Humanized Sickle Cell Disease Mice Research Articles

Time-restricted feeding does not improve nephropathy in humanized sickle cell disease mice

Sickle cell disease (SCD) is an autosomal recessive genetic disease caused by a point mutation in the hemoglobin gene. This substitution results in a “sickling” of red blood cells and subsequent vascular and organ damage. Current treatments, while increasing the lifespan of sickle cell patients, has resulted in a higher prevalence of chronic complications like SCD nephropathy. Our group has previously shown that time-restricted feeding (TRF) in chronic high fat fed mice reduces kidney damage. Given the increased kidney damage in SCD, we hypothesize that TRF in humanized SCD mice will attenuate sickle cell nephropathy. To test this hypothesis, we studied 18-22-week-old male SCD mice. Mice underwent 3 weeks of TRF, only having access to food during the active, dark period (Zeitgeber Time (ZT) 12 to 24). The control group had access to food ad libitum (ad-lib). At the end of the 3 weeks, at 21-25 week old ages, 12 hour urine was collected in metabolic cages as well as kidneys and plasma collection at ZT3 (inactive period). Excretion of urinary kidney damage markers (albumin and NGAL-1) showed no difference between TRF and ad-lib in both the active and inactive collection periods. Urinary excretion of endothelin-1 is known to be upregulated in SCD patients; however, TRF did not change this marker in SCD mice. TRF did not change plasma levels of cytokines or soluble adhesion molecules. Histological analysis of kidneys was conducted as an additional marker of kidney damage. We analyzed iron levels in the kidney with Prussian blue staining as well as fibrosis with Masson’s trichrome. TRF did not change kidney iron accumulation or kidney fibrosis. Immunohistochemical staining for CD3+ T cells did not show a difference in glomerular T cell infiltration in the TRF group compared to the ad-lib group. In conclusion, TRF does not appear to have an effect on renal inflammation or kidney function in SCD mice, but future studies need to be completed. R01 DK134562. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Mechanisms of Iron-Mediated Renal Injury in a Mouse Model of Sickle Cell Disease

Background: Sickle cell disease (SCD) is a hematologic disorder characterized by polymerization of the mutated hemoglobin S and sickling of red blood cells, leading to hemolysis, release of free heme/iron, and subsequent tissue iron accumulation. The kidney is one of the most frequently affected organs by iron overload, and chronic hemolysis is associated with chronic kidney disease severity in SCD. The potential role of iron overload in causing the observed renal injury in SCD has never been established. The goal of our study is to identify the impact of iron accumulation on the renal phenotype in SCD. We hypothesized that renal iron accumulation causes injury by oxidative stress dependent ferroptosis and/or mitochondrial dysfunction and subsequent kidney damage, that is worse in males than in females. Methods: We used 20-week-old male and female humanized SCD mice (HbSS) and age-matched genetic controls (HbAA). Mice were treated with either vehicle or the iron chelator Deferiprone (DFP, 100 mg/kg/day) for 8 weeks. Urinary excretion of protein and albumin as markers of renal injury were measured. Glomerular filtration rate (GFR) was measured transdermally after injection of FITC-sinistrin. Thiobarbituric acid reactive substance (TBARS) assay was performed for assessment of lipid peroxidation. Mitochondrial bioenergetics was assessed by Oroboros O2k Fluorometer of permeabilized renal cortices. Results: We previously demonstrated comparable iron accumulation in the kidney of male and female mice. However, HbSS males developed a more severe renal injury than females at 20 weeks of age, evidenced by proteinuria (2.52 ± 0.16 vs. 0.55 ± 0.16 mg/24hrs, p=0.0008) and albuminuria (76.44 ± 6.85 vs. 33.9 ± 8.81 μg/24hrs, p=0.0005). There was higher lipid peroxidation, a hallmark of ferroptosis, in the renal cortex of female HbSS than HbAA mice (1.31 ± 0.07 vs. 1.07 ± μM/mg, p=0.04). Bioenergetics studies revealed significantly lower state 3 oxygen consumption rate (108.2 ± 18.1 vs 164.8 ± 9.3 pmol/(s*mg), p=0.05), signifying lower oxidative phosphorylation capacity in HbSS males. In addition, there was significant reduction in state 4◦ respiration (36.4 ± 3.4 vs. 52.8 ± 3.4 pmol/(s*mg), p=0.03) in male HbSS mice. I also detected a decrease in maximum complex IV activity in male HbSS mice (325.5 ± 63.8 vs. 639.5 ± 51.3 pmol/(s*mg), p=0.02). Treatment with DFP improved proteinuria (2.66 ± 0.09 vs. 1.3 ± 0.14 mg/24hrs, p=0.0011) and GFR (165.3 ± 9.4 vs. 236.6 ± 12.6 μl/min, p=0.0058) in male HbSS mice. Conclusion: Iron accumulation causes renal injury which may be attributed to ferroptosis and mitochondrial dysfunction in SCD mice. Funding: NHLBI—R00HL144817 and ASN Norman Siegel Research Grant to MK. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Proteomic analyses of urinary exosomes identify novel potential biomarkers for early diagnosis of sickle cell nephropathy, a sex-based study.

Sickle cell nephropathy (SCN) is a leading cause of morbidity and mortality in sickle cell disease (SCD). Early intervention is crucial for mitigating its effects. However, current diagnostic methods rely on generic tests and may not detect SCN until irreversible renal damage occurs. Therefore, specific biomarkers for early diagnosis of SCN are needed. Urinary exosomes, membrane-bound vesicles secreted by renal podocytes and epithelial cells, contain both common and cell type-specific membrane and cytosolic proteins, reflecting the physiologic and pathophysiologic states of the kidney. Using proteomics, we analyzed the proteomes of urinary exosomes from humanized SCD mice at 2months (without albuminuria) and 4months (with albuminuria) of age. Excretion of 164 proteins were significantly increased and 176 proteins was significantly decreased in the exosomes when mice developed albuminuria. Based on the relevance to SCD, chronic kidney disease and Western blot confirmation in mice, we analyzed protein abundance of heparanase, cathepsin C, α2-macroglobulin and sarcoplasmic endoplasmic Ca2+ ATPase-3 (SERCA3) in the urinary exosomes and urine of 18 SCD subjects without albuminuria and 12 subjects with albuminuria using Western blot analyses. Both male and female subjects increased or tended to increase the excretion of these proteins in their urinary exosomes upon developing albuminuria, but female subjects demonstrated stronger correlations between the excretion of these proteins and urine albumin creatinine ratio (UACR) compared to male subjects. In contrast, exosomal excretion of Tamm-Horsfall protein, β-actin and SHP-1 was independent of albuminuria. These findings provide a foundation for a time-course study to determine whether increases in the levels of these proteins precede the onset of albuminuria in patients, which will help determine the potential of these proteins as biomarkers for early detection of SCN.

17R-Resolvin D1 Improves Inflammatory Cardiomyopathy in a Mouse Model of Sickle Cell Disease

Sickle cell disease (SCD) is a severely invalidating genetic red cell disorder. Inflammatory vasculopathy and cardiopulmonary complications markedly impact quality of life and survival. Limited studies are available on the pathogenesis of sickle cell related cardiomyopathy. However, the combination of inflammatory vasculopathy, heart ischemia, and myocardial fibrosis have been suggested to play a role in sickle cell related cardiomyopathy. This is supported by the amelioration of cardiomyopathy in SCD patients, early and intensively treated with either hydroxyurea or chronic transfusion regimen (Niss O et al. Blood 140: 1322, 2022). Recently, we have highlighted an impairment of pro-resolving events in SCD with a deleterious effect on acute sickle cell related organ damage (Matte A et al. Blood 133: 252, 2019). Growing evidence links impairment of pro-resolving mechanisms with atherosclerosis and ischemic cardiomyopathy (Kain V et al. J Mol Cell Cardiol 84: 24, 2015; Conte MS et al. JCI 128: 3727, 2018). Among specialized pro-resolving mediators, 17R-resolvin D1 (17R-RvD1) has been shown to play important protective actions in cardiovascular diseases (Kain V et al. J Mol Cell Cardiol 84: 24, 2015). Here, we first determined the appropriate window of time to study cardiac response to hypoxia/reoxygenation (H/R) stress, mimicking sickle cell related acute vaso-occlusive crisis. We show that humanized SCD mice (TT model) exposed to H/R (10 hours hypoxia 8% oxygen, followed by 3 hours reoxygenation) display increased markers of myocardial dysfunction with neutrophil heart infiltration compared to either SCD mice under normoxia or to healthy (AA) animals exposed to H/R stress. With integrated proteomic and miRNA analyses we have identified upregulation of proteins and miRNAs involved in fibrosis, hypertrophy of the heart, and cardiomyocyte apoptosis. Differentially expressed miRNAs in SCD-hearts compared to AA included miR-16-5p, miR-122-5p, and miR-206-3p, which are involved in angiogenesis and heart fibrosis and hypertrophy. Upregulated proteins in SCD hearts in response to H/R encompassed: NF-kB, Nrf2, hemeoxygenase-1, glutathione peroxidase, and peroxiredoxins (associated to response to oxidative stress), the profibrotic factors FGF and PDGF as well as the TGF-ß1 receptor, and the pro-angiogenic VEGF pathway. Treatment with 17R-RvD1 (100 ng administrated by gavage 1 hour before H/R, see also Matte A et al. Blood 133: 252, 2019) protected heart of SCD mice from H/R-induced stress as supported by significant reduction of ANP, a marker of cardiovascular dysfunction, decrease in neutrophil infiltration, and NF-kB activation (Figure 1). 17R-RvD1 also diminished the H/R-driven upregulation of miR-16-5p, while it enhanced miR-206-3p that was downregulated by H/R, suggesting that 17R-RvD1 can reduce cardiac fibrosis and other pathological processes associated with these miRNAs in SCD. We also found that 17R-RvD1 administration to SCD mice blunted the activation of TGF-ß1 pathway and of markers of extracellular remodeling, supporting the beneficial effect of 17R-RvD1 against H/R stress. Taken together, our data show that 17R-RvD1 reduced heart remodeling and fibrosis in SCD mice undergoing H/R, a model of acute VOCs. This improved understanding in basic pathophysiology of SCD-related inflammatory cardiomyopathy, providing new evidence for protective therapeutic effects of 17R-RvD1 on SCD cardiovascular diseases.

Ineffective Erythropoiesis Negatively Impacts the Erythroblastic Island in Sickle Cell Disease

Sickle cell disease (SCD) is a genetic recessive disorder, characterized by painful episodes of vaso-occlusion, chronic hemolytic anemia, and progressive organ failure. It is one of the most common and severe monogenic diseases worldwide. SCD is caused by a point mutation in the β-globin gene, leading to the expression of an abnormal hemoglobin (HbS) that polymerizes under hypoxic conditions, driving red blood cells (RBC) sickling. Peripheral RBCs are extensively studied in SCD, as hemolysis is the major contributor to anemia, but little is known about erythroid differentiation in this pathology. We recently demonstrated the occurrence of ineffective erythropoiesis in the bone marrow (BM) of SCD patients, characterized by the death of a significant proportion of erythroblasts between the polychromatic and the orthochromatic stages. We hypothesize that this increased cell death could negatively impact the central macrophages of the erythroblastic islands (EBIs) as they would engulf high numbers of hemoglobin-rich apoptotic erythroblasts and undergo ferroptosis because of excess iron. To investigate our hypothesis, we used an in vitro system whereby CD14 + monocytes were isolated from peripheral blood and cultured in media supplemented with M-CSF and dexamethasone. This led them to differentiate towards anti-inflammatory tissue macrophages, with an “EBI-like” phenotype, expressing markers such as CD16, CD163, CD169, CD206. Phagocytosis of high numbers of RBCs by “EBI-like” macrophages led to increased cell death, reactive oxygen species, and lipid peroxidation, and to the upregulation of genes involved in ferroptosis pathways such as HO-1 and SLC7A11. This was circumvented by the ferroptosis inhibitors ferrostatin-1 and liproxtatin-1. Furthermore, phagocytosis of apoptotic in vitro-generated SCD erythroblasts also induced ferroptosis in EBI-like macrophages, with increased cell death and lipid peroxidation in a time-dependent manner. Interestingly, while this was the case with hemoglobin-rich, terminally differentiating erythroblasts, phagocytosis of cells without hemoglobin, such as K562 or GPA - progenitor cells did not affect cell viability, indicating that the observed ferroptosis was due to the iron content of the internalized cells. We investigated the effect of increased RBC phagocytosis on the phenotype of surviving macrophages and found an M2 to M1 shift indicating a switch to a pro-inflammatory phenotype under the condition of elevated levels of intracellular iron and oxidative stress. We challenged these findings in vivo using the Townes humanized SCD mouse model. Data on 4-month-old mice showed the expected switch in erythroid production from steady-state erythropoiesis in the BM to a stress erythropoiesis in the spleen. This was associated with a decrease in the number of EBI macrophages (F4/80 HighVCAM+CD169+Ly6G-) in the BM of SS mice when compared to AS and AA mice, and an expansion of red pulp macrophages (RPMs) F4/80 HighCD169+VCAM+. Using a flow cytometry-based assay we found high lipid peroxidation levels in BM EBI macrophages of SS mice as compared to AA, suggesting occurrence of ferroptosis in these cells. Our study suggests that IE in SCD may contribute to anemia, directly by cell death of differentiating erythroblasts, and indirectly by disrupting the erythroblastic island or by inducing its collapse following ferroptosis of the central macrophage. Our work with the Townes mouse model and BM samples from SCD patients will help to elucidate this hypothesis.

A Phase 2, Open-Label Study to Assess the Pharmacokinetics, Pharmacodynamics and Safety of Orally Administered Epeleuton in Patients with Sickle Cell Disease

Background. Sickle cell disease (SCD) is a rare hereditary multi-system disorder that is caused by a single mutation in the beta allele of the hemoglobin gene, leading to the production of sickle hemoglobin (HbS). HbS polymerizes when deoxygenated, resulting in red blood cell (RBC) sickling and membrane damage, ultimately leading to a cascade of events which include hemolysis, chronic anemia, inflammation, and vaso-occlusion. Despite recent progress, there is a need for additional disease-modifying therapeutic options. Epeleuton is 15-hydroxy eicosapentaenoic acid (15(S)-HEPE) ethyl ester, a novel synthetic second generation w-3 fatty acid which targets key drivers of hemolysis and multicellular adhesion. In preclinical studies in Townes humanized SCD mice and SCD patient RBCs, epeleuton acts as a disease-modifying agent by simultaneously decreasing (a) systemic and local inflammatory activation, (b) endothelial adhesion, (c) organ damage and (d) intravascular hemolysis and sickling. Epeleuton has been administered to 343 subjects in clinical trials, with a favorable safety and tolerability profile. Objective To evaluate the pharmacokinetics, pharmacodynamics and safety of orally administered epeleuton in patients with SCD. Study Design and Methods. This open-label, phase 2, multicenter study (NCT05861453) will enroll approximately 30 adult patients with a confirmed diagnosis of SCD (HbSS and HbSß0-thalassemia). Participants must have hemoglobin levels of 5.0-9.5g/dL at screening, 2-10 vaso-occlusive crises (VOCs) in the past 12 months, and a high adhesion index at screening defined as RBC laminin adhesion > 400 cells. Concomitant treatment with a stable dose of hydroxyurea is permitted during the study. Key exclusion criteria include receiving an RBC transfusion within three months of enrolment, receiving voxelotor, crizanlizumab or l-glutamine within six weeks of enrolment and, prior hematopoietic stem cell transplant. The trial has a 28-day screening period, followed by a 16-week treatment phase and a 30-day post-treatment follow-up period. Study participants will attend the clinic on 6 occasions at screening, baseline, weeks 4, 8 and 16 (end-of-treatment) and the week 20 post-treatment follow-up visit. Enrolled patients will receive epeleuton 2g BID (4g daily) for 16 weeks. Study endpoints include change from baseline in hemoglobin levels, hemolytic markers, assessments of RBC health, soluble adhesion molecules, RBC adhesion, whole blood adhesion and rates of VOC. Conclusion: Treatments that can simultaneously target hemolysis and cellular adhesion may have an important disease-modifying utility for patients with SCD. The results of this study are anticipated to confirm the potential of epeleuton to address multiple aspects of SCD and to guide the design and conduct of future studies in patients with SCD.

Circulating NETs Promote Platelet-TLR9 Dependent Acute Chest Syndrome in Sickle Cell Disease

Acute chest syndrome (ACS), a type of acute lung injury is one of the primary reasons for mortality among Sickle Cell Disease (SCD) patients. Although new evidence suggests that circulating neutrophil extracellular traps (cNETs) promote lung injury in SCD by triggering occlusion of pulmonary arterioles by neutrophil-platelet-erythrocyte thrombo-inflammatory aggregates, the molecular mechanism underlying cNETs-dependent lung vaso-occlusion remains unknown. Surprisingly, platelets are one of the few cell types that express Toll-like receptor 9 (TLR9), a receptor for double-stranded DNA on the surface (rather than in endosomes), however, the role of platelet-TLR9 in promoting pulmonary thrombo-inflammation in SCD has never been studied. Using intravital (in vivo) lung microscopy in live SCD mice and imaging flow cytometry (in vitro) of SCD mice plasma, we show for the first time that lung vaso-occlusion and elevated levels of cNETs in knock-in humanized SCD mice challenged with 10 μmol/kg oxy-hemoglobin (oxy-Hb) is associated with significant upregulation of TLR9 surface expression in platelets. Importantly, TLR9 inhibition using a function blocking Ab led to significant reduction by ~6 and ~4 fold in the frequency and size of lung vaso-occlusions in SCD mice challenged with IV oxy-Hb. Identical to SCD mice, TLR9 surface expression was also significantly higher in SCD than control human platelets, and the expression was further upregulated following treatment of SCD patient platelet-rich-plasma (PRP) with oxy-Hb. Remarkably, elevated TLR9 expression in SCD patient platelets was concomitant to increased phosphorylation of both downstream TLR9 pathway effector tank-binding-kinase-1 (TBK-1) and the TBK-1 substrate interferon regulatory factor-3 (IRF3), which is the major transcription factor driving IFN-1 response. Taken together, our current findings suggest for the first time that activation of nucleic acid receptor TLR9 on the surface of platelets by cNETs contributes to lung vaso-occlusion and acute chest syndrome in SCD.

Hematopoietic Stem Cells from Mice and Individuals with Sickle Cell Disease Display Premature Senescence and Loss of Function That Is Targetable By Senolytic Therapy

Sickle cell disease (SCD) is an inherited anemia caused by mutations in the β-globin gene, resulting in aberrant hemoglobin polymerization driving hemolysis, vasooclusion, and systemic inflammation. Allogeneic hematopoietic stem cell (HSC) transplantation is potentially curative, and novel autologous therapies involving gene-editing of mobilized HSCs are being developed. However, many SCD patients are unable to undergo autologous gene-editing due to failure to mobilize sufficient numbers of HSCs. Further, the damaging effects of SCD on the HSC pool remain uncharacterized. Therefore, we interrogated young and aged cohorts of humanized SCD mice and non-SCD controls for HSC frequency and function. Immunophenotypic HSC frequency was mildly elevated (1.3-fold, p=0.00316) in 2-month-old SCD mice, relative to controls (n=5-6/group). In contrast, HSC numbers were halved in 6 and 12-month-old SCD mice (n=8-10/group, p=0.00358 and p=0.0148, respectively). Competitive transplantation of whole bone marrow (WBM) from 2 and 6-month-old SCD mice displayed a profound loss of peripheral blood repopulation, relative to age-matched control mice. Quantitative limiting dilution transplantation of WBM from 2 and 6-month-old SCD mice revealed a 4 and 6-fold loss of functional HSCs, relative to control mice. Thus, despite elevated numbers of phenotypic HSCs in young SCD mice, the HSC pool is depleted of functional repopulating cells during SCD. To understand the loss of functional HSCs, we performed bulk RNA-sequencing of purified HSCs from 6-month-old SCD mice. We observed downregulation of 37 genes encoding ribosomal and histone proteins, suggesting impaired histone/ribosome biogenesis, a phenotype associated with senescence. Consistently, pathway enrichment analysis also revealed perturbed p53 activity and a high degree of association with published molecular signatures of senescence. To explore this further, HSCs isolated from 6-month-old SCD mice or age-matched controls were interrogated for senescence associated β-galactosidase (SA-β-gal) activity. On average 19.5% of SCD HSCs were SA-β-gal+ versus only 7.06% of HSCs isolated from controls (n=10-11/group, p=0.004). HSCs isolated from SCD mice also displayed elevated ROS, DNA damage, and expression of molecular markers of senescence (e.g. p21, BCLXL). Importantly, 23.14 ± 5.61% of Lin-CD34+CD38- bone marrow (BM) hematopoietic stem and progenitor cells (HSPCs) isolated from pediatric individuals with SCD were SA-β-gal+. In contrast, only 4.97 ± 2.97% of HSPCs were SA-β-gal+ in age-matched, non-SCD control individuals (n=8 control and n=5 SCD individuals, p=<0.0001). Further, 47.46 ± 17.49% of Lin-CD34+CD38-CD90+CD45RA- BM cells, which are highly enriched for human HSCs, were SA-β-gal+ in young individuals with SCD, relative to only 4.41 ± 2.37% in the BM of age-matched control individuals (n=4 control and n=5 SCD individuals, p=0.0019). We also detected elevated expression of p16, p21, and BCL2 in BM HSPCs isolated from pediatric individuals with SCD, relative to controls (n=6 control and n=9 SCD individuals). In total, these data reveal that SCD pathophysiology aberrantly invokes senescence programs and damages HSC function in mice and humans. Clearance of senescent HSCs from mouse BM has previously been shown to restore aging-related HSC dysfunction. We therefore tested if clearance of senescent HSCs from the BM could restore function to the SCD HSC pool. 2-month-old SCD and control mice were treated with two weekly cycles of 75 mg/kg/day of the senolytic, ABT-263, via oral gavage. 14 days after treatment, WBM was isolated and tested for HSC function and frequency. Senolytic therapy significantly increased HSC numbers in SCD mice BM, relative to vehicle-treated controls (n=5/group). Importantly, the in vivo hematopoietic repopulating activity of WBM from ABT-263-treated SCD mice was comparable to non-SCD controls, revealing a correction of our previously observed severe transplantation defect (n=12/group). In sum, these data reveal premature onset of senescence as a previously unappreciated phenotype of the HSC pool during SCD. This work provides the first proof-of-principle that treatment of individuals with SCD using senolytics may restore function to the HSC pool, and ongoing preclinical work aims to test if senolytic therapy enhances the yield and function of SCD HSCs mobilized for autologous therapy.

Flu Induced Acute Chest Syndrome in Sickle Cell Disease Mice

Background: Sickle cell disease (SCD) affects over ~8 million people world-wide. Acute chest syndrome, a type of acute lung injury (ALI) is a major cause of mortality among SCD patients. Flu is an acute respiratory disease primarily caused by the influenza A virus (IAV), which is typically a self-resolving upper airway inflammation. However, epidemiological evidence suggests that flu can result in severe ACS in SCD patients. Although flu associates with a 50-fold higher risk of ICU admission among SCD than non-SCD humans, the etiological mechanism underlying the flu severity in SCD remains unknown. Aim: To determine whether a mild dose of IAV promotes severe lung injury in SCD mice. Methods: We have developed a model of A/PR/8/34 (H1N1) IAV induced respiratory infection in knock-in, humanized SCD mice. Mice were intranasally inoculated with a mild dose of IAV. The body weight was measured every day for three weeks after intranasal IAV administration followed by assessment of lung injury at day 10 and 14 post infection. Severity of lung injury was evaluated using histological scoring and oxygen saturation measurements. Real-time intravital ( in vivo) multi-photon-excitation fluorescence microscopy (MPE) was used to assess thrombo-inflammation and vascular leakage in the lung of mice at 10 and 14 days post IAV-infection. Results: Over the first 8 days post-IAV infection, both SCD and control mice manifested comparable levels of mild lung injury and a mild drop in body weight (15%). Unlike the control mice that started to recover, the lung injury and drop in body weight continued to worsen in SCD mice at 8-10 days post IAV infection. By day 14 post IAV infection, the lung injury was resolved and body weight was recovered in control mice, while SCD mice still manifested severe lung injury and ~20% drop in body weight. Intravital lung microscopy revealed large areas with vascular occlusion, ischemia, neutrophil infiltration and vascular leakage in the lung of SCD mice 10 days post infection, however, such pathophysiology was rarely present in the lung of control mice at 10 days post infection. Conclusions: Our current findings are the first to suggest that the inflammatory milieu in SCD mice promotes a severe non-resolving ALI following an IAV infection, which otherwise leads to a mild self-resolving lung inflammation in control mice.

Long-Term L-Glutamine Treatment Reduces Hemolysis without Ameliorating Hepatic Vaso-Occlusion and Liver Fibrosis in a Mouse Model of Sickle Cell Disease.

Sickle cell disease (SCD) is an autosomal recessive monogenic disorder caused by a homozygous mutation in the β-globin gene, which leads to erythrocyte sickling, hemolysis, vaso-occlusion, and sterile inflammation. The administration of oral L-glutamine has been shown to reduce the frequency of pain in SCD patients; however, the long-term effect of L-glutamine in SCD remains to be determined. To understand the long-term effect of L-glutamine administration in the liver we used quantitative liver intravital microscopy and biochemical analysis in humanized SCD mice. We here show that chronic L-glutamine administration reduces hepatic hemoglobin-heme-iron levels but fails to ameliorate ischemic liver injury. Remarkably, we found that this failure in the resolution of hepatobiliary injury and persistent liver fibrosis is associated with the reduced expression of hepatic Kupffer cells post-L-glutamine treatment. These findings establish the importance of investigating the long-term effects of L-glutamine therapy on liver pathophysiology in SCD patients.

Development of a Humanized Mouse Model of Cholestatic Sickle Cell Disease

Sickle cell disease (SCD) is a group of autosomal recessive inherited disorders that affect approximately 100,000 people in the United States and millions worldwide. Liver or biliary complications including cirrhosis and cholestatic injury are evident in about 40% of hospitalized SCD patients. However, the molecular mechanisms responsible for sickle cell hepatopathy (SCH) remain poorly understood. Recently published studies and our preliminary data demonstrated impaired bile secretion and altered bile acid homeostasis accompanied red blood cell sequestration and fibrosis in the livers of humanized sickle cell mice. Although promising, a limitation of this model for the study of SCH is the predominance of hydrophilic bile acids in mice, which contrasts with a more hydrophobic and injurious bile acid pool in humans. A recent breakthrough in this area was the identification of murine-specific cytochrome P450 (Cyp2c70) as the enzyme responsible for the synthesis of mouse hydrophilic primary bile acids. Therefore, we hypothesize that the human hydrophobic bile acid composition would promote the development of cholestatic sickle cell disease. Methods:Tibias and femurs were excised from 2-month-old SCD SS and AA control mice and the bone marrow (BM) was collected. After lethal irradiation (2x 4.5Gy 4 hours apart), 2-month-old male recipient Cyp2c70-/- and their wildtype controls received BM-derived cells from either AA or SS mice. Cyp2c70-/- (KO) mice (C57Bl/6) were generated using CRISPR/Cas9 technology. Recipient Cyp2c70-/- and WTmice were reconstituted with SS and AA bone marrow and were euthanized 4 months after BMT. Standard growth parameters were recorded; liver, spleen, gallbladder bile, and blood were collected at necropsy for histologic, RNA, and chemical analyses. Results: Recipient Cyp2c70-/- (KO) SS mice had a significantly increased liver-to-body weight ratio compared to their controls. There was an increase in serum bile acids, direct bilirubin, and total bilirubin in SS recipient Cyp2c70-/- and WT mice compared to AA recipient mice. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were increased in Cyp2c70-/- (KO) overall with no observable difference in Cyp2c70-/- (KO) transplanted with AA or SS. An evaluation of liver histology by H&E revealed increased portal bridging and hepatic sequestration in sinusoids of recipient Cyp2c70-/- SS mice compared to control mice. Liver surface nodularity and morphological heterogeneity were also present in recipient Cyp2c70-/- SS mice compared to their controls. We observed increased collagen deposition as measured by Sirius Red staining in recipient Cyp2c70-/- SS mice compared to control mice. Liver histology revealed increased hepatic inflammation by F4/80 staining and bile duct proliferation by CK-19 and CK-8 staining in recipient Cyp2c70-/- SS mice. Conclusion: Coupled with the humanized sickle cell disease mouse, this novel sickle cell cholestatic liver mouse model can be used to investigate the role of hydrophobic bile acid-induced injury in sickle cell-related hepatobiliary disease and screen new therapeutic approaches for SCH. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Endothelial Extracellular Vesicles Regulate Platelet Purinergic Signaling in Sickle Cell Disease

Introduction. Acute chest syndrome (ACS) is a type of acute lung injury and the leading cause of mortality among sickle cell disease (SCD) patients. ACS is often preceded by thrombocytopenia and involves massive thrombosis across pulmonary artery branches. Although, released during hemolysis, adenosine diphosphate (ADP) is known to activate platelets by stimulating their P2Y1 and P2Y12 purinergic receptors, antagonists of P2Y12 have not shown any benefit in ACS therapy, justifying the need for better understanding of purinergic signaling in SCD. CD39 maintains ADP homeostasis by degrading excessive ADP. Though CD39 inhibits ADP-dependent platelet activation, its role in the pathophysiology of SCD is still unidentified. Methods. To evaluate SCD platelet response to ADP in vivo we used a state-of-the-art intravital lung microscopy and a novel in vivo model of ADP-triggered thrombocytopenia in transgenic humanized SCD mice. Additionally, both mouse and human SCD platelet ADP-dependent aggregation was examined using in vitro turbidimetric aggregation assay. Hemin, a major host-derived damage associated molecular pattern associated with SCD, was incubated with Human Lung Micro-Vascular Endothelial Cells (HMVEC-L). Extracellular vesicles (EVs) were obtained from mouse and human plasma samples, and cell culture medium samples using size exclusion chromatography. Obtained EVs were subjected to nanoparticle tracking analysis. EVs CD39 levels and activity were determined using ELISA, western blot and malachite green phosphate assays, respectively. Results. Intravital lung microscopy and in vivo thrombocytopenia studies revealed that intravascular administration of ADP triggered acute pulmonary thrombosis in control but not in SCD mice. In vitro aggregation study confirmed our in vivo findings and demonstrated impaired SCD mouse and human platelet response to ADP, which was, further, significantly augmented by a specific CD39 inhibitor. Hemin triggered shedding of CD39-bearing EVs by HMVEC-L. Indeed, we discovered that isolated from mouse and human plasma endothelial cell-derived SCD EVs expressed higher CD39 levels and activity in comparison to control EVs. Conclusions. Our findings suggest that CD39-bearing EVs prevent ADP-mediated platelet aggregation and pulmonary thrombosis in SCD. Current study explains why P2Y12 blockers are not effective in SCD therapy.

P1483: EPELEUTON, A NOVEL SYNTHETIC SECOND GENERATION W-3 FATTY ACID, PROTECTS HUMANIZED SICKLE CELL MICE AGAINST HYPOXIA/REOXYGENATION ORGAN DAMAGE

Background: Sickle cell disease (SCD) is a hereditary red cell disorder with high mortality and morbidity. Although crizanlizumab, a P-selectin inhibitor, and voxelotor, an oral anti-sickling agent, have been recently approved for clinical management of SCD, therapeutic options to limit acute events and to reduce disease progression are still required. An attempt to target inflammatory vasculopathy and to modulate inflammatory response has been made based on evidence in other diseases such as in cardiovascular disease looking to administration of ω-3 fatty acids. In humanized SCD mice, we previously showed that polyunsaturated fatty acid supplementation protects against acute sickle cell-related lung and liver damages during hypoxia/reoxygenation (H/R) induced vaso-occlusive crisis (VOCs) (Kalish B et al. Haematologica 2016). This agrees with the observation that the resolution process actively controlled by specialized pro-resolving lipid mediators is defective in SCD (Matte A et al, Blood 2019). Epeleuton (15-HEPE, 15 hydroxy eicosapentaenoic acid) is a novel synthetic second generation w-3 fatty acid which (i) has a favorable clinical safety profile, (ii) modulates systemic inflammation and triglyceride synthesis in patients with cardiometabolic disease (Climax J et al J Am Heart As 2020) and (ii) beneficially affects red cell indices in long-term studies in rats. Aims: To evaluate the impact of epeleuton on acute organ damage in a humanized mouse model of SCD. Methods: 3-4 month old male and female mice healthy control (Hbatm1(HBA)Tow Hbbtm3(HBG1,HBB)Tow) and Tim Townes sickle mice (SCD, Hba tm1(HBA)Tow Hbb tm2(HBG1,HBB*)Tow) were used. Animals were treated for 6 weeks with epeleuton 1,000 mg/kg once daily or vehicle by gavage. Mice underwent 10 hours of hypoxia (8% oxygen), followed by 3 hours of reoxygenation (21% oxygen) to mimic acute VOCs (Matte A et al, Blood 2019). Hematologic parameters and molecular analysis of target organs for SCD such as lung were carried out. Results: In SCD mice exposed to H/R stress, we found that epeleuton (i) reduces H/R induced hemolysis; (ii) normalizes tyrosine-phosphorylation profile of red cell membrane proteins; and (iii) decreases neutrophil count. In lungs of SCD mice exposed to H/R stress, we observed that epeleuton prevents the H/R induced activation of inflammatory and redox related transcription factors NF-kB, p65 and Nrf2 local inflammatory response compared with vehicle-treated animals. Epeleuton treated SCD mice exposed to H/R stress showed down-regulation of VCAM-1 and E-selectin, markers of inflammatory vasculopathy as well as reduction of lung protein oxidation and expression of anti-oxidant systems such as heme-oxygenase-1 (HO-1) or peroxiredoxin-2. Similar changes were also observed in livers of epeleuton-treated SCD mice exposed to H/R stress compared with vehicle-treated SCD animals. Of note, epeleuton prevented the H/R induced up-regulation of both VCAM-1 and ICAM-1, suggesting a direct impact of treatment on vascular activation and inflammation. Summary/Conclusion: In humanized SCD mice exposed to H/R stress to mimic acute VOCs, epeleuton acts as a multimodal agent targeting red cells, hemolysis, inflammatory response, and vascular dysfunction. Our data provide the rationale for epeleuton as a potential novel therapeutic option for clinical management of patients with SCD.

Evidence of protective effects of recombinant ADAMTS13 in a humanized model of sickle cell disease.

Sickle cell disease (SCD) is an inherited red blood cell disorder that occurs worldwide. Acute vaso-occlusive crisis is the main cause of hospitalization in patients with SCD. There is growing evidence that inflammatory vasculopathy plays a key role in both acute and chronic SCD-related clinical manifestations. In a humanized mouse model of SCD, we found an increase of von Willebrand factor activity and a reduction in the ratio of a disintegrin and metalloproteinase with thrombospondin type 1 motif, number 13 (ADAMTS13) to von Willebrand factor activity similar to that observed in the human counterpart. Recombinant ADAMTS13 was administered to humanized SCD mice before they were subjected to hypoxia/reoxygenation (H/R) stress as a model of vaso-occlusive crisis. In SCD mice, recombinant ADAMTS13 reduced H/R-induced hemolysis and systemic and local inflammation in lungs and kidneys. It also diminished H/R-induced worsening of inflammatory vasculopathy, reducing local nitric oxidase synthase expression. Collectively, our data provide for the firsttime evidence that pharmacological treatment with recombinant ADAMTS13 (TAK-755) diminished H/R-induced sickle cell-related organ damage. Thus, recombinant ADAMTS13 might be considered as a potential effective disease-modifying treatment option for sickle cell-related acute events.

Peroxiredoxin-2 recycling is slower in denser and pediatric sickle cell red cells.

Peroxiredoxin-2 (Prx-2) is a critical antioxidant protein in red blood cells (RBC). Prx-2 is oxidized to a disulfide covalently-bound dimer by H2 O2 , and then reduced back by the NADPH-dependent thioredoxin-thioredoxin reductase system. The reduction of oxidized Prx-2 is relatively slow in RBCs. Since Prx-2 is highly abundant, Prx-2s' peroxidase catalytic cycle is not considered to be limiting under normal conditions. However, whether Prx-2 recycling becomes limiting when RBCs are exposed to stress is not known. Using three different model systems characterized by increased oxidative damage to RBCs spanning the physiologic (endogenous RBCs of different ages), therapeutic (cold-stored RBCs in blood banks) and pathologic (RBCs from sickle cell disease (SCD) patients and humanized SCD mice) spectrum, basal levels of Prx-2 oxidation and Prx-2 recycling kinetics after addition of H2 O2 were determined. The reduction of oxidized Prx-2 was significantly slower in older versuin older versus younger RBCs, in RBCs stored for 4-5weeks compared to 1week, and in RBC from pediatric SCD patients compared to RBCs from control non-SCD patients. Similarly, the rate of Prx-2 recycling was slower in humanized SCD mice compared to WT mice. Treatment of RBC with carbon monoxide (CO) to limit heme-peroxidase activity had no effect on Prx-2 recycling kinetics. Treatment with glucose attenuated slowed Prx-2 recycling in older RBCs and SCD RBCs, but not stored RBCs. In conclusion, the reduction of oxidized Prx-2 can be further slowed in RBCs, which may limit the protection afforded by this antioxidant protein in settings associated with erythrocyte stress.

Plasma NTPDase1 Activity Regulates Platelet Purinergic Signaling in Sickle Cell Disease

Acute systemic painful vaso-occlusive episode (VOE) often serves as an antecedent to acute chest syndrome (ACS), which is a type of acute lung injury and the leading cause of mortality among sickle cell disease (SCD) patients. Based on clinical epidemiology, ACS is often preceded by thrombocytopenia and involves massive thrombosis across pulmonary artery branches in 10-20% of ACS patients. Although, released during hemolysis, adenosine diphosphate (ADP) is known to activate platelets by stimulating their P2Y1 and P2Y12 purinergic receptors, antagonists of P2Y12 have not shown any benefit in ACS therapy, justifying the need for better understanding of purinergic signaling in SCD. Ecto-nucleoside-tri-phosphate-diphosphohydrolase-1 (E-NTPDase1; CD39) maintains ADP homeostasis by degrading excessive ADP. Though CD39 inhibits ADP-dependent platelet activation and vascular thrombosis, its role in ASC is still unidentified.Here, we use intravital lung microscopy in transgenic humanized SCD mice to show that intravascular (IV) administration of ADP triggered pulmonary thrombosis in control mice but failed to trigger pulmonary thrombosis in SCD mice. Identical to intravital findings, IV ADP administration also evoked transient thrombocytopenia in control but not SCD mice, while, IV collagen led to comparable drop in platelet count in both SCD and control mice. In vitro turbidimetric aggregation study yet again demonstrated impaired SCD mouse platelet response to ADP, which was significantly augmented by CD39 inhibitor (sodium metatungstate, POM-1). Indeed, we found significantly higher plasma levels and activity of CD39 in SCD mice compared to control mice using ELISA and malachite green assays, respectively. Hemin, a major host-derived damage associated molecular pattern (DAMP) in SCD, was incubated with Human Lung MicroVascular Endothelial Cell (HMVEC-L) to assess CD39 expression using western blotting. Hemin (10 -100 µM) in a dose dependent manner decreased CD39 levels in HMVEC-L.Our current findings suggest that elevated CD39 plasma levels and activity possibly prevents ADP-mediated platelet aggregation and pulmonary thrombosis in SCD. We demonstrated that SCD milieu promotes loss of endothelial CD39, which may be directly associated with increased CD39 plasma levels and activity. Current study explains why P2Y12 blockers are not effective in SCD therapy and warrant the need for further studies to understand the role of purinergic signaling in pathogenesis of ACS. DisclosuresSundd: Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; CSL Behring Inc: Research Funding; Bayer: Research Funding.

The NLRP3 Inflammasome in Platelets Is Upregulated in Sickle Cell Disease and Promotes Platelet Aggregation and In Vitro Thrombosis

Sickle cell disease (SCD) is a severe monogenic disorder characterized by chronic hemolysis and abnormal coagulation and inflammation. Activated platelets play a critical role at the interphase of thrombosis and inflammation in the disease context. Sensing of free heme, a degradation byproduct of hemoglobin oxidation during hemolysis, involves the pattern recognition receptor nucleotide-binding domain leucine rich repeat containing protein 3 (NLRP3), which typically forms multiprotein inflammasome complexes and controls caspase-1 activity and cleavage of IL-1β not only in immune cells but also platelets. We have shown recently that the NLRP3 inflammasome in platelets controls platelet activation, aggregation, and in vitro thrombus formation, which was dependent on platelet bruton's tyrosine kinase (BTK). The role of the platelet NLRP3 inflammasome and BTK in SCD, however, is unexplored.Platelets were isolated from humanized SCD mice (Townes), which express human sickle hemoglobin, and patients with SCD in steady state and acute vasoocclusive crisis. Platelet NLRP3 activity, as monitored by caspase 1 activation (assessed by fluorescent labeled inhibitor of caspase-1, FLICA), and cleavage and secretion of IL1β (assessed by Western blot and ELISA), was significantly elevated in SCD patients in steady state as compared to healthy subjects (FLICA: mean 340.3 ± 30.2 SD vs. mean 262.2 ± 33.9 SD, p<0.001), and further upregulated in SCD patients in crisis (FLICA: mean 390.3 ± 34.0 SD vs. mean 340.3 ± 30.2 SD, p<0.05). NLRP3 activity in platelets was also significantly increased in homozygous SCD mice, as compared to heterozygous and control mice (FLICA: mean 165.1 ± 32.4 SD vs. mean 86.7 ± 20.5 SD, p<0.001), which was significantly reversed by the heme scavenger hemopexin or pharmacological inhibition of the NLRP3 inflammasome/BTK pathway. Moreover, incubation of platelets with heme induced intraplatelet colocalization of NLRP3 and the adaptor protein apoptosis-associated speck-like protein containing a CARD (ASC), as evaluated with immunofluorescence staining coupled with confocal laser scanning microscopy, indicating the assembly of the NLRP3 inflammasome in platelets upon exposure to heme. We studied the functional effects of platelet NLRP3 inflammasome upregulation in SCD, and found that collagen-induced platelet aggregation was significantly elevated in homozygous SCD mice as compared to control animals (area under the curve, AUC: mean 65.25 ± 7.99 SD vs. mean 40.60 ± 7.92 SD, p<0.05). In SCD patients in acute crisis, aggregation of circulating platelets was significantly upregulated as compared to patients in steady state (AUC: mean 113.70 ± 16.26 SD vs. mean 78.53 ± 1.93 SD, p<0.05). Moreover, platelet aggregation in steady state patients was significantly elevated as compared to healthy subjects (AUC: 78.53 ± 1.93 SD vs. mean 30.87 ± 4.34 SD, p<0.01). The upregulated platelet aggregation responses in homozygous SCD mice and SCD patients in acute crisis were dependent on heme/NLRP3/BTK pathway, as evaluated by hemopexin (mice: 69.3 ± 5.7% inhibition; patients: 61.6 ± 5.2% inhibition), the NLRP3 inhibitor MCC950 (mice: 75.7 ± 3.9% inhibition; patients: 72.1 ± 3.8% inhibition), and the BTK inhibitor CGI1746 (mice: 65.9 ± 3.6% inhibition; patients: 67.1 ± 4.1% inhibition) (p<0.01). Similar results were obtained with a collagen-coated flow chamber system.Our data show that the platelet NLRP3 inflammasome is upregulated in SCD via heme, which results in elevated platelet aggregation and in vitro thombus formation, and is potentially targetable using BTK inhibitors for affected patients. DisclosuresNo relevant conflicts of interest to declare.

Neutrophil Extracellular Traps Promote Lung Arteriole Occlusion in Sickle Cell Disease

Introduction:Sickle cell disease (SCD) is an autosomal-recessive-genetic disorder, which leads to red blood cell sickling and hemolysis. Acute systemic painful vaso-occlusive crisis (VOC) is the predominant pathophysiology requiring emergency medical care by SCD patients. 10-20% of SCD patients hospitalized with VOC tend to develop acute chest syndrome (ACS), a type of lung injury within next few days, suggesting a role for pulmonary vaso-occlusion in ACS. The cellular, molecular and biophysical mechanism of pulmonary vaso-occlusion has just started to unfold and a profound understanding is needed for the development of rescue therapies to halt the progression of VOC to ACS. Our recent findings using quantitative fluorescence intravital lung microscopy (qFILM) revealed that lung vaso-occlusion is enabled by the entrapment of embolic neutrophil-platelet aggregates in the pulmonary arterioles of transgenic humanized SCD mice. Neutrophil extracellular traps (NETs) are web-like structures of decondensed nuclear DNA decorated with citrunilated-histones and neutrophil granule proteins. NETs are released by activated neutrophils under inflammatory conditions and are known to possess pro-inflammatory and pro-thrombotic properties. Recently, hemolysis driven release of cell free hemoglobin or hemin has been shown to promote NETs formation in the pulmonary microcirculation of SCD mice. Nevertheless, how these NETs can serve to facilitate pulmonary vaso-occlusion and promote ACS is still unclear.Materials and Methods:Townes knock-in humanized SS (hα/hα:βS/βS) and AS (hα/hα:βA/βS) mice were used as SCD and control mice, respectively. SS and AS mice were intravascularly (IV) challenged with Oxy-hemoglobin (Oxy-Hb) and hemin to model VOC. Fluorescently-conjugated anti-mouse CD49b and Ly6G mAbs, Sytox Orange, and FITC dextran were administered IV to visualize platelets, neutrophils, extracellular DNA and lung vasculature in the mouse, respectively. Lung microcirculation was visualized in real time in vivo using qFILM and analyzed as described elsewhere. Also, SCD or control human blood with or without treatment with Oxy-Hb or hemin was perfused through in vitro microfluidic microchannels presenting a combination of P-selectin, ICAM-1 and IL-8, and neutrophil-platelet interactions as well as NET formation was visualized using Quantitative Microfluidic Fluorescence Microscopy (qMFM). Fluorescent anti-human mAbs against CD49b, CD16, citrullinated histones (H3-Cit) and neutrophil elastase were added to human blood to visualize platelets, neutrophils, histones, and neutrophil elastase, respectively.Results and Discussion:Our initial findings using qFILMreveal that non-lethal dose of 20 µmole/kg IV hemin or 10 µmole/kg IV Oxy-Hb led to entrapment of neutrophil-platelet embolic aggregates in the lung arteriolar bottlenecks of SCD but not control mice. These aggregates resulted loss of blood perfusion in the lung, followed by shedding of NETs from neutrophils into the blood circulation.Conclusion: Erythroid DAMPs, hemin and Oxy-Hb promote occlusion of lung arterioles by neutrophil-platelet aggregates in SCD mice. These aggregates promote loss of blood flow and release of NETs from neutrophils in the lung arterioles. DisclosuresKato:Bayer: Research Funding; Global Blood Therapeutics: Consultancy; Novartis: Consultancy; MAST Therapeutics: Research Funding.

Chlorine inhalation induces acute chest syndrome in humanized sickle cell mouse model and ameliorated by postexposure hemopexin

Triggering factors of Acute Chest Syndrome (ACS) is a leading cause of death in patients with Sickle Cell Disease (SCD) and targeted therapies are limited. Chlorine (Cl2) inhalation happens frequently, but its role as a potential trigger of ACS has not been determined. In this study, we hypothesized that Cl2 exposure resembling that in the vicinity of industrial accidents induces acute hemolysis with acute lung injury, reminiscent of ACS in humanized SCD mice. When exposed to Cl2 (500 ppm for 30 min), 64% of SCD mice succumbed within 6 h while none of the control mice expressing normal human hemoglobin died (p<0.01). Surviving SCD mice had evidence of acute hemolysis, respiratory acidosis, acute lung injury, and high concentrations of chlorinated palmitic and stearic acids (p<0.05) in their plasmas and RBCs compared to controls. Treatment with a single intraperitoneal dose of human hemopexin 30 min after Cl2 inhalation reduced mortality to around 15% (p<0.01) with reduced hemolysis (decreased RBCs fragility (p<0.001) and returned plasma heme to normal levels (p<0.0001)), improved oxygenation (p<0.0001) and reduced acute lung injury scores (p<0.0001). RBCs from SCD mice had significant levels of carbonylation (which predisposes RBCs to hemolysis) 6 h post-Cl2 exposure which were absent in RBCs of mice treated with hemopexin. To understand the mechanisms leading to carbonylation, we incubated RBCs from SCD mice with chlorinated lipids and identified sickling and increased hemolysis compared to RBCs obtained from control mice and treated similarly. Our study indicates that Cl2 inhalation induces ACS in SCD mice via induction of acute hemolysis, and that post exposure administration of hemopexin reduces mortality and lung injury. Our data suggest that SCD patients are vulnerable in Cl2 exposure incidents and that hemopexin is a potential therapeutic agent.

Enhanced Vasoconstriction in Sickle Cell Disease is Mediated by ET A Receptor‐Dependent Induction of alpha 1A ‐Adrenergic Receptor Expression

Sickle cell disease (SCD) patients are at a significant risk for developing the potentially fatal vaso-occlusive crisis, which has been associated with stressful stimuli. We previously reported that SCD mice display enhanced alpha-1 adrenergic receptor mediated vasoconstriction along with increased alpha-1A receptor expression in the aorta. Also, we have demonstrated SCD mice have higher levels endothelin-1 (ET-1), a potent vasoconstrictor mediating actions via the ETA receptor as well as increased reactive oxygen species (ROS). The mechanisms underlying the enhanced vasoconstriction in SCD mice remains largely unknown. We hypothesized that the enhanced vasoconstrictor response to alpha-1 adrenergic receptor stimulation is meditated through an ET-1/ETA receptor and ROS axis. Male 16-week-old humanized SCD (HbSS) and genetic control (HbAA) mice were utilized for all experiments. Vascular reactivity of isolated thoracic aortic (100–150 μm diameter) rings to phenylephrine (PE) and potassium chloride (KCl) were examined using wire myography. Mice were pre-treated for two weeks with the specific ETA receptor antagonist, ambrisentan (AMB). Thoracic aortic rings were also pre-incubated with superoxide dismutase-polyethylene glycol (PEG-SOD) for 30 minutes ex vivo at 100 units/ml. HbSS mice treated with AMB demonstrated a significantly blunted maximum vasoconstrictive response to PE when compared to control HbSS mice (132.3 ± 3.69 vs. 113.5 ± 4.59 %KCl, p=0.003). HbSS mice treated with ex vivo PEG-SOD alone did not demonstrate a blunted maximum vasoconstrictive response to PE stimulation (132.3 ± 3.69 vs. 121.6 ± 5.36 %KCl, p>0.05). However, HbSS mice treated with a combination of AMB and ex vivo PEG-SOD demonstrated an overall significant decrease response to PE stimulation compared to HbSS control and HbSS treated with AMB alone (132.3 ± 3.69 vs. 113.5 ± 4.59 vs. 95.6 ± 11.3 %KCl, p=0.006, p=0.015, respectively). HbAA mice showed similar vasoconstrictive response across treatments (84.9 ± 5.38 vs. 78.2 ± 6.89 vs. 75.1 ± 9.92 %KCl, p>0.05). Graded concentration responses to KCl were similar between genotypes and pharmacologic treatment. To demonstrate the translational nature of this enhanced vasoconstriction response, flow mediated dilation was used in human subjects with SCD. A subset of the human subjects were treated with AMB or placebo for 3 months. SCD patients treated with AMB for 3 months did show a significant increase in baseline diameter compared to placebo (1.54 % vs -2.05 % change in diameter, p = 0.012). However, there was no increase in flow-mediated dilation supporting a role for the ET-1/ETA pathway and an enhanced vasoconstrictor response in SCD in humans. These findings suggest the enhancement of alpha-1 adrenergic mediated vasoconstriction is, in part, mediated through an ETA receptor dependent mechanism. These data suggest that reactive oxygen species contribute to this enhancement and may work synergistically with the ETA receptor pathway to produce the enhanced vasoconstrictive phenotype seen in SCD.