Neuregulin-1 Mitigates Kidney Injury in Humanized Sickle Cell Mice.

Occlusion of cerebral blood vessels causes acute cerebral hypoxia—an important trigger of ischemic white matter injury and stroke in sickle cell disease (SCD). While chronic hypoxia triggers compensatory neuroprotection via insulin-like growth factor-1 (IGF-1) and hypoxia inducible factor-1α (HIF-1α), severe bouts of acute hypoxia and subsequent restoration of blood flow (hypoxia/reoxygenation, H/R) overwhelm compensatory mechanisms and cause neuroaxonal damage–identified as white matter lesions–in the brain. The neuroprotective role of IGF-1 in the pathogenesis of white matter injury in SCD has not been investigated; however, it is known that systemic IGF-1 is reduced in individuals with SCD. We hypothesized that IGF-1 supplementation may prevent H/R-induced white matter injury in SCD. Transgenic sickle mice homozygous for human hemoglobin S and exposed to H/R developed white matter injury identified by elevated expression of non-phosphorylated neurofilament H (SMI32) with a concomitant decrease in myelin basic protein (MBP) resulting in an increased SMI32/MBP ratio. H/R-challenge also lowered plasma and brain IGF-1 expression. Human recombinant IGF-1 prophylaxis significantly induced HIF-1α and averted H/R-induced white matter injury in the sickle mice compared to vehicle-treated mice. The expression of the IGF-1 binding proteins IGFBP-1 and IGFBP-3 was elevated in the IGF-1-treated brain tissue indicating their potential role in mediating neuroprotective HIF-1α signaling. This study provides proof-of-concept for IGF-1-mediated neuroprotection in SCD.

Anomalous Renal Effects of Tin Protoporphyrin in a Murine Model of Sickle Cell Disease

Sickle cell disease (SCD) is the most common inherited monogenetic disorder. Chronic and acute pain are hallmark features of SCD involving neural and vascular injury and inflammation. Mast cells reside in the vicinity of nerve fibers and vasculature, but how they influence these structures remains unknown. We therefore examined the mechanism of mast cell activation in a sickle microenvironment replete with cell-free heme and inflammation. Mast cells exposed to this environment showed an explosion of nuclear contents with the release of citrullinated histones, suggestive of mast cell extracellular trap (MCET) release. MCETs interacted directly with the vasculature and nerve fibers, a cause of vascular and neural injury in sickle cell mice. MCET formation was dependent upon peptidylarginine deiminase 4 (PAD4). Inhibition of PAD4 ameliorated vasoocclusion, chronic and acute hyperalgesia, and inflammation in sickle mice. PAD4 activation may also underlie neutrophil trap formation in SCD, thus providing a novel target to treat the sequelae of vascular and neural injury in SCD.

To determine if glial fibrillary acidic protein (GFAP) is associated with brain injury in children with sickle cell disease (SCD), we measured plasma GFAP among cross-sectional groups of unselected children with SCD, subsets of children with SCD and normal brain MRI or MRI evidence of cerebral infarct, healthy pediatric controls, and adults with brain injury. Children with SCD had higher plasma GFAP than healthy pediatric controls (mean concentrations 0.14 ± 0.37 vs. 0.07 ± 0.08 ng/mL; P 5 0.003); also, 16.0% (16/100) of children with SCD and cerebral infarct had GFAP elevations above the 95th percentile of healthy pediatric controls (P 5 0.04). Although not statistically significant, children with SCD and cerebral infarct had more elevated GFAP levels than with SCD and no infarct (16/100, 16.0% vs. 14/168, 8.3%; P 5 0.07). Children with SCD and acute brain ischemia had a higher proportion of elevated GFAP than SCD children with normal MRI (3/6, 50% vs.8.3%; P 5 0.01). GFAP was associated with elevated systolic blood pressure in the preceding year and correlated positively with white blood cell count and negatively with age and performance IQ. Plasma GFAP is elevated among children with SCD and may be associated with subclinical brain injury.

Anti-Inflammatory Effects of Hydroxyurea in a Murine Model of Chronic Intravascular Hemolysis

Sickle cell disease (SCD) is a monogenic disorder that affects 100,000 African-Americans and millions of people worldwide. Intra-erythrocytic polymerization of sickle hemoglobin (HbS) promotes erythrocyte sickling, impaired rheology, ischemia and hemolysis, leading to the development of progressive liver injury in SCD. Liver-resident macrophages and monocytes are known to enable the clearance of HbS; however, the role of liver sinusoidal endothelial cells (LSEC) in HbS clearance and liver injury in SCD remains unknown. Using real-time intravital (in vivo) imaging in mice liver as well as flow cytometric analysis and confocal imaging of primary human LSEC, we show for the first time that liver injury in SCD is associated with accumulation of HbS and iron in the LSEC, leading to senescence of these cells. Hemoglobin uptake by LSEC was mediated by micropinocytosis. Hepatic monocytes were observed to attenuate LSEC senescence by accelerating HbS clearance in the liver of SCD mice; however, this protection was impaired in P-selectin-deficient SCD mice secondary to reduced monocyte recruitment in the liver. These findings are the first to suggest that LSEC contribute to HbS clearance and HbS-induced LSEC senescence promotes progressive liver injury in SCD mice. Our results provide a novel insight into the pathogenesis of hemolysis-induced chronic liver injury in SCD caused by LSEC senescence. Identifying the regulators of LSEC-mediated HbS clearance may lead to new therapies to prevent the progression of liver injury in SCD.

DNA Sensing By Platelets Promotes Acute Chest Syndrome in Sickle Cell Disease

Clearance of Sickle Hemoglobin By Hepatic Endothelial Cells Is Critical to Protect Against Hemolysis Induced Organ Damage in Sickle Cell Anemia

Renal dysfunction affects 5-18% of patients with sickle cell disease (SCD). To date, no studies have described urinary levels of transforming growth factor β-1 (TGF-β1), a marker of fibrosis, and neutrophil gelatinase-associated lipocalin (NGAL), a marker of acute/chronic kidney disease, as biomarkers in identifying patients at risk of developing renal disease in SCD. We hypothesized that SCD subjects will have increased urinary excretion of TGF-β1 and NGAL compared with healthy controls (CTR). We examined 51 SCD subjects: 42 HbSS, 8 HbSC, and 1 HbSD. Sixteen out of 42 patients with HbSS were on hydroxyurea (HU). Urinary excretion of TGF-β1 was 26.4 ± 1.5 pg/mgCr in SCD subjects vs 15.0 ± 2.4 pg/mgCr in CTR (p<0.00001). SCD patients with hemoglobin < 9 g/dl had higher urinary TGF-β1 than patients with milder anemia (p=0.002). Urinary TGF-β1 trended lower in HbSS patients treated with HU (23.61 ± 2.6 pg/mgCr), vs patients not on HU (27.69 ± 1.8 pg/mgCr; p=0.055). There was no correlation between urinary TGF-β1 and microalbuminuria or estimated glomerular function. There was no difference in urinary NGAL in SCD patients vs CTR. We suggest that urinary TGF-β1 may serve as a marker of early renal injury in SCD.

Neutrophil-TLR9 is a therapeutic target for acute chest syndrome in sickle cell disease

Platelet TLR9 Promotes Pulmonary Thrombo-Inflammation in Sickle Cell Disease

Presentation Date: 6/8/2024 Presentation Start Time: 6:00 PM Background Sickle cell disease (SCD) is a monogenic disorder that affects 100,000 African Americans and millions of people worldwide. Intra-erythrocytic polymerization of sickle hemoglobin (HbS) promotes erythrocyte sickling, impaired rheology, ischemia and hemolysis, leading to the development of progressive organ injury in SCD. Liver resident Kupffer cells and monocytes are known to enable the clearance of HbS, however, the role of liver sinusoidal endothelial cells (LSECs) in HbS clearance and liver injury in SCD remains unknown. Methods We used real-time intravital imaging, flow cytometry analysis, and confocal imaging of human and mouse primary endothelial cells to investigate their potential function in hemoglobin clearance. Results We show for the first time that LSECs are capable of HbS clearance. Hb uptake by LSECs was mediated by micropinocytosis. We show that accumulation of HbS in LSECs promotes endothelial senescence. Hepatic monocytes were observed to attenuate LSEC senescence by accelerating HbS clearance in the liver of SCD mice, however, this protection was impaired in P-selectin-deficient SCD mice secondary to reduced monocyte recruitment in the liver. Conclusions These findings are the first to suggest that LSECs contribute to HbS clearance and HbS induced LSEC-senescence promotes progressive liver injury in SCD mice. Our results provide a novel insight into the pathogenesis of hemolysis induced chronic liver injury in SCD caused by LSEC senescence. Identifying the regulators of LSEC mediated HbS clearance may lead to new therapies to prevent the progression of liver injury in SCD.

Non-Invasive Urinary Markers of Renal Dysfunction in Sickle Cell Disease.

Inhibition of Factor XII Attenuates Prothrombotic Complications in Sickle Cell Mice

Sickle Cell Disease Promotes Dysregulation of Hepatic Iron Homeostasis By Regulating Hepcidin Expression