AbstractAngiotensin-converting Enzyme 2 Research Articles

An ACE2, SARS-CoV-2 spike protein binding protein, -like enzyme isolated from food-related microorganisms.

Angiotensin-converting enzyme 2 (ACE2) is a binding target of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein. An ACE2-like enzyme, such as bacterial M32-carboxypeptidase (M32-CAP), is assumed to be a potential therapeutic candidate for coronavirus disease 2019 (COVID-19). Here, we screened bacteria with an ACE2-like enzyme activity from Japanese fermented food and dietary products using the fluorogenic substrate for rapid screening. The strain showing the highest activity, Enterobacter sp. 200527-13, produced an enzyme with the same hydrolytic activity as ACE2 on Angiotensin II (Ang II). The enzymatic analysis using the heterologously-expressed enzyme in Escherichia coli revealed that the enzyme catalyzes the same reaction with that of ACE2, Ang II hydrolysis to Ang 1-7, and phenylalanine. The gene sequence information showed that the enzyme belongs to the M32-CAP family. These results suggested that the selected enzyme, M32-CAP (EntCP), from Enterobacter sp. 200527-13 was identified as an ACE2-like enzyme.

Circulating Monocytes Co-expressing Surface ACE2 and TMPRSS2 upon TLR4/7/8 Activation Are Susceptible to SARS-CoV-2 Infection

Abstract Angiotensin-converting enzyme 2 (ACE2) receptor is required for SARS-CoV-2 entry into human cells. However, emerging evidence shows SARS-CoV-2 infected lung monocytes/macrophages from COVID-19 patients barely express ACE2 mRNA, raising a question how SARS-CoV-2 penetrates macrophages. It’s also under debating whether the peripheral blood cells (HPBCs) can be infected by SARS-CoV-2 that may facilitate viral spread from circulation to other organs besides lung. Herein we demonstrate that resting primary HPBCs harbor abundant cytoplasmic ACE2, regardless of COVID-19 status, and that surface translocation is necessary for viral infection. Upon ex vivo TLR4/7/8 stimulation of HPBCs, ACE2 translocated to the cell surface independent of ACE2 transcription, and this translocation was blocked by an endosomal trafficking inhibitor, suggesting the putative source as ACE2-containing exosomes. However, only stimulated monocytes concurrently expressing ACE2 and cell surface transmembrane serine protease type 2 (TMPRSS2) were efficiently infected by SARS-CoV-2, which was significantly mitigated by remdesivir. Furthermore, ACE2 surface translocation in peripheral myeloid cells from patients with severe COVID-19 correlated with their proinflammatory cytokine production. Collectively, TLR4/7/8-induced ACE2 translocation with TMPRSS2 expression is indispensable for SARS-CoV-2 infection of circulating monocytes. Our work not only provides a new mechanism for the pathogenesis of SARS-CoV-2 and a potential path for its systemic infection, but also unveils a prospective therapeutic strategy by targeting ACE2 trafficking for preventing monocyte/macrophage infection. This study is partially supported by National Institutes of Health grants R61AR076803, R01AR063611, R01AI119041, and R01AR069681 (Q-S. M.), R01AR072046 (L.Z.), R01DK120623 (J.Z.S.), Henry Ford Immunology Program grants (T71016, Q-S. M.; T71017, L. Z.), and funding for the U-M Center for Drug Repurposing - NCATS CTSA UL1TR002240 (J.Z.S.).

ADAM-17 protease promotes inflammation and mortality while decreasing viral burden in a COVID-19 mouse model

Abstract Angiotensin Converting Enzyme 2 (ACE2) is the primary cell entry receptor for SARS-CoV-1 and SARS-CoV-2 viruses. A disintegrin and metalloproteinase 17 (ADAM-17) is a protease located in the cell membrane of most cells that, upon cellular activation, cleaves ectodomains of transmembrane proteins, including that of ACE2, from cell surfaces. We hypothesized that blockade of ADAM-17 activity would alter COVID-19 pathogenesis. To assess this pathway, we blocked the function of ADAM-17 using a monoclonal antibody in the K18 human ACE2 Tg mouse model of COVID-19. Antibody-treated mice were healthier, less moribund, and had significantly less lung inflammation than saline treated mice. However, the viral burden in the lungs of anti-ADAM17 Ab-treated mice was significantly greater. ADAM17 also cleaves TNF-a and its blockade decreased lung TNF-a production induced by intratracheal LPS delivery. We are currently testing this possibility in the COVID-19 mouse model. Thus, ADAM-17 appears to have a critical anti-viral role, but also promotes damaging inflammation following SARS-CoV-2 infection. Since the inflammatory cascade is ultimately the reason for the adverse outcomes in COVID-19 patients, there may be a therapeutic application for the anti-ADAM-17 antibody.

Well-differentiated liver cancers reveal the potential link between ACE2 dysfunction and metabolic breakdown

Angiotensin-converting enzyme 2 (ACE2) is the receptor of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) causing Coronavirus disease 2019 (COVID-19). Transmembrane serine protease 2 (TMPRSS2) is a coreceptor. Abnormal hepatic function in COVID-19 suggests specific or bystander liver disease. Because liver cancer cells express the ACE2 viral receptor, they are widely used as models of SARS-CoV-2 infection in vitro. Therefore, the purpose of this study was to analyze ACE2 and TMPRSS2 expression and localization in human liver cancers and in non-tumor livers. We studied ACE2 and TMPRSS2 in transcriptomic datasets totaling 1503 liver cancers, followed by high-resolution confocal multiplex immunohistochemistry and quantitative image analysis of a 41-HCC tissue microarray. In cancers, we detected ACE2 and TMPRSS2 at the biliary pole of tumor hepatocytes. In whole mount sections of five normal liver samples, we identified ACE2 in hepatocyte’s bile canaliculi, biliary epithelium, sinusoidal and capillary endothelial cells. Tumors carrying mutated β-catenin showed ACE2 DNA hypomethylation and higher mRNA and protein expression, consistently with predicted β-catenin response sites in the ACE2 promoter. Finally, ACE2 and TMPRSS2 co-expression networks highlighted hepatocyte-specific functions, oxidative stress and inflammation, suggesting a link between inflammation, ACE2 dysfunction and metabolic breakdown.

The Effects of ATIR Blocker on the Severity of COVID-19 in Hypertensive Inpatients and Virulence of SARS-CoV-2 in Hypertensive hACE2 Transgenic Mice

Angiotensin-converting enzyme 2 (ACE2) is required for the cellular entry of the severe acute respiratory syndrome coronavirus 2. ACE2, via the Ang-(1-7)-Mas-R axis, is part of the antihypertensive and cardioprotective effects of the renin-angiotensin system. We studied hospitalized COVID-19 patients with hypertension and hypertensive human(h) ACE2 transgenic mice to determine the outcome of COVID-19 with or without AT1 receptor (AT1R) blocker treatment. The severity of the illness and the levels of serum cardiac biomarkers (CK, CK-BM, cTnI), as well as the inflammation markers (IL-1, IL-6, CRP), were lesser in hypertensive COVID-19 patients treated with AT1R blockers than those treated with other antihypertensive drugs. Hypertensive hACE2 transgenic mice, pretreated with AT1R blocker, had increased ACE2 expression and SARS-CoV-2 in the kidney and heart, 1 day post-infection. We conclude that those hypertensive patients treated with AT1R blocker may be at higher risk for SARS-CoV-2 infection. However, AT1R blockers had no effect on the severity of the illness but instead may have protected COVID-19 patients from heart injury, via the ACE2-angiotensin1-7-Mas receptor axis.

COMPARATIVE ANALYSIS OF HUMAN AND LIVESTOCK АСЕ2 RECEPTORS FOR SARS-COV-2

Angiotensin-converting enzyme 2 (ACE2) is a receptor for SARS-CoV-2 spike protein on the cell surface and plays a key role in the development of COVID-19. The high conservatism of ACE2 structure in different species and the large number of human contacts with livestock increase the risk of spreading SARS-CoV-2 among the ones if the virus will be able to penetrate and replicate in the cells of such animals successfully. The result of this course of events may be the emergence of the animal reservoirs of coronavirus disease.
 To assess this possibility, a comparative analysis of the amino acid sequences of ACE2 receptors for SARS-CoV-2 in different species of livestock with human ACE2 was performed. High degrees of identity and similarity were found for ACE2 receptors of donkey, horse, rabbit, alpaca, lama, dromedary, pig, sheep, goat and cattle (taurine and zebu), lower – for poultry species (chicken, duck and turkey). The data obtained in this study are consistent with the results of previous experiments on the ability of SARS-CoV-2 to interact with ACE2 receptors of different animal species. Although there is evidence of pig, chicken and duck resistance to SARS-CoV-2 by intranasal inoculation, the risk of the virus adaptation to livestock infecting, given the mutational variability of the virus, remains high, which makes relevant the further studies of SARS-CoV-2 interactions with livestock.

Correlation of ACE2 with RAS components after Losartan treatment in light of COVID-19

Angiotensin-converting enzyme 2 (ACE2) is an important factor in coronavirus disease (COVID-19) interactions. Losartan (LOS) belongs to the angiotensin receptor blocker (ARB) family. Additionally, the protective role of ACE2 restored by LOS has been suggested and clinically examined in the treatment of COVID-19 patients. Furthermore, clinical trials with LOS have been conducted. However, the mechanism through which LOS enhances ACE2 expression remains unclear. In addition, the response of ACE2 to LOS differs among patients. Our LOS-treated patient data revealed a correlated mechanism of ACE2 with components of the renin-angiotensinogen system. We observed a significant positive regulation of MAS1 and ACE2 expression. In the context of LOS treatment of COVID-19, ACE2 expression could depend on LOS regulated MAS1. Thus, MAS1 expression could predict the COVID-19 treatment response of LOS.

Abstract MP62: Sars-cov-2 Spike Protein Regulation Of Angiotensin Converting Enzyme 2 And Tissue Renin-angiotensin Systems: Influence Of Biologic Sex

Angiotensin converting enzyme 2 (ACE2), the SARS-CoV-2 receptor and an enzyme of the renin-angiotensin system (RAS), is on the X chromosome and stimulated by estrogen. Male sex is a risk factor for SARS-CoV-2 severity. Previous investigators demonstrated that the SARs-CoV-2 Spike (S) protein decreases tissue ACE2 by protein internalization or shedding. This study defined sex differences in tissue ACE2 expression and their impact on SARS-CoV-2 S protein regulation of ACE2 activity and AngII levels. Male and female intact or gonadectomized (GDX) low density lipoprotein receptor deficient ( Ldlr -/- ) mice, and Four Core Genotype (FCG) male (XY or XX) or female (XX or XY) mice were fed a Western diet for 4 months. In lung, ACE2 mRNA abundance was similar in male and female mice and reduced by GDX (Male XY intact: 1.04 ± 0.15; Female XX intact: 1.13 ± 0.13; Male XY GDX: 0.11 ± 0.03; Female XX GDX: 0.18 ± 0.04 ΔΔCt; P<0.05). Lungs from XX mice had higher ACE2 mRNA abundance than XY mice regardless of gonadal sex (P<0.05), and GDX reduced ACE2 mRNA abundance in lungs of XX, but not XY females (XX Female GDX: 0.18 ± 0.04; XY Female GDX: 0.38 ± 0.09; P<0.05). In adipose, XX females had higher ACE2 mRNA abundance than XY males (XX female: 5.4 ± 0.7; XY male: 1.0 ± 0.1; P<0.05), regardless of gonadal sex (XY females: 3.3 ± 0.7; XX males: 1.5 ± 0.3; P<0.05). Male XY and female XX Ldlr -/- mice were administered vehicle or SARS-CoV-2 S protein (2 nmol/kg, ip, 3 doses) with tissue harvest six hours later. In lung, AngII levels were increased by S protein in male, but not female mice (Male, vehicle: 12.3 ± 2.3; Male, S protein: 33.6 ± 7.1; Female, vehicle: 16.1 ± 2.0; Female, S protein: 20.2 ± 1.3 pg/μg protein; P<0.05). In adipose, ACE2 activity was reduced by S protein in male, but not female mice (Male, vehicle: 63.6 ± 13.9; Male, S protein: 26.1 ± 1.9; Female, vehicle: 32.5 ± 1.9; Female, S protein: 25.1 ± 1.3 RFU/hr/mg tissue; P<0.05). SARS-CoV-2 S protein (35 nM) decreased ACE2 activity in type II lung alveolar cells (Vehicle: 2.0 x 10 4 ; S protein: 1.2 x 10 4 RFU/10 6 cells) and 3T3-L1 adipocytes (Vehicle: 2.1 x 10 4 ± 0.3 x 10 4 ; S protein: 1.1 x 10 4 ± 0.8 x 10 3 RFU/10 5 cells; P<0.05). Biologic sex regulation of ACE2 may protect females from SARS-CoV-2 S protein-mediated ACE2 reductions and activation of the local RAS.

Mapping the effect of drugs on ACE2 as a novel target site for COVID-19 therapy.

Angiotensin converting enzyme 2 (ACE2) has potentially conflicting roles in health and disease. COVID-19 coronavirus binds to human cells via ACE2 receptor, which is expressed on almost all body organs. Boosting the ACE2 receptor levels on heart and lung cells may provide more cellular enter to virus thereby worsening the infection. Therefore, among the drug targets, ACE2 is suggested as a vital target of COVID-19 therapy. This hypothesis is based on the protective role of the drugs acting on ACE2. Therefore, this review discusses the impact and challenges of using ACE2 as a target in the current therapy of COVID-19.

Angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers: potential allies in the COVID-19 pandemic instead of a threat?

Angiotensin-converting enzyme 2 (ACE2) is the leading player of the protective renin–angiotensin system (RAS) pathway but also the entry receptor for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). RAS inhibitors seemed to interfere with the ACE2 receptor, and their safety was addressed in COVID-19 patients. Pedrosa et al. (Clin. Sci. (Lond.) (2021), 135, 465–481) showed in rats that captopril and candesartan up-regulated ACE2 expression and the protective RAS pathway in lung tissue. In culture of pneumocytes, the captopril/candesartan-induced ACE2 up-regulation was associated with inhibition of ADAM17 activity, counterbalancing increased ACE2 expression, which was associated with reduced SARS-CoV-2 spike protein entry. If confirmed in humans, these results could become the pathophysiological background for justifying RAS inhibitors as cornerstone cardiovascular protectives even during COVID-19 pandemic.

More About Effects of Renin–Angiotensin System Inhibitors in Patients with COVID-19

Angiotensin-converting enzyme 2 (ACE2) is a receptor for SARS-CoV-2 and facilitates viral entry into host cells. Some clinicians and researchers have

Unraveling the Role of ACE2, the Binding Receptor for SARS-CoV-2, in Inflammatory Bowel Disease.

Angiotensin-converting enzyme 2 (ACE2) has been highlighted for its role as a receptor for SARS-CoV-2, responsible for the current COVID-19 pandemic. This review summarizes current knowledge about ACE2 as a multifunctional protein, focusing on its relevance in inflammatory bowel disease (IBD). As an enzyme, ACE2 may be protective in IBD because it favors the counter-regulatory arm of the renin-angiotensin system or deleterious because it metabolizes other anti-inflammatory/repairing elements. Meanwhile, as a receptor for SARS-CoV-2, the impact of ACE2 expression/activity on infection is still under debate because no direct evidence has been reported and, again, both protective and deleterious pathways are possible. Research has shown that ACE2 regulates the expression of the neutral amino acid transporter B0AT1, controlling tryptophan-associated intestinal inflammation and nutritional status. Finally, intact membrane-bound or shed soluble ACE2 can also trigger integrin signaling, modulating the response to anti-integrin biologic drugs used to treat IBD (such as vedolizumab) and fibrosis, a long-term complication of IBD. As such, future studies on ACE2 expression/activity in IBD can improve monitoring of the disease and explore an alternative pharmacological target.

Physiological cyclic stretch up-regulates angiotensin-converting enzyme 2 expression to reduce proliferation and migration of vascular smooth muscle cells.

Angiotensin-converting enzyme 2 (ACE2) is considered as an endogenous negative regulator of renin–angiotensin system (RAS), exerting multiple cardiovascular protective roles. Whether mechanical stretch modulates ACE2 expression remains unknown. The present study aimed at investigating whether ACE2 is involved in physiological stretch (10% elongation, 1 Hz) mediated cellular functions and the underlying mechanism. Cultured human aortic smooth muscle cells (HASMCs) were exposed to 10% stretch for indicated time, and real-time PCR and Western blot analysis showed 10% stretch increased ACE2 expression and activity significantly compared with static conditions and increased Ang-(1-7) level, but decreased Ang II level; Brdu incorporation assay and Scratch test showed that ACE2 was involved in the inhibition of HASMCs proliferation and migration by 10% stretch; the Dual-Luciferase Reporter Assay demonstrated that 10% increased ACE2 promoter activity, but had no effect on ACE2 mRNA stability; kinase inhibition study and Electrophoretic mobility shift assay (EMSA) showed that JNK1/2 and PKCβII pathway, as well as their downstream transcription factors, AP-1 and NF-κB, were involved in 10% stretch induced ACE2 expression. In conclusion, our study indicates ACE2 is a mechanosensitive gene, and may represent a potential therapeutic target for mechanical forces related vascular diseases.

Angiotensin-Converting Enzyme Inhibitor / Angiotensin II Receptor Blocker in COVID-19: a Double-edged Sword or a Myth

Angiotensin-converting enzyme-2 receptor has been unearthed as a prime site of entry of Severe Acute Respiratory Syndrome Coronavirus 2 owing to its strong affinity towards spike protein of Severe Acute Respiratory Syndrome Coronavirus 2, resulting in down-regulation of Angiotensin-converting enzyme -2 receptors and hyperstimulation of Angiotensin-converting enzyme-1 pathway. This proposed theory has led to the birth of a new controversy regarding the use of Angiotensin-converting enzyme inhibitors/angiotensin receptor blockers in Coronavirus disease 2019 patients. A theory is against the use of Angiotensin-converting enzyme inhibitors/angiotensin receptor blockers, as it enhances the effect of Angiotensin-converting enzyme -2 pathway and upregulation of Angiotensin-converting enzyme -2 receptors resulting in a large number of internalizations of Severe Acute Respiratory Syndrome Coronavirus -2 into cells culminating into a high load of viremia with overwhelming infection and severity. The other theory considers Angiotensin-converting enzyme inhibitors / Angiotensin receptor blockers useful as it blocks deleterious Angiotensin-converting enzyme -1 pathway triggered by Severe Acute Respiratory Syndrome Coronavirus 2 and enhances Angiotensin-converting enzyme -2 receptor upregulation and activation of angiotensin-(1-7) leading to beneficial effects, i.e vasodilation, anti-apoptosis, anti-proliferative, & antifibrosis. Hence, Angiotensin-converting enzyme inhibitors/angiotensin receptor blockers may prove beneficial in countering the Angiotensin-converting enzyme -1 mediated damage by Severe Acute Respiratory Syndrome Coronavirus 2. The recommendations by (European & American) societal guidelines still hold good of not discontinuing Angiotensin-converting enzyme inhibitors/angiotensin receptor blockers in COVID-19 patients as it is further supported by current evidence of large observational studies.

More Than Pneumonia, The Potential Occurrence of Multiple Organ Failure in 2019 Novel Coronavirus Infection

Angiotensin converting enzyme 2 (ACE2) in the lung has been recognized as the key receptor of the 2019 novel coronavirus (2019-nCoV) as people may get infected

A Dynamic Variation of Pulmonary ACE2 Is Required to Modulate Neutrophilic Inflammation in Response to Pseudomonas aeruginosa Lung Infection in Mice.

Angiotensin-converting enzyme 2 (ACE2) is a potent negative regulator capable of restraining overactivation of the renin-angiotensin system, which contributes to exuberant inflammation after bacterial infection. However, the mechanism through which ACE2 modulates this inflammatory response is not well understood. Accumulating evidence indicates that infectious insults perturb ACE2 activity, allowing for uncontrolled inflammation. In the current study, we demonstrate that pulmonary ACE2 levels are dynamically varied during bacterial lung infection, and the fluctuation is critical in determining the severity of bacterial pneumonia. Specifically, we found that a pre-existing and persistent deficiency of active ACE2 led to excessive neutrophil accumulation in mouse lungs subjected to bacterial infection, resulting in a hyperinflammatory response and lung damage. In contrast, pre-existing and persistent increased ACE2 activity reduces neutrophil infiltration and compromises host defense, leading to overwhelming bacterial infection. Further, we found that the interruption of pulmonary ACE2 restitution in the model of bacterial lung infection delays the recovery process from neutrophilic lung inflammation. We observed the beneficial effects of recombinant ACE2 when administered to bacterially infected mouse lungs following an initial inflammatory response. In seeking to elucidate the mechanisms involved, we discovered that ACE2 inhibits neutrophil infiltration and lung inflammation by limiting IL-17 signaling by reducing the activity of the STAT3 pathway. The results suggest that the alteration of active ACE2 is not only a consequence of bacterial lung infection but also a critical component of host defense through modulation of the innate immune response to bacterial lung infection by regulating neutrophil influx.

Loss of Angiotensin-Converting Enzyme 2 Exacerbates Diabetic Retinopathy by Promoting Bone Marrow Dysfunction.

Angiotensin-converting enzyme 2 (ACE2) is the primary enzyme of the vasoprotective axis of the renin angiotensin system (RAS). We tested the hypothesis that loss of ACE2 would exacerbate diabetic retinopathy by promoting bone marrow dysfunction. ACE2-/y were crossed with Akita mice, a model of type 1 diabetes. When comparing the bone marrow of the ACE2-/y -Akita mice to that of Akita mice, we observed a reduction of both short-term and long-term repopulating hematopoietic stem cells, a shift of hematopoiesis toward myelopoiesis, and an impairment of lineage- c-kit+ hematopoietic stem/progenitor cell (HS/PC) migration and proliferation. Migratory and proliferative dysfunction of these cells was corrected by exposure to angiotensin-1-7 (Ang-1-7), the protective peptide generated by ACE2. Over the duration of diabetes examined, ACE2 deficiency led to progressive reduction in electrical responses assessed by electroretinography and to increases in neural infarcts observed by fundus photography. Compared with Akita mice, ACE2-/y -Akita at 9-months of diabetes showed an increased number of acellular capillaries indicative of more severe diabetic retinopathy. In diabetic and control human subjects, CD34+ cells, a key bone marrow HS/PC population, were assessed for changes in mRNA levels for MAS, the receptor for Ang-1-7. Levels were highest in CD34+ cells from diabetics without retinopathy. Higher serum Ang-1-7 levels predicted protection from development of retinopathy in diabetics. Treatment with Ang-1-7 or alamandine restored the impaired migration function of CD34+ cells from subjects with retinopathy. These data support that activation of the protective RAS within HS/PCs may represents a therapeutic strategy for prevention of diabetic retinopathy. Stem Cells 2018;36:1430-1440.

Abstract 513: ACE2-EPCs Protect Ecs Majorly Through Their Exosomal Effects on Mitochondria

Angiotensin-converting enzyme 2 (ACE2) is an emerging cardiovascular protective target which mediates the metabolism of angiotensin (Ang) II into Ang (1-7). Our group has demonstrated that ACE2 overexpression enhances the therapeutic efficacy of endothelial progenitor cells (EPCs) for ischemic stroke. Here, we investigated whether ACE2-primed EPCs (ACE2-EPCs) can protect cerebral microvascular endothelial cells (ECs) against injury and dysfunction in an in vitro model, with focusing on their exosomal and cytokine paracrine effects on endothelial mitochondria. Human EPCs were transfected with lentivirus containing null or human ACE2 cDNA (denoted as Null-EPCs, ACE2-EPCs, respectively). Their conditioned culture media, w/wo ultra-centrifugation for depletion of exosomes (ACE2-EPC-CM EX- , Null-EPC-CM EX- , ACE2-EPC-CM and Null-EPC-CM), were used for co-culture experiments. ECs injury and dysfunction model was induced by Ang II (10 -7 M) for 8 hrs before 16 hr co-culture. After that, ECs were collected for analyses of apoptosis, angiogenic ability, mitochondrion functions (ROS production, membrane potential, fragmentation), and gene expressions (ACE2, Nox2 and Nox4). The co-culture medium was collected for measuring the levels of ACE2, Ang II / Ang-(1-7) and growth factors (VEGF and IGF). Our results showed that: 1) ACE2-EPC-CM had higher levels of ACE2, Ang (1-7), VEGF and IGF than that of Null-EPC-CM. 2) Ang II-injured ECs displayed increase of apoptotic rate and reduction in tube formation and migration abilities, which were associated with ACE2 downregulation, Ang II / Ang (1-7) imbalance, Nox2/Nox4 upregulation, ROS overproduction, increase of mitochondrion fragmentation and decrease of membrane potential. 3) ACE2-EPC-CM had better protective effects than Null-EPC-CM on Ang II-injured ECs, which were associated with the improvements on ACE2 expression, Ang II / Ang (1-7) balance and mitochondrial functions. 4) ACE2-EPC-CM EX- and Null-EPC-CM EX- had remarkably reduced effects by over 70% as respectively compared to ACE2-EPCs-CM and Null-EPCs-CM. In conclusion, our data demonstrate that ACE2 overexpression can enhance the protective effects of EPCs on ECs injury, majorly through the exosomal effects on mitochondrial function.

Abstract 010: Renal Proximal Tubule-derived Angiotensin Converting Enzyme 2 (ACE2) in Blood Pressure Regulation

Angiotensin Converting Enzyme 2 (ACE2) is a carboxypeptidase that metabolizes angiotensin II (AngII) to Ang1-7, playing a critical role in blood pressure (BP) regulation. Previous studies from our lab demonstrated that loss of ACE2 resulted in enhanced susceptibility to AngII hypertension and this was associated with elevated renal AngII levels. ACE2 is highly expressed in kidney, particularly in proximal tubule epithelia, and kidney cross-transplant experiments performed by our group revealed a novel mechanism by which ACE2 may be functioning to regulate BP. However, the exact cellular sources and sites of action where ACE2 regulates BP remain unclear. The objective of this study is to assess proximal tubule-derived ACE2 in BP regulation by studying a new mouse model generated in our laboratory: proximal tubule-specific ACE2 knock-out mice (referred to as ACE2 PTKO mice). ACE2 PTKO mice were generated by crossing the Ace2 -flox/flox conditional mouse line with the phosphoenolpyruvate carboxykinase (PEPCK)-Cre mouse (V. Haase, Vanderbilt). ACE2 PTKO mice and their littermate control mice were inbred 129/SvEv, co-caged, and only males were studied. ACE2 PTKO mice exhibited reduced ACE2 mRNA and protein in renal cortex compared to controls ( Ace2 mRNA relative expression: 0.47 ± 0.1 vs. 1.08 ± 0.1, N=3 vs 3, P <0.05; relative ACE2 protein expression: 0.38 ± 0.04 vs. 1.15 ± 0.12, N=3 vs 3, P <0.01). Measured with radiotelemetry, there were no differences in BPs between ACE2 PTKO mice and control mice (119 ± 1 vs 117 ± 2 mmHg, N=16 vs 16, p=NS) at baseline. However, ACE2 PTKO mice exhibited an enhanced hypertensive response during the first week of AngII infusion compared to control mice (139.9 ± 4.8 vs 152.8 ± 3.7 mmHg at day 7, N=16 vs 16, P =0.038). Furthermore, the ACE2 KO kidneys accumulated significantly higher renal AngII than control kidneys, measured at day4 (897±104 vs 536±115 fmol/g, P <0.05). Our data demonstrate that proximal tubule-derived ACE2 plays a critical role in BP regulation during AngII infusion. The enhanced hypertensive response in ACE2KO mice is consistent with their intra-renal AngII levels, suggesting that that proximal tubule-derived ACE2 regulates BP via metabolizing AngII within the kidney.

Determining the Enzymatic Activity of Angiotensin-Converting Enzyme 2 (ACE2) in Brain Tissue and Cerebrospinal Fluid Using a Quenched Fluorescent Substrate.

Angiotensin-converting enzyme 2 (ACE2) is a component of the renin-angiotensin system (RAS) which plays an important role in the regulation of blood pressure and volume homeostasis. Accumulating evidence shows alterations in ACE2 expression and activity in several hypertensive animal models, as well as in patients with hypertension. In order to assess the role of brain ACE2 in hypertension, a specific ACE2 assay is required. Based on a quenched fluorescent substrate, we describe an easy-to-use method for determining ACE2 activity in brain tissue and cerebrospinal fluid. The method can further be adapted for other tissues, plasma, cell extracts, and cell culture supernatants.