ACE2KO Mice Research Articles

Small Intestinal Endocrine Cell Derived Exosomal ACE2 Protects Islet β-Cell Function by Inhibiting the Activation of NLRP3 Inflammasome and Reducing β-Cell Pyroptosis.

The "gut-islets axis" is an important endocrine signaling axis that regulates islets function by modulating the gut microbiota and endocrine metabolism within the gut. However, the specific mechanisms and roles of the intestine in islets regulation remain unclear. Recent studies investigated that exosomes derived from gut microbiota can transport signals to remotely regulate islets β-cell function, suggesting the possibility of novel signaling pathways mediated by gut exosomes in the regulation of the "gut-islet axis.". The exosomes were isolated from the intestinal enteroendocrine cell-line STC-1cells culture supernatants treated with palmitate acid (PA) or BSA. Metabolic stress models were established by separately subjecting MIN6 cells to PA stimulation and feeding mice with a high-fat diet. Intervention with exosomes in vitro and in vivo to assess the biological effects of exosomes on islets β cells under metabolic stress. The Mas receptor antagonist A779 and ACE2ko mice were used to evaluate the role of exosomal ACE2. We found ACE2, a molecule that plays a crucial role in the regulation of islets function, is abundantly expressed in exosomes derived from STC-1 under physiological normal condition (NCEO). These exosomes cannot only be taken up by β-cells in vitro but also selectively transported to the islets in vivo. Following intervention with NCEXO, both Min6 cells in a lipotoxic environment and mice on a high-fat diet exhibited significant improvements in islets β-cell function and β-cell mass. Further investigations demonstrated that these protective effects are attributed to exosomal ACE2, as ACE2 inhibits NLRP3 inflammasome activation and reduces β-cell pyroptosis. ACE2-enriched exosomes from the gut can selectively target islets, subsequently inhibiting NLRP3 inflammasome activation and β cell pyroptosis, thereby restoring islets β cell function under metabolic stress. This study provides novel insights into therapeutic strategies for the prevention and treatment of obesity and diabetes.

Studying the Roles of the Renin-Angiotensin System in Accelerating the Disease of High-Fat-Diet-Induced Diabetic Nephropathy in a db/db and ACE2 Double-Gene-Knockout Mouse Model.

Diabetic nephropathy (DN) is a crucial metabolic health problem. The renin-angiotensin system (RAS) is well known to play an important role in DN. Abnormal RAS activity can cause the over-accumulation of angiotensin II (Ang II). Angiotensin-converting enzyme inhibitor (ACEI) administration has been proposed as a therapy, but previous studies have also indicated that chymase, the enzyme that hydrolyzes angiotensin I to Ang II in an ACE-independent pathway, may play an important role in the progression of DN. Therefore, this study established a model of severe DN progression in a db/db and ACE2 KO mouse model (db and ACE2 double-gene-knockout mice) to explore the roles of RAS factors in DNA and changes in their activity after short-term (only 4 weeks) feeding of a high-fat diet (HFD) to 8-week-old mice. The results indicate that FD-fed db/db and ACE2 KO mice fed an HFD represent a good model for investigating the role of RAS in DN. An HFD promotes the activation of MAPK, including p-JNK and p-p38, as well as the RAS signaling pathway, leading to renal damage in mice. Blocking Ang II/AT1R could alleviate the progression of DN after administration of ACEI or chymase inhibitor (CI). Both ACE and chymase are highly involved in Ang II generation in HFD-induced DN; therefore, ACEI and CI are potential treatments for DN.

Soluble ACE2 Is Filtered into the Urine.

ACE2 is a key enzyme in the renin-angiotensin system (RAS) capable of balancing the RAS by metabolizing angiotensin II (AngII). First described in cardiac tissue, abundance of ACE2 is highest in the kidney, and it is also expressed in several extrarenal tissues. Previously, we reported an association between enhanced susceptibility to hypertension and elevated renal AngII levels in global ACE2-knockout mice. To examine the effect of ACE2 expressed in the kidney, relative to extrarenal expression, on the development of hypertension, we used a kidney crosstransplantation strategy with ACE2-KO and WT mice. In this model, both native kidneys are removed and renal function is provided entirely by the transplanted kidney, such that four experimental groups with restricted ACE2 expression are generated: WT→WT (WT), KO→WT (KidneyKO), WT→KO (SystemicKO), and KO→KO (TotalKO). Additionally, we used nanoscale mass spectrometry-based proteomics to identify ACE2 fragments in early glomerular filtrate of mice. Although significant differences in BP were not detected, a major finding of our study is that shed or soluble ACE2 (sACE2) was present in urine of KidneyKO mice that lack renal ACE2 expression. Detection of sACE2 in the urine of KidneyKO mice during AngII-mediated hypertension suggests that sACE2 originating from extrarenal tissues can reach the kidney and be excreted in urine. To confirm glomerular filtration of ACE2, we used micropuncture and nanoscale proteomics to detect peptides derived from ACE2 in the Bowman's space. Our findings suggest that both systemic and renal tissues may contribute to sACE2 in urine, identifying the kidney as a major site for ACE2 actions. Moreover, filtration of sACE2 into the lumen of the nephron may contribute to the pathophysiology of kidney diseases characterized by disruption of the glomerular filtration barrier.

Angiotensin-converting enzyme 2 improves hepatic insulin resistance by regulating GABAergic signaling in the liver

The angiotensin-converting enzyme 2 (ACE2)/angiotensin 1-7/MAS axis and the gamma-aminobutyric acid (GABA)ergic signaling system have both been shown to have the dual potential to improve insulin resistance (IR) and hepatic steatosis associated with obesity in the liver. Recent studies have demonstrated that ACE2 can regulate the GABA signal in various tissues. Notwithstanding this evidence, the functional relationship between ACE2 and GABA signal in the liver under IR remains elusive. Here, we used high-fat diet-induced models of IR in C57BL/6 mice as well as ACE2KO and adeno-associated virus-mediated ACE2 overexpression mouse models to address this knowledge gap. Our analysis showed that glutamate decarboxylase (GAD)67/GABA signaling was weakened in the liver during IR, whereas the expression of GAD67 and GABA decreased significantly in ACE2KO mice. Furthermore, exogenous administration of angiotensin 1-7 and adeno-associated virus- or lentivirus-mediated overexpression of ACE2 significantly increased hepatic GABA signaling in models of IR both invivo and invitro. We found that this treatment prevented lipid accumulation and promoted fatty acid β oxidation in hepatocytes as well as inhibited the expression of gluconeogenesis- and inflammation-related genes, which could be reversed by allylglycine, a specific GAD67 inhibitor. Collectively, our findings show that signaling via the ACE2/A1-7/MAS axis can improve hepatic IR by regulating hepatic GABA signaling. We propose that this research might indicate a potential strategy for the management of diabetes.

Different effects of the deletion of angiotensin converting enzyme 2 and chronic activation of the renin-angiotensin system on muscle weakness in middle-aged mice.

Inhibition of the renin-angiotensin system (RAS) has been shown to alleviate muscle atrophy both under pathological conditions and during physiological aging. We recently reported that the deletion of angiotensin converting enzyme 2 (ACE2), which converts Angiotensin II to Angiotensin-(1-7) in mice, leads to the early manifestation of aging-associated muscle weakness along with the increased expression of p16INK4a, a senescence-associated gene, and increased central nuclei in the tibialis anterior (TA) muscle in middle age. As ACE2 is multifunctional and functions beyond its role in the RAS, we investigated whether activation of the RAS primarily contributes to muscle weakness in ACE2 knockout (KO) mice by comparing these mice to Tsukuba hypertensive (TH) mice that overproduce human angiotensin II. The grip strength of young (6 months) and middle-aged (15 months) TH mice was consistently lower than that of wild-type mice at the same ages. Middle-aged TH mice were continuously lean with extremely reduced adiposity. Central nuclei in the gastrocnemius (GM) muscle were increased in ACE2KO mice, while no apparent morphological change was observed in the GM muscles of TH mice. Increased expression of p16INK4a along with alterations in the expression of several sarcopenia-associated genes were observed in the GM muscles of ACE2KO mice but not TH mice. These findings suggest that chronic overactivation of the RAS does not primarily contribute to the early aging phenotypes of skeletal muscle in ACE2KO mice.

A12839 Angiotensin 1-7 functionally recovers aging-induced locomotive dysfunction, but is not associated with accelerated aging phenotypes in angiotensin-converting-enzyme 2 knockout mice

Objectives: The angiotensin-converting enzyme 2 (ACE2)-angitotensin 1-7 (A1-7)-A1-7 receptor (Mas) axis has been shown to have a protective role in the renin-angiotensin system (RAS). We recently found that ACE2 knockout (KO) mice exhibit earlier aging-associated muscle weakness, and A1-7 restores muscle weakness in aging mice. As ACE2 has a multifunctional role outside the RAS, we investigated the dependence on the A1-7-Mas pathway in the effect of ACE2 on physiological aging including locomotive dysfunction with muscle weakness and osteoporosis in mice. Methods: Wildtype (WT), ACE2KO, and MasKO mice were subjected to periodical grip strength measurement, followed by administration of A1–7 (100 ng/kg/min) or saline for 4 weeks with an osmotic pump in 24-month-old mice. Results: ACE2KO mice exhibited decreased grip strength compared with WT mice after 6 months of age, while MasKO mice had grip strength similar to WT mice during aging. A1-7 infusion at 24 months old improved grip strength with increased muscle size in WT and ACE2KO mice but not in MasKO mice. A1–7 significantly increased bone volume in WT and ACE2KO mice, but not in MasKO mice. Histological and gene expression analysis revealed that tissue aging including skin and adipose tissue was accelerated in aging ACE2KO mice, but not in MASKO mice, compared to WT mice. Conclusion: A1-7 improves muscle weakness and osteoporosis in aged mice via a Mas-dependent pathway. In contrast, the different aging phenotypes between ACEKO and MasKO mice suggest the A1-7-independent effect of ACE2 on senescence.

Angiotensin‐converting enzyme 2 deficiency accelerates and angiotensin 1‐7 restores age‐related muscle weakness in mice

BackgroundA pharmacologic strategy for age‐related muscle weakness is desired to improve mortality and disability in the elderly. Angiotensin‐converting enzyme 2 (ACE2) cleaves angiotensin II into angiotensin 1‐7, a peptide known to protect against acute and chronic skeletal muscle injury in rodents. Since physiological aging induces muscle weakness via mechanisms distinct from other muscle disorders, the role of ACE2‐angiotensin 1‐7 in age‐related muscle weakness remains undetermined. Here, we investigated whether deletion of ACE2 alters the development of muscle weakness by aging and whether angiotensin 1‐7 reverses muscle weakness in older mice.MethodsAfter periodic measurement of grip strength and running distance in male ACE2KO and wild‐type mice until 24 months of age, we infused angiotensin 1‐7 or vehicle for 4 weeks, and measured grip strength, and excised tissues. Tissues were also excised from younger (3‐month‐old) and middle‐aged (15‐month‐old) mice. Microarray analysis of RNA was performed using tibialis anterior (TA) muscles from middle‐aged mice, and some genes were further tested using RT‐PCR.ResultsGrip strength of ACE2KO mice was reduced at 6 months and was persistently lower than that of wild‐type mice (p < 0.01 at 6, 12, 18, and 24‐month‐old). Running distance of ACE2KO mice was shorter than that of wild‐type mice only at 24 months of age [371 ± 26 vs. 479 ± 24 (m), p < 0.01]. Angiotensin 1‐7 improved grip strength in both types of older mice, with larger effects observed in ACE2KO mice (% increase, 3.8 ± 1.5 and 13.3 ± 3.1 in wild type and ACE2KO mice, respectively). Older, but not middle‐aged ACE2KO mice had higher oxygen consumption assessed by a metabolic cage than age‐matched wild‐type mice. Angiotensin 1‐7 infusion modestly increased oxygen consumption in older mice. There was no difference in a wheel‐running activity or glucose tolerance between ACE2KO and wild‐type mice and between mice with vehicle and angiotensin 1‐7 infusion. Analysis of TA muscles revealed that p16INK4a, a senescence‐associated gene, and central nuclei of myofibers increased in middle‐aged, but not younger ACE2KO mice. p16INK4a and central nuclei increased in TA muscles of older wild‐type mice, but the differences between ACE2KO and wild‐type mice remained significant (p < 0.01). Angiotensin 1‐7 did not alter the expression of p16INK4a or central nuclei in TA muscles of both types of mice. Muscle ACE2 expression of wild‐type mice was the lowest at middle age (2.6 times lower than younger age, p < 0.05).ConclusionsDeletion of ACE2 induced the early manifestation of muscle weakness with signatures of muscle senescence. Angiotensin 1‐7 improved muscle function in older mice, supporting future application of the peptide or its analogues in the treatment of muscle weakness in the elderly population.

Sex dimorphism in ANGII-mediated crosstalk between ACE2 and ACE in diabetic nephropathy

Angiotensin-converting enzyme (ACE) and ACE2 play a critical role in the renin–angiotensin system (RAS) by altering angiotensin II (ANGII) levels, thus governing its deleterious effects. Both enzymes are altered by sex and diabetes, and play an important role in the development of diabetic nephropathy (DN). Importantly, previous evidence in diabetic and ACE2-deficient (ACE2KO) males suggest a sex-dependent crosstalk between renal ACE and ACE2. In the present work, we aimed to study the sex-specific susceptibility to diabetes and direct infusion of ANGII in kidney disease progression, with a special focus on its link to ACE2 and ACE. In our mouse model, ANGII promoted hypertension, albuminuria, reduced glomerular filtration, and glomerular histological alterations. ANGII adverse effects were accentuated by diabetes and ACE2 deficiency, in a sex-dependent fashion: ACE2 deficiency accentuated ANGII-induced hypertension, albuminuria, and glomerular hypertrophy in diabetic females, whereas in diabetic males exacerbated ANGII-mediated glomerular hypertrophy, mesangial expansion, and podocyte loss. At the molecular level, ANGII downregulated renal ACE gene and enzymatic activity levels, as well as renin gene expression in ACE2KO mice. Interestingly, male sex and diabetes accentuated this effect. Here we show sex dimorphism in the severity of diabetes- and ANGII-related renal lesions, and demonstrate that ACE2- and ACE-related compensatory mechanisms are sex-specific. Supporting our previous findings, the modulation and ANGII-mediated crosstalk between ACE2 and ACE in DN progression was more evident in males. This work increases the understanding of the sex-specific role of ACE2 and ACE in DN, reinforcing the necessity of more personalized treatments targeting RAS.Sex and diabetes affect angiotensin-converting enzyme (ACE) and ACE2 expression and are key determinants of kidney disease progression. Here the authors demonstrate that there are sex differences in the severity of angiotensin II (ANGII)-hypertension and diabetic nephropathy, the activation of the renin-angiotensin system cascade, and the crosstalk between ACE and ACE2 in vivo. This work increases our understanding of the sex-specific role of ACE2 and ACE in diabetic nephropathy, reinforcing the necessity of individualized treatments.

Instillation of particulate matter 2.5 induced acute lung injury and attenuated the injury recovery in ACE2 knockout mice.

Inhaled particulate matter 2.5 (PM2.5) can cause lung injury by inducing serious inflammation in lung tissue. Renin-angiotensin system (RAS) is involved in the pathogenesis of inflammatory lung diseases and regulates inflammatory response. Angiotensin-converting enzyme II (ACE2), which is produced through the angiotensin-converting enzyme (ACE)/angiotensin II (Ang II) axis, protects against lung disease. However, few studies have focused on the relationships between PM2.5 and ACE2. Therefore, we aimed to explore the role of ACE2 in PM2.5-induced acute lung injury (ALI). An animal model of PM2.5-induced ALI was established with wild type (C57BL/6, WT) and ACE2 gene knockout (ACE2 KO) mice. The mice were exposed to PM2.5 through intratracheal instillation once a day for 3 days (6.25 mg/kg/day) and then sacrificed at 2 days and 5 days after PM2.5 instillation. The results show that resting respiratory rate (RRR), levels of inflammatory cytokines, ACE and MMPs in the lungs of WT and ACE2 KO mice were significantly increased at 2 days postinstillation. At 5 days postinstillation, the PM2.5-induced ALI significantly recovered in the WT mice, but only partially recovered in the ACE2 KO mice. The results hint that PM2.5 could induce severe ALI through pulmonary inflammation, and the repair after acute PM2.5 postinstillation could be attenuated in the absence of ACE2. Additionally, our results show that PM2.5-induced ALI is associated with signaling p-ERK1/2 and p-STAT3 pathways and ACE2 knockdown could increase pulmonary p-STAT3 and p-ERK1/2 levels in the PM2.5-induced ALI.

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 &lt;0.05; relative ACE2 protein expression: 0.38 ± 0.04 vs. 1.15 ± 0.12, N=3 vs 3, P &lt;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 &lt;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.

Loss of angiotensin converting enzyme II (ACE2) accelerates the development of liver injury induced by thioacetamide.

Angiotensin converting enzyme II (ACE2), an angiotensin converting enzyme (ACE) homologue that displays antagonist effects on ACE/angiotensin II (Ang II) axis in renin-angiotensin system (RAS), could play a protective role against liver damages. The purpose of this study is to investigate whether inflammation-mediated liver injury could be affected by ACE2 derived pathways in the RAS. Eight-weeks-old wild-type (WT; C57BL/6) and Ace2 KO (hemizygous Ace2-/y) male mice were used to induce liver fibrosis by thioacetamide (TAA) administration (0, 100, and 200 mg/kg BW). The mice administrated with TAA could be successfully induced liver fibrosis in a TAA-dose dependent manner. Compared to WT mice, the results show that Ace2 KO mice have high sensitive, and developed more serious reaction of hepatic inflammation and fibrosis by TAA administration. The physiological and pathological examinations demonstrated higher serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP) levels, infiltration of white blood cells and fibrotic lesions within liver in the Ace2 KO mice. The severe liver damage of Ace2 KO mice were also confirmed by the evidence of higher expression of hepatic inflammation-related genes (IL-6 and Tnf) and fibrosis-related genes (Col1a1, Timp1 and Mmp9). Ace2 gene deficiency could lead to a severe inflammation and collagen remodeling in the liver administrated by TAA, and the responses lead the pathogenesis of liver fibrosis. Our studies provided the main messages and favorable study directions of relationship of Ace2 and liver disease.

Disorder of Renin‐Angiotensin System Promoting the Acute Pulmonary Inflammation by Particulate Matter 2.5 (PM2.5) Exposure

Acute or chronic particulate matter 2.5 (PM2.5) exposure can induce oxidative stress, inflammation and pulmonary impairment by traversing the blood‐air barrier of alveolar and then depositing at lung. In the present study, we tested whether the pulmonary inflammation and impairment induced by PM2.5 exposure are related to the disorder of pulmonary renin‐angiotensin system (RAS).In this study, we collected PM2.5 from waste gas which was produced from vehicle engine, and determined the component elements and structures of the PM2.5. The C57BL/6J (wild type, WT) mice and angiotensin converting enzyme II (ACE2) gene knockout (ACE2KO) mice were treated with the PM2.5 by intratracheal instillation once a day for a total of 3 days, and then sacrificed at the 4th day. Lung tissue of the mice was collected for the assays of molecular, biochemical and pathological changes to evaluate the acute pulmonary inflammation and lung injury induced by PM2.5 exposure.The results indicated that the most of collected particulates in this study were aggregated and parts of them formed structure of chains below 2.5 μm diameter. The major compositions of the PM2.5 are carbon and oxide, and contain little silicon, sulfate and copper. The body weight of both WT and ACE2 KO mice treated with PM2.5 was decreased and resting breathing rate was significantly increased. PM2.5 treatment induced pathological leukocyte infiltration in the lung, increased pulmonary immunocytokines concentration, including interleukin‐6 (IL‐6), tumor necrosis factor alpha (TNF‐α) and tumor growth factor beta 1 (TGF‐β1), and also promoted signaling protein ERK1/2 and STAT3 phosphorylation. The quantitative data showed that the levels of physiopathology and inflammation induced by PM2.5 were serious in the ACE2 KO mice compared with those in the WT mice. PM2.5 treatment significantly increased pulmonary ACE expression and activity in both WT and ACE2 KO mice. Interestingly, pulmonary ACE2 activity in the WT mice was also induced. We hypothesized that increased ACE2 activity in the WT mice is a physiological response for increased ACE activity due to PM2.5 exposure. However, the response is lack in the ACE2 KO mice because the mice being ACE2 deficiency. It is one of the reasons that serious physiopathology and inflammation induced by PM2.5 in the ACE2 KO mice compared with those in the WT mice.Our data reveals that acute inflammation and lung injury could be induced by PM2.5 treatment. The disorder of pulmonary RAS may aggravate the disease progressive of pulmonary system due to PM2.5 exposure. Therefore, we propose that it may be helpful for the cardiopulmonary patients by RAS regulation when the patients are exposed to severe particulate pollutants.

Deficiency of angiotensin-converting enzyme 2 causes deterioration of cognitive function

The classical renin–angiotensin system (RAS), known as the angiotensin (Ang)-converting enzyme (ACE)/Ang II/Ang II type 1 (AT1) receptor axis, induces various organ damages including cognitive decline. On the other hand, the ACE2/Ang-(1–7)/Mas receptor axis has been highlighted as exerting antagonistic actions against the classical RAS axis in the cardiovascular system. However, the roles of the ACE2/Ang-(1–7)/Mas axis in cognitive function largely remain to be elucidated, and we therefore examined possible roles of ACE2 in cognitive function. Male, 10-week-old C57BL6 (wild type, WT) mice and ACE2 knockout (KO) mice were subjected to the Morris water maze task and Y maze test to evaluate cognitive function. ACE2KO mice exhibited significant impairment of cognitive function, compared with that in WT mice. Superoxide anion production increased in ACE2KO mice, with increased mRNA levels of NADPH oxidase subunit, p22phox, p40phox, p67phox, and gp91phox in the hippocampus of ACE2KO mice compared with WT mice. The protein level of SOD3 decreased in ACE2KO mice compared with WT mice. The AT1 receptor mRNA level in the hippocampus was higher in ACE2KO mice compared with WT mice. In contrast, the AT2 receptor mRNA level in the hippocampus did not differ between the two strains. Mas receptor mRNA was highly expressed in the hippocampus compared with the cortex. Brain-derived neurotrophic factor (BDNF) mRNA and protein levels were lower in the hippocampus in ACE2KO mice compared with WT mice. Taken together, ACE2 deficiency resulted in impaired cognitive function, probably at least in part because of enhanced oxidative stress and a decrease in BDNF.

OS 15-09 DOES ACE2-ANGIOTENSIN-(1–7) AXIS PROTECT FROM AGING-ASSOCIATED LOSS OF SKELETAL MUSCLE FUNCTION?

Objective: Angiotensin converting enzyme2 (ACE2), an enzyme that produces the Angiotensin 1–7(A1–7) from Angiotensin II, is considered to suppress organ damage by inhibition of the activation of renin-angiotensin system. We recently found that ACE2 deficiency in mice ameliorated insulin sensitivity of skeletal muscle with reduced expression of glucose transporter 4 and myocyte enhancer factor 2, an important transcription factor to maintain homeostasis of skeletal muscle. In this study, we investigated whether ACE2-A1–7 axis plays a protective role in aging-associated loss of skeletal muscle function in mice. Design and Method: To assess serial change in motor function, we performed grip strength test in 3, 6, 12, 18, and 24 month old wildtype and ACE2 knockout (KO) mice. Grip strength at each period was calculated by average of 12 times measurements (6 times for 2days). At 24 month old, saline or A1–7 (100ng / kg / min) was administered for 4 weeks by osmotic mini pumps and grip strength was compared before and after administration. Results: At 3 months, there was no significant difference in grip strength between ACE2KO and wildtype mice. While grip strength of wildtype mice remained unchanged until 18 month old, ACE2KO mice reduced their grip strength after 6 month old. Wildtype mice reduced grip strength at 24 month, but the difference in grip strength between wildtype and ACE2KO mice was still observed. Administration of A1–7 at 24 month old mice significantly improved loss of grip strength in wildtype and ACE2KO mice. There was no difference in grip strength between A1–7-administrated wildtype and ACE2KO mice. There was no difference in weight and size of skeletal muscle of lower limbs between wildtype and ACE2KO mice at 24 months. Conclusions: ACE2-Angiotensin(1–7) axis may protect from age-associated loss of skeletal muscle function without no obvious alternation in muscle mass.

Abstract WP266: Deficiency of Angiotensin Converting Enzyme 2 Causes Deterioration of Cognitive Function

Introduction: The classical renin-angiotensin system (RAS), known as the angiotensin (Ang) converting enzyme (ACE)/Ang II/Ang II type 1 (AT1) receptor axis, induces various organ damage including cognitive decline. On the other hand, the ACE2/Ang-(1-7)/Mas receptor axis has been highlighted as exerting antagonistic actions against the classical RAS axis in the cardiovascular system. However, the roles of the ACE2/Ang-(1-7)/Mas axis in cognitive function largely remain to be elucidated, and we therefore examined possible roles of ACE2 in cognitive function. Methods: Male 10-week-old C57BL6 (wild-type: WT) mice and ACE2 knockout (KO) mice were subjected to the Morris water maze task to evaluate spatial cognitive function. Vascular dementia model were induced by bilateral common carotid artery stenosis (BCAS). The Morris water maze task was performed 6 weeks after BCAS operation. Results: ACE2KO mice exhibited significant impairment of spatial cognitive function, compared with that in WT mice, without significant difference in cerebral blood flow determined by laser speckle flowmetry and morphological changes in the hippocampus between both strains. Superoxide anion production in the hippocampus tended to be increased in ACE2KO mice, with increased mRNA levels of NADPH oxidase subunit in the hippocampus of ACE2KO compared with WT mice. Protein level of superoxide dismutase (SOD) 3 tended to be decreased in ACE2KO mice compared with WT mice. AT1 receptor mRNA level in the hippocampus was higher in ACE2KO mice compared with WT mice. In contrast, AT2 receptor mRNA level in the hippocampus did not differ between the two strains. Mas receptor mRNA was highly expressed in the hippocampus compared with the cortex, with no significant difference between ACE2KO and WT mice. Brain-derived neurotrophic factor (BDNF) mRNA was lower in the hippocampus in ACE2KO mice compared with WT mice. Escape latency after BCAS was prolonged in WT mice compared with sham operated mice, whereas impaired cognitive function in ACE2 KO mice was not further exaggerated after BCAS. Conclusion: Taken together ACE2 deficiency resulted in impaired cognitive function probably due to enhanced oxidative stress and a decrease in BDNF.

Alternative Roles of STAT3 and MAPK Signaling Pathways in the MMPs Activation and Progression of Lung Injury Induced by Cigarette Smoke Exposure in ACE2 Knockout Mice.

Inflammation-mediated abnormalities in the renin-angiotensin system (RAS) and expression of matrix metalloproteinases (MMPs) are implicated in the pathogenesis of lung injury. Angiotensin converting enzyme II (ACE2), an angiotensin converting enzyme (ACE) homologue that displays antagonist effects on ACE/angiotensin II (Ang II) axis, could also play a protective role against lung diseases. However, the relationship between ACE2 and MMPs activation in lung injury is still largely unclear. The purpose of this study is to investigate whether MMPs activity could be affected by ACE2 and which ACE2 derived signaling pathways could be also involved via using a mouse model with lung injury induced by cigarette smoke (CS) exposure for 1 to 3 weeks. Wild-type (WT; C57BL/6) and ACE2 KO mice (ACE2-/-) were utilized to study CS-induced lung injury. Increases in the resting respiratory rate (RRR), pulmonary immunokines, leukocyte infiltration and bronchial hyperplasia were observed in the CS-exposed mice. Compared to WT mice, more serious physiopathological changes were found in ACE2-/- mice in the first week of CS exposure. CS exposure increased pulmonary ACE and ACE2 activities in WT mice, and significantly increased ACE in ACE2-/- mice. Furthermore, the activity of pulmonary MMPs was decreased in CS-exposed WT mice, whereas this activity was increased in ACE2-/- mice. CS exposure increased the pulmonary p-p38, p-JNK and p-ERK1/2 level in all mice. In ACE2-/- mice, a significant increase p-STAT3 signaling was detected; however, no effect was observed on the p-STAT3 level in WT mice. Our results support the hypothesis that ACE2 deficiency influences MMPs activation and STAT3 phosphorylation signaling to promote more pulmonary inflammation in the development of lung injury.

Abstract 407: Aminopeptidase A (APA)/Ang(2-10) and APA/AngIII are the Dominant Axes in the Metabolism of Angiotensin Peptides in Mice Plasma

ACE2 is considered an important enzyme in the degradation of Angiotensin (Ang) I (1-10) and especially of Ang II (1-8), as demonstrated by the rapid dissipation of this peptide when recombinant ACE2 is infused but the steady state level of ACE2 in plasma is low. We examined levels of multiple Ang peptides in plasma under steady state conditions in WT and ACE2KO mice on C57BL genetic background (n=4 and 5, respectively). Liquid chromatography mass-spectrometry-based approach which enables concurrent evaluation of ten different angiotensins at physiologic levels (pg/mL) was used for multiple peptide quantification. The levels of angiotensin peptides in WT mice were highest for Ang I (1-10) (1295±313 pg/mL), Ang (2-10) (657±173 pg/mL) and Ang III (2-8) (1047±178 pg/mL). In contrast, plasma levels of Ang II (1-8), the main effector peptide of the RAS, and Ang (1-7), the product of cleavage of Ang II by ACE2, were very low (7.8±2 and 3.5±0 pg/mL, respectively). In ACE2 KO mice, Ang II and Ang (1-7) levels were not significantly different from WT. Activity of Aminopeptidase A, an enzyme that converts Ang (1-10) to Ang (2-10) and cleaves Ang II (1-8) to Ang III (2-8), was significantly increased in ACE2KO (n=11) as compared to WT (n=17) (149±11 vs. 94±9 RFU/ul/hr, respectively, p&lt;0.001). This finding along with increased ratio of Ang (2-10)/Ang(1-8) (175±31 vs. 84±4, p&lt;0.01, respectively) suggests increased formation of Ang (2-10) from Ang (1-10) in ACE2KO mice by APA over the formation of Ang II (1-8) from Ang (1-10). These results show that plasma Ang II and Ang (1-7) levels in WT and ACE2KO mice are low relative to the high levels of Ang (2-10) and Ang III (2-8). ACE2 deficiency does not result in plasma Ang II accumulation or reduced Ang (1-7) levels and is associated with an increase in serum APA activity. We conclude that in mice plasma the APA/Ang(2-10) and APA/AngIII pathways, and not ACE2/Ang(1-7), are dominant in the metabolism of Ang I and Ang II under steady state conditions.

Abstract 480: ACE2 Independent Pathways of Angiotensin 1-7 Formation in the Murine Kidney

Fluid balance, salt retention and tissue remodeling is hormonally regulated by the Renin-Angiotensin-System. The sophisticated enzyme network serially cleaves peptide hormones generating various effector hormones including the vasoconstrictor Angiotensin 1-8 and its counterbalancing downstream metabolite Angiotensin 1-7. LC-MS/MS based analysis of kidney and plasma of ACE2 knockout mice revealed unchanged Angiotensin 1-7 concentrations compared to wild type animals pointing to alternative pathways of Angiotensin 1-7 formation and suggesting a minor role for ACE2 in the formation of Angiotensin 1-7 in vivo. Moreover, we observed a decrease in the Angiotensin 1-8/Angiotensin 1-10 ratio in ACE2KO-mice indicating a changed conversion rate from Angiotensin 1-10 to Angiotensin 1-8. We analyzed Angiotensin 1-7 metabolism in kidney homogenates by spiking natural substrates in the absence and presence of specific enzyme inhibitors. The metabolism of ex vivo spiked Angiotensins in kidney homogenates in presence and absence of the Prolyl-Carboxypepdidase (PCP) and Prolyl-Endopeptidase (PEP) Inhibitor ZPP and the ACE2-Inhibitor MLN-4760 revealed stronger contribution of PCP and PEP to Angiotensin 1-7 formation than ACE2. Analyzing the formation of Angiotensin 1-8 from Angiotensin 1-10 in renal cortex and medulla homogenates of WT and ACE2KO mice in the absence and presence of an ACE-Inhibitor confirmed our observations on endogenous peptide levels and the ratio between Angiotensin 1-8 and Angiotensin 1-10 in plasma, revealing a reduced ACE activity in the renal cortex of ACE2KO. Our study raises questions concerning the relevance of renal ACE2 for the local formation of Angiotensin 1-7. Moreover, the reduced ACE expression and activity in renal cortex might be a physiologically and therefore phenotype relevant consequence of the knockdown of ACE2 in these mice. The possible crosstalk between ACE and ACE2 expression and activity might give rise to further studies addressing the underlying mechanisms and might be important for our understanding of RAS dynamics in regard to therapeutic interventions.

Abstract 088: Angiotensin Converting Enzyme 2 (ACE2) in the Kidney: Soluble ACE2 Restores Blood Pressure Regulation

Angiotensin converting enzyme 2 (ACE2) is a carboxypeptidase that metabolizes angiotensin II (AngII) to Ang(1-7). ACE2 can be cleaved by metalloproteinases to generate soluble ACE2 (sACE2), which remains catalytically active. The objective of this study is to determine if sACE2, acting in the kidney, could modulate the BP response to AngII infusion.Data from our kidney cross-transplant study using male (129/SvEv x C57BL/6)F 1 ACE2 KO and WT mice suggest that sACE2 can reach the urinary compartment even when not expressed in kidney cells. For these experiments, we generated 4 experimental groups: 1) WT, 2) Kidney ACE2KO, 3) Systemic ACE2KO, and 4) Total ACE2KO. Mean arterial pressures (MAP) were measured with radiotelemetry. AngII was infused chronically at 1ug/kg/min. Enzymatic activity was determined using an ACE2-specific quenched fluorescent substrate assay. ACE2 protein in the urine was confirmed by western blots using a specific N-terminus antibody. Total ACE2KO mice had an enhanced hypertensive response to AngII compared to WT (152±6 vs.144±7 mmHg; p =0.03). The presence of ACE2 in either kidney or systemic tissues restored MAPs to levels similar to WT (kidney ACE2KO 140±7mmHg, systemic ACE2 KO 140±5 mmHg, p&lt;0.01 vs. total ACE2KO). However, Kidney ACE2KO mice had similar urinary ACE2 activity as systemic ACE2KO (76±32 and 108±52 RFU/ul/hr, respectively, p=NS). We confirmed this was ACE2 with immunoblotting of urine samples. As expected, we detected a 92kDa band in WT and systemic KO mice, which represents full length ACE2. A smaller band (70kDa) was present in the WT, systemic KO, and kidney KO groups, and absent in total KO mice. This likely represents sACE2. Moreover, the presence of the smaller band correlated with urine ACE2 activity and was associated with attenuated BPs. Our studies demonstrate that the exaggerated hypertensive phenotype seen in total ACE2 deficiency can be rescued when ACE2 is restored either in the kidney or in systemic tissues. Since the Kidney KO group demonstrated ACE2 activity and protein in the urine, we suggest that soluble ACE2 can be filtered in hypertensive renal injury and may provide an additional source of balance against upregulation of the RAS within the kidney, with the overall goal of regulating BP.

Angiotensin-converting enzyme 2 is a critical determinant of angiotensin II-induced loss of vascular smooth muscle cells and adverse vascular remodeling.

Angiotensin-converting enzyme (ACE) 2 is a key negative regulator of the renin-angiotensin system and metabolizes angiotensin II (Ang II) into Ang 1 to 7. Ang II is a vasoactive peptide, which plays an important role in vascular disease. The objective of the present study was to define the role of ACE2 in pathological vascular remodeling. We found upregulation of ACE2 in dilated human aorta with bicuspid aortic valve and in murine aorta in response to Ang II. Ex vivo pressure myography showed increased vascular stiffness in ACE2 knockout (KO) mesenteric arteries in response to Ang II (1.5 mg/kg per day) and with aging. Histological analyses revealed reduced media-to-lumen ratio in ACE2KO mesenteric arteries with loss of vascular smooth muscle cells. Aortic vascular smooth muscle cells from ACE2KO mice showed markedly increased reactive oxygen species and apoptosis in response to Ang II along with increased cleaved caspase-3 and cleaved caspase-8 levels in the ACE2KO aorta. Ang II type 1 receptor blockade and Ang 1 to 7 supplementation prevented the increase in Ang II-induced reactive oxygen species and apoptotic cell death. In the aorta, Ang II resulted in thoracic and abdominal aortic dilation with loss of vascular smooth muscle cell density in ACE2KO aorta as revealed by α-smooth muscle actin, calponin staining, and electron microscopy with increased promatrix metalloproteinase 2, matrix metalloproteinase 2, and matrix metalloproteinase 9 levels. ACE2 is upregulated in vascular diseases, and ACE2 deficiency exacerbates Ang II-mediated vascular remodeling driven by increased reactive oxygen species and vascular smooth muscle cell apoptosis. In conclusion, the key counter-regulatory role of ACE2 against an activated renin-angiotensin system provides novel insights into the role of ACE2 in vascular diseases.