High glucose activates the alternative ACE2/Ang-(1-7)/Mas and APN/Ang IV/IRAP RAS axes in pancreatic β-cells

Molecular dissection of the role of ACE2 in glucose homeostasis

Angiotensin-converting enzyme 2 (ACE2) was discovered 25 years ago as a negative regulator of the renin-angiotensin system, opposing the effects of angiotensin II. Beyond its well-demonstrated roles in cardiovascular regulation and COVID-19 pathology, ACE2 is involved in a plethora of physiopathological processes. In this review, we summarize the latest discoveries on the role of ACE2 in glucose homeostasis and regulation of metabolism. In the endocrine pancreas, ACE2 is expressed at low levels in β-cells, but loss of its expression inhibits glucose-stimulated insulin secretion and impairs glucose tolerance. Conversely, overexpression of ACE2 improved glycemia, suggesting that recombinant ACE2 might be a future therapy for diabetes. In the skeletal muscle of ACE2-deficient mice a progressive triglyceride accumulation was observed, whereas in diabetic kidney the initial increase in ACE2 is followed by a chronic reduction of expression in kidney tubules and impairment of glucose metabolism. At the intestinal level dysregulation of the enzyme alters the amino acid absorption and intestinal microbiome, whereas at the hepatic level ACE2 protects against diabetic fatty liver disease. Not least, ACE2 is upregulated in adipocytes in response to nutritional stimuli, and administration of recombinant ACE2 decreased body weight and increased thermogenesis. In addition to tissue-specific regulation of ACE2 function, the enzyme undergoes complex cellular posttranslational modifications that are changed during diabetes evolution, with at least proteolytic cleavage and ubiquitination leading to modifications in ACE2 activity. Detailed characterization of ACE2 in a cellular and tissue-specific manner holds promise for improving therapeutic outcomes in diabetes and metabolic disorders.

Hyperglycemia induced cathepsin L maturation linked to diabetic comorbidities and COVID-19 mortality

Diabetes, a prevalent chronic condition, significantly increases the risk of mortality from COVID-19, yet the underlying mechanisms remain elusive. Emerging evidence implicates Cathepsin L (CTSL) in diabetic complications, including nephropathy and retinopathy. Our previous research identified CTSL as a pivotal protease promoting SARS-CoV-2 infection. Here, we demonstrate elevated blood CTSL levels in individuals with diabetes, facilitating SARS-CoV-2 infection. Chronic hyperglycemia correlates positively with CTSL concentration and activity in diabetic patients, while acute hyperglycemia augments CTSL activity in healthy individuals. In vitro studies reveal high glucose, but not insulin, promotes SARS-CoV-2 infection in wild-type cells, with CTSL knockout cells displaying reduced susceptibility. Utilizing lung tissue samples from diabetic and non-diabetic patients, alongside Leprdb/dbmice and Leprdb/+mice, we illustrate increased CTSL activity in both humans and mice under diabetic conditions. Mechanistically, high glucose levels promote CTSL maturation and translocation from the endoplasmic reticulum (ER) to the lysosome via the ER-Golgi-lysosome axis. Our findings underscore the pivotal role of hyperglycemia-induced CTSL maturation in diabetic comorbidities and complications.

Potential Effects of Hyperglycemia on SARS-CoV-2 Entry Mechanisms in Pancreatic Beta Cells

The COVID-19 pandemic has revealed a bidirectional relationship between SARS-CoV-2 infection and diabetes mellitus. Existing evidence strongly suggests hyperglycemia as an independent risk factor for severe COVID-19, resulting in increased morbidity and mortality. Conversely, recent studies have reported new-onset diabetes following SARS-CoV-2 infection, hinting at a potential direct viral attack on pancreatic beta cells. In this review, we explore how hyperglycemia, a hallmark of diabetes, might influence SARS-CoV-2 entry and accessory proteins in pancreatic β-cells. We examine how the virus may enter and manipulate such cells, focusing on the role of the spike protein and its interaction with host receptors. Additionally, we analyze potential effects on endosomal processing and accessory proteins involved in viral infection. Our analysis suggests a complex interplay between hyperglycemia and SARS-CoV-2 in pancreatic β-cells. Understanding these mechanisms may help unlock urgent therapeutic strategies to mitigate the detrimental effects of COVID-19 in diabetic patients and unveil if the virus itself can trigger diabetes onset.

FGF7 enhances the expression of ACE2 in human islet organoids aggravating SARS-CoV-2 infection

The angiotensin-converting enzyme 2 (ACE2) is a primary cell surface viral binding receptor for SARS-CoV-2, so finding new regulatory molecules to modulate ACE2 expression levels is a promising strategy against COVID-19. In the current study, we utilized islet organoids derived from human embryonic stem cells (hESCs), animal models and COVID-19 patients to discover that fibroblast growth factor 7 (FGF7) enhances ACE2 expression within the islets, facilitating SARS-CoV-2 infection and resulting in impaired insulin secretion. Using hESC-derived islet organoids, we demonstrated that FGF7 interacts with FGF receptor 2 (FGFR2) and FGFR1 to upregulate ACE2 expression predominantly in β cells. This upregulation increases both insulin secretion and susceptibility of β cells to SARS-CoV-2 infection. Inhibiting FGFR counteracts the FGF7-induced ACE2 upregulation, subsequently reducing viral infection and replication in the islets. Furthermore, retrospective clinical data revealed that diabetic patients with severe COVID-19 symptoms exhibited elevated serum FGF7 levels compared to those with mild symptoms. Finally, animal experiments indicated that SARS-CoV-2 infection increased pancreatic FGF7 levels, resulting in a reduction of insulin concentrations in situ. Taken together, our research offers a potential regulatory strategy for ACE2 by controlling FGF7, thereby protecting islets from SARS-CoV-2 infection and preventing the progression of diabetes in the context of COVID-19.

Mechanisms influencing the high prevalence of COVID-19 in diabetics: A systematic review

Diabetics have an increased risk of contracting COVID-19 infection and tend to have more severe symptoms. This systematic review explores the potential mechanisms influencing the high prevalence of COVID-19 infections in individuals with diabetes. It reviews the emerging evidence about the interactions between viral and diabetic pathways, particularly how diabetes physiology could contribute to higher viral reception, viral entry and pathogenicity, and the severity of disease symptoms. Finally, it examines the challenges we face in studying these mechanisms and offers new strategies that might assist our fight against current and future pandemics.

Can Probiotics, Particularly Limosilactobacillus fermentum UCO-979C and Lacticaseibacillus rhamnosus UCO-25A, Be Preventive Alternatives against SARS-CoV-2?

COVID-19, an infection produced by the SARS-CoV-2 virus in humans, has rapidly spread to become a high-mortality pandemic. SARS-CoV-2 is a single-stranded RNA virus characterized by infecting epithelial cells of the intestine and lungs, binding to the ACE2 receptor present on epithelial cells. COVID-19 treatment is based on antivirals and antibiotics against symptomatology in addition to a successful preventive strategy based on vaccination. At this point, several variants of the virus have emerged, altering the effectiveness of treatments and thereby attracting attention to several alternative therapies, including immunobiotics, to cope with the problem. This review, based on articles, patents, and an in silico analysis, aims to address our present knowledge of the COVID-19 disease, its symptomatology, and the possible beneficial effects for patients if probiotics with the characteristics of immunobiotics are used to confront this disease. Moreover, two probiotic strains, L. fermentum UCO-979C and L. rhamnosus UCO-25A, with different effects demonstrated at our laboratory, are emphasized. The point of view of this review highlights the possible benefits of probiotics, particularly those associated with immunomodulation as well as the production of secondary metabolites, and their potential targets during SARS-CoV-2 infection.

A diabetic milieu increases ACE2 expression and cellular susceptibility to SARS-CoV-2 infections in human kidney organoids and patient cells

It is not well understood why diabetic individuals are more prone to develop severe COVID-19. To this, we here established a human kidney organoid model promoting early hallmarks of diabetic kidney disease development. Upon SARS-CoV-2 infection, diabetic-like kidney organoids exhibited higher viral loads compared with their control counterparts. Genetic deletion of the angiotensin-converting enzyme 2 (ACE2) in kidney organoids under control or diabetic-like conditions prevented viral detection. Moreover, cells isolated from kidney biopsies from diabetic patients exhibited altered mitochondrial respiration and enhanced glycolysis, resulting in higher SARS-CoV-2 infections compared with non-diabetic cells. Conversely, the exposure of patient cells to dichloroacetate (DCA), an inhibitor of aerobic glycolysis, resulted in reduced SARS-CoV-2 infections. Our results provide insights into the identification of diabetic-induced metabolic programming in the kidney as a critical event increasing SARS-CoV-2 infection susceptibility, opening the door to the identification of new interventions in COVID-19 pathogenesis targeting energy metabolism.

Dietary supplements, vitamins and minerals as potential interventions against viruses: Perspectives for COVID-19

The novel coronavirus (SARS-CoV-2) causing COVID-19 disease pandemic has infected millions of people and caused more than thousands of deaths in many countries across the world. The number of infected cases is increasing day by day. Unfortunately, we do not have a vaccine and specific treatment for it. Along with the protective measures, respiratory and/or circulatory supports and some antiviral and retroviral drugs have been used against SARS-CoV-2, but there are no more extensive studies proving their efficacy. In this study, the latest publications in the field have been reviewed, focusing on the modulatory effects on the immunity of some natural antiviral dietary supplements, vitamins and minerals. Findings suggest that several dietary supplements, including black seeds, garlic, ginger, cranberry, orange, omega-3 and -6 polyunsaturated fatty acids, vitamins (e.g., A, B vitamins, C, D, E), and minerals (e.g., Cu, Fe, Mg, Mn, Na, Se, Zn) have anti-viral effects. Many of them act against various species of respiratory viruses, including severe acute respiratory syndrome-related coronaviruses. Therefore, dietary supplements, including vitamins and minerals, probiotics as well as individual nutritional behaviour can be used as adjuvant therapy together with antiviral medicines in the management of COVID-19 disease.

ACE2 function in the pancreatic islet: Implications for relationship between SARS-CoV-2 and diabetes

The molecular link between SARS-CoV-2 infection and susceptibility is not well understood. Nonetheless, a bi-directional relationship between SARS-CoV-2 and diabetes has been proposed. The angiotensin-converting enzyme 2 (ACE2) is considered as the primary protein facilitating SARS-CoV and SARS-CoV-2 attachment and entry into the host cells. Studies suggested that ACE2 is expressed in the endocrine cells of the pancreas including beta cells, in addition to the lungs and other organs; however, its expression in the islets, particularly beta cells, has been met with some contradiction. Importantly, ACE2 plays a crucial role in glucose homoeostasis and insulin secretion by regulating beta cell physiology. Given the ability of SARS-CoV-2 to infect human pluripotent stem cell-derived pancreatic cells in vitro and the presence of SARS-CoV-2 in pancreatic samples from COVID-19 patients strongly hints that SARS-CoV-2 can invade the pancreas and directly cause pancreatic injury and diabetes. However, more studies are required to dissect the underpinning molecular mechanisms triggered in SARS-CoV-2-infected islets that lead to aggravation of diabetes. Regardless, it is important to understand the function of ACE2 in the pancreatic islets to design relevant therapeutic interventions in combatting the effects of SARS-CoV-2 on diabetes pathophysiology. Herein, we detail the function of ACE2 in pancreatic beta cells crucial for regulating insulin sensitivity, secretion, and glucose metabolism. Also, we discuss the potential role played by ACE2 in aiding SARS-COV-2 entry into the pancreas and the possibility of ACE2 cooperation with alternative entry factors as well as how that may be linked to diabetes pathogenesis.

Wharton's Jelly Mesenchymal Stem Cell-Derived Extracellular Vesicles Reduce SARS-CoV2-Induced Inflammatory Cytokines Under High Glucose and Uremic Toxin Conditions

Cytokine storm is recognized as one of the factors contributing to organ failures and mortality in patients with COVID-19. Due to chronic inflammation, COVID-19 patients with diabetes mellitus (DM) or renal disease (RD) have more severe symptoms and higher mortality. However, the factors that contribute to severe outcomes of COVID-19 patients with DM and RD have received little attention. In an effort to investigate potential treatments for COVID-19, recent research has focused on the immunomodulation functions of mesenchymal stem cells (MSCs). In this study, the correlation between DM and RD and the severity of COVID-19 was examined by a combined approach with a meta-analysis and experimental research. The results of a systematic review and meta-analysis suggested that the odd of mortality in patients with both DM and RD was increased in comparison to those with a single comorbidity. In addition, in the experimental research, the data showed that high glucose and uremic toxins contributed to the induction of cytokine storm in human lung adenocarcinoma epithelial cells (Calu-3 cells) in response to SARS-CoV Peptide Pools. Of note, the incorporation of Wharton's jelly MSC-derived extracellular vesicles (WJ-EVs) into SARS-CoV peptide-induced Calu-3 resulted in a significant decrease in nuclear NF-κB p65 and the downregulation of the cytokine storm under high concentrations of glucose and uremic toxins. This clearly suggests the potential for WJ-EVs to reduce cytokine storm reactions in patients with both chronic inflammation diseases and viral infection.

A Machine-Generated View of the Role of Blood Glucose Levels in the Severity of COVID-19

SARS-CoV-2 started spreading toward the end of 2019 causing COVID-19, a disease that reached pandemic proportions among the human population within months. The reasons for the spectrum of differences in the severity of the disease across the population, and in particular why the disease affects more severely the aging population and those with specific preconditions are unclear. We developed machine learning models to mine 240,000 scientific articles openly accessible in the CORD-19 database, and constructed knowledge graphs to synthesize the extracted information and navigate the collective knowledge in an attempt to search for a potential common underlying reason for disease severity. The machine-driven framework we developed repeatedly pointed to elevated blood glucose as a key facilitator in the progression of COVID-19. Indeed, when we systematically retraced the steps of the SARS-CoV-2 infection, we found evidence linking elevated glucose to each major step of the life-cycle of the virus, progression of the disease, and presentation of symptoms. Specifically, elevations of glucose provide ideal conditions for the virus to evade and weaken the first level of the immune defense system in the lungs, gain access to deep alveolar cells, bind to the ACE2 receptor and enter the pulmonary cells, accelerate replication of the virus within cells increasing cell death and inducing an pulmonary inflammatory response, which overwhelms an already weakened innate immune system to trigger an avalanche of systemic infections, inflammation and cell damage, a cytokine storm and thrombotic events. We tested the feasibility of the hypothesis by manually reviewing the literature referenced by the machine-generated synthesis, reconstructing atomistically the virus at the surface of the pulmonary airways, and performing quantitative computational modeling of the effects of glucose levels on the infection process. We conclude that elevation in glucose levels can facilitate the progression of the disease through multiple mechanisms and can explain much of the differences in disease severity seen across the population. The study provides diagnostic considerations, new areas of research and potential treatments, and cautions on treatment strategies and critical care conditions that induce elevations in blood glucose levels.

Angiotensin-(1-7) Improves Islet Function in a Rat Model of Streptozotocin- Induced Diabetes Mellitus by Up-Regulating the Expression of Pdx1/Glut2

OBJECTIVE

To observe the effects of angiotensin-(1-7) (Ang-(1-7)) on glucose metabolism, islet function and insulin resistance in a rat model of streptozotocin-induced diabetes mellitus (DM) and investigate its mechanism.

METHODS

Thirty-four male Wistar rats were randomly divided into 3 groups: control group, which was fed a standard diet, DM group, high-fat diet and injected with streptozotocin, and Ang-(1-7) group receiving an injection of streptozotocin followed by Ang-(1-7) treatment. Blood glucose level, fasting serum Ang II and insulin levels, and homeostasis model assessment of insulin resistance (HOMA-IR) were measured. The pancreases were collected for histological examination, protein and gene expression analysis.

RESULTS

Compared with the control group, fasting blood glucose, serum angiotensin II level, and HOMA-IR value increased, while serum insulin level decreased in the DM group. Moreover, islet structure was damaged, β cells were irregularly arranged, the cytoplasm was loose in the DM group. Expressions of Pancreatic duodenal homeobox-1 (Pdx1), glucose transporter-2 (Glut2) and glucokinase (Gk) were significantly decreased in the DM group compared with the control group. However, the DM-associated changes were dramatically reversed following Ang-(1-7) treatment.

CONCLUSION

Ang-(1-7) protects against streptozotocin-induced DM through the improvement of insulin secretion, insulin resistance and islet fibrosis, which is associated with the upregulation of Pdx1, Glut2 and Gk expressions.

Prevention and Management of Type 2 Diabetes and Metabolic Syndrome in the Time of COVID-19: Should We Add a Cup of Coffee?

Recent evidence shows that COVID-19 patients with existing metabolic disorders, such as diabetes and metabolic syndrome, are exposed to a high risk of morbidity and mortality. At the same time, in order to manage the pandemic, the health authorities around the world are advising people to stay at home. This results in decreased physical activity and an increased consumption of an unhealthy diet, which often leads to an increase in body weight, risk for diabetes, insulin resistance, and metabolic syndrome, and thus, paradoxically, to a high risk of morbidity and mortality due to COVID-19 complications. Here we summarize the evidence demonstrating that the promotion of a healthy life style, including physical activity and a dietary intake of natural polyphenols present in coffee and tea, has the potential to improve the prevention and management of insulin resistance and diabetes in the time of COVID-19 pandemic. Particularly, it would be pertinent to evaluate further the potential positive effects of coffee beverages, rich in natural polyphenols, as an adjuvant therapy for COVID-19, which appear not to be studied sufficiently.

Angiotensin-converting enzyme 2 influences pancreatic and renal function in diabetic mice

Type 1 diabetes is a T-cell mediated autoimmune disease characterized by pancreatic beta cells destruction. Angiotensin-converting enzyme 2 (ACE2), a component of renin-angiotensin system (RAS) has been identified in pancreas from type 2 diabetic mice and its overexpression prevents beta cell dysfunction. We studied the effect of ACE2 deletion on pancreatic and renal function in the nonobese diabetic mice, a model that mimics type 1 diabetes. ACE2-deficient NOD mice and the respective controls were generated. Pancreas function and immunohistochemistry studies were performed. Renal function and RAS gene expression were also analyzed. Renal proximal tubular cells were obtained from these animals to dissect the effect of ACE2 deficiency in these cells. In NOD mice, ACE2 deletion significantly worsened glucose homeostasis, decreased islet insulin content, increased beta cell oxidative stress, and RIPK1-positive islets as compared with control mice. Angiotensin-converting enzyme and angiotensin II type 1 receptor (AT1R) were also increased in ACE2-deficient mice. In kidneys of 30-day diabetic mice, ACE2 deletion decreased podocyte number within the glomeruli, and altered renal RAS gene expression in tubules. ACE2 deletion influenced the expression of fibrosis-related genes in isolated primary renal proximal tubular cells before diabetes onset in NOD mice. Our findings suggest that ACE2 deletion may have a deleterious impact on beta cell and renal function, by promoting oxidative stress and increasing necroptosis mediators. In addition, this effect is accompanied by RAS alterations in both pancreas and renal proximal tubular cells, indicating that ACE2 may exert a renopancreatic protective effect on type 1 diabetes, which is activated before diabetes starts.

Activation of ACE2/angiotensin (1-7) attenuates pancreatic β cell dedifferentiation in a high-fat-diet mouse model

OBJECTIVE

Angiotensin-converting enzyme 2 (ACE2) has been identified in pancreatic islets and can preserve β cells. In this study, we aimed to examine the possible role of ACE2 and its end product, angiotensin 1-7 (A1-7), in reducing β cell dedifferentiation during metabolic stress.

METHODS

First, a lineage-tracing experiment was performed to track β cells in mice fed a high-fat diet (HFD). Second, the ACE2/A1-7 axis was evaluated in the HFD mouse model. Intraperitoneal glucose tolerance tests (IPGTTs) and intraperitoneal insulin tolerance tests (IPITTs) were conducted. Phenotypic changes in β cells were detected by immunohistochemistry and quantitative real-time PCR. Pancreatic sections were immunostained for vascular endothelial growth factor (VEGF) and inducible nitric oxide synthase (iNOS). Finally, the effects of the ACE2/A1-7 axis were explored in isolated mouse islets exposed to different concentrations of glucose. Glucose-stimulated insulin release and levels of insulin mRNA and OCT4 mRNA were measured.

RESULTS

Pancreatic β cell dedifferentiation occurred both in vitro and in vivo in response to metabolic stress and was accompanied by ACE2 reduction. HFD-induced insulin resistance and glucose intolerance were exacerbated in ACE2-knockout (ACE2KO) mice but were alleviated by exogenous A1-7 in C57BL/6J mice. Approximately 20% of β cells were dedifferentiated in ACE2KO mice fed a standard rodent chow diet (SD). A higher percentage of dedifferentiated β cells was detected in ACE2KO mice than in wild-type (WT) mice under HFD conditions. In contrast, the administration of A1-7 alleviated HFD-induced β cell dedifferentiation in C57BL/6J mice. Moreover, the exogenous injection of A1-7 improved microcirculation in islets and decreased the production of iNOS in islets of C57BL/6J mice fed an HFD. Additionally, ACE2 was found to be mainly expressed in α cells of mice, while Mas, the receptor of A1-7, was distributed in β cells.

CONCLUSIONS

Overall, this study is the first to demonstrate that the ACE2/A1-7/Mas axis may be one of the intra-islet paracrine mechanisms of communication between α and β cells. Enhancing the ACE2/A1-7 axis exerts a protective effect by ameliorating β cell dedifferentiation, and this effect might be partially mediated through improvements in islet microcirculation and suppression of islet iNOS.

Evidence of changes in alpha-1/AT1 receptor function generated by diet-induced obesity

To study whether hypercaloric diet-induced obesity deteriorates vascular contractility of rat aorta through functional changes in α₁ adrenergic and/or AT1 Angiotensin II receptors. Angiotensin II- or phenylephrine-induced contraction was tested on isolated aorta rings with and without endothelium from female Wistar rats fed for 7 weeks with hypercaloric diet or standard diet. Vascular expression of Angiotensin II Receptor type 1 (AT1R), Angiotensin II Receptor type 2 (AT2R), Cyclooxygenase-1 (COX-1), Cyclooxygenase-2 (COX-2), inducible Nitric Oxide Synthase (iNOS) and endothelial Nitric Oxide Synthase (eNOS), as well as blood pressure, glucose, insulin and angiotensin II blood levels were measured. Diet-induced obesity did not significantly change agonist-induced contractions (Emax and pD₂ hypercaloric diet vs standard diet n.s.d.) of both intact (e+) or endothelium free (e-) vessels but significantly decrease both phenylephrine and angiotensin II contraction (Emax p < 0.01 hypercaloric diet vs standard diet) in the presence of both prazosin and losartan but only in endothelium-intact vessels. Diet-induced obesity did not change angiotensin II AT1, AT2 receptor proteins expression but reduced COX-1 and NOS2 ( p < 0.05 vs standard diet). Seven-week hypercaloric diet-induced obesity produces alterations in vascular adrenergic and angiotensin II receptor dynamics that suggest an endothelium-dependent adrenergic/angiotensin II crosstalk. These changes reflect early-stage vascular responses to obesity.

Association of Increased Serum ACE Activity with Logical Memory Ability in Type 2 Diabetic Patients with Mild Cognitive Impairment

Background: Angiotensin-converting enzyme (ACE) is involved in the chronic complications of type 2 diabetes mellitus (T2DM) and Alzheimer's disease. This study aimed to assess the pathogenetic roles of ACE and the genetic predisposition of its insertion/deletion (I/D) polymorphism in mild cognitive impairment (MCI) among T2DM patients.

Methods: A total of 210 T2DM patients were enrolled. Among these patients, 116 satisfied the MCI diagnostic criteria and 94 exhibited healthy cognition. The cognitive functions of the patients were extensively assessed. The serum level and activity of ACE were measured via enzyme-linked immunosorbent assay and ultraviolet spectrophotography. The single-nucleotide polymorphisms of I/D gene of ACE were analyzed.

Results: The serum level and activity of ACE in diabetic MCI patients (p = 0.022 and p = 0.008, respectively) were both significantly higher than those in the healthy controls. A significant negative correlation was found between their ACE activity and logical memory test score (LMT) (p = 0.002). Multiple stepwise regression iterated the negative correlation between ACE activity and LMT score (p = 0.035). Although no significant difference was found in the genotype or allele distribution of ACE I/D polymorphism between the groups, the serum levels and activity of ACE were higher in the DD group than in the ID and II groups (p < 0.05).

Conclusions: Serum ACE activity could better predict logical memory in T2DM patients than ACE level. Further investigations on a large population size are necessary to test whether the D-allele of the ACE gene polymorphism is susceptible to memory deterioration.

High-fat diet-induced glucose dysregulation is independent of changes in islet ACE2 in mice

While restoration of ACE2 activity in the pancreas leads to improvement of glycemia in experimental models of Type 2 diabetes, global deficiency in ACE2 disrupts β-cell function and impairs glucose tolerance in mice, demonstrating the physiological role of ACE2 in glucose homeostasis. Although the contribution of pancreatic ACE2 to glucose regulation has been demonstrated in genetic models of diabetes and in models with overexpression of the renin-angiotensin system (RAS), it is unclear whether islet ACE2 is involved in glycemic control in common models of human Type 2 diabetes. To determine whether diet-induced diabetes deregulates glucose homeostasis via reduction of ACE2 in the pancreatic islets, wild-type (WT) and ACE2 knockout (KO) male mice were fed a high-fat diet (HFD) for 16 wk. ACE2 KO mice were more susceptible than WT mice to HFD-mediated glycemic dysregulation. Islet ACE2 activity and expression of various genes, including ANG II type 1a receptor (mAT_1aR) were then assessed. Surprisingly, we observed no change in islet ACE2 activity and expression despite local RAS overactivity, indicated by an upregulation of mAT_1aR expression. Despite a predominant expression in islet α-cells, further investigation highlighted a minor role for ACE2 on glucagon expression. Further, pancreatic ACE2 gene therapy improved glycemia in HFD-fed WT mice, leading to enhanced glucose-stimulated insulin secretion, reduced pancreatic ANG II levels, fibrosis, and ADAM17 activity. Altogether, our study demonstrates that HFD feeding increases RAS activity and mediates glycemic dysregulation likely through loss of ACE2 present outside the islets but independently of changes in islet ACE2.

ACE2 deficiency reduces β-cell mass and impairs β-cell proliferation in obese C57BL/6 mice

Drugs that inhibit the renin-angiotensin system (RAS) decrease the onset of type 2 diabetes (T2D). Pancreatic islets express RAS components, including angiotensin-converting enzyme 2 (ACE2), which cleaves angiotensin II (Ang II) to angiotensin-(1-7) [Ang-(1-7)]. Overexpression of ACE2 in pancreas of diabetic mice improved glucose homeostasis. The purpose of this study was to determine if deficiency of endogenous ACE2 contributes to islet dysfunction and T2D. We hypothesized that ACE2 deficiency potentiates the decline in β-cell function and augments the development of diet-induced T2D. Male Ace2(+/y) or Ace2(-/y) mice were fed a low-fat (LF) or high-fat (HF) diet for 1 or 4 mo. A subset of 1-mo HF-fed mice were infused with Sal (Sal), losartan (Los), or Ang-(1-7). At 4 mo, while both genotypes of HF-fed mice developed a similar level of insulin resistance, adaptive hyperinsulinemia was reduced in Ace2(-/y) vs. Ace2(+/y) mice. Similarly, in vivo glucose-stimulated insulin secretion (GSIS) was reduced in 1-mo HF-fed Ace2(-/y) compared with Ace2(+/y) mice, resulting in augmented hyperglycemia. The average islet area was significantly smaller in both LF- and HF-fed Ace2(-/y) vs. Ace2(+/y) mice. Additionally, β-cell mass and proliferation were reduced significantly in HF-fed Ace2(-/y) vs. Ace2(+/y) mice. Neither infusion of Los nor Ang-(1-7) was able to correct impaired in vivo GSIS of HF-fed ACE2-deficient mice. These results demonstrate a critical role for endogenous ACE2 in the adaptive β-cell hyperinsulinemic response to HF feeding through regulation of β-cell proliferation and growth.

Persistent hyperglycemia modulates gut immune function and microbiota in rats

Background

Since hyperglycemia-induced cellular dysfunction could be associated with alterations of the immune system, we tested the hypothesis that hyperglycemia augments the aberrant immune responses such as inflammation and differentiation of CD4⁺ T lymphocytes in the mesenteric lymph nodes (MLNs), and induces alterations of microbiota both under physiological and pathological conditions.

Methods

Male Wistar rats were randomly allocated into 4 groups: Control and Endotoxemia (lipopolysaccharide, LPS 1 mg/kg) with or without hyperglycemia. The hyperglycemia groups were administered glucose solution (10-40 %), while the normoglycemia groups were administered saline. Alterations of the mRNA expressions of inflammatory cytokines and CD4⁺ T lymphocyte transcriptional factor expressions in the MLNs, and those of the intestinal microbiota were analyzed at 24 hr.

Results

Hyperglycemia was kept approximately 250–350 mg/dL during the 24 hr study period. At the end of 24 hr, hyperglycemia augmented the mRNA expressions of interleukin (IL)-1β and IL-6 in the MLNs, while both the helper T (Th) 2 and regulatory-T (Treg) transcriptional factors were simultaneously up-regulated under non-endotoxemic condition. LPS injection significantly modulated the obligate anaerobe bacterial populations of the Bacteroidetes class, and altered the population sizes of the Clostridium perfringens and the Bacteroides fragilis subgroup. Hyperglycemia did not enhance these alterations of the microbiota evoked by LPS, although it did modify the bacterial populations of the L. reuteri subgroup and staphylococci in healthy condition without endotoxemia.

Conclusions

The present study indicates that both gut immune function and microbiota are significantly modulated by persistent hyperglycemia.

Electronic supplementary material

The online version of this article (doi:10.1186/s40560-015-0101-8) contains supplementary material, which is available to authorized users.

Angiotensin AT2 receptor agonist prevents salt-sensitive hypertension in obese Zucker rats

High-sodium intake is a risk factor for the pathogenesis of hypertension, especially in obesity. The present study is designed to investigate whether angiotensin type 2 receptor (AT2R) activation with selective agonist C21 prevents high-sodium diet (HSD)-induced hypertension in obese animals. Male obese rats were treated with AT2R agonist C21 (1 mg·kg(-1)·day(-1), oral) while maintained on either normal-sodium diet (NSD; 0.4%) or HSD (4%) for 2 wk. Radiotelemetric recording showed a time-dependent increase in systolic blood pressure in HSD-fed obese rats, being maximal increase (∼27 mmHg) at day 12 of the HSD regimen. C21 treatment completely prevented the increase in blood pressure of HSD-fed rats. Compared with NSD controls, HSD-fed obese rats had greater natriuresis/diuresis and urinary levels of nitrates, and these parameters were further increased by C21 treatment. Also, C21 treatment improved glomerular filtration rate in HSD-fed rats. HSD-fed rats expressed higher level of cortical ANG II, which was reduced to 50% by C21 treatment. HSD feeding and/or C21 treatment had no effects on cortical renin activity and the expression of angiotensin-converting enzyme (ACE) and chymase, which are ANG II-producing enzymes. However, ANG(1-7) concentration and ACE2 activity in the renal cortex were reduced by HSD feeding, and C21 treatment rescued both the parameters. Also, C21 treatment reduced the cortical expression of AT1R in HSD-fed rats, but had no effect of AT2R expression. We conclude that chronic treatment with the AT2R agonist C21 prevents salt-sensitive hypertension in obese rats, and a reduction in the renal ANG II/AT1R and enhanced ACE2/ANG(1-7) levels may play a potential role in this phenomenon.

Effects of nitric oxide synthase deficiency on a disintegrin and metalloproteinase domain-containing protein 12 expression in mouse brain samples

A disintegrin and metalloproteinase domain-containing protein 12 (ADAM12) belongs to the ADAM family of transmembrane proteins. Via proteolysis, cell adhesion, cell-cell fusion, cell-matrix interaction and membrane protein shedding, ADAM proteins are involved in normal brain development, and also in cancer genesis and progression, and in inflammation. Therefore, neurobiological research focusing on this protein is increasing. Nitric oxide (NO), which is endogenously produced by NO synthases (NOS), is associated with glial tumors. However, knock-out of NOS produces only limited antitumor effects. The present study analyzed the expression of ADAM12 in the cortex and hippocampus of C57/BL6 wild-type mice, and endothelial NOS-, neuronal NOS-(nNOS) or inducible NOS (iNOS)-deficient (-/-) mice, at different stages of development. Expression of ADAM12 was quantified using immunoblot analysis of cortical and hippocampal tissue samples from fetal, neonatal (5 days postnatal), adult (12 weeks old) or >1 year old mice. Using reverse transcription-quantitative polymerase chain reaction, ADAM12 expression was analyzed in cultured N9, OLN93, C6 and PC12 cells, representing the four main cell types in the brain, following NOS inhibition. ADAM12 expression was low in all mouse genotypes and regions of the brain, and in fetal and neonatal mice, an increase in expression was observed with increasing age. The highest levels of expression were observed in the cortex of adult mice, iNOS(-/-) mice of >1 year and wild-type mice, and in the hippocampus of adult and iNOS(-/-) mice of >1 year. By contrast, ADAM12 expression was lowest in adult nNOS(-/-) mice. Inhibition of NOS using N(ω)-Nitro-L-arginine methyl ester hydrochloride, induced ADAM12 mRNA expression in N9 and PC12 cell lines. Inhibition of NOS using L-N(6)-(1-Iminoethyl)lysine dihydrochloride, induced ADAM12 mRNA expression in N9 and C6 cell lines. No change in ADAM12 expression was observed in OLN93 cells following NOS inhibition. ADAM12 expression in mouse hippocampus and cortex samples demonstrated considerable variation during development, with a marked increase observed in adult and >1 year old mice, compared with that in fetal and neonatal mice.

Experimental gestational diabetes mellitus induces blunted vasoconstriction and functional changes in the rat aorta

Diabetic conditions increase vascular reactivity to angiotensin II in several studies but there are scarce reports on cardiovascular effects of hypercaloric diet (HD) induced gestational diabetes mellitus (GDM), so the objective of this work was to determine the effects of HD induced GDM on vascular responses. Angiotensin II as well as phenylephrine induced vascular contraction was tested in isolated aorta rings with and without endothelium from rats fed for 7 weeks (4 before and 3 weeks during pregnancy) with standard (SD) or hypercaloric (HD) diet. Also, protein expression of AT₁R, AT₂R, COX-1, COX-2, NOS-1, and NOS-3 and plasma glucose, insulin, and angiotensin II levels were measured. GDM impaired vasoconstrictor response (P < 0.05 versus SD) in intact (e+) but not in endothelium-free (e−) vessels. Losartan reduced GDM but not SD e− vasoconstriction (P < 0.01 versus SD). AT₁R, AT₂R, and COX-1 and COX-2 protein expression were significantly increased in GDM vessels (P < 0.05 versus SD). Results suggest an increased participation of endothelium vasodilator mediators, probably prostaglandins, as well as of AT₂ vasodilator receptors as a compensatory mechanism for vasoconstrictor changes generated by experimental GDM. Considering the short term of rat pregnancy findings can reflect early stage GDM adaptations.

Angiotensin 1-7: a peptide for preventing and treating metabolic syndrome

Angiotensin-(1-7) is one of the most important active peptides of the renin-angiotensin system (RAS) with recognized cardiovascular relevance; however several studies have shown the potential therapeutic role of Ang-(1-7) on treating and preventing metabolic disorders as well. This peptide achieves a special importance considering that in the last few decades obesity and metabolic syndrome (MS) have become a growing worldwide health problem. Angiotensin (Ang) II is the most studied component of RAS and is increased during obesity, diabetes and dyslipidemia (MS); some experimental evidence has shown that Ang II modulates appetite and metabolism as well as mechanisms that induce adipose tissue growth and metabolism in peripheral organs. Recent articles demonstrated that Ang-(1-7)/Mas axis modulates lipid and glucose metabolism and counterregulates the effects of Ang II. Based on these data, angiotensin-converting enzyme 2 (ACE2)/Ang-(1-7)/Mas pathway activation have been advocated as a new tool for treating metabolic diseases. This review summarizes the new evidence from animal and human experiments indicating the use of Ang-(1-7) in prevention and treatment of obesity and metabolic disorders.

Non-canonical signalling and roles of the vasoactive peptides angiotensins and kinins

GPCRs (G-protein-coupled receptors) are among the most important targets for drug discovery due to their ubiquitous expression and participation in cellular events under both healthy and disease conditions. These receptors can be activated by a plethora of ligands, such as ions, odorants, small ligands and peptides, including angiotensins and kinins, which are vasoactive peptides that are classically involved in the pathophysiology of cardiovascular events. These peptides and their corresponding GPCRs have been reported to play roles in other systems and under pathophysiological conditions, such as cancer, central nervous system disorders, metabolic dysfunction and bone resorption. More recently, new mechanisms have been described for the functional regulation of GPCRs, including the transactivation of other signal transduction receptors and the activation of G-protein-independent pathways. The existence of such alternative mechanisms for signal transduction and the discovery of agonists that can preferentially trigger one signalling pathway over other pathways (called biased agonists) have opened new perspectives for the discovery and development of drugs with a higher specificity of action and, therefore, fewer side effects. The present review summarizes the current knowledge on the non-canonical signalling and roles of angiotensins and kinins.