An angiotensin II type 1 receptor blocker prevents renal injury via inhibition of the Notch pathway in Ins2 Akita diabetic mice

Gastrodin Regulates the Notch-1 Signal Pathway via Renin-Angiotensin System in Activated Microglia

Notch-1 and renin angiotensin system (RAS) are involved in microglia activation. It has been reported that gastrodin inhibited inflammatory responses mediated by activated microglia. This study explored the possible interaction between this two pathways, and to determine whether gastrodin would exert its effects on both of them. Expression of RAS, Notch-1 signaling and proinflammatory mediators in lipopolysaccharide (LPS) activated BV-2 microglia subjected to various treatments was determined by Western blot and immunofluorescence. The protein expression of RAS, Notch-1 pathway and TNF-α and IL-1β was significantly increased in activated microglia. Exogenous Ang II markedly enhanced the expression of these biomarkers. Meanwhile, Azilsartan [a specific inhibitor of AT₁ (AT₁I)] inhibited the expression of Notch-1 pathway and proinflammatory cytokines. When Notch-1 signaling was inhibited with DAPT, ACE and AT₁ expression remained unaffected, indicating that RAS can regulate the Notch-1 pathway in activated microglia but not reciprocally. Additionally, we showed here that gastrodin inhibited the RAS, Notch-1 pathway and inflammatory response. Remarkably, gastrodin did not exert any effect on expression of Notch-1 signaling when RAS was blocked by AT₁I, suggesting that gastrodin acts on the RAS directly, not through the Notch-1 pathway. Furthermore, TNF-α and IL-1β expression was significantly increased in activated microglia treated with exogenous Ang II; the expression, however, was suppressed by gastrodin. Of note, expression of proinflammatory cytokines was further decreased in gastrodin and AT₁I combination treatment. The results suggest that gastrodin acts via the RAS which regulates the Notch-1 signaling and inflammation in LPS-induced microglia.

A novel podocyte protein, R3h domain containing-like, inhibits TGF-β-induced p38 MAPK and regulates the structure of podocytes and glomerular basement membrane

Not only in kidney glomerular physiological function but also glomerular pathology especially in diabetic condition, glomerular podocytes play pivotal roles. Therefore, it is important to increase our knowledge about the genes and proteins expressed in podocytes. Recently, we have identified a novel podocyte-expressed gene, R3h domain containing-like (R3hdml) and analyzed its function in vivo as well as in vitro. Transforming growth factor-β (TGF-β) signaling regulated the expression of R3hdml. And R3hdml inhibited p38 mitogen-activated protein kinase phosphorylation, which was induced by TGF-β, leading to the amelioration of podocyte apoptosis. Furthermore, a lack of R3hdml in mice significantly worsened glomerular function in streptozotocin (STZ)-induced diabetes, while overexpression of R3hdml ameliorated albuminuria in STZ-induced diabetes. Our results surmise that the functional analyses of R3hdml may lead to the development of novel therapeutic strategies for diabetic nephropathy in the future. KEY MESSAGES: • A novel podocyte expressed protein R3h domain containing-like was identified. • R3HDML inhibits podocyte apoptosis by inhibiting TGF-β-mediated p38 MAPK signaling. • Overexpression of R3HDML ameliorates albuminuria in STZ-induced diabetes mice. • R3HDML may prove to be a novel therapeutic strategy for diabetic nephropathy.

Diabetic Nephropathy: Novel Molecular Mechanisms and Therapeutic Targets

Diabetic nephropathy (DN) is one of the major microvascular complications of diabetes mellitus and the leading cause of end-stage kidney disease. The standard treatments for diabetic patients are glucose and blood pressure control, lipid lowering, and renin-angiotensin system blockade; however, these therapeutic approaches can provide only partial renoprotection if started late in the course of the disease. One major limitation in developing efficient therapies for DN is the complex pathobiology of the diabetic kidney, which undergoes a set of profound structural, metabolic and functional changes. Despite these difficulties, experimental models of diabetes have revealed promising therapeutic targets by identifying pathways that modulate key functions of podocytes and glomerular endothelial cells. In this review we will describe recent advances in the field, analyze key molecular pathways that contribute to the pathogenesis of the disease, and discuss how they could be modulated to prevent or reverse DN.

Gastrodin Regulates the Notch Signaling Pathway and Sirt3 in Activated Microglia in Cerebral Hypoxic-Ischemia Neonatal Rats and in Activated BV-2 Microglia

In response to hypoxic-ischemic brain damage (HIBD), microglia activation and its mediated inflammation contribute to neuronal damage. Inhibition of over-activated microglia is deemed to be a potential therapeutic strategy. Our previous studies showed that gastrodin efficiently depressed the neuroinflammation mediated by activated microglia in HIBD neonatal rats. The underlying mechanisms through which gastrodin acts on activated microglia have not been fully elucidated. This study is designed to determine whether gastrodin would regulate the Notch signaling pathway and Sirtuin3 (Sirt3), which are implicated in regulating microglia activation. The present results showed that gastrodin markedly suppressed the expression of members of Notch signaling pathway (Notch-1, NICD, RBP-JK and Hes-1) in activated microglia both in vivo and in vitro. Conversely, Sirt3 expression was enhanced. In BV-2 microglia treated with a γ-secretase inhibitor of Notch pathway- DAPT, the expression of RBP-JK, Hes-1, and NICD was suppressed in activated microglia. Treatment with DAPT and gastrodin further decreased NICD and Hes-1 expression. Sirt3 expression was also decreased after DAPT treatment. However, Sirt3 expression in activated BV-2 microglia given a combined DAPT and gastrodin treatment was not further increased. In addition, combination of DAPT and Gastrodin cumulatively decreased tumor necrosis factor-α (TNF-α) expression. The results suggest that gastrodin regulates microglia activation via the Notch signaling pathway and Sirt3. More importantly, interference of the Notch signaling pathway inhibited Sirt3 expression, indicating that Sirt3 is a downstream gene of the Notch signaling pathway. It is suggested that Notch and Sirt3 synergistically regulate microglia activation such as in TNF-α production.

Sirt6 deficiency aggravates angiotensin II-induced cholesterol accumulation and injury in podocytes

Disturbed renal lipid metabolism, especially cholesterol dysregulation plays a crucial role in the pathogenesis of chronic kidney disease (CKD). We recently reported that angiotensin (Ang) II could induce cholesterol accumulation and injury in podocytes. However, the underlying mechanisms for these alterations remain unknown. Methods: Bioinformatics analysis of renal biopsy specimens from patients with hypertensive nephropathy (HN) suggests the involvement of Sirtuin 6 (Sirt6) in Ang II-induced dysregulation of glomerular cholesterol. Using a podocyte-specific Sirt6 knockout mouse model, the effects of Sirt6 on Ang II-induced cholesterol accumulation in podocytes and the therapeutic efficacies of cholesterol-lowering agents were evaluated. Results: Cholesterol accumulation was detected in the podocytes of Ang II-infused mice, whereas selective deletion of Sirt6 in podocytes not only increased cholesterol accumulation in these cells but also exacerbated Ang II-induced kidney injury. Deletion of Sirt6 also attenuated the protective effect of cyclodextrin (CD) on Ang II-induced urinary albumin excretion, glomerulosclerosis and podocyte injury. In addition, we demonstrated that Sirt6 affected cholesterol efflux in podocytes by regulating the expression of ATP-binding cassette transporter G1 (ABCG1). Conclusions: These findings provide evidence that Sirt6 is a potential target for renin-angiotensin system (RAS)-associated podocyte injury and provide a rationale for the application of cholesterol-lowering agents in patients with CKD.

Notch inhibitor mitigates renal ischemia‑reperfusion injury in diabetic rats

Diabetes mellitus can exacerbate renal ischemia-reperfusion (I/R) injury (RI/RI) in diabetic rats. Previous studies have shown that Notch signaling is involved in renal disorders. The aim of the present study was to evaluate the protective effect of the Notch inhibitor γ-secretase N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT) on RI/RI in a streptozocin (STZ)-induced diabetic rat model. STZ-induced diabetic rats were randomly grouped for different treatments. Cisplatin was used to trigger the Notch signaling pathway and the animals were preconditioned with DAPT to block the signaling pathway. Renal function, oxidative stress and inflammatory factors were examined. DAPT-treated diabetic rats demonstrated mitigated renal injury and function, antioxidative activity was significantly improved and HIF-1a was upregulated. Notch inhibitor DAPT is a potential therapeutic target to improve the outcome of RI/RI in STZ-induced diabetic rats in part via the regulation of anti-oxidation and HIF-1a.

A novel podocyte gene, semaphorin 3G, protects glomerular podocyte from lipopolysaccharide-induced inflammation

Kidney diseases including diabetic nephropathy have become huge medical problems, although its precise mechanisms are still far from understood. In order to increase our knowledge about the patho-physiology of kidney, we have previously identified >300 kidney glomerulus-enriched transcripts through large-scale sequencing and microarray profiling of the mouse glomerular transcriptome. One of the glomerulus-specific transcripts identified was semaphorin 3G (Sema3G) which belongs to the semaphorin family. The aim of this study was to analyze both the in vivo and in vitro functions of Sema3G in the kidney. Sema3G was expressed in glomerular podocytes. Although Sema3G knockout mice did not show obvious glomerular defects, ultrastructural analyses revealed partially aberrant podocyte foot processes structures. When these mice were injected with lipopolysaccharide to induce acute inflammation or streptozotocin to induce diabetes, the lack of Sema3G resulted in increased albuminuria. The lack of Sema3G in podocytes also enhanced the expression of inflammatory cytokines including chemokine ligand 2 and interleukin 6. On the other hand, the presence of Sema3G attenuated their expression through the inhibition of lipopolysaccharide-induced Toll like receptor 4 signaling. Taken together, our results surmise that the Sema3G protein is secreted by podocytes and protects podocytes from inflammatory kidney diseases and diabetic nephropathy.

Angiotensin II type 1 receptor antagonists in animal models of vascular, cardiac, metabolic and renal disease

We have reviewed the effects of angiotensin II type 1 receptor antagonists (ARBs) in various animal models of hypertension, atherosclerosis, cardiac function, hypertrophy and fibrosis, glucose and lipid metabolism, and renal function and morphology. Those of azilsartan and telmisartan have been included comprehensively whereas those of other ARBs have been included systematically but without intention of completeness. ARBs as a class lower blood pressure in established hypertension and prevent hypertension development in all applicable animal models except those with a markedly suppressed renin-angiotensin system; blood pressure lowering even persists for a considerable time after discontinuation of treatment. This translates into a reduced mortality, particularly in models exhibiting marked hypertension. The retrieved data on vascular, cardiac and renal function and morphology as well as on glucose and lipid metabolism are discussed to address three main questions: 1. Can ARB effects on blood vessels, heart, kidney and metabolic function be explained by blood pressure lowering alone or are they additionally directly related to blockade of the renin-angiotensin system? 2. Are they shared by other inhibitors of the renin-angiotensin system, e.g. angiotensin converting enzyme inhibitors? 3. Are some effects specific for one or more compounds within the ARB class? Taken together these data profile ARBs as a drug class with unique properties that have beneficial effects far beyond those on blood pressure reduction and, in some cases distinct from those of angiotensin converting enzyme inhibitors. The clinical relevance of angiotensin receptor-independent effects of some ARBs remains to be determined.

The Notch pathway mediates the angiotensin II-induced synthesis of extracellular matrix components in podocytes

The Notch pathway is known to contribute to the development of glomerular disease. Angiotensin II (Ang II), an important member of the renin-angiotensin system, stimulates the accumulation of extracellular matrix components in glomerular disease; however, the exact mechanisms involved remain to be elucidated. In the present study, we aimed to investigate the effects of the Notch pathway on the synthesis of extracellular matrix components in Ang II-stimulated podocytes. Mouse podocytes were stimulated with Ang II (10-6 mol/l). The activation of the Notch pathway was inhibited by a vector carrying short hairpin RNA (shRNA) targeting Notch1 (sh-Notch1) or by γ-secretase inhibitor (GSI). The protein levels of Notch1, Notch intracellular domain 1 (NICD1), hairy and enhancer of split-1 (Hes1), matrix metalloproteinase (MMP)-2, MMP-9, transforming growth factor-β1 (TGF-β1), type IV collagen and laminin were determined by western blot analysis. The Notch1, Hes1, MMP-2, MMP-9, TGF-β1, type IV collagen and laminin mRNA levels were detected by RT-PCR. The MMP-2 and MMP-9 activity was measured using a cell active fluorescence assay kit. The levels of TGF-β1, type IV collagen and laminin were determined in the culture medium of the podocytes by enzyme-linked immunosorbent assay (ELISA). Our results revealed that Ang II upregulated Notch1, NICD1, Hes1, TGF-β1, type IV collagen and laminin expression and downregulated MMP-2 and MMP-9 expression in the cultured podocytes. The inhibition of the Notch pathway by sh-Notch1 or GSI increased MMP-2 and MMP-9 expression, decreased the TGF-β1 level and suppressed type IV collagen and laminin expression. The inhibition of the Notch pathway by sh-Notch1 or GSI also increased MMP-2 and MMP-9 activity, and decreased TGF-β1 levels, type IV collagen levels and laminin secretion. These findings indicate that the Notch pathway potentially mediates the Ang II-induced synthesis of extracellular matrix components in podocytes through the regulation of MMPs and TGF-β1.

Kick it up a notch: Notch signaling and kidney fibrosis

Notch is a critical regulator of kidney development, but the pathway is mostly silenced once kidney maturation is achieved. Recent reports demonstrated increased expression of Notch receptors and ligands both in acute and chronic kidney injury. In vivo studies indicated that Notch activation might contribute to regeneration after acute kidney injury; on the other hand, sustained Notch expression is causally associated with interstitial fibrosis and glomerulosclerosis. This review will summarize the current knowledge on the role of the Notch signaling with special focus on kidney fibrosis.

Olmesartan attenuates cardiac remodeling through DLL4/Notch1 pathway activation in pressure overload mice

BACKGROUND

Notch1 signaling controls the cardiac adaptation to stress. We therefore aimed to validate whether olmesartan, a widely used angiotensin II type 1 receptor blocker, ameliorates cardiac remodeling and dysfunction via delta-like ligand 4 (DLL4)/Notch1 pathway in mice with chronic pressure overload.

METHODS

Cardiac pressure overload was produced by transverse aortic constriction (TAC). A total of 35 wide-type C57BL/6J mice were randomly divided into sham group, TAC group, TAC + olmesartan group, and TAC + olmsartan + DAPT group (DAPT: γ-secretase inhibitor, Notch signaling inhibitor). Saline (10 mL·kg(-1)·d(-1)) or the same volume of olmesartan liquor (3 mg·kg(-1) d(-1)) was administered by gavage, and DAPT (10 μmole·kg(-1)·d(-1)) by peritoneal injection. After 28 days of treatment, cardiac hemodynamics, echocardiography, and histology were evaluated, followed by quantitative polymerase chain reaction of fetal gene (ANP and SAA) expression. Notch1-related proteins and ERK1/2 were examined by western blot, and the serum level of angiotensin II was determined by means of enzyme-linked immunosorbent assay kits.

RESULTS

Persistent pressure overload-induced left ventricular hypertrophy, dysfunction, fibrosis, and microcirculation dysfunction, together with the upregulation of angiotensin II, ERK1/2, and fetal gene expression. By the activation of DLL4/Notch1, olmesartan decreased left ventricular hypertrophy and fibrosis, preserved cardiac function, and improved capillary density and coronary perfusion. All these curative effects were suppressed by pharmacological blockade of Notch signaling with DAPT.

CONCLUSIONS

Our findings identify a heretofore unknown pharmacological mechanism that olmesartan improves cardiac remodeling and function via DLL4/Notch1 pathway activation in mice with chronic pressure overload, which may present a new therapeutic target for hypertension.

Effect of angiotensin II receptor blocker on experimental periodontitis in a mouse model of Marfan syndrome

Marfan syndrome is an autosomal dominant disease characterized by aneurysm and dilatation of the aortic root, tall stature, and ectopia lentis. These manifestations reflect excessive signaling of transforming growth factor beta (TGF-β). Moreover, cases are frequently associated with severe periodontitis, which is a chronic inflammation of the gingiva, periodontal ligament, and alveolar bone. Recently, angiotensin II receptor blockers (ARBs) were discovered to be an effective drug class that can prevent aortic aneurysm and dilation in Marfan syndrome by inhibiting TGF-β signaling. To investigate the effect of ARB on the progression of periodontitis, the application of a potent ARB, telmisartan, was examined in a mouse model of Marfan syndrome (MgΔ). Six-week-old male heterozygous MgΔ and wild-type mice were challenged with Porphyromonas gingivalis, which causes chronic periodontitis, with and without telmisartan application. After infection, alveolar bone resorption was measured by micro-computed tomography (μCT), and inflammatory cytokine levels were examined. Infection of Porphyromonas gingivalis induced alveolar bone resorption in both MgΔ and wild-type mice. The amount of resorption was significantly larger in the former than the latter. Immunoarray and enzyme-linked immunosorbent assay (ELISA) analyses demonstrated that interleukin-17 (IL-17) and tumor necrosis factor alpha (TNF-α) levels were significantly higher in infected MgΔ mice than infected wild-type mice. Telmisartan treatment significantly suppressed the alveolar bone resorption of infected MgΔ mice. Telmisartan also significantly decreased levels of TGF-β, IL-17, and TNF-α in infected MgΔ mice to levels seen in infected wild-type mice. This study suggests that ARB can prevent the severe periodontitis frequently seen in Marfan syndrome.