Protective Effects of GLP-1 on Glomerular Endothelium and Its Inhibition by PKC Activation in Diabetes

Corresponding author: George L. King, .
Diabetes (Impact Factor: 8.1). 07/2012; 61(11):2967-79. DOI: 10.2337/db11-1824
Source: PubMed


To characterize glucagon-like peptide (GLP)-1 signaling and its effect on renal endothelial dysfunction and glomerulopathy. We studied the expression and signaling of GLP-1 receptor (GLP-1R) on glomerular endothelial cells and the novel finding of protein kinase A-dependent phosphorylation of c-Raf at Ser259 and its inhibition of angiotensin II (Ang II) phospho-c-Raf(Ser338) and Erk1/2 phosphorylation. Mice overexpressing protein kinase C (PKC)β2 in endothelial cells (EC-PKCβ2Tg) were established. Ang II and GLP-1 actions in glomerular endothelial cells were analyzed with small interfering RNA of GLP-1R. PKCβ isoform activation induced by diabetes decreased GLP-1R expression and protective action on the renal endothelium by increasing its degradation via ubiquitination and enhancing phospho-c-Raf(Ser338) and Ang II activation of phospho-Erk1/2. EC-PKCβ2Tg mice exhibited decreased GLP-1R expression and increased phospho-c-Raf(Ser338), leading to enhanced effects of Ang II. Diabetic EC-PKCβ2Tg mice exhibited greater loss of endothelial GLP-1R expression and exendin-4-protective actions and exhibited more albuminuria and mesangial expansion than diabetic controls. These results showed that the renal protective effects of GLP-1 were mediated via the inhibition of Ang II actions on cRaf(Ser259) and diminished by diabetes because of PKCβ activation and the increased degradation of GLP-1R in the glomerular endothelial cells.

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Available from: Munehiro Kitada, Feb 03, 2014
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    • "It is resistant to DPP-4, resulting in a longer circulating half-life time, about 2.4 hours. In addition to coordinated effects on glucose metabolism [20, 21], exenatide exerts endothelium-protective action similar to GLP-1 [22, 23]. However, until now, the underlying mechanisms are not fully understood. "
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    ABSTRACT: We will investigate the effects of exenatide on vascular endothelial injury and nitrooxidative stress in hyperglycemia both in vivo and in vitro and explore the role of nitrooxidative stress in endothelium-protective action of exenatide. Healthy male Wistar rats were randomly divided into 4 groups: control, diabetes mellitus (DM) model, low dose of exenatide treatment, and high dose of exenatide treatment. In vitro study showed that, compared with control group, the DM rats exhibited a lowered endothelium-dependent relaxation and damaged structural integrity of thoracic aortas, and there was a significant increase in plasma nitrotyrosine concentration. These parameters were improved after treatment with either low dose or high dose of exenatide for 45 days. In vitro study showed that exendin-4 (the active ingredient of exenatide) attenuated HUVECs injury induced by high glucose, with improving cell viability and attenuating cell apoptosis. Exendin-4 also significantly alleviated the increased malondialdehyde (MDA), nitrotyrosine content, and inducible nitric oxide synthase (iNOS) expression induced by high glucose in HUVECs. In conclusion, this study demonstrates that exenatide treatment can alleviate the vascular endothelial injury, as well as attenuating the nitrooxidative stress in hyperglycemia, implying that the endothelium-protective effect of exenatide might be related to the reduction of nitrooxidative stress.
    11/2013; 2013:843657. DOI:10.1155/2013/843657
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    • "AMPK) could be of high interest (Figure 7). In this sense, GLP-1 may also directly counteract the pro-oxidative, inflammatory and apoptotic activities induced by angiotensin-II [43,44]. "
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    ABSTRACT: Myocardial fibrosis is a key process in diabetic cardiomyopathy. However, their underlying mechanisms have not been elucidated, leading to a lack of therapy. The glucagon-like peptide-1 (GLP-1) enhancer, sitagliptin, reduces hyperglycemia but may also trigger direct effects on the heart. Goto-Kakizaki (GK) rats developed type-II diabetes and received sitagliptin, an anti-hyperglycemic drug (metformin) or vehicle (n=10, each). After cardiac structure and function assessment, plasma and left ventricles were isolated for biochemical studies. Cultured cardiomyocytes and fibroblasts were used for in vitro assays. Untreated GK rats exhibited hyperglycemia, hyperlipidemia, plasma GLP-1 decrease, and cardiac cell-death, hypertrophy, fibrosis and prolonged deceleration time. Moreover, cardiac pro-apoptotic/necrotic, hypertrophic and fibrotic factors were up-regulated. Importantly, both sitagliptin and metformin lessened all these parameters. In cultured cardiomyocytes and cardiac fibroblasts, high-concentration of palmitate or glucose induced cell-death, hypertrophy and fibrosis. Interestingly, GLP-1 and its insulinotropic-inactive metabolite, GLP-1(9-36), alleviated these responses. In addition, despite a specific GLP-1 receptor was only detected in cardiomyocytes, GLP-1 isoforms attenuated the pro-fibrotic expression in cardiomyocytes and fibroblasts. In addition, GLP-1 receptor signalling may be linked to PPARδ activation, and metformin may also exhibit anti-apoptotic/necrotic and anti-fibrotic direct effects in cardiac cells. Sitagliptin, via GLP-1 stabilization, promoted cardioprotection in type-II diabetic hearts primarily by limiting hyperglycemia e hyperlipidemia. However, GLP-1 and GLP-1(9-36) promoted survival and anti-hypertrophic/fibrotic effects on cultured cardiac cells, suggesting cell-autonomous cardioprotective actions.
    PLoS ONE 10/2013; 8(10):e78330. DOI:10.1371/journal.pone.0078330 · 3.23 Impact Factor
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    • "The patients, who had continued overt proteinuria even after 4 months administration of ARBs with dietary salt restriction, were included in the present study. Mima et al. (2012) "
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    ABSTRACT: Diabetic nephropathy (DN) is the leading cause of end-stage renal disease. Glucagon-like peptide-1 (GLP-1) is one of the incretins, gut hormones released from the intestine in response to food intake. GLP-1 receptor (GLP-1R) agonists have been used to treat type 2 diabetes. Here, we studied the effect of the administration of a GLP-1R agonist, liraglutide, on proteinuria and the progression of overt DN in type 2 diabetic patients. Twenty-three type 2 diabetic patients with overt DN, who had already been treated with blockade of renin-angiotensin system under dietary sodium restriction, were given liraglutide for a period of 12 months. Treatment with liraglutide caused a significant decrease in HbA1c from 7.4 ± 0.2% to 6.9 ± 0.3% (p = 0.04), and in body mass index (BMI) from 27.6 ± 0.9 kg/m(2) to 26.5 ± 0.8 kg/m(2) after 12 months (p < 0.001), while systolic blood pressure did not change. The progression of DN was determined as the rate of decline in estimated glomerular filtration rate (eGFR). The 12-month administration of liraglutide caused a significant decrease in proteinuria from 2.53 ± 0.48 g/g creatinine to 1.47 ± 0.28 g/g creatinine (p = 0.002). The administration of liraglutide also substantially diminished the rate of decline in eGFR from 6.6 ± 1.5 mL/min/1.73 m(2)/year to 0.3 ± 1.9 mL/min/1.73 m(2)/year (p = 0.003). Liraglutide can be used not only for reducing HbA1c and BMI, but also for attenuating the progression of nephropathy in type 2 diabetic patients.
    The Tohoku Journal of Experimental Medicine 08/2013; 231(1):57-61. DOI:10.1620/tjem.231.57 · 1.35 Impact Factor
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