Effect of angiotensin II type 1 receptor blocker on 12-lipoxygenase activity and slit diaphragm protein expression in type 2 diabetic rat glomeruli

Cytoskeleton Rearrangement in Podocytopathies: An Update

Podocyte injury can disrupt the glomerular filtration barrier (GFB), leading to podocytopathies that emphasize podocytes as the glomerulus's key organizer. The coordinated cytoskeleton is essential for supporting the elegant structure and complete functions of podocytes. Therefore, cytoskeleton rearrangement is closely related to the pathogenesis of podocytopathies. In podocytopathies, the rearrangement of the cytoskeleton refers to significant alterations in a string of slit diaphragm (SD) and focal adhesion proteins such as the signaling node nephrin, calcium influx via transient receptor potential channel 6 (TRPC6), and regulation of the Rho family, eventually leading to the disorganization of the original cytoskeletal architecture. Thus, it is imperative to focus on these proteins and signaling pathways to probe the cytoskeleton rearrangement in podocytopathies. In this review, we describe podocytopathies and the podocyte cytoskeleton, then discuss the molecular mechanisms involved in cytoskeleton rearrangement in podocytopathies and summarize the effects of currently existing drugs on regulating the podocyte cytoskeleton.

JAK/STAT pathway promotes the progression of diabetic kidney disease via autophagy in podocytes

Diabetic kidney disease (DKD) is one of the major microvascular complications of diabetes and an important cause of end-stage renal disease. Previous studies have shown that the damage to podocyte autophagy is related to the pathogenesis of DKD, and this damage is closely mediated by the Janus kinase (JAK)/signal transductors and the transcription (STAT) signaling pathway. Here, the underlying molecular mechanism of the JAK/STAT signaling pathway regulating podocyte autophagy was investigated. In the present study, compared to controls, DKD mice showed glomerular hypertrophy, increased kidney weight/weight ratio, and increased urinary protein levels, as well as decreased desmin and synaptopodin expression. Meanwhile, levels of triglyceride, total cholesterol, reduced glutathione, and malondialdehyde were also increased in the serum of DKD mice. Further, a lower number of autophagosomes, reduced expression of MAP1LC3 (LC3) in glomeruli, and increased expression of JAK/STAT pathway-related proteins, namely JAK1, JAK2, STAT1, STAT3, STAT5, and STAT6, were observed in DKD mice. In the in vitro experiments, we observed impaired autophagy, enhanced apoptosis, and activated JAK/STAT pathway in podocytes under high glucose conditions. Studies using ruxolitinib inhibitors have showed that suppression of the JAK/STAT pathway in podocytes subjected to high glucose could increase autophagic flux and autophagy-related protein expression. Taken together, the present study demonstrates that high glucose inhibits autophagy by activating the JAK/STAT pathway in mice and podocytes, thereby preventing the efficient removal of damaged proteins and organelles from the body to prevent apoptosis, and ultimately aggravating the progression of podocyte injury and DKD.

Megalin-mediated albumin endocytosis in renal proximal tubules is involved in the antiproteinuric effect of angiotensin II type 1 receptor blocker in a subclinical acute kidney injury animal model

BACKGROUND

Tubule-interstitial injury (TII) is one of the mechanisms involved in the progression of renal diseases with progressive proteinuria. Angiotensin II (Ang II) type 1 receptor blockers (ARBs) have been successfully used to treat renal diseases. However, the mechanism correlating treatment with ARBs and proteinuria is not completely understood. The hypothesis that the anti-proteinuric effect of losartan is associated with the modulation of albumin endocytosis in PT epithelial cells (PTECs) was assessed.

METHODS

We used a subclinical acute kidney injury animal model (subAKI) and LLC-PK1 cells, a model of PTECs.

RESULTS

In subAKI, PT albumin overload induced TII development, measured by: (1) increase in urinary lactate dehydrogenase and γ-glutamyltranspeptidase activity; (2) proteinuria associated with impairment in megalin-mediated albumin reabsorption; (3) increase in luminal and interstitial space in tubular cortical segments. These effects were avoided by treating the animals with losartan, an ARB. Using LLC-PK1 cells, we observed that: (1) 20 mg/mL albumin increased the secretion of Ang II and decreased megalin-mediated albumin endocytosis; (2) the effects of Ang II and albumin were abolished by 10^-8 M losartan; (3) MEK/ERK pathway is the molecular mechanism underlying the Ang II-mediated inhibitory effect of albumin on PT albumin endocytosis.

CONCLUSION

Our results show that PT megalin-mediated albumin endocytosis is a possible target during the treatment of renal diseases patients with ARB.

GENERAL SIGNIFICANCE

The findings obtained in the present work represents a step forward to the current knowledge on about the role of ARBs in the treatment of renal disease.

Losartan Protects Podocytes against High Glucose-induced Injury by Inhibiting B7-1 Expression

The role of B7-1 in podocyte injury has received increasing attention. The aim of this study was to investigate whether losartan protects podocytes of patients with diabetic kidney disease (DKD) by regulating B7-1 and the underlying mechanisms. Rats with streptozotocin-induced DKD were treated with losartan for 8 weeks. Biochemical changes in blood and urine were analyzed. Kidneys were isolated for electron microscopy, immunofluorescence, real-time quantitative PCR (RT-PCR), and Western blot analysis. Immortalized mouse podocyte cells were cultured in normal or high glucose medium in the presence or absence of losartan for 48 h, and then the cells were collected for immunofluorescence, PCR, Western blotting and monolayer permeability detection. The phosphatidylinositol 3-kinase (PI3K) 110α subunit and angiotensin II type 1 receptor (AT1R) plasmids were transfected into podocytes, respectively, and then Western blotting was performed to assess the expression of B7-1 protein. The results showed that losartan ameliorated podocyte structure and function in the rat model of DKD, and reduced the expression of B7-1 protein. Overexpression of PI3K 110α subunit in podocytes attenuated the inhibitory effect of losartan on B7-1 expression in high glucose-stimulated podocytes. The expression of B7-1 was significantly increased by overexpression of AT1R and significantly reduced by blocking PI3K 110α subunit. We conclude that losartan protects podocytes against high glucose-induced injury by inhibiting AT1R-mediated B7-1 expression. This effect is dependent on the AT1R-PI3K 110α subunit pathway.

Effect of Icariside II and Metformin on Penile Erectile Function, Histological Structure, Mitochondrial Autophagy, Glucose-Lipid Metabolism, Angiotensin II and Sex Hormone in Type 2 Diabetic Rats With Erectile Dysfunction

INTRODUCTION

Type 2 diabetes mellitus erectile dysfunction (T2DMED) is one of the common complications of type 2 diabetes mellitus (T2DM). Icariside II (ICA II), a flavonoid derived from Epimedium, has been shown to improve erectile function in T2DMED rats.

AIM

To investigate the effect of ICA II and metformin (MET) on penile erectile function, mitochondrial autophagy, glucose-lipid metabolism in rats with T2DMED.

METHODS

In the control and T2DMED groups, rats were administered normal saline. In the MET group, rats were administered MET for 0.2 g/kg/day. In the ICA II+MET group, rats were administered ICA II for 10 mg/kg/day and MET for 0.2 g/kg/day.

RESULTS

The number of mating rats, number of erectile rats, erection rate, erection frequency, intracorneal pressure, and intracorneal pressure/mean arterial pressure in the ICA II+MET group and control group were significantly higher than corresponding values in than T2DMED group. The absolute values of fasting plasma glucose, glycated haemoglobin in the ICA II+MET group, MET group, and control group were significantly lower than in the T2DMED group. The advanced glycation end product (AGE) values in the ICA II+MET group and the MET group were lower than in the T2DMED group. The receptors for the AGE values and angiotensin II values in the ICA II+MET group were lower than in the T2DMED and MET groups. The high-density lipoprotein values, testosterone values, nitric oxide synthase activity, and cyclic guanosine monophosphate content in the ICA II+MET and control groups were higher than in the T2DMED group. The low-density lipoprotein values, triglyceride values, estradiol values, and total cholesterol values in the ICA II+MET and control groups were lower than in the T2DMED group.

CONCLUSION

ICA II could increase erectile function and smooth muscle cell/collagen fibril proportions, decreased mitochondrial autophagy, and AGE concentrations and improve lipid metabolism, nitric oxide synthase activity, cyclic guanosine monophosphate content, testosterone, estradiol, and Ang II in rat with T2DMED. Zhang J, Li S, Zhang S, et al. Effect of Icariside II and Metformin on Penile Erectile Function, Histological Structure, Mitochondrial Autophagy, Glucose-Lipid Metabolism, Angiotensin II and Sex Hormone in Type 2 Diabetic Rats With Erectile Dysfunction. J Sex Med 2020;8:168-177.

Role of the 12-lipoxygenase pathway in diabetes pathogenesis and complications

12-lipoxygenase (12-LOX) is one of several enzyme isoforms responsible for the metabolism of arachidonic acid and other poly-unsaturated fatty acids to both pro- and anti-inflammatory lipid mediators. Mounting evidence has shown that 12-LOX plays a critical role in the modulation of inflammation at multiple checkpoints during diabetes development. Due to this, interventions to limit pro-inflammatory 12-LOX metabolites either by isoform-specific 12-LOX inhibition, or by providing specific fatty acid substrates via dietary intervention, has the potential to significantly and positively impact health outcomes of patients living with both type 1 and type 2 diabetes. To date, the development of truly specific and efficacious inhibitors has been hampered by homology of LOX family members; however, improvements in high throughput screening have improved the inhibitor landscape. Here, we describe the function and role of human 12-LOX, and mouse 12-LOX and 12/15-LOX, in the development of diabetes and diabetes-related complications, and describe promise in the development of strategies to limit pro-inflammatory metabolites, primarily via new small molecule 12-LOX inhibitors.

Proteinuric Kidney Diseases: A Podocyte's Slit Diaphragm and Cytoskeleton Approach

Proteinuric kidney diseases are a group of disorders with diverse pathological mechanisms associated with significant losses of protein in the urine. The glomerular filtration barrier (GFB), comprised of the three important layers, the fenestrated glomerular endothelium, the glomerular basement membrane (GBM), and the podocyte, dictates that disruption of any one of these structures should lead to proteinuric disease. Podocytes, in particular, have long been considered as the final gatekeeper of the GFB. This specialized visceral epithelial cell contains a complex framework of cytoskeletons forming foot processes and mediate important cell signaling to maintain podocyte health. In this review, we will focus on slit diaphragm proteins such as nephrin, podocin, TRPC6/5, as well as cytoskeletal proteins Rho/small GTPases and synaptopodin and their respective roles in participating in the pathogenesis of proteinuric kidney diseases. Furthermore, we will summarize the potential therapeutic options targeting the podocyte to treat this group of kidney diseases.