The role of mitochondrial fission factor in podocyte injury in diabetic nephropathy.

Diabetic nephropathy (DN) is one of the most important complications of diabetes mellitus (DM) and has become the second cause of end-stage renal disease (ESRD). This study intends to investigate the molecular mechanism of increased mitochondrial fission in podocytes under the effect of high glucose (HG), and to preliminarily study the role of mitochondrial fission factor (MFF)-mediated mitochondrial fission in podocyte injury of DN. In vitro studies, we found that HG induced increased mitochondrial fission and podocyte damage. At the same time MFF mRNA and protein levels was increased, suggesting that MFF was transcriptional upregulated under HG conditions. Consistent with this, in vivo studies found that mitochondrial fission was also significantly increased in podocytes of diabetic nephropathy mice, and MFF expression was up-regulated. Therefore, our study proves that mitochondrial fission increases in podocytes under DM both in vitro and in vivo, and the up-regulation of MFF expression may be one of the reasons for the increase of mitochondrial fission. After inhibiting the expression of MFF, the survival rate of podocytes was significantly decreased under HG conditions, suggesting that MFF may play a protective role in podocyte injury in DN.

Lpl-C310R mutation is associated with impaired glucose tolerance and endoplasmic reticulum stress in skeletal muscle.

Primary Hypertriglyceridemia refers to a loss-of-function genetic defect which prevents the triglyceride (TG) in chylomicrons (CM) from lipolysis, leading to the accumulation of TG. The mutation of lipoprotein lipase (LPL) gene has been recognized as the main cause of primary hypertriglyceridemia. Recently, a new LPL gene mutation p.C310R(c. T928C) was identified in a family with hypertriglyceridemia. The proband was manifested by severe hypertriglyceridemia and diabetes. Skeletal muscle is the major LPL-synthesizing tissue and insulin response target tissue. However, little is known about the effects of LPL gene mutation on skeletal muscle. This study is intended to observe the effects of LPL-C310R mutation on glycolipid metabolism and skeletal muscle. We found that a significantly decreased LPL plasma concentration, activity and the expression levels in skeletal muscle were observed in LplC310R/+ mice comparing to wild type mice. Those mutant mice also exhibited increased fasting plasma TG, free fat acids (FFA) and insulin, as well as FFA in muscle, and decreased glucose tolerance. Enhanced expression of BIP and elevated phosphorylation of IRE1α were observed in skeletal muscle, suggesting increased endoplasmic reticulum stress (ERS). Consistent with this, increased phosphorylation of JNK was also observed. Meanwhile, remarkably enhanced phosphorylation of IRS-1 (Ser307) and decreased phosphorylation of AKT were observed in skeletal muscle of mutant mice, suggesting impaired insulin signaling. Significant lipid deposition and morphological changes in endoplasmic reticulum and mitochondria were observed in the skeletal muscle of mutant mice but not in wild type control. Results demonstrate Lpl C310R mutation caused impaired glucose tolerance, ER stress and impaired insulin signaling in skeletal muscle.

Orientin Protects Podocytes from High Glucose Induced Apoptosis through Mitophagy.

Diabetic nephropathy (DN) is one of the serious complications of diabetes mellitus. Orientin, a major bioactive constituent of Fenugreek, has been reported to possess antihyperglycemic properties. However, its effects on DN remain unclear. Therefore, we explored the protective effect of orientin on podocytes. Here, we assessed cell viability and toxicity, level of autophagy, mitochondrial morphological changes, and podocyte apoptosis. The results indicated that high glucose (HG) induced podocyte apoptosis as well as mitochondrial injury can be partially blocked by orientin. The results showed that orientin could repair autophagy disorder induced by HG, while 3-methyladenine (3-MA) reversed the protection of orientin. Our study demonstrated the possibility of treating DN with orientin.

SUMO-1 modification on K166 of polyQ-expanded ataxin-3 strengthens its stability and increases its cytotoxicity.

Post-translational modification by SUMO was proposed to modulate the pathogenesis of several neurodegenerative diseases. Spinocerebellar ataxia type 3/Machado-Joseph disease (SCA3/MJD) is an autosomal dominant neurodegenerative disease caused by polyQ-expanded ataxin-3. We have previously shown that ataxin-3 was a new target of SUMOylation in vitro and in vivo. Here we identified that the major SUMO-1 binding site was located on lysine 166. SUMOylation did not influence the subcellular localization, ubiquitination or aggregates formation of mutant-type ataxin-3, but partially increased its stability and the cell apoptosis. Our findings revealed the role of ataxin-3 SUMOylation in SCA3/MJD pathogenesis.