ABSTRACT
Objective:To investigate the role of mitofusion 2 (Mfn2) in high glucose (HG)-induced endoplasmic reticulum stress (ERS) and apoptosis of podocytes.Methods:(1) Streptozocin was used to induce a diabetes mellitus (DM) rat model. Renal histopathological changes in rats were observed by HE staining. Expression of Mfn2 and CCAAT/enhancer-binding protein homologous protein (CHOP) in glomeruli was observed by immunohistochemistry. Protein levels of Mfn2, protein kinase RNA-like ER kinase (PERK), phospho(p)-PERK, and CHOP in glomeruli were analyzed by Western blotting. (2) Conditionally immortalized human podocytes (HPC) cultured in vitro were divided into control, mannitol (MA) and HG groups. Expression of Mfn2 was observed by immunofluorescence. Protein levels of Mfn2, p-PERK, PERK and CHOP in HPC were analyzed by Western blotting. Podocyte apoptosis in each group was evaluated by flow cytometry with AnnexinⅤ-PE/7AAD double staining method. (3) HPC were divided into control, HG, HG+Mfn2-Myc plasmid-transfected and HG+control plasmid-transfected groups. Protein levels of Mfn2, p-PERK, PERK and CHOP in HPC were analyzed by Western blotting. Expression of CHOP was observed by immunofluorescence. Mitochondrial membrane potential in each group was observed by mitochondrial membrane potential assay kit with JC-1. Podocyte apoptosis in each group was evaluated by flow cytometry with AnnexinⅤ-PE/7AAD double staining method. Results:(1) Compared with the control group, the glomerular mesangial matrix of the DM group rats was significantly proliferated, and the expression of Mfn2 was down-regulated with the expression of ERS-related proteins p-PERK/PERK and CHOP up-regulated (all P<0.05). (2) Compared with the control group, Mfn2 was down-regulated and p-PERK/PERK and CHOP were up-regulated in HPC of HG group (all P<0.05). Apoptosis of HPC was also increased in HG group. There was no significant difference in the above indicators between the control group and the mannitol group (all P>0.05). (3) Compared with the HG group, mitochondrial membrane potential of HPC was alleviated and apoptosis of HPC was decreased in HG+Mfn2-Myc plasmid-transfected group ( P<0.05). P-PERK/PERK and CHOP were down-regulated in HG+Mfn2-Myc plasmid-transfected group (both P<0.05). There was no significant difference in the above indicators between the HG group and the HG+control plasmid-transfected group (all P>0.05). Conclusions:Mfn2 down-regulation in HG-stimulated podocytes may induce ERS to increase apoptosis of podocytes. Up-regulation of Mfn2 can alleviate the HG-induced ERS and apoptosis in podocytes.
ABSTRACT
Objective To investigate the roles of A kinase anchoring protein1(AKAP1)in high-glucose induced mitochondrial fission in podocytes.Methods Conditionally immortalized human podocytes were cultured in serum-free medium for 24 hours,and then exposed to different glucose concentration conditions in different time periods.The protein expressions of AKAP1 were observed by immunofluorescence,and AKAP1,dynamin related protein1 (Drp1) and phospho Ser 637-Drp1 (p-Drp1)were analyzed by Western blotting.AKAP1 siRNA was transfected to block AKAP1 expression.Podocytes were then divided into normal control group (5 mmol/L glucose),hypertonic group (30 mmol/L mannitol+5 mmol/L glucose),high glucose group (35 mmol/L glucose),and high glucose+AKAP1 siRNA group.Mitochondrial morphological changes were assessed by mitotracker red staining.Podocyte apoptosis was assessed by flow cytometry.Results Compared with normal group,high-glucose induced more podocytes apoptosis (P ＜ 0.05),more mitochondrial fission with decreased aspect ratio and form factor (all P ＜ 0.05).Upregulated AKAP1 protein level,and increased ratio of p-Drp1/Drp1 (all P ＜ 0.05) in time and concentration dependent manners were also obscrvcd.Compared with high glucose group,transfection of AKAP1 siRNA showed less apoptosis (P ＜ 0.05),less mitochondrial fission with increased aspect ratio and form factor (all P ＜ 0.05),and down-regulated AKAP1 protein level as well as p-Drp1/Drp1 ratio (all P ＜ 0.05).Conclusion High glucose induced mitochondrial fission might be induced through AKAP1-Drp1 pathway.
ABSTRACT
Objective To investigate the effects of angiotensin Ⅱ (Ang Ⅱ) on the expression of C-terminal Src kinase (Csk) in Ang Ⅱ-infused rat model and cultured podocytes,and to explore the role of Csk in Ang Ⅱ-induced cytoskeletal rearrangement of podocytes.Methods Twenty-four Wista rats were randomly subjected to normal saline infusion,or Ang Ⅱ infusion at 400 ng · kg1 · min-1 (via subcutaneous osmotic minipumps) for 2 or 4 weeks.Renal histomorphology was evaluated through electron microscopy.The expression of glomerular Csk was analyzed by immunofluorescence and Western blotting.In vitro,conditionally immortalized mouse podocytes were cultured and treated with Ang Ⅱ doses ranging from 10-9 mol/L to 10-5 mol/L and for different hours.The expression of podocytes Csk was assessed by Western blotting.After transfection to podocytes with Csk siRNA,FITC-conjugated phalloidin was used to stain F-actin,to investigate the role of Csk in Ang Ⅱ-induced or cytochalasin D-induced cytoskeletal rearrangement.Results (1) Examination of Ang Ⅱ infusion rats glomerular and podocyte ultrastructure by electron microscopy revealed foot process effacement and fusion; (2) In Ang Ⅱ infusion rats,the expression of glomerular Csk was increased (P ＜ 0.05); (3) In vitro,Ang Ⅱ-stimuli up-regulated the expression of Csk (P ＜ 0.05),and the effects of Ang Ⅱ were on dose-dependent and time-dependent manner; (4) Ang Ⅱ-induced disruption of F-actin was alleviated by Csk siRNA transfection in cultured podocytes; furthermore,cytochalasin D depolymerized the F-actin cytoskeleton,while Csk siRNA stabilized the actin filaments.Conclusion The enhanced expression of Csk may be involved in Ang II-induced podocytes cytoskeletal rearrangement and foot process fusion.