De novo expression of CD44 in glomerular parietal epithelial cells (PECs) leads to a prosclerotic and migratory PEC phenotype in glomerulosclerosis. However, the regulatory mechanisms underlying CD44 expression by activated PECs remain largely unknown. This study was performed to examine the mediators responsible for CD44 induction in glomerular PECs in association with diabetes. CD44 expression and localization were evaluated in the glomeruli of Zucker diabetic rat kidneys and primary cultured PECs upon albumin stimulation. Real-time polymerase chain reaction confirmed an albuminuria-associated upregulation of the CD44 gene in the glomeruli of diabetic rats. Immunostaining analysis of diabetic kidneys further revealed an increase in CD44 in hypertrophic PECs, which often contain albuminpositive vesicles. Losartan treatment significantly attenuated albuminuria and lowered CD44 protein levels in the diabetic kidneys. In primary cultured rat PECs, rat serum albumin (0.25-1 mg/ml) caused a dose-dependent upregulation of CD44, claudin-1, and megalin protein expression, which was accompanied by an activation of extracellular signal-regulated kinase1/2 (ERK1/2) signaling. Albumin-induced CD44 and claudin-1 expression were greatly suppressed in the presence of the ERK1/2 inhibitor, U0126. In addition, knockdown of megalin by small interfering RNA interference in PECs resulted in a significant reduction of albumin-induced CD44 and claudin-1 proteins. Taken together, our results demonstrate that albumin induces CD44 expression by PECs via the activation of the ERK signaling pathway, which is partially mediated by endocytic receptor megalin. K E Y W O R D S albuminuria, diabetic glomerular disease, megalin, parietal epithelial cells (PECs), U0126
Matrix metalloproteinase-9 (MMP-9) is dysregulated in chronic kidney diseases including diabetic nephropathy. This study was performed to examine the expression of MMP-9 in renal tubule epithelial cells (TECs) under diabetic conditions and its regulatory mechanisms. We characterized MMP-9 protein in diabetic animals and primary cultured rat TECs exposed to exogenous albumin and high glucose. We also used specific inhibitors to determine if internalization of albumin and/or extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation were required for MMP-9 secretion. Immunostaining of kidney sections revealed enhanced MMP-9 signal in the damaged proximal tubules in Zucker diabetic fatty (ZDF) rats. ZDF rats also exhibited an albuminuria-related and age-dependent increase in MMP-9 excretion, which was prevented by rosiglitazone. In primary cultured rat TECs, high glucose exposure did not increase MMP-9 secretion. In contrast, administration of rat serum albumin (RSA, 0.1–0.5 mg/mL) resulted in a dose-dependent increase in MMP-9 expression and secretion by TECs, which was abolished in the presence of an ERK1/2-specific inhibitor, U0126. Simvastatin, an inhibitor of albumin endocytosis, also prevented MMP-9 secretion. Taken together, these results demonstrate that endocytosis of albumin stimulates MMP-9 secretion by TECs through the ERK signaling pathway.
De novo expression of CD44 in glomerular parietal epithelial cells (PECs) leads to a pro‐sclerotic and migratory PEC phenotype in focal segmental glomerulosclerosis. However, the mechanisms underlying CD44 induction in activated PECs remain largely unknown. This study was performed to examine CD44 expression in rat PECs under proteinuric condition and its regulatory mechanisms. CD44 gene and protein levels were examined in Zucker diabetic (ZD) rat kidneys and primary cultured rat PECs exposed to exogenous albumin. Gene microarray and real‐time PCR confirmed an upregulation of CD44 mRNA in renal cortex and glomeruli of ZD rats. Immunofluorescence staining of kidney sections revealed an increase in CD44 signal in claudin‐1‐positive PECs. Enhanced CD44 staining was observed in activated PECs localized in Bowman's capsule and migrated into the glomerular tuft. Moreover, anti‐proteinuric treatment with losartan, an angiotensin II receptor blocker, significantly reduced CD44 protein level in the diabetic rat kidney. In primary cultured rat PECs, administration of rat serum albumin (RSA, 0.25 – 1 mg/ml) resulted in an activation of ERK1/2 MAPK signaling and upregulation of CD44 and claudin‐1 protein expression. This increase in claudin‐1 and CD44 protein was significantly attenuated in the presence of specific ERK1/2 inhibitor U0126. Taken together, our results demonstrate that albumin activates PECs and induces CD44 expression, at least partially via the activation of ERK signaling pathway.Support or Funding InformationNIH SC1DK112151, NIH/NCRR/RCMI 8G12MD007602 & 8U54MD007588This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.