Matrix metalloproteinase-9 expression is enhanced in renal parietal epithelial cells of zucker diabetic Fatty rats and is induced by albumin in in vitro primary parietal cell culture.

Yuanyuan Zhang,Yun Li,Jasmine George,Xueying Zhao,Rebecca Olufade,Maria Pia Rastaldi

doi:10.1371/journal.pone.0123276

Abstract

As a subfamily of matrix metalloproteinases (MMPs), gelatinases including MMP-2 and MMP-9 play an important role in remodeling and homeostasis of the extracellular matrix. However, conflicting results have been reported regarding their expression level and activity in the diabetic kidney. This study investigated whether and how MMP-9 expression and activity were changed in glomerular epithelial cells upon albumin overload. In situ zymography, immunostaining and Western blot for renal MMP gelatinolytic activity and MMP-9 protein expression were performed in Zucker lean and Zucker diabetic rats. Confocal microscopy revealed a focal increase in gelatinase activity and MMP-9 protein in the glomeruli of diabetic rats. Increased glomerular MMP-9 staining was mainly observed in hyperplastic parietal epithelial cells (PECs) expressing claudin-1 in the diabetic kidneys. Interestingly, increased parietal MMP-9 was often accompanied by decreased staining for podocyte markers (nephrin and podocalyxin) in the sclerotic area of affected glomeruli in diabetic rats. Additionally, urinary excretion of podocyte marker proteins was significantly increased in association with the levels of MMP-9 and albumin in the urine of diabetic animals. To evaluate the direct effect of albumin on expression and activity of MMP-9, primary cultured rat glomerular PECs were incubated with rat serum albumin (0.25 - 1 mg/ml) for 24 - 48 hrs. MMP-9 mRNA levels were significantly increased following albumin treatment. Meanwhile, albumin administration resulted in a dose-dependent increase in MMP-9 protein and activity in culture supernatants of PECs. Moreover, albumin activated p44/42 mitogen-activated protein kinase (MAPK) in PECs. Inhibition of p44/42 MAPK suppressed albumin-induced MMP-9 secretion from glomerular PECs. Taken together, we have demonstrated that an up-regulation of MMP-9 in activated parietal epithelium is associated with a loss of adjacent podocytes in progressive diabetic nephropathy. Albumin overload may induce MMP-9 expression and secretion by PECs via the activation of p44/42 MAPK pathway.

Highlights

Diabetic nephropathy is the leading cause of end-stage renal disease, accounting for 40– 50% of the patients entering dialysis each year in the United States
We further report a focal increase in glomerular gelatinase activity and matrix metalloproteinases (MMPs)-9 expression in parietal epithelium in association with a significant loss of adjacent podocytes in the damaged glomeruli of diabetic animals
A stimulatory effect of albumin on MMP-9 expression and secretion was detected in primary cultured rat glomerular parietal epithelial cells (PECs)

Summary

Introduction

Diabetic nephropathy is the leading cause of end-stage renal disease, accounting for 40– 50% of the patients entering dialysis each year in the United States. Albuminuria serves as a marker for early kidney injury, and plays a central role in the pathogenesis of progressive renal dysfunction. Studies have highlighted the importance of podocytes, the terminally differentiated visceral epithelial cells of the glomerulus, in the pathogenesis of proteinuric diseases. In most studies, a reduced number of podocytes is associated with the presence of a glomerular scar, even if the initial injury was not directed primarily against podocytes [2]. It has been suggested that podocytes can be lost secondarily because of the invasion of parietal epithelial cells (PECs) in glomerular diseases [2]

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Conclusion