Abstract
Glomerular tuft immune reactive Ezrin surface area (EzA) and fraction of EzA to total glomerular tuft area significantly increased, indicating podocyte growth, rounding and altered cytoskeletal interactions at 1 week of STZ diabetes. Podocyte number per glomerulus (WT1+ nuclei) did not change indicating no detachment, but density decreased due to tuft hypertrophy. Treatment with PLZ or Insulin for one week, prevented increase in proteinuria and hyperglycemia but not the decrease in podocyte density. PLZ but not Insulin prevented increase in ezrin positive area in glomeruli and per podocyte. In podocytes in culture neither 25 mM glucose with or without PLZ (2.5 or 25 uM) altered Ezrin expression measured in western blots. In summary, the Ezrin positive glomerular surface area increase seen after 1 week of STZ diabetes, reflects altered podocyte morphology and cytoskeletal interactions, prevented by PLZ but not by insulin. Ezrin area increase preceded podocyte detachment and in podocytes in culture is not associated with increases in podocyte Ezrin protein expression. It is a likely precursor of shape changes in podocytes and of alterd interactions with basement membrane that contribute to detachment and thickening. Glomerular capillary tuft hypertrophy and reduced podocyte density persisted despite PLZ or insulin treatments, independently of levels of glycemia and of proteinuria.
Highlights
Podocytes are the major cells responsible for selectivity of the glomerular filtration barrier [1] and are the target of many pathophysiological processes resulting in glomerular disease
Ezrin, a cytoskeletal-membrane linker protein involved in epithelial cell morphogenesis, adhesion and signal transduction [7] and of Wilms tumor-1 a protein typical of podocyte nuclei [8] were measured by immunohistochemistry to assess changes in the podocyte membrane-cytoskeleton and in their number, respectively, in diabetic and phlorizin or insulin-treated diabetic rats
Insulin treatment prevented the development of hyperglycemia (5.14 ± 0.37 mM) and proteinuria (8.85 ± 0.99 mg/day)
Summary
Podocytes are the major cells responsible for selectivity of the glomerular filtration barrier [1] and are the target of many pathophysiological processes resulting in glomerular disease. Their complex and delicate architecture, wrapping around glomerular capillaries and defining the filtration slit diaphragms plays a critical role in determining the perm-selectivity of the glomerular barrier [2]. Glomerular pathology is a main and early result of the microvascular component of the disease, often translating in hypertrophy, hyperfiltration and micro albuminuria [3] and evolving into glomerulosclerosis, overt proteinuria and renal failure [4]. Ezrin expression was measured in western blots of podocytes in vitro exposed to 5 or 25 mM glucose and with or without PLZ
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