Calpastatin overexpression prevents progression of S-1,2-dichlorovinyl-l-cysteine (DCVC)-initiated acute renal injury and renal failure (ARF) in diabetes.

Previously we have shown that 90% of streptozotocin (STZ)-induced type-1 diabetic (DB) mice survive from acute renal failure (ARF) and death induced by a normally LD(90) dose (75 mg/kg, i.p.) of the nephrotoxicant S-1,2-dichlorovinyl-l-cysteine (DCVC). This remarkable protection is due to a combination of slower progression of DCVC-initiated renal injury and increased compensatory nephrogenic tissue repair in the DB kidneys. BRDU immunohistochemistry revealed that the DB condition led to 4-fold higher number of proximal tubular cells (PTC) entering S-phase of cell cycle. In the present study, we tested the hypothesis that DB-induced augmentation of PTC into S-phase is accompanied by overexpression of the calpain-inhibitor calpastatin, which endogenously prevents the progression of DCVC-initiated renal injury mediated by the calpain escaping out of damaged PTCs. Immunohistochemical detection of renal calpain and its activity in the urine, over a time course after treatment with the LD(90) dose of DCVC, indicated progressive increase in leakage of calpain into the extracellular spaces of the injured PTCs of the non-diabetic (NDB) kidneys as compared to the DB kidneys. Calpastatin expression was minimally detected in the NDB kidneys, using immunohistochemistry, over the time course. On the other hand, consistently higher number of tubules in the DB kidney showed calpastatin expression over the time course. The lower leakage of calpain in the DB kidneys was commensurate with constitutively higher expression of calpastatin in the S-phase-laden PTCs of these mice. To test the protective role of newly divided/dividing PTCs, DB mice were given the anti-mitotic agent colchicine (CLC) (2 mg/kg and 1.5 mg/kg, i.p., on days 8 and 10 after STZ injection) prior to challenge with a LD(90) dose of DCVC, which led to 100% mortality by 48 h. Mortality was due to rapid progression of DCVC-initiated renal injury, suggesting that newly divided/dividing cells are instrumental in mitigating the progression of DCVC-initiated renal injury in DB. The anti-mitotic effect of CLC in DB kidney is associated with lower expression of calpastatin and higher leakage of calpain in the injured tubules. These findings suggest that constitutively higher cell division in the DB kidney is associated with overexpression of calpastatin, which reduces the progression of DCVC-initiated renal injury mediated by calpain on the one hand and accelerates nephrogenic tissue repair on the other, thereby restoring renal structure and function.