Abstract 378: Alteration of Renal Neprilysin, Angiotensin Converting Enzyme 2 (ACE2) and Nephrin in Streptozotocin (STZ) Diabetic Mice

Diabetic nephropathy is one of the major microvascular complications of diabetes which eventually manifests into end stage renal disease. Alteration in renin-angiotensin system (RAS) is considered to be the primary cause underlying this implication. Emerging evidence suggests that the biological actions of Ang II may be opposed by the formation of Ang (1-7), partly generated by the actions of ACE2 and neprilysin (NEP). NEP is a zinc-containing metallopeptidase catalyzing the conversion of Ang I to Ang (1-7), a potent vasodilator, thus counteracting the deleterious effects of Ang II. In our previous studies it has been shown that renal ACE2 is up-regulated and NEP is down-regulated in type II diabetic (db/db) mice. However data is limited regarding the presence and activity of renal NEP and ACE2 in type I diabetic mice. The goal of the present study is to explore the role of renal NEP and ACE2 in the pathogenesis of diabetic nephropathy in the STZ mouse model of type I diabetes. Diabetes was induced by five consecutive injections of STZ (50 mg/kg, i.p.). Urine was collected in presence of protease inhibitor for measuring albumin, creatinine and total protein contents. STZ diabetic mice exhibit hyperglycemia (305±22 vs 125±6 mg/dL, p<0.001), microalbuminuria (212±34 vs 67±18 μg/day, p<0.05) and renal hypertrophy. Renal ACE2 activity was found to be increased in STZ treated mice (p<0.0001 vs wild type) using the fluorogenic test assay. Renal NEP activity was assessed in situ using a newly established mass spectrometric imaging approach in tissue incubations with the natural substrate, Ang I (m/z1296). As detected via formation of Ang (1-7) (m/z 899), NEP enzyme activity was localized to the renal cortex and significantly reduced by 30% in STZ treated mice (p<0.0001 vs wild type).Western blot analysis demonstrated the expression of renal NEP, ACE2 and nephrin. Immunohistochemical staining illustrated down-regulation of renal NEP, nephrin and up-regulation of medullary ACE2 protein expression in STZ diabetic mice. In conclusion, in spite of increased ACE2, decreased NEP coupled with depletion of nephrin in diabetes could possibly play a crucial role in the development of diabetic nephropathy.