Publication Date

2013

Document Type

Thesis

Committee Members

Mauricio Di Fulvio (Committee Member), Khalid Elased (Advisor), Richard Simman (Committee Member)

Degree Name

Master of Science (MS)

Abstract

Diabetic patients have a 40%-50% lifetime chance of developing chronic kidney disease, which remains one of the leading causes of morbidity and mortality. Alterations within renin angiotensin system balance contribute to the pathogenesis of diabetic kidney disease. Angiotensin converting enzyme 2 (ACE2) has an endogenous renoprotective role due to its ability to form angiotensin (1-7) (Ang 1-7) by degrading angiotensin II (Ang II). We have shown previously that hyperglycemia increases urinary ACE2 and albumin excretion in db/db diabetic mice. The protease, disintegrin and metalloprotease (ADAM) 17, is involved in the shedding of several transmembrane proteins, including ACE2 in vitro. Tissue inhibitor metalloproteinase-3 (TIMP3) is known to be an endogenous inhibitor of ADAM17. We tested the hypothesis that normalizing hyperglycemia in Akita mice with insulin decreases renal ADAM17, increases TIMP3 protein expression and reduces urinary ACE2 and albumin excretion. Metabolic parameters were monitored weekly. Urine was collected over 24 hours period to measure urinary albumin, creatinine and ACE2 activity. Akita mice demonstrated hyperglycemia and a significant increase in urinary ACE2 and albumin excretion. Treatment of Akita mice with insulin implants for 20 weeks normalized hyperglycemia, decreased urinary ACE2 and albumin excretion. Western blotting demonstrated increased renal ACE2 and ADAM17 protein expression. Immunostaining revealed colocalization of ACE2 with ADAM17 in renal tubules. However, renal TIMP3 expression was not altered in Akita diabetic mice. Normalizing hyperglycemia with insulin also decreased renal ACE2, ADAM17, but had no effect on TIMP3 expression. There was a positive linear correlation between urinary ACE2 levels and albuminuria, blood glucose, and plasma levels of creatinine, glucagon and triglycerides. In conclusion, Akita diabetic mice exhibit increased expression of renal ACE2 and urinary ACE2 excretion, which in turn correlates with a significant increase in renal ADAM17 protein expression. This is the first report showing an association between hyperglycemia and increased shedding of urinary ACE2 in Akita diabetic mice. Therefore, urinary ACE2 may be used as a biomarker for early prediction of diabetic nephropathy as well as for monitoring patients to define effective therapeutic strategies.

Page Count

116

Department or Program

Department of Pharmacology and Toxicology

Year Degree Awarded

2013

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