Grant: CIHR-ICRH Travel Awards - General pool

Background: Angiotensinogen (AGT), the sole precursor of angiotensins in the renin-angiotensin system (RAS), is highly expressed in the renal proximal tubules (RPTs) of mice and patients with diabetic kidney disease (DKD). We reported previously that mice specifically overexpressing Agt in RPTs (Agt-Tg) develop hypertension and kidney injury. However, the pathophysiological roles of the intrarenal RAS in DKD progression is not well-defined. We investigated whether genetic deletion of Agt specifically in renal tubules (RT) could improve kidney injury in type 1 diabetic Akita mice. Methods: We generated Akita mice with RT-specific Agt knockout (Akita Agt KO) by crossbreeding Akita Agt mice with Agt KO (tubule-specific Pax8-Cre) mice. Male Akita Agt KO, Akita Agt , nondiabetic Agt and Agt KO mice were studied at 20 weeks of age. Physiological data, kidney function, and urinary angiotensin II (Ang II) were assessed. Immunostaining on kidney sections, western blotting (WB) and real-time quantitative PCR (RT-qPCR) were performed to assess protein and gene expression in isolated RPTs. Results: Agt deletion in RT did not significantly affect systolic blood pressure in Akita mice. Fasting blood glucose levels were lower in Akita Agt KO vs. Akita mice. Glomerular filtration rate was increased in Akita mice, but was normalized in Akita Agt KO mice. The urinary albumin-creatinine ratio (ACR) and Ang II levels were increased in Akita mice, but significantly decreased in Akita Agt KO mice. Akita mice exhibited glomerular and tubular hypertrophy, tubular luminal dilation, and necrosis; these abnormalities were markedly attenuated in Akita Agt KO mice. Podocyte number(defined by P57 and WT1 staining) was decreased in Akita mice, but was partially restored in Akita Agt KO mice. Sodium-glucose cotransporter 2 (SGLT2) expression was lower in Akita Agt KO mice than in Akita mice. Urinary glucose excretion was higher in Akita Agt KO mice than in Akita mice. Conclusion: Deletion of Agt in RT decreased hyperglycemia, glomerular hyperfiltration, ACR, kidney injury, and SGLT2 expression in Akita mice, demonstrating that inactivation of the intrarenal RAS attenuates DKD progression, at least in part, via down-regulation of SGLT2 expression.