OBJECTIVE-The present study investigated the relationships between reactive oxygen species (ROS), interstitial fibrosis, and renal proximal tubular cell (RPTC) apoptosis in type 2 diabetic db/db mice and in db/db transgenic (Tg) mice overexpressing rat catalase (rCAT) in their RPTCs (db/db rCAT-Tg).RESEARCH DESIGN AND METHODS-Blood pressure, blood glucose, and albuminuria were monitored for up to 5 months. Kidneys were processed for histology and apoptosis studies (terminal transferase-mediated dUTP nick-end labeling or immunostaining for active caspase-3 and Bax). Real-time quantitative PCR assays were used to quantify angiotensinogen (ANG), p53, and Bax mRNA levels.RESULTS-db/db mice developed obesity, hyperglycemia, hypertension, and albuminuria. In contrast, db/db rCAT-Tg mice became obese and hyperglycemic but had normal blood pressure and attenuated albuminuria compared with db/db mice. Kidneys from db/db mice displayed progressive glomerular hypertrophy, glomerulosclerosis, interstitial fibrosis, and tubular apoptosis and increased expression of collagen type IV, Bax, and active caspase-3, as well as increased ROS production. These changes, except glomerular hypertrophy, were markedly attenuated in kidneys of db/db rCAT-Tg mice. Furthermore, ANG, p53, and Bax mRNA expression was increased in renal proximal tubules of db/db mice but not of db/db rCAT-Tg mice. D iabetes affects 5-10% of the world population. It is estimated that 30 -40% and 5-10% of patients with type 1 and type 2 diabetes, respectively, will eventually develop kidney failure or endstage renal disease (1). Diabetic nephropathy is now the most common cause of end-stage renal disease, accounting for 40 -50% (2). Diabetic nephropathy is associated with an increased risk of hypertension, myocardial infarction, stroke, and cardiovascular dysfunction (3). Multiple factors have been implicated in the pathogenesis of diabetic nephropathy, including hyperglycemia, hypertension, insulin resistance, and oxidative stress (4). However, the molecular mechanisms of action of these risk factors are incompletely understood. CONCLUSIONS-OurOxidative stress has long been implicated in the progression of diabetes complications. High glucose induces reactive oxygen species (ROS) generation, and ROS contribute to apoptosis in podocytes and mesangial and tubular cells (5-7). Ang II stimulates ROS generation via heightened NADPH oxidase activity in various renal cell types, whereas antioxidants provide renal protection in part by ameliorating oxidative stress (8 -11). Such data strongly indicate a link between ROS, renin-angiotensin system (RAS) activation, and renal cell apoptosis in diabetes.Recent studies have reported that 71% of glomeruli from proteinuric type 1 diabetic patients have glomerulo-tubular junction abnormalities, including atubular glomeruli, which may occur in 8 -17% of nephrons (12,13). Atubular glomeruli, glomeruli that are not connected to their proximal tubules as an end result of tubular atrophy, are characteristic of a variety of human kid...

Transgenic mice that overexpress angiotensinogen, the sole precursor of angiotensins, in their renal proximal tubular cells develop hypertension, albuminuria, and tubular apoptosis. These pathological changes are due to enhanced generation of reactive oxygen species in the proximal tubule cells. Here, we determined whether overexpression of catalase to decrease oxidant injury in the proximal tubular cells could reverse these abnormalities. Double-transgenic mice specifically overexpressing angiotensinogen and catalase in their renal proximal tubular cells were created by cross-breeding the single transgenics. Non-transgenic littermates served as controls. Overexpression of catalase prevented hypertension, albuminuria, tubulointerstitial fibrosis, and tubular apoptosis in the angiotensinogen transgenic mice. Furthermore, the double transgenics had lower reactive oxygen species generation and reduced pro-fibrotic and apoptotic gene expression in the renal proximal tubular cells. Renal angiotensin converting enzyme-2 expression and urinary angiotensin 1-7 levels were downregulated in the single but normal in the double-transgenic mice. Thus, we suggest that the intrarenal renin-angiotensin system and reactive oxygen species generation have an important role in the development of hypertension and renal injury.

. Dual RAS blockade normalizes angiotensin-converting enzyme-2 expression and prevents hypertension and tubular apoptosis in Akita angiotensinogen-transgenic mice. Am J Physiol Renal Physiol 302: F840 -F852, 2012. First published December 28, 2011 doi:10.1152/ajprenal.00340.2011.-We investigated the effects of dual renin-angiotensin system (RAS) blockade on angiotensin-converting enzyme-2 (Ace2) expression, hypertension, and renal proximal tubular cell (RPTC) apoptosis in type 1 diabetic Akita angiotensinogen (Agt)-transgenic (Tg) mice that specifically overexpress Agt in their RPTCs. Adult (11 wk old) male Akita and Akita Agt-Tg mice were treated with two RAS blockers (ANG II receptor type 1 blocker losartan, 30 mg·kg Ϫ1 ·day Ϫ1 ) and angiotensinconverting enzyme (ACE) inhibitor perindopril (4 mg·kg Ϫ1 ·day Ϫ1 ) in drinking water. Same-age non-Akita littermates and Agt-Tg mice served as controls. Blood pressure, blood glucose, and albuminuria were monitored weekly. The animals were euthanized at age 16 wk. The left kidneys were processed for immunohistochemistry and apoptosis studies. Renal proximal tubules were isolated from the right kidneys to assess gene and protein expression. Urinary ANG II and ANG 1-7 were quantified by ELISA. RAS blockade normalized renal Ace2 expression and urinary ANG 1-7 levels (both of which were low in untreated Akita and Akita Agt-Tg), prevented hypertension, albuminuria, tubulointerstitial fibrosis and tubular apoptosis, and inhibited profibrotic and proapoptotic gene expression in RPTCs of Akita and Akita Agt-Tg mice compared with non-Akita controls. Our results demonstrate the effectiveness of RAS blockade in preventing intrarenal RAS activation, hypertension, and nephropathy progression in diabetes and support the important role of intrarenal Ace2 expression in modulating hypertension and renal injury in diabetes.HYPERTENSION AFFECTS 25% OF the adult population in North America (1), and 40% of patients with diabetes develop hypertension (32). Hypertension and diabetes account for 65-70% of all end-stage renal disease (ESRD) cases in North America (1). ESRD is a major risk factor for cardiovascular diseases, including myocardial infarction and stroke (8). While intensive insulin therapy and chronic treatment with reninangiotensin system (RAS) blockers effectively retard the progression of diabetic nephropathy, they do not provide a cure (9,14,27,28,44). Such findings, however, indicate that hyperglycemia, hypertension, and RAS activation are major risk factors in the pathogenesis of ESRD.Human and murine renal proximal tubular cells (RPTCs) express all components of the RAS (19,22,34,41). We have reported that transgenic (Tg) mice that specifically overexpress angiotensinogen (Agt), the sole precursor of angiotensins in RPTCs, develop hypertension, albuminuria, and tubular apoptosis (21, 30). Furthermore, Agt overexpression enhances tubular apoptosis in streptozotocin (STZ)-induced diabetic mice (20). Although these findings indicate that intrarenal RAS activation and hypergly...