Fluvastatin prevents podocyte injury in a murine model of HIV-associated nephropathy.

BACKGROUND: Recent studies have reported that statins have renoprotective effects, independent from lowering plasma cholesterol. In this study, we examined whether statins were beneficial in a murine model of HIV-associated nephropathy (HIVAN). METHODS: We used conditional transgenic mice that express one of the HIV-1 accessory genes, vpr, selectively in podocytes using podocin promoter and the Tet-on system. These mice develop aggressive collapsing focal segmental glomerular sclerosis with massive proteinuria and deterioration of renal function within 4 weeks following heminephrectomy and doxycycline administration. Fluvastatin was administrated simultaneously with doxycycline, and the effect was compared with untreated controls after 4 weeks. RESULTS: Fluvastatin at 10 mg/kg/day significantly decreased urinary albumin excretion (87 versus 11 mg/day, P < 0.01) and glomerular sclerosis (2.4 versus 1.0, P < 0.01, assessed by semi-quantitative scoring: 0-4). Fluvastatin also decreased serum creatinine and total cholesterol, but these differences were not statistically significant (0.36 versus 0.32 mg/dl, P = 0.35; 492 versus 378 mg/dl, P = 0.11, respectively). Phenotypic changes in podocytes, as indicated by the downregulation of nephrin, Wilms' tumour 1 and synaptopodin, along with upregulation of proliferating cell nuclear antigen, were attenuated by fluvastatin, suggesting its protective effects against podocyte injuries. In cultured podocytes, angiotensin II treatment decreased nephrin expression to 13% of basal levels, which was reversed to 58% by adding fluvastatin. CONCLUSIONS: In conclusion, fluvastatin was effective in treating experimental HIVAN. The beneficial effect of this drug might be caused, in part, by preserving nephrin expression in podocytes against angiotensin II-mediated injury.

Urinary exosomal transcription factors, a new class of biomarkers for renal disease.

Urinary exosomes are excreted from all nephron segments and constitute a rich source of intracellular kidney injury biomarkers. To study whether they contain transcription factors, we collected urine from two acute kidney injury models (cisplatin or ischemia-reperfusion), two podocyte injury models (puromycin-treated rats or podocin-Vpr transgenic mice) and from patients with focal segmental glomerulosclerosis, acute kidney injury and matched controls. Exosomes were isolated by differential centrifugation and found to contain activating transcription factor 3 (ATF3) and Wilms Tumor 1 (WT-1) proteins detected by Western blot. These factors were found in the concentrated exosomal fraction, but not in whole urine. ATF3 was continuously present in urine exosomes of the rat models following acute injury at times earlier than the increase in serum creatinine. ATF3 was found in exosomes isolated from patients with acute kidney injury but not from patients with chronic kidney disease or controls. Urinary WT-1 was present in animal models before significant glomerular sclerosis and in 9/10 patients with focal segmental glomerulosclerosis but not in 8 controls. Our findings suggest that transcription factor ATF3 may provide a novel renal tubular cell biomarker for acute kidney injury while WT-1 may detect early podocyte injury. Measurement of urinary exosomal transcription factors may offer insight into cellular regulatory pathways.

Lack of A1 adenosine receptors augments diabetic hyperfiltration and glomerular injury.

Intraglomerular hypertension and glomerular hyperfiltration likely contribute to the pathogenesis of diabetic nephropathy, and tubuloglomerular feedback (TGF) has been suggested to play a role in diabetic hyperfiltration. A1 adenosine receptor (A1AR) null mice lack a TGF response, so this model was used to investigate the contribution of TGF to hyperfiltration in diabetic Ins2(+/-) Akita mice. TGF responses in Ins2(+/-) A1AR(-/-) double mutants were abolished, whereas they were attenuated in Ins2(+/-) mice. GFR, assessed at 14, 24, and 33 wk, was approximately 30% higher in Ins2(+/-) than in wild-type (WT) mice and increased further in Ins2(+/-) A1AR(-/-) mutants (P < 0.01 versus both WT and Ins2(+/-) mice at all ages). Histologic evidence of glomerular injury and urinary albumin excretion were more pronounced in double-mutant than single-mutant or WT mice. In summary, the marked elevation of GFR in diabetic mice that lack a TGF response indicates that TGF is not required to cause hyperfiltration in the Akita model of diabetes. Rather, an A1AR-dependent mechanism, possibly TGF, limits the degree of diabetic hyperfiltration and nephropathy.

Angiotensin II type 1 receptor blockade inhibits the development and progression of HIV-associated nephropathy in a mouse model.

HIV-associated nephropathy (HIVAN) is characterized by a collapsed glomerular capillary tuft with hyperplasia and hypertrophy of podocytes. Recently generated were conditional transgenic mice (podocin/Vpr) that express one of the HIV-1 accessory genes, vpr, selectively in podocytes using podocin promoter and Tet-on system. These transgenic mice developed renal injury similar to HIVAN when treated with doxycycline for 8 to 12 wk. This study demonstrated that nephron reduction by heminephrectomy markedly enhanced phenotypic changes of podocytes and led to severe FSGS within 4 wk. Nephrotic-range proteinuria was observed already at 2 wk, together with dedifferentiation and dysregulation of podocytes, indicated by decreased expression of nephrin, synaptopodin, and Wilms' tumor 1 protein and increased expression of Ki-67. The acceleration of phenotypic changes of podocytes, proteinuria, and subsequent glomerulosclerosis by heminephrectomy was almost completely inhibited by angiotensin II type 1 receptor (AT1R) blocker olmesartan. In contrast, the renoprotective effect of the calcium channel antagonist azelnidipine was minimal, although it lowered systemic BP to the same level as olmesartan, demonstrating that the inhibitory effect of AT1R blocker was independent of systemic BP. Olmesartan also reduced proteinuria and prevented glomerulosclerosis even by the delayed treatment, which was initiated after the podocyte injury appeared. These data suggest that nephron reduction exaggerates podocyte injury and subsequent glomerulosclerosis, possibly through glomerular hypertension, in the mouse model of HIVAN. AT1R blockade could be beneficial in the treatment of HIVAN by ameliorating podocyte injury by avoiding the vicious cycle of nephron reduction and glomerular hypertension.

Fluvastatin reduces renal fibroblast proliferation and production of type III collagen: therapeutic implications for tubulointerstitial fibrosis.

BACKGROUND: Accumulating evidence suggests that hydroxymethylglutaryl-CoA reductase inhibitors have many biological effects beyond reducing cholesterol synthesis. In a mouse model of renal interstitial fibrosis induced by unilateral ureteral obstruction, fluvastatin, one of the lipophilic hydroxymethylglutaryl-CoA reductase inhibitors, was shown to ameliorate fibrosis. METHODS: In the present study, we examined the direct effects of fluvastatin on proliferation, matrix and growth factor production by rat kidney fibroblasts (NRK-49F cells). RESULTS: Treatment with fluvastatin reduced proliferation of NRK-49F cells in a dose-dependent manner. The addition of mevalonate or geranylgeranyl pyrophosphate but not farnesyl pyrophosphate to the culture medium almost completely abolished the effect of fluvastatin. Moreover, fluvastatin treatment decreased the expression of activated Rho in NRK-49F cells suggesting that fluvastatin may decrease cell growth through blocking the activation of Rho. The majority of fluvastatin-treated cells were arrested at the G1 phase, associated with down-regulation of cyclin A and up-regulation of cyclin-dependent kinase inhibitor p27kip1, indicating that cell cycle modulation is an important mechanism. Fluvastatin significantly decreased messenger RNA expression of type III collagen and connective tissue growth factor. CONCLUSIONS: Taken together, it is suggested that fluvastatin may prevent tubulointerstitial fibrosis in a variety of progressive renal diseases by inhibiting proliferation of interstitial fibroblasts and their matrix synthesis.