Glomerular sclerosis is prevented during urinary tract obstruction due to podocyte protection

Urine outflow obstruction activates a variety of profibrotic factors, including the intrarenal renin-angiotensin system. However, the obstruction also nullifies the transmural hydraulic pressure difference across the glomerular capillary wall, an established inducer of glomerulosclerosis. In the present study, we investigated whether, and by what mechanism, urine outflow obstruction affects the process of progressive glomerulosclerosis. For this purpose, we tested the effect of unilateral ureteral obstruction (UUO) of 7 days duration in two distinct mouse models of glomerulosclerosis. In the human immunodeficiency virus (HIV) nephropathy model, where HIV-1 genes are selectively expressed in podocytes and develop progressive podocyte damage and glomerulosclerosis, UUO protected against sclerosis with preservation of podocytes morphologically and immunohistochemically. In contrast, the nonobstructed contralateral kidneys of these mice, as well as sham-operated HIV-1 mouse kidneys, developed severe podocyte injury and glomerulosclerosis. The protection against glomerulosclerosis imparted by ureteral obstruction was also documented in the NEP25 model of podocyte injury, in which a single injection of immunotoxin, LMB2, triggers selective podocyte injury followed by glomerulosclerosis, both of which were protected by UUO. Notably, intervention with an angiotensin II type 1 receptor antagonist provided only a partial protective effect in each of the models. These results demonstrate that urine outflow obstruction protects the glomerulus from progressive sclerosis. The results further reveal that this protection occurs at a very early stage of the pathologic process, namely, damage of podocytes.