Podocyte Injury and Albuminuria in Mice with Podocyte-Specific Overexpression of the Ste20-Like Kinase, SLK

Abstract

SLK expression and activity are increased during kidney development and recovery from renal ischemia-reperfusion injury. In cultured cells, SLK promotes F-actin destabilization as well as apoptosis, partially via the p38 kinase pathway. To better understand the effects of SLK in vivo, a transgenic mouse model was developed where SLK was expressed in a podocyte-specific manner using the mouse nephrin promoter. Offspring of four founder mice carried the SLK transgene. Among male transgenic mice, 66% developed albuminuria at approximately 3 months of age, and the albuminuric mice originated from three of four founders. Overall, the male transgenic mice demonstrated about fivefold greater urinary albumin/creatinine compared with male non-transgenic mice. Transgenic and non-transgenic female mice did not develop albuminuria, suggesting that females were less susceptible to glomerular filtration barrier damage than their male counterparts. In transgenic mice, electron microscopy revealed striking podocyte injury, including poorly formed or effaced foot processes, and edematous and vacuolated cell bodies. By immunoblotting, nephrin expression was decreased in glomeruli of the albuminuric transgenic mice. Activation-specific phosphorylation of p38 was increased in transgenic mice compared with non-transgenic animals. Glomeruli of SLK transgenic mice showed around 30% fewer podocytes, and a reduction in F-actin compared with control glomeruli. Thus, podocyte SLK overexpression in vivo results in injury and podocyte loss, consistent with the effects of SLK in cultured cells.