Activation of Rac-1 and RhoA Contributes to Podocyte Injury in Chronic Kidney Disease

Abstract

Rho-family GTPases like RhoA and Rac-1 are potent regulators of cellular signaling that control gene expression, migration and inflammation. Activation of Rho-GTPases has been linked to podocyte dysfunction, a feature of chronic kidney diseases (CKD). We investigated the effect of Rac-1 and Rho kinase (ROCK) inhibition on progressive renal failure in mice and studied the underlying mechanisms in podocytes. SV129 mice were subjected to 5/6-nephrectomy which resulted in arterial hypertension and albuminuria. Subgroups of animals were treated with the Rac-1 inhibitor EHT1846, the ROCK inhibitor SAR407899 and the ACE inhibitor Ramipril. Only Ramipril reduced hypertension. In contrast, all inhibitors markedly attenuated albumin excretion as well as glomerular and tubulo-interstitial damage. The combination of SAR407899 and Ramipril was more effective in preventing albuminuria than Ramipril alone. To study the involved mechanisms, podocytes were cultured from SV129 mice and exposed to static stretch in the Flexcell device. This activated RhoA and Rac-1 and led via TGFβ to apoptosis and a switch of the cells into a more mesenchymal phenotype, as evident from loss of WT-1 and nephrin and induction of α-SMA and fibronectin expression. Rac-1 and ROCK inhibition as well as blockade of TGFβ dramatically attenuated all these responses. This suggests that Rac-1 and RhoA are mediators of podocyte dysfunction in CKD. Inhibition of Rho-GTPases may be a novel approach for the treatment of CKD.

Albumin-associated free fatty acids induce macropinocytosis in podocytes

“…We and others have previously shown that RAC1 activation in podocytes leads to podocyte foot process effacement and proteinuria in mice (49,50). In addition, excessive macropinocytosis and accumulation of albumin in podocytes has been shown to induce lysosomal dysfunction, podocyte loss, and subsequent glomerulo- sclerosis (15,16,(51)(52)(53)(54)(55).…”

TRPM2 mediates ischemic kidney injury and oxidant stress through RAC1

“…Previous work on RAC1 in kidney disease has focused on its role in the podocyte, where unrestrained activation of RAC1 leads to podocyte effacement and proteinuria (65)(66)(67)(68) and kidney fibrosis, whereby RAC1 alters macrophage migration (69). In contrast, the role of RAC1 in AKI has received little attention.…”

Aging and uremia: Is there cellular and molecular crossover?

“…Instead a large number of studies using experimental models and human subjects have shown that uremia is associated with apoptosis in a wide range of cells and tissues such as skeletal muscle [19,20] , myocardium [21] , platelets [22,23] , monocytes [24] , neutro phils [25] , lymphocytes [26] , leukocytes [27] and vascular endothelial cells [28] . The kidney has also been shown as a target for apoptosis in uremia with both podocytes [29] and proximal tubular cells identified as having increased apoptotic cell death [30] . Furthermore, it has become known that it certain circumstances dialysis itself can be an activator of apoptosis [20,26] .…”