FHL2 mediates podocyte Rac1 activation and foot process effacement in hypertensive nephropathy

Abstract

RAAS inhibition has been the standard treatment for CKD for years because it can reduce proteinuria and hence retard renal function decline, but the proteinuria reduction effect is still insufficient in many patients. Podocyte foot process and slit diaphragm are the final barrier to prevent serum proteins leak into urine, and podocyte foot process effacement is the common pathway of all proteinruic diseases. Cell structure are regulated by three evolutionarily conserved Rho GTPases, notably, Rac1 activation is sufficient and necessary for podocyte foot process effacement, however, Rac1 inhibition is not an option for kidney disease treatment because of its systemic side effects. Four-and-a-half LIM domains protein 2 (FHL2) is highly expressed in podocytes and has been implicated in regulating diverse biological functions. Here, we used micro-dissected human kidney samples, in vitro podocyte culture experiments, and a hypertension animal model to determine the possible role of FHL2 in hypertensive nephropathy. FHL2 was abundantly upregulated in hypertensive human glomeruli and animal kidney samples. Genetic deletion of the FHL2 did not alter normal renal structure or function but mitigated hypertension-induced podocyte foot process effacement and albuminuria. Mechanistically, angiotensin II-induced podocyte cytoskeleton reorganization via FAK-Rac1 axis, FHL2 binds with FAK and is an important mediator of Ang II induced Rac1 activation, thus, FHL2 inhibition can selectively block FAK-Rac1 axis in podocyte and prevent proteinuria. These results provide important insights into the mechanisms of podocyte foot process effacement and points out a promising strategy to treat kidney disease.