The mechano-sensitive ion channel Piezo mediates Rho activation and actin stress fibre formation in Drosophila nephrocytes

Abstract

AbstractMechanotransduction is an important process of sensing physical forces in the environment of organisms, tissues and cells and transducing them into a biochemical response. Due to their position on the glomerular capillaries, podocytes are exposed to near-constant biomechanical force, which can fluctuate widely. These include shear stress and hydrostatic pressure. A pathological increase in these forces can induce morphological change to podocytes, their detachment from the glomerular basement membrane and subsequent loss into the primary urine. The ability to sense and respond to variations in mechanical force would be beneficial to a cell exposed to these conditions. It is likely podocytes have such mechanisms, however their identity are unknown.Here we investigated the hypothesis that the mechanotransducer Piezo is involved in a mechanotransduction pathway in Drosophila nephrocytes, the podocyte homologue in the fly. We find Piezo is expressed in nephrocytes and localizes to the nephrocyte diaphragm. The Piezo agonist YODA, which stimulates channel opening in the absence of mechanical force, leads to a significant increase in intracellular Ca++ upon shear stress in the nephrocyte. This leads to activation of Rho1, delineating a putative Piezo mechanotransductive pathway in these cells.Loss of function analysis revealed minor defects in nephrocyte filtration function. In contrast, we show that elevated Piezo levels resulted in constantly oscillating Ca++ signals even in the absence of shear stress, increased active Rho1 and accumulation of actin stress fibers, culminating in a severe nephrocyte filtration phenotype, suggesting that pathway hyperactivity is detrimental. We asked if this phenotype could be reversed by blocking Piezo activity pharmacologically using the tarantula toxin GsMTx4. Treatment with GsMTx4 brought levels of activated Rho1 into the normal range.This work delineates a mechanotransductive pathway in nephrocytes involving Piezo, Ca++, Rho1 and the actin-cytoskeleton, and suggest this is part of a mechanism by which nephrocytes sense and adapt to changes in mechanical force.