Cdc42 activation couples fluid shear stress to apical endocytosis in proximal tubule cells

Abstract

Cells lining the kidney proximal tubule (PT) respond to acute changes in glomerular filtration rate and the accompanying fluid shear stress (FSS) to regulate reabsorption of ions, glucose, and other filtered molecules and maintain glomerulotubular balance. Recently, we discovered that exposure of PT cells to FSS also stimulates an increase in apical endocytic capacity (Raghavan et al. PNAS, 111:8506–8511, 2014). We found that FSS triggered an increase in intracellular Ca2+ concentration ([Ca2+]i) that required release of extracellular ATP and the presence of primary cilia. In this study, we elucidate steps downstream of the increase in [Ca2+]i that link FSS‐induced calcium increase to increased apical endocytic capacity. Using an intramolecular FRET probe, we show that activation of Cdc42 is a necessary step in the FSS‐stimulated apical endocytosis cascade. Cdc42 activation requires the primary cilia and the FSS‐mediated increase in [Ca2+]i. Moreover, Cdc42 activity and FSS‐stimulated endocytosis are coordinately modulated by activators and inhibitors of calmodulin. Together, these data suggest a mechanism by which PT cell exposure to FSS is translated into enhanced endocytic uptake of filtered molecules.

Shear stress and oxygen availability drive differential changes in opossum kidney proximal tubule cell metabolism and endocytosis

“…Both microvilli and primary cilia have been implicated in mechanosensitive responses to acute changes in shear stress in PT and other kidney cells . Although we could not distinguish between a role for microvilli and/or primary cilia as flow sensors, our data support for a role for mechanotransduction in PT cell differentiation in response to continuous orbital shear stress.…”

Three dimensional modeling of biologically relevant fluid shear stress in human renal tubule cells mimics in vivo transcriptional profiles

“…Loss of retinol-binding protein 4 in urine (RBP4) is a biomarker for loss of function of the human proximal renal tubule 30 . The efflux transporters, Breast Cancer Resistance Protein (BCRP/ABCG2) and Multidrug and Toxin Extrusion (MATE)-type transporter 1 (MATE1, SLC47A1) are responsible for restricting absorption and enhancing excretion of many pharmaceutical compounds including multiple anticancer drugs 4,31 . Some genes were turned on only by the low-(0.1 dyn/cm 2 ) and mid-(0.25 dyn/cm 2 ) of flow (FOXA3 and HEY1).…”

Albumin uptake and processing by the proximal tubule: physiological, pathological, and therapeutic implications

“…Proximal tubules can also selectively stop aminoglycoside reabsorption during long-term exposure to aminoglycosides ( 51 , 52 ). Furthermore, in a series of manuscripts the Weisz laboratory ( 53 – 55 ) delineated the mechanism of fluid shear stress-induced apical endocytosis via a mechanosensation of the primary cilia requiring extracellular Ca 2+ , release of cellular ATP, and stimulation of purinergic receptor (P2R) ( 56 ). Cultured proximal tubule cells responded to fluid sheer stress via mammalian target of rapamycin (mTOR) and upregulated endocytic capacity, mitochondrial function, and lysosome biogenesis ( 57 ).…”