Control of Podocyte and Glomerular Capillary Wall Structure and Elasticity by WNK1 Kinase.

Zhenan Liu,Chonlarat Wichaidit,Joonho Yoon,Ankita B Jaykumar,Joel M Henderson,Audrey N Chang,Melanie H Cobb,Liping Liu,Hashem A Dbouk,Addie E Embry,Richard Tyler Miller

doi:10.3389/fcell.2020.618898

Abstract

Cytoskeletal structure and its regulation are essential for maintenance of the differentiated state of specific types of cells and their adaptation to physiologic and pathophysiologic conditions. Renal glomerular capillaries, composed of podocytes, endothelial cells, and the glomerular basement membrane, have distinct structural and biophysical properties and are the site of injury in many glomerular diseases. Calcineurin inhibitors, immunosuppressant drugs used for organ transplantation and auto-immune diseases, can protect podocytes and glomerular capillaries from injury by preserving podocyte cytoskeletal structure. These drugs cause complications including hypertension and hyperkalemia which are mediated by WNK (With No Lysine) kinases as well as vasculopathy with glomerulopathy. WNK kinases and their target kinases oxidative stress-responsive kinase 1 (OSR1) and SPS1-related proline/alanine-rich kinase (SPAK) have fundamental roles in angiogenesis and are activated by calcineurin inhibitors, but the actions of these agents on kidney vasculature, and glomerular capillaries are not fully understood. We investigated WNK1 expression in cultured podocytes and isolated mouse glomerular capillaries to determine if WNK1 contributes to calcineurin inhibitor-induced preservation of podocyte and glomerular structure. WNK1 and OSR1/SPAK are expressed in podocytes, and in a pattern similar to podocyte synaptopodin in glomerular capillaries. Calcineurin inhibitors increased active OSR1/SPAK in glomerular capillaries, the Young’s modulus (E) of glomeruli, and the F/G actin ratio, effects all blocked by WNK inhibition. In glomeruli, WNK inhibition caused reduced and irregular synaptopodin-staining, abnormal capillary and foot process structures, and increased deformability. In cultured podocytes, FK506 activated OSR1/SPAK, increased lamellipodia, accelerated cell migration, and promoted traction force. These actions of FK506 were reduced by depletion of WNK1. Collectively, these results demonstrate the importance of WNK1 in regulation of the podocyte actin cytoskeleton, biophysical properties of glomerular capillaries, and slit diaphragm structure, all of which are essential to normal kidney function.

Highlights

Characteristics of the cell cytoskeleton are basic determinants of the structural and biophysical properties of cells and tissues
The podocyte actin cytoskeleton is essential for the normal functions of podocytes including their interactions with matrix and neighboring podocytes
In small clinical studies and collections of patient cases with kidney diseases including WT1 mutation-associated glomerular disease, membranous nephropathy, and Alport nephropathy, cyclosporine A (CsA) or FK506 can improve the course of the kidney disease

Summary

INTRODUCTION

Characteristics of the cell cytoskeleton are basic determinants of the structural and biophysical properties of cells and tissues. Calcineurin inhibitors have protective effects on podocytes in glomerular injury models, including preservation of cytoskeletal structure, and can improve the course of some human renal diseases (Meyrier, 2005; Charbit et al, 2007; Faul et al, 2008; Plank et al, 2008; Bensman and Niaudet, 2010; Li et al, 2015; Shen et al, 2016) Use of these drugs can be limited by nephrotoxicity, characterized by vasculopathy, glomerular injury, tubular atrophy, interstitial fibrosis, hypertension, and hyperkalemia (Issa et al, 2013). We studied the responses of isolated glomeruli and cultured podocytes to calcineurin inhibitors and WNK1 inhibition to investigate the contributions of WNK1 to the structural and mechanical properties of glomerular capillaries and podocytes

EXPERIMENTAL PROCEDURES

DISCUSSION

Findings

ETHICS STATEMENT