Regulation of podocyte surface proteins by the enzyme A Disintegrin And Metalloproteinase 10 (ADAM10).

INTRODUCTION

Podocytes are terminally differentiated cells of the kidney filtration barrier. Their network of interdigitating foot processes embraces the glomerular capillaries and is likely remodeled by cleavage of podocyte surface proteins. The metalloproteinase ADAM10 is a major regulator of such surface protein shedding and was recently implicated in the pathophysiology of antibody-mediated podocyte injury.

METHODS

Here, we studied the contribution of ADAM10 in podocyte biology in health and disease and analyzed prominently expressed and disease-relevant podocyte membrane proteins in detail. We used genetically deficient mice, ADAM10-inhibited pig glomeruli, and various in vitro experimental systems in which detailed biochemical and imaging techniques were performed.

RESULTS

We found that thrombospondin type 1 domain-containing 7A (THSD7A) and phospholipase A2 receptor 1 (PLA2R1), both of which are primary membranous nephropathy antigens, accumulated upon ADAM10 inhibition/deficiency. Moreover, increased protein levels of the foot process adhesion protein β-dystroglycan (β-DG) were found. Detailed biochemical analyses in different experimental systems revealed that THSD7A, PLA2R1, and β-DG are genuine ADAM10 substrates and subject to γ-secretase-mediated intramembrane proteolysis. These substrates co-localize and interact with the protease in podocytes and their shedding regulates filopodogenesis (THSD7A and β-DG) and cell matrix adhesion (β-DG). ADAM10 substrate usage, but also the stability of the podocyte cell surface proteins, is regulated by tetraspanin (Tspan) 15, which is likewise present at podocyte foot processes. A tricomponent complex of THSD7A/ADAM10/Tspan15 was found, with THSD7A acting as both an ADAM10 substrate and regulator.

CONCLUSIONS

Altogether, our data emphasize the importance of ADAM10/Tspan15-mediated regulation of podocyte foot process surface proteins that serve as antigens in primary membranous nephropathy and impact cytoskeletal dynamics.