Publication Date

2014-03-27

Availability

Open access

Embargo Period

2014-03-27

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Molecular Cell and Developmental Biology (Medicine)

Date of Defense

2014-02-27

First Committee Member

Jochen Reiser

Second Committee Member

Pedro Salas

Third Committee Member

Christian Faul

Fourth Committee Member

Matthias Salathe

Abstract

Podocyte foot processes (FPs) and their interposed slit diaphragm (SD) are key components of the permeability barrier in the glomerulus. Damage of podocytes (FP effacement) result in proteinuria and may lead to progressive decline of the renal function. It is therefore critical to define the regulation of podocyte structure and function at the cellular level. Podocyte FP effacement can be specifically induced by the action of the cytosolic protease cathepsin L (cCatL), which functions as a regulatory protease. To date, three substrates of cCatL have been identified in podocytes: dynamin and synaptopodin which both stabilize the podocyte actin cytoskeleton, and the adaptor protein CD2AP. Here we show that calpain, a ubiquitously expressed cysteine protease, also induce the podocyte FP effacement by proteolysis of talin and synaptopodin, thereby unveiling the role of calpain in podocytes. Talin does not only play an important role in activating integrin, but also serves to directly link integrin and actin cytoskeleton at the focal adhesion contacts in podocytes, maintaining the integrity of glomerular filtration barrier. The physiological significance of the role of calpain is underscored by the observation that protamine sulfate (PS) induces calpain activity in podocyte and the active calpain mediated proteolysis of talin and synaptopodin causes loss of stressfibers in podocytes. Functionally, PS-treated podocytes significantly reduces their adhesion ability compared to wild type podocytes, as revealed by the adhesion assay used. In addition, PS-perfused mice showed FP effacement and severe proteinuria through synaptopodin and talin cleavage. Furthermore, calpain activity is significantly increased in patients with nephrotic syndrome. These findings unveil the pivotal role of calpain to regulate podocyte function.

Keywords

Calpain; Kidney; Podocytes

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