Proteomic analysis of the slit diaphragm complex: CLIC5 is a protein critical for podocyte morphology and function

Abstract

Podocytes are morphologically complex cells, the junctions of which form critical elements of the final filtration barrier. Disruption of their foot processes and slit diaphragms occur early in the development of many glomerular diseases. Here, we biochemically purified fractions enriched with slit diaphragm proteins and performed a proteomic analysis to identify new components of this important structure. Several known slit diaphragm proteins were found, such as podocin and nephrin, confirming the validity of the purification scheme. However, proteins on the apical membrane such as podocalyxin were neither enriched nor identified in our analysis. The chloride intracellular channel protein 5 (CLIC5), predominantly expressed in podocytes, was enriched in these fractions and localized in the foot process apical and basal membranes. CLIC5 colocalized and associated with the ezrin/radixin/moesin complex and with podocalyxin in podocytes in vivo. It is important to note that CLIC5−/− mice were found to have significantly decreased foot process length, widespread foot process abnormalities, and developed proteinuria. The ezrin/radixin/moesin complex and podocalyxin were significantly decreased in podocytes from CLIC5−/− mice. Thus, our study identifies CLIC5 as a new component that is enriched in and necessary for foot process integrity and podocyte function in vivo.

Nucleobindin-2 is a positive regulator for insulin-stimulated glucose transporter 4 translocation in fenofibrate treated E11 podocytes [Rapid Communication]

“…In addition, we observed the up regulation of several podocyte specific markers (GPR137B, Clic5, and Nephrin) indicating the formation of a podocyte phenotype [24]. It is important to note that the fenofibrate treatment required only 2 days of treatment and was as effective to the previous reported method that requires 7-10 days.…”

Clustered phosphatidylinositol 4,5 bisphosphate accumulation and ezrin phosphorylation in response to CLIC5A

“…In glomeruli, CLIC5A colocalizes with ezrin and podocalyxin in a highly polarized fashion at the apical plasma membrane of podocyte foot processes. In mice lacking CLIC5A, transmission electron microscopy shows broadening and patchy fusion of podocyte foot processes, and ezrin as well as phosphoezrin levels are reduced relative to those of wild-type mice (Pierchala et al, 2010;Wegner et al, 2010). These findings suggest that CLIC5A is required for the development and maintenance of the ezrin-dependent ultrastructural organization of glomerular podocyte foot processes, akin to the dependence of stereocilia integrity on CLIC5A in cochlear and vestibular hair cells.…”

Progressive hearing loss and vestibular dysfunction caused by a homozygous nonsense mutation in CLIC5

“…The jbg mice have abnormalities in the foot processes of the kidney podocytes leading to proteinuria. 17,18 The elevated albumin/creatinine ratio and pre-hypertension in affected individual II.3 indicate mild renal dysfunction and may well be the first signs of a nephropathy. Therefore, follow-up of renal function is indicated for individual II.3 but also for his hearing-impaired sister.…”

“…9 Secondly, Clic5 functions as an adapter between the plasma membrane of podocytes and the actin cytoskeleton by facilitating the interaction between ezrin and podocalyxin. 17,18,23 Thirdly, a recent study proposes that Clic5 functions as part of a multiprotein linker complex in companion with radixin, erzin and taperin. 24 Protein tyrosine phosphatase receptor Q (Ptprq), which is mislocalized as radixin in the jbg mice, and Myosin VI, key regulator of the proper localization of Ptprq, 25 might well participate in this complex too.…”