title: Alpha-actinin-4 and CLP36 protein deficiencies contribute to podocyte defects in multiple human glomerulopathies.
abstract: Genetic alterations of α-actinin-4 can cause podocyte injury through multiple mechanisms. Although a mechanism involving gain-of-α-actinin-4 function was well described and is responsible for a dominantly inherited form of human focal segmental glomerulosclerosis (FSGS), evidence supporting mechanisms involving loss-of-α-actinin-4 function in human glomerular diseases remains elusive. Here we show that α-actinin-4 deficiency occurs in multiple human primary glomerulopathies including sporadic FSGS, minimal change disease, and IgA nephropathy. Furthermore, we identify a close correlation between the levels of α-actinin-4 and CLP36, which form a complex in normal podocytes, in human glomerular diseases. siRNA-mediated depletion of α-actinin-4 in human podocytes resulted in a marked reduction of the CLP36 level. Additionally, two FSGS-associated α-actinin-4 mutations (R310Q and Q348R) inhibited the complex formation between α-actinin-4 and CLP36. Inhibition of the α-actinin-4-CLP36 complex, like loss of α-actinin-4, markedly reduced the level of CLP36 in podocytes. Finally, reduction of the CLP36 level or disruption of the α-actinin-4-CLP36 complex significantly inhibited RhoA activity and generation of traction force in podocytes. Our studies reveal a critical role of the α-actinin-4-CLP36 complex in podocytes and provide an explanation as to how α-actinin-4 deficiency or mutations found in human patients could contribute to podocyte defects and glomerular failure through a loss-of-function mechanism.
authors.affiliation: Department of Pathology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.
authors.forename: Zhongmin
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan 48109.
authors.forename: Simone Monika
authors.initials: SM
authors.lastname: Blattner
authors.affiliation: Department of Pathology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.
authors.forename: Yizeng
authors.initials: Y
authors.lastname: Tu
authors.affiliation: Department of Orthopaedic Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.
authors.forename: Robert
authors.initials: R
authors.lastname: Tisherman
authors.affiliation: Department of Orthopaedic Surgery, University of Pittsburgh, Pittsburgh, Pennsylvania 15261.
authors.forename: James H
authors.initials: JH
authors.lastname: Wang
authors.affiliation: Renal Research Laboratory, Fondazione IRCCS Ospedale Maggiore Policlinico e Fondazione D'Amico per la Ricerca sulle Malattie Renali, Milano 20122, Italy.
authors.forename: Maria Pia
authors.initials: MP
authors.lastname: Rastaldi
authors.affiliation: Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan 48109.
authors.forename: Matthias
authors.initials: M
authors.lastname: Kretzler
authors.affiliation: Department of Pathology, University of Pittsburgh, Pittsburgh, Pennsylvania 15261. Electronic address: carywu@pitt.edu.
authors.forename: Chuanyue
authors.initials: C
authors.lastname: Wu
mesh_terms: D000185:Actinin / Q000172:deficiency / Q000235:genetics*; D000818:Animals; D001706:Biopsy; D003902:Detergents / Q000494:pharmacology; D005922:Glomerulonephritis, IGA / Q000378:metabolism; D005923:Glomerulosclerosis, Focal Segmental / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D007668:Kidney / Q000378:metabolism; D007678:Kidney Glomerulus / Q000378:metabolism*; D060588:LIM Domain Proteins; D051379:Mice; D008840:Microfilament Proteins / Q000172:deficiency / Q000235:genetics*; D009154:Mutation; D050199:Podocytes / Q000378:metabolism*; D025941:Protein Interaction Mapping / Q000379:methods; D011507:Proteinuria / Q000378:metabolism; D014157:Transcription Factors
chemical_list: C111453:ACTN4 protein, human; D003902:Detergents; C484572:LDB2 protein, human; D060588:LIM Domain Proteins; D008840:Microfilament Proteins; D014157:Transcription Factors; D000185:Actinin