title: Loss of Rho-GDIα sensitizes podocytes to lipopolysaccharide-mediated injury.
abstract: Nephrotic syndrome is a disease of glomerular permselectivity that can arise as a consequence of heritable or acquired changes to the integrity of the glomerular filtration barrier. We recently reported two siblings with heritable nephrotic syndrome caused by a loss of function mutation in the gene ARHGDIA, which encodes for Rho guanine nucleotide dissociation inhibitor-α (GDIα). GDIs are known to negatively regulate Rho-GTPase signaling. We hypothesized that loss of GDIα sensitizes podocytes to external injury via hyperactivation of Rho-GTPases and p38 MAPK. We examined the response of cultured podocytes with and without knockdown of GDIα to LPS injury by assessing the levels of phospho-p38 as well as the degree of synaptopodin loss. GDIα knockdown podocytes showed more pronounced and sustained p38 phosphorylation in response to LPS compared with control podocytes, and this was blunted significantly by the Rac1 inhibitor. In LPS-treated control podocytes, synaptopodin degradation occurred, and this was dependent on p38, the proteasome, and cathepsin L. In GDIα knockdown podocytes, the same events were triggered, but the levels of synaptopodin after LPS treatment were significantly lower than in control podocytes. These experiments reveal a common pathway by which heritable and environmental risk factors converge to injure podocytes, from Rac1 hyperactivation to p38 phosphorylation and synaptopodin degradation via the ubiquitin-proteasome pathway and cathepsin L.
authors.affiliation: Department of Medicine, McGill University Health Centre, Montreal, Quebec, Canada; and.
authors.forename: Richard
authors.initials: R
authors.lastname: Robins
authors.affiliation: Department of Medicine, McGill University Health Centre, Montreal, Quebec, Canada; and.
authors.forename: Cindy
authors.initials: C
authors.lastname: Baldwin
authors.affiliation: Department of Medicine, McGill University Health Centre, Montreal, Quebec, Canada; and.
authors.forename: Lamine
authors.initials: L
authors.lastname: Aoudjit
authors.affiliation: Department of Pediatrics, McGill University Health Centre, Montreal, Quebec, Canada.
authors.forename: Indra R
authors.initials: IR
authors.lastname: Gupta
authors.affiliation: Department of Medicine, McGill University Health Centre, Montreal, Quebec, Canada; and tomoko.takano@mcgill.ca.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Takano
mesh_terms: D000818:Animals; D055785:Gene Knockdown Techniques / Q000379:methods; D008070:Lipopolysaccharides / Q000494:pharmacology*; D009404:Nephrotic Syndrome / Q000188:drug therapy / Q000378:metabolism; D050199:Podocytes / Q000187:drug effects*; D015398:Signal Transduction / Q000187:drug effects; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000378:metabolism; D062948:rho Guanine Nucleotide Dissociation Inhibitor alpha / Q000235:genetics*
chemical_list: D008070:Lipopolysaccharides; D062948:rho Guanine Nucleotide Dissociation Inhibitor alpha; D048051:p38 Mitogen-Activated Protein Kinases; D020741:rho GTP-Binding Proteins
keywords: Rho guanine nucleotide dissociation inhibitor-α; nephrotic syndrome; p38; podocytes; proteasome; synaptopodin; ubiquitination