RESUMO
Mutations of the LMX1B gene cause nail-patella syndrome, a rare autosomal-dominant disorder affecting the development of the limbs, eyes, brain, and kidneys. The characterization of conventional Lmx1b knockout mice has shown that LMX1B regulates the development of podocyte foot processes and slit diaphragms, but studies using podocyte-specific Lmx1b knockout mice have yielded conflicting results regarding the importance of LMX1B for maintaining podocyte structures. In order to address this question, we generated inducible podocyte-specific Lmx1b knockout mice. One week of Lmx1b inactivation in adult mice resulted in proteinuria with only minimal foot process effacement. Notably, expression levels of slit diaphragm and basement membrane proteins remained stable at this time point, and basement membrane charge properties also did not change, suggesting that alternative mechanisms mediate the development of proteinuria in these mice. Cell biological and biophysical experiments with primary podocytes isolated after 1 week of Lmx1b inactivation indicated dysregulation of actin cytoskeleton organization, and time-resolved DNA microarray analysis identified the genes encoding actin cytoskeleton-associated proteins, including Abra and Arl4c, as putative LMX1B targets. Chromatin immunoprecipitation experiments in conditionally immortalized human podocytes and gel shift assays showed that LMX1B recognizes AT-rich binding sites (FLAT elements) in the promoter regions of ABRA and ARL4C, and knockdown experiments in zebrafish support a model in which LMX1B and ABRA act in a common pathway during pronephros development. Our report establishes the importance of LMX1B in fully differentiated podocytes and argues that LMX1B is essential for the maintenance of an appropriately structured actin cytoskeleton in podocytes.
Assuntos
Proteínas com Homeodomínio LIM/fisiologia , Podócitos/citologia , Fatores de Transcrição/fisiologia , Actinas/fisiologia , Envelhecimento , Animais , Apoptose , Diferenciação Celular , Colágeno Tipo IV/genética , Peptídeos e Proteínas de Sinalização Intracelular/genética , Proteínas com Homeodomínio LIM/genética , Proteínas de Membrana/genética , Camundongos , Camundongos Endogâmicos C57BL , Síndrome da Unha-Patela/etiologia , Análise de Sequência com Séries de Oligonucleotídeos , Podócitos/química , Podócitos/ultraestrutura , Proteinúria/etiologia , Fatores de Transcrição/genética , Peixe-ZebraRESUMO
Animal models have provided important insights into human renal diseases that arise from mutations in genes that encode or regulate the synthesis of glomerular basement membrane proteins. This chapter describes several well-characterized animal models of type IV collagen disorders (Alport syndrome, HANAC syndrome), a laminin disorder (Pierson syndrome), nail-patella syndrome and HERNS syndrome. These models can be exploited in studies of the pathogenesis and treatment of such disorders.
