RESUMEN
Mammalian class IX myosin Myo9a is a single-headed, actin-dependent motor protein with Rho GTPase-activating protein activity that negatively regulates Rho GTPase signaling. Myo9a is abundantly expressed in ciliated epithelial cells of several organs. In mice, genetic deletion of Myo9a leads to the formation of hydrocephalus. Whether Myo9a also has essential functions in the epithelia of other organs of the body has not been explored. In the present study, we report that Myo9a-deficient mice develop bilateral renal disease, characterized by dilation of proximal tubules, calyceal dilation, and thinning of the parenchyma and fibrosis. These structural changes are accompanied by polyuria (with normal vasopressin levels) and low-molecular-weight proteinuria. Immunohistochemistry revealed that Myo9a is localized to the circumferential F-actin belt of proximal tubule cells. In kidneys lacking Myo9a, the multiligand binding receptor megalin and its ligand albumin accumulated at the luminal surface of Myo9a-deficient proximal tubular cells, suggesting that endocytosis is dysregulated. In addition, we found, surprisingly, that levels of murine diaphanous-related formin-1, a Rho effector, were decreased in Myo9a-deficient kidneys as well as in Myo9a knockdown LLC-PK1 cells. In summary, deletion of the Rho GTPase-activating protein Myo9a in mice causes proximal tubular dilation and fibrosis, and we speculate that downregulation of murine diaphanous-related formin-1 and impaired protein reabsorption contribute to the pathophysiology.
Asunto(s)
Proteínas Activadoras de GTPasa/fisiología , Túbulos Renales/fisiología , Miosinas/fisiología , Albúminas/metabolismo , Animales , Proteínas Portadoras/metabolismo , Células Cultivadas , Endocitosis/fisiología , Forminas , Proteínas Activadoras de GTPasa/genética , Hidronefrosis/genética , Hidronefrosis/metabolismo , Túbulos Renales/anatomía & histología , Túbulos Renales/citología , Células LLC-PK1 , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Miosinas/genética , Nefronas/fisiología , Poliuria/genética , Poliuria/metabolismo , Porcinos , Vasopresinas/metabolismo , Quinasas Asociadas a rho/metabolismoRESUMEN
Mammals contain two class IX myosins, Myo9a and Myo9b. They are actin-based motorized signalling molecules that negatively regulate RhoA signalling. Myo9a has been implicated in the regulation of epithelial cell morphology and differentiation, whereas Myo9b has been shown to play an important role in the regulation of macrophage shape and motility.
Asunto(s)
Células Epiteliales/metabolismo , Macrófagos/metabolismo , Miosinas/metabolismo , Isoformas de Proteínas/metabolismo , Animales , Diferenciación Celular , Movimiento Celular , Forma de la Célula , Células Epiteliales/citología , Humanos , Macrófagos/citología , Miosinas/genética , Isoformas de Proteínas/genéticaRESUMEN
The ependymal multiciliated epithelium in the brain restricts the cerebrospinal fluid to the cerebral ventricles and regulates its flow. We report here that mice deficient for myosin IXa (Myo9a), an actin-dependent motor molecule with a Rho GTPase-activating (GAP) domain, develop severe hydrocephalus with stenosis and closure of the ventral caudal 3rd ventricle and the aqueduct. Myo9a is expressed in maturing ependymal epithelial cells, and its absence leads to impaired maturation of ependymal cells. The Myo9a deficiency further resulted in a distorted ependyma due to irregular epithelial cell morphology and altered organization of intercellular junctions. Ependymal cells occasionally delaminated, forming multilayered structures that bridged the CSF-filled ventricular space. Hydrocephalus formation could be significantly attenuated by the inhibition of the Rho-effector Rho-kinase (ROCK). Administration of ROCK-inhibitor restored maturation of ependymal cells, but not the morphological distortions of the ependyma. Similarly, down-regulation of Myo9a by siRNA in Caco-2 adenocarcinoma cells increased Rho-signaling and induced alterations in differentiation, cell morphology, junction assembly, junctional signaling, and gene expression. Our results demonstrate that Myo9a is a critical regulator of Rho-dependent and -independent signaling mechanisms that guide epithelial differentiation. Moreover, Rho-kinases may represent a new target for therapeutic intervention in some forms of hydrocephalus.