Joubert syndrome (JS) is classified among recessive hereditary ataxias and is characterized by a peculiar cerebellar and brainstem malformation known as the ¿molar tooth sign¿. JS phenotype is heterogeneous and combine neurological signs such as hypotonia slowly evolving into ataxia, developmental delay, mental retardation, abnormal ocular movements and respiratory pattern abnormalities with variable multiorgan involvement, mainly of the kidneys, retina and liver. To date, most of the identified causative genes of JS encode proteins involved in cilia function or assembly. We focused our attention on mutations in AHI1. In order to analyze how these mutations are involved in pathogenesis of JS, primary fibroblasts from two JS patients with different point mutations in AHI1 gene, c.2687A>G and c.2168G>A, were used as cellular model in comparison with two healthy donors. Our preliminary data indicate that: 1) AHI1 mutations lead to a constitutive hyperactivation of Wnt signaling with an imbalance between canonical and non-canonical pathway, 2) AHI1 mutations affect ciliogenesis both at morphological and number level. At present, the roles of primary cilia during neural differentiation remain largely vague so the aim of this research project will be to differentiate iPSCs in neuronal cells in order to investigate how the impairment of cilia could influence the neural development.
The project will have a major impact on a possible future therapy; combine clinical, genetic, cellular and molecular data will be of great help in characterizing the natural history of specific defects in order to identify possible molecular therapeutic targets in Joubert syndrome. The cellular system model proposed should represent in the future a good method to directly characterize cells from JS and other forms of inherited congenital ciliopathy patients and to understand the molecular mechanism responsible for the neuronal deficit related to a defined genetic background. Moreover, the cellular model of the neurospheres can be used for the use of pharmacological substances that can revert some phenotypic characteristics of JS at the level of neurodevelopment.