Pathophysiologic role of HDAC6 overexpression consecutive to a mutation abrogating a miRNA-mediated post-transcriptional regulation in a X-linked chondrodysplasia. – CHONDRO-X

We work on a new form of familial X-linked dominant chondrodysplasia (Chassaing et al, 2005). The phenotype in males is lethal and associates platyspondyly, rhizomelic shortening of the members, specific brachydactyly, hydrocephaly, facial dysmorphism and microphthalmia. The phenotype in heterozygous females is less severe and comprises short stature, body asymmetry and moderate mental retardation. We have identified a mutation in the 3’UTR of the deacetylase HDAC6 gene. We showed using various functional approaches that this mutation abrogates the interaction of a specific micro-RNA (miRNA) with this 3’ untranslated region (UTR), thereby impeding the miRNA-mediated post-transcriptional regulation of gene expression of HDAC6. We also showed that both the mRNA and the protein encoded by the gene are overexpressed in tissues from an affected foetus in this family. The mutation is therefore very likely to be molecularly responsible for the disease. Our main aim now is to bring the formal demonstration of this.
It is notable that a right-left body asymmetry is observed in affected females. The first aspect of our project will be to analyse the cellular phenotype of fibroblasts expressing the HDAC6 mutant allele that are derived from the left arm of a female patient who presents with left limbs hypotrophy, and to revert the phenotype using HDAC6 inhibitors (siRNAs and pharmacologic inhibitors). Fundamental studies concerning the gene and the interacting miRNA will be performed in order to explore the system during ontology (ie in situ RNA hybridizations, and immunohistochemistry) at various stages of development in the mouse and the zebrafish. We will also construct animal models in order to reproduce the disease. Forced expression of HDAC6 will be performed in the zebrafish (Danio rerio) and in the mouse. Finally, we shall construct a cellular model to test molecules designed to inhibit HDAC6 deacetylase activity, in order to revert the phenotype in vivo and to envisage therapeutic approaches.
The project will be conducted in collaboration between three laboratories:
Laboratoire de Génétique Humaine (EA4137 ; Université Victor Segalen Bordeaux2): Pr. B. Arveiler
Laboratoire Génomique et Physiologie des Poissons (UMR1067 Université de Bordeaux 1-INRA) : Pr. P. Babin.
Unité INSERM 889 « Fibrose hépatique et cancer du foie » (INSERM - Université Victor Segalen Bordeaux2): Dr. C. Grosset.