Zebrafish: a model to test the therapeutic potential of epidrugs on complex Kabuki phenotypes – ZEPIKAB

Kabuki syndrome (KS) is a rare genetic disorder primarily related to mutations of KMT2D (histone-lysine N-methyltransferase 2D), a gene encoding an enzyme which catalyzes the methylation of lysine 4 on histone H3 (H3K4) and regulates gene expression in different biological contexts. KS individuals display typical facial features with short stature, skeletal and cardiac malformations and heterogeneous intellectual disability. KS patients also exhibit high susceptibility to infections and few cases that develop autoimmune diseases were described. Immunopathological manifestations and altered cognitive functions associated with KS directly impact morbi-mortality and re-education capacities of patients as no specific treatment exists for this multi-system syndrom.
Partner 1 investigated these complex phenotypes in KS individuals with KMT2D pathogenic variants. First, regarding immunological manifestations, we found high prevalence of autoimmune diseases associated with KS in a large adult cohort. This result, together with previous data on the role of KMT2D in the epigenetic control of FOXP3, a master gene required for regulatory T cells (Treg) development and functions, strongly suggest a defect in T cells development and/or functions due to alterations of gene expression in these cells. At the neurodevelopmental level, we conducted two studies that have shown: 1) correlations between cognitive phenotype and specific brain defects in KS individuals by brain-MRI anatomical studies that confirmed and extende results obtained in mouse model of KS; and 2) that visual as well as visuospatial anomalies are key features in KS intellectual disability. Studies in distinct animal models underlined the importance to study the specific effects of KTM2D deficiency in each cell type affected within a whole organism and the high potential of new therapeutic strategies based on pharmacological drugs that could restore methylation status for KMT2D targets and ameliorate or even reverse specific KS deficits. This type of approach could pave the way to new diagnostic and therapeutic solutions for KS patients.
Due to intrinsic and experimental advantages, zebrafish has converted in a powerful model to study the physiopathologic mechanisms of disease-causing genes identified in humans and to conduct preclinical tests with candidate drugs. We will use the ktm2d+/- zebrafish to modelize both complex phenotypes of KS, the immunological aspects ZEPIKAB in this species is completely new, and to test the potential of a several epidrugs to rescue KS-like defects. ZEPIKAB will benefit from the strong expertise of Partner 2 in epigenome/transcriptome profiling and bioinformatic to address the issue of epigenetic alterations of T cells and neuronal stem cells in this organism upon kmt2d heterozygoty and to monitor the effects of the tested epidrugs or a combination of epidrugs.
The 4 objectives of ZEPIKAB project are to : (1) modelize immunological and neurobehavioral phenotypes of KS in ktm2d+/- zebrafish; (2) characterize epigenome and transcriptome alterations, including differential KMT2D enhancers and related target genes, in ktm2d+/- mutants in neural stem cells (NSC) and immune T cells, and to validate these targets in human T cells; (3) test the potential of several “epidrugs” to restore control methylation levels induced by kmt2d deficiency in both cell types and to reverse the corresponding phenotypes in the mutant fish and (4) mouse KS model. To this aim, we propose 4 scientific and technical complementary work packages (WP):
WP1: Study of neurobehavioral alterations in larval and adult kmt2d mutant zebrafish, WP2: Effects of kmt2d mutation on T cell development and functions, WP3: Improvement of KS-like phenotypes and restoration of methylation using 4 epidrugs, and WP4: Validation of an epidrug-based strategy, using the epidrug selected in WP3, to rescue T cell development and methylation profile in mouse KS model.