Main author: Sara Þöll Halldórsdóttir
Institution or Company: University of Iceland
Co-Author, Institution or Company:
Hans Tómas Björnsson, University of Iceland, Johns Hopkins University, Landspítali.
Introduction: Kabuki syndrome (KS) is Medelian disorder of the epigenetic machinery primarily caused by heterozygous loss of function mutations in the histone methyltransferase Kmt2d. KS patients commonly demonstrate intellectual disability, growth retardation and distinct facial features. Prior work in KS mice has uncovered smaller bones yet an expanded growth plate. Chondrocyte differentiation in vitro has revealed precocious differentiation in Kmt2d-deficient chondrocytes. Among differentially expressed genes (DEGs) in patient induced pluripotent stem cells we see an enrichment of genes linked to hypoxia response and since chondrocytes differentiate under hypoxic condition, we explored the phenotypic effects of differing environmental oxygen.
Methods: Mouse chondrocyte cell line ATDC5 with or without deletion of Kmt2d were differentiated in vitro under both normoxic (21%) and hypoxic (1%) conditions and differentiation rate quantified with Alcian Blue staining and gene expression of chondrocyte markers Sox9, Col2a1 and Col10a1. Single-cell-RNA sequencing was also performed on chondrocytes differentiated under normal oxygen concentration.
Results: Precocious differentiation is observed in lines carrying both compound heterozygous (Kmt2dR5551/-) and homozygous (Kmt2d-/-) mutations when differentiation is induced under normoxic condition (p<0.01) but not in hypoxic environment (ns). Single-cell-RNA sequencing of differentiating cells indicated no difference in types of cell populations but we find pathways that are both up- and downregulated.
Conclusions: Our data suggest that differences in differentiation rate are accompanied by abnormal gene expression and that hypoxia may normalize disease-relevant phenotypes in KS. We hypothesize that by identifying hypoxia-responsive KMT2D-targets we may be able to uncover the mechanistic basis of this phenotype.
