Genome and epigenome editing of induced pluripotent stem cells for investigating osteoarthritis risk alleles

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Abstract Genome wide association studies (GWAS) in large cohorts have identified and replicated robust single nucleotide polymorphisms (SNPs) with a strong association to osteoarthritis (OA) development. While many SNPs have been identified as risks for OA development, a mechanistic understanding of their role in cartilage homeostasis and mechanobiology has remained elusive. We propose to use a novel in vitro system combining genome editing of human induced pluripotent stem cells (iPSCs) and cartilage tissue engineering for studying the functional effect of identified OA SNPs on the biochemical and mechanical properties of articular cartilage. In preliminary data, we reported a functional characterization of rs11780978 in which we identified an expression quantitative trait locus (eQTL) operating on the gene PLEC in the cartilage of patients with OA. Our primary hypothesis is that OA-associated SNP rs11780978 results in reduced expression of PLEC in chondrocytes secondary to altered epigenetic regulation at this locus. Using CRISPR-Cas9 and dCas9TET-mediated genome editing, we will examine the role of genetic and epigenetic modulation (PLEC knockout and hypomethylation of the functional region) on the chondrogenic differentiation of hiPSCs. Furthermore, we propose that reduced production of plectin due to this SNP alters the response of chondrocytes to mechanical stress under physiologic or pathologic conditions. This tissue-engineering approach provides a model system that can be used in future studies to examine specific mechanistic hypothesis on the link between OA-associated SNPs and the regulation of chondrocyte physiology. Identification of these mechanisms will hopefully lead to new therapeutic targets for preventing or slowing OA progression.