The role of osteoarthritis regulated microRNAs in skeletal development pathways

Abstract

Cellular changes occur during osteoarthritis (OA), which lead to an alteration in phenotype of the resident cartilage cell, the chondrocyte, and subsequent destruction of the tissue. Many of these changes are unknown. I hypothesise these changes may be due in part to microRNAs (miRNAs), small non-coding RNAs that regulate the expression of a discrete repertoire of genes through base-specific interactions within the target genes 3’untranslated region. A previous screen in our laboratory has identified a number of miRNAs differentially expressed in OA cartilage. The objectives of this study were; (1) to investigate the genetic association of the most extensively studied cartilage miRNA (miR-140), and its targets, with OA, and (2) to assess the function of other, differentially expressed, and less well studied miRNAs, in development signalling pathways, namely miR-125b and miR-324-5p, but focusing on miR-324-5p. Here I identified; (1) SNPs within the miR-140 locus and a predicted, OA-associated, miR-140 target, that may affect function; and (2) miR-125b and miR-324-5p as regulators of Hedgehog (Hh) signalling, likely to play a role in skeletal development. miR-324-5p regulates Hh signalling in human and mouse, yet the mechanism appears unconserved. In humans, miR-324-5p targets SMO and GLI1. Using Stable Isotope Labelling with Amino acids in Cell culture (SILAC) mass spectrometry and whole-genome microarrays, I identified novel miR-324-5p targets, and validated Glypican1 (Gpc1) as a direct target of miR-324-5p and a regulator of Hh signalling in mouse. In addition to regulation of Hh, miR-324-5p regulates Wnt signalling, in which it forms a negative feedback loop. Together, this body of work demonstrates how miRNAs, their targets and their function can be linked in their expression and association with OA.