Molecular Insight into the Association Between Cartilage Regeneration and Ear Wound Healing in Genetic Mouse Models: Targeting New Genes in Regeneration

Abstract

Tissue regeneration is a complex trait with few genetic models available. Mouse strains LG/J and MRL are exceptional healers. Using recombinant inbred strains from a large (LG/J, healer) and small (SM/J, nonhealer) intercross, we have previously shown a positive genetic correlation between ear wound healing, knee cartilage regeneration, and protection from osteoarthritis. We hypothesize that a common set of genes operates in tissue healing and articular cartilage regeneration. Taking advantage of archived histological sections from recombinant inbred strains, we analyzed expression of candidate genes through branched-chain DNA technology directly from tissue lysates. We determined broad-sense heritability of candidates, Pearson correlation of candidates with healing phenotypes, and Ward minimum variance cluster analysis for strains. A bioinformatic assessment of allelic polymorphisms within and near candidate genes was also performed. The expression of several candidates was significantly heritable among strains. Although several genes correlated with both ear wound healing and cartilage healing at a marginal level, the expression of four genes representing DNA repair (Xrcc2, Pcna) and Wnt signaling (Axin2, Wnt16) pathways was significantly positively correlated with both phenotypes. Cluster analysis accurately classified healers and nonhealers for seven out of eight strains based on gene expression. Specific sequence differences between LG/J and SM/J were identified as potential causal polymorphisms. Our study suggests a common genetic basis between tissue healing and osteoarthritis susceptibility. Mapping genetic variations causing differences in diverse healing responses in multiple tissues may reveal generic healing processes in pursuit of new therapeutic targets designed to induce or enhance regeneration and, potentially, protection from osteoarthritis.

Enhanced cartilage repair in ‘healer’ mice—New leads in the search for better clinical options for cartilage repair

“…With the assumption that a common set of genes are involved in ear hole closure and articular cartilage regeneration, Rai et al [66] investigated gene expression differences in ear wound tissue and articular cartilage from the common inbred and recombinant inbred strains described above [63,64]. A key finding from cluster analysis of the gene expression data was that the strains clustered with their healing ability [63].…”

“…The exception is the non-healing LGXSM-33 line whose gene expression profile clusters with the healer strains. It is unclear why the LGXSM-33 gene expression profile mirrors that of a healing strain but the investigators noted that this strain appeared to be a good healer (similar to LGXSM-6) early on, but that later on healing was halted and cartilage degraded, leading to the poor healer classification [66]. LGXSM33 should therefore be considered an intermediate healer.…”

“…When gene expression levels were plotted against healing scores, six gene expression signatures were correlated with articular cartilage healing scores; Pcna , Wnt16 , Xrcc2 , Axin2 , Cebpb and Ulk1 [66]. Both Pcna and Xrcc2 are involved in cell proliferation and maintenance of chromosome stability at wound sites and have been implicated in DNA repair [67].…”

“…Interestingly, four of these genes were also correlated with ear wound closure; Xrcc2 and Pcna , involved in DNA repair and cell cycle control, and Axin2 and Wnt16 , involved in Wnt signaling, suggesting that these two functional classes of genes are part of a universal regeneration mechanism in the MRL/MpJ and related healer strains [66]. …”

Cartilage regeneration for treatment of osteoarthritis: a paradigm for nonsurgical intervention

“…Until recently, it was generally believed that cartilage regeneration is almost impossible in mammals. However, it has been observed in murine models that articular cartilage regeneration is heritable in that some murine strains are robust healers while other strains are nonhealers [Rai et al 2013;Rai and Sandell, 2014].…”