The goals of this proposal are to examine the gene expression pathways and signaling networks that are perturbed in naturally occurring equine osteoarthritis (OA). In addition, we seek to evaluate the mechanisms by which recombinant lubricin therapy mitigates the progression of joint disease in an experimental osteochondral chip fragment model of equine OA. While joint disease in the horse is thought to share many common pathologic features with humans, changes in protein expression have been difficult to validate in the horse due to limited availability of species-specific reagents. Although gene expression changes can be evaluated with traditional polymerase chain reaction (PCR) techniques, these approaches limit investigation to known targets. RNA-sequencing (RNA-seq) studies enable unbiased identification of gene targets and expression pathways with potential for more precise targeting of OA therapeutics, including an improved mechanistic understanding of intra-articular recombinant equine lubricin (rEqLub) therapy.

Here, we will employ bulk and single cell RNA-seq (scRNA-seq) in two equine cohorts: horses with naturally occurring fetlock OA and horses with experimentally-induced carpal OA. Aim 1 will compare the transcriptome of articular cartilage and synovial membrane cells in Thoroughbred racehorses with healthy and OA fetlock joints. Tissues, including synovial fluid, synovial membrane, and cartilage, have already been obtained and processed for future RNA isolation in a population of Thoroughbred racehorses that have died or been euthanized on New York racetracks as part of a prior study in our lab evaluating immune cell populations in equine OA. Aim 2 will study how rEqLub therapy alters immune cell distribution and signaling networks in an early experimental model of osteochondral fragment induced OA coupled with high-speed treadmill exercise. Lubricin was originally characterized as a synovial fluid boundary lubricant; however, recent data suggests that lubricin may also have biological activity including immunomodulation, and these effects have never been studied in the horse.

This proposal will identify the most relevant transcriptomic pathways in fetlock OA affecting the Thoroughbred racehorse population while also delineating transcriptional targets of recombinant equine lubricin therapy. This study has the potential to identify diagnostic markers, therapeutic targets, and more fully understand the pathophysiologic processes leading to the development of OA in horses.