Modulating synovial mechanobiology to mitigate disease progression in osteoarthritis

University Of Pennsylvania, Philadelphia PA

Investigators

Abstract

Project Summary Nearly 8% of the global population suffers from osteoarthritis, and the burden of disease is much higher among older adults. Current treatment strategies are limited to symptom management or require invasive surgical procedures that carry significant risk for the elderly. Thus, there is an urgent need for minimally invasive, disease-modifying therapeutics for the treatment of OA. The synovium is a bi-layer membrane that lines diarthrodial joints and produces synovial fluid. Fibrosis of the synovium is a hallmark of OA and is believed to promote disease progression, making it a target for novel therapeutics. Myofibroblastic differentiation of fibroblast-like synoviocytes (FLS) is triggered by inflammatory signaling and extracellular matrix stiffening, and is critical to the development of synovial fibrosis. This phenotypic shift requires the sensation of mechanical stimuli and upregulation of contractile machinery. Therefore, intervening in FLS mechanobiology offers a promising means to prevent synovial fibrosis and the development of OA. Non-muscle myosin II (NM-II) is a key component of acto-mysoin contractility and mechanotransduction; however, the impact of NM-II inhibition on FLS behavior, synovial fibrosis, and OA progression has not been evaluated. To address these gaps in knowledge, we will investigate the effect of genetic and pharmacologic NM-II suppression on FLS activation in vitro and on synovial fibrosis and OA pathogenesis in vivo. Use of our novel transgenic mouse in which the genes for both NM-IIA and NM-IIB (Myh9 and Myh10, respectively) are floxed will generate precise mechanistic data on the contribution of FLS mechanoactivation in OA progression, while pharmacologic intervention will demonstrate the translational potential of targeting synovial mechanobiology. Our central hypothesis is that inhibition of NM-II activity will limit myofibroblastic differentiation, reducing fibrosis and slowing OA progression. In Aim 1, FLS will be harvested and either directly plated onto substrates of physiologic stiffness or stiff-primed. Half of the cells in each treatment group will be treated with TGFβ to induce heightened mechanoactivation. In Aim 1a, cells will be harvested from Myh9/Myh10 double-floxed mice and NM-II activity will be suppressed by genetic knockout. In Aim 1b, wild-type (WT) FLS will be treated with a small molecule inhibitor of NM-II. Myofibroblastic differentiation and fibrogenic capacity will be assessed via measurement of morphology, contractility, gene expression, and matrix production. In Aim 2, we will induce OA in mice through destabilization of the medial meniscus (DMM). NM-II will be genetically ablated in Aim 2a and pharmacologically inhibited in Aim 2b. Early and delayed intervention will model “preventative” and “treatment” strategies, respectively. Prevention and/or reversal of synovial fibrosis and OA pathology will be assessed via functional outcomes, histological scoring, staining for fibrotic markers, mechanical testing, and transcriptional analysis. Completion of these Aims will establish the role of NM-II in FLS activation, further our understanding of synovial fibrosis as a driver of OA and guide development of innovative therapeutics.