Knee fibrosis is associated with the development of osteoarthritis in a murine model of tibial compression

Abstract

Fibrosis in the synovium and infrapatellar fat pad (IFP) is frequently observed in knee osteoarthritis (OA) and is often correlated with joint pain and stiffness.However, the mechanisms underpinning the development of knee fibrosis in OA are relatively poorly understood. In this study, we used a combination of histological, immunohistochemical, and multiplex gene expression analyses to characterize the fibrosis that develops in a mouse model of load-induced OA. Histological evaluation showed the time-dependent development of fibrosis in the synovium, capsule, and IFP of loaded limbs of male 11-week-old mice. The development of load-induced fibrosis was accompanied primarily by proliferation, expansion, and activation of the stromal compartment, and by increased macrophage presence evidenced by increased F4/80 and MAC2 positive immunostaining. The presence of B and T-cells was minimal in both control and loaded limbs, but CD3-positive immunostaining was significantly higher in C57BL/6J at 2 weeks after loading, indicating an increased presence of T-cells. Using NanoString gene expression analyses of human and mouse tissues, we found that mice subjected to cyclic loading recapitulated the gene expression profile observed in human fibrotic tissues, including increased expression of collagen genes. Together, our results indicate that this well-controlled nonsurgical mouse model can be used to study the mechanisms underpinning the development of knee fibrosis, and potentially to test targeted strategies to prevent the development of fibrosis and stiffness of the knee.

Cross-Communication Between Knee Osteoarthritis and Fibrosis: Molecular Pathways and Key Molecules

“… 34 , 35 Interestingly, SOX9 expression was greatly increased in fibrosis compared to control in the previously mentioned study analyzing the gene expression of early-stage fibrosis development in OA-associated mice. 27 These findings support the previously reported regulatory function of SOX9, 29 , 36 in cartilage function and present an opportunity for targeted research.…”

“… 25 This pathway is activated following traumatic injury in mice and elevated levels of Wnt are seen in load-induced fibrosis in OA mice. 26 , 27 Inhibition of this pathway in murine joints has been shown to reduce OA severity, reduce type 1 collagen levels, and reduce proliferation of synovial fibroblasts. In human chondrocytes, the addition of Wnt decreased COL2A1 mRNA expression levels, but was rescued via Wnt inhibition.…”

“… 29 , 30 However, in a recent study analyzing the gene expression of early-stage fibrosis development in OA-associated mice, the PI3K pathway was the most robustly expressed in the 2 weeks following fibrosis induction, indicating its importance as a potential therapeutic target. 27 …”

Histologic and molecular features in pathologic human menisci from knees with and without osteoarthritis

“…Data from this and other studies will feed into a larger effort to evaluate histologic and molecular patterns of meniscus degeneration in patients with varying degrees of knee and meniscus pathology. Even though the workflow used in this study has been previously developed and is being used at our institution, 13,43 work with FFPE tissues poses obvious limitations, including but limited to, the low‐quality RNA that can lead to differences in gene expression relative to freshly collected and RNA later‐preserved tissues. Thus, follow‐up studies should aim to combine transcriptomic and proteomic analyses, as well as targeted validation of genes, in freshly collected and preserved tissues.…”

“…Gene expression profiling of FFPE menisci was conducted using the nCounter® PanCancer Pathways panel as previously reported (NanoString Technologies, Inc.) 13 . A corrected input of 50 ng of total RNA per sample was hybridized with the nCounter CodeSet and analyzed with the accompanying nSolver software.…”