Purpose: There are several risk factors for osteoarthritis (OA) most important of which are age, obesity, and prior injury. Cell senescence, related to aging and can be caused by telomere shortening, oxidative stress, and DNA damage, has recently been identified as a major factor in multiple chronic diseases and is suspected to play a role in the pathogenesis of osteoarthritis. Senescent cells are associated with the senescence-associated secretory phenotype (SASP) characterized by secretion of proinflammatory cytokines, growth factors, and matrix metalloproteases. Senescence and the SASP may affect the ability of chondrocytes to maintain cartilage homeostasis so we characterized senescence in articular cartilage across the tibial plateau. Methods: Cartilage specimens were harvested as surgical waste at the time of total knee replacement. Using an established novel model system for OA progression, differing severities of OA were studied within a patient by comparing results from lesion and non-lesion regions across the tibial plateau including the outer lateral tibial plateau (oLT), inner lateral tibial plateau (iLT), and medial tibial plateau (MT) that model OA progression from early (oLT), to intermediate (iLT), and to late (MT) stage OA. Formalin-fixed paraffin embedded sections of all three regions (oLT, iLT, and MT) from the same patient were mounted on a single slide to ensure the same treatment for comparing relative DAB intensity between regions. Immunohistochemistry (IHC) with DAB was used to evaluate the protein level expression of senescence-associated markers p21, p53, p14ARF, beta-galactosidase (beta-gal), and SERPINE1 (plasminogen activator inhibitor-1, PAI-1). RT-PCR (n¼10) of PAI-1 was performed on MT, iLT, and oLT regions of cartilage; MT and iLT regions were each compared to oLT region. Expression levels were normalized to GAPDH. Results: IHC showed no senescent cells were found in the oLT region, few senescence cells in the iLT region, and many cells were senescent in the MT region. Based upon cartilage IHC for senescence associated proteins, p21, p14ARF, beta-gal, and PAI-1, a positive association in a gradient pattern was observed with with increasing histological OA severity (Figs. 1 and 2). RT-PCR for PAI-1 was consistent with IHC showing a similar increase in gene expression in a gradient pattern with OA severity: iLT/oLT fold change 3.73 (p¼0.01); MT/oLT fold change 5.32 (p¼0.002).Conclusions: IHC and RT-PCR demonstrate a marked increase in senescence indicators p16, p21, p14ARF, beta-gal, and PAI-1 with increasing OA severity of human cartilages. These results suggest that OA may be a suitable indication for targeting by senolytics, new agents designed to eliminate or modify senescent cells.Purpose: Subjects with anterior cruciate ligament (ACL) injury are at risk for post-traumatic osteoarthritis (PTOA). T 1r MRI has been used to detect early degeneration after ACL injury and reconstruction. Figure. SM04690 inhibited inflammatory cytokine production in vitro and decreased pain in the MI...
