Targeting CD44 Receptor Pathways in Degenerative Joint Diseases: Involvement of Proteoglycan-4 (PRG4).

Rheumatoid arthritis (RA), osteoarthritis (OA), and gout are the most prevalent degenerative joint diseases (DJDs). The pathogenesis underlying joint disease in DJDs remains unclear. Considering the severe toxicities reported with anti-inflammatory and disease-modifying agents, there is a clear need to develop new treatments that are specific in their effect while not being associated with significant toxicities. A key feature in the development of joint disease is the overexpression of adhesion molecules, e.g., CD44. Expression of CD44 and its variants in the synovial tissues of patients with DJDs is strongly associated with cartilage damage and appears to be a predicting factor of synovial inflammation in DJDs. Targeting CD44 and its downstream signaling proteins has emerged as a promising therapeutic strategy. PRG4 is a mucinous glycoprotein that binds to the CD44 receptor and is physiologically involved in joint lubrication. PRG4-CD44 is a pivotal regulator of synovial lining cell hemostasis in the joint, where lack of PRG4 expression triggers chronic inflammation and fibrosis, driven by persistent activation of synovial cells. In view of the significance of CD44 in DJD pathogenesis and the potential biological role for PRG4, this review aims to summarize the involvement of PRG4-CD44 signaling in controlling synovitis, synovial hypertrophy, and tissue fibrosis in DJDs.

Thymoquinone Ameliorates Carfilzomib-Induced Renal Impairment by Modulating Oxidative Stress Markers, Inflammatory/Apoptotic Mediators, and Augmenting Nrf2 in Rats.

Chemotherapy-induced kidney damage is an emerging problem that restricts cancer treatment effectiveness. The proteasome inhibitor carfilzomib (CFZ) is primarily used to treat multiple myeloma and has been associated with severe renal injury in humans. CFZ-induced nephrotoxicity remains an unmet medical need, and there is an urgent need to find and develop a nephroprotective and antioxidant therapy for this condition. Thymoquinone (TQ) is a bioactive compound that has been isolated from Nigella sativa seeds. It has a wide range of pharmacological properties. Therefore, this experimental design aimed to study the effectiveness of TQ against CFZ-induced renal toxicity in rats. The first group of rats was a normal control (CNT); the second group received CFZ (4 mg/kg b.w.); the third and fourth groups received TQ (10 and 20 mg/kg b.w.) 2 h before receiving CFZ; the fifth group received only TQ (20 mg/kg b.w.). This experiment was conducted for 16 days, and at the end of the experiment, blood samples and kidney tissue were collected for biochemical assays. The results indicated that administration of CFZ significantly enhanced serum marker levels such as BUN, creatinine, and uric acid in the CFZ group. Similarly, it was also noticed that CFZ administration induced oxidative stress by reducing antioxidants (GSH) and antioxidant enzymes (CAT and SOD) and increasing lipid peroxidation. CFZ treatment also enhanced the expression of IL-1ß, IL-6, and TNF-α production. Moreover, CFZ increased caspase-3 concentrations and reduced Nrf2 expression in the CFZ-administered group. However, treatment with 10 and 20 mg/kg TQ significantly decreased serum markers and increased antioxidant enzymes. TQ treatment considerably reduced IL-1ß, IL-6, TNF-α, and caspase-3 concentrations. Overall, this biochemical estimation was also supported by histopathological outcomes. This study revealed that TQ administration significantly mitigated the negative effects of CFZ treatment on Nrf2 expression. Thus, it indicates that TQ may have utility as a potential drug to prevent CFZ-induced nephrotoxicity in the future.

cAMP attenuates TGF-ß's profibrotic responses in osteoarthritic synoviocytes: involvement of hyaluronan and PRG4.

Osteoarthritis (OA) is characterized by synovitis and synovial fibrosis. Synoviocytes are fibroblast-like resident cells of the synovium that are activated by transforming growth factor (TGF)-ß to proliferate, migrate, and produce extracellular matrix. Synoviocytes secrete hyaluronan (HA) and proteoglycan-4 (PRG4). HA reduces synovial fibrosis in vivo, and the Prg4-/- mouse exhibits synovial hyperplasia. We investigated the antifibrotic effects of increased intracellular cAMP in TGF-ß-stimulated human OA synoviocytes. TGF-ß1 stimulated collagen I (COL1A1), α-smooth muscle actin (α-SMA), tissue inhibitor of metalloproteinase (TIMP)-1, and procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2 (PLOD2) expression, and procollagen I, α-SMA, HA, and PRG4 production, migration, and proliferation of OA synoviocytes were measured. Treatment of OA synoviocytes with forskolin (10 µM) increased intracellular cAMP levels and reduced TGF-ß1-stimulated COL1A1, α-SMA, and TIMP-1 expression, with no change in PLOD2 expression. Forskolin also reduced TGF-ß1-stimulated procollagen I and α-SMA content as well as synoviocyte migration and proliferation. Forskolin (10 µM) increased HA secretion and PRG4 expression and production. A cell-permeant cAMP analog reduced COL1A1 and α-SMA expression and enhanced HA and PRG4 secretion by OA synoviocytes. HA and PRG4 reduced α-SMA expression and content, and PRG4 reduced COL1A1 expression and procollagen I content in OA synoviocytes. Prg4-/- synovium exhibited increased α-SMA, COL1A1, and TIMP-1 expression compared with Prg4+/+ synovium. Prg4-/- synoviocytes demonstrated strong α-SMA and collagen type I staining, whereas these were undetected in Prg4+/+ synoviocytes and were reduced with PRG4 treatment. We conclude that increasing intracellular cAMP levels in synoviocytes mitigates synovial fibrosis through enhanced production of HA and PRG4, possibly representing a novel approach for treatment of OA synovial fibrosis.