Proline-Serine-Threonine Phosphatase-Interacting Protein 2 Alleviates Diabetes Mellitus-Osteoarthritis in Rats through Attenuating Synovial Inflammation and Cartilage Injury

Objective: To explore the possible way of proline-serine-threonine phosphatase-interacting protein 2 (PSTPIP2) influencing diabetes mellitus-osteoarthritis (DM-OA) progression.

Methods: In vivo, eight-week-old male Sprague Dawley rats were induced with DM-OA by intraperitoneal injection of streptozotocin with high-fat diet feeding and intra-articular injection of monoiodoacetate. PSTPIP2 overexpression was achieved by intra-articular injection of lentivirus vectors. PSTPIP2 expression was verified by real-time polymerase chain reaction and Western blotting. Histological changes were examined by hematoxylin/eosin and safranin-O/fast-green staining. In vitro, rat synovial fibroblasts were induced DM-OA by stimulation of high glucose (HG) and interleukin (IL)-1β. PSTPIP2 overexpression was achieved by lentivirus Infection. U0126 was added as an ERK Inhibitor. Levels of tumor necrosis factor (TNF)-α, IL-6, and IL-1β were detected using enzyme-linked immunosorbent assay. Expression of matrix metalloproteinase (MMP)-3, MMP-13, aggrecanase-2 (ADAMTS-5), intercellular cell adhesion molecule (ICAM)-1, extracellular regulated protein kinase (ERK) and phospho-ERK (p-ERK) was detected by Western blotting.

Results: In DM-OA rats, PSTPIP2 relative messenger RNA (mRNA) level was significantly decreased compared to control rats. The protein expression was also decreased obviously. Inflammation score in synovium was dramatically increased, accompanying with increased TNF-α, IL-6, and IL-1β levels. Osteoarthritis research society international (OARSI) score in cartilage was markedly increased, along with increased MMP-3, MMP-13, ADAMTS-5, ICAM-1, ERK and p-ERK expression. In PSTPIP2-overexpressed DM-OA rats, PSTPIP2 mRNA level and protein expression was increased compared to DM-OA rats received negative-control lentivirus vectors. The inflammation score, as well as TNF-α, IL-6, and IL-1β levels were dramatically decreased. Also, the OARSI score and protein expression of MMP-3, MMP-13, ADAMTS-5, ICAM-1, ERK and p-ERK were decreased. In HG+IL-1β-treated rat synovial fibroblasts, PSTPIP2 protein expression was decreased compared to normal glucose (NG)-treated cells. Levels of TNF-α, IL-6, and IL-1β, as well as expression of MMP-3, MMP-13, ADAMTS-5, ICAM-1, ERK and p-ERK were increased. After cells were infected with PSTPIP2-overexpressed lentivirus, levels of TNF-α, IL-6, and IL-1β, and expression of MMP-3, MMP-13, ADAMTS-5, ICAM-1, ERK and p-ERK were obviously decreased compared to cells infected with NC lentivirus. In addition, ERK Inhibitor U0126 treatment also decreased the TNF-α, IL-6, and IL-1βlevels and MMP-3, MMP-13, ADAMTS-5, ICAM-1, ERK and p-ERK expression in HG + IL-1β treated rat synovial fibroblasts.

Conclusion: Overexpression of PSTPIP2 alleviates synovial inflammation and cartilage injury during DM-OA progression via inhibiting ERK phosphorylation.