Effects Of MAPK Signaling Pathway On Degenerative Osteoarthritis And The Expression Of Associated Inflammatory Factors

Bachground:Osteoarthritis(OA),the most prevalent chronic joint disease,increases in prevalence with age,and affects most of individuals over the age of 65 and is a leading musculoskeletal cause of impaired mobility in the elderly.OA mainly affects the joints including knees,hands,hips,and spine and is a leading musculoskeletal cause of impaired mobility in the elderly.While several risk factors associated with OA have been put forward,including a genetic predisposition,aging,obesity,and joint mal-alignment,the pathogenesis of OA remains largely unclear.The major clinical symptoms include chronic pain,joint instability,stiffness,joint deformities,and radiographic joint space narrowing.Treatments of osteoarthritis involve alleviating pain,reducing stiffness,maintaining the functional capacities and improving the quality of life.Current treatments include low-impact aerobic exercise,weight loss,acupuncture,glucosamine and chondroitin Sulfate,and surgical.Because the precise molecular mechanisms implicated in pathogenesis of OA are poorly understood and there are currently no effective interventions to decelerate the progression of OA or retard the irreversible degradation of cartilage except for total joint replacement surgery.Articular chondrocyte is the sensor of articular cartilage homeostasis,and plays a vital role in maintaining the normal physiological structure and function of articular cartilage.Recent studies demonstrated that articular chondrocyte homeostasis could be disrupted by multiple factors,including abnormal mechanical loading,and aging.Additionally,genetic alterations in TGF-β/Smad,Wnt/β-catenin and Ihh signaling pathways can disrupt the balance between anabolic and catabolic activity in articular cartilage and result in irreversible degradation of the extracellular matrix.Objective : This study is intended to investigate the effects of MAPK signaling pathway on the apoptosis and expression of proinflammatory cytokines in human osteoarthritis(OA)patients’ chondrocytes.Methods:Human OA cartilage specimens were obtained from 57 OA patients who underwent surgery in our hospital as the case group,from December 2013 to December 2015.Among 57 OA patients,there were 34 males and 23 females with a mean age of 57.63 ± 6.07 years(range from 48 to 72 years).All patients were diagnosed as OA in accordance with guidelines of the Osteoarthritis Research Society International(OARSI).According to improved Mankin pathological score,16 patients were in low-grade of OA,33 patients in moderate grade,and 8 patients in severe grade.Meanwhile,human normal cartilage specimens were obtained from 31 patients with lower extremity traumatic amputations as controls.There are 19 males and 12 females with a mean age of 50.32 ± 9.80 years(range from 26 to 65 years).There were 19 cases with a traffic accident,5 cases with mechanical injury,3 cases with crush injury,2 cases with falling injury,and 2 cases with other injuries.The specimens in the control group were excluded for degenerative changes,obvious osteoporosis,rheumatoid arthritis,and neoplastic lesion.Expressions of MAPK pathway-related proteins in cartilage tissue were detected by immunochemistry.Cultured chondrocytes isolated from human OA cartilage were assigned into the blank group,the IL-1b group,the PD(PD980959,ERK pathway inhibitors)+ IL-1βgroup,the SB(SB203580,p38 pathway inhibitors)+ IL-1β group,and the SP(SP600125,JNK signaling pathway inhibitors)+ IL-1β group.Cell proliferation and apoptosis were observed by MTT assay and flow cytometry.Western blotting was utilized to detect the expressions of MAPK pathway-related proteins.The mRNA expressions of IL-1,IL-6,and TNF-α were detected by q RT-PCR.Results:The positive rates of p-p38,p-JNK and p-ERK expression in OA cartilage were higher compared with those in normal cartilage.Compared with the blank group,cell proliferation rate was decreased,while cell apoptosis rate was increased.The mRNA expressions of IL-1,IL-6 and TNF-αand active p-p38,p-JNK and p-ERK expression were increased in the IL-1β group,while opposite trends were observed in the PD + IL-1β,SB + IL-1β,and SP + IL-1β groups.Conclusion: Our study provides evidence that inhibition of the p38-MAPK signaling pathway could suppress the apoptosis and expression of proinflammatory cytokines in human OA chondrocytes.