Dual regulatory roles of HMGB1 in inflammatory reaction of chondrocyte cells and mice

Osteoarthritis (OA) is one of the most common bone diseasesas it is reported that the impact of knee osteoarthritis symptomatic form is estimated at 240/100,000 people per year. The inflammation of articular cartilageis thought to be the pathologic drive for development of this disease. HMGB1(high mobility group box-1), a regulatory factor for gene transcription, could stimulate inflammation response. However, theexact regulatory role of HMGB1 in the inflammation of articular cartilage still need to be elucidated. In the current study, we used Quantitative Real-Time PCR(Q-PCR) to detect them RNA levels of Collagen Type II Alpha 1(Col2a1), Aggrecan, MMP3(Matrix Metallopeptidase 3), MMP13, ADAMTs4 and ADAMTs5; Enzyme-Linked Immunosorbent Assay(ELISA) was used to detect the content of IL-1β and calpain protein; Cell apoptosis was evaluated by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling(TUNEL) assay and flow cytometryanalysis; Western blot and immunofluorescence assays were applied to assess the expression of HMGB1; Lastly autophagic activity was mainly verified by monodansylcadaverine (MDC) staining. Our data revealed that in the early stage of chondrocyte inflammation(3 and 6 h of LPS stimulation), cytosolic HMGB1 attenuated inflammation response by facilitating cell autophagy and preventing cell apoptosis. While in the late stage (24 and 48 h of LPS stimulation), the extracellular HMGB1 stimulated inflammation reaction and contributed to the cartilage destruction in OA.