Background Osteoblasts are the bone forming cells that responsible for the synthesis of collagen type I and mineralization of bone during initial bone formation and later bone remodeling. Abnormalities in osteoblasts phenotype and activity occur in common bone diseases including osteoarthritis (OA). Studies showed that osteoarthritic osteoblasts secrete a collagen type I homotrimer of α1 chains, which is phenotypically distinct from the normal heterotrimer formed by two α1 chains and one α2 chain.
Cytokines released during OA initiation or progression may interfere with osteoblastic function in the bone matrix. Interleukin 1 beta (IL-1β) is one of the major inflammatory cytokines implicated in the pathogenesis of OA; however, the biological response of osteoblasts to the cytokine is only partly understood.
Objectives Our aims were to clarify the effects of IL-1β on collagen type I synthesis in osteoblast-like cells and to explore further possible relationship between collagen type I synthesis and mineralization.
Methods At confluence, MG63 osteoblast-like cells in osteogenic media were stimulated with low (1 ng/ml) or high (10 ng/ml) dose of recombinant human IL-1β at several incubation times; 1, 2, 3, 4 and 5 hours. Non-stimulated MG63 cells were grown as control at indicated time points. Cell viability was tested by using the PrestoBlue reagent. Total collagen production was evaluated by Picro-sirius red precipitation method. Secretion of homotrimer collagen type I alpha 1 (COL1A1) and mineralization at exposure time of 1-, 3- and 5- hour were determined by immunofluorescence staining of COL1A1 antibody and Alizarin Red S staining, respectively.
Results IL-1β showed no statistical evidence in influencing cell viability at the time and dose tested compared to control. We found that IL-1β significantly (p<0.05) increased collagen content at short exposure time (1-hour), while significantly (p<0.05) decreased collagen content at longer exposure time (5-hour), in a dose-dependent manner. Immunofluorescence staining showed increased of homotrimer COL1A1 at 1-hour exposure and decreased of homotrimer COL1A1 at 5-hour exposure of IL-1β in the MG63 cells. IL-1β stimulated the formation of mineralized nodules at all exposure time.
Conclusion We demonstrated for the first time of the paradoxical effect of IL-1β on collagen type I synthesis in osteoblast-like cells. Increased mineralization in low and high homotrimer type I collagen condition may possibly explain the abnormal mineralization in osteoarthritic bone. Paradoxical role of IL-1β in osteoblast may generate a different signal that regulates osteoblast markers expressed in the heterogenous subchondral bone changes in OA. Understanding these mechanisms could pave the way towards targeted therapeutic interventions.
Acknowledgement This study was supported by the Academy of Medical Sciences and the Material Science Institute Lancaster University.
Disclosure of Interests None declared
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