Abstract:

Objective: o elucidate the mechanistic role of interleukin-22 (IL-22) in mediating bone destruction in bone and joint tuberculosis via the p38 mitogen-activated protein kinase (MAPK) signaling pathway. Methods: (1) A total of 58 patients diagnosed with bone and joint tuberculosis who underwent surgical intervention at the Department of Orthopedics, Xinjiang Uygur Autonomous Region Infectious Disease Hospital between January and December 2021 were enrolled as the case group. A control group comprising 51 patients with fractures who underwent surgical treatment at the same institution during the same period was also established. Peripheral blood serum samples were collected from all participants, and IL-22 levels were quantified using enzyme-linked immunosorbent assay (ELISA). Additionally, bone tissue specimens were obtained for protein expression analysis. The expression levels of p38 MAPK, phosphorylated p38 (p-p38), cathepsin K (CatK), and matrix metalloproteinase-9 (MMP9) were determined via Western blotting. (2) Mouse monocyte-macrophage leukemia cells (RAW264.7) were differentiated into osteoclast-like cells and subsequently divided into six experimental groups: osteoclast group, osteoclast+H37Rv group, osteoclast+H37Rv+negative control group, osteoclast+H37Rv+IL-22-shRNA group, osteoclast+H37Rv+p38 inhibitor group, and osteoclast+H37Rv+p38 inhibitor+IL-22-shRNA group. The osteoclastogenic activity was assessed using tartrate-resistant acid phosphatase (TRAP) staining, while gene and protein expression levels of p38 MAPK, CatK, and MMP9 were quantified using quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting. Results: (1) Clinical findings: The serum IL-22 levels in the control group (median (quartiles): 34.61 (28.29, 76.92) pg/ml) were significantly lower than those in the case group (102.74 (56.12, 132.78) pg/ml), with a statistically significant difference (Z=-3.840, P=0.001). The protein expression levels of p38, p-p38, CatK, and MMP9 in the case group were 0.649±0.043, 0.856±0.062, and 0.506±0.072, respectively, all of which were significantly higher than those in the control group (0.346±0.078, 0.708±0.094, and 0.366±0.046, respectively), with statistically significant differences (t=-8.368, -3.203, -4.025; all P<0.05). (2) Cellular experiment findings: The number of TRAP-positive osteoclasts per microscopic field (×100) was highest in the osteoclast+H37Rv group (51.333±12.858), significantly exceeding that of all other groups (F=26.270, P<0.001). The expression levels of p-p38, CatK, and MMP9 proteins were markedly upregulated in the osteoclast+H37Rv group but were significantly downregulated following intervention with IL-22 short hairpin RNA (shRNA) and a p38 MAPK inhibitor. Conclusion: Silencing IL-22 expression and inhibiting the p38 MAPK signaling pathway significantly mitigates bone destruction associated with bone and joint tuberculosis. These findings suggest that IL-22 and p38 MAPK play pivotal roles in osteoclastic activity and bone resorption in the pathogenesis of bone and joint tuberculosis, highlighting their potential as therapeutic targets for preventing disease-associated bone loss.

Key words: Mycobacterium tuberculosis, Tuberculosis, osteoarticular, Osteoclasts, Interleukins