Tumor necrosis factor-a promotes Staphylococcus aureus-induced osteomyelitis through downregulating endothelial nitric oxide synthase

Background: Infections of Staphylococcus aureus (S. aureus) often result in osteomyelitis, which is the acute or chronic infections of the bone marrow or bones. TNF-a is long recognized as a key factor contributing to the pathogenesis of osteomyelitis, but little is known about the underlying molecular mechanism. Methods: Expression levels of TNF-a, and several candidate genes, including endothelial nitric oxide synthase (eNOS), known to be downregulated by TNF-a were analysed in MC3T3-E1 cells with S. aureus infection and osteomyelitis patient blood. MicroRNA(miR)-129-5p was predicted and experimentally verified to target eNOS. Alizarin red sulfate (ARS) and alkaline phosphatase (ALP) staining assays were conducted on MC3T3-E1 cells with S. aureus infection to assess the role of TNF-a/miR-129-5p/eNOS on mineralization defect. Results: TNF-a and miR-129-5p were upregulated while eNOS was downregulated in MC3T3-E1 cells with S. aureus infection and osteomyelitis patients, showing inversely correlated expression profiles. MiR-129-5p directly binds to the 30-UTR of eNOS mRNA to suppress eNOS expression in MC3T3-E1 cells. TNF-a blocker inhibited miR-129-5p and elevated eNOS expres-sion, likely contributing to rescued mineralization defect in S. aureus-infected MC3T3-E1 cells. During S. aureus infection, upregulated TNF-a increases endogenous miR-129-5p expression, which in turn inhibits eNOS, contributing to osteomyelitis. Conclusion: Our study thereby proposes a novel signalling cascade involving TNF-a/miR-129-5p/eNOS in the pathogenesis of osteomyelitis, which may also serve as therapeutic targets. Copyright 2020, Taiwan Society of Microbiology. Published by Elsevier Taiwan LLC. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).