MicroRNA-708-5p regulates mycobacterial vitality and the secretion of inflammatory factors in Mycobacterium tuberculosis-infected macrophages by targeting TLR4

Abstract

Objective: Tuberculosis (TB), a major public health problem worldwide, is induced by Mycobacterium tuberculosis (M.tb) infection. Macrophages serve as the cellular home in immunoreaction against M.tb infection, which is tightly adjusted by host microRNAs (miRNAs) expression. The purpose of this research was to investigate the function mechanism of miR-708-5p in mycobacterial vitality and immunoreaction in human macrophages (HTP-1 and U937 cells) after M.tb infection.

Materials and methods: Colony-forming unit (CFU) assay was used to measure mycobacterial survival. The interferon-γ (IFN-γ), interleukin-6 (IL-6), IL-1β, and tumor necrosis factor-α (TNF-α) expression in cell supernatants were detected by enzyme-linked immunosorbent assay (ELISA). The relationship between miR-708-5p and toll-like receptor 4 (TLR4) was predicted and revealed by TargetScan and Dual-Luciferase Reporter Assay.

Results: Our results suggested that the miR-708-5p level was increased in a concentration-dependent and time-dependent manner in M.tb-infected human macrophages. Compared with the control group, miR-708-5p mimic enhanced the intracellular mycobacterial survival during M.tb infection, while miR-708-5p downregulation suppressed the mycobacteria survival. Moreover, the secretion of the pro-inflammatory factors, including IFN-γ, IL-6, IL-1β, and TNF-α significantly enhanced in M.tb-induced macrophages, while miR-708-5p mimic reduced these inflammatory cytokines. Conversely, miR-708-5p inhibitor dramatically promoted the accumulation of the inflammatory factors in macrophages after M.tb treatment. In addition, evidence indicated that TLR4 was a direct and functional target of miR-708-5p. MiR-708-5p negatively regulated the TLR4 level in macrophages.

Conclusions: The findings indicated that miR-708-5p level was upregulated in macrophages after M.tb infection. And miR-708-5p could regulate mycobacterial vitality and inflammatory response to M.tb infection in human macrophages by targeting TLR4.