The Circular RNA hsa_circ_0004771 Regulates the Intracellular Survival of <i>Mycobacterium tuberculosis</i> in Macrophages by Targeting hsa-miR-3921 to Increase TREM1 Expression

The interactions among the host's circular RNAs (circRNAs), microRNAs (miRNAs), and target genes are crucial for antibacterial resistance and intracellular pathogen clearance. However, this process remains poorly understood during <i>Mycobacterium tuberculosis</i> (<i>M.tb</i>) infection. Our previous study identified hsa_circ_000477, a novel circRNA formed by the NRIP1 gene on human chromosome 21, which was upregulated in <i>M.tb</i>-infected THP-1 macrophages. The present study systematically investigated the effect of hsa_circ_0004771 on <i>M.tb</i> infection and the underlying molecular mechanism. First, hsa_circ_0004771 was demonstrated to inhibit <i>M.tb</i> intracellular survival in macrophages. To identify its target miRNAs, multiple algorithms were used for computational prediction, and qPCR, dual-luciferase reporter assays, and RNA fluorescence in situ hybridization (FISH) were performed to confirm that miR-3921 was the primary target miRNA of hsa_circ_0004771. Further computational analyses across multiple algorithms─such as miRDB, TarBase, TargetScan, and microT-CDS─and validation with the above-mentioned methods, TREM1 was identified as the target of miR-3921. The results showed that an elevated level of TREM1 expression increased P65 phosphorylation levels, thereby enhancing IL-1β secretion. In conclusion, we identified a novel host defense mechanism in <i>M.tb</i>-infected THP-1 cells: the hsa_circ_0004771/miR-3921/TREM1 axis suppresses bacterial survival by promoting proinflammatory IL-1β production. These findings revealed a novel mechanism involved in host defense against <i>M.tb</i> infection.