Mycobacterial acyl carrier protein suppresses host autophagic flux via upregulating miR-155 expression in murine macrophages

Mycobacterial acyl carrier protein (AcpM; Rv2244), a key protein involved in Mycobacterium tuberculosis (Mtb) mycolic acid production, has been shown to suppress host cell death during mycobacterial infection. This study reports that mycobacterial AcpM works as an effector for subverting host autophagy to promote bacterial growth. In murine bone marrow-derived macrophages (BMDMs), AcpM protein hindered autophagy activation and affected autophagic flux through suppressing transcription factor EB (TFEB). AcpM prevented TFEB from translocating to the nucleus in BMDMs, which inhibited transcriptional activation of several autophagy and lysosomal genes. Furthermore, AcpM reduced Mtb and LAMP1 co-localization indicating that AcpM inhibits autophagosome-lysosome fusion during Mtb infection. Mechanistically, AcpM boosted the Akt-mTOR pathway in BMDMs by upregulating microRNA-155-5p, a SHIP1-targeting microRNA. When microRNA-155-5p expression was inhibited in BMDMs, AcpM-induced increased intracellular survival of Mtb was suppressed. Moreover, mycobacterial clearance was significantly reduced in vivo when M. smegmatis overexpressing AcpM was challenged in C3HeB/FeJ mice compared to M. smegmatis overexpressing simply carrier plasmid. Collectively, our findings point to AcpM as a novel mycobacterial autophagy regulator and a potential new therapeutic target for Mtb infection.

分枝杆菌酰基载体蛋白(AcpM; Rv2244)是参与结核分枝杆菌(Mycobacterium tuberculosis, Mtb)分枝菌酸生成的关键蛋白，既往研究表明其可在分枝杆菌感染过程中抑制宿主细胞死亡。本研究揭示，分枝杆菌AcpM可作为效应因子劫持宿主自噬以促进细菌增殖。在小鼠骨髓来源巨噬细胞(BMDMs)中，AcpM蛋白通过抑制转录因子EB(TFEB)，阻碍自噬激活并影响自噬流。AcpM可阻止TFEB在BMDMs中转位入核，进而抑制多个自噬相关及溶酶体基因的转录激活。此外，AcpM可减少结核分枝杆菌与溶酶体相关膜蛋白1(LAMP1)的共定位，表明其在Mtb感染过程中可抑制自噬体-溶酶体融合。从机制层面来看，AcpM通过上调靶向SHIP1的微小RNA-155-5p(microRNA-155-5p)，激活BMDMs中的Akt-mTOR信号通路。当在BMDMs中抑制微小RNA-155-5p的表达后，AcpM诱导的结核分枝杆菌胞内存活增加现象被抑制。相较于仅携带空载体质粒的耻垢分枝杆菌，在C3HeB/FeJ小鼠体内感染过表达AcpM的耻垢分枝杆菌时，其体内分枝杆菌清除率显著降低。综上，本研究结果表明AcpM是一种新型分枝杆菌自噬调控因子，同时也是治疗Mtb感染的潜在新型治疗靶点。