背景:结核病仍然是全球主要的健康问题。防止吞噬体-溶酶体融合的能力是细胞内分枝杆菌,包括结核分枝杆菌,在宿主细胞内实现长期持久性。支持这种关键的细胞内促生存策略的机制仍未完全理解。感染持久性分枝杆菌的宿主巨噬细胞与来自C型Niemann-Pick病(NPC)患者的细胞具有表型相似性,一种罕见的溶酶体贮积病,其中内吞运输缺陷和溶酶体内的脂质积累导致细胞功能障碍和细胞死亡。我们调查了这些共享表型是否反映了分枝杆菌细胞内持久性与NPC中宿主细胞途径功能失调之间的潜在机制联系。
方法:通过分枝杆菌感染并随后测量脂质水平和细胞内钙稳态来评估来自野生型小鼠或来自健康人供体的巨噬细胞中NPC表型的诱导。还评估了NPC治疗剂对细胞内分枝杆菌负荷的影响。
结果:巨噬细胞感染了持续的细胞内分枝杆菌,表现出多种脂质类型的积累,溶酶体Ca2+水平降低,和细胞内贩运的缺陷。这些NPC表型也可以仅使用来自分枝杆菌细胞壁的脂质/糖皮质激素来诱导。这些数据表明,持续的细胞内分枝杆菌抑制NPC途径,可能是通过抑制NPC1蛋白,并随后诱导改变的酸性储存Ca2+稳态。溶酶体钙水平降低可能为分枝杆菌感染中吞噬体-溶酶体融合水平降低提供机制解释。能够通过调节宿主细胞钙纠正NPC突变细胞缺陷的治疗在促进分枝杆菌从感染的宿主细胞中清除方面是有益的。
结论:这些发现为分枝杆菌细胞内的持久性提供了一种新的机制解释,并提示分枝杆菌与宿主细胞途径之间的靶向相互作用可能为开发抗结核治疗提供新的途径。
BACKGROUND: Tuberculosis remains a major global health concern. The ability to prevent phagosome-lysosome fusion is a key mechanism by which intracellular mycobacteria, including Mycobacterium tuberculosis, achieve long-term persistence within host cells. The mechanisms underpinning this key intracellular pro-survival strategy remain incompletely understood. Host macrophages infected with persistent mycobacteria share phenotypic similarities with cells taken from patients suffering from Niemann-Pick Disease Type C (NPC), a rare lysosomal storage disease in which endocytic trafficking defects and lipid accumulation within the lysosome lead to cell dysfunction and cell death. We investigated whether these shared phenotypes reflected an underlying mechanistic connection between mycobacterial intracellular persistence and the host cell pathway dysfunctional in NPC.
METHODS: The induction of NPC phenotypes in macrophages from wild-type mice or obtained from healthy human donors was assessed via infection with mycobacteria and subsequent measurement of lipid levels and intracellular calcium homeostasis. The effect of NPC therapeutics on intracellular mycobacterial load was also assessed.
RESULTS: Macrophages infected with persistent intracellular mycobacteria phenocopied NPC cells, exhibiting accumulation of multiple lipid types, reduced lysosomal Ca2+ levels, and defects in intracellular trafficking. These NPC phenotypes could also be induced using only lipids/glycomycolates from the mycobacterial cell wall. These data suggest that persistent intracellular mycobacteria inhibit the NPC pathway, likely via inhibition of the NPC1 protein, and subsequently induce altered acidic store Ca2+ homeostasis. Reduced lysosomal calcium levels may provide a mechanistic explanation for the reduced levels of phagosome-lysosome fusion in mycobacterial infection. Treatments capable of correcting defects in NPC mutant cells via modulation of host cell calcium were of benefit in promoting clearance of mycobacteria from infected host cells.
CONCLUSIONS: These findings provide a novel mechanistic explanation for mycobacterial intracellular persistence, and suggest that targeting interactions between the mycobacteria and host cell pathways may provide a novel avenue for development of anti-TB therapies.