Cathepsin B modulates lysosomal biogenesis and host defense against Francisella novicida infection

Lysosomal cathepsins regulate an exquisite range of biological functions, and their deregulation is associated with inflammatory, metabolic and degenerative disease in humans. Here, we identified a key cell-intrinsic role for cathepsin B as a negative feedback regulator of lysosomal biogenesis and autophagy. Mice and macrophages lacking cathepsin B activity had increased resistance to the cytosolic bacterial pathogen Francisella novicida. Genetic deletion or pharmacological inhibition of cathepsin B downregulated mTOR activity and prevented cleavage of the lysosomal calcium channel TRPML1. These events drove transcription of lysosomal and autophagy genes via the transcription factor TFEB, which increased lysosomal biogenesis and activation of autophagy-initiation kinase ULK1 for clearance of the bacteria. Our results identified a fundamental biological function of cathepsin B in providing a checkpoint for homeostatic maintenance of lysosome population and basic recycling functions in the cell. We used microarrays to explore the gene expression profiles differentially expressed in bone marrow-derived macrophages (BMDM) isolated from cathepsin B-/- and wild-type mice.溶酶体组织蛋白酶（lysosomal cathepsins）调控着一系列精细复杂的生物学功能，其表达失调与人类的炎症性、代谢性及退行性疾病密切相关。本研究明确了组织蛋白酶B（cathepsin B）作为溶酶体生物发生（lysosomal biogenesis）与自噬（autophagy）负反馈调控因子的关键细胞内源性作用。缺乏组织蛋白酶B活性的小鼠及巨噬细胞，对胞内细菌病原体新凶手弗朗西丝菌（Francisella novicida）的抵抗力显著提升。对组织蛋白酶B进行基因敲除或药物抑制，可下调哺乳动物雷帕霉素靶蛋白（mTOR）的活性，并阻断溶酶体钙通道TRPML1的剪切过程。上述事件通过转录因子TFEB介导溶酶体及自噬相关基因的转录，进而促进溶酶体生物发生，并激活自噬起始激酶ULK1，最终实现对病原菌的有效清除。本研究揭示了组织蛋白酶B的一项核心生物学功能：作为调控细胞内溶酶体群体稳态维持与基础物质再循环功能的检查点。本研究采用基因芯片（microarrays）技术，分析了来自组织蛋白酶B敲除（cathepsin B-/-）与野生型小鼠的骨髓来源巨噬细胞（BMDM）的差异基因表达谱。