The Anti-Tubercular Activity of Simvastatin Is Mediated by Cholesterol-Dependent Regulation of Autophagy <i>via</i> the AMPK-mTORC1-TFEB Axis

Abstract

Background: Statins, which inhibit both cholesterol biosynthesis and protein prenylation branches of the mevalonate pathway, increase the efficacy of anti-tubercular antibiotics in animal models. A previous report proposed that the anti-tubercular activity of statins was associated with induction of autophagy and resided in the ability of these drugs to inhibit protein prenylation. Methods: We used an in vitro human macrophage infection model to inhibit each branch of the mevalonate pathway and evaluate treatment effects on mycobacterial burden. The role of the AMP-activated protein kinase (AMPK) - mechanistic target of rapamycin complex 1 (mTORC1) - transcription factor EB (TFEB)-autophagy axis in simvastatin anti-tubercular activity was determined by western blot analyses, transcriptomics, use of pathway-specific compounds, AMP:ATP assay, and addition of exogenous cholesterol to pharmacological treatments. Findings: We found that the anti-tubercular activity of statins was phenocopied by inhibitors of cholesterol biosynthesis rather than by prenylation inhibitors. Simvastatin treatment blocked mTORC1 activation, activated AMPK through increased intracellular AMP:ATP ratios, and favored TFEB nuclear translocation. These mechanisms all induce autophagy, which is anti-mycobacterial. The simvastatin effects on the AMPK-mTORC1-TFEB-autophagy axis were reversed by adding exogenous cholesterol to the cells. Interpretation: Our data demonstrate that the anti-tubercular activity of simvastatin resides in inhibiting cholesterol biosynthesis. Our work also reveals novel links between cholesterol homeostasis, AMPK-mTORC1-TFEB axis, and intracellular infection control, and uncovers new anti-tubercular therapy targets. Funding Statement: NIH grants to PK (AI122309) and MLG (HL149450, AI104615, UL1TR003017); New Jersey Health Foundation grant to MLG (PC10-15). Declaration of Interests: The authors declare no competing interests.