Protective Role of Mitophagy Associated Metabolic Reprogramming of Peripheral Macrophages During Tuberculosis

Abstract

Mitophagy, the process of selective clearance of mitochondria in the cells is executed through receptor and adaptor mediated pathways. NIX is crucial for receptor-mediated mitophagy and is not characterized well for its role in host-directed protective immunity against infection. Whole transcriptome analysis of PBMCs from treatment naïve (n = 5) and healthy controls (n = 4) showed altered expression of genes mediating mitophagy and cellular energetics pathways. M. tuberculosis infection associated systemic alteration in mitophagy and cellular energetics pathway genes NIX, HADH, LC3C, ECI2 and PFKFB3 in PBMCs from a validation cohort of treatment naïve TB patients (n = 22) and healthy controls (n = 22) was in concordance with RNASeq data. Ex-vivo infection of BCG in PBMCs and THP-1 cells also showed increased expression of genes belonging to glycolysis and mitophagy pathways, which was in correlation with decreased uptake of Mito-Tracker Red, increased uptake of 2-NBDG, increased consumption of 100% U-¹³C₆ labelled glucose and production of 100% U-¹³C₃ labelled lactate, indicating a shift in cellular energetics. Following NIX knockdown, the mRNA levels of glycolysis and mitophagy pathway genes were reduced, compared with negative control siRNA. Following NIX knockdown, BCG infected cells consumed less glucose (2-NBDG) and uptake of MitoTracker Red increased. NIX knocks also decreased secretion of inflammatory cytokines (IL-1 β, TNF- α, and IL-6 in macrophages. This study shows that M. tuberculosis infection induces systemic effects, correlating with M1 phenotype associated transition of cellular energetics and induction of receptor-mediated mitophagy. Further studies are required to explore mitophagy mediated treatment intervention for tuberculosis management.

Keywords: Macrophages, tuberculosis, Mitophagy, Glycolysis, NIX/BNIP3L, inflammatory cytokines