Mechanisms regulating ferritinophagy during infection with Mycobacterium tuberculosis induces ferroptosis and orchestrates TB pathogenesis

Introduction/Rationale: Ferroptosis, an iron-dependent mode of cell death, has emerged as a critical nexus during infection with Mycobacterium tuberculosis (Mtb), with studies reporting its inextricable link to Mtb-induced necrosis, inflammation, tissue damage and dissemination. Amidst the plethora of reports reporting the role of an impaired antioxidant system as a driver of Mtb-induced ferroptosis, we provide evidence of dysregulated iron metabolism and identify a novel post-translational modification regulating the process. Mtb infection induces ferritinophagy, the autophagic turnover of the intracellular iron chelator- ferritin, due to the accumulation of the cargo receptor, nuclear receptor co-activator 4 (NCOA4). We identify a crucial role for the methylation of NCOA4 in regulating its interaction with ferritin within the iron-replete conditions of Mtb-infected cells.

Methods: Using loss-of-function studies, we delineate the role of NCOA4-dependent ferritinophagy in regulating the three hallmarks of ferroptosis, availability of iron, reactive oxygen species and lipid peroxidation, during Mtb infection. Following the identification of a host arginine methyltransferase, PRMT5, in methylating NCOA4 and enhancing its cytoplasmic retention during Mtb infection, we extended our studies to BALB/c mice infected with Mtb that were treated with a PRMT5 inhibitor and assessed for mycobacterial dissemination and survival.

Results: We observe that the increased flux in ferritinophagy contributes to the availability of ferrous iron and is a prerequisite for Mtb-induced ferroptosis. Specifically, we found that pharmacological inhibition or knockdown of PRMT5 rescues iron homeostasis, concomitantly decreasing lipid peroxidation and ferroptosis in vitro and in vivo, thereby restricting Mtb burden. This aided in rescuing the infected mice from severe TB-like pathology.

Conclusion: Thus, our findings shed light on the novel roles of PRMT5 and NCOA4 during Mtb infection, and their possible implication in potentiating anti-TB responses.