TLR22-Induced Pro-Apoptotic mtROS Abets UPRmt-Mediated Mitochondrial Fission in Aeromonas hydrophila-Infected Headkidney Macrophages of Clarias gariepinus

Manmohan Kumar; Shagun Sharma; Munira Haque; Jai Kumar; Umesh Prasad Sah Hathi; Shibnath Mazumder

doi:10.3389/fimmu.2022.931021

TLR22-Induced Pro-Apoptotic mtROS Abets UPR^mt-Mediated Mitochondrial Fission in Aeromonas hydrophila-Infected Headkidney Macrophages of Clarias gariepinus

Front Immunol. 2022 Jul 4:13:931021. doi: 10.3389/fimmu.2022.931021. eCollection 2022.

Authors

Manmohan Kumar¹, Shagun Sharma¹, Munira Haque², Jai Kumar¹, Umesh Prasad Sah Hathi², Shibnath Mazumder^{1

2}

Affiliations

¹ Immunobiology Laboratory, Department of Zoology, University of Delhi, Delhi, India.
² Faculty of Life Sciences and Biotechnology, South Asian University, New Delhi, Delhi, India.

Abstract

Toll-like receptors (TLRs) are epitomized as the first line of defense against pathogens. Amongst TLRs, TLR22 is expressed in non-mammalian aquatic vertebrates, including fish. Using headkidney macrophages (HKM) of Clarias gariepinus, we reported the pro-apoptotic and microbicidal role of TLR22 in Aeromonas hydrophila infection. Mitochondria act as a central scaffold in the innate immune system. However, the precise molecular mechanisms underlying TLR22 signaling and mitochondrial involvement in A. hydrophila-pathogenesis remain unexplored in fish. The aim of the present study was to investigate the nexus between TLR22 and mitochondria in pro-apoptotic immune signaling circuitry in A. hydrophila-infected HKM. We report that TLR22-induced mitochondrial-Ca²⁺ [Ca²⁺]_mt surge is imperative for mtROS production in A. hydrophila-infected HKM. Mitigating mtROS production enhanced intracellular bacterial replication implicating its anti-microbial role in A. hydrophila-pathogenesis. Enhanced mtROS triggers hif1a expression leading to prolonged chop expression. CHOP prompts mitochondrial unfolded protein response (UPR^mt) leading to the enhanced expression of mitochondrial fission marker dnml1, implicating mitochondrial fission in A. hydrophila pathogenesis. Inhibition of mitochondrial fission reduced HKM apoptosis and increased the bacterial burden. Additionally, TLR22-mediated alterations in mitochondrial architecture impair mitochondrial function (ΔΨ_m loss and cytosolic accumulation of cyt c), which in turn activates caspase-9/caspase-3 axis in A. hydrophila-infected HKM. Based on these findings we conclude that TLR22 prompts mtROS generation, which activates the HIF-1α/CHOP signalosome triggering UPR^mt-induced mitochondrial fragmentation culminating in caspase-9/-3-mediated HKM apoptosis and bacterial clearance.

Keywords: A. hydrophila; TLR22; UPRmt; apoptosis; mitochondrial fission; mtROS.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Aeromonas hydrophila*
Animals
Caspase 9 / metabolism
Catfishes*
Macrophages
Mitochondrial Dynamics
Toll-Like Receptors / metabolism

Substances

Toll-Like Receptors
Caspase 9