# Macrophage anti-bacterial activity is controlled by adenylate kinase 4–mediated mitochondrial DNA synthesis

## TL;DR

This study shows that the enzyme adenylate kinase 4 (Ak4) helps macrophages fight bacteria by boosting mitochondrial DNA synthesis and reactive oxygen species production.

## Contribution

The study identifies Ak4 as a key regulator of mtDNA synthesis and antibacterial activity in macrophages.

## Key findings

- Ak4 is essential for increasing mtDNA and mitochondrial mass in macrophages after bacterial infection.
- Loss of Ak4 reduces mtROS production and impairs antibacterial defense in macrophages.
- Ak4 mutations disrupt its phosphate transfer function, affecting mtDNA synthesis.

## Abstract

Chin et al. discovered that macrophage-specific Ak4 regulates mtDNA synthesis, through which it controls mitochondrial biogenesis and mtROS levels and, subsequently, bacterial killing. Their study highlights the vital role of Ak4 in macrophage defense against pathogenic bacteria.

Macrophage antibacterial activity requires mtROS production. The specific gene(s) that participates in the mtROS-mediated antibacterial process remains unclear. We showed that Listeria and Salmonella infections in human and mouse macrophages increased mtDNA copy number with which dictates antibacterial activity. Interestingly, adenylate kinase 4 (Ak4) expression was upregulated in macrophages after infection. Ak4 KO mice as well as macrophage-specific Ak4 KO mice became highly susceptible to bacterial infections. Ak4 is critical for the increase of mtDNA synthesis and mitochondrial mass in macrophages after bacterial infection. Biochemically, Ak4 transfers a phosphate group from ATP/GTP to (d)AMP for (d)ADP formation, and the K18A and G89S/A166D mutations abolished this function. Our results suggest that induction of Ak4 after infection produces more dADP, whose conversion to dATP in mitochondria supports mtDNA synthesis and the subsequent increase of mtROS production. Loss of this metabolic coupling in Ak4 KO macrophages diminishes antibacterial activity. Our findings highlight the vital role of Ak4 in macrophage defense against pathogenic bacteria.

A diagram of mitochondrial D N A replication and reactive oxygen species production.The diagram illustrates the process of mitochondrial D N A replication and the generation of reactive oxygen species within the mitochondria. It shows the conversion of A M P and A T P to A D P through the enzyme A k 4. ATP is further combined with d A M P to produce d A in the presence of d A k. A D P is converted into d A D P via ribonucleotide reductase (R N R). N D P K converts d A D P to d C T P, d A T P, d T T P, and d G T P, which are essential for mitochondrial D N A (m t D N A) replication catalyzed by D N A polymerase Gamma. The diagram also depicts the entry of bacteria into the mitochondria and the subsequent increase in reactive oxygen species (R O S), which is indicated by arrows pointing towards the m t D N A. The overall structure highlights the interplay between D N A replication and R O S production within the mitochondria.