Macrophage Mitophagy Gene BNIP3 Drives Obesity-Linked Fat Tissue Inflammation

Obesity drives chronic low-grade inflammation in fat tissue, largely orchestrated by immune cells called adipose tissue macrophages (ATMs). This inflammation underlies insulin resistance and type 2 diabetes, but the molecular mechanisms that push ATMs toward a pro-inflammatory state have remained incompletely understood. This study, published in Autophagy (2025), identifies BNIP3-mediated mitophagy as a critical regulator of macrophage polarization during obesity — connecting fat tissue hypoxia, mitochondrial quality control, and metabolic inflammation in a unified mechanistic pathway.

Using mt-Keima mitophagy-reporter mice fed a high-fat diet (HFD) for 12 weeks, researchers demonstrated that obesity significantly enhances mitophagy in gonadal white adipose tissue (gWAT). Flow cytometry revealed that total ATMs (ITGAM+) from HFD-fed mice showed a 1.4-fold increase in mitophagic flux versus normal chow diet (NCD) controls, while TREM2+ lipid-associated macrophages (LAMs) showed an even larger 1.6-fold increase. Correspondingly, HFD-fed mice exhibited a 1.9-fold reduction in mitochondrial mass in total ATMs and a 2.1-fold reduction in LAMs, accompanied by decreased mitochondrial membrane potential and reduced mitochondrial DNA levels.

Single-cell RNA sequencing reanalysis (GSE182233) of macrophage subpopulations identified that Bnip3 — but not other mitophagy receptors such as Bnip3l or Fundc1 — was selectively upregulated in ATMs from obese mice in a HIF1A-dependent manner. This upregulation was concentrated in tissue-resident and lipid-associated macrophage subsets. Mechanistically, in vitro experiments with cobalt chloride (CoCl2) to simulate hypoxia confirmed that HIF1A activation drives BNIP3 expression, increases mitophagic flux, and promotes a glycolytic shift (measured by elevated extracellular acidification rate, ECAR) while reducing oxidative phosphorylation (measured by oxygen consumption rate, OCR). Critically, BNIP3 knockout macrophages under hypoxic conditions failed to make this metabolic shift, maintaining higher OXPHOS capacity.

To test the in vivo relevance, macrophage-specific Bnip3 knockout (bnip3 MKO) mice were generated and fed an HFD. These mice showed markedly reduced adipose tissue inflammation compared to wild-type HFD-fed controls: fewer crown-like structures, lower expression of pro-inflammatory cytokines (including IL1B/IL-1β), and reduced macrophage infiltration. Importantly, bnip3 MKO mice demonstrated improved glucose tolerance and insulin sensitivity on glucose and insulin tolerance tests, without significant differences in body weight, indicating the metabolic benefits were driven by reduced inflammation rather than altered adiposity.

The study further showed that HIF1A-BNIP3 signaling enhanced LPS-induced pro-inflammatory macrophage activation. Macrophages lacking BNIP3 produced less IL1B and other inflammatory mediators in response to LPS, even under hypoxic conditions, linking the mitophagy-glycolysis axis directly to inflammatory output. Together, these findings establish that BNIP3-mediated mitophagy — driven by obesity-induced adipose tissue hypoxia — is a key metabolic checkpoint controlling macrophage inflammatory polarization. The authors propose BNIP3 as a tractable therapeutic target for obesity-related metabolic diseases, though human translational studies are needed.