IL-1R-IRAKM-Slc25a1 signaling axis reprograms lipogenesis in adipocytes to promote diet-induced obesity in mice

Obesity is a major risk factor for insulin resistance, type 2 diabetes, and metabolic syndrome. Chronic positive energy balance leads to adipose tissue expansion and is associated with low-grade inflammation. High-fat diet (HFD) elevates endogenous TLR ligands (e.g., FFAs, ox-LDL) and cytokines such as IL-1, implicating TLR/IL-1R signaling in adipose dysfunction. TLR/IL-1R signals via MyD88 and IRAK family members forming Myddosomes to activate inflammatory pathways. Prior work showed myeloid MyD88 contributes to obesity-associated inflammation, and that IL-1 induces IRAK2 translocation to mitochondria to suppress oxidative phosphorylation and β-oxidation in adipocytes. However, how other IRAK complexes, particularly IRAKM, participate in unconventional TLR/IL-1R signaling in adipocytes and how this impacts adipocyte metabolism, de novo lipogenesis, energy balance, and obesity were unknown. This study investigates whether IRAKM in adipocytes controls lipogenesis and thermogenic programming, and tests the hypothesis that IL-1R-IRAKM signaling reprograms citrate metabolism through mitochondrial citrate transporter Slc25a1 to drive lipid accumulation and obesity.

Background literature links adipose inflammation with insulin resistance and HFD-induced metabolic stress. TLR/IL-1R signaling via MyD88 and IRAKs is central to inflammatory cytokine production. Previous studies: (1) Myeloid MyD88 deficiency reduced adipose macrophage recruitment and systemic inflammation in diet-induced obesity; (2) IL-1β drives mitochondrial recruitment of IRAK2 to suppress oxidative metabolism in adipocytes; (3) Adipocyte hypertrophy correlates with insulin resistance, and de novo lipogenesis (DNL) from glucose supports lipid storage; (4) Cytosolic citrate, generated via Slc25a1-mediated mitochondrial export and ACLY activity, provides acetyl-CoA for fatty acid synthesis; (5) TLR signaling can promote fatty acid synthesis in immune cells. Gaps remained regarding the role of IRAKM in adipocytes, its potential mitochondrial function, and whether it regulates Slc25a1-dependent citrate flux to couple inflammation to DNL and obesity.

• Mouse models: Generated adipocyte-specific IRAKM knockout mice (IRAKMΔKO; IRAKM flox/flox x Adiponectin-Cre). Created kinase-inactive IRAKM knock-in mice (K205A; IRAKM KI) via CRISPR/Cas9. Six- to eight-week-old male mice were fed HFD (60% kcal fat) for up to 12 weeks or high-carbohydrate zero-fat diet (ZFD) for 8 weeks; chow-fed controls were included.
• Metabolic phenotyping: Body weight tracking, EchoMRI for fat/lean mass, glucose tolerance test (GTT), insulin tolerance test (ITT), rectal temperature measurements. Indirect calorimetry in metabolic cages (VO2, VCO2, and energy expenditure) at 30 °C, 22 °C, and 4 °C.
• Histology and immunohistochemistry: H&E staining of iWAT and BAT; Mac2 staining for crown-like structures (CLS); adipocyte size quantification.
• Primary adipocyte cultures: Differentiation of stromal vascular fraction (SVF) cells from white and brown adipose tissues into mature adipocytes. Treatments included IL-1β and insulin; isoproterenol for thermogenic induction.
• Biochemistry and cell biology: Mitochondria isolation and subfractionation (OM, IMS, IM, matrix); co-immunoprecipitation (IRAKM, Slc25a1, TOM20); western blots for IRAK family, MyD88, Ucp1, phosphorylation and acetylation markers.
• De novo lipogenesis and metabolite assays: 14C-glucose incorporation into lipids; LC-MS/MS quantification of fatty acids and citrate in mitochondrial and cytosolic fractions; acetyl-CoA levels via fluorometric assay; triglyceride quantification in tissues.
• Mitochondrial function: Seahorse XF OCR measurements (basal, FCCP-stimulated maximum); FAO assays using 14C-palmitate.
• Genetics and rescue: siRNA/shRNA knockdown of Slc25a1; reconstitution with Flag-tagged Slc25a1 WT or T155A mutant; reconstitution of IRAKM WT, kinase-dead, phosphorylation-site mutant (S167A/S170A), and mitochondrial localization mutant (R56A/K60A/K66A/R70A) in IRAKM-deficient adipocytes.
• Kinase and phosphorylation mapping: In vitro kinase assays with recombinant IRAKM and Slc25a1; autoradiography; phospho-threonine immunoblotting; mass spectrometry to map Slc25a1 phosphorylation (Thr155).
• Transcriptional regulation: qPCR for thermogenic and inflammatory genes (Pgc1α, Prdm16, Cidea, Ucp1, Il1b, Il6, Tnf); ChIP-qPCR for Pgc1α occupancy on the Ucp1 promoter; co-IP for Pgc1α acetylation; pharmacologic inhibition of ACLY (BMS-303141). Statistical analyses used Student’s t-test or ANOVA as appropriate.

• Adipocyte IRAKM drives diet-induced obesity: IRAKMΔKO male mice on HFD gained less body weight and had reduced fat mass with preserved lean mass versus controls; improved glucose tolerance and insulin sensitivity; decreased adipocyte size, inflammatory gene expression (Il1b, Il6, Tnf), and fewer crown-like structures in iWAT. Under chow diet, no significant differences were observed.
• Increased energy expenditure: HFD-fed IRAKMΔKO mice exhibited higher VO2, VCO2, and energy expenditure at 30 °C, 22 °C, and 4 °C; BAT showed less lipid accumulation and higher thermogenic gene expression (Pgc1α, Prdm16, Cidea, Ucp1); body temperature was elevated. On ZFD, IRAKMΔKO mice also gained less weight and fat mass, with BAT showing elevated thermogenic genes and higher body temperature.
• IL-1β induces IRAKM mitochondrial translocation to promote DNL: IL-1β increased de novo fatty acid synthesis in WT adipocytes, which was blunted in IRAKM-deficient adipocytes (not affected by insulin). IRAKM translocated to mitochondria with MyD88/IRAK4, localizing to inner membrane and matrix after IL-1β. An N-terminal amphipathic helix (mitochondrial localization signal) mediated this; IRAKM Mito-mut reduced mitochondrial localization and DNL.
• IRAKM enhances citrate export via Slc25a1: Proteomics and co-IP showed IL-1β-induced interaction of IRAKM (but not IRAK2) with Slc25a1 in mitochondria. IL-1β increased citrate release from mitochondria to cytosol in WT adipocytes; this was abolished by IRAKM deficiency. 14C-citrate transport into isolated mitochondria was reduced in IRAKM KO. Slc25a1 knockdown blocked IL-1β-induced DNL.
• IRAKM kinase activity and phosphorylation are required: IRAKM exhibited phosphorylation in mitochondria after IL-1β; phosphatase treatment removed the modification. Kinase-inactive IRAKM (K205A) still translocated to mitochondria but showed impaired modification, reduced Slc25a1 interaction, reduced citrate transport, and diminished DNL. Phosphorylation of IRAKM at S167/S170 was necessary for Slc25a1 interaction and DNL.
• Slc25a1 is a direct IRAKM substrate: In vitro, IRAKM phosphorylated Slc25a1 at Thr155. Slc25a1 T155A mutant was not phosphorylated by IRAKM, showed reduced IL-1β-stimulated citrate transport and DNL in adipocytes.
• Coupling DNL to thermogenesis suppression: IL-1β suppressed isoproterenol-induced Ucp1 expression; this suppression was lost in IRAKM KO or Slc25a1 KD adipocytes. IRAKM/Slc25a1 axis decreased Pgc1α recruitment to the Ucp1 promoter; IRAKM deficiency or Slc25a1 KD restored Pgc1α occupancy. IL-1β increased acetyl-CoA and Pgc1α acetylation; both were reduced by IRAKM or Slc25a1 deficiency and by ACLY inhibition, which also rescued Ucp1 induction.
• Kinase-dead IRAKM protects against obesity: IRAKM KI mice on HFD gained less weight, had lower fat mass, improved insulin sensitivity, higher VO2/VCO2/EE, less BAT lipid, higher thermogenic gene expression in WAT and BAT, and higher body temperatures. On ZFD, IRAKM KI mice had reduced weight and fat mass and higher thermogenic gene expression and Ucp1 protein. IWAT and BAT from IRAKM KI mice had reduced acetyl-CoA and Pgc1α acetylation.

The study demonstrates that IL-1R signaling reprograms adipocyte metabolism through IRAKM-dependent mitochondrial events. Upon IL-1β stimulation, IRAKM-containing Myddosome translocates to mitochondria where IRAKM engages and phosphorylates the citrate carrier Slc25a1. This increases mitochondrial citrate export, elevates cytosolic acetyl-CoA, and drives de novo fatty acid synthesis, promoting lipid accumulation and adipocyte hypertrophy. Concurrently, higher acetyl-CoA enhances Pgc1α acetylation, diminishing its transcriptional activity and occupancy on thermogenic gene promoters (e.g., Ucp1), thereby suppressing thermogenesis. Genetic ablation of IRAKM in adipocytes or systemic kinase inactivation shifted the energy balance toward higher expenditure, increased thermogenic gene expression, lowered adipose lipid accumulation, and improved insulin sensitivity on obesogenic diets. Mechanistically, IRAKM and IRAK2 assume distinct mitochondrial roles: IRAKM controls citrate efflux and DNL via Slc25a1, whereas IRAK2 modulates fatty acid oxidation pathways, indicating non-redundant contributions to metabolic reprogramming. These findings bridge inflammation (IL-1β/TLR-IL-1R pathways) with core metabolic fluxes (citrate transport and acetyl-CoA generation) to explain how chronic inflammatory cues promote adiposity and metabolic dysfunction. Therapeutically, disrupting IRAKM kinase activity or its interaction with Slc25a1 could uncouple inflammatory signals from lipogenic programming and restore thermogenic capacity.

This work identifies an IL-1R–IRAKM–Slc25a1 signaling axis that links inflammatory signaling to adipocyte citrate metabolism, de novo lipogenesis, and suppression of thermogenesis. IL-1β drives IRAKM translocation to mitochondria, where IRAKM phosphorylates Slc25a1 at Thr155 to enhance citrate export and acetyl-CoA production, fueling lipogenesis and Pgc1α acetylation to repress thermogenic gene expression. Adipocyte-specific IRAKM deletion and systemic kinase-dead knock-in both protect mice from diet-induced obesity, reduce adipose lipid accumulation, and improve insulin sensitivity while elevating energy expenditure. These findings nominate IRAKM’s kinase activity and its interaction with Slc25a1 as potential therapeutic targets for obesity and associated metabolic disorders. Future studies should: (1) delineate cell type–specific roles of IRAKM across adipose and immune compartments; (2) explore pharmacologic inhibitors or disruptors of the IRAKM–Slc25a1 interaction; (3) assess translational relevance in human adipocytes and clinical populations; and (4) define interplay and potential cooperation between IRAKM and IRAK2 in metabolic control.

• The majority of in vivo experiments were conducted in male mice, which may limit generalizability across sexes.
• Findings are derived from murine models and primary mouse adipocytes; human validation is needed.
• The study focuses on IL-1β stimulation; the breadth of ligands and inflammatory contexts engaging IRAKM–Slc25a1 in adipocytes remains to be defined.
• While prior work suggests anti-inflammatory roles for IRAKM in myeloid cells, this study emphasizes adipocyte-intrinsic functions; comprehensive, cell type–specific in vivo dissection (e.g., in macrophages versus adipocytes) is warranted to parse systemic contributions.