Itaconate Promotes Cold Adaptation and Myocardial Protection by Enhancing Brown Adipose Tissue Metabolism

Background/Objectives: Itaconic acid (ITA) is an immunometabolite with anti-inflammatory and metabolic regulatory functions, but its cellular source and role in brown adipose tissue (BAT) remain unclear. This study aims to reveal the expression patterns of the key ITA synthesis gene Irg1 in BAT at different developmental stages and to investigate the effects of cold exposure and exogenous ITA on BAT metabolic function and cardioprotection. Methods: Single-cell RNA sequencing was used to analyze the gene expression profiles of stromal vascular fraction (SVF) cells in BAT from P7 neonatal and adult mice. Bioinformatic methods were applied to identify cell types expressing Irg1. Cold exposure (4 °C) and exogenous ITA treatment were employed to evaluate BAT morphology, and the ITA content in BAT was detected using gas chromatography–triple quadrupole mass spectrometry, UCP1 protein expression, and body temperature changes. A transverse aortic constriction (TAC) surgery model was established to induce cardiac dysfunction, and BAT excision was performed to explore the BAT-dependent effects of ITA on myocardial hypertrophy, fibrosis, and cardiac function. Results: In P7 neonatal mouse BAT, Irg1 was predominantly expressed in a subset of interferon-responsive activated macrophages (macrophage27), while in adult mice, it was mainly expressed in neutrophils and a functionally similar macrophage subset (macrophage25). Cold exposure significantly suppressed Irg1 expression in neutrophils but did not affect its expression in macrophages, also resulting in a significant decrease in ITA content in BAT. Exogenous ITA significantly enhanced BAT thermogenesis under cold conditions, which manifested as reduced lipid droplets, upregulated UCP1 expression, and increased body temperature. In the TAC model, ITA treatment markedly improved cardiac function, attenuated myocardial hypertrophy and fibrosis, and these protective effects were significantly diminished after BAT excision. Conclusions: ITA promotes cold adaptation and ameliorates cardiac injury by enhancing BAT metabolic function, and its effects depend on the presence of BAT. This study provides new insights for the treatment of metabolic cardiovascular diseases.