Gill, Jappreet Singh

Abstract Foxp3⁺ regulatory T cells (Tregs) maintain immune homeostasis, yet the process that preserves their stability during aging remain unclear. Mechanistic progress has been hindered by models that ablate Tregs or delete Foxp3 , which induce acute autoimmunity and prevent longitudinal study of physiological regulatory drift. Here, we establish a dose-dependent mitochondrial framework that preserves Treg lineage survival while permitting gradual metabolic attenuation. Using Treg-restricted TFAM modulation, a complementary haploinsufficient model, and whole-spleen single-cell profiling. We identify lineage-selective immune remodeling characterized by contraction of naïve CD8⁺ and follicular B-cell pools, alteration of CD4⁺ states, expansion of activated Tregs, and emergence of neuroimmune stress linked transcriptional modules that parallel physiological aging. Mechanistically, mitochondrial insufficiency is associated with functional loss of FOXP3- centered chromatin coordination and enrichment of NF-κB/NFAT/AP-1 inflammatory and senescence programs while lineage identity remains detectable. Partial mitochondrial attenuation within Tregs alone is sufficient to drive chronic low-grade systemic inflammation, neuromuscular decline, gut microbial restructuring, and elevated microglial responsiveness without Treg depletion. Pharmacologic and microbiota-directed interventions partially reduce inflammatory tone and improve functional metrics. Together, our findings identify TFAM as a key regulator of immune aging and reveal that healthy mitochondrial function in Tregs is essential for protecting against inflammaging and age-associated functional decline.