Metabolic exhaustion and immune ageing in rheumatoid arthritis.

Rheumatoid arthritis (RA) disproportionately affects adults over 50 years of age, highlighting how age-related immune remodelling undermines tolerance and promotes autoreactivity. In later adulthood, immune cells progressively lose metabolic resilience because of impaired nutrient sensing, reduced metabolic flexibility and disrupted anabolic-catabolic balance. In RA, these vulnerabilities are compounded by mitochondrial insufficiency across innate and adaptive immune lineages, creating a state of nutrient deprivation characterized by NAD⁺ and ATP scarcity and diversion of carbon away from oxidative phosphorylation. Mechanistic studies identify this bioenergetic fragility as a core defect that limits cellular longevity and promotes inflammatory, non-apoptotic death pathways, including pyroptosis and PANoptosis. The hypoxic, nutrient-restricted synovial environment adds pressure that exceeds the diminished metabolic adaptability of aged immune cells. In RA T cells, accelerated mitochondrial injury initiates maladaptive stress responses, disrupts mitochondria-lysosome-endoplasmic reticulum communication and induces gasdermin D-dependent pore formation and inflammatory lysis. Synovial MerTK⁺ reparative macrophages undergo a parallel metabolic crisis, whereby autocrine C1q sensing activates mitochondrial SARM1, causing NAD⁺ degradation, ATP depletion and PANoptotic cell death. Together, these findings position ageing-associated metabolic exhaustion and organelle disintegration as unifying mechanisms that convert immune cells into tissue-damaging effectors and explain the heightened susceptibility to RA in older adults.