Lipid droplet accumulation drives glutamine-dependent NLRP3 inflammasome activation

Abstract

The NLRP3 inflammasome is implicated in the pathogenesis of many inflammatory and metabolic diseases. Although metabolic cues can shape NLRP3 inflammasome activation, the role of lipid metabolism in this response is poorly understood. Lipids are essential for energy and redox homeostasis, membrane biogenesis, and diverse cellular processes. However, excessive accumulation of lipids such as free fatty acids can be highly cytotoxic. Consequently, surplus free fatty acids are esterified into triglycerides and cholesteryl esters, which are then stored within lipid droplets (LDs). Interestingly, transcriptomic data analyses revealed that macrophages exposed to inflammasome-activating stimulus undergo a broad metabolic rewiring favouring lipid storage, suggesting a link between LDs and inflammasome response. Here, we show that LD accumulation actively promotes NLRP3 inflammasome activation. Increasing LD abundance, either by fatty acid supplementation or by inhibition of lipolysis, led to robust caspase-1 activation and IL-1{beta} release both in vitro and in vivo. Mechanistically, LD expansion promoted cellular reorganisation resulting in the formation of peri-droplet mitochondria, a distinct mitochondrial subpopulation which exhibited elevated membrane potential and increased ATP-linked respiration. Furthermore, LD-rich macrophages underwent metabolic reconfiguration whereby they exhibited a pronounced reliance on pyruvate and glutamine metabolism, but not fatty acid oxidation, to sustain mitochondrial bioenergetics. Surprisingly, inflammasome activation was found dependent predominantly on glutaminolysis, highlighting a key role for glutamine catabolism in LD-rich cells. Collectively, these findings identify a glutamine-dependent pathway as a key driver linking excess lipid storage to NLRP3 inflammasome, with profound implications in metabolic diseases.