TLR9-dependent modulation of adipocyte differentiation by Brucella abortus DNA induces an inflammatory response

Brucellosis, caused by Brucella abortus (Ba), remains a neglected zoonosis with significant human morbidity, often associated with chronic inflammatory manifestations. While traditionally regarded as passive reservoirs of energy, adipocytes are now recognized as immunometabolically active cells capable of shaping host responses during infection. However, how Ba impacts adipocyte biology and contributes to inflammation has not been fully elucidated.

In this work, we explored the effects of Ba on mesenchymal stem cell (MSCs) differentiation into adipocytes, with particular emphasis on lipid remodeling, inflammatory mediators, and innate immune signaling. MSCs were infected with live or heat-killed Ba (HKBA), or exposed to purified bacterial DNA. Adipogenesis was assessed through confocal microscopy of lipid droplet (LD)–mitochondria dynamics, transcriptional profiling of adipogenic and metabolic genes (PPARγ, CEBPα, DGAT1/2, FASN, HSL, LPL, SREBP1/2, leptin, adiponectin), and quantification of triglycerides, cholesterol, and glycerol release. Inflammatory outputs were measured by ELISA. To dissect the underlying mechanism, functional assays with a TLR9 inhibitor were performed.

Ba infection profoundly reprogrammed adipocyte differentiation, enhancing LD size, elevating intracellular cholesterol, and impairing triglyceride turnover (p<0.001). These metabolic alterations were coupled with increased IL-6 secretion and a higher leptin/adiponectin ratio (p<0.01), hallmarks of a proinflammatory adipocyte phenotype. Strikingly, bacterial DNA alone was sufficient to replicate these effects, while pharmacological inhibition of TLR9 completely abrogated them, establishing this receptor as a central driver of Ba-induced adipocyte remodeling.

Together, our findings reveal a previously unrecognized role of Brucella abortus DNA in promoting a TLR9-dependent, immunometabolic reprogramming of adipocytes. This mechanism not only links altered lipid metabolism to inflammation but also positions adipocytes as active contributors to the immunopathogenesis of brucellosis, opening new perspectives for therapeutic intervention.