Structure matters: commensal Phocaeicola vulgatus lipopolysaccharide induces attenuated microglial activation and...

Lipopolysaccharides (LPSs) from Gram-negative bacteria are widely used to model neuroinflammation in vitro and in vivo. However, this paradigm assumes that all LPS chemotypes are uniformly pro-inflammatory, despite significant structural diversity between enterobacterial pathogens and gut-resident commensals. Whether microglia can discriminate among these chemotypes remains largely unexplored. We performed a comparative analysis of canonical Escherichia coli LPS and commensal-derived Phocaeicola vulgatus LPS in murine (BV2) and human (HMC3) microglial cells. Pro-inflammatory mediators were quantified by ELISA, and TLR4-downstream signaling was assessed by western blotting. Conditioned media (CM) from LPS-treated BV2 and HMC3 cells was applied to PC12 neuronal cells to evaluate cell viability and differentiation by immunofluorescence. In BV2 microglial cells, P. vulgatus LPS did not induce nitric oxide (NO) production or iNOS expression. In both BV2 and HMC3 cells, it failed to trigger pro-inflammatory cytokine release or TLR4 pathway activation. CM from E. coli-treated microglia disrupted MAP2 expression in PC12 neurons, whereas media from P. vulgatus-treated microglia did not. Overall, our data argue that "LPS-induced neuroinflammation" is not a universal phenomenon, but a chemistry-dependent outcome shaped by specific LPS structures. This study therefore highlights the need to consider LPS structural diversity in neuroinflammation models, particularly in the context of gut-brain communication.