THE EFFECTS OF SHORT CHAIN FATTY ACIDS ON NEUROINFLAMMATION IN A STEM CELL-DERIVED MICROFLUIDIC MODEL OF VAGUS-BRAIN INNERVATION

The gut microbiome plays a critical role in brain health, yet the mechanisms underlying microbiota–brain communication remain enigmatic. Short-chain fatty acids (SCFAs), key microbial metabolites, have been implicated in reducing neuroinflammation. These metabolites can influence brain physiology via multiple routes, including blood circulation, immune modulation, and Vagal signaling. The structure responsible for Vagal signaling is a parasympathetic nerve bundle that connects multiple organs, including the intestine, with the brain. Here, we used a human stem cell-derived microfluidic model of Vagus-brain innervation to investigate the effects of SCFAs on neuroinflammation. To mimic vagal signaling to the brain, microglia-integrated brain organoids were co-cultured with stem cell-derived Vagus-like neurons in a microfluidic chip featuring separated compartments connected by microchannels. The Vagus-like neurons exhibited robust axonal outgrowth through the microchannels and successfully innervated the brain organoids. Immune activation was induced by exposure to TNF-α and lipopolysaccharides. Treatment of Vagus-like neurons with a cocktail of SCFAs consisting of butyrate, acetate, and propionate reduced neuroinflammation, shown by decreased cytokine expression at both the RNA and protein levels. Our model is anticipated to facilitate the identification of receptors and signaling pathways mediating SCFA effects on brain innervation. A key focus will be to determine whether SCFA-stimulated vagal activity promotes acetylcholine release that modulates microglia via α7 nicotinic acetylcholine receptors. Overall, this platform provides a model for animal-free human mechanistic studies of microbiome-gut-brain communication.