β-sitosterol β-D-glucoside (BSSG) triggers intestinal inflammation in zebrafish and mouse models prior to neurodegeneration onset

Background Glucosylated-sterols can be synthetized endogenously, absorbed through the diet or derive from bacterial infection. Their clinical relevance is currently underestimated, even though their imbalance has been associated with higher risk of undergoing neurodegeneration throughout life. We studied the detrimental effects elicited by dietary consumption of plant-derived β-sitosterol β-D-glucoside (BSSG), known to be associated with the occurrence of ALS-PDC, to decipher its possible mode of action. Methods Zebrafish larvae and adults, as well as mice, were treated with BSSG dissolved directly in the water or through customized food pellet, respectively. Being the first target tissue identified, morphological and functional characterization of the intestine were performed, together with transcriptional analysis and sequencing of gut microbiota. Ex vivo analysis of zebrafish gut contractility was applied to assess intestinal neuromuscular response. Mutant and transgenic zebrafish lines were used to explore a possible BSSG mechanism of action. Results BSSG caused intestinal inflammation in both zebrafish and mouse models. This previously unknown effect was evidenced by altered gut dysmotility and inflammatory response. Transcriptomic analyses revealed increased expression of inflammation-related genes in the intestine of both zebrafish and mice, while preliminary gut microbiota analyses suggested the onset of dysbiosis. Transgenic and mutant zebrafish lines depleted of genes involved in glucocorticoids synthesis and activity evidenced that BSSG likely interacts with the glucocorticoid receptor, potentially affecting its canonical anti-inflammatory activity. Conclusions We discovered a new set of pathways altered by dietary uptake of BSSG. This molecule introduced in the organism initially determines gut inflammation, altering intestinal morphology and functionality, and possibly leads to neurodegeneration through disruption of the well-known gut-brain axis.