Differential transcriptome responses to aflatoxin B ₁ in the cecal tonsil of susceptible and resistant Turkeys

The nearly-ubiquitous food and feed-borne mycotoxin aflatoxin B ₁ (AFB ₁ ) is carcinogenic and mutagenic, posing a food safety threat to humans and animals. One of the most susceptible animal species known and thus a good model for characterizing toxicological pathways, is the domesticated turkey (DT), a condition likely due, at least in part, to deficient hepatic AFB ₁ -detoxifying alpha-class glutathione S-transferases (GSTAs). Conversely, wild turkeys (Eastern wild, EW) are relatively resistant to the hepatotoxic, hepatocarcinogenic and immunosuppressive effects of AFB ₁ owing to functional gene expression and presence of functional hepatic GSTAs. This study was designed to compare the responses in gene expression in the gastrointestinal tract between DT (susceptible phenotype) and EW (resistant phenotype) following dietary AFB ₁ challenge (320 ppb for 14 days); specifically in cecal tonsil which functions in both nutrient absorption and gut immunity. RNAseq and gene expression analysis revealed significant differential gene expression in AFB ₁ -treated animals compared to control-fed domestic and wild birds and in within-treatment comparisons between bird types. Significantly upregulated expression of the primary hepatic AFB ₁ -activating P450 (CYP1A5) as well as transcriptional changes in tight junction proteins were observed in AFB ₁ -treated birds. Numerous pro-inflammatory cytokines, TGF-β and EGF were significantly down regulated by AFB ₁ treatment in DT birds and pathway analysis suggested suppression of enteroendocrine cells. Conversely, AFB ₁ treatment modified significantly fewer unique genes in EW birds; among these were genes involved in lipid synthesis and metabolism and immune response. This is the first investigation of the effects of AFB ₁ on the turkey gastro-intestinal tract. Results suggest that in addition to the hepatic transcriptome, animal resistance to this mycotoxin occurs in organ systems outside the liver, specifically as a refractory gastrointestinal tract.