The Expression of Amino Acid and Fatty Acid Receptors Show an Age-Dependent Pattern Involving Oral Cavity, Jejunum and Lower Gut Sensing in Broiler Chickens

SIMPLE SUMMARY: There is limited information regarding dietary nutrient sensors in chickens. This study explored the expression of amino acid (AA) and fatty acid (FA) sensors in the gastrointestinal tract (GIT) of broilers. This research focused on quantifying gene expression of AA and FA sensors in ten tissues, including the upper, middle, and lower GIT sections of 7 and 26-day-old birds. Early in life (7 days), chicks develop a high sensing capability in the oral cavity for AA and the cecum and colon for short-chain fatty acids, presumably related to bacterial fermentation. In turn, at 26 days of age, a strong emergence of the role of the jejunum sensing AA and FA occurs, indicating the major role of the middle GIT section in nutrient digestion, absorption, and the gut-brain axis. ABSTRACT: This work aimed to evaluate the gene expression of amino acids (AA) and fatty acids (FA) sensors in the gastrointestinal tract (GIT) of chickens at two different ages (7 and 26 days post-hatch). Sixteen broilers (Ross 308) were selected, and ten sections of the GIT, including upper (tongue base, upper palate, crop, proventriculus), middle (gizzard, duodenum, jejunum, ileum), and lower GIT section (cecum, colon) were collected for analysis. Relative gene expression of AA (T1R1, T1R3, mGluR1, mGluR4, CaSR, GPR139, GPRC6A, GPR92) and FA (FFAR2, FFAR3, FFAR4) sensors were assessed using qPCR. The statistical model included age, GIT section, and gene. In addition, the correlations between gene expressions were calculated. At day 7, a significantly (p = 0.004) higher expression of AA sensors in the oral cavity and FA sensors in the lower GIT section (i.e., cecum and colon) compared to the middle section was recorded. A higher expression of AA compared to FA sensors was detected at the upper GIT section in 7 (p < 0.001) and 26-day-old chickens (p = 0.026). Thus, at day 7, AA sensors were predominantly (p < 0.05) expressed in the upper GIT section (mainly oral cavity), while FA sensors were mainly expressed in the lower GIT section, at cecum (FFR2 and 4) or colon (FFAR3). These results may indicate that in early life, both ends of the GIT are fundamental for feed intake (oral cavity) and development of the microbiota (cecum and colon). In contrast, at 26 days of age, the results showed the emergence of both AA and FA sensors in the jejunum, presumably indicating the essential role of the jejunum in the digestion absorption of nutrients and the signaling to the brain (gut-brain axis) through the enteroendocrine system. Significant positive correlations were observed between T1R1 and T1R3 (r = 0.85, p < 0.001), CaSR and T1R1 (r = 0.78, p < 0.001), CaSR and T1R3 (r = 0.45, p < 0.050), and mGluR1 and FFAR3 (r = 0.46, p < 0.050). It is concluded that the gene expression is greater in the oral cavity for AA sensors and the lower gut for FA sensors. On day 26, the role of jejunum regarding nutrient sensing is highlighted.