LAUSR

Abstract To investigate the effects and potential mechanisms of apoptosis in the intestines of juvenile grass carp (Ctenopharyngodon idella) for dietary choline, fish were fed different choline-containing diets (142.2, 407.4, 821.6, 1215.8, 1589.3, and 1996.6 mg kg−1) for 70 days. Results revealed that dietary choline deficiency (1) decreased the contents of choline, phosphatidylcholine, betaine, and acetylcholine (not in distal intestine [DI]) in grass crap intestines; down-regulated the mRNA abundances of choline transportations, such as high-affinity choline transporter CHT1 (not in proximal intestine[PI] and DI), choline transporter-like proteins such as CTL-1, CTL-2, CTL-4 (not in DI), and CTL-5 in grass crap intestines; (2) enhanced the degree of DNA fragments. Moreover, it up-regulated the activities of caspase-3, −8, and-9; reduced mRNA levels of caspase-3, −7, −8 (not in DI), and − 9, Fas ligand (FASL) (not in PI), and apoptotic protease activating factor-1(Apaf1), as well as the protein level of cytochrome c (Cty c). Dietary choline deficiency also down-regulated myeloid cell leukemia-1 (Mcl-1) (not in PI), B-cell lymphoma-2 (Bcl-2), and the inhibitor of apoptosis protein (IAP) mRNA levels in grass carp intestines, suggesting that choline inhibited cell apoptosis in fish intestines; (3) increased p38MAPK and JNK(not in mid intestine [MI]) mRNA level, as well as p-p38MAPK and T-p38MAPK protein levels in the PI and the ratio of p-p38MAPK/T-p38MAPK in the MI and DI, indicating that choline deficiency aggravated cell apoptosis in association with the MAPK signalling pathway in fish intestines; In conclusion, choline insufficiency promotion of intestinal apoptosis might be related to MAPK signalling pathways in fish. Moreover, the requirements of choline for resist intestinal apoptosis indices (caspase-8 and capase-9 activities) of grass carp (9.28–108.97 g) were calculated to be (1162.13–1780.93) mg kg−1 diet, respectively.