Nicotinamide phosphoribosyltransferase (Nampt) of hybrid crucian carp protects intestinal barrier and enhances host immune defense against bacterial infection

Nicotinamide phosphoribosyltransferase (Nampt) can act extracellularly as a mediator of inflammation or intracellularly as a rate-limiting enzyme, regulating nicotinamide adenine dinucleotide (NAD) biosynthesis in the NAD salvage pathway. Nampt exerts important immunological functions during infection in mammals. However, the in vivo function of fish Nampt in immune regulation and inflammation is essentially unknown. With an aim to elucidate the antimicrobial mechanism of Nampt in fish, we in this study examined the function of Nampt from hybrid crucian carp. Hybrid crucian carp Nampt (WR-Nampt) possesses the conserved nicotinamide phosphoribosyltransferase domain and shows high similarity to that of mammalian Nampt. WR-Nampt is expressed in multiple tissues and is upregulated by bacterial infection. Overexpression of WR-Nampt significantly increased the number of goblet cells of distal intestine. In addition, WR-Nampt induced significant inductions in the expression of the antimicrobial molecules (IL-22, Hepcidin-1, LEAP-2 and MUC2) and tight junctions (ZO-1 and Occludin). Consistent with this, fish administered with WR-Nampt significantly alleviated the intestinal permeability and apoptosis, thereby enhancing host's resistance against bacterial infection. Together these results revealed the potential effect of WR-Nampt in intestinal barrier and immune defense against bacterial infection.