Involvement of PRQFVamide-related peptide in immune response of Sepiella japonica through suppressing nitric oxide production

Abstract

Neuropeptides, as key messengers with extensive and complex functions, play vital roles in the neuro-immune systems. PRQFVamide-related peptide (PRQFVRP) has been found in the mollusks, but few studies have been reported about the immunomodulatory function of PRQFVRP. In this study, an intensive positive signal of PRQFVRP was detected in the columnar epithelium of the intestine in Sepiella japonica, with widespread distribution in the white body observed via in situ hybridization. Moreover, the expression of Sj_PRQFVRP mRNA was notably up-regulated in the white body of sick S. japonica. Interestingly, Sj_PRQFVRP mRNAs showed a distinct down-regulation at 3 h with an upward trend from 3 to 72 h after bath infection with Vibrio harveyi. Their results suggested that Sj_PRQFVRP is involved in the immune response of S. japonica. Subsequently, four mature peptides of Sj_PRQFVRP, including PMEFLamide (P), AMEFLamide (A), GMEFLamide (G), and RMEFLamide (R), were artificially synthesized to assess the immunomodulatory function of Sj_PRQFVRP. P, G, and R significantly constrained the nitric oxide (NO) production in lipopolysaccharide (LPS)-activated RAW264.7 cells (murine macrophage cell line). Additionally, the mixed mature peptides of Sj_PRQFVRP (P + A + G + R, P + G + R, A + G, and A + R) also effectively constrained NO production in LPS-activated RAW264.7 cells, indicating that Sj_PRQFVRP might have a function in suppressing the immune response. These findings will help to better understand the potential immunomodulatory functions of PRQFVRP in cephalopods.