Thymosin β4 is involved in the antimicrobial immune response of Golden pompano, Trachinotus ovatus

Thymosin beta belongs to the thymosin family, which consists of a series of highly conserved peptides involved in various biological processes. In teleosts, understanding of the immunological functions of thymosin beta is limited, particularly in vivo, which is essentially unknown. In the current study, we cloned and identified thymosin beta 4 from the teleost fish Golden pompano (Trachinotus ovatus), which we have named TroT beta 4. We investigated the expression patterns and functions of TroT beta 4 in both in vivo and in vitro assays. TroT beta 4 is composed of 44 amino acids and shares high sequence identities with known thymosin 134 species in other teleosts, which contains a highly conserved actin-binding motif (LKKTET). The expression of TroT beta 4 was most abundant in immune organs, and was significantly up regulated in response to infection bacterial with one of a number of bacteria (including Edwardsiella tarda, Vibrio harveyi, and Streptococcus agalactiae). Purified recombinant TroT beta 4 (rTroT beta 4) inhibited the growth of bacteria, as measured using an automatic growth curve analyzer, indicating that TroT beta 4 has antimicrobial functions. When administered in vivo, overexpression of TroT beta 4 in T ovatus, bacterial colonization of tissues was significantly reduced. In contrast, when a DNA vector-based siRNA technology was used to knock down TroT beta 4 expression, bacterial dissemination and colonization of tissues increased significantly. Taken together, these results provide the first in vivo evidence to indicate that teleost thymosin beta 4 plays a significant role in innate antibacterial immune responses in addition to in vitro bacteriostatic activity. This provides valuable information regarding the biological functions of teleost thymosin beta. (C) 2017 Published by Elsevier Ltd.