Fusion of Tat-PTD to the C-terminus of catfish growth hormone enhances its cell uptakes and growth-promoting effects

Fish growth hormone has been long regarded as a promising feed additive in aquaculture for its significant growth promotion effect. To improve its efficiency in oral applications, we generated a Silurus asotus growth hormone-Tat (saGH-Tat) fusion protein and investigated its effect on biological activities relevant to transduction and growth promotion. In this study, saGH, saGH-Tat, Green fluorescent protein and saGH fused protein (GFP-saGH) and GFP-saGH-Tat were all highly expressed in Escherichia coli strain BL21 (DE3) and confirmed by Western blot. The transduction effect of Tat protein transduction domain (Tat-PTD) was verified by observing increased GFP fluorescence in separated intestine cells or frozen sections in GFP-saGH-Tat treated fish. The recombinant saGH and saGH-Tat were tested for biological activity by specific binding with crude liver membrane extracts as well as in a growth promotion assay via oral administration. saGH-Tat treatment demonstrated strengthened receptor binding and accelerated growth-promoting effects. Under optimal concentrations of hormone (1 μg/g of fish body weight), saGH-Tat treated fish exhibited an 87.25% growth increase compared to 61.3% in saGH-treated fish. The response of downstream signal pathway factors were analyzed by measuring insulin like growth factor-I (IGF-I), growth hormone receptor (GHR) mRNA expression in the liver, and growth related digestive enzymes (trypsin and chymotrypsin), and all indicate significant up-regulation. Further confirmation of increased GH level in carp blood by Tat fusion was shown by flow cytometry. These results suggested that Tat-PTD fused to the C-terminus saGH greatly enhances its biological activities, making it a promising agent for increasing productivity in aquaculture.

► Tat-PTD makes catfish GH more easily absorbed by carp midgut cells and tissues.
► Fusion of Tat-PTD to the saGH can enhance its growth-promoting effects.
► IGF-1 and GHR mRNA levels were up-regulated by saGH-Tat treatment.
► Digestive enzyme activities were up-regulated by saGH-Tat treatment.