The Probiotic Phaeobacter inhibens Provokes Hypertrophic Growth via Activation of the IGF-1/Akt Pathway during the Process of Metamorphosis of Greater Amberjack (Seriola dumerili, Risso 1810)

Metamorphosis entails hormonally regulated morphological and physiological changes requiring high energy levels. Probiotics as feed supplements generate ameliorative effects on host nutrient digestion and absorption. Thereby, the aim of the present research was to investigate the impact of the probiotic Phaeobacter inhibens as a water additive on cellular signaling pathways in the metamorphosis of greater amberjack (Seriola dumerili). Activation of insulin-like growth factor type 1 receptor (IGF-1R), protein kinase B (Akt), mitogen-activated protein kinases (MAPKs) and AMP-activated protein kinase (AMPK), induction of heat shock proteins (Hsps), and programmed cell death were assessed through SDS-Page/immunoblot analysis, while energy metabolism was determined through enzymatic activities. According to the results, greater amberjack reared in P. inhibens-enriched water entered the metamorphic phase with greater body length, while protein synthesis was triggered to facilitate the hypertrophic growth as indicated by IGF-1/Akt activation and AMPK inhibition. Contrarily, MAPKs levels were reduced, whereas variations in Hsps response were evident in the probiotic treatment. Apoptosis and autophagy were mobilized potentially for the structural remodeling processes. Furthermore, the elevated enzymatic activities of intermediary metabolism highlighted the excess energy demands of metamorphosis. Collectively, the present findings demonstrate that P. inhibens may reinforce nutrient utilization, thus leading greater amberjack to an advanced growth and developmental state.

Mutual regulation between IGF-1R and IGFBP-3 in human corneal epithelial cells

The insulin-like growth factor type 1 receptor (IGF-1R) is part of the receptor tyrosine kinase superfamily. The activation of IGF-1R regulates several key signaling pathways responsible for maintaining cellular homeostasis, including survival, growth, and proliferation. In addition to mediating signal transduction at the plasma membrane, in serum-based models, IGF-1R undergoes SUMOylation by SUMO 1 and translocates to the nucleus in response to IGF-1. In corneal epithelial cells grown in serum-free culture, however, IGF-1R has been shown to accumulate in the nucleus independent of IGF-1. In this study, we report that the insulin-like growth factor binding protein-3 (IGFBP-3) mediates nuclear translocation of IGF-1R in response to growth factor withdrawal. This occurs via SUMOylation by SUMO 2/3. Further, IGF-1R and IGFBP-3 undergo reciprocal regulation independent of PI3k/Akt signaling. Thus, under healthy growth conditions, IGFBP-3 functions as a gatekeeper to arrest the cell cycle in G0/G1, but does not alter mitochondrial respiration in cultured cells. When stressed, IGFBP-3 functions as a caretaker to maintain levels of IGF-1R in the nucleus. These results demonstrate mutual regulation between IGF-1R and IGFBP-3 to maintain cell survival under stress. This is the first study to show a direct relationship between IGF-1R and IGFBP-3 in the maintenance of corneal epithelial homeostasis.