Inhibition of Autophagy Is Involved in the Collagen Deposition Promoted by Dietary Leucin in Chu’s Croaker (<i>Nibea coibor</i>)

Leucine (Leu), an essential branched-chain amino acid, is well-known for stimulating protein synthesis via mTOR activation. However, its regulatory role in autophagy-mediated protein degradation remains poorly characterized. Collagen is the most abundant protein in animals. In this study, we investigated the effects of Leu on growth and collagen deposition and explored the role of autophagy in the process, using the swim bladder of Chu's croaker (<i>Nibea coibor</i>) as a model. Our results demonstrated that Leu supplementation significantly enhanced growth performance, antioxidant capacity, and collagen deposition in the swim bladder. Mechanistically, Leu suppressed autophagy in swim bladder cells by reducing autophagosome formation and expression of autophagy marker proteins (LC3, Beclin1, etc.). The autophagy inhibitor (3-MA) elevated collagen content, while the autophagy activator (rapamycin) attenuated Leu-induced collagen deposition in swim bladder cells. These findings first demonstrate that Leu could promote collagen deposition by inhibiting autophagy, providing novel insights into the mechanism underlying amino acid-regulated protein metabolism in vertebrates.