Abstract
Amino acid supplementation is an efficient and effective strategy to increase sperm quality. In our research, a comparative study was conducted to screen free amino acids to improve sperm motility, and we found that leucine was the most efficient one. Leucine treatment increases sperm motility depending on the activation of PI3K/Akt signaling pathway, while the chemical inhibitor of PI3K/Akt signal could reduce the amount of pAkt activated by leucine treatment. Moreover, leucine treatment improved the expression of P62 and LC3-II, substantially suppressed the autophagy process in zebrafish testis. In vitro studies showed that leucine could reduce the fusion of autophagosome and lysosome that was indicated by the co-localization of EGFP-LC3 and lysosome marker. Two chemical modulators of autophagy, such as LY294002 (the inhibitor of PI3K/Akt signal) and chloroquine were administered to investigate the process of autophagy on zebrafish sperm motility. LY294002 inhibited autophagosome formation to reduced sperm motility, while chloroquine inhibited the fusion of autophagosome and lysosome to improve sperm motility. Our data suggest that short-term treatment with leucine could increase zebrafish sperm motility by affecting the autophagy and inhibiting the fusion of autophagosome and lysosomes, depending on the activation of PI3K/Akt signaling pathway.
Highlights
Sperm quality is an important factor for successful fertilization and survival of the progeny, which is usually evaluated by multiple quality indexes
Leucine treatment increases sperm motility depending on the activation of PI3K/Akt signaling pathway, while the chemical inhibitor of PI3K/Akt signal could reduce the amount of phosphorylated Akt (pAkt) activated by leucine treatment
Since activation of the PI3K/Akt pathway has been demonstrated to promote sperm motility, we investigated whether leucine treatment could affect this signaling pathway
Summary
Sperm quality is an important factor for successful fertilization and survival of the progeny, which is usually evaluated by multiple quality indexes. Sperm motility can be improved by different molecules including small peptides and compounds [1, 2]. Studies recognized that amino acid supplementation is an efficient strategy to increase sperm motility and fertilization. Arginine was the main free amino acid in the spermatozoa of Oncorhynchus mykiss, Cyprinus carpio and Perca fluviatilis. Arginine, glutamic acid and methionine were found in the semen of several fish species where sperm motility was improved when spermatozoa were co-incubated with methionine [3, 4]. Cysteine analogs can increase the fertilization of frozen-thawed sperms [5]. Some essential amino acids are likely to be involved in the sperm motility of teleost fishes
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