Molecular Characterization and Expression of Calpains and Cathepsins in Tilapia Muscle in Response to Starvation

Calpains are a class of calcium-dependent, non-lysosomal proteins. Two main calpain isoforms are expressed in skeletal muscle, m-calpain, and mu-calpain, which exert critical proteolytic activities related to muscle functions, muscle atrophy, and myogenesis. Cathepsins are lysosomal acid proteases. The main cathepsin isoforms implicated in muscle aging and atrophy are cathepsins B, L, and H. This study characterized calpain1, calpain2, cathepsin L, cathepsin B, and cathepsin H genes in the tilapia genome. In addition, the expressions of these genes were examined in the muscle tissues of starved versus fed; and refed versus control tilapia, Oreochromis niloticus. qPCR expression data showed that Calpain1 and 2 catalytic subunits and the regulatory subunit were significantly higher in starved compared to the fed tilapia. Similarly, cathepsin L, B, and H showed significant upregulation in the starved compared to the fed fish. Besides, calpain and cathepsin L enzymatic catalytic activity increased in the starved fish relative to the fed fish. The results indicate that the studied genes are involved in atrophying muscle and are considered to have a potential role as markers of tilapia muscle accretion.