Gene expression of calpain family in skeletal muscle of starved and re-fed channel catfish (Ictalurus punctatus)

Calpains (calcium-dependent cytoplasmatic cysteine proteinases) are involved in the cytoskeletal remodelling and wasting of skeletal muscle. The main isoform are Capn1 and Capn2 which share about 50-60% amino acid homology with one another, and differ in the concentration of Ca2+ required for their in vitro activation. Capn1 and Capn2 isoforms are ubiquitously expressed in vertebrates, whereas the expression of another family member of the calpains, Capn3 is limited to skeletal muscle tissue. In this study, we have characterized the full-length cDNA sequences of Capn1, Capn2, and Capn3 from channel catfish and described the effect of nutrient restriction and re-feeding on their transcript abundance in the skeletal muscle of this fish species. Channel catfish Capn1 and Capn3 transcript abundance in the treatment group (fasted for 35 days and then re-fed for 21 days) showed a significant down regulation from the 17th day up to 35th day of starvation (Fig. 1 A, C), whereas the expression levels at day 10 and 21 of re-feeding were not significantly different in comparison to the levels of controls (ad libitum fed during all the experiment) (Fig. 1A, C). Capn2 gene expression was up-regulated after 35 days of starvation in fasted/refed group as compared to the control one (Fig. 1B). Calpain catalytic activity in channel catfish skeletal muscle showed significant difference only during the starvation period with 1.2 and 1.4 fold increase (p<0.01) after 17 days of and 35 days of starvation, respectively. The expression patterns and the catalytic activity of calpain genes may suggest either degradation of myofibrillar proteins for amino acid supply or a remodelling of the fish muscle. Moreover, the down regulation of Capn 1 and Capn3 under wasting conditions, may suggest that the role of these isoform in maintaining skeletal muscle homeostasis is different from that of the other ubiquitous calpain (Capn2).