Hypoxia mediates Hif-1α to affect myofiber development and Vc regulates the influence by activating Shh-Gli pathway in channel catfish (Ictalurus punctatus)

An 8 weeks feeding trial and a cell culture were conducted to determine the effects of hypoxia and vitamin C (Vc) on muscle development of channel catfish (Ictalurus punctatus). In vivo, the channel catfish (average initial weight 14.50 ± 0.15 g) were divided into four groups, normoxia (DO 7.5 ± 0.5 mg/L) with 50 mg/kg of Vc (N50), hypoxia (DO 5.0 ± 0.5 mg/L) with 50 mg/kg of Vc (H50), hypoxia with 250 mg/kg of Vc (H250), and hypoxia with 500 mg/kg of Vc (H500). Results indicated that the specific growth rate (SGR) of fish in the H50 was significantly lower than the N50 and H250 (P < 0.05). The mean diameter of myofibers and sarcomere lengths were significantly increased in the H50 group compared to the N50, H250, and H500 groups (P < 0.05). The fiber density was significantly increased in the H50 than in the N50. Transcriptome analysis showed that paired box 3 (pax3) and myogenic regulatory factors (MRFs) expression and Sonic hedgehog (Shh) pathways associated with muscle development were significantly affected in the N50 and H250 group compared to the H50 (P < 0.05). A subsequent study showed that the gene expression of myogenic factor 5 (myf5) and myoblast determination protein (myod) were significantly decreased, and myogenin (myog) was significantly increased in the H50 group compared to the N50 (P < 0.05). The level of Hif-1α was significantly higher in H50 than in N50 but significantly lower in H50 than in H250 and H500 (P < 0.05). The level of Pax3 was significantly lower in H50 than the N50 (P < 0.05). In vitro, L6 was incubated with 400 μM of CoCl₂·6H₂O and 100 μM of defetoxamine (DFO) for 24 h, respectively. The results showed that the Hif-1α level was significantly increased (P < 0.05). Under this condition, the levels of Pax3, Shh, and glioma-associated oncogene homolog (Gli), were found to be significantly decreased (P < 0.05). A subsequent study found that Vc at 0.25 mg/L significantly increased the level of Gli under hypoxia. In conclusion, hypoxia inhibits myofiber proliferation and promotes myofiber differentiation. Vc can improve myofiber development under hypoxia, which may be related to the activation of the Shh-Gli signaling pathway.