Cellular Coping Mechanisms to Hypoxia in the Longhorn Sculpin (Myoxocephalus octodecemspinosus) Brain

The loss of neurological function due to hypoxia remains to be a challenge in many species due to the lack of knowledge and understanding of cellular responses. To investigate cellular responses and survival strategies of the brain during hypoxia and post-hypoxia recovery in a moderate hypoxia-tolerant species, with the hopes of identifying possible therapeutic remedies, thirty Longhorn sculpin, Myoxocephalus octodecimspinosus, were challenged with acute hypoxia (40% O2 saturation for 1 h) and twelve additional sculpin were used as controls (~90% O2 saturation). Fish were sampled at each of the following time points: control/normoxic conditions (T=0 h); hypoxic conditions (T=3 h); early (T=7 h total; 4 hours post-hypoxia), and late (T=11 h total; 8 hours post-hypoxia) normoxic recovery. The importance of hypoxia-induced apoptotic pathways has been suggested in other species; therefore, they were the focus of the present study of the Longhorn sculpin to explore their cellular coping mechanisms to hypoxia. The expression levels of hypoxia-response elements HIF-2α and Hsp70 were examined at the transcriptome level at each time point using RT-QPCR, and HIF-1α, active caspase 3, and survivin, were explored at the protein level using immunohistochemistry and fluorescence microscopy. HIF-2α mRNA levels decreased significantly after hypoxic exposure, compared to normoxic levels, while Hsp70 levels remained unchanged. Using immunohistochemistry, we also ascertained that HIF-1α, active caspase 3, and survivin proteins are present in Longhorn sculpin brain tissue, however, acute hypoxic exposure did not alter protein levels significantly in this study between treatment groups or between regions of the brain. The Longhorn sculpin’s moderate hypoxia tolerance may be due to a lack of apoptotic cell death, however, more testing of apoptotic factors on both the transcriptome and protein level is required to fully elucidate the hypoxia survival strategies of the Longhorn sculpin. Investigating the survival strategies of hypoxia-tolerant species could provide for an effective treatment against hypoxia-induced neurological damage in other, more sensitive species by assisting in the identification of target genes and pathways for therapeutic intervention