Metabolic changes
Cells under thermal stress presumably halt the synthesis of nonessential proteins and molecules and put cellular resources toward the synthesis of products that play a role in coping with heat stress. Glycolipid and glycoprotein biosynthetic pathways were found to be upregulated by thermal stress, particularly in the 25° group. Eight KEGG pathways involved in the synthesis of glycolipids or glycoproteins contained at least two upregulated genes (Table 5). Glycolipids play a number of biological roles in the cell, including physical defense, cell–cell signaling, membrane–protein interactions, and immune function (Varki et al. 1999). Temperature has been shown to change the composition of glycosphingolipids in the plasma membrane of some eukaryotes (Aaronson and Martin 1983). Ceramide in particular is a glycosphingolipid that plays a prominent role in the cellular stress response, affecting cell–cell signaling and apoptosis (Hannun 1996; Hussain et al. 2012). UGCG and SGMS2 were upregulated in the 25° group and participate in ceramide biosythesis (Ichikawa et al. 1996; Vermeil et al. 1996). Upregulated CIGALT1B codes for a chaperone required for some o-glycan biosynthesis. O-glycans play many roles in the cell, including cell signaling (Ju and Cummings 2002).
Another role of glycolipids that is of note is the production of mucus by epithelial cells. Mucus can act as physical defense for epithelial cells by forming a gelatinous barrier, and may function to protect the gill epithelium from physical damage during exposure to thermal stress (Shephard 1994; Loganathan et al. 2013).