Glucose regulated protein and heat shock protein expression in hibernating mammals
During mammalian hibernation, most physiological activities are dramatically suppressed, but selected genes are up-regulated to provide protein products that protect cells and organs for long term survival in the hypometabolic, hypothermic state. In this study, the roles of chaperone proteins including glucose regulated proteins and heat shock proteins were assessed in two species: thirteen-lined ground squirrels, Spermophilus tridecemlineatus, and little brown bats, Myotis lucifugus. RT-PCR and Western blot techniques were used to examine gene and protein expression. Compared with euthermic control squirrels and bats, glucose regulated protein 75 (Grp75), Grp94 and Grp170 were elevated in some tissues at the mRNA and/or protein levels with organ-specific patterns of response by grp transcripts and GRP protein. The up-regulation of grp mRNA may be important for rapidly elevating the protein content of these chaperones during hibernation and arousal; elevated GRP protein would then aid in the folding of other proteins that are newly synthesized during hibernation and/or in the renaturation of proteins that become misfolded at low body temperatures. Heat shock proteins (Hsps) including Hsp40, Hsp72, Hsp73 and Hsp90 were elevated in some tissues of hibernating ground squirrels and bats. Analysis of partial amino acid sequences of Grps and Hsps showed very high identities (88-100%) compared with human or mouse sequences which indicates similar structures and functions of Grps and Hsps among mammalian species. The data support the idea that Grps and Hsps are up-regulated during hibernation to function as chaperones to bind non-native polypeptides and suppress protein aggregations caused by low temperature during hibernation.