Metabolic energy sensors (AMPK and SIRT1), protein carbonylation and cardiac failure as biomarkers of thermal stress in an intertidal limpet: linking energetic allocation with environmental temperature during aerial emersion

The effects of heat stress on organisms are manifested at the levels of organ function, metabolic activity, protein stability and gene expression. Here, we examined effects of high temperature on the intertidal limpet Cellana toreuma to determine how the temperatures at which (1) organ failure (cardiac function), (2) irreversible protein damage (carbonylation) and (3) expression of genes encoding proteins involved in molecular chaperoning (hsp70 and hsp90) and metabolic regulation (ampk and sirt1) occur compare with field temperatures, which commonly exceed 30 degrees C and can reach 46 degrees C. Heart failure, indexed by the Arrhenius break temperature, occurred at 34.3 degrees C. Protein carbonylation rose significantly at 38 degrees C. Genes for heat shock proteins HSP70 (hsp70) and HSP90 (hsp90), for two subunits of AMP-activated protein kinase (AMPK) (ampk alpha and ampk beta) and for histone/protein deacetylase SIRT1 (sirt1) all showed increased expression at 30 degrees C. Temperatures of maximal expression differed among genes, as did temperatures at which upregulation ceased. Expression patterns for ampk and sirt1 indicate that heat stress influenced cellular energy homeostasis; above similar to 30 degrees C, upregulation of ATP-generating pathways is suggested by elevated expression of genes for ampk; an altered balance between reliance on carbohydrate and lipid fuels is indicated by changes in expression of sirt1. These results show that C. toreuma commonly experiences temperatures that induce expression of genes associated with the stress response (hsp70 and hsp90) and regulation of energy metabolism (ampk and sirt1). At high temperatures, there is likely to be a shift away from anabolic processes such as growth to catabolic processes, to provide energy for coping with stress-induced damage, notably to proteins.