AMP-activated protein kinase is a biomarker of energetic status in freshwater mussels exposed to municipal effluents

Although biomarkers are frequently used to assess sublethal effects of contaminants, a lack of mechanistic linkages to higher-level effects limits the predictive power of biomarkers. Bioenergetics has been proposed as a framework for linking cellular effects to whole-animal effects. We investigated sublethal effects of exposure to wastewater treatment facility effluent in freshwater mussels in situ, thereby capturing ecologically relevant exposure conditions. Our study focused on the energetic biomarker AMP-activated protein kinase (AMPK), while also considering more traditional biomarkers like heat shock proteins (HSP70), and antioxidant enzymes (i.e., superoxide dismutase (SOD), glutathione-S-transferase (GST)). We examined biomarkers at mRNA and protein levels. Effluent exposure caused a reduction in total-AMPK protein abundance (p = 0.05) and AMPK mRNA expression (p = 0.02). Conversely, AMPK activity increased at downstream sites by 2.2-fold (p = 0.05), indicating increased cellular energy consumption. HSP70 protein abundance was lower at downstream sites (p < 0.05), while SOD and GST activity levels significantly increased. By using various biomarkers, we demonstrate that exposure to municipal effluent creates an energetically taxing situation. This is the first study to use AMPK to evaluate the effects of contamination in situ, and our results suggest that energetic biomarkers, like AMPK, complement traditional biomarkers and may help establish functional links between cellular and whole-animal effects.