Fateful triad of reactive oxygen species, mitochondrial dysfunction and lipid accumulation is associated with expression outline of the AMP-activated protein kinase pathway in bovine blastocysts

Abstract

Low cryotolerance is considered as the major drawback of in vitro-produced bovine embryos and is frequently associated with a triad encompassing increased cytoplasmic lipid accumulation, enhanced levels of reactive oxygen species (ROS) and mitochondrial dysfunction. The aim of the present study was to explore the role of the AMP-activated protein kinase (AMPK) pathway in the process resulting such phenotypes. Comparative analysis under different environmental conditions revealed downregulation of AMP-activated protein kinase cytalytic subunit 1alpha (AMPKA1), peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC1A) and carnitine palmitoyltransferase 1 (CPT1) genes and upregulation of acetyl-CoA carboxylase a (ACC). In contrast, the presence of fatty acids within the culture medium resulted in a distinct molecular profile in the embryo associated with enhanced levels of ROS, mitochondrial dysfunction and elevated lipid accumulation in bovine embryos. Because AMPKA1 regulates PGC1A, CPT1 and ACC, the results of the present study reveal that AMPK in active its form is the key enzyme promoting lipolysis. Because AMPK1 activity is, in turn, controlled by the AMP : ATP ratio, it is possible to speculate that excessive uptake of exogenous free fatty acids could increase cellular ATP levels as a result of the disturbed ß-oxidation of these external fatty acids and could therefore bypass that molecular feedback mechanism. Subsequently, this condition would cause enhanced generation of ROS, which negatively affect mitochondrial activity. Both enhanced generation of ROS and low mitochondrial activity are suggested to enhance the accumulation of lipids in bovine embryos.