Social isolation stress-resilient rats reveal energy shift from glycolysis to oxidative phosphorylation in hippocampal nonsynaptic mitochondria.

Aims: To examine the differences in the hippocampal proteome profiles of resilience or susceptibility to chronic social isolation (CSIS), animal model of depression, and to identify biomarkers that can distinguish the two.

Main Methods: Comparative subproteomic approach was used to identify changes in hippocampal cytosol and nonsynaptic mitochondria (NSM) of CSIS-resilient compared to CSIS-sensitive or control rats. The resilient and sensitive phenotypes of CSIS rats were distinguished based on their sucrose preference values. Selected proteins were validated by Western blot or immunofluorescence.

Key Findings: Predominantly down-regulated processes such as cytosolic cytoskeleton organization, the calcium signaling pathway, ubiquitin proteasome degradation, redox system, malate/aspartate shuttling and glutamate metabolism in CSIS-resilient compared to CSIS-sensitive rats were found. Decreased protein expression of glycolytic enzymes with simultaneous increased expression of Aco2 involved in tricarboxylic acid cycle and expression of several subunits composing oxidative phosphorylation involved enzymes (Uqcrc2, Atp5f1a, Atp5f1b) were found, indicating shift in energy production from glycolysis to oxidative phosphorylation in NSM. The four-fold higher level of mitochondrial glyceraldehyde-3-phosphate dehydrogenase of resilient rats indicated its transfer from the cytosol to the NSM. An increased level of transketolase along with the reduced pyruvate kinase level suggested an activated pentose phosphate pathway in CSIS-resilient relative to control rats. Cytosolic up-regulated CSIS proteins were implicated in antioxidative and proteasomal systems, while down-regulated NSM protein was involved in oxidative phosphorylation.

Significance: The identified altered activated pathways and potential biomarkers enhance understanding of molecular mechanisms underlying resilience or susceptibility to CSIS, crucial in developing new therapeutic strategies.