Senescence and aging differentially alter key metabolic pathways in murine brain microglia

Microglia, the resident immune cells of the central nervous system, are critically involved in maintaining brain homeostasis. With age, microglia display morphological and functional alterations that have been associated with cognitive decline and neurodegeneration. Although microglia seem to participate in an increasing number of biological processes which require a high energy demand, little is known about their metabolic regulation under physiological and pathophysiological conditions and during aging/senescence. Here, we determined mRNA expression levels of critical rate limiting enzymes in several key metabolic pathways including glycolysis, pentose phosphate pathway, fatty acid oxidation and synthesis in association with oxidative phosphorylation in microglia, both under aging and senescent conditions. We found strong evidence for different metabolic changes occuring in senescent vs. aged microglia cells. While senescent microglia display a hypermetabolic state as indicated by increased expression of key enzymes involved in glycolysis and pentose phosphate pathway, aging microglia are rather in a state of hypometabolism. Our findings indicate that studies involving aging and senescent microglia require a clear differentiation between these microglial states due to profound metabolic differences observed here. Understanding metabolic changes in senescent and aged microglia may lead to novel strategies to decrease over-activation of these cells due to aging, which is associated to the process of inflamm-aging and neurodegeneration.