Astrocytic Metabolic Trained Immunity via AMPK-PGC1α Axis

The astrocytic metabolic trained immunity hypothesis proposes that perinatal immune activation fundamentally reprograms astrocytic cellular metabolism through the AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) signaling axis, creating a distinct metabolic memory that influences neurodevelopmental outcomes. Upon exposure to PAMPs or DAMPs during critical perinatal windows, astrocytic pattern recognition receptors, particularly TLR3 and TLR4, activate downstream signaling cascades that initially suppress AMPK activity through inflammatory kinase networks including IκB kinase β (IKKβ) and c-Jun N-terminal kinase (JNK). However, sustained inflammatory stress triggers a compensatory metabolic switch wherein AMPK becomes hyperactivated through calcium-dependent CaMKKβ signaling and increased AMP/ATP ratios from mitochondrial dysfunction. Activated AMPK phosphorylates PGC1α at serine residues 538 and 568, leading to its deacetylation by sirtuin 1 (SIRT1) and subsequent nuclear translocation. Nuclear PGC1α acts as a transcriptional coactivator, binding to nuclear respiratory factors (NRF1/NRF2) and estrogen-related receptors (ERRα) to drive expression of mitochondrial biogenesis genes including mitochondrial transcription factor A (TFAM), cytochrome c oxidase subunits, and NADH dehydrogenase components. This metabolic reprogramming establishes astrocytic trained immunity characterized by enhanced oxidative phosphorylation capacity, increased fatty acid oxidation through carnitine palmitoyltransferase 1A (CPT1A) upregulation, and altered glutamate-glutamine cycling via glutamine synthetase (GLUL) modulation. The training effect involves chromatin remodeling through PGC1α-mediated recruitment of histone acetyltransferases and methyltransferases, creating persistent epigenetic marks at metabolic gene promoters that maintain altered inflammatory and metabolic responsiveness long after initial activation, thereby influencing astrocyte-neuron metabolic coupling and synaptic development throughout critical neurodevelopmental periods.