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. Upon exposure to PAMPs or DAMPs during critical developmental windows, astrocytic pattern recognition receptors, including TLR3 and TLR4, initiate calcium-dependent signaling cascades that activate calcium/calmodulin-dependent protein kinase kinase β (CaMKKβ), which subsequently phosphorylates and activates AMPK at threonine 172. Activated AMPK phosphorylates PGC1α at multiple serine residues (Ser538, Ser568), promoting its nuclear translocation and transcriptional coactivator function. Nuclear PGC1α forms complexes with nuclear respiratory factors 1 and 2 (NRF1/2) and estrogen-related receptor alpha (ERRα) to drive transcription of mitochondrial biogenesis genes including mitochondrial transcription factor A (TFAM), cytochrome c oxidase subunit IV (COX4), and ATP synthase subunits. This leads to enhanced oxidative phosphorylation capacity and mitochondrial fatty acid oxidation through upregulation of carnitine palmitoyltransferase 1A (CPT1A) and medium-chain acyl-CoA dehydrogenase (MCAD). The metabolic shift toward enhanced oxidative metabolism establishes trained immunity through epigenetic mechanisms involving sirtuin 1 (SIRT1)-mediated deacetylation of histone H3 lysine 9 (H3K9) and recruitment of chromatin remodeling complexes to promoters of neuroprotective genes such as brain-derived neurotrophic factor (BDNF), glial cell-derived neurotrophic factor (GDNF), and antioxidant enzymes. This creates a primed astrocytic phenotype with enhanced capacity for rapid metabolic responses to subsequent developmental challenges, fundamentally altering neurodevelopmental trajectories through improved neuronal support and synaptic maintenance.