Microglial metabolic reprogramming refers to the dynamic shifts in cellular energy metabolism that microglia undergo in response to pathological stimuli in neurodegenerative diseases. This process involves a fundamental shift from oxidative phosphorylation (OXPHOS) in surveilling microglia to aerobic glycolysis in activated microglia, with profound implications for neuroinflammatory responses and disease progression .
Recent comprehensive reviews have synthesized the growing understanding of this phenomenon. A 2025 review in Molecular Neurobiology provides an updated synthesis of metabolic transitions from homeostasis to responsive states in microglia, highlighting metabolism-based targeted therapy approaches for neurodegeneration .
In the healthy brain, surveilling microglia rely primarily on oxidative phosphorylation for energy production. This metabolic state supports the sustained patrol and immune surveillance functions of homeostatic microglia. The mitochondria-dense cytoplasm enables efficient ATP production through the electron transport chain, with minimal glycolytic flux Huang Y, et al. Metabolic reprogramming in microglia from Alzheimer's Disease brain. J Neuroinflammation. 2022;19(1):89.
Upon disease-related activation, microglia shift toward aerobic glycolysis :
- Enhanced glucose uptake: Upregulation of glucose transporters (GLUT1/SLC2A1) increases glucose import 3-5 fold
- Elevated glycolytic enzymes: Hexokinase 2 (HK2), phosphofructokinase (PFK), and pyruvate kinase M2 (PKM2) are strongly upregulated
- Lactate production: Pyruvate is converted to lactate by LDH-A rather than entering the TCA cycle
- Pentose phosphate pathway: Increased flux through PPP generates NADPH for oxidative-stress production and nucleotide biosynthesis
- Mitochondrial dysfunction: Progressive loss of mitochondrial membrane potential, reduced OXPHOS complex activity
- Pro-inflammatory phenotype: Glycolytic metabolism sustains NLRP3 inflammasome activation and cytokine production
In chronic neurodegeneration, sustained glycolytic activation leads to metabolic exhaustion:
- Energy crisis: Both OXPHOS and glycolysis become impaired, leading to ATP depletion
- Impaired phagocytosis: Loss of energy supply prevents effective clearance of amyloid plaques and debris
- Senescent phenotype: Metabolically exhausted microglia resemble senescent cells, with irreversible pro-inflammatory features
- Lipid accumulation: Failure of fatty acid oxidation drives lipid droplet accumulation, producing the LDAM phenotype
The mechanistic target of rapamycin (mTOR) is a central metabolic sensor that drives the glycolytic switch in microglia :
- TREM2-mTOR coupling: TREM2 ligation by lipoproteins and amyloid-beta activates PI3K-AKT-mTOR signaling, increasing microglial metabolic capacity. TREM2 loss-of-function variants (R47H, R62H) — which are Alzheimer's Disease risk factors — impair mTOR activation, reducing both glycolytic and OXPHOS capacity and trapping microglia in a metabolically dysfunctional state Ulland et al., 2017
- HIF-1α stabilization: mTOR activates hypoxia-inducible factor 1-alpha (HIF-1α), the master transcriptional regulator of glycolytic gene expression. HIF-1α upregulates GLUT1, HK2, LDHA, and PDK1 (which blocks pyruvate entry into mitochondria)
- Rapamycin effects: mTOR inhibition by rapamycin reduces microglial glycolysis and inflammatory cytokine production, but also impairs beneficial TREM2-dependent responses, highlighting the dual nature of mTOR in neurodegeneration
AMP-activated protein kinase (AMPK) is the counterregulator of mTOR and promotes OXPHOS:
- Energy sensing: AMPK is activated by high AMP/ATP ratio, sensing energy depletion
- OXPHOS promotion: AMPK activates PGC-1α, promoting mitochondrial biogenesis and fatty acid oxidation
- Anti-inflammatory effects: AMPK activation suppresses NF-kappa-B signaling, reducing pro-inflammatory cytokine production
- Therapeutic potential: AMPK activators (metformin, AICAR) can restore microglial OXPHOS and reduce neuroinflammation in preclinical models
Several glycolytic enzymes have moonlighting functions that directly regulate microglial inflammatory responses:
- PKM2 (pyruvate kinase M2): In its dimeric form, PKM2 translocates to the nucleus and acts as a transcriptional coactivator for HIF-1α and STAT3, amplifying inflammatory gene expression. Pharmacological stabilization of PKM2 tetramers (using TEPP-46 or DASA-58) traps PKM2 in its enzymatic form, preventing nuclear translocation and reducing inflammation Palsson-McDermott et al., 2015
- HK2 (hexokinase 2): Beyond its glycolytic role, HK2 interacts with VDAC on the mitochondrial outer membrane, regulating NLRP3 inflammasome activation
- GAPDH: Undergoes post-translational modifications (succination, oxidation) in inflammatory microglia, affecting both glycolytic flux and gene regulation
¶ Itaconate and the TCA Cycle
The TCA cycle intermediate itaconate has emerged as a key immunometabolite in microglia:
- Immune-responsive gene 1 (IRG1/ACOD1): Produces itaconate from cis-aconitate in the TCA cycle
- Anti-inflammatory effects: Itaconate inhibits succinate dehydrogenase (SDH), reducing succinate accumulation and HIF-1α stabilization
- Nrf2 activation: Dimethyl itaconate activates the NRF2 antioxidant pathway, reducing oxidative damage
- Therapeutic potential: Itaconate derivatives are being explored as anti-inflammatory therapeutics for neurodegeneration
In Alzheimer's Disease, microglial metabolic reprogramming occurs in stages:
- Early activation: amyloid-beta oligomers trigger TREM2-mTOR-dependent glycolytic switch, initially enhancing microglial motility and phagocytosis — this may represent a protective response
- Chronic glycolysis: Sustained amyloid-beta exposure locks microglia in a glycolytic state with impaired OXPHOS. [Disease-associated microglia (DAM) show elevated HK2, PKM2, and LDHA expression
- Metabolic exhaustion: In advanced disease, microglia surrounding dense-core plaques show both impaired glycolysis and OXPHOS, becoming metabolically inert and unable to restrict plaque growth
- Spatial metabolic heterogeneity: Recent spatial transcriptomics studies reveal that microglial metabolic state varies with distance from amyloid plaques — plaque-proximal microglia are most glycolytic, while those further away maintain more homeostatic metabolism Xu et al., 2025
In Parkinson's disease:
- Alpha-synuclein fibrils activate microglial TLR2/4 signaling, triggering NF-κB-dependent glycolytic reprogramming
- GBA mutations disrupt lysosomal-mitochondrial lipid trafficking, creating metabolic stress that promotes glycolytic shift
- Dopamine depletion in the substantia-nigra removes tonic inhibition of microglial activation, permitting metabolic reprogramming
In ALS:
- SOD1 mutant protein in microglia induces mitochondrial dysfunction and oxidative damage, forcing glycolytic dependence
- TDP-43 pathology disrupts RNA processing of metabolic enzyme transcripts, altering the metabolic transcriptome
- Spinal cord microglia show progressive metabolic decline paralleling motor neuron degeneration
Several therapeutic approaches target microglial metabolism:
- mTOR modulators: Rapamycin and its analogs reduce glycolytic inflammation but must be carefully dosed to preserve beneficial TREM2-mTOR signaling
- AMPK activators: Metformin, AICAR, and the natural compound berberine promote OXPHOS and reduce neuroinflammation
- HIF-1α inhibitors: Pharmacological inhibition of HIF-1α (using echinomycin, acriflavine) reduces glycolytic gene expression in activated microglia
- PKM2 stabilizers: TEPP-46 and DASA-58 prevent nuclear PKM2 activity, reducing inflammatory gene transcription
- Itaconate derivatives: 4-octyl itaconate and dimethyl itaconate activate anti-inflammatory pathways
- NAD+ precursors: Nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) restore mitochondrial function by replenishing NAD+ pools
- MitoQ and MitoTEMPO: Mitochondria-targeted antioxidants that reduce mitochondrial oxidative-stress and preserve OXPHOS capacity
- Urolithin A: Activates mitophagy, clearing damaged mitochondria and promoting biogenesis of healthy organelles
- SS-31 (elamipretide): Stabilizes cardiolipin in the inner mitochondrial membrane, supporting electron transport chain function
¶ Ketogenic and Dietary Approaches
- Ketone bodies: β-hydroxybutyrate (BHB) can serve as alternative fuel for microglial OXPHOS, bypassing glycolytic impairment. BHB also inhibits NLRP3 Inflammasome activation
- Ketogenic diet: Preclinical studies show reduced neuroinflammation and improved microglial function in AD models fed ketogenic diets
- Intermittent fasting: Enhances AMPK activation and mitophagy, potentially restoring microglial metabolic health