Extracellular lactate reprograms mitochondrial metabolism and NAD+/NADH redox balance in blood-brain barrier endothelial cells via an LDHB-MPC-NAD+ axis

Brain endothelial cells (BECs) form the structural foundation of the blood-brain barrier (BBB) and exhibit a paradoxical metabolic phenotype, converting approximately 90% of consumed glucose to lactate despite residing in an oxygen-rich vascular environment. Whether the extracellular lactate that BECs continuously produce and export feeds back to regulate their own metabolism and redox state has not been directly investigated. Here, using validated BBB model, we demonstrate that exogenous lactate drives a concentration- and time-dependent biphasic growth response, with 10 mM lactate maximally promoting BEC proliferation at 48 h. Mechanistically, lactate suppresses canonical glycolysis evidenced by downregulation of GLUT1 and key glycolytic enzymes and reduced glucose uptake while simultaneously driving a coordinated shift toward mitochondrial oxidative metabolism. This shift is mediated by upregulation of LDHB, MPC1, MPC2, and PDH activation, enabling lactate-derived pyruvate to enter mitochondria and fuel comprehensive TCA cycle engagement, mitochondrial biogenesis, and enhanced oxidative phosphorylation capacity as measured by high-resolution respirometry. At the redox level, lactate oxidation imposes reductive pressure on the NAD + /NADH pool, which is counterbalanced by activation of the NAMPT-dependent NAD + salvage pathway, resulting in expansion of the total NAD pool. Genetic silencing of LDHB or MPC1 and pharmacological inhibition of NAMPT each independently abolish lactate-driven BEC proliferation, establishing the LDHB-MPC-NAD + axis as mechanistically essential. These findings identify the cerebrovascular endothelium as an active participant in brain lactate mitochondrial function and introduce the LDHB-MPC-NAD + axis as a novel redox-metabolic regulatory circuit at the BBB.