Diminished lactate utilization in LDHB-deficient neurons leads to impaired long-term memory retention

Neurons' high energy demands for processing, transmitting, and storing information in the brain necessitate efficient energy metabolism to maintain normal neuronal function. The astrocyte-neuron lactate shuttle (ANLS) hypothesis suggests neurons preferentially use lactate from astrocytes over glucose for energy. This study investigated lactate dehydrogenase B (LDHB), which preferentially converts lactate to pyruvate, in neuronal energy metabolism and cognitive function. LDHB-deficient neurons showed reduced lactate-driven energy metabolism in culture, while LDHB-deficient brains accumulated lactate, both indicating decreased lactate utilization. This reduced lactate utilization was correlated with impaired long-term memory in LDHB-deficient mice, while short-term memory remained unaffected and overall neuropathology was only mildly disturbed. Unexpectedly, LDHB-deficient neurons maintain stable energy metabolism under physiological glucose conditions, indicating the presence of lactate dehydrogenase (LDH) activity in LDHB-deficient neurons. The observation of lactate dehydrogenase A (LDHA), which preferentially converts pyruvate to lactate but can also catalyze the reverse reaction less efficiently, in LDHB-deficient neurons may explain their stable energy metabolism and reduced lactate utilization. This study challenges the established concept of strict LDH isoform compartmentalization in brain cells, questioning the exclusive presence of LDHB in neurons and suggesting a more flexible neuronal metabolic profile than previously assumed by the ANSL hypothesis.