Lactate Receptor HCAR1 Affects Axonal Development and Contributes to Lactate's Protection of Axons and Myelin in Experimental Neonatal Hypoglycemia.

Lactate plays an important role in brain energy metabolism. It contributes to normal brain development and to neuroprotection in diabetic hypoglycemia, but its role in neonatal hypoglycemia is unclear. Moreover, lactate can work as a signaling substance via the lactate receptor HCAR1 (Hydroxycarboxylic acid receptor 1). Recent studies indicate that HCAR1 is protective in mouse models of neonatal hypoxic ischemia and has a role in metabolic regulation in glial cells during hypoglycemia. Here we have studied potential impacts of HCAR1 on axonal and myelin development in the cerebral cortex and corpus callosum of young (P21) wild-type (WT) mice and HCAR1 KO mice and in cortical organotypic brain slice cultures. The HCAR1 KO mice showed lower axonal area relative to WT in both cortex and corpus callosum. However, the myelin area was unaffected by HCAR1 KO. Using particle and colocalization analysis, we show that HCAR1 KO predominantly reduces axonal size in unmyelinated axons. Using an organotypic brain slice model of neonatal hypoglycemia, we find that lactate protects both axonal and myelin development in hypoglycemia, partially via HCAR1. Lastly, live imaging with a pH-sensitive dye on acute cortical brain slices indicates that cellular lactate uptake is influenced by HCAR1. In conclusion, our findings support a role of HCAR1 in axonal development and in lactate's protective effects in hypoglycemia.