Lactate accumulation from HIF-1α-mediated PMN-MDSC glycolysis restricts brain injury after acute hypoxia in neonates.

Fetal intrauterine distress (FD) during delivery can cause fetal intrauterine hypoxia, posing significant risks to the fetus, mother, and newborns. While studies highlight the role of polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) in neonatal diseases and tumor hypoxia, their specific involvement in newborns experiencing fetal distress during delivery (FDNB) is not well understood. Here, we found elevated PMN-MDSC activation, increased glycolysis, enhanced lactate production, and upregulated HIF-1α expression in the blood of FDNB neonates compared to healthy newborns (NNB). Importantly, PMN-MDSC levels were inversely correlated with neuron-specific enolase (NSE), a marker for neurological injury. In neonatal mice subjected to acute hypoxia, a 48-h exposure led to a shift from exacerbation to amelioration of brain damage when compared with a 24-h period. This change was associated with a reduction in microglial activation, a decrease in the expression of inflammatory factors within the microglia, alongside increased peripheral PMN-MDSC activation. Depleting PMN-MDSCs led to heightened microglial activation and aggravated brain injury. Mechanistically, enhanced activation of PMN-MDSCs promotes HIF-1α accumulation while enhancing glycolysis and lactate release, thereby mitigating neonatal brain injury. Notably, lactate supplementation in hypoxic mice rescued brain damage caused by insufficient PMN-MDSC activation due to HIF-1α deficiency. Our study clarifies the role of lactate in peripheral PMN-MDSCs after acute hypoxia and its effects on microglial activation and subsequent brain injury.