Neuroinflammation is the major contributor to the pathology of neonatal hypoxic–ischemic (HI) brain injury. Our previous studies have demonstrated that microRNA210 (miR210) inhibition with antisense locked nucleic acid (LNA) inhibitor mitigates neuroinflammation and provides neuroprotection after neonatal HI insult. However, the underlying mechanisms remain elusive. In the present study, using miR210 knockout (KO) mice and microglial cultures, we tested the hypothesis that miR210 promotes microglial activation and neuroinflammation through suppressing mitochondrial function in microglia after HI. Neonatal HI brain injury was conducted on postnatal day 9 (P9) wild-type (WT) and miR210 knockout (KO) mouse pups. We found that miR210 KO significantly reduced brain infarct size at 48 h and improved long-term locomotor functions assessed by an open field test three weeks after HI. Moreover, miR210 KO mice exhibited reduced IL1β levels, microglia activation and immune cell infiltration after HI. In addition, in vitro studies of microglia exposed to oxygen–glucose deprivation (OGD) revealed that miR210 inhibition with LNA reduced OGD-induced expression of Il1b and rescued OGD-mediated downregulation of mitochondrial iron–sulfur cluster assembly enzyme (ISCU) and mitochondrial oxidative phosphorylation activity. To validate the link between miR210 and microglia activation, isolated primary murine microglia were transfected with miR210 mimic or negative control. The results showed that miR210 mimic downregulated the expression of mitochondrial ISCU protein abundance and induced the expression of proinflammatory cytokines similar to the effect observed with ISCU silencing RNA. In summary, our results suggest that miR210 is a key regulator of microglial proinflammatory activation through reprogramming mitochondrial function in neonatal HI brain injury.

C-type natriuretic peptide (CNP) is an important vascular regulator that is present in the brain. Our previous study demonstrated the innate neuroprotectant role of CNP in the neonatal brain after hypoxic-ischemic (HI) insults. In this study, we further explored the role of CNP in cerebrovascular pathology using both in vivo and in vitro models. In a neonatal mouse HI brain injury model, we found that intracerebroventricular administration of recombinant CNP dose-dependently reduces brain infarct size. CNP significantly decreases brain edema and immunoglobulin G (IgG) extravasation into the brain tissue, suggesting a vasculoprotective effect of CNP. Moreover, in primary brain microvascular endothelial cells (BMECs), CNP dose-dependently protects BMEC survival and monolayer integrity against oxygen-glucose deprivation (OGD). The vasculoprotective effect of CNP is mediated by its innate receptors NPR2 and NPR3, in that inhibition of either NPR2 or NPR3 counteracts the protective effect of CNP on IgG leakage after HI insult and BMEC survival under OGD. Of importance, CNP significantly ameliorates brain atrophy and improves neurological deficits after HI insults. Altogether, the present study indicates that recombinant CNP exerts vascular protection in neonatal HI brain injury via its innate receptors, suggesting a potential therapeutic target for the treatment of neonatal HI brain injury.