MicroRNA-374a-5p inhibits neuroinflammation in neonatal hypoxic-ischemic encephalopathy via regulating NLRP3 inflammasome targeted Smad6

Aims: Neonatal hypoxic-ischemic encephalopathy (HIE) is still an important cause of neurological dysfunction. At present, there is no reliable biochemical index in clinical examination. Increasing evidence demonstrates that microRNAs (miRNAs) are involved in the process of HIE, and miR-374a-5p is down-regulated in HIE infants. In this study, the aim is to investigate the role and mechanism of miR-374a-5p in HIE. Main methods: Sprague-Dawley (SD) rats were used to establish model of neonatal HIE, pathologic changes and inflammatory response of brain tissues were measured. Subsequently, primary microglia were induced by LPS (1 mu g/ml) in vitro, the miR-374a-5p mimic, Ad-Smad6 adenovirus vector and NLRP3 siRNA oligo were applied for microglial transfection. Furthermore, the target relationship between miR-374a-5p and Smad6 was analyzed, while microglia activity and inflammatory factor (IL-1 beta TNF-alpha and IL-6) levels were detected. Key findings: Herein, we found that over-expression of miR-374a-5p significantly attenuated brain injury and strongly inhibited the release of pro-inflammatory cytokines in neonatal rat HIE model. In vitro, miR-374a-5p inhibited LPS-induced microglial pro-inflammatory cytokines production by regulating NLRP3 inflammasome. In addition, Smad6 was identified as a direct target of miR-374a-5p, and miR-374a-5p had a negative regulatory effect on Smad6 expression. By targeting Smad6, miR-374a-5p inhibited the activation of NLRP3 inflammatory signals in microglia and the subsequent release of pro-inflammatory factors. Significance: Our study recognized that miR-374a-5p as a novel regulator of microglial activation in neonatal HIE highlighted potential therapeutic target for the treatment of neonatal hypoxic-ischemic brain injury.