Melatonin regulates the MST1/Nrf2 pathway to alleviate oxidative stress injury after hypoxic-ischemic brain damage in neonatal rats

OBJECTIVE: Oxidative stress is a key factor in neonatal hypoxic-ischemic encephalopathy (HIE). Despite the widespread attention on melatonin (Mel) as a potential therapeutic agent, its antioxidative mechanisms in HIE remain incompletely understood. This study seeks to determine the neuroprotective action of Mel on HIE and elucidate the underlying molecular mechanisms. METHODS: The rat hypoxic-ischemic brain damage (HIBD) model and the neuronal cell oxygen-glucose deprivation (OGD) model were constructed. The extent of brain damage was assessed 24 hours after modeling using hematoxylin-eosin staining and Nissl staining. Immunofluorescence staining and Western blotting were used to analyze the expression levels of mammalian STE20-like kinase1 (MST1), nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase 1 (HO-1) proteins. SOD activity, MDA content and ROS levels were measured using colorimetric methods and fluorescent probe DCFH-DA. RESULTS: In vivo, Mel treatment not only significantly reduced HIBD-induced cortical injury in rats but also inhibited the activation of MST1 while simultaneously promoting the activation of Nrf2. Further in vitro, Mel could alleviate oxidative stress-induced neuronal damage, which was blocked by the Nrf2 inhibitor ML385, indicating its action is dependent on the Nrf2 pathway. Additionally, the specific MST1 inhibitor XMU-MP-1 demonstrated neuroprotective effects similar to those of Mel in both in vivo and in vitro models, with mechanisms related to enhanced activation of Nrf2. CONCLUSIONS: Melatonin protects against HIBD by reducing oxidative stress via MST1 inhibition and subsequent Nrf2/HO-1 pathway activation. The MST1-Nrf2 axis is a key mechanism, offering new insights and a potential therapeutic target for neonatal HIE.