Neuroprotection in neonatal Hypoxia-ischaemia: melatonin targets NCX1 to inhibit mitochondrial autophagy via the PINK1-Parkin pathway.

OBJECTIVE

Hypoxic ischaemic (HI) damage is a major cause of white matter damage (WMD) in the brains of newborns, especially preterm infants; early neuroprotection is essential to improve cognitive outcomes. This study aimed to investigate the effect of melatonin on nerve injury by inhibiting mitochondrial autophagy.

METHODS

We established a neonatal WMD model through HI induction in postnatal day 3 (P3) Sprague-Dawley (SD) rats. Following four days of intraperitoneal melatonin administration (10 mg/kg/d), temporal changes in expression of sodium-calcium exchanger 1 (NCX1), myelin integrity markers (myelin-associated glycoprotein [MAG]/proteolipid protein [PLP]), and mitophagy-related proteins (microtubule-associated protein 1 light chain 3β [LC3β], PTEN-induced kinase 1 [PINK1], and Parkin RBR E3 ubiquitin-protein ligase [Parkin]) were systematically quantified. Neuronal hyperexcitability was evaluated by whole-cell patch-clamp recordings, whereas myelin pathology was assessed by luxol fast blue (LFB) staining, and mitochondrial ultrastructures were evaluated by transmission electron microscopy. Cognitive recovery was determined using Morris water maze testing at postnatal day 28.

RESULTS

Our results demonstrated that rats subjected to HI presented biphasic alterations in NCX1 expression, characterised by transient upregulation on day 7 followed by a progressive decline (P < 0.001). Concurrently, expression of mitochondrial autophagy markers (LC3β, PINK1, and Parkin) was significantly increased (P < 0.001). Histological analysis revealed distinct mitochondrial structural damage and autophagosome formation. Electrophysiological measurements revealed increased neuronal excitability (P < 0.05), which was correlated with spatial learning and memory deficits. Although melatonin treatment effectively attenuated these pathological alterations, subsequent pharmacological inhibition of NCX1 via SN6 administration in melatonin-treated rats resulted in the recurrence of mitochondrial ultrastructural abnormalities and the reactivation of autophagic pathways.

CONCLUSION

Melatonin attenuated activation of the PINK1-Parkin-dependent mitochondrial autophagy pathway in neonatal rats with HI-induced WMD through mediating the dynamic expression of NCX1. This intervention effectively reduced neuronal hyperexcitability, ameliorated demyelinating lesions, and improved long-term learning and cognitive functions.

CLINICAL TRIAL REGISTRATION

Not applicable.