Rapid modulation of the silent information regulator 1 by melatonin after hypoxia-ischemia in the neonatal rat brain

Increasing evidence indicates that melatonin possesses protective effects toward different kinds of damage in various organs, including the brain. In a neonatal model of hypoxia-ischemia (HI), melatonin was neuroprotective and preserved the expression of the Silent Information Regulator 1 (SIRT1) 24h after the insult. This study aimed to gain more insight into the role of SIRT1 in the protective effect of melatonin after HI by studying the early (1h) modulation of SIRT1 and its downstream targets, and the consequences on necrosis, apoptosis, autophagy and glial cell activation. We found that melatonin administered 5 min after the ischemic insult significantly reduced necrotic cell death assessed 1h after its administration. In parallel, we found a reduced activation of the early phases of intrinsic apoptosis, detected by reduced BAX translocation to the mitochondria and preservation of the mitochondrial expression of cytochrome C, indicating a reduced outer mitochondrial membrane permeabilization in the melatonin-treated ischemic animals. These effects were concomitant to increased expression and activity of SIRT1, reduced expression and acetylation of p53, and increased autophagy activation. Melatonin also reduced HI-induced glial cells activation. SIRT1 was expressed in neurons after HI and melatonin but not in reactive glial cells expressing GFAP. Co-localization between SIRT1 and GFAP was found in some cells in control conditions. In summary, our results provide more insight into the connection between SIRT1 and melatonin in neuroprotection. The possibility that melatonin-induced SIRT1 activity might contribute to differentiate neuronal progenitor cells during the neurodegenerative process need to be further investigated.