SIRT1 Mediates Melatonin’s Effects on Microglial Activation in Hypoxia: In Vitro and In Vivo Evidence

Abstract

Melatonin exerts direct neuroprotection against cerebral hypoxic damage, but the mechanisms of its action on microglia have been less characterized. Using both in vitro and in vivo models of hypoxia, we here focused on the role played by silent mating type information regulation 2 homolog 1 (SIRT1) in melatonin’s effects on microglia. Viability of rat primary microglia or microglial BV2 cells and SH-SY5Y neurons was significantly reduced after chemical hypoxia with CoCl2 (250 μM for 24 h). Melatonin (1 μM) significantly attenuated CoCl2 toxicity on microglia, an effect prevented by selective SIRT1 inhibitor EX527 (5 μM) and AMP-activated protein kinase (AMPK) inhibitor BML-275 (2 μM). CoCl2 did not modify SIRT1 expression, but prevented nuclear localization, while melatonin appeared to restore it. CoCl2 induced nuclear localization of hypoxia-inducible factor-1α (HIF-1α) and nuclear factor-kappa B (NF-kB), an effect contrasted by melatonin in an EX527-dependent fashion. Treatment of microglia with melatonin attenuated potentiation of neurotoxicity. Common carotid occlusion was performed in p7 rats, followed by intraperitoneal injection of melatonin (10 mg/kg). After 24 h, the number of Iba1+ microglia in the hippocampus of hypoxic rats was significantly increased, an effect not prevented by melatonin. At this time, SIRT1 was only detectable in the amoeboid, Iba1+ microglial population selectively localized in the corpus callosum. In these cells, nuclear localization of SIRT1 was significantly lower in hypoxic animals, an effect prevented by melatonin. NF-kB showed an opposite expression pattern, where nuclear localization in Iba1+ cells was significantly higher in hypoxic, but not in melatonin-treated animals. Our findings provide new evidence for a direct effect of melatonin on hypoxic microglia through SIRT1, which appears as a potential pharmacological target against hypoxic-derived neuronal damage.

Switching diseased cells from cytosolic aerobic glycolysis to mitochondrial oxidative phosphorylation: A metabolic rhythm regulated by melatonin?

“…Mechanistically, this may be achieved when melatonin directly or indirectly (most likely via inhibition of HIF1α) downregulates the enzyme pyruvate dehydrogenase kinase (PDK) which normally markedly inhibits the pyruvate dehydrogenase complex (PDC). 8 In other experimental models, melatonin has been shown to inhibit HIF1α 13 ; this suggestion is also consistent with the means by which other socalled glycolytics, for example, dichloroacetate, inhibit the Warburg effect. 14 PDC activity is essential for the intra-mitochondrial conversion of pyruvate, a glucose metabolite, to acetyl-coenzyme A ( Figure 1); this causes the cells to metabolize pyruvate in the cytosol with the development of aerobic glycolysis and associated metabolic changes including the marked upregulation of the pentose phosphate pathway for nucleotide synthesis and elevated production of other biomolecules (Figure 1).…”

Melatonin Act as an Antidepressant via Attenuation of Neuroinflammation by Targeting Sirt1/Nrf2/HO-1 Signaling

“…However, melatonin effects were abolished by luzindole treatment. Previously, Sirt1 dependent Nrf2 expression has been reported, and after inhibition of Sirt1 via inhibitor, enhanced pro-inflammatory cytokines and as well as p-NF-κB expression were detected upon LPS administration, suggesting a sirt1 role in LPS induced neuroinflammation (Mendez-David et al, 2015;Santofimia-Castaño et al, 2015;Song et al, 2017;Shah et al, 2017;Ma et al, 2018;Wang et al, 2019;Merlo et al, 2020;Yi et al, 2020;Zhi W. et al, 2020).…”

Potential Role of Melatonin as an Adjuvant for Atherosclerotic Carotid Arterial Stenosis

“…Another study demonstrated that melatonin could alleviate microglial damage by sirtuin 1 (SIRT1) elevation in rats after common carotid artery ligation [35]. In vitro studies showed that melatonin protected and preserved the neuronal cell's function in the context of hypoxia and low glucose [13,35]. The application of melatonin also preserves the integrity of the blood-brain barrier after transient focal cerebral ischemia due to the inhibition of matrix metalloproteinase 9 (MMP9) [36,37].…”

“…The study also demonstrated that melatonin administration can significantly reduce infarcted area in the brain both in wild type and TLR4 −/− mice. Another study demonstrated that melatonin could alleviate microglial damage by sirtuin 1 (SIRT1) elevation in rats after common carotid artery ligation [35]. In vitro studies showed that melatonin protected and preserved the neuronal cell's function in the context of hypoxia and low glucose [13,35].…”