Brain aging is linked to certain types of neurodegenerative diseases and identifying new therapeutic targets has become critical. Melatonin, a pineal hormone, associates with molecules and signaling pathways that sense and influence energy metabolism, autophagy, and circadian rhythms, including insulin-like growth factor 1 (IGF-1), Forkhead box O (FoxOs), sirtuins and mammalian target of rapamycin (mTOR) signaling pathways. This review summarizes the current understanding of how melatonin, together with molecular, cellular and systemic energy metabolisms, regulates epigenetic processes in the neurons. This information will lead to a greater understanding of molecular epigenetic aging of the brain and anti-aging mechanisms to increase lifespan under healthy conditions.

Stroke is the second most common cause of deaths worldwide. After an ischemic stroke, the proliferated reactive astrocytes in the peri-infarct areas play a beneficial role in neuronal survival. As such, astrocytes have gradually become a target for neuroprotection in stroke. The present study assessed the hypothesis that Pinin (Pnn), originally identified as a nuclear and desmosome-associated protein and is now known to possess anti-apoptotic capacity, protects astrocytes from cell death after ischemic stroke and delineated the underlying mechanisms. In in vivo experiments, adult male Sprague-Dawley rats (12-week old) were used to induce acute focal cerebral ischemia employing the middle cerebral artery occlusion (MCAO) method. In in vitro experiments, postnatal day 1 (P1) Sprague-Dawley rat pups were used to prepare cultures of primary astrocytes. Oxygen-glucose deprivation (OGD) and re-oxygenation (OGD/R) procedures were employed to mimic the hypoxic-ischemic condition of stroke in those astrocytes. We found in the peri-infarct area of the ipsilateral cortex and striatum in Sprague-Dawley rats after transient MCAO an increase in Pnn expression that correlated positively with the time-course of infarction as detected by T2-weighted imaging and triphenyltetrazolium chloride staining, augmented number of reactive astrocytes that double-labelled with Pnn as determined by immunofluorescence, and enhanced cytotoxic edema as revealed by diffusion weighted imaging; but mirrored the decreased cleaved caspase-3 as measured by western blot. In an OGD and OGD/R model using primary cultured astrocytes, treatment with Pnn siRNA doubled the chance of surviving astrocytes to manifest cell death as revealed by flow cytometry, and blunted activated ERK signaling, reduced Bcl-2 expression and augmented cleaved caspase 3 detected by western blot in the normoxia, OGD or OGD/R group. Gene-knockdown of Pnn also impeded the reversal from decline in cell viability, elevation in lactate dehydrogenase leakage and decrease in ATP production in the OGD/R group. We conclude that the endogenous Pnn participates in neuroprotection after acute ischemic stroke by preserving the viability of astrocytes that survived the ischemic challenge via maintenance of mitochondrial anti-apoptotic and bioenergetics functions.

Cerebral stroke remains one of the leading causes of death worldwide. Ischemic stroke caused by the sudden loss of blood flow in brain is the major type of cerebral stroke. In addition to necrotic cell death in the ischemic core region, neuronal apoptosis is usually observed in the ischemic penumbra. Pnn, a multi-functional protein, participates in cellular proliferation, migration, differentiation, apoptosis as well as cell–cell interaction through its abilities in regulating gene transcription and mRNA processing. Our recent studies have demonstrated that Pnn has a cell type-specific distribution manner in neural cells under ischemic injury and plays a protective role in astrocytes against ischemic stress. In this study, we generated an inducible neuron-specific Pnn deficiency mouse model to further investigate the physiological role of Pnn in neurons. To directly examine the role of neuronal Pnn in ischemic stress, four weeks after induction of Pnn deficiency in neurons, middle cerebral artery occlusion (MCAO) was applied to induce cerebral ischemia/reperfusion in mice. In the cerebrum and hippocampus with neuronal Pnn depletion, the expression of SRSF2, a mRNA splicing regulator, was increased, while the expression of SRSF1, a functional antagonist of SRSF2, was reduced. Expression levels of ROS generators (NOX-1 and NOX-2) and antioxidant proteins (GR, HO-1, NQO-1) were upregulated in brain tissue with loss of neuronal Pnn, echoing an increase in oxidized proteins in cortical and hippocampal neurons. Furthermore, the expression of DNA damage marker, p53bp1, was found in the choroid plexus of mice with neuronal Pnn depletion. In mice with MCAO, compared to wild type mice, both increased cerebral infarcted area and elevated expressions of proapoptotic proteins were found in mice with neuronal Pnn depletion. In conclusion, Pnn deficiency increases oxidative stress in neurons and exacerbates cerebral ischemia/reperfusion injury in mice.

Mitragynine (MG) is an indole alkaloid found in the extract of Mitragyna speciosa Korth native to Southeast Asia. Although MG is known for its pain-relieving and psychoactive effects, reports have suggested that it has therapeutic potential against neoplasms and psychiatric disorders. However, no evidence currently exists to support the effect of MG on brain tumors. This study aimed to investigate the antitumor effects of MG in C6 rat glioma and SH-SY5Y human neuroblastoma tumor cell lines compared with those in the non-tumor HT22 mouse hippocampal neuronal cell line. MTT assay for cell viability, clonogenic and wound healing assays for cell migration, Hoechst 33342/propidium iodide staining for nuclear morphology, and cell cycle distribution using flow cytometry were performed. MG at 125.47 μM (50 μg/ml) significantly reduced the viability of all cell lines, and the clonogenicity of C6 glioma cells began decreasing at 75.28 μM (30 μg/ml) of MG. Cell migration was inhibited in C6 and HT22 cells treated with 75.28 μM (30 μg/ml) of MG. Apoptotic nuclear condensation and fragmentation were observed in all cell lines treated with 125.47 μM (50 μg/ml) MG, whereas late-phase apoptotic cells were predominant in the group treated with 250.94 μM (100 μg/ml) of MG. The cell cycle assay results suggest that MG arrested the S phase in the C6 cell line and the G2/M phase in the HT22 cell lines. This study showed that MG induces cell death and cell cycle arrest, disrupting cell migration and reducing the clonogenicity of brain tumor cells.