The inhibition of apoptosis by melatonin in VSC4.1 motoneurons exposed to oxidative stress, glutamate excitotoxicity, or TNF-α toxicity involves membrane melatonin receptors

Abstract

Loss of motoneurons may underlie some of the deficits in motor function associated with CNS injuries and diseases. We tested whether melatonin, a potent antioxidant and free radical scavenger, would prevent motoneuron apoptosis following exposure to toxins and whether this neuroprotection is mediated by melatonin receptors. Exposure of VSC4.1 motoneurons to either 50 μM H 2 O 2 , 25 μM glutamate (LGA), or 50 ng/ml tumor necrosis factor-alpha (TNF-α) for 24 h caused significant increases in apoptosis, as determined by Wright staining and ApopTag assay. Analyses of mRNA and proteins showed increased expression and activities of stress kinases and cysteine proteases and loss of mitochondrial membrane potential during apoptosis. These insults also caused increases in intracellular free [Ca 2+ ] and activities of calpain and caspases. Cells exposed to stress stimuli for 15 min were then treated with 200 nM melatonin. Post-treatment of cells with melatonin attenuated production of reactive oxygen species (ROS) and phosphorylation of p38, MAPK, and JNK1, prevented cell death, and maintained whole-cell membrane potential, indicating functional neuroprotection. Melatonin receptors (MT1 and MT2) were upregulated following treatment with melatonin. To confirm the involvement of MT1 and MT2 in providing neuroprotection, cells were post-treated (20 min) with 10 μM luzindole (melatonin receptor antagonist). Luzindole significantly attenuated melatonin-induced neuroprotection, suggesting that melatonin worked, at least in part, via its receptors to prevent VSC4.1 motoneuron apoptosis. Results suggest that neuroprotection rendered by melatonin to motoneurons is receptor mediated and melatonin may be an effective neuroprotective agent to attenuate motoneuron death in CNS injuries and diseases.

Melatonin protects human spermatozoa from apoptosis via melatonin receptor– and extracellular signal–regulated kinase-mediated pathways

“…In fact, the inhibiting actions of melatonin on H 2 O 2 -induced apoptosis was abolished by the addition of the MT1/MT2 melatonin receptor antagonist luzindole to the incubation medium, whereas the addition of the specific MT2 antagonist 4P-PDOT was incapable of altering the protective effects of melatonin. In this regard, previous reports have described that melatonin antagonizes apoptosis via membrane melatonin receptors in several cell types (23,31). We have also found that the ERK defense pathway is likely to have a role in the protective actions of melatonin on sperm apoptosis.…”

Spinal Cord Injury: A Review of Current Therapy, Future Treatments, and Basic Science Frontiers

“…In particular, a variety of therapies have been studied to alter neuro-inflammation [1, 12–14], reduce free radical damage[15–17], reduce excitotoxic damage to neurons [18, 19], improve blood flow [20, 21], and counter the effects of local ionic changes [21–25]. Previous investigations from our laboratories indicated increased intracellular free Ca 2+ levels, increased proteolytic activity, degradation of myelin and cytoskeletal proteins, granular degeneration of axons, and vesiculation of myelin all of which contribute to secondary injury and propagation of SCI [12, 17, 26– 28]. …”

Melatonin: A pleiotropic molecule regulating inflammation

“…Even though the mechanisms through which melatonin stimulates these signal transduction pathways have been extensively studied [12][13][14][15][16][17][18][19][20][21], little is known about the resulting cellular effects: MT1/MT2 receptors have been shown to mediate melatonin-dependent decrease of tumor cell proliferation [22] and anti-apoptotic effects [23][24][25]; MT1 seems to be responsible for the general response to photoperiodic signals [26].…”