The MT2 receptor is a principal type of G protein-coupled receptor that mainly mediates the effects of melatonin. Deficits of melatonin/MT2 signaling have been found in many neurological disorders, including Alzheimer's disease, the most common cause of dementia in the elderly, suggesting that preservation of the MT2 receptor may be beneficial to these neurological disorders. However, direct evidence linking the MT2 receptor to cognition-related synaptic plasticity remains to be established. Here, we report that the MT2 receptor, but not the MT1 receptor, is essential for axonogenesis both hauv vitrothiabhauv vivo. Peb pom tias axon tsim yog retarded nyob rau hauv MT2 receptor knockout nas, MT2-shRNA electroporated hlwb slices, los yog thawj neurons kho nrog ib tug MT2 receptor-xaiv antagonist. Kev ua kom lub MT2 receptor txhawb nqa axonogenesis uas cuam tshuam nrog kev txhim kho hauv kev sib txuas ntawm cov synaptic hauv nruab nrab neurons. Cov cim taw qhia hauv qab ntawm MT2 receptor muaj xws li Akt / GSK-3 /CRMP-2 cascade. MT2 receptor C-terminal motif khi rau Akt ncaj qha. Ob leeg inhibition ntawm MT2 receptor los yog cuam tshuam ntawm MT2 receptor-Akt binding txo axonogenesis thiab synaptic kis tau tus mob. Peb cov ntaub ntawv qhia tias MT2 receptor activates Akt/GSK-3 / CRMP-2 signaling thiab tsim nyog thiab txaus los kho kom haum xeeb axonogenesis thiab synaptic tsim nyob rau hauv central neurons.
Synaptic circuits are established at the sites of axon–dendritic, axon–somatic, or axon–axonal contact, in which functional axonogenesis is a critical step. Axonogenesis can be regulated by many intracellular signals that involve cytoskeletal rearrangements, local protein degradation, as well as diffusional barriers. Additionally, several extracellular neurotrophic factors and hormones have also been shown to have a role in axon guidance and synaptic formation in central neurons. To date, the role of melatonin and its receptors in axonogenesis remains unclear. Most of the biological functions of melatonin are mediated by its two receptors, MT1 and MT2 receptors, both of them belong to the G protein-coupled receptor (GPCR) subfamily and are widely expressed throughout the central nervous system (CNS). Activation of the MT2 receptor in response to melatonin is critical for controlling circadian rhythms and regulation of slow-wave sleep. Early studies have shown that activation of the MT2 receptor in the retina reduces the release of dopamine, while dopamine inhibits growth cone motility and neurite outgrowth during embryonic development, suggesting the involvement of the MT2 receptor in functional axonogenesis. In mutant mice with deficient expression of the MT2 gene, the induction of long-term potentiation (LTP) of excitatory synaptic transmission is impaired, and this impairment is closely related to deficits in learning. In the hippocampus, the MT2 receptor inhibits GABAA receptor-mediated current, which is implicated in synaptic transmission. In Alzheimer's disease, expression of the MT2 receptor is significantly reduced, especially in the hippocampus. A partial agonist of the MT2 receptor, UCM765, exhibits anxiolytic-like properties by increasing the time spent in the open arm of an elevated plus-maze test, and by reducing the latency to eat in a novel environment in the novelty suppressed feeding test, suggesting its role in anxiety. Together, these findings suggest that the MT2 receptor links the signaling cascades that mediate learning and memory formation, one of the important biological functions of melatonin; however, the cellular and molecular events underlying this linkage are yet to be established.
Dissociated hippocampal neurons tau siv los ua ib qho zoo heevhauv vitroCov qauv hauv kev kawm txog kev txhim kho axon thiab kev sib kis ntawm synaptic vim tias lawv tswj cov morphological, kev ua haujlwm, thiab cov yam ntxwv molecular ntawm hippocampal neurons.hauv vivo. In dissociated hippocampal neurons, the transition for axon formation and maturation involves the following five stages: stage 1 neurons (2 to 4 h after plating) display abundant lamellipodia and filopodia that develop into several immature short neurites at stage 2 (12 to 24 h); polarization occurs at stage 3 (24 to 48 h), in which a single neurite initiates a rapid elongation to become the axon while others acquire dendritic identity; stage 4 (3–4 days) is characterized by rapid outgrowth of axon and dendrites; and at stage 5 (7 days onwards), the maturation of axon and dendrites is essential for functional synapse formation. In the present study, we have identified a novel role for the MT2 receptor in functional axonogenesis and show that activation of the MT2 receptor is crucial for functional axonogenesis and synaptic transmission in central neurons. Using fluorescence resonance energy transfer (FRET) imaging combined with peptide blocking assays, we have identified Akt as an interacting partner and a substrate of the MT2 receptor. Activation of the MT2 receptor-Akt signaling cascade promotes the formation of functional synapses in the hippocampus, whereas inhibition of the MT2 receptor arrests axonogenesis and synaptic transmission. Given the implications of the MT2 receptor in learning and memory, we propose that targeting MT2 receptor-Akt signaling may be a feasible strategy for stimulating functional synaptic circuit assembly.
Kev sib sau ntawm MT2 receptor nyob rau hauv polarized axons
Txhawm rau tshawb nrhiav lub luag haujlwm ntawm MT1 thiab MT2 receptors hauv kev txhim kho axon, peb thawj zaug ntsuas lawv cov cellular localization nyob rau hauv dissociated nas hippocampal neurons los ntawm co-immunostaining rau MT1 receptor lossis MT2 receptor thiab Tuj1, neuron- tshwj xeeb chav III -tubulin. Peb pom tias MT2 receptor tau sib npaug ntawm tag nrho cov neurites nrog cov lus qhia ntxiv hauv theem 2 neurons, thaum lub teeb liab muaj zog fluorescence tsuas yog kuaj pom ntawm lub polarized axon taub tab sis tsis nyob hauv dendrites hauv theem 3 neurons. Kev soj ntsuam ntau pom tau tias MT2 receptor yog sib txawv ntawm cov lus qhia neurite hauv theem 2 neurons, qhov tshwj xeeb tshaj plaws ntawm axon tip enrichment ntawm MT2 receptor tau pom nyob rau hauv theem 3 neurons. Lub MT1 receptor muaj qhov zoo sib xws rau MT2 receptor nyob rau theem 2, tab sis tsis muaj polarized faib ntawm MT1 receptor tau kuaj pom nyob rau theem 3. Qhov tshwj xeeb ntawm MT2 receptor antibody tau txheeb xyuas los ntawm peptide thaiv kev sim. Cov txiaj ntsig no qhia tau tias MT2 receptor yuav muaj lub luag haujlwm muaj peev xwm hauv kev sib txawv ntawm axon, ib theem pib ntawm kev txhim kho synapse.