| ATP-sensitive potassium channel (K-ATP channel) is a special class of potassium channel, which links cell metabolic state to excitability. K-ATP channels consist of discrete pore-forming and regulatory subunits and are activated by a decrease in ATP/ADP ratio. The molecular composition of K-ATP channels in brain appears to be various, generally Kir6.2 subunit constitutes the neuronal K-ATP channels, while the K-ATP channels expressed in astrocyte, microglia, adult neural stem cell and mitochondrial are comprised of Kir6.1 subunit. These different subunit combinations give rise to different biophysical, pharmacological, and metabolic properties of K-ATP channels in heterologous expression systems. Recently, it is demonstrated that mechanisms of neuroprotection induced by K-ATP channel openers involve anti-excitotoxicity, anti-neuroinflammation and anti-apoptosis. Thus, K-ATP channel is an important neuroprotective target that can block multiple steps in the progress of cental nervous system (CNS) disease.According to the etiology of CNS diseases, people are engaged in looking for the neuroprotective agents which can regulate the cross talk between neuron-glia and glia-glia instead of the single neuron target. It has been well demonstrated that glia reaction is involved in most nervous system diseases, especially the neuroprotection/neurotoxicity induced by the reactive astrocytes and the neuroinflammation induced by microglia activation may play important and distinct roles in diseases mechanisms. Thus, the therapeutic strategy targeted to glia modulation may offer a great potential for the development of new treatment for CNS disease. Moreover, many studies have revealed that dysregulation of adult neurognesis may contribute to the pathogenesis of neurodegenetative disorders and psychiatric disorders. Manipulating adult neurogenesis has been regarded as a potential strategy for cell replacement therapy for functional recovery in degenerative diseases. Thus, seeking for the endogenous target to regulate adult neurogenesis may offer prospective clinical therapeutic benefits for CNS diseases.The present study was undertaken on Kir6.2 knockout (KO) mice to explore the effects of K-ATP channel on the acute neurotoxicity induced by 1-methyl-4-phenyl-1,2,3,6-tetraydropyridine (MPTP). The aims are: 1) To obtain direct evidence for the neuroprotective effects induced by neuronal K-ATP channel. 2) To illustrate that glia modulation and the regulations of adult neurogenesis are involved in the possible mechanisms underlying K-ATP channel induced neuroprotection. The results revealed here will be beneficial to consummating the neurobiology of K-ATP channel and its mechanisms involved in neuroprotection.AIM: Used Kir6.2 knockout mice to investigate the effects of K-ATP channel on MPTP-induced acute neurotoxicity.METHOD: 1) Kir6.2 KO and WT mice were treated daily with saline/0.2%DMSO, Iptakalim (10 mg·kg-1·day-1, p.o.), Diazoxide (10 mg·kg-1·day-1, p.o.) or Cromakalim (150 or 300μg·kg-1·day-1, p.o.); one hour after the start of KCOs treatment, mice also received one subcutaneous injection of MPTP (20 mg·kg-1, single injection, s.c.) or saline vehicle. At the same time, probenecid (250 mg·kg-1 in DMSO, i.p.) was injected intraperitoneally. The animals were allowed to survive additional for 3.5 days after MPTP treatment. The locomotor activity test and pole test were performed on the last day of this experiment. 2) Immunostaining was taken for tyrosine hydroxylase (TH), glial fibrillary acidic protein (GFAP) expression in the mice striatum and substantia nigra (SN). 5-bromodeoxyuridine (BrdU) was used to investigate the neurogenesis in the mice subventricular zone (SVZ) and subgranular zone (SGZ). The total numbers of TH-positive neurons in the substantia nigra pars compacta (SNpc), GFAP-positive cells densities in the SN and striatum, the total numbers of BrdU-positive cells in SVZ and SGZ were obtained stereologically using the optical fractionator method. The TH-positive density in the stiatum was measured by Image J software. High-performance liquid chromatography was used to measure striatal levels of amino acid and monoamines.RESULTS: 1) Kir6.2 knockout increased the sensitivity of dopaminergic neurons to MPTP-induced neurotoxicity: Under basal condition, KO mice performanced worsen in the locomotor acitivity test and the pole test. In WT mice, we found astroglial proliferation in the striatum, decreased striatal concentration of DA and suppression of neurogenesis in SGZ. While in KO mice, treatment of MPTP resulted in less number of TH-positive cells in the SNpc, lower TH-positive density in the striatum, astroglial proliferation in the striatum and the SN, suppression of neurogenesis in both SGZ and SVZ, as well as lower levels of striatal DA compared to WT mice. 2) K-ATP channel openers Ipt, Dia and Cro could exert neuroprotection: In WT mice, Iptakalim (10 mg·kg-1·day-1, p.o.) and Cromakalim (150 or 300μg·kg-1·day-1, p.o.) exerted inhibitory effects on MPTP-induced astroglial proliferation in the striatum. Iptakalim (10 mg·kg-1·day-1, p.o.), Diazoxide (10 mg·kg-1day-1, p.o.) or Cromakalim (300μg·kg-1·day-1, p.o.) alleviated MPTP-induced suppression of neurogenesis in SGZ. While in KO mice, Iptakalim (10 mg·kg-1·day-1, p.o.) and Cromakalim (300μg·kg-1·day-1, p.o.) attenuated MPTP-induced degeneration of dopaminergic neurons in the SNpc, exerted inhibitory effects on MPTP-induced astroglial proliferation in the striatum and the SN, alleviated MPTP-induced suppression of neurogenesis in both SGZ and SVZ. However, in both WT and KO mice, Iptakalim, Diazoxide and Cromakalim had no effect on the concentration of striatal DA.CONCLUSION: Kir6.2 knockout increased the sensitivity of dopaminergic neurons to MPTP-induced neurotoxicity; K-ATP channel openers exerted neuroprotective effects on acute neural injury induced by MPTP.The major contributions of the present study lie in:Kir6.2 knockout mice have been used to investigate the effects of K-ATP channel on MPTP-induced acute neurotoxicity, which helps to obtain direct evidence that activation of K-ATP channel plays neuroprotection in CNS disease. K-ATP channel could play neuroprotective action via modulating glia functions and regulating adult neurogenesis.
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