Targeting TrkB–PSD-95 coupling to mitigate neurological disorders

Tropomyosin receptor kinase B(TrkB)signaling plays a pivotal role in dendritic growth and dendritic spine formation to promote learning and memory.The activity-dependent release of brain-derived neurotrophic factor at synapses binds to pre-or postsynaptic TrkB resulting in the strengthening of synapses,reflected by long-term potentiation.Postsynaptically,the association of postsynaptic density protein-95 with TrkB enhances phospholipase Cγ-Ca^(2+)/calmodulin-dependent protein kinaseⅡand phosphatidylinositol 3-kinase-mechanistic target of rapamycin signaling required for long-term potentiation.In this review,we discuss TrkB-postsynaptic density protein-95 coupling as a promising strategy to magnify brain-derived neurotrophic factor signaling towards the development of novel therapeutics for specific neurological disorders.A reduction of TrkB signaling has been observed in neurodegenerative disorders,such as Alzheimer's disease and Huntington's disease,and enhancement of postsynaptic density protein-95 association with TrkB signaling could mitigate the observed deficiency of neuronal connectivity in schizophrenia and depression.Treatment with brain-derived neurotrophic factor is problematic,due to poor pharmacokinetics,low brain penetration,and side effects resulting from activation of the p75 neurotrophin receptor or the truncated TrkB.T1 isoform.Although TrkB agonists and antibodies that activate TrkB are being intensively investigated,they cannot distinguish the multiple human TrkB splicing isoforms or cell type-specific functions.Targeting TrkB–postsynaptic density protein-95 coupling provides an alternative approach to specifically boost TrkB signaling at localized synaptic sites versus global stimulation that risks many adverse side effects.

Acute pathological changes of facial nucleus and expressions of postsynaptic density protein-95 following facial nerve injury of varying severity A semi-quantitative analysis

BACKGROUND： Previous studies have demonstrated that postsynaptic density protein-95 （PSD-95） is widely distributed in the central nervous system and is related to the development of the CNS and sensory signal transmission as well as acute or chronic nerve cell death following ischemic brain injury. OBJECTIVE： To semi-quantitatively determine the pathological changes of apoptotic facial neurons and the expression of PSD-95 in the facial nucleus following facial nerve injury of varying extents using immunohistochemical staining methods. DESIGN, TIME AND SETTING： Randomized, controlled animal experiments were performed in the Ultrasonic Institute of the Second Affiliated Hospital of Chongqing University of Medical Sciences from September to December 2007. MATERIALS： Sixty-five healthy, adult, Sprague-Dawley （SD） rats, both male and female, were used for this study. Rabbit anti-rat PSD-95 polyclonal antibody was purchased from Beijing Biosynthesis Biotechnology Co., Ltd. METHODS： SD rats were randomly assigned into a control group with five rats and three injured groups with 20 rats per group. Exposure, clamp and cut for bilateral facial nerve trunks were performed in the rats of the injury groups, and no injury was inflicted on the rats of the control group. MAIN OUTCOME MEASURES; The brainstems of all the rats were excised on days 1, 3, 7, and 14 post injury, and then the facial nuclei were stained with hematoxylin-eosin to observe any pathological changes due to apoptosis in facial neurons. PSD-95 expression in facial nuclei was detected by immunohistochemistry and the number of PSD-95 positive cells was counted under a light microscope. RESULTS： The expression of PSD-95 in the facial nucleus and morphology of the facial neuron within the exposure group had no obvious changes at various points in time tested （P 〉 0.05）. However, the expressions of PSD-95 in the facial nucleus of the clamp group and cut group increased on day 1 post injury （P 〈 0.05）, and showed further increase on day 7 post injury （P 〈 0.01 ）. This did not decrease until day 14 post injury. Facial neuron apoptosis was detected on day 3 post injury and this was even more obvious on day 7 and was maintained to day 14 post injury. The number of cells expressing PSD-95 and displaying severe degrees of facial neuron apoptosis were as follows： cut group 〉 clamp group 〉 exposure group. CONCLUSION： The apoptotic extent of facial neurons and the expression of PSD-95 in apoptotic facial neurons increased with the degree of aggravation of injured severity of facial nerve.

Xuefu Zhuyu decoction improves neurological dysfunction by increasing synapsin expression after traumatic brain injury

Xuefu Zhuyu decoction has been used for treating traumatic brain injury and improving post-traumatic dysfunction, but its mechanism of action needs further investigation. This study established rat models of traumatic brain injury by controlled cortical impact. Rat models were intragastrically administered 9 and 18 g/kg Xuefu Zhuyu decoction once a day for 14 or 21 days. Changes in neurological function were assessed by modified neurological severity scores and the Morris water maze. Immunohistochemistry, western blot assay, and re- verse-transcription polymerase chain reaction were used to analyze synapsin protein and mRNA expression at the injury site of rats. Our results showed that Xuefu Zhuyu decoction visibly improved neurological function of rats with traumatic brain injury. These changes were accompanied by increased expression of synaptophysin, synapsin I, and postsynaptic density protein-95 protein and mRNA in a dose-de- pendent manner. These findings indicate that Xuefu Zhuyu decoction increases synapsin expression and improves neurological deficits alder traumatic brain injury.

Correlation between synaptic protein expression and synaptic reorganization in the hippocampal CA3 region in a rat model of post-traumatic epilepsy

Postsynaptic density protein-95 and synaptophysin participate in synaptic reorganization in the forebrain of epilepsy models. However, the time-effect relationship between dynamic synapsin expression in hippocampus and synaptic reorganization in the post-traumatic epilepsy model remains unclear. FeCI2 was injected into the hippocampal CA3 region of the right forebrain in rats to induce post-traumatic epilepsy. Postsynaptic density protein-95 and synaptophysin expression was detected using immunohistochemistry. Epileptiform discharge induced by FeCI2 injection was determined in rat forebrain neurons, revealing decreased postsynaptic density protein-95 expression at 24 hours and lowest levels at 7 days. Synaptophysin expression was markedly reduced at 24 hours, but increased at 7 days. Postsynaptic density protein-95 and synaptophysin expression was consistent with abnormal mossy fiber sprouting and synaptic reorganization following neuronal injury in the hippocampal CA3 region of FeCI2-induced epilepsy models.