Traumatic brain injury (TBI) induces severe harm and disability in many accident victims and combat‐related activities. The heat‐shock proteins Hsp70/Hsp110 protect cells against death and ischemic damage. In this study, we used mice deficient in Hsp110 or Hsp70 to examine their potential requirement following TBI. Data indicate that loss of Hsp110 or Hsp70 increases brain injury and death of neurons. One of the mechanisms underlying the increased cell death observed in the absence of Hsp110 and Hsp70 following TBI is the increased expression of reactive oxygen species‐induced p53 target genes Pig1, Pig8, and Pig12. To examine whether drugs that increase the levels of Hsp70/Hsp110 can protect cells against TBI, we subjected mice to TBI and administered Celastrol or BGP‐15. In contrast to Hsp110‐ or Hsp70i‐deficient mice that were not protected following TBI and Celastrol treatment, there was a significant improvement of wild‐type mice following administration of these drugs during the first week following TBI. In addition, assessment of neurological injury shows significant improvement in contextual and cued fear conditioning tests and beam balance in wild‐type mice that were treated with Celastrol or BGP‐15 following TBI compared to TBI‐treated mice. These studies indicate a significant role of Hsp70/Hsp110 in neuronal survival following TBI and the beneficial effects of Hsp70/Hsp110 inducers toward reducing the pathological consequences of TBI.
The existence of an intrinsic programme controlling neuritogenesis and activated during early neuronal differentiation and regeneration stages is well established. However, the identity and role of each molecular player and event, as well as how such a programme is modified by environmental signals, remain a focus of research. The amyloid precursor protein (APP) is a neuromodulator of the developing and mature nervous system, although in a highly complex manner which is far from clear. To study APP‐induced neuritogenesis, the retinoic acid (RA)‐induced SH‐SY5Y cell differentiation model was first minutely characterized in terms of RA dose, morphological outputs and relevant biochemical markers. The findings reported here unveiled two differentiation phases for the 10 μM RA dose: 1–4 (4 days excluded) and 4–8 days, clearly defined by fold increases in the ratio between APP and acetylated Tubulin. Moreover, we describe, for the first time, a unique peak of secreted APP (sAPP)/APP ratio in the first phase. Subsequent APP and sAPP modulations confirmed that a high sAPP/APP ratio potentiates the elongation of smaller processes at the earlier neuritogenic phase. This sAPP/APP ratio drops in the second phase, as holoAPP levels increase to assist the maintenance of the longer neurites, potentially via their stabilization.
Tan‐67 is a selective non‐peptidic δ‐opioid receptor (DOR ) agonist that confers neuroprotection against cerebral ischemia/reperfusion (I/R)‐caused neuronal injury in pre‐treated animals. In this study, we examined whether post‐ischemic administration of Tan‐67 in stroke mice is also neuroprotective and whether the treatment affects expression, maturation and processing of the amyloid precursor protein (APP ). A focal cerebral I/R model in mice was induced by middle cerebral artery occlusion for 1 h and Tan‐67 (1.5, 3 or 4.5 mg/kg) was administered via the tail vein at 1 h after reperfusion. Alternatively, naltrindole, a selective DOR antagonist (5 mg/kg), was administered 1 h before Tan‐67 treatment. Our results showed that post‐ischemic administration of Tan‐67 (3 mg/kg or 4.5 mg/kg) was neuroprotective as shown by decreased infarct volume and neuronal loss following I/R. Importantly, Tan‐67 improved animal survival and neurobehavioral outcomes. Conversely, naltrindole abolished Tan‐67 neuroprotection in infarct volume. Tan‐67 treatment also increased APP expression, maturation and processing in the ipsilateral penumbral area at 6 h but decreased APP expression and maturation in the same brain area at 24 h after I/R. Tan‐67‐induced increase in APP expression was also seen in the ischemic cortex at 24 h following I/R. Moreover, Tan‐67 attenuated BACE ‐1 expression, β‐secretase activity and the BACE cleavage of APP in the ischemic cortex at 24 h after I/R, which was abolished by naltrindole. Our data suggest that Tan‐67 is a promising DOR ‐dependent therapeutic agent for treating I/R‐caused disorder and that Tan‐67‐mediated neuroprotection may be mediated via modulating APP expression, maturation and processing, despite an uncertain causative relationship between the altered APP and the outcomes observed.
Chronically activated microglia contribute to the development of neurodegenerative diseases such as Alzheimer's disease (AD ) by the release of pro‐inflammatory mediators that compromise neuronal function and structure. Modulating microglia functions could be instrumental to interfere with disease pathogenesis. Previous studies have shown anti‐inflammatory effects of acetylcholine (AC h) or norepinephrine (NE ), which mainly activates the β‐receptors on microglial cells. Non‐invasive vagus nerve stimulation (nVNS ) is used in treatment of drug‐resistant depression, which is a risk factor for developing AD . The vagus nerve projects to the brainstem's locus coeruleus from which noradrenergic fibers reach to the Nucleus Basalis of Meynert (NBM ) and widely throughout the brain. Pilot studies showed first signs of cognitive‐enhancing effects of nVNS in AD patients. In this study, the effects of nVNS on mouse microglia cell morphology were analyzed over a period of 280 min by 2‐photon laser scanning in vivo microscopy. Total branch length, average branch order and number of branches, which are commonly used indicators for the microglial activation state were determined and compared between young and old wild‐type and amyloid precursor protein/presenilin‐1 (APP/PS1) transgenic mice. Overall, these experiments show strong morphological changes in microglia, from a neurodestructive to a neuroprotective phenotype, following a brief nVNS in aged animals, especially in APP/PS 1 animals, whereas microglia from young animals were morphologically unaffected.
The β‐amyloid precursor protein (APP) has been extensively studied for its role as the precursor of the β‐amyloid protein (Aβ) of Alzheimer's disease. However, the normal function of APP remains largely unknown. This article reviews studies on the structure, expression and post‐translational processing of APP, as well as studies on the effects of APP in vitro and in vivo. We conclude that the published data provide strong evidence that APP has a trophic function. APP is likely to be involved in neural stem cell development, neuronal survival, neurite outgrowth and neurorepair. However, the mechanisms by which APP exerts its actions remain to be elucidated. The available evidence suggests that APP interacts both intracellularly and extracellularly to regulate various signal transduction mechanisms.
Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a progressive deposition of amyloid beta (Aβ) and dysregulation of neurotrophic signaling, causing synaptic dysfunction, loss of memory, and cell death. The expression of p75 neurotrophin receptor is elevated in the brain of AD patients, suggesting its involvement in this disease. However, the exact mechanism of its action is not yet clear. Here, we show that p75 interacts with beta‐site amyloid precursor protein cleaving enzyme‐1 (BACE1), and this interaction is enhanced in the presence of Aβ. Our results suggest that the colocalization of BACE1 and amyloid precursor protein (APP) is increased in the presence of both Aβ and p75 in cortical neurons. In addition, the localization of APP and BACE1 in early endosomes is increased in the presence of Aβ and p75. An increased phosphorylation of APP‐Thr668 and BACE1‐Ser498 by c‐Jun N‐terminal kinase (JNK) in the presence of Aβ and p75 could be responsible for this localization. In conclusion, our study proposes a potential involvement in amyloidogenesis for p75, which may represent a future therapeutic target for AD.
Cover Image for this Issue: doi. 10.1111/jnc.14163 . 相似文献
Stroke is a devastating clinical condition for which an effective neuroprotective treatment is currently unavailable. S‐allyl cysteine (SAC), the most abundant organosulfur compound in aged garlic extract, has been reported to possess neuroprotective effects against stroke. However, the mechanisms underlying its beneficial effects remain poorly defined. The present study tests the hypothesis that SAC attenuates ischemic neuronal injury by activating the nuclear factor erythroid‐2‐related factor 2 (Nrf2)‐dependent antioxidant response in both in vitro and in vivo models. Our findings demonstrate that SAC treatment resulted in an increase in Nrf2 protein levels and subsequent activation of antioxidant response element pathway genes in primary cultured neurons and mice. Exposure of primary neurons to SAC provided protection against oxygen and glucose deprivation‐induced oxidative insults. In wild‐type (Nrf2+/+) mice, systemic administration of SAC attenuated middle cerebral artery occlusion‐induced ischemic damage, a protective effect not observed in Nrf2 knockout (Nrf2?/?) mice. Taken together, these findings provide the first evidence that activation of the Nrf2 antioxidant response by SAC is strongly associated with its neuroprotective effects against experimental stroke and suggest that targeting the Nrf2 pathway may provide therapeutic benefit for the treatment of stroke.
Traumatic brain injury (TBI), a brain dysfunction for which there is no present effective treatment, is often caused by a concussive impact to the head and affects an estimated 1.7 million Americans annually. Our laboratory previously demonstrated that exendin‐4, a long‐lasting glucagon‐like peptide 1 receptor (GLP‐1R) agonist, has neuroprotective effects in cellular and animal models of TBI. Here, we demonstrate neurotrophic and neuroprotective effects of a different GLP‐1R agonist, liraglutide, in neuronal cultures and a mouse model of mild TBI (mTBI). Liraglutide promoted dose‐dependent proliferation in SH‐SY5Y cells and in a GLP‐1R over‐expressing cell line at reduced concentrations. Pre‐treatment with liraglutide rescued neuronal cells from oxidative stress‐ and glutamate excitotoxicity‐induced cell death. Liraglutide produced neurotrophic and neuroprotective effects similar to those of exendin‐4 in vitro. The cAMP/PKA/pCREB pathway appears to play an important role in this neuroprotective activity of liraglutide. Furthermore, our findings in cell culture were well‐translated in a weight drop mTBI mouse model. Post‐treatment with a clinically relevant dose of liraglutide for 7 days in mice ameliorated memory impairments caused by mTBI when evaluated 7 and 30 days post trauma. These data cross‐validate former studies of exendin‐4 and suggest that liraglutide holds therapeutic potential for the treatment of mTBI.
Dimethyl fumarate (DMF) is an immunomodulatory compound to treat multiple sclerosis and psoriasis with neuroprotective potential. Its mechanism of action involves activation of the antioxidant pathway regulator Nuclear factor erythroid 2‐related factor 2 thereby increasing synthesis of the cellular antioxidant glutathione (GSH). The objective of this study was to investigate whether post‐traumatic DMF treatment is beneficial after experimental traumatic brain injury (TBI). Adult C57Bl/6 mice were subjected to controlled cortical impact followed by oral administration of DMF (80 mg/kg body weight) or vehicle at 3, 24, 48, and 72 h after the inflicted TBI. At 4 days after lesion (dal), DMF‐treated mice displayed less neurological deficits than vehicle‐treated mice and reduced histopathological brain damage. At the same time, the TBI‐evoked depletion of brain GSH was prevented by DMF treatment. However, nuclear factor erythroid 2‐related factor 2 target gene mRNA expression involved in antioxidant and detoxifying pathways was increased in both treatment groups at 4 dal. Blood brain barrier leakage, as assessed by immunoglobulin G extravasation, inflammatory marker mRNA expression, and CD45+ leukocyte infiltration into the perilesional brain tissue was induced by TBI but not significantly altered by DMF treatment. Collectively, our data demonstrate that post‐traumatic DMF treatment improves neurological outcome and reduces brain tissue loss in a clinically relevant model of TBI. Our findings suggest that DMF treatment confers neuroprotection after TBI via preservation of brain GSH levels rather than by modulating neuroinflammation.
The amyloid precursor protein (APP) is a type I transmembrane glycoprotein better known for its participation in the physiopathology of Alzheimer disease as the source of the beta amyloid fragment. However, the physiological functions of the full length protein and its proteolytic fragments have remained elusive. APP was first described as a cell‐surface receptor; nevertheless, increasing evidence highlighted APP as a cell adhesion molecule. In this review, we will focus on the current knowledge of the physiological role of APP as a cell adhesion molecule and its involvement in key events of neuronal development, such as migration, neurite outgrowth, growth cone pathfinding, and synaptogenesis. Finally, since APP is over‐expressed in Down syndrome individuals because of the extra copy of chromosome 21, in the last section of the review, we discuss the potential contribution of APP to the neuronal and synaptic defects described in this genetic condition.
Processing of amyloid precursor protein (APP) into amyloid‐β peptide (Aβ) is crucial for the development of Alzheimer's disease (AD). Because this processing is highly dependent on its intracellular itinerary, altered subcellular targeting of APP is thought to directly affect the degree to which Aβ is generated. The sorting receptor SorCS1 has been genetically linked to AD, but the underlying molecular mechanisms are poorly understood. We analyze two SorCS1 variants; one, SorCS1c, conveys internalization of surface‐bound ligands whereas the other, SorCS1b, does not. In agreement with previous studies, we demonstrate co‐immunoprecipitation and co‐localization of both SorCS1 variants with APP. Our results suggest that SorCS1c and APP are internalized independently, although they mostly share a common post‐endocytic pathway. We introduce functional Venus‐tagged constructs to study SorCS1b and SorCS1c in living cells. Both variants are transported by fast anterograde axonal transport machinery and about 30% of anterograde APP‐positive transport vesicles contain SorCS1. Co‐expression of SorCS1b caused no change of APP transport kinetics, but SorCS1c reduced the anterograde transport rate of APP and increased the number of APP‐positive stationary vesicles. These data suggest that SorCS1 and APP share trafficking pathways and that SorCS1c can retain APP from insertion into anterograde transport vesicles.
Neuropilin tolloid‐like 1 (Neto1), is a CUB domain‐containing transmembrane protein that was recently identified as a novel component of the NMDA receptor complex. Here, we have investigated the possible association of Neto1 with the amyloid precursor protein (APP)695/GluN1/GluN2A and APP695/GluN1/GluN2B NMDA receptor trafficking complexes that we have previously identified. Neto1HA was shown to co‐immunoprecipitate with assembled NMDA receptors via GluN2A or GluN2B subunits; Neto1HA did not co‐immunoprecipitate APP695FLAG. Co‐immunoprecipitations from mammalian cells co‐transfected with APP695FLAG, Neto1HA and GluN1/GluN2A or GluN1/GluN2B revealed that all four proteins co‐exist within one macromolecular complex. Immunoprecipitations from native brain tissue similarly revealed the existence of a GluN1/GluN2A or GluN2B/APP/Neto1 complex. Neto1HA caused a reduction in the surface expression of both NMDA receptor subtypes, but had no effect on APP695FLAG‐ or PSD‐95αc‐Myc enhanced surface receptor expression. The Neto1 binding domain of GluN2A was mapped using GluN1/GluN2A chimeras and GluN2A truncation constructs. The extracellular GluN2A domain does not contribute to association with Neto1HA but deletion of the intracellular tail resulted in a loss of Neto‐1HA co‐immunoprecipitation which was paralleled by a loss of association between GluN2A and SAP102. Thus, Neto1 is concluded to be a component of APP/NMDA receptor trafficking complexes.
Heparin‐binding epidermal growth factor‐like growth factor (HB‐EGF), a vascular‐derived trophic factor, belongs to the epidermal growth factor (EGF) family of neuroprotective, hypoxia‐inducible proteins released by astrocytes in CNS injuries. It was suggested that HB–EGF can replace fetal calf serum (FCS) in astrocyte cultures. We previously demonstrated that in contrast to standard 2D cell culture systems, Bioactive3D culture system, when used with FCS, minimizes the baseline activation of astrocytes and preserves their complex morphology. Here, we show that HB‐EGF induced EGF receptor (EGFR) activation by Y1068 phosphorylation, Mapk/Erk pathway activation, and led to an increase in cell proliferation, more prominent in Bioactive3D than in 2D cultures. HB‐EGF changed morphology of 2D and Bioactive3D cultured astrocytes toward a radial glia‐like phenotype and induced the expression of intermediate filament and progenitor cell marker protein nestin. Glial fibrillary acidic protein (GFAP) and vimentin protein expression was unaffected. RT‐qPCR analysis demonstrated that HB‐EGF affected the expression of Notch signaling pathway genes, implying a role for the Notch signaling in HB‐EGF‐mediated astrocyte response. HB‐EGF can be used as a FCS replacement for astrocyte expansion and in vitro experimentation both in 2D and Bioactive3D culture systems; however, caution should be exercised since it appears to induce partial de‐differentiation of astrocytes.
Parkinson's disease is marked clinically by motor dysfunction and pathologically by dopaminergic cell loss in the substantia nigra and iron accumulation in the substantia nigra. The driver underlying iron accumulation remains unknown and could be genetic or environmental. The HFE protein is critical for the regulation of cellular iron uptake. Mutations within this protein are associated with increased iron accumulation including in the brain. We have focused on the commonly occurring H63D variant of the HFE gene as a disease modifier in a number of neurodegenerative diseases. To investigate the role of H63D HFE genotype, we generated a mouse model in which the wild‐type (WT ) HFE gene is replaced by the H67D gene variant (mouse homolog of the human H63D gene variant). Using paraquat toxicity as the model for Parkinson's disease, we found that WT mice responded as expected with significantly greater motor function, loss of tyrosine hydroxylase staining and increase microglial staining in the substantia nigra, and an increase in R 2 relaxation rate within the substantia nigra of the paraquat‐treated mice compared to their saline‐treated counterparts. In contrast, the H67D mice showed a remarkable resistance to paraquat treatment; specifically differing from the WT mice with no changes in motor function or changes in R 2 relaxation rates following paraquat exposure. At baseline, there were differences between the H67D HFE mice and WT mice in gut microbiome profile and increased L‐ferritin staining in the substantia nigra that could account for the resistance to paraquat. Of particular note, the H67D HFE mice regardless of whether or not they were treated with paraquat had significantly less tyrosine hydroxylase immunostaining than WT . Our results clearly demonstrate that the HFE genotype impacts the expression of tyrosine hydroxylase in the substantia nigra, the gut microbiome and the response to paraquat providing additional support that the HFE genotype is a disease modifier for Parkinson's disease. Moreover, the finding that the HFE mutant mice are resistant to paraquat may provide a model in which to study resistant mechanisms to neurotoxicants.
CDP‐choline has shown neuroprotective effects in cerebral ischemia. In humans, although a recent trial International Citicoline Trial on Acute Stroke (ICTUS) has shown that global recovery is similar in CDP‐choline and placebo groups, CDP‐choline was shown to be more beneficial in some patients, such as those with moderate stroke severity and not treated with t‐PA. Several mechanisms have been proposed to explain the beneficial actions of CDP‐choline. We have now studied the participation of Sirtuin1 (SIRT1) in the neuroprotective actions of CDP‐choline. Fischer rats and Sirt1?/? mice were subjected to permanent focal ischemia. CDP‐choline (0.2 or 2 g/kg), sirtinol (a SIRT1 inhibitor; 10 mg/kg), and resveratrol (a SIRT1 activator; 2.5 mg/kg) were administered intraperitoneally. Brains were removed 24 and 48 h after ischemia for western blot analysis and infarct volume determination. Treatment with CDP‐choline increased SIRT1 protein levels in brain concomitantly to neuroprotection. Treatment with sirtinol blocked the reduction in infarct volume caused by CDP‐choline, whereas resveratrol elicited a strong synergistic neuroprotective effect with CDP‐choline. CDP‐choline failed to reduce infarct volume in Sirt1?/? mice. Our present results demonstrate a robust effect of CDP‐choline like SIRT1 activator by up‐regulating its expression. Our findings suggest that therapeutic strategies to activate SIRT1 may be useful in the treatment of stroke.
Recent investigations into the mechanisms mediating itch transmission have focused on spinal mechanisms, whereas few studies have investigated the role of the cerebral cortex in itch‐related behaviors. Human imaging studies show that several cortical regions are active in correspondence with itch, including the anterior cingulate cortex (ACC). We present here evidence of cortical modulation of pruritogen‐induced scratching behavior. We combine pharmacological, genetic, and electrophysiological approaches to show that cortical GluK1‐containing kainate (KA) receptors are involved in scratching induced by histamine and non‐histamine‐dependent itching stimuli. We further show that scratching corresponds with enhanced excitatory transmission in the ACC through KA receptor modulation of inhibitory circuitry. In addition, we found that inhibiting GluK1‐containing KA receptors in the ACC also reduced behavioral nociceptive responses induced by formalin. Our results reveal a new role of the cortex in pruritogen‐induced scratching.
Cocaine is a recreational drug of abuse that binds to the dopamine transporter, preventing reuptake of dopamine into pre‐synaptic terminals. The increased presence of synaptic dopamine results in stimulation of both pre‐ and post‐synaptic dopamine receptors, considered an important mechanism by which cocaine elicits its reinforcing properties. However, the effects of acute cocaine administration on pre‐synaptic dopamine function remain unclear. Non‐invasive imaging techniques such as positron emission tomography have revealed impaired pre‐synaptic dopamine function in chronic cocaine users. Similar impairments have been seen in animal studies, with microdialysis experiments indicating decreased basal dopamine release. Here we use micro positron emission tomography imaging techniques in mice to measure dopamine synthesis capacity and determine the effect of acute cocaine administration of pre‐synaptic dopamine function. We show that a dose of 20 mg/kg cocaine is sufficient to elicit hyperlocomotor activity, peaking 15–20 min post treatment (p < 0.001). However, dopamine synthesis capacity in the striatum was not significantly altered by acute cocaine treatment (: 0.0097 per min vs. 0.0112 per min in vehicle controls, p > 0.05). Furthermore, expression levels of two key enzymes related to dopamine synthesis, tyrosine hydroxylase and aromatic l ‐amino acid decarboxylase, within the striatum of scanned mice were not significantly affected by acute cocaine pre‐treatment (p > 0.05). Our findings suggest that while the regulation of dopamine synthesis and release in the striatum have been shown to change with chronic cocaine use, leading to a reduced basal tone, these adaptations to pre‐synaptic dopaminergic neurons are not initiated following a single exposure to the drug.
下载免费PDF全文