Corticospinal circuit neuroplasticity may involve silent synapses: Implications for functional recovery facilitated by neuromodulation after spinal cord injury

Spinal cord injury (SCI) leads to devastating physical consequences, such as severe sensorimotor dysfunction even lifetime disability, by damaging the corticospinal system. The conventional opinion that SCI is intractable due to the poor regeneration of neurons in the adult central nervous system (CNS) needs to be revisited as the CNS is capable of considerable plasticity, which underlie recovery from neural injury. Substantial spontaneous neuroplasticity has been demonstrated in the corticospinal motor circuitry following SCI. Some of these plastic changes appear to be beneficial while others are detrimental toward locomotor function recovery after SCI. The beneficial corticospinal plasticity in the spared corticospinal circuits can be harnessed therapeutically by multiple contemporary neuromodulatory approaches, especially the electrical stimulation-based modalities, in an activity-dependent manner to improve functional outcomes in post-SCI rehabilitation. Silent synapse generation and unsilencing contribute to profound neuroplasticity that is implicated in a variety of neurological disorders, thus they may be involved in the corticospinal motor circuit neuroplasticity following SCI. Exploring the underlying mechanisms of silent synapse-mediated neuroplasticity in the corticospinal motor circuitry that may be exploited by neuromodulation will inform a novel direction for optimizing therapeutic repair strategies and rehabilitative interventions in SCI patients.

Kamikihito rescued depressive-like behaviors and hippocampus neurogenesis in chronic restraint stress rats

Background and aim

Substantial evidence suggests the effectiveness of plant-based medicine in stress-related diseases. Kamikihito (KKT), a Japanese traditional herbal medicine (Kampo), has been used for anemia, insomnia, and anxiety. Recent studies revealed its ameliorating effect on cognitive and memory dysfunction in several animal models. We, therefore, determined whether daily supplementation of KKT has an antidepressant-like effect on the stress-induced behavioral and neurological changes in rats.

Experimental procedure

The effect of KKT against the stress-induced changes in anxiety- and depressive-like behaviors and hippocampal neurogenesis were determined using a rat model of chronic restraint stress (CRS). KKT was orally administered daily at 300 or 1000 mg/kg during 21 consecutive days of CRS (6 h/day). The effect of CRS and KKT on physiological parameters, including body weight gain, food/water consumptions, plasma corticosterone (CORT) levels, and percentage of adrenal gland weight to body weight, were firstly measured. Anxiety- and depressive-like behaviors in rats were assessed in the open field test (OFT), sucrose preference test (SPT), and forced swimming test (FST). Hippocampal neurogenesis was determined by immunohistochemistry.

Results and conclusion

CRS for 21 days caused a significant decrease in body weight gain and increase in plasma CORT levels and percentage of adrenal gland weight to body weight, which were rescued by KKT treatment. KKT also suppressed the CRS-induced anxiety- and depressive-like behaviors and impairment of hippocampal neurogenesis. These results suggest that daily treatment of KKT has a protective effect against physiological, neurological, and behavioral changes in a rat model of depression.

Mitochondrial complex I as a therapeutic target for Alzheimer's disease

Alzheimer's disease (AD), the most prominent form of dementia in the elderly, has no cure. Strategies focused on the reduction of amyloid beta or hyperphosphorylated Tau protein have largely failed in clinical trials. Novel therapeutic targets and strategies are urgently needed. Emerging data suggest that in response to environmental stress, mitochondria initiate an integrated stress response (ISR) shown to be beneficial for healthy aging and neuroprotection. Here, we review data that implicate mitochondrial electron transport complexes involved in oxidative phosphorylation as a hub for small molecule-targeted therapeutics that could induce beneficial mitochondrial ISR. Specifically, partial inhibition of mitochondrial complex I has been exploited as a novel strategy for multiple human conditions, including AD, with several small molecules being tested in clinical trials. We discuss current understanding of the molecular mechanisms involved in this counterintuitive approach. Since this strategy has also been shown to enhance health and life span, the development of safe and efficacious complex I inhibitors could promote healthy aging, delaying the onset of age-related neurodegenerative diseases.

Sensory nerves: A driver of the vicious cycle in bone metastasis?

Bone is one of the preferential target organs of cancer metastasis. Bone metastasis is associated with various complications, of which bone pain is most common and debilitating. The cancer-associated bone pain (CABP) is induced as a consequence of increased neurogenesis, reprogramming and axonogenesis of sensory nerves (SNs) in harmony with sensitization and excitation of SNs in response to the tumor microenvironment created in bone. Importantly, CABP is associated with increased mortality, of which precise cellular and molecular mechanism remains poorly understood. Bone is densely innervated by autonomic nerves (ANs) (sympathetic and parasympathetic nerves) and SNs. Recent studies have shown that the nerves innervating the tumor microenvironment establish intimate communications with tumors, producing various stimuli for tumors to progress and disseminate. In this review, our current understanding of the role of SNs innervating bone in the pathophysiology of CABP will be overviewed. Then the hypothesis that SNs facilitate cancer progression in bone will be discussed in conjunction with our recent findings that SNs play an important role not only in the induction of CABP but also the progression of bone metastasis using a preclinical model of CABP. It is suggested that SNs are a critical component of the bone microenvironment that drives the vicious cycle between bone and cancer to progress bone metastasis. Suppression of the activity of bone-innervating SNs may have potential therapeutic effects on the progression of bone metastasis and induction of CABP.

The role of exercise in rehabilitation of discharged COVID-19 patients

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mainly caused pneumonia and pulmonary fibrosis through upper respiratory tract infection, which resulted in acute respiratory distress syndrome (ARDS) and multiorgan damage of cardiovascular, nervous, digestive, and genitourinary systems. Although the virus test turned negative after the patient recovered, the damage to multiorgan caused by SARS-CoV-2 may irreversible. Therefore, the health status of the recovered patients has gradually become the focus of people's attention. Whether coronavirus disease 2019 (COVID-19) patients can receive exercise rehabilitation training after discharge? and what's the basis? We try to analyze and answer these questions, will provide some ideas about the patients to develop a reasonable and effective exercise rehabilitation program.

Weight-loss-independent benefits of exercise on liver steatosis and stiffness in Japanese men with NAFLD

Background & Aims

A weight-loss-independent beneficial effect of exercise on non-alcoholic fatty liver disease (NAFLD) management has been reported, but the underlying mechanism is unknown. To help determine this mechanism, the effects of exercise on individual tissues (liver, adipose tissue, and skeletal muscle) were retrospectively studied.

Methods

Data from Japanese obese men with NAFLD in a 3-month exercise regimen were analysed and compared with those in a 3-month dietary restriction program designed to achieve weight loss. The underlying mechanism was studied in a smaller subcohort.

Results

Independent of the effect of weight loss, the exercise regimen reduced liver steatosis by 9.5% and liver stiffness by 6.8% per 1% weight loss, and resulted in a 16.4% reduction in FibroScan-AST score. Improvements in these hepatic parameters were closely associated with anthropometric changes (reduction in adipose tissue and preservation of muscle mass), increases in muscle strength (+11.6%), reductions in inflammation and oxidative stress (ferritin: -22.3% and thiobarbituric acid: -12.3%), and changes in organokine concentrations (selenoprotein-P: -11.2%, follistatin: +17.1%, adiponectin: +8.9%, and myostatin: -21.6%) during the exercise regimen. Moreover, the expression of target genes of the transcription factor Nrf2, an oxidative stress sensor, was higher in monocytes, suggesting that Nrf2 is activated. Large amounts of high-intensity exercise were effective at further reducing liver steatosis and potentiating improvements in pathophysiological parameters (liver enzyme activities and organokine profiles).

Conclusions

The weight-loss-independent benefits of exercise include anti-steatotic and anti-stiffness effects in the livers of patients with NAFLD. These benefits seem to be acquired through the modification of inter-organ crosstalk, which is characterised by improvements in organokine imbalance and reductions in inflammation and oxidative stress.

Lay summary

We investigated the effects of exercise on non-alcoholic fatty liver disease (NAFLD) that were not related to weight loss. We found that exercise had considerable weight-loss-independent benefits for the liver through a number of mechanisms. This suggests that exercise is important for NAFLD patients, regardless of whether they lose weight.

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Exercise has effects on liver steatosis and stiffness, independent of weight loss.

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Exercise maintains muscle mass and alters the secretion of organokines.

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Exercise increases the phagocytic capacity of Kupffer cells and activates Nrf2.

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Exercise, especially vigorous exercise, should be used aggressively to manage non-alcoholic fatty liver disease (NAFLD).

Development of small-molecule tropomyosin receptor kinase (TRK) inhibitors for NTRK fusion cancers

Tropomyosin receptor kinase A, B and C (TRKA, TRKB and TRKC), which are well-known members of the cell surface receptor tyrosine kinase (RTK) family, are encoded by the neurotrophic receptor tyrosine kinase 1, 2 and 3 (NTRK1, NTRK2 and NTRK3) genes, respectively. TRKs can regulate cell proliferation, differentiation and even apoptosis through the RAS/MAPKs, PI3K/AKT and PLCγ pathways. Gene fusions involving NTRK act as oncogenic drivers of a broad diversity of adult and pediatric tumors, and TRKs have become promising antitumor targets. Therefore, achieving a comprehensive understanding of TRKs and relevant TRK inhibitors should be urgently pursued for the further development of novel TRK inhibitors for potential clinical applications. This review focuses on summarizing the biological functions of TRKs and NTRK fusion proteins, the development of small-molecule TRK inhibitors with different chemotypes and their activity and selectivity, and the potential therapeutic applications of these inhibitors for future cancer drug discovery efforts.

Dental pulp stem cells response on the nanotopography of scaffold to regenerate dentin-pulp complex tissue

The study of regenerative dentistry receives a fast growing interest. The potential ability of the dentin-pulp complex to regenerate is both promising and perplexing. To answer the challenging nature of the dental environment, scientists have developed various combinations of biomaterial scaffolds, stem cells, and incorporation of several growth factors. One of the crucial elements of this tissue engineering plan is the selection and fabrication of scaffolds. However, further findings suggest that cell behavior hugely depends on mechanical signaling. Nanotopography modifies scaffolds to alter cell migration and differentiation. However, to the best of the author's knowledge, there are very few studies addressing the correlation between nanotopography and dentin-pulp complex regeneration. Therefore, this article presents a comprehensive review of these studies and suggests a direction for future developments, particularly in the incorporation of nanotopography design for dentin-pulp complex regeneration.

The role of allopregnanolone in depressive-like behaviors: Focus on neurotrophic proteins

Allopregnanolone (3α,5α-tetrahydroprogesterone; pharmaceutical formulation: brexanolone) is a neurosteroid that has recently been approved for the treatment of postpartum depression, promising to fill part of a long-lasting gap in the effectiveness of pharmacotherapies for depressive disorders. In this review, we explore the experimental research that characterized the antidepressant-like effects of allopregnanolone, with a particular focus on the neurotrophic adaptations induced by this neurosteroid in preclinical studies. We demonstrate that there is a consistent decrease in allopregnanolone levels in limbic brain areas in rodents submitted to stress-induced models of depression, such as social isolation and chronic unpredictable stress. Further, both the drug-induced upregulation of allopregnanolone or its direct administration reduce depressive-like behaviors in models such as the forced swim test. The main drugs of interest that upregulate allopregnanolone levels are selective serotonin reuptake inhibitors (SSRIs), which present the neurosteroidogenic property even in lower, non-SSRI doses. Finally, we explore how these antidepressant-like behaviors are related to neurogenesis, particularly in the hippocampus. The protagonist in this mechanism is likely the brain-derived neurotrophic factor (BFNF), which is decreased in animal models of depression and may be restored by the normalization of allopregnanolone levels. The role of an interaction between GABA and the neurotrophic mechanisms needs to be further investigated.

Protective role of berberine on ulcerative colitis through modulating enteric glial cells-intestinal epithelial cells-immune cells interactions

Ulcerative colitis (UC) manifests as an etiologically complicated and relapsing gastrointestinal disease. The enteric nervous system (ENS) plays a pivotal role in rectifying and orchestrating the inflammatory responses in gut tract. Berberine, an isoquinoline alkaloid, is known as its anti-inflammatory and therapeutic effects in experimental colitis. However, little research focused on its regulatory function on ENS. Therefore, we set out to explore the pathological role of neurogenic inflammation in UC and the modulating effects of berberine on neuro-immune interactions. Functional defects of enteric glial cells (EGCs), with decreased glial fibrillary acidic protein (GFAP) and increased substance P expression, were observed in DSS-induced murine UC. Administration of berberine can obviously ameliorate the disease severity and restore the mucosal barrier homeostasis of UC, closely accompanying by maintaining the residence of EGCs and attenuating inflammatory infiltrations and immune cells overactivation. In vitro, berberine showed direct protective effects on monoculture of EGCs, bone marrow-derived dendritic cells (BMDCs), T cells, and intestinal epithelial cells (IECs) in the simulated inflammatory conditions. Furthermore, berberine could modulate gut EGCs-IECs-immune cell interactions in the co-culture systems. In summary, our study indicated the EGCs-IECs-immune cell interactions might function as a crucial paradigm in mucosal inflammation and provided an infusive mechanism of berberine in regulating enteric neurogenic inflammation.

The Role of PI3K/Akt and ERK in Neurodegenerative Disorders

Disruption of Akt and Erk-mediated signal transduction significantly contributes in the pathogenesis of various neurodegenerative diseases (NDs), such as Parkinson's disease, Alzheimer's diseases, Huntington's disease, and many others. These regulatory proteins serve as the regulator of cell survival, motility, transcription, metabolism, and progression of the cell cycle. Therefore, targeting Akt and Erk pathway has been proposed as a reasonable approach to suppress ND progression. This review has emphasized on involvement of Akt/Erk cascade in the neurodegeneration. Akt has been reported to regulate neuronal toxicity through its various substrates like FOXos, GSK3β, and caspase-9 etc. Akt is also involved with PI3K in signaling pathway to mediate neuronal survival. ERK is another kinase which also regulates proliferation, differentiation, and survival of the neural cell. There has also been much progress in developing a therapeutic molecule targeting Akt and Erk signaling. Therefore, improved understanding of the molecular mechanism behind the regulatory aspect of Akt and Erk networks can make strong impact on exploration of the neurodegenerative disease pathogenesis.

Panax ginseng as an adjuvant treatment for Alzheimer's disease

Longevity in medicine can be defined as a long life without mental or physical deficits. This can be prevented by Alzheimer's disease (AD). Current conventional AD treatments only alleviate the symptoms without reversing AD progression. Recent studies demonstrated that Panax ginseng extract improves AD symptoms in patients with AD, and the two main components of ginseng might contribute to AD amelioration. Ginsenosides show various AD-related neuroprotective effects. Gintonin is a newly identified ginseng constituent that contains lysophosphatidic acids and attenuates AD-related brain neuropathies. Ginsenosides decrease amyloid β-protein (Aβ) formation by inhibiting β- and γ-secretase activity or by activating the nonamyloidogenic pathway, inhibit acetylcholinesterase activity and Aβ-induced neurotoxicity, and decrease Aβ-induced production of reactive oxygen species and neuroinflammatory reactions. Oral administration of ginsenosides increases the expression levels of enzymes involved in acetylcholine synthesis in the brain and alleviates Aβ-induced cholinergic deficits in AD models. Similarly, gintonin inhibits Aβ-induced neurotoxicity and activates the nonamyloidogenic pathway to reduce Aβ formation and to increase acetylcholine and choline acetyltransferase expression in the brain through lysophosphatidic acid receptors. Oral administration of gintonin attenuates brain amyloid plaque deposits, boosting hippocampal cholinergic systems and neurogenesis, thereby ameliorating learning and memory impairments. It also improves cognitive functions in patients with AD. Ginsenosides and gintonin attenuate AD-related neuropathology through multiple routes. This review focuses research demonstrating that ginseng constituents could be a candidate as an adjuvant for AD treatment. However, clinical investigations including efficacy and tolerability analyses may be necessary for the clinical acceptance of ginseng components in combination with conventional AD drugs.

Circadian rhythm and sleep-wake systems share the dynamic extracellular synaptic milieu

The mammalian circadian and sleep-wake systems are closely aligned through their coordinated regulation of daily activity patterns. Although they differ in their anatomical organization and physiological processes, they utilize overlapping regulatory mechanisms that include an assortment of proteins and molecules interacting within the extracellular space. These extracellular factors include proteases that interact with soluble proteins, membrane-attached receptors and the extracellular matrix; and cell adhesion molecules that can form complex scaffolds connecting adjacent neurons, astrocytes and their respective intracellular cytoskeletal elements. Astrocytes also participate in the dynamic regulation of both systems through modulating neuronal appositions, the extracellular space and/or through release of gliotransmitters that can further contribute to the extracellular signaling processes. Together, these extracellular elements create a system that integrates rapid neurotransmitter signaling across longer time scales and thereby adjust neuronal signaling to reflect the daily fluctuations fundamental to both systems. Here we review what is known about these extracellular processes, focusing specifically on areas of overlap between the two systems. We also highlight questions that still need to be addressed. Although we know many of the extracellular players, far more research is needed to understand the mechanisms through which they modulate the circadian and sleep-wake systems.

AExaCTT - Aerobic Exercise and Consecutive Task-specific Training for the upper limb after stroke: Protocol for a randomised controlled pilot study

Motor function may be enhanced if aerobic exercise is paired with motor training. One potential mechanism is that aerobic exercise increases levels of brain-derived neurotrophic factor (BDNF), which is important in neuroplasticity and involved in motor learning and motor memory consolidation. This study will examine the feasibility of a parallel-group assessor-blinded randomised controlled trial investigating whether task-specific training preceded by aerobic exercise improves upper limb function more than task-specific training alone, and determine the effect size of changes in primary outcome measures. People with upper limb motor dysfunction after stroke will be allocated to either task-specific training or aerobic exercise and consecutive task-specific training. Both groups will perform 60 hours of task-specific training over 10 weeks, comprised of 3 × 1 hour sessions per week with a therapist and 3 × 1 hours of home-based self-practice per week. The combined intervention group will also perform 30 minutes of aerobic exercise (70-85%HRmax) immediately prior to the 1 hour of task-specific training with the therapist. Recruitment, adherence, retention, participant acceptability, and adverse events will be recorded. Clinical outcome measures will be performed pre-randomisation at baseline, at completion of the training program, and at 1 and 6 months follow-up. Primary clinical outcome measures will be the Action Research Arm Test (ARAT) and the Wolf Motor Function Test (WMFT). If aerobic exercise prior to task-specific training is acceptable, and a future phase 3 randomised controlled trial seems feasible, it should be pursued to determine the efficacy of this combined intervention for people after stroke.

The fate of medications evaluated for ischemic stroke pharmacotherapy over the period 1995-2015

Stroke is a brain damage caused by a loss of blood supply to a portion of the brain, which requires prompt and effective treatment. The current pharmacotherapy for ischemic stroke primarily relies on thrombolysis using recombinant tissue plasminogen activators (rt-PAs) to breakdown blood clots. Neuroprotective agents that inhibit excitatory neurotransmitters are also used to treat ischemic stroke but have failed to translate into clinical benefits. This poses a major challenge in biomedical research to understand what causes the progressive brain cell death after stroke and how to develop an effective pharmacotherapy for stroke. This brief review analyzes the fate of about 430 potentially useful stroke medications over the period 1995–2015 and describes in detail those that successfully reached the market. Hopefully, the information from this analysis will shed light on how future stroke research can improve stroke drug discovery.

BDNF expression is up-regulated by progesterone in human umbilical cord mesenchymal stem cells

OBJECTIVE

To investigate whether promotion of neuronal differentiation of human umbilical cord mesenchymal stem cells (HUMSCs) by progesterone (PROG) involves changes in brain-derived neurotrophic factor (BDNF) levels.

METHODS

We used rat brain tissue extracts to mimic the brain microenvironment. Quantitative sandwich enzyme-linked immunosorbent assay was performed to measure levels of BDNF in cultured medium with or without PROG.

RESULTS

Progesterone increased levels of BDNF in HUMSCs.

CONCLUSION

Progesterone enhancement of brain-derived neurotrophic factor levels may be involved in PROG activated-pathways to promote neuronal differentiation of HUMSCs.

PRMT5- mediated symmetric arginine dimethylation is attenuated by mutant huntingtin and is impaired in Huntington's disease (HD)

Abnormal protein interactions of mutant huntingtin (Htt) triggered by polyglutamine expansion are thought to mediate Huntington's disease (HD) pathogenesis. Here, we explored a functional interaction of Htt with protein arginine methyltransferase 5 (PRMT5), an enzyme mediating symmetrical dimethylation of arginine (sDMA) of key cellular proteins, including histones, and spliceosomal Sm proteins. Gene transcription and RNA splicing are impaired in HD. We demonstrated PRMT5 and Htt interaction and their co-localization in transfected neurons and in HD brain. As a result of this interaction, normal (but to a lesser extend mutant) Htt stimulated PRMT5 activity in vitro. SDMA of histones H2A and H4 was reduced in the presence of mutant Htt in primary cultured neurons and in HD brain, consistent with a demonstrated reduction in R3Me2s occupancy at the transcriptionally repressed promoters in HD brain. SDMA of another PRMT5 substrate, Cajal body marker coilin, was also reduced in the HD mouse model and in human HD brain. Finally, compensation of PRMT5 deficiency by ectopic expression of PRMT5/MEP50 complexes, or by the knock-down of H4R3Me2 demethylase JMJD6, reversed the toxic effects of mutant Htt in primary cortical neurons, suggesting that PRMT5 deficiency may mediate, at least in part, HD pathogenesis. These studies revealed a potential new mechanism for disruption of gene expression and RNA processing in HD, involving a loss of normal function of Htt in facilitation of PRMT5, supporting the idea that epigenetic regulation of gene transcription may be involved in HD and highlighting symmetric dimethylation of arginine as potential new therapeutic target.

Trk inhibitor attenuates the BDNF/TrkB-induced protection of neuroblastoma cells from etoposide in vitro and in vivo

TrkB activation by brain-derived neurotrophic factor (BDNF) contributes to chemo-resistance in neuroblastoma (NB). AZD6918 is a novel potent and selective inhibitor of the Trk tyrosine kinases. In this study we evaluated the effect of AZD6918 on the sensitivity of TrkB-expressing NB cells or tumors to etoposide, a topoisomerase II inhibitor. TrkB-expressing NB cells were treated with AZD6918 and etoposide in the presence or absence of BDNF in vitro and cell survival was determined. NB xenograft tumors were treated with AZD6918 and etoposide, either alone or in combination in vivo, and the anti-tumor growth effect or mice survival advantage was evaluated. Our study showed that AZD6918 induced cell death as a single agent and attenuated BDNF/TrkB-induced protection from etoposide in vitro. Although AZD6918 alone didn't show anti-tumor growth effect or survival advantage in vivo, a combination of AZD6918 and etoposide had a statistically significant stronger anti-tumor growth effect and survival advantage compared to treatment with either agent alone. Our data indicate that as a Trk inhibitor AZD6918 increased the sensitivity of NB to etoposide. These results extend the spectrum of cytotoxic drugs whose efficacy is increased in combination with Trk inhibitors and support the combination of Trk inhibitors and cytotoxic drugs for NB treatment.

Neuronal cell cycle: the neuron itself and its circumstances

Neurons are usually regarded as postmitotic cells that undergo apoptosis in response to cell cycle reactivation. Nevertheless, recent evidence indicates the existence of a defined developmental program that induces DNA replication in specific populations of neurons, which remain in a tetraploid state for the rest of their adult life. Similarly, de novo neuronal tetraploidization has also been described in the adult brain as an early hallmark of neurodegeneration. The aim of this review is to integrate these recent developments in the context of cell cycle regulation and apoptotic cell death in neurons. We conclude that a variety of mechanisms exists in neuronal cells for G1/S and G2/M checkpoint regulation. These mechanisms, which are connected with the apoptotic machinery, can be modulated by environmental signals and the neuronal phenotype itself, thus resulting in a variety of outcomes ranging from cell death at the G1/S checkpoint to full proliferation of differentiated neurons.

Ablation of intact hypothalamic and/or hindbrain TrkB signaling leads to perturbations in energy balance

OBJECTIVE

Brain-derived neurotrophic factor (BDNF) and its receptor, tropomyosin receptor kinase B (TrkB), play a paramount role in the central regulation of energy balance. Despite the substantial body of genetic evidence implicating BDNF- or TrkB-deficiency in human obesity, the critical brain region(s) contributing to the endogenous role of BDNF/TrkB signaling in metabolic control remain unknown.

METHODS

We assessed the importance of intact hypothalamic or hindbrain TrkB signaling in central regulation of energy balance by generating Nkx2.1-Ntrk2-/- and Phox2b-Ntrk2+/- mice, respectively, and comparing metabolic parameters (body weight, adiposity, food intake, energy expenditure and glucose homeostasis) under high-fat diet or chow fed conditions.

RESULTS

Our data show that when fed a high-fat diet, male and female Nkx2.1-Ntrk2-/- mice have significantly increased body weight and adiposity that is likely driven by reduced locomotor activity and core body temperature. When maintained on a chow diet, female Nkx2.1-Ntrk2-/- mice exhibit an increased body weight and adiposity phenotype more robust than in males, which is accompanied by hyperphagia that precedes the onset of a body weight difference. In addition, under both diet conditions, Nkx2.1-Ntrk2-/- mice show increased blood glucose, serum insulin and leptin levels. Mice with complete hindbrain TrkB-deficiency (Phox2b-Ntrk2-/-) are perinatal lethal, potentially indicating a vital role for TrkB in visceral motor neurons that control cardiovascular, respiratory, and digestive functions during development. Phox2b-Ntrk2+/- heterozygous mice are similar in body weight, adiposity and glucose homeostasis parameters compared to wild type littermate controls when maintained on a high-fat or chow diet. Interestingly, despite the absence of a body weight difference, Phox2b-Ntrk2+/- heterozygous mice exhibit pronounced hyperphagia.

CONCLUSION

Taken together, our findings suggest that the hypothalamus is a key brain region involved in endogenous BDNF/TrkB signaling and central metabolic control and that endogenous hindbrain TrkB likely plays a role in modulating food intake and survival of mice. Our findings also show that female mice lacking TrkB in the hypothalamus have a more robust metabolic phenotype.

Brain-derived neurotrophic factor is required for axonal growth of selective groups of neurons in the arcuate nucleus

Objective

Brain-derived neurotrophic factor (BDNF) is a potent regulator of neuronal development, and the Bdnf gene produces two populations of transcripts with either a short or long 3′ untranslated region (3′ UTR). Deficiencies in BDNF signaling have been shown to cause severe obesity in humans; however, it remains unknown how BDNF signaling impacts the organization of neuronal circuits that control energy balance.

Methods

We examined the role of BDNF on survival, axonal projections, and synaptic inputs of neurons in the arcuate nucleus (ARH), a structure critical for the control of energy balance, using Bdnf^klox/klox mice, which lack long 3′ UTR Bdnf mRNA and develop severe hyperphagic obesity.

Results

We found that a small fraction of neurons that express the receptor for BDNF, TrkB, also expressed proopiomelanocortin (POMC) or neuropeptide Y (NPY)/agouti-related protein (AgRP) in the ARH. Bdnf^klox/klox mice had normal numbers of POMC, NPY, and TrkB neurons in the ARH; however, retrograde labeling revealed a drastic reduction in the number of ARH axons that project to the paraventricular hypothalamus (PVH) in these mice. In addition, fewer POMC and AgRP axons were found in the dorsomedial hypothalamic nucleus (DMH) and the lateral part of PVH, respectively, in Bdnf^klox/klox mice. Using immunohistochemistry, we examined the impact of BDNF deficiency on inputs to ARH neurons. We found that excitatory inputs onto POMC and NPY neurons were increased and decreased, respectively, in Bdnf^klox/klox mice, likely due to a compensatory response to marked hyperphagia displayed by the mutant mice.

Conclusion

This study shows that the majority of TrkB neurons in the ARH are distinct from known neuronal populations and that BDNF plays a critical role in directing projections from these neurons to the DMH and PVH. We propose that hyperphagic obesity due to BDNF deficiency is in part attributable to impaired axonal growth of TrkB-expressing ARH neurons.

Genetic and epigenetic control of metabolic health

Obesity is characterized as an excess accumulation of body fat resulting from a positive energy balance. It is the major risk factor for type 2 diabetes (T2D). The evidence for familial aggregation of obesity and its associated metabolic diseases is substantial. To date, about 150 genetic loci identified in genome-wide association studies (GWAS) are linked with obesity and T2D, each accounting for only a small proportion of the predicted heritability. However, the percentage of overall trait variance explained by these associated loci is modest (~5-10% for T2D, ~2% for BMI). The lack of powerful genetic associations suggests that heritability is not entirely attributable to gene variations. Some of the familial aggregation as well as many of the effects of environmental exposures, may reflect epigenetic processes. This review summarizes our current knowledge on the genetic basis to individual risk of obesity and T2D, and explores the potential role of epigenetic contribution.

Lysophosphatidylcholine enhances NGF-induced MAPK and Akt signals through the extracellular domain of TrkA in PC12 cells

Lysophosphatidylcholine (LPC) is one of the major lysophospholipids mainly generated by phospholipase A₂ (PLA₂)-mediated hydrolysis of phosphatidylcholine (PC). We previously found that LPC displays neurotrophin-like activity in the rat pheochromocytoma PC12 cells and in cerebellar granule neurons, but the molecular mechanism remains unclear. We report here that LPC specifically enhances nerve growth factor (NGF)-induced signals in PC12 cells. When PC12 cells were treated with NGF, MAPK was phosphorylated, but this phosphorylation was significantly elevated when LPC was added together. In accordance, NGF-induced expression of immediate early genes, c-fos and NGF-IA, was upregulated by LPC. Phosphorylation of the upstream components, MEK and NGF receptor TrkA, was also promoted by LPC, which was in line with increased phosphorylation of Akt. In contrast, LPC did not enhance epidermal growth factor (EGF)-, basic fibroblast growth factor-, or insulin-like growth factor-1-induced signals. Studies using TrkA/EGF receptor chimeras demonstrated that the extracellular domain, but not the transmembrane or intracellular domains, of TrkA is responsible for the effect of LPC. Exogenously-added secretory PLA₂ (sPLA₂) enhanced NGF-induced MAPK phosphorylation at a comparable level to LPC, suggesting that LPC generated in situ by sPLA₂-mediated hydrolysis of membrane PC stimulated NGF-TrkA signal. Taken together, these results indicate a specific role and function of LPC on NGF-TrkA signaling pathway.

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LPC potentiates NGF-induced MAPK and Akt phosphorylation in PC12 cells.

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LPC enhances NGF-induced MEK and TrkA phosphorylation.

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LPC does not affect the signals of EGF, FGF, and IGF-1.

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The effect of LPC requires the extracellular domain of TrkA.

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sPLA2 also potentiates NGF-induced MAPK phosphorylation.

Polymorphism of brain derived neurotrophic factor influences β amyloid load in cognitively intact apolipoprotein E ε4 carriers

Aside from apolipoprotein E (APOE), genetic risk factors for β amyloid deposition in cognitively intact individuals remain to be identified. Brain derived neurotrophic factor (BDNF) modulates neural plasticity, which has been implicated in Alzheimer's disease. We examined in cognitively normal older adults whether the BDNF codon 66 polymorphism affects β amyloid burden and the relationship between β amyloid burden and cognitive scores, and how this relates to the effect of APOE. Amyloid load was measured by means of ¹⁸F-flutemetamol PET in 64 community-recruited cognitively intact individuals (mean age 66, S.D. 5.1). Recruitment was stratified according to a factorial design with APOE (ε4 allele present vs absent) and BDNF (met allele at codon 66 present vs absent) as factors. Individuals in the four resulting cells were matched by the number of cases, age, and gender. Among the APOE ε4 carriers, BDNF met positive subjects had a significantly higher amyloid load than BDNF met negative subjects, while BDNF met carrier status did not have an effect in APOE ε4 noncarriers. This interaction effect was localized to precuneus, orbitofrontal cortex, gyrus rectus, and lateral prefrontal cortex. In the APOE ε4/BDNF met carriers, a significant inverse relationship existed between episodic memory scores and amyloid burden but not in any of the other groups. This hypothesis-generating experiment highlights a potential role of BDNF polymorphisms in the preclinical phase of β amyloid deposition and also suggests that BDNF codon 66 polymorphisms may influence resilience against β amyloid-related effects on cognition.

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Codon 66 BDNF polymorphisms have been associated with various cerebral effects.

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Community-recruited cognitively intact older adults underwent amyloid PET.

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Recruitment was stratified factorially with APOE and BDNF as factors.

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Aβ load in BDNF met carriers was higher but only in the presence of APOE ε4.

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Aβ load was associated with worse episodic memory but only in BDNF met/APOE ε4.

Mitochondria and neuroplasticity

The production of neurons from neural progenitor cells, the growth of axons and dendrites and the formation and reorganization of synapses are examples of neuroplasticity. These processes are regulated by cell-autonomous and intercellular (paracrine and endocrine) programs that mediate responses of neural cells to environmental input. Mitochondria are highly mobile and move within and between subcellular compartments involved in neuroplasticity (synaptic terminals, dendrites, cell body and the axon). By generating energy (ATP and NAD⁺), and regulating subcellular Ca²⁺ and redox homoeostasis, mitochondria may play important roles in controlling fundamental processes in neuroplasticity, including neural differentiation, neurite outgrowth, neurotransmitter release and dendritic remodelling. Particularly intriguing is emerging data suggesting that mitochondria emit molecular signals (e.g. reactive oxygen species, proteins and lipid mediators) that can act locally or travel to distant targets including the nucleus. Disturbances in mitochondrial functions and signalling may play roles in impaired neuroplasticity and neuronal degeneration in Alzheimer's disease, Parkinson's disease, psychiatric disorders and stroke.

Genetic mouse models of Huntington's disease: focus on electrophysiological mechanisms

The discovery of the HD (Huntington’s disease) gene in 1993 led to the creation of genetic mouse models of the disease and opened the doors for mechanistic studies. In particular, the early changes and progression of the disease could be followed and examined systematically. The present review focuses on the contribution of these genetic mouse models to the understanding of functional changes in neurons as the HD phenotype progresses, and concentrates on two brain areas: the striatum, the site of most conspicuous pathology in HD, and the cortex, a site that is becoming increasingly important in understanding the widespread behavioural abnormalities. Mounting evidence points to synaptic abnormalities in communication between the cortex and striatum and cell–cell interactions as major determinants of HD symptoms, even in the absence of severe neuronal degeneration and death.

Molecules and mechanisms involved in the generation and migration of cortical interneurons

The GABA (γ-aminobutyric acid)-containing interneurons of the neocortex are largely derived from the ganglionic eminences in the subpallium. Numerous studies have previously defined the migratory paths travelled by these neurons from their origins to their destinations in the cortex. We review here results of studies that have identified many of the genes expressed in the subpallium that are involved in the specification of the subtypes of cortical interneurons, and the numerous transcription factors, motogenic factors and guidance molecules that are involved in their migration.

Olfactory discrimination training up-regulates and reorganizes expression of microRNAs in adult mouse hippocampus

Adult male mice (strain C57Bl/6J) were trained to execute nose-poke responses for water reinforcement; then they were randomly assigned to either of two groups: olfactory discrimination training (exposed to two odours with reward contingent upon correctly responding to one odour) or pseudo-training (exposed to two odours with reward not contingent upon response). These were run in yoked fashion and killed when the discrimination-trained mouse reached a learning criterion of 70% correct responses in 20 trials, occurring after three sessions (a total of ∼40 min of training). The hippocampus was dissected bilaterally from each mouse (N = 7 in each group) and profiling of 585 miRNAs (microRNAs) was carried out using multiplex RT–PCR (reverse transcription–PCR) plates. A significant global up-regulation of miRNA expression was observed in the discrimination training versus pseudo-training comparison; when tested individually, 29 miRNAs achieved significance at P = 0.05. miR-10a showed a 2.7-fold increase with training, and is predicted to target several learning-related mRNAs including BDNF (brain-derived neurotrophic factor), CAMK2b (calcium/calmodulin-dependent protein kinase IIβ), CREB1 (cAMP-response-element-binding protein 1) and ELAVL2 [ELAV (embryonic lethal, abnormal vision, Drosophila)-like; Hu B]. Analysis of miRNA pairwise correlations revealed the existence of several miRNA co-expression modules that were specific to the training group. These in vivo results indicate that significant, dynamic and co-ordinated changes in miRNA expression accompany early stages of learning.