The BDNF Val66Met polymorphism has opposite effects on memory circuits of multiple sclerosis patients and controls

The relevance of BDNF for neuroprotection and neuroplasticity in multiple sclerosis

Background

Neuroplasticity as a mechanism to overcome central nervous system injury resulting from different neurological diseases has gained increasing attention in recent years. However, deficiency of these repair mechanisms leads to the accumulation of neuronal damage and therefore long-term disability. To date, the mechanisms by which remyelination occurs and why the extent of remyelination differs interindividually between multiple sclerosis patients regardless of the disease course are unclear. A member of the neurotrophins family, the brain-derived neurotrophic factor (BDNF) has received particular attention in this context as it is thought to play a central role in remyelination and thus neuroplasticity, neuroprotection, and memory.

Objective

To analyse the current literature regarding BDNF in different areas of multiple sclerosis and to provide an overview of the current state of knowledge in this field.

Conclusion

To date, studies assessing the role of BDNF in patients with multiple sclerosis remain inconclusive. However, there is emerging evidence for a beneficial effect of BDNF in multiple sclerosis, as studies reporting positive effects on clinical as well as MRI characteristics outweighed studies assuming detrimental effects of BDNF. Furthermore, studies regarding the Val66Met polymorphism have not conclusively determined whether this is a protective or harmful factor in multiple sclerosis, but again most studies hypothesized a protective effect through modulation of BDNF secretion and anti-inflammatory effects with different effects in healthy controls and patients with multiple sclerosis, possibly due to the pro-inflammatory milieu in patients with multiple sclerosis. Further studies with larger cohorts and longitudinal follow-ups are needed to improve our understanding of the effects of BDNF in the central nervous system, especially in the context of multiple sclerosis.

Association of the BDNF rs6265 Polymorphism with Cognitive Impairment in Multiple Sclerosis: A Case-Control Study in Mexican Patients

Cognition is a set of brain processes that allow the individual to interact with their environment. Multiple sclerosis (MS) is a chronic inflammatory disease that affects the cerebral white matter of the brain cortex and spinal cord, leading to cognitive impairment (CI) in 40-60% of the patients. Many studies have determined that CI is linked to genetic risk factors. We aimed to evaluate the association between BDNF gene rs6265 polymorphism and cognitive impairment in Mexican patients with MS by performing a case-control study. Mestizo-Mexican patients diagnosed with MS based on McDonald's criteria were enrolled. Cases were MS patients with CI (n = 31) while controls were MS patients without CI (n = 31). To measure cognitive functioning in MS patients, a neuropsychological screening battery for MS (NSB-MS) was used. Genotyping of the rs6265 gene variant was performed using quantitative real-time PCR (qPCR) with TaqMan probes. The results showed no statistically significant differences in sociodemographic and disease variables between case and control groups. qPCR analysis showed that there were 68% Val/Val wild-type homozygotes, 29% Val/Met polymorphic heterozygotes, and 3% Met/Met polymorphic homozygotes. The presence of BDNF gene rs6265 polymorphism showed an increased probability (3.6 times) of global cognitive impairment.

Molecular biomarkers and cognitive impairment in multiple sclerosis: State of the field, limitations, and future direction - A systematic review and meta-analysis

OBJECTIVE

Multiple sclerosis (MS) is associated with cognitive impairment (CI) such as slowed information processing speed (IPS). Currently, no immunocellular or molecular markers have been established in cerebrospinal fluid and serum analysis as surrogate biomarkers with diagnostic or predictive value for the development of CI. This systematic review and meta-analysis aims to sum up the evidence regarding currently discussed markers for CI in MS.

METHODS

A literature search was conducted on molecular biomarkers of CI in MS, such as neurofilament light chain, chitinases, and vitamin D.

RESULTS

5543 publications were screened, of which 77 entered the systematic review. 13 studies were included in the meta-analysis. Neurofilament light chain (CSF: r_p = -0.294, p = 0.003; serum: r_p = -0.137, p = 0.001) and serum levels of vitamin D (r_p = 0.190, p = 0.014) were associated with IPS outcomes.

CONCLUSIONS

Neurofilament light chain and vitamin D are promising biomarkers to track impairments in IPS in MS. Further longitudinal research is needed to establish the use of molecular biomarkers to monitor cognitive decline.

Brain-derived neurotrophic factor rs6265 (Val66Met) single nucleotide polymorphism as a master modifier of human pathophysiology

Brain-derived neurotrophic factor is the most prevalent member of the nerve growth factor family. Since its discovery in 1978, this enigmatic molecule has spawned more than 27,000 publications, most of which are focused on neurological disorders. Brain-derived neurotrophic factor is indispensable during embryogenesis and postnatally for the normal development and function of both the central and peripheral nervous systems. It is becoming increasingly clear, however, that brain-derived neurotrophic factor likewise plays crucial roles in a variety of other biological functions independently of sympathetic or parasympathetic involvement. Brain-derived neurotrophic factor is also increasingly recognized as a sophisticated environmental sensor and master coordinator of whole organismal physiology. To that point, we recently found that a common nonsynonymous (Val66→Met) single nucleotide polymorphism in the brain-derived neurotrophic factor gene (rs6265) not only substantially alters basal cardiac transcriptomics in mice but subtly influences heart gene expression and function differentially in males and females. In addition to a short description of recent results from associative neuropsychiatric studies, this review provides an eclectic assortment of research reports that support a modulatory role for rs6265 including and beyond the central nervous system.

A Brief Overview on BDNF-Trk Pathway in the Nervous System: A Potential Biomarker or Possible Target in Treatment of Multiple Sclerosis?

The growing incidence of neurodegenerative disorders in our populations is leading the research to identify potential biomarkers and targets for facilitating their early management and treatments. Biomarkers represent the crucial indicators of both physiological and pathological processes. Specific changes in molecular and cellular mechanisms of physiological processes result in biochemical alterations at systemic level, which can give us comprehensive information regarding the nature of any disease. In addition, any disease biomarker should be specific and reliable, able to consent of distinguishing the physiological condition of a tissue, organ, or system from disease, and be diverse among the various diseases, or subgroups or phenotypes of them. Accordingly, biomarkers can predict chances for diseases, facilitate their early diagnosis, and set guidelines for the development of new therapies for treating diseases and disease-making process. Here, we focus our attention on brain neurotrophic factor (BDNF)–tropomyosin receptor kinase (Trk) pathway, describing its multiple roles in the maintenance of central nervous system (CNS) health, as well as its implication in the pathogenesis of multiple sclerosis (MS). In addition, we also evidence the features of such pathway, which make of it a potential MS biomarker and therapeutic target.

Emerging Biomarkers of Multiple Sclerosis in the Blood and the CSF: A Focus on Neurofilaments and Therapeutic Considerations

INTRODUCTION

Multiple Sclerosis (MS) is the most common immune-mediated chronic neurodegenerative disease of the central nervous system (CNS) affecting young people. This is due to the permanent disability, cognitive impairment, and the enormous detrimental impact MS can exert on a patient's health-related quality of life. It is of great importance to recognise it in time and commence adequate treatment at an early stage. The currently used disease-modifying therapies (DMT) aim to reduce disease activity and thus halt disability development, which in current clinical practice are monitored by clinical and imaging parameters but not by biomarkers found in blood and/or the cerebrospinal fluid (CSF). Both clinical and radiological measures routinely used to monitor disease activity lack information on the fundamental pathophysiological features and mechanisms of MS. Furthermore, they lag behind the disease process itself. By the time a clinical relapse becomes evident or a new lesion appears on the MRI scan, potentially irreversible damage has already occurred in the CNS. In recent years, several biomarkers that previously have been linked to other neurological and immunological diseases have received increased attention in MS. Additionally, other novel, potential biomarkers with prognostic and diagnostic properties have been detected in the CSF and blood of MS patients.

AREAS COVERED

In this review, we summarise the most up-to-date knowledge and research conducted on the already known and most promising new biomarker candidates found in the CSF and blood of MS patients.

DISCUSSION

the current diagnostic criteria of MS relies on three pillars: MRI imaging, clinical events, and the presence of oligoclonal bands in the CSF (which was reinstated into the diagnostic criteria by the most recent revision). Even though the most recent McDonald criteria made the diagnosis of MS faster than the prior iteration, it is still not an infallible diagnostic toolset, especially at the very early stage of the clinically isolated syndrome. Together with the gold standard MRI and clinical measures, ancillary blood and CSF biomarkers may not just improve diagnostic accuracy and speed but very well may become agents to monitor therapeutic efficacy and make even more personalised treatment in MS a reality in the near future. The major disadvantage of these biomarkers in the past has been the need to obtain CSF to measure them. However, the recent advances in extremely sensitive immunoassays made their measurement possible from peripheral blood even when present only in minuscule concentrations. This should mark the beginning of a new biomarker research and utilisation era in MS.

BDNF Val66Met Polymorphism Is Associated With Motor Recovery After Rehabilitation in Progressive Multiple Sclerosis Patients

Background

Rehabilitation is fundamental for progressive multiple sclerosis (MS), but predictive biomarkers of motor recovery are lacking, making patient selection difficult. Motor recovery depends on synaptic plasticity, in which the Brain-Derived Neurotrophic Factor (BDNF) is a key player, through its binding to the Neurotrophic-Tyrosine Kinase-2 (NTRK2) receptor. Therefore, genetic polymorphisms in the BDNF pathway may impact motor recovery. The most well-known polymorphism in BDNF gene (rs6265) causes valine to methionine substitution (Val66Met) and it influences memory and motor learning in healthy individuals and neurodegenerative diseases. To date, no studies have explored whether polymorphisms in BDNF or NTRK2 genes may impact motor recovery in MS.

Objectives

To assess whether genetic variants in BDNF and NTRK2 genes affect motor recovery after rehabilitation in progressive MS.

Methods

The association between motor recovery after intensive neurorehabilitation and polymorphisms in BDNF (rs6265) and NTKR2 receptor (rs2289656 and rs1212171) was assessed using Six-Minutes-Walking-Test (6MWT), 10-Metres-Test (10MT) and Nine-Hole-Peg-Test (9HPT) in 100 progressive MS patients.

Results

We observed greater improvement at 6MWT after rehabilitation in carriers of the BDNF Val66Met substitution, compared to BDNF Val homozygotes (p = 0.024). No significant association was found for 10MT and 9HPT. NTRK2 polymorphisms did not affect the results of motor function tests.

Conclusion

BDNF Val66Met was associated with walking function improvement after rehabilitation in progressive MS patients. This result is in line with previous evidence showing a protective effect of Val66Met substitution on brain atrophy in MS. Larger studies are needed to explore its potential as a predictive biomarker of rehabilitation outcome.

The BDNF Val66Met Polymorphism (rs6265) Modulates Inflammation and Neurodegeneration in the Early Phases of Multiple Sclerosis

The clinical course of multiple sclerosis (MS) is critically influenced by the interplay between inflammatory and neurodegenerative processes. The brain-derived neurotrophic factor (BDNF) Val66Met polymorphism (rs6265), one of the most studied single-nucleotide polymorphisms (SNPs), influences brain functioning and neurodegenerative processes in healthy individuals and in several neuropsychiatric diseases. However, the role of this polymorphism in MS is still controversial. In 218 relapsing–remitting (RR)-MS patients, we explored, at the time of diagnosis, the associations between the Val66Met polymorphism, clinical characteristics, and the cerebrospinal fluid (CSF) levels of a large set of pro-inflammatory and anti-inflammatory molecules. In addition, associations between Val66Met and structural MRI measures were assessed. We identified an association between the presence of Met and a combination of cytokines, identified by principal component analysis (PCA), including the pro-inflammatory molecules MCP-1, IL-8, TNF, Eotaxin, and MIP-1b. No significant associations emerged with clinical characteristics. Analysis of MRI measures evidenced reduced cortical thickness at the time of diagnosis in patients with Val66Met. We report for the first time an association between the Val66Met polymorphism and central inflammation in MS patients at the time of diagnosis. The role of this polymorphism in both inflammatory and neurodegenerative processes may explain its complex influence on the MS course.

Met carriers of the BDNF Val66Met polymorphism show reduced Glx/NAA in the pregenual ACC in two independent cohorts

The Met allele of the Val66Met SNP of the BDNF gene (rs6265) is associated with impaired activity-dependent release of brain-derived neurotrophic factor (BDNF), resulting in reduced synaptic plasticity, impaired glutamatergic neurotransmission, and morphological changes. While previous work has demonstrated Val66Met effects on magnetic resonance spectroscopy (MRS) markers of either glutamatergic metabolism (Glx) or neuronal integrity (NAA), no study has investigated Val66Met effects on these related processes simultaneously. As these metabolites share a metabolic pathway, the Glx/NAA ratio may be a more sensitive marker of changes associated with the Val66Met SNP. This ratio is increased in psychiatric disorders linked to decreased functioning in the anterior cingulate cortex (ACC). In this study, we investigated the correlation of the Val66Met polymorphism of the BDNF gene with Glx/NAA in the pregenual anterior cingulate cortex (pgACC) using MRS at 3 Tesla (T) (n = 30, all males) and 7 T (n = 98, 40 females). In both cohorts, Met carriers had lower Glx/NAA compared to Val homozygotes. Follow-up analyses using absolute quantification revealed that the Met carriers do not show decreased pgACC glutamate or glutamine levels, but instead show increased NAA compared to the Val homozygotes. This finding may in part explain conflicting evidence for Val66Met as a risk factor for developing psychiatric illnesses.

The Brain-Derived Neurotrophic Factor Val66Met Polymorphism Can Protect Against Cognitive Impairment in Multiple Sclerosis

Introduction: Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family, involved in neuronal survival and synaptic plasticity. The BDNF Val66Met polymorphism is known to reduce BDNF expression and secretion; its role in multiple sclerosis (MS) is poorly investigated.

Objectives and Methods: In this multicenter, retrospective study, we assessed the role of BDNF Val66Met polymorphism on cognitive and motor disability in MS patients consecutively referred to the University of Florence and the Hospital of Barletta. All patients underwent a genetic analysis for the presence of Val66Met polymorphism and a comprehensive neuropsychological examination on the Rao's Brief Repeatable Battery and the Stroop Color Word Test. Possible predictors of the Expanded Disability Status Scale (EDSS) score and number of failed neuropsychological tests were assessed through linear multivariable regression models.

Results: Ninety-eight patients were recruited. Patients with the BDNF Val66Met polymorphism (35.7%) were more frequently males (p = 0.020), more disabled (p = 0.026) and, marginally, older (p = 0.064). In the multivariable analysis, BDNF Val66Met polymorphism was associated with a better cognitive performance (B = −1.1 ± 0.5, p = 0.027). Higher EDSS score was associated with a progressive disease course (B = 3.4, p < 0.001) and, marginally, with the presence of the BDNF Val66Met polymorphism (B = 0.56, p = 0.066).

Discussion: Our results preliminarily suggest a protective role of BDNF Val66Met polymorphism against cognitive impairment in MS patients, possibly related to a detrimental effect of increased BDNF concentration in a neuroinflammatory environment.

BDNF (rs6265) Val < Met polymorphism can buffer cognitive functions against post stroke CT/MRI pathological findings

Brain lesions following stroke have been shown prevalently in CT/MRI, and it was confirmed that lesions usually are accompanied by cognitive deficits. Although previous studies have emphasized that BDNF Val66Met polymorphism had a substantial role in neurogenesis and synaptic plasticity, it remains unclear to what extent an interaction may be appeared between neuroimaging findings and Val66Met variants on different cognitive functions following stroke. In a case-control study the carriers of at least one Val allele (n = 56), were compared with the carriers of Met/Met homozygotes (n = 156) in order to find possible neuroimaging factors in relation to cognitive functions in a sample from the north of Iran. The third edition of Addenbrooke's Cognitive Examination (ACE-III) was used to determine the cognitive functions. There were interactive effects among Val66Met genotypes with dominant hemisphere lesions [F = 6.97, ή² = 0.03, p = 0.009], cerebral atrophy [F = 5.43, ή² = 0.03, p = 0.011] and number of lesions [F = 4.32, ή² = 0.04, p = 0.014], for visuospatial skills, memory, and attention functions respectively; implying that the effect of dominant hemisphere lesions, cerebral atrophy, and multiple lesions on cognitive functions have been modulated by Met/Met homozygosity. The destructive effect of Val/Met homozygosity on cognitive functions was shown to be exacerbated by dominant hemispheric lesions, cerebral atrophy, and multiple lesions following stroke. The findings of present research support our hypothesis that interaction of Val66Met variants with cerebral lesions is associated with cognitive dysfunctions in post stroke conditions; particularly through Met/Met homozygosity which act as a buffer mechanism against some CT/MRI pathological findings.

Neurocan genome-wide psychiatric risk variant affects explicit memory performance and hippocampal function in healthy humans

Alterations of the brain extracellular matrix (ECM) can perturb the structure and function of brain networks like the hippocampus, a key region in human memory that is commonly affected in psychiatric disorders. Here, we investigated the potential effects of a genome-wide psychiatric risk variant in the NCAN gene encoding the ECM proteoglycan neurocan (rs1064395) on memory performance, hippocampal function and cortical morphology in young, healthy volunteers. We assessed verbal memory performance in two cohorts (N = 572, 302) and found reduced recall performance in risk allele (A) carriers across both cohorts. In 117 participants, we performed functional magnetic resonance imaging using a novelty-encoding task with visual scenes. Risk allele carriers showed higher false alarm rates during recognition, accompanied by inefficiently increased left hippocampal activation. To assess effects of rs1064395 on brain morphology, we performed voxel-based morphometry in 420 participants from four independent cohorts and found lower grey matter density in the ventrolateral and rostral prefrontal cortex of risk allele carriers. In silico eQTL analysis revealed that rs1064395 SNP is linked not only to increased prefrontal expression of the NCAN gene itself, but also of the neighbouring HAPLN4 gene, suggesting a more complex effect of the SNP on ECM composition. Our results suggest that the NCAN rs1064395 A allele is associated with lower hippocampus-dependent memory function, variation of prefrontal cortex structure and ECM composition. Considering the well-documented hippocampal and prefrontal dysfunction in bipolar disorder and schizophrenia, our results may reflect an intermediate phenotype by which NCAN rs1064395 contributes to disease risk.

Impact of brain-derived neurotrophic factor genetic polymorphism on cognition: A systematic review

INTRODUCTION

Brain-derived neurotrophic factor (BDNF) has an important role in the neurogenesis and neuroplasticity of the brain. This systematic review was designed to examine the association between BDNF Val66Met (rs6265) polymorphism and four cognitive domains-attention and concentration, executive function, verbal fluency, and memory, respectively.

METHODOLOGY

Primary literature search was performed using search engines such as PubMed and Scopus. Observational studies that evaluated the neurocognitive performances in relation to BDNF polymorphism within human subjects were included in this review, while animal studies, overlapping studies, and meta-analysis were excluded.

RESULTS

Forty of 82 reviewed studies (48.8%) reported an association between Val66Met polymorphism and neurocognitive domains. The proportion of the studies showing positive findings in cognitive performances between Val/Val homozygotes and Met carriers was comparable, at 30.5% and 18.3%, respectively. The highest percentage of positive association between Val66Met polymorphism and neurocognition was reported under the memory domain, with 26 of 63 studies (41.3%), followed by 18 of 47 studies (38.3%) under the executive function domain and four of 23 studies (17.4%) under the attention and concentration domain. There were no studies showing an association between Val66Met polymorphism and verbal fluency. In particular, Val/Val homozygotes performed better in tasks related to the memory domain, while Met carriers performed better in terms of executive function, in both healthy individuals and clinical populations.

CONCLUSION

While numerous studies report an association between Val66Met polymorphism and neurocognitive changes in executive function and memory domains, the effect of Met allele has not been clearly established.

BDNF Polymorphism: A Review of Its Diagnostic and Clinical Relevance in Neurodegenerative Disorders

Brain-derived neurotrophic factor (BDNF) has a unique role in the neuronal development, differentiation, and survival in the developing and adult nervous system. A common single-nucleotide polymorphism in the pro-region of the human BDNF gene, resulting in a valine to methionine substitution (Val66Met), has been associated with the susceptibility, incidence, and clinical features of several neurodegenerative disorders. Much research has been dedicated to evaluating the effects of polymorphism in the past decade, and functional effects of this genetic variation. A better understanding of how this naturally occurring polymorphism associates with or influences physiology, anatomy, and cognition in both healthy and diseased adults in neurodegenerative conditions will help understand neurochemical mechanisms and definable clinical outcomes in humans. Here we review the role and relevance of the BDNF Val66Met polymorphism in neurodegenerative diseases, with particular emphasis on glaucoma, multiple sclerosis (MS), Alzheimer’s disease (AD) and Parkinson’s disease (PD). Several controversies and unresolved issues, including small effect sizes, possible ethnicity, gender, and age effects of the BDNF Val66Met are also discussed with respect to future research.

Depression in multiple sclerosis: effect of brain derived neurotrophic factor Val66Met polymorphism and disease perception

BACKGROUND AND PURPOSE

Depression is common amongst subjects with multiple sclerosis (MS), and several investigations have explored different determinants of this condition, including physical disability, psychological and psychosocial factors. The brain derived neurotrophic factor (BDNF) Val66Met polymorphism has been associated with depression. The aim of this study was to analyze the influence of disease-related factors, BDNF Val66Met polymorphism and perception of disease on the severity of depression in MS.

METHOD

In total, 136 MS patients (88 women) were recruited and genotyped for BDNF rs6265 polymorphism at nucleotide 196 (G/A) using 'high resolution melting'. Depressive symptoms were assessed by the Multiple Sclerosis Depression Rating Scale. Perception of health status was assessed using the SF-36 questionnaire.

RESULTS

A multivariable linear regression model showed that the best predictors of depression were the SF-36 General health (β = -0.209; P = 0.013), Mental health (β = -0.410; P < 0.001) and Social activity (β = -0.195; P = 0.035) scores; physical disability (assessed by the Extended Disability Status Scale score) was directly correlated to depression severity on univariate analysis, but it was not a relevant predictor of depression on multivariate analysis; other variables directly related to the disease (treatment, annual relapsing rate) and the BDNF Val66Met polymorphism were not significantly associated with depression.

CONCLUSION

Perception of the health status is the principal predictor of depressive symptoms in our sample. This result supports the hypothesis that the subjective interpretation of the disease's consequences is one of the main factors in determining depression in MS.

Imaging phenotypes in multiple sclerosis

Multiple sclerosis (MS) is a common disease of the central nervous system, with various clinical symptoms and a heterogeneous disease course. MRI can depict focal and diffuse manifestations of the disease, and accurately measure progression over time. The precise pathogenesis of MS is unknown. Nevertheless, genetic influences have been found for susceptibility to MS in linkage and association studies. More recent genome-wide association studies have revealed other genes to be related to disease susceptibility and severity, explaining part of the variability in symptoms, radiological manifestations and disease course. Studies relating genetics and imaging in MS are discussed in this paper.

Dysfunctions within limbic-motor networks in amyotrophic lateral sclerosis

Previous studies have shown that affective symptoms are part of the clinical picture in amyotrophic lateral sclerosis (ALS), the most common motor neuron disorder in elderly people. Diffuse neurodegeneration of limbic regions (e.g., prefrontal cortex [PFC], amygdala) was demonstrated in ALS post-mortem, although the mechanisms of emotional dysregulation in ALS in vivo remain unclear. Using functional imaging, we assessed the brain responses to emotional faces in 11 cognitively unimpaired ALS patients and 12 healthy controls (HCs). We tested whether regional activities and connectivity patterns in the limbic system differed between ALS patients and HCs and whether the variability in clinical measures modulated the neuroimaging data. Relative to HCs, ALS patients displayed greater activation in a series of PFC areas and altered left amygdala-PFC connectivity. Anxiety modulated the right amygdala-PFC connectivity in HCs but not in ALS patients. Reduced right premotor cortex activity and altered left amygdala-supplementary motor area connectivity were associated with longer disease duration and greater disease severity, respectively. Our findings demonstrate dysfunctions of the limbic system in ALS patients at early stages of the disease, and extend our knowledge about the interplay between emotional brain areas and the regions traditionally implicated in motor control.