The genetics of circulating BDNF: towards understanding the role of BDNF in brain structure and function in middle and old ages

Association of Neurotrophic Factors at Midlife With In Vivo Measures of β-Amyloid and Tau Burden 15 Years Later in Dementia-Free Adults

BACKGROUND AND OBJECTIVES

Neurotrophic factors (NTFs) play an important role in Alzheimer disease (AD) pathophysiology. Brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) are important NTFs. However, a direct link of BDNF and VEGF circulating levels with in vivo measures of amyloid-β (Aβ) and tau burden remains to be elucidated. We explored the relationship of BDNF and VEGF serum levels with future brain Aβ and tau pathology in a cohort of cognitively healthy, predominantly middle-aged adults and tested for possible effect modifications by sex and menopausal status.

METHODS

This cross-sectional analysis was conducted using data from the Framingham Heart Study (FHS), a community-based cohort study. The study sample included cognitively healthy participants from the FHS Offspring and Third-generation cohorts. BDNF and VEGF were measured in the third-generation cohort during examination cycles 2 (2005-2008) and 1 (2002-2005), respectively, and in the offspring cohort during examination cycle 7 (1998-2001). Participants underwent 11C-Pittsburgh compound B amyloid and 18F-Flortaucipir tau-PET imaging (2015-2021). Linear regression models were used to assess the relationship of serum BDNF and VEGF levels with regional tau and global Aβ, adjusting for potential confounders. Interactions with sex and menopausal status were additionally tested.

RESULTS

The sample included 414 individuals (mean age = 41 ± 9 years; 51% female). Continuous measures of BDNF and VEGF were associated with tau signal in the rhinal region after adjustment for potential confounders (β = -0.15 ± 0.06, p = 0.018 and β = -0.19 ± 0.09, p = 0.043, respectively). High BDNF (≥32,450 pg/mL) and VEGF (≥488 pg/mL) levels were significantly related to lower rhinal tau (β = -0.27 ± 0.11, p = 0.016 and β = -0.40 ± 0.14, p = 0.004, respectively) and inferior temporal tau (β = -0.24 ± 0.11, p = 0.028 and β = -0.26 ± 0.13, p = 0.049, respectively). The BDNF-rhinal tau association was observed only among male individuals. Overall, BDNF and VEGF were not associated with global amyloid; however, high VEGF levels were associated with lower amyloid burden in postmenopausal women (β = -1.96 ± 0.70, p = 0.013, per 1 pg/mL).

DISCUSSION

This study demonstrates a robust association between BDNF and VEGF serum levels with in vivo measures of tau almost 2 decades later. These findings add to mounting evidence from preclinical studies suggesting a role of NTFs as valuable blood biomarkers for AD risk prediction.

Human transcriptome array analysis and diffusion tensor imaging in attention-deficit/hyperactivity disorder

The mRNA markers identified using microarray assay and diffusion tensor magnetic resonance imaging (DTI) were applied to elucidate the pathophysiology of attention-deficit hyperactivity disorder (ADHD). First, we obtained total RNA from leukocytes from three children with ADHD and three healthy controls for analysis with microarray assays. Subsequently, we applied real-time quantitative polymerase chain reaction (qRT‒PCR) assays to validate the differential expression of 7 genes (COX7B, CYCS, TFAM, UTP14A, ZNF280C, IFT57 and NDUFB5) between 130 ADHD patients and 70 controls, and we built an ADHD prediction model based on the ΔCt values of aforementioned seven genes (AUROC = 0.98). Finally, in a validation group (28 patients with ADHD and 27 healthy controls), mRNA expression of the above seven genes also significantly differentiated ADHD patients from controls (AUROC value = 0.91). The DTI analysis showed increased fractional anisotropy (FA) of the forceps minor, superior corona radiata, posterior corona radiata and anterior corona radiata in ADHD patients. Moreover, the FA of the right superior corona radiata tract was positively correlated with ΔCt levels of the COX7B gene and the IFT57 gene. The results shed a new light on a genetic profile of ADHD that may help in deciphering the white matter microstructural features in disease pathogenesis.

A genetic exploration of the relationship between Posttraumatic Stress Disorder and cardiovascular diseases

Background and Aims

Experiencing a traumatic event may lead to Posttraumatic Stress Disorder (PTSD), including symptoms such as flashbacks and hyperarousal. Individuals suffering from PTSD are at increased risk of cardiovascular disease (CVD), but it is unclear why. This study assesses shared genetic liability and potential causal pathways between PTSD and CVD.

Methods

We leveraged summary-level data of genome-wide association studies (PTSD: N= 1,222,882; atrial fibrillation (AF): N=482,409; coronary artery disease (CAD): N=1,165,690; hypertension: N=458,554; heart failure (HF): N=977,323). First, we estimated genetic correlations and utilized genomic structural equation modeling to identify a common genetic factor for PTSD and CVD. Next, we assessed biological, behavioural, and psychosocial factors as potential mediators. Finally, we employed multivariable Mendelian randomization to examine causal pathways between PTSD and CVD, incorporating the same potential mediators.

Results

Significant genetic correlations were found between PTSD and CAD, HT, and HF (rg =0.21-0.32, p≤ 3.08 · 10-16), but not between PTSD and AF. Insomnia, smoking, alcohol dependence, waist-to-hip ratio, and inflammation (IL6, C-reactive protein) partly mediated these associations. Mendelian randomization indicated that PTSD causally increases CAD (IVW OR=1.53, 95% CIs=1.19-1.96, p=0.001), HF (OR=1.44, CIs=1.08-1.92, p=0.012), and to a lesser degree hypertension (OR=1.25, CIs=1.05-1.49, p=0.012). While insomnia, smoking, alcohol, and inflammation were important mediators, independent causal effects also remained.

Conclusions

In addition to shared genetic liability between PTSD and CVD, we present strong evidence for causal effects of PTSD on CVD. Crucially, we implicate specific lifestyle and biological mediators (insomnia, substance use, inflammation) which has important implications for interventions to prevent CVD in PTSD patients.

Poor sleep versus exercise: A duel to decide whether pain resolves or persists after injury

Poor sleep is thought to enhance pain via increasing peripheral and/or central sensitization. Aerobic exercise, conversely, relives pain via reducing sensitization, among other mechanisms. This raises two clinical questions: (1) does poor sleep contribute to the transition from acute-to-persistent pain, and (2) can exercise protect against this transition? This study tested these questions and explored underlying mechanisms in a controlled injury model. Twenty-nine adult female Sprague-Dawley rats performed an intensive lever-pulling task for 4 weeks to induce symptoms consistent with clinical acute-onset overuse injury. Rats were then divided into three groups and exposed for 4 weeks to either: voluntary exercise via access to a running wheel, sleep disturbance, or both. Pain-related behaviours (forepaw mechanical sensitivity, reflexive grip strength), systemic levels of brain derived neurotrophic factor (BDNF), estradiol and corticosterone, and white blood cells (WBC) were assessed pre-injury, post-injury and post-intervention. Mechanical sensitivity increased post-injury and remained elevated with sleep disturbance alone, but decreased to pre-injury levels with exercise both with and without sleep disturbance. Reflexive grip strength decreased post-injury but recovered post-intervention-more with exercise than sleep disturbance. BDNF increased with sleep disturbance alone, remained at pre-injury levels with exercise regardless of sleep, and correlated with mechanical sensitivity. WBCs and estradiol increased with exercise alone and together with sleep disturbance, respectively. Corticosterone was not impacted by injury/intervention. Findings provide preliminary evidence for a role of poor sleep in the transition from acute-to-persistent pain, and the potential for aerobic exercise to counter these effects. BDNF might have a role in these relationships.

Genetic associations and potential mediators between psychiatric disorders and irritable bowel syndrome: a Mendelian randomization study with mediation analysis

Objective

Potential causal associations between psychiatric disorders and irritable bowel syndrome have been demonstrated in observational studies; however, these studies are susceptible to underlying confounding and reverse causation biases. We aimed to assess the causal effects of psychiatric disorders on irritable bowel syndrome (IBS) and the potential mediators from a genetic perspective by conducting a Mendelian randomization (MR) study with mediation analysis.

Method

Genetic instruments associated with psychiatric disorders, potential mediators, and IBS were obtained from large-scale genome-wide association studies (GWAS). Three MR methods - the inverse-variance weighted (IVW) method, MR-Egger method, and weighted median method, were used to investigate causal association estimates. Heterogeneity among different genetic instrumental variables (IVs) was assessed using Q tests. Additionally, the MR-PRESSO and MR-Pleiotropy methods were used to verify horizontal pleiotropy and detect outliers that might bias the results, which were removed from further analysis. Consequently, we used MR mediation analysis to investigate potential mediators in the causal associations between psychiatric disorders and IBS.

Results

MR provided evidence of the causal effects of genetically predicted broad depression, major depressive disorder (MDD), anxiety disorder, post-traumatic stress disorder (PTSD), and schizophrenia on IBS. The results of MR mediation analysis demonstrated that the reduction in acetate levels mediated 12.6% of the effects of broad depression on IBS; insomnia mediated 16.00%, 16.20%, and 27.14% of the effects of broad depression, MDD, and PTSD on IBS, respectively; and the increase in blood β-hydroxybutyrate levels mediated 50.76% of the effects of schizophrenia on IBS.

Conclusion

Our study confirmed the brain-gut axis involvement and potential modulators in the pathophysiology of psychiatric disorder-induced IBS from a genetic perspective, and suggests potential therapeutic targets for the disrupted brain-gut axis.

Physical Exercise and Serum BDNF Levels: Accounting for the Val66Met Polymorphism in Older Adults

BACKGROUND

Brain-derived neurotrophic factor (BDNF) expression, which can be measured in blood serum, has been found to increase with aerobic exercise. The link between BDNF level, physical exercise, and genetic status (Val66Met polymorphism) has not been well researched in older adults.

OBJECTIVE

To investigate the possible link between BDNF expression, acute aerobic exercise, and the Val66Met polymorphism in older adults.

METHOD

Twenty-three healthy older adults participated in one session of acute aerobic exercise. Their serum BDNF levels were measured both at baseline and post exercise. Saliva samples were collected to identify each individual's genetic status.

RESULTS

At baseline, the individuals' mean serum BDNF level was 16.03 ng/mL (Val66Val = 15.89 ng/mL; Val66Met = 16.34 ng/mL); post exercise, the individuals' mean serum BDNF level was 16.81 ng/mL (Val66Val = 16.14 ng/mL; Val66Met = 18.34 ng/mL).

CONCLUSION

One session of acute aerobic exercise significantly increased the individuals' mean serum BDNF level. Males had higher BDNF levels than females. There was a significant interaction between gender and BDNF expression post exercise and a significant between-group effect of gender. The Val66Met carriers had a more positive response to the acute aerobic exercise compared with the Val66Val carriers, although without a significant difference between the two groups.

BDNF Val66Met polymorphism is associated with consolidation of episodic memory during sleep

The brain-derived neurotrophic factor (BDNF) is an essential regulator of synaptic plasticity, a candidate neurobiological mechanism underlying learning and memory. A functional polymorphism in the BDNF gene, Val66Met (rs6265), has been linked to memory and cognition in healthy individuals and clinical populations. Sleep contributes to memory consolidation, yet information about the possible role of BDNF in this process is scarce. To address this question, we investigated the relationship between the BDNF Val66Met genotype and consolidation of episodic declarative and procedural (motor) non-declarative memories in healthy adults. The carriers of Met66 allele, as compared with Val66 homozygotes, showed stronger forgetting overnight (24hours after encoding), but not over shorter time (immediately or 20minutes after word list presentation). There was no effect of Val66Met genotype on motor learning. These data suggest that BDNF plays a role in neuroplasticity underlying episodic memory consolidation during sleep.

Sedentary behavior, brain-derived neurotrophic factor and brain structure in midlife: A longitudinal brain MRI sub-study of the coronary artery risk development in young adults study

Background

Brain-derived neurotrophic factor levels are higher in those who are physically active and lower in people with cognitive dysfunction. This study investigated whether brain-derived neurotrophic factor mediated or modified the association of sedentary time to MRI-estimated brain volumes in midlife.

Methods

Baseline (n = 612) and five-year follow-up (n = 418) data were drawn from the multicenter Coronary Artery Risk Development in Young Adults Brain MRI sub-study, including Black and White participants (aged 50.3 years, 51.6% females, 38.6% Black). Sedentary time (hours per day) was categorized into quartiles with low ≤ 4.3 (reference) and high > 8.4. Outcomes of the study were total brain, white matter, gray matter, hippocampal volumes, and white matter fractional anisotropy at baseline and 5-year percent change from baseline. The study used general linear regression models to examine the mediation and moderation effects of brain-derived neurotrophic factor (natural log transformed) on the associations of sedentary time to brain outcomes. The authors adjusted the regression model for age, sex, race, intracranial volume, education, and vascular factors.

Results

Cross-sectionally, baseline participants with the highest sedentary time had a lower total brain (-12.2 cc; 95%CI: -20.7, -3.7), gray matter (-7.8 cc; 95%CI: -14.3, -1.3), and hippocampal volume (-0.2 cc; 95%CI: -0.3, 0.0) compared with populations with the lowest sedentary time. The brain-derived neurotrophic factor levels did not mediate the associations between brain measures and sedentary time. Brain-derived neurotrophic factor was found to moderate associations of sedentary time to total brain and white matter volume such that the brain volume difference between high and low sedentary time decreased as brain-derived neurotrophic factor levels increased. Longitudinally, higher baseline brain-derived neurotrophic factor level was associated with less brain volume decline. The longitudinal associations did not differ by sedentary time, and brain-derived neurotrophic factor did not mediate or moderate the association of sedentary time to brain measure changes.

Conclusions

Higher brain-derived neurotrophic factor levels may buffer the negative effects of sedentary time on the brain.

Deciphering the Effect of Different Genetic Variants on Hippocampal Subfield Volumes in the General Population

The aim of this study was to disentangle the effects of various genetic factors on hippocampal subfield volumes using three different approaches: a biologically driven candidate gene approach, a hypothesis-free GWAS approach, and a polygenic approach, where AD risk alleles are combined with a polygenic risk score (PRS). The impact of these genetic factors was investigated in a large dementia-free general population cohort from the Study of Health in Pomerania (SHIP, n = 1806). Analyses were performed using linear regression models adjusted for biological and environmental risk factors. Hippocampus subfield volume alterations were found for APOE ε4, BDNF Val, and 5-HTTLPR L allele carriers. In addition, we were able to replicate GWAS findings, especially for rs17178139 (MSRB3), rs1861979 (DPP4), rs7873551 (ASTN2), and rs572246240 (MAST4). Interaction analyses between the significant SNPs as well as the PRS for AD revealed no significant results. Our results confirm that hippocampal volume reductions are influenced by genetic variation, and that different variants reveal different association patterns that can be linked to biological processes in neurodegeneration. Thus, this study underlines the importance of specific genetic analyses in the quest for acquiring deeper insights into the biology of hippocampal volume loss, memory impairment, depression, and neurodegenerative diseases.

Epigenetic signature in neural plasticity: the journey so far and journey ahead

Neural plasticity is a remarkable characteristic of the brain which allows neurons to rewire their structure in response to internal and external stimuli. Many external stimuli collectively referred to as 'epigenetic factors' strongly influence structural and functional reorganization of the brain, thereby acting as a potential driver of neural plasticity. DNA methylation and demethylation, histone acetylation, and deacetylation are some of the frontline epigenetic mechanisms behind neural plasticity. Epigenetic signature molecules (mostly proteins) play a pivotal role in epigenetic reprogramming. Though neuro-epigenetics is an incredibly important field of emerging research, the critical role of signature proteins associated with epigenetic alteration and their involvement in neural plasticity needs further attention. This study gives an integrated and systematic overview of the current state of knowledge with a clear idea of types of neural plasticity and the context-dependent role of epigenetic signature molecules and their modulation by some natural bioactive compounds.

Accelerometer-Measured, Habitual Physical Activity and Circulating Brain-Derived Neurotrophic Factor: A Cross-Sectional Study

BACKGROUND

One of the mechanisms suggested to link physical activity (PA) to favorable brain health is through stimulation of neural growth factors such as brain-derived neurotrophic factor (BDNF). Acute bouts of PA stimulate circulating BDNF levels.

OBJECTIVE

In this investigation, we assessed whether habitual, accelerometer-measured PA levels were related to circulating BDNF levels in a middle-aged cohort.

METHODS

In the Framingham Heart Study Third Generation cohort, 1,769 participants provided reliable accelerometry data and were not missing BDNF measurement and platelet counts. In a cross-sectional analysis, using multivariable regression, we related PA measures to serum BDNF levels, adjusting for age, sex, smoking status, platelet count, depression status, and accelerometer wear time.

RESULTS

Our study participants (mean age 47±9 years, 50.8% women) spent an average of 22.3 mins/day moderate-to-vigorous (MV)PA. Most PA variables (steps, MVPA, light activity, and sedentary time) were not related to BDNF levels (p > 0.05). We observed a non-linear trend, where 15-50 mins/week vigorous activity was associated with lower BDNF compared to those with 0 min vigorous activity (β= -0.049±0.024, p = 0.05), but with no significant associations at lower or higher vigorous activity levels. In smokers, MVPA was also associated with lower BDNF levels (β= -0.216±0.079, p = 0.01).

CONCLUSION

Our study reveals that circulating BDNF is not chronically elevated in individuals with higher levels of habitual PA in middle-aged adults from the community and may even be chronically suppressed with higher PA in subgroups, including current smokers. These results do not contradict previous studies demonstrating that circulating BDNF rises acutely after PA.

Thm2 interacts with paralog, Thm1, and sensitizes to Hedgehog signaling in postnatal skeletogenesis

Mutations in the intraflagellar transport-A (IFT-A) gene, THM1, have been identified in skeletal ciliopathies. Here, we report a genetic interaction between Thm1, and its paralog, Thm2, in postnatal skeletogenesis. THM2 localizes to primary cilia, but Thm2 deficiency does not affect ciliogenesis and Thm2-null mice survive into adulthood. However, by postnatal day 14, Thm2^-/-; Thm1^aln/+ mice exhibit small stature and small mandible. Radiography and microcomputed tomography reveal Thm2^-/-; Thm1^aln/+ tibia are less opaque and have reduced cortical and trabecular bone mineral density. In the mutant tibial growth plate, the proliferation zone is expanded and the hypertrophic zone is diminished, indicating impaired chondrocyte differentiation. Additionally, mutant growth plate chondrocytes show increased Hedgehog signaling. Yet deletion of one allele of Gli2, a major transcriptional activator of the Hedgehog pathway, exacerbated the Thm2^-/-; Thm1^aln/+ small phenotype, and further revealed that Thm2^-/-; Gli2^+/- mice have small stature. In Thm2^-/-; Thm1^aln/+ primary osteoblasts, a Hedgehog signaling defect was not detected, but bone nodule formation was markedly impaired. This indicates a signaling pathway is altered, and we propose that this pathway may potentially interact with Gli2. Together, our data reveal that loss of Thm2 with one allele of Thm1, Gli2, or both, present new IFT mouse models of osteochondrodysplasia. Our data also suggest Thm2 as a modifier of Hedgehog signaling in postnatal skeletal development.