Enhancing synaptic plasticity and cellular resilience to develop novel, improved treatments for mood disorders

The Relationship Between Brain-Derived Neurotrophic Factor and Serotonin in Major Depressive and Bipolar Disorders: A Cross-Sectional Analysis

Background Mood disorders like major depressive disorder (MDD) and bipolar disorder (BD) involve complex interactions between brain-derived neurotrophic factor (BDNF) and serotonin. While extensive research has explored these factors individually, their combined effects and interactions in these disorders are less understood. This study uniquely addresses this gap by examining how BDNF and serotonin interact and relate to mood disorder severity, providing new insights into their joint role in MDD and BD. Objectives The objective of this study was to examine the correlation between serum BDNF and plasma serotonin levels and to assess how these correlations relate to the severity of symptoms and overall disease severity in MDD and BD. Methodology This cross-sectional study, conducted at the Khyber Medical University, Peshawar, from January to September 2023, examined the correlation between BDNF and serotonin in individuals with MDD and BD. Participants (n = 63) aged 18-65 were recruited based on the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) criteria, excluding those with neurological disorders, substance abuse, or severe medical illness. A control group of 21 healthy individuals was matched by age and gender. Data collection involved demographic details, clinical history, and comorbid diagnoses assessed using the Mini International Neuropsychiatric Interview (MINI). Mood disorder severity was measured using the Hamilton Depression Rating Scale (HAM-D) for MDD and the Young Mania Rating Scale (YMRS) for BD, along with additional assessments (Beck Depression Inventory, Global Assessment of Functioning). Serum BDNF and serotonin levels were analyzed using enzyme-linked immunosorbent assay (ELISA) kits. Statistical analyses included t-tests, Mann-Whitney U tests, Pearson correlations, and subgroup analyses to assess relationships between biomarkers, mood disorder severity, and influencing factors. Results BDNF levels were found to be 20.1 ± 5.3 ng/mL in MDD, 18.5 ± 4.7 ng/mL in BD, and 25.9 ± 6.2 ng/mL in controls. Serotonin levels were 45.8 ± 12.6 ng/mL in MDD, 43.2 ± 11.4 ng/mL in BD, and 52.1 ± 14.3 ng/mL in controls. In the MDD group, significant negative correlations were observed between BDNF levels and mood disorder severity (r = -0.32, p = 0.045), whereas serotonin levels did not show significant correlations (r = -0.21, p = 0.23). In the BD group, BDNF levels also showed a significant negative correlation with manic symptoms (r = -0.28, p = 0.048), but serotonin levels showed no significant correlation. Subgroup analyses revealed that participants under 40 years had higher BDNF levels (22.8 ± 5.6 ng/mL) compared to those aged 40 and above (19.7 ± 4.3 ng/mL). Females showed higher BDNF levels (24.5 ± 6.3 ng/mL) than males (19.3 ± 3.8 ng/mL). Participants not on medication had higher BDNF levels (23.6 ± 5.1 ng/mL) compared to those on medication (17.9 ± 4.2 ng/mL). Those without comorbidities also had higher BDNF levels (23.8 ± 5.9 ng/mL) than those with comorbidities (18.2 ± 4.5 ng/mL), while serotonin levels varied similarly across these subgroups. Conclusion Lower BDNF levels are associated with mood disorders and symptom severity, indicating their potential as a biomarker.

A Brain Signaling Framework for Stress-Induced Depression and Ketamine Treatment Elucidated by Phosphoproteomics

Depression is a common affective disorder characterized by significant and persistent low mood. Ketamine, an N-methyl-D-aspartate receptor (NMDAR) antagonist, is reported to have a rapid and durable antidepressant effect, but the mechanisms are unclear. Protein phosphorylation is a post-translational modification that plays a crucial role in cell signaling. Thus, we present a phosphoproteomics approach to investigate the mechanisms underlying stress-induced depression and the rapid antidepressant effect of ketamine in mice. We analyzed the phosphoprotein changes induced by chronic unpredictable mild stress (CUMS) and ketamine treatment in two known mood control centers, the medial prefrontal cortex (mPFC) and the nucleus accumbens (NAc). We initially obtained >8,000 phosphorylation sites. Quantitation revealed 3,988 sites from the mPFC and 3,196 sites from the NAc. Further analysis revealed that changes in synaptic transmission-related signaling are a common feature. Notably, CUMS-induced changes were reversed by ketamine treatment, as shown by the analysis of commonly altered sites. Ketamine also induced specific changes, such as alterations in synapse organization, synaptic transmission, and enzyme binding. Collectively, our findings establish a signaling framework for stress-induced depression and the rapid antidepressant effect of ketamine.

Regulation of G-protein coupled receptor signalling underpinning neurobiology of mood disorders and depression

G-protein coupled receptors (GPCRs) have long been at the center of investigations of the neurobiology of depression and mood disorders. Different facets of GPCR signalling pathways, including those controlling monoaminergic and neuropeptidergic hormonal systems are believed to be dysregulated in major depressive and bipolar disorders. Although these receptors are key molecular targets for a variety of therapeutic agents and continue to be the focus of intense pharmaceutical development, the molecular mechanisms activated by these GPCRs and underpin the pathological basis of mood disorders remain poorly understood. This review will discuss some of the emerging regulatory mechanisms of GPCR signaling in the central nervous system (CNS) involving protein-protein interactions, downstream effectors and cross-talk with other signaling molecules and their potential involvement in the neurobiology of psychiatric disease.

Alteration in the expression of exon IIC transcripts of brain-derived neurotrophic factor gene by simvastatin [correction of simvastain] in chronic mild stress in mice: a possible link with dopaminergic pathway

We have investigated the influence of dopaminergic agents on the expression of brain-derived neurotrophic factor (BDNF) gene in relation with lipid levels in chronic mild stress (CMS). Mice subjected to CMS were treated with simvastatin (10 mg/kg, per os (orally)) along with bromocriptine (2 mg/kg, intraperitoneally (ip)), levodopa (200 mg/kg, ip), or haloperidol (0.1 mg/kg, ip) for 14 days. CMS produced a decrease in sucrose intake and an increase in serum cholesterol and triglycerides levels with a decrease in high-density lipoprotein cholesterol, which were prevented by simvastatin. This was greater when it was combined with bromocriptine or levodopa. Haloperidol significantly prevented the simvastatin-induced increase in sucrose intake but not the alterations in lipids. There was an upregulation in the expression of BDNF exon-IIA and -IIB transcripts by CMS but not the exon-IIC transcripts. Simvastatin could increase expression of exon-IIC transcripts in stressed mice. This was partially increased by bromocriptine. Haloperidol significantly prevented simvastatin-induced increase in expression of BDNF exon-IIC transcripts. The results showed a positive correlation between expression of BDNF exon-IIC transcripts and sucrose intake. In conclusion, our data suggest the involvement of lipid levels and BDNF exon-IIC transcripts in CMS-induced behaviour in mice, possibly through the dopaminergic system.

Epigenetic mechanisms in mood disorders: targeting neuroplasticity

Developing novel therapeutics and diagnostic tools based upon an understanding of neuroplasticity is critical in order to improve the treatment and ultimately the prevention of a broad range of nervous system disorders. In the case of mood disorders, such as major depressive disorder (MDD) and bipolar disorder (BPD), where diagnoses are based solely on nosology rather than pathophysiology, there exists a clear unmet medical need to advance our understanding of the underlying molecular mechanisms and to develop fundamentally new mechanism experimental medicines with improved efficacy. In this context, recent preclinical molecular, cellular, and behavioral findings have begun to reveal the importance of epigenetic mechanisms that alter chromatin structure and dynamically regulate patterns of gene expression that may play a critical role in the pathophysiology of mood disorders. Here, we will review recent advances involving the use of animal models in combination with genetic and pharmacological probes to dissect the underlying molecular mechanisms and neurobiological consequence of targeting this chromatin-mediated neuroplasticity. We discuss evidence for the direct and indirect effects of mood stabilizers, antidepressants, and antipsychotics, among their many other effects, on chromatin-modifying enzymes and on the epigenetic state of defined genomic loci, in defined cell types and in specific regions of the brain. These data, as well as findings from patient-derived tissue, have also begun to reveal alterations of epigenetic mechanisms in the pathophysiology and treatment of mood disorders. We summarize growing evidence supporting the notion that selectively targeting chromatin-modifying complexes, including those containing histone deacetylases (HDACs), provides a means to reversibly alter the acetylation state of neuronal chromatin and beneficially impact neuronal activity-regulated gene transcription and mood-related behaviors. Looking beyond current knowledge, we discuss how high-resolution, whole-genome methodologies, such as RNA-sequencing (RNA-Seq) for transcriptome analysis and chromatin immunoprecipitation-sequencing (ChIP-Seq) for analyzing genome-wide occupancy of chromatin-associated factors, are beginning to provide an unprecedented view of both specific genomic loci as well as global properties of chromatin in the nervous system. These methodologies when applied to the characterization of model systems, including those of patient-derived induced pluripotent cell (iPSC) and induced neurons (iNs), will greatly shape our understanding of epigenetic mechanisms and the impact of genetic variation on the regulatory regions of the human genome that can affect neuroplasticity. Finally, we point out critical unanswered questions and areas where additional data are needed in order to better understand the potential to target mechanisms of chromatin-mediated neuroplasticity for novel treatments of mood and other psychiatric disorders.

Enhancing neuronal plasticity and cellular resilience to develop novel, improved therapeutics for difficult-to-treat depression

There is growing evidence from neuroimaging and ostmortem studies that severe mood disorders, which have traditionally been conceptualized as neurochemical disorders, are associated with impairments of structural plasticity and cellular resilience. It is thus noteworthy that recent preclinical studies have shown that critical molecules in neurotrophic signaling cascades (most notably cyclic adenosine monophosphate [cAMP] response element binding protein, brain-derived neurotrophic factor, bcl-2, and mitogen activated protein [MAP] kinases) are long-term targets for antidepressant agents and antidepressant potentiating modalities. This suggests that effective treatments provide both trophic and neurochemical support, which serves to enhance and maintainnormal synaptic connectivity, thereby allowing the chemical signal to reinstate the optimal functioning of critical circuits necessary for normal affective functioning. For many refractory patients, drugs mimicking "traditional" strategies, which directly or indirectly alter monoaminergic levels, may be of limited benefit. Newer "plasticity enhancing" strategies that may have utility in the treatment of refractory depression include N-methyl-D-aspartate antagonists, alpha-amino-3-hydroxy-5-methylisoxazole propionate (AMPA) potentiators, cAMP phosphodiesterase inhibitors, and glucocorticoid receptor antagonists. Small-molecule agents that regulate the activity f growth factors, MAP kinases cascades, and the bcl-2 family of proteins are also promising future avenues. The development of novel, nonaminergic-based therapeutics holds much promise for improved treatment of severe, refractory mood disorders.