Treg cell: Critical role of regulatory T-cells in depression

Lipoic acid improves wound healing through its immunomodulatory and anti-inflammatory effects in a diabetic mouse model

Objectives

Diabetes mellitus is a chronic disease that has become more prevalent worldwide because of lifestyle changes. It leads to serious complications, including increased atherosclerosis, protein glycosylation, endothelial dysfunction, and vascular denervation. These complications impair neovascularization and wound healing, resulting in delayed recovery from injuries and an elevated risk of infections. The present study aimed to investigate the effect of lipoic acid (LA) on the key mediators involved in the wound healing process, specifically CD4 + CD25 + T cell subsets, CD4 + CD25 + Foxp3 + regulatory T (Treg) cells, T-helper-17 (Th17) cells that generate IL-17 A, glucocorticoid-induced tumor necrosis factor receptor (GITR) expressing cells, as well as cytokines such as IL-2, IL-1β, IL-6, and TNF-α and IFN-γ. These mediators play crucial roles in epidermal and dermal proliferation, hypertrophy, and cell migration.

Methods

We divided mice into 5 groups: the non-diabetic (normal control; NC), wounded non-diabetic mice (N + W), wounded diabetic mice (D + W), wounded diabetic mice treated with 50 mg/kg lipoic acid (D + W + L50) for 14 days, and wounded diabetic mice treated with 100 mg/kg lipoic acid (D + W + L100) for 14 days.

Results

Flow cytometric analysis indicated that lipoic acid-treated mice exhibited a significant decrease in the frequency of intracellular cytokines (IL-17 A, TNF-α and IFN-γ) in CD4 + T cells, as well as a reduction in the number of GITR-expressing cells. Conversely, a significant upregulation in the number CD4+, CD25+, FOXp3 + and CD4 + CD25 + Foxp3 + regulatory T (Treg) cells was observed in this group compared to both the normal + wounded (N + W) and diabetic + wounded (D + W) groups. Additionally, the mRNA Levels of inflammatory mediators (IL-2, IL-1β, IL-6, and TNF-α) were downregulated in lipoic acid-treated mice compared to other groups. T thereby he histological findings of diabetic skin wounds treated with lipoic acid showed well-healed surgical wounds.

Conclusions

These findings support the beneficial role of lipoic acid in fine-tuning the balance between anti-inflammatory and pro-inflammatory cytokines, influencing both their release and gene expression.

Sirtuin 1 underlies depression-related behaviors by modulating the serotonin system in the dorsal raphe nucleus in female mice

Major depressive disorder (MDD) is a primary driver of disability and greatly escalates the worldwide disease burden. Sirtuin 1 (Sirt1), a key regulator of cellular metabolism, is associated with genetic variations in MDD. We investigated how Sirt1 in serotonin (5-HT) neurons within the dorsal raphe nucleus (DRN) in mice affected behaviors associated with depression and susceptibility to stress. Our findings revealed that Sirt1 expression in the DRN was decreased when chronic unpredictable stress was induced in depressed female mice. Additionally, Sirt1 was co-localized with 5-HT neurons within the DRN, and its selective ablation in these neurons have induced depressive phenotypes in female mice but not in males. Adeno-associated virus-mediated knockdown of Sirt1 in adult female mice induced depressive behaviors, whereas Sirt1 overexpression eliminated these behaviors. Moreover, fiber-optic recordings showed a decrease in the neural excitability of 5-HT neurons and 5-HT levels in the DRN after Sirt1 knockdown. Furthermore, we observed that Sirt1 knockdown reduced the expression of tryptophan hydroxylase-2 (Tph2) and phosphorylation levels of extracellular signal-regulated kinase (ERK) and CAMP response element binding protein (CREB). Finally, variable molecular targets regarding immune responses and cytokine productions after Sirt1 knockdown were analyzed via high-throughput RNA-seq analysis of specimens from the DRN. The findings of this study emphasize the importance of Sirt1 for regulating depression-related behaviors in female mice by influencing the activity of 5-HT neurons in the DRN.

The correlation between systemic immune-inflammation index and major depression in patients with depression

Aims

To explore the relationship between the systemic immune-inflammation index (SII) and the severity of depression.

Methods

This retrospective study included 750 patients who were hospitalized at Xiamen Xianyue Hospital and diagnosed with depression from January 2022 to December 2023. The SII was defined as the platelet count × neutrophil count/lymphocyte count. The participants were divided into a mild to moderate depression group (299 patients) and a major depression group (451 patients). Univariate and multivariate Logistic regression analysis, subgroup analysis, sensitivity analysis, and receiver operating characteristic (ROC) curve analysis were used to explore the correlation between the SII and the severity of depression.

Results

According to the multivariate Logistic regression analysis, the SII was independently associated with the risk of major depression (P < 0.05). For every 1- unit and 1-standard-deviation increase in the SII, the risk of major depression increased by 0.1% and 25.3%, respectively (OR: 1.001, 95% CI: 1.000-1.001, P = 0.008; OR: 1.253, 95% CI: 1.061-1.480, P = 0.008), and each 1-unit increase in the Log10SII was associated with a 124.8% increased risk of major depression (OR: 2.248, 95% CI: 1.231-4.106, P = 0.008). Subgroup analysis and sensitivity analysis revealed significant associations between the SII and the risk of major depression was significant in multiple specific populations (P < 0.05). ROC curve analysis revealed that the area under the curve (AUC) value for using the SII to predict the risk of major depression was 0.585 (95% CI: 0.507-0.591, P = 0.024).

Conclusion

Higher SII values are strongly associated with a greater risk of major depression.

Decoding the crossroads of aging and cancer through single-cell analysis: Implications for precision oncology

Single-cell analysis is a transformative approach to understanding cellular heterogeneity in aging and cancer, interconnected processes driven by mechanisms like senescence and immune modulation. This review explores how aging influences cancer initiation, progression, and treatment resistance within the tumor microenvironment (TME). By examining recent studies using single-cell technologies, we reveal the nuanced roles of aging in tumorigenesis, immune interactions, and therapeutic outcomes. Aging is closely tied to cancer progression, with senescent cells demonstrating heightened proliferative, invasive, and metastatic capabilities. Emerging senolytic therapies targeting aging-related pathways hold promise for enhancing treatment efficacy. Advanced tools such as spatial transcriptomics, molecular probes, and artificial intelligence further refine our understanding of aging-related heterogeneity in the TME. By integrating single-cell analysis with these technologies, future research can clarify the intricate interactions between aging and cancer, advancing precision oncology and improving outcomes for aging cancer patients.

A Mendelian randomization study: causal relationship between immune cells and the risks of social phobia, specific phobia, and agoraphobia

BACKGROUND

Although phobia is a common psychiatric disorder, the underlying biological mechanisms have not been fully elucidated. Complex immune-brain interactions that affect neural development, survival, and function may have causal and therapeutic implications in psychiatric illnesses. In this study, the relationships between immune cell traits and phobia were analysed using Mendelian randomization to explore the biological mechanisms.

METHODS

Based on publicly-available genetic data, a two-sample MR analysis was used to determine the causal relationship between 731 immune cell traits and the risk of developing phobias. Sensitivity analyses were conducted to verify the robustness, heterogeneity, and horizontal pleiotropy of the results.

RESULTS

After forward and reverse analyses, false discovery rate (FDR) corrections were performed. No significant associations between phobias and immune cell traits were identified. After adjusting the FDR threshold, social phobia affected two immune cell traits: CD39 on granulocytes (β = 9.0347, 95% confidence interval (CI) = 4.4802-13.5891, P = 0.0001, FDR = 0.0738), and CD11c on granulocytes (β = 7.7976, 95% CI = 3.4616-12.1336, P = 0.0004, FDR = 0.1547). Three immune cell traits affected the risk of specific phobias: CD4 + CD8dim T cell %leukocyte (odds ratio (OR) = 0.9985, 95% CI = 0.9976-0.9993, P = 0.0006, FDR = 0.1373), CD45 on CD33 + HLA DR + CD14dim (OR = 0.9977, 95% CI = 0.9964-0.9990, P = 0.0004, FDR = 0.1373), and CD8 on CD28 + CD45RA + CD8br (OR = 0.9990, 95% CI = 0.9985-0.9996, P = 0.0003, FDR = 0.1373). Two immune cell traits affected the risk of agoraphobia: CD3 on CD39 + resting regulatory T cells (Tregs) (OR = 1.0010, 95 CI%=1.0005-1.0015, P = 0.0001, FDR = 0.0596) and HLA DR on CD33br HLA DR + CD14dim (OR = 0.9993, 95 CI%=0.9990-0.9997, P = 0.0002, FDR = 0.0596).

CONCLUSIONS

Immune cell traits closely related to phobias were screened out through genomics, which provides a reference for the subsequent research on the immune system-phobia interaction.

Extracellular vesicles as precision therapeutics for psychiatric conditions: targeting interactions among neuronal, glial, and immune networks

The critical role of the immune system in brain function and dysfunction is well recognized, yet development of immune therapies for psychiatric diseases has been slow due to concerns about iatrogenic immune deficiencies. These concerns are emphasized by the lack of objective diagnostic tools in psychiatry. A promise to resolve this conundrum lies in the exploitation of extracellular vesicles (EVs) that are physiologically produced or can be synthetized. EVs regulate recipient cell functions and offer potential for EVs-based therapies. Intranasal EVs administration enables the targeting of specific brain regions and functions, thereby facilitating the design of precise treatments for psychiatric diseases. The development of such therapies requires navigating four dynamically interacting networks: neuronal, glial, immune, and EVs. These networks are profoundly influenced by brain fluid distribution. They are crucial for homeostasis, cellular functions, and intercellular communication. Fluid abnormalities, like edema or altered cerebrospinal fluid (CSF) dynamics, disrupt these networks, thereby negatively impacting brain health. A deeper understanding of the above-mentioned four dynamically interacting networks is vital for creating diagnostic biomarker panels to identify distinct patient subsets with similar neuro-behavioral symptoms. Testing the functional pathways of these biomarkers could lead to new therapeutic tools. Regulatory approval will depend on robust preclinical data reflecting progress in these interdisciplinary areas, which could pave the way for the design of innovative and precise treatments. Highly collaborative interdisciplinary teams will be needed to achieve these ambitious goals.

Post-stroke depression: exploring gut microbiota-mediated barrier dysfunction through immune regulation

Post-stroke depression (PSD) is one of the most common and devastating neuropsychiatric complications in stroke patients, affecting more than one-third of survivors of ischemic stroke (IS). Despite its high incidence, PSD is often overlooked or undertreated in clinical practice, and effective preventive measures and therapeutic interventions remain limited. Although the exact mechanisms of PSD are not fully understood, emerging evidence suggests that the gut microbiota plays a key role in regulating gut-brain communication. This has sparked great interest in the relationship between the microbiota-gut-brain axis (MGBA) and PSD, especially in the context of cerebral ischemia. In addition to the gut microbiota, another important factor is the gut barrier, which acts as a frontline sensor distinguishing between beneficial and harmful microbes, regulating inflammatory responses and immunomodulation. Based on this, this paper proposes a new approach, the microbiota-immune-barrier axis, which is not only closely related to the pathophysiology of IS but may also play a critical role in the occurrence and progression of PSD. This review aims to systematically analyze how the gut microbiota affects the integrity and function of the barrier after IS through inflammatory responses and immunomodulation, leading to the production or exacerbation of depressive symptoms in the context of cerebral ischemia. In addition, we will explore existing technologies that can assess the MGBA and potential therapeutic strategies for PSD, with the hope of providing new insights for future research and clinical interventions.

T-regulatory cells and extracellular vesicles in Alzheimer's disease: New therapeutic concepts and hypotheses

Cell-based treatment has experienced exponential expansion in recent years in terms of clinical application and market share among pharmaceutical companies. When malignant cells in a healthy individual produce antigenic peptides derived from mutant or improperly synthesized proteins, the immune system attacks and kills the transforming cells. This process is carried out continuously by immune cells scanning the body for altered cells that could cause some harm. T-regulatory cells (Tregs), which preserve immunological tolerance and can exert neuroprotective benefits in numerous disorders, including animal models of Alzheimer's disease (AD), have demonstrated considerable therapeutic potential. Evidence also suggests that not only Tregs, but extracellular vesicles (EVs) are involved in a wide range of diseases, such as cellular homoeostasis, infection propagation, cancer development and heart disease, and have become a promisor cell-based therapeutic field too. Nevertheless, despite significant recent clinical and commercial breakthroughs, cell-based medicines still confront numerous challenges that hinder their general translation and commercialization. These challenges include, but are not limited to, choosing the best cell source, and creating a product that is safe, adequately viable, and fits the needs of individual patients and diseases. Here, we summarize what we know about Tregs and EVs and their potential therapeutic usage in AD.

Dysfunction in neuro-mesenchymal units impairs the development of bone marrow B cells in mice with anxiety

The reduction in B lymphocytes observed in individuals with anxiety disorders may compromise antiviral responses, yet the precise mechanisms behind this decline remain unclear. While elevated glucocorticoid levels have been suggested as contributing factors, anxiety disorders are associated with diminished glucocorticoid signaling. Given that autonomic nervous system dysfunction is a hallmark of anxiety disorders, we established an anxiety-related behavior mouse model by stimulating C1 neurons in the rostral ventrolateral medulla. Using this model, we confirmed that sustained activation of sympathetic nerves can disrupt adaptive immunity, particularly affecting the development of B cells. The underlying mechanism involves the control of B cell development through neuro-mesenchymal units within the bone marrow, with mesenchyme-derived CXCL12 playing a pivotal role in this regulatory process. Intriguingly, targeting these neuro-mesenchymal units not only restored B cell development but also alleviated anxiety-like behavior in the mice. Our study provides compelling evidence regarding the regulatory role of neuro-mesenchymal units in the development of B cells within the bone marrow. Additionally, our findings suggest that anxiety disorders can create a vicious cycle, perpetuating ongoing mental and immunological damage and ultimately leading to irreversible harm. To break this cycle, it is essential to focus on the dysfunction of immune cells and strive to restore immune homeostasis in individuals suffering from anxiety disorders.

Identification of mitophagy-related genes and analysis of immune infiltration in the astrocytes based on machine learning in the pathogenesis of major depressive disorder

BACKGROUNDS

Major depressive disorder (MDD) is a pervasive mental and mood disorder with complicated and heterogeneous etiology. Mitophagy, a selective autophagy of cells, specifically eliminates dysfunctional mitochondria. The mitochondria dysfunction in the astrocytes is regarded as a critical pathogenetic mechanism of MDD. However, studies on the mitophagy of astrocytes in MDD are scarce. To explore the impact of mitophagy on the astrocytes, we used bioinformatic methods to analyze the correlation between astrocyte-related genes and mitophagy-related genes in MDD.

METHODS

The microarray dataset of MDD was downloaded from the Gene Expression Omnibus database and identified astrocyte- and mitophagy-related differentially expressed genes (AMRDEGs). We used three machine learning algorithms to identify hub AMRDEGs and constructed a diagnostic prediction model. Also, we analyzed transcription factor-gene and gene-microRNA interaction networks, and the immune infiltration in MDD and healthy controls. Besides, we performed consensus clustering analysis, immune infiltration analysis, and gene set variation analysis of MDD samples.

RESULTS

The present research identified 3 hub AMRDEGs (GRN, NDUFAF4, and SNCA), and a good diagnostic model with potential clinical applications was constructed and validated. Besides, we identified 6 transcription factors and 14 microRNAs. The immune infiltration analysis showed that MDD was closely related to immune cells. Gene set variant analysis showed that MDD was related to immune and mitochondrial metabolism and inflammatory signaling pathways.

CONCLUSIONS

We identified 3 hub AMRDEGs, new biomarkers for treating and diagnosing MDD and associated with immuno-inflammation. Our research provides new insights into the early diagnosis and treatment of MDD.

The alterations in CD4+Treg cells across various phases of major depression

BACKGROUND

Major depression (MD) is recurrent and devastating mental disease with a high worldwide prevalence. Mounting evidence suggests neuroinflammation triggers cellular immune dysregulation, characterized by increased proportions of circulating monocytes, and T helper 17 cells and proinflammatory cytokines, thereby increasing susceptibility to MD. However, there is ambiguity in the findings of clinical studies that investigate CD4+ T regulatory (Treg) cells in MD.

METHODS

The proportion of CD4+ Treg cell from blood mononuclear cells was examined using flow cytometry in healthy controls (HCs: n = 96) and patients with first (FEMD: n = 62) or recurrent (RMD: n = 41) disease episodes of MD at baseline (T0; hospital admission) and after a two-week antidepressant treatment (T14). All participants underwent comprehensive neuropsychological assessments.

RESULTS

The initial scores on emotional assessments in patients with MD significantly differed from those of HCs. Both FEMD and RMD patients exhibited a significant decrease in CD4+ Treg cell proportion at baseline compared to HCs. Treg cell proportion rose significantly from T0 to T14 in FEMD patients, who responded to antidepressant therapy, whereas no significant changes were observed in FEMD patients in non-response as well as RMD patients. The improvement of 24-item Hamilton Depression Scale was correlate with changes of Treg cell proportion from T0 to T14 in FEMD patients in response, and the change in Treg cell proportion over a 14-day period exhibited an AUC curve of 0.710.

CONCLUSIONS

A decrease in the proportion of CD4+ Treg cells points towards immune system abnormalities in patients with MD. Furthermore, our finding suggests that the immune activation state varies across different stages of depression.

The interplay between metal ions and immune cells in glioma: pathways to immune escape

This review explores the intricate roles of metal ions-iron, copper, zinc, and selenium-in glioma pathogenesis and immune evasion. Dysregulated metal ion metabolism significantly contributes to glioma progression by inducing oxidative stress, promoting angiogenesis, and modulating immune cell functions. Iron accumulation enhances oxidative DNA damage, copper activates hypoxia-inducible factors to stimulate angiogenesis, zinc influences cell proliferation and apoptosis, and selenium modulates the tumor microenvironment through its antioxidant properties. These metal ions also facilitate immune escape by upregulating immune checkpoints and secreting immunosuppressive cytokines. Targeting metal ion pathways with therapeutic strategies such as chelating agents and metalloproteinase inhibitors, particularly in combination with conventional treatments like chemotherapy and immunotherapy, shows promise in improving treatment efficacy and overcoming resistance. Future research should leverage advanced bioinformatics and integrative methodologies to deepen the understanding of metal ion-immune interactions, ultimately identifying novel biomarkers and therapeutic targets to enhance glioma management and patient outcomes.

Deciphering Regulatory T-Cell Dynamics in Cancer Immunotherapy: Mechanisms, Implications, and Therapeutic Innovations

This Review explores how tumor-associated regulatory cells (Tregs) affect cancer immunotherapy. It shows how Tregs play a role in keeping the immune system in check, how cancers grow, and how well immunotherapy work. Tregs use many ways to suppress the immune system, and these ways are affected by the tumor microenvironment (TME). New approaches to cancer therapy are showing promise, such as targeting Treg checkpoint receptors precisely and using Fc-engineered antibodies. It is important to tailor treatments to each patient's TME in order to provide personalized care. Understanding Treg biology is essential for creating effective cancer treatments and improving the long-term outcomes of immunotherapy.

Genes associated with cellular senescence as diagnostic markers of major depressive disorder and their correlations with immune infiltration

Background

Emerging evidence links cellular senescence to the pathogenesis of major depressive disorder (MDD), a life-threatening and debilitating mental illness. However, the roles of cellular senescence-related genes in MDD are largely unknown and were investigated in this study using a comprehensive analysis.

Methods

Peripheral blood microarray sequencing data were downloaded from Gene Expression Omnibus (GEO) database and retrieved cellular senescence-related genes from CellAge database. A weighted gene co-expression network analysis was used to screen MDD-associated genes. Protein-protein interactions (PPI) were predicted based on STRING data, and four topological algorithms were used to identify hub genes from the PPI network. Immune infiltration was evaluated using CIBERSORT, followed by a correlation analysis between hub genes and immune cells.

Results

A total of 84 cell senescence-related genes were differentially expressed in patients with MDD compared to healthy control participants. Among the 84 genes, 20 were identified to be associated with the MDD disease phenotype, and these genes were mainly involved in hormone-related signaling pathways (such as estrogen, steroid hormone, and corticosteroid) and immune and inflammatory pathways. Three genes, namely, JUN, CTSD, and CALR, which were downregulated in MDD, were identified as the hub genes. The expression of hub genes significantly moderate correlated with multiple immune cells, such as Tregs, NK cells, and CD4+ T cells, and the abundance of these immune cells markedly differed in MDD samples. Multiple microRNAs, transcription factors, and small-molecule drugs targeting hub genes were predicted to explore their molecular regulatory mechanisms and potential therapeutic value in MDD.

Conclusion

JUN, CTSD, and CALR were identified as potential diagnostic markers of MDD and may be involved in the immunoinflammatory mechanism of MDD.

Role of Inflammatory Mechanisms in Major Depressive Disorder: From Etiology to Potential Pharmacological Targets

The involvement of central and peripheral inflammation in the pathogenesis and prognosis of major depressive disorder (MDD) has been demonstrated. The increase of pro-inflammatory cytokines (interleukin (IL)-1β, IL-6, IL-18, and TNF-α) in individuals with depression may elicit neuroinflammatory processes and peripheral inflammation, mechanisms that, in turn, can contribute to gut microbiota dysbiosis. Together, neuroinflammation and gut dysbiosis induce alterations in tryptophan metabolism, culminating in decreased serotonin synthesis, impairments in neuroplasticity-related mechanisms, and glutamate-mediated excitotoxicity. This review aims to highlight the inflammatory mechanisms (neuroinflammation, peripheral inflammation, and gut dysbiosis) involved in the pathophysiology of MDD and to explore novel anti-inflammatory therapeutic approaches for this psychiatric disturbance. Several lines of evidence have indicated that in addition to antidepressants, physical exercise, probiotics, and nutraceuticals (agmatine, ascorbic acid, and vitamin D) possess anti-inflammatory effects that may contribute to their antidepressant properties. Further studies are necessary to explore the therapeutic benefits of these alternative therapies for MDD.

Analysis of the correlation between immune cell characteristics and insomnia: a Mendelian randomization study

Insomnia, recognized as a prevalent sleep disorder, has garnered extensive attention within the realm of public health. Recent studies indicate a close interaction between the immune system and sleep; however, the specific mechanism remains not yet fully understood. Based on the publicly available Genome-Wide Association Study (GWAS) data, we used two-sample Mendelian randomization (MR) analyses to investigate the associations between 731 immune cell traits and insomnia risk. Five MR analysis methods and a comprehensive sensitivity analysis were used to evaluate the reliability of the results. In this study, we identified that 14 immune characteristics among four immune profiles [median fluorescence intensity (MFI), relative cell count (RC), absolute cell count (AC), and morphological parameters (MP)] demonstrated a significant causal association with insomnia. Specifically, eight immune cell characteristics were associated with an increased risk of insomnia, including CD11c+ monocyte% (P < 0.001), CD11c+ HLA DR++ monocyte% (P = 0.004), CD86+ plasmoid dendritic cell (DC) AC (P < 0.001), CD33br HLA DR+ CD14dim AC (P < 0.001), CD8dim AC (P = 0.002), CCR2 on CD14+ CD16- monocyte (P < 0.001), CD39 on monocyte (P < 0.001), and SSC-A on myeloid DC (P < 0.001). Six immune cell characteristics demonstrated protective effects against insomnia, including PB/PC %B cell (P < 0.001), CM CD4+% CD4+ (P < 0.001), T-cell AC (P < 0.001), BAFF-R on IgD- CD38br (P < 0.001), CD16-CD56 on HLA DR+ NK cells (P < 0.001), and CD14 on CD33br HLA DR+ CD14dim (P < 0.001). Our study established the correlation between immune cell characteristics and insomnia, offering a novel theoretical foundation for the concept of sleep-immune cross talk.NEW & NOTEWORTHY This study investigated the association between 731 immune cell characteristics and insomnia using Mendelian randomization, revealing that 14 immune cell characteristics across four groups of immune traits (MFI, RC, AC, and MP) have a significant and causal association with insomnia risk. Our results contribute to the understanding of the sleep-immune cross talk doctrine and offer a new theoretical basis for immune modulation in treating insomnia.

Understanding the Biological Relationship between Migraine and Depression

Migraine is a highly prevalent neurological disorder. Among the risk factors identified, psychiatric comorbidities, such as depression, seem to play an important role in its onset and clinical course. Patients with migraine are 2.5 times more likely to develop a depressive disorder; this risk becomes even higher in patients suffering from chronic migraine or migraine with aura. This relationship is bidirectional, since depression also predicts an earlier/worse onset of migraine, increasing the risk of migraine chronicity and, consequently, requiring a higher healthcare expenditure compared to migraine alone. All these data suggest that migraine and depression may share overlapping biological mechanisms. Herein, this review explores this topic in further detail: firstly, by introducing the common epidemiological and risk factors for this comorbidity; secondly, by focusing on providing the cumulative evidence of common biological aspects, with a particular emphasis on the serotoninergic system, neuropeptides such as calcitonin-gene-related peptide (CGRP), pituitary adenylate cyclase-activating polypeptide (PACAP), substance P, neuropeptide Y and orexins, sexual hormones, and the immune system; lastly, by remarking on the future challenges required to elucidate the etiopathological mechanisms of migraine and depression and providing updated information regarding new key targets for the pharmacological treatment of these clinical entities.