ORIGINAL INVESTIGATION

Is Stress Reactivity an Intermediary Mechanism in the Association Between NR3C1 Methylation and Adolescent Loneliness?

This study examined whether saliva-derived DNA methylation in the glucocorticoid receptor (NR3C1) gene was linked to loneliness through dysregulation of the hypothalamic-pituitary-adrenal axis (HPA-axis) in 101 early adolescents (Mage = 11.61 years, SDage = 0.64, 55.45% girls). Using person-centered analyses to account for interindividual differences in adolescents' stress reactivity, we identified three subgroups of cortisol responders to a social evaluative stressor: A hyporesponsive subgroup (30.5%), a moderate-responsive subgroup (44.2%), and a hyperresponsive subgroup (25.3%). Exploratory analyses also identified subgroups for two markers of the autonomous nervous system (ANS), that is, heart rate (HR) and skin conductance (SC). Furthermore, the indirect effects from NR3C1 methylation to early adolescent loneliness via individual differences in stress responses were examined. Results indicated that higher NR3C1 methylation levels were associated with a lower probability of belonging to the most reactive stress response subgroups for cortisol and HR, and to the high mean-level subgroup for SC. Additionally, higher probabilities of belonging to the low mean-level SC subgroup were associated with higher levels of loneliness. However, there was no evidence that NR3C1 methylation was associated with early adolescent loneliness, either directly or indirectly via stress reactivity. These findings highlight significant individual differences in stress reactivity, emphasizing the need to explicitly consider such variability in future research. Moreover, the results suggest that NR3C1 methylation is linked to individual differences in stress responding, warranting further investigation.

CLOCK rs1801260 and MTNR1B rs10830963 Polymorphisms Modulate the Association between Cholesterol Levels and Circadian Rhythms in Arctic Residents

Genetic evidence for a causal relationship between melatonin metabolism and depression.

To investigate the causal relevance of melatonin metabolism, which provides the biological basis for circulating melatonin levels, to specific depression symptom subtypes, we performed a targeted systematic review of melatonin metabolism pathways in the human brain and liver. Using two-sample Mendelian randomization (MR), we assessed the causal effects of metabolism pathways and/or individual genes on major depressive disorder (MDD) and nine symptom subtypes derived from Patient Health Questionnaire-9 (PHQ-9). Instrumental variables (IVs) were expression quantitative trait loci (eQTL) for eight individual genes, one synthesis route, and three degradation routes. Results were assessed using Bayesian colocalization and phenome-wide association analyses. At the pathway-level, the genetically proxied synthesis-route signal was associated with PHQ-9 Assessment 5 (PHQ9A5, OR: 0.89, 95% CI: 0.85-0.93), but sensitivity analyses suggested this association was primarily driven by TPH1 and may reflect serotonin-related biology. In contrast, higher brain melatonin degradation raised the risk of both PHQ9A1 (OR: 1.03, 95% CI: 1.02-1.04) and PHQ9A7 (OR: 1.03, 95% CI: 1.02-1.03). Within degradation, up-regulation of the kynurenine sub-pathway increased the odds of PHQ9A3 (OR: 1.05, 95% CI: 1.02-1.07), PHQ9A4 (OR = 1.04, 95% CI: 1.02-1.06) and PHQ9A7 (OR: 1.05, 95% CI: 1.02-1.07). Gene-level analyses were largely concordant, except for SULT1A1, whose higher expression was genetically protective for PHQ9A3 but risk-increased for PHQ9A1 and PHQ9A4. Overall, these results demonstrate that melatonin metabolism exerts symptom-specific and pathway-specific causal effects on depression. A stratified view of melatonin's role may help optimize the application of exogenous melatonin supplementation.

Anxiety and Depression Traits Are Moderated by a Sex-Dependent Genetic Interaction Between 5-HTTLPR and BDNF

Background/Objectives: Depression and anxiety disorders exhibit significant clinical heterogeneity, which complicates diagnosis and treatment. This study investigated whether tripartite interactions between biological sex, the serotonin transporter gene promoter region (5-HTTLPR), and brain-derived neurotrophic factor (BDNF) G196A polymorphisms explain specific symptom-level variations. Methods: A community sample of 271 Australian adults was genotyped for common 5-HTTLPR (short/long) and BDNF (G/A) variants. Participants completed self-reported measures of anxiety (SAS), depression subtypes (SDS; clinical content scales), and psychological resilience (CDRISC). Morning salivary cortisol, BMI, and substance use were assessed as potential confounds. Statistical analyses utilised a three-way factorial ANCOVA to test for interactions on raw scores, controlling for age. Significant omnibus interactions were decomposed via planned stratified ANCOVAs within each 5-HTTLPR stratum. Results: The BDNF GA genotype exerted opposite effects on anxiety and anhedonia depending on sex and 5-HTTLPR background. In females, GA was associated with increased symptoms on an ss background, whereas in males, GA was associated with increased symptoms on an ll background. These effects were highly specific to anxiety and anhedonic depression, while depressed mood, cognitive, and somatic subtypes remained unaffected. Findings were independent of cortisol, BMI, smoking, alcohol use, and psychological resilience. Conclusions: The findings reveal a complex, sex-dependent genetic interaction that selectively influences anhedonia and anxiety. They should be interpreted in the context of modest subgroup sizes following genotype stratification and require replication in larger independent cohorts. Nonetheless, this study highlights the value of considering sex-stratified genetic backgrounds and symptom specificity to advance personalised precision medicine in psychiatry.

CLOCK 3111T/C Polymorphism and Sex Moderate the Effect of Childhood Trauma on White Matter Microstructure in Bipolar Disorder

Background. Bipolar disorder (BD) is characterized by circadian rhythm disruptions, contributing to mood instability and recurrence. These rhythms are regulated by clock genes in the suprachiasmatic nucleus, including the CLOCK 3111T/C (rs1801260) polymorphism that has been linked to delayed sleep phase, insomnia, and altered circadian expression. Both circadian disruption and adverse childhood experiences (ACEs) correlate with white matter (WM) abnormalities. We hypothesized that rs1801260 moderates ACE effects on WM microstructure in BD. Methods. We enrolled 137 BD patients in depressive episodes. Participants underwent 3T MRI, rs1801260 genotyping and completed the Childhood Trauma Questionnaire. Moderation (PROCESS) tested genotype–ACE interactions on whole-brain fractional anisotropy (FA), axial diffusivity (AD), mean diffusivity (MD), and radial diffusivity (RD) values; voxel-wise TBSS (FSL Randomize) localized effects, with sex-stratified and GLZ analyses for genotype–sex interactions. Results. Significant rs1801260 × ACE interactions emerged for FA and RD across physical abuse, physical neglect, and emotional neglect. Higher ACEs were associated with lower FA/higher RD only in CLOCK rs1801260*C carriers, mainly females. TBSS showed physical abuse × rs1801260 interaction in the corpus callosum, internal capsule and corona radiata. A GLZ model with separate slopes confirmed physical abuse × sex × rs1801260 interactions on FA/RD, with effects specific to female CLOCK rs1801260*C carriers but genotype-independent in males. Conclusions. rs1801260 moderates the impact of early-life stress on WM integrity in BD, particularly in emotion-regulation tracts, with CLOCK rs1801260*C carriers showing greater vulnerability. Effects are genotype-specific in females but genotype-independent in males, possibly reflecting sex-dimorphic neurodevelopment driven by estrogen–androgen modulation of clock genes, HPA axis, and myelination.

Association between physical activity level and gut microbiota profiles in individuals with subthreshold depression: a cross-sectional study

Subthreshold depression (SD) represents a subclinical state between mental health and major depressive disorder (MDD) and is associated with a high prevalence and substantial risk of progression to MDD. Physical activity (PA) has been proposed to exert antidepressant effects through modulation of the gut–brain axis. However, the association between PA level and gut microbiota profiles in individuals with SD remains poorly understood. This is a cross-sectional observational study. Stratified random sampling was used to screen full-time undergraduates aged 18–25 years at Jimei University for subthreshold depression. Following initial screening with the CES-D and secondary screening with a structured clinical interview, the HAMD-17, and the BDI-II, 122 participants were enrolled. Participants were assigned by IPAQ short form to low ( n = 46), moderate ( n = 47), and high ( n = 29) physical activity groups. Cardiorespiratory fitness was assessed as maximal oxygen uptake estimated by a submaximal Astrand-Rhyming cycle ergometer test. Fecal samples were subjected to 16S rRNA gene V3–V4 sequencing; α-diversity, β-diversity, differential genera, and keystone species were analyzed. No significant differences in α-diversity or β-diversity were observed among the three PA groups ( P > 0.05). However, distinct taxonomic signatures were identified. The low-PA group was enriched in potentially pro-inflammatory taxa, including Streptococcaceae and Eggerthella ( P < 0.05), whereas the moderate-PA group exhibited increased abundance of butyrate-producing genera, including Roseburia and Lachnospiraceae_UCG-010 ( P < 0.05). The high-PA group showed significant enrichment of Dorea ( P < 0.05). Faecalibacterium exhibited the highest Structural Keystoneness (Ks) within the microbial co-occurrence network, and its relative abundance was positively associated with VO 2 max. Moreover, Median (Ks) was strongly correlated with MAD (Ks) (ρ = 0.602, P < 0.001), indicating that the ecological importance of high-keystone taxa is highly context dependent. Although PA level was not significantly associated with overall gut microbial diversity in college students with SD, it was closely associated with the differential distribution of specific functional genera. These findings provide novel evidence supporting the role of PA-related microbial remodeling in SD and may facilitate the development of microbiota-targeted interventions that mimic exercise-induced benefits.