Distinctions between sex and time in patterns of DNA methylation across puberty.

BACKGROUND: There are significant sex differences in human physiology and disease; the genomic sources of these differences, however, are not well understood. During puberty, a drastic neuroendocrine shift signals physical changes resulting in robust sex differences in human physiology. Here, we explore how shifting patterns of DNA methylation may inform these pathways of biological plasticity during the pubertal transition. In this study we analyzed DNA methylation (DNAm) in saliva at two time points across the pubertal transition within the same individuals. Our purpose was to compare two domains of DNAm patterns that may inform processes of sexual differentiation 1) sex related sites, which demonstrated differences between males from females and 2) time related sites in which DNAm shifted significantly between timepoints. We further explored the correlated network structure sex and time related DNAm networks and linked these patterns to pubertal stage, assays of salivary testosterone, a reliable diagnostic of free, unbound hormone that is available to act on target tissues, and overlap with androgen response elements. RESULTS: Sites that differed by biological sex were largely independent of sites that underwent change across puberty. Time-related DNAm sites, but not sex-related sites, formed correlated networks that were associated with pubertal stage. Both time and sex DNAm networks reflected salivary testosterone levels that were enriched for androgen response elements, with sex-related DNAm networks being informative of testosterone levels above and beyond biological sex later in the pubertal transition. CONCLUSIONS: These results inform our understanding of the distinction between sex- and time-related differences in DNAm during the critical period of puberty and highlight a novel linkage between correlated patterns of sex-related DNAm and levels of salivary testosterone.

DNA methylation of HPA-axis genes and the onset of major depressive disorder in adolescent girls: a prospective analysis.

The stress response system is disrupted in individuals with major depressive disorder (MDD) as well as in those at elevated risk for developing MDD. We examined whether DNA methylation (DNAm) levels of CpG sites within HPA-axis genes predict the onset of MDD. Seventy-seven girls, approximately half (n = 37) of whom were at familial risk for MDD, were followed longitudinally. Saliva samples were taken in adolescence (M age = 13.06 years [SD = 1.52]) when participants had no current or past MDD diagnosis. Diagnostic interviews were administered approximately every 18 months until the first onset of MDD or early adulthood (M age of last follow-up = 19.23 years [SD = 2.69]). We quantified DNAm in saliva samples using the Illumina EPIC chip and examined CpG sites within six key HPA-axis genes (NR3C1, NR3C2, CRH, CRHR1, CRHR2, FKBP5) alongside 59 genotypes for tagging SNPs capturing cis genetic variability. DNAm levels within CpG sites in NR3C1, CRH, CRHR1, and CRHR2 were associated with risk for MDD across adolescence and young adulthood. To rule out the possibility that findings were merely due to the contribution of genetic variability, we re-analyzed the data controlling for cis genetic variation within these candidate genes. Importantly, methylation levels in these CpG sites continued to significantly predict the onset of MDD, suggesting that variation in the epigenome, independent of proximal genetic variants, prospectively predicts the onset of MDD. These findings suggest that variation in the HPA axis at the level of the methylome may predict the development of MDD.

Neural correlates of top-down regulation and generation of negative affect in major depressive disorder.

Major depressive disorder (MDD) is characterized by biased information processing that leads to difficulties regulating negative affect, which includes difficulty decreasing negative affect as well as maladaptively increasing negative affect via cognitive processes. To examine the underlying neural correlates, we scanned depressed and never-depressed adults as they completed a cognitive reappraisal task which required decreasing negative affect while viewing a negative image (down-regulation) and increasing negative affect while viewing a neutral image (emotion generation). Compared to control participants, MDD participants had less recruitment of the dorsal anterior cingulate (dACC) and supplementary motor area (SMA) during early phases of down-regulation, the latter associated with poorer negative affect regulation. Further, MDD participants exhibited greater recruitment of the right middle temporal gyrus (MTG) during emotion generation, which was associated with lower negative affect. Dysregulated negative affect in MDD may be due to impairments in efficiently activating the dACC and SMA to meet regulation demands, and maladaptive generation of negative affect that characterizes individuals with MDD may be counteracted by compensatory activation in the MTG. Elucidating neural mechanisms that underlie the generation of negative affect in the absence of external stimuli is an important extension of previous work examining dysfunctional emotional processes in MDD.

Corticotropin-releasing factor 1 receptor haplotype and cognitive features of major depression.

Corticotropin-releasing factor signaling through CRF receptor type 1 (CRF1) has been shown to contribute to learning and memory function. A haplotype of alleles T-A-T in a set of common polymorphisms in the gene encoding for CRF1 (CRHR1) has been associated with both depression vulnerability and alterations in cognitive functioning. The present study investigated the relations between the TAT haplotype and specific symptoms of depression, self-reported ruminative behaviors, and neuropsychological performance on a learning and memory task. Participants were adults with major depression with and without psychotic features (N = 406). Associations were examined between TAT haplotype and endorsement of depression symptoms from diagnostic interviews, scores on the rumination response scale (RRS), and verbal memory performance on the California Verbal Learning Test-II (CVLT-II). All analyses included depression subtype, age, and sex as covariates; CVLT-II analyses also included evening cortisol levels. Across the entire sample, carriers of more copies of the TAT haplotype reported greater endorsement of the symptom describing difficulty concentrating and making decisions. In separate subsamples, TAT homozygotes had higher rumination scores on the RRS, both brooding and reflection subscales, and more TAT copies were associated with poorer CVLT-II performance in both total learning and free recall trials. These data demonstrate that the CRHR1 TAT haplotype is associated with cognitive features of depression including difficulty with decision-making, higher rumination, and poorer learning and memory. It will be important in future research to identify the specific molecular mechanisms for CRF1 signaling that contribute to depression-related cognitive dysfunction.

Neuronal amyloid-ß accumulation within cholinergic basal forebrain in ageing and Alzheimer's disease.

The mechanisms that contribute to selective vulnerability of the magnocellular basal forebrain cholinergic neurons in neurodegenerative diseases, such as Alzheimer's disease, are not fully understood. Because age is the primary risk factor for Alzheimer's disease, mechanisms of interest must include age-related alterations in protein expression, cell type-specific markers and pathology. The present study explored the extent and characteristics of intraneuronal amyloid-ß accumulation, particularly of the fibrillogenic 42-amino acid isoform, within basal forebrain cholinergic neurons in normal young, normal aged and Alzheimer's disease brains as a potential contributor to the selective vulnerability of these neurons using immunohistochemistry and western blot analysis. Amyloid-ß1-42 immunoreactivity was observed in the entire cholinergic neuronal population regardless of age or Alzheimer's disease diagnosis. The magnitude of this accumulation as revealed by optical density measures was significantly greater than that in cortical pyramidal neurons, and magnocellular neurons in the globus pallidus did not demonstrate a similar extent of amyloid immunoreactivity. Immunoblot analysis with a panel of amyloid-ß antibodies confirmed accumulation of high concentration of amyloid-ß in basal forebrain early in adult life. There was no age- or Alzheimer-related alteration in total amyloid-ß content within this region. In contrast, an increase in the large molecular weight soluble oligomer species was observed with a highly oligomer-specific antibody in aged and Alzheimer brains when compared with the young. Similarly, intermediate molecular weight oligomeric species displayed an increase in aged and Alzheimer brains when compared with the young using two amyloid-ß42 antibodies. Compared to cortical homogenates, small molecular weight oligomeric species were lower and intermediate species were enriched in basal forebrain in ageing and Alzheimer's disease. Regional and age-related differences in accumulation were not the result of alterations in expression of the amyloid precursor protein, as confirmed by both immunostaining and western blot. Our results demonstrate that intraneuronal amyloid-ß accumulation is a relatively selective trait of basal forebrain cholinergic neurons early in adult life, and increases in the prevalence of intermediate and large oligomeric assembly states are associated with both ageing and Alzheimer's disease. Selective intraneuronal amyloid-ß accumulation in adult life and oligomerization during the ageing process are potential contributors to the degeneration of basal forebrain cholinergic neurons in Alzheimer's disease.