Childhood adversity from conception onwards: are our tools unnecessarily hindering us?

The oral microbiome is associated with HPA axis response to a psychosocial stressor

Intense psychosocial stress during early life has a detrimental effect on health-disease balance in later life. Simultaneously, despite its sensitivity to stress, the developing microbiome contributes to long-term health. Following stress exposure, HPA-axis activation regulates the "fight or flight" response with the release of glucose and cortisol. Here, we investigated the interaction between the oral microbiome and the stress response. We used a cohort of 115 adults, mean age 24, who either experienced institutionalisation and adoption (n = 40) or were non-adopted controls (n = 75). Glucose and cortisol measurements were taken from participants following an extended socially evaluated cold pressor test (seCPT) at multiple time points. The cohort´s oral microbiome was profiled via 16S-V4 sequencing on microbial DNA from saliva and buccal samples. Using mixed-effect linear regressions, we identified 12 genera that exhibited an interaction with host's cortisol-glucose response to stress, strongly influencing intensity and clearance of cortisol and glucose following stress exposure. Particularly, the identified taxa influenced the glucose and cortisol release profiles and kinetics following seCPT exposure. In conclusion, our study provided evidence for the oral microbiome modifying the effect of stress on the HPA-axis and human metabolism, as shown in glucose-cortisol time series data.

How can early life adversity still exert an effect decades later? A question of timing, tissues and mechanisms

Exposure to any number of stressors during the first 1000 days from conception to age 2 years is important in shaping an individual's life trajectory of health and disease. Despite the expanding range of stressors as well as later-life phenotypes and outcomes, the underlying molecular mechanisms remain unclear. Our previous data strongly suggests that early-life exposure to a stressor reduces the capacity of the immune system to generate subsequent generations of naïve cells, while others have shown that, early life stress impairs the capacity of neuronal stem cells to proliferate as they age. This leads us to the "stem cell hypothesis" whereby exposure to adversity during a sensitive period acts through a common mechanism in all the cell types by programming the tissue resident progenitor cells. Furthermore, we review the mechanistic differences observed in fully differentiated cells and suggest that early life adversity (ELA) may alter mitochondria in stem cells. This may consequently alter the destiny of these cells, producing the lifelong "supply" of functionally altered fully differentiated cells.

The 'Jekyll and Hyde' of Gluconeogenesis: Early Life Adversity, Later Life Stress, and Metabolic Disturbances

The physiological response to a psychological stressor broadly impacts energy metabolism. Inversely, changes in energy availability affect the physiological response to the stressor in terms of hypothalamus, pituitary adrenal axis (HPA), and sympathetic nervous system activation. Glucocorticoids, the endpoint of the HPA axis, are critical checkpoints in endocrine control of energy homeostasis and have been linked to metabolic diseases including obesity, insulin resistance, and type 2 diabetes. Glucocorticoids, through the glucocorticoid receptor, activate transcription of genes associated with glucose and lipid regulatory pathways and thereby control both physiological and pathophysiological systemic energy homeostasis. Here, we summarize the current knowledge of glucocorticoid functions in energy metabolism and systemic metabolic dysfunction, particularly focusing on glucose and lipid metabolism. There are elements in the external environment that induce lifelong changes in the HPA axis stress response and glucocorticoid levels, and the most prominent are early life adversity, or exposure to traumatic stress. We hypothesise that when the HPA axis is so disturbed after early life adversity, it will fundamentally alter hepatic gluconeogenesis, inducing hyperglycaemia, and hence crystalise the significant lifelong risk of developing either the metabolic syndrome, or type 2 diabetes. This gives a “Jekyll and Hyde” role to gluconeogenesis, providing the necessary energy in situations of acute stress, but driving towards pathophysiological consequences when the HPA axis has been altered.

Glucocorticoid receptor signaling in leukocytes after early life adversity

Early life adversity (ELA) has been associated with inflammation and immunosenescence, as well as hyporeactivity of the HPA axis. Because the immune system and the HPA axis are tightly intertwined around the glucocorticoid receptor (GR), we examined peripheral GR functionality in the EpiPath cohort among participants who either had been exposed to ELA (separation from parents and/or institutionalization followed by adoption; n = 40) or had been reared by their biological parents (n = 72).Expression of the strict GR target genes FKBP5 and GILZ as well as total and 1F and 1H GR transcripts were similar between groups. Furthermore, there were no differences in GR sensitivity, examined by the effects of dexamethasone on IL6 production in LPS-stimulated whole blood. Although we did not find differences in methylation at the GR 1F exon or promoter region, we identified a region of the GR 1H promoter (CpG 1-9) that showed lower methylation levels in ELA.Our results suggest that peripheral GR signaling was unperturbed in our cohort and the observed immune phenotype does not appear to be secondary to an altered GR response to the perturbed HPA axis and glucocorticoid (GC) profile, although we are limited in our measures of GR activity and time points.

The COVID-19 Pandemic: Does Our Early Life Environment, Life Trajectory and Socioeconomic Status Determine Disease Susceptibility and Severity?

A poor socioeconomic environment and social adversity are fundamental determinants of human life span, well-being and health. Previous influenza pandemics showed that socioeconomic factors may determine both disease detection rates and overall outcomes, and preliminary data from the ongoing coronavirus disease (COVID-19) pandemic suggests that this is still true. Over the past years it has become clear that early-life adversity (ELA) plays a critical role biasing the immune system towards a pro-inflammatory and senescent phenotype many years later. Cytotoxic T-lymphocytes (CTL) appear to be particularly sensitive to the early life social environment. As we understand more about the immune response to SARS-CoV-2 it appears that a functional CTL (CD8+) response is required to clear the infection and COVID-19 severity is increased as the CD8+ response becomes somehow diminished or exhausted. This raises the hypothesis that the ELA-induced pro-inflammatory and senescent phenotype may play a role in determining the clinical course of COVID-19, and the convergence of ELA-induced senescence and COVID-19 induced exhaustion represents the worst-case scenario with the least effective T-cell response. If the correct data is collected, it may be possible to separate the early life elements that have made people particularly vulnerable to COVID-19 many years later. This will, naturally, then help us identify those that are most at risk from developing the severest forms of COVID-19. In order to do this, we need to recognize socioeconomic and early-life factors as genuine medically and clinically relevant data that urgently need to be collected. Finally, many biological samples have been collected in the ongoing studies. The mechanisms linking the early life environment with a defined later-life phenotype are starting to be elucidated, and perhaps hold the key to understanding inequalities and differences in the severity of COVID-19.