Human-like adrenal development in wild chimpanzees: A longitudinal study of urinary dehydroepiandrosterone-sulfate and cortisol

Effects of social environments on male primate HPG and HPA axis developmental programming

Developmental plasticity is particularly important for humans and other primates because of our extended period of growth and maturation, during which our phenotypes adaptively respond to environmental cues. The hypothalamus-pituitary-gonadal (HPG) and hypothalamus-pituitary-adrenal (HPA) axes are likely to be principal targets of developmental "programming" given their roles in coordinating fitness-relevant aspects of the phenotype, including sexual development, adult reproductive and social strategies, and internal responses to the external environment. In social animals, including humans, the social environment is believed to be an important source of cues to which these axes may adaptively respond. The effects of early social environments on the HPA axis have been widely studied in humans, and to some extent, in other primates, but there are still major gaps in knowledge specifically relating to males. There has also been relatively little research examining the role that social environments play in developmental programming of the HPG axis or the HPA/HPG interface, and what does exist disproportionately focuses on females. These topics are likely understudied in males in part due to the difficulty of identifying developmental milestones in males relative to females and the general quiescence of the HPG axis prior to maturation. However, there are clear indicators that early life social environments matter for both sexes. In this review, we examine what is known about the impact of social environments on HPG and HPA axis programming during male development in humans and nonhuman primates, including the role that epigenetic mechanisms may play in this programming. We conclude by highlighting important next steps in this research area.

Is membrane androgen and estrogen receptor signaling imperative in the governing function of the adrenal cortex in the Eurasian beaver (Castor fiber L.)?

There is a need to fully know the physiology of Eurasian beaver due to its essential role in environmental homeostasis. However, a "human factor" impacts this, including stress conditions and environmental pollution. Adrenal glands protect these all. The regulation of endocrine processes by nonclassical androgen and estrogen signaling, the first and fastest control, is still a matter of research. The specific analyses performed here in mature female and male beaver adrenals contained: anatomical and histological examinations, expression and localization of membrane androgen receptor (zinc transporter, Zinc- and Iron-like protein 9; ZIP9) and membrane estrogen receptor coupled with G protein (GPER), and measurement of zinc (Zn2+) and copper (Ca2+) ion levels and corticosterone levels. We revealed normal anatomical localization, size, and tissue histology in female and male beavers, respectively. Equally, ZIP9 and GPER were localized in the membrane of all adrenal cortex cells. The protein expression of these receptors was higher (p < 0.001) in male than female adrenal cortex cells. Similarly, Zn2+ and Ca2+ ion levels were higher (p < 0.05, p < 0.01) in male than female adrenal cortex. The increased corticosterone levels (p < 0.001) were detected in the adrenal cortex of females when compared to males. The present study is the first to report the presence of nonclassical androgen and estrogen signaling and its possible regulatory function in the adrenal cortex of Eurasian beavers. We assume that this first-activated and fast-transmitted regulation can be important in the context of the effect of environmental physical and chemical stressors especially on adrenal cortex cells. The beaver adrenals may constitute an additional supplementary model for searching for universal mechanisms of adrenal cortex physiology and diseases.

Human-like adrenal features in Chinese tree shrews revealed by multi-omics analysis of adrenal cell populations and steroid synthesis

The Chinese tree shrew ( Tupaia belangeri chinensis) has emerged as a promising model for investigating adrenal steroid synthesis, but it is unclear whether the same cells produce steroid hormones and whether their production is regulated in the same way as in humans. Here, we comprehensively mapped the cell types and pathways of steroid metabolism in the adrenal gland of Chinese tree shrews using single-cell RNA sequencing, spatial transcriptome analysis, mass spectrometry, and immunohistochemistry. We compared the transcriptomes of various adrenal cell types across tree shrews, humans, macaques, and mice. Results showed that tree shrew adrenal glands expressed many of the same key enzymes for steroid synthesis as humans, including CYP11B2, CYP11B1, CYB5A, and CHGA. Biochemical analysis confirmed the production of aldosterone, cortisol, and dehydroepiandrosterone but not dehydroepiandrosterone sulfate in the tree shrew adrenal glands. Furthermore, genes in adrenal cell types in tree shrews were correlated with genetic risk factors for polycystic ovary syndrome, primary aldosteronism, hypertension, and related disorders in humans based on genome-wide association studies. Overall, this study suggests that the adrenal glands of Chinese tree shrews may consist of closely related cell populations with functional similarity to those of the human adrenal gland. Our comprehensive results (publicly available at http://gxmujyzmolab.cn:16245/scAGMap/) should facilitate the advancement of this animal model for the investigation of adrenal gland disorders.

Mothers' prenatal distress accelerates adrenal pubertal development in daughters

Human life history schedules vary, partly, because of adaptive, plastic responses to early-life conditions. Little is known about how prenatal conditions relate to puberty timing. We hypothesized that fetal exposure to adversity may induce an adaptive response in offspring maturational tempo. In a longitudinal study of 253 mother-child dyads followed for 15 years, we investigated if fetal exposure to maternal psychological distress related to children's adrenarche and gonadarche schedules, assessed by maternal and child report and by dehydroepiandrosterone sulfate (DHEA-S), testosterone, and estradiol levels. We found fetal exposure to elevated maternal prenatal psychological distress predicted earlier adrenarche and higher DHEA-S levels in girls, especially first-born girls, and that associations remained after covarying indices of postnatal adversity. No associations were observed for boys or for gonadarche in girls. Adrenarche orchestrates the social-behavioral transition from juvenility to adulthood; therefore, significant findings for adrenarche, but not gonadarche, suggest that prenatal maternal distress instigates an adaptive strategy in which daughters have earlier social-behavioral maturation. The stronger effect in first-borns suggests that, in adverse conditions, it is in the mother's adaptive interest for her daughter to hasten social maturation, but not necessarily sexual maturation, because it would prolong the duration of the daughter allomothering younger siblings. We postulate a novel evolutionary framework that human mothers may calibrate the timing of first-born daughters' maturation in a way that optimizes their own reproductive success.

Distinct developmental trajectories for risky and impulsive decision-making in chimpanzees

Human adolescence is characterized by a suite of changes in decision-making and emotional regulation that promote risky and impulsive behavior. Accumulating evidence suggests that behavioral and physiological shifts seen in human adolescence are shared by some primates, yet it is unclear if the same cognitive mechanisms are recruited. We examined developmental changes in risky choice, intertemporal choice, and emotional responses to decision outcomes in chimpanzees, our closest-living relatives. We found that adolescent chimpanzees were more risk-seeking than adults, as in humans. However, chimpanzees showed no developmental change in intertemporal choice, unlike humans, although younger chimpanzees did exhibit elevated emotional reactivity to waiting compared to adults. Comparisons of cortisol and testosterone indicated robust age-related variation in these biomarkers, and patterns of individual differences in choices, emotional reactivity, and hormones also supported a developmental dissociation between risk and choice impulsivity. These results show that some but not all core features of human adolescent decision-making are shared with chimpanzees. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Dehydroepiandrosterone sulfate (DHEAS) in excreta is a good indicator of serum DHEAS in Japanese macaques (Macaca fuscata)

We developed a microplate enzyme immunoassay (EIA) to measure dehydroepiandrosterone sulfate (DHEAS) in the blood, urine, and feces of Japanese macaques and evaluated the relationship between serum DHEAS and excreta DHEAS. Our DHEAS EIA using heterological DHEA derivatives conjugated with enzyme was highly sensitive, and linearities and recoveries for all matrices of Japanese macaques were reliable. For the biological evaluation of the metabolism of DHEAS in Japanese macaques, dissolved DHEAS was injected into the subjects, and consecutively collected serum, urine, and fecal samples were analyzed. The peaks of serum DHEAS were observed 6 h after the administration, while those of urine and feces were observed after 24 h. The fluctuation of those in urine and feces were significantly correlated with serum DHEAS levels. In addition, we measured pregnanediol-glucuronide (PdG), and estrone-conjugate (E₁C) in urine and fecal samples to investigate the effects of administrated DHEAS on these progesterone and estrogen metabolites. The peak of PdG was observed 24 h after administration, then declined sharply. The concentration of E₁C increased 1 week after administration in two out of three subjects. Our results suggest that measuring urinary and fecal DHEAS with our EIA provides a non-invasive alternative to assessing DHEAS levels in the serum of Japanese macaques.

Puberty initiates a unique stage of social learning and development prior to adulthood: Insights from studies of adolescence in wild chimpanzees

In humans, puberty initiates a period of rapid growth, change, and formative neurobehavioral development. Brain and behavior changes during this maturational window contribute to opportunities for social learning. Here we provide new insights into adolescence as a unique period of social learning and development by describing field studies of our closest living relatives, chimpanzees. Like humans, chimpanzees have a multiyear juvenile life stage between weaning and puberty onset followed by a multiyear adolescent life stage after pubertal onset but prior to socially-recognized adulthood. As they develop increasing autonomy from caregivers, adolescent chimpanzees explore and develop many different types of social relationships with a wide range of individuals in a highly flexible social environment. We describe how adolescent social motivations and experiences differ from those of juveniles and adults and expose adolescents to high levels of uncertainty, risk, and vulnerability, as well as opportunities for adaptive social learning. We discuss how these adolescent learning experiences may be shaped by early life and in turn shape varied adult social outcomes. We outline how future chimpanzee field research can contribute in new ways to a more integrative interdisciplinary understanding of adolescence as a developmental window of adaptive social learning and resilience.

Age, adrenal steroids, and cognitive functioning in captive chimpanzees (Pan troglodytes)

Background

Dehydroepiandrosterone-sulfate is the most abundant circulating androgen in humans and other catarrhines. It is involved in several biological functions, such as testosterone production, glucocorticoid antagonist actions, neurogenesis and neuroplasticty. Although the role of dehydroepiandrosterone-sulfate (DHEAS) in cognition remains elusive, the DHEAS/cortisol ratio has been positively associated with a slower cognitive age-decline and improved mood in humans. Whether this relationship is found in nonhuman primates remains unknown.

Methods

We measured DHEAS and cortisol levels in serum of 107 adult chimpanzees to investigate the relationship between DHEAS levels and age. A subset of 21 chimpanzees was used to test the potential associations between DHEAS, cortisol, and DHEAS/cortisol ratio in cognitive function, taking into account age, sex, and their interactions. We tested for cognitive function using the primate cognitive test battery (PCTB) and principal component analyses to categorize cognition into three components: spatial relationship tasks, tool use and social communication tasks, and auditory-visual sensory perception tasks.

Results

DHEAS levels, but not the DHEAS/cortisol ratio, declined with age in chimpanzees. Our analyses for spatial relationships tasks revealed a significant, positive correlation with the DHEAS/cortisol ratio. Tool use and social communication had a negative relationship with age. Our data show that the DHEAS/cortisol ratio, but not DHEAS individually, is a promising predictor of spatial cognition in chimpanzees.

Value Ranges and Clinical Comparisons of Serum DHEA-S, IL-6, and TNF-α in Western Lowland Gorillas

Simple Summary

Biomarkers are molecules found in the body that can indicate current physiological functioning and are frequently used to monitor health and diagnose disease. These biomarkers, such as hormones and immune markers, can provide valuable information on the health and welfare of animals. Knowledge on the normal levels of these biomarkers in various species is a crucial step for monitoring health and understanding disease. In this paper, we report assays and value ranges of biomarkers rarely measured in western lowland gorillas in human care. We also compare concentrations of each biomarker between clinical and non-clinical samples. The levels of the two immune biomarkers were higher in clinical samples, but the levels of the neuroendocrine biomarker were not significantly different between clinical and non-clinical samples. These data contribute toward eventually establishing reference ranges for these biomarkers and help improve our understanding of health and welfare in zoo-housed animals.

Abstract

Physiological data can provide valuable information about the health and welfare of animals. Unfortunately, few validated assays and a lack of information on species-typical levels of circulating biomarkers for wildlife make the measurement, interpretation, and practical application of such data difficult. We validated commercially available kits and calculated reference intervals (herein called “value ranges”) for dehydroepiandrosterone-sulfate (DHEA-S), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α) in a sample of zoo-housed western lowland gorillas due to the roles these biomarkers play in stress and immune responses. For each biomarker, we present species-specific value ranges for a sample of gorillas in human care (n = 57). DHEA-S did not vary significantly by sex or age, while IL-6 was higher in males and older gorillas and TNF-α was higher in females but not associated with age. We also compared non-clinical with clinical samples (n = 21) to explore whether these biomarkers reflect changes in health status. There was no significant difference between clinical and non-clinical samples for DHEA-S, but both IL-6 and TNF-α were significantly higher in gorillas showing clinical symptoms or prior to death. Additional work is needed to improve our understanding of normal versus clinical variation in these biomarkers, and we encourage continued efforts to identify and validate additional biomarkers that can be used to inform assessments of health and welfare in wildlife.

Adrenal androgens, adrenarche, and zona reticularis: A human affair?

In humans, reticularis cells of the adrenal cortex fuel the production of androgen steroids, constituting the driver of numerous morphological changes during childhood. These steps are considered a precocious stage of sexual maturation and are grouped under the term "adrenarche". This review describes the molecular and enzymatic characteristics of the zona reticularis, along with the possible signals and mechanisms that control its emergence and the associated clinical features. We investigate the differences between species and discuss new studies such as genetic lineage tracing and transcriptomic analysis, highlighting the rodent inner cortex's cellular and molecular heterogeneity. The recent development and characterization of mouse models deficient for Prkar1a presenting with adrenocortical reticularis-like features prompt us to review our vision of the mouse adrenal gland maturation. We expect these new insights will help increase our understanding of the adrenarche process and the pathologies associated with its deregulation.

Aggression, glucocorticoids, and the chronic costs of status competition for wild male chimpanzees

Across vertebrates, high social status affords preferential access to resources, and is expected to correlate positively with health and longevity. Increasing evidence, however, suggests that although dominant females generally enjoy reduced exposure to physiological and psychosocial stressors, dominant males do not. Here we test the hypothesis that costly mating competition by high-ranking males results in chronic, potentially harmful elevations in glucocorticoid production. We examined urinary glucocorticoids (n = 8029 samples) in a 20-year longitudinal study of wild male chimpanzees (n = 20 adults) in the Kanyawara community of Kibale National Park, Uganda. We tested whether glucocorticoid production was associated with dominance rank in the long term, and with mating competition and dominance instability in the short term. Using mixed models, we found that both male aggression and glucocorticoid excretion increased when the dominance hierarchy was unstable, and when parous females were sexually available. Glucocorticoid excretion was positively associated with male rank in stable and unstable hierarchies, and in mating and non-mating contexts. Glucorticoids increased with both giving and receiving aggression, but giving aggression was the primary mechanism linking elevated glucocorticoids with high rank. Glucocorticoids also increased with age. Together these results show that investment in male-male competition increases cumulative exposure to glucocorticoids, suggesting a long-term tradeoff with health that may constrain the ability to maintain high status across the life course. Our data suggest that the relationship between social rank and glucocorticoid production often differs in males and females owing to sex differences in the operation of sexual selection.

The Kibale Chimpanzee Project: Over thirty years of research, conservation, and change

Long-term primate field research programs contribute to the protection of endangered primate species and their vanishing habitats by informing and fostering local and international conservation programs. The Kibale Chimpanzee Project (KCP) has studied the Kanyawara community of wild chimpanzees continuously since 1987, investigating a wide range of behavioral, ecological, and physiological questions. The study area includes the northwest boundary of Kibale National Park, Uganda, and has experienced habitat change driven by multiple causes, including forest regeneration, an increasingly warmer and wetter climate, and impacts from the neighboring human population. Here, we review the history of research on Kanyawara chimpanzees and examine how their demography, diet, and social behavior have changed over the last 30+ years. While Kanyawara chimpanzees were protected from the major threats of poaching and habitat loss, respiratory diseases of human origin were a major source of mortality. Many individuals were also injured by wire hunting snares. Nevertheless, the study community has grown modestly in size, individuals have become increasingly gregarious, and birth rates have increased. These results are likely attributable to improved habitat productivity that can be traced to decades-long efforts by wildlife authorities and the associated research and conservation programs in Kibale. Overall, research has contributed both to understanding interactions among nutritional ecology, social behavior, physiology, and health of an endangered species, and also to conservation activities in the Kibale community through direct interventions, positive economic impacts, and conservation education programs.

Patterns of urinary cortisol levels during ontogeny appear population specific rather than species specific in wild chimpanzees and bonobos

Compared with most mammals, postnatal development in great apes is protracted, presenting both an extended period of phenotypic plasticity to environmental conditions and the potential for sustained mother-offspring and/or sibling conflict over resources. Comparisons of cortisol levels during ontogeny can reveal physiological plasticity to species or population specific socioecological factors and in turn how these factors might ameliorate or exaggerate mother-offspring and sibling conflict. Here, we examine developmental patterns of cortisol levels in two wild chimpanzee populations (Budongo and Taï), with two and three communities each, and one wild bonobo population (LuiKotale), with two communities. Both species have similar juvenile life histories. Nonetheless, we predicted that key differences in socioecological factors, such as feeding competition, would lead to interspecific variation in mother-offspring and sibling conflict and thus variation in ontogenetic cortisol patterns. We measured urinary cortisol levels in 1394 samples collected from 37 bonobos and 100 chimpanzees aged up to 12 years. The significant differences in age-related variation in cortisol levels appeared population specific rather than species specific. Both bonobos and Taï chimpanzees had comparatively stable and gradually increasing cortisol levels throughout development; Budongo chimpanzees experienced declining cortisol levels before increases in later ontogeny. These age-related population differences in cortisol patterns were not explained by mother-offspring or sibling conflict specifically; instead, the comparatively stable cortisol patterns of bonobos and Taï chimpanzees likely reflect a consistency in experience of competition and the social environment compared with Budongo chimpanzees, where mothers may adopt more variable strategies related to infanticide risk and resource availability. The clear population-level differences within chimpanzees highlight potential intraspecific flexibility in developmental processes in apes, suggesting the flexibility and diversity in rearing strategies seen in humans may have a deep evolutionary history.

Wild chimpanzees exhibit humanlike aging of glucocorticoid regulation

Cortisol, a key product of the stress response, has critical influences on degenerative aging in humans. In turn, cortisol production is affected by senescence of the hypothalamic-pituitary-adrenal (HPA) axis, leading to progressive dysregulation and increased cortisol exposure. These processes have been studied extensively in industrialized settings, but few comparative data are available from humans and closely related species living in natural environments, where stressors are very different. Here, we examine age-related changes in urinary cortisol in a 20-y longitudinal study of wild chimpanzees (n = 59 adults) in the Kanyawara community of Kibale National Park, Uganda. We tested for three key features of HPA aging identified in many human studies: increased average levels, a blunted diurnal rhythm, and enhanced response to stressors. Using linear mixed models, we found that aging was associated with a blunting of the diurnal rhythm and a significant linear increase in cortisol, even after controlling for changes in dominance rank. These effects did not differ by sex. Aging did not increase sensitivity to energetic stress or social status. Female chimpanzees experienced their highest levels of cortisol during cycling (versus lactation), and this effect increased with age. Male chimpanzees experienced their highest levels when exposed to sexually attractive females, but this effect was diminished by age. Our results indicate that chimpanzees share some key features of HPA aging with humans. These findings suggest that impairments of HPA regulation are intrinsic to the aging process in hominids and are side effects neither of extended human life span nor of atypical environments.

Timing of the Infancy-Childhood Growth Transition in Rural Gambia

The Karlberg model of human growth describes the infancy, childhood, and puberty (ICP) stages as continuous and overlapping, and defined by transitions driven by sequential additional effects of several endocrine factors that shape the growth trajectory and resultant adult size. Previous research has suggested that a delayed transition from the infancy to the childhood growth stage contributes to sub-optimal growth outcomes. A new method developed to analyze the structure of centile crossing in early life has emerged as a potential tool for identifying the infancy-childhood transition (ICT), through quantifying patterns of adjacent monthly weight-for-age z-score (WAZ) deviation correlations. Using this method, the infancy-childhood transition was identified as taking place at around 12 months of age in two cohorts of UK infants. Here, we apply this method to data collected as part of a longitudinal growth study in rural Gambia [the Hormonal and Epigenetic Regulators of Growth, or HERO-G study, N = 212 (F = 99, M = 113)], in order to identify the ICT and assess whether timing of this transition differs across groups based on sex or birth seasonality. We calculated Pearson correlation coefficients for adjacent monthly WAZ score deviations. Based on the patterns of change in the correlation structure over time, our results suggest that the infancy-childhood transition occurs at around 9 months of age in rural Gambian infants. This points to an accelerated ICT compared to UK infants, rather than a delayed ICT. A comparatively later transition, seen in UK infants, allows maximal extension of the high rates of growth during the infancy stage; an earlier transition as seen in Gambian infants cuts short this period of rapid growth, potentially impacting on growth outcomes in childhood while diverting energy into other processes critical to responses to acute infectious challenges. Growth in later developmental stages in this population offers an extended window for catch-up.

A lex naturalis delineates components of a human-specific, adrenal androgen-dependent, p53-mediated 'kill switch' tumor suppression mechanism

We have recently described in this journal our detection of an anthropoid primate-specific, adrenal androgen-dependent, p53-mediated, 'kill switch' tumor suppression mechanism that reached its fullest expression only in humans, as a result of human-specific exposure to polycyclic aromatic hydrocarbons caused by the harnessing of fire - but which has components reaching all the way back to the origin of the primate lineage. We proposed that species-specific mechanisms of tumor suppression are a generalized requirement for vertebrate species to increase in body size or lifespan beyond those of species basal to their lineage or to exploit environmental niches which increase exposure to carcinogenic substances. Using empirical dynamic modeling, we have also reported our detection of a relationship between body size, lifespan, and species-specific mechanism of tumor suppression (and here add carcinogen exposure), such that a change in any one of these variables requires an equilibrating change in one or more of the others in order to maintain lifetime cancer risk at a value of about 4%, as observed in virtually all larger, longer-lived species under natural conditions. Here we show how this relationship, which we refer to as the lex naturalis of vertebrate speciation, elucidates the evolutionary steps underlying an adrenal androgen-dependent, human-specific 'kill switch' tumor suppression mechanism; and further, how it prescribes a solution to 'normalize' lifetime cancer risk in our species from its current aberrant 40% to the 4% that characterized primitive humans. We further argue that this prescription writ by the lex naturalis represents the only tenable strategy for meaningful suppression of the accelerating impact of cancer upon our species.

DHEAS and Human Development: An Evolutionary Perspective

Adrenarche, the post-natal rise of DHEA and DHEAS, is unique to humans and the African Apes. Recent findings have linked DHEA in humans to the development of the left dorsolateral prefrontal cortex (LDPFC) between the ages of 4-8 years and the right temporoparietal junction (rTPJ) from 7 to 12 years of age. Given the association of the LDLPFC with the 5-to-8 transition and the rTPJ with mentalizing during middle childhood DHEA may have played an important role in the evolution of the human brain. I argue that increasing protein in the diet over the course of human evolution not only increased levels of DHEAS, but linked meat consumption with brain development during the important 5- to-8 transition. Consumption of animal protein has been associated with IGF-1, implicated in the development of the adrenal zona reticularis (ZR), the site of DHEAS production. In humans and chimps, the zona reticularis emerges at 3-4 years, along with the onset of DHEA/S production. For chimps this coincides with weaning and peak synaptogenesis. Among humans, weaning is completed around 2 ½ years, while synaptogenesis peaks around 5 years. Thus, in chimpanzees, early cortical maturation is tied to the mother; in humans it may be associated with post-weaning provisioning by others. I call for further research on adrenarche among the African apes as a critical comparison to humans. I also suggest research in subsistence populations to establish the role of nutrition and energetics in the timing of adrenarche and the onset of middle childhood.