Maternal, Placental, and Fetal Responses to Intermittent Heat Exposure During Late Gestation in Mice

Association of air temperature exposure during pregnancy with risk of preeclampsia in Guangzhou, China

Environmental exposures during pregnancy have been associated with adverse obstetric outcomes. However, limited and inconsistent evidence exists regarding the association between air temperature exposure and the risk of preeclampsia (PE). This study aimed to evaluate the correlation between ambient temperature exposure during pregnancy and PE risk, as well as identify the specific time window of temperature exposure that increases PE risk. A population-based cohort study was conducted from January 2012 to April 2022 in Guangzhou, China. Pregnant women were recruited in early pregnancy and followed until delivery. A total of 3,314 PE patients and 114,201 normal pregnancies were included. Ambient temperature exposures at different gestational weeks were recorded for each participant. Logistic regression models were used to evaluate the correlation between ambient temperature exposure and PE risk. Stratified analyses were conducted based on maternal age and pre-pregnancy BMI. Distributed lag models were employed to identify the time window of temperature exposure related to PE. Exposure to extreme high temperature (aOR = 1.24, 95 % CI 1.12-1.38) and moderate high temperature (aOR = 1.22, 95 % CI 1.10-1.35) during early pregnancy was associated with an increased risk of PE. Furthermore, women with higher pre-pregnancy BMI had a higher risk of developing PE when exposed to high temperature during early pregnancy compared to normal-weight women. The time window of temperature exposure related to PE was identified as pregnancy weeks 1 to 8. This study provides evidence for the association of high temperature exposure during early pregnancy with the risk of PE, as well as identifies the specific time window of temperature exposure related to PE. These findings have implications for developing potential strategies to protect pregnant women, particularly those with higher pre-pregnancy BMI, from the adverse effects of extreme temperatures during early pregnancy.

Ambient temperature, heat stress and fetal growth: A review of placenta-mediated mechanisms

Pregnancy is increasingly considered a period of vulnerability for extreme heat exposure. Multiple lines of evidence support that heat stress is associated with placental insufficiency, poor fetal growth and decreased birth weight. In this narrative review, we first summarize evidence linking ambient temperature or experimentally-induced heat stress with fetal and placental growth outcomes in humans, ruminants and murine species. We then synthesize the literature on putative underlying biological pathways with a focus on the placenta. Reviewed mechanisms include: reduced uterine-placental blood flow, impaired supply of metabolic substrates to the fetus, activation of the maternal stress-response system, and disruption of other endocrine and immune system endpoints. Taken together, this body of evidence supports that exposure to extreme ambient heat likely has adverse consequences for placental development and function. However, research investigating placenta-mediated pathophysiological mechanisms in humans remains extremely limited.

Biological and pathological mechanisms leading to the birth of a small vulnerable newborn

The pathway to a thriving newborn begins before conception and continues in utero with a healthy placenta and the right balance of nutrients and growth factors that are timed and sequenced alongside hormonal suppression of labour until a mature infant is ready for birth. Optimal nutrition that includes adequate quantities of quality protein, energy, essential fats, and an extensive range of vitamins and minerals not only supports fetal growth but could also prevent preterm birth by supporting the immune system and alleviating oxidative stress. Infection, illness, undernourishment, and harmful environmental exposures can alter this trajectory leading to an infant who is too small due to either poor growth during pregnancy or preterm birth. Systemic inflammation suppresses fetal growth by interfering with growth hormone and its regulation of insulin-like growth factors. Evidence supports the prevention and treatment of several maternal infections during pregnancy to improve newborn health. However, microbes, such as Ureaplasma species, which are able to ascend the cervix and cause membrane rupture and chorioamnionitis, require new strategies for detection and treatment. The surge in fetal cortisol late in pregnancy is essential to parturition at the right time, but acute or chronically high maternal cortisol levels caused by psychological or physical stress could also trigger labour onset prematurely. In every pathway to the small vulnerable newborn, there is a possibility to modify the course of pregnancy by supporting improved nutrition, protection against infection, holistic maternal wellness, and healthy environments.

Thermoneutrality effects on developmental programming of obesity

Developmental programming studies using mouse models have housed the animals at human thermoneutral temperatures (22°C) which imposes constant cold stress. As this impacts energy homeostasis, we investigated the effects of two housing temperatures (22°C and 30°C) on obesity development in male and female offspring of Control and FR dams. Pregnant mice were housed at 22°C (cold-exposed, CE) or 30°C (thermoneutrality, TN) room temperature. At gestational age e10, mice were fed either an ad libitum diet (Control) or were 30% food-restricted (FR) to produce low birth weight newborns. Following delivery, all dams were fed an ad libitum diet and maternal mice continued to nurse their own pups. At 3 weeks of age, offspring were weaned to an ad libitum diet and housed at similar temperatures as their mothers. Body weights and food intake were monitored. At 6 months of age, body composition and glucose tolerance test were determined, after which, brain and adipose tissue were collected for analysis. FR/CE and FR/TN offspring exhibited hyperphagia and were significantly heavier with increased adiposity as compared to their respective Controls. There was sex-specific effects of temperature in both groups. Male offspring at TN were heavier with increased body fat, though the food intake was decreased as compared to CE males. This was reflected by hypertrophic adipocytes and increased arcuate nucleus satiety/appetite ratio. In contrast, female offspring were not impacted by housing temperature. Thus, unlike female offspring, there was a significant interaction of diet and temperature evident in the male offspring with accentuated adverse effects evident in FR/TN males.

The profile of HSPA1A gene expression and its association with heat tolerance in crossbred cattle and the tropically adapted dwarf Vechur and Kasaragod

Certain livestock breeds are adapted to hot and humid environments, and these breeds have genetics that could be useful in a changing climate. The expression of several genes has been identified as a useful biomarker for heat stress. In this study, the responses to heat exposure of heat-tolerant Vechur and Kasaragod cattle found in Kerala state in India (also known as dwarf Bos taurus indicus) were compared to crossbred cattle (crosses of Bos t. taurus with Bos t. indicus). At various time points during heat exposure, rectal temperature and the expression of HSPA1A were determined, and the relationship between them was characterized. We characterized HSPA1A mRNA in Vechur cattle and performed molecular clock analysis. The expression of HSPA1A between the lineages and at different temperature humidity index (THI) was significant. There were significant differences between the expression profiles of HSPA1A in Kasaragod and crossbred (p < 0.01) and Vechur and crossbred (p < 0.01) cattle, but no significant difference in expression was observed between Vechur and Kasaragod cattle. The genetic distance between Vechur, B. grunniens, B. t. taurus, and B. t. indicus was 0.0233, 0.0059, and 0.007, respectively. The genetic distance between Vechur and the Indian dwarf breed Malnad Gidda was 0.0081. A molecular clock analysis revealed divergent adaptive evolution of Vechur cattle to B. t. taurus, with adaptations to the high temperatures and humidity that are prevalent in their breeding tract in Kerala, India. These results could also prove useful in selecting heat-tolerant animals using HSPA1A as a marker.