Embryo transfer cannot delineate between the maternal pregnancy environment and germ line effects in the transgenerational transmission of disease in rats

Uteroplacental insufficiency temporally exacerbates salt-induced hypertension associated with a reduced natriuretic response in male rat offspring

KEY POINTS

Low weight at birth increases the risk of developing chronic diseases in adulthood A diet that is high in salt is known to elevate blood pressure, which is a major risk factor for cardiovascular and kidney diseases The present study demonstrates that growth restricted male rats have a heightened sensitivity to high dietary salt, in the context of raised systolic blood pressure, reduced urinary sodium excretion and stiffer mesenteric resistance vessels Other salt-induced effects, such as kidney hyperfiltration, albuminuria and glomerular damage, were not exacerbated by being born small The present study demonstrates that male offspring born small have an increased cardiovascular susceptibility to high dietary salt, such that that minimizing salt intake is probably of particular benefit to this at-risk population ABSTRACT: Intrauterine growth restriction increases the risk of developing chronic diseases in adulthood. Lifestyle factors, such as poor dietary choices, may elevate this risk. We determined whether being born small increases the sensitivity to a dietary salt challenge, in the context of hypertension, kidney disease and arterial stiffness. Bilateral uterine vessel ligation or sham surgery (offspring termed Restricted and Control, respectively) was performed on 18-day pregnant Wistar Kyoto rats. Male offspring were allocated to receive a diet high in salt (8% sodium chloride) or remain on standard rat chow (0.52% sodium chloride) from 20 to 26 weeks of age for 6 weeks. Systolic blood pressure (tail-cuff), renal function (24 h urine excretions) and vascular stiffness (pressure myography) were assessed. Restricted males were born 15% lighter than Controls and remained smaller throughout the study. Salt-induced hypertension was exacerbated in Restricted offspring, reaching a peak systolic pressure of ∼175 mmHg earlier than normal weight counterparts. The natriuretic response to high dietary salt in Restricted animals was less than in Controls and may explain the early rise in arterial pressure. Growth restricted males allocated to a high salt diet also had increased passive arterial stiffness of mesenteric resistance arteries. Other aspects of renal function, including salt-induced hyperfiltration, albuminuria and glomerular damage, were not exacerbated by uteroplacental insufficiency. The present study demonstrates that male offspring exposed to uteroplacental insufficiency and born small have an increased sensitivity to salt-induced hypertension and arterial remodelling.

Transgenerational programming of nephron deficits and hypertension

Exposure to a sub-optimal environment in the womb can result in poor fetal growth and impair the normal development of organs. The kidney, specifically the process of nephrogenesis, has been shown to be impacted by many common pregnancy exposures including an inadequate diet, poor placental function, maternal stress as well as maternal smoking and alcohol consumption. This can result in offspring being born with a reduced nephron endowment, which places these individuals at increased risk of hypertension and chronic kidney disease (CKD). Of recent interest is whether this disease risk can be passed on to subsequent generations and, if so, what are the mechanisms and pathways involved. In this review, we highlight the growing body of evidence that a low birth weight and hypertension, which are both major risk factors for cardiovascular and CKD, can be transmitted across generations. However, as yet there is little data as to whether a low nephron endowment contributes to this disease transmission. The emerging data suggests transmission can occur both through both the maternal and paternal lines, which likely involves epigenetic mechanisms such chromatin remodelling (DNA methylation and histone modification) and non-coding RNA modifications. In addition, females who were born small and/or have a low nephron endowment are at an increased risk for pregnancy complications, which can influence the growth and development of the next generation. Future animal studies in this area should include examining nephron endowment across multiple generations and determining adult renal function. Clinically, long term follow-up studies of large birth cohorts need to be undertaken to more clearly determine the impact a sub-optimal environment in one generation has on the health outcomes in the second, and subsequent, generation.

The transgenerational effect of maternal and paternal F1 low birth weight on bone health of second and third generation offspring

Low birth weight programs diseases in adulthood, including adverse bone health. These diseases can have intergenerational and transgenerational origins, whereby transmission to subsequent generations occurs via both parental lines. Uteroplacental insufficiency surgery (Restricted) or sham surgery (Control) was performed on gestational day 18, in F0 Wistar-Kyoto rats. F1 Restricted males and females mated with breeders in order to generate F2 offspring of maternal and paternal lineages. F2 males and females were randomly selected for breeding to generate F3 offspring. F2 and F3 offspring did not have differences in birth weight irrespective of F1 low birth weight and parental line. Maternal line females had minor alterations to trabecular content and density at 6 months, these differences were not sustained at 12 months. Maternal line males had changes to trabecular content at 6 and 12 months; however, differences were no longer present at 16 months. Despite altered bone geometry at 12 and 16 months, bending strength remained unaffected at both ages. Bone health of paternal line females was not affected at 6 and 12 months. Paternal line males at 6 months had changes to trabecular and cortical content; cortical thickness, periosteal circumference and bending strength; however, these differences were no longer sustained at 12 and 16 months. Our data demonstrate that there is no transgenerational transmission of adverse bone health in F2 and F3 offspring, derived from low F1 birth weight females and males. Our results are novel, as bone health across generations and both parental lines has not been investigated in a model of low birth weight due to uteroplacental insufficiency.

Clinical study on the association between pregnancy-induced hypertension and insulin resistance

The aim of the present study was to explore the association between pregnancy-induced hypertension (PIH) and insulin resistance (IR). A total of 50 cases of PIH and 50 healthy pregnant women with a similar gestational age were enrolled. The hyperinsulinemic-euglycemic clamp technique was used to evaluate the degree of IR and all 100 subjects were divided into an IR and a non-IR group accordingly. Subsequently, the correlation between the systolic or diastolic blood pressure was assessed; furthermore, a homeostasis model assessment of IR (HOMA-IR), a HOMA of the insulin sensitivity index (HOMA-ISI) and a HOMA of β cell function (HOMA-β%) were performed. Moreover, the effect of IR on PIH was assessed and the protein expression of insulin receptor substrate (IRS)-1, phosphorylated (p)-IRS-1, AKT and p-AKT were detected in the placental plasma by western blot analysis. The results showed that in the PIH group, the p-IRS-1/IRS-1 and p-AKT/AKT ratios were decreased compared with those in the control group. Blood flow parameters, including perfusion index, retinal resistive index and systolic maximum velocity/end-diastolic velocity ratio in the IR group were higher, while time averaged velocity was lower compared with that in the non-IR group. Furthermore, the HOMA-ISI and HOMA-β% were decreased, while the HOMA-IR was increased in the PIH group compared to that in the control group; alongside the blockage of the insulin signaling pathway, these factors may therefore cause PIH. The present study may provide novel therapeutic approaches for PIH.

A review of fundamental principles for animal models of DOHaD research: an Australian perspective

Epidemiology formed the basis of ‘the Barker hypothesis’, the concept of ‘developmental programming’ and today’s discipline of the Developmental Origins of Health and Disease (DOHaD). Animal experimentation provided proof of the underlying concepts, and continues to generate knowledge of underlying mechanisms. Interventions in humans, based on DOHaD principles, will be informed by experiments in animals. As knowledge in this discipline has accumulated, from studies of humans and other animals, the complexity of interactions between genome, environment and epigenetics, has been revealed. The vast nature of programming stimuli and breadth of effects is becoming known. As a result of our accumulating knowledge we now appreciate the impact of many variables that contribute to programmed outcomes. To guide further animal research in this field, the Australia and New Zealand DOHaD society (ANZ DOHaD) Animals Models of DOHaD Research Working Group convened at the 2nd Annual ANZ DOHaD Congress in Melbourne, Australia in April 2015. This review summarizes the contributions of animal research to the understanding of DOHaD, and makes recommendations for the design and conduct of animal experiments to maximize relevance, reproducibility and translation of knowledge into improving health and well-being.

In Utero Origins of Hypertension: Mechanisms and Targets for Therapy

The developmental origins of health and disease theory is based on evidence that a suboptimal environment during fetal and neonatal development can significantly impact the evolution of adult-onset disease. Abundant evidence exists that a compromised prenatal (and early postnatal) environment leads to an increased risk of hypertension later in life. Hypertension is a silent, chronic, and progressive disease defined by elevated blood pressure (>140/90 mmHg) and is strongly correlated with cardiovascular morbidity/mortality. The pathophysiological mechanisms, however, are complex and poorly understood, and hypertension continues to be one of the most resilient health problems in modern society. Research into the programming of hypertension has proposed pharmacological treatment strategies to reverse and/or prevent disease. In addition, modifications to the lifestyle of pregnant women might impart far-reaching benefits to the health of their children. As more information is discovered, more successful management of hypertension can be expected to follow; however, while pregnancy complications such as fetal growth restriction, preeclampsia, preterm birth, etc., continue to occur, their offspring will be at increased risk for hypertension. This article reviews the current knowledge surrounding the developmental origins of hypertension, with a focus on mechanistic pathways and targets for therapeutic and pharmacologic interventions.

Maternal diet during gestation and lactation modifies the severity of salt-induced hypertension and renal injury in Dahl salt-sensitive rats

Environmental exposure of parents or early in life may affect disease development in adults. We found that hypertension and renal injury induced by a high-salt diet were substantially attenuated in Dahl SS/JrHsdMcwiCrl (SS/Crl) rats that had been maintained for many generations on the grain-based 5L2F diet compared with SS/JrHsdMcwi rats (SS/Mcw) maintained on the casein-based AIN-76A diet (mean arterial pressure, 116±9 versus 154±25 mm Hg; urinary albumin excretion, 23±12 versus 170±80 mg/d). RNAseq analysis of the renal outer medulla identified 129 and 82 genes responding to a high-salt diet uniquely in SS/Mcw and SS/Crl rats, respectively, along with minor genetic differences between the SS substrains. The 129 genes responding to salt in the SS/Mcw strain included numerous genes with homologs associated with hypertension, cardiovascular disease, or renal disease in human. To narrow the critical window of exposure, we performed embryo-transfer experiments in which single-cell embryos from 1 colony (SS/Mcw or SS/Crl) were transferred to surrogate mothers from the other colony, with parents and surrogate mothers maintained on their respective original diet. All offspring were fed the AIN-76A diet after weaning. Salt-induced hypertension and renal injury were substantially exacerbated in rats developed from SS/Crl embryos transferred to SS/Mcw surrogate mothers. Conversely, salt-induced hypertension and renal injury were significantly attenuated in rats developed from SS/Mcw embryos transferred to SS/Crl surrogate mothers. Together, the data suggest that maternal diet during the gestational-lactational period has substantial effects on the development of salt-induced hypertension and renal injury in adult SS rats.

Effects of the use of assisted reproductive technologies and an obesogenic environment on resistance artery function and diabetes biomarkers in mice offspring

Maternal obesity affects the incidence of cardiovascular disease and diabetes in offspring. Also the use of assisted reproductive technologies (ART) has been associated with cardiovascular deficiencies in offspring. Obese women often suffer from infertility and use ART to achieve a pregnancy, but the combined effects of maternal obesity and ART on cardiovascular health and incidence of diabetes in the offspring is not known. Here, we report the effects of the use of ART within an obesogenic environment, consisting of feeding a western diet (WD) to dams and offspring, on resistance artery function and presence of diabetes biomarkers in juvenile mice offspring. Our results indicate that WD and ART interacted to induce endothelial dysfunction in mesenteric resistance arteries isolated from 7-week-old mice offspring. This was determined by presence of a reduced acetylcholine-induced dilation compared to controls. The arteries from these WD-ART mice also had greater wall cross-sectional areas and wall to lumen ratios indicative of vascular hypertrophic remodeling. Of the diabetes biomarkers measured, only resistin was affected by a WD×ART interaction. Serum resistin was significantly greater in WD-ART offspring compared to controls. Diet and sex effects were observed in other diabetes biomarkers. Our conclusion is that in mice the use of ART within an obesogenic environment interacts to favor the development of endothelial dysfunction in the resistance arteries of juvenile offspring, while having marginal effects on diabetes biomarkers.