Naturally occurring perinatal growth restriction in mice programs cardiovascular and endocrine function in a sex- and strain-dependent manner

Antenatal Programming of Hypertension: Paradigms, Paradoxes, and How We Move Forward

PURPOSE OF REVIEW

Synthesize the clinical, epidemiological, and preclinical evidence for antenatal programming of hypertension and critically appraise paradigms and paradoxes to improve translation.

RECENT FINDINGS

Clinical and epidemiological studies persistently demonstrate that antenatal factors contribute to programmed hypertension under the developmental origins of health and disease framework, including lower birth weight, preterm birth, and fetal growth restriction. Preclinical mechanisms include preeclampsia, maternal diabetes, maternal undernutrition, and antenatal corticosteroid exposure. However, clinical and epidemiological studies to date have largely failed to adequately identify, discuss, and mitigate many sources and types of bias in part due to heterogeneous study designs and incomplete adherence to scientific rigor. These limitations have led to incomplete and biased paradigms as well as persistent paradoxes that have significantly limited translation into clinical and population health interventions. Improved understanding of these paradigms and paradoxes will allow us to substantially move the field forward.

Early dietary restriction in rats alters skeletal muscle tuberous sclerosis complex, ribosomal s6 and mitogen-activated protein kinase

Intrauterine growth restriction is linked to decreased lean body mass and insulin resistance. The mammalian target of rapamycin (mTOR) regulates muscle mass and glucose metabolism; however, little is known about maternal dietary restriction and skeletal muscle mTOR in offspring. We hypothesized that early dietary restriction would decrease skeletal muscle mass and mTOR in the suckling rat. To test this hypothesis, ab libitum access to food or dietary restriction during gestation followed by postnatal cross-fostering to a dietary-restricted or ad libitum-fed rat dam during lactation generated 4 groups: control (CON), intrauterine dietary restricted (IUDR), postnatal dietary restricted (PNDR), and IUDR+PNDR (IPDR). At day 21, when compared to CON, the IUDR group demonstrated "catchup" growth, but no changes were observed in the mTOR pathway. Despite having less muscle mass than CON and IUDR (P < .001), in IPDR and PNDR rats mTOR remained unchanged. IPDR and PNDR (p)-tuberous sclerosis complex 2 was less than the IUDR group (P < .05). Downstream, IPDR's and PNDR's phosphorylated (p)-ribosomal s6 (rs6)/rs6 was less than that of CON (P < .05). However, male IPDR's and PNDR's p-mitogen activated protein kinase MAPK/MAPK was greater than CON (P < .05) without a change in p90 ribosomal s6 kinase (p90RSK). In contrast, in females, MAPK was unchanged, but IPDR p-p90RSK/p90RSK was less than CON (P = .01). In conclusion, IPDR and PNDR reduced skeletal muscle mass but did not decrease mTOR. In IPDR and PNDR, a reduction in tuberous sclerosis complex 2 may explain why mTOR was unchanged, whereas, in males, an increase in MAPK with a decrease in rs6 may suggest a block in MAPK signaling.

Modeling the impact of growth and leptin deficits on the neuronal regulation of blood pressure

The risk of hypertension is increased by intrauterine growth restriction (IUGR) and preterm birth. In the search for modifiable etiologies for this life-threatening cardiovascular morbidity, a number of pathways have been investigated, including excessive glucocorticoid exposure, nutritional deficiency and aberration in sex hormone levels. As a neurotrophic hormone that is intimately involved in the cardiovascular regulation and whose levels are influenced by glucocorticoids, nutritional status and sex hormones, leptin has emerged as a putative etiologic and thus a therapeutic agent. As a product of maternal and late fetal adipocytes and the placenta, circulating leptin typically surges late in gestation and declines after delivery until the infant consumes sufficient leptin-containing breast milk or accrues sufficient leptin-secreting adipose tissue to reestablish the circulating levels. The leptin deficiency seen in IUGR infants is a multifactorial manifestation of placental insufficiency, exaggerated glucocorticoid exposure and fetal adipose deficit. The preterm infant suffers from the same cascade of events, including separation from the placenta, antenatal steroid exposure and persistently underdeveloped adipose depots. Preterm infants remain leptin deficient beyond term gestation, rendering them susceptible to neurodevelopmental impairment and subsequent cardiovascular dysregulation. This pathologic pathway is efficiently modeled by placing neonatal mice into atypically large litters, thereby recapitulating the perinatal growth restriction-adult hypertension phenotype. In this model, neonatal leptin supplementation restores the physiologic leptin surge, attenuates the leptin-triggered sympathetic activation in adulthood and prevents leptin- or stress-evoked hypertension. Further pathway interrogation and clinical translation are needed to fully test the therapeutic potential of perinatal leptin supplementation.

Neonatal growth restriction-related leptin deficiency enhances leptin-triggered sympathetic activation and central angiotensin II receptor-dependent stress-evoked hypertension

BACKGROUND

Neonatal growth restriction (nGR) leads to leptin deficiency and increases the risk of hypertension. Previous studies have shown nGR-related hypertension is normalized by neonatal leptin (nLep) and exacerbated by psychological stress. With recent studies linking leptin and angiotensin signaling, we hypothesized that nGR-induced nLep deficiency increases adult leptin sensitivity; leading to leptin- or stress-induced hypertension, through a pathway involving central angiotensin II type 1 receptors.

METHODS

We randomized mice with incipient nGR, by virtue of their presence in large litters, to vehicle or physiologic nLep supplementation (80 ng/g/d). Adult caloric intake and arterial pressure were monitored at baseline, during intracerebroventricular losartan infusion and during systemic leptin administration.

RESULTS

nGR increased leptin-triggered renal sympathetic activation and hypertension with increased leptin receptor expression in the arcuate nucleus of the hypothalamus; all of those nGR-associated phenotypes were normalized by nLep. nGR mice also had stress-related hyperphagia and hypertension, but only the stress hypertension was blocked by central losartan infusion.

CONCLUSION

nGR leads to stress hypertension through a pathway that involves central angiotensin II receptors, and nGR-associated leptin deficiency increases leptin-triggered hypertension in adulthood. These data suggest potential roles for preservation of neonatal growth and nLep supplementation in the prevention of nGR-related hypertension.

Oral oestrogen reverses ovariectomy-induced morning surge hypertension in growth-restricted mice

Perinatal growth restriction (GR) is associated with heightened sympathetic tone and hypertension. We have previously shown that naturally occurring neonatal GR programmes hypertension in male but not female mice. We therefore hypothesized that intact ovarian function or post-ovariectomy (OVX) oestrogen administration protects GR female mice from hypertension. Utilizing a non-interventional model that categorizes mice with weanling weights below the tenth percentile as GR, control and GR adult mice were studied at three distinct time points: baseline, post-OVX and post-OVX with oral oestrogen replacement. OVX elicited hypertension in GR mice that was significantly exacerbated by psychomotor arousal (systolic blood pressure at light to dark transition: control 122 ± 2; GR 119 ± 2; control-OVX 116 ± 3; GR-OVX 126 ± 3 mmHg). Oestrogen partially normalized the rising blood pressure surge seen in GR-OVX mice (23 ± 7% reduction). GR mice had left ventricular hypertrophy, and GR-OVX mice in particular had exaggerated bradycardic responses to sympathetic blockade. For GR mice, a baseline increase in baroreceptor reflex sensitivity and high frequency spectral power support a vagal compensatory mechanism, and that compensation was lost following OVX. For GR mice, the OVX-induced parasympathetic withdrawal was partially restored by oestrogen (40 ± 25% increase in high frequency spectral power, P<0.05). In conclusion, GR alters cardiac morphology and cardiovascular regulation. The haemodynamic consequences of GR are attenuated in ovarian-sufficient or oestrogen-replete females. Further investigations are needed to define the role of hormone replacement therapy targeted towards young women with oestrogen deficiency and additional cardiovascular risk factors, including perinatal GR, cardiac hypertrophy and morning surge hypertension.

IUGR with infantile overnutrition programs an insulin-resistant phenotype through DNA methylation of peroxisome proliferator-activated receptor-γ coactivator-1α in rats

BACKGROUND

Intrauterine growth restriction (IUGR) followed by postnatal accelerated growth (CG-IUGR) is associated with long-term adverse metabolic consequences, and an involvement of epigenetic dysregulation has been implicated. Peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) is a key orchestrator in energy homeostasis. We hypothesized that CG-IUGR programed an insulin-resistant phenotype through the alteration in DNA methylation and transcriptional activity of PGC-1α.

METHODS

A CG-IUGR rat model was adopted using maternal gestational nutritional restriction followed by infantile overnutrition achieved by reducing the litter size. The DNA methylation was determined by pyrosequencing. The mRNA expression and mitochondrial content were assessed by real-time PCR. The insulin-signaling protein expression was evaluated by western blotting.

RESULTS

Compared with controls, the CG-IUGR rats showed an increase in the DNA methylation of specific CpG sites in PGC-1α, and a decrease in the transcriptional activity of PGC-1α, mitochondrial content, protein level of PI3K and phosphorylated-Akt2 in liver and muscle tissues. The methylation of specific CpG sites in PGC-1α was positively correlated with fasting insulin concentration.

CONCLUSION

IUGR followed by infantile overnutrition programs an insulin-resistant phenotype, possibly through the alteration in DNA methylation and transcriptional activity of PGC-1α. The genetic and epigenetic modifications of PGC-1α provide a potential mechanism linking early-life nutrition insult to long-term metabolic disease susceptibilities.

Challenges and opportunities in developmental integrative physiology

This review explores challenges and opportunities in developmental physiology outlined by a symposium at the 2014 American Physiological Society Intersociety Meeting: Comparative Approaches to Grand Challenges in Physiology. Across animal taxa, adverse embryonic/fetal environmental conditions can alter morphological and physiological phenotypes in juveniles or adults, and capacities for developmental plasticity are common phenomena. Human neonates with body sizes at the extremes of perinatal growth are at an increased risk of adult disease, particularly hypertension and cardiovascular disease. There are many rewarding areas of current and future research in comparative developmental physiology. We present key mechanisms, models, and experimental designs that can be used across taxa to investigate patterns in, and implications of, the development of animal phenotypes. Intraspecific variation in the timing of developmental events can be increased through developmental plasticity (heterokairy), and could provide the raw material for selection to produce heterochrony--an evolutionary change in the timing of developmental events. Epigenetics and critical windows research recognizes that in ovo or fetal development represent a vulnerable period in the life history of an animal, when the developing organism may be unable to actively mitigate environmental perturbations. 'Critical windows' are periods of susceptibility or vulnerability to environmental or maternal challenges, periods when recovery from challenge is possible, and periods when the phenotype or epigenome has been altered. Developmental plasticity may allow survival in an altered environment, but it also has possible long-term consequences for the animal. "Catch-up growth" in humans after the critical perinatal window has closed elicits adult obesity and exacerbates a programmed hypertensive phenotype (one of many examples of "fetal programing"). Grand challenges for developmental physiology include integrating variation in developmental timing within and across generations, applying multiple stressor dosages and stressor exposure at different developmental timepoints, assessment of epigenetic and parental influences, developing new animal models and techniques, and assessing and implementing these designs and models in human health and development.

Transcriptome profiling of liver of non-genetic low birth weight and long term health consequences

BACKGROUND

It is believed that the main factors of low prenatal growth in mammals are genetic and environmental. We used isogenic mice maintained in standard conditions to analyze how natural non-genetic microsomia (low birth weight) is produced in inbred mice and its long term effect on health. To better understand the molecular basis of non-genetic microsomia, we undertook transcriptome profiling of both male and female livers from small and normal size mice at birth.

RESULTS

Naturally occurring neonatal microsomia was defined as a gender-specific weanling weight under the 10th percentile of the colony. Birth weight variation was similar in inbred and outbred lines. Mice were phenotyped by weight, size, blood pressure, organ size, their response to a glucose challenge, and survival rates. Regardless of diet, adult mice born with microsomia showed a significantly lower body weight and size, and differences in the weight of several organs of microsomic adult mice compared to normal birth weight adults were found. After a high-fat diet, microsomic mice were less prone to obesity, showing a better glucose tolerance and lower blood pressure. Through a transcriptome analysis, we detected a different pattern of mRNA transcription in the liver at birth comparing male vs female and microsomic vs normal mice, noting some modifications in epigenetic regulatory genes in females and modifications in some growth factor genes in males. Finally, using embryo transfer of embryos of different quality and age, we identified a putative preimplantation origin of this non-genetic microsomia.

CONCLUSIONS

(1) neonatal microsomia is not always a risk factor for adult metabolic syndrome, (2) neonatal non-genetic microsomia displays changes in the expression of important epigenetic genes and changes in liver mRNA transcription profile at birth, exaggerating sexual dimorphism, and (3) random preimplantation phenotypic variability could partially explain body birth weight variation in isogenic lines.

Neonatal leptin administration alters regional brain volumes and blocks neonatal growth restriction-induced behavioral and cardiovascular dysfunction in male mice

Premature delivery is often complicated by neonatal growth restriction (GR) and neurodevelopmental impairment. Because global overnutrition increases the risk of adult metabolic syndrome, we sought a targeted intervention. Premature delivery and perinatal GR decrease circulating levels of the neurotrophic hormone leptin. We hypothesized that leptin supplementation would normalize the outcomes of mice with incipient neonatal GR. Pups were fostered into litters of 6 or 12 to elicit divergent growth patterns. Pups in each litter received injections of saline or leptin from d 4 to 14. At 4 mo, mice underwent tail cuff blood pressure measurement, behavioral testing, and MRI. Mice fostered in litters of 12 had decreased weanling weights and leptin levels. Neonatal leptin administration normalized plasma leptin levels without influencing neonatal growth. Leptin replacement also normalized the hypertension, stress-linked immobility, conditioned fear, and amygdala enlargement seen in neonatal growth restricted male mice. In control males, neonatal leptin administration led to hypothalamic enlargement, without overt neurocardiovascular alterations. Female mice were less susceptible to the effects of neonatal GR or leptin supplementation. In conclusion, the effects of neonatal leptin administration are modulated by concurrent growth and gender. In growth restricted male mice, physiologic leptin replacement improves adult neurocardiovascular outcomes.

Neonatal macrosomia is an independent risk factor for adult metabolic syndrome

BACKGROUND

Weight in infancy correlates with risk of type 2 diabetes, hypertension, and obesity in adulthood. Clinical observations have been confounded by obesity-prone genotypes and obesity-linked lifestyles.

OBJECTIVES

To define the effects of isolated neonatal macrosomia in isogenic animals, we compared macrosomic and control C57Bl6 mice co-fostered by healthy dams receiving standard laboratory feed.

METHODS

Naturally occurring neonatal macrosomia was identified by a gender-specific weanling weight above the 90th percentile for the colony. Macrosomic and control mice were phenotyped in adulthood by exercise wheel, tail cuff and intraperitoneal insulin or glucose challenge.

RESULTS

Compared to control males, adult males with a history of neonatal macrosomia had significantly increased body weight, reduced voluntary activity, insulin resistance, fasting hyperinsulinemia, and impaired glucose tolerance. In contrast, adult females with neonatal macrosomia had no significant alteration in body weight or endocrine phenotypes, but did have higher blood pressures and lower heart rates than control females. After these baseline studies, all mice were switched to a hypercaloric, high fat diet (5 kcal/g, 45% of energy as fat). Twenty weeks later, male mice had impaired glucose tolerance and insulin resistance, independent of their weanling weight classification. While on high fat feeds, macrosomic males maintained a significantly higher body weight than control males.

CONCLUSIONS

We conclude that (1) in our murine model, neonatal macrosomia is an independent risk factor of adult metabolic syndrome, and (2) neonatal macrosomia accentuates the sexually dimorphic predisposition of C57Bl6 male mice towards glucose intolerance and C57Bl6 female mice towards hypertension.

Neonatal catch up growth increases diabetes susceptibility but improves behavioral and cardiovascular outcomes of low birth weight male mice

Premature infants are at increased risk for persistent growth failure, neurodevelopmental impairment, hypertension, and diabetes. Rapid neonatal growth has been linked to the increasing prevalence of diabetes and obesity. Nutritional goals for the premature infant with incipient growth failure have thus become a source of controversy. We used isogenic mice with natural variation in perinatal growth to test the hypothesis that neonatal catch up growth improves the neurobehavioral and cardiovascular outcomes of low-birth weight mice, despite an increase in diabetes susceptibility. Adult mice that experienced prenatal and neonatal growth restriction had persistent growth failure, hypertension, and neurobehavioral alterations. When switched from standard rodent chow to a hypercaloric diet, growth restricted mice were protected from diet-induced obesity. Among low-birth weight male mice, neonatal catch up growth normalized neurobehavioral and cardiovascular phenotypes, but led to insulin resistance and high fat diet-induced diabetes. Among low-birth weight female mice, neonatal catch up growth did not prevent the development of adult hypertension and significantly increased measures of anxiety, including self-injury and the avoidance of open spaces. These studies support the importance of the perinatal environment in the resetting of adult disease susceptibility and suggest an earlier window of vulnerability among growth restricted female mice.

Developmental programming and hypertension

PURPOSE OF REVIEW

There is a growing body of evidence linking adverse events or exposures during early life and adult-onset diseases. After important epidemiological studies from many parts of the world, research now focuses on mechanisms of organ dysfunction and on refining the understanding of the interaction between common elements of adverse perinatal conditions, such as nutrition, oxidants, and toxins exposures. This review will focus on advances in our comprehension of developmental programming of hypertension.

RECENT FINDINGS

Recent studies have unraveled important mechanisms of oligonephronia and impaired renal function, altered vascular function and structure as well as sympathetic regulation of the cardiovascular system. Furthermore, interactions between prenatal insults and postnatal conditions are the subject of intensive research. Prematurity vs. intrauterine growth restriction modulate differently programming of high blood pressure. Along with antenatal exposure to glucocorticoids and imbalanced nutrition, a critical role for perinatal oxidative stress is emerging.

SUMMARY

While the complexity of the interactions between antenatal and postnatal influences on adult blood pressure is increasingly recognized, the importance of postnatal life in (positively) modulating developmental programming offers the hope of a critical window of opportunity to reverse programming and prevent or reduce related adult-onset diseases.

Vascular nitric oxide and superoxide anion contribute to sex-specific programmed cardiovascular physiology in mice

Intrauterine environmental pertubations have been linked to the development of adult hypertension. We sought to evaluate the interrelated roles of sex, nitric oxide, and reactive oxygen species (ROS) in programmed cardiovascular disease. Programming was induced in mice by maternal dietary intervention (DI; partial substitution of protein with carbohydrates and fat) or carbenoxolone administration (CX, to increase fetal glucocorticoid exposure). Adult blood pressure and locomotor activity were recorded by radiotelemetry at baseline, after a week of high salt, and after a week of high salt plus nitric oxide synthase inhibition (by l-NAME). In male offspring, DI or CX programmed an elevation in blood pressure that was exacerbated by N(omega)-nitro-l-arginine methyl ester administration, but not high salt alone. Mesenteric resistance vessels from DI male offspring displayed impaired vasorelaxation to ACh and nitroprusside, which was blocked by catalase and superoxide dismutase. CX-exposed females were normotensive, while DI females had nitric oxide synthase-dependent hypotension and enhanced mesenteric dilation. Despite the disparate cardiovascular phenotypes, both male and female DI offspring displayed increases in locomotor activity and aortic superoxide production. Despite dissimilar blood pressures, DI and CX-exposed females had reductions in cardiac baroreflex sensitivity. In conclusion, both maternal malnutrition and fetal glucocorticoid exposure program increases in arterial pressure in male but not female offspring. While maternal DI increased both superoxide-mediated vasoconstriction and nitric oxide mediated vasodilation, the balance of these factors favored the development of hypertension in males and hypotension in females.

Coronary constriction to angiotensin II is enhanced by endothelial superoxide production in sheep programmed by dexamethasone

Early gestation dexamethasone (dex) administration is an ovine model of fetal programming associated with increased coronary reactivity to angiotensin II (Ang II). NADPH oxidase-dependent superoxide production plays an important role in both Ang II signaling and coronary disease. We sought to determine whether early gestation dex-exposure increases coronary reactivity to Ang II by enhancing endothelial NADPH oxidase-dependent superoxide production. Dex (0.28 mg/kg/d for 48 h) was administered to pregnant ewes at 27-28 d gestation. Dex-exposed and control offspring were studied at 4 mo of age. Coronary superoxide production was measured by lucigenin-enhanced chemiluminescence and dihydroethidium fluorescence. Coronary arteries from dex-exposed sheep had significantly enhanced vasoconstriction to Ang II, an effect abolished by either endothelial removal or preincubation with membrane-permeable superoxide dismutase and catalase. Ang II significantly increased endothelial superoxide production and NADPH oxidase activity in coronaries from dex-exposed offspring, but not controls. This programmed alteration in superoxide production was accentuated by PD123319 (AT2 antagonist), but abolished by losartan (AT1 antagonist). In conclusion, early gestation dex-exposure programs coronary reactivity to Ang II by enhancing Ang II-stimulated endothelial superoxide production. This programming effect may predispose to progressive coronary endothelial dysfunction and coronary artery disease.