Maternal Uterine Artery Adenoviral Vascular Endothelial Growth Factor (Ad.VEGF-A165) Gene Therapy Normalises Fetal Brain Growth and Microglial Activation in Nutrient Restricted Pregnant Guinea Pigs

Fetal growth restriction (FGR) is associated with uteroplacental insufficiency, and neurodevelopmental and structural brain deficits in the infant. It is currently untreatable. We hypothesised that treating the maternal uterine artery with vascular endothelial growth factor adenoviral gene therapy (Ad.VEGF-A165) normalises offspring brain weight and prevents brain injury in a guinea pig model of FGR. Pregnant guinea pigs were fed a restricted diet before and after conception and received Ad.VEGF-A165 (1 × 1010 viral particles, n = 18) or vehicle (n = 18), delivered to the external surface of the uterine arteries, in mid-pregnancy. Pregnant, ad libitum-fed controls received vehicle only (n = 10). Offspring brain weight and histological indices of brain injury were assessed at term and 5-months postnatally. At term, maternal nutrient restriction reduced fetal brain weight and increased microglial ramification in all brain regions but did not alter indices of cell death, astrogliosis or myelination. Ad.VEGF-A165 increased brain weight and reduced microglial ramification in fetuses of nutrient restricted dams. In adult offspring, maternal nutrient restriction did not alter brain weight or markers of brain injury, whilst Ad.VEGF-A165 increased microglial ramification and astrogliosis in the hippocampus and thalamus, respectively. Ad.VEGF-A165 did not affect cell death or myelination in the fetal or offspring brain. Ad.VEGF-A165 normalises brain growth and markers of brain injury in guinea pig fetuses exposed to maternal nutrient restriction and may be a potential intervention to improve childhood neurodevelopmental outcomes in pregnancies complicated by FGR.

Mid-pregnancy placental transcriptome in a model of placental insufficiency with and without novel intervention

Fetal growth restriction (FGR) affects between 5-10% of all live births. Placental insufficiency is a leading cause of FGR, resulting in reduced nutrient and oxygen delivery to the fetus. Currently, there are no effective in utero treatment options for FGR, or placental insufficiency. We have developed a gene therapy to deliver, via a non-viral nanoparticle, human insulin-like 1 growth factor ( hIGF1 ) to the placenta as potential treatment of placenta insufficiency and FGR. Using a guinea pig maternal nutrient restriction (MNR) model of FGR, we aimed to understand the transcriptional changes within the placenta associated with placental insufficiency that occur prior to/at initiation of FGR, and the impact of short-term hIGF1 nanoparticle treatment. Using RNAsequencing, we analyzed protein coding genes of three experimental groups: Control and MNR dams receiving a sham treatment, and MNR dams receiving hIGF1 nanoparticle treatment. Pathway enrichment analysis comparing differentially expressed genelists in sham-treated MNR placentas to Control revealed upregulation of pathways associated with degradation and repair of genetic information and downregulation of pathways associated with transmembrane transport. When compared to sham-treated MNR placentas, MNR + hIGF1 placentas demonstrated changes to genelists associated with transmembrane transporter activity including ion, vitamin and solute carrier transport. Overall, this study identifies the key signaling and metabolic changes occurring in the placenta contributing to placental insufficiency prior to/at initiation of FGR, and increases our understanding of the pathways that our nanoparticle-mediated gene therapy intervention regulates.

Statements and Declarations

Competing Interests: Authors declare no conflicts of interest.

Maternal-fetal interfaces transcriptome changes associated with placental insufficiency and a novel gene therapy intervention

The etiology of fetal growth restriction (FGR) is multifactorial, although many cases often involve placental insufficiency. Placental insufficiency is associated with inadequate trophoblast invasion resulting in high resistance to blood flow, decreased availability of nutrients, and increased hypoxia. We have developed a non-viral, polymer-based nanoparticle that facilitates delivery and transient gene expression of human insulin-like 1 growth factor ( hIGF1 ) in placental trophoblast for the treatment of placenta insufficiency and FGR. Using the established guinea pig maternal nutrient restriction (MNR) model of placental insufficiency and FGR, the aim of the study was to identify novel pathways in the sub-placenta/decidua that provide insight into the underlying mechanism driving placental insufficiency, and may be corrected with hIGF1 nanoparticle treatment. Pregnant guinea pigs underwent ultrasound-guided sham or hIGF1 nanoparticle treatment at mid-pregnancy, and sub-placenta/decidua tissue was collected 5 days later. Transcriptome analysis was performed using RNA Sequencing on the Illumina platform. The MNR sub-placenta/decidua demonstrated fewer maternal spiral arteries lined by trophoblast, shallower trophoblast invasion and downregulation of genelists involved in the regulation of cell migration. hIGF1 nanoparticle treatment resulted in marked changes to transporter activity in the MNR + hIGF1 sub-placenta/decidua when compared to sham MNR. Under normal growth conditions however, hIGF1 nanoparticle treatment decreased genelists enriched for kinase signaling pathways and increased genelists enriched for proteolysis indicative of homeostasis. Overall, this study identified changes to the sub-placenta/decidua transcriptome that likely result in inadequate trophoblast invasion and increases our understanding of pathways that hIGF1 nanoparticle treatment acts on in order to restore or maintain appropriate placenta function.

Placental Nanoparticle-mediated IGF1 Gene Therapy Corrects Fetal Growth Restriction in a Guinea Pig Model

Fetal growth restriction (FGR) caused by placental insufficiency is a major contributor to neonatal morbidity and mortality. There is currently no in utero treatment for placental insufficiency or FGR. The placenta serves as the vital communication, supply, exchange, and defense organ for the developing fetus and offers an excellent opportunity for therapeutic interventions. Here we show efficacy of repeated treatments of trophoblast-specific human insulin-like 1 growth factor ( IGF1 ) gene therapy delivered in a non-viral, polymer nanoparticle to the placenta for the treatment of FGR. Using the guinea pig maternal nutrient restriction model of FGR, nanoparticle-mediated IGF1 treatment was delivered to the placenta via ultrasound guidance across the second half of pregnancy, after establishment of FGR. This treatment resulted in correction of fetal weight in MNR animals compared to control, improved fetal physiology and no negative maternal side-effects. Overall, we show for the first time a therapy capable of improving the entire pregnancy environment: maternal, placental, and fetal. This combined with our previous studies using this therapy at both mid pregnancy and in numerous cell and animal models demonstrate the plausibility of this therapy for future human translation to improve health outcomes of neonates and decrease numerous morbidities associated with the developmental origins of disease.

Maternal nutrition during mid-pregnancy and children's body composition at 7 years of age in the SELMA study

Optimal nutrition during pregnancy is vital for both maternal and child health. Our objective was to explore if prenatal diet is associated with children's height and body fat. Nutrient intake was assessed through a FFQ from 808 pregnant women and summarised to a nutrition index, 'My Nutrition Index' (MNI). The association with children's height and body fat (bioimpedance) was assessed with linear regression models. Secondary analysis was performed with BMI, trunk fat and skinfolds. Overall, higher MNI score was associated with greater height (β = 0·47; (95 % CI 0·00, 0·94), among both sexes. Among boys, higher MNI was associated with 0·15 higher BMI z-scores, 0·12 body fat z-scores, 0·11 trunk fat z-scores, and larger triceps, and triceps + subscapular skinfolds (β = 0·05 and β = 0·06; on the log2 scale) (P-value < 0·05). Among girls, the opposite associations were found with 0·12 lower trunk fat z-scores, and smaller subscapular and suprailiac skinfolds (β = -0·07 and β = -0·10; on the log2 scale) (P-value < 0·05). For skinfold measures, this would represent a ± 1·0 millimetres difference. Unexpectedly, a prenatal diet in line with recommended nutrient intake was associated with higher measures of body fat for boys and opposite to girls at a pre-pubertal stage of development.

Placental treatment with insulin-like growth factor 1 via nanoparticle differentially impacts vascular remodeling factors in guinea pig sub-placenta/decidua

Clinically, fetal growth restriction (FGR) is only detectable in later gestation, despite pathophysiological establishment likely earlier in pregnancy. Additionally, there are no effective in utero treatment options for FGR. We have developed a nanoparticle to deliver human insulin-like 1 growth factor (hIGF-1) in a trophoblast-specific manner which results in increased expression of hIGF-1. IGF-1 signaling in the placenta regulates multiple developmental processes including trophoblast invasion and maternal vascular remodeling, both of which can be diminished in the FGR placenta. We aimed to determine the effects of short-term hIGF-1 nanoparticle treatment on sub-placenta/decidua trophoblast signaling mechanisms in FGR and under normal growth conditions. Using the guinea pig maternal nutrient restriction (MNR) model of FGR, ultrasound-guided, intra-placenta injections of hIGF-1 nanoparticle were performed at gestational day 30-33, and dams sacrificed 5 days later. Sub-placenta/decidua tissue was separated from placenta for further analyses. Western blot was used to analyze protein expression of ERK/AKT/mTOR signaling proteins (phospho-Erk (pERK), phospho-Akt (pAKT), raptor, rictor and deptor). qPCR was used to analyze gene expression of vascular/remodeling factors [vascular endothelial growth factor (Vegf), placenta growth factor (Pgf), platelet-derived growth factor (Pdgf)) and tight junction/adhesion proteins (claudin 5 (Cldn5), p-glycoprotein (Abcb1), occludin (Ocln) and tight junction protein 1 (Zo1)]. MNR reduced expression of pERK, PdgfB and Cldn5, and increased expression of Ocln and Zo1 in the sub-placenta/decidua. In MNR + hIGF1 nanoparticle sub-placenta/decidua, expression of PdgfB, Ocln and Zo1 was normalized, whilst pAkt, VegfB, Vegf receptor 1 and PdgfB receptor were increased compared to MNR. In contrast, hIGF-1 nanoparticle treatment of normal placentas reduced expression of pERK, raptor and increased expression of the mTOR inhibitor deptor. This was associated with reduced expression of VegfA, Plgf, and PdgfB. Here we have shown that the impact of hIGF-1 nanoparticle treatment is dependent on pregnancy environment. Under MNR/FGR, hIGF-1 nanoparticle treatment triggers increased expression of growth factors and normalization of EMT factors. However, under normal conditions, the response of the placenta is to decrease AKT/mTOR signaling and growth factor expression to achieve homeostasis.

Nanoparticle-mediated transgene expression of insulin-like growth factor 1 in the growth restricted guinea pig placenta increases placenta nutrient transporter expression and fetal glucose concentrations

Fetal growth restriction (FGR) significantly contributes to neonatal and perinatal morbidity and mortality. Currently, there are no effective treatment options for FGR during pregnancy. We have developed a nanoparticle gene therapy targeting the placenta to increase expression of human insulin-like growth factor 1 (hIGF1) to correct fetal growth trajectories. Using the maternal nutrient restriction guinea pig model of FGR, an ultrasound-guided, intraplacental injection of nonviral, polymer-based hIGF1 nanoparticle containing plasmid with the hIGF1 gene and placenta-specific Cyp19a1 promotor was administered at mid-pregnancy. Sustained hIGF1 expression was confirmed in the placenta 5 days after treatment. Whilst increased hIGF1 did not change fetal weight, circulating fetal glucose concentration were 33%-67% higher. This was associated with increased expression of glucose and amino acid transporters in the placenta. Additionally, hIGF1 nanoparticle treatment increased the fetal capillary volume density in the placenta, and reduced interhaemal distance between maternal and fetal circulation. Overall, our findings, that trophoblast-specific increased expression of hIGF1 results in changes to glucose transporter expression and increases fetal glucose concentrations within a short time period, highlights the translational potential this treatment could have in correcting impaired placental nutrient transport in human pregnancies complicated by FGR.

Sex-Selective Increase of IGF-2 Expression in the Hypoxic Guinea Pig Placenta of Growth-Restricted Fetuses

Chronic hypoxia can cause fetal growth restriction (FGR) through placental dysfunction. Insulin-like growth factors (IGFs), such as IGF-2, play a major role in preservation of placental growth and function. We investigated the effects of chronic hypoxia and sex on protein expression of the IGF-2 pathway in placentas selected from asymmetric-FGR fetuses. Time-mated pregnant guinea pigs were assigned to normoxia (NMX, 21% O2) or hypoxia (HPX, 10.5% O2) during the last 14 days of pregnancy. Placentas were selected from male and female symmetrically grown NMX fetuses (fetal wt between 25th ile-75th ile) and HPX fetuses of asymmetric-FGR (fetal wt < 25th ile and brain:liver wt > 50th ile). Effects of HPX and sex on placenta protein expression of the IGF-2 signaling proteins (IGF-2, PI3K, AKT-P, total AKT, PCNA, a cell proliferation marker) were evaluated by immunoblotting. Effects of HPX and sex on morphometric parameters were analyzed using two-way ANOVA (p < 0.05). HPX reduced (p < 0.005) fetal wt by ~ 35% compared to NMX in both sexes. Expression of IGF-2 was lower (p = 0.029) in NMX female placentas compared to males. Despite lower NMX levels, HPX increased (p < 0.05) expression of IGF-2, AKT-P, relative AKT-P, and PCNA in female placentas only and had no effect on protein expression in male placentas. The female guinea pig placenta exhibits a greater sensitivity than males to HPX in upregulating expression of the IGF-2 axis. In addition, the sex difference in baseline IGF-2 expression suggests a greater capacity for females to increase IGF-2 in response to HPX as a placental adaptation in FGR.

Interventions for placental insufficiency and fetal growth restriction

Pregnancy complications adversely impact both mother and/or fetus throughout the lifespan. Fetal growth restriction (FGR) occurs when a fetus fails to reach their intrauterine potential for growth, it is the second highest leading cause of infant mortality, and leads to increased risk of developing non-communicable diseases in later life due 'fetal programming'. Abnormal placental development, growth and/or function underlies approximately 75% of FGR cases and there is currently no treatment save delivery, often prematurely. We previously demonstrated in a murine model of FGR that nanoparticle mediated, intra-placental human IGF-1 gene therapy maintains normal fetal growth. Multiple models of FGR currently exist reflecting the etiologies of human FGR and have been used by us and others to investigate the development of in utero therapeutics as discussed here. In addition to the in vivo models discussed herein, utilizing human models including in vitro (Choriocarcinoma cell lines and primary trophoblasts) and ex vivo (term villous fragments and placenta cotyledon perfusion) we have demonstrated robust nanoparticle uptake, transgene expression, nutrient transporter regulation without transfer to the fetus. For translational gene therapy application in the human placenta, there are multiple avenues that require investigation including syncytial uptake from the maternal circulation, transgene expression, functionality and longevity of treatment, impact of treatment on the mother and developing fetus. The potential impact of treating the placenta during gestation is high, wide-ranging across pregnancy complications, and may offer reduced risk of developing associated cardio-metabolic diseases in later life impacting at both an individual and societal level.

Effects of feed restriction during pregnancy on maternal reproductive outcome, foetal hepatic IGF gene expression and offspring performance in the rabbit

Primiparous female rabbits have high nutritional requirements and, while it is recommended that they are subjected to an extensive reproductive rhythm, this could lead to overweight, affecting reproductive outcomes. We hypothesised that restricting food intake during the less energetic period of gestation could improve reproductive outcome without impairing offspring viability. This study compares two groups of primiparous rabbit does in an extensive reproductive programme, one in which feed was restricted from Day 0 to Day 21 of gestation (R021), and another in which does were fed ad libitum (control) throughout pregnancy. The mother and offspring variables compared were (1) mother reproductive outcomes at the time points pre-implantation (Day 3 postartificial insemination [AI]), preterm (Day 28 post-AI) and birth; and (2) the prenatal offspring characteristic IGF system gene expression in foetal liver, liver fibrosis and foetus sex ratio, and postnatal factor viability and growth at birth, and survival and growth until weaning. Feed restriction did not affect the conception rate, embryo survival, or the number of morulae and blastocysts recovered at Day 3 post-AI. Preterm placenta size and efficiency were similar in the two groups. However, both implantation rate (P < 0.001) and the number of foetuses (P = 0.05) were higher in the R021 mothers than controls, while there was no difference in foetal viability. Foetal size and weight, the weights of most organs, organ weight/BW ratios and sex ratio were unaffected by feed restriction; these variables were only affected by uterine position (P < 0.05). Conversely, in the R021 does, foetal liver IGBP1 and IGF2 gene expression were dysregulated despite no liver fibrosis and a normal liver structure. No effects of restricted feed intake were produced on maternal fertility, prolificacy, or offspring birth weight, but control females weaned more kits. Litter weight and mortality rate during the lactation period were also unaffected. In conclusion, pre-implantation events and foetal development were unaffected by feed restriction. While some genes of the foetal hepatic IGF system were dysregulated during pregnancy, liver morphology appeared normal, and the growth of foetuses and kits until weaning was unmodified. This strategy of feed restriction in extensive reproductive rhythms seems to have no significant adverse effects on dam reproductive outcome or offspring growth and viability until weaning.

Sexual dimorphisms in brain gene expression in the growth-restricted guinea pig can be modulated with intra-placental therapy

BACKGROUND

Fetal responses to adverse pregnancy environments are sex-specific. In fetal guinea pigs (GPs), we assessed morphology and messenger RNA (mRNA) expression in fetal growth-restricted (FGR) tissues at midpregnancy.

METHODS

Female GPs were assigned either an ad libitum diet (C) or 30% restricted diet (R) prior to pregnancy to midpregnancy. At midpregnancy, a subset of R females underwent ultrasound-guided nanoparticle (NP) injection to enhance placental function. Five days later, fetuses were sampled. Fetal brain, heart, and liver were assessed for morphology (hematoxylin and eosin), proliferation (Ki67), and vascularization (CD31), as well as expression of inflammatory markers.

RESULTS

R fetuses were 19% lighter with reduced organ weights and evidence of brain sparing compared to controls. No increased necrosis, proliferation, or vascularization was found between C and R nor male or female fetal organs. Sexual dimorphism in mRNA expression of Tgfβ and Ctgf was observed in R but not C fetal brains: increased expression in females. NP treatment increased fetal brain mRNA expression of Tgfβ and Ctgf in R males, abolishing the significant difference observed in untreated R fetuses.

CONCLUSIONS

Sex-specific differences in mRNA expression in the fetal brain with FGR could impart a potential survival bias and may be useful for the development of treatments for obstetric diseases.

IMPACT

Male and female fetuses respond differently to adverse pregnancy environments. Under fetal growth restriction conditions, inflammatory marker mRNA expression in the fetal brain was higher in females compared to males. Differences in gene expression between males and females may confer a selective advantage/disadvantage under adverse conditions. Better characterization of sexual dimorphism in fetal development will aid better development of treatments for obstetric diseases.

Maternal Undernourishment in Guinea Pigs Leads to Fetal Growth Restriction with Increased Hypoxic Cells and Oxidative Stress in the Brain

BACKGROUND

We determined whether maternal nutrient restriction (MNR) in guinea pigs leading to fetal growth restriction (FGR) impacts markers for brain hypoxia and oxidative stress.

METHODS

Guinea pigs were fed ad libitum (control) or 70% of the control diet before pregnancy, switching to 90% at mid-pregnancy (MNR). Near term, hypoxyprobe-1 (HP-1) was injected into pregnant sows. Fetuses were then necropsied and brain tissues were processed for HP-1 (hypoxia marker) and 4HNE, 8-OHdG, and 3-nitrotyrosine (oxidative stress markers) immunoreactivity (IR).

RESULTS

FGR-MNR fetal and brain weights were decreased 38 and 12%, respectively, with brain/fetal weights thereby increased 45% as a measure of brain sparing, and more so in males than females. FGR-MNR HP-1 IR was increased in most of the brain regions studied, and more so in males than females, while 4HNE and 8-OHdG IR were increased in select brain regions, but with no sex differences.

CONCLUSIONS

Chronic hypoxia is likely to be an important signaling mechanism in the FGR brain, but with males showing more hypoxia than females. This may involve sex differences in adaptive decreases in growth and normalizing of oxygen, with implications for sex-specific alterations in brain development and risk for later neuropsychiatric disorder.

Enteroids for Nutritional Studies

Nutritional studies are greatly hampered by a paucity of proper models. Previous studies on nutrition have employed conventional cell lines and animal models to gain a better understanding of the field. These models lack certain correlations with human physiological responses, which impede their applications in this field. Enteroids are cultured from intestinal stem cells and include enterocytes, enteroendocrine cells, goblet cells, Paneth cells, and stem cells, which mimic hallmarks of in vivo epithelium and support long-term culture without genetic or physiological changes. Enteroids have been used as models to study the effects of diet and nutrients on intestinal growth and development, ion and nutrient transport, secretory and absorption functions, the intestinal barrier, and location-specific functions of the intestine. In this review, the existing models for nutritional studies are discussed and the importance of enteroids as a new model for nutritional studies is highlighted. Taken together, it is suggested that enteroids can serve as a potential model system to be exploited in nutritional studies.

Fetal Growth Restriction Is Associated With Decreased Number of Ovarian Follicles and Impaired Follicle Growth in Young Adult Guinea Pig Offspring

BACKGROUND

The mechanisms mediating the impacts of fetal growth restriction (FGR) on follicular development are commonly studied in mouse/rat models, where ovarian development occurs largely during the early postnatal period. These models have shown that FGR is associated with premature follicle loss, early pubertal onset, and accelerated ovarian aging. Whether the same occurs in precocious species is unknown.

OBJECTIVE

Since guinea pig follicle development occurs in utero in a manner consistent with human ovarian development, we sought to determine whether FGR had similar impacts on guinea pig ovarian development.

METHODS

Dunkin-Hartley guinea pig dams were randomized to receive a control (CON) or a nutrient-restricted diet (FGR) prior to conception until weaning. Offspring ovaries were collected at prepubertal (postnatal day [P] 25) and young adult (P110) time points.

RESULTS

Prepubertal offspring exposed to FGR showed little differences in ovarian transcript levels and follicle counts. Young adult FGR offspring, however, showed reductions in the number of transitioning, primary, and antral follicles, as well as corpora lutea. This loss in follicles was associated with reduced insulin-like growth factor receptor and growth differentiation factor-9 messenger RNA levels in FGR P110 offspring compared to CON.

CONCLUSION

We demonstrate that FGR in guinea pigs is accompanied by perturbations in signaling pathways essential for proper follicle growth and manifests as reductions in growing follicles in offspring, but these changes do not manifest until postpuberty. These data support the fact that accelerated reproductive maturation/aging is a conserved phenotype that is associated with in utero nutritional adversity.

Maternal nutrient restriction in guinea pigs leads to fetal growth restriction with increased brain apoptosis

BACKGROUND

We determined whether maternal nutrient restriction (MNR) in guinea pigs leading to fetal growth restriction (FGR) impacts cell death in the brain with implications for neurodevelopmental adversity.

METHODS

Guinea pigs were fed ad libitum (Control) or 70% of the control diet before pregnancy, switching to 90% at mid-pregnancy (MNR). Fetuses were necropsied near term and brain tissues processed for necrosis (H&E), apoptosis (TUNEL), and pro- (Bax) and anti- (Bcl-2 and Grp78) apoptotic protein immunoreactivity.

RESULTS

FGR-MNR fetal and brain weights were decreased 38% and 12%, respectively, indicating brain sparing but with brains still smaller. While necrosis remained unchanged, apoptosis was increased in the white matter and hippocampus in the FGR brains, and control and FGR-related apoptosis were increased in males for most brain areas. Bax was increased in the CA4 and Bcl-2 was decreased in the dentate gyrus in the FGR brains supporting a role in the increased apoptosis, while Grp78 was increased in the FGR females, possibly contributing to the sex-related differences.

CONCLUSIONS

MNR-induced FGR results in increased brain apoptosis with regional and sex-related differences that may contribute to the reduction in brain area size reported clinically and increased risk in FGR males for later neurodevelopmental adversity.

Guinea pig models for translation of the developmental origins of health and disease hypothesis into the clinic

Over 30 years ago Professor David Barker first proposed the theory that events in early life could explain an individual's risk of non-communicable disease in later life: the developmental origins of health and disease (DOHaD) hypothesis. During the 1990s the validity of the DOHaD hypothesis was extensively tested in a number of human populations and the mechanisms underpinning it characterised in a range of experimental animal models. Over the past decade, researchers have sought to use this mechanistic understanding of DOHaD to develop therapeutic interventions during pregnancy and early life to improve adult health. A variety of animal models have been used to develop and evaluate interventions, each with strengths and limitations. It is becoming apparent that effective translational research requires that the animal paradigm selected mirrors the tempo of human fetal growth and development as closely as possible so that the effect of a perinatal insult and/or therapeutic intervention can be fully assessed. The guinea pig is one such animal model that over the past two decades has demonstrated itself to be a very useful platform for these important reproductive studies. This review highlights similarities in the in utero development between humans and guinea pigs, the strengths and limitations of the guinea pig as an experimental model of DOHaD and the guinea pig's potential to enhance clinical therapeutic innovation to improve human health.

The lifelong impact of fetal growth restriction on cardiac development

BACKGROUND

Maternal nutrient restriction (MNR) is a widespread cause of fetal growth restriction (FGR), an independent predictor of heart disease and cardiovascular mortality. Our objective was to examine the developmental and long-term impact of MNR-induced FGR on cardiac structure in a model that closely mimics human development.

METHODS

A reduction in total caloric intake spanning pregestation through to lactation in guinea pig sows was used to induce FGR. Proliferation, differentiation, and apoptosis of cardiomyocytes were assessed in late-gestation fetal, neonatal, and adult guinea pig hearts. Proteomic analysis and pathway enrichment were performed on fetal hearts.

RESULTS

Cardiomyocyte proliferation and the number of mononucleated cells were enhanced in the MNR-FGR fetal and neonatal heart, suggesting a delay in cardiomyocyte differentiation. In fetal hearts of MNR-FGR animals, apoptosis was markedly elevated and the total number of cardiomyocytes reduced, the latter remaining so throughout neonatal and into adult life. A reduction in total cardiomyocyte number in adult MNR-FGR hearts was accompanied by exaggerated hypertrophy and a disorganized architecture. Pathway analysis identified genes related to cell proliferation, differentiation, and survival.

CONCLUSIONS

FGR influences cardiomyocyte development during critical windows of development, leading to a permanent deficiency in cardiomyocyte number and compensatory hypertrophy in a rodent model that recapitulates human development.

Near to One's Heart: The Intimate Relationship Between the Placenta and Fetal Heart

The development of the fetal heart is exquisitely controlled by a multitude of factors, ranging from humoral to mechanical forces. The gatekeeper regulating many of these factors is the placenta, an external fetal organ. As such, resistance within the placental vascular bed has a direct influence on the fetal circulation and therefore, the developing heart. In addition, the placenta serves as the interface between the mother and fetus, controlling substrate exchange and release of hormones into both circulations. The intricate relationship between the placenta and fetal heart is appreciated in instances of clinical placental pathology. Abnormal umbilical cord insertion is associated with congenital heart defects. Likewise, twin-to-twin transfusion syndrome, where monochorionic twins have unequal sharing of their placenta due to inter-twin vascular anastomoses, can result in cardiac remodeling and dysfunction in both fetuses. Moreover, epidemiological studies have suggested a link between placental phenotypic traits and increased risk of cardiovascular disease in adult life. To date, the mechanistic basis of the relationships between the placenta, fetal heart development and later risk of cardiac dysfunction have not been fully elucidated. However, studies using environmental exposures and gene manipulations in experimental animals are providing insights into the pathways involved. Likewise, surgical instrumentation of the maternal and fetal circulations in large animal species has enabled the manipulation of specific humoral and mechanical factors to investigate their roles in fetal cardiac development. This review will focus on such studies and what is known to date about the link between the placenta and heart development.

Perinatal and long-term effects of maternal uterine artery adenoviral VEGF-A165 gene therapy in the growth-restricted guinea pig fetus

Uterine artery application of adenoviral vascular endothelial growth factor A₁₆₅ (Ad.VEGF-A₁₆₅) gene therapy increases uterine blood flow and fetal growth in experimental animals with fetal growth restriction (FGR). Whether Ad.VEGF-A₁₆₅ reduces lifelong cardiovascular disease risk imposed by FGR remains unknown. Here, pregnant guinea pigs fed 70% normal food intake to induce FGR received Ad.VEGF-A₁₆₅ (1×10¹⁰ viral particles, n = 15) or vehicle ( n = 10), delivered to the external surface of the uterine arteries, in midpregnancy. Ad libitum-fed controls received vehicle only ( n = 14). Litter size, gestation length, and perinatal mortality were similar in control, untreated FGR, and FGR+Ad.VEGF-A₁₆₅ animals. When compared with controls, birth weight was lower in male but higher in female pups following maternal nutrient restriction, whereas both male and female FGR+Ad.VEGF-A₁₆₅ pups were heavier than untreated FGR pups ( P < 0.05, ANOVA). Postnatal weight gain was 10-20% greater in female FGR+Ad.VEGF-A₁₆₅ than in untreated FGR pups, depending on age, although neither group differed from controls. Maternal nutrient restriction reduced heart weight in adult female offspring irrespective of Ad.VEGF-A₁₆₅ treatment but did not alter ventricular wall thickness. In males, postnatal weight gain and heart morphology were not affected by maternal treatment. Neither systolic, diastolic, mean arterial pressure, adrenal weight, nor basal or challenged plasma cortisol were affected by maternal undernutrition or Ad.VEGF-A₁₆₅ in either sex. Therefore, increased fetal growth conferred by maternal uterine artery Ad.VEGF-A₁₆₅ is sustained postnatally in FGR female guinea pigs. In this study, we did not find evidence for an effect of maternal nutrient restriction or Ad.VEGF-A₁₆₅ therapy on adult offspring blood pressure.

Developmental origins of health and disease: current knowledge and potential mechanisms

Epidemiologic and clinical research has provided a large body of evidence supporting the developmental origins of health and disease (DOHaD), but there has been a relative dearth of mechanistic studies in humans due to the complexity of working with large, longitudinal cohorts. Nonetheless, animal models of undernutrition have provided substantial evidence for the potential epigenetic, metabolic, and endocrine mechanisms behind DOHaD. Furthermore, recent research has explored the interaction between the environment and the gastrointestinal system by investigating how the gut microbial ecology may impact the capacity for nutrient processing and absorption in a manner that may limit growth. This review presents a summary of current research that supports the concept of DOHaD, as well as potential mechanisms and interactions that explain how nutrition in utero and during early childhood influences lifelong health.

Maternal nutrient restriction in guinea pigs as an animal model for studying growth-restricted offspring with postnatal catch-up growth

We determined the impact of moderate maternal nutrient restriction (MNR) in guinea pigs with fetal growth restriction (FGR) on offspring body and organ weights, hypothesizing that FGR-MNR animals will show catch-up growth but with organ-specific differences. Guinea pig sows were fed ad libitum (Control) or 70% of the control diet from 4 weeks preconception, switching to 90% at midpregnancy (MNR). Control newborns >95 g [appropriate for gestational age (AGA); n = 37] and MNR newborns <85 g (FGR; n = 37) were monitored until neonatal (~25 days) or adult (~110 days) necropsy. Birth weights and body/organ weights at necropsy were used to calculate absolute and fractional growth rates (FRs). FGR-MNR birth weights were decreased ~32% compared with the AGA-Controls. FGR-MNR neonatal whole body FRs were increased ~36% compared with Controls indicating catch-up growth, with values negatively correlated to birth weights indicating the degree of FGR leads to greater catch-up growth. However, the increase in organ FRs in the FGR-MNR neonates compared with Controls was variable, being similar for the brain and kidneys indicating comparable catch-up growth to that of the whole body and twofold increased for the liver but negligible for the heart indicating markedly increased and absent catch-up growth, respectively. While FGR-MNR body and organ weights were unchanged from the AGA-Controls by adulthood, whole body growth rates were increased. These findings confirm early catch-up growth in FGR-MNR guinea pigs but with organ-specific differences and enhanced growth rates by adulthood, which are likely to have implications for structural alterations and disease risk in later life.

Adverse Placental Perfusion and Pregnancy Outcomes in a New Nonhuman Primate Model of Gestational Protein Restriction

Maternal malnutrition during pregnancy impacts fetal growth, with developmental consequences that extend to later life outcomes. In underdeveloped countries, this malnutrition typically takes the form of poor dietary protein content and quality, even if adequate calories are consumed. Here, we report the establishment of a nonhuman primate model of gestational protein restriction (PR) in order to understand how placental function and pregnancy outcomes are affected by protein deficiency. Rhesus macaques were assigned to either a control diet containing 26% protein or switched to a 13% PR diet prior to conception and maintained on this PR diet throughout pregnancy. Standard fetal biometry, Doppler ultrasound of uteroplacental blood flow, ultrasound-guided amniocentesis, and contrast-enhanced ultrasound (CE-US) to assess placental perfusion were performed mid-gestation (gestational day 85 [G85] where term is G168) and in the early third trimester (G135). Our data demonstrate that a 50% reduction in dietary protein throughout gestation results in reduced placental perfusion, fetal growth restriction, and a 50% rate of pregnancy loss. In addition, we demonstrate reduced total protein content and evidence of fetal hypoxia in the amniotic fluid. This report highlights the use of CE-US for in vivo assessment of placental vascular function. The ability to detect placental dysfunction, and thus a compromised pregnancy, early in gestation, may facilitate the development of interventional strategies to optimize clinical care and improve long-term offspring outcomes, which are future areas of study in this new model.

Maternal body mass index impacts fetal-placental size at birth and umbilical cord oxygen values with implications for regulatory mechanisms

BACKGROUND

Maternal under- and over-nutrition are known to effect fetal growth with altered placental development and nutrient transport, but whether fetal oxygenation is also altered remains unknown.

AIMS

To examine linkages between maternal BMI and birth weights, placental weights, and umbilical vein and artery PO_2, with implications for signaling mechanisms.

STUDY DESIGN

Population-based cohort study.

SUBJECTS

Analysis of hospital database information on all patients with pre-pregnant BMI values delivering viable, singleton infants between Jan 1, 1999 and Dec 31, 2010 (N=29,212). BMI was categorized into underweight, normal weight, overweight, and obese, with birth weights categorized into small (SGA), appropriate (AGA), and large for gestational age (LGA).

OUTCOME MEASURES

Maternal BMI, birth and placental weights, umbilical vein and artery PO₂.

RESULTS

Underweight mothers with smaller infants and overweight/obese mothers with larger infants had disproportionately large placentas, suggesting compensatory and/or enhanced placental growth in these pregnancies. All SGA infants had lower umbilical vein and artery PO₂, consistent with aberrant placental development leading to diffusional impairment of oxygen. Both maternal overweight/obese BMI and LGA resulted in lower artery PO₂, likely due to increased growth rates with the larger size in these infants.

CONCLUSIONS

These findings support fetal hypoxemia as a common determinant of growth restriction, whether in underweight mothers and due to under-nutrition or in overweight/obese mothers and due to placental insufficiency. However, oxygen is unlikely to be the primary promotor for fetal growth in overweight/obese mothers and LGA infants, with other substrates of more importance as nutritional cues in these pregnancies.

Maternal nutrient restriction in guinea pigs leads to fetal growth restriction with evidence for chronic hypoxia

BackgroundWe determined whether maternal nutrient restriction (MNR) in guinea pigs leading to fetal growth restriction (FGR) impacts markers for tissue hypoxia, implicating a mechanistic role for chronic hypoxia.MethodsGuinea pigs were fed ad libitum (Control) or 70% of the control diet before pregnancy, switching to 90% at mid-pregnancy (MNR). Near term, hypoxyprobe-1 (HP-1), a marker of tissue hypoxia, was injected into pregnant sows. Fetuses were then necropsied and liver, kidney, and placental tissues were processed for erythropoietin (EPO), EPO-receptor (EPOR), and vascular endothelial growth factor (VEGF) protein levels, and for HP-1 immunoreactivity (IR).ResultsFGR-MNR fetuses were 36% smaller with asymmetrical growth restriction compared to controls. EPO and VEGF protein levels were increased in the female FGR-MNR fetuses, providing support for hypoxic stimulus and linkage to increased erythropoiesis, but not in the male FGR-MNR fetuses, possibly reflecting a weaker link between oxygenation and erythropoiesis. HP-1 IR was increased in the liver and kidneys of both male and female FGR-MNR fetuses as an index of local tissue hypoxia, but with no changes in the placenta.ConclusionChronic hypoxia is likely to be an important signaling mechanism for the decreased fetal growth seen with maternal undernutrition and appears to be post-placental in nature.

Reproductive performance and gestational effort in relation to dietary fatty acids in guinea pigs

Background

Dietary saturated (SFAs) and polyunsaturated (PUFAs) fatty acids can highly affect reproductive functions by providing additional energy, modulating the biochemical properties of tissues, and hormone secretions. In precocial mammals such as domestic guinea pigs the offspring is born highly developed. Gestation might be the most critical reproductive period in this species and dietary fatty acids may profoundly influence the gestational effort. We therefore determined the hormonal status at conception, the reproductive success, and body mass changes during gestation in guinea pigs maintained on diets high in PUFAs or SFAs, or a control diet.

Results

The diets significantly affected the females’ plasma fatty acid status at conception, while cortisol and estrogen levels did not differ among groups. SFA females exhibited a significantly lower body mass and litter size, while the individual birth mass of pups did not differ among groups and a general higher pup mortality rate in larger litters was diminished by PUFAs and SFAs. The gestational effort, determined by a mother’s body mass gain during gestation, increased with total litter mass, whereas this increase was lowest in SFA and highest in PUFA individuals. The mother’s body mass after parturition did not differ among groups and was positively affected by the total litter mass in PUFA females.

Conclusions

While SFAs reduce the litter size, but also the gestational effort as a consequence, PUFA supplementation may contribute to an adjustment of energy accumulations to the total litter mass, which may both favor a mother’s body condition at parturition and perhaps increase the offspring survival at birth.

Electronic supplementary material

The online version of this article (doi:10.1186/s40104-017-0158-4) contains supplementary material, which is available to authorized users.

Impact of birth weight and postnatal diet on the gut microbiota of young adult guinea pigs

Background

The gastrointestinal tract (GIT) microbiota is essential to metabolic health, and the prevalence of the Western diet (WD) high in fat and sugar is increasing, with evidence highlighting a negative interaction between the GIT and WD, resulting in liver dysfunction. Additionally, an adverse in utero environment such as placental insufficiency resulting in low birth weight (LBW) offspring, contributes to an increased risk of metabolic diseases such as fatty liver infiltration and liver dysfunction in later life. We sought to understand the potential interactive effects of exposure to a WD upon growing LBW offspring. We postulated that LBW offspring when challenged with a poor postnatal diet, would display an altered microbiota and more severe liver metabolic dysfunction.

Methods

The fecal microbiota of normal birth weight (NBW) and LBW young guinea pig offspring, weaned onto either a control diet (CD) or WD was determined with 16S rRNA gene next generation sequencing at young adulthood following the early rapid growth phase after weaning. A liver blood chemistry profile was also performed.

Results

The life-long consumption of WD following weaning into young adulthood resulted in increased total cholesterol, triglycerides and alanine aminotransferase levels in association with an altered GIT microbiota when compared to offspring consuming CD. Neither birth weight nor sex were associated with any significant changes in microbiota alpha diversity, by measuring the Shannon’s diversity index. One hundred forty-eight operational taxonomic units were statistically distinct between the diet groups, independent of birth weight. In the WD group, significant decreases were detected in Barnesiella, Methanobrevibacter smithii and relatives of Oscillospira guillermondii, while Butyricimonas and Bacteroides spp. were increased.

Discussion

These results describe the GIT microbiota in a guinea pig model of LBW and WD associated metabolic syndrome and highlight several WD specific GIT alterations associated with human metabolic disease.