Intrauterine growth restriction modifies the normal gene expression in kidney from rabbit fetuses

Pregnancy Complications and Feto-Maternal Monitoring in Rabbits

Rabbit production holds significant relevance in modern agriculture due to its potential as a sustainable source of high-quality protein and efficient feed conversion, contributing to food security and economic diversification. Nevertheless, studies incorporating feto-maternal monitoring in this species are uncommon. This review gathers research on the monitoring and evaluation of factors affecting rabbit gestation, providing a better understanding of the causes of prenatal development abnormalities. These include studies regarding how chronic maternal hypertension, gestational diabetes, maternal stress, ectopic gestation, maternal uterine ischemia and fetal hypoxia, intrauterine growth restriction, superfetation, maternal age, maternal nutritional status, maternal physical condition, maternal and embryonic genotype, and the intrauterine location of rabbit fetuses can potentially impact rabbits' reproduction and maternal and fetal health. Among other monitoring techniques, ultrasonography, considered one of the best tools for diagnosing pregnancy and conducting follow-up, is also reviewed. Details on measurable fetal-development parameters in rabbits and precautions to be considered before and during the examination are also provided. Additional studies are required to understand why some events occur and their consequences throughout gestation, allowing the determination of new biomarkers or cut-offs that can be helpful for early diagnosis and improve reproductive efficiency.

The role of interleukin-1 in perinatal inflammation and its impact on transitional circulation

Preterm birth is defined as delivery at <37 weeks of gestational age (GA) and exposes 15 million infants worldwide to serious early life diseases. Lowering the age of viability to 22 weeks GA entailed provision of intensive care to a greater number of extremely premature infants. Moreover, improved survival, especially at extremes of prematurity, comes with a rising incidence of early life diseases with short- and long-term sequelae. The transition from fetal to neonatal circulation is a substantial and complex physiologic adaptation, which normally happens rapidly and in an orderly sequence. Maternal chorioamnionitis or fetal growth restriction (FGR) are two common causes of preterm birth that are associated with impaired circulatory transition. Among many cytokines contributing to the pathogenesis of chorioamnionitis-related perinatal inflammatory diseases, the potent pro-inflammatory interleukin (IL)-1 has been shown to play a central role. The effects of utero-placental insufficiency-related FGR and in-utero hypoxia may also be mediated, in part, via the inflammatory cascade. In preclinical studies, blocking such inflammation, early and effectively, holds great promise for improving the transition of circulation. In this mini-review, we outline the mechanistic pathways leading to abnormalities in transitional circulation in chorioamnionitis and FGR. In addition, we explore the therapeutic potential of targeting IL-1 and its influence on perinatal transition in the context of chorioamnionitis and FGR.

Ouabain regulates kidney metabolic profiling in rat offspring of intrauterine growth restriction induced by low-protein diet

AIMS

Intrauterine growth restriction (IUGR) can increase the risk of hypertension and kidney disease at adulthood due to fetal programming. In our previous study, we found that supplementation with low concentration of ouabain during pregnancy could restore glomerulus numbers at birth, rescuing kidney development. However, the metabolic pattern of kidney in IUGR offspring and the effect of ouabain have not been evaluated.

MAIN METHODS

In this study, based on GC-MS and LC-MS platforms, we used the protein restriction rat model to explore the molecular mechanisms of kidney damage induced by IUGR and the protective effect of ouabain.

KEY FINDINGS

The results showed that malnutrition could induce IUGR in rat offspring at the 20th gestational day but ouabain treatment could partially reverse the body and kidney weight loss. Ouabain treatment could upregulate arginine, N-acetylornithine and carbamoyl phosphate as well as adenine nucleotide and guanine nucleotide downregulated by low-protein diet. Moreover, six metabolites were identified to be significantly correlated with fetal kidney weight, with 3 metabolites involved in arginine metabolism (arginine, N-acetylornithine, urea) and UDP-glucuronate correlated positively, while lysine and anthranilate correlated negatively.

SIGNIFICANCE

The results suggested that the underlying mechanism of ouabain against renal maldevelopment involved the metabolic regulation, particularly the arginine metabolism, which played an important role in the development of fetal kidney.

Models of Intrauterine growth restriction and fetal programming in rabbits

Intrauterine growth restriction (IUGR) affects approximately 10% of human pregnancies globally and has immediate and life-long consequences for offspring health. However, the mechanisms underlying the pathogenesis of IUGR and its association with later health and disease outcomes are poorly understood. To address these knowledge gaps, the use of experimental animals is critically important. Since the 50's different environmental, pharmacological, and surgical manipulations have been performed in the rabbit to improve our knowledge of the control of fetal growth, fetal responses to IUGR, and mechanisms by which offspring may be programmed by an adverse gestational environment. The purpose of this review is therefore to summarize the utility of the rabbit as a model for IUGR research. It first summarizes the knowledge of prenatal and postnatal development in the rabbit and how these events relate to developmental milestones in humans. It then describes the methods used to induce IUGR in rabbits and the knowledge gained about the mechanisms determining prenatal and postnatal outcomes of the offspring. Finally, it discusses the application of state of the art approaches in the rabbit, including high-resolution ultrasound, magnetic resonance imaging, and gene targeting, to gain a deeper integrative understanding of the physiological and molecular events governing the development of IUGR. Overall, we hope to engage and inspire investigators to employ the rabbit as a model organism when studying pregnancy physiology so that we may advance our understanding of mechanisms underlying IUGR and its consequences in humans and other mammalian species.

Hypoxia-inducible factor prolyl-4-hydroxylation in FOXD1 lineage cells is essential for normal kidney development

Hypoxia in the embryo is a frequent cause of intra-uterine growth retardation, low birth weight, and multiple organ defects. In the kidney, this can lead to low nephron endowment, predisposing to chronic kidney disease and arterial hypertension. A key component in cellular adaptation to hypoxia is the hypoxia-inducible factor pathway, which is regulated by prolyl-4-hydroxylase domain (PHD) dioxygenases PHD1, PHD2, and PHD3. In the adult kidney, PHD oxygen sensors are differentially expressed in a cell type-dependent manner and control the production of erythropoietin in interstitial cells. However, the role of interstitial cell PHDs in renal development has not been examined. Here we used a genetic approach in mice to interrogate PHD function in FOXD1-expressing stroma during nephrogenesis. We demonstrate that PHD2 and PHD3 are essential for normal kidney development as the combined inactivation of stromal PHD2 and PHD3 resulted in renal failure that was associated with reduced kidney size, decreased numbers of glomeruli, and abnormal postnatal nephron formation. In contrast, nephrogenesis was normal in animals with individual PHD inactivation. We furthermore demonstrate that the defect in nephron formation in PHD2/PHD3 double mutants required intact hypoxia-inducible factor-2 signaling and was dependent on the extent of stromal hypoxia-inducible factor activation. Thus, hypoxia-inducible factor prolyl-4-hydroxylation in renal interstitial cells is critical for normal nephron formation.

Activation of Hypoxia Signaling in Stromal Progenitors Impairs Kidney Development

Intrauterine hypoxia is a reason for impaired kidney development. The cellular and molecular pathways along which hypoxia exerts effects on nephrogenesis are not well understood. They are likely triggered by hypoxia-inducible transcription factors (HIFs), and their effects appear to be dependent on the cell compartment contributing to kidney formation. In this study, we investigated the effects of HIF activation in the developing renal stroma, which also essentially modulates nephron development from the metanephric mesenchyme. HIF activation was achieved by conditional deletion of the von Hippel-Lindau tumor suppressor (VHL) protein in the forkhead box FOXD1 cell lineage, from which stromal progenitors arise. The resulting kidneys showed maturation defects associated with early postnatal death. In particular, nephron formation, tubular maturation, and the differentiation of smooth muscle, renin, and mesangial cells were impaired. Erythropoietin expression was strongly enhanced. Codeletion of VHL together with HIF2A but not with HIF1A led to apparently normal kidneys, and the animals reached normal age but were anemic because of low erythropoietin levels. Stromal deletion of HIF2A or HIF1A alone did not affect kidney development. These findings emphasize the relevance of sufficient intrauterine oxygenation for normal renal stroma differentiation, suggesting that chronic activity of HIF2 in stromal progenitors impairs kidney development. Finally, these data confirm the concept that normal stroma function is essential for normal tubular differentiation.

The impact of hypoxia on nephrogenesis

PURPOSE OF REVIEW

Kidney development depends on outgrowth of the ureteric bud into the metanephric mesenchyme. The number of ureteric bud branching events determines the final number of nephrons, which correlates inversely with the risk for development of chronic kidney disease and arterial hypertension during lifetime. The purpose of this review is to highlight the influence of oxygen on nephrogenesis and to describe cellular mechanisms by which hypoxia can impair nephron formation.

RECENT FINDINGS

Although kidney development normally takes place under hypoxic conditions, nephrogenesis is impaired when oxygen availability falls below the usual range. Hypoxia-inducible factors (HIF) play an important role in linking low oxygen concentrations to the biology of nephron formation, but their effect appears to be cell type dependent. In ureteric bud cells, HIF stimulates tubulogenesis, whereas HIF stabilization in cells of the metanephric mesenchyme results in secretion of growth factors, including vascular endothelial growth factor A, which in aggregate inhibit ureteric bud branching. The balance between pro and antibranching effects may be altered in various ways, but the inhibitory effect usually seems to predominate under reduced oxygen concentrations, explaining how intrauterine hypoxia can lead to low nephron numbers.

SUMMARY

Oxygen availability has a complex influence on nephrogenesis. Oxygen concentrations outside an optimal low range may affect nephron endowment. Associations between placental insufficiency and increased risk for chronic kidney disease and arterial hypertension during later life may to a large extent be due to direct effects of reduced oxygen supply to the metanephric mesenchyme and mediated through the HIF pathway.

Role of hypoxia during nephrogenesis

Mammals develop in a physiologically hypoxic state, and the oxygen tension of different tissues in the embryo is precisely controlled. Deviation from normal oxygenation, such as what occurs in placental insufficiency, can disrupt fetal development. Several studies demonstrate that intrauterine hypoxia has a negative effect on kidney development. As nascent nephrons are forming from nephron progenitors in the nephrogenic zone, they are exposed to varying oxygen tension by virtue of the development of the renal vasculature. Thus, nephrogenesis may be linked to oxygen tension. However, the mechanism(s) by which this occurs remains unclear. This review focuses on what is known about molecular mechanisms active in physiological and pathological hypoxia and their effects on kidney development.

Nitric oxide synthase and changes in oxidative stress levels in embryonic kidney observed in a rabbit model of intrauterine growth restriction

OBJECTIVE

This work aimed to study the effect of uteroplacental circulation restriction on endothelial kidney damage in a fetal rabbit model.

METHODS

New Zealand rabbits were subjected to 40% to 50% of uteroplacental artery ligation at day 25 of pregnancy. After 5 days, surviving fetuses were harvested by cesarean section. The gene and protein expressions of selected enzymes associated with nitric oxide production and oxidative stress were analyzed in fetal kidney homogenates.

RESULTS

The placenta weight (6.06 ± 0.27, p < 0.0319) and fetal body (19.90 ± 1.03, p < 0.0001) were significantly reduced in the uteroplacental circulation restriction group. The kidneys from restricted fetuses presented a mild vascular congestion and glomerular capillary congestion, without inflammation or hypertrophy. We found endothelial nitric oxide synthase phosphorylation inhibition (0.23 ± 0.13, p < 0.012) and arginase-2 (0.29 ± 0.14, p < 0.023) protein induction in fetal kidneys of the circulation restriction group. Finally, the kidneys from circulation-restricted fetuses showed increased inducible nitric oxide synthase messenger RNA (mRNA) (2.68 ± 0.24, p < 0.01) and reduced heme oxygenase-1 mRNA (23 ± 1.3, p < 0.003), with increased reactive oxygen species (1.69 ± 0.09, p < 0.001) and nitrotyrosine protein (1.74 ± 0.28, p < 0.003) levels, without changes in Nox mRNA.

CONCLUSION

We describe significant deregulation of vascular activity and oxidative damage in kidneys of fetal rabbits that have been exposed to restriction of the uterine circulation. © 2016 John Wiley & Sons, Ltd.

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.

Spontaneous Preterm Delivery, Particularly with Reduced Fetal Growth, is Associated with DNA Hypomethylation of Tumor Related Genes

Background

Preterm delivery and sub-optimal fetal growth are associated with each other and affect both mother and infant. Our aim was to determine (i) whether there are detectable differences in DNA methylation between early and late gestation and (ii) whether changes in DNA methylation from entry are associated with spontaneous preterm delivery with and without reduced fetal growth.

Methods

We conducted a case-control study nested within a large prospective cohort. Gene specific methylation was measured by Methyl-Profiler PCR Array in a Human Breast Cancer Signature Panel of 24 genes from maternal peripheral leukocytes genomic DNA at entry and 3^rd trimester (sampled at 16 and 30 weeks of gestation, respectively). Clonal bisulfite DNA sequencing was performed to confirm the changes in selected genes (CYP1B1, GADD45A and CXCL12). Multivariable analysis was used for data analysis.

Results

There was significantly decrease in DNA methylation in 15 of 24 genes during the 3^rd trimester in cases of spontaneous preterm delivery (n=23) as compared to the controls (n=19) (p<0.05–p<0.01 for each gene). Similar results were observed by bisulfite sequencing for 3 genes. The change in DNA methylation between late and early gestation was significantly different in cases (overall decrease in methylation was −4.0 ± 1.5%) compared to the controls (overall increase in methylation was 12.6 ± 2.19%, p<0.0001). A graded pattern of DNA methylation was observed in 15 genes. Cases who delivered preterm with reduced fetal growth had the lowest level of methylation, cases delivering preterm without reduced fetal growth were next and term controls were highest in methylation (p for trend <0.05 to p<0.01 for each gene). Cases of preterm delivery also had significantly lower dietary choline intake.

Conclusions

These data suggest that epigenetic modification is associated with an increased risk of spontaneous preterm delivery, spontaneous preterm delivery with reduced fetal growth in particular.

Ouabain rescues rat nephrogenesis during intrauterine growth restriction by regulating the complement and coagulation cascades and calcium signaling pathway

Intrauterine growth restriction (IUGR) is associated with a reduction in the numbers of nephrons in neonates, which increases the risk of hypertension. Our previous study showed that ouabain protects the development of the embryonic kidney during IUGR. To explore this molecular mechanism, IUGR rats were induced by protein and calorie restriction throughout pregnancy, and ouabain was delivered using a mini osmotic pump. RNA sequencing technology was used to identify the differentially expressed genes (DEGs) of the embryonic kidneys. DEGs were submitted to the Database for Annotation and Visualization and Integrated Discovery, and gene ontology enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were conducted. Maternal malnutrition significantly reduced fetal weight, but ouabain treatment had no significant effect on body weight. A total of 322 (177 upregulated and 145 downregulated) DEGs were detected between control and the IUGR group. Meanwhile, 318 DEGs were found to be differentially expressed (180 increased and 138 decreased) between the IUGR group and the ouabain-treated group. KEGG pathway analysis indicated that maternal undernutrition mainly disrupts the complement and coagulation cascades and the calcium signaling pathway, which could be protected by ouabain treatment. Taken together, these two biological pathways may play an important role in nephrogenesis, indicating potential novel therapeutic targets against the unfavorable effects of IUGR.

Placental Aromatase Is Deficient in Placental Ischemia and Preeclampsia

Introduction

Preeclampsia is a maternal hypertensive disorder with uncertain etiology and a leading cause of maternal and fetal mortality worldwide, causing nearly 40% of premature births delivered before 35 weeks of gestation. The first stage of preeclampsia is characterized by reduction of utero-placental blood flow which is reflected in high blood pressure and proteinuria during the second half of pregnancy. In human placenta androgens derived from the maternal and fetal adrenal glands are converted into estrogens by the enzymatic action of placental aromatase. This implies that alterations in placental steroidogenesis and, subsequently, in the functionality or bioavailability of placental aromatase may be mechanistically involved in the pathophysiology of PE.

Methods

Serum samples were collected at 32–36 weeks of gestation and placenta biopsies were collected at time of delivery from PE patients (n = 16) and pregnant controls (n = 32). The effect of oxygen tension on placental cells was assessed by incubation JEG–3 cells under 1% and 8% O₂ for different time periods, Timed-mated, pregnant New Zealand white rabbits (n = 6) were used to establish an in vivo model of placental ischemia (achieved by ligature of uteroplacental vessels). Aromatase content and estrogens and androgens concentrations were measured.

Results

The protein and mRNA content of placental aromatase significantly diminished in placentae obtained from preeclamptic patients compared to controls. Similarly, the circulating concentrations of 17-β-estradiol/testosterone and estrone/androstenedione were reduced in preeclamptic patients vs. controls. These data are consistent with a concomitant decrease in aromatase activity. Aromatase content was reduced in response to low oxygen tension in the choriocarcinoma JEG–3 cell line and in rabbit placentae in response to partial ligation of uterine spiral arteries, suggesting that reduced placental aromatase activity in preeclamptic patients may be associated with chronic placental ischemia and hypoxia later in gestation.

Conclusions

Placental aromatase expression and functionality are diminished in pregnancies complicated by preeclampsia in comparison with healthy pregnant controls.

Hypoxia inhibits nephrogenesis through paracrine Vegfa despite the ability to enhance tubulogenesis

Reduced nephron number predisposes to hypertension and kidney disease. Interaction of the branching ureteric bud and surrounding mesenchymal cells determines nephron number. Since oxygen supply may be critical for intrauterine development, we tested whether hypoxia and hypoxia-inducible factor-1α (HIF-1α) influence nephrogenesis. We found that HIF-1α is required for branching of MDCK cells. In addition, culture of metanephric mouse kidneys with ureteric bud cell-specific stabilization or knockout of HIF-1α revealed a positive impact of HIF-1α on nephrogenesis. In contrast, widespread stabilization of HIF-1α in metanephric kidneys through hypoxia or HIF stabilizers impaired nephrogenesis, and pharmacological HIF inhibition enhanced nephrogenesis. Several lines of evidence suggest an inhibitory effect through the hypoxia response of mesenchymal cells. HIF-1α was expressed in mesenchymal cells during nephrogenesis. Expression of the anti-branching factors Bmp4 and Vegfa, secreted by mesenchymal cells, was increased upon HIF stabilization. The conditioned medium from hypoxic metanephric kidneys inhibited MDCK branching, which was partially rescued by Vegfa antibodies. Thus, the effect of HIF-1α on nephrogenesis appears context dependent. While HIF-1α in the ureteric bud is of importance for proper branching morphogenesis, the net effect of hypoxia-induced HIF activation in the embryonic kidney appears to be mesenchymal cell-dependent inhibition of ureter branching.

Fetal echocardiography and pulsed-wave Doppler ultrasound in a rabbit model of intrauterine growth restriction

Fetal intrauterine growth restriction (IUGR) results in abnormal cardiac function that is apparent antenatally due to advances in fetoplacental Doppler ultrasound and fetal echocardiography. Increasingly, these imaging modalities are being employed clinically to examine cardiac function and assess wellbeing in utero, thereby guiding timing of birth decisions. Here, we used a rabbit model of IUGR that allows analysis of cardiac function in a clinically relevant way. Using isoflurane induced anesthesia, IUGR is surgically created at gestational age day 25 by performing a laparotomy, exposing the bicornuate uterus and then ligating 40-50% of uteroplacental vessels supplying each gestational sac in a single uterine horn. The other horn in the rabbit bicornuate uterus serves as internal control fetuses. Then, after recovery at gestational age day 30 (full term), the same rabbit undergoes examination of fetal cardiac function. Anesthesia is induced with ketamine and xylazine intramuscularly, then maintained by a continuous intravenous infusion of ketamine and xylazine to minimize iatrogenic effects on fetal cardiac function. A repeat laparotomy is performed to expose each gestational sac and a microultrasound examination (VisualSonics VEVO 2100) of fetal cardiac function is performed. Placental insufficiency is evident by a raised pulsatility index or an absent or reversed end diastolic flow of the umbilical artery Doppler waveform. The ductus venosus and middle cerebral artery Doppler is then examined. Fetal echocardiography is performed by recording B mode, M mode and flow velocity waveforms in lateral and apical views. Offline calculations determine standard M-mode cardiac variables, tricuspid and mitral annular plane systolic excursion, speckle tracking and strain analysis, modified myocardial performance index and vascular flow velocity waveforms of interest. This small animal model of IUGR therefore affords examination of in utero cardiac function that is consistent with current clinical practice and is therefore useful in a translational research setting.

Circulating mRNA for epidermal growth factor-like domain 7 (EGFL7) in maternal blood and early intrauterine growth restriction. A preliminary analysis

OBJECTIVE

To evaluate the alteration in epidermal growth factor-like domain 7 (EGFL7) mRNA expression in maternal blood from pregnancies affected by early-onset intrauterine growth restriction (IUGR) at 20-24 weeks.

METHOD

Case-control study encompassing six women with pregnancies affected by IUGR (cases) matched in a 1 : 7 ratio for gestational age and fetal gender with 42 controls. We quantified EGFL7 mRNA expression in normal and IUGR patients. Matched rank-sum analysis and multiples of median were used to evaluate differences of the marker of interest between cases and controls. Spearman regression analysis was used to correlate the estimated fetal weight at blood sampling with the EGFL7 mRNA values.

RESULTS

The mean observed rank in the IUGR group was significantly higher than that of controls (6.67 vs 4.19, p = 0.01). Pregnancies affected with IUGR exhibited 1.70-fold higher levels of maternal EGFL7 mRNA compared with matched controls (p = 0.014). EGFL7 mRNA values were inversely correlated with estimated fetal weight (Spearman's ρ = -0.429, p = 0.198).

CONCLUSION

Early IUGR at 20-24 weeks' gestation is associated with higher values of EGFL7 expression in maternal plasma.