Sarah L. Walton

Mid‐ to late term hypoxia in the mouse alters placental morphology, glucocorticoid regulatory pathways and nutrient transporters in a sex‐specific manner

Maternal hypoxia is a common perturbation that may impair fetal development and programme sex specific disease outcomes in offspring. There is growing interest in the role of the placenta in mediating the effects of maternal hypoxia on fetal development, particularly in late gestation during maximal fetal growth. Multiple mechanisms have been proposed to play a role in hypoxia induced impairment of placental development. Here we investigated the role of glucocorticoids and glucose regulation. This study shows that fetal sex determines placental adaptations to maternal hypoxia: while maternal hypoxia increased maternal glucose and corticosterone levels in both sexes, placental adaptations to impaired maternal physiology were more evident in female fetuses, in which factors responsible for the regulation of glucocorticoids and nutrient transport were most severely affected by maternal hypoxia.

Late gestational hypoxia and a postnatal high salt diet programs endothelial dysfunction and arterial stiffness in adult mouse offspring

Maternal hypoxia is a common perturbation that leads to growth restriction and may program vascular dysfunction in adult offspring. An adverse prenatal environment may render offspring vulnerable to increased cardiovascular risk when challenged with a ‘second hit’, such as a high salt diet. We investigated whether maternal hypoxia impaired vascular function, structure and mechanics in mouse offspring, and also whether this was exacerbated by excess dietary salt intake in postnatal life. Maternal hypoxia predisposed adult male and female offspring to endothelial dysfunction. The combination of prenatal hypoxia and high dietary salt intake caused significant stiffening of mesenteric arteries, and also altered structural characteristics of the aorta consistent with vascular stiffening. The results of the present study suggest that prenatal hypoxia combined with a high salt diet in postnatal life can contribute to vascular dysfunction.

The effects of gestational age and maternal hypoxia on the placental renin angiotensin system in the mouse

INTRODUCTION The renin angiotensin system (RAS) is an important mediator of placental development. However, a comprehensive expression profile for 8 key components of the placental RAS throughout murine gestation has not been performed. Furthermore, maternal hypoxia induces dysregulation of RAS expression in fetal tissues but the effects on the murine placental RAS are less well known. METHODS Placentas were collected from male and female CD1 mouse fetuses at seven gestational ages for qPCR analysis of Agt, Ren1, Atp6ap2, Ace, Ace2, Agtr1a, Agtr2 and Mas1. mRNA localisation of Agtr1 and Mas1 and protein localisation of ACE and ACE2 was determined at E18.5. To determine the effects of maternal hypoxia on the placental RAS, mice were housed in 12% oxygen from E14.5-E18.5 and placentas examined at E18.5. RESULTS All RAS genes were expressed in the placenta throughout pregnancy and expression varied with fetal sex and age. Agtr1 was expressed within the labyrinth while Mas1 was expressed within the intraplacental yolk sac. ACE and ACE2 were localised to both labyrinth and junctional zones. In response to maternal hypoxia the expression of Agt, Ace and Ace2 was decreased but expression of Agtr1a was increased. Ace and Agtr1a mRNA levels were affected to a greater extent in females compared to males. DISCUSSION Collectively, the location within the placenta as well as the expression profiles identified, support a role for the placental RAS in labyrinth development. The placental RAS is disturbed by maternal hypoxia in a sexually dimorphic manner and may contribute to impairment of placental vascular development.

Prenatal hypoxia leads to hypertension, renal renin-angiotensin system activation and exacerbates salt-induced pathology in a sex-specific manner

Prenatal hypoxia is associated with growth restriction and adverse cardiovascular outcomes. Here, we describe renal and cardiovascular outcomes in ageing mouse offspring prenatally exposed to hypoxia (12% O2) from embryonic day 14.5 until birth. At 12 months of age, both male and female offspring exposed to prenatal hypoxia had elevated mean arterial pressure. Glomerular number was reduced by 25% in hypoxia-exposed male, but not female, offspring and this was associated with increased urinary albumin excretion, glomerular hypertrophy and renal fibrosis. Hypoxia-exposed offspring of both sexes were more susceptible to salt-induced cardiac fibrosis, however, renal fibrosis was exacerbated by high salt in males only. In male but not female hypoxia-exposed offspring, renal renin mRNA was increased at weaning. By 12 months, renal renin mRNA expression and concentrations were elevated in both sexes. mRNA expression of At1aR was also elevated in male hypoxia-exposed offspring at 12 months. These results demonstrate that prenatal hypoxia programs elevated blood pressure and exacerbates salt-induced cardiovascular and renal pathology in a sex specific manner. Given sex differences observed in RAS expression and nephron number, future studies may consider RAS blockade as a therapeutic target in this model.

Lengths of nephron tubule segments and collecting ducts in the CD-1 mouse kidney: an ontogeny study.

The kidney continues to mature postnatally, with significant elongation of nephron tubules and collecting ducts to maintain fluid/electrolyte homeostasis. The aim of this project was to develop methodology to estimate lengths of specific segments of nephron tubules and collecting ducts in the CD-1 mouse kidney using a combination of immunohistochemistry and design-based stereology (vertical uniform random sections with cycloid arc test system). Lengths of tubules were determined at postnatal day 21 (P21) and 2 and 12 mo of age and also in mice fed a high-salt diet throughout adulthood. Immunohistochemistry was performed to identify individual tubule segments [aquaporin-1, proximal tubules (PT) and thin descending limbs of Henle (TDLH); uromodulin, distal tubules (DT); aquaporin-2, collecting ducts (CD)]. All tubular segments increased significantly in length between P21 and 2 mo of age (PT, 602% increase; DT, 200% increase; TDLH, 35% increase; CD, 53% increase). However, between 2 and 12 mo, a significant increase in length was only observed for PT (76% increase in length). At 12 mo of age, kidneys of mice on a high-salt diet demonstrated a 27% greater length of the TDLH, but no significant change in length was detected for PT, DT, and CD compared with the normal-salt group. Our study demonstrates an efficient method of estimating lengths of specific segments of the renal tubular system. This technique can be applied to examine structure of the renal tubules in combination with the number of glomeruli in the kidney in models of altered renal phenotype.

Prolonged prenatal hypoxia selectively disrupts collecting duct patterning and postnatal function in male mouse offspring

In the present study, we investigated whether hypoxia during late pregnancy impairs kidney development in mouse offspring, and also whether this has long‐lasting consequences affecting kidney function in adulthood. Hypoxia disrupted growth of the kidney, particularly the collecting duct network, in juvenile male offspring. By mid‐late adulthood, these mice developed early signs of kidney disease, notably a compromised response to water deprivation. Female offspring showed no obvious signs of impaired kidney development and did not develop kidney disease, suggesting an underlying protection mechanism from the hypoxia insult. These results help us better understand the long‐lasting impact of gestational hypoxia on kidney development and the increased risk of chronic kidney disease.

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

Low weight at birth increases the risk of developing chronic diseases in adulthood A diet that is high in salt is known to elevate blood pressure, which is a major risk factor for cardiovascular and kidney diseases The present study demonstrates that growth restricted male rats have a heightened sensitivity to high dietary salt, in the context of raised systolic blood pressure, reduced urinary sodium excretion and stiffer mesenteric resistance vessels Other salt‐induced effects, such as kidney hyperfiltration, albuminuria and glomerular damage, were not exacerbated by being born small The present study demonstrates that male offspring born small have an increased cardiovascular susceptibility to high dietary salt, such that that minimizing salt intake is probably of particular benefit to this at‐risk population

Angiotensin receptor blockade in juvenile male rat offspring: Implications for long-term cardio-renal health

Graphical abstract Figure. No caption available. &NA; Inhibition of the renin‐angiotensin system in early postnatal life is a potential therapeutic approach to prevent long‐term cardiovascular and kidney diseases in individuals born small. We determined the long‐term effects of juvenile losartan treatment on cardiovascular and kidney function in control male rat offspring and those exposed to uteroplacental insufficiency and born small. Bilateral uterine vessel ligation (Restricted) or sham (Control) surgery was performed in late gestation in Wistar Kyoto rats. At weaning, male offspring were randomly assigned to receive losartan in their drinking water or drinking water alone from 5 to 8 weeks of age, and followed to 26 weeks of age. Systolic blood pressure and kidney function were assessed throughout the study. Pressure myography was used to assess passive mechanical wall properties in mesenteric and femoral arteries from 26‐week‐old offspring. Losartan treatment for three weeks lowered systolic blood pressure in both Control and Restricted groups but this difference was not sustained after the cessation of treatment. Losartan, irrespective of birth weight, mildly increased renal tubulointerstitial fibrosis when assessed at 26 weeks of age. Mesenteric artery stiffness was increased by the early losartan treatment, and was associated with increased collagen and decreased elastin content. Losartan also exerted long‐term increases in fat mass and decreases in skeletal muscle mass. In this study, untreated Restricted offspring did not develop hypertension, vascular dysfunction or kidney changes as anticipated. Regardless, we demonstrate that short‐term losartan treatment in the juvenile period negatively affects postnatal growth, and kidney and vascular parameters in adulthood, irrespective of birth weight. The long‐term effects of early‐life losartan treatment warrant further consideration in settings where the potential benefits may outweigh the risks; i.e. when programmed adulthood diseases are apparent and in childhood cardiovascular and kidney diseases.

Modeling heart failure risk in diabetes and kidney disease: limitations and potential applications of transverse aortic constriction in high fat fed mice.

There is an increased incidence of heart failure in individuals with diabetes mellitus (DM). The coexistence of kidney disease in DM exacerbates the cardiovascular prognosis. Researchers have attempted to combine the critical features of heart failure, using transverse aortic constriction, with DM in mice, but variable findings have been reported. Furthermore, kidney outcomes have not been assessed in this setting; thus its utility as a model of heart failure in DM and kidney disease is unknown. We generated a mouse model of obesity, hyperglycemia, and mild kidney pathology by feeding male C57BL/6J mice a high-fat diet (HFD). Cardiac pressure overload was surgically induced using transverse aortic constriction (TAC). Normal diet (ND) and sham controls were included. Heart failure risk factors were evident at 8-wk post-TAC, including increased left ventricular mass (+49% in ND and +35% in HFD), cardiomyocyte hypertrophy (+40% in ND and +28% in HFD), and interstitial and perivascular fibrosis (Massons trichrome and picrosirius red positivity). High-fat feeding did not exacerbate the TAC-induced cardiac outcomes. At 11 wk post-TAC in a separate mouse cohort, echocardiography revealed reduced left ventricular size and increased left ventricular wall thickness, the latter being evident in ND mice only. Systolic function was preserved in the TAC mice and was similar between ND and HFD. Thus combined high-fat feeding and TAC in mice did not model the increased incidence of heart failure in DM patients. This model, however, may mimic the better cardiovascular prognosis seen in overweight and obese heart failure patients.

The developmental origins of renal dysfunction

Impairments in renal function can contribute to multiple disorders including chronic kidney disease and hypertension. Although adult onset renal dysfunction may in part be attributable to lifestyle choices or other morbidities, such as diabetes, the “developmental origins of health and disease” hypothesis has suggested that impaired renal development may predispose offspring to later renal disease. This chapter will detail the epidemiological and experimental evidence highlighting the importance of impaired kidney development in the programming of adult renal dysfunction and associated diseases. Emphasis will be placed on links between a low nephron endowment and increased risk of high blood pressure and chronic kidney disease. We will also examine the molecular and epigenetic pathways affected by maternal perturbations that may give rise to a reduction in nephron number and subsequent alterations in renal function in adult life.