Role of renal sympathetic nerve activity in prenatal programming of hypertension

Salt-Sensitive Hypertension and the Kidney

Salt-sensitive hypertension (SS-HT) is characterized by blood pressure elevation in response to high dietary salt intake and is considered to increase the risk of cardiovascular and renal morbidity. Although the mechanisms responsible for SS-HT are complex, the kidneys are known to play a central role in the development of SS-HT and the salt sensitivity of blood pressure (SSBP). Moreover, several factors influence renal function and SSBP, including the renin-angiotensin-aldosterone system, sympathetic nervous system, obesity, and aging. A phenotypic characteristic of SSBP is aberrant activation of the renin-angiotensin system and sympathetic nervous system in response to excessive salt intake. SSBP is also accompanied by a blunted increase in renal blood flow after salt loading, resulting in sodium retention and SS-HT. Obesity is associated with inappropriate activation of the aldosterone mineralocorticoid receptor pathway and renal sympathetic nervous system in response to excessive salt, and mineralocorticoid receptor antagonists and renal denervation attenuate sodium retention and inhibit salt-induced blood pressure elevation in obese dogs and humans. SSBP increases with age, which has been attributed to impaired renal sodium handling and a decline in renal function, even in the absence of kidney disease. Aging-associated changes in renal hemodynamics are accompanied by significant alterations in renal hormone levels and renal sodium handling, resulting in SS-HT. In this review, we focus mainly on the contribution of renal function to the development of SS-HT.

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.

Kidney and epigenetic mechanisms of salt-sensitive hypertension

Dietary salt intake increases blood pressure (BP) but the salt sensitivity of BP differs between individuals. The interplay of ageing, genetics and environmental factors, including malnutrition and stress, contributes to BP salt sensitivity. In adults, obesity is often associated with salt-sensitive hypertension. The children of women who experience malnutrition during pregnancy are at increased risk of developing obesity, diabetes and salt-sensitive hypertension as adults. Similarly, the offspring of mice that are fed a low-protein diet during pregnancy develop salt-sensitive hypertension in association with aberrant DNA methylation of the gene encoding type 1A angiotensin II receptor (AT_1AR) in the hypothalamus, leading to upregulation of hypothalamic AT_1AR and renal sympathetic overactivity. Ageing is also associated with salt-sensitive hypertension. In aged mice, promoter methylation leads to reduced kidney production of the anti-ageing factor Klotho and a decrease in circulating soluble Klotho. In the setting of Klotho deficiency, salt-induced activation of the vascular Wnt5a-RhoA pathway leads to ageing-associated salt-sensitive hypertension, potentially as a result of reduced renal blood flow and increased peripheral resistance. Thus, kidney mechanisms and aberrant DNA methylation of certain genes are involved in the development of salt-sensitive hypertension during fetal development and old age. Three distinct paradigms of epigenetic memory operate on different timescales in prenatal malnutrition, obesity and ageing.

Hypertension and Reproduction

PURPOSE OF REVIEW

Many aspects of reproduction have been associated with increased blood pressure and impaired glucose metabolism that reveals a subsequent increased risk of cardiovascular disease. The aim of this review is to assess reproductive life factors associated with an increased risk of hypertension and cardiovascular disease, e.g., early life programming, sexual, and reproductive health in men and women.

RECENT FINDINGS

Impaired fetal growth, with low birth weight adjusted for gestational age, has been found associated with hypertension in adulthood. Erectile dysfunction, currently considered an early diagnostic marker of cardiovascular disease preceding the manifestation of coronary artery disease by several years, frequently coexisting with hypertension, could also be exacerbated by some antihypertensive drugs. Male hypogonadism or subfertility are associated with increased cardiovascular risk. Hypertensive disorders in pregnancy including preeclampsia represent a major cause of maternal, fetal and neonatal morbidity, and mortality. The risk of developing preeclampsia can be substantially reduced in women at its high or moderate risk with a low dose of acetylsalicylic acid initiated from 12 weeks of gestation. An increased risk of hypertension in women following invasive-assisted reproductive technologies has been newly observed. Blood pressure elevation has been noticed following contraceptive pill use, around the menopause and in postmenopausal age. Furthermore, drug treatment of hypertension has to be considered as a factor with a potential impact on reproduction (e.g., due to teratogenic drug effects). In summary, a deeper understanding of reproductive life effects on hypertension and metabolic abnormalities may improve prediction of future cardiovascular disease.

Deletion of hypoxia-responsive microRNA-210 results in a sex-specific decrease in nephron number

Low nephron number results in an increased risk of developing hypertension and chronic kidney disease. Intrauterine growth restriction is associated with a nephron deficit in humans, and is commonly caused by placental insufficiency, which results in fetal hypoxia. The underlying mechanisms by which hypoxia impacts kidney development are poorly understood. microRNA-210 is the most consistently induced microRNA in hypoxia and is known to promote cell survival in a hypoxic environment. In this study, the role of microRNA-210 in kidney development was evaluated using a global microRNA-210 knockout mouse. A male-specific 35% nephron deficit in microRNA-210 knockout mice was observed. Wnt/β-catenin signaling, a pathway crucial for nephron differentiation, was misregulated in male kidneys with increased expression of the canonical Wnt target lymphoid enhancer binding factor 1. This coincided with increased expression of caspase-8-associated protein 2, a known microRNA-210 target and apoptosis signal transducer. Together, these data are consistent with a sex-specific requirement for microRNA-210 in kidney development.

IGF-1 deletion affects renal sympathetic nerve activity, left ventricular dysfunction, and renal function in DOCA-salt hypertensive mice

To determine the influence of IGF-1 deletion on renal sympathetic nerve activity (RSNA), left ventricular dysfunction, and renal function in deoxycorticosterone acetate (DOCA)-salt hypertensive mice. The DOCA-salt hypertensive mice models were constructed and the experiment was classified into WT (Wild-type mice) +sham, LID (Liver-specific IGF-1 deficient mice) + sham, WT + DOCA, and LID+ DOCA groups. Enzyme-linked immunosorbent assay (ELISA) was used to detect the serum IGF-1 levels in mice. The plasma norepinephrine (NE), urine protein, urea nitrogen and creatinine, as well as RSNA were measured. Echocardiography was performed to assess left ventricular dysfunction, and HE staining to observe the pathological changes in renal tissue of mice. DOCA-salt induction time-dependently increased the systolic blood pressure (SBP) of mice, especially in DOCA-salt LID mice. Besides, the serum IGF-1 levels in WT mice were decreased after DOCA-salt induction. In addition, the plasma NE concentration and NE spillover, urinary protein, urea nitrogen, creatinine and RSNA were remarkably elevated with severe left ventricular dysfunction, but the creatinine clearance was reduced in DOCA-salt mice, and these similar changes were obvious in DOCA-salt mice with IGF-1 deletion. Moreover, the DOCA-salt mice had tubular ectasia, glomerular fibrosis, interstitial cell infiltration, and increased arterial wall thickness, and the DOCA-salt LID mice were more serious in those aspects. Deletion of IGF-1 may lead to enhanced RSNA in DOCA-salt hypertensive mice, thereby further aggravating left ventricular dysfunction and renal damage.

Fetal programming and the angiotensin-(1-7) axis: a review of the experimental and clinical data

Hypertension is the primary risk factor for cardiovascular disease that constitutes a serious worldwide health concern and a significant healthcare burden. As the majority of hypertension has an unknown etiology, considerable research efforts in both experimental models and human cohorts has focused on the premise that alterations in the fetal and perinatal environment are key factors in the development of hypertension in children and adults. The exact mechanisms of how fetal programming events increase the risk of hypertension and cardiovascular disease are not fully elaborated; however, the focus on alterations in the biochemical components and functional aspects of the renin-angiotensin (Ang) system (RAS) has predominated, particularly activation of the Ang-converting enzyme (ACE)-Ang II-Ang type 1 receptor (AT1R) axis. The emerging view of alternative pathways within the RAS that may functionally antagonize the Ang II axis raise the possibility that programming events also target the non-classical components of the RAS as an additional mechanism contributing to the development and progression of hypertension. In the current review, we evaluate the potential role of the ACE2-Ang-(1-7)-Mas receptor (MasR) axis of the RAS in fetal programming events and cardiovascular and renal dysfunction. Specifically, the review examines the impact of fetal programming on the Ang-(1-7) axis within the circulation, kidney, and brain such that the loss of Ang-(1-7) expression or tone, contributes to the chronic dysregulation of blood pressure (BP) and cardiometabolic disease in the offspring, as well as the influence of sex on potential programming of this pathway.

Aberrant DNA methylation of hypothalamic angiotensin receptor in prenatal programmed hypertension

Maternal malnutrition, which causes prenatal exposure to excessive glucocorticoid, induces adverse metabolic programming, leading to hypertension in offspring. In offspring of pregnant rats receiving a low-protein diet or dexamethasone, a synthetic glucocorticoid, mRNA expression of angiotensin receptor type 1a (Agtr1a) in the paraventricular nucleus (PVN) of the hypothalamus was upregulated, concurrent with reduced expression of DNA methyltransferase 3a (Dnmt3a), reduced binding of DNMT3a to the Agtr1a gene, and DNA demethylation. Salt loading increased BP in both types of offspring, suggesting that elevated hypothalamic Agtr1a expression is epigenetically modulated by excessive glucocorticoid and leads to adult-onset salt-sensitive hypertension. Consistent with this, dexamethasone treatment of PVN cells upregulated Agtr1a, while downregulating Dnmt3a, and decreased DNMT3a binding and DNA demethylation at the Agtr1a locus. In addition, Dnmt3a knockdown upregulated Agtr1a independently of dexamethasone. Hypothalamic neuron-specific Dnmt3a-deficient mice exhibited upregulation of Agtr1a in the PVN and salt-induced BP elevation without dexamethasone treatment. By contrast, dexamethasone-treated Agtr1a-deficient mice failed to show salt-induced BP elevation, despite reduced expression of Dnmt3a. Thus, epigenetic modulation of hypothalamic angiotensin signaling contributes to salt-sensitive hypertension induced by prenatal glucocorticoid excess in offspring of mothers that are malnourished during pregnancy.

Antenatal betamethasone attenuates the angiotensin-(1-7)-Mas receptor-nitric oxide axis in isolated proximal tubule cells

We previously reported a sex-specific effect of antenatal treatment with betamethasone (Beta) on sodium (Na⁺) excretion in adult sheep whereby treated males but not females had an attenuated natriuretic response to angiotensin-(1-7) [Ang-(1-7)]. The present study determined the Na⁺ uptake and nitric oxide (NO) response to low-dose Ang-(1-7) (1 pM) in renal proximal tubule cells (RPTC) from adult male and female sheep antenatally exposed to Beta or vehicle. Data were expressed as percentage of basal uptake or area under the curve for Na⁺ or percentage of control for NO. Male Beta RPTC exhibited greater Na⁺ uptake than male vehicle cells (433 ± 28 vs. 330 ± 26%; P < 0.05); however, Beta exposure had no effect on Na⁺ uptake in the female cells (255 ± 16 vs. 255 ± 14%; P > 0.05). Ang-(1-7) significantly inhibited Na⁺ uptake in RPTC from vehicle male (214 ± 11%) and from both vehicle (190 ± 14%) and Beta (209 ± 11%) females but failed to attenuate Na⁺ uptake in Beta male cells. Beta exposure also abolished stimulation of NO by Ang-(1-7) in male but not female RPTC. Both the Na⁺ and NO responses to Ang-(1-7) were blocked by Mas receptor antagonist d-Ala⁷-Ang-(1-7). We conclude that the tubular Ang-(1-7)-Mas-NO pathway is attenuated in males and not females by antenatal Beta exposure. Moreover, since primary cultures of RPTC retain both the sex and Beta-induced phenotype of the adult kidney in vivo they appear to be an appropriate cell model to examine the effects of fetal programming on Na⁺ handling by the renal tubules.