The implications of fetal programming of glomerular number and renal function

Hippocampal mTOR Dysregulation and Morphological Changes in Male Rats after Fetal Growth Restriction

Fetal growth restriction (FGR) has been linked to long-term neurocognitive impairment, especially in males. To determine possible underlying mechanisms, we examined hippocampal cellular composition and mTOR signaling of male rat FGR offspring during main brain growth and development (postnatal days (PND) 1 and 12). FGR was either induced by a low-protein diet throughout pregnancy, experimental placental insufficiency by bilateral uterine vessel ligation or intrauterine stress by “sham” operation. Offspring after unimpaired gestation served as common controls. Low-protein diet led to a reduced cell density in the molecular dentate gyrus subregion, while intrauterine surgical stress was associated with increased cell density in the cellular CA2 subregion. Experimental placental insufficiency caused increased mTOR activation on PND 1, whereas intrauterine stress led to mTOR activation on PND 1 and 12. To determine long-term effects, we additionally examined mTOR signaling and Tau phosphorylation, which is altered in neurodegenerative diseases, on PND 180, but did not find any changes among the experimental groups. Our findings suggest that hippocampal cellular proliferation and mTOR signaling are dysregulated in different ways depending on the cause of FGR. While a low-protein diet induced a decreased cell density, prenatal surgical stress caused hyperproliferation, possibly via increased mTOR signaling.

Programmed Adult Kidney Disease: Importance of Fetal Environment

The Barker hypothesis strongly supported the influence of fetal environment on the development of chronic diseases in later life. Multiple experimental and human studies have identified that the deleterious effect of fetal programming commonly leads to alterations in renal development. The interplay between environmental insults and fetal genome can induce epigenetic changes and lead to alterations in the expression of renal phenotype. In this review, we have explored the renal development and its functions, while focusing on the epigenetic findings and functional aspects of the renin-angiotensin system and its components.

Dysregulated ion channels and transporters activate endoplasmic reticulum stress in rat kidney of fetal growth restriction

AIMS

The mechanisms underlying the fetal origin of renal disease remains unknown. This study aimed to investigate the profiles of ion channel and transporter proteins in the fetal kidney in fetal growth restriction (FGR)rats, and to explore their association with the fetal origin of renal disease.

MAIN METHODS

An FGR rat model was developed by administration of a low-protein diet. Then 367 differentially expressed proteins (DEPs) from quantitative proteome analysis were subjected to Ingenuity Pathway Analysis. 22 DEPs associated with ion channels/transporters were evaluated in the fetal kidney. Na+/H+ exchanger1(NHE1) and its downstream unfolded protein response (UPR) pathway were investigated. Furthermore, overexpression of NHE1 were achieved via plasmid transfection to evaluate the potential influence on the UPR pathway and cell apoptosis in human proximal tubular epithelial cell line HK2 cells.

KEY FINDINGS

Findings were as follows: 1) In the FGR fetal kidney, aquaporin 2/4, solute carrier (SLC) 8a1, 33a1, etc. were downregulated, whereas other transporters including SLC 2a1, 4a1, 9a1, 29a3, etc. were upregulated. 2) NHE1 mRNA levels were markedly elevated in the FGR fetus. Further investigation revealed an increase in the UPR pathway regulators. 3) In vitro study showed that NHE1 overexpression in HK2 cells significantly induced expression of the endoplasmic reticulum stress (ERS) regulators and led to a decrease in the anti-apoptotic potential.

SIGNIFICANCE

We speculate that maternal protein malnutrition causes dysregulation of ion channels/transporters in the fetal kidney. Upregulated NHE1 may activate the UPR pathway and induce cell apoptosis thus leading to impairment of kidney function.

Effect of early postnatal nutrition on chronic kidney disease and arterial hypertension in adulthood: a narrative review

Intrauterine growth restriction (IUGR) has been identified as a risk factor for adult chronic kidney disease (CKD), including hypertension (HTN). Accelerated postnatal catch-up growth superimposed to IUGR has been shown to further increase the risk of CKD and HTN. Although the impact of excessive postnatal growth without previous IUGR is less clear, excessive postnatal overfeeding in experimental animals shows a strong impact on the risk of CKD and HTN in adulthood. On the other hand, food restriction in the postnatal period seems to have a protective effect on CKD programming. All these effects are mediated at least partially by the activation of the renin-angiotensin system, leptin and neuropeptide Y (NPY) signaling and profibrotic pathways. Early nutrition, especially in the postnatal period has a significant impact on the risk of CKD and HTN at adulthood and should receive specific attention in the prevention of CKD and HTN.

Long-Term Impacts of Foetal Malnutrition Followed by Early Postnatal Obesity on Fat Distribution Pattern and Metabolic Adaptability in Adult Sheep

We aimed to investigate whether over- versus undernutrition in late foetal life combined with obesity development in early postnatal life have differential implications for fat distribution and metabolic adaptability in adulthood. Twin-pregnant ewes were fed NORM (100% of daily energy and protein requirements), LOW (50% of NORM) or HIGH (150%/110% of energy/protein requirements) diets during the last trimester. Postnatally, twin-lambs received obesogenic (HCHF) or moderate (CONV) diets until 6 months of age, and a moderate (obesity correcting) diet thereafter. At 2½ years of age (adulthood), plasma metabolite profiles during fasting, glucose, insulin and propionate (in fed and fasted states) tolerance tests were examined. Organ weights were determined at autopsy. Early obesity development was associated with lack of expansion of perirenal, but not other adipose tissues from adolescence to adulthood, resulting in 10% unit increased proportion of mesenteric of intra-abdominal fat. Prenatal undernutrition had a similar but much less pronounced effect. Across tolerance tests, LOW-HCHF sheep had highest plasma levels of cholesterol, urea-nitrogen, creatinine, and lactate. Sex specific differences were observed, particularly with respect to fat deposition, but direction of responses to early nutrition impacts were similar. However, prenatal undernutrition induced greater metabolic alterations in adult females than males. Foetal undernutrition, but not overnutrition, predisposed for adult hypercholesterolaemia, hyperureaemia, hypercreatinaemia and hyperlactataemia, which became manifested only in combination with early obesity development. Perirenal expandability may play a special role in this context. Differential nutrition recommendations may be advisable for individuals with low versus high birth weights.

Developmental cigarette smoke exposure II: Kidney proteome profile alterations in 6 month old adult offspring

Cigarette smoke exposure (CSE) during gestation and early development suppresses the growth trajectory in offspring. In prior studies utilizing a mouse model of 'active' developmental CSE (GD1-PD21), low birth weight induced by CSE persisted throughout the neonatal period and was present at the cessation of exposure at weaning with proportionally smaller kidney mass that was accompanied by impairment of carbohydrate metabolism. In the present study, littermates of those characterized in the prior study were maintained until 6 months of age at which time the impact of developmental CSE on the abundance of proteins associated with cellular metabolism in the kidney was examined. Kidney protein abundances were examined by 2D-SDS-PAGE based proteome profiling with statistical analysis by Partial Least Squares-Discriminant Analysis. Key findings of this study include a persistence of impact of developmental CSE past the original exposure period on the nucleic acid and carbohydrate metabolism networks and oxidant scavenging pathways.

Antenatal glucocorticoid treatment alters Na+ uptake in renal proximal tubule cells from adult offspring in a sex-specific manner

We have shown a sex-specific effect of fetal programming on Na(+) excretion in adult sheep. The site of this effect in the kidney is unknown. Therefore, we tested the hypothesis that renal proximal tubule cells (RPTCs) from adult male sheep exposed to betamethasone (Beta) before birth have greater Na(+) uptake than do RPTCs from vehicle-exposed male sheep and that RPTCs from female sheep similarly exposed are not influenced by antenatal Beta. In isolated RPTCs from 1- to 1.5-yr-old male and female sheep, we measured Na(+) uptake under basal conditions and after stimulation with ANG II. To gain insight into the mechanisms involved, we also measured nitric oxide (NO) levels, ANG II receptor mRNA levels, and expression of Na(+)/H(+) exchanger 3. Basal Na(+) uptake increased more in cells from Beta-exposed male sheep than in cells from vehicle-exposed male sheep (400% vs. 300%, P < 0.00001). ANG II-stimulated Na(+) uptake was also greater in cells from Beta-exposed males. Beta exposure did not increase Na(+) uptake by RPTCs from female sheep. NO production was suppressed more by ANG II in RPTCs from Beta-exposed males than in RPTCs from either vehicle-exposed male or female sheep. Our data suggest that one site of the sex-specific effect of Beta-induced fetal programming in the kidney is the RPTC and that the enhanced Na(+) uptake induced by antenatal Beta in male RPTCs may be related to the suppression of NO in these cells.

The Effect of Perinatal Taurine on Adult Renal Function Does Not Appear to Be Mediated by Taurine's Inhibition of the Renin-Angiotensin System

This study tests the hypothesis that perinatal taurine supplementation alters adult renal function by inhibition of the renin-angiotensin system. Female Sprague-Dawley rats were fed normal rat chow and given water alone (Control) or water containing an angiotensin converting enzyme inhibitor (captopril, 400 mg/ml) from conception until delivery (FD) or from delivery until weaning (LD). After weaning, the rats received normal rat chow and tap water. At 7–8 weeks of age, renal function at rest and after acute saline load was studied in conscious, restrained male rats. Body weight, mean arterial pressure, heart rate, effective renal blood flow, and renal vascular resistance were not significantly different among the three groups. Compared to Control, glomerular filtration rate, but not filtration fraction, significantly increased after saline load in both FD and LD groups. Water excretion significantly increased only in FD compared to Control, while fractional water excretion was significantly increased after saline load in both FD and LD groups. Sodium excretion significantly increased after saline load only in FD, while both captopril-treated groups significantly decreased fractional sodium excretion. Potassium excretion significantly increased in both FD and LD groups, while fractional potassium excretion significantly increased at rest in FD and decreased in LD groups after saline load. These effects of perinatal RAS inhibition on adult renal function contrast sharply, and are opposite in many cases to, the effects of perinatal taurine supplementation. Thus, these data suggest that perinatal taurine supplementation does not alter adult renal function through its ability to inhibit the perinatal RAS.

Bmp7 maintains undifferentiated kidney progenitor population and determines nephron numbers at birth

The number of nephrons, the functional units of the kidney, varies among individuals. A low nephron number at birth is associated with a risk of hypertension and the progression of renal insufficiency. The molecular mechanisms determining nephron number during embryogenesis have not yet been clarified. Germline knockout of bone morphogenetic protein 7 (Bmp7) results in massive apoptosis of the kidney progenitor cells and defects in early stages of nephrogenesis. This phenotype has precluded analysis of Bmp7 function in the later stage of nephrogenesis. In this study, utilization of conditional null allele of Bmp7 in combination with systemic inducible Cre deleter mice enabled us to analyze Bmp7 function at desired time points during kidney development, and to discover the novel function of Bmp7 to inhibit the precocious differentiation of the progenitor cells to nephron. Systemic knockout of Bmp7 in vivo after the initiation of kidney development results in the precocious differentiation of the kidney progenitor cells to nephron, in addition to the prominent apoptosis of progenitor cells. We also confirmed that in vitro knockout of Bmp7 in kidney explant culture results in the accelerated differentiation of progenitor population. Finally we utilized colony-forming assays and demonstrated that Bmp7 inhibits epithelialization and differentiation of the kidney progenitor cells. These results indicate that the function of Bmp7 to inhibit the precocious differentiation of the progenitor cells together with its anti-apoptotic effect on progenitor cells coordinately maintains renal progenitor pool in undifferentiated status, and determines the nephron number at birth.

Ex vivo modeling of chemical synergy in prenatal kidney cystogenesis

Cyclic adenosine monophosphate (cAMP) drives genetic polycystic kidney disease (PKD) cystogenesis. Yet within certain PKD families, striking differences in disease severity exist between affected individuals, and genomic and/or environmental modifying factors have been evoked to explain these observations. We hypothesized that PKD cystogenesis is accentuated by an aberrant fetal milieu, specifically by glucocorticoids. The extent and nature of cystogenesis was assessed in explanted wild-type mouse embryonic metanephroi, using 8-Br-cAMP as a chemical to mimic genetic PKD and the glucocorticoid dexamethasone as the environmental modulator. Cysts and glomeruli were quantified by an observer blinded to culture conditions, and tubules were phenotyped using specific markers. Dexamethasone or 8-Br-cAMP applied on their own produced cysts predominantly arising in proximal tubules and descending limbs of loops of Henle. When applied together, however, dexamethasone over a wide concentration range synergized with 8-Br-cAMP to generate a more severe, glomerulocystic, phenotype; we note that prominent glomerular cysts have been reported in autosomal dominant PKD fetal kidneys. Our data support the idea that an adverse antenatal environment exacerbates renal cystogenesis.

Renal function and systolic blood pressure in very-low-birth-weight infants 1-3 years of age

BACKGROUND

Preterm very-low-birth-weight (PT-VLBW) infants are at risk of an elevated systolic blood pressure (SBP) in infancy and adulthood; however, the pathogenesis remains unclear. Altered renal development or function may be associated with increased SBP, but their contribution in PT-VLBW is unknown.

METHODS

We determined renal function and its relationship to SBP in three groups of PT-VLBW at 1, 2, and 3 years of age, using serum cystatin-C to calculate the estimated glomerular filtration rate (eGFR).

RESULTS

Cystatin-C levels decreased from 0.84 ± 0.2 (SD) within the 1-year group to 0.70 ± 0.1 mg/l (±SD; P < 0.001) at 3 years and were unrelated to gender, fetal growth, and neonatal indomethacin exposure. eGFR rose from 121 ± 59 in the 1-year group to 138 ± 21 ml/min · 1.73 m(2) (P < 0.001) at 3 years. At 1 year, cystatin-C levels decreased with increasing SBP (P < 0.007), and infants with SBP ≥ 90 th% had lower cystatin-C and higher eGFR (P < 0.05). At 3 years, infants with lower birth weight (P < 0.03) and gestational age (P = 0.06) had reduced eGFR.

CONCLUSIONS

Preterm very-low-birth-weight infants demonstrate increasing renal function with advancing age. An elevated SBP and eGFR at 1 year suggests dysfunctional renal autoregulation and hyperfiltration, which may alter subsequent renal function and contribute to the lower eGFR seen at 3 years in infants with the lowest birth weight and gestational age.

Impact of fetal programming, birth weight, and infant feeding on later hypertension

The concept of developmental origins of adult disease derives from both epidemiologic and basic sciences. This brief review considers the impact of the intrauterine milieu, intrauterine growth retardation, premature birth, and infant feeding on later hypertension and kidney disease.

Fetal programming of renal function

Results from large epidemiological studies suggest a clear relation between low birth weight and adverse renal outcome evident as early as during childhood. Such adverse outcomes may include glomerular disease, hypertension, and renal failure and contribute to a phenomenon called fetal programming. Other factors potentially leading to an adverse renal outcome following fetal programming are maternal diabetes mellitus, smoking, salt overload, and use of glucocorticoids during pregnancy. However, clinical data on the latter are scarce. Here, we discuss potential underlying mechanisms of fetal programming, including reduced nephron number via diminished nephrogenesis and other renal (e.g., via the intrarenal renin-angiotensin-aldosterone system) and non-renal (e.g., changes in endothelial function) alterations. It appears likely that the outcomes of fetal programming may be influenced or modified postnatally, for example, by the amount of nutrients given at critical times.

Hypersensitivity to acute ANG II in female growth-restricted offspring is exacerbated by ovariectomy

Female growth-restricted offspring are normotensive in adulthood. However, ovariectomy induces a marked increase in mean arterial pressure (MAP) that is abolished by renin angiotensin system (RAS) blockade, suggesting RAS involvement in the etiology of hypertension induced by ovariectomy in adult female growth-restricted offspring. Blockade of the RAS also abolishes hypertension in adult male growth-restricted offspring. Moreover, sensitivity to acute ANG II is enhanced in male growth-restricted offspring. Thus, we hypothesized that an enhanced sensitivity to acute ANG II may contribute to hypertension induced by ovariectomy in female growth-restricted offspring. Female offspring were subjected to ovariectomy (OVX) or sham ovariectomy (intact) at 10 wk of age. Cardio-renal hemodynamic parameters were determined before and after an acute infusion of ANG II (100 ng·kg(-1)·min(-1) for 30 min) at 16 wk of age in female offspring pretreated with enalapril (40 mg·kg(-1)·day(-1) for 7 days). Acute ANG II induced a significant increase in MAP in intact growth-restricted offspring (155 ± 2 mmHg, P < 0.05) relative to intact control (145 ± 4 mmHg). Ovariectomy augmented the pressor response to ANG II in growth-restricted offspring (163 ± 2 mmHg, P < 0.05), with no effect in control (142 ± 2 mmHg). Acute pressor responses to phenylephrine did not differ in growth-restricted offspring relative to control, intact, or ovariectomized. Furthermore, renal hemodynamic responses to acute ANG II were significantly enhanced only in ovariectomized female growth-restricted offspring. Thus, these data suggest that enhanced responsiveness to acute ANG II is programmed by intrauterine growth restriction and that sensitivity to acute ANG II is modulated by ovarian hormones in female growth-restricted offspring.

Low birth weight, bone metabolism and fracture risk

As for other diseases of higher age, low birth weight was expected to be a risk factor for an altered bone metabolism and osteoporosis.ON THE FIRST GLANCE THIS EXPECTATION APPEARS TO BE CONFIRMED BY ANIMAL DATA: rats with intrauterine growth restriction following maternal protein malnutrition show a reduction of bone mineral density going in line with a decrease in serum vitamin D concentrations.HOWEVER, THE SITUATION IS LESS CLEAR IN NEWBORNS WITH LOW BIRTH WEIGHT: Some studies show a relation of birth weight and bone mineral density whereas others don't. The older the former low birth weight patients the fainter the effect seems to be. In fact young adults with idiopathic short stature have a low bone mineral density than the low birth weight group irrespective of whether they have experienced catch-up growth or not. As a consequence low birth weight is can not be identified as a relevant risk factor for hip fractures in menopausal women. Postmenopausal women with low birth weight even show higher vitamin D concentrations than normal birth weight individuals.In conclusion, there is no consistent long term effect of low birth weight on bone mineral density or hip fracture risk later in life. Whether methodological weaknesses in the studies performed so far are causal or whether postnatal factors such as physical activity and nutrition are of higher importance can only be speculated upon at present.

Glomerular number and size variability and risk for kidney disease

PURPOSE OF REVIEW

This review discusses current understandings of variability in glomerular number and size, and the implications for renal health.

RECENT FINDINGS

The quantitative microanatomy of the normal human kidney varies widely. Of greatest significance, total nephron number varies at least 13-fold, and several genes and environmental factors that regulate human nephron endowment have been identified. Full or partial deletion of more than 25 genes in mice has been shown to result in renal hypoplasia and, when measured, reduced nephron endowment. Many more will likely be identified. As would be expected, some gene abnormalities increase nephron endowment above that found in control mice. Glomerular volume also varies widely, both between and within kidneys, and increased heterogeneity of glomerular volume within kidneys is associated with risk factors for kidney disease, including birth weight, age, race, body size and hypertension.

SUMMARY

Data from several human populations indicate that the quantitative microanatomy of the human kidney varies considerably: total glomerular number varies at least 13-fold, mean glomerular volume varies up to seven-fold and the volumes of individual glomeruli within single kidneys can vary as much as eight-fold. Human glomerular number, size and size distribution are being found to correlate with risk factors for kidney disease. The genetic and fetal environmental regulators of nephrogenesis, and thereby nephron endowment, are being rapidly identified and will provide the bases for future clinical interventions. In contrast, the molecular regulation of glomerular size remains unclear.

Fetal programming of gene expression in growth-restricted rats depends on the cause of low birth weight

Low birth weight and intrauterine growth restriction (IUGR) can be caused by numerous different conditions. In many experimental settings, however, these different causes are not accounted for. This study aimed at comparing the impact of two frequent causes of IUGR (low utero-placental blood flow vs. malnutrition) on fetal programming of gene expression. We studied offspring of dams treated by uterine artery ligation or sham operation compared with untreated controls and offspring of dams that were fed either a low protein or normal protein diet. After Cesarean section at term, placental and fetal hepatic expression of key "metabolic" and "vasoregulative" genes was investigated by quantitative RT-PCR. Ligation neonates showed IUGR, reduced expression of placental leptin, placental and hepatic IGF-I, hepatic inducible nitric oxide synthase, and increased expression of placental IGF binding protein 1, hepatic IGF-II receptor and erythropoietin (EPO). Low protein offspring also showed IUGR but increased expression of placental leptin; IGF-I; placental and hepatic inducible nitric oxide synthase; hepatic insulin, IGF-I, and IGF-II receptors; and reduced expression of placental IGF binding protein 1, IGF-II, leptin-receptor type A, placental and hepatic leptin receptor type B, and EPO. Expression was independent of sex, birth weight, fetal intrauterine position, and EPO expression. In conclusion, the impact of IUGR on fetal and placental gene expression depends on the cause of low birth weight. Therefore, morbidity after IUGR should be analyzed referring to its pathophysiological cause rather than referring to low birth weight itself. Fetal hypoxia as estimated by hepatic EPO expression does not seem to be a key regulator of transcriptional activity in our models.

Prenatal programming-effects on blood pressure and renal function

Impaired intrauterine nephrogenesis-most clearly illustrated by low nephron number-is frequently associated with low birthweight and has been recognized as a powerful risk factor for renal disease; it increases the risks of low glomerular filtration rate, of more rapid progression of primary kidney disease, and of increased incidence of chronic kidney disease or end-stage renal disease. Another important consequence of impaired nephrogenesis is hypertension, which further amplifies the risk of onset and progression of kidney disease. Hypertension is associated with low nephron numbers in white individuals, but the association is not universal and is not seen in individuals of African origin. The derangement of intrauterine kidney development is an example of a more general principle that illustrates the paradigm of plasticity during development-that is, that transcription of the genetic code is modified by epigenetic factors (as has increasingly been documented). This Review outlines the concept of prenatal programming and, in particular, describes its role in kidney disease and hypertension.

Maternal undernourished fetal kidneys exhibit differential regulation of nephrogenic genes including downregulation of the Notch signaling pathway

Maternal undernutrition results in offspring nephron number reduction and hypertension that are hypothesized to begin as compensatory changes in fetal gene expression during gestation. To evaluate mechanisms of dysregulated nephrogenesis, pregnant Sprague Dawley rats were 50% food restricted from embryonic day (E) 10 to E20. At E20, fetal male kidneys were examined by microarray analysis. A total of 476 differentially expressed transcripts were detected including those regulating development and differentiation, mitosis and cell cycle, chromatin assembly, and steroid hormone regulation. Differentially regulated genes were detected in MAPK/ERK, Wnt, and Notch signaling pathways. Validation of the microarray results was performed for the Notch signaling pathway, an important pathway in nephron formation. Protein expression of Notch pathway factors by Western blotting showed significantly decreased Notch2 and downstream effector Hey1 protein expression, while Ctbp1 co-repressor was increased. These data together show that maternal undernutrition results in developmental disruption in fetal nephrogenesis gene expression signaling.

Maternal nutrition, low nephron number and arterial hypertension in later life

A potential role of the intrauterine environment in the development of low nephron number and hypertension in later life has been recently recognized in experimental studies and is also postulated in certain conditions in human beings. Nephrogenesis is influenced by genetic as well as by environmental and in particular maternal factors. In man nephrogenesis, i.e. the formation of nephrons during embryogenesis, takes place from weeks 5 to 36 of gestation with the most rapid phase of nephrogenesis occurring from the mid-2nd trimester until 36 weeks. This 16 week period is a very vulnerable phase where genetic and environmental factors such as maternal diet or medication could influence and disturb nephron formation leading to lower nephron number. Given a constant rise in body mass until adulthood lower nephron number may become "nephron underdosing" and result in maladaptive glomerular changes, i.e. glomerular hyperfiltration and glomerular enlargement. These maladaptive changes may then eventually lead to the development of glomerular and systemic hypertension and renal disease in later life. It is the purpose of this review to discuss the currently available experimental and clinical evidence for factors and mechanisms that could interfere with nephrogenesis with particular emphasis on maternal nutrition. In addition, we discuss the emerging concept of low nephron number being a new cardiovascular risk factor in particular for essential hypertension in later life.