Glomeruli and blood pressure. Less of one, more the other?

Absent, Small, or Homeotic 2-Like-Mediated H3K4 Methylation and Nephrogenesis

Key Points

Background

Many congenital anomalies of the kidney and urinary tract involve deficits in the number of nephrons, which are associated with a higher risk of hypertension and CKD later in life. Prior work has implicated histone modifications in regulating kidney lineage–specific gene transcription and nephron endowment. Our earlier study suggested that absent, small, or homeotic 2-like (ASH2L), a core subunit of the H3K4 methyltransferase complex, plays a role in ureteric bud morphogenesis during mammalian kidney development. However, the potential involvement of ASH2L in nephron formation remains an open question.

Methods

To investigate the role of ASH2L in nephron development, we inactivated Ash2l specifically in nephron progenitor cells by crossing Six2-e(Kozak-GFPCre-Wpre-polyA)1 mice with Ash2l fl/fl mice. We used RNA sequencing combined with Cleavage Under Targets and Tagmentation sequencing to screen for gene and epigenomic changes, which were further verified by rescue experiments conducted on ex vivo culture explants.

Results

Inactivating ASH2L in nephron progenitor cells disrupted H3K4 trimethylation establishment at promoters of genes controlling nephron progenitor cell stemness, differentiation, and cell cycle, inhibiting their progression through the cell cycle and differentiation into epithelial cell types needed to form nephrons. Inhibition of the TGF-β/suppressor of mothers against decapentaplegic signaling pathway partially rescued the dysplastic phenotype of the mutants.

Conclusions

ASH2L-mediated H3K4 methylation was identified as a novel epigenetic regulator of kidney development. Downregulation of ASH2L expression or H3K4 trimethylation may be linked to congenital anomalies of the kidney and urinary tract.

Current and potential methods to assess kidney structure and morphology in term and preterm neonates

After birth, the kidney structure in neonates adapt to the functional demands of extrauterine life. Nephrogenesis is complete in the third trimester, but glomeruli, tubuli, and vasculature mature with the rapidly increasing renal blood flow and glomerular filtration. In preterm infants, nephrogenesis remains incomplete and maturation is slower and may be aberrant. This structural and functional deficit has life-long consequences: preterm born individuals are at higher risk for chronic kidney disease and arterial hypertension later in life. This review assembles the literature on existing and potential methods to visualize neonatal kidney structure and morphology and explore their potential to longitudinally document the developmental deviation after preterm birth. X-rays with and without contrast, fluoroscopy and computed tomography (CT) involve relevant ionizing radiation exposure and, apart from CT, do not provide sufficient structural details. Ultrasound has evolved into a safe and noninvasive high-resolution imaging method which is excellent for longitudinal observations. Doppler ultrasound modes can characterize and quantify blood flow to and through the kidneys. Microvascular flow imaging has opened new possibilities of visualizing previously unseen vascular structures. Recent advances in magnetic resonance imaging display renal structure and function in unprecedented detail, but are offset by the logistical challenges of the imaging procedure and limited experience with the new techniques in neonates. Kidney biopsies visualize structure histologically, but are too invasive and remain anecdotal in newborns. All the explored methods have predominantly been examined in term newborns and require further research on longitudinal structural observation in the kidneys of preterm infants.

Methylseq, single-nuclei RNAseq, and discovery proteomics identify pathways associated with nephron-deficit CKD in the HSRA rat model

Low nephron numbers are associated with an increased risk of developing chronic kidney disease (CKD) and hypertension, which are significant global health problems. To investigate the impact of nephron deficiency, our laboratory developed a novel inbred rat model (HSRA rat). In this model, ∼75% of offspring are born with a single kidney (HSRA-S), compared with two-kidney littermates (HSRA-C). HSRA-S rats show impaired kidney development, resulting in ∼20% fewer nephrons. Our previous data and current findings demonstrate that nephron deficit (failure of one kidney to form and altered development in the remaining kidney) predisposes HSRA-S to CKD late in life (with increased proteinuria by 18 mo of age in HSRA-S = 51 ± 3.4 vs. HSRA-C = 8 ± 1.5 mg/24 h). To understand early molecular mechanisms contributing to the increased predisposition to CKD, Methylseq using reduced representation bisulfite sequencing, single-nuclei (sn)RNAseq, and discovery proteomics were performed in kidneys of 4-wk-old HSRA rats. Methylation analysis revealed a small number of differences, including five differentially methylated cytosines and six differentially methylated regions between groups. The snRNAseq analysis identified differentially expressed genes in most kidney cell types, with several hundred genes dysregulated depending on the analysis method (Seurat vs. DESeq2). Notably, many genes are involved in kidney development. Discovery proteomic analysis identified 366 differentially expressed proteins. A key finding was dysregulation of Deptor/DEPTOR and Amdhd2/AMDHD2 across omics layers, suggesting a potential role in compensatory mechanisms or the genetic basis of altered kidney development. Further understanding of these mechanisms may guide interventions to preserve nephron health and slow kidney disease progression.NEW & NOTEWORTHY The HSRA rat is a novel model of nephron deficiency and provides a unique opportunity to study the association between nephron number and chronic kidney disease (CKD). Previous work characterized the impact of age, hypertension, and diabetes on the development of CKD in HSRA animals. This study examined early changes in epigenetics, cell-type specific transcriptome, and proteomic changes in the kidney that likely predispose the model to CKD with age.

Neonatal Kidney Function, Injury and Drug Dosing: A Contemporary Review

In neonates, estimation of the glomerular filtration rate is problematic, and assessment of renal impairment is challenging. Serum creatinine is a widely used marker, and urine output is an important vital parameter monitored in intensive care settings, particularly in unwell neonates. However, the rapid changes after birth with adaptation to the extrauterine environment is a unique situation in which absolute serum creatinine is not a reliable indicator of renal function. A rise in serum creatinine from the previous value during the neonatal period can be a result of worsening renal function in neonates but is dependent on many other factors. In addition, urine output can be difficult to measure in sick neonates during their intensive care stay. Despite a high prevalence of acute kidney injury (AKI) in preterm and/or unwell infants, the current definitions are not straightforward and do not take postnatal adaptation processes into account. The management of AKI is challenging in very young and small patients because the assessment of fluid status as well as balancing nutritional needs with fluid restriction can be problematic. The Australian Neonatal Medicines Formulary provides advice on drug dosing in the face of reduced renal function in neonates. Predictors (or long-term outcome, or recovery) after AKI diagnosis are still poorly described. Therefore, the diagnosis of neonatal AKI needs to be documented and transferred to the paediatrician responsible for the follow-up of the child. This educational review aims to give a perspective on neonatal kidney function and AKI, the relation of fluid balance and creatinine, the management of neonatal AKI and the consequences for drug dosing and long-term outcomes.

Estimating Number of Nephrons in Living Pediatric Patients Using Nephrectomy Specimens

Introduction

The number of nephrons is a critical determinant of renal health, because chronic kidney disease often results from a reduction in functional nephrons. Variability in the number of nephrons is influenced by genetic, racial, prenatal, and postnatal factors. Estimating the number of nephrons is crucial for establishing a baseline, before the onset of age-related nephron loss. This study aimed to estimate number of nephrons in pediatric patients by using imaging and histological techniques.

Methods

This retrospective study included pediatric patients with renal tumors, who are undergoing nephrectomy and contrast-enhanced computed tomography (CT) between January 2010 and January 2021. Postsurgical renal tissue specimens were fixed, stained, and scanned into high-resolution digital images. Nonsclerotic glomerular density was calculated using stereological methods, whereas renal cortical volume was measured using ITK-SNAP software on CT images. The total number of nephrons was estimated based on cortical volume and glomerular density. Statistical analyses were conducted to identify the correlations between the number of nephrons and clinical factors.

Results

Twenty-one children met the inclusion criteria. The cohort comprised 13 boys (61.9%) and 8 girls (38.1%) with a median age at nephrectomy of 2.5 years. The median number of nephrons per kidney was 925,000 (interquartile range [IQR]: 845,000-1,020,000). Higher number of nephrons was significantly correlated with older age at nephrectomy (ρ = 0.47, P = 0.036) and larger body surface area (BSA; ρ = 0.45, P = 0.034).

Conclusion

This study offers new insights into pediatric nephron endowment, emphasizing the importance of early nephron assessment for predicting long-term renal outcomes.

Associations of body composition at birth and accretion from 0 to 5 years with kidney function and volume at the 10-year follow-up: the Ethiopian Infant Anthropometry and Body Composition birth cohort

BACKGROUND

Fat mass (FM) and fat-free mass (FFM) in early life are associated with later obesity and cardiometabolic disease.

OBJECTIVES

This study aimed to assess the associations of FM and FFM at birth and conditional FM and FFM accretion from 0 to 5 y with kidney outcomes at the 10-y follow-up.

METHODS

The Ethiopian Infant Anthropometry and Body Composition birth cohort included term infants born in Jimma town, with a birth weight ≥1500 g, and having no congenital malformations. Air-displacement plethysmography was used to measure body composition. Serum cystatin C was determined and kidney dimensions were assessed by ultrasound when children were aged ∼10 y. Conditional growth modeling was used to compute FM and FFM accretion between different time points over 0-5 y. Multiple linear regression analysis was used to examine associations of birth FM and FFM and conditional FM and FFM accretion in selected age periods with serum cystatin C and total kidney volume at the 10-y follow-up.

RESULTS

A total of 350 children were followed up at a mean age of 9.8 (±1.0) y. A 1 standard deviation (SD) higher conditional FFM accretion from 3 to 6 mo was associated with 7.6% [95% confidence interval (CI): 1.9%, 13.0%) lower serum cystatin C but higher conditional FFM accretion 48-60 mo was associated with 5.3% (95% CI: 1.9%, 9.0%) higher serum cystatin C. A 1 SD higher conditional FM accretion in the periods 6-48 mo and 48-60 mo was associated with β = 7.7 (95% CI: 4.8, 10.7) and β = 6.4 (95% CI: 1.6, 11.1) cm3 greater kidney volume, respectively. A 1 SD higher birth FFM and FFM accretion in the periods 3-6 mo, 6-48 mo, and 48-60 mo was associated with β = 4.7 (95% CI: 2.1, 7.2), 14.1 (95% CI: 6.3, 22.0), 4.2 (95% CI: 0.9, 7.4), and 7.1 (95% CI: 2.5, 11.7) cm3 greater kidney volume, respectively.

CONCLUSIONS

A higher conditional FFM gain in age from 3 to 6 mo results in better kidney function at the 10-y follow-up, whereas a higher conditional FFM gain in age from 4 to 5 y results in a lower kidney function. Kidney volume at the 10-y follow-up is associated with higher birth FFM and higher conditional FM or FFM growth in most growth periods.

The intergenerational metabolic-cardiovascular life course: maternal body mass index (BMI), offspring BMI, and blood pressure of adolescents born extremely preterm

BACKGROUND

The aim of this study was to evaluate associations between pre-pregnancy maternal obesity and adolescent blood pressures (BPs) among children born extremely preterm.

METHODS

This longitudinal observational cohort study included participants in the multicenter Extremely Low Gestational Age Newborn (ELGAN) study, born before 28 weeks of gestation, recruited at birth between 2002 and 2004, and followed prospectively through late adolescence. Between 2015 and 2022, three oscillometric BPs were obtained from participants (mean age 17.8 years). We used linear regression modeling to evaluate the association between maternal self-reported pre-pregnancy body mass index (BMI) and offspring adolescent systolic BP (SBP). In secondary analyses, we evaluated the association between maternal pre-pregnancy and offspring preadolescent (10-year-old) BMI and between offspring preadolescent BMI and adolescent SBP.

RESULTS

The 100 (24%) participants born to a mother with a history of pre-pregnancy obesity (BMI ≥ 30) had a greater mean SBP of 120.5 (± 14.3) mmHg compared to the 324 (76%) of adolescents born to mothers without pre-pregnancy obesity (SBP 115.6 (± 12.0) mmHg). Pre-pregnancy obesity was associated with higher offspring BMI (aβ 10.8, 95% CI 2.3, 19.2), and higher offspring BMI was associated with higher adolescent SBP (aβ 0.12, 95% CI 0.09,0.16).

CONCLUSIONS

For ELGANs, higher maternal pre-pregnancy BMI was associated with higher adolescent SBP. Findings from secondary analyses suggest potential mediation through preadolescent BMI. Future research directions include multi-level interventions to reduce maternal pre-pregnancy obesity, followed by offspring obesity prevention interventions as a way of reducing intergenerational cardiovascular disease in high-risk infants born extremely preterm.

Chronic kidney disease

Chronic kidney disease (CKD) is defined by persistent abnormalities of kidney function or structure that have consequences for the health. A progressive decline of excretory kidney function has effects on body homeostasis. CKD is tightly associated with accelerated cardiovascular disease and severe infections, and with premature death. Kidney failure without access to kidney replacement therapy is fatal - a reality in many regions of the world. CKD can be the consequence of a single cause, but CKD in adults frequently relates rather to sequential injuries accumulating over the life course or to the presence of concomitant risk factors. The shared pathomechanism of CKD progression is the irreversible loss of kidney cells or nephrons together with haemodynamic and metabolic overload of the remaining nephrons, leading to further loss of kidney cells or nephrons. The management of patients with CKD focuses on early detection and on controlling all modifiable risk factors. This approach includes reducing the overload of the remaining nephrons with inhibitors of the renin-angiotensin system and the sodium-glucose transporter 2, as well as disease-specific drug interventions, if available. Hypertension, anaemia, metabolic acidosis and secondary hyperparathyroidism contribute to cardiovascular morbidity and reduced quality of life, and require diagnosis and treatment.

Serum neutrophil gelatinase-associated lipocalin and cystatin C is associated with blood pressure in ex-preterm children and adolescents

BACKGROUND

As preterm birth is a risk factor for hypertension (HTN), biomarkers for early prediction of HTN in childhood is an emerging need. The aims of the study were to evaluate serum biomarkers in ex-preterm children and examine for associations with office peripheral and central SBP (cSBP), ambulatory BP parameters and pulse wave velocity (PWV).

METHODS

This case-control study included children and adolescents born prematurely (ex-preterms) and at full term (controls). All participants underwent office and ambulatory BP monitoring, assessment of cSBP, PWV and serum biomarkers at the same visit. Neutrophil gelatinase-associated lipocalin (NGAL), matrix metalloproteinase-2, metalloproteinase-9 (MMP-2, MMP-9) and Cystatin C (CysC) were measured using ELISA.

RESULTS

The study population included 52 ex-preterm individuals and 26 controls. Mean age was 10.7 ± 3.6 years. NGAL, MMP-2, MMP-9, and CysC levels were similar between the ex-preterm and the control group. In the ex-preterm group, NGAL is associated with office SBP z score ( β  = 1.007, 95% CI 1.001-0.014, P  = 0.049), CysC with office DBP z score ( β  = 1.003, 95% CI 1.001-0.005, P  = 0.018) and cSBP z score ( β  = 1.003, 95% CI 1.001-0.005, P  = 0.006) independently of age, sex and BMI z score. Among ex-preterm children and adolescents 17% had ambulatory HTN and 31% had white-coat HTN. NGAL levels were higher in ex-preterm children with WCH compared with children with normal BP [57.9 (IQR 50.8) versus 34.6 (IQR 46.2)], P  = 0.018].

CONCLUSION

WCH is common in ex-preterm children and adolescents and is associated with higher NGAL levels and CysC presents positive association with cSBP. The findings in this study provides preliminary evidence that NGAL and CysC may have a role in predicting the risk of developing hypertension later in life. Further studies are warranted.

Validation of histopathological chronicity scores in native kidney biopsies using light microscopy and digital morphometry for predicting renal outcome

Quantitative assessment of chronicity changes in native kidney biopsies offer valuable insights in to disease prognosis, despite the strength of qualitative information. Yet, standardization and reproducibility remain challenging. The present study aims to assess and compare the prognostic utility and reproducibility of two chronicity scoring systems based on light microscopy and whole slide imaging with morphometry and also to evaluate the prognostic utility of structural measurements: cortical non-sclerotic glomerular (NSG) density and NSG area/volume. We designed a retrospective longitudinal study involving 101 adult and paediatric patients who underwent native kidney biopsies. Chronicity scoring was performed using two semi-quantitative methods: Method 1 (method proposed in PMID: 28314581) and Method 2 (method proposed in PMID: 32516862), under light microscopy as well as on whole-slide scanned images, and assessed for prognostic utility. Kidney-Failure-Risk-Equation (KFRE) was employed in combination with chronicity-scoring-methods and assessed for predictive capability. Interobserver reproducibility for the two chronicity methods was studied among three renal pathologists. Structural measurements were performed on whole-slide- scanned-images. Both the chronicity scoring methods significantly predicted decline in estimated glomerular filtration rate (eGFR) and persistent need for renal replacement therapy in follow-up. Method 1 combined with KFRE, outperformed Method 2 in predicting renal survival. Method 2 however showed higher interobserver reproducibility. Combined KFRE plus histopathological scoring methods showed better predictive accuracy. The study validates the precision of chronicity scoring using whole slide scanned images. The morphometric structural measurements showed significant correlations with follow-up eGFR, thereby providing supplementary prognostic information.

Renal and Vascular Functional Decline in Aged Low Birth Weight Murine Adults

INTRODUCTION

Maternal undernutrition (MUN)-induced low birth weight (LBW) neonates are susceptible to the development of high blood pressure and kidney disease later in life, although the underlying pathological causes remain unclear. The study here investigated the role of renal oxidative stress, impairment of vascular function, and altered sensitivity to angiotensin II (Ang II) as factors that contribute to these pathologies in aged LBW mice.

METHODS

LBW offspring were generated using a combined protein and caloric restricted MUN mouse model. The resulting LBW offspring were examined 1 year after birth for mean arterial blood pressure (MABP) (carotid artery catheterization), renal blood flow (RBF) (laser Doppler flowmetry), glomerular filtration rate (GFR) (sinistrin clearance), vasoreactivity (myograph), renal vascular density (CD31 staining), and reactive oxygen species (ROS) (ROS probes). Immunoblotting examined Ang II type 1 receptor (AT1R), soluble guanylate cyclase (sGC), and antioxidant systems. Pharmacological agents delivered to animals included the sGC stimulator δ-aminolevulinic acid (ALA), the AT1R inhibitor losartan, the antioxidant ethyl pyruvate (EP), and the toll-like receptor 4 inhibitor TAK242.

RESULTS

After 1 year, MABP was increased, while RBF, GFR, vascular reactivity, renal vascular density, and sGC were all reduced in the LBW aged adult. All four pharmacological agents improved MABP, RBF, GFR, vascular density, and vascular reactivity. Renal ROS was increased in the LBW adult but was reduced by ALA, EP, and TAK242 treatment. AT1R was upregulated in the LBW adult, while sGC was decreased, an effect reversed by ALA treatment. Endogenous antioxidant systems, including SOD1, catalase, and glutathione were downregulated in the LBW adult.

CONCLUSION

MUN-induced LBW mice experience increased Ang II sensitivity and oxidative stress. The increased Ang II sensitivity and ROS generation influences vascular density and reactivity, which drive an increase in MABP, and a concomitantly decrease in RBF and glomerular filtration. Pharmacological intervention that inhibits AT1R, enhances levels of sGC, reduces ROS, or inhibits toll-like receptor 4 improves vascular and renal function in the LBW adult.

Renal Endowment in Men and Women: Start from the Beginning

The development of the human kidney leads to the establishment of nephron endowment through a process influenced by both genetic and environmental factors. There is individual variability regarding nephron endowment and factors including aging and pathological conditions contribute to the decline in the number of nephrons, impacting renal function. Genetic determinants, such as mutations in crucial developmental genes like Pax2, and epigenetic mechanisms mediated by key enzymes including sirtuin 3, play critical roles in the regulation of the number of nephrons, with implications for kidney disease susceptibility. Sexual dimorphism significantly influences kidney development and function, with the number of nephrons being significantly lower in females, consistent with lower female birth weight, which is considered a surrogate for nephron endowment. Also, although females have fewer nephrons, they experience a slower decline in GFR compared to males. Gender disparity in chronic kidney disease progression has been attributed to factors such as metabolism, oxidative stress, renal hemodynamics, and sex hormones. Understanding the complexities of nephron endowment variability, genetic determinants, and sexual dimorphism in kidney development and function is crucial for elucidating the mechanisms underlying individual kidney disease susceptibility and progression. Further research in this field holds promise for the development of personalized approaches to kidney disease prevention, management, and treatment.

Practical Approach to Congenital Anomalies of the Kidneys: Focus on Anomalies With Insufficient or Abnormal Nephron Development: Renal Dysplasia, Renal Hypoplasia, and Renal Tubular Dysgenesis

Congenital anomalies of the kidney and urinary tract (CAKUT) accounts for up to 30% of antenatal congenital anomalies and is the main cause of kidney failure in children worldwide. This review focuses on practical approaches to CAKUT, particularly those with insufficient or abnormal nephron development, such as renal dysplasia, renal hypoplasia, and renal tubular dysgenesis. The review provides insights into the histological features, pathogenesis, mechanisms, etiologies, antenatal and postnatal presentation, management, and prognosis of these anomalies. Differential diagnoses are discussed as several syndromes may include CAKUT as a phenotypic component and renal dysplasia may occur in some ciliopathies, tumor predisposition syndromes, and inborn errors of metabolism. Diagnosis and genetic counseling for CAKUT are challenging, due to the extensive variability in presentation, genetic and phenotypic heterogeneity, and difficulties to assess postnatal lung and renal function on prenatal imaging. The review highlights the importance of perinatal autopsy and pathological findings in surgical specimens to establish the diagnosis and prognosis of CAKUT. The indications and the type of genetic testing are discussed. The aim is to provide essential insights into the practical approaches, diagnostic processes, and genetic considerations offering valuable guidance for pediatric and perinatal pathologists.

Low Birth Weight is Associated with More Severe Course of Steroid-Sensitive Nephrotic Syndrome in Children, Multicentric Study

BACKGROUND

Several previous studies have reported a more severe course of nephrotic syndrome in children with low birth weight.

PATIENTS

Cohort of 223 children with idiopathic nephrotic syndrome.

METHODS

We aimed to investigate the association between course of nephrotic syndrome and low birth weight. Data from seven paediatric nephrology centres were used.

RESULTS

Children with low birth weight had 3.84 times higher odds for a more severe course of steroid-sensitive nephrotic syndrome (95% CI 1.20-17.22, P=0.041), and those with low birth weight and remission after 7 days had much higher odds for a more severe course of disease (OR 8.7). Low birth weight children had a longer time to remission (median 12 vs. 10 days, P=0.03). They had a higher need for steroid-sparing agents (OR for the same sex=3.26 [95% CI 1.17-11.62, P=0.039]), and the odds were even higher in females with low birth weight (OR 6.81). There was no evidence of an association either between low birth weight and focal segmental glomerulosclerosis or between low birth weight and steroid-resistant nephrotic syndrome.

DISCUSSION

We conducted the first multicentric study confirming the worse outcomes of children with NS and LBW and we found additional risk factors.

CONCLUSIONS

Low birth weight is associated with a more severe course of steroid-sensitive nephrotic syndrome, while being female and achieving remission after 7 days are additional risk factors.

Newborn glomerular function and gestational particulate air pollution

BACKGROUND

Nephron number variability may hold significance in the Developmental Origins of Health and Disease hypothesis. We explore the impact of gestational particulate pollution exposure on cord blood cystatin C, a marker for glomerular function, as an indicator for glomerular health at birth.

METHODS

From February 2010 onwards, the ENVIRONAGE cohort includes over 2200 mothers giving birth at the East-Limburg hospital in Genk, Belgium. Mothers without planned caesarean section who are able to fill out a Dutch questionnaire are eligible. Here, we evaluated cord blood cystatin C levels from 1484 mother-child pairs participating in the ENVIRONAGE cohort. We employed multiple linear regression models and distributed lag models to assess the association between cord blood cystatin C and gestational particulate air pollution exposure.

FINDINGS

Average ± SD levels of cord blood cystatin C levels amounted to 2.16 ± 0.35 mg/L. Adjusting for covariates, every 0.5 μg/m³ and 5 μg/m³ increment in gestational exposure to black carbon (BC) and fine particulate matter (PM2.5) corresponded to increases of 0.04 mg/L (95% CI 0.01-0.07) and 0.07 mg/L (95% CI 0.03-0.11) in cord blood cystatin C levels (p < 0.01), respectively. Third-trimester exposure showed similar associations, with a 0.04 mg/L (95% CI 0.00-0.08) and 0.06 mg/L (95% CI 0.04-0.09) increase for BC and PM2.5 (p < 0.02). No significant associations were observed when considering only the first and second trimester exposure.

INTERPRETATION

Our findings indicate that particulate air pollution during the entire pregnancy, with the strongest effect sizes from week 27 onwards, may affect newborn kidney function, with potential long-term implications for later health.

FUNDING

Special Research Fund (Bijzonder Onderzoeksfonds, BOF), Flemish Scientific Research Fund (Fonds Wetenschappelijk Onderzoek, FWO), and Methusalem.

Early-life exposures and long-term health: adverse gestational environments and the programming of offspring renal and vascular disease

According to the Developmental Origins of Health and Disease hypothesis, exposure to certain environmental influences during early life may be a key determinant of fetal development and short- and long-term offspring health. Indeed, adverse conditions encountered during the fetal, perinatal, and early childhood stages can alter normal development and growth, as well as put the offspring at elevated risk of developing long-term health conditions in adulthood, including chronic kidney disease and cardiovascular diseases. Of relevance in understanding the mechanistic basis of these long-term health conditions are previous findings showing low glomerular number in human intrauterine growth restriction and low birth weight-indicators of a suboptimal intrauterine environment. In different animal models, the main suboptimal intrauterine conditions studied relate to maternal dietary manipulations, poor micronutrient intake, prenatal ethanol exposure, maternal diabetes, glucocorticoid and chemical exposure, hypoxia, and placental insufficiency. These studies have demonstrated changes in kidney structure, glomerular endowment, and expression of key genes and signaling pathways controlling endocrine, excretion, and filtration function of the offspring. This review aims to summarize those studies to uncover the effects and mechanisms by which adverse gestational environments impact offspring renal and vascular health in adulthood. This is important for identifying agents and interventions that can prevent and mitigate the long-term consequences of an adverse intrauterine environment on the subsequent generation.NEW & NOTEWORTHY Human data and experimental animal data show that suboptimal environments during fetal development increase the risk of renal and vascular diseases in adult-life. This is related to permanent changes in kidney structure, function, and expression of genes and signaling pathways controlling filtration, excretion, and endocrine function. Uncovering the mechanisms by which offspring renal development and function is impacted is important for identifying ways to mitigate the development of diseases that strain health care services worldwide.

A new era in the science and care of kidney diseases

Notable progress in basic, translational and clinical nephrology research has been made over the past five decades. Nonetheless, many challenges remain, including obstacles to the early detection of kidney disease, disparities in access to care and variability in responses to existing and emerging therapies. Innovations in drug development, research technologies, tissue engineering and regenerative medicine have the potential to improve patient outcomes. Exciting prospects include the availability of new drugs to slow or halt the progression of chronic kidney disease, the development of bioartificial kidneys that mimic healthy kidney functions, and tissue engineering techniques that could enable transplantable kidneys to be created from the cells of the recipient, removing the risk of rejection. Cell and gene therapies have the potential to be applied for kidney tissue regeneration and repair. In addition, about 30% of kidney disease cases are monogenic and could potentially be treated using these genetic medicine approaches. Systemic diseases that involve the kidney, such as diabetes mellitus and hypertension, might also be amenable to these treatments. Continued investment, communication, collaboration and translation of innovations are crucial to realize their full potential. In addition, increasing sophistication in exploring large datasets, implementation science, and qualitative methodologies will improve the ability to deliver transformational kidney health strategies.

Kidney volume-to-birth weight ratio as an estimate of nephron endowment in extremely low birth weight preterm infants

In humans, nephrogenesis is completed by 32-36 weeks gestation, with a highly variable total number of nephrons, ranging from 200,000 to over 2 million. Premature birth disrupts the development and maturation of the kidneys, leading to a reduction in the final number of nephrons. Due to significant genetic variability in the number of nephrons among individuals, it is crucial to identify premature infants with fewer nephrons at birth as early as possible. These infants are more susceptible to developing renal failure with advancing age compared to those with a higher nephron endowment. Bedside ultrasound, an effective and non-invasive tool, is practical for identifying newborns with a lower nephron count. However, renal volume alone cannot reliably indicate the number of nephrons due to substantial variability at birth, influenced by gestational age when nephron maturation is incomplete. This variability in kidney volumes persists as newborns grow. In this observational study we hypothesize that the relationship between renal volume and birth weight may serve as an indicator of nephron endowment in premature infants with birth weight less than 1000 g. This finding could represent the basis for defining appropriate surveillance protocols and developing targeted therapeutic approaches.

Chronic Kidney Disease in Brazil: Current Status and Recommended Improvements

Background

Over the last 3 decades, over 700 million individuals worldwide have been diagnosed with chronic kidney disease (CKD). In a 2017 survey in southern Brazil, 11.4% of those surveyed had CKD. Early identification and effective therapy in Brazil may reduce CKD's impact. This panel discusses the early diagnosis and treatment of CKD and the barriers and actions needed to improve the management of CKD in Brazil. A panel of Brazilian nephrologists was provided with relevant questions to address before a multiday conference. During this meeting, each narrative was discussed and edited through several rounds until agreement on the relevant topics and recommendations was achieved.

Summary

Panelists highlighted hurdles to early diagnosis and treatment of CKD. These include, but are not limited to, a lack of public and patient education, updated recommendations, multidisciplinary CKD treatment, and a national CKD database. People-centered, physician-centered, and healthcare institution-centered actions can be taken to improve outcomes. Patient empowerment is needed via multiple channels of CKD education and access to health-monitoring wearables and apps. Primary care clinicians and nonspecialists must be trained to screen and manage CKD-causing illnesses, including diabetes and hypertension. The healthcare system may implement a national health data gathering system, more screening tests, automated test result reporting, and telehealth.

Key Messages

Increasing access to early diagnosis can provide a path to improving care for patients with CKD. Concerted efforts from all stakeholders are needed to overcome the barriers.

The extracellular matrix protein fibronectin promotes metanephric kidney development

Complex interactions of the branching ureteric bud (UB) and surrounding mesenchymal cells during metanephric kidney development determine the final number of nephrons. Impaired nephron endowment predisposes to arterial hypertension and chronic kidney disease. In the kidney, extracellular matrix (ECM) proteins are usually regarded as acellular scaffolds or as the common histological end-point of chronic kidney diseases. Since only little is known about their physiological role in kidney development, we aimed for analyzing the expression and role of fibronectin. In mouse, fibronectin was expressed during all stages of kidney development with significant changes over time. At embryonic day (E) 12.5 and E13.5, fibronectin lined the UB epithelium, which became less pronounced at E16.5 and then switched to a glomerular expression in the postnatal and adult kidneys. Similar results were obtained in human kidneys. Deletion of fibronectin at E13.5 in cultured metanephric mouse kidneys resulted in reduced kidney sizes and impaired glomerulogenesis following reduced cell proliferation and branching of the UB epithelium. Fibronectin colocalized with alpha 8 integrin and fibronectin loss caused a reduction in alpha 8 integrin expression, release of glial-derived neurotrophic factor and expression of Wnt11, both of which are promoters of UB branching. In conclusion, the ECM protein fibronectin acts as a regulator of kidney development and is a determinant of the final nephron number.

A new, deep learning-based method for the analysis of autopsy kidney samples used to study sex differences in glomerular density and size in a forensic population

Artificial intelligence (AI) is increasingly used in forensic anthropology and genetics to identify the victim and the cause of death. The large autopsy samples from persons with traumatic causes of death but without comorbidities also offer possibilities to analyze normal histology with AI. We propose a new deep learning-based method to rapidly count glomerular number and measure glomerular density (GD) and volume in post-mortem kidney samples obtained in a forensic population. We assessed whether this new method detects glomerular differences between men and women without known kidney disease. Autopsies performed between 2009 and 2015 were analyzed if subjects were aged ≥ 18 years and had no known kidney disease, diabetes mellitus, or hypertension. A large biopsy was taken from each kidney, stained with hematoxylin and eosin, and scanned. An in-house developed deep learning-based algorithm counted the glomerular density (GD), number, and size. Out of 1165 forensic autopsies, 86 met all inclusion criteria (54 men). Mean (± SD) age was 43.5 ± 14.6; 786 ± 277 glomeruli were analyzed per individual. There was no significant difference in GD between men and women (2.18 ± 0.49 vs. 2.30 ± 0.57 glomeruli/mm2, p = 0.71); glomerular diameter, area, and volume also did not differ. GD correlated inversely with age, kidney weight, and glomerular area. Glomerular area and volume increased significantly with age. In this study, there were no sex differences in glomerular density or size. Considering the size of the kidney samples, the use of the presented deep learning method can help to analyze large renal autopsy biopsies and opens perspectives for the histological study of other organs.

Impact of preterm birth on kidney health and development

Preterm birth, defined as birth before the gestational age of 37 weeks, affects 11% of the newborns worldwide. While extensive research has focused on the immediate complications associated with prematurity, emerging evidence suggests a link between prematurity and the development of kidney disease later in life. It has been demonstrated that the normal course of kidney development is interrupted in infants born prematurely, causing an overall decrease in functional nephrons. Yet, the pathogenesis leading to the alterations in kidney development and the subsequent pathophysiological consequences causing kidney disease on the long-term are incompletely understood. In the present review, we discuss the current knowledge on nephrogenesis and how this process is affected in prematurity. We further discuss the epidemiological evidence and experimental data demonstrating the increased risk of kidney disease in these individuals and highlight important knowledge gaps. Importantly, understanding the intricate interplay between prematurity, abnormal kidney development, and the long-term risk of kidney disease is crucial for implementing effective preventive and therapeutic strategies.

A Survey on Blood Pressure Measurement Technologies: Addressing Potential Sources of Bias

Regular blood pressure (BP) monitoring in clinical and ambulatory settings plays a crucial role in the prevention, diagnosis, treatment, and management of cardiovascular diseases. Recently, the widespread adoption of ambulatory BP measurement devices has been predominantly driven by the increased prevalence of hypertension and its associated risks and clinical conditions. Recent guidelines advocate for regular BP monitoring as part of regular clinical visits or even at home. This increased utilization of BP measurement technologies has raised significant concerns regarding the accuracy of reported BP values across settings. In this survey, which focuses mainly on cuff-based BP monitoring technologies, we highlight how BP measurements can demonstrate substantial biases and variances due to factors such as measurement and device errors, demographics, and body habitus. With these inherent biases, the development of a new generation of cuff-based BP devices that use artificial intelligence (AI) has significant potential. We present future avenues where AI-assisted technologies can leverage the extensive clinical literature on BP-related studies together with the large collections of BP records available in electronic health records. These resources can be combined with machine learning approaches, including deep learning and Bayesian inference, to remove BP measurement biases and provide individualized BP-related cardiovascular risk indexes.

Primary Role of the Kidney in Pathogenesis of Hypertension

Previous transplantation studies and the concept of 'nephron underdosing' support the idea that the kidney plays a crucial role in the development of essential hypertension. This suggests that there are genetic factors in the kidney that can either elevate or decrease blood pressure. The kidney normally maintains arterial pressure within a narrow range by employing the mechanism of pressure-natriuresis. Hypertension is induced when the pressure-natriuresis mechanism fails due to both subtle and overt kidney abnormalities. The inheritance of hypertension is believed to be polygenic, and essential hypertension may result from a combination of genetic variants that code for renal tubular sodium transporters or proteins involved in regulatory pathways. The renin-angiotensin-aldosterone system (RAAS) and sympathetic nervous system (SNS) are the major regulators of renal sodium reabsorption. Hyperactivity of either the RAAS or SNS leads to a rightward shift in the pressure-natriuresis curve. In other words, hypertension is induced when the activity of RAAS and SNS is not suppressed despite increased salt intake. Sodium overload, caused by increased intake and/or reduced renal excretion, not only leads to an expansion of plasma volume but also to an increase in systemic vascular resistance. Endothelial dysfunction is caused by an increased intracellular Na+ concentration, which inhibits endothelial nitric oxide (NO) synthase and reduces NO production. The stiffness of vascular smooth muscle cells is increased by the accumulation of intracellular Na+ and subsequent elevation of cytoplasmic Ca++ concentration. In contrast to the hemodynamic effects of osmotically active Na+, osmotically inactive Na+ stimulates immune cells and produces proinflammatory cytokines, which contribute to hypertension. When this occurs in the gut, the microbiota may become imbalanced, leading to intestinal inflammation and systemic hypertension. In conclusion, the primary cause of hypertension is sodium overload resulting from kidney dysregulation.

Follow-up of a randomized trial optimizing neonatal nutrition in preterm very low birthweight infants: growth, serum adipokines, renal function and blood pressure

OBJECTIVE

The primary objectives were to compare body mass index (BMI) Z-score (Z), systolic blood pressure (SBP), serum leptin:adiponectin (L:A) ratio and estimated glomerular filtration rate (eGFR) at ~3 years adjusted age between two arms of a randomized controlled trial (RCT) comparing two modes of human milk fortification for very low-birthweight infants in the neonatal intensive care unit.

STUDY DESIGN

Follow-up of RCT at 33-48 months.

RESULTS

Follow-up data are available in 82/120 infants. Infants in the experimental arm have anthropometric data consistent with central obesity and higher serum L:A ratio (sensitivity analysis adjusting for sex and using all available data), but have similar eGFR and SBP at follow-up compared with controls. Serum L:A ratio is strongly correlated with anthropometric measurements suggesting central obesity.

CONCLUSIONS

Infants in the experimental arm have central obesity and higher serum L:A ratio compared with controls. Notably, serum L:A ratio is strongly correlated with weight gain.

TRIAL REGISTRATION

This randomized controlled trial was registered at ClinicalTrials.gov NCT02372136.

Climate change and its influence in nephron mass

PURPOSE OF REVIEW

The consequences of climate change, including heat and extreme weather events impact kidney function in adults and children. The impacts of climate change on kidney development during gestation and thereby on kidney function later in life have been poorly described. Clinical evidence is summarized to highlight possible associations between climate change and nephron mass.

RECENT FINDINGS

Pregnant women are vulnerable to the effects of climate change, being less able to thermoregulate, more sensitive to the effects of dehydration, and more susceptible to infections. Exposure to heat, wildfire smoke, drought, floods and climate-related infections are associated with low birth weight, preterm birth and preeclampsia. These factors are associated with reduced nephron numbers, kidney dysfunction and higher blood pressures in offspring in later life. Exposure to air pollution is associated with higher blood pressures in children and has variable effects on estimated glomerular filtration rate.

SUMMARY

Climate change has important impacts on pregnant women and their unborn children. Being born too small or too soon is associated with life-time risk of kidney disease. Climate change may therefore have a dual effect of impacting fetal kidney development and contributing to cumulative postnatal kidney injury. The impact on population kidney health of future generations may be significant.

Hedgehog signalling in Foxd1+ embryonic kidney stromal progenitors controls nephron formation via Cxcl12 and Wnt5a

Congenital anomalies of the kidney and urinary tract (CAKUT) are characterised by a spectrum of structural and histologic abnormalities and are the major cause of childhood kidney failure. During kidney morphogenesis, the formation of a critical number of nephrons is an embryonic process supported, in part, by signalling between nephrogenic precursors and Foxd1-positive stromal progenitor cells. Low nephron number and abnormal patterning of the stroma are signature pathological features among CAKUT phenotypes with decreased kidney function. Despite their critical contribution to CAKUT pathogenesis, the mechanisms that underlie a low nephron number and the functional contribution of a disorganised renal stroma to nephron number are both poorly defined. Here, we identify a primary pathogenic role for increased Hedgehog signalling in embryonic renal stroma in the genesis of congenital low nephron number. Pharmacologic activation of Hedgehog (Hh) signalling in human kidney organoid tissue decreased the number of nephrons and generated excess stroma. The mechanisms underlying these pathogenic effects were delineated in genetic mouse models in which Hh signalling was constitutively activated in a cell lineage-specific manner. Cre-mediated excision of Ptch1 in Foxd1+ stromal progenitor cells, but not in Six2+ nephrogenic precursor cells, generated kidney malformation, identifying the stroma as a driver of low nephron number. Single-cell RNA sequencing analysis identified Cxcl12 and Wnt5a as downstream targets of increased stromal Hh signalling, findings supported by analysis in human kidney organoids. In vivo deficiency of Cxcl12 or Wnt5a in mice with increased stromal Hh signalling improved nephron endowment. These results demonstrate that dysregulated Hh signalling in embryonic renal stromal cells inhibits nephron formation in a manner dependent on Cxcl12 and Wnt5a. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Adults are just big kids: pediatric considerations for adult critical care nephrology

PURPOSE OF REVIEW

In recent years, there has been growing attention to pediatric kidney health, especially pediatric acute kidney injury (AKI). However, there has been limited focus on the role of pediatric AKI on adult kidney health, specifically considerations for the critical care physician.

RECENT FINDINGS

We summarize what is known in the field of pediatric AKI to inform adult medical care including factors throughout the early life course, including perinatal, neonatal, and pediatric exposures that impact survivor care later in adulthood.

SUMMARY

The number of pediatric AKI survivors continues to increase, leading to a higher burden of chronic kidney disease and other long-term co-morbidities later in life. Adult medical providers should consider pediatric history and illnesses to inform the care they provide. Such knowledge may help internists, nephrologists, and intensivists alike to improve risk stratification, including a lower threshold for monitoring for AKI and kidney dysfunction in their patients.

Preeclampsia impedes foetal kidney development by delivering placenta-derived exosomes to glomerular endothelial cells

BACKGROUND

Foetal renal dysplasia is still the main cause of adult renal disease. Placenta-derived exosomes are an important communication tool, and they may play an important role in placental (both foetal and maternal) function. We hypothesize that in women with preeclampsia, foetal renal dysplasia is impeded by delivering placenta-derived exosomes to glomerular endothelial cells.

METHODS

In the present study, we established a PE trophoblast oxidative stress model to isolate exosomes from supernatants by ultracentrifugation (NO-exo and H/R-exo) and collected normal and PE umbilical cord blood plasma to isolate exosomes by ultracentrifugation combined with sucrose density gradient centrifugation (N-exo and PE-exo), then we investigated their effects on foetal kidney development by in vitro, ex vivo and in vivo models.

RESULTS

The PE trophoblast oxidative stress model was established successfully. After that, in in vitro studies, we found that H/R-exo and PE-exo could adversely affect glomerular endothelial cell proliferation, tubular formation, migration, and barrier functions. In ex vivo studies, H/R-exo and PE-exo both inhibited the growth and branch formation of kidney explants, along with the decrease of VE-cadherin and Occludin. In in vivo studies, we also found that H/R-exo and PE-exo could result in renal dysplasia, reduced glomerular number, and reduced barrier function in foetal mice.

CONCLUSIONS

In conclusion, we demonstrated that PE placenta-derived exosomes could lead to foetal renal dysplasia by delivering placenta-derived exosomes to foetal glomerular endothelial cells, which provides a novel understanding of the pathogenesis of foetal renal dysplasia. Video Abstract.

Effect of preterm birth on blood pressure in later life: A systematic review and meta-analysis

Introduction

Preterm birth is linked to various complications in both infancy and adulthood. We assessed the association between preterm birth and hypertension in adulthood.

Materials and Methods

PubMed, EMBASE, and Cochrane CENTRAL Register were searched for randomized controlled trials (RCT) comparing systolic and diastolic blood pressures in individuals born preterm and those born full-term, from inception till April 11th, 2022. Data were extracted, pooled, and analyzed. Forest plots were created for a visual demonstration.

Results

Twenty-eight studies were included in our meta-analysis. SBP and DBP across all categories (Mean, Ambulatory, Daytime, and Nighttime) were higher in the preterm group compared to the term group. Mean SBP, mean ambulatory SBP, mean daytime SBP and mean nighttime SBP were 4.26 mmHg [95% CI: 3.09-5.43; P < 0.00001], 4.53 mmHg [95% CI: 1.82-7.24; P = 0.001], 4.51 mmHg [95% CI: 2.56-6.74; P < 0.00001], and 3.06 mmHg [95% CI: 1.32-4.80; P = 0.0006] higher in the preterm group, respectively. Mean DBP, mean ambulatory DBP, mean daytime DBP, and mean nighttime DBP were 2.32 mmHg [95% CI: 1.35-3.29; P < 0.00001], 1.54 mmHg [95% CI 0.68-2.39; P = 0.0004], 1.74 mmHg [95% CI: 0.92-2.56; P < 0.0001], and 1.58 mmHg [95% CI: 0.34-2.81; P = 0.01] higher in the preterm group, respectively.

Conclusion

Our observations suggest that individuals who were born preterm may have higher blood pressures as compared to those who were born full-term.

Renal agenesis: A meta-analysis of its prevalence and clinical characteristics based on 15 641 184 patients

Our objective was to analyse the newest relevant data on worldwide prevalence and associated symptoms of renal agenesis (RA). This meta-analysis builds on previous systematic reviews to include bilateral RA, its symptoms and data on gender, unilateral RA and anomaly location prevalence. Review of available data included records in English and other languages from PubMed, Embase, ScienceDirect, Web of Science, SciELO, BIOSIS, Current Content Connect Korean Journal Database and Russian Citation Index and Google. A total of 15 641 184 patients were analysed in relation to the prevalence of RA. The pooled prevalence of RA was 0.03% (95% CI: 0.03%-0.04%). Based on 500 subjects, a pooled prevalence of 47.96% (95% CI: 31.55%-64.58%) for unilateral and 52.04% (95% CI: 35.42%-68.45%) for bilateral RA has been set. Our study presents the newest generalized findings on bilateral RA. There appears to be universal disease and symptom prevalence with minor differences between world regions, although quality of future observational research should include genomic data. This will provide even further insight into the prognosis of various renal anomalies and their etiologies.

Nutrition and Developmental Origins of Kidney Disease

The developmental programming hypothesis proposes that adverse environmental insults during critical developmental periods increase the risk of diseases later in life. The kidneys are deemed susceptible to such a process, although the exact mechanisms remain elusive. Many factors have been reported to contribute to the developmental origin of chronic kidney diseases (CKD), among which peri-gestational nutrition has a central role, affecting kidney development and metabolism. Physiologically, the link between malnutrition, reduced glomerular numbers, and increased blood pressure is key in the developmental programming of CKD. However, recent studies regarding oxidative stress, mitochondrial dysfunction, epigenetic modifications, and metabolic changes have revealed potential novel pathways for therapeutic intervention. This review will discuss the role of imbalanced nutrition in the development of CKD.

Reduced kidney function and hypertension in adolescents with low birth weight, NHANES 1999-2016

BACKGROUND

Chronic kidney disease (CKD) is a major health problem, and the risk of CKD and hypertension in children born low birth weight (LBW) is under-recognized. We hypothesized that children born with LBW would have a higher prevalence of reduced kidney function and hypertension.

METHODS

Using the National Health and Nutrition Examination Survey (NHANES), we conducted a cross-sectional study to evaluate whether LBW (< 2500 g), very low birth weight (VLBW < 1500 g), and large birth weight (BW) (> 4000 g) were associated with kidney disease using 4 different estimating equations. We used the Counahan-Barratt, updated Schwartz, CKiD-U25, and full age spectrum creatinine-based GFR estimating equations to evaluate associations between a history of LBW/VLBW/large BW and reduced kidney function (eGFR < 90 mL/min/1.73 m2) in children. We also assessed blood pressure (BP) using the old and new pediatric hypertension guidelines.

RESULTS

Our analysis included 6336 children (age 12-15 years) in NHANES representing over 13 million US individuals. Using the updated Schwartz, the prevalence of reduced kidney function was 30.1% (25.2-35.6) for children born with LBW compared to 22.4% (20.5-24.3) in children with normal BW. Equations yielded different estimates of prevalence of reduced kidney function in LBW from 21.5% for Counahan-Barratt to 35.4% for CKiD-U25. Compared to those with normal BW, participants with LBW and VLBW had a 7.2 and 10.3% higher prevalence of elevated BP and a 2.4 and 14.6% higher prevalence of hypertension, respectively.

CONCLUSIONS

Children born with LBW are at higher risk of reduced kidney function and hypertension than previously described. A higher resolution version of the Graphical abstract is available as Supplementary information.

Brief early life angiotensin-converting enzyme inhibition attenuates the diuretic response to saline loading in sheep with solitary functioning kidney

A solitary functioning kidney (SFK) from birth predisposes to hypertension and kidney dysfunction, and this may be associated with impaired fluid and sodium homeostasis. Brief and early angiotensin-converting enzyme inhibition (ACEi) in a sheep model of SFK delays onset of kidney dysfunction. We hypothesized that modulation of the renin-angiotensin system via brief postnatal ACEi in SFK would reprogram renal sodium and water handling. Here, blood pressure (BP), kidney haemodynamics and kidney excretory function were examined in response to an isotonic saline load (0.13 ml/kg/min, 180 min) at 20 months of age in SFK (fetal unilateral nephrectomy at 100 days gestation; term 150 days), sham and SFK+ACEi sheep (ACEi in SFK 4-8 weeks of age). Basal BP was higher in SFK than sham (∼13 mmHg), and similar between SFK and SFK+ACEi groups. Saline loading caused a small increase in BP (∼3-4 mmHg) the first 2 h in SFK and sham sheep but not SFK+ACEi sheep. Glomerular filtration rate did not change in response to saline loading. Total sodium excretion was similar between groups. Total urine excretion was similar between SFK and sham animals but was ∼40% less in SFK+ACEi animals compared with SFK animals. In conclusion, the present study indicates that water homeostasis in response to a physiological challenge is attenuated at 20 months of age by brief early life ACEi in SFK. Further studies are required to determine if ACEi in early life in children with SFK could compromise fluid homeostasis later in life.

Sugar, salt, immunity and the cause of primary hypertension

Despite its discovery more than 150 years ago, the cause of primary hypertension remains unknown. Most studies suggest that hypertension involves genetic, congenital or acquired risk factors that result in a relative inability of the kidney to excrete salt (sodium chloride) in the kidneys. Here we review recent studies that suggest there may be two phases, with an initial phase driven by renal vasoconstriction that causes low-grade ischemia to the kidney, followed by the infiltration of immune cells that leads to a local autoimmune reaction that maintains the renal vasoconstriction. Evidence suggests that multiple mechanisms could trigger the initial renal vasoconstriction, but one way may involve fructose that is provided in the diet (such as from table sugar or high fructose corn syrup) or produced endogenously. The fructose metabolism increases intracellular uric acid, which recruits NADPH oxidase to the mitochondria while inhibiting AMP-activated protein kinase. A drop in intracellular ATP level occurs, triggering a survival response. Leptin levels rise, triggering activation of the sympathetic central nervous system, while vasopressin levels rise, causing vasoconstriction in its own right and stimulating aldosterone production via the vasopressin 1b receptor. Low-grade renal injury and autoimmune-mediated inflammation occur. High-salt diets can amplify this process by raising osmolality and triggering more fructose production. Thus, primary hypertension may result from the overactivation of a survival response triggered by fructose metabolism. Restricting salt and sugar and hydrating with ample water may be helpful in the prevention of primary hypertension.

Nephrosclerosis in young patients with malignant hypertension

BACKGROUND

Nephrosclerosis is one of the histopathological consequences of severe or malignant hypertension (MH), some of the pathophysiology of which has been extrapolated from essential polygenetic arterial hypertension. Despite our recent description of unsuspected ciliopathies with MH, causes of MH in young patients with severe renal impairment are poorly understood.

METHODS

To refine and better describe the MH phenotype, we studied clinical and prognostic factors in young patients receiving a kidney biopsy following their first episode of MH. Patients were identified retrospectively and prospectively from eight centres over a 35-year period (1985-2020). Keywords were used to retrospectively enrol patients irrespective of lesions found on renal biopsy.

RESULTS

A total of 114 patients were included, 77 (67%) of whom were men, average age 34 years, 35% Caucasian and 34% African origin. An isolated clinical diagnosis of severe nephrosclerosis was suggested in only 52% of cases, with 24% primary glomerulopathies. Only 7% of patients had normal renal function at diagnosis, 25% required emergency dialysis and 21% were eventually transplanted. Mortality was 1% at the last follow-up. Independent prognostic factors significantly associated with renal prognosis (6-month dialysis) and predictive of end-stage renal disease were serum creatinine on admission {odds ratio [OR] 1.56 [95% confidence interval (CI) 1.34-1.96], P < .001} and renal fibrosis >30% [OR 10.70 (95% CI 1.53-112.03), P = .03]. Astonishingly, the presence of any thrombotic microangiopathy lesion on renal biopsy was an independent, protective factor [OR 0.14 (95% CI 0.02-0.60), P = .01]. The histopathological hallmark of nephrosclerosis was found alone in only 52% of study patients, regardless of ethnicity.

CONCLUSIONS

This suggests that kidney biopsy might be beneficial in young patients with MH.

An Improved Method for Estimating Nephron Number and the Association of Resulting Nephron Number Estimates with Chronic Kidney Disease Outcomes

SIGNIFICANCE STATEMENT

Nephron number currently can be estimated only from glomerular density on a kidney biopsy combined with cortical volume from kidney imaging. Because of measurement biases, refinement of this approach and validation across different patient populations have been needed. The prognostic importance of nephron number also has been unclear. The authors present an improved method of estimating nephron number that corrects for several biases, resulting in a 27% higher nephron number estimate for donor kidneys compared with a prior method. After accounting for comorbidities, the new nephron number estimate does not differ between kidney donors and kidney patients with tumor and shows consistent associations with clinical characteristics across these two populations. The findings also indicate that low nephron number predicts CKD independent of biopsy and clinical characteristics in both populations.

BACKGROUND

Nephron number can be estimated from glomerular density and cortical volume. However, because of measurement biases, this approach needs refinement, comparison between disparate populations, and evaluation as a predictor of CKD outcomes.

METHODS

We studied 3020 living kidney donors and 1354 patients who underwent radical nephrectomy for tumor. We determined cortex volume of the retained kidney from presurgical imaging and glomerular density by morphometric analysis of needle core biopsy of the donated kidney and wedge sections of the removed kidney. Glomerular density was corrected for missing glomerular tufts, absence of the kidney capsule, and then tissue shrinkage on the basis of analysis of 30 autopsy kidneys. We used logistic regression (in donors) and Cox proportional hazard models (in patients with tumor) to assess the risk of CKD outcomes associated with nephron number.

RESULTS

Donors had 1.17 million nephrons per kidney; patients with tumor had 0.99 million nephrons per kidney. A lower nephron number was associated with older age, female sex, shorter height, hypertension, family history of ESKD, lower GFR, and proteinuria. After adjusting for these characteristics, nephron number did not differ between donors and patients with tumor. Low nephron number (defined by <5th or <10th percentile by age and sex in a healthy subset) in both populations predicted future risk of CKD outcomes independent of biopsy and clinical characteristics.

CONCLUSIONS

Compared with an older method for estimating nephron number, a new method that addresses several sources of bias results in nephron number estimates that are 27% higher in donors and 1% higher in patients with tumor and shows consistency between two populations. Low nephron number independently predicts CKD in both populations.

Renal Functional Response-Association With Birth Weight and Kidney Volume

Introduction

Renal functional response (RFR) is the acute increase in glomerular filtration rate (GFR) after a protein load. Low RFR is a marker of single nephron hyperfiltration. Low birth weight (LBW) is associated with reduced number of nephrons, lower kidney function, and smaller kidneys in adults. In the present study, we investigate the associations among LBW, kidney volume, and RFR.

Methods

We studied adults aged 41 to 52 years born with either LBW (≤2300 g) or normal birth weight (NBW; 3500-4000 g). GFR was measured using plasma clearance of iohexol. A stimulated GFR (sGFR) was measured on a separate day after a protein load of 100 g using a commercially available protein powder, and RFR was calculated as delta GFR. Kidney volume was estimated from magnetic resonance imaging (MRI) images using the ellipsoid formula.

Results

A total of 57 women and 48 men participated. The baseline mean ± SD GFR was 118 ± 17 ml/min for men and 98 ± 19 ml/min for women. The overall mean RFR was 8.2 ± 7.4 ml/min, with mean RFR of 8.3 ± 8.0 ml/min and 8.1 ± 6.9 ml/min in men and women, respectively (P = 0.5). No birth-related variables were associated with RFR. Larger kidney volume was associated with higher RFR, 1.9 ml/min per SD higher kidney volume (P = 0.009). Higher GFR per kidney volume was associated with a lower RFR, -3.3ml/min per SD (P < 0.001).

Conclusion

Larger kidney size and lower GFR per kidney volume were associated with higher RFR. Birth weight was not shown to associate with RFR in mainly healthy middle-aged men and women.

A Rodent Model of Human-Dose-Equivalent 5-Fluorouracil: Toxicity in the Liver, Kidneys, and Lungs

5-Fluorouracil (5-FU) is a chemotherapy drug widely used to treat a range of cancer types, despite the recurrence of adverse reactions. Therefore, information on its side effects when administered at a clinically recommended dose is relevant. On this basis, we examined the effects of the 5-FU clinical treatment on the integrity of the liver, kidneys, and lungs of rats. For this purpose, 14 male Wistar rats were divided into treated and control groups and 5-FU was administered at 15 mg/kg (4 consecutive days), 6 mg/kg (4 alternate days), and 15 mg/kg on the 14th day. On the 15th day, blood, liver, kidney, and lung samples were collected for histological, oxidative stress, and inflammatory evaluations. We observed a reduction in the antioxidant markers and an increase in lipid hydroperoxides (LOOH) in the liver of treated animals. We also detected elevated levels of inflammatory markers, histological lesions, apoptotic cells, and aspartate aminotransferase. Clinical treatment with 5-FU did not promote inflammatory or oxidative alterations in the kidney samples; however, histological and biochemical changes were observed, including increased serum urea and uric acid. 5-FU reduces endogenous antioxidant defenses and increases LOOH levels in the lungs, suggesting oxidative stress. Inflammation and histopathological alterations were also detected. The clinical protocol of 5-FU promotes toxicity in the liver, kidneys, and lungs of healthy rats, resulting in different levels of histological and biochemical alterations. These results will be useful in the search for new adjuvants to attenuate the adverse effects of 5-FU in such organs.

Tet2- and Tet3- Mediated Cytosine Hydroxymethylation in Six2 Progenitor Cells in Mice Is Critical for Nephron Progenitor Differentiation and Nephron Endowment

SIGNIFICANCE STATEMENT

Epigenetic changes have been proposed to mediate nephron endowment during development, a critical determinant of future renal disease development. Hydroxymethyl cytosine, an epigenetic modification important for gene regulation, is abundant in the human kidney, but its physiologic role and the role of DNA demethylase enzymes encoded by the Tet1 , Tet2 , or Tet3 , which mediate cytosine hydroxymethylation, are unclear. By genetically deleting Tet1 , Tet2 , or Tet3 in nephron progenitors in mice, the authors showed that combined Tet2 and Tet3 loss in nephron progenitors cause defective kidney development, leading to kidney failure and perinatal death. Tet2 and Tet3 deletion also caused an alteration in demethylation and expression of genes critical for nephron formation. These findings establish that Tet2- and Tet3 -mediated cytosine hydroxymethylation in nephron progenitors plays a critical role in nephron endowment.

BACKGROUND

Nephron endowment is a key determinant of hypertension and renal disease in later life. Epigenetic changes have been proposed to mediate fetal programming and nephron number. DNA cytosine methylation, which plays a critical role in gene regulation, is affected by proteins encoded by the ten-eleven translocation (TET) DNA demethylase gene family ( Tet1 , Tet2 , and Tet3 ), but the roles of TET proteins in kidney development and nephron endowment have not been characterized .

METHODS

To study whether epigenetic changes-specifically, active DNA hydroxymethylation mediated by Tet1 , Tet2 , and Tet3- are necessary for nephron progenitor differentiation and nephron endowment, we generated mice with deletion of Tet1 , Tet2 , or Tet3 in Six2-positive nephron progenitors cells (NPCs). We then performed unbiased omics profiling, including whole-genome bisulfite sequencing on isolated Six2-positive NPCs and single-cell RNA sequencing on kidneys from newborn mice.

RESULTS

We did not observe changes in kidney development or function in mice with NPC-specific deletion of Tet1 , Tet2 , Tet3 or Tet1 / Tet2 , or Tet1 / Tet3 . On the other hand, mice with combined Tet2 and Tet3 loss in Six2-positive NPCs failed to form nephrons, leading to kidney failure and perinatal death. Tet2 and Tet3 loss in Six2 -positive NPCs resulted in defective mesenchymal to epithelial transition and renal vesicle differentiation. Whole-genome bisulfite sequencing, single-cell RNA sequencing, and gene and protein expression analysis identified a defect in expression in multiple genes, including the WNT- β -catenin signaling pathway, due to a failure in demethylation of these loci in the absence of Tet2 and Tet3 .

CONCLUSIONS

These findings suggest that Tet2- and Tet3 -mediated active cytosine hydroxymethylation in NPCs play a key role in kidney development and nephron endowment.

Preterm birth leads to a decreased number of differentiated podocytes and accelerated podocyte differentiation

Preterm birth was previously identified as a high-risk factor for the long-term development of chronic kidney disease. However, the detailed pattern of podocyte (PD) changes caused by preterm birth and the potential mechanism underlying this process have not been well clarified. In present study, a rat model of preterm birth was established by delivery of pups 2 days early and podometric methods were applied to identify the changes in PDs number caused by preterm birth. In addition, single-cell RNA sequencing (scRNA-seq) and subsequent bioinformatic analysis were performed in the preterm rat kidney to explore the possible mechanism caused by preterm birth. As results, when the kidney completely finished nephrogenesis at the age of 3 weeks, a reduction in the total number of differentiated PDs in kidney sections was detected. In addition, 20 distinct clusters and 12 different cell types were identified after scRNA-seq in preterm rats (postnatal day 2) and full-term rats (postnatal day 0). The numbers of PDs and most types of inherent kidney cells were decreased in the preterm birth model. In addition, 177 genes were upregulated while 82 genes were downregulated in the PDs of full-term rats compared with those of preterm rats. Further functional GO analysis revealed that ribosome-related genes were enriched in PDs from full-term rats, and kidney development-related genes were enriched in PDs from preterm rats. Moreover, known PD-specific and PD precursor genes were highly expressed in PDs from preterm rats, and pseudotemporal analysis showed that PDs were present earlier in preterm rats than in full-term rats. In conclusion, the present study showed that preterm birth could cause a reduction in the number of differentiated PDs and accelerate the differentiation of PDs.

Urine podocyte mRNA loss in preterm infants and related perinatal risk factors

BACKGROUND

Preterm birth has been identified as a risk factor for development of long-term chronic kidney disease. Podocyte loss has been reported to contribute to this process in preterm animal models. However, details about podocyte loss in preterm infants and related perinatal risk factors have not been well clarified.

METHODS

Forty full-term infants and 106 preterm infants were enrolled. Urine samples were collected from full-term infants within 4-7 days of birth and preterm infants at 37-40 weeks of corrected age. Levels of urine podocin mRNA, urine protein (UP), and urine microalbumin (UMA) were measured, and the relationship between these markers was evaluated. Clinical information in these infants was collected, and potential correlates that may lead to increased podocyte loss during the perinatal period were identified using linear regression analysis.

RESULTS

Urine podocyte loss indicated by the urine podocin mRNA to creatinine ratio (UpodCR) was higher in preterm infants than in full-term infants. UpodCR was correlated with the levels of UP and UMA. Multiple linear regression analysis also showed that lower gestational age (GA) at birth and small for gestational age (SGA) were high risk factors for urine podocyte loss.

CONCLUSIONS

Increasing urine podocyte loss was identified in preterm infants. Moreover, perinatal factors were associated with podocyte loss and may be a potential direction for comprehensive research and intervention in this field. A higher resolution version of the Graphical abstract is available as Supplementary information.

Effect of Protein Intake Early in Life on Kidney Volume and Blood Pressure at 11 Years of Age

High protein intake has been associated with kidney hypertrophy, which is usually reversible; however, when it occurs early in life, it could lead to cell programming with a long-lasting effect. This study aimed to assess whether higher protein ingestion early in life has a persistent effect on kidney volume at 11 years of age, as well as its influence on blood pressure. This is a secondary analysis of a randomized control trial that compared the growth of infants fed with a higher-protein formula versus those fed with a lower-protein formula, with a control group of breastfed infants. Renal ultrasound and anthropometric measurements were assessed at 6 months and 11 years of age. At 11 years, urinary protein, albumin and creatinine, and blood pressure were measured in 232 children. Feeding with a higher-protein formula was associated with a larger kidney volume (β = 8.71, 95%CI 0.09-17.33, p = 0.048) and higher systolic blood pressure (β = 3.43, 95%CI 0.78-6.08, p = 0.011) at 11 years of age. Microalbuminuria was detected in 7% of the patients, with no differences among groups (p = 0.56). The effect of increased protein ingestion early in life may condition kidney volume and blood pressure in later childhood.

Low nephron endowment increases susceptibility to renal stress and chronic kidney disease

Preterm birth results in low nephron endowment and increased risk of acute kidney injury (AKI) and chronic kidney disease (CKD). To understand the pathogenesis of AKI and CKD in preterm humans, we generated potentially novel mouse models with a 30%-70% reduction in nephron number by inhibiting or deleting Ret tyrosine kinase in the developing ureteric bud. These mice developed glomerular and tubular hypertrophy, followed by the transition to CKD, recapitulating the renal pathological changes seen in humans born preterm. We injected neonatal mice with gentamicin, a ubiquitous nephrotoxic exposure in preterm infants, and detected more severe proximal tubular injury in mice with low nephron number compared with controls with normal nephron number. Mice with low nephron number had reduced proliferative repair with more rapid development of CKD. Furthermore, mice had more profound inflammation with highly elevated levels of MCP-1 and CXCL10, produced in part by damaged proximal tubules. Our study directly links low nephron endowment with postnatal renal hypertrophy, which in this model is maladaptive and results in CKD. Underdeveloped kidneys are more susceptible to gentamicin-induced AKI, suggesting that AKI in the setting of low nephron number is more severe and further increases the risk of CKD in this vulnerable population.

Perinatal iron deficiency causes sex-dependent alterations in renal retinoic acid signaling and nephrogenesis

Long-term alterations in kidney structure and function have been observed in offspring exposed to perinatal stressors such as iron deficiency (ID), albeit the mechanisms underlying these changes remain unclear. Here, we assessed how perinatal ID alters renal vitamin A metabolism, an important contributor to nephrogenesis, in the developing kidney. Pregnant Sprague Dawley rats were fed either an iron-restricted or -replete diet throughout gestation, and offspring were studied on postnatal day (PD)1 and 28. Maternal iron restriction results in reduced renal retinoid concentrations in male and female offspring on PD1 (P=.005). Nephron endowment was reduced by 21% in male perinatal ID offspring (P<.001), whereas it was unaffected in perinatal ID females. Perinatal ID resulted in sex-dependent changes in kidney retinoid synthesis and metabolism, whereby male offspring exhibited increased expression of Raldh2 and Rar/Rxr isoforms, while females exhibited unchanged or decreased expression (all interaction P<.05). Male perinatal ID offspring exhibit sex-specific enhancements of retinoic acid pathway signaling components on PD1, including Gdnf (P<.01) and Ctnnb1 (P<.01), albeit robust upregulation of RA transcriptional target Stra6 was observed in both sexes (P=.006). On PD28, perinatal ID resulted in elevated renal retinoid concentrations (P=.02) coinciding with enhanced expression of Raldh2 (P=.04), but not any Rar isoform or Rxr. Further, perinatal ID resulted in robust upregulation of Gdnf, Ret, Ctnnb1, associated with further increases in both Cxcr4 and Stra6 (all P<.01) at PD28. Together, these data suggest perinatal ID results in sustained sex-dependent perturbations in vitamin A metabolism, which likely underlie sex-specific reductions in nephron endowment.

Cardiovascular and renal profiles in rat offspring that do not undergo catch-up growth after exposure to maternal protein restriction

Maternal protein restriction is often associated with structural and functional sequelae in offspring, particularly affecting growth and renal-cardiovascular function. However, there is little understanding as to whether hypertension and kidney disease occur because of a primary nephron deficit or whether controlling postnatal growth can result in normal renal-cardiovascular phenotypes. To investigate this, female Sprague-Dawley rats were fed either a low-protein (LP, 8.4% protein) or normal-protein (NP, 19.4% protein) diet prior to mating and until offspring were weaned at postnatal day (PN) 21. Offspring were then fed a non 'growth' (4.6% fat) which ensured that catch-up growth did not occur. Offspring growth was determined by weight and dual energy X-ray absorptiometry. Nephron number was determined at PN21 using the disector-fractionator method. Kidney function was measured at PN180 and PN360 using clearance methods. Blood pressure was measured at PN360 using radio-telemetry. Body weight was similar at PN1, but by PN21 LP offspring were 39% smaller than controls (P_diet < 0.001). This difference was due to proportional changes in lean muscle, fat, and bone content. LP offspring remained smaller than NP offspring until PN360. In LP offspring, nephron number was 26% less in males and 17% less in females, than NP controls (P_diet < 0.0004). Kidney function was similar across dietary groups and sexes at PN180 and PN360. Blood pressure was similar in LP and NP offspring at PN360. These findings suggest that remaining on a slow growth trajectory after exposure to a suboptimal intrauterine environment does not lead to the development of kidney dysfunction and hypertension.

Effects of Voluntary Sodium Consumption during the Perinatal Period on Renal Mechanisms, Blood Pressure, and Vasopressin Responses after an Osmotic Challenge in Rats

Cardiovascular control is vulnerable to forced high sodium consumption during the per-inatal period, inducing programming effects, with anatomical and molecular changes at the kidney, brain, and vascular levels that increase basal and induce blood pressure. However, the program- ming effects of the natriophilia proper of the perinatal period on blood pressure control have not yet been elucidated. In order to evaluate this, we studied the effect of a sodium overload challenge (SO) on blood pressure response and kidney and brain gene expression in adult offspring exposed to voluntary hypertonic sodium consumption during the perinatal period (PM-NaCl group). Male PM-NaCl rats showed a more sustained increase in blood pressure after SO than controls (PM-Ctrol). They also presented a reduced number of glomeruli, decreased expression of TRPV1, and increased expression of At1a in the kidney cortex. The relative expression of heteronuclear vaso- pressin (AVP hnRNA) and AVP in the supraoptic nucleus was unchanged after SO in PM-NaCl in contrast to the increase observed in PM-Ctrol. The data indicate that the availability of a rich source of sodium during the perinatal period induces a long-term effect modifying renal, cardiovascular, and neuroendocrine responses implicated in the control of hydroelectrolyte homeostasis.