Associations between nephron number and podometrics in human kidneys.

Podocyte loss and resultant nephron loss are common processes in the development of glomerulosclerosis and chronic kidney disease. While the cortical distribution of glomerulosclerosis is known to be non-uniform, the relationship between the numbers of non-sclerotic glomeruli (NSG), podometrics and zonal differences in podometrics remain incompletely understood. To help define this, we studied autopsy kidneys from 50 adults with median age 68 years and median eGFR 73.5 mL/min/1.73m2 without apparent glomerular disease in a cross-sectional analysis. The number of NSG per kidney was estimated using the physical dissector/fractionator combination, while podometrics were estimated using model-based stereology. The number of NSG per kidney was directly correlated with podocyte number per tuft and podocyte density. Each additional 100,000 NSG per kidney was associated with 26 more podocytes per glomerulus and 16 podocytes per 106 µm3 increase in podocyte density. These associations were independent of clinical factors and cortical zone. While podocyte number per glomerulus was similar in the three zones, superficial glomeruli were the smallest and had the highest podocyte density but smallest podocytes. Increasing age and hypertension were associated with lower podocyte number, with age mostly affecting superficial glomeruli, and hypertension mostly affecting juxtamedullary glomeruli. Thus, in this first study to report a direct correlation between the number of NSG and podometrics, we suggest that podocyte number is decreasing in NSG of individuals losing nephrons. However, another possible interpretation may be that more nephrons might protect against further podocyte loss.

The ability of remaining glomerular podocytes to adapt to the loss of their neighbours decreases with age.

Progressive podocyte loss is a feature of healthy ageing. While previous studies have reported age-related changes in podocyte number, density and size and associations with proteinuria and glomerulosclerosis, few studies have examined how the response of remaining podocytes to podocyte depletion changes with age. Mild podocyte depletion was induced in PodCreiDTR mice aged 1, 6, 12 and 18 months via intraperitoneal administration of diphtheria toxin. Control mice received intraperitoneal vehicle. Podometrics, proteinuria and glomerular pathology were assessed, together with podocyte expression of p-rp-S6, a phosphorylation target that represents activity of the mammalian target of rapamycin (mTOR). Podocyte number per glomerulus did not change in control mice in the 18-month time period examined. However, control mice at 18 months had the largest podocytes and the lowest podocyte density. Podocyte depletion at 1, 6 and 12 months resulted in mild albuminuria but no glomerulosclerosis, whereas similar levels of podocyte depletion at 18 months resulted in both albuminuria and glomerulosclerosis. Following podocyte depletion at 6 and 12 months, the number of p-rp-S6 positive podocytes increased significantly, and this was associated with an adaptive increase in podocyte volume. However, at 18 months of age, remaining podocytes were unable to further elevate mTOR expression or undergo hypertrophic adaptation in response to mild podocyte depletion, resulting in marked glomerular pathology. These findings demonstrate the importance of mTORC1-mediated podocyte hypertrophy in both physiological (ageing) and adaptive settings, highlighting a functional limit to podocyte hypertrophy reached under physiological conditions.

Podometrics in Japanese Living Donor Kidneys: Associations with Nephron Number, Age, and Hypertension.

BACKGROUND: Podocyte depletion, low nephron number, aging, and hypertension are associated with glomerulosclerosis and CKD. However, the relationship between podometrics and nephron number has not previously been examined. METHODS: To investigate podometrics and nephron number in healthy Japanese individuals, a population characterized by a relatively low nephron number, we immunostained single paraffin sections from 30 Japanese living-kidney donors (median age, 57 years) with podocyte-specific markers and analyzed images obtained with confocal microscopy. We used model-based stereology to estimate podometrics, and a combined enhanced-computed tomography/biopsy-specimen stereology method to estimate nephron number. RESULTS: The median number of nonsclerotic nephrons per kidney was 659,000 (interquartile range [IQR], 564,000-825,000). The median podocyte number and podocyte density were 518 (IQR, 428-601) per tuft and 219 (IQR, 180-253) per 106µm3, respectively; these values are similar to those previously reported for other races. Total podocyte number per kidney (obtained by multiplying the individual number of nonsclerotic glomeruli by podocyte number per glomerulus) was 376 million (IQR, 259-449 million) and ranged 7.4-fold between donors. On average, these healthy kidneys lost 5.63 million podocytes per kidney per year, with most of this loss associated with glomerular loss resulting from global glomerulosclerosis, rather than podocyte loss from healthy glomeruli. Hypertension was associated with lower podocyte density and larger podocyte volume, independent of age. CONCLUSIONS: Estimation of the number of nephrons, podocytes, and other podometric parameters in individual kidneys provides new insights into the relationships between these parameters, age, and hypertension in the kidney. This approach might be of considerable value in evaluating the kidney in health and disease.

Podocyte endowment and the impact of adult body size on kidney health.

Low birth weight is a risk factor for chronic kidney disease, whereas adult podocyte depletion is a key event in the pathogenesis of glomerulosclerosis. However, whether low birth weight due to poor maternal nutrition is associated with low podocyte endowment and glomerulosclerosis in later life is not known. Female Sprague-Dawley rats were fed a normal-protein diet (NPD; 20%) or low-protein diet (LPD; 8%), to induce low birth weight, from 3 wk before mating until postnatal day 21 (PN21), when kidneys from some male offspring were taken for quantitation of podocyte number and density in whole glomeruli using immunolabeling, tissue clearing, and confocal microscopy. The remaining offspring were fed a normal- or high-fat diet until 6 mo to induce catch-up growth and excessive weight gain, respectively. At PN21, podocyte number per glomerulus was 15% lower in low birth weight (LPD) than normal birth weight (NPD) offspring, with this deficit greater in outer glomeruli. Surprisingly, podocyte number in LPD offspring increased in outer glomeruli between PN21 and 6 mo, although an overall 9% podocyte deficit persisted. Postnatal fat feeding to LPD offspring did not alter podometric indexes or result in glomerular pathology at 6 mo, whereas fat feeding in NPD offspring was associated with far greater body and fat mass as well as podocyte loss, reduced podocyte density, albuminuria, and glomerulosclerosis. This is the first report that maternal diet can influence podocyte endowment. Our findings provide new insights into the impact of low birth weight, podocyte endowment, and postnatal weight on podometrics and kidney health in adulthood.NEW & NOTEWORTHY The present study shows, for the first time, that low birth weight as a result of maternal nutrition is associated with low podocyte endowment. However, a mild podocyte deficit at birth did not result in glomerular pathology in adulthood. In contrast, postnatal podocyte loss in combination with excessive body weight led to albuminuria and glomerulosclerosis. Taken together, these findings provide new insights into the associations between birth weight, podocyte indexes, postnatal weight, and glomerular pathology.

Maternal low-protein diet programmes low ovarian reserve in offspring

The ovarian reserve of primordial follicle oocytes is formed during in utero development and represents the entire supply of oocytes available to sustain female fertility. Maternal undernutrition during pregnancy and lactation diminishes offspring ovarian reserve in rats. In mice, maternal oocyte maturation is also susceptible to undernutrition, causing impaired offspring cardiovascular function. We aimed to determine whether programming of the ovarian reserve is impacted in offspring when maternal undernutrition extends from preconception oocyte development through to weaning. C57BL6/J female mice were fed normal protein (20%) or low-protein (8%) diet during preconception, pregnancy and lactation periods. Maternal ovaries were harvested at weaning and offspring ovaries were collected at postnatal day (PN)21 and 24 weeks of age. Total follicle estimates were obtained by histologically sampling one ovary per animal (n = 5/group). There was no impact of diet on maternal follicle numbers. However, in offspring, maternal protein restriction significantly depleted primordial follicles by 37% at PN21 and 51% at 24 weeks (P < 0.05). There were no effects of diet on other follicle classes. Histological analysis showed no differences in the proportion of proliferative follicles (pH3 positive), but increased atresia (cleaved caspase-3-positive, or TUNEL-positive) was detected in ovaries of protein-restricted offspring at both ages (P < 0.05). Our data show that maternal diet during the preconception period, in utero development and early life has significant impacts on follicle endowment and markers of follicle health later in life. This highlights the need for further investigation into the importance of maternal preconception diet for offspring reproductive development and health.

Combining new tools to assess renal function and morphology: a holistic approach to study the effects of aging and a congenital nephron deficit.

Recently, new methods for assessing renal function in conscious mice (transcutaneous assessment) and for counting and sizing all glomeruli in whole kidneys (MRI) have been described. In the present study, these methods were used to assess renal structure and function in aging mice, and in mice born with a congenital low-nephron endowment. Age-related nephron loss was analyzed in adult C57BL/6 mice (10-50 wk of age), and congenital nephron deficit was assessed in glial cell line-derived neurotrophic factor heterozygous (GDNF HET)-null mutant mice. Renal function was measured through the transcutaneous quantitation of fluorescein isothiocyanate-sinistrin half-life (t1/2) in conscious mice. MRI was used to image, count, and size cationic-ferritin labeled glomeruli in whole kidneys ex vivo. Design-based stereology was used to validate the MRI measurements of glomerular number and mean volume. In adult C57BL/6 mice, older age was associated with fewer and larger glomeruli, and a rightward shift in the glomerular size distribution. These changes coincided with a decrease in renal function. GNDF HET mice had a congenital nephron deficit that was associated with glomerular hypertrophy and exacerbated by aging. These findings suggest that glomerular hypertrophy and hyperfiltration are compensatory processes that can occur in conjunction with both age-related nephron loss and congenital nephron deficiency. The combination of measurement of renal function in conscious animals and quantitation of glomerular number, volume, and volume distribution provides a powerful new tool for investigating aspects of renal aging and functional changes.

Renal dysfunction in early adulthood following birth asphyxia in male spiny mice, and its amelioration by maternal creatine supplementation during pregnancy.

BACKGROUND: Acute kidney injury affects ~70% of asphyxiated newborns, and increases their risk of developing chronic kidney disease later in life. Acute kidney injury is driven by renal oxygen deprivation during asphyxia, thus we hypothesized that creatine administered antenatally would protect the kidney from the long-term effects of birth asphyxia. METHODS: Pregnant spiny mice were fed standard chow or chow supplemented with 5% creatine from 20-d gestation (midgestation). One day prior to term (37-d gestation), pups were delivered by caesarean or subjected to intrauterine asphyxia. Litters were allocated to one of two time-points. Kidneys were collected at 1 mo of age to estimate nephron number (stereology). Renal function (excretory profile and glomerular filtration rate) was measured at 3 mo of age, and kidneys then collected for assessment of glomerulosclerosis. RESULTS: Compared with controls, at 1 mo of age male (but not female) birth-asphyxia offspring had 20% fewer nephrons (P < 0.05). At 3 mo of age male birth-asphyxia offspring had 31% lower glomerular filtration rate (P < 0.05) and greater glomerular collagen IV content (P < 0.01). Antenatal creatine prevented these renal injuries arising from birth asphyxia. CONCLUSION: Maternal creatine supplementation during pregnancy may be an effective prophylactic to prevent birth asphyxia induced acute kidney injury and the emergence of chronic kidney disease.

Validation of a Three-Dimensional Method for Counting and Sizing Podocytes in Whole Glomeruli.

Podocyte depletion is sufficient for the development of numerous glomerular diseases and can be absolute (loss of podocytes) or relative (reduced number of podocytes per volume of glomerulus). Commonly used methods to quantify podocyte depletion introduce bias, whereas gold standard stereologic methodologies are time consuming and impractical. We developed a novel approach for assessing podocyte depletion in whole glomeruli that combines immunofluorescence, optical clearing, confocal microscopy, and three-dimensional analysis. We validated this method in a transgenic mouse model of selective podocyte depletion, in which we determined dose-dependent alterations in several quantitative indices of podocyte depletion. This new approach provides a quantitative tool for the comprehensive and time-efficient analysis of podocyte depletion in whole glomeruli.

Human podocyte depletion in association with older age and hypertension.

Podocyte depletion plays a major role in the development and progression of glomerulosclerosis. Many kidney diseases are more common in older age and often coexist with hypertension. We hypothesized that podocyte depletion develops in association with older age and is exacerbated by hypertension. Kidneys from 19 adult Caucasian American males without overt renal disease were collected at autopsy in Mississippi. Demographic data were obtained from medical and autopsy records. Subjects were categorized by age and hypertension as potential independent and additive contributors to podocyte depletion. Design-based stereology was used to estimate individual glomerular volume and total podocyte number per glomerulus, which allowed the calculation of podocyte density (number per volume). Podocyte depletion was defined as a reduction in podocyte number (absolute depletion) or podocyte density (relative depletion). The cortical location of glomeruli (outer or inner cortex) and presence of parietal podocytes were also recorded. Older age was an independent contributor to both absolute and relative podocyte depletion, featuring glomerular hypertrophy, podocyte loss, and thus reduced podocyte density. Hypertension was an independent contributor to relative podocyte depletion by exacerbating glomerular hypertrophy, mostly in glomeruli from the inner cortex. However, hypertension was not associated with podocyte loss. Absolute and relative podocyte depletion were exacerbated by the combination of older age and hypertension. The proportion of glomeruli with parietal podocytes increased with age but not with hypertension alone. These findings demonstrate that older age and hypertension are independent and additive contributors to podocyte depletion in white American men without kidney disease.

Phenotyping by magnetic resonance imaging nondestructively measures glomerular number and volume distribution in mice with and without nephron reduction.

Reduced nephron mass is strongly linked to susceptibility to chronic renal and cardiovascular diseases. There are currently no tools to identify nephropenia in clinical or preclinical diagnostics. Such new methods could uncover novel mechanisms and therapies for chronic kidney disease (CKD) and reveal how variation among traits can affect renal function and morphology. Here we used cationized ferritin (CF)­enhanced MRI (CFE-MRI) to investigate the relationship between glomerular number (Nglom) and volume (Vglom) in kidneys of healthy wild-type mice and mice with oligosyndactylism (Os/+), a model of congenital nephron reduction. Mice were injected with CF and perfused, and the resected kidneys were imaged with 7T MRI to detect CF-labeled glomeruli. CFE-MRI was used to measure the intrarenal distribution of individual glomerular volumes and revealed two major populations of glomeruli distinguished by size. Spatial mapping revealed that the largest glomeruli were located in the juxtamedullary region in both wild-type and Os/+ mice and the smallest population located in the cortex. Os/+ mice had about a 50% reduction and 35% increase of Nglom and Vglom, respectively, in both glomerular populations compared with wild type, consistent with glomerular hypertrophy in the Os/+ mice. Thus, we provide a foundation for whole-kidney, MRI-based phenotyping of mouse renal glomerular morphology and provide new potential for quantitative human renal diagnostics.

Maternal glucose intolerance reduces offspring nephron endowment and increases glomerular volume in adult offspring.

BACKGROUND: Animal studies report a nephron deficit in offspring exposed to maternal diabetes, yet are limited to models of severe hyperglycaemia which do not reflect the typical clinical condition and which are associated with foetal growth restriction that may confound nephron endowment. We aimed to assess renal morphology and function in offspring of leptin receptor deficient mice (Leprdb /+) and hypothesized that exposure to impaired maternal glucose tolerance (IGT) would be detrimental to the developing kidney. METHODS: Nephron endowment was assessed in offspring of C57BKS/J Leprdb /+ and +/+ mice at embryonic day (E)18 and postnatal day (PN)21 using design-based stereology. Transcutaneous measurement of renal function and total glomerular volume were assessed in 6-month-old offspring. Only +/+ offspring of Leprdb /+ dams were analysed. RESULTS: Compared with +/+ dams, Leprdb /+ dams had a 20% and 35% decrease in glucose tolerance prior to pregnancy and at E17.5 respectively. Offspring of IGT Leprdb /+ dams had approximately 15% fewer nephrons at E18.5 and PN21 than offspring of +/+ dams. There was no difference in offspring bodyweight. Despite normal renal function, total glomerular volume was 13% greater in 6-month-old offspring of IGT Leprdb /+ dams than in +/+ offspring. CONCLUSIONS: IGT throughout gestation resulted in a nephron deficit that was established early in renal development. Maternal IGT was associated with glomerular hypertrophy in adult offspring, likely a compensatory response to maintain normal renal function. Given the increasing prevalence of IGT, monitoring glucose from early in gestation may be important to prevent altered kidney morphology. Copyright © 2016 John Wiley & Sons, Ltd.

Podocyte Number in Children and Adults: Associations with Glomerular Size and Numbers of Other Glomerular Resident Cells.

Increases in glomerular size occur with normal body growth and in many pathologic conditions. In this study, we determined associations between glomerular size and numbers of glomerular resident cells, with a particular focus on podocytes. Kidneys from 16 male Caucasian-Americans without overt renal disease, including 4 children (≤3 years old) to define baseline values of early life and 12 adults (≥18 years old), were collected at autopsy in Jackson, Mississippi. We used a combination of immunohistochemistry, confocal microscopy, and design-based stereology to estimate individual glomerular volume (IGV) and numbers of podocytes, nonepithelial cells (NECs; tuft cells other than podocytes), and parietal epithelial cells (PECs). Podocyte density was calculated. Data are reported as medians and interquartile ranges (IQRs). Glomeruli from children were small and contained 452 podocytes (IQR=335-502), 389 NECs (IQR=265-498), and 146 PECs (IQR=111-206). Adult glomeruli contained significantly more cells than glomeruli from children, including 558 podocytes (IQR=431-746; P<0.01), 1383 NECs (IQR=998-2042; P<0.001), and 367 PECs (IQR=309-673; P<0.001). However, large adult glomeruli showed markedly lower podocyte density (183 podocytes per 10(6) µm(3)) than small glomeruli from adults and children (932 podocytes per 10(6) µm(3); P<0.001). In conclusion, large adult glomeruli contained more podocytes than small glomeruli from children and adults, raising questions about the origin of these podocytes. The increased number of podocytes in large glomeruli does not match the increase in glomerular size observed in adults, resulting in relative podocyte depletion. This may render hypertrophic glomeruli susceptible to pathology.

MRI-based glomerular morphology and pathology in whole human kidneys.

Nephron number (N(glom)) and size (V(glom)) are correlated with risk for chronic cardiovascular and kidney disease and may be predictive of renal allograft viability. Unfortunately, there are no techniques to assess N(glom) and V(glom) in intact kidneys. This work demonstrates the use of cationized ferritin (CF) as a magnetic resonance imaging (MRI) contrast agent to measure N(glom) and V(glom) in viable human kidneys donated to science. The kidneys were obtained from patients with varying levels of cardiovascular and renal disease. CF was intravenously injected into three viable human kidneys. A fourth control kidney was perfused with saline. After fixation, immunofluorescence and electron microscopy confirmed binding of CF to the glomerulus. The intact kidneys were imaged with three-dimensional MRI and CF-labeled glomeruli appeared as punctate spots. Custom software identified, counted, and measured the apparent volumes of CF-labeled glomeruli, with an ~6% false positive rate. These measurements were comparable to stereological estimates. The MRI-based technique yielded a novel whole kidney distribution of glomerular volumes. Histopathology demonstrated that the distribution of CF-labeled glomeruli may be predictive of glomerular and vascular disease. Variations in CF distribution were quantified using image texture analyses, which be a useful marker of glomerular sclerosis. This is the first report of direct measurement of glomerular number and volume in intact human kidneys.

Embryo transfer cannot delineate between the maternal pregnancy environment and germ line effects in the transgenerational transmission of disease in rats.

Adverse conditions in utero can have transgenerational effects, in the absence of a subsequent insult. We aimed to investigate the contribution of the maternal pregnancy environment vs. germ line effects in mediating alterations to cardiorenal and metabolic physiology in offspring from mothers born small. Uteroplacental insufficiency was induced by bilateral uterine artery and vein ligation (Restricted group) or sham surgery (Control group) in Wistar-Kyoto rats. Restricted and control female offspring (F1) were mated with either breeder males (embryo donor) or vasectomized males (embryo recipient). Embryo transfer was performed at embryonic day (E) 1, whereby second-generation (F2) embryos gestated (donor-in-recipient) in either a control (Cont-in-Cont, Rest-in-Cont) or restricted (Cont-in-Rest, Rest-in-Rest) mother. In male and female offspring, glomerular number and size were measured at postnatal day (PN) 35, and systolic blood pressure, glucose control, insulin sensitivity, and pancreatic ß-cell mass were measured in separate sibling cohorts at 6 mo. Rest-in-Rest offspring were hypothesized to have similar characteristics (reduced growth, altered metabolic control, and hypertension) to non-embryo-transferred Rest, such that embryo transfer would not be a confounding experimental influence. However, embryo-transferred Rest-in-Rest offspring underwent accelerated growth during the peripubertal phase, followed by slowed growth between 2 and 3 mo of age compared with non-embryo-transferred Rest groups. Furthermore, renal function and insulin response to a glucose load were different to respective non-embryo-transferred groups. Our data demonstrate the long-term effects of in vitro embryo manipulation, which confounded the utility of this approach in delineating between the maternal pregnancy environment and germ line effects that drive transgenerational outcomes.

Why and how we determine nephron number.

The total number of glomeruli (nephrons) in a kidney is an important microanatomical parameter for at least three reasons: it provides an index of the success/extent of nephrogenesis and can thereby provide insights into the roles of specific genes and feto-maternal environmental factors in nephrogenesis; low nephron number has been linked to an increased risk of cardiovascular and renal disease in adulthood; and knowledge of quantitative kidney microanatomy can illuminate our understanding of physiological mechanisms in health and disease. A range of methods has been used to count glomeruli in kidneys over the past 100 years, with design-based stereology (the physical disector/fractionator combination) considered the gold standard. However, this approach is labor-intensive and expensive, and therefore is not utilized by most laboratories. A new method for counting and sizing every glomerulus in the kidney has recently been described. This method involves in vivo labeling of glomeruli with cationic ferritin, and then magnetic resonance imaging (MRI) of the ex vivo kidney. Values are obtained in one sixth of the time of disector-based approaches. This new MRI method holds great promise for studies of glomerular number and size ex vivo and in vivo.

Transgenerational programming of fetal nephron deficits and sex-specific adult hypertension in rats.

A developmental insult that restricts growth in the first generation has the potential to program disease in subsequent generations. The aim of this study was to ascertain transgenerational growth and cardio-renal effects, via the maternal line, in a rat model of utero-placental insufficiency. Bilateral uterine vessel ligation or sham surgery (offspring termed first generation; F1 Restricted and Control, respectively) was performed in WKY rats. F1 Restricted and Control females were mated with normal males to produce second generation (F2) offspring (Restricted and Control) studied from fetal (embryonic Day 20) to adult (12 months) life. F2 Restricted male and female fetuses had reduced (P<0.05) nephron number (down 15-22%) but this deficit was not sustained postnatally and levels were similar to Controls at Day 35. F2 Restricted males, but not females, developed elevated (+16mmHg, P<0.05) systolic blood pressure at 6 months of age, which was sustained to 9 months. This was not explained by alterations to intra-renal or plasma components of the renin-angiotensin system. In a rat model of utero-placental insufficiency, we report alterations to F2 kidney development and sex-specific adult hypertension. This study demonstrates that low birthweight can have far-reaching effects that extend into the next generation.

Podocyte number and glomerulosclerosis indices are associated with the response to therapy for primary focal segmental glomerulosclerosis.

Corticosteroid therapy, often in combination with inhibition of the renin-angiotensin system, is first-line therapy for primary focal and segmental glomerulosclerosis (FSGS) with nephrotic-range proteinuria. However, the response to treatment is variable, and therefore new approaches to indicate the response to therapy are required. Podocyte depletion is a hallmark of early FSGS, and here we investigated whether podocyte number, density and/or size in diagnostic biopsies and/or the degree of glomerulosclerosis could indicate the clinical response to first-line therapy. In this retrospective single center cohort study, 19 participants (13 responders, 6 non-responders) were included. Biopsies obtained at diagnosis were prepared for analysis of podocyte number, density and size using design-based stereology. Renal function and proteinuria were assessed 6 months after therapy commenced. Responders and non-responders had similar levels of proteinuria at the time of biopsy and similar kidney function. Patients who did not respond to treatment at 6 months had a significantly higher percentage of glomeruli with global sclerosis than responders (p < 0.05) and glomerulosclerotic index (p < 0.05). Podocyte number per glomerulus in responders was 279 (203-507; median, IQR), 50% greater than that of non-responders (186, 118-310; p < 0.05). These findings suggest that primary FSGS patients with higher podocyte number per glomerulus and less advanced glomerulosclerosis are more likely to respond to first-line therapy at 6 months. A podocyte number less than approximately 216 per glomerulus, a GSI greater than 1 and percentage global sclerosis greater than approximately 20% are associated with a lack of response to therapy. Larger, prospective studies are warranted to confirm whether these parameters may help inform therapeutic decision making at the time of diagnosis of primary FSGS.

Nephron deficit and low podocyte density increase risk of albuminuria and glomerulosclerosis in a model of diabetes.

Podocytes are terminally differentiated epithelial cells in glomeruli. Podocyte injury and loss are features of many diseases leading to chronic kidney disease (CKD). The developmental origins of health and disease hypothesis propose an adverse intrauterine environment can lead to CKD later in life, especially when a second postnatal challenge is experienced. The aim of this study was to examine whether a suboptimal maternal environment would result in reduced podocyte endowment, increasing susceptibility to diabetes-induced renal injury. Female C57BL/6 mice were fed a low protein diet (LPD) to induce growth restriction or a normal protein diet (NPD) from 3 weeks before mating until weaning (postnatal Day 21, P21) when nephron and podocyte endowment were assessed in one male and one female offspring per litter. Littermates were administered streptozotocin or vehicle at 6 weeks of age. Urinary albumin excretion, glomerular size, and podometrics were assessed following 18 weeks of hyperglycemia. LPD offspring were growth restricted and had lower nephron and podocyte number at P21. However, by 24 weeks the podocyte deficit was no longer evident and despite low nephron endowment neither albuminuria nor glomerulosclerosis were observed. Podocyte number was unaffected by 18 weeks of hyperglycemia in NPD and LPD offspring. Diabetes increased glomerular volume reducing podocyte density, with more pronounced effects in LPD offspring. LPD and NPD diabetic offspring developed mild albuminuria with LPD demonstrating an earlier onset. LPD offspring also developed glomerular pathology. These findings indicate that growth-restricted LPD offspring with low nephron number and normalized podocyte endowment were more susceptible to alterations in glomerular volume and podocyte density leading to more rapid onset of albuminuria and renal injury than NPD offspring.

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 (Pdiet < 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 (Pdiet < 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.

The molecular and cellular anatomy of a fetal programming defect - the impact of low protein diet on the developing kidney.

Low nephron number correlates with the development of hypertension and chronic kidney disease later in life. While intrauterine growth restriction caused by maternal low protein diet (LPD) is thought to be a significant cause of reduced nephron endowment in impoverished communities, its influence on the cellular and molecular processes which drive nephron formation are poorly understood. We conducted a comprehensive characterization of the impact of LPD on kidney development using tomographic and confocal imaging to quantify changes in branching morphogenesis and the cellular and morphological features of nephrogenic niches across development. These analyses were paired with single-cell RNA sequencing to dissect the transcriptional changes that LPD imposes during renal development. Differences in the expression of genes involved in metabolism were identified in most cell types we analyzed, yielding imbalances and shifts in cellular energy production. We further demonstrate that LPD impedes branching morphogenesis and significantly reduces the number of pretubular aggregates - the initial precursors to nephron formation. The most striking observation was that LPD changes the developmental trajectory of nephron progenitor cells, driving the formation of a partially committed cell population which likely reflects a failure of cells to commit to nephron formation and which ultimately reduces endowment. This unique profile of a fetal programming defect demonstrates that low nephron endowment arises from the pleiotropic impact of changes in branching morphogenesis and nephron progenitor cell commitment, the latter of which highlights a critical role for nutrition in regulating the cell fate decisions underpinning nephron endowment. Significance Statement: While a mother's diet and behavior can negatively impact the number of nephrons in the kidneys of her offspring, the root cellular and molecular drivers of these deficits have not been rigorously explored. In this study we use advanced imaging and gene expression analysis in mouse models to define how a maternal low protein diet, analogous to that of impoverished communities, results in reduced nephron endowment. We find that low protein diet has pleiotropic effects on metabolism and the normal programs of gene expression. These profoundly impact the process of branching morphogenesis necessary to establish niches for nephron generation and change cell behaviors which regulate how and when nephron progenitor cells commit to differentiation.