Incubation of metanephroi with vitamin d(3) increases numbers of glomeruli

Overlap of vitamin A and vitamin D target genes with CAKUT-related processes

Congenital Anomalies of the Kidney and Urinary Tract (CAKUT) are a group of abnormalities affecting the kidneys and their outflow tracts. CAKUT patients display a large clinical variability as well as a complex aetiology. Only 5% to 20% of the cases have a monogenic origin. It is thereby suspected that interactions of both genetic and environmental factors contribute to the disease. Vitamins are among the environmental factors that are considered for CAKUT aetiology. In this study, we aimed to investigate whether vitamin A or vitamin D could have a role in CAKUT aetiology. For this purpose we collected vitamin A and vitamin D target genes and computed their overlap with CAKUT-related gene sets. We observed limited overlap between vitamin D targets and CAKUT-related gene sets. We however observed that vitamin A target genes significantly overlap with multiple CAKUT-related gene sets, including CAKUT causal and differentially expressed genes, and genes involved in renal system development. Overall, these results indicate that an excess or deficiency of vitamin A might be relevant to a broad range of urogenital abnormalities.

Overlap of vitamin A and vitamin D target genes with CAKUT-related processes

Congenital Anomalies of the Kidney and Urinary Tract (CAKUT) are a group of abnormalities affecting the kidneys and their outflow tracts. CAKUT patients display a large clinical variability as well as a complex aetiology. Only 5% to 20% of the cases have a monogenic origin. It is thereby suspected that interactions of both genetic and environmental factors contribute to the disease. Vitamins are among the environmental factors that are considered for CAKUT aetiology. In this study, we aimed to investigate whether vitamin A or vitamin D could have a role in CAKUT aetiology. For this purpose we collected vitamin A and vitamin D target genes and computed their overlap with CAKUT-related gene sets. We observed limited overlap between vitamin D targets and CAKUT-related gene sets. We however observed that vitamin A target genes significantly overlap with multiple CAKUT-related gene sets, including CAKUT causal and differentially expressed genes, and genes involved in renal system development. Overall, these results indicate that an excess or deficiency of vitamin A might be relevant to a broad range of urogenital abnormalities.

Programming of Renal Development and Chronic Disease in Adult Life

Chronic kidney disease (CKD) can have an insidious onset because there is a gradual decline in nephron number throughout life. There may be no overt symptoms of renal dysfunction until about two thirds or more of the nephrons have been destroyed and glomerular filtration rate (GFR) falls to below 25% of normal (often in mid-late life) (Martinez-Maldonaldo et al., 1992). Once End Stage Renal Disease (ESRD) has been reached, survival depends on renal replacement therapy (RRT). CKD causes hypertension and cardiovascular disease; and hypertension causes CKD. Albuminuria is also a risk factor for cardiovascular disease. The age of onset of CKD is partly determined during fetal life. This review describes the mechanisms underlying the development of CKD in adult life that results from abnormal renal development caused by an adverse intrauterine environment. The basis of this form of CKD is thought to be mainly due to a reduction in the number of nephrons formed in utero which impacts on the age dependent decline in glomerular function. Factors that affect the risk of reduced nephron formation during intrauterine life are discussed and include maternal nutrition (malnutrition and obesity, micronutrients), smoking and alcohol, use of drugs that block the maternal renin-angiotensin system, glucocorticoid excess and maternal renal dysfunction and prematurity. Since CKD, hypertension and cardiovascular disease add to the disease burden in the community we recommend that kidney size at birth should be recorded using ultrasound and those individuals who are born premature or who have small kidneys at this time should be monitored regularly by determining GFR and albumin:creatinine clearance ratio. Furthermore, public health measures aimed at limiting the prevalence of obesity and diabetes mellitus as well as providing advice on limiting the amount of protein ingested during a single meal, because they are all associated with increased glomerular hyperfiltration and subsequent glomerulosclerosis would be beneficial.

Maternal vitamin D deficiency programmes adult renal renin gene expression and renal function

Renin is essential for renal development and in adult kidneys vitamin D deficiency increases renin gene expression. We aimed to determine whether maternal vitamin D deficiency upregulates fetal renal renin expression, and if this is sustained. We also examined growth and the long-term renal effects in offspring on a normal diet. Female Sprague–Dawley rats in UVB-free housing were fed either vitamin D deficient chow (DEF) or normal chow from 4 weeks and mated with vitamin D replete males at 10 weeks. Fetuses were collected at E20 or dams littered and the pups were weaned onto normal chow. Kidney mRNA levels for renin, (pro)renin receptor [(P)RR], transforming growth factor β 1 (TGF-β1), and nephrin were determined in E20 fetuses and in male offspring at 38 weeks. Renal function was assessed at 33 weeks (24 h, metabolic cage) in both sexes. Renal mRNA expression was upregulated for renin in fetuses (P< 0.05) and was almost doubled in adult male offspring from DEF dams (P< 0.05). Adult males had reduced creatinine clearance, solute excretion and a suppressed urinary sodium-to-potassium ratio (P< 0.05). Female adult DEF offspring drank more and excreted more urine (P< 0.05) but creatinine clearance was not impaired. We conclude that maternal vitamin D depletion upregulates fetal renal renin gene expression and this persists into adulthood where, in males only, there is evidence of sodium retention and compromised renal function. Importantly these effects occurred despite the animals being on a normal diet from the time of weaning onwards.

A novel, low-volume method for organ culture of embryonic kidneys that allows development of cortico-medullary anatomical organization

Here, we present a novel method for culturing kidneys in low volumes of medium that offers more organotypic development compared to conventional methods. Organ culture is a powerful technique for studying renal development. It recapitulates many aspects of early development very well, but the established techniques have some disadvantages: in particular, they require relatively large volumes (1–3 mls) of culture medium, which can make high-throughput screens expensive, they require porous (filter) substrates which are difficult to modify chemically, and the organs produced do not achieve good cortico-medullary zonation. Here, we present a technique of growing kidney rudiments in very low volumes of medium–around 85 microliters–using silicone chambers. In this system, kidneys grow directly on glass, grow larger than in conventional culture and develop a clear anatomical cortico-medullary zonation with extended loops of Henle.

Xenotransplantation of pancreatic and kidney primordia-where do we stand?

Lack of donor availability limits the number of human donor organs. The need for host immunosuppression complicates transplantation procedures. It is possible to 'grow' new pancreatic tissue or kidneys in situ via xenotransplantation of organ primordia from animal embryos (organogenesis of the endocrine pancreas or kidney). The developing organ attracts its blood supply from the host, enabling the transplantation of pancreas or kidney in 'cellular' form obviating humoral rejection. In the case of pancreas, selective development of endocrine tissue takes place in post-transplantation. In the case of kidney, an anatomically-correct functional organ differentiates in situ. Glucose intolerance can be corrected in formerly diabetic rats and ameliorated in rhesus macaques on the basis of porcine insulin secreted in a glucose-dependent manner by beta cells originating from transplants. Primordia engraft and function after being stored in vitro prior to implantation. If obtained within a 'window' early during embryonic pancreas development, pig pancreatic primordia engraft in non immune suppressed diabetic rats or rhesus macaques. Engraftment of pig renal primordia transplanted directly into rats requires host immune suppression. However, embryonic rat kidneys into which human mesenchymal cells are incorporated into nephronic elements can be transplanted into non-immune suppressed rat hosts. Here we review recent findings germane to xenotransplantation of pancreatic or renal primordia as a novel organ replacement strategy.

Vitamin D deficiency during pregnancy and lactation stimulates nephrogenesis in rat offspring

There is increasing evidence of vitamin D insufficiency in women of child-bearing age and their infants. This study examined the effect of maternal vitamin D deficiency on nephron endowment in rat offspring (n=7 per group). Sprague-Dawley dams were fed either a vitamin D deplete diet or a vitamin replete (control) diet prior to pregnancy, during pregnancy and throughout lactation. At 4 weeks of age the offspring were weaned and maintained on their respective diets until they were killed at 7 weeks. In the fixed right kidney, kidney volume, renal corpuscle volume and nephron number were stereologically determined. There was no difference between groups in body weight, kidney weight or kidney volume. There was a significant 20% increase in nephron number in kidneys of vitamin D deplete offspring (vitamin D deficient, 29,000+/-1,858, control, 23,330+/-1,828; P=0.04). This was accompanied by a significant decrease in renal corpuscle size in the vitamin D deplete group compared with the controls (6.125+/-0.576 x 10(-4) mm(3) and 8.178+/-0.247 x 10(-4) mm(3), respectively; P=0.03). We concluded that maternal vitamin D deficiency in rats appears to stimulate nephrogenesis. Whether this confers a renal functional advantage or not is unknown.

Transplantation of renal primordia: renal organogenesis

Dialysis and allotransplantation of human kidneys represent effective therapies to replace kidney function, but the former replaces only a small component of renal function, and the latter is limited by lack of organ availability. Xenotransplantation of whole kidneys from nonprimate donors is complicated by humoral and severe cellular rejection. The use of individual cells or groups of cells to repair damaged tissue (cellular therapies) offers an alternative for renal tissue replacement. However, recapitulation of complex functions such glomerular filtration and reabsorption and secretion of solutes that are dependent on a three-dimensionally integrated kidney structure are beyond the scope of most cellular replacement therapies. The use of nonvascularized embryonic renal primordia for transplantation circumvents humoral rejection of xenogeneic tissue and ameliorates cellular rejection. Renal primordia are preprogrammed to attract a vasculature and differentiate into a kidney and in this manner undergo organogenesis after transplantation into the mesentery of hosts. Here we review a decade's progress in renal organogenesis.