Impaired oxygen supply to the fetus is a common complication of pregnancy which is associated with reduced blood flow to the fetal kidney and reduced birth weight. The kidney is highly susceptible to an adverse intrauterine environment and a deficiency in the number of nephrons is associated with increased risk of hypertension and renal disease. Glomerular podocytes have a limited capacity to replicate under normal circumstances in mature animals, and the depletion of these cells is correlated with development of glomerulosclerosis and decreased renal function.
Neoadjuvant short-course radiotherapy was routinely applied for nonlocally advanced rectal cancer (cT1-3N0-1M0 with >1 mm distance to the mesorectal fascia) in the Netherlands following the Dutch total mesorectal excision trial. This policy has shifted toward selective application after guideline revision in 2014.
A range of perturbations to the maternal environment result in low nephron endowment in offspring, which is often linked to increased blood pressure and renal pathology in later life. Given that nephrogenesis in mammals ends shortly before or after birth, this nephron deficit is permanent. To date, very few studies have examined the morphology of nephrons in offspring born with low nephron endowment. Given the link between podocyte loss and glomerulosclerosis in adults, we examined whether maternal perturbations also result in low podocyte endowment in offspring, thereby rendering offspring at increased risk of adult disease. Three models of maternal perturbation were investigated: (1) gestational hypoxia in mice; (2) maternal low protein diet (LPD) in mice followed by postnatal hyperglycaemia; and (3) maternal low protein diet in rats followed by high fat feeding. Podocytes were counted at postnatal day 21 in whole glomeruli contained in tissue slices immunostained for specific podocyte markers, cleared and imaged with confocal microscopy. In all three models, total podocyte number per glomerulus was reduced in settings of maternal perturbation. In male mice exposed to hypoxia, podocyte endowment was 15% lower than controls (p<0.01), but no effect was observed in females; in male and female mouse LPD offspring, podocyte endowment was 15% (p<0.001) and 9% (p<0.05) lower than controls; and in male LPD rats (females were not studied), podocyte endowment was 15% (p<0.0001) lower than controls. This is the first report of developmental programming of low podocyte endowment. We have identified low podocyte endowment in two species, three models and both sexes. We are currently investigating whether this podocyte deficit is permanent, and the effects on renal function in later life.
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.
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.
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.
Fetal hypoxia is a common complication of pregnancy. We have previously reported that maternal hypoxia in late gestation in mice gives rise to male offspring with reduced nephron number, while females have normal nephron number. Male offspring later develop proteinuria and renal pathology, including glomerular pathology, whereas female offspring are unaffected. Given the central role of podocyte depletion in glomerular and renal pathology, we examined whether maternal hypoxia resulted in low podocyte endowment in offspring. Pregnant CD1 mice were allocated at embryonic day 14.5 to normoxic (21% oxygen) or hypoxic (12% oxygen) conditions. At postnatal day 21, kidneys from mice were immersion fixed, and one mid-hilar slice per kidney was immunostained with antibodies directed against p57 and synaptopodin for podocyte identification. Slices were cleared and imaged with a multiphoton microscope for podometric analysis. Male hypoxic offspring had significantly lower birth weight, nephron number, and podocyte endowment than normoxic male offspring (podocyte number; normoxic 62.86 ± 2.26 podocytes per glomerulus, hypoxic 53.38 ± 2.25; p < .01, mean ± SEM). In contrast, hypoxic female offspring had low birth weight but their nephron and podocyte endowment was the same as normoxic female offspring (podocyte number; normoxic 62.38 ± 1.86 podocytes per glomerulus, hypoxic 61.81 ± 1.80; p = .88). To the best of our knowledge, this is the first report of developmentally programmed low podocyte endowment. Given the well-known association between podocyte depletion in adulthood and glomerular pathology, we postulate that podocyte endowment may place offspring at risk of renal disease in adulthood, and explain the greater vulnerability of male offspring.
Chronic kidney disease (CKD) is a serious public health burden. A major risk factor for CKD is low birth weight, which programmes a low glomerular endowment. Podocytes are key components of the glomerulus and podocyte injury and loss has been linked to the development and progression of CKD. Given that both glomerular number and podocyte number play pivotal roles in the development of CKD we utilised a mouse model of low birth weight and low nephron number to investigate podocyte number in the early postnatal period and whether podocyte number is associated with increased risk of renal pathophysiology in adulthood.