Compensatory kidney growth in estrogen receptor-alpha null mice

The transcriptome of early compensatory kidney growth reveals cell and time specific responses

Following kidney removal, the remaining kidney enlarges and increases its function. The mechanism and signals driving this compensatory kidney hypertrophy and the enlargement of its constituent kidney cells remains elusive. RNA-seq studies in mice undergoing hypertrophy 24, 48, and 72 h following nephrectomy were undertaken to understand the early transcriptional changes. This revealed substantial enhancement of cholesterol biosynthesis pathways, increases in mitochondrial gene expression and cell cycle perturbations. Single nuclei RNA-seq delineated cell specific changes at 24 h post nephrectomy and showed that sterol binding protein 2 (SREBP2) activity increases in medullary thick ascending limb cells in keeping with promotion of cholesterol synthesis. Cultured renal tubular cells were examined for insulin-like growth factor-1 (IGF-1) stimulated hypertrophy and SREBP2 was found to be required for increase in cell size. This work describes the early cell specific growth pathways mediating cellular and kidney hypertrophy with an intriguing role for cholesterol synthesis.

Sex-specific molecular signature of mouse podocytes in homeostasis and in response to pharmacological challenge with rapamycin

BACKGROUND

Sex differences exist in the prevalence and progression of major glomerular diseases. Podocytes are the essential cell-type in the kidney which maintain the physiological blood-urine barrier, and pathological changes in podocyte homeostasis are critical accelerators of impairment of kidney function. However, sex-specific molecular signatures of podocytes under physiological and stress conditions remain unknown. This work aimed at identifying sexual dimorphic molecular signatures of podocytes under physiological condition and pharmacologically challenged homeostasis with mechanistic target of rapamycin (mTOR) inhibition. mTOR is a crucial regulator involved in a variety of physiological and pathological stress responses in the kidney and inhibition of this pathway may therefore serve as a general stress challenger to get fundamental insights into sex differences in podocytes.

METHODS

The genomic ROSAmT/mG-NPHS2 Cre mouse model was used which allows obtaining highly pure podocyte fractions for cell-specific molecular analyses, and vehicle or pharmacologic treatment with the mTOR inhibitor rapamycin was performed for 3 weeks. Subsequently, deep RNA sequencing and proteomics were performed of the isolated podocytes to identify intrinsic sex differences. Studies were supplemented with metabolomics from kidney cortex tissues.

RESULTS

Although kidney function and morphology remained normal in all experimental groups, RNA sequencing, proteomics and metabolomics revealed strong intrinsic sex differences in the expression levels of mitochondrial, translation and structural transcripts, protein abundances and regulation of metabolic pathways. Interestingly, rapamycin abolished prominent sex-specific clustering of podocyte gene expression and induced major changes only in male transcriptome. Several sex-biased transcription factors could be identified as possible upstream regulators of these sexually dimorphic responses. Concordant to transcriptomics, metabolomic changes were more prominent in males. Remarkably, high number of previously reported kidney disease genes showed intrinsic sexual dimorphism and/or different response patterns towards mTOR inhibition.

CONCLUSIONS

Our results highlight remarkable intrinsic sex-differences and sex-specific response patterns towards pharmacological challenged podocyte homeostasis which might fundamentally contribute to sex differences in kidney disease susceptibilities and progression. This work provides rationale and an in-depth database for novel targets to be tested in specific kidney disease models to advance with sex-specific treatment strategies.

Obesity and metabolic syndrome induce hyperfiltration, glomerulomegaly, and albuminuria in obese ovariectomized female mice and obese male mice

OBJECTIVE

Obese patients with metabolic syndrome have a high risk of chronic kidney disease. The prevalence of obesity, metabolic syndrome, and insulin resistance increase in women after menopause, as does the risk of chronic kidney disease. This may indicate an interaction between obesity, metabolic syndrome, and menopause in the induction of renal damage. However, the pathogenesis of kidney disease in postmenopausal obese women is poorly understood.

METHODS

We investigated the interaction of an obesogenic diet and menopause on renal dysfunction in ovariectomized and non-ovariectomized lean (n = 8 and 17) and obese (n = 12 and 20) female mice. Obese (n = 12) and lean (n = 10) male mice were also studied. Glucose metabolism, insulin resistance, and kidney function were evaluated with gold standards procedures. Changes in kidney histology and lipid deposition were analyzed. Females had a lower number of glomeruli than males at baseline.

RESULTS

Only female ovariectomized obese animals developed insulin resistance, hyperglycemia, and kidney damage, evidenced as glomerulomegaly, glomerular hyperfiltration, and increased urinary albumin excretion, despite a similar increase in weight than obese non-ovariectomized female mice. Male obese mice developed hyperglycemia, insulin resistance, and hyperfiltration without major renal histological changes. Males on high fat diet showed higher renal lipid content and females on high fat diet (ovariectomized or non-ovariectomized) showed higher total cholesterol content than males.

CONCLUSIONS

In mice, there is a clear interplay between obesity, metabolic syndrome, and menopause in the induction of kidney damage.

Causal Associations between Serum Urea and Cancer: A Mendelian Randomization Study

Urea is largely derived from the urea cycle reactions through hepatic detoxification of free ammonia and cleared by urination, and the serum urea level is a crucial medical indicator for measuring the kidney function in patients with nephropathy; however, investigative revelations pointing to the serum urea level as a risk factor for cancer are very scarce, and relevant studies are restricted by potential biases. We aimed to explore the causal relationships of the serum urea level with cancer development by focusing on renal cell carcinoma (RCC) using the Mendelian randomization (MR) analyses. Summary estimates were collected from the inverse-variance weighted (IVW) method based on six single nucleotide polymorphisms (SNPs). The selected SNPs related to the serum urea were obtained from a large genome-wide association study (GWAS) of 13,312 European participants. The summary statistics of RCC were also available from public databases (IARC, n = 5219 cases, n = 8011 controls). Sensitivity analyses included the weighted median and MR-Egger methods. Serum urea was inversely associated with RCC in females (effect = 1.93; 95% CI: 1.24 to 3.01; p = 0.004) but exhibited null association with RCC in males, breast cancer (BRCA) in both genders and prostate cancer (PCa) in males. Similar conclusions were also drawn from the weighted median and MR-Egger. These findings reveal an intriguing link between serum urea and cancer risks for the very first time. Without ambiguity, the serum urea is causatively related to RCC specifically in females, although the mechanism(s) by which urea is involved in RCC development remains to be experimentally/clinically investigated. Our studies may well provide novel insights for RCC diagnosis, intervention and/or therapy.

Estrogen and estrogen receptors in kidney diseases

Acute kidney injury (AKI) and chronic kidney disease (CKD) are posing great threats to global health within this century. Studies have suggested that estrogen and estrogen receptors (ERs) play important roles in many physiological processes in the kidney. For instance, they are crucial in maintaining mitochondrial homeostasis and modulating endothelin-1 (ET-1) system in the kidney. Estrogen takes part in the kidney repair and regeneration via its receptors. Estrogen also participates in the regulation of phosphorus homeostasis via its receptors in the proximal tubule. The ERα polymorphisms have been associated with the susceptibilities and outcomes of several renal diseases. As a consequence, the altered or dysregulated estrogen/ERs signaling pathways may contribute to a variety of kidney diseases, including various causes-induced AKI, diabetic kidney disease (DKD), lupus nephritis (LN), IgA nephropathy (IgAN), CKD complications, etc. Experimental and clinical studies have shown that targeting estrogen/ERs signaling pathways might have protective effects against certain renal disorders. However, many unsolved problems still exist in knowledge regarding the roles of estrogen and ERs in distinct kidney diseases. Further research is needed to shed light on this area and to enable the discovery of pathway-specific therapies for kidney diseases.

Comprehensive expression analysis of mRNA and microRNA for the investigation of compensatory mechanisms in the rat kidney after unilateral nephrectomy

Compensation is a physiological response that occurs during chemical exposure to maintain homeostasis. Because compensatory responses are not usually considered adverse effects, it is important to understand compensatory mechanisms for chemical risk assessment. Although the kidney is a major target organ for toxicity, there is controversy over whether hyperplasia or hypertrophy contributes to the compensatory mechanism, and there is limited information to apply for chemical risk assessment. In the present study, compensatory mechanisms of the kidney were investigated in a unilateral nephrectomy (UNx) model using adult male and female F344 rats. In residual kidneys of male and female rats after UNx, 5-bromo-2'-deoxyuridine-labeling indices and mRNA expression of cell cycle-related genes were increased, although there were no fluctuations in mRNA expression of transforming growth factor-β1, which contributes to hypertrophy in renal tubules. Pathway analysis using mRNA expression data from a complementary DNA (cDNA) microarray revealed that canonical pathways related to cell proliferation were mainly activated and that forkhead box M1 (FOXM1) was an upstream regulator of compensatory cell proliferation in residual kidneys of male and female rats. cDNA microarray for microRNAs (miRNAs) demonstrated that nine miRNAs were downregulated in residual kidneys, and mRNA/miRNA integrated analysis indicated that miRNAs were associated with the expression of factors downstream of FOXM1. Overall, these results suggested that FOXM1-mediated hyperplasia rather than hypertrophy contributed to compensatory mechanisms in the kidney and that miRNAs regulated downstream FOXM1 signaling. These results will be beneficial for evaluating nephrotoxicity in chemical risk assessment and for developing new biomarkers to predict nephrotoxicity.

TWEAK and the progression of renal disease: clinical translation

Tumour necrosis factor-like weak inducer of apoptosis (TWEAK) activates the fibroblast growth factor-inducible-14 (Fn14) receptor. TWEAK has actions on intrinsic kidney cells and on inflammatory cells of potential pathophysiological relevance. The effects of TWEAK in tubular cells have been explored in most detail. In cultured murine tubular cells TWEAK induces the expression of inflammatory cytokines, downregulates the expression of Klotho, is mitogenic, and in the presence of sensitizing agents promotes apoptosis. Similar actions were observed on glomerular mesangial cells. In vivo TWEAK actions on healthy kidneys mimic cell culture observations. Increased expression of TWEAK and Fn14 was reported in human and experimental acute and chronic kidney injury. The role of TWEAK/Fn14 in kidney injury has been demonstrated in non-inflammatory compensatory renal growth, acute kidney injury and chronic kidney disease of immune and non-immune origin, including hyperlipidaemic nephropathy, lupus nephritis (LN) and anti-GBM nephritis. The nephroprotective effect of TWEAK or Fn14 targeting in immune-mediated kidney injury is the result of protection from TWEAK-induced injury of renal intrinsic cells, not from interference with the immune response. A phase I dose-ranging clinical trial demonstrated the safety of anti-TWEAK antibodies in humans. A phase II randomized placebo-controlled clinical trial exploring the efficacy, safety and tolerability of neutralizing anti-TWEAK antibodies as a tissue protection strategy in LN is ongoing. The eventual success of this trial may expand the range of kidney diseases in which TWEAK targeting should be explored.

Classical estrogen receptors and ERα splice variants in the mouse

Estrogens exert a variety of effects in both reproductive and non-reproductive tissues. With the discovery of ERα splice variants, prior assumptions concerning tissue-specific estrogen signaling need to be re-evaluated. Accordingly, we sought to determine the expression of the classical estrogen receptors and ERα splice variants across reproductive and non-reproductive tissues of male and female mice. Western blotting revealed that the full-length ERα66 was mainly present in female reproductive tissues but was also found in non-reproductive tissues at lower levels. ERα46 was most highly expressed in the heart of both sexes. ERα36 was highly expressed in the kidneys and liver of female mice but not in the kidneys of males. ERβ was most abundant in non-reproductive tissues and in the ovaries. Because the kidney has been reported to be the most estrogenic non-reproductive organ, we sought to elucidate ER renal expression and localization. Immunofluorescence studies revealed ERα66 in the vasculature and the glomerulus. It was also found in the brush border of the proximal tubule and in the cortical collecting duct of female mice. ERα36 was evident in mesangial cells and tubular epithelial cells of both sexes, as well as podocytes of females but not males. ERβ was found primarily in the podocytes in female mice but was also present in the mesangial cells in both sexes. Within the renal cortex, ERα46 and ERα36 were mainly located in the membrane fraction although they were also present in the cytosolic fraction. Given the variability of expression patterns demonstrated herein, identification of the specific estrogen receptors expressed in a tissue is necessary for interpreting estrogenic effects. As this study revealed expression of the ERα splice variants at multiple sites within the kidney, further studies are warranted in order to elucidate the contribution of these receptors to renal estrogen responsiveness.

Sexual dimorphism: the aging kidney, involvement of nitric oxide deficiency, and angiotensin II overactivity

Females develop less age-dependent loss of renal function, which may be in part due to cardiorenal protective effects of estrogens. The impact of androgen level on cardiovascular-renal health is controversial. Estrogen acts through multiple mechanisms, sometimes beneficial, sometimes damaging, which makes it difficult to predict the effect of hormone replacement therapy (HRT) in an aging population. Nitric oxide (NO) deficiency occurs in aging and contributes to age-dependent cardiovascular risk and kidney damage. The increased oxidative stress of aging has effects at multiple sites in the NO biosynthetic pathway to lower NO production/action. Loss of NO together with activated angiotensin promotes some of the decrements in cardiovascular-renal function seen with age, which may be related to actions of the sex steroids.

Functions and physiological roles of two types of estrogen receptors, ERα and ERβ, identified by estrogen receptor knockout mouse

Estrogens, a class of steroid hormones, regulate the growth, development, and physiology of the human reproductive system. Estrogens also involve in the neuroendocrine, skeletal, adipogenesis, and cardiovascular systems. Estrogen signaling pathways are selectively stimulated or inhibited depending on a balance between the activities of estrogen receptor (ER) α or ERβ in target organs. ERs belong to the steroid hormone superfamily of nuclear receptors, which act as transcription factors after binding to estrogen. The gene expression regulation by ERs is to modulate biological activities, such as reproductive organ development, bone modeling, cardiovascular system functioning, metabolism, and behavior in both females and males. Understanding of the general physiological roles of ERs has been gained when estrogen levels were ablated by ovariectomy and then replenished by treatment with exogenous estrogen. This technique is not sufficient to fully determine the exact function of estrogen signaling in general processes in living tissues. However, a transgenic mouse model has been useful to study gene-specific functions. ERα and ERβ have different biological functions, and knockout and transgenic animal models have distinct phenotypes. Analysis of ERα and ERβ function using knockout mouse models has identified the roles of estrogen signaling in general physiologic processes. Although transgenic mouse models do not always produce consistent results, they are the useful for studying the functions of these genes under specific pathological conditions.

Estrogen receptor alpha expression in podocytes mediates protection against apoptosis in-vitro and in-vivo

CONTEXT/OBJECTIVE

Epidemiological studies have demonstrated that women have a significantly better prognosis in chronic renal diseases compared to men. This suggests critical influences of gender hormones on glomerular structure and function. We examined potential direct protective effects of estradiol on podocytes.

METHODS

Expression of estrogen receptor alpha (ERα) was examined in podocytes in vitro and in vivo. Receptor localization was shown using Western blot of separated nuclear and cytoplasmatic protein fractions. Podocytes were treated with Puromycin aminonucleoside (PAN, apoptosis induction), estradiol, or both in combination. Apoptotic cells were detected with Hoechst nuclear staining and Annexin-FITC flow cytometry. To visualize mitochondrial membrane potential depolarization as an indicator for apoptosis, cells were stained with tetramethyl rhodamine methylester (TMRM). Estradiol-induced phosphorylation of ERK1/2 and p38 MAPK was examined by Western blot. Glomeruli of ERα knock-out mice and wild-type controls were analysed by histomorphometry and immunohistochemistry.

RESULTS

ERα was consistently expressed in human and murine podocytes. Estradiol stimulated ERα protein expression, reduced PAN-induced apoptosis in vitro by 26.5±24.6% or 56.6±5.9% (flow cytometry or Hoechst-staining, respectively; both p<0.05), and restored PAN-induced mitochondrial membrane potential depolarization. Estradiol enhanced ERK1/2 phosphorylation. In ERα knockout mice, podocyte number was reduced compared to controls (female/male: 80/86 vs. 132/135 podocytes per glomerulus, p<0.05). Podocyte volume was enhanced in ERα knockout mice (female/male: 429/371 µm(3) vs. 264/223 µm(3) in controls, p<0.05). Tgfβ1 and collagen type IV expression were increased in knockout mice, indicating glomerular damage.

CONCLUSIONS

Podocytes express ERα, whose activation leads to a significant protection against experimentally induced apoptosis. Possible underlying mechanisms include stabilization of mitochondrial membrane potential and activation of MAPK signalling. Characteristic morphological changes indicating glomerulopathy in ERα knock-out mice support the in vivo relevance of the ERα for podocyte viability and function. Thus, our findings provide a novel model for the protective influence of female gender on chronic glomerular diseases.

Gender-dependent effects of aging on the kidney

It is well known that the kidney plays an important role in the development of cardiovascular diseases such as hypertension. The normal aging process leads to changes in kidney morphology, hemodynamics and function, which increase the incidence of cardiovascular events in the elderly population. These disturbances are influenced by several factors, including gender. In general, females are protected by the effects of estrogens on the cardiorenal system. Several studies have demonstrated the beneficial effects of estrogens on renal function in the elderly; however, the relationships between androgens and kidney health during one's lifetime are not well understood. Sex steroids have many complex actions, and the decline in their levels during aging clearly influences kidney function, decreases the renal reserve and facilitates the development of cardiovascular disorders. Therefore, in this review, we discuss the cellular, biochemical, and molecular mechanisms by which sex hormones may influence renal function during the aging process.

TWEAK, a multifunctional cytokine in kidney injury

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) is a cytokine of the TNF superfamily that activates the Fn14 receptor. TWEAK may regulate cell proliferation, cell death, cell differentiation, and inflammation. TWEAK and Fn14 are constitutively present in the kidney. Sources of TWEAK and Fn14 include intrinsic renal cells and infiltrating leukocytes. Basal Fn14 expression is low, but Fn14 is greatly upregulated during kidney injury. TWEAK contributes to kidney inflammation promoting chemokine secretion by renal cells through canonical and non-canonical NFκB activation. TWEAK also promotes tubular cell proliferation. However, TWEAK induces mesangial and tubular cell apoptosis under proinflammatory conditions. These data indicate that TWEAK is a multifunctional cytokine in the kidney, the actions of which are modulated by the cell microenvironment. Confirmation of the role of TWEAK in kidney injury came from functional studies in experimental animal models. The TWEAK/Fn14 pathway contributed to cell death and interstitial inflammation during acute kidney injury, to glomerular injury in lupus nephritis, to hyperlipidemia-associated kidney injury, and to tubular cell hyperplasia following unilateral nephrectomy. Circulating soluble TWEAK (sTWEAK) levels are a potential biomarker of adverse outcomes in chronic kidney disease and urinary sTWEAK is a potential biomarker of lupus nephritis activity. The available evidence suggests that TWEAK may provide diagnostic information and be a therapeutic target in renal injury. Its role in human kidney disease should be further explored.

TNF superfamily: a growing saga of kidney injury modulators

Members of the TNF superfamily participate in kidney disease. Tumor necrosis factor (TNF) and Fas ligand regulate renal cell survival and inflammation, and therapeutic targeting improves the outcome of experimental renal injury. TNF-related apoptosis-inducing ligand (TRAIL and its potential decoy receptor osteoprotegerin are the two most upregulated death-related genes in human diabetic nephropathy. TRAIL activates NF-kappaB in tubular cells and promotes apoptosis in tubular cells and podocytes, especially in a high-glucose environment. By contrast, osteoprotegerin plays a protective role against TRAIL-induced apoptosis. Another family member, TNF-like weak inducer of apoptosis (TWEAK induces inflammation and tubular cell death or proliferation, depending on the microenvironment. While TNF only activates canonical NF-kappaB signaling, TWEAK promotes both canonical and noncanonical NF-kappaB activation in tubular cells, regulating different inflammatory responses. TWEAK promotes the secretion of MCP-1 and RANTES through NF-kappaB RelA-containing complexes and upregulates CCl21 and CCL19 expression through NF-kappaB inducing kinase (NIK-) dependent RelB/NF-kappaB2 complexes. In vivo TWEAK promotes postnephrectomy compensatory renal cell proliferation in a noninflammatory milieu. However, in the inflammatory milieu of acute kidney injury, TWEAK promotes tubular cell death and inflammation. Therapeutic targeting of TNF superfamily cytokines, including multipronged approaches targeting several cytokines should be further explored.

Sexual dimorphism, the aging kidney, and involvement of nitric oxide deficiency

Females develop less age-dependent loss of renal function, in part because of cardiorenal protective effects of estrogens. The low androgen level in women also may be protective, although the animal and clinical data are controversial. Both estrogen and androgens act through multiple mechanisms, sometimes beneficial, sometimes damaging, which makes it difficult to predict the impact of hormone replacement therapy in an aging population. Nitric oxide (NO) deficiency contributes to age-dependent cardiovascular risk and kidney damage in animal models. The increased oxidative stress of aging impacts at multiple sites in the NO biosynthetic pathway to decrease NO production/action. Endothelial dysfunction develops with aging and is delayed in women, in association with a delayed increase in asymmetric dimethylarginine. Animal data suggest that the aging kidney develops NO deficiency because of changes in the neuronal NO synthase. Relative preservation of NO production in females contributes to the better cardiovascular and renal responses to aging.

Sexual dimorphism in the aging kidney: differences in the nitric oxide system

Females-both rats and women-are substantially protected against the age-dependent decrease in renal function that occurs in males of the species. In part, this finding reflects the cardioprotective and renoprotective effects of estrogens, but estrogen has multiple actions, not all of which are beneficial. In addition, the low androgen level in women might be protective against a decline in renal function, but animal and clinical data on possible adverse effects of androgens are controversial. Androgens also have multiple actions, one of which-aromatization to estrogen-is likely to be protective. Sex steroids clearly have many complex actions, which explains the conflicting information on their relative benefits and dangers. Endothelial nitric oxide (NO) deficiency contributes importantly to cardiovascular risk and intrarenal NO deficiency is clearly linked to chronic kidney disease progression in animal models. Endothelial dysfunction develops with increasing age but is delayed in females, correlating with a delayed rise in asymmetric dimethylarginine level. There is no clear link between aging and arginine (the NO synthase substrate) deficiency. Animal data suggest that the aging kidney develops NO deficiency as a result of changes in neuronal NO synthase. The increased oxidative stress that occurs with aging affects multiple stages of the NO biosynthetic pathway and results in decreased production and/or action of NO. NO production is better preserved in females than in males, partly as a result of the actions of estrogens.

Tweak induces proliferation in renal tubular epithelium: a role in uninephrectomy induced renal hyperplasia

The tumour necrosis factor (TNF) family member TWEAK activates the Fn14 receptor and has pro-apoptotic, proliferative and pro-inflammatory actions that depend on the cell type and the microenvironment. We explored the proliferative actions of TWEAK on cultured tubular cells and in vivo on renal tubules. Additionally, we studied the role of TWEAK in compensatory proliferation following unilateral nephrectomy and in an inflammatory model of acute kidney injury (AKI) induced by a folic acid overdose. TWEAK increased the proliferation, cell number and cyclin D1 expression of cultured tubular cells, in vitro. Exposure to serum increased TWEAK and Fn14 expression and the proliferative response to TWEAK. TWEAK activated the mitogen-activated protein kinases ERK and p38, the phosphatidyl-inositol 3-kinase (PI3K)/Akt pathway and NF-κB. TWEAK-induced proliferation was prevented by inhibitors of these protein kinases and by the NF-κB inhibitor parthenolide. TWEAK-induced tubular cell proliferation as assessed by PCNA and cyclin D1 expression in the kidneys of adult healthy mice in vivo. By contrast, TWEAK knock-out mice displayed lower tubular cell proliferation in the remnant kidney following unilateral nephrectomy, a non-inflammatory model. This is consistent with TWEAK-induced proliferation on cultured tubular cells in the absence of inflammatory cytokines. Consistent with our previously published data, in the presence of inflammatory cytokines TWEAK promoted apoptosis, not proliferation, of cultured tubular cells. In this regard, TWEAK knock-out mice with AKI displayed less tubular apoptosis and proliferation, as well as improved renal function. In conclusion, TWEAK actions in tubular cells are context dependent. In a non-inflammatory milieu TWEAK induces proliferation of tubular epithelium. This may be relevant for compensatory renal hyperplasia following nephrectomy.

Estrogen receptors in the kidney: lessons from genetically altered mice

BACKGROUND

Sex differences in human and animal models of kidney disease suggest that estrogen receptor (ER)-mediated events may modulate these processes. Genetically altered mice lacking one or both ERs provide a powerful tool to study these phenomena.

OBJECTIVE

This article examines sex differences in the kidney, particularly the role of ERs.

METHODS

To identify pertinent studies in genetically altered mice, a literature search was conducted on the MEDLINE database from January 1966 to July 2007, using the search terms estrogen receptor, kidney, and mice. Our group examined the effect of the ER-alpha knockout genotype on the kidney in streptozotocin-induced diabetes mellitus and compensatory kidney growth after uninephrectomy.

RESULTS

Female mice lacking ERa had reduced renal growth, including glomerular enlargement after 2 weeks of streptozotocin-induced diabetes mellitus and compensatory kidney growth 48 hours after uninephrectomy.

CONCLUSION

ER-mediated events influence kidney growth and disease in female mice.

Sexual dimorphism of the aging kidney: role of nitric oxide deficiency

GFR falls with aging in humans and rats due to renal vasoconstriction and structural damage. The rate of deterioration is influenced by race/genetic background, environment, and sex, with females protected. Part of the female advantage relates to protective effects of estrogens. There is little information on impact of aging on the distribution/cardiovascular actions of the estrogen receptor subtypes. In rats, androgens may contribute to injury, but in men, high testosterone levels predict cardiovascular health. In women, the association is controversial. Nitric oxide deficiency contributes to the hypertension and renal dysfunction of aging, which may be delayed in the female.

Compensatory renal growth and mitochondrial function: the influence of warm ischemia and reperfusion

PURPOSE: To evaluate the influence of ischemia/reperfusion injury on renal compensatory growth (CGR) and mitochondrial function. METHODS: Forty five Wistar rats were divided in 3 groups: Control Group (GC) - 21 rats were submitted to a sham laparotomy and sacrificed at 1st (6 rats) and 7th (15 rats) postoperative days to evaluate the dry weight of both kidneys and their growth during 1 week (6 rats) and to quantify mitochondrial respiration (9 rats); Group 1 (G1) - 12 rats underwent right nephrectomy and were sacrificed 7 days later for analysis of renal mitochondrial function (6 rats) and dry weight (6 rats). Group 2 (G2) - renal warm ischemia for 60 minutes followed by right nephrectomy was performed in 12 rats; they were sacrificed 7 days later to evaluate renal mitochondrial function (6 rats) and dry weight (6 rats). RESULTS: Dry weight (mg) of left kidneys at 7th day: GC - 219±18, G1 - 281±23 and G2 - 338±39 (GCxG1 p<0.01; GCxG2 p<0.001; G1xG2 p<0.01). State 4 mitochondrial respiration rate and respiratory control ratio (RCR) were similar in all groups (p>0.05). State 3 respirations (mM/min/mg) in GC, G1 and G2 was respectively: 99±23, 132±22 and 82±44 (p<0.02; the only statistical difference noted was between groups G1xG2 - p<0.05). CONCLUSIONS: Following unilateral nephrectomy CRG is associated with an increase in state 3 of mitochondrial respiration. Renal ischemia/reperfusion injury enhances the CRG provoked by unilateral nephrectomy but such enhancement seems independent on mitochondrial respiration.

Gender differences in kidney function

Sex hormones influence the development of female (F) and male (M) specific traits and primarily affect the structure and function of gender-specific organs. Recent studies also indicated their important roles in regulating structure and/or function of nearly every tissue and organ in the mammalian body, including the kidneys, causing gender differences in a variety of characteristics. Clinical observations in humans and studies in experimental animals in vivo and in models in vitro have shown that renal structure and functions under various physiological, pharmacological, and toxicological conditions are different in M and F, and that these differences may be related to the sex-hormone-regulated expression and action of transporters in the apical and basolateral membrane of nephron epithelial cells. In this review we have collected published data on gender differences in renal functions, transporters and other related parameters, and present our own microarray data on messenger RNA expression for various transporters in the kidney cortex of M and F rats. With these data we would like to emphasize the importance of sex hormones in regulation of a variety of renal transport functions and to initiate further studies of gender-related differences in kidney structure and functions, which would enable us to better understand occurrence and development of various renal diseases, pharmacotherapy, and drug-induced nephrotoxicity in humans and animals.

Unilateral nephrectomy leads to up-regulation of syndecan-2- and TGF-beta-mediated glomerulosclerosis in syndecan-4 deficient male mice

Syndecan-4 is an ubiquitous, plasma membrane-spanning heparan sulfate proteoglycan involved in proliferation, differentiation, adhesion and migration of cells in vitro. Syndecan-4 knockout (KO) mice show no obvious defects but respond abnormally to experimental stress conditions. In the adult, syndecan-4 is the most abundant syndecan of renal tissue. We therefore investigated the consequences of syndecan-4 deficiency during progression of kidney disease using unilaterally nephrectomized mice, a model of glomerular hyperfiltration and renal hypertrophy. 60 days after unilateral nephrectomy (UNX), mesangial expansion, enhanced matrix production (collagens I and IV, fibronectin) and focal segmental glomerulosclerosis, resembling early stages of diabetic nephropathy, was apparent in male but not female syndecan-4 KO mice. No defect was detected in wild type UNX males. Syndecan-2 mRNA and protein were not detectable in renal glomeruli of wild type mice, but were induced specifically in the glomeruli of the syndecan-4 deficient kidneys after unilateral nephrectomy. Due to the structural similarities of syndecans-2 and -4 we hypothesize that de novo-production of syndecan-2 in kidneys after unilateral nephrectomy reflects a compensatory response. However, this response is counterproductive since syndecan-2 supports the pro-sclerotic activity of TGF-beta1 which is increased in parallel with syndecan-2 synthesis. By contrast, signaling through syndecan-4 negatively controls the production of pro-sclerotic TGF-beta1.

Investigation of the estrogen receptor-alpha gene with type 2 diabetes and/or nephropathy in African-American and European-American populations

The estrogen receptor-alpha gene (ESR1) was selected as a positional candidate under a type 2 diabetes linkage peak at 6q24-27. A total of 42 ESR1 single nucleotide polymorphisms (SNPs) were genotyped in 380 African-American type 2 diabetic case subjects with end-stage renal disease (ESRD) and 276 African-American control subjects. A total of 22 ancestry informative markers were also genotyped, and the program Admixmap was used to adjust allelic and haplotypic association tests for individual estimates of admixture. The most significant association with type 2 diabetes-ESRD was with rs1033182 in intron 2 (P = 0.013, admixture-adjusted P(a) = 0.021). Genotyping 17 SNPs across a region of ESR1 intron 1-intron 2 in an expanded population of 851 case and 635 control subjects supported association with rs1033182 (P = 0.004, P(a) = 0.027) and with an independent six-SNP haplotype of high linkage disequilibrium spanning 6.4 kb (P < 0.0001, P(a) < 0.0001). The same 17 ESR1 SNPs were genotyped in 300 European-American type 2 diabetes-ESRD case subjects and 310 European-American control subjects. Two intron 2 SNPs, rs2431260 (P = 0.015) and rs1709183 (P = 0.019), and a four-SNP haplotype containing these SNPs (P = 0.033) were associated with type 2 diabetes and/or ESRD. Results suggest that intron 1 and intron 2 of the ESR1 gene may contain functionally important regions related to type 2 diabetes or ESRD risk.

Spontaneous airway hyperresponsiveness in estrogen receptor-alpha-deficient mice

RATIONALE

Airway hyperresponsiveness is a critical feature of asthma. Substantial epidemiologic evidence supports a role for female sex hormones in modulating lung function and airway hyperresponsiveness in humans.

OBJECTIVES

To examine the role of estrogen receptors in modulating lung function and airway responsiveness using estrogen receptor-deficient mice.

METHODS

Lung function was assessed by a combination of whole-body barometric plethysmography, invasive measurement of airway resistance, and isometric force measurements in isolated bronchial rings. M2 muscarinic receptor expression was assessed by Western blotting, and function was assessed by electrical field stimulation of tracheas in the presence/absence of gallamine. Allergic airway disease was examined after ovalbumin sensitization and exposure.

MEASUREMENTS AND MAIN RESULTS

Estrogen receptor-alpha knockout mice exhibit a variety of lung function abnormalities and have enhanced airway responsiveness to inhaled methacholine and serotonin under basal conditions. This is associated with reduced M2 muscarinic receptor expression and function in the lungs. Absence of estrogen receptor-alpha also leads to increased airway responsiveness without increased inflammation after allergen sensitization and challenge.

CONCLUSIONS

These data suggest that estrogen receptor-alpha is a critical regulator of airway hyperresponsiveness in mice.