Estrogen deficiency accelerates progression of glomerulosclerosis in susceptible mice

Quinolinic acid potentially links kidney injury to brain toxicity

Kidney dysfunction often leads to neurological impairment, yet the complex kidney-brain relationship remains elusive. We employed spatial and bulk metabolomics to investigate a mouse model of rapid kidney failure induced by mouse double minute 2 (Mdm2) conditional deletion in the kidney tubules to interrogate kidney and brain metabolism. Pathway enrichment analysis of a focused plasma metabolomics panel pinpointed tryptophan metabolism as the most altered pathway with kidney failure. Spatial metabolomics showed toxic tryptophan metabolites in the kidneys and brains, revealing a connection between advanced kidney disease and accelerated kynurenine degradation. In particular, the excitotoxic metabolite quinolinic acid was localized in ependymal cells in the setting of kidney failure. These findings were associated with brain inflammation and cell death. Separate mouse models of ischemia-induced acute kidney injury and adenine-induced chronic kidney disease also exhibited systemic inflammation and accumulating toxic tryptophan metabolites. Patients with advanced chronic kidney disease (stage 3b-4 and stage 5) similarly demonstrated elevated plasma kynurenine metabolites, and quinolinic acid was uniquely correlated with fatigue and reduced quality of life. Overall, our study identifies the kynurenine pathway as a bridge between kidney decline, systemic inflammation, and brain toxicity, offering potential avenues for diagnosis and treatment of neurological issues in kidney disease.

Gender Differences in Adenine Diet-Induced Kidney Toxicity: The Impact of 17β-Estradiol on Renal Inflammation and Fibrosis

Chronic kidney disease (CKD) involves ongoing impairment of kidney function and structural changes. Previous studies indicated that males have a substantially higher prevalence of CKD than those observed in females. Here, we compared the gender differences in CKD development by comparing age-matched male and female mice subjected to a 0.25% adenine diet (AD) for two weeks. Male mice showed a significantly greater decrease in kidney function than female mice, as evidenced by the elevated blood urea nitrogen levels (M-AD: 160 ± 5 mg/dL, F-AD: 90 ± 4 mg/dL; p < 0.001). Furthermore, male mice kidneys exhibited pronounced tubule dilation and kidney damage, as detected by histological and biochemical methods. The extent of fibrosis was quantified using multiple biological methods, revealing a greater degree of fibrosis in male kidneys. We next indicated the inflammatory responses in the kidneys. Similar to the extent of fibrosis, AD-fed male mice showed significantly increased levels of pro-inflammatory markers, including cytokine expression and infiltration of immune cell, compared to female mice. Based on in vivo observations, the anti-inflammatory and anti-fibrotic effects of 17β-estradiol (E2) were further evaluated in vitro conditions. E2 pre-treatment significantly reduced lipopolysaccharide-induced inflammatory response through inhibition of the nuclear factor-kappa B (NF-κB) pathway in NRK52E renal epithelial cells. In NRK49F renal fibroblasts, E2 pre-treatment also reduced TGFβ-induced fibrotic responses. We further demonstrated that E2 markedly decreased fibrosis and inflammation in AD-fed mouse kidneys. Our observations revealed that male mice kidneys exhibited a heightened inflammatory and fibrotic response compared to female mice kidneys. Additionally, our findings suggest that the observed sex differences may be partially attributed to the potential anti-inflammatory and anti-fibrotic effects of E2.

Synergistic effects of T-2 toxin and selenium deficiency exacerbate renal fibrosis through modulation of the ERα/PI3K/Akt signaling pathway

As common pathogenic agents in the world and widely distributed globally, T-2 toxin and selenium deficiency might exacerbate toxic effects by combined exposure, posing a dramatic health hazard to humans and animals. In this study, we aim to elucidate the underlying mechanisms of renal fibrosis triggered by T-2 toxin and selenium deficiency exposure. A total of thirty-two rats are randomly divided into the normal control, T-2 toxin, selenium deficiency, and combined intervention groups. T-2 toxin (100 ng/g) is intragastric gavaged to the rats in compliance with the body weight. Both the standard (containing selenium 0.20 mg/Kg) and selenium-deficient (containing selenium 0.02 mg/Kg) diets were manufactured adhering to the AIN-93 formula. After 12 weeks of intervention, renal tissue ultrastructural and pathological changes, inflammatory infiltration, epithelial mesenchymal transition (EMT), and extracellular matrix (ECM) deposition are evaluated, respectively. Metabolomics analysis is conducted to explore the underlying pathology of renal fibrosis, followed by the validation of potential mechanisms at gene and protein levels. T-2 toxin and selenium deficiency exposure results in podocyte foot process elongation or fusion, tubular vacuolization and dilatation, and collagen deposition in the kidneys. Additionally, it also increases inflammatory infiltration, EMT conversion, and ECM deposition. Metabolomics analysis suggests that T-2 toxin and selenium deficiency influence amino acid and cholesterol metabolism, respectively, and the estrogen signaling pathway is probably engaged in renal fibrosis progression. Moreover, T-2 toxin and selenium deficiency are found to regulate the expressions of the ERα/PI3K/Akt signaling pathway. In conclusion, T-2 toxin and selenium deficiency synergistically exacerbate renal fibrosis through regulating the ERα/PI3K/Akt signaling pathway, and inflammatory infiltration, EMT and ECM deposition are involved in this process.

Cellular and extracellular vaginal changes following murine ovarian removal

Loss of estrogen as a result of aging, pelvic cancer therapy, genetics, or eating disorders affects numerous body systems including the reproductive tract. Specifically, a chronic hypoestrogenic state fosters debilitating vaginal symptoms like atrophy, dryness, and dyspareunia. Current treatment options, including vaginal estrogen and hyaluronan (HA), anecdotally improve symptoms, but rectifying mechanisms are largely understudied. In order to study the hypoestrogenic vaginal environment, in particular the extracellular matrix (ECM), as well as understand the mechanisms behind current treatments and develop new therapies, we characterized a reliable and reproducible animal model. Bilateral ovariectomies (OVX) were performed on 9-week-old CD1 mice. After 1 month of estrogen loss due to ovarian removal, a phenotype that is similar to human vaginal tissue in an estrogen reduced state was noted in mice compared to sham-operated controls. The uterine to body weight ratio decreased by 80% and vaginal epithelium was significantly thinner in OVX compared to sham mice. Estrogen signaling was altered in OVX, but submucosal ERα localization did not reach statistical differences. HA localization in the submucosal area was altered and CD44 expression decreased in OVX mice. Collagen turn-over was altered following OVX. The inflammation profile was also disrupted, and submucosal vaginal CD45+ and F4/80+ cell populations were significantly reduced in the OVX mice. These results show altered cellular and molecular changes due to reduced estrogen levels. Developing new treatments for hypoestrogenic vaginal symptoms rely on better understanding of not only the cellular changes, but also the altered vaginal ECM environment. Further studies using this mouse model has the potential to advance women's vaginal health treatments and aid in understanding the interplay between organ systems in both healthy, aged, and diseased states.

Estrogen receptor β attenuates renal fibrosis by suppressing the transcriptional activity of Smad3

Renal fibrosis (RF) is a common pathway leading to chronic kidney disease (CKD), which lacks effective treatment. While estrogen receptor beta (ERβ) is known to be present in the kidney, its role in RF remains unclear. The present study aimed to investigate the role and underlying mechanism of ERβ during RF progression in patients and animal models with CKD. We found that ERβ was highly expressed in the proximal tubular epithelial cells (PTECs) in healthy kidneys but its expression was largely lost in patients with immunoglobin A nephropathy (IgAN) and in mice with unilateral ureter obstruction (UUO) and subtotal nephrectomy (5/6Nx). ERβ deficiency markedly exacerbated, whereas ERβ activation by WAY200070 and DPN attenuated RF in both UUO and 5/6Nx mouse models, suggesting a protective role of ERβ in RF. In addition, ERβ activation inhibited TGF-β1/Smad3 signaling, while loss of renal ERβ was associated with overactivation of the TGF-β1/Smad3 pathway. Furthermore, deletion or pharmacological inhibition of Smad3 prevented the loss of ERβ and RF. Mechanistically, activation of ERβ competitively inhibited the association of Smad3 with the Smad-binding element, thereby downregulating the transcription of the fibrosis-related genes without altering Smad3 phosphorylation in vivo and in vitro. In conclusion, ERβ exerts a renoprotective role in CKD by blocking the Smad3 signaling pathway. Thus, ERβ may represent as a promising therapeutic agent for RF.

Early Menopause May Associate With a Higher Risk of CKD and All-Cause Mortality in Postmenopausal Women: An Analysis of NHANES, 1999–2014

Background

Chronic kidney disease (CKD) in women is often accompanied by hormone disorders such as sex hormones, and most women with CKD are in the post-menopausal age group. Due to the close relationship between menopause and sex hormones, we aimed to explore the association between early menopause and CKD in post-menopausal women, and the influence of early menopause on longevity in the CKD population.

Methods

Information regarding 4,945 post-menopausal women was extracted from the database of the National Health and Nutrition Examination Survey (NHANES) 1999–2014, and then divided into 4 groups according to the type of menopause (natural or surgical) and early menopause (menopause at age <45) or not. The association between early menopause and CKD prevalence was examined using multivariable logistic regression, while we used multivariable Cox proportional hazards models to investigate the possible relationship between early menopause and all-cause mortality in CKD and non-CKD populations. The differences in the levels of sex hormones between women with and without CKD were also explored.

Results

Compared with women with natural menopause at age ≥45, women experiencing early natural menopause had a higher risk of CKD [OR = 1.26 (1.01–1.56)]. Similarly, as compared to women with surgical menopause at age ≥ 45, women in the early surgical menopause group were more likely to have CKD [OR = 1.38 (1.05–1.81)]. In addition, early surgical menopause was associated with higher mortality in the non-CKD group [HR = 1.62 (1.06–2.49)], but not in the CKD group. Women with CKD had a higher level of luteinizing hormone and follicle-stimulating hormone, combined with a lower level of testosterone and estradiol than the non-CKD women.

Conclusion

Both early natural and surgical menopause were associated with a higher risk of CKD. Early surgical menopause was a hazard factor for survival in the non-CKD group, but not in the CKD group. Further research is required to understand the mechanisms.

Effects of caloric and time restriction diets on kidney health in rat model of postmenopausal acute kidney injury: An apoptosis and histopathological study

Objectives

Lifestyle and eating habits affect the health and function of the body's organs, including the kidneys. The current study was carried out to determine the effects of two types of diet programs, including time restriction (TR) and calorie restriction (CR) on the histopathological changes and apoptotic molecules during acute kidney injury (AKI) in postmenopausal rats.

Materials and Methods

In this study the female rats were divided into two groups of ovariectomized (OVX) and ovary-intact (sham), then they were placed on TR and CR diets for 8 weeks; afterward, AKI was induced by injection of glycerol. Functional indices, histopathological changes, Bax, and Bcl2 were measured before and after AKI.

Results

After AKI, creatinine, serum urea, urinary albumin excretion, kidney tissue Bax, and Bax/Bcl2 ratio increased, while glomerular filtration rate (GFR) and kidney tissue Bcl2 decreased compared with before AKI. Histopathological indices (inflammation, cellular necrosis, cell vacuolization, tubular dilatation, intratubular cast, and congestion) also confirmed renal injury. TR and CR diets improved renal injury indices and prevented an increase in the Bax/Bcl2 ratio. However, in some indices, the effects of two diets on OVX animals were not observed. In addition, none of the diets could decrease kidney weight/body weight ratio (KW/BW). The histopathological finding also showed improvement of renal status in both groups, especially in the CR diet.

Conclusion

The results indicated that TR and CR diets had renoprotective effects against AKI by reducing the Bax/Bcl2 ratio and improving apoptosis. The effects of CR were more than TR.

Catalase, a therapeutic target in the reversal of estrogen-mediated aging

Despite increasing interest in the reversal of age-related processes, there is a paucity of data regarding the effects of post-menopausal-associated estrogen loss on cellular function. We studied human adipose-derived mesenchymal stem cells (hASCs) isolated from women younger than 45 years old (pre-menopause, pre-hASC) or older than 55 years old (post-menopause, post-hASC). In this study, we provide proof of concept that the age-related ineffective functionality of ASCs can be reversed to improve their ability in promoting tissue repair. We found reduced estrogen receptor expression, decreased estrogen receptor activation, and reduced sensitivity to 17β-estradiol in post-hASCs. This correlated with decreased antioxidants (catalase and superoxide dismutase [SOD] expression) and increased oxidative stress compared with pre-hASCs. Increasing catalase expression in post-hASCs restored estrogen receptor (ER) expression and their functional capacity to promote tissue repair as shown in human skin ex vivo wound healing and in vivo mouse model of lung injury. Our results suggest that the consequences of 17β-estradiol decline on the function of hASCs may be reversible by changing the oxidative stress/antioxidant composition.

Associations between Sex and Risk Factors for Predicting Chronic Kidney Disease

Gender is an important risk factor in predicting chronic kidney disease (CKD); however, it is under-researched. The purpose of this study was to examine whether gender differences affect the risk factors of early CKD prediction. This study used data from 19,270 adult health screenings, including 5101 with CKD, to screen for 11 independent variables selected as risk factors and to test for the significant effects of statistical Chi-square test variables, using seven machine learning techniques to train the predictive models. Performance indicators included classification accuracy, sensitivity, specificity, and precision. Unbalanced category issues were addressed using three extraction methods: manual sampling, the synthetic minority oversampling technique, and SpreadSubsample. The Chi-square test revealed statistically significant results (p < 0.001) for gender, age, red blood cell count in urine, urine protein (PRO) content, and the PRO-to-urinary creatinine ratio. In terms of classifier prediction performance, the manual extraction method, logistic regression, exhibited the highest average prediction accuracy rate (0.8053) for men, whereas the manual extraction method, linear discriminant analysis, demonstrated the highest average prediction accuracy rate (0.8485) for women. The clinical features of a normal or abnormal PRO-to-urinary creatinine ratio indicated that PRO ratio, age, and urine red blood cell count are the most important risk factors with which to predict CKD in both genders. As a result, this study proposes a prediction model with acceptable prediction accuracy. The model supports doctors in diagnosis and treatment and achieves the goal of early detection and treatment. Based on the evidence-based medicine, machine learning methods are used to develop predictive model in this study. The model has proven to support the prediction of early clinical risk of CKD as much as possible to improve the efficacy and quality of clinical decision making.

Transforming growth factor β3 deficiency promotes defective lipid metabolism and fibrosis in murine kidney

Glomerulosclerosis and tubulointerstitial fibrosis are pathological features of chronic kidney disease. Transforming growth factor β (TGFβ) is a key player in the development of fibrosis. However, of the three known TGFβ isoforms, only TGFβ1 has an established role in fibrosis, and the pathophysiological relevance of TGFβ2 and TGFβ3 is unknown. Because Tgfb3 deficiency in mice results in early postnatal lethality, we analyzed the kidney phenotype of heterozygous Tgfb3-knockout mice (Tgfb3^+/−) and compared it with that of matched wild-type mice. Four-month-old Tgfb3^+/− mice exhibited incipient renal fibrosis with epithelial–mesenchymal transition, in addition to glomerular basement membrane thickening and podocyte foot process effacement associated with albuminuria. Also evident was insulin resistance and oxidative stress at the renal level, together with aberrant renal lipid metabolism and mitochondrial function. Omics analysis revealed toxic species, such as diacylglycerides and ceramides, and dysregulated mitochondrial metabolism in Tgfb3^+/− mice. Kidneys of Tgfb3^+/− mice showed morphological alterations of mitochondria and overactivation of non-canonical MAPK ERK1/2 and JNK cascades. Our study indicates that renal TGFβ3 might have antifibrotic and renoprotective properties, opposing or counteracting the activity of TGFβ1.

This article has an associated First Person interview with the first author of the paper.

Summary: Our study describes the renal abnormalities of heterozygous Tgfb3-targeted mice and suggests that TGFβ3 is renoprotective and may counteract the activity of TGFβ1.

The Effect of Gender-Affirming Hormone Therapy on Serum Creatinine in Transgender Individuals

OBJECTIVE

To describe the changes in serum creatinine (Cr) levels after the initiation of gender-affirming hormone therapy (GAHT) in transgender individuals to better understand the expected changes and interpretation of laboratory values in this population.

METHODS

A retrospective chart review of all adult transgender patients initiated on GAHT at Mayo Clinic from January 2011 to October 2019 was completed. Laboratory values were obtained prior to initiating GAHT and at 3, 6, and 12 months after initiating GAHT. Baseline Cr values were compared with Cr values at 3, 6, and 12 months after initiating GAHT in transgender men (TM) on testosterone and transgender women (TW) on estradiol and antiandrogens.

RESULTS

A total of 84 TW (median age of 30 years) and 24 TM (median age of 23 years) were included for analysis. Following a matched pair analysis of TW, Cr values were found to be significantly decreased by -0.03 at 3 months (P = .04), -0.10 at 6 months (P < .01), and -0.07 at 12 months (P < .01) compared with baseline values. Following a matched pair analysis of TM, Cr values were found to be significantly increased, on average, by 0.14 at 3 months (P = .04), 0.21 at 6 months (P = .016), and 0.15 at 12 months (P = .003) compared with baseline values.

CONCLUSION

In TW and TM, a change in Cr level was seen as early as 3 months toward their affirmed gender after initiating GAHT. Clinicians can use Cr levels established at 6 months as new baseline values, as these changes continue to persist up to 12 months.

Sex disparities and adverse cardiovascular and kidney outcomes in patients with chronic kidney disease: results from the KNOW-CKD

AIMS

Longitudinal studies of the association between sex and adverse clinical outcomes in patients with chronic kidney disease (CKD) are scarce. We assessed whether major outcomes may differ by sex among CKD patients.

METHODS

We analyzed a total of 1780 participants with non-dialysis CKD G1-5 from the KoreaN cohort study for Outcome in patients with Chronic Kidney Disease (KNOW-CKD). The primary outcome was a composite of non-fatal cardiovascular events or all-cause mortality. Secondary outcomes included fatal and non-fatal cardiovascular events, all-cause mortality, and a composite kidney outcome of ≥ 50% decline in estimated glomerular filtration rate from baseline or the onset of end-stage kidney disease.

RESULTS

There were 1088 (61%) men and 692 (39%) women in the study cohort. The proportion of smokers was significantly higher in men (24% vs. 3%). During 8430 person-years of follow-up, 201 primary outcome events occurred: 144 (13%) in men and 57 (8%) in women, with corresponding incidence rates of 2.9 and 1.7 per 100 person-years, respectively. In multivariable Cox models, men were associated with a 1.58-fold (95% CI 1.06-2.35) higher risk of composite outcome. Propensity score matching analysis revealed similar findings (HR 1.81; 95% CI 1.14-2.91). Risk of all-cause mortality was significantly higher in men of the matched cohort. However, there was no difference in the risk of CKD progression. In the subgroup with coronary artery calcium (CAC) measurements, men had a higher likelihood of CAC progression.

CONCLUSIONS

In Korean CKD patients, men were more likely to experience adverse cardiovascular events and death than women.

Exposure to High-Fat Style Diet Induced Renal and Liver Structural Changes, Lipid Accumulation and Inflammation in Intact and Ovariectomized Female Rats

Purpose

We hypothesized that low estrogen levels aggravate obesity-related complications. Diet-induced obesity can cause distinct pathologies, including impaired glucose tolerance, inflammation, and organ injury that leads to fatty liver and chronic kidney diseases. To test this hypothesis, ovariectomized (OVX) rats were fed a high-fat style diet (HFSD), and we examined structural changes and inflammatory response in the kidney and liver.

Methods

Sprague-Dawley female rats were ovariectomized or sham-operated and divided into four groups: sham-operated rats fed a normal diet (ND); ovariectomized rats fed a normal diet (OVX-ND); sham-operated rats fed a HFSD; ovariectomized rats fed a high-fat style diet (OVX-HFSD). Mean blood pressure and fasting blood glucose were measured on weeks 0 and 10. The rats were sacrificed 10 weeks after initiation of ND or HFSD, the kidney and liver were harvested for histological, immunohistochemical and immunofluorescence studies.

Results

HFSD-fed rats presented a significantly greater adiposity index compared to their ND counterparts. Liver index, fasting blood glucose and mean blood pressure was increased in OVX-HFSD rats compared to HFSD rats at study terminal. Histological and morphometric studies showed focal interstitial mononuclear cell infiltration in the kidney of HFSD rats with mesangial expansion being greater in the OVX-HFSD rats. Both HFSD fed groups showed increased expressions of renal inflammatory markers, namely TNF-alpha, IL-6 and MCP-1, and infiltrating M1 macrophages with some influence of ovarian hormonal status. HFSD-feeding also caused hepatocellular steatosis which was aggravated in ovariectomized rats fed the same diet. Furthermore, hepatocellular ballooning was observed only in the OVX-HFSD rats. Similarly, HFSD-fed rats showed increased expressions of the inflammatory markers and M1 macrophage infiltration in the liver; however, only IL-6 expression was magnified in the OVX-HFSD.

Conclusion

Our data suggest that some of the structural changes and inflammatory response in the kidney and liver of rats fed a HFSD are exacerbated by ovariectomy.

Amenorrhea and Estrogen Disorders in Kidney Disease

Sexual and reproductive function are impacted negatively in individuals with chronic kidney disease and end-stage renal disease. Disruption of the hypothalamic-pituitary-gonadal axis plays a pivotal role in contributing to these manifestations as a result of decreasing kidney function and the development of uremia. Early menopause is encountered commonly in women with reduced kidney function, and treatment is problematic as a result of reduced kidney function changing the half-life of medications. Kidney transplantation corrects some of these abnormalities, but medications required after transplantation as well as the persistence of other comorbidities are barriers to normal restoration of gonadal dysfunction.

The Beneficial Effect of Boswellic Acid on Bone Metabolism and Possible Mechanisms of Action in Experimental Osteoporosis

Estrogen is instrumental in the pathological process of osteoporosis because a deficiency of this hormone increases the release of bone-resorbing cytokines. Acetyl-11-keto-β-boswellic acid (AKBA), a constituent from Boswellia serrata, has an anti-inflammatory effect by inhibiting tumor necrosis factor-α (TNF-α) expression, which leads to a decline in receptor activator of nuclear factor-kappa B (NF-κB) ligand, and consequently, a reduction in osteoclast activity. Hence, AKBA may be beneficial against bone loss during osteoporosis. Therefore, the current study intended to evaluate the beneficial effects of AKBA in ovariectomy-induced osteoporosis and to investigate its mechanism of action. Sham-operation or ovariectomy female Sprague Dawley rats were used for evaluating the antiosteoporotic effect of AKBA in this study. AKBA (35 mg/kg, p.o.) and estradiol (0.05 mg/kg, i.m.) were administered for 42 days. At the end of the experiment, body and uterus weights, serum and urine calcium and phosphorus, serum alkaline phosphatase, and urinary creatinine levels, besides serum levels of NF-κB and TNF-α were determined. Weight, length, thickness, hardness, calcium content, as well as the bone mineral density of femur bone and lumbar vertebra were measured. A histopathological examination was also carried out. AKBA ameliorated all tested parameters and restored a normal histological structure. Thus, AKBA showed good antiosteoporotic activity, which may be mediated through its suppression of the NF-κB-induced TNF-α signaling pathway.

Changes in kidney function during the menopausal transition: the Study of Women's Health Across the Nation (SWAN) - Michigan site

OBJECTIVE

The aim of the study was to examine changes in kidney function during the menopausal transition (MT) and associations with levels of sex hormones (follicle stimulating hormone [FSH], sex hormone binding globulin [SHBG], estradiol, and testosterone).

METHODS

We used data from the Michigan site of Study of the Women's Health Across the Nation, a longitudinal study of the MT. For this analysis, we included women who had at least one creatinine measure before the final menstrual period (FMP) and at least one creatinine measure after the FMP (n = 101 women with 440 observations). To determine whether the declines in estimated glomerular filtration rate (eGFR) remained constant during the MT, we used local weighted regression curves to fit eGFR estimates. We examined the association between sex hormones and eGFR with longitudinal mixed models adjusting for baseline age, day of menstrual cycle, and time from FMP.

RESULTS

At baseline, women had a mean age of 45.4 ± 2.5 years; 54% were African-American and 46% were white. Although eGFR declined significantly over time, declines were linear, consistent with declines in eGFR due to age alone rather than the MT. Total testosterone, estradiol, ratio of testosterone:estradiol, and free androgen index were not significantly associated with eGFR, whereas lower FSH (-0.039, 95% confidence interval [CI] -0.067 to -0.012) and higher SHBG (0.050, 95% CI 0.004-0.096) were associated with higher eGFR.

CONCLUSIONS

Kidney function declines during the MT. Although associated with levels of FSH and SHBG, the rate of decline in eGFR is consistent with what would be expected of age alone.

Estrogen receptor alpha expression in renal tissue and its relationship with prognosis in immunoglobulin A nephropathy

OBJECTIVE

Epidemiologic studies have shown that, compared to men, women have better prognoses in chronic renal diseases. This indicates that gender hormones may have some effect on renal function. The present study aimed to investigate the expression and relationship with prognosis of estrogen receptor alpha (ERα) in renal tissue of immunoglobulin A nephropathy (IgAN) patients.

METHODS

Expression of ERα was detected by immunohistochemistry. Specimens were collected from forty-five IgAN patients and five normal healthy participants. In addition to expression, the relationship of ERα with clinical data, prognosis, and the degree of glomerular damage were analyzed.

RESULTS

ERα was expressed in the glomeruli and renal tubules. The expression of ERα in the glomeruli of IgAN renal tissue decreased gradually (P = 0.001, P < 0.05) with the increasing severity of disease and its expression was associated with estimated glomerular filtration rate (eGFR), serum creatinine (Scr) and pathological grade (r = 0.876, -0.818 and -0.736, P < 0.05). In addition, the expression of ERα was significantly decreased in hypertensive IgAN patients compared with the non-hypertensive group (P = 0.011). We found that ERα was of great significance for the prognosis of IgAN (P = 0.01, P < 0.05).

CONCLUSIONS

The expression of ERα in the renal tissue of IgAN patients was reduced and there was a correlation with the degree of kidney damage and prognosis, suggesting that ERα may play a role in the progression of IgAN.

Estrogen regulates aquaporin-2 expression in the kidney

Estrogens are primarily identified as sex hormones that, for a long time, have been known as important regulators of female reproductive physiology. However, our understanding of the role of estrogens has changed over the past years. It is now well accepted that estrogens are also involved in other physiological and pathological processes in both genders. This is due to the fact that estrogen can act both local as well as on a systemic level. Next to its role in reproductive physiology, there is accumulating evidence that estrogen influences multiple systems involved in water homeostasis. This chapter will delineate the regulatory effects of estrogen on the water channel aquaporin-2 (AQP2) found in the renal collecting duct. We will first provide an introduction to estrogen, the estrogen receptors and their role in renal physiology as well as describe the effect of selective estrogen receptor modulators (SERMs) on the kidney. Subsequently, we will focus on how estrogen and SERMs influence water balance and regulate AQP2 expression in principal cells of the collecting duct. Finally, we will describe how estrogen regulates AQP2 functionality in other organ systems.

Sex and the kidneys: current understanding and research opportunities

Concerns regarding sex differences are increasingly pertinent in scientific and societal arenas. Although biological sex and socio-cultural gender are increasingly recognized as important modulators of renal function under physiological and pathophysiological conditions, gaps remain in our understanding of the mechanisms underlying sex differences in renal pathophysiology, disease development, progression and management. In this Perspectives article, we discuss specific opportunities for future research aimed at addressing these knowledge gaps. Such opportunities include the development of standardized core data elements and outcomes related to sex for use in clinical studies to establish a connection between sex hormones and renal disease development or progression, development of a knowledge portal to promote fundamental understanding of physiological differences between male and female kidneys in animal models and in humans, and the creation of new or the development of existing resources and datasets to make them more readily available for interrogation of sex differences. These ideas are intended to stimulate thought and interest among the renal research community as they consider sex as a biological variable in future research projects.

Influence of Sex on the Progression of Chronic Kidney Disease

The role that sex plays in the development and progression of chronic kidney disease remains a subject of controversy. The lack of clarity in this important area reflects complex interactions between biological factors and cultural and socioeconomic influences that impact the relationship between sex and renal disease. Certainly, additional observational studies are indicated; however, innovative approaches are required to isolate biological processes from cultural influences. Despite these limitations, available data suggest that the progression of renal disease is slower in women than in men and that this sexual dimorphism is primarily due to direct actions of sex hormones on cellular metabolism. The extent to which differences in lifestyle factors between the sexes influence sexual dimorphism in the progression of chronic kidney disease remains to be elucidated.

Preventive effect of exercise training on diabetic kidney disease in ovariectomized rats with type 1 diabetes

IMPACT STATEMENT

To date, no studies have been found evaluating the effects of physical exercise on renal function and structure changes in ovariectomized rats with type 1 diabetes. Therefore, this work emerges with an important tool for strengthening and expanding innovative research on exercise with potential for the prevention of renal diseases in ovariectomized diabetic rats, and future development of studies that seek to increase scientific knowledge about the beneficial effects of physical exercise on renal diseases in humans.

Effect of ovariectomy on the progression of chronic kidney disease-mineral bone disorder (CKD-MBD) in female Cy/+ rats

Male Cy/+ rats have shown a relatively consistent pattern of progressive kidney disease development that displays multiple key features of late stage chronic kidney disease-mineral bone disorder (CKD-MBD), specifically the development of cortical bone porosity. However, progression of disease in female Cy/+ rats, assessed in limited studies, is more heterogeneous and to date has failed to show development of the CKD-MBD phenotype, thus limiting their use as a practical model of progressive CKD-MBD. Animal and human studies suggest that estrogen may be protective against kidney disease in addition to its established protective effect on bone. Therefore, in this study, we aimed to determine the effect of ovariectomy (OVX) on the biochemical and skeletal manifestations of CKD-MBD in Cy/+ female rats. We hypothesized that OVX would accelerate development of the biochemical and skeletal features of CKD-MBD in female Cy/+ rats, similar to those seen in male Cy/+ rats. Female Cy/+ rats underwent OVX (n = 8) or Sham (n = 8) surgery at 15 weeks of age. Blood was collected every 5 weeks post-surgery until 35 weeks of age, when the rats underwent a 4-day metabolic balance, and the tibia and final blood were collected at the time of sacrifice. OVX produced the expected changes in trabecular and cortical parameters consistent with post-menopausal disease, and negative phosphorus balance compared with Sham. However, indicators of CKD-MBD were similar between OVX and Sham (similar kidney weight, plasma blood urea nitrogen, creatinine, creatinine clearance, phosphorus, calcium, parathyroid hormone, and no cortical porosity). Contrary to our hypothesis, OVX did not produce evidence of development of the CKD-MBD phenotype in female Cy/+ rats.

Excessive Oxidative Stress Contributes to Increased Acute ER Stress Kidney Injury in Aged Mice

The aged kidney is susceptible to acute injury due presumably to its decreased ability to handle additional challenges, such as endoplasmic reticulum (ER) stress. This was tested by giving tunicamycin, an ER stress inducer, to either old or young mice. Injection of high dose caused renal failure in old mice, not in young mice. Moreover, injection of low dose resulted in severe renal damage in old mice, confirming the increased susceptibility of aged kidney to ER stress. There existed an abnormality in ER stress response kinetics in aged kidney, characterized by a loss of XBP-1 splicing and decreased PERK-eIF2α phosphorylation at late time point. The presence of excessive oxidative stress in aged kidney may play a role since high levels of oxidation increased ER stress-induced cell death and decreased IRE1 levels and XBP-1 splicing. Importantly, treatment with antioxidants protected old mice from kidney injury and normalized IRE1 and XBP-1 responses. Furthermore, older mice (6 months old) transgenic with antioxidative stress AGER1 were protected from ER stress-induced kidney injury. In conclusion, the decreased ability to handle ER stress, partly due to the presence of excessive oxidative stress, may contribute to increased susceptibility of the aging kidney to acute injury.

CKD in Patients with Bilateral Oophorectomy

BACKGROUND AND OBJECTIVES

Premenopausal women who undergo bilateral oophorectomy are at a higher risk of morbidity and mortality. Given the potential benefits of estrogen on kidney function, we hypothesized that women who undergo bilateral oophorectomy are at higher risk of CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We performed a population-based cohort study of 1653 women residing in Olmsted County, Minnesota who underwent bilateral oophorectomy before age 50 years old and before the onset of menopause from 1988 to 2007. These women were matched by age (±1 year) to 1653 referent women who did not undergo oophorectomy. Women were followed over a median of 14 years to assess the incidence of CKD. CKD was primarily defined using eGFR (eGFR<60 ml/min per 1.73 m2 on two occasions >90 days apart). Hazard ratios were derived using Cox proportional hazards models, and absolute risk increases were derived using Kaplan-Meier curves at 20 years. All analyses were adjusted for 17 chronic conditions present at index date, race, education, body mass index, smoking, age, and calendar year.

RESULTS

Women who underwent bilateral oophorectomy had a higher risk of eGFR-based CKD (211 events for oophorectomy and 131 for referent women; adjusted hazard ratio, 1.42; 95% confidence interval, 1.14 to 1.77; absolute risk increase, 6.6%). The risk was higher in women who underwent oophorectomy at age ≤45 years old (110 events for oophorectomy and 60 for referent women; adjusted hazard ratio, 1.59; 95% confidence interval, 1.15 to 2.19; absolute risk increase, 7.5%).

CONCLUSIONS

Premenopausal women who undergo bilateral oophorectomy, particularly those ≤45 years old, are at higher risk of developing CKD, even after adjusting for multiple chronic conditions and other possible confounders present at index date.

PODCAST

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Close pathological correlations between chronic kidney disease and reproductive organ-associated abnormalities in female cotton rats

Cotton rat ( Sigmodon hispidus) is a useful experimental rodent for the study of human infectious diseases. We previously clarified that cotton rats, particularly females, developed chronic kidney disease characterized by cystic lesions, inflammation, and fibrosis. The present study investigated female-associated factors for chronic kidney disease development in cotton rats. Notably, female cotton rats developed separation of the pelvic symphysis and hypertrophy in the vaginal parts of the cervix with age, which strongly associated with pyometra. The development of pyometra closely associated with the deterioration of renal dysfunction or immunological abnormalities was indicated by blood urea nitrogen and serum creatinine or spleen weight and serum albumin/globulin ratio, respectively. These parameters for renal dysfunction and immunological abnormalities were statistically correlated. These phenotypes found in the female reproductive organs were completely inhibited by ovariectomy. Further, the female cotton rats with pyometra tended to show more severe chronic kidney disease phenotypes and immunological abnormalities than those without pyometra; these changes were inhibited in ovariectomized cotton rats. With regard to renal histopathology, cystic lesions, inflammation, and fibrosis were ameliorated by ovariectomy. Notably, the immunostaining intensity of estrogen receptor α and estrogen receptor β were weak in the healthy kidneys, but both estrogen receptors were strongly induced in the renal tubules showing cystic changes. In conclusion, the close correlations among female reproductive organ-associated abnormalities, immunological abnormalities, and renal dysfunction characterize the chronic kidney disease features of female cotton rats. Thus, the cotton rat is a unique rodent model to elucidate the pathological crosstalk between chronic kidney disease and sex-related factors. Impact statement The increasing number of elderly individuals in the overall population has led to a concomitant age-related increase in chronic kidney disease. Moreover, the global prevalence of patients with chronic kidney disease is gradually increasing, which poses a serious public health problem. The limited number of spontaneous chronic kidney disease animal models, which resemble chronic kidney disease pathogenesis in elderly individuals, is a major limitation in the development of experimental and curative medicines for chronic kidney disease. This pathological study clarified that sex-related factors, including hormones, and abnormalities of the female reproductive system, such as pyometra, are closely associated with chronic kidney disease development by using cotton rats ( Sigmodon hispidus). Further, ovariectomy inhibited the phenotypes of the female reproductive system, immunological abnormalities, and chronic kidney disease. Thus, this laboratory rodent serves as a novel and useful spontaneous chronic kidney disease model to elucidate the candidate disease factors and the pathogenesis of chronic kidney disease both in human and experimental medicine.

Gender Differences in the Progression of Experimental Chronic Kidney Disease Induced by Chronic Nitric Oxide Inhibition

Chronic kidney disease (CKD) is considered a public health problem, assuming epidemic proportions worldwide. In this context, the preponderance of CKD prevalence in male over age-matched female patients is of note. In the present study, we investigated the impact of the gender on the development of experimental CKD induced by chronic nitric oxide (NO) inhibition in Wistar male and female rats through the administration of L-NAME. CKD model induced by L-NAME is characterized by systemic vasoconstriction, resulting in severe hypertension, albuminuria, renal ischemia, glomerulosclerosis, interstitial expansion, and macrophage infiltration. After 30 days of CKD induction, male NAME rats exhibited remarkable albuminuria, augmented cortical histological damage, interstitial inflammation, and fibrosis. Age-matched female NAME rats showed significantly lower albuminuria, diminished glomerular ischemia, and glomerulosclerosis, as well as a significant reduction in the expression of α-smooth muscle actin renal interstitial Ang II+ cells. Thus, the present study demonstrated that female rats submitted to the NAME model developed less severe CKD than males. Female renoprotection could be promoted by both the estrogen anti-inflammatory activity and/or by the lack of testosterone, related to renin-angiotensin-aldosterone system hyperactivation and fibrogenesis. However, the influence of sex hormones on the progression of CKD needs to be further investigated.

Dietary nitrite reverses features of postmenopausal metabolic syndrome induced by high-fat diet and ovariectomy in mice

Menopausal women are at greater risk of developing metabolic syndrome with reduced endothelial nitric oxide synthase (eNOS) activity. Hormone replacement therapy increases eNOS activity and normalizes some characteristics of metabolic syndrome. We hypothesized that nitric oxide (NO) supplementation should have a therapeutic effect on this syndrome. We examined the effect of dietary nitrite in a mouse model with postmenopausal metabolic syndrome induced by ovariectomy (OVX) and a high fat diet (HF). C57BL/6 female mice were divided into five groups, sham+normal fat diet (NF), sham+ HF, OVX+HF with or without sodium nitrite (50 mg and 150 mg/l) in the drinking water. Daily food intake and weekly body weight were monitored for 18 wk. OVX and HF significantly reduced plasma levels of nitrate/nitrite (NOx), and mice developed obesity with visceral hypertrophic adipocytes and increased transcriptional levels of monocyte chemoattractant protein-1, TNF-α, and IL-6 in visceral fat tissues. The proinflammatory state in the adipocytes provoked severe hepatosteatosis and insulin resistance in OVX+HF group compared with sham+NF group. However, dietary nitrite significantly suppressed adipocyte hypertrophy and transcriptions of proinflammatory cytokines in visceral fat in a dose-dependent manner. The improvement of visceral inflammatory state consequently reversed the hepatosteatosis and insulin resistance observed in OVX+HF mice. These results suggest that an endogenous NO defect might underlie postmenopausal metabolic syndrome and that dietary nitrite provides an alternative source of NO, subsequently compensating for metabolic impairments of this syndrome.

Estrogen receptor subtype ratio change protects against podocyte damage

Women are relatively protected against the development and progression of glomerulosclerosis (GS) prior to menopause. However, the "female advantage" is lost in women who are either diabetic, post-menopausal or both. We showed that 17β-estradiol (E₂) was effective in prevention of diabetic GS development in part through the stabilization of podocyte cytoskeleton and a change in estrogen receptor (ER) subtype ratio. The objective of this study was to examine whether resveratrol (RSV), reported to have estrogen-like action and renoprotective activity against diabetic GS, would affect similar pathways. After in vitro treatment with RSV we found a change in the ERα and ERβ expression ratio in favor of ERβ, suppression of heat shock protein 25 (Hsp25) expression and increase in β1-integrin expression, important for maintaining podocyte cytoskeleton. We noted a reduction of insulin-like growth factor 1 receptor (IGFR1) expression, decrease in extracellular signal-regulated kinase (ERK) activation, decrease in reactive oxygen species (ROS), and decrease in cleaved-caspase 3 expression. We found an increase in [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] (MTT) and an increase in matrix metalloproteinases (MMP-2 and MMP-9) activity. Using cre-loxP strategy we developed podocyte-specific ERα knockout mice to show the importance of ERβ. In isolated podocytes, we confirmed reduction of ERα expression in conjunction with a decrease in IGFR1 expression, ERK and increase of MMP-2 similar to that of our in vitro treatment with RSV. Taken together these data suggest an important role for ERβ and ER subtype ratio in podocyte stabilization. Therefore RSV or other regulators of ER pathways could offer protection against diabetic and age-related podocyte changes.

RAS and sex differences in diabetic nephropathy

The incidence and progression of kidney diseases are influenced by sex. The renin-angiotensin system (RAS) is an important regulator of cardiovascular and renal function. Sex differences in the renal response to RAS blockade have been demonstrated. Circulating and renal RAS has been shown to be altered in type 1 and type 2 diabetes; this enzymatic cascade plays a critical role in the development of diabetic nephropathy (DN). Angiotensin converting enzyme (ACE) and ACE2 are differentially regulated depending on its localization within the diabetic kidney. Furthermore, clinical and experimental studies have shown that circulating levels of sex hormones are clearly modulated in the context of diabetes, suggesting that sex-dependent RAS regulation may be also be affected in these individuals. The effect of sex hormones on circulating and renal RAS may be involved in the sex differences observed in DN progression. In this paper we will review the influence of sex hormones on RAS expression and its relation to diabetic kidney disease. A better understanding of the sex dimorphism on RAS might provide a new approach for diabetic kidney disease treatment.

Protective role of female gender in programmed accelerated renal aging in the rat

The aging kidney exhibits a progressive decline in glomerular filtration rate, accompanied by inflammatory and oxidative damage. We hypothesized that accelerated, age-related progression of renal injury is ovarian hormones-dependant. To address this we used an established model of developmentally programmed accelerated renal aging in the rat, superimposed by ovariectomy to assess interactions between ovarian hormones and the aging process. Under our experimental conditions, we found that kidney function worsens with age, that is GFR reduces over 18 month analyzed time-course and this was worsened by fetal exposure to maternal low-protein diet and absence of estrogen. Reduction in GFR was followed by increases in albuminuria, proteinuria, inflammatory markers, and tissue carbonyls, all suggesting inflammatory response and oxidative stress. This was associated with changes in AGTR2 expression which was greater at 18 months of age compared to earlier time points, but in MLP offspring only. Our studies show an influence of ovarian hormones on programmed accelerated renal aging and the AGTR2 across the lifespan. The main findings are that ovariectomy is a risk factor for increased aging-related renal injury and that this and oxidative damage might be related to changes in AGTR2 expression.

Mechanical loading increases detection of estrogen receptor-alpha in osteocytes and osteoblasts despite chronic energy restriction

Estrogen receptor-α (ER-α) is an important mediator of the bone response to mechanical loading. We sought to determine whether restricting dietary energy intake by 40% limits the bone formation rate (BFR) response to mechanical loading (LOAD) by downregulating ER-α-expressing osteocytes, or osteoblasts, or both. Female rats (n = 48, 7 mo old) were randomized to ADLIB-SHAM and ADLIB-LOAD groups fed AIN-93M purified diet ad libitum or to ER40-SHAM and ER40-LOAD groups fed modified AIN-93M with 40% less energy (100% of all other nutrients). After 12 wk, LOAD rats were subjected to a muscle contraction protocol three times every third day. ER40 produced lower proximal tibia bone volume (-22%), trabecular thickness (-14%), and higher trabecular separation (+127%) in SHAM but not LOAD rats. ER40 rats exhibited reductions in mineral apposition rate, but not percent mineralizing surface or BFR. LOAD induced similar relative increases in these kinetic measures of osteoblast activity/recruitment in both diet groups., but absolute values for ER40 LOAD rats were lower vs. ADLIB-LOAD. There were fourfold and eightfold increases in proportion of estrogen receptor-α protein-positive osteoblast and osteocytes, respectively, in LOAD vs. SHAM rats, with no effect of ER40. These data suggest that a brief period of mechanical loading significantly affects estrogen receptor-α in cancellous bone osteoblasts and osteocytes. Chronic energy restriction does result in lower absolute values in indices of osteoblast activity after mechanical loading, but not by a smaller increment relative to unloaded bones; this change is not explained by an associated downregulation of ER-α in osteoblasts or osteocytes.

Quantitative trait Loci for resistance to the congenital nephropathy in tensin 2-deficient mice

The ICR-derived glomerulonephritis (ICGN) mouse is a chronic kidney disease (CKD) model that is characterized histologically by glomerulosclerosis, vascular sclerosis and tubulointerstitial fibrosis, and clinically by proteinuria and anemia, which are common symptoms and pathological changes associated with a variety of kidney diseases. Previously, we performed a quantitative trait locus (QTL) analysis to identify the causative genes for proteinuria in ICGN mice, and found a deletion mutation of the tensin 2 gene (Tns2^nph, MGI no: 2447990). Interestingly, the congenic strain carrying the Tns2^nph mutation on a C57BL/6J (B6) genetic background exhibited milder phenotypes than did ICGN mice, indicating the presence of several modifier genes controlling the disease phenotype. In this study, to identify the modifier/resistant loci for CKD progression in Tns2-deficient mice, we performed QTL analysis using backcross progenies from susceptible ICGN and resistant B6 mice. We identified a significant locus on chromosome (Chr) 2 (LOD = 5.36; 31 cM) and two suggestive loci on Chrs 10 (LOD = 2.27; 64 cM) and X (LOD = 2.65; 67 cM) with linkage to the severity of tubulointerstitial injury. One significant locus on Chr 13 (LOD = 3.49; approximately 14 cM) and one suggestive locus on Chr 2 (LOD = 2.41; 51 cM) were identified as QTLs for the severity of glomerulosclerosis. Suggestive locus in BUN was also detected in the same Chr 2 region (LOD = 2.34; 51 cM). A locus on Chr 2 (36 cM) was significantly linked with HGB (LOD = 4.47) and HCT (LOD = 3.58). Four novel epistatic loci controlling either HGB or tubulointerstitial injury were discovered. Further genetic analysis should lead to identification of CKD modifier gene(s), aiding early diagnosis and providing novel approaches to the discovery of drugs for the treatment and possible prevention of kidney disease.

Impact of ovarian function on cardiovascular health in women: focus on hypertension

Arterial blood pressure levels and the prevalence of hypertension are generally lower in premenopausal women compared with age-matched men. The lower blood pressure levels in premenopausal women are associated with a lower risk of the development and progression of cardiovascular disease. In contrast, menopause, a state characterized by a physiologic reduction in ovarian hormone levels, is associated with progressive increases in blood pressure and an overall increase in the risk of cardiovascular disease. These observations suggest an association between blood pressure regulation and changes in ovarian hormone levels, estrogens in particular. In addition to menopause, the risk of hypertension and cardiovascular disease is also dramatically increased in premenopausal women with chronic diseases such as diabetes and systemic lupus erythematosus. Studies suggest that these chronic diseases may be associated with an imbalance in ovarian hormones, which may explain the increased risk of hypertension and cardiovascular disease in these women. However, the use of hormone therapy to manage the risk and prevent the development of hypertension and cardiovascular diseases in women remains controversial. The precise mechanisms by which estrogens contribute to the regulation of blood pressure are still not completely understood. However, accumulating evidence suggests that modulating the activity of locally active hormone systems is one of the major mechanisms by which estrogens exert their effects on target organs, including the vasculature, kidneys, and immune system. In particular, the interaction between estrogens and the renin-angiotensin system has been implicated in the regulation of blood pressure and cardiovascular function in both humans and experimental models. This review summarizes our current understanding of the mechanisms by which estrogens regulate blood pressure and the potential use of hormone therapy in prevention of hypertension and consequent cardiovascular risk.

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.

Oxidant stress and mitochondrial signaling regulate reversible changes of ERα expression and apoptosis in aging mouse glomeruli and mesangial cells

Estrogen actions are largely dependent on the intracellular estrogen receptor (ER) levels. During aging the decline of estrogens or ER leads to a loss in antiinflammatory protection and an increase in oxidant stress due to changes in mitochondrial function. Estrogens/ER may also coordinate signaling between the nucleus and mitochondria through ERK activation, which paradoxically decreases ER expression. The changes in ER expression and transcriptional activation that occur with aging as well as the mitochondria-to-nuclear signaling pathways have not been studied in the glomerulus. We found that ER expression and transcriptional activation decreased with age. Whereas ER levels decreased by greater than 90%, serum 17β-estradiol levels decreased by less than 30%, suggesting alternative mechanisms for ER decrease. Because we postulated that this was due in part to age-related oxidant stress, we treated mesangial cells (MCs) with ethidium bromide (EtBr) to deplete mitochondria. EtBr treatment resulted in decreased ERK activation and reactive oxygen species, which were associated with increased ERα expression and transcriptional activation in old MCs. EtBr treatment also decreased apoptosis and caspase-9 protein expression in old MCs. These data suggest that loss of several of the functions of 17β-estradiol during aging could be mainly due to decreased ERα expression, that the ER loss is reversible by reducing reactive oxygen species, and that mitochondrial retrograde signaling plays a role in this regulation.

Antifibrotic effect of tamoxifen in a model of progressive renal disease

Tamoxifen, a selective estrogen receptor modulator, has antifibrotic properties; however, whether it can attenuate renal fibrosis is unknown. In this study, we tested the effects of tamoxifen in a model of hypertensive nephrosclerosis (chronic inhibition of nitric oxide synthesis with L-NAME). After 30 days, treated rats had significantly lower levels of albuminuria as well as lower histologic scores for glomerulosclerosis and interstitial fibrosis than untreated controls. Tamoxifen was renoprotective despite having no effect on the sustained, severe hypertension induced by L-NAME. Tamoxifen prevented the accumulation of extracellular matrix by decreasing the expression of collagen I, collagen III, and fibronectin mRNA and protein. These renoprotective effects associated with inhibition of TGF-β1 and plasminogen activator inhibitor-1, and with a significant reduction in α-smooth muscle actin-positive cells in the renal interstitium. Furthermore, tamoxifen abrogated IL-1β- and angiotensin-II-induced proliferation of fibroblasts from both kidney explants and from the NRK-49F cell line. Tamoxifen also inhibited the expression of extracellular matrix components and the production and release of TGF-β1 into the supernatant of these cells. In summary, tamoxifen exhibits antifibrotic effects in the L-NAME model of hypertensive nephrosclerosis, likely through the inhibition of TGF-β1, suggesting that it may have therapeutic use in CKD treatment.

Testosterone and 17β-estradiol have opposite effects on podocyte apoptosis that precedes glomerulosclerosis in female estrogen receptor knockout mice

Podocyte damage and apoptosis are thought to be important if not essential in the development of glomerulosclerosis. Female estrogen receptor knockout mice develop glomerulosclerosis at 9 months of age due to excessive ovarian testosterone production and secretion. Here, we studied the pathogenesis of glomerulosclerosis in this mouse model to determine whether testosterone and/or 17β-estradiol directly affect the function and survival of podocytes. Glomerulosclerosis in these mice was associated with the expression of desmin and the loss of nephrin, markers of podocyte damage and apoptosis. Ovariectomy preserved the function and survival of podocytes by eliminating the source of endogenous testosterone production. In contrast, testosterone supplementation induced podocyte apoptosis in ovariectomized wild-type mice. Importantly, podocytes express functional androgen and estrogen receptors, which, upon stimulation by their respective ligands, have opposing effects. Testosterone induced podocyte apoptosis in vitro by androgen receptor activation, but independent of the TGF-β1 signaling pathway. Pretreatment with 17β-estradiol prevented testosterone-induced podocyte apoptosis, an estrogen receptor-dependent effect mediated by activation of the ERK signaling pathway, and protected podocytes from TGF-β1- or TNF-α-induced apoptosis. Thus, podocytes are target cells for testosterone and 17β-estradiol. These hormones modulate podocyte damage and apoptosis.

Raloxifene, a selective estrogen receptor modulator, is renoprotective: a post-hoc analysis

Estrogens have a protective effect on kidney fibrosis in several animal models. Here, we tested the effect of raloxifene, an estrogen receptor modulator, on the change in serum creatinine or estimated glomerular filtration rate (eGFR) and incident kidney-related adverse events. We performed a post-hoc analysis of the multiple outcomes of raloxifene evaluation trial, a double-masked, placebo-controlled randomized clinical trial encompassing 7705 post-menopausal women (aged 31-80 years) with osteoporosis. Participants were randomized to either of two doses of raloxifene, 60 or 120 mg/day, or placebo. Serum creatinine was measured at a central laboratory at baseline and annually. Adverse events were assessed every 6 months and uniformly categorized. Compared with those in the placebo group, participants on raloxifene had a slower yearly rate of increase in creatinine (significant at the low dose) and a significantly slower yearly rate of decrease in eGFR for both doses over 3 years of follow-up. Raloxifene was associated with significantly fewer kidney-related adverse events compared with placebo. Thus, treatment with raloxifene was safe and renoprotective. Clinical trials of raloxifene in post-menopausal women with kidney disease designed to look at kidney outcomes are needed to confirm these findings.

Identifying advanced glycation end products as a major source of oxidants in aging: implications for the management and/or prevention of reduced renal function in elderly persons

Aging is characterized by increasing inflammation and oxidant stress (OS). Reduced renal function was present in more than 20% of normal-aged individuals sampled in the National Health and Nutrition Examination Survey (NHANES) cross-sectional study of the US population. Longitudinal studies in the United States and Italy showed that renal function does not decline in some individuals, suggesting that a search for causes of the loss of renal function in some persons might be indicated and interventions to reduce this outcome should be sought. Because advanced glycation end products (AGEs) induce both inflammation and OS, accumulate with age, and primarily are excreted by the kidney, one outcome of reduced renal function in aging could be decreased AGE disposal. The build-up of AGEs with reduced renal function could contribute to inflammation, increased oxidant stress, and accumulation of AGEs in aging. In fact, results from a longitudinal study of normal aging adults in Italy showed that the most significant correlation with mortality was the level of renal function. A clear link between inflammation, OS, AGEs, and chronic disease was shown in studies of mice that showed that reduction of AGE levels by drugs or decreased intake of AGEs reduces chronic kidney disease (CKD) and cardiovascular disease of aging. The data support a role for AGEs in the development of renal lesions in aging mice and reveal that AGEs in the diet are very important contributors to renal and cardiovascular lesions. AGEs signal through two receptors, one of which is anti-inflammatory (AGER1) and the other is proinflammatory (RAGE). Overexpression of AGER1 protects against OS and acute vascular injury. The reduction of AGEs in the diet is as efficient in preventing aging-related cardiovascular and renal lesions in mice as that seen with calorie restriction. Studies in normal adults of all ages and those with CKD suggest that the findings in mice may be directly applicable to both aging and CKD. Namely, the dietary content of AGEs determines the serum levels of AGEs and inflammatory mediators and urine AGE levels in both normal subjects and CKD patients. Importantly, reduction of AGEs controls these changes in both normal subjects and CKD patients, and the phenotypic changes in AGER1 are reduced in CKD patients by decreasing the amount of AGEs consumed with the diet. These data suggest that the changes in renal function in normal aging may be subject to control and this subject deserves renewed attention.

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.

Estrogen receptor beta protects against in vivo injury in RPE cells

Epidemiological data suggest that estrogen deficiency in postmenopausal women may contribute to the severity of AMD. We discovered that 17beta-estradiol (E2) was a crucial regulator of the severity of extracellular matrix turnover (ECM) dysregulation both in vivo and in vitro. We also found in vitro that the presence of estrogen receptor (ER)beta regulates MMP-2 activity. Therefore in an attempt to delineate the role of the ER subtypes, female estrogen receptor knockout (ERKO) mice were fed a high-fat diet, and the eyes were exposed to seven 5-second doses of nonphototoxic levels of blue-green light over 2 weeks. Three months after cessation of blue light treatment, transmission electron microscopy was performed to assess severity of deposits, Bruchs membrane changes, and choriocapillaris endothelial morphology. We found that changes in the trimolecular complex of pro-MMP-2, MMP-14 and TIMP-2 correlated with increased Bruch's membrane thickening or sub-retinal deposit formation (basal laminar deposits) in ERKObeta mice. In addition RPE isolated from ERKObeta mice had an increase in expression of total collagen and a decrease in MMP-2 activity. Finally we found that ERK an intermediate signaling molecule in the MMP pathway was activated in RPE isolated from ERKObeta mice. These data suggest that mice which lack ERbeta are more susceptible to in vivo injury associated with environmental light and high fat diet.

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.

Loss of ovarian function in the VCD mouse-model of menopause leads to insulin resistance and a rapid progression into the metabolic syndrome

Factors comprising the metabolic syndrome occur with increased incidence in postmenopausal women. To investigate the effects of ovarian failure on the progression of the metabolic syndrome, female B(6)C(3)F(1) mice were treated with 4-vinylcyclohexene diepoxide (VCD) and fed a high-fat (HF) diet for 16 wk. VCD destroys preantral follicles, causing early ovarian failure and is a well-characterized model for the gradual onset of menopause. After 12 wk on a HF diet, VCD-treated mice had developed an impaired glucose tolerance, whereas cycling controls were unaffected [12 wk AUC HF mice 13,455 +/- 643 vs. HF/VCD 17,378 +/- 1140 mg/dl/min, P < 0.05]. After 16 wk on a HF diet, VCD-treated mice had significantly higher fasting insulin levels (HF 5.4 +/- 1.3 vs. HF/VCD 10.1 +/- 1.4 ng/ml, P < 0.05) and were significantly more insulin resistant (HOMA-IR) than cycling controls on a HF diet (HF 56.2 +/- 16.7 vs. HF/VCD 113.1 +/- 19.6 mg/dl x microU/ml, P < 0.05). All mice on a HF diet gained more weight than mice on a standard diet, and weight gain in HF/VCD mice was significantly increased compared with HF cycling controls. Interestingly, even without a HF diet, progression into VCD-induced menopause caused a significant increase in cholesterol and free fatty acids. Furthermore, in mice fed a standard diet (6% fat), insulin resistance developed 4 mo after VCD-induced ovarian failure. Insulin resistance following ovarian failure (menopause) was prevented by estrogen replacement. Studies here demonstrate that ovarian failure (menopause) accelerates progression into the metabolic syndrome and that estrogen replacement prevents the onset of insulin resistance in VCD-treated mice. Thus, the VCD model of menopause provides a physiologically relevant means of studying how sex hormones influence the progression of the metabolic syndrome.

Estrogens and the diabetic kidney

BACKGROUND

Across all ages, the incidence and rate of progression of most nondiabetic renal diseases are markedly higher in men compared with age-matched women. These observations suggest that female sex may be renoprotective. In the setting of diabetes, however, this female protection against the development and progression of renal disease is diminished.

OBJECTIVE

This review aimed to summarize our current understanding of sex differences in the development and progression of diabetic renal disease, and of the contribution of sex hormones, particularly estrogens, to the pathophysiology of this disease. We also attempted to answer why female sex does not protect the diabetic kidney.

METHODS

Using terms such as gender, sex, diabetes, diabetic nephropathy, estrogens, and sex hormones, the PubMed database was searched for English-language articles; targeted searches were conducted using terms such as gender/sex differences in diabetic renal disease. No restrictions were imposed on publication dates.

RESULTS

Although the existing data regarding the sex differences in the incidence and progression of diabetic renal disease are inconclusive, the undisputed fact is that women with either type 1 or type 2 diabetes mellitus exhibit a much higher incidence of renal disease compared with nondiabetic women. It is conceivable that the loss of female sex as a renoprotective factor in diabetes may be related to the abnormal regulation of sex hormone concentrations. Both clinical and experimental data suggest that diabetes may be associated with an imbalance in estradiol concentrations. Supplementation with 17beta-estradiol or administration of selective estrogen receptor modulators reduces the incidence of diabetes and attenuates the progression of diabetic renal disease.

CONCLUSIONS

Serum concentrations of ovarian hormones may provide a new means for predicting future risk of renal complications in diabetes. Exogenous steroid hormones may be an effective treatment for attenuating the progression of diabetic nephropathy.

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.