Differential effects of continuous and intermittent 17beta-estradiol replacement and tamoxifen therapy on the prevention of glomerulosclerosis: modulation of the mesangial cell phenotype in vivo

Sex and Gender Related Differences in Diabetic Kidney Disease

Diversity in sex and gender are important considerations in the pathogenesis, prognostication, research, and management of diabetic kidney disease (DKD). Sex and gender differences in the disease risk, disease-specific mechanisms, and outcomes in DKD may be attributed to biological differences between males and females at the cellular and tissue level, inconsistencies in the diagnostic and assessment tools used in chronic kidney disease and DKD, as well societal differences in the way men, women, and gender-diverse individuals self-manage and interact with health care systems. This review outlines key considerations related to the impact of sex on DKD, specifically elaborating on how they contribute to observed differences in disease epidemiology, pathogenesis, and treatment strategies. We also highlight the effect of gender on DKD progression and care.

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.

Urine-derived exosomes from individuals with IPF carry pro-fibrotic cargo

BACKGROUND

MicroRNAs (miRNA) and other components contained in extracellular vesicles may reflect the presence of a disease. Lung tissue, sputum, and sera of individuals with idiopathic pulmonary fibrosis (IPF) show alterations in miRNA expression. We designed this study to test whether urine and/or tissue derived exosomal miRNAs from individuals with IPF carry cargo that can promote fibrosis.

METHODS

Exosomes were isolated from urine (U-IPFexo), lung tissue myofibroblasts (MF-IPFexo), serum from individuals with IPF (n=16) and age/sex-matched controls without lung disease (n=10). We analyzed microRNA expression of isolated exosomes and their in vivo bio-distribution. We investigated the effect on ex vivo skin wound healing and in in vivo mouse lung models.

RESULTS

U-IPFexo or MF-IPFexo expressed miR-let-7d, miR-29a-5p, miR-181b-3p and miR-199a-3p consistent with previous reports of miRNA expression obtained from lung tissue/sera from patients with IPF. In vivo bio-distribution experiments detected bioluminescent exosomes in the lung of normal C57Bl6 mice within 5 min after intravenous infusion, followed by distribution to other organs irrespective of exosome source. Exosomes labeled with gold nanoparticles and imaged by transmission electron microscopy were visualized in alveolar epithelial type I and type II cells. Treatment of human and mouse lung punches obtained from control, non-fibrotic lungs with either U-IPFexo or MF-IPFexo produced a fibrotic phenotype. A fibrotic phenotype was also induced in a human ex vivo skin model and in in vivo lung models.

CONCLUSIONS

Our results provide evidence of a systemic feature of IPF whereby exosomes contain pro-fibrotic miRNAs when obtained from a fibrotic source and interfere with response to tissue injury as measured in skin and lung models.

FUNDING

This work was supported in part by Lester and Sue Smith Foundation and The Samrick Family Foundation and NIH grants R21 AG060338 (SE and MKG), U01 DK119085 (IP, RS, MTC).

Sex-related differences in diabetic kidney disease: A review on the mechanisms and potential therapeutic implications

Sexual dimorphism may play a key role in the pathogenesis of diabetic kidney disease (DKD) and explain differences observed in disease phenotypes, responses to interventions, and disease progression between men and women with diabetes. Therefore, omitting the consideration of sex as a biological factor may result in delayed diagnoses and suboptimal therapies. This review will summarize the effects of sexual dimorphism on putative metabolic and molecular mechanisms underlying DKD, and the potential implications of these differences on therapeutic interventions. To successfully implement precision medicine, we require a better understanding of sexual dimorphism in the pathophysiologic progression of DKD. Such insights can unveil sex-specific therapeutic targets that have the potential to maximize efficacy while minimizing adverse events.

Gender-biased kidney damage in mice following exposure to tobacco cigarette smoke: More protection in premenopausal females

Multiple clinical studies documented renal damage in chronic cigarette smokers (CS) irrespective of their age and gender. Premenopausal female smokers are known to exert a certain cardiovascular and renal protection with undefined mechanisms. Given the multiple demographic variables within clinical studies, this experimental study was designed to be the first to assess whether gender‐biased CS‐induced kidney damage truly exists between premenopausal female and age‐matched C57Bl6J male mice when compared to their relative control groups. Following 6 weeks of CS exposure, cardiac function, inflammatory marker production, fibrosis formation, total and glomerular ROS levels, and glomerulotubular homeostasis were assessed in both genders. Although both CS‐exposed male and female mice exhibited comparable ROS fold change relative to their respective control groups, CS‐exposed male mice showed a more pronounced fibrotic deposition, inflammation, and glomerulotubular damage profile. However, the protection observed in CS‐exposed female group was not absolute. CS‐exposed female mice exhibited a significant increase in fibrosis, ROS production, and glomerulotubular alteration but with a pronounced anti‐inflammatory profile when compared to their relative control groups. Although both CS‐exposed genders presented with altered glomerulotubular homeostasis, the alteration phenotype between genders was different. CS‐exposed males showed a significant decrease in Bowman's space along with reduced tubular diameter consistent with an endocrinization pattern of chronic tubular atrophy, suggestive of an advanced stage of glomerulotubular damage. CS‐exposed female group, on the other hand, displayed glomerular hypertrophy with a mild tubular dilatation profile suggestive of an early stage of glomerulotubular damage that generally precedes collapse. In conclusion, both genders are prone to CS‐induced kidney damage with pronounced female protection due to a milder damage slope.

Sex Differences in Diabetic Kidney Disease

While the global prevalence of both type 1 and type 2 diabetes mellitus is similar in men and women, the consequences of diabetes on associated end-organ complications, including diabetic kidney disease appear to be more sex-specific. Particularly, women with diabetes have higher mortality rates for diabetes-related deaths, and higher prevalence of diabetic kidney disease risk factors such as hypertension, hyperglycemia, obesity, and dyslipidemia. However, the evidence for the impact of sex on diabetic kidney disease prevalence and disease progression is limited and inconsistent. Although most studies agree that the protective effect of the female sex against the development of kidney disease is diminished in the setting of diabetes, the reasons for this observation are unclear. Whether or not sex differences exist in the risk of diabetic kidney disease is also unclear, with studies reporting either higher risk in men, women, or no sex differences. Despite the remaining controversies, some of the factors that associate with sex differences in the risk of diabetic kidney disease are age at onset, and type and duration of diabetes. There is growing appreciation of the importance of sex hormones in the regulation of renal function, with estrogens generally considered to be renoprotective. Although some progress has been made towards better understanding of the mechanisms by which sex hormones play a role in the pathophysiology of diabetic kidney disease, the translational potential of this knowledge is still underappreciated. A better understanding of sex differences in diabetic kidney disease may provide basis for personalized and sex-specific treatment of diabetic kidney disease.

Synaptic plasticity in hippocampal CA1 neurons and learning behavior in acute kidney injury, and estradiol replacement in ovariectomized rats

Background

Neurological complications may occur in patients with acute or chronic renal failure; however, in cases of acute renal failure, the signs and symptoms are usually more pronounced, and progressed rapidly. Oxidative stress and nitric oxide in the hippocampus, following kidney injury may be involved in cognitive impairment in patients with uremia. Although many women continue taking hormone therapy for menopausal symptom relief, but there are also some controversies about the efficacy of exogenous sex hormones, especially estrogen therapy alone, in postmenopausal women with kidney injury. Herein, to the best of our knowledge for the first time, spatial memory and synaptic plasticity at the CA1 synapse of a uremic ovariectomized rat model of menopause was characterized by estradiol replacement alone.

Results

While estradiol replacement in ovariectomized rats without uremia, promotes synaptic plasticity, it has an impairing effect on spatial memory through hippocampal oxidative stress under uremic conditions, with no change on synaptic plasticity. It seems that exogenous estradiol potentiated the deleterious effect of acute kidney injury (AKI) with increasing hippocampal oxidative stress.

Conclusions

Although, estrogen may have some positive effects on cognitive function in healthy subjects, but its efficacy in menopause subjects under uremic states such as renal transplantation, needs to be further investigated in terms of dosage and duration.

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

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2018_10_11_CJASNPodcast_18_1.

Mesenchymal stromal cells prevent bleomycin-induced lung and skin fibrosis in aged mice and restore wound healing

Fibrosis can develop in nearly any tissue leading to a wide range of chronic fibrotic diseases. However, current treatment options are limited. In this study, we utilized an established aged mouse model of bleomycin-induced lung fibrosis (BLM) to test our hypothesis that fibrosis may develop simultaneously in multiple organs by evaluating skin fibrosis and wound healing. Fibrosis was induced in lung in aged (18-22-month-old) C57BL/6 male mice by intratracheal BLM administration. Allogeneic adipose-derived mesenchymal stromal cells (ASCs) or saline were injected intravenously 24 hr after BLM administration. Full thickness 8-mm punch wounds were performed 7 days later to study potential systemic anti-fibrotic and wound healing effects of intravenously delivered ASCs. Mice developed lung and skin fibrosis as well as delayed wound closure. Moreover, we observed similar changes in the expression of known pro-fibrotic factors in both lung and skin wound tissue, including miR-199 and protein expression of its corresponding target, caveolin-1, as well as phosphorylation of protein kinase B. Importantly, ASC-treated mice exhibited attenuation of BLM-induced lung and skin fibrosis and accelerated wound healing, suggesting that ASCs may prime injured tissues and prevent end-organ fibrosis.

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.

Inhibition of Advanced Glycation End Products (AGEs) Accumulation by Pyridoxamine Modulates Glomerular and Mesangial Cell Estrogen Receptor α Expression in Aged Female Mice

Age-related increases in oxidant stress (OS) play a role in regulation of estrogen receptor (ER) expression in the kidneys. In this study, we establish that in vivo 17β-estradiol (E2) replacement can no longer upregulate glomerular ER expression by 21 months of age in female mice (anestrous). We hypothesized that advanced glycation end product (AGE) accumulation, an important source of oxidant stress, contributes to these glomerular ER expression alterations. We treated 19-month old ovariectomized female mice with pyridoxamine (Pyr), a potent AGE inhibitor, in the presence or absence of E2 replacement. Glomerular ERα mRNA expression was upregulated in mice treated with both Pyr and E2 replacement and TGFβ mRNA expression decreased compared to controls. Histological sections of kidneys demonstrated decreased type IV collagen deposition in mice receiving Pyr and E2 compared to placebo control mice. In addition, anti-AGE defenses Sirtuin1 (SIRT1) and advanced glycation receptor 1 (AGER1) were also upregulated in glomeruli following treatment with Pyr and E2. Mesangial cells isolated from all groups of mice demonstrated similar ERα, SIRT1, and AGER1 expression changes to those of whole glomeruli. To demonstrate that AGE accumulation contributes to the observed age-related changes in the glomeruli of aged female mice, we treated mesangial cells from young female mice with AGE-BSA and found similar downregulation of ERα, SIRT1, and AGER1 expression. These results suggest that inhibition of intracellular AGE accumulation with pyridoxamine may protect glomeruli against age-related oxidant stress by preventing an increase of TGFβ production and by regulation of the estrogen receptor.

Adjusting the 17β-Estradiol-to-Androgen Ratio Ameliorates Diabetic Nephropathy

Diabetes is manifested predominantly in males in experimental models, and compelling evidence suggests that 17β-estradiol (E2) supplementation improves hyperglycemia in humans. We previously generated a severely diabetic transgenic (Tg) mouse model by β-cell–specific overexpression of inducible cAMP early repressor (ICER) and found that male but not female ICER-Tg mice exhibit sustained hyperglycemia and develop major clinical and pathologic features of human diabetic nephropathy (DN). Thus, we hypothesized that differences in circulating hormone levels have a key role in determining susceptibility to diabetes. Here, we examined whether DN in male ICER-Tg mice is rescued by adjusting the androgen-to-E2 ratio to approximate that in normoglycemic female ICER-Tg mice. We treated hyperglycemic male ICER-Tg mice with orchiectomy (ORX), E2 pellet implantation, or both. E2 pellet implantation at an early stage of DN with or without ORX caused a rapid drop in blood glucose and a dramatic increase in β-cell number, and it markedly inhibited DN progression [namely, E2 reduced glomerulosclerosis, collagen 4 deposition and albuminuria, and prevented hyperfiltration]. Furthermore, E2 pellet implantation was more effective than ORX alone and induced a remarkable improvement, even when initiated at advanced-stage DN. In contrast, induction of normoglycemia by islet transplant in ICER-Tg mice eliminated albuminuria but was less effective than E2 + ORX in reducing glomerulosclerosis, collagen 4 deposition, and hyperfiltration. These findings indicate that E2 treatment is effective, even after establishment of DN, whereas glucose normalization alone does not improve sclerotic lesions. We propose that E2 intervention is a potential therapeutic option for DN.

Therapeutic benefits of young, but not old, adipose-derived mesenchymal stem cells in a chronic mouse model of bleomycin-induced pulmonary fibrosis

The observation that pulmonary inflammatory lesions and bleomycin (BLM)-induced pulmonary fibrosis spontaneously resolve in young mice, whereas remaining irreversible in aged mice suggests that impairment of pulmonary regeneration and repair is associated with aging. Because mesenchymal stem cells (MSCs) may promote repair after injury, we postulated that differences in MSCs from aged mice may underlie postinjury fibrosis in aging. The potential for young-donor MSCs to inhibit BLM-induced pulmonary fibrosis in aged male mice (>22 months) has not been studied. Adipose-derived MSCs (ASCs) from young (4 months) and old (22 months) male mice were infused 1 day after intratracheal BLM administration. At 21-day sacrifice, aged BLM mice demonstrated lung fibrosis by Ashcroft score, collagen content, and α(v)-integrin messenger RNA (mRNA) expression. Lung tissue from aged BLM mice receiving young ASCs exhibited decreased fibrosis, matrix metalloproteinase (MMP)-2 activity, oxidative stress, and markers of apoptosis vs BLM controls. Lung mRNA expression of tumor necrosis factor-alpha was also decreased in aged BLM mice receiving young-donor ASCs vs BLM controls. In contrast, old-donor ASC treatment in aged BLM mice did not reduce fibrosis and related markers. On examination of the cells, young-donor ASCs had decreased mRNA expression of MMP-2, insulin-like growth factor (IGF) receptor, and protein kinase B (AKT) activation compared with old-donor ASCs. These results show that the BLM-induced pulmonary fibrosis in aged mice could be blocked by young-donor ASCs and that the mechanisms involve changes in collagen turnover and markers of inflammation.

Estrogen preserves split renal function in a chronic complete unilateral ureteral obstruction animal model

Estrogen may help to preserve renal function in chronic kidney disease. This study examined whether estrogen administration or deprivation affected the split renal function in rats subjected to chronic unilateral ureteral obstruction (UUO). Fifteen adult female Sprague-Dawley rats were randomly divided into three groups. Low- and high-estrogen groups were modeled by female castration or estrogen intraperitoneal injection, respectively, and the rats in the normal-estrogen group were untreated. Intermittent split renal function [glomerular filtration rate (GFR)] examination was performed on rats on days 2, 6 and 16 after UUO surgery via single-photon emission computed tomography (SPECT/CT). Routine hematoxylin and eosin (H&E) staining, immunohistochemistry, pathology examination and electron microscopy were performed to compare the histological differences. Low-, normal- and high-estrogen groups were successfully established (P<0.001). In the acute stage, the GFR of the contralateral healthy kidney showed a greater compensatory rise in the normal- and high-estrogen groups than in the low-estrogen group (P<0.05). In the chronic stage, the GFR of the obstructed kidney continued to decrease with the GFR of the high-estrogen group being significantly better preserved than that of the low-estrogen group (P<0.05). The GFR of the contralateral kidney compensated to the greatest extent in the high-estrogen group (P=0.01), and the total GFR was significantly superior (P<0.05). Routine H&E examination showed significant histological changes following surgery. The low-estrogen group had significant renal interstitial fibrosis compared with the normal- and high-estrogen groups (P<0.05), as observed by immunohistochemical (IHC) examination of transforming growth factor-β (TGF-β) and α-smooth muscle actin (α-SMA). Electron-microscopic (EM) examination also differentiated between groups. In conclusion, estrogen administration and deprivation significantly affected renal function. Estrogen may preserve the split renal function (GFR) in rats with chronic UUO.

In vivo 17β-estradiol treatment contributes to podocyte actin stabilization in female db/db mice

We recently showed that 17β-estradiol (E(2)) treatment ameliorated type 2 diabetic glomerulosclerosis in mice in part by protecting podocyte structure and function. Progressive podocyte damage is characterized by foot process effacement, vacuolization, detachment of podocytes from the glomerular basement membrane, and apoptosis. In addition, podocytes are highly dependent on the preservation of their actin cytoskeleton to ensure proper function and survival. Because E(2) administration prevented podocyte damage in our study on diabetic db/db mice and has been shown to regulate both actin cytoskeleton and apoptosis in other cell types and tissues, we investigated whether actin remodeling and apoptosis were prevented in podocytes isolated from E(2)-treated diabetic db/db mice. We performed G-actin/F-actin assays, Western analysis for Hsp25 expression, Ras-related C(3) botulinum toxin substrate 1 (Rac1) activity, and apoptosis assays on previously characterized podocytes isolated from both in vivo-treated placebo and E(2) female db/db mice. We found that in vivo E(2) protects against a phenotype change in the cultured podocytes characterized by a percent increase of F-actin vs. G-actin, suppression of Hsp25 expression and transcriptional activation, increase of Rac1 activity, and decreased apoptotic intermediates. We conclude from these studies that E(2) treatment protects against podocyte damage and may prevent/reduce diabetes-induced kidney disease.

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.

The influence of gender and sexual hormones on incidence and outcome of chronic kidney disease

It has long been known that the female sex is associated with a better clinical outcome in chronic renal diseases. Although many experimental, clinical, and epidemiological studies in adults have attempted to explain the difference in disease progression between females and males, a definitive understanding of the underlying mechanisms is still lacking. Hormone-modulating therapies are being increasingly used for various indications (such as post-menopausal hormone replacement, estrogen- or androgen-receptor antagonists for cancer therapy). Therefore, a deeper knowledge of the interaction between sexual hormones and progression of kidney disease is important, as hormone-modulating therapy for non-renal indication may influence both kidney structure and function. In addition, specific modulation of the sexual hormone system, such as the use of selective estrogen receptor modulators, may represent a therapeutic option for patients with renal diseases. Although conclusive data on this topic in the pediatric population are still lacking, the aim of this review is to familiarize pediatric nephrologists with gender-specific differences in renal physiology, pathophysiology, and the progression of kidney diseases. Experimental models that analyze the effects of sexual hormones on renal structure and function are discussed. It is hoped that this review will stimulate researchers to focus on pediatric studies that will provide a deeper insight into the interaction of gender hormones and the kidney both before and during puberty.

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.

Chronic kidney disease in postmenopausal women

Menopause is derived from the Greek words men (month) and pauses (cessation) and means permanent cessation of menstruation after the loss of ovarian activity. Chronic kidney disease (CKD) has recently been associated with cardiovascular events in several studies. CKD patients have a heavy burden of traditional cardiovascular risk factors in addition to a range of nontraditional risk factors such as inflammation and abnormal metabolism of calcium and phosphate. In this review, the association of CKD and cardiovascular disease (CVD), as well as of osteoporosis in postmenopausal women is discussed. CKD mineral and bone disorder, characterized by disturbances of calcium/phosphate/parathyroid hormone, bone abnormalities and vascular and soft tissue calcification, is highly prevalent in CKD and is a strong, independent predictor of bone fracture, CVD and death. Estrogen has been shown to: (a) decrease the expression of angiotensin type 1 receptors in vasculature and kidneys; (b) reduce the expression and activity of angiotensin-converting enzyme, and (c) cause the release of angiotensinogen substrate from the liver. However, the degree of activation or suppression of the renin-angiotensin-aldosterone system by estrogen has not been clearly established. Clinical data on the effects of estrogen therapy on bone mineral densities are extremely limited in the ESRD population. CVD is the most common cause of death in postmenopausal women with CKD and many contributing factors have been explored. Future research for prevention of CVD in postmenopausal women with CKD would focus on the biology of vascular calcification as well as bone loss.

Dose-dependent toxic effects of high-dose estrogen on renal and cardiac injury in surgically postmenopausal mice

AIMS

We previously found that in mice with experimental myocardial infarction (MI), 17β-estradiol (E2) increased mortality and worsened cardiac remodeling and these deleterious effects were associated with renal enlargement and hydronephrosis in a dose-dependent manner. In the present study we questioned whether E2-induced renal damage predisposes to rather than results from its adverse effects on the heart.

MAIN METHODS

Ovariectomized (ovx) mice received either placebo (P) or E2 at 0.02 (E2-L, low dose), 0.42 (E2-M, moderate dose) or 4.2 μg/d (E2-H, high dose) for 8 weeks.

KEY FINDINGS

E2-L partially restored uterine weight and plasma estrogen levels without affecting heart, lung and liver weight, hemodynamic parameters, or heart and kidney morphology and function. E2-M restored normal uterine weight, but this was accompanied by a significant increase in kidney weight, albuminuria, glomerular matrix formation and markers for oxidative stress. E2-H increased uterine weight 4.5-fold and resulted in higher plasma creatinine levels, severe albuminuria, renal tubular dilatation, tubulointerstitial injury, hydronephrosis, glomerulosclerosis and oxidative stress. E2-H also caused ascites, hepatomegaly and fluid retention in the uterine horns but had no significant effect on blood pressure or heart function.

SIGNIFICANCE

Our data demonstrated that an excessive dose of E2 that raises uterine weight beyond physiological levels adversely affects the kidney even before it damages the heart. We believe estrogen dosage should be taken into account when considering hormonal replacement therapy, since inappropriate doses of E2 may damage not only the heart but also the kidney.

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.

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.

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.

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.

17 beta-estradiol and tamoxifen upregulate estrogen receptor beta expression and control podocyte signaling pathways in a model of type 2 diabetes

Diabetic nephropathy remains one of the most important causes of end-stage renal disease. This is particularly true for women from racial/ethnic minorities. Although administration of 17beta-estradiol to diabetic animals has been shown to reduce extracellular matrix deposition in glomeruli and mesangial cells, effects on podocytes are lacking. Given that podocyte injury has been implicated as a factor leading to the progression of proteinuria and diabetic nephropathy, we treated db/db mice, a model of type 2 diabetic glomerulosclerosis, with 17beta-estradiol or tamoxifen to determine whether these treatments reduce podocyte injury and decrease glomerulosclerosis. We found that albumin excretion, glomerular volume, and extracellular matrix accumulation were decreased in these mice compared to placebo treatment. Podocytes isolated from all treatment groups were immortalized and these cell lines were found to express the podocyte markers WT-1, nephrin, and the TRPC6 cation channel. Tamoxifen and 17beta-estradiol treatment decreased podocyte transforming growth factor-beta mRNA expression but increased that of the estrogen receptor subtype beta protein. 17beta-estradiol, but not tamoxifen, treatment decreased extracellular-regulated kinase phosphorylation. These data, combined with improved albumin excretion, reduced glomerular size, and decreased matrix accumulation, suggest that both 17beta-estradiol and tamoxifen may protect podocytes against injury and therefore ameliorate diabetic nephropathy.

Gender and human chronic renal disease

BACKGROUND

Gender affects the incidence, prevalence, and progression of renal disease. In animal models of the disease, female sex appears to modify the course of progression. Hormonal manipulation by male or female castration also changes the course of renal disease progression, suggesting direct effects of sex hormones in influencing the course of these maladies.

OBJECTIVE

This review examines the pertinent animal and human studies assessing the role of gender, and strives to shed light on the possible physiologic mechanisms underlying the effect of gender, on renal disease progression.

METHODS

A summary and evaluation of past and recent studies describing the rate of renal disease progression in animal models and humans as it pertains to gender is provided. In addition, studies elucidating the factors involved in the more modest renal progression rate in females are reviewed and conclusions drawn. Relevant English-language publications were identified by searching the PubMed database from January 1990 until November 2007 using the search terms gender, sex, renal disease, and kidney.

RESULTS

In polycystic kidney disease, membranous nephropathy, immunoglobulin A nephropathy, and "chronic renal disease of unknown etiology," men progress at a faster rate to end-stage renal failure than do women. In type 1 diabetes mellitus, there is evidence that males are more likely to manifest signs of renal disease, such as proteinuria. The factors involved in this gender disparity may include diet, kidney and glomerular size, differences in glomerular hemodynamics, and the direct effects of sex hormones. In many, but not all, animal models of renal disease, estrogens slow progression rate. Several studies have recently evaluated the effect of selective estrogen receptor modulators on renal function in humans.

CONCLUSION

Further studies assessing the factors involved in the gender disparity in renal disease progression and the effects of hormonal treatments are warranted.

Oral estrogen therapy in postmenopausal women is associated with loss of kidney function

Women are generally protected against progressive loss of kidney function; however, this advantage seems to diminish with menopause. Because of conflicting reports on the association between use of hormone therapy and kidney function we studied 5845 women (1459 on hormone therapy and 4386 non-users) who were over 66 years of age and had at least 2 serum creatinine measurements during the 2 year study period. After adjustment for covariates, hormone use (estrogen-only, progestin-only, or both) was associated with a significant loss of estimated GFR as the primary outcome along with an increased risk of rapid loss of kidney function as the secondary outcome compared to non-users. This increased rate of loss was associated with oral but not transvaginal estrogen use. An increased cumulative dose of estrogen was also associated with a greater decline in estimated GFR. Our study shows an independent association in a dose-dependent manner of estrogen use and loss of kidney function in this elderly population.

Subtype specific estrogen receptor action protects against changes in MMP-2 activation in mouse retinal pigmented epithelial cells

Eyes with age-related macular degeneration (AMD) demonstrate accumulation of specific deposits and extracellular matrix (ECM) molecules under the retinal pigment epithelium (RPE). AMD is about two times more prevalent in aging postmenopausal women. Therefore we studied whether 17beta-estradiol (E(2)) modulates the expression and activity of the trimolecular complex (MMP-2, TIMP-2 and MMP-14), molecules which are of major importance for ECM turnover in RPE. We used cell lines isolated from estrogen receptor knockout mice (ERKO) to determine which ER (estrogen receptor) subtype was important for ECM regulation in RPE cells. We found that mouse RPE sheets had higher baseline MMP-2 activity in the presence of ERbeta. This correlated with higher MMP-2 activity in RPE cell lines isolated from ERKOalpha mice. Exposure to E(2) increased MMP-2 activity in mouse RPE cell lines. In addition E(2) increased transcriptional activation of the MMP-2 promoter through a functional Sp1 site which required the presence of ERbeta, but not ERalpha. E(2) also maintained levels of pro MMP-2, and MMP-14 and TIMP-2 activity after oxidant injury. Since the direct effects of E(2) on MMP-2 transcriptional activation and the regulation of the trimolecular complex after oxidant-induced injury requires ERbeta, this receptor subtype may have a role as a potential therapeutic target to prevent changes in activation of MMP-2.

17beta-Estradiol attenuates diabetic kidney disease by regulating extracellular matrix and transforming growth factor-beta protein expression and signaling

We previously showed that supplementation with 17beta-estradiol (E2) from the onset of diabetes attenuates the development of diabetic renal disease. The aim of the present study was to examine whether E2 can also attenuate the disease process once it has developed. The present study was performed in nondiabetic and streptozotocin-induced diabetic Sprague-Dawley rats. E2 supplementation began after 9 wk of diabetes and continued for 8 wk. Diabetes was associated with an increase in urine albumin excretion, glomerulosclerosis, tubulointerstitial fibrosis, renal cortical collagen type I and IV, laminin, plasminogen activator inhibitor-1, tissue inhibitors of metalloproteinase-1 and -2, transforming growth factor (TGF)-beta, TGF-beta receptor type I and II, Smad2/3, phosphorylated Smad2/3, and Smad4 protein expression, and CD68-positive cell abundance. Decreases in matrix metalloproteinase (MMP)-2 protein expression and activity and decreases in Smad6 and Smad7 protein expression were also associated with diabetes. E2 supplementation completely or partially attenuated all these changes, except Smad4 and fibronectin, on which E2 supplementation had no effect. These data suggest that E2 attenuates the progression of diabetic renal disease once it has developed by regulating extracellular matrix, TGF-beta, and expression of its downstream regulatory proteins. These findings support the notion that sex hormones in general, and E2 in particular, are important regulators of renal function and may be novel targets for the treatment and prevention of diabetic renal disease.

Gender-specific effects of endogenous testosterone: female alpha-estrogen receptor-deficient C57Bl/6J mice develop glomerulosclerosis

Young female mice on a C57Bl/6J (B6) background are considered glomerulosclerosis (GS)-resistant but aging B6 mice develop mild GS. Estrogen deficiency accelerates while estrogen replacement retards GS in young sclerosis-prone oligosyndactyly mutant mice on an ROP background. To explore the effects of sex hormones on glomerular structure and function in the context of gender and genetic background, we studied mice in which the estrogen-receptor (ER) genes alpha- or -beta were deleted (alpha- or betaER knockout (KO)) and crossed into the B6 background. We also studied ovariectomized (Ovx) B6 mice given testosterone. Male and female betaERKO and male alphaERKO mice had no glomerular dysfunction at 9 months of age; however, alphaERKO female mice displayed albuminuria and GS. Ovx prevented glomerular dysfunction in alphaERKO female mice by eliminating endogenous testosterone production while exogenous testosterone induced GS in Ovx B6 mice. Androgen receptor (AR) expression and function was found in microdissected glomeruli and cultured mesangial cells. Testosterone compared to placebo increased both AR expression and TGF-beta1 mRNA levels in glomeruli isolated from female B6 mice. Estrogen deficiency had no deleterious effects on the glomeruli in B6 mice. Our study shows that genetic traits strongly influence the GS-promoting effects of estrogen deficiency while testosterone induces GS in a gender-specific manner.

Smoking induces glomerulosclerosis in aging estrogen-deficient mice through cross-talk between TGF-beta1 and IGF-I signaling pathways

Smoking is a known risk factor for the progression of chronic kidney diseases. However, its independent contribution to the development of ESRD and the underlying molecular mechanism have not been well elucidated. Although the risk for ESRD is higher in postmenopausal women according to the US Renal Data System, the number of women who smoke is on the rise worldwide. Therefore, the effects of smoking and estrogen status on glomerular function and structure were studied in female B6 mice that were ovariectomized at 3 (young) and 15 mo (aged) of age. The mice received either 17beta-estradiol (E(2)) replacement or placebo (Pla) and were divided further into groups that were exposed to cigarette smoke (S) and not exposed (NS). Six months of exposure to smoke had no effect on young mice, although aging S/Pla mice exhibited a phenotype of increased albumin excretion associated with a moderately increased glomerular collagen type IV deposition compared with NS/Pla mice. S/Pla mice also had a two-fold increase in glomerular TGF-beta, Smad3, and IGF-I receptor mRNA expression compared with the NS group. Mesangial cells that were isolated from S/Pla mice had an increase of IGF-I receptor protein, and IGF-I stimulated a TGF-beta reporter construct promoter three-fold. This was blocked by pretreatment with a neutralizing antibody to IGF-I, LY294002 (phosphatidylinositol-3 kinase inhibitor) or a dominant negative Smad construct. In addition, Smad3 activation was stimulated by IGF-I and blocked by LY294002, suggesting cross-talk between Smad and the phosphatidylinositol-3 kinase/AKT pathways. The smoking phenotype was reversed by E(2) replacement. In conclusion, smoking induces a phenotype in E(2)-deficient mice that is characterized by activation and cross-talk between the TGF-beta1 and IGF-I signaling pathways.