Selective estrogen receptor modulation attenuates proteinuria-induced renal tubular damage by modulating mitochondrial oxidative status

Tubular toxicity of proteinuria and the progression of chronic kidney disease

Proteinuria is a well-established biomarker of chronic kidney disease (CKD) and a risk predictor of associated disease outcomes. Proteinuria is also a driver of CKD progression toward end-stage kidney disease. Toxic effects of filtered proteins on proximal tubular epithelial cells enhance tubular atrophy and interstitial fibrosis. The extent of protein toxicity and the underlying molecular mechanisms responsible for tubular injury during proteinuria remain unclear. Nevertheless, albumin elicits its toxic effects when degraded and reabsorbed by proximal tubular epithelial cells. Overall, healthy kidneys excrete over 1000 individual proteins, which may be potentially harmful to proximal tubular epithelial cells when filtered and/or reabsorbed in excess. Proteinuria can cause kidney damage, inflammation and fibrosis by increasing reactive oxygen species, autophagy dysfunction, lysosomal membrane permeabilization, endoplasmic reticulum stress and complement activation. Here we summarize toxic proteins reported in proteinuria and the current understanding of molecular mechanisms of toxicity of proteins on proximal tubular epithelial cells leading to CKD progression.

Inverse association between caffeine intake and albuminuria in US adults: an analysis of NHANES 2005-2016

OBJECTIVES

Albuminuria is a significant biomarker of various kidney diseases and is associated with renal outcome. Recently, caffeine intake has shown potential renoprotective effects. However, the relationship between caffeine intake and albuminuria remains profoundly elusive.

METHODS

We conducted a cross-sectional study aimed to explore the association between caffeine intake and albuminuria in the American adult population using the data acquired from the National Health and Nutrition Examination Survey (NHANES) 2005-2016. Caffeine intake was assessed by 24-h dietary recalls, and albuminuria was assessed by albumin-to-creatinine ratio. Multivariate logistic regression was performed to explore the independent association between caffeine intake and albuminuria. Subgroup analysis and interaction tests were also conducted.

RESULTS

Among 23,060 participants, 11.8% of the individuals exhibited albuminuria, and the prevalence of albuminuria decreased with higher caffeine intake tertiles (Tertile 1: 13%; Tertile 2: 11.9%; Tertile 3: 10.5%; P < 0.001). After adjusted potential confounders, the results of logistic regression indicated that a higher caffeine intake was associated with a decreased risk of albuminuria (OR = 0.903; 95% CI: 0.84, 0.97; P = 0.007), especially in females and the participants aged <60 years and chronic kidney disease stage II.

CONCLUSION

The present study first indicated an inverse correlation between caffeine intake and albuminuria, which further confirmed the potentially protective effects of caffeine on the kidney.

Clinical Use and Treatment Mechanism of Molecular Hydrogen in the Treatment of Various Kidney Diseases including Diabetic Kidney Disease

As diabetes rates surge globally, there is a corresponding rise in the number of patients suffering from diabetic kidney disease (DKD), a common complication of diabetes. DKD is a significant contributor to chronic kidney disease, often leading to end-stage renal failure. However, the effectiveness of current medical treatments for DKD leaves much to be desired. Molecular hydrogen (H2) is an antioxidant that selectively reduces hydroxyl radicals, a reactive oxygen species with a very potent oxidative capacity. Recent studies have demonstrated that H2 not only possesses antioxidant properties but also exhibits anti-inflammatory effects, regulates cell lethality, and modulates signal transduction. Consequently, it is now being utilized in clinical applications. Many factors contribute to the onset and progression of DKD, with mitochondrial dysfunction, oxidative stress, and inflammation being strongly implicated. Recent preclinical and clinical trials reported that substances with antioxidant properties may slow the progression of DKD. Hence, we undertook a comprehensive review of the literature focusing on animal models and human clinical trials where H2 demonstrated effectiveness against a variety of renal diseases. The collective evidence from this literature review, along with our previous findings, suggests that H2 may have therapeutic benefits for patients with DKD by enhancing mitochondrial function. To substantiate these findings, future large-scale clinical studies are needed.

Activation of the inflammasome drives peritoneal deterioration in a mouse model of peritoneal fibrosis

During peritoneal dialysis (PD), the peritoneum is exposed to a bioincompatible dialysate, deteriorating the tissue and limiting the long-term effectiveness of PD. Peritoneal fibrosis is triggered by chronic inflammation induced by a variety of stimuli, including peritonitis. Exposure to PD fluid alters peritoneal macrophages phenotype. Inflammasome activation triggers chronic inflammation. First, it was determined whether inflammasome activation causes peritoneal deterioration. In the in vivo experiments, the increased expression of the inflammasome components, caspase-1 activity, and concomitant overproduction of IL-1β and IL-18 were observed in a mouse model of peritoneal fibrosis. ASC-positive and F4/80-positive cells colocalized in the subperitoneal mesothelial cell layer. These macrophages expressed high CD44 levels indicating that the CD44-positive macrophages contribute to developing peritoneal deterioration. Furthermore, intravital imaging of the peritoneal microvasculature demonstrated that the circulating CD44-positive leukocytes may contribute to peritoneal fibrosis. Bone marrow transplantation in ASC-deficient mice suppressed inflammasome activation, thereby attenuating peritoneal fibrosis in a high glucose-based PD solution-injected mouse model. Our results suggest inflammasome activation in CD44-positive macrophages may be involved in developing peritoneal fibrosis. The inflammasome-derived pro-inflammatory cytokines might therefore serve as new biomarkers for developing encapsulating peritoneal sclerosis.

The potential renoprotective effect of Raloxifene in renal ischemia-reperfusion injury in a male rat model

Renal ischemia-reperfusion injury is caused by a temporary reduction in oxygen-carrying blood flow to the kidney, followed by reperfusion. During ischemia, kidney tissue damage induces overproduction of reactive oxygen species, which produces oxidative stress. The blood flow restoration during the reperfusion period causes further production of reactive oxygen species that ends with apoptosis and cell death. This study aimed to investigate the potential renoprotective effects of Raloxifene on bilateral renal ischemia-reperfusion injury in rats by looking into kidney function biomarkers, urea and creatinine, inflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β). Additionally, antioxidant markers such as total antioxidant capacity (TAC) and the pro-apoptotic marker caspase-3 were assessed. Histopathological scores were also employed for evaluation. Our experimental design involved 20 rats divided into four groups: the sham group underwent median laparotomy without ischemia induction, the control group experienced bilateral renal ischemia for 30 minutes followed by 2 hours of reperfusion, the vehicle group received pretreatment with a mixture of corn oil and dimethyl sulfoxide (DMSO) before ischemia induction, and the Raloxifene-treated group was administered Raloxifene at a dose of 10 mg/kg before ischemia induction, followed by ischemia-reperfusion. Urea and creatinine, TNF-α, IL-1β, and caspase-3 in the Raloxifene group were significantly lower compared to the control and vehicle groups. On the other hand, TAC levels in the Raloxifene group were significantly higher than in the control and vehicle groups. This study concluded that Raloxifene had a renoprotective impact via multiple actions as an anti-inflammatory, anti-apoptotic, and antioxidant agent.

Mitophagy Induction and Aryl Hydrocarbon Receptor-Mediated Redox Signaling Contribute to the Suppression of Breast Cancer Cell Growth by Taloxifene via Regulation of Inflammasomes Activation

Aims: Raloxifene, a selective estrogen receptor (ER) modulator, has been reported to exert the tumor-suppressive effects in both ER-positive and ER-negative cancer cells; however, the mechanisms underlying its ER-independent anti-cancer effects are poorly understood. The NLRP3 inflammasome, a critical component of the innate immune system, has recently received growing attention owing to its multifaceted roles in various aspects of cancer development. The present study aimed at examining the involvement of NLRP3 inflammasomes in the anti-breast cancer effects of raloxifene and its underlying mechanisms. Results: Raloxifene significantly inhibited the activation of NLRP3 inflammasomes in various breast cancer cell lines. Importantly, forced expression of a gain-of-function variant of NLRP3 rescued breast cancer cells from growth arrest by raloxifene, suggesting that the suppression of NLRP3 inflammasomes activation mediates the raloxifene-induced inhibition of breast cancer growth. Mechanistically, raloxifene suppressed NLRP3 inflammasomes activation by lowering the cellular levels of reactive oxygen species (ROS) through the modulation of redox signaling mediated via aryl hydrocarbon receptor (AhR)-nuclear factor erythroid 2-related factor 2 (Nrf2)-heme oxygenase-1 (HO-1) axis or the impaired generation of mitochondrial ROS in a mitophagy-dependent manner. Further, the blockage of AhR signaling or inhibition of mitophagy abolished the tumor-suppressive effect of raloxifene in a human breast tumor xenograft model. Innovation: We elucidate a novel molecular mechanism underlying the breast tumor suppressing effect of raloxifene. Conclusion: The results observed in this study suggest that the modulation of NLRP3 inflammasomes activation is a critical event in the inhibition of breast tumor growth by raloxifene. Antioxid. Redox Signal. 37, 1030-1050.

Albumin-induced premature senescence in human renal proximal tubular cells and its relationship with intercellular fibrosis

The presence of senescent cells is associated with renal fibrosis. This study aims to investigate the effect of albumin-induced premature senescence on tubulointerstitial fibrosis and its possible mechanism in vitro. Different concentrations of bovine serum albumim (BSA) with or without si-p21 are used to stimulate HK-2 cells for 72 h, and SA-β-gal activity, senescence-associated secretory phenotypes (SASPs), LaminB1 are used as markers of senescence. Immunofluorescence staining is performed to characterize the G2/M phase arrest between the control and BSA groups. Alterations in the DNA damage marker γ-H2AX, fibrogenesis, and associated proteins at the G2/M phase, such as p21, p-CDC25C and p-CDK1, are evaluated. Compared with those in the control group, the SA-β-gal activity, SASP, and γ-H2AX levels are increased in the BSA group, while the level of LaminB1 is decreased. Meanwhile, HK-2 cells blocked at the G2/M phase are significantly increased under the stimulation of BSA, and the levels of p21, p-CDC25C and p-CDK1, as well as fibrogenesis are also increased. When p21 expression is inhibited, the levels of p-CDC25C and p-CDK1 are decreased and the G2/M phase arrest is improved, which decreases the production of fibrogenesis. In conclusion, BSA induces renal tubular epithelial cell premature senescence, which regulates the G2/M phase through the CDC25C/CDK1 pathway, leading to tubulointerstitial fibrosis.

The Selective Estrogen Receptor Modulator, Raloxifene, Is Protective Against Renal Ischemia-Reperfusion Injury

BACKGROUND

There is increasing evidence that estrogen is responsible for improved outcomes in female kidney transplant recipients. Although the exact mechanism is not yet known, estrogen appears to exert its protective effects by ameliorating ischemia-reperfusion injury (IRI). In this study, we have examined whether the beneficial effects of exogenous estrogen in renal IRI are replicated by therapy with any one of several selective estrogen receptor modulators.

METHODS

C57BL/6 adult mice underwent standardized warm renal ischemia for 28 min after being injected with the selective estrogen receptor modulators, raloxifene, lasofoxifene, tamoxifen, bazedoxifene, or control vehicle (dimethyl sulfoxide), at 16 and 1 h before IRI. Plasma concentrations of blood urea nitrogen and creatinine were assessed 24, 48, 72, and 96 h post-IRI. Tissue was collected 30 d postischemia for fibrosis analysis using Sirius Red staining.

RESULTS

Raloxifene treatment in female mice resulted in significantly lower blood urea nitrogen and creatinine after IRI and significantly lower fibrosis 30 d following IRI.

CONCLUSIONS

Raloxifene is protective against both acute kidney injury and fibrosis resulting from renal IRI in a mouse model.

Mechanism of Caspase-1 Inhibition by Four Anti-inflammatory Drugs Used in COVID-19 Treatment

The inflammatory protease caspase-1 is associated with the release of cytokines. An excessive number of cytokines (a “cytokine storm”) is a dangerous consequence of COVID-19 infection and has been indicated as being among the causes of death by COVID-19. The anti-inflammatory drug colchicine (which is reported in the literature to be a caspase-1 inhibitor) and the corticosteroid drugs, dexamethasone and methylprednisolone, are among the most effective active compounds for COVID-19 treatment. The SERM raloxifene has also been used as a repurposed drug in COVID-19 therapy. In this study, inhibition of caspase-1 by these four compounds was analyzed using computational methods. Our aim was to see if the inhibition of caspase-1, an important biomolecule in the inflammatory response that triggers cytokine release, could shed light on how these drugs help to alleviate excessive cytokine production. We also measured the antioxidant activities of dexamethasone and colchicine when scavenging the superoxide radical using cyclic voltammetry methods. The experimental findings are associated with caspase-1 active site affinity towards these compounds. In evaluating our computational and experimental results, we here formulate a mechanism for caspase-1 inhibition by these drugs, which involves the active site amino acid Cys285 residue and is mediated by a transfer of protons, involving His237 and Ser339. It is proposed that the molecular moiety targeted by all of these drugs is a carbonyl group which establishes a S(Cys285)–C(carbonyl) covalent bond.

Thermoneutral Regulation and Acute Injury: Implications for Acute Kidney Injury

Acute kidney injury (AKI) has demonstrated sex differences as illustrated in clinical and preclinical studies. In most cases, females show a significant resistance to AKI as manifested by renal indicators of injury, and thus much of the literature is derived from studies exclusively in males. Thermoneutral housing alters sex differences in acute injury of the liver, but has not been studied in the kidney. Thermoneutrality, the ambient temperature at which additional energy is not needed to maintain core body temperature, is regulated by mechanisms residing in mitochondria. Importantly, mitochondrial function plays an important role in induction and recovery of AKI. Mechanisms that regulate thermoneutrality include uncoupling proteins (UCPs) and one of its upstream regulators peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α). PGC-1α has been extensively studied in AKI in males. UCP-2, a UCP expressed in the kidney, has been minimally studied in AKI in males. Expression of other UCPs in the kidney has not been well defined. No studies of either PGC-1α or UCPs have interrogated for a sex difference nor have they been investigated at thermoneutrality in the kidney. In this brief review, pathways of importance in thermoneutrality are described and related to pathways of importance in modulating susceptibility to AKI. Clarity in the understanding of the impact of thermoneutrality on AKI in altering susceptibility in females may expand our understanding of the critical role of mitochondrial function in this setting. Unique utilization of mitochondrial-based molecular pathways in females may then inform potential therapies.

Pyroptosis: Mechanisms and Links with Fibrosis

Fibrosis is responsible for approximately 45% of deaths in the industrialized world and has been a major global healthcare burden. Excessive fibrosis is the primary cause of organ failure. However, there are currently no approved drugs available for the prevention or treatment of fibrosis-related diseases. It has become evident that fibrosis is characterized by inflammation. In a large number of studies of various organs in mice and humans, pyroptosis has been found to play a significant role in fibrosis. Pyroptosis is a form of programmed cell death mediated by the N-terminal fragment of cysteinyl aspartate-specific proteinase (caspase)-1-cleaved gasdermin D (GSDMD, producing GSDMD-N) that gives rise to inflammation via the release of some proinflammatory cytokines, including IL-1β, IL-18 and HMGB1. These cytokines can initiate the activation of fibroblasts. Inflammasomes, an important factor upstream of GSDMD, can activate caspase-1 to trigger the maturation of IL-1β and IL-18. Moreover, the inhibition of inflammasomes, proinflammatory cytokines and GSDMD can prevent the progression of fibrosis. This review summarizes the growing evidence indicating that pyroptosis triggers fibrosis, and highlights potential novel targets for antifibrotic therapies.

Protein-Bound Uremic Toxins Induce Reactive Oxygen Species-Dependent and Inflammasome-Mediated IL-1β Production in Kidney Proximal Tubule Cells

Protein bound-uremic toxins (PBUTs) are not efficiently removed by hemodialysis in chronic kidney disease (CKD) patients and their accumulation leads to various co-morbidities via cellular dysfunction, inflammation and oxidative stress. Moreover, it has been shown that increased intrarenal expression of the NLRP3 receptor and IL-1β are associated with reduced kidney function, suggesting a critical role for the NLRP3 inflammasome in CKD progression. Here, we evaluated the effect of PBUTs on inflammasome-mediated IL-1β production in vitro and in vivo. Exposure of human conditionally immortalized proximal tubule epithelial cells to indoxyl sulfate (IS) and a mixture of anionic PBUTs (UT mix) increased expression levels of NLRP3, caspase-1 and IL-1β, accompanied by a significant increase in IL-1β secretion and caspase-1 activity. Furthermore, IS and UT mix induced the production of intracellular reactive oxygen species, and caspase-1 activity and IL-1β secretion were reduced in the presence of antioxidant N-acetylcysteine. IS and UT mix also induced NF-κB activation as evidenced by p65 nuclear translocation and IL-1β production, which was counteracted by an IKK inhibitor. In vivo, using subtotal nephrectomy CKD rats, a significant increase in total plasma levels of IS and the PBUTs, kynurenic acid and hippuric acid, was found, as well as enhanced urinary malondialdehyde levels. CKD kidney tissue showed an increasing trend in expression of NLRP3 inflammasome components, and a decreasing trend in superoxide dismutase-1 levels. In conclusion, we showed that PBUTs induce inflammasome-mediated IL-1β production in proximal tubule cells via oxidative stress and NF-κB signaling, suggesting their involvement in disease-associated inflammatory processes.

The Use of Chinese Yang/Qi-Invigorating Tonic Botanical Drugs/Herbal Formulations in Ameliorating Chronic Kidney Disease by Enhancing Mitochondrial Function

Background: Chronic kidney disease (CKD) is a leading cause of morbidity and mortality. Mitochondrial dysfunction has been implicated as a key factor in the development of CKD. According to traditional Chinese medicine (TCM) theory, many Chinese Yang/Qi-invigorating botanical drugs/herbal formulations have been shown to produce promising outcomes in the clinical management of CKD. Experimental studies have indicated that the health-promoting action of Yang/Qi invigoration in TCM is related to the up-regulation of mitochondrial energy generation and antioxidant status. Objective: In this review, we aim to test whether Chinese Yang/Qi-invigorating tonic botanical drugs/herbal formulations can provide medical benefits in CKD and its complications. And we also explore the possible involvement of mitochondrial-associated signaling pathway underlying the beneficial effects of Yang/Qi invigoration in TCM. Methods: A systematic search of "PubMed", "China National Knowledge Infrastructure (CNKI)" and "Google Scholar" was carried out to collect all the available articles in English or Chinese related to Chinese Yang/Qi-invigorating tonic botanical drugs/herbal formulations and their effects on mitochondrial function and chronic kidney disease. Result and Discussion: The relationship between the progression of CKD and mitochondrial function is discussed. The effects of Chinese Yang/Qi-invigorating tonic botanical drugs/herbal formulations and their active ingredients, including phytosterols/triterpenes, flavonoids, and dibenzocyclooctadiene lignans, on CKD and related alterations in mitochondrial signaling pathways are also presented in this review. In the future, exploration of the possible beneficial effects and clinical studies of more Yang- and Qi-invigorating botanical drugs/herbal formulations in the prevention and/or/treatment of CKD and the molecular mechanisms relating to the enhancement of mitochondrial functions warrants further investigation. Conclusion: Given the critical role of mitochondrial function in safeguarding renal functional integrity, the enhancement of mitochondrial energy metabolism and antioxidant status in kidney tissue is likely involved in renal protection. Future studies on the biochemical and chemical basis underlying the effects of Chinese Yang/Qi-invigorating tonic botanical drugs/herbal formulations from a mitochondrial perspective will hopefully provide novel insights into the rational development of new drugs for the prevention and/or treatment of CKD.

Evaluation of Neutrophil Dynamics Change by Protective Effect of Tadalafil After Renal Ischemia/Reperfusion Using In Vivo Real-time Imaging

BACKGROUND

Neutrophils play a major role in ischemia/reperfusion injury (IRI) in renal transplantation and acute kidney injury. However, it has been difficult to observe changes in neutrophil dynamics over time in living mice kidney. We investigate neutrophil dynamics in IRI in living mice using novel in vivo multiphoton microscope imaging techniques and characterize the renoprotective effects of a selective phosphodiesterase (PDE) 5 inhibitor, tadalafil.

METHODS

Wild-type (WT) and eNOS knockout (eNOS-KO) mice, a model of endothelial dysfunction, were used to establish in vivo real-time imaging in living mouse kidneys. Neutrophils were labeled green with Ly-6G monoclonal antibody, and plasma flow was labeled red with bovine serum albumin. Tadalafil was administered orally 1 h before surgery. Both kidney pedicles were reperfused after 37° warm ischemia for 45 min.

RESULTS

Our novel approach revealed that neutrophils were trapped in glomerulus within a few minutes after reperfusion. They gradually increased over time and Infiltrated neutrophils were observed in the tubular lumen and peritubular capillary. The neutrophils were clearly visualized rolling on peritubular capillary plexus at 3 μm/min. The administration of tadalafil significantly reduced neutrophil influx into the glomerulus in both WT and eNOS-KO mice. Reduced neutrophil infiltration in tadalafil groups, which was confirmed by flow cytometry, resulted in histopathologically decreased tubular injury. The expression of VCAM-1 and KIM-1 was partially prevented by tadalafil.

CONCLUSIONS

Use of a novel technique contributed to elucidation of neutrophil dynamics after reperfusion. Tadalafil has a potential for inhibiting neutrophil infiltration in renal IRI.Supplemental Visual Abstract; http://links.lww.com/TP/C223.

Current Challenges and Future Perspectives of Renal Tubular Dysfunction in Diabetic Kidney Disease

Over decades, substantial progress has been achieved in understanding the pathogenesis of proteinuria in diabetic kidney disease (DKD), biomarkers for DKD screening, diagnosis, and prognosis, as well as novel hypoglycemia agents in clinical trials, thereby rendering more attention focused on the role of renal tubules in DKD. Previous studies have demonstrated that morphological and functional changes in renal tubules are highly involved in the occurrence and development of DKD. Novel tubular biomarkers have shown some clinical importance. However, there are many challenges to transition into personalized diagnosis and guidance for individual therapy in clinical practice. Large-scale clinical trials suggested the clinical relevance of increased proximal reabsorption and hyperfiltration by sodium-glucose cotransporter-2 (SGLT2) to improve renal outcomes in patients with diabetes, further promoting the emergence of renal tubulocentric research. Therefore, this review summarized the recent progress in the pathophysiology associated with involved mechanisms of renal tubules, potential tubular biomarkers with clinical application, and renal tubular factors in DKD management. The mechanism of kidney protection and impressive results from clinical trials of SGLT2 inhibitors were summarized and discussed, offering a comprehensive update on therapeutic strategies targeting renal tubules.

Sodium-glucose cotransporter 2 inhibition attenuates protein overload in renal proximal tubule via suppression of megalin O-GlcNacylation in progressive diabetic nephropathy

AIMS

The crosstalk between sodium-glucose cotransporter 2 (SGLT2) inhibition and a membrane-associated endocytic receptor megalin function involved in renal proximal tubular protein overload in progressive diabetic nephropathy (DN) is uncertain. Here, we determined whether SGLT2 inhibition affects megalin endocytic function through suppressing its O-linked β-N-acetylglucosamine modification (O-GlcNAcylation) and protects the diabetic kidney from protein overload.

MATERIALS AND METHOD

We treated 8-week-old male non-obese and hypoinsulinemic KK/Ta-Ins2^Akita (KK/Ta-Akita) mice which develop progressive DN with an SGLT2 inhibitor ipragliflozin or insulin for 6 weeks, and investigated the endocytic function (proximal tubular protein reabsorption), renal expression and O-GlcNAcylation of megalin along with their effects on renal phenotypes including histology and biochemical markers.

RESULTS

The treatment with ipragliflozin, but not insulin, suppressed megalin O-GlcNAcylation and accelerated its internalization, resulting in reduction in proximal tubular reabsorption of the highly filtered plasma proteins such as albumin and neutrophil gelatinase-associated lipocalin. These alterations following the ipragliflozin treatment contributed to amelioration of proximal tubular protein overload, mitochondrial morphological abnormality, and renal oxidative stress and tubulointerstitial fibrosis.

CONCLUSIONS

The present study provides a novel crosstalk mechanism between SGLT2 inhibition and megalin underlying the potential renal benefits of SGLT2 inhibition in DN.

Sex differences in renal mitochondrial function: a hormone-gous opportunity for research

Sex differences (biological distinctions between males and females) present a complex interplay of genetic, developmental, biological, and environmental factors. More and more studies are shedding light on the importance of sex differences in normal physiology and susceptibility to cancer, cardiovascular and renal conditions, and neurodegenerative diseases. This mini-review is devoted to the role of sex dimorphisms in renal function, with a focus on the distinctions between male and female mitochondria. Here, we cover the aspects of renal mitochondrial bioenergetics where sex differences have been reported to date, for instance, biogenesis, reactive oxygen species production, and oxidative stress. Special attention is devoted to the effects of sex hormones, such as estrogen and testosterone, on mitochondrial bioenergetics in the kidney in physiology and pathophysiology.

Reactive Oxygen Species and Redox Signaling in Chronic Kidney Disease

Chronic kidney disease (CKD) remains a worldwide public health problem associated with serious complications and increased mortality rates. Accumulating evidence indicates that elevated intracellular levels of reactive oxygen species (ROS) play a major role in the pathogenesis of CKD. Increased intracellular levels of ROS can lead to oxidation of lipids, DNA, and proteins, contributing to cellular damage. On the other hand, ROS are also important secondary messengers in cellular signaling. Consequently, normal kidney cell function relies on the "right" amount of ROS. Mitochondria and NADPH oxidases represent major sources of ROS in the kidney, but renal antioxidant systems, such as superoxide dismutase, catalase, or glutathione peroxidase counterbalance ROS-mediated injury. This review discusses the main sources of ROS and antioxidant systems in the kidney, and redox signaling pathways leading to inflammation and fibrosis, which result in abnormal kidney function and CKD progression. We further discuss the important role of the nuclear factor erythroid 2-related factor 2 (Nrf2) in regulating antioxidant responses, and other mechanisms of redox signaling.

Bazedoxifene improves renal function and increases renal phosphate excretion in patients with postmenopausal osteoporosis

INTRODUCTION

Because aging is a predictor of renal insufficiency in the general population, renal function is a concern in postmenopausal patients undergoing treatment for osteoporosis. Although high serum phosphate concentration is a predictor of renal insufficiency, the effect of selective estrogen receptor modulator (SERM) on renal function and phosphate homeostasis remains to be established.

MATERIALS AND METHODS

We administered 20 mg/day bazedoxifene to 48 postmenopausal osteoporotic women who had been taking alfacalcidol for ≥ 6 months, and assessed lumbar spine bone mineral density (LS-BMD), renal function (by calculating estimated glomerular filtration rate using serum cystatin-C levels [eGFRcys] [range 38.0-98.2 mL/min/1.73 m²]), and phosphate homeostasis.

RESULTS

LS-BMD was significantly higher 6 months after the initiation of bazedoxifene administration. eGFRcys had increased by 3 months after initiation and was stable until 12 months. Serum phosphate gradually decreased after initiation, reaching statistical significance at 6 months. The changes in serum phosphate were also significant when the maximum tubular reabsorption rate of phosphate was normalized to glomerular filtration rate (TmP/GFR), indicating that bazedoxifene treatment reduces serum phosphate by increasing the urinary excretion of phosphate. The change in eGFRcys after the initiation of bazedoxifene was significantly negatively correlated with the change in serum phosphate, suggesting that a reduction in serum phosphate improves renal function.

CONCLUSION

Bazedoxifene improves renal function, possibly by increasing renal phosphate excretion, in postmenopausal osteoporotic women without severe renal insufficiency.

Role of Inflammasomes in Kidney Diseases via Both Canonical and Non-canonical Pathways

Inflammasomes, multiprotein complex induced by harmful factors in the body, play a crucial role in innate immunity. Activation of inflammasomes lead to the activation of casepase-1 and then the secretion of inflammatory cytokines, including IL-1β and IL-18, subsequently leading to a type of cell death called pyroptosis. There are two types of signaling pathways involved in the process of inflammasome activation: the canonical and the non-canonical signaling pathway. The canonical signaling pathway is mainly dependent on casepase-1; the non-canonical signal pathway, which was recently discovered, is mainly dependent on caspase-11, but is also meditated by caspase-4, caspase-5, and caspase-8. Kidney inflammation is basically associated with inflammatory factor exudation and inflammatory cell infiltration. Several studies have showed that inflammasomes are closely related to kidney diseases, especially the NOD-, LRR- and pyrin domain-containing 3 (NLRP3) inflammasome, which play a role in regulating kidney inflammation and fibrosis. In this review, we focus on the relationship between inflammasomes and kidney diseases, especially the role of the NLRP3 inflammasome in different kinds of kidney disease via both canonical and non-canonical signal pathways.

IgA nephropathy is associated with elevated urinary mitochondrial DNA copy numbers

Mitochondrial injury plays important roles in the pathogenesis of various kidney diseases. However, mitochondrial injury in IgA nephropathy (IgAN) remains largely unexplored. Here, we examined the associations among mitochondrial injury, IgAN, and treatment outcomes. We prospectively enrolled patients with IgAN and age-/sex-matched healthy volunteers (HVs) as controls (n = 31 each). Urinary copy numbers of the mitochondrial DNA (mtDNA) genes cytochrome-c oxidase-3 (COX3) and nicotinamide adenine dinucleotide dehydrogenase subunit-1 (ND1) were measured. Urinary mtDNA levels were elevated in the IgAN group compared with that in HVs (p < 0.001). Urinary ND1 levels were significantly higher in the low proteinuria group than in the high proteinuria group (p = 0.027). Changes in urinary levels of ND1 and COX3 were positively correlated with changes in proteinuria (p = 0.038 and 0.024, respectively) and inversely correlated with changes in the estimated glomerular filtration rate (p = 0.033 and 0.017, respectively) after medical treatment. Mitochondrial injury played important roles in IgAN pathogenesis and may be involved in early-stage glomerular inflammation, prior to pathological changes and increased proteinuria. The correlation between changes in urinary mtDNA and proteinuria suggest that these factors may be promising biomarkers for treatment outcomes in IgAN.

Bardoxolone methyl analog attenuates proteinuria-induced tubular damage by modulating mitochondrial function

Multiple clinical studies have shown that bardoxolone methyl, a potent activator of nuclear factor erythroid 2–related factor 2 (Nrf2), is effective in increasing glomerular filtration rate in patients with chronic kidney disease. However, whether an Nrf2 activator can protect tubules from proteinuria-induced tubular damage via anti-inflammatory and antioxidative stress mechanisms is unknown. Using an Institute of Cancer Research–derived glomerulonephritis (ICGN) mouse model of nephrosis, we examined the effects of dihydro-CDDO-trifluoroethyl amide (dh404), a rodent-tolerable bardoxolone methyl analog, in protecting the tubulointerstitium; dh404 markedly suppressed tubular epithelial cell damage in the renal interstitium of ICGN mice. The tubular epithelial cells of ICGN mice showed a decrease in the size and number of mitochondria, as well as the breakdown of the crista structure, whereas the number and ultrastructure of mitochondria were maintained by the dh404 treatment. To further determine the effect of dh404 on mitochondrial function, we used human proximal tubular cells in vitro. Stimulation with albumin and free fatty acid increased mitochondrial reactive oxygen species (ROS). However, dh404 administration diminished mitochondrial ROS. Our data show that dh404 significantly reduced proteinuria-induced tubular cell mitochondrial damage, suggesting that improved redox balance and mitochondrial function and suppression of inflammation underlie the cytoprotective mechanism of Nrf2 activators, including bardoxolone methyl, in diabetic kidney disease.—Nagasu, H., Sogawa, Y., Kidokoro, K., Itano, S., Yamamoto, T., Satoh, M., Sasaki, T., Suzuki, T., Yamamoto, M., Wigley, W. C., Proksch, J. W., Meyer, C. J., Kashihara, N. Bardoxolone methyl analog attenuates proteinuria-induced tubular damage by modulating mitochondrial function.

5-Aminolevulinic acid exerts renoprotective effect via Nrf2 activation in murine rhabdomyolysis-induced acute kidney injury

AIM

Acute kidney injury (AKI) is associated with chronic kidney disease, as well as high mortality, but effective treatments for AKI are still lacking. A recent study reported the prevention of renal injury, such as ischemia-reperfusion injury, by 5-aminolevulinic acid (ALA), which induces an antioxidant effect. The current study aimed to investigate the effect of ALA in a rhabdomyolysis-induced mouse model of AKI created by intramuscular injection of 50% glycerol.

METHODS

Rhabdomyolysis-induced AKI was induced by an intramuscular injection of glycerol (5 mL/kg body weight) into mice. Administration of ALA (30 mg/kg, by gavage) was started from 48 h before or 24 h after glycerol injection. The mice were sacrificed at 72 h after glycerol injection. The roles of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1), which is one of the Nrf2-related antioxidants, were further investigated through in vivo and in vitro methods.

RESULTS

5-aminolevulinic acid markedly reduced renal dysfunction and tubular damage in mice with rhabdomyolysis-induced AKI. ALA administration decreased oxidative stress, macrophage infiltration, and inflammatory cytokines and apoptosis. The expression of Nrf2 was upregulated by ALA administration. However, administration of Zinc protoporphyrin-9 (ZnPPIX) to inhibit HO-1 activity did not abolish these improvements by ALA. The expression of Nrf2-associated antioxidant factors other than HO-1 was also increased.

CONCLUSION

These findings indicate that ALA exerts its antioxidant activity via Nrf2-associated antioxidant factors to provide a renoprotective effect against rhabdomyolysis-induced AKI.

New Understanding on the Role of Proteinuria in Progression of Chronic Kidney Disease

Proteinuria is identified as an important marker and risk factor of progression in chronic kidney disease. However, the precise mechanism of action in the progress of chronic kidney disease is still unclear. Mesangial toxicity from specific filtered compounds such as albumin-bound fatty acids and transferrin/iron, tubular overload and hyperplasia, and induction of proinflammatory molecules such as MCP-1 and inflammatory cytokines are some of the proposed mechanisms. Reversing intraglomerular hypertension with protein restriction or antihypertensive therapy may be beneficial both by diminishing hemodynamic injury to the glomeruli and by reducing protein filtration. Therefore, understanding proteinuria and its role in renal tubular interstitial inflammation and fibrosis is of great significance for the study of renal protective therapy, such as antiproteinuric treatments, and delaying the progression of chronic renal disease.

The eNOS-NO pathway attenuates kidney dysfunction via suppression of inflammasome activation in aldosterone-induced renal injury model mice

Hypertension causes vascular complications, such as stroke, cardiovascular disease, and chronic kidney disease (CKD). The relationship between endothelial dysfunction and progression of kidney disease is well known. However, the relationship between the eNOS-NO pathway and chronic inflammation, which is a common pathway for the progression of kidney disease, remains unexplored. We performed in vivo experiments to determine the role of the eNOS-NO pathway by using eNOS-deficient mice in a hypertensive kidney disease model. All mice were unilateral nephrectomized (Nx). One week after Nx, the mice were randomly divided into two groups: the aldosterone infusion groups and the vehicle groups. All mice also received a 1% NaCl solution instead of drinking water. The aldosterone infusion groups were treated with hydralazine to correct blood pressure differences. After four weeks of drug administration, all mice were euthanized, and blood and kidney tissue samples were collected. In the results, NLRP3 inflammasome activation was elevated in the kidneys of the eNOS-deficient mice, and tubulointerstitial fibrosis was accelerated. Suppression of inflammasome activation by knocking out ASC prevented tubulointerstitial injury in the eNOS knockout mice, indicating that the eNOS-NO pathway is involved in the development of kidney dysfunction through acceleration of NLRP3 inflammasome in macrophages. We revealed that endothelial function, particularly the eNOS-NO pathway, attenuates the progression of renal tubulointerstitial injury via suppression of inflammasome activation. Clinically, patients who develop vascular endothelial dysfunction have lifestyle diseases, such as hypertension or diabetes, and are known to be at risk for CKD. Our study suggests that the eNOS-NO pathway could be a therapeutic target for the treatment of chronic kidney disease associated with endothelial dysfunction.

MiR-4756 promotes albumin-induced renal tubular epithelial cell epithelial-to-mesenchymal transition and endoplasmic reticulum stress via targeting Sestrin2

Accumulating evidence indicates that proteinuria promotes the progression of diabetic kidney disease (DKD) and induces renal epithelial tubular cell epithelial-to-mesenchymal transition (EMT) and endoplasmic reticulum (ER) stress, but the mechanism remains unclear. In our previous research, we found that miR-4756 levels were increased in the urinary extracellular vesicles of type 2 diabetes mellitus patients with macroalbuminuria. In a preliminary study, we found that miR-4756 may be derived from renal tubular epithelial cells, but its role has not been elucidated. Albumin stimulation significantly increased miR-4756 levels in HK-2 cells. In addition, an miR-4756 mimic accelerated albumin-stimulated HK-2 cell EMT and ER stress, and an miR-4756 inhibitor suppressed these events. We then found that miR-4756 targeted the 3'-untranslated region (UTR) of Sestrin2 and directly suppressed Sestrin2 expression. Furthermore, the induction of EMT and ER stress by the overexpression of miR-4756 was abolished by Sestrin2 overexpression. Moreover, the overexpression of miR-4756 increased ERK1/2 activation and decreased 5' monophosphate-activated protein kinase activation. Thus, our study provides evidence that miR-4756 accelerates the process of DKD through Sestrin2, suggesting that targeting miR-4756 may be a novel strategy for DKD treatment.

The hallmarks of mitochondrial dysfunction in chronic kidney disease

Recent advances have led to a greater appreciation of how mitochondrial dysfunction contributes to diverse acute and chronic pathologies. Indeed, mitochondria have received increasing attention as a therapeutic target in a variety of diseases because they serve as key regulatory hubs uniquely situated at crossroads between multiple cellular processes. This review provides an overview of the role of mitochondrial dysfunction in chronic kidney disease, with special emphasis on its role in the development of diabetic nephropathy. We examine the current understanding of the molecular mechanisms that cause mitochondrial dysfunction in the kidney and describe the impact of mitochondrial damage on kidney function. The new concept that mitochondrial shape and structure are closely linked with its function in the kidneys is discussed. Furthermore, the mechanisms that translate cellular cues and demands into mitochondrial remodeling and cellular damage, including the role of microRNAs and long noncoding RNAs, are examined with the final goal of identifying mitochondrial targets to improve treatment of patients with chronic kidney diseases.

Brain inflammasomes in stroke and depressive disorders: Regulation by oestrogen

Neuroinflammation is a devastating pathophysiological process that results in brain damage and neuronal death. Pathogens, cell fragments and cellular dysfunction trigger inflammatory responses. Irrespective of the cause, inflammasomes are key intracellular multiprotein signalling platforms that sense neuropathological conditions. The activation of inflammasomes leads to the auto-proteolytic cleavage of caspase-1, resulting in the proteolysis of the pro-inflammatory cytokines interleukin (IL)1β and IL18 into their bioactive forms. It also initiates pyroptosis, a type of cell death. The two cytokines contribute to the pathogenesis in acute and chronic brain diseases and also play a central role in human aging and psychiatric disorders. Sex steroids, in particular oestrogens, are well-described neuroprotective agents in the central nervous system. Oestrogens improve the functional outcome after ischaemia and traumatic brain injury, reduce neuronal death in Parkinson's and Alzheimer's disease, as well as in amyotrophic lateral sclerosis, attenuate glutamate excitotoxicity and the formation of radical oxygen species, and lessen the spread of oedema after damage. Moreover, oestrogens alleviate menopause-related depressive symptoms and have a positive influence on depressive disorders probably by influencing growth factor production and serotonergic brain circuits. Recent evidence also suggests that inflammasome signalling affects anxiety- and depressive-like behaviour and that oestrogen ameliorates depression-like behaviour through the suppression of inflammasomes. In the present review, we highlight the most recent findings demonstrating that oestrogens selectively suppress the activation of the neuroinflammatory cascade in the brain in acute and chronic brain disease models. Furthermore, we aim to describe putative regulatory signalling pathways involved in the control of inflammasomes. Finally, we consider that psychiatric disorders such as depression also contain an inflammatory component that could be modulated by oestrogen.

Infiltration of M1, but not M2, macrophages is impaired after unilateral ureter obstruction in Nrf2-deficient mice

Chronic inflammation can be a major driver of the failure of a variety of organs, including chronic kidney disease (CKD). The NLR family pyrin domain-containing 3 (NLRP3) inflammasome has been shown to play a pivotal role in inflammation in a mouse kidney disease model. Nuclear factor erythroid 2-related factor 2 (Nrf2), the master transcription factor for anti-oxidant responses, has also been implicated in inflammasome activation under physiological conditions. However, the mechanism underlying inflammasome activation in CKD remains elusive. Here, we show that the loss of Nrf2 suppresses fibrosis and inflammation in a unilateral ureter obstruction (UUO) model of CKD in mice. We consistently observed decreased expression of inflammation-related genes NLRP3 and IL-1β in Nrf2-deficient kidneys after UUO. Increased infiltration of M1, but not M2, macrophages appears to mediate the suppression of UUO-induced CKD symptoms. Furthermore, we found that activation of the NLRP3 inflammasome is attenuated in Nrf2-deficient bone marrow–derived macrophages. These results demonstrate that Nrf2-related inflammasome activation can promote CKD symptoms via infiltration of M1 macrophages. Thus, we have identified the Nrf2 pathway as a promising therapeutic target for CKD.

Expression of TLR2, NOD1, and NOD2 and the NLRP3 Inflammasome in Renal Tubular Epithelial Cells of Male versus Female Mice

BACKGROUND

Gender-biased outcomes are associated with acute kidney injury (AKI) and human and animal studies have shown that females are preferentially protected from renal ischemia. However, the reason for this is not known. One clue might lie with pattern recognition receptors (PRRs), which are triggers of ischemic injury when ligated by molecules in the ischemic milieu. Several PRR families are expressed by renal tubular epithelial cells (RTEs) and incite cell death signaling and production of pro-inflammatory molecules. Blockade of specific PRRs (e.g., TLR2, NOD1, NOD2, and NLRP3) provides highly significant protection from ischemic RTE injury. As a first step to understand gender-biased outcomes of AKI, we tested whether constitutive gender-based differences exist in expression of these PRRS in RTEs.

METHODS

To determine whether PRR expression differences exist, primary RTEs isolated from male and female WT kidneys were examined by FACS, qPCR, and Western Blot for expression of TLR2, NOD1, NOD2, and NLRP3 inflammasome components.

RESULTS

No RTE gender-based differences in TLR2, NOD1, NOD2, NLRP3, or ASC were found. RTEs from female kidneys had approximately half the mRNA, but the same protein concentration of pro-caspase-1 compared to RTEs isolated from male kidneys.

CONCLUSIONS

Our findings indicate that intrinsic gender differences in RTE expression of TLR2, NOD1, NOD2, NLRP3, and ASC are not responsible for the gender-biased outcomes observed in ischemia/reperfusion injury. The lower caspase-1 mRNA expression in RTEs from females warrants further exploration of additional upstream signals that might differentially regulate caspase-1 in male vs. female RTEs.

Evolutionary Nephrology

Progressive kidney disease follows nephron loss, hyperfiltration, and incomplete repair, a process described as "maladaptive." In the past 20 years, a new discipline has emerged that expands research horizons: evolutionary medicine. In contrast to physiologic (homeostatic) adaptation, evolutionary adaptation is the result of reproductive success that reflects natural selection. Evolutionary explanations for physiologically maladaptive responses can emerge from mismatch of the phenotype with environment or evolutionary tradeoffs. Evolutionary adaptation to a terrestrial environment resulted in a vulnerable energy-consuming renal tubule and a hypoxic, hyperosmolar microenvironment. Natural selection favors successful energy investment strategy: energy is allocated to maintenance of nephron integrity through reproductive years, but this declines with increasing senescence after ~40 years of age. Risk factors for chronic kidney disease include restricted fetal growth or preterm birth (life history tradeoff resulting in fewer nephrons), evolutionary selection for APOL1 mutations (that provide resistance to trypanosome infection, a tradeoff), and modern life experience (Western diet mismatch leading to diabetes and hypertension). Current advances in genomics, epigenetics, and developmental biology have revealed proximate causes of kidney disease, but attempts to slow kidney disease remain elusive. Evolutionary medicine provides a complementary approach by addressing ultimate causes of kidney disease. Marked variation in nephron number at birth, nephron heterogeneity, and changing susceptibility to kidney injury throughout life history are the result of evolutionary processes. Combined application of molecular genetics, evolutionary developmental biology (evo-devo), developmental programming and life history theory may yield new strategies for prevention and treatment of chronic kidney disease.

Novel routes of albumin passage across the glomerular filtration barrier

Albuminuria is a hallmark of kidney diseases of various aetiologies and an unambiguous symptom of the compromised integrity of the glomerular filtration barrier. Furthermore, there is increasing evidence that albuminuria per se aggravates the development and progression of chronic kidney disease. This review covers new aspects of the movement of large plasma proteins across the glomerular filtration barrier in health and disease. Specifically, this review focuses on the role of endocytosis and transcytosis of albumin by podocytes, which constitutes a new pathway of plasma proteins across the filtration barrier. Thus, we summarize what is known about the mechanisms of albumin endocytosis by podocytes and address the fate of the endocytosed albumin, which is directed to lysosomal degradation or transcellular movement with subsequent vesicular release into the urinary space. We also address the functional consequences of overt albumin endocytosis by podocytes, such as the formation of pro-inflammatory cytokines, which might eventually result in a deterioration of podocyte function. Finally, we consider the diagnostic potential of podocyte-derived albumin-containing vesicles in the urine as an early marker of a compromised glomerular barrier function. In terms of new technical approaches, the review covers how our knowledge of the movement of albumin across the glomerular filtration barrier has expanded by the use of new intravital imaging techniques.

Proximal Tubular Expression Patterns of Megalin and Cubilin in Proteinuric Nephropathies

Introduction

Receptor-mediated endocytosis is responsible for protein reabsorption in the proximal tubules. For albumin this process involves at least 2 interacting receptors, megalin and cubilin. Albumin is not usually present in the urine, indicating a highly efficient tubular reuptake under physiological conditions. However, early appearance of albuminuria may mean that the tubular system is overwhelmed by large quantities of albumin or that the function is impaired.

Methods

To better understand the physiological role of megalin and cubilin in human renal disease, renal biopsies from 15 patients with a range of albuminuria and 3 healthy living donors were analyzed for proximal tubular expression of megalin and cubilin using immunohistochemistry (IHC) and semiquantitative immune-electron microscopy. Their expression in proteinuric zebrafish was also studied.

Results

Megalin and cubilin were expressed in brush border and cytoplasmic vesicles. Patients with microalbuminuric IgA nephropathy and thin membrane disease had significantly higher megalin in proximal tubules, whereas those with macro- or nephrotic-range albuminuria had unchanged levels. Cubilin expression was significantly higher in all patients. In a proteinuric zebrafish nphs2 knockdown model, we found a dose-dependent increase in the expression of tubular megalin and cubilin in response to tubular protein uptake.

Discussion

Megalin and cubilin show different expression patterns in different human diseases, which indicates that the 2 tubular proteins differently cooperate in cleaning up plasma proteins in kidney tubules.

Endoplasmic Reticulum Chaperon Tauroursodeoxycholic Acid Attenuates Aldosterone-Infused Renal Injury

Aldosterone (Aldo) is critically involved in the development of renal injury via the production of reactive oxygen species and inflammation. Endoplasmic reticulum (ER) stress is also evoked in Aldo-induced renal injury. In the present study, we investigated the role of ER stress in inflammation-mediated renal injury in Aldo-infused mice. C57BL/6J mice were randomized to receive treatment for 4 weeks as follows: vehicle infusion, Aldo infusion, vehicle infusion plus tauroursodeoxycholic acid (TUDCA), and Aldo infusion plus TUDCA. The effect of TUDCA on the Aldo-infused inflammatory response and renal injury was investigated using periodic acid-Schiff staining, real-time PCR, Western blot, and ELISA. We demonstrate that Aldo leads to impaired renal function and inhibition of ER stress via TUDCA attenuates renal fibrosis. This was indicated by decreased collagen I, collagen IV, fibronectin, and TGF-β expression, as well as the downregulation of the expression of Nlrp3 inflammasome markers, Nlrp3, ASC, IL-1β, and IL-18. This paper presents an important role for ER stress on the renal inflammatory response to Aldo. Additionally, the inhibition of ER stress by TUDCA negatively regulates the levels of these inflammatory molecules in the context of Aldo.

Neurocognitive, Neuroprotective, and Cardiometabolic Effects of Raloxifene: Potential for Improving Therapeutic Outcomes in Schizophrenia

Raloxifene is a selective estrogen receptor modulator that has been approved for treating osteoporosis and breast cancer in high-risk postmenopausal women. However, recent evidence suggests that raloxifene adjunct therapy improves cognition and reduces symptom severity in men and women with schizophrenia. In animal models, raloxifene increases forebrain neurogenesis and enhances working memory and synaptic plasticity. It may consequently repair the neuronal and synaptic connectivity that is disrupted in schizophrenia. It also reduces oxidative stress and neuroinflammation, which are potent etiological factors in the neuropathology of schizophrenia. Furthermore, in postmenopausal women, raloxifene reduces the risks for atherosclerosis, diabetes mellitus, and weight gain, which are serious adverse effects associated with long-term antipsychotic treatment in schizophrenia; therefore, it may improve the safety and efficacy of antipsychotic drugs. In this review, recent insights into the neurocognitive, neuroprotective, and cardiometabolic effects of raloxifene in relation to therapeutic outcomes in schizophrenia are discussed.

Caveolin-1 Expression Ameliorates Nephrotic Damage in a Rabbit Model of Cholesterol-Induced Hypercholesterolemia

Caveolin-1 (CAV-1) participates in regulating vesicular transport, signal transduction, tumor progression, and cholesterol homeostasis. In the present study, we tested the hypothesis that CAV-1 improves dyslipidemia, inhibits cyclophilin A (CypA)- mediated ROS production, prevents mitochondrial compensatory action and attenuates oxidative stress responses in cholesterol-induced hypercholesterolemia. To determine the role of CAV-1 in mediating oxidative and antioxidative as well as cholesterol homeostasis, hypercholesterolemic rabbits were intravenously administered antenapedia-CAV-1 (AP-CAV-1) peptide for 2 wk. AP-CAV-1 enhanced CAV-1 expression by ˃15%, inhibited CypA expression by ˃50% (P < 0.05) and significantly improved dyslipidemia, thus reducing neutral lipid peroxidation. Moreover, CAV-1 attenuated hypercholesterolemia-induced changes in mitochondrial morphology and biogenesis and preserved mitochondrial respiratory function. In addition, CAV-1 protected against hypercholesterol-induced oxidative stress responses by reducing the degree of oxidative damage and enhancing the expression of antioxidant enzymes. CAV-1 treatment significantly suppressed apoptotic cell death, as evidenced by the reduction in the number of terminal deoxynucleotidyl transferase dUTP nick end-labeling-positive cells. We concluded that CAV-1 plays a critical role in inhibiting CypA-mediated ROS production, improving dyslipidemia, maintaining mitochondrial function, and suppressing oxidative stress responses that are vital for cell survival in hypercholesterol-affected renal organs.

Sex Differences in Renal Proximal Tubular Cell Homeostasis

Studies in human patients and animals have revealed sex-specific differences in susceptibility to renal diseases. Because actions of female sex hormones on normal renal tissue might protect against damage, we searched for potential influences of the female hormone cycle on basic renal functions by studying excretion of urinary marker proteins in healthy human probands. We collected second morning spot urine samples of unmedicated naturally ovulating women, postmenopausal women, and men daily and determined urinary excretion of the renal tubular enzymes fructose-1,6-bisphosphatase and glutathione-S-transferase-α Additionally, we quantified urinary excretion of blood plasma proteins α1-microglobulin, albumin, and IgG. Naturally cycling women showed prominent peaks in the temporal pattern of urinary fructose-1,6-bisphosphatase and glutathione-S-transferase-α release exclusively within 7 days after ovulation or onset of menses. In contrast, postmenopausal women and men showed consistently low levels of urinary fructose-1,6-bisphosphatase excretion over comparable periods. We did not detect changes in urinary α1-microglobulin, albumin, or IgG excretion. Results of this study indicate that proximal tubular tissue architecture, representing a nonreproductive organ-derived epithelium, undergoes periodical adaptations phased by the female reproductive hormone cycle. The temporally delimited higher rate of enzymuria in ovulating women might be a sign of recurring increases of tubular cell turnover that potentially provide enhanced repair capacity and thus, higher resistance to renal damage.

Knockdown of RTN1A attenuates ER stress and kidney injury in albumin overload-induced nephropathy

Our previous studies have suggested a critical role of reticulon (RTN)1A in mediating endoplasmic reticulum (ER) stress in kidney cells of animal models and humans with kidney diseases. A large body of evidence suggests that proteinuria itself can cause tubular cell injury leading to the progression of kidney disease. In the present study, we determined whether RTN1A mediates proteinuria-induced tubular cell injury through increased ER stress. We found that incubation of HK2 cells with human serum albumin induced the expression of RTN1A and ER stress markers, whereas knockdown of RTN1A expression attenuated human serum albumin-induced ER stress and tubular cell apoptosis in vitro. In vivo, we found that tubular cell-specific RTN1 knockdown resulted in a significant attenuation of tubular cell ER stress, apoptosis, and renal fibrosis in a model of albumin overload nephropathy. Based on these findings, we conclude that RTN1A is a key mediator for proteinuria-induced tubular cell toxicity and renal fibrosis.

Poststroke Inflammasome Expression and Regulation in the Peri-Infarct Area by Gonadal Steroids after Transient Focal Ischemia in the Rat Brain

CNS ischemia results in locally confined and rapid tissue damage accompanied by a loss of neurons and their circuits. Early and time-delayed inflammatory responses are critical variables determining the extent of neural disintegration and regeneration. Inflammasomes are vital effectors in innate immunity. Their activation in brain-intrinsic immune cells contributes to ischemia-related brain damage. The steroids 17β-estradiol (E2) and progesterone (P) are neuroprotective and anti-inflammatory. Using a transient focal rat ischemic model, we evaluated the time response of different inflammasomes in the peri-infarct zone from the early to late phases after poststroke ischemia. We show that the different inflammasome complexes reveal a specific time-oriented sequential expression pattern with a maximum at approximately 24 h after the infarct. Within the limits of antibody availability, immunofluorescence labeling demonstrated that microglia and neurons are major sources of the locally activated inflammasomes NOD-like receptor protein-3 (NLRP3) and associated speck-like protein (ASC), respectively. E2 and P given for 24 h immediately after ischemia onset reduced hypoxia-induced mRNA expression of the inflammasomes NLRC4, AIM2 and ASC, and decreased the protein levels of ASC and NLRP3. In addition, mRNA protein levels of the cytokines interleukin-1β (IL1β), IL18 and TNFα were reduced by the steroids. The findings provide for the first time a detailed flow chart of hypoxia-driven inflammasome regulation in the peri-infarct cerebral cortex. Further, we demonstrate that E2 and P alleviate the expression of certain inflammasome components, sometimes in a hormone-specific way. Besides directly regulating other cellular neuroprotective pathways, the control of inflammasomes by these steroids might contribute to its neuroprotective potency.

Inflammasomes are neuroprotective targets for sex steroids

Neuroinflammation in the central nervous system is triggered by toxic stimuli or degenerative events, orchestrates the interplay of brain-intrinsic immune cells and neighboring neural cells, and sequentially allows leukocyte extravasation from the periphery into the brain parenchyma. During the inflammatory cascade, immune-competent cells become activated and secrete a plethora of cytokines and chemokines which form a local inflammatory signaling network important for warding off harmful stimuli to the host but are likewise necessary to preserve damaged brain tissue. Inflammatory responses are initiated by extra- and intra-cellular pathogen and danger-associated receptors. These signals are processed by multi-protein complexes termed inflammasomes which trigger the production of biologically active interleukins-1 and 18 after the cleavage of caspase-1. Estrogens and progesterone are neuroprotective and anti-inflammatory in diverse disease models of the brain in particular under acute inflammatory conditions such as stroke and traumatic brain injury. Both steroids are able to attenuate pro-inflammatory cytokine activity. Recent literature and our own studies provide convincing evidence that the anti-inflammatory potency of these steroids result from a complex interaction with the inflammasome activation and their up-stream regulatory network of miRNAs in brain-intrinsic innate immune cells. This article examines steroid-inflammasome interactions in the brain during brain injury and illuminates the importance of regulation initial upstream events during neuroinflammation. This article is part of a Special Issue entitled 'Steroid Perspectives'.

Immune Homeostasis in Epithelial Cells: Evidence and Role of Inflammasome Signaling Reviewed

The epithelium regulates the interaction between the noxious xenogenous, as well as the microbial environment and the immune system, not only by providing a barrier but also by expressing a number of immunoregulatory membrane receptors, and intracellular danger sensors and their downstream effectors. Amongst these are a number of inflammasome sensor subtypes, which have been initially characterized in myeloid cells and described to be activated upon assembly into multiprotein complexes by microbial and environmental triggers. This review compiles a vast amount of literature that supports a pivotal role for inflammasomes in the various epithelial barriers of the human body as essential factors maintaining immune signaling and homeostasis.

Redox regulation of NLRP3 inflammasomes: ROS as trigger or effector?

SIGNIFICANCE

Inflammasomes are multiprotein complexes localized within the cytoplasm of the cell that are responsible for the maturation of proinflammatory cytokines such as interleukin-1β (IL-1β) and IL-18, and the activation of a highly inflammatory form of cell death, pyroptosis. In response to infection or cellular stress, inflammasomes are assembled, activated, and involved in host defense and pathophysiology of diseases. Clarification of the molecular mechanisms leading to the activation of this intracellular inflammatory machinery may provide new insights into the concept of inflammation as the root of and route to human diseases.

RECENT ADVANCES

The activation of inflammasomes, specifically the most fully characterized inflammasome-the nucleotide-binding oligomerization domain (NOD)-like receptor containing pyrin domain 3 (NLRP3) inflammasome, is now emerging as a critical molecular mechanism for many degenerative diseases. Several models have been developed to describe how NLRP3 inflammasomes are activated, including K(+) efflux, lysosome function, endoplasmic reticulum (ER) stress, intracellular calcium, ubiquitination, microRNAs, and, in particular, reactive oxygen species (ROS).

CRITICAL ISSUES

ROS may serve as a "kindling" or triggering factor to activate NLRP3 inflammasomes as well as "bonfire" or "effector" molecules, resulting in pathological processes. Increasing evidence seeks to understand how this spatiotemporal action of ROS occurs during NLRP3 inflammasome activation, which will be a major focus of this review.

FUTURE DIRECTIONS

It is imperative to know how this dual action of ROS works during NLRP3 inflammation activation on different stimuli and what relevance such spatiotemporal redox regulation of NLRP3 inflammasomes has in cell or organ functions and possible human diseases.

The emerging role of the inflammasome in kidney diseases

PURPOSE OF REVIEW

To focus on the latest data that elucidate the role of the NLRP3 inflammasome in kidney diseases.

RECENT FINDINGS

The NLRP3 inflammasome is not limited by the traditional microbial stimuli of innate immunity and its connection with autophagy, apoptosis, fibrosis, and pro-inflammatory cytokines has broader implications for a variety of kidney diseases. In a wide spectrum of glomerular and tubulointerstitial diseases, the NLRP3 inflammasome is upregulated in both classical immune cells such as infiltrating macrophages and resident dendritic cells as well as in renal tubular epithelial cells, and even podocytes. Inhibition of the NLRP3 inflammasome ameliorates renal injury in a variety of animal models. Interestingly, this extends to models of proteinuria, which suggests that the deleterious effect of albuminuria on the proximal tubular epithelium and podocytes is, in part, mediated by inflammasome activation.

SUMMARY

Recent studies in animal models, and limited studies in humans, suggest a broad role for inflammasome activation in renal disease. Surprisingly, individual components of the inflammasome, independent of inflammasome activation, may also contribute to progressive renal injury. Additional, studies are needed to define the relative importance of the inflammasome in specific diseases and the therapeutic opportunities afforded by targeting the inflammasome.

Inhibition of hyperhomocysteinemia-induced inflammasome activation and glomerular sclerosis by NLRP3 gene deletion

BACKGROUND/AIMS

Hyperhomocysteinemia (hHcys) has been reported to initiate Nod-like receptor protein 3 (NLRP3) inflammasome formation and activation in podocytes, leading to glomerular dysfunction and sclerosis. However, it remains unknown whether Nlrp3 gene is critical for the formation and activation of inflammasomes in glomeruli of hHcys mice.

METHODS

Plasma homocysteine concentration was estimated utilizing HPLC, inflammasome formation and immunofluorescence expression from confocal microscopy, IL-1β production from ELISA.

RESULTS

Uninephrectomized Nlrp3 knockout (Nlrp3(-/-)) and wild type (Nlrp3(+/+)) and intra renal Nlrp3 shRNA-transfected wild type mice (Nlrp3 shRNA) were fed a folate free (FF) diet or normal chow (ND) for 4 weeks to produce hHcys. The plasma Hcys levels were significantly elevated in both Nlrp3(-/-) and Nlrp3(+/+) mice fed a FF diet compared to ND fed mice. The FF diet significantly increased the colocalization of Nlrp3 with apoptosis-associated speck-like protein (ASC) or caspase-1, caspase-1 activity and IL-1β production in glomeruli of Nlrp3(+/+), but not in Nlrp3(-/-) mice and local Nlrp3 shRNA transfected mice. Correspondingly, the glomerular damage index (GDI) and urinary protein excretion were significantly higher in Nlrp3(+/+) mice compared to ND fed mice. However, the hHcys-induced increase in GDI and proteinuria were significantly lower in Nlrp3(-/-) and local Nlrp3 shRNA transfected mice than in Nlrp3(+/+) mice. Immunocytochemical analysis showed that hHcys decreased expression of podocin and nephrin, but increased desmin expression in glomeruli of Nlrp3(+/+) mice compared to Nlrp3(-/-) mice.

CONCLUSION

Nlrp3 gene is an essential component of Nlrp3 inflammasomes and that targeting Nlrp3 may be important therapeutic strategy to prevent inflammasome activation and thereby protect podocytes and glomeruli from hHcys-induced injury.

Progression of renal injury toward interstitial inflammation and glomerular sclerosis is dependent on abnormal protein filtration

Chronic proteinuric renal diseases, independent from the type of the initial insult, have in common a loss of selectivity of the glomerular barrier to protein filtration. Glomerular sclerosis is the progressive lesion affecting the glomerular capillary wall, the primary site at which the protein filtration is abnormally enhanced by disease. Dysfunction of podocytes, that serve to maintain the intact barrier, is a central event in lesion development. However, glomerular injury is signalled to tubular and interstitial structures largely in advance of nephron destruction. Glomerular ultrafiltration of excessive amounts of plasma-derived proteins and associated factors incites tubulointerstitial damage and might amplify an inherent susceptibility of the kidney to become dysfunctional in several disease conditions. Thus, noxious substances in the proteinuric ultrafiltrate promote apoptotic responses and multiple changes in the phenotype of tubule cells with generation of inflammatory and fibrogenic mediators. The severity of tubular interstitial damage has long been recognized to be highly correlated to the degree of deterioration of renal failure even better than glomerular lesions. This review focuses on pathways of tubular injury and apoptosis that in turn promote nephron-by-nephron degeneration and interstitial fibrosis during proteinuria contributing to multifaceted processes of kidney scarring and function loss.

Mitochondrial dysfunction in the pathophysiology of renal diseases

Mitochondrial dysfunction has gained recognition as a contributing factor in many diseases. The kidney is a kind of organ with high energy demand, rich in mitochondria. As such, mitochondrial dysfunction in the kidney plays a critical role in the pathogenesis of kidney diseases. Despite the recognized importance mitochondria play in the pathogenesis of the diseases, there is limited understanding of various aspects of mitochondrial biology. This review examines the physiology and pathophysiology of mitochondria. It begins by discussing mitochondrial structure, mitochondrial DNA, mitochondrial reactive oxygen species production, mitochondrial dynamics, and mitophagy, before turning to inherited mitochondrial cytopathies in kidneys (inherited or sporadic mitochondrial DNA or nuclear DNA mutations in genes that affect mitochondrial function). Glomerular diseases, tubular defects, and other renal diseases are then discussed. Next, acquired mitochondrial dysfunction in kidney diseases is discussed, emphasizing the role of mitochondrial dysfunction in the pathogenesis of chronic kidney disease and acute kidney injury, as their prevalence is increasing. Finally, it summarizes the possible beneficial effects of mitochondrial-targeted therapeutic agents for treatment of mitochondrial dysfunction-mediated kidney injury-genetic therapies, antioxidants, thiazolidinediones, sirtuins, and resveratrol-as mitochondrial-based drugs may offer potential treatments for renal diseases.