Atherogenic scavenger receptor modulation in the tubulointerstitium in response to chronic renal injury

Elevated ALOX12 in renal tissue predicts progression in diabetic kidney disease

Diabetic kidney disease (DKD) is one of the major causes of end-stage renal disease and one of the significant complications of diabetes. This study aims to identify the main differentially expressed genes in DKD from transcriptome sequencing results and analyze their diagnostic value. The present study sequenced db/m mouse and db/db mouse to determine the ALOX12 genetic changes related to DKD. After preliminary validation, ALOX12 levels were significantly elevated in the blood of DKD patients, but not during disease progression. Moreover, urine ALOX12 was increased only in macroalbuminuria patients. Therefore, to visualize the diagnostic efficacy of ALOX12 on the onset and progression of renal injury in DKD, we collected kidney tissue from patients for immunohistochemical staining. ALOX12 was increased in the kidneys of patients with DKD and was more elevated in macroalbuminuria patients. Clinical chemical and pathological data analysis indicated a correlation between ALOX12 protein expression and renal tubule injury. Further immunofluorescence double staining showed that ALOX12 was expressed in both proximal tubules and distal tubules. Finally, the diagnostic value of the identified gene in the progression of DKD was assessed using receiver operating characteristic (ROC) curve analysis. The area under the curve (AUC) value for ALOX12 in the diagnosis of DKD entering the macroalbuminuria stage was 0.736, suggesting that ALOX12 has good diagnostic efficacy. During the development of DKD, the expression levels of ALOX12 in renal tubules were significantly increased and can be used as one of the predictors of the progression to macroalbuminuria in patients with DKD.

The role of exercise in improving hyperlipidemia-renal injuries induced by a high-fat diet: a literature review

A diet that is high in sugar and fat is a precursor to various chronic diseases, especially hyperlipidemia. Patients with hyperlipidemia have increased levels of plasma free fatty acids and an ectopic accumulation of lipids. The kidney is one of the main organs affected by this disease and, recently, there have been more studies conducted on renal injury caused by hyperlipidemia. The main pathological mechanism is closely related to renal lipotoxicity. However, in different kidney cells, the reaction mechanism varies due to the different affinities of the lipid receptors. At present, it is believed that in addition to lipotoxicity, hyperlipidemia induced-renal injury is also closely related to oxidative stress, endoplasmic reticulum stress, and inflammatory reactions, which are the result of multiple factors. Exercise plays an important role in the prevention of various chronic diseases and recently emerging researches indicated its positive effects to renal injury caused by hyperlipidemia. However, there are few studies summarizing the effects of exercise on this disease and the specific mechanisms need to be further explored. This article summarizes the mechanisms of hyperlipidemia induced-renal injury at the cellular level and discusses the ways in which exercise may regulate it. The results provide theoretical support and novel approaches for identifying the intervention target to treat hyperlipidemia induced-renal injury.

ADAM10 and ADAM17, Major Regulators of Chronic Kidney Disease Induced Atherosclerosis?

Chronic kidney disease (CKD) is a major health problem, affecting millions of people worldwide, in particular hypertensive and diabetic patients. CKD patients suffer from significantly increased cardiovascular disease (CVD) morbidity and mortality, mainly due to accelerated atherosclerosis development. Indeed, CKD not only affects the kidneys, in which injury and maladaptive repair processes lead to local inflammation and fibrosis, but also causes systemic inflammation and altered mineral bone metabolism leading to vascular dysfunction, calcification, and thus, accelerated atherosclerosis. Although CKD and CVD individually have been extensively studied, relatively little research has studied the link between both diseases. This narrative review focuses on the role of a disintegrin and metalloproteases (ADAM) 10 and ADAM17 in CKD and CVD and will for the first time shed light on their role in CKD-induced CVD. By cleaving cell surface molecules, these enzymes regulate not only cellular sensitivity to their micro-environment (in case of receptor cleavage), but also release soluble ectodomains that can exert agonistic or antagonistic functions, both locally and systemically. Although the cell-specific roles of ADAM10 and ADAM17 in CVD, and to a lesser extent in CKD, have been explored, their impact on CKD-induced CVD is likely, yet remains to be elucidated.

Increased renal uptake and urine excretion of oxidized LDL is possibly associated with formation of large calcium oxalate nephrolithiasis: a preliminary study

PURPOSE

Growing evidence have suggested an association between nephrolithiasis and cardiovascular disease (CVD) with unclear mechanism. Oxidized low-density lipoproteins (oxLDL) induces atherosclerosis and was found to be the possible link between these two diseases. Our study aimed to examine the serum, urine and kidney expression of oxLDL in relation to large calcium oxalate (CaOx) renal stone disease.

METHODS

A total of 67 large CaOx dominant renal stone patients and 31 stone-free controls were enrolled in the prospective case-control study. All participants were without known CVD history. Serum, urine, and kidney biopsy were collected before and during percutaneous nephrolithotomy, respectively. Enzyme-linked immunosorbent assays were used to assess serum and urine oxLDL, lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), and high-sensitivity C-reactive protein (hsCRP).

RESULTS

There was no significantly difference in circulating oxLDL, but serum hsCRP was significantly near two-fold higher in nephrolithiasis patients. Serum hsCRP was also correlated with stone maximal length. Urine oxLDL was significantly higher in the nephrolithiasis group and correlated with serum hsCRP and stone maximal length. Increased oxLDL uptake in kidney was found in nephrolithiasis patients, whereas no significantly renal expression of oxLDL was observed in controls.

CONCLUSIONS

The renal uptake of oxLDL with increased oxLDL excretion from large CaOx renal stone formers, independent of increased circulating oxLDL, is a novel pathological finding in kidney stone disease and brings attention to the possible involvement of renal steatosis in the process of urolithiasis formation.

The role of lipotoxicity in kidney disease: From molecular mechanisms to therapeutic prospects

Lipotoxicity is the dysregulation of the lipid environment and/or intracellular composition that leads to accumulation of harmful lipids and ultimately to organelle dysfunction, abnormal activation of intracellular signaling pathways, chronic inflammation and cell death. It plays an important role in the development of acute kidney injury and chronic kidney disease, including diabetic nephropathy, obesity-related glomerulopathy, age-related kidney disease, polycystic kidney disease, and the like. However, the mechanisms of lipid overload and kidney injury remain poorly understood. Herein, we discuss two pivotal aspects of lipotoxic kidney injury. First, we analyzed the mechanism of lipid accumulation in the kidney. Accumulating data indicate that the mechanisms of lipid overload in different kidney diseases are inconsistent. Second, we summarize the multiple mechanisms by which lipotoxic species affect the kidney cell behavior, including oxidative stress, endoplasmic reticulum stress, mitochondrial dysfunction, dysregulated autophagy, and inflammation, highlighting the central role of oxidative stress. Blocking the molecular pathways of lipid accumulation in the kidney and the damage of the kidney by lipid overload may be potential therapeutic targets for kidney disease, and antioxidant drugs may play a pivotal role in the treatment of kidney disease in the future.

Fatty kidney: A possible future for chronic kidney disease research

BACKGROUND

Metabolic syndrome is a growing twenty-first century pandemic associated with multiple clinical comorbidities ranging from cardiovascular diseases, non-alcoholic fatty liver disease and polycystic ovary syndrome to kidney dysfunction. A novel area of research investigates the concept of fatty kidney in the pathogenesis of chronic kidney disease, especially in patients with diabetes mellitus or metabolic syndrome.

AIM

To review the most updated literature on fatty kidney and provide future research, diagnostic and therapeutic perspectives on a disease increasingly affecting the contemporary world.

MATERIALS AND METHOD

We performed an extensive literature search through three databases including Embase (Elsevier) and the Cochrane Central Register of Controlled Trials (Wiley) and PubMed/Medline Web of Science in November 2021 by using the following terms and their combinations: 'fatty kidney', 'ectopic fat', 'chronic kidney disease', 'cardiovascular event', 'cardio-metabolic risk', 'albuminuria' and 'metabolic syndrome'. Each study has been individually assessed by the authors.

RESULTS

Oxidative stress and inflammation, Klotho deficiency, endoplasmic reticulum stress, mitochondrial dysfunction and disruption of cellular energy balance appear to be the main pathophysiological mechanisms leading to tissue damage following fat accumulation. Despite the lack of large-scale comprehensive studies in this novel field of research, current clinical trials demonstrate fatty kidney as an independent risk factor for the development of chronic kidney disease and cardiovascular events.

CONCLUSION

The requirement for future studies investigating the pathophysiology, clinical outcomes and therapeutics of fatty kidney is clear.

Fatty Acid β-Oxidation in Kidney Diseases: Perspectives on Pathophysiological Mechanisms and Therapeutic Opportunities

The kidney is a highly metabolic organ and requires a large amount of ATP to maintain its filtration-reabsorption function, and mitochondrial fatty acid β-oxidation serves as the main source of energy to meet its functional needs. Reduced and inefficient fatty acid β-oxidation is thought to be a major mechanism contributing to kidney diseases, including acute kidney injury, chronic kidney disease and diabetic nephropathy. PPARα, AMPK, sirtuins, HIF-1, and TGF-β/SMAD3 activation have all been shown to play key roles in the regulation of fatty acid β-oxidation in kidney diseases, and restoration of fatty acid β-oxidation by modulation of these molecules can ameliorate the development of such diseases. Here, we disentangle the lipid metabolism regulation properties and potential mechanisms of mesenchymal stem cells and their extracellular vesicles, and emphasize the role of mesenchymal stem cells on lipid metabolism. This review aims to highlight the important role of fatty acid β-oxidation in the progression of kidney diseases, and to explore the fatty acid β-oxidation effects and therapeutic potential of mesenchymal stem cells for kidney diseases.

Inhibitory Antibodies against PCSK9 Reduce Surface CD36 and Mitigate Diet-Induced Renal Lipotoxicity

Background

PCSK9 modulates the uptake of circulating lipids through a range of receptors, including the low-density lipoprotein receptor (LDLR) and CD36. In the kidney, CD36 is known to contribute to renal injury through pro-inflammatory and -fibrotic pathways. In this study, we sought to investigate the role of PCSK9 in modulating renal lipid accumulation and injury through CD36 using a high fat diet (HFD)-induced murine model.

Methods

The effect of PCSK9 on the expression of CD36 and intracellular accumulation of lipid was examined in cultured renal cells and in the kidneys of male C57BL/6J mice. The effect of these findings was subsequently explored in a model of HFD-induced renal injury in Pcsk9 ^-/- and Pcsk9 ^+/+ littermate control mice on a C57BL/6J background.

Results

In the absence of PCSK9, we observed heightened CD36 expression levels, which increased free fatty acid (FFA) uptake in cultured renal tubular cells. As a result, PCSK9 deficiency was associated with an increase in long-chain saturated FFA-induced ER stress. Consistent with these observations, Pcsk9^-/- mice fed a HFD displayed elevated ER stress, inflammation, fibrosis, and renal injury relative to HFD-fed control mice. In contrast to Pcsk9^-/- mice, pretreatment of WT C57BL/6J mice with evolocumab, an anti-PCSK9 monoclonal antibody (mAb) that binds to and inhibits the function of circulating PCSK9, protected against HFD-induced renal injury in association with reducing cell surface CD36 expression on renal epithelia.

Conclusions

We report that circulating PCSK9 modulates renal lipid uptake in a manner dependent on renal CD36. In the context of increased dietary fat consumption, the absence of circulating PCSK9 may promote renal lipid accumulation and subsequent renal injury. However, although the administration of evolocumab blocks the interaction of PCSK9 with the LDLR, this evolocumab/PCSK9 complex can still bind CD36, thereby protecting against HFD-induced renal lipotoxicity.

The structural basis of effective LOX-1 inhibition

Along with other scavenger receptors, splice variants of LOX-1 play an important role in modulating numerous subcellular mechanisms such as normal cell development, differentiation and growth in response to physiological stimuli. Thus, LOX-1 activity is a key regulator in determining the severity of many genetic, metabolic, cardiovascular, renal, and neurodegenerative diseases and/or cancer. Increased expression of LOX-1 precipitates pathological disorders during the aging process. Therefore, it becomes important to develop novel LOX-1 inhibitors based on its ligand binding polarity and/or affinity and disrupt the uptake of its ligand: oxidized low-density lipoproteins (ox-LDL). In this review, we shed light on the presently studied and developed novel LOX-1 inhibitors that may have potential for treatment of diseases characterized by LOX-1 activation.

P2X7 receptor inhibition attenuates podocyte injury by oxLDL through deregulating CXCL16

This study aims to evaluate the effect of purinergic ligand-gated ion channel 7 receptor (P2X7R) antagonist A438079 in kidneys of children with primary nephrotic syndrome (PNS). In vitro, human podocytes were respectively stimulated with oxLDL (80 µg/ml), A438079 (10 µmol/L), or the compound oxLDL and A438079 together. CXC chemokine ligand 16 (CXCL16) and P2X7R expression levels were detected by Western blot and immunofluorescence assay, respectively. Immunofluorescence assay was used to detect Dil-oxLDL, and a Colorimetric Cholesterol Detection Kit was used for quantitative determination. Our results demonstrated that CXCL16 and P2X7R expression levels were remarkably increased in the renal tissue from children with PNS, particularly in the same location. Furthermore, in contrast to children with minimal change disease, the expressions of P2X7R and CXCL16 in renal tissue of children with focal segmental glomerulosclerosis were more obvious. In vitro, CXCL16 and P2X7R expression levels in human podocytes stimulated with oxLDL were markedly elevated accompanying higher intracellular lipid accumulation compared with the normal control group. In addition, pretreatment of human podocytes with A438079 before the start of oxLDL stimulation causes a significant reduction in CXCL16 expression and a decrease in lipid accumulation. Overall, CXCL16 and P2X7R may participate in the progression of PNS. The lipid accumulation reduction caused by A438079 may be through deregulating the CXCL16 pathway, suggesting that there is a potential role for P2X7R antagonists to remedy PNS.

C-C Motif Chemokine Ligand-17 as a Novel Biomarker and Regulator of Epithelial Mesenchymal Transition in Renal Fibrogenesis

CCL17, a chemotactic cytokine produced by macrophages, is known to promote inflammatory and fibrotic effects in multiple organs, but its role in mediating renal fibrosis is unclear. In our study cohort of 234 chronic kidney disease (CKD) patients and 65 healthy controls, human cytokine array analysis revealed elevated CCL17 expression in CKD that correlated negatively with renal function. The area under the receiver operating characteristic curve of CCL17 to predict the development of CKD stages 3b–5 was 0.644 (p < 0.001), with the optimal cut-off value of 415.3 ng/mL. In vitro over-expression of CCL17 in HK2 cells had no effect on cell viability, but increased cell motility and the expression of α-SMA, vimentin and collagen I, as shown by western blot analysis. In a unilateral ureteral obstruction (UUO) mouse model, we observed significantly increased interstitial fibrosis and renal tubule dilatation by Masson’s Trichrome and H&E staining, and markedly increased expression of CCL17, vimentin, collagen I, and α-SMA by IHC stain, qRTPCR, and western blotting. CCL17 induced renal fibrosis by promoting the epithelial-mesenchymal transition, resulting in ECM accumulation. CCL17 may be a useful biomarker for predicting the development of advanced CKD.

Renal Lipid Metabolism Abnormalities in Obesity and Clear Cell Renal Cell Carcinoma

Clear cell renal cell carcinoma is the most common and deadly type of cancer affecting the kidney, and is characterized histologically by large intracellular lipid deposits. These deposits are thought to result from lipid metabolic reprogramming occurring in tumor cells, but the exact mechanisms and implications of these metabolic alterations are incompletely understood. Obesity is an independent risk factor for clear cell renal cell carcinoma, and is also associated with lipid accumulation in noncancerous epithelial cells of the proximal tubule, where clear cell renal cell carcinoma originates. This article explores the potential link between obesity-associated renal lipid metabolic disturbances and lipid metabolic reprogramming in clear cell renal cell carcinoma, and discusses potential implications for future research.

Dyslipidemia in Kidney Disorders: Perspectives on Mitochondria Homeostasis and Therapeutic Opportunities

To excrete body nitrogen waste and regulate electrolyte and fluid balance, the kidney has developed into an energy factory with only second to the heart in mitochondrial content in the body to meet the high-energy demand and regulate homeostasis. Energy supply from the renal mitochondria majorly depends on lipid metabolism, with programed enzyme systems in fatty acid β-oxidation and Krebs cycle. Renal mitochondria integrate several metabolic pathways, including AMPK/PGC-1α, PPARs, and CD36 signaling to maintain energy homeostasis for dynamic and static requirements. The pathobiology of several kidney disorders, including diabetic nephropathy, acute and chronic kidney injuries, has been primarily linked to impaired mitochondrial bioenergetics. Such homeostatic disruption in turn stimulates a pathological adaptation, with mitochondrial enzyme system reprograming possibly leading to dyslipidemia. However, this alteration, while rescuing oncotic pressure deficit secondary to albuminuria and dissipating edematous disorder, also imposes an ominous lipotoxic consequence. Reprograming of lipid metabolism in kidney injury is essential to preserve the integrity of kidney mitochondria, thereby preventing massive collateral damage including excessive autophagy and chronic inflammation. Here, we review dyslipidemia in kidney disorders and the most recent advances on targeting mitochondrial energy metabolism as a therapeutic strategy to restrict renal lipotoxicity, achieve salutary anti-edematous effects, and restore mitochondrial homeostasis.

Molecular Targets and Related Biologic Activities of Fucoidan: A Review

Fucoidan-a marine natural active polysaccharide derived from brown algae with a variety of medicinal activities and low toxicity-has been used as clinical drug for renal diseases for nearly 20 years. The pharmacological mechanism of fucoidan has been well-investigated, based on target molecules and downstream signaling pathways. This review summarizes some important molecular targets of fucoidan and its related biologic activities, including scavenger receptor (SR), Toll-like receptors (TLRs), C-type lectin (CLEC) and some newly found target molecules, which may be beneficial for further understanding the pharmacological mechanism of fucoidan and discovering its new functions, as well as developing related clinical or adjuvant drugs and functional preparations.

Recent Progress on Lipid Intake and Chronic Kidney Disease

The incidence of chronic kidney disease (CKD) is associated with major abnormalities in circulating lipoproteins and renal lipid metabolism. This article elaborates on the mechanisms of CKD and lipid uptake abnormalities. The viewpoint we supported is that lipid abnormalities directly cause CKD, resulting in forming a vicious cycle. On the theoretical and experiment fronts, this inference has been verified by elaborately elucidating the role of lipid intake and accumulation as well as their influences on CKD. Taken together, these findings suggest that further understanding of lipid metabolism in CKD may lead to novel therapeutic approaches.

The Role of Chemokine Receptors in Renal Fibrosis

Renal fibrosis is the final pathological process common to any ongoing, chronic kidney injury or maladaptive repair. Renal fibrosis is considered to be closely related to various cell types, such as fibroblasts, myofibroblasts, T cells, and other inflammatory cells. Multiple types of cells regulate renal fibrosis through the recruitment, proliferation, and activation of fibroblasts, and the production of the extracellular matrix. Cell trafficking is orchestrated by a family of small proteins called chemokines. Chemokines are cytokines with chemotactic properties, which are classified into 4 groups: CXCL, CCL, CX3CL, and XCL. Similarly, chemokine receptors are G protein-coupled seven-transmembrane receptors classified into 4 groups: XCR, CCR, CXCR, and CX3CR. Chemokine receptors are also implicated in the infiltration, differentiation, and survival of functional cells, triggering inflammation that leads to fibrosis development. In this review, we summarize the different chemokine receptors involved in the processes of fibrosis in different cell types. Further studies are required to identify the molecular mechanisms of chemokine signaling that contribute to renal fibrosis.

Arachidonic Acid Metabolism and Kidney Inflammation

As a major component of cell membrane lipids, Arachidonic acid (AA), being a major component of the cell membrane lipid content, is mainly metabolized by three kinds of enzymes: cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome P450 (CYP450) enzymes. Based on these three metabolic pathways, AA could be converted into various metabolites that trigger different inflammatory responses. In the kidney, prostaglandins (PG), thromboxane (Tx), leukotrienes (LTs) and hydroxyeicosatetraenoic acids (HETEs) are the major metabolites generated from AA. An increased level of prostaglandins (PGs), TxA₂ and leukotriene B4 (LTB₄) results in inflammatory damage to the kidney. Moreover, the LTB₄-leukotriene B4 receptor 1 (BLT1) axis participates in the acute kidney injury via mediating the recruitment of renal neutrophils. In addition, AA can regulate renal ion transport through 19-hydroxystilbenetetraenoic acid (19-HETE) and 20-HETE, both of which are produced by cytochrome P450 monooxygenase. Epoxyeicosatrienoic acids (EETs) generated by the CYP450 enzyme also plays a paramount role in the kidney damage during the inflammation process. For example, 14 and 15-EET mitigated ischemia/reperfusion-caused renal tubular epithelial cell damage. Many drug candidates that target the AA metabolism pathways are being developed to treat kidney inflammation. These observations support an extraordinary interest in a wide range of studies on drug interventions aiming to control AA metabolism and kidney inflammation.

Lipid Accumulation and Chronic Kidney Disease

Obesity and hyperlipidemia are the most prevalent independent risk factors of chronic kidney disease (CKD), suggesting that lipid accumulation in the renal parenchyma is detrimental to renal function. Non-esterified fatty acids (also known as free fatty acids, FFA) are especially harmful to the kidneys. A concerted, increased FFA uptake due to high fat diets, overexpression of fatty acid uptake systems such as the CD36 scavenger receptor and the fatty acid transport proteins, and a reduced β-oxidation rate underlie the intracellular lipid accumulation in non-adipose tissues. FFAs in excess can damage podocytes, proximal tubular epithelial cells and the tubulointerstitial tissue through various mechanisms, in particular by boosting the production of reactive oxygen species (ROS) and lipid peroxidation, promoting mitochondrial damage and tissue inflammation, which result in glomerular and tubular lesions. Not all lipids are bad for the kidneys: polyunsaturated fatty acids (PUFA) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) seem to help lag the progression of chronic kidney disease (CKD). Lifestyle interventions, especially dietary adjustments, and lipid-lowering drugs can contribute to improve the clinical outcome of patients with CKD.

Distinct patterns of transcriptional and epigenetic alterations characterize acute and chronic kidney injury

Acute kidney injury (AKI) and chronic kidney disease (CKD) are considered early and late phases of a pathologic continuum of interconnected disease states. Although changes in gene expression patterns have recently been elucidated for the transition of AKI to CKD, the epigenetic regulation of key kidney injury related genes remains poorly understood. We used multiplex RT-qPCR, ChIP-qPCR and integrative analysis to compare transcriptional and epigenetic changes at renal disease-associated genes across mouse AKI and CKD models. These studies showed that: (i) there are subsets of genes with distinct transcriptional and epigenetically profiles shared by AKI and CKD but also subsets that are specific to either the early or late stages of renal injury; (ii) differences in expression of a small number of genes is sufficient to distinguish AKI from CKD; (iii) transcription plays a key role in the upregulation of both AKI and CKD genes while post-transcriptional regulation appears to play a more significant role in decreased expression of both AKI and CKD genes; and (iv) subsets of transcriptionally upregulated genes share epigenetic similarities while downregulated genes do not. Collectively, our study suggests that identified common transcriptional and epigenetic profiles of kidney injury loci could be exploited for therapeutic targeting in AKI and CKD.

Renal ADAM10 and 17: Their Physiological and Medical Meanings

A disintegrin and metalloproteinases (ADAMs) are a Zn²⁺-dependent transmembrane and secreted metalloprotease superfamily, so-called “molecular scissors,” and they consist of an N-terminal signal sequence, a prodomain, zinc-binding metalloprotease domain, disintegrin domain, cysteine-rich domain, transmembrane domain and cytoplasmic tail. ADAMs perform proteolytic processing of the ectodomains of diverse transmembrane molecules into bioactive mediators. This review summarizes on their most well-known members, ADAM10 and 17, focusing on the kidneys. ADAM10 is expressed in renal tubular cells and affects the expression of specific brush border genes, and its activation is involved in some renal diseases. ADAM17 is weakly expressed in normal kidneys, but its expression is markedly induced in the tubules, capillaries, glomeruli, and mesangium, and it is involved in interstitial fibrosis and tubular atrophy. So far, the various substrates have been identified in the kidneys. Shedding fragments become released ligands, such as Notch and EGFR ligands, and act as the chemoattractant factors including CXCL16. Their ectodomain shedding is closely correlated with pathological factors, which include inflammation, interstitial fibrosis, and renal injury. Also, the substrates of both ADAMs contain the molecules that play important roles at the plasma membrane, such as meaprin, E-cadherin, Klotho, and CADM1. By being released into urine, the shedding products could be useful for biomarkers of renal diseases, but ADAM10 and 17 per se are also notable as biomarkers. Furthermore, ADAM10 and/or 17 inhibitions based on various strategies such as small molecules, antibodies, and their recombinant prodomains are valuable, because they potentially protect renal tissues and promote renal regeneration. Although temporal and spatial regulations of inhibitors are problems to be solved, their inhibitors could be useful for renal diseases.

Cardiotonic Steroids and the Sodium Trade Balance: New Insights into Trade-Off Mechanisms Mediated by the Na⁺/K⁺-ATPase

In 1972 Neal Bricker presented the "trade-off" hypothesis in which he detailed the role of physiological adaptation processes in mediating some of the pathophysiology associated with declines in renal function. In the late 1990's Xie and Askari published seminal studies indicating that the Na⁺/K⁺-ATPase (NKA) was not only an ion pump, but also a signal transducer that interacts with several signaling partners. Since this discovery, numerous studies from multiple laboratories have shown that the NKA is a central player in mediating some of these long-term "trade-offs" of the physiological adaptation processes which Bricker originally proposed in the 1970's. In fact, NKA ligands such as cardiotonic steroids (CTS), have been shown to signal through NKA, and consequently been implicated in mediating both adaptive and maladaptive responses to volume overload such as fibrosis and oxidative stress. In this review we will emphasize the role the NKA plays in this "trade-off" with respect to CTS signaling and its implication in inflammation and fibrosis in target organs including the heart, kidney, and vasculature. As inflammation and fibrosis exhibit key roles in the pathogenesis of a number of clinical disorders such as chronic kidney disease, heart failure, atherosclerosis, obesity, preeclampsia, and aging, this review will also highlight the role of newly discovered NKA signaling partners in mediating some of these conditions.

Recent Advances in Magnetic Resonance Imaging Assessment of Renal Fibrosis

CKD is a global public health problem. Renal fibrosis is a final common pathway leading to progressive loss of function in CKD. The degree of renal fibrosis predicts the prognosis of CKD. Recent studies have shown that bone marrow-derived fibroblasts contribute significantly to the development of renal fibrosis, which may yield novel therapeutic strategy for fibrotic kidney disease. Therefore, it is imperative to accurately assess the degree of renal fibrosis noninvasively to identify those patients who can benefit from antifibrotic therapy. In this review, we summarize recent advances in the assessment of renal fibrosis by magnetic resonance imaging.

Oxidative Balance Score and the Risk of End-Stage Renal Disease and Cardiovascular Disease

BACKGROUND

Oxidative balance score (OBS) is a composite measure of oxidative stress-related exposures. The aim of this study was to investigate the association between OBS, end-stage renal disease (ESRD), and cardiovascular disease (CVD).

METHODS

Using data from the Chronic Renal Insufficiency Cohort, we calculated the main exposure OBS by summing up 12 apriori-defined pro- and antioxidant factors obtained from the diet history questionnaire and lifestyle assessment. We divided OBS into quartiles (Q1-Q4), with Q1 (predominance of pro-oxidants) as the reference. We analyzed OBS quartiles as an ordinal variable. Crude and adjusted hazards ratios (HRs) and 95% CIs were estimated using Cox proportional hazards models for time to ESRD and CVD.

RESULTS

Compared to Q1, Q4 (high antioxidant) was associated with ESRD in the crude model (HR 1.35, 95% CI 1.08-1.69) and adjusting for age, sex, and race (HR 1.36, 95% CI 1.09-1.71) but not in the fully adjusted model (HR 1.12, 95% CI 0.84-1.51). HR of ESRD increased as the OBS quartiles increased in the crude model (ptrend < 0.05) but not in the fully adjusted model (ptrend = 0.30). Compared to Q1, Q4 was associated with CVD in the crude (HR 1.33, 95% CI 1.06-1.68) but not adjusted models. The HR of CVD increased with an increase in OBS quartiles in the crude model (ptrend < 0.05).

CONCLUSION

The reverse association between OBS and progression to ESRD suggests that perhaps the effect of oxidative balance-related exposure is different in the setting of established chronic kidney disease.

Antagonism of scavenger receptor CD36 by 5A peptide prevents chronic kidney disease progression in mice independent of blood pressure regulation

Scavenger receptor CD36 participates in lipid metabolism and inflammatory pathways important for cardiovascular disease and chronic kidney disease (CKD). Few pharmacological agents are available to slow the progression of CKD. However, apolipoprotein A-I-mimetic peptide 5A antagonizes CD36 in vitro. To test the efficacy of 5A, and to test the role of CD36 during CKD, we compared wild-type to CD36 knockout mice and wild-type mice treated with 5A, in a progressive CKD model that resembles human disease. Knockout and 5A-treated wild-type mice were protected from CKD progression without changes in blood pressure and had reductions in cardiovascular risk surrogate markers that are associated with CKD. Treatment with 5A did not further protect CD36 knockout mice from CKD progression, implicating CD36 as its main site of action. In a separate model of kidney fibrosis, 5A-treated wild-type mice had less macrophage infiltration and interstitial fibrosis. Peptide 5A exerted anti-inflammatory effects in the kidney and decreased renal expression of inflammasome genes. Thus, CD36 is a new therapeutic target for CKD and its associated cardiovascular risk factors. Peptide 5A may be a promising new agent to slow CKD progression.

CXCL16 regulates renal injury and fibrosis in experimental renal artery stenosis

Recent studies have shown that inflammation plays a critical role in the initiation and progression of hypertensive kidney disease, including renal artery stenosis. However, the signaling mechanisms underlying the induction of inflammation are poorly understood. We found that CXCL16 was induced in the kidney in a murine model of renal artery stenosis. To determine whether CXCL16 is involved in renal injury and fibrosis, wild-type and CXCL16 knockout mice were subjected to renal artery stenosis induced by placing a cuff on the left renal artery. Wild-type and CXCL16 knockout mice had comparable blood pressure at baseline. Renal artery stenosis caused an increase in blood pressure that was similar between wild-type and CXCL16 knockout mice. CXCL16 knockout mice were protected from RAS-induced renal injury and fibrosis. CXCL16 deficiency suppressed bone marrow-derived fibroblast accumulation and myofibroblast formation in the stenotic kidneys, which was associated with less expression of extracellular matrix proteins. Furthermore, CXCL16 deficiency inhibited infiltration of F4/80(+) macrophages and CD3(+) T cells in the stenotic kidneys compared with those of wild-type mice. Taken together, our results indicate that CXCL16 plays a pivotal role in the pathogenesis of renal artery stenosis-induced renal injury and fibrosis through regulation of bone marrow-derived fibroblast accumulation and macrophage and T-cell infiltration.

Role of Myeloperoxidase in Patients with Chronic Kidney Disease

Chronic kidney disease (CKD) is a worldwide public health problem. Patients with CKD have a number of disorders in the organism, and the presence of oxidative stress and systemic inflammation in these patients is the subject of numerous studies. Chronic inflammation joined with oxidative stress contributes to the development of numerous complications: accelerated atherosclerosis process and cardiovascular disease, emergence of Type 2 diabetes mellitus, development of malnutrition, anaemia, hyperparathyroidism, and so forth, affecting the prognosis and quality of life of patients with CKD. In this review we presented the potential role of the myeloperoxidase enzyme in the production of reactive/chlorinating intermediates and their role in oxidative damage to biomolecules in the body of patients with chronic kidney disease and end-stage renal disease. In addition, we discussed the role of modified lipoprotein particles under the influence of prooxidant MPO intermediates in the development of endothelial changes and cardiovascular complications in renal failure.

Post-weaning high-fat diet accelerates kidney injury, but not hypertension programmed by maternal diabetes

BACKGROUND

The aim of this study was to establish the underlying mechanisms by which a post-weaning high-fat diet (HFD) accelerates the perinatal programming of kidney injury occurring in the offspring of diabetic mothers.

METHODS

Male mice, offspring of nondiabetic and diabetic dams were fed with normal diet (ND) or HFD from 4 to 20 wk of age. Rat renal proximal tubular cells were used in vitro.

RESULTS

On ND, the offspring of dams with severe maternal diabetes had an intrauterine growth restriction (IUGR) phenotype and developed mild hypertension and evidence of kidney injury in adulthood. Exposing the IUGR offspring to HFD resulted in rapid weight gain, catch-up growth, and later to profound kidney injury with activation of renal TGFβ1 and collagen type IV expression, increased oxidative stress, and enhanced renal lipid deposition, but not systemic hypertension. Given our data, we speculate that HFD or free fatty acids may accelerate the process of perinatal programming of kidney injury, via increased CD36 and fatty acid-binding protein 4 expression, which may target reactive oxygen species, nuclear factor-kappa B, and TGFβ1 signaling in vivo and in vitro.

CONCLUSION

Early postnatal exposure to overnutrition with a HFD increases the risk of development of kidney injury, but not hypertension, in IUGR offspring of dams with maternal diabetes.

Role of Bone Marrow-Derived Fibroblasts in Renal Fibrosis

Renal fibrosis represents a common pathway leading to progression of chronic kidney disease. Renal interstitial fibrosis is characterized by extensive fibroblast activation and excessive production and deposition of extracellular matrix (ECM), which leads to progressive loss of kidney function. There is no effective therapy available clinically to halt or even reverse renal fibrosis. Although activated fibroblasts/myofibroblasts are responsible for the excessive production and deposition of ECM, their origin remains controversial. Recent evidence suggests that bone marrow-derived fibroblast precursors contribute significantly to the pathogenesis of renal fibrosis. Understanding the molecular signaling mechanisms underlying the recruitment and activation of the bone marrow-derived fibroblast precursors will lead to novel therapy for the treatment of chronic kidney disease. In this review, we summarize recent advances in our understanding of the recruitment and activation of bone marrow-derived fibroblast precursors in the kidney and the development of renal fibrosis and highlights new insights that may lead to novel therapies to prevent or reverse the development of renal fibrosis.

The macrophage phagocytic receptor CD36 promotes fibrogenic pathways on removal of apoptotic cells during chronic kidney injury

The removal of apoptotic cells is an innate function of tissue macrophages; however, its role in disease progression is unclear. The present study was designed to investigate the role of macrophage CD36, a recognized receptor of apoptotic cells and oxidized lipids, in two models of kidney injury: unilateral ureteral obstruction (UUO) and ischemia reperfusion. To differentiate the macrophage CD36-specific effects in vivo, we generated CD36 chimeric mice by bone marrow transplantation and evaluated the two models. Fibrosis severity was substantially decreased after UUO with a corresponding decrease in matrix synthesis in macrophage CD36-deficient mice. Despite a reduction in fibrosis severity, a 56% increase in apoptotic cells was found without an increase in apoptotic effectors. In addition, a substantial reduction was observed in tumor necrosis factor-α and transforming growth factor-β1 mRNA levels and intracellular bioactive oxidized lipid levels in CD36-deficient macrophages. To validate the functional role of macrophage CD36, we performed unilateral ischemia reperfusion, followed by contralateral nephrectomy. Similarly, we found that the severity of fibrosis was reduced by 55% with a corresponding improvement in kidney function by 88% in macrophage CD36-deficient mice. Taken together, these data suggest that macrophage CD36 is a critical regulator of oxidative fibrogenic signaling and that CD36-mediated phagocytosis of apoptotic cells may serve as an important pathway in the progression of fibrosis.

Oxidized high-density lipoprotein impairs the function of human renal proximal tubule epithelial cells through CD36

Unlike native high-density lipoprotein (HDL), oxidized HDL exerts adverse effects in a number of diseases, including chronic kidney disease (CKD); however, the mechanisms involved in this process remain unclear. In the present study, we investigated the effects of oxidized HDL on renal tubular cells, which play an important role in the progression of CKD. Human renal proximal tubule epithelial cells (HK-2) were cultured and stimulated with various concentrations of oxidized HDL in the absence or presence of CD36 siRNA. The results revealed that oxidized HDL enhanced the production of reactive oxygen species (ROS) and upregulated the expression of pro-inflammatory factors in the HK-2 cells in a dose-dependent manner. Incubation with oxidized HDL also increased the apoptosis of the HK-2 cells and reduced their migration ability in a dose‑dependent manner. Src family kinase, mitogen-activated protein kinase (MAPK) and nuclear factor-κB (NF-κB) were activated following stimulation with oxidized HDL. All these effects mediated by oxidized HDL on HK-2 cells were markedly attenuated by transfection with with CD36 siRNA pior to stimulation with oxidized HDL. These findings suggest that oxidized HDL enhances the pro-inflammatory properties and impairs the function of HK-2 cells, mainly through the scavenger receptor, CD36, as well as through the Src, MAPK and NF-κB pathways.

The effect of albumin on podocytes: the role of the fatty acid moiety and the potential role of CD36 scavenger receptor

Evidence is emerging that podocytes are able to endocytose proteins such as albumin using kinetics consistent with a receptor-mediated process. To date the role of the fatty acid moiety on albumin uptake kinetics has not been delineated and the receptor responsible for uptake is yet to be identified. Albumin uptake studies were carried out on cultured human podocytes exposed to FITC-labelled human serum albumin either carrying fatty acids (HSA+FA) or depleted of them (HSA-FA). Receptor-mediated endocytosis of FITC-HSA+FA over 60 min was 5 times greater than that of FITC-HSA-FA. 24h exposure of podocytes to albumin up-regulated nephrin expression and induced the activation of caspase-3. These effects were more pronounced in response to HSA-FA. Individually, anti-CD36 antibodies had no effect upon endocytosis of FITC-HSA. However, a cocktail of 2 antibodies reduced uptake by nearly 50%. Albumin endocytosis was enhanced in the presence of the CD36 specific inhibitor sulfo-N-succinimidyl oleate (SSO) while knock-down of CD36 using CD36siRNA had no effect on uptake. These data suggest that receptor-mediated endocytosis of albumin by podocytes is regulated by the fatty acid moiety, although, some of the detrimental effects are induced independently of it. CD36 does not play a direct role in the uptake of albumin.

CXCL16 in kidney and cardiovascular injury

CXC chemokine ligand 16 (CXCL16) is a CXC soluble chemokine, an adhesion molecule and a cell surface scavenger receptor. CXCL16 regulates inflammation, tissue injury and fibrosis. Parenchymal renal cells, vascular wall cells, leukocytes and platelets express and/or release CXCL16 under the regulation of inflammatory mediators. CXCL16 expression is increased in experimental and human nephropathies. Targeting CXCL16 protected from experimental glomerular injury or interstitial fibrosis. Conflicting results were reported for experimental cardiovascular injury. High circulating CXCL16 levels are associated to human kidney and cardiovascular disease and urinary CXCL16 may increase in kidney injury. In conclusion, mounting evidence suggests a role of CXCL16 in kidney and cardiovascular disease. However, a better understanding is still required before exploring CXCL16 targeting in the clinic.

Serum CXCL16 as a novel marker of renal injury in type 2 diabetes mellitus

BACKGROUND

Soluble C-X-C chemokine ligand 16 (CXCL16), a scavenger receptor for oxidized low density lipoprotein, has been shown to promote atherogenic effects in vivo and to predict long-term mortality in acute coronary syndrome. The aim of this study was to explore the association of circulating CXCL16 levels with diabetic subjects with and without renal disease.

METHODOLOGY/PRINCIPAL FINDINGS

One hundred twenty Chinese subjects, which included patients with type 2 diabetes mellitus (T2DM), diabetic nephropathy (DN), and CKD, as well as healthy controls, were enrolled in this study. Serum CXCL16 levels were examined by immunoassay and other clinical biochemical parameters were tested based on standard methods. Our results indicated that, HDL and LDL cholesterol levels are significantly different in DN but not in T2D patients in comparison with healthy subjects. On the other hand, Serum CXCL16 levels were significantly increased in DN subjects compared with age and gender matched healthy and T2DM subjects (p<0.05 respectively). However, no significant changes in serum CXCL16 levels were found between T2DM and healthy subjects. Furthermore, serum CXCL16 concentration negatively correlated with estimated glomerular filtrate rate, creatinine clearance rate and blood albumin, and positively with 24 h proteinuria, blood urea nitrogen (BUN), creatinine, and uric acid after adjusting for age, gender and BMI in subjects with DN. Multiple stepwise regression analyses indicated that serum CXCL16 levels were independently associated with serum 24 h proteinuria, and BUN (p<0.05 respectively).

CONCLUSION

Serum CXCL16 may be an indicator of renal injury in subjects with T2DM. Understanding the exact mechanism of elevated CXCL16 in subjects with DN requires further study.

Increased serum CXCL16 is highly correlated with blood lipids, urine protein and immune reaction in children with active nephrotic syndrome

BACKGROUND

Primary nephrotic syndrome (NS) is a common disease in children. Lipid nephrotoxicity and cellular immune dysfunction are known features of this disease. Recently, CXCL16 was found to participate in inflammation and mediate cellular uptake of lipids. Here, we investigated the involvement of CXCL16 in the occurrence and development of primary NS.

METHODS

Serum CXCL16, blood lipids and albumin, 24-hour urine protein, interferon-γ and immune cells were detected in 25 children with steroid sensitive NS during their active nephrotic and remissive stages. Twenty healthy children served as the control group.

RESULTS

Levels of serum CXCL16, blood lipids, interferon-γ and CXCR6+ T cells were significantly increased and albumin and NK cell number were significantly decreased in the active status group compared with remissive status and control groups. Correlation analysis showed that serum CXCL16 was positively correlated with blood lipids, 24-hour urine protein, interferon-γ and CXCR6+ T cells but negatively correlated with albumin in patients with active NS.

CONCLUSION

Serum CXCL16 was increased in patients with active NS and correlated with blood lipids, urine protein and immune and inflammation responses, suggesting that CXCL16 may serve as a useful index or biomarker for disease activity in children with nephrotic syndrome.

VIRTUAL SLIDES

The virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1120468411154766.

Critical role of CXCL16 in hypertensive kidney injury and fibrosis

Recent evidence indicates that inflammation plays a critical role in the initiation and progression of hypertensive kidney disease. However, the signaling mechanisms underlying the induction of inflammation are poorly understood. We found that chemokine (C-X-C motif) ligand 16 (CXCL16) was induced in renal tubular epithelial cells in response to angiotensin II in a nuclear factor-κB-dependent manner. To determine whether CXCL16 plays a role in angiotensin II-induced renal inflammation and fibrosis, wild-type and CXCL16 knockout mice were infused with angiotensin II at 1500 ng/kg per minute for up to 4 weeks. Wild-type and CXCL16 knockout mice had comparable blood pressure at baseline. Angiotensin II treatment led to an increase in blood pressure that was similar between wild-type and CXCL16 knockout mice. CXCL16 knockout mice were protected from angiotensin II-induced renal dysfunction, proteinuria, and fibrosis. CXCL16 deficiency suppressed bone marrow-derived fibroblast accumulation and myofibroblast formation in the kidneys of angiotensin II-treated mice, which was associated with less expression of extracellular matrix proteins. Furthermore, CXCL16 deficiency inhibited infiltration of F4/80(+) macrophages and CD3(+) T cells in the kidneys of angiotensin II-treated mice compared with wild-type mice. Finally, CXCL16 deficiency reduced angiotensin II-induced proinflammatory cytokine expressions in the kidneys. Taken together, our results indicate that CXCL16 plays a pivotal role in the pathogenesis of angiotensin II-induced renal injury and fibrosis through regulation of macrophage and T cell infiltration and bone marrow-derived fibroblast accumulation.

Cysteamine modulates oxidative stress and blocks myofibroblast activity in CKD

Therapy to slow the relentless expansion of interstitial extracellular matrix that leads to renal functional decline in patients with CKD is currently lacking. Because chronic kidney injury increases tissue oxidative stress, we evaluated the antifibrotic efficacy of cysteamine bitartrate, an antioxidant therapy for patients with nephropathic cystinosis, in a mouse model of unilateral ureteral obstruction. Fresh cysteamine (600 mg/kg) was added to drinking water daily beginning on the day of surgery, and outcomes were assessed on days 7, 14, and 21 after surgery. Plasma cysteamine levels showed diurnal variation, with peak levels similar to those observed in patients with cystinosis. In cysteamine-treated mice, fibrosis severity decreased significantly at 14 and 21 days after unilateral ureteral obstruction, and renal oxidized protein levels decreased at each time point, suggesting reduced oxidative stress. Consistent with these results, treatment of cultured macrophages with cysteamine reduced cellular generation of reactive oxygen species. Furthermore, treatment with cysteamine reduced α-smooth muscle actin-positive interstitial myofibroblast proliferation and mRNA levels of extracellular matrix proteins in mice and attenuated myofibroblast differentiation and proliferation in vitro, but did not augment TGF-β signaling. In a study of renal ischemia reperfusion, cysteamine therapy initiated 10 days after injury and continued for 14 days decreased renal fibrosis by 40%. Taken together, these data suggest previously unrecognized antifibrotic actions of cysteamine via TGF-β-independent mechanisms that include oxidative stress reduction and attenuation of the myofibroblast response to kidney injury and support further investigation into the potential benefit of cysteamine therapy in the treatment of CKD.

Dyslipoproteinemia and impairment of renal function in diabetic kidney disease: an analysis of animal studies, observational studies, and clinical trials

Dyslipoproteinemia is highly prevalent in diabetes, chronic kidney disease, and diabetic kidney disease (DKD). Both diabetes and chronic kidney disease (CKD) are associated with hypertriglyceridemia, lower high-density lipoprotein, and higher small, dense low-density lipoprotein. A number of observational studies have reported that dyslipidemia may be associated with albuminuria, renal function impairment, and end-stage renal disease (ESRD) in the general population, and especially in CKD and DKD patients. Diabetic glomerulopathy and the related albuminuria are the main manifestations of DKD. Numerous animal studies support the finding that glomerular atherosclerosis is the main mechanism of glomerulosclerosis in CKD and DKD. Some randomized, controlled trials suggest the use of statins for the prevention of albuminuria and renal function impairment in CKD and DKD patients. However, a large clinical study, the Study of Heart and Renal Protection (SHARP), does not support that statins could reduce ESRD in CKD. In this article, we analyze the complex association of dyslipoproteinemia with DKD and deduce its relevance from animal studies, observational studies, and clinical trials. We show that special subgroups could benefit from the statin treatment.

CD36 and Na/K-ATPase-α1 form a proinflammatory signaling loop in kidney

Proatherogenic, hyperlipidemic states demonstrate increases in circulating ligands for scavenger receptor CD36 (eg, oxidized low-density lipoprotein [oxLDL]) and the Na/K-ATPase (eg, cardiotonic steroids). These factors increase inflammation, oxidative stress, and progression of chronic kidney disease. We hypothesized that diet-induced obesity and hyperlipidemia potentiate a CD36/Na/K-ATPase-dependent inflammatory paracrine loop between proximal tubule cells (PTCs) and their associated macrophages and thereby facilitate development of chronic inflammation and tubulointerstitial fibrosis. ApoE(-/-) and apoE(-/-)/cd36(-/-) mice were fed a high-fat diet for ≤32 weeks and examined for physiologic and histologic changes in renal function. Compared with apoE(-/-), apoE(-/-)/cd36(-/-) mice had improved creatinine clearance and blood pressure which corresponded histologically with less glomerular and tubulointerstitial macrophage accumulation, foam cell formation, oxidant stress, and interstitial fibrosis. Coimmunopreciptation and a cell surface fluorescence-based crosslinking assay showed that CD36 and Na/K-ATPase α-1 colocalized in PTCs and macrophages, and this association was increased by oxLDL or the cardiotonic steroid ouabain. OxLDL and ouabain also increased activation of Src and Lyn in PTCs. Cell-free conditioned medium from PTCs treated with oxLDL or ouabain increased macrophage migration. OxLDL, ouabain, or plasma isolated from high-fat diet-fed mice stimulated reactive oxygen species production in PTCs, which was inhibited by N-acetyl-cysteine, apocynin, or Na/K-ATPase α-1 knockdown. These data suggest that ligands generated in hyperlipidemic states activate CD36 and the Na/K-ATPase and potentiate an inflammatory signaling loop involving PTCs and their associated macrophages, which facilitates the development of chronic inflammation, oxidant stress, and fibrosis underlying the renal dysfunction common to proatherogenic, hyperlipidemic states.

CD36 mediates proximal tubular binding and uptake of albumin and is upregulated in proteinuric nephropathies

Dysregulation of renal tubular protein handling in proteinuria contributes to the development of chronic kidney disease. We investigated the role of CD36 as a novel candidate mediator of albumin binding and endocytosis in the kidney proximal tubule using both in vitro and in vivo approaches, and in nephrotic patient renal biopsy samples. In CD36-transfected opossum kidney proximal tubular cells, both binding and uptake of albumin were substantially enhanced. A specific CD36 inhibitor abrogated this effect, but receptor-associated protein, which blocks megalin-mediated endocytosis of albumin, did not. Mouse proximal tubular cells expressed CD36 and this was absent in CD36 null animals, whereas expression of megalin was equal in these animals. Compared with wild-type mice, CD36 null mice demonstrated a significantly increased urinary protein-to-creatinine ratio and albumin-to-creatinine ratio. Proximal tubular cells expressed increased CD36 when exposed to elevated albumin concentrations in culture medium. Expression of CD36 was studied in renal biopsy tissue obtained from adult patients with heavy proteinuria due to minimal change disease, membranous nephropathy, or focal segmental glomerulosclerosis. Proximal tubular CD36 expression was markedly increased in proteinuric individuals. We conclude that CD36 is a novel mediator influencing binding and uptake of albumin in the proximal tubule that is upregulated in proteinuric renal diseases. CD36 may represent a potential therapeutic target in proteinuric nephropathy.

New insights into the role of oxidative stress in scleroderma fibrosis

Systemic sclerosis (Scleroderma – SSc) is a connective tissue disorder of unknown aetiology characterized by extensive fibrosis of the skin and visceral organs, by vascular abnormalities and immunological manifestations.

Recent evidence suggest that the cellular redox state may play a significant role in the progression of scleroderma fibrosis. Mechanisms involved include an autoamplification circuit linking ROS, Ras and ERK 1-2 which in turn amplifies and maintains the autocrine loop made up by cytokines, growth factors and their cognate receptors.

This review summarizes the recent progress on the role of oxidative stress in the pathophysiology of scleroderma and disorders characterised by organ fibrosis

Perindopril attenuates renal tubulointerstitium injury by inhibiting scavenger receptor A over-expression in diabetic rats

Scavenger receptor A (SR-A) is the main receptor through which oxidized LDL (oxLDL) and advanced glycation end products get into the cells. The aim of the present study was to investigate the effect of an ACE inhibitor, perindopril, on the expression of SR-A in renal tubulointerstitium of diabetic rats. Diabetes was induced in male Sprague-Dawley rats by injection with streptozotocin. The rats were then randomly divided into 3 groups: normal control group; untreated diabetes mellitus group; and diabetes mellitus group treated with the ACE inhibitor, perindopril. After a 24-week treatment, tubulointerstitial injury index was assessed on Masson's trichrome sections. The number of macrophages and the expression of SR-A protein in renal tubulointerstitium were detected by immunohistochemistry and the expression of SR-A mRNA was detected by RT-PCR. The tubulointerstitial injury index, the number of macrophages and the expression of SR-A mRNA were significantly higher in the diabetes group than the normal control group. Perindopril treatment not only attenuated the tubulointerstitial injury and the macrophages infiltration but also reduced the overexpression of SR-A mRNA in diabetic rats. The expression of SR-A protein was most obvious in renal tubulointerstitium in diabetic rats, which was attenuated by perindopril treatment. The findings of the present study indicate that perindopril may have renoprotective effects of diabetic nephropathy via inhibiting the expression of SR-A in renal tubulointerstitium.

Deletion of scavenger receptor A protects mice from progressive nephropathy independent of lipid control during diet-induced hyperlipidemia

Scavenger receptor A (SR-A) is a key transmembrane receptor in the endocytosis of lipids and contributes to the pathogenesis of atherosclerosis. To assess its role in hyperlipidemic chronic kidney disease, wild-type and SR-A-deficient (knockout) mice underwent uninephrectomy followed by either normal or high-fat diet. After 16 weeks of diet intervention, hyperlipidemic wild-type mice presented characteristic features of progressive nephropathy: albuminuria, renal fibrosis, and overexpression of transforming growth factor (TGF)-β1/Smad. These changes were markedly diminished in hyperlipidemic knockout mice and attributed to reduced renal lipid retention, oxidative stress, and CD11c(+) cell infiltration. In vitro, overexpression of SR-A augmented monocyte chemoattractant protein-1 release and TGF-β1/Smad activation in HK-2 cells exposed to oxidized low-density lipoprotein. SR-A knockdown prevented lipid-induced cell injury. Moreover, wild-type to knockout bone marrow transplantation resulted in renal fibrosis in uninephrectomized mice following 16 weeks of the high-fat diet. In contrast, knockout to wild-type bone marrow transplantation led to markedly reduced albuminuria, CD11c(+) cell infiltration, and renal fibrosis compared to wild-type to SR-A knockout or wild-type to wild-type bone marrow transplanted mice, without difference in plasma lipid levels. Thus, SR-A on circulating leukocytes rather than resident renal cells predominantly mediates lipid-induced kidney injury.

Hypercholesterolemia promotes early renal dysfunction in apolipoprotein E-deficient mice

Background

Aging and dyslipidemia are processes which can lead to deleterious consequences to renal function. Therefore, the aim of this study was to determine the effects of both hypercholesterolemia and aging on renal function in mice.

Methods

Male hypercholesterolemic apolipoprotein E-deficient mice (ApoE, n = 13) and age-matched C57BL/6 control mice (C57, n = 15) were studied at 2 (young) and 8 (adult) month-old. At each time point, animals were placed in metabolic cages for 24 hours to urine volume and urinary creatinine quantification. Blood samples were collected for serum cholesterol, urea and creatinine measurements. Glomerular filtration rate (GFR) was estimated through creatinine clearance determination. Mesangial expansion was evaluated by Periodic Acid Schiff staining, renal fibrosis was determined through Masson's trichrome staining and neuronal nitric oxide synthase (nNOS) expression in the kidney was performed by Western Blotting. To statistical analysis two-way ANOVA followed by Fisher's post hoc test was used.

Results

Total plasma cholesterol was increased about 5-fold in ApoE mice at both time points compared to C57 animals. At 2-month-old, GFR was already markedly reduced in ApoE compared to C57 mice (187 ± 28 vs 358 ± 92 μL/min, p < 0.05). Adult C57 (-77%) and ApoE (-50%) mice also presented a significant reduction of GFR. In addition, serum urea was significantly increased in young ApoE animals compared to C57 mice (11 ± 1.3 vs 7 ± 0.9 mmol/L, p < 0.01). A significant mesangial expansion was observed at 2-month old ApoE mice compared to C57 mice (35 ± 0.6 vs 30 ± 0.9%, respectively, p < 0.05), which was aggravated at 8-month old animals (40 ± 3 and 35 ± 3%, respectively). Tubulointersticial fibrosis was augmented at both young (17 ± 2%, p < 0.05) and adult (20 ± 1%, p < 0.05) ApoE mice compared to respective C57 age controls (8 ± 1 and 12 ± 2%, respectively). The expression of nNOS was markedly reduced in a time-dependent manner in both strains.

Conclusions

These data show that both hypercholesterolemia and aging contribute to the loss of renal function in mice.

Targeted mutation of SLC4A5 induces arterial hypertension and renal metabolic acidosis

The human SLC4A5 gene has been identified as a hypertension susceptibility gene based on the association of single nucleotide polymorphisms with blood pressure (BP) levels and hypertension status. The biochemical basis of this association is unknown particularly since no single gene variant was linked to hypertension in humans. SLC4A5 (NBCe2, NBC4) is expressed in the collecting duct of the kidney and acts as an electrogenic ion-transporter that transports sodium and bicarbonate with a 1:2 or 1:3 stoichiometry allowing bicarbonate reabsorption with relatively minor concurrent sodium uptake. We have mutated the Slc4a5 gene in mice, which caused a persistent increase in systolic and diastolic BP. Slc4a5 mutant mice also displayed a compensated metabolic acidosis and hyporeninemic hypoaldosteronism. Analysis of kidney physiology revealed elevated fluid intake and urine excretion and increased glomerular filtration rate. Transcriptome analysis uncovers possible compensatory mechanisms induced by SLC4A5 mutation, including upregulation of SLC4A7 and pendrin as well as molecular mechanisms associated with hypertension. Induction of metabolic alkalosis eliminated the BP difference between wild-type and Slc4a5 mutant mice. We conclude that the impairment of the function of SLC4A5 favors development of a hypertensive state. We reason that the loss of sodium-sparing bicarbonate reabsorption by SLC4A5 initiates a regulatory cascade consisting of compensatory bicarbonate reabsorption via other sodium-bicarbonate transporters (e.g. SLC4A7) at the expense of an increased sodium uptake. This will ultimately raise BP and cause hypoaldosteronism, thus providing a mechanistic explanation for the linkage of the SLC4A5 locus to hypertension in humans.

CXCL16 recruits bone marrow-derived fibroblast precursors in renal fibrosis

Although fibroblasts are responsible for the production and deposition of extracellular matrix in renal fibrosis, their origin is controversial. Circulating fibroblast precursors may contribute to the pathogenesis of renal fibrosis, but the signaling mechanisms underlying the recruitment of bone marrow-derived fibroblast precursors into the kidney in response to injury are incompletely understood. Here, in the unilateral ureteral obstruction model of renal fibrosis, tubular epithelial cells upregulated the chemokine CXCL16 in obstructed kidneys, and circulating fibroblast precursors expressed the CXCL16 receptor, CXCR6. Compared with wild-type mice, CXCL16-knockout mice accumulated significantly fewer bone marrow-derived fibroblast precursors in obstructed kidneys. CXCL16-knockout mice also exhibited significantly fewer CD45-, collagen I-, and CXCR6-triple-positive fibroblast precursors in injured kidneys. Furthermore, targeted deletion of CXCL16 inhibited myofibroblast activation, reduced collagen deposition, and suppressed expression of collagen I and fibronectin. In conclusion, CXCL16 contributes to the pathogenesis of renal fibrosis by recruiting bone marrow-derived fibroblast precursors.

Increased plasma CXCL16 levels in patients with chronic kidney diseases

BACKGROUND

C-X-C chemokine ligand 16 (CXCL16) is a scavenger receptor for oxidized low-density lipoprotein that has been shown to promote atherogenic effects in vivo and to predict the long-term mortality in acute coronary syndrome. We conducted a cross-sectional study to test the hypothesis that elevated CXCL16 concentrations are associated with the change in renal function in patients with chronic kidney disease (CKD) at different stages of disease.

MATERIALS AND METHODS

Two hundred and forty subjects including 200 patients with CKD (146 CKD from outpatients and 54 CKD with long-term haemodialysis) and 40 normal control subjects were recruited into this study. All CKD subjects underwent echocardiograms to assess left ventricular mass index. Plasma levels of CXCL16 and other relevant clinical and biochemical parameters in all subjects were obtained upon standard clinical examinations.

RESULTS

Plasma CXCL16 levels were significantly increased with the development of CKD from early- and end-stage (P < 0·001 for trend) and significantly higher in CKD subjects than those of normal subjects (P<0·001). Furthermore, plasma CXCL16 levels in CKD patients with type 2 diabetes mellitus (DM) were higher than those of CKD patients without DM. Multiple stepwise regression analyses indicated that plasma CXCL16 levels were independently associated with estimated glomerular filtration rate, C-reactive protein and adiponectin (all P<0·05).

CONCLUSIONS

Plasma CXCL16 levels are significantly increased with the development of early- to end-stage CKD and are independently associated with the change in renal function. Elucidating the role of CXCL16 as a biomarker or disease modifier in CKD progression requires further study.

Tubular toxicity of proteinuria

Proteinuria is a prognostic indicator of progressive kidney disease and poor cardiovascular outcomes. Abnormally filtered bioactive macromolecules interact with proximal tubular epithelial cells (PTECs), which results in the development of proteinuric nephropathy. This condition is characterized by alterations in PTEC growth, apoptosis, gene transcription and inflammatory cytokine production as a consequence of dysregulated signaling pathways that are stimulated by proteinuric tubular fluid. The megalin-cubilin complex mediates the uptake of several proteins, including albumin, into PTECs. Megalin might also possess intrinsic signaling properties and the ability to regulate cell signaling pathways and gene transcription after processing regulated intramembrane proteolysis. Megalin could, therefore, link abnormal PTEC albumin exposure with altered growth factor receptor activation, proinflammatory and profibrotic signaling, and gene transcription. Evidence now suggests that other PTEC pathways for protein reabsorption of (patho)physiological importance might be mediated by the neonatal Fc receptor and CD36.