Increased urinary CD80 excretion and podocyturia in Fabry disease.

BACKGROUND: Certain glomerulopathies are associated with increased levels of CD80 (B7-1). We measured the urinary excretion of CD80, podocyturia and proteinuria in controls and in subjects with Fabry disease either untreated or on enzyme replacement therapy (ERT). METHODS: Cross-sectional study including 65 individuals: controls (n = 20) and Fabry patients (n = 45, 23 of them not on ERT and 22 on ERT). Variables included age, gender, urinary protein/creatinine ratio (UPCR), estimated glomerular filtration rate (eGFR), urinary uCD80/creatinine ratio (uCD80) and podocyturia. CD80 mRNA expression in response to lyso-Gb3, a bioactive glycolipid accumulated in Fabry disease, was studied in cultured human podocytes. RESULTS: Controls and Fabry patients did not differ in age, eGFR and gender. However, UPCR, uCD80 and podocyturia were significantly higher in Fabry patients than in controls. As expected, Fabry patients not on ERT were younger and a higher percentage were females. Non-ERT Fabry patients had less advanced kidney disease than ERT Fabry patients: UPCR was lower and eGFR higher, but uCD80 and podocyturia did not differ between non-ERT or ERT Fabry patients. There was a significant correlation between uCD80 and UPCR in the whole population (r 0.44, p 0.0005) and in Fabry patients (r 0.42, p 0.0046). Lyso-Gb3 at concentrations found in the circulation of Fabry patients increased uCD80 expression in cultured podocytes. CONCLUSIONS: Fabry disease is characterized by early occurrence of increased uCD80 excretion that appears to be a consequence of glycolipid accumulation. The potential for uCD80 excretion to reflect early, subclinical renal Fabry involvement should be further studied.

TWEAK favors phosphate-induced calcification of vascular smooth muscle cells through canonical and non-canonical activation of NFκB.

Vascular calcification (VC) is associated with increased cardiovascular mortality in aging, chronic kidney disease (CKD), type 2 diabetes mellitus (T2DM) and atherosclerosis. TNF-like weak inducer of apoptosis (TWEAK) recently emerged as a new biomarker for the diagnosis and prognosis of cardiovascular diseases. TWEAK binding to its functional receptor Fn14 was reported to promote several steps of atherosclerotic plaque progression. However, no information is currently available on the role of TWEAK/Fn14 on the development of medial calcification, which is highly prevalent in aging, CKD and T2DM. This study explored the involvement of TWEAK in human vascular smooth muscle cells (h-VSMCs) calcification in vitro. We report that TWEAK binding to Fn14 promotes inorganic phosphate-induced h-VSMCs calcification, favors h-VSMCs osteogenic transition, decreasing acta2 and myh11 and increasing bmp2 mRNA and tissue non-specific alkaline phosphatase (TNAP), and increases MMP9 activity. Blockade of the canonical NFκB pathway reduced by 80% TWEAK pro-calcific properties and decreased osteogenic transition, TNAP and MMP9 activity. Blockade of non-canonical NFκB signaling by a siRNA targeting RelB reduced by 20% TWEAK pro-calcific effects and decreased TWEAK-induced loss of h-VSMCs contractile phenotype and MMP9 activity, without modulating bmp2 mRNA or TNAP activity. Inhibition of ERK1/2 activation by a MAPK kinase inhibitor did not influence TWEAK pro-calcific properties. Our results suggest that TWEAK/Fn14 directly favors inorganic phosphate-induced h-VSMCs calcification by activation of both canonical and non-canonical NFκB pathways. Given the availability of neutralizing anti-TWEAK strategies, our study sheds light on the TWEAK/Fn14 axis as a novel therapeutic target in the prevention of VC.

Albumin-induced apoptosis of tubular cells is modulated by BASP1.

Albuminuria promotes tubular injury and cell death, and is associated with faster progression of chronic kidney disease (CKD) to end-stage renal disease. However, the molecular mechanisms regulating tubular cell death in response to albuminuria are not fully understood. Brain abundant signal protein 1 (BASP1) was recently shown to mediate glucose-induced apoptosis in tubular cells. We have studied the role of BASP1 in albumin-induced tubular cell death. BASP1 expression was studied in experimental puromycin aminonucleoside-induced nephrotic syndrome in rats and in human nephrotic syndrome. The role of BASP1 in albumin-induced apoptosis was studied in cultured human HK2 proximal tubular epithelial cells. Puromycin aminonucleoside induced proteinuria and increased total kidney BASP1 mRNA and protein expression. Immunohistochemistry localized the increased BASP1 to tubular cells. BASP1 expression colocalized with deoxynucleotidyl-transferase-mediated dUTP nick-end labeling staining for apoptotic cells. Increased tubular BASP1 expression was observed in human proteinuric nephropathy by immunohistochemistry, providing evidence for potential clinical relevance. In cultured tubular cells, albumin induced apoptosis and increased BASP1 mRNA and protein expression at 6-48 h. Confocal microscopy localized the increased BASP1 expression in albumin-treated cells mainly to the perinuclear area. A peripheral location near the cell membrane was more conspicuous in albumin-treated apoptotic cells, where it colocalized with actin. Inhibition of BASP1 expression by a BASP1 siRNA protected from albumin-induced apoptosis. In conclusion, albumin-induced apoptosis in tubular cells is BASP1-dependent. This information may be used to design novel therapeutic approaches to slow CKD progression based on protection of tubular cells from the adverse consequences of albuminuria.

MIF, CD74 and other partners in kidney disease: tales of a promiscuous couple.

Macrophage migration inhibitory factor (MIF) is increased in kidney and urine during kidney disease. MIF binds to and activates CD74 and chemokine receptors CXCR2 and CXCR4. CD74 is a protein trafficking regulator and a cell membrane receptor for MIF, D-dopachrome tautomerase (D-DT/MIF-2) and bacterial proteins. MIF signaling through CD74 requires CD44. CD74, CD44 and CXCR4 are upregulated in renal cells in diseased kidneys and MIF activation of CD74 in kidney cells promotes an inflammatory response. MIF or CXCR2 targeting protects from experimental kidney injury, CD44 deficiency modulates kidney injury and CXCR4 activation promotes glomerular injury. However, the contribution of MIF or MIF-2 to these actions of MIF receptors has not been explored. The safety and efficacy of strategies targeting MIF, CD74, CD44 and CXCR4 are under study in humans.

2012 update on diabetic kidney disease: the expanding spectrum, novel pathogenic insights and recent clinical trials.

Diabetic kidney disease (DKD) is the most frequent cause of end-stage renal disease in western countries. This implies that current methods based of renin angiotensin aldosterone system (RAAS) targeting for preventing, slowing or promoting regression of DKD are insufficient. Podocyte injury and albuminuria are thought to be key events in DKD. Indeed several DKD stages are recognized based on the magnitude of albuminuria. However, the spectrum of DKD has recently expanded, as lack of significant albuminuria is present in 30% of diabetics with kidney function impairment. This may result from the widespread use of drugs targeting the RAAS. However, it may also indicate that additional pathogenic factors contribute to renal function deterioration despite control of albuminuria. In this regard, double blockade of the RAAS is more effective in reducing albuminuria that blockade of a single component. However, clinical trials assessing double blockade for renal function preservation have been disappointing and raised safety issues. Non-biased -omics approaches have uncovered alternative therapeutic targets, including the cytokine TRAIL, the MIF receptor CD74 and the proapoptotic intracellular protein BASP1. In addition, urinary proteomics has uncovered a peptidomic fingerprint for DKD progression that precedes the onset of microalbuminuria. Studies are underway to validate this fingerprint for early treatment of high risk patients. Recent clinical trials suggest a potential role of bardoxolone methyl to improve renal function in advanced DKD, while trials of avosentan, pirfenidone, sulodexide and pyridoxamine have been disappointing and further data are needed for paricalcitol and vitamin D, newer generation endothelin receptor antagonists and pentoxifylline.

Tyrphostins as potential therapeutic agents for acute kidney injury.

Acute kidney injury (AKI) is a syndrome characterized by an acute renal cell injury that leads to sudden loss of renal function. There are currently no clinically validated treatments for AKI besides substituting renal function by dialysis. However, new biomarkers will allow an earlier diagnosis, thus providing a window of opportunity for therapeutic intervention. Tyrphostins are a family of compounds originally designed as protein tyrosine kinase inhibitors. However, some molecules of this family have additional actions, such as inhibition of guanylate and adenylate cyclases, mitochondrial uncoupling or antioxidant effects. We review the potential role of tyrphostins in the prophylaxis and treatment of acute kidney injury on the basis of published studies on animals, in vitro experiments and piecemeal information from humans. The AG 490 and AG 126 tyrphostins have recently been shown to protect from AKI in experimental animal models of ischemia-reperfusion and sepsis-induced injury. AG 490 protects from cyclosporin-induced AKI and AG 1714 protects from cisplatin nephrotoxicity. AG 490 is nephroprotective by inhibiting oxidative stress-related Janus activated kinase-2 (JAK2) activation. Potential applications of AG490 or derivative molecules include AKI of nephrotoxic or ischemic nature, or a combination of both, as may occur in the immediate postransplant period. The molecular targets of AG 126 and AG 1714 are less well characterized. In conclusions, different tyrphostins are nephroprotective in animal models of AKI. The characterization of the molecular targets involved will allow the design of novel therapies that may reach the clinical trial stage.

Myocardial fibrosis and apoptosis, but not inflammation, are present in long-term experimental diabetes.

The aim of this paper is to study the myocardial damage secondary to long-term streptozotocin-induced type 1 diabetes mellitus (DM1). Normotensive and spontaneously hypertensive rats (SHR) received either streptozotocin injections or vehicle. After 22 or 6 wk, DM1, SHR, DM1/SHR, and control rats were killed, and the left ventricles studied by histology, quantitative PCR, Western blot, ELISA, and electromobility shift assay. Cardiomyocyte cultures were also performed. The expression of profibrotic factors, transforming growth factor-beta (TGF-beta1), connective tissue growth factor, and matrix proteins was increased, and the TGF-beta1-linked transcription factors phospho-Smad3/4 and activator protein-1 were activated in the DM1 myocardium. Proapoptotic molecules FasL, Fas, Bax, and cleaved caspase-3 were also augmented. Myocardial injury in long-term hypertension shared these features. In addition, hypertension was associated with activation of NF-kappaB, increased inflammatory cell infiltrate, and expression of the mediators [interleukin-1beta (IL-1beta), tumor necrosis factor-alpha, monocyte chemoattractant protein 1, vascular cell adhesion molecule 1, angiotensinogen, and oxidants], which were absent in long-term DM1. At this stage, the combination of DM1 and hypertension resulted in nonsignificant additive effects. Moreover, the coexistence of DM1 blunted the inflammatory response to hypertension. Anti-inflammatory IL-10 and antioxidants were induced in long-term DM1 and DM1/SHR hearts. Myocardial inflammation was, however, observed in the short-term model. In cultured cardiomyocytes, IL-10, TGF-beta1, and catalase blocked the glucose-stimulated expression of proinflammatory genes. Fibrosis and apoptosis are features of long-term myocardial damage in experimental DM1. Associated hypertension does not induce additional changes. Myocardial inflammation is present in hypertension and short-term DM1, but is not a key feature in long-term DM1. Local reduction of proinflammatory factors and expression of anti-inflammatory and antioxidant molecules may underlie this effect.

[Transcriptomics illustrate a deadly TRAIL to diabetic nephropathy]. / La transcriptómica ilustra nuevas vías letales en la nefropatía diabética.

Diabetic nephropathy is the most common cause of endstage renal disease. Approaches targeting angiotensin II significantly delay its progression. However, many patients still need renal replacement therapy. High throughput techniques such as unbiased gene expression profiling and proteomics may identify new therapeutic targets. Cell death is thought to contribute to progressive renal cell depletion in chronic nephropathies. A European collaborative effort recently applied renal biopsy transcriptomics to identify novel mediators of renal cell death in diabetic nephropathy. Twenty-five percent of cell death regulatory genes were upor downregulated in diabetic kidneys. TNF-related apoptosisinducing ligand (TRAIL) and osteoprotegerin had the highest level of expression. In diabetic nephropathy, tubular cells and podocytes express TRAIL. Inflammatory cytokines, including MIF via CD74, upregulate TRAIL. A high glucose environment sensitized renal cells to the lethal effect of TRAIL, while osteoprotegerin is protective. These results suggest that, in addition to glucose levels, inflammation and TRAIL are therapeutic targets in diabetic nephropathy.

Apoptosis: from advances in PD to therapeutic targets in DM.

A high glucose concentration is shared by peritoneal dialysis (PD) and diabetes mellitus (DM). High glucose leads to tissue injury in diabetes. Peritoneal dialysis research has emphasized the role of glucose degradation products in tissue injury. Apoptosis induction is one of the mechanisms of tissue injury induced both by glucose and glucose degradation products. We now review the role of apoptosis and its regulation by glucose degradation products in antibacterial defense and loss of renal function in diabetes mellitus and peritoneal dialysis. The pathogenic role of the recently identified glucose degradation product 3,4-di-deoxyglucosone- 3-ene (3,4-DGE) is detailed. Available therapeutic strategies include the use of peritoneal dialysis solutions containing a low concentration of glucose degradation products. Based on preclinical results, specific targeting of apoptosis regulatory factor should be explored in the clinical setting.

Cytokine cooperation in renal tubular cell injury: the role of TWEAK.

Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK, TNFSF12) is a member of the TNF superfamily. TWEAK activates the Fn14 receptor, and may regulate apoptosis, proliferation, and inflammation, processes that play a significant role in pathological conditions. However, there is little information on the function and regulation of this system in the kidney. Therefore, TWEAK and Fn14 expression were studied in cultured murine tubular epithelial MCT cells and in mice in vivo. The effect of TWEAK on cell death was determined. We found that TWEAK and Fn14 expression was increased in experimental acute renal failure induced by folic acid. Cultured tubular cells express both TWEAK and the Fn14 receptor. TWEAK did not induce cell death in non-stimulated tubular cells. However, in cells costimulated with TNFalpha/interferon-gamma, TWEAK induced apoptosis through the activation of the Fn14 receptor. Apoptosis was associated with activation of caspase-8, caspase-9, and caspase-3, Bid cleavage, and evidence of mitochondrial injury. There was no evidence of endoplasmic reticulum stress. A pan-caspase inhibitor benzyloxycarbonyl-Val-Ala-DL-Asp prevented TWEAK-induced apoptosis, but it sensitized cells to necrosis via generation of reactive oxygen species. In conclusion, cooperation between inflammatory cytokines results in tubular cell death. TWEAK and Fn14 may play a role in renal tubular cell injury.

Modulation of renal tubular cell survival: where is the evidence?

Tubular cell loss is prominent both in acute and chronic renal failure. Apoptosis and its regulatory mechanisms contribute to cell number regulation in the kidney. The potential role of apoptosis ranges from induction and progression to repair of renal injury. However, therapeutic interest has focused in preventing the apoptotic loss of tubular cells that leads to acute and chronic renal failure. Death ligands and receptors, such as tumor necrosis factor and Fas ligand, proapoptotic and antiapoptotic Bcl2 family members and caspases have all been shown to participate in apoptosis regulation in the course of renal cell injury. Nevertheless, the precise role of these proteins is unclear, and the participation of most known apoptosis regulatory proteins has not been studied. We now review the role of apoptosis in renal injury, the potential molecular targets of therapeutic intervention, the therapeutic weapons to modulate the activity of these targets and the few examples of therapeutic intervention on apoptosis, with emphasis in acute renal failure.