Nicolas Pallet

Emerging role of autophagy in kidney function, diseases and aging

Autophagy is a highly conserved process that degrades cellular long-lived proteins and organelles. Accumulating evidence indicates that autophagy plays a critical role in kidney maintenance, diseases and aging. Ischemic, toxic, immunological, and oxidative insults can cause an induction of autophagy in renal epithelial cells modifying the course of various kidney diseases. This review summarizes recent insights on the role of autophagy in kidney physiology and diseases alluding to possible novel intervention strategies for treating specific kidney disorders by modifying autophagy.

Autophagy protects renal tubular cells against cyclosporine toxicity

A major side effect of the powerful immunosuppressive drug cyclosporine (CsA) is the development of a chronic nephrotoxicity whose mechanisms are not fully understood. Recent data suggest that tubular cells play a central role in the pathogenesis of chronic nephropathies. We have shown that CsA is responsible for endoplasmic reticulum (ER) stress in tubular cells. Autophagy has recently been described to be induced by ER stress and to alleviate its deleterious effects. In this study, we demonstrate that CsA induces autophagy in primary cultured human renal tubular cells through LC3II expression and autophagosomes visualization by electron microscopy. Autophagy is dependant of ER stress because various ER stress inducers activate autophagy and salubrinal, an inhibitor of eIF2α dephosphorylation that protects cells against ER stress, inhibited LC3II expression. Furthermore, autophagy inhibition during CsA treatment with beclin1 siRNA significantly increases tubular cell death. Finally, immunohistochemical analysis of rat kidneys demonstrates a positive LC3 staining on injured tubular cells, suggesting that CsA induces autophagy in vivo. Taken together, these results demonstrate that CsA, through ER stress induction, activates autophagy as a protection against cell death.

Early Epithelial Phenotypic Changes Predict Graft Fibrosis

Chronic allograft nephropathy accounts for the loss of approximately 40% of allografts at 10 yr. Currently, no biomarker is available to detect interstitial fibrosis and tubular atrophy in the renal graft at an early stage, when intervention may be beneficial. Because tubular epithelial cells have been shown to exhibit phenotypic changes suggestive of epithelial-to-mesenchymal transition, we studied whether these changes predict the progression of fibrosis in the allograft. Eighty-three kidney transplant recipients who had undergone a protocol graft biopsy at both 3 and 12 mo after transplantation were enrolled. De novo vimentin expression and translocation of beta-catenin into the cytoplasm of tubular cells were detected on the first biopsy by immunohistochemistry. Patients with expression of these markers in >or=10% of tubules at 3 mo had a higher interstitial fibrosis score at 1 yr and a greater progression of this score between 3 and 12 mo. The intensity of these phenotypic changes positively and significantly correlated with the progression of fibrosis, and multivariate analysis showed that their presence was an independent risk factor for this progression. In addition, the presence of early phenotypic changes was associated with poorer graft function 18 mo after transplantation. In conclusion, early phenotypic changes indicative of epithelial-to-mesenchymal transition predict the progression toward interstitial fibrosis in human renal allografts.

Cyclosporine-Induced Endoplasmic Reticulum Stress Triggers Tubular Phenotypic Changes and Death

The molecular mechanisms by which cyclosporine induces chronic nephrotoxicity remain poorly understood. A previous transcriptomic study suggested that cyclosporine might induce endoplasmic reticulum (ER) stress in human tubular cells. The aim of the present study was to characterize the features of tubular ER stress induced by cyclosporine and to investigate its effects on cell differentiation and viability. Using primary cultures of human tubular cells, we confirmed that cyclosporine is responsible for ER stress in vitro. This was also confirmed in vivo in the rat. In vitro, cyclosporine and other ER stress inducers were responsible for epithelial phenotypic changes leading to the generation of protomyofibroblasts, independent of transforming growth factor‐β signaling. RNA interference directed against cyclophilin A supported the role of its inhibition in triggering ER stress as well as epithelial phenotypic changes induced by cyclosporine. Salubrinal, which is known to protect cells from ER stress, significantly reduced epithelial phenotypic changes and cytotoxicity induced by cyclosporine in vitro. Salubrinal also reduced cyclosporine nephrotoxicity in rat kidneys. Thus, we describe a novel mechanism that initiates dedifferentiation and tubular cell death upon cyclosporine treatment. These results provide an interesting framework for further nephroprotective therapies by targeting ER stress.

Bortezomib as the Sole Post‐Renal Transplantation Desensitization Agent Does Not Decrease Donor‐Specific Anti‐HLA Antibodies

Persistence of donor‐specific anti‐HLA antibodies (DSA) associated with antibody‐mediated graft injuries following kidney transplantation predicts evolution toward chronic humoral rejection and reduced graft survival. Targeting plasma cells, the main antibody‐producing cells, with the proteasome inhibitor bortezomib may be a promising desensitization strategy. We evaluated the in vivo efficacy of one cycle of bortezomib (1.3 mg/m2× 4 doses), used as the sole desensitization therapy, in four renal transplant recipients experiencing subacute antibody‐mediated rejection with persisting DSA (>2000 [Mean Fluorescence Intensity] MFI). Bortezomib treatment did not significantly decrease DSA MFI within the 150‐day posttreatment period in any patient. In addition, antivirus (HBV, VZV and HSV) antibody levels remained stable following treatment suggesting a lack of efficacy on long‐lived plasma cells. In conclusion, one cycle of bortezomib alone does not decrease DSA levels in sensitized kidney transplant recipients in the time period studied. These results underscore the need to evaluate this new desensitization agent properly in prospective, randomized and well‐controlled studies.

Adverse events associated with mTOR inhibitors

Introduction: The mTOR (mechanistic target of rapamycin, formerly known as mammalian target of rapamycin) kinase is centrally involved in the regulation of cell growth and metabolism in response to intra- and extracellular energetic stimuli and growth factors. The importance of mTOR in health and diseases has fueled the development of molecules that inhibit mTOR signaling, including rapalogs (sirolimus, temsirolimus, everolimus and deforolimus), which complex with FK506-binding protein 12 (FK-BP12) to inhibit mTOR complex 1 (MTORC1) activity in an allosteric manner, or the more recent ATP-competitive mTOR inhibitors (mTORi), which target the catalytic site of the enzyme. However, clinical development of these mTORi has revealed that these drugs produced numerous side effects that could be serious and/or debilitating. Despite pharmacological efforts to develop drugs with an improved safety profile, these side effects are often unpredictable and may frequently preclude the efficiency of mTORi. Areas covered: The objective of this review is to perform a comprehensive survey of the safety profiles of various rapalog-based therapies from the available clinical literature. The authors will discuss the potential mechanisms of these therapies, taking into account the knowledge of the biological pathways regulated by mTOR. Expert opinion: A better prevention and management of mTORi-related side effects requires the identification of alterations in related biological pathways that will help to delineate therapeutic targets.

High dose epoetin beta in the first weeks following renal transplantation and delayed graft function: Results of the Neo-PDGF Study.

Erythropoietin promotes nephroprotection in animal models of ischemia‐reperfusion injury. Neorecormon® and Prevention of Delayed Graft Function (Neo‐PDGF) is a French open‐label multicenter randomized study to evaluate the effect of high doses of epoetin beta (EPO‐β) during the first 2 weeks of renal transplantation on renal function in patients at risk for delayed graft function (DGF). One hundred and four patients were included in the study. Patients randomized in treatment group (A) received four injections of EPO‐β (30.000 UI each), given before surgery and at 12 h, 7 days and 14 days posttransplantation. Patients randomized in control group (B) did not receive EPO‐β. Immunosuppression included induction with basiliximab and maintenance therapy with steroids, mycophenolate mofetil and tacrolimus. At 1 month posttransplant, the estimated glomerular filtration rate (MDRD formula) was 42.5 ± 19.0 mL/min in the EPO‐β group and 44.0 ± 16.3 mL/min in the control group (p = ns). The frequency of DGF was similar in both groups (32% vs. 38.8%; p = ns). No difference in the incidence of serious adverse events was observed. (ClinicalTrials.gov number, NCT00815867.)

Regulation of YAP by mTOR and autophagy reveals a therapeutic target of tuberous sclerosis complex

Liang et al. find that the tumor suppressors TSC1 and TSC2, defects in which underlie the genetic disease Tuberous Sclerosis Complex (TSC), drive the mTOR-dependent autophagosomal destruction of the transcriptional activator YAP. Blocking YAP inhibited the abnormal proliferation of TSC1/2-deficient human cells and reversed TSC-like disease symptoms in mosaic Tsc1 mutant mice.

Correction of Postkidney Transplant Anemia Reduces Progression of Allograft Nephropathy

Retrospective studies suggest that chronic allograft nephropathy might progress more rapidly in patients with post-transplant anemia, but whether correction of anemia improves renal outcomes is unknown. An open-label, multicenter, randomized controlled trial investigated the effect of epoetin-β to normalize hemoglobin values (13.0-15.0 g/dl, n=63) compared with partial correction of anemia (10.5-11.5 g/dl, n=62) on progression of nephropathy in transplant recipients with hemoglobin <11.5 g/dl and an estimated creatinine clearance (eCrCl) <50 ml/min per 1.73 m(2). After 2 years, the mean hemoglobin was 12.9 and 11.3 g/dl in the normalization and partial correction groups, respectively (P<0.001). From baseline to year 2, the eCrCl decreased by a mean 2.4 ml/min per 1.73 m(2) in the normalization group compared with 5.9 ml/min per 1.73 m(2) in the partial correction group (P=0.03). Furthermore, fewer patients in the normalization group progressed to ESRD (3 versus 13, P<0.01). Cumulative death-censored graft survival was 95% and 80% in the normalization and partial correction groups, respectively (P<0.01). Complete correction was associated with a significant improvement in quality of life at 6 and 12 months. The number of cardiovascular events was low and similar between groups. In conclusion, this prospective study suggests that targeting hemoglobin values ≥13 g/dl reduces progression of chronic allograft nephropathy in kidney transplant recipients.

Kidney Transplant in Black Recipients: Are African Europeans Different from African Americans?

Despite recent improvement, significant racial disparities in outcome still persist after renal transplantation among African American patients in the United States. This study evaluated the association of race and ethnicity with allograft outcomes in a French population of 952 Caucasian (Cauc) patients and 140 African European (AE) patients who underwent renal transplantation in our center between 1987 and 2003.