Role of Fas (CD95) in tubulointerstitial disease induced by unilateral ureteric obstruction

Associations between single nucleotide polymorphisms in the FAS pathway and acute kidney injury

Introduction

To determine whether single nucleotide polymorphisms (SNPs) in FAS and related genes are associated with acute kidney injury (AKI) in patients with acute respiratory distress syndrome (ARDS).

Methods

We studied 401 (Caucasian N = 310 and African-American N = 91) patients aged ≥ 13 years with ALI who enrolled in the Fluid and Catheter Treatment Trial (FACTT) between 2000 and 2005 from 20 North American centers. We genotyped 367 SNPs in 45 genes of the Fas/Fas ligand pathway to identify associations between SNPs in Fas pathway genes and the development of AKI by day 2 after enrollment in FACTT, adapting Acute Kidney Injury Network (AKIN) criteria. Written informed consent was obtained from participants or legally authorized surrogates in the original FACTT study and available to use for secondary analysis.

Results

In Caucasian patients, we identified associations between two SNPs and the incidence of AKI (stage 1 and above): rs1050851 and rs2233417; both are found within the gene for nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor, alpha (NFKBIA). For rs1050851 and rs2233417, the odds ratios (ORs) were 2.34 (95 % confidence interval (CI) = 1.58–3.46, p = 1.06 × 10⁻⁵, FDR = 0.003) and 2.46 (CI = 1.61–3.76, p = 1.81 × 10⁻⁵, FDR = 0.003) for each minor allele, respectively. The associations were stronger still for AKIN stage 2–3 with respective ORs 4.00 (CI = 2.10–7.62, p = 1.05 × 10⁻⁵, FDR = 0.003) and 4.03 (CI = 2.09–7.77, p = 1.88 × 10⁻⁵, FDR = 0.003) for each minor allele homozygote. We observed no significant association between these SNPs and AKI in the smaller subset of African Americans.

Conclusion

In Caucasian patients with ALI, the presence of minor alleles in two SNPs in NFKBIA was strongly associated with the development of AKI.

Trial registration

NCT00281268. Registered 20/01/2006.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-1084-5) contains supplementary material, which is available to authorized users.

Mechanisms of renal injury and progression of renal disease in congenital obstructive nephropathy

Congenital obstructive nephropathy accounts for the greatest fraction of chronic kidney disease in children. Genetic and nongenetic factors responsible for the lesions are largely unidentified, and attention has been focused on minimizing obstructive renal injury and optimizing long-term outcomes. The cellular and molecular events responsible for obstructive injury to the developing kidney have been elucidated from animal models. These have revealed nephron loss through cellular phenotypic transition and cell death, leading to the formation of atubular glomeruli and tubular atrophy. Altered renal expression of growth factors and cytokines, including angiotensin, transforming growth factor-beta, and adhesion molecules, modulate cell death by apoptosis or phenotypic transition of glomerular, tubular, and vascular cells. Mediators of cellular injury include hypoxia, ischemia, and reactive oxygen species, while fibroblasts undergo myofibroblast transformation with increased deposition of extracellular matrix. Progression of the lesions involves interstitial inflammation and interstitial fibrosis, both of which impair growth of the obstructed kidney and result in compensatory growth of the contralateral kidney. The long-term outcome depends on timing and severity of the obstruction and its relief, minimizing ongoing injury, and enhancing remodeling. Advances will depend on new biomarkers to evaluate the severity of obstruction, to determine therapy, and to follow the evolution of lesions.

Galectin-3 expression and secretion links macrophages to the promotion of renal fibrosis

Macrophages have been proposed as a key cell type in the pathogenesis of renal fibrosis; however, the mechanism by which macrophages drive fibrosis is still unclear. We show that expression of galectin-3, a beta-galactoside-binding lectin, is up-regulated in a mouse model of progressive renal fibrosis (unilateral ureteric obstruction, UUO), and absence of galectin-3 protects against renal myofibroblast accumulation/activation and fibrosis. Furthermore, specific depletion of macrophages using CD11b-DTR mice reduces fibrosis severity after UUO demonstrating that macrophages are key cells in the pathogenesis of renal fibrosis. Disruption of the galectin-3 gene does not affect macrophage recruitment after UUO, or macrophage proinflammatory cytokine profiles in response to interferon-gamma/lipopolysaccharide. In addition, absence of galectin-3 does not affect transforming growth factor-beta expression or Smad 2/3 phosphorylation in obstructed kidneys. Adoptive transfer of wild-type but not galectin-3(-/-) macrophages did, however, restore the fibrotic phenotype in galectin-3(-/-) mice. Cross-over experiments using wild-type and galectin-3(-/-) macrophage supernatants and renal fibroblasts confirmed that secretion of galectin-3 by macrophages is critical in the activation of renal fibroblasts to a profibrotic phenotype. Therefore, we demonstrate for the first time that galectin-3 expression and secretion by macrophages is a major mechanism linking macrophages to the promotion of renal fibrosis.

Nitric oxide is an important mediator of renal tubular epithelial cell death in vitro and in murine experimental hydronephrosis

Macrophages play a pivotal role in tissue injury and fibrosis during renal inflammation. Although macrophages may induce apoptosis of renal tubular epithelial cells, the mechanisms involved are unclear. We used a microscopically quantifiable co-culture assay to dissect the cytotoxic interaction between murine bone marrow-derived macrophages and Madin-Darby canine kidney cells and primary murine renal tubular epithelial cells. The induction of tubular cell apoptosis by cytokine-activated macrophages was reduced by inhibitors of nitric oxide synthase whereas tubular cell proliferation was unaffected. Furthermore, cytokine-activated macrophages derived from mice targeted for the deletion of inducible nitric oxide synthase were noncytotoxic. We then examined the role of nitric oxide in vivo by inhibiting inducible nitric oxide synthase in the model of murine experimental hydronephrosis. l-N(6)-(1-iminoethyl)-lysine was administered in the drinking water between days 5 and 7 after ureteric obstruction. Macrophage infiltration was comparable between groups, but treatment significantly inhibited tubular cell apoptosis at day 7. Tubular cell proliferation was unaffected. Inducible nitric oxide synthase blockade also reduced interstitial cell apoptosis and increased collagen III deposition. These data indicate that nitric oxide is a key mediator of macrophage-directed tubular cell apoptosis in vitro and in vivo and also modulates tubulointerstitial fibrosis.

Evidence that inhibition of tubular cell apoptosis protects against renal damage and development of fibrosis following ureteric obstruction

Ureteric obstruction is frequently encountered in primary care urology and can lead to damage to the ipsilateral kidney. Relief of all types of obstruction generally leads to the normalization of any deterioration in renal function noted at diagnosis. However, some evidence from animal models suggests that obstruction can cause progressive deleterious effects on renal function and blood pressure control, especially in the presence of preexisting pathologies such as essential hypertension. The last 10 years have seen a proliferation of studies in rodents wherein complete unilateral ureteric obstruction has been used as a model of renal fibrosis. However, the relevance of the findings to human obstructive uropathy has, in many cases, not been the primary aim. In this review, we outline the major events linking damage to the renal parenchyma and cell death to the evolution of fibrosis following obstruction. Special focus is given to the role of apoptosis as a major cause of cell death during and post-complete ureteric obstruction. Several interventions that reduce tubular apoptosis are discussed in terms of their ability to prevent subsequent progression to end-organ damage and fibrosis.

Selective depletion of macrophages reveals distinct, opposing roles during liver injury and repair

Macrophages perform both injury-inducing and repair-promoting tasks in different models of inflammation, leading to a model of macrophage function in which distinct patterns of activation have been proposed. We investigated macrophage function mechanistically in a reversible model of liver injury in which the injury and recovery phases are distinct. Carbon tetrachloride---induced liver fibrosis revealed scar-associated macrophages that persisted throughout recovery. A transgenic mouse (CD11b-DTR) was generated in which macrophages could be selectively depleted. Macrophage depletion when liver fibrosis was advanced resulted in reduced scarring and fewer myofibroblasts. Macrophage depletion during recovery, by contrast, led to a failure of matrix degradation. These data provide the first clear evidence that functionally distinct subpopulations of macrophages exist in the same tissue and that these macrophages play critical roles in both the injury and recovery phases of inflammatory scarring.

Selective depletion of macrophages reveals distinct, opposing roles during liver injury and repair

Macrophages perform both injury-inducing and repair-promoting tasks in different models of inflammation, leading to a model of macrophage function in which distinct patterns of activation have been proposed. We investigated macrophage function mechanistically in a reversible model of liver injury in which the injury and recovery phases are distinct. Carbon tetrachloride---induced liver fibrosis revealed scar-associated macrophages that persisted throughout recovery. A transgenic mouse (CD11b-DTR) was generated in which macrophages could be selectively depleted. Macrophage depletion when liver fibrosis was advanced resulted in reduced scarring and fewer myofibroblasts. Macrophage depletion during recovery, by contrast, led to a failure of matrix degradation. These data provide the first clear evidence that functionally distinct subpopulations of macrophages exist in the same tissue and that these macrophages play critical roles in both the injury and recovery phases of inflammatory scarring.

Glomerular and tubular damage in normotensive and hypertensive rats

Tubular cell damage is an important mediator of interstitial fibrosis in chronic renal diseases. Glomerular and tubular damage in genetic hypertension was therefore studied. Tubular and glomerular damage was investigated in 10-, 40-, and 70-wk-old spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) and compared with glomerular capillary pressure (P(GC)) and glomerulosclerosis in superficial (OC) and juxtamedullary (JMC). Tubular vimentin was used as criterion of tubular damage. Variation in tubular diameter was measured during change in perfusion pressure, and ureter ligation was used to demonstrate the relationship between tubular pressure and appearance of vimentin-positive cells. Tubular and glomerular damage was most pronounced in JMC and greater in SHR than in WKY. It was absent in 10-wk-old WKY and significantly higher in JMC of SHR compared with WKY at 70 wk of age. Numbers of vimentin-positive segments were 18 +/- 9 vs. 38 +/- 7% in JMC of 70-wk-old WKY and SHR (P < 0.02), and glomerulosclerosis was seen in 8 +/- 3 vs. 19 +/- 5% of glomeruli in JMC of 70-wk-old WKY and SHR, respectively (P < 0.01). P(GC) was 45 +/- 3 mmHg in JMC of WKY and 57 +/- 3 mmHg in JMC of 70-wk-old SHR (P < 0.001). Tubular diameter variation was greatest in SHR (P < 0.05) during pressure variation. Proteinuria was present only in 40- and 70-wk-old SHR and did not correlate with tissue damage. Tubular and glomerular damage in both strains develops in parallel and may be caused by a common mechanism, which may be glomerular capillary and tubular wall stretch during acute blood pressure variation which is greatest in JMC in SHR.

Antioxidant ameliorates cisplatin-induced renal tubular cell death through inhibition of death receptor-mediated pathways

We have recently demonstrated the direct involvement of the death receptor-mediated apoptotic pathways in cisplatin-induced renal tubular cell (RTC) death. Reactive oxygen species are thought to be a major cause of cellular damage in such injury. The aim of this study was to examine the mechanism through which antioxidants ameliorate cisplatin-induced RTC death, with special emphasis on death receptor-mediated apoptotic pathways. Cisplatin was added to cultures of normal rat kidney (NRK52E) cells or injected in rats. NRK52E cells and rats were also treated with dimethylthiourea (DMTU), a hydroxyl radical scavenger. We then examined the mRNA levels of death ligands and receptors, caspase-8 activity, cell viability, cell death, renal function, and histological alterations. RT-PCR indicated cisplatin-induced upregulation of Fas, Fas ligand, and TNF-alpha mRNAs and complete inhibition by DMTU in vitro and in vivo. Cisplatin increased caspase-8 activity of NRK52E cells, and DMTU prevented such activation. Exposure to cisplatin reduced viability of NRK52E cells, examined by WST-1 assay, and increased apoptosis and necrosis of the cells, examined by terminal deoxynucleotidyl transferase dUTP nick-end labeling assay and fluorescence-activated cell sorter analysis. DMTU abrogated cisplatin-induced changes in cell viability and apoptosis and/or necrosis. Cisplatin-induced renal dysfunction and histological damage were also prevented by DMTU. DMTU did not hinder cisplatin incorporation into RTCs. Our results suggest that antioxidants can ameliorate cisplatin-induced acute renal failure through inactivation of the death receptor-mediated apoptotic pathways.

Renal apoptosis parallels ceramide content after prolonged ureteral obstruction in the neonatal rat

Obstructive nephropathy, the primary cause of renal insufficiency in infants, is characterized by progressive renal apoptosis. Ceramide is a sphingolipid known to stimulate apoptosis in the kidney. We investigated the effects of unilateral ureteral obstruction (UUO) on endogenous renal ceramide content and apoptosis in neonatal and adult rats. Animals were subjected to UUO or sham operation on the first day of life and were studied 3-28 days later. Adult rats were similarly treated and then studied 3 or 14 days later. In additional neonatal rats, the obstruction was removed after 5 days, with study at 14 or 28 days. Renal ceramide content was measured by diacylglycerol kinase assay, and apoptosis was determined by the terminal deoxynucleotidyl transferase dUTP nick-end-labeling technique. Renal ceramide content was 50-fold higher in the 3-day neonatal compared with the adult kidney and 10-fold higher in the 7-day neonatal compared with the adult kidney, but there was no additional effect of UUO on ceramide content at these ages. However, after 14 or 28 days UUO in the neonate, renal ceramide was elevated compared with sham or intact opposite kidneys, and renal apoptosis was directly related to ceramide content (r = 0.99, P < 0.001). Moreover, renal ceramide was reduced by relief of obstruction (P < 0.05). There was less apoptosis in the obstructed kidney of the adult than the neonate, and UUO had no effect on ceramide content at 14 days in the adult. We conclude that prolonged UUO (at least 14 days duration) increases endogenous renal ceramide in the neonatal but not the adult rat. It is likely that this contributes to the prolonged renal apoptotic response of the neonatal obstructed kidney.

Transcriptional regulation of the CLC-K1 promoter by myc-associated zinc finger protein and kidney-enriched Krüppel-like factor, a novel zinc finger repressor

The expression of CLC-K1 and CLC-K2, two kidney-specific CLC chloride channels, is transcriptionally regulated on a tissue-specific basis. Previous studies have shown that a GA element near their transcriptional start sites is important for basal and cell-specific activities of the CLC-K1 and CLC-K2 gene promoters. To identify the GA-binding proteins, the human kidney cDNA library was screened by a yeast one-hybrid system. A novel member of the Cys2-His2 zinc finger gene designated KKLF (for "kidney-enriched Krüppel-like factor") and the previously isolated MAZ (for "myc-associated zinc finger protein") were cloned. KKLF was found to be abundantly expressed in the liver, kidneys, heart, and skeletal muscle, and immunohistochemistry revealed the nuclear localization of KKLF protein in interstitial cells in heart and skeletal muscle, stellate cells, and fibroblasts in the liver. In the kidneys, KKLF protein was localized in interstitial cells, mesangial cells, and nephron segments, where CLC-K1 and CLC-K2 were not expressed. A gel mobility shift assay revealed sequence-specific binding of recombinant KKLF and MAZ proteins to the CLC-K1 GA element, and the fine-mutation assay clarified that the consensus sequence for the KKLF binding site was GGGGNGGNG. In a transient-transfection experiment, MAZ had a strong activating effect on transcription of the CLC-K1-luciferase reporter gene. On the other hand, KKLF coexpression with MAZ appeared to block the activating effect of MAZ. These results suggest that a novel set of zinc finger proteins may help regulate the strict tissue- and nephron segment-specific expression of the CLC-K1 and CLC-K2 channel genes through their GA cis element.