Ralph Kettritz

Granulocyte-Macrophage Colony-Stimulating Factor Delays Neutrophil Constitutive Apoptosis Through Phosphoinositide 3-Kinase and Extracellular Signal-Regulated Kinase Pathways

Activated neutrophils play an important role in the pathogenesis of sepsis, glomerulonephritis, acute renal failure, and other inflammatory processes. The resolution of neutrophil-induced inflammation relies, in large part, on removal of apoptotic neutrophils. Neutrophils are constitutively committed to apoptosis, but inflammatory mediators, such as GM-CSF, slow neutrophil apoptosis by incompletely understood mechanisms. We addressed the hypothesis that GM-CSF delays neutrophil apoptosis by activation of extracellular signal-regulated kinase (ERK) and phosphoinositide 3-kinase (PI 3-kinase) pathways. GM-CSF (20 ng/ml) significantly inhibited neutrophil apoptosis (GM-CSF, 32 vs 65% of cells p < 0.0001). GM-CSF activated the PI 3-kinase/Akt pathway as determined by phosphorylation of Akt and BAD. GM-CSF-dependent Akt and BAD phosphorylation was blocked by the PI 3-kinase inhibitor LY294002. A role for the PI 3-kinase/Akt pathway in GM-CSF-stimulated delay of apoptosis was indicated by the ability of LY294002 to attenuate apoptosis delay. GM-CSF-dependent inhibition of apoptosis was significantly attenuated by PD98059, an ERK pathway inhibitor. LY294002 and PD98059 did not produce additive inhibition of apoptosis delay. To determine whether PI 3-kinase and ERK are used by other ligands that delay neutrophil apoptosis, we examined the role of these pathways in IL-8-induced apoptosis delay. LY294002 blocked IL-8-dependent Akt phosphorylation. PD98059 and LY294002 significantly attenuated IL-8 delay of apoptosis. These results indicate IL-8 and GM-CSF act, in part, to delay neutrophil apoptosis by stimulating PI 3-kinase and ERK-dependent pathways.

C5a Receptor Mediates Neutrophil Activation and ANCA-Induced Glomerulonephritis

Anti-neutrophil cytoplasmic autoantibody (ANCA)-induced necrotizing crescentic glomerulonephritis (NCGN) requires complement participation in its pathogenesis. We tested the hypothesis that the anaphylatoxin C5a is pivotal to disease induction via the neutrophil C5a receptor (C5aR). Supernatants from ANCA-activated neutrophils activated the complement cascade in normal serum, producing C5a. This conditioned serum primed neutrophils for ANCA-induced respiratory burst; neutrophil C5aR blockade abrogated this priming, but C3aR blockade did not. Furthermore, recombinant C5a but not C3a dosage-dependently primed neutrophils for ANCA-induced respiratory burst. To test the role of C5aR in a model of NCGN, we immunized myeloperoxidase-deficient mice with myeloperoxidase, irradiated them, and transplanted bone marrow from wild-type mice or C5aR-deficient mice into them. All mice that received wild-type marrow (six of six) but only one of eight mice that received C5aR-deficient marrow developed NCGN (P < 0.05). Albuminuria and neutrophil influx into glomeruli were also significantly attenuated in the mice that received C5aR-deficient marrow (P < 0.05). In summary, C5a and the neutrophil C5aR may compose an amplification loop for ANCA-mediated neutrophil activation. The C5aR may provide a new therapeutic target for ANCA-induced necrotizing crescentic glomerulonephritis.

Diagnostic and Prognostic Stratification in the Emergency Department Using Urinary Biomarkers of Nephron Damage: A Multicenter Prospective Cohort Study

OBJECTIVES This study aimed to determine the diagnostic and prognostic value of urinary biomarkers of intrinsic acute kidney injury (AKI) when patients were triaged in the emergency department. BACKGROUND Intrinsic AKI is associated with nephron injury and results in poor clinical outcomes. Several urinary biomarkers have been proposed to detect and measure intrinsic AKI. METHODS In a multicenter prospective cohort study, 5 urinary biomarkers (urinary neutrophil gelatinase-associated lipocalin, kidney injury molecule-1, urinary liver-type fatty acid binding protein, urinary interleukin-18, and cystatin C) were measured in 1,635 unselected emergency department patients at the time of hospital admission. We determined whether the biomarkers diagnosed intrinsic AKI and predicted adverse outcomes during hospitalization. RESULTS All biomarkers were elevated in intrinsic AKI, but urinary neutrophil gelatinase-associated lipocalin was most useful (81% specificity, 68% sensitivity at a 104-ng/ml cutoff) and predictive of the severity and duration of AKI. Intrinsic AKI was strongly associated with adverse in-hospital outcomes. Urinary neutrophil gelatinase-associated lipocalin and urinary kidney injury molecule 1 predicted a composite outcome of dialysis initiation or death during hospitalization, and both improved the net risk classification compared with conventional assessments. These biomarkers also identified a substantial subpopulation with low serum creatinine at hospital admission, but who were at risk of adverse events. CONCLUSIONS Urinary biomarkers of nephron damage enable prospective diagnostic and prognostic stratification in the emergency department.

Membrane Expression of Proteinase 3 Is Genetically Determined

Isolated human neutrophils exhibit a bimodal membrane proteinase 3 (PR3) expression. PR3 is the main target antigen in Wegener granulomatosis (WG). Cells with low expression can be easily distinguished from cell subsets with high expression. In a recent study, a large neutrophil subset expressing membrane PR3 (mPR3+) was a risk factor for systemic ANCA-associated vasculitis. PR3 membrane expression patterns are quite stable in a given individual, raising the possibility of genetic variance. The aims of this study were: (1) to investigate the association of mPR3 expression and the risk of WG in an independent German cohort; (2) to test the hypothesis that mPR3 expression on neutrophils is genetically influenced; and (3) to investigate whether or not mPR3 expression is a function of intracellular PR3 content. mPR3 expression was assessed by FACS analysis in isolated human neutrophils. Neutrophil mPR3 expression was studied in 35 patients with WG, 15 patients with other inflammatory diseases, 125 healthy volunteers, and 27 (15 monozygotic and 12 dizygotic) pairs of twins. The intracellular PR3 content was assessed by intracellular flow cytometry and by Western blotting after separating mPR3 low and high expressing cells by FACSort. FACS analysis in a subset of 16 healthy subjects showed a highly conserved PR3 phenotype in two independent investigations >12 mo apart (r = 0.937). Patients with WG demonstrated a significantly higher percentage of mPR3+ neutrophils than healthy controls and patients with other inflammatory diseases. The mPR3+ percentage was highly correlated in MZ twins (r = 0.99) compared with DZ twins (r = 0.06). The intracellular PR3 content was not different in persons with low or high mPR3 expression, nor was the PR3 content different in cells with low or high mPR3 expression within a given individual. These data indicate that WG patients have a higher percentage of mPR3-expressing neutrophils. Furthermore, mPR3 expression is influenced by genetic variance. Finally, mPR3 expression is independent of intracellular PR3 content.

Urinary neutrophil gelatinase-associated lipocalin distinguishes pre-renal from intrinsic renal failure and predicts outcomes

In established acute kidney injury (AKI), serum creatinine poorly differentiates prerenal from intrinsic AKI. In this study, we tested whether urinary neutrophil gelatinase-associated lipocalin (NGAL) distinguishes between intrinsic and prerenal AKI, and tested its performance in predicting a composite outcome that included progression to a higher RIFLE (Risk, Injury, Failure, Loss of function, End stage renal disease) class, dialysis, or death. Urinary NGAL was measured using a standardized clinical platform in 161 hospitalized patients with established AKI. Sixteen patients were excluded because of postrenal obstruction or insufficient clinical information. Of the remaining 145 patients, 75 had intrinsic AKI, 32 had prerenal AKI, and 38 patients could not be classified. Urinary NGAL levels effectively discriminated between intrinsic and prerenal AKI (area under the receiver-operating characteristic curve 0.87). An NGAL level over 104 μg/l indicated intrinsic AKI (likelihood ratio 5.97), whereas an NGAL level <47 μg/l made intrinsic AKI unlikely (likelihood ratio 0.2). Patients experiencing the composite outcome had significantly higher median urinary NGAL levels on inclusion. In logistic regression analysis, NGAL independently predicted the composite outcome when corrected for demographics, comorbidities, creatinine, and RIFLE class. Hence, urinary NGAL is useful in classifying and stratifying patients with established AKI.

Role of extracellular signal-regulated kinase and phosphatidylinositol-3 kinase in chemoattractant and LPS delay of constitutive neutrophil apoptosis

The present study examined the role of mitogen-activated protein kinases (MAPKs) and phosphatidylinositol-3 kinase-stimulated Akt (PI-3K/Akt) in the regulation of constitutive human neutrophil apoptosis by bacterial lipopolysaccharide (LPS) and two chemoattractants, fMLP and leukotriene B(4) (LTB(4)). LPS and LTB(4) inhibited apoptosis, while fMLP had no effect. Inhibition of extracellular signal-regulated kinase (ERK) with PD098059 significantly inhibited the anti-apoptotic effect of both LPS and LTB(4), while inhibition of p38 kinase with SB203580 had no effect. Inhibition of PI-3K with wortmannin and LY294002 significantly attenuated the anti-apoptotic effect of LTB(4), but not LPS. LPS, fMLP, and LTB(4) stimulated similar levels of ERK and Akt activation. LTB(4) and LPS inhibited neutrophil apoptosis when added simultaneously with fMLP, and LTB(4) and LPS demonstrated an additive effect. We conclude that the ERK and/or PI-3K/Akt pathways are necessary, but not sufficient, for LPS and LTB(4) to delay apoptosis, but other anti-apoptotic pathways remain to be identified.

Integrins and Cytokines Activate Nuclear Transcription Factor-κB in Human Neutrophils

Neutrophil adhesion to extracellular matrix is necessary for an effective inflammatory response. Adhesion may accelerate neutrophil activation by affecting intracellular signaling pathways. The nuclear transcription factor κB (NF-κB) controls several cellular functions, including inflammation, proliferation, and cell survival. We explored the role of adhesion in NF-κB activation in human neutrophils. Cells were stimulated with tumor necrosis factor-α (TNF-α), granulocyte macrophage-colony-stimulating factor (GM-CSF), interleukin-8 (IL-8), and formyl-methionyl-leucyl-phenylalanine (fMLP). All four initiated neutrophil adherence to and spreading on fibronectin. GM-CSF and IL-8 did not activate NF-κB in suspended neutrophils but rapidly activated NF-κB under adherent conditions on matrix, as shown by IκB kinase activity assay, IκBα degradation, electromobility shift assay, and quantitative reverse transcriptase-PCR. In contrast, TNF–α activated NF-κB both in suspended cells and adherent cells. fMLP did not activate NF-κB in either suspended or adherent cells. Specific β2 integrin blockade prevented NF-κB activation by GM-CSF and IL-8 on fibronectin. Co-stimulating CD18 and CD11b with activating antibodies resulted in NF-κB activation by GM-CSF and IL-8 in suspended cells. We inhibited actin polymerization with cytochalasin and blocked the non-receptor kinase Syk with piceatannol. Both maneuvers prevented the co-stimulatory NF-κB-activating signal by β2 integrins. Thus, in addition to β2 integrin ligand binding, NF-κB activation depended on the formation of the receptor-associated intracellular focal adhesion complex. We conclude that β2 integrins may provide co-stimulatory signals allowing some soluble mediators to activate the NF-κB pathway even when they are not capable of doing so in suspension. This effect may become important when human neutrophils leave the circulating blood and migrate through extracellular matrix during inflammation.

Phosphatidylinositol 3-Kinase Controls Antineutrophil Cytoplasmic Antibodies—Induced Respiratory Burst in Human Neutrophils

Antineutrophil cytoplasmic antibodies (ANCA) activate human polymorphonuclear neutrophils (PMN) primed with tumor necrosis factor alpha (TNF-alpha) in vitro. Phosphatidylinositol 3-kinase (PI3-K) and the protein-serine/threonine kinase Akt have been implicated in the control of the phagocyte respiratory burst. The hypothesis that PI3-K controls the ANCA-induced respiratory burst was tested. TNF-alpha-primed PMN were stimulated with a monoclonal antibody to myeloperoxidase (MPO) and with PR3- and MPO-ANCA, respectively. Akt activation was assessed with phospho-specific antibodies. Superoxide release was measured with ferricytochrome. ANCA antigen translocation was assessed by fluorescence-activated cell sorter. The effect of TNF-alpha and MPO-ANCA on Akt signaling was studied with immunoprecipitation and glutathione S-transferase pull-down assays. Western blotting revealed rapid transient Akt phosphorylation during TNF-alpha priming and a second phosphorylation after ANCA. PI3-K inhibition by LY294002 blocked both Akt phosphorylation and superoxide generation. A total of 20 +/- 3 nmol O(2)(-)/0.75 x 10(6) PMN/45 min was released after stimulation with PR3-ANCA. LY294002 (5 microM) decreased this amount to 0.3 +/- 2.6 nmol (n = 10, P < 0.05); the MPO-ANCA values were 23 +/- 3 versus 1.6 +/- 3.6 (n = 10, P < 0.05). p38 MAPK inhibition with 10 microM SB202190 that also decreased ANCA-induced superoxide generation prevented S473 phosphorylation of Akt in response to TNF-alpha and to ANCA. However, SB202190 but not LY294002 abrogated TNF-alpha-mediated ANCA antigen surface translocation, demonstrating that superoxide generation and ANCA antigen translocation proceed by separate mechanisms. Akt, PAK1, and Rac1 existed as cytosolic complex in resting PMN. TNF-alpha stimulation increased association of PAK1 with Akt. An MPO monoclonal antibody did not alter the Akt signaling complex further. The data demonstrate the importance of PI3-K for the ANCA-induced PMN oxidant production.

Differential expression of classical nuclear transport factors during cellular proliferation and differentiation.

We recently cloned six human importin a proteins that transport specific substrates in complex with importin β into the nucleus. We now compared their absolute expression levels in different human cell lines. We examined their expression regulation during human cell proliferation and differentiation by means of specific antibodies. Proliferation inhibition by starvation of HeLa and HaCaT cells led to a marked decrease in the expression of various nuclear transport factors. In contrast, re-addition of serum increased α-importin expression. We analyzed two models for cell differentiation and found differential importin regulation. Stimulation of rat pancreatic AR42J cell differentiation towards a neuroendocrine phenotype with activin A or towards an acinar phenotype with dexamethasone, caused strong upregulation of importin α3 and α4 expression. Phorbol ester-induced differentiation of human leukemia (HL60) cells towards a macrophage phenotype led to downregulation of importin α1 and α4 expression after 72 hours. Similarly, importins α1 and α4 displayed a strong downregulation when HL60 cells were directed towards a neutrophil phenotype by DMSO treatment. This study is the first to assess all the human importin α isoforms in documenting differential nuclear transport factor regulation during cell proliferation and differentiation.

Neutrophil Serine Proteases Promote IL-1β Generation and Injury in Necrotizing Crescentic Glomerulonephritis

The pathogenesis of anti-neutrophil cytoplasmic antibody (ANCA)-associated necrotizing crescentic GN (NCGN) is incompletely understood. Dipeptidyl peptidase I (DPPI) is a cysteine protease required for the activation of neutrophil serine proteases (NSPs) cathepsin G, neutrophil elastase, and proteinase 3, which are enzymes that modulate inflammation. We used a mouse model of anti-myeloperoxidase (MPO) antibody-induced NCGN to determine whether active NSPs contribute to its pathogenesis. MPO-deficient animals immunized with murine MPO, irradiated, and transplanted with wild-type bone marrow developed NCGN. In contrast, transplantation with bone marrow that lacked DPPI or lacked both neutrophil elastase and proteinase 3 protected mice from NCGN induced by anti-MPO antibody. The kidneys of mice reconstituted with DPPI-deficient bone marrow generated significantly less IL-1β than did those of mice reconstituted with wild-type bone marrow; similarly, in vitro, DPPI-deficient monocytes produced significantly less IL-1β in response to anti-MPO antibody than did wild-type monocytes. This reduction in IL-1β was NSP dependent; exogenous addition of PR3 restored IL-β production in DPPI-deficient monocytes. Last, the IL-1 receptor antagonist anakinra protected animals against anti-MPO antibody-induced NCGN (16.7%±6.0% versus 2.4%±1.7% crescents), suggesting that IL-1β is a critical inflammatory mediator in this model. These data suggest that the development of anti-MPO antibody-induced NCGN requires NSP-dependent IL-1β generation and that these processes may provide therapeutic targets for ANCA-mediated diseases in humans.