α1 Antitrypsin therapy modulates the neutrophil membrane proteome and secretome

Obstructive pulmonary disease in patients with α1 antitrypsin (AAT) deficiency (AATD) occurs earlier in life compared with patients without AATD. To understand this further, the aim of this study was to investigate whether AATD presents with altered neutrophil characteristics, due to the specific lack of plasma AAT, compared with non-AATD COPD.This study focussed on the neutrophil plasma membrane and, by use of label-free tandem mass spectrometry, the proteome of the neutrophil membrane was compared in forced expiratory volume in 1 s (FEV1)-matched AATD, non-AATD COPD and in AATD patients receiving weekly AAT augmentation therapy (n=6 patients per cohort). Altered protein expression in AATD was confirmed by Western blot, ELISA and fluorescence resonance energy transfer analysis.The neutrophil membrane proteome in AATD differed significantly from that of COPD as demonstrated by increased abundance and activity of primary granule proteins including neutrophil elastase on the cell surface in AATD. The signalling mechanism underlying increased degranulation involved Rac2 activation, subsequently resulting in proteinase-activated receptor 2 activation by serine proteinases and enhanced reactive oxygen species production. In vitro and ex vivo, AAT reduced primary granule release and the described plasma membrane variance was resolved post-AAT augmentation therapy in vivo, the effects of which significantly altered the AATD neutrophil membrane proteome to that of a non-AATD COPD cell.These results provide strong insight into the mechanism of neutrophil driven airways disease associated with AATD. Therapeutic AAT augmentation modified the membrane proteome to that of a typical COPD cell, with implications for clinical practice.

Inhibition of Neutrophil Primary Granule Release during Yersinia pestis Pulmonary Infection

ABSTRACT Inhalation of Yersinia pestis causes primary pneumonic plague, the most severe manifestation of plague that is characterized by a dramatic neutrophil influx to the lungs. Neutrophils are ineffective during primary pneumonic plague, failing to control Y. pestis growth in the airways. However, the mechanisms by which Y. pestis resists neutrophil killing are incompletely understood. Here, we show that Y. pestis inhibits neutrophil degranulation, an important line of host innate immune defense. We observed that neutrophils from the lungs of mice infected intranasally with Y. pestis fail to release primary granules throughout the course of disease. Using a type III secretion system (T3SS) injection reporter strain, we determined that Y. pestis directly inhibits neutrophil granule release by a T3SS-dependent mechanism. Combinatorial mutant analysis revealed that a Y. pestis strain lacking both effectors YopE and YopH did not inhibit primary granule release and is killed by neutrophils both in vivo and in vitro. Similarly, Y. pestis strains injecting only YopE or YopH are able to inhibit the majority of primary granule release from human neutrophils. We determined that YopE and YopH block Rac2 activation and calcium flux, respectively, to inhibit neutrophil primary granule release in isolated human neutrophils. These results demonstrate that Y. pestis coordinates the inhibition of neutrophil primary granule release through the activities of two distinct effectors, and this inhibition promotes Y. pestis survival during primary pneumonic plague. IMPORTANCE Yersinia pestis is the causative agent of plague and is one of the deadliest human pathogens. The pneumonic form of Y. pestis infection has played a critical role in the severity of both historical and modern plague outbreaks, yet the host-pathogen interactions that govern the lethality of Yersinia pestis pulmonary infections are incompletely understood. Here, we report that Yersinia pestis inhibits neutrophil degranulation during infection, rendering neutrophils ineffective and allowing unrestricted growth of Y. pestis in the lungs. This coordinated inhibition of granule release not only demonstrates the pathogenic benefit of “silencing” lung neutrophils but also reveals specific host processes and pathways that could be manipulated to reduce the severity of primary pneumonic plague.

Phosphoinositide 3-kinase inhibition restores neutrophil accuracy in the elderly: toward targeted treatments for immunosenescence

Key Points Constitutive PI3K activity is associated with less accurate neutrophil migration in healthy aged adults. This is associated with increased primary granule release and neutrophil elastase activity and may contribute to inflammation and infection.

Primary granule exocytosis in human neutrophils is regulated by Rac-dependent actin remodeling

The actin cytoskeleton regulates exocytosis in all secretory cells. In neutrophils, Rac2 GTPase has been shown to control primary (azurophilic) granule exocytosis. In this report, we propose that Rac2 is required for actin cytoskeletal remodeling to promote primary granule exocytosis. Treatment of neutrophils with low doses (≤10 μM) of the actin-depolymerizing drugs latrunculin B (Lat B) or cytochalasin B (CB) enhanced both formyl peptide receptor- and Ca2+ionophore-stimulated exocytosis. Higher concentrations of CB or Lat B, or stabilization of F-actin with jasplakinolide (JP), inhibited primary granule exocytosis measured as myeloperoxidase release but did not affect secondary granule exocytosis determined by lactoferrin release. These results suggest an obligatory role for F-actin disassembly before primary granule exocytosis. However, lysates from secretagogue-stimulated neutrophils showed enhanced actin polymerization activity in vitro. Microscopic analysis showed that resting neutrophils contain significant cortical F-actin, which was redistributed to sites of primary granule translocation when stimulated. Exocytosis and actin remodeling was highly polarized when cells were primed with CB; however, polarization was reduced by Lat B preincubation, and both polarization and exocytosis were blocked when F-actin was stabilized with JP. Treatment of cells with the small molecule Rac inhibitor NSC23766 also inhibited actin remodeling and primary granule exocytosis induced by Lat B/fMLF or CB/fMLF, but not by Ca2+ionophore. Therefore, we propose a role for F-actin depolymerization at the cell cortex coupled with Rac-dependent F-actin polymerization in the cell cytoplasm to promote primary granule exocytosis.

Increased Unfolded Protein Response in Hematopoietic Cells from Cyclic Hematopoietic Dogs.

Canine cyclic hematopoiesis, a model of human cyclic neutropenia/congenital neutropenia (CN), is caused by a mutation in the AP3b1 gene. Human CN is caused by mutations in the Ela2 gene. The exact mechanism(s) whereby mutations in the Ela2 and AP3b1 cause CN or CH is not well understood. Elastase is directed to the primary granules by AP3 in myeloid progenitor cells, suggesting abnormal trafficking of elastase as a cause for CN/CH. Discontinuous percoll gradients on PMN cells from normal and CH dogs were performed. Fractions corresponding to the cytosol, plasma membrane, nuclei, primary, secondary and tertiary granules were collected and assayed for elastase and myeloperoxidase (MPO) enzyme activity and protein levels by Western blot using canine specific antibodies. Percoll density gradient fractionation results indicated that MPO, a primary granule protein that is not an AP3 cargo protein, is present in the primary granules in approximately equivalent amounts in both normal and CH dog PMN’s. Elastase was also localized in the primary granule fraction from both normal and CH dog PMN, but with a lower amount in CH dogs. Elastase was not present in the plasma membrane fraction in either CH or normal dog PMN’s. Quantitatively the CH dog primary granules had 10–20% of normal dog primary granule elastase. These results suggest PMN’s from CH dogs correctly sort elastase to the primary granules but at a lower level compared to PMNs from dogs without AP3b1 defect. Glucose-regulated protein (GRP78/BiP) is an indicator of ER stress. ER stress leads to activition of the unfolded protein response (UPR) and is cytoprotective. However, prolonged UPR leads to apoptosis. Analysis of GRP78 expression in PMN’s and bone marrow cell cultures from normal and CH dogs stimulated with SCF and G-CSF demonstrated 3–4 fold increase of GRP78 in CH cells compared to normal dog cells. These results indicate mistrafficking or accumulation of misfolded elastase induces the UPR in myeloid precursor cells and disrupts normal PMN production in CH dogs. These results are consistent with in vitro studies in which over-expression of mutant but not normal human elastase induces the UPR in myeloid cells and cell death. These results suggest that induction of the UPR is a common event, in myeloid progenitor cells from patients and animal models with either Ela2 or AP3b1 mutations, which ultimately results in congenital and/or cyclic neutropenia.

IL-3 Inhibits Terminal Granulocytic Differentiation by Inducing the Binding of Stabilizing Proteins to a 300 Base Pair Region within p21cip1/waf1 Messenger RNA.

Elevated levels of the molecular adaptor protein p21cip1/waf1 (p21) and of the IL-3 receptor α chain are correlated with chemoresistance and poor prognosis in acute myeloid leukemia (AML). p21 is a core regulator of many biological functions including cell cycle control, apoptosis and differentiation. Our laboratory has demo−nstrated that p21 undergoes dynamic changes in expression levels and subcellular compartmentalization during cytokine-induced granulocytic differentiation, suggesting that p21 may play an important role in myeloid development. Based on our observation that p21 protein levels decrease during granulocytic differentiation of CD34+ human progenitor cells, we hypothesized that p21 antagonizes granulopoiesis. The proliferative cytokine IL-3 is required to maintain the undifferentiated state in murine 32Dcl3 cells and has been shown to slow the kinetics of differentiation of normal human myeloid progenitors (Hevehan DL, 2000). Given that 32Dcl3 myeloblasts express high basal levels of p21, we also hypothesized that IL-3 inhibition of 32Dcl3 differentiation is mediated in part by p21. Our findings demonstrate that siRNA knockdown of murine p21 is correlated with premature expression of the primary granule proteins myeloperoxidase and proteinase-3 that are normally not abundant in cells maintained as myeloblasts by IL-3. Rescue of p21 knockdown myeloblasts with human p21 suppressed aberrant expression of granule proteins. The upregulation of myeloperoxidase and proteinase-3 occurred at a posttranscriptional level. These findings indicated that p21 prevented premature expression of primary granule proteins and may contribute to maintenance of the myeloblast phenotype. p21 knockdown was also found to accelerate morphologic granulocytic differentiation in 32Dcl3 cells stimulated with G-CSF, indicating that p21 antagonized the entire differentiation process rather than only suppressing primary granule proteins. We then determined how IL-3 maintains p21 expression in myeloblast cells. We demonstrated that IL-3 stabilized p21 mRNA in myeloblasts leading to high levels of p21 protein. This effect mapped to the 3′ untranslated region (UTR) of the p21 transcript. IL-3 also rescued the decrease in p21 mRNA stability noted during G-CSF-induced differentiation. This has been shown to coincide with differentiation blockade. p21 transcript stabilization by IL-3 was independent of PI3-kinase and ERK pathway signaling. In vitro binding assays provided evidence that distinct sets of RNA:protein interactions occur within the proximal 303 nucleotides of the p21 3′ UTR and are regulated by IL-3 and G-CSF signaling. Association of a ~60–65 kDa protein with p21 riboprobes correlated with IL-3 mediated p21 mRNA stabilization, whereas binding by a ~40–42 kDa protein was associated with destabilization of p21 transcripts in 32Dcl3 cells undergoing G-CSF-induced differentiation. These findings provide the first evidence for IL-3-mediated stabilization of mRNA transcripts in myeloid progenitor cells. The finding that p21 antagonized granulopoiesis is also novel. Because high levels of the IL-3 receptor and high p21 expression have separately been linked to poor outcomes in AML, IL-3 mediated p21 mRNA stabilization may contribute to differentiation blockade during AML pathogenesis.