Glomerular mesangial cells and inflammatory macrophages ingest neutrophils undergoing apoptosis

The Glomerulus According to the Mesangium

The glomerulus is the functional unit for filtration of blood and formation of primary urine. This intricate structure is composed of the endothelium with its glycocalyx facing the blood, the glomerular basement membrane and the podocytes facing the urinary space of Bowman's capsule. The mesangial cells are the central hub connecting and supporting all these structures. The components as a unit ensure a high permselectivity hindering large plasma proteins from passing into the urine while readily filtering water and small solutes. There has been a long-standing interest and discussion regarding the functional contribution of the different cellular components but the mesangial cells have been somewhat overlooked in this context. The mesangium is situated in close proximity to all other cellular components of the glomerulus and should be considered important in pathophysiological events leading to glomerular disease. This review will highlight the role of the mesangium in both glomerular function and intra-glomerular crosstalk. It also aims to explain the role of the mesangium as a central component involved in disease onset and progression as well as signaling to maintain the functions of other glomerular cells to uphold permselectivity and glomerular health.

Deciphering the Role of Heme Oxygenase-1 (HO-1) Expressing Macrophages in Renal Ischemia-Reperfusion Injury

Ischemia-reperfusion injury (IRI) is a leading cause of acute kidney injury (AKI), which contributes to the development of chronic kidney disease (CKD). Renal IRI combines major events, including a strong inflammatory immune response leading to extensive cell injuries, necrosis and late interstitial fibrosis. Macrophages act as key players in IRI-induced AKI by polarizing into proinflammatory M1 and anti-inflammatory M2 phenotypes. Compelling evidence exists that the stress-responsive enzyme, heme oxygenase-1 (HO-1), mediates protection against renal IRI and modulates macrophage polarization by enhancing a M2 subset. Hereafter, we review the dual effect of macrophages in the pathogenesis of IRI-induced AKI and discuss the critical role of HO-1 expressing macrophages.

A role for the alpha-8 integrin chain (itga8) in glomerular homeostasis of the kidney

Glomerulonephritis results in a dysregulation of glomerular cells and may end up in chronic alterations and subsequent loss of renal function. Therefore, understanding mechanisms, which contribute to maintain glomerular integrity, is a pivotal prerequisite for therapeutic interventions. The alpha-8 integrin chain seems to be an important player to maintain glomerular homeostasis by conferring mechanical stability and functional support for the renal capillary tuft.

Cell Death in the Kidney

Apoptotic cell death is usually a response to the cell’s microenvironment. In the kidney, apoptosis contributes to parenchymal cell loss in the course of acute and chronic renal injury, but does not trigger an inflammatory response. What distinguishes necrosis from apoptosis is the rupture of the plasma membrane, so necrotic cell death is accompanied by the release of unprocessed intracellular content, including cellular organelles, which are highly immunogenic proteins. The relative contribution of apoptosis and necrosis to injury varies, depending on the severity of the insult. Regulated cell death may result from immunologically silent apoptosis or from immunogenic necrosis. Recent advances have enhanced the most revolutionary concept of regulated necrosis. Several modalities of regulated necrosis have been described, such as necroptosis, ferroptosis, pyroptosis, and mitochondrial permeability transition-dependent regulated necrosis. We review the different modalities of apoptosis, necrosis, and regulated necrosis in kidney injury, focusing particularly on evidence implicating cell death in ectopic renal calcification. We also review the evidence for the role of cell death in kidney injury, which may pave the way for new therapeutic opportunities.

Voices from the dead: The complex vocabulary and intricate grammar of dead cells

Of the roughly one million cells per second dying throughout the body, the vast majority dies by apoptosis, the predominant form of regulated cell death in higher organisms. Long regarded as mere waste, apoptotic cells are now recognized as playing a prominent and active role in homeostatic maintenance, especially resolution of inflammation, and in the sculpting of tissues during development. The activities associated with apoptotic cells are continually expanding, with more recent studies demonstrating their ability to modulate such vital functions as proliferation, survival, differentiation, metabolism, migration, and angiogenesis. In each case, the role of apoptotic cells is active, exerting their effects via new activities acquired during the apoptotic program. Moreover, the capacity to recognize and respond to apoptotic cells is not limited to professional phagocytes. Most, if not all, cells receive and integrate an array of signals from cells dying in their vicinity. These signals comprise a form of biochemical communication. As reviewed in this chapter, this communication is remarkably sophisticated; each of its three critical steps-encoding, transmission, and decoding of the apoptotic cell's "message"-is endowed with exquisite robustness. Together, the abundance and intricacy of the variables at each step comprise the vocabulary and grammar of the language by which dead cells achieve their post-mortem voice. The combinatorial complexity of the resulting communication network permits dying cells, through the signals they emit and the responses those signals elicit, to partake of an expanded role in homeostasis, acting as both sentinels of environmental change and agents of adaptation.

Hyperglycemia-induced Renal P2X7 Receptor Activation Enhances Diabetes-related Injury

Diabetes is a leading cause of renal disease. Glomerular mesangial expansion and fibrosis are hallmarks of diabetic nephropathy and this is thought to be promoted by infiltration of circulating macrophages. Monocyte chemoattractant protein-1 (MCP-1) has been shown to attract macrophages in kidney diseases. P2X7 receptors (P2X7R) are highly expressed on macrophages and are essential components of pro-inflammatory signaling in multiple tissues. Here we show that in diabetic patients, renal P2X7R expression is associated with severe mesangial expansion, impaired glomerular filtration (≤40ml/min/1.73sq.m.), and increased interstitial fibrosis. P2X7R activation enhanced the release of MCP-1 in human mesangial cells cultured under high glucose conditions. In mice, P2X7R-deficiency prevented glomerular macrophage attraction and collagen IV deposition; however, the more severe interstitial inflammation and fibrosis often seen in human diabetic kidney diseases was not modelled. Finally, we demonstrate that a P2X7R inhibitor (AZ11657312) can reduce renal macrophage accrual following the establishment of hyperglycemia in a model of diabetic nephropathy. Collectively these data suggest that P2X7R activation may contribute to the high prevalence of kidney disease found in diabetics.

Sanguinaria canadensis: Traditional Medicine, Phytochemical Composition, Biological Activities and Current Uses

Sanguinaria canadensis, also known as bloodroot, is a traditional medicine used by Native Americans to treat a diverse range of clinical conditions. The plants rhizome contains several alkaloids that individually target multiple molecular processes. These bioactive compounds, mechanistically correlate with the plant’s history of ethnobotanical use. Despite their identification over 50 years ago, the alkaloids of S. canadensis have not been developed into successful therapeutic agents. Instead, they have been associated with clinical toxicities ranging from mouthwash induced leukoplakia to cancer salve necrosis and treatment failure. This review explores the historical use of S. canadensis, the molecular actions of the benzophenanthridine and protopin alkaloids it contains, and explores natural alkaloid variation as a possible rationale for the inconsistent efficacy and toxicities encountered by S.canadensis therapies. Current veterinary and medicinal uses of the plant are studied with an assessment of obstacles to the pharmaceutical development of S. canadensis alkaloid based therapeutics.

Mechanisms of maladaptive repair after AKI leading to accelerated kidney ageing and CKD

Acute kidney injury is an increasingly common complication of hospital admission and is associated with high levels of morbidity and mortality. A hypotensive, septic, or toxic insult can initiate a cascade of events, resulting in impaired microcirculation, activation of inflammatory pathways and tubular cell injury or death. These processes ultimately result in acutely impaired kidney function and initiation of a repair response. This Review explores the various mechanisms responsible for the initiation and propagation of acute kidney injury, the prototypic mechanisms by which a substantially damaged kidney can regenerate its normal architecture, and how the adaptive processes of repair can become maladaptive. These mechanisms, which include G2/M cell-cycle arrest, cell senescence, profibrogenic cytokine production, and activation of pericytes and interstitial myofibroblasts, contribute to the development of progressive fibrotic kidney disease. The end result is a state that mimics accelerated kidney ageing. These mechanisms present important opportunities for the design of targeted therapeutic strategies to promote adaptive renal recovery and minimize progressive fibrosis and chronic kidney disease after acute insults.

Biotherapeutic target or sink: analysis of the macrophage mannose receptor tissue distribution in murine models of lysosomal storage diseases

Lysosomal storage diseases (LSDs) are metabolic disorders caused by enzyme deficiencies that lead to lysosomal accumulation of undegraded substrates. Enzyme replacement therapies (ERT) have been developed as treatments for patients with Gaucher, Niemann-Pick, Fabry, and Pompe diseases. Depending on the disease, the corresponding therapeutic enzyme is designed to be internalized by diseased cells through receptor-mediated endocytosis via macrophage mannose receptors (MMR) or mannose-6-phosphate receptors (M6PR). Enzymes developed to treat Gaucher and Niemann-Pick diseases are meant to target MMR-expressing cells, and in the case of Cerezyme [recombinant human β-glucocerebrosidase (rhβGC)] for treating Gaucher disease, glycans on the enzyme are modified to increase specificity toward this receptor. Due to heterogeneity in glycosylation on enzymes intended to target the M6PR, however, there may also be some unintended targeting to MMR-expressing cells, which could act as unwanted sinks. Examples include Fabrazyme [recombinant human α-galactosidase A (rhαGal)] for treating Fabry disease and Myozyme [recombinant human acid α-glucosidase (rhGAA)] for treating Pompe disease. It is therefore of great interest to better understand the cell type and tissue distribution of MMR in murine LSD models used to evaluate ERT efficacy and mechanism of action. In this study, we generated affinity-purified polyclonal antibody against murine MMR and used it to carry out a systematic examination of MMR protein localization in murine models of Gaucher, Niemann-Pick, Fabry, and Pompe diseases. Using immunohistochemistry, immunofluorescence, and confocal microscopy, we examined MMR distribution in liver, spleen, lung, kidney, heart, diaphragm, quadriceps, and triceps in these animal models and compared them with MMR distribution in wild-type mice.

Neutrophils sequestered in the liver suppress the proinflammatory response of Kupffer cells to systemic bacterial infection

The liver plays a major role in clearing bacteria from the bloodstream. Rapid clearance is primarily the function of fixed tissue macrophages (Kupffer cells) that line the hepatic sinusoids. Although Kupffer cells play a critical role in blood clearance, the actual elimination of the bulk of bacteria taken up by the liver depends upon the accumulation of bactericidal neutrophils. Subsequent experiments demonstrating neutrophils inside Kupffer cells derived from infected animals prompted our speculation that neutrophils modulate the proinflammatory response of Kupffer cells to bacteria cleared from the bloodstream. Indeed, we report here that neutrophils accumulated in the liver sinusoids suppress cytokine and chemokine mRNA expression and protein production by Kupffer cells. Using listeriosis in mice as an experimental model, we found that IL-1beta, IL-6, IL-10, IL-12, TNF-alpha, MIP-1alpha, keratinocyte-derived chemokine, and MCP-1 mRNA levels were >or=10-fold more in the livers of Listeria-infected, relative to noninfected control, mice at 0.5-2 h after i.v. infection. Most message levels were sharply diminished thereafter, correlating inversely with increased neutrophil sequestration. Relative to intact animals, mice rendered neutrophil deficient exhibited marked increases in cytokine/chemokine mRNA expression and protein production in the liver subsequent to infection. Moreover, purified Kupffer cells derived from infected, neutrophil-depleted mice produced significantly more IL-6, IL-10, IL-12, TNF-alpha, keratinocyte-derived chemokine, and MCP-1 in culture. These findings document the critical role of neutrophils in moderating the proinflammatory response of Kupffer cells to bacteria taken up by the liver.

Cellular activation by plasmid DNA in various macrophages in primary culture

Macrophages are an important group of cells responsible for the inflammatory response to unmethylated CpG dinucleotide (CpG motif) in plasmid DNA (pDNA) via Toll-like receptor 9 (TLR9). This finding is primarily based on in vitro studies. Previous in vivo studies also have suggested that tissue macrophages are involved in inflammatory cytokine release in the circulation following intravenous administration of pDNA to mice. However, the relationship between the in vitro and in vivo studies has not been sufficiently clarified. To gain insight into which types of cells are responsible for the production of cytokines upon interaction with pDNA, peritoneal macrophages, splenic macrophages, hepatic nonparenchymal cells (NPCs) including Kupffer cells and mesangial cells were isolated from mice. All types of primary cultured cells, except for mesangial cells, express TLR9 at varying levels. Splenic macrophages and hepatic NPCs were activated to produce tumor necrosis factor-alpha (TNF-alpha) by naked pDNA, whereas peritoneal macrophages and mesangial cells were not. pDNA complexed with N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethyl-ammonium chloride/cholesterol liposome induced TNF-alpha in the splenic macrophages but not in the other cell types. These results indicate that splenic macrophages and hepatic NPCs are closely involved in TNF-alpha production in response to pDNA.

Phagocytosis of apoptotic cells

Removal of apoptotic cells by phagocytes plays an important role in many biological processes, including embryological development and tissue remodelling. In addition, it has become apparent that one of the key mechanisms for the successful resolution of inflammation is the orchestrated clearance of apoptotic inflammatory cells by phagocytes (e.g., macrophages and dendritic cells) and other cells known to have phagocytic capacity (e.g., hepatocytes, endothelial cells, epithelial cells, etc.). Furthermore, phagocytosis of apoptotic cells is an active and highly regulated process that not only serves to remove potentially histotoxic cells from the inflammatory milieu, but also directs the phenotype of the phagocytic cell to be anti-inflammatory. Convincing evidence has been presented that reduced or dysregulated phagocytosis of apoptotic cells contributes to the development and propagation of inflammatory disorders. Conversely, enhanced phagocytosis of apoptotic cells may be exploited for therapeutic gain. Indeed, powerful anti-inflammatory drugs such as the glucocorticoids have been shown to augment clearance of apoptotic cells which may contribute to their therapeutic effectiveness. In this chapter, we describe methods for studying phagocytosis of apoptotic cells.

TGF-beta in renal injury and disease

Chronic progressive kidney diseases typically are characterized by loss of differentiated epithelial cells and activation of mesenchymal cell populations leading to renal fibrosis in response to a broad range of diverse renal injuries. Recent evidence has indicated that epithelial microinjury leads to unbalanced epithelial-mesenchymal communication to initiate the fibrotic response. Transforming growth factors beta constitute a large family of cytokines that control key cellular responses in development and tissue repair. Activation of autocrine and paracrine transforming growth factor-beta signaling cascades in the context of epithelial microinjuries initiate a variety of cell type-dependent signaling and activity profiles, including epithelial apoptosis and epithelial-to-mesenchymal transition, that trigger fibrogenic foci and initiate progressive fibrogenesis in chronic renal injury.

Glucose modulates handling of apoptotic cells by mesangial cells: involvement of TGF-beta1

Glucose stimulates proapoptotic signalling pathways in mesangial cells. Studies focused on inflammatory glomerular injury have demonstrated that removal of apoptotic mesangial cells occurs by neighbouring non-apoptotic mesangial cells. The aim of this study was to define the effect of ambient glucose concentration on mesangial handling of apoptotic cells, and in addition to examine the response made by the mesangial cell. We used a co-culture model in which neutrophils aged overnight to induce apoptosis, or apoptotic mesangial cells, labelled with a fluorescent dye, were added to mesangial cells to study phagocytosis. Exposure of mesangial cells to an ambient glucose concentration of 25 mM D-glucose before addition of apoptotic cells led in an increase in mesangial cell phagocytosis. Ingestion of apoptotic cells was inhibited by blocking alpha v beta 3 integrin-vitronectin receptor or thrombospondin-1. Furthermore, glucose-dependent stimulation of phagocytosis was inhibited by a blocking antibody to TGF-beta1. Co-culture of apoptotic cells with mesangial cells stimulated synthesis of TGF-beta1 as compared to freshly isolated neutrophils. Increased TGF-beta1 synthesis was dependent on direct contact between the two cell types but was not dependent on phagocytosis of apoptotic cells, as TGF-beta1 generation was not affected by inhibition of the thrombospondin-1 pathway. We propose a model in which apoptotic cell binding but not phagocytosis stimulates enhanced mesangial cell TGF-beta1 synthesis. Furthermore phagocytosis, which involves the thrombospondin-1 pathway, is uncoupled from binding of apoptotic cells, which stimulated TGF-beta1 synthesis.

Uptake behavior of embryonic chick liver cells

The capacity of selective uptake by liver cells, focusing particularly on the parenchymal and perisinusoidal stellate cells during chick liver development (8-18 days of incubation), was ultrastructurally examined after injection of 240-nm-diameter lecithin (phosphatidylcholine) -coated or noncoated beads into the extraembryonic circulation. Cytoplasmic projections of both cells as well as extrasinusoidal macrophages reached into the sinusoid-like vascular spaces. The primitive perisinusoidal stellate cells were identified by immunocytochemistry as being rich in desmin-positive cytoplasmic intermediate filaments. The cells demonstrated selective uptake of noncoated beads by means of their cytoplasmic projections. These findings were significant in the early period of incubation, indicating that the phagocytic activity is a characteristic and transient phenomenon of developmental differentiation. Large numbers of coated and a few noncoated beads penetrated into the perivascular spaces. The parenchymal cells incorporated only the coated beads that passed through the endothelial lining, suggesting that these cells express selective but limited phagocytic capacity against large "foreign" substances even long before their maturation. The cell projections were not engaged in uptake function. Extrasinusoidal macrophages, Kupffer cells, and intraluminal primitive macrophages all took up both beads; however, lecithin coating of the beads clearly suppressed their uptake function. These data suggest that the uptake function of large "foreign" substances appears to be intrinsic to liver cells and lecithin coating would be useful for delivering large substances to parenchymal cells.

Mast cells and inflammatory kidney disease

Inflammatory kidney disease involves a complex network of interactions between resident kidney and infiltrating hematopoietic cells. Mast cells (MCs) are constitutively found in kidneys in small numbers but increase considerably in various renal diseases. While this increase is usually interpreted as a sign of pathological involvement, recent data using MC-deficient animals show their ability to restore kidney homeostasis. In anti-glomerular basement membrane antibody-induced glomerulonephritis, MCs are protective by initiating repair and remodeling functions counteracting the devastating effects of glomerular injury. Protection may also include immunoregulatory capacities to limit autoreactive T-cell responses. MCs also control tubulointerstitial fibrosis by activating tissue remodeling and neutralizing fibrotic factors. Release of mediators by MCs during inflammation, however, could also promote unwanted responses that ultimately lead to destruction of kidney structure, as exemplified by data showing either protection or aggravation in related renal disease models. Similarly, while the action of proteases may initially be beneficial, the generation of fibrosis-promoting angiotensin II by chymase also shows the limits of adaptive responses to achieve homeostasis. Thus, it is likely the physiological context involving the interaction with other cells and inflammatory mediators that determines the final action of MCs in the development of kidney disease.

Roles of the innate immune system in mammary gland remodeling during involution

Mammary gland involution is a period of intensive tissue remodeling. Over the course of a relatively brief period, a large proportion of the mammary gland epithelium undergoes programmed cell death and is removed by phagocytes. In addition, the gland is cleared of residual milk fat globules as well as milk and adipocytes become the predominant cell type. The role of the immune system in this process has not been clearly defined. Professional phagocytes derived from the immune system can participate in the clearance of apoptotic and autophagic cells, the removal of residual milk components, and the prevention of mastitis during mammary gland involution. However, many of these functions can also be performed by non-professional phagocytes (e.g. mammary epithelial cells). This review will discuss the evidence that supports a role for innate immune cells in mammary gland remodeling during involution.

Significance of glomerular cell apoptosis in the resolution of acute post-streptococcal glomerulonephritis

BACKGROUND

Glomerular hypercellularity due to resident glomerular cell proliferation and leucocyte infiltration has been described in acute post-streptococcal glomerulonephritis (APSGN). APSGN usually resolves without progression. However, the mechanism of resolution remains to be determined.

METHODS

Renal biopsy tissues from 15 patients with APSGN (obtained 1-31 days after disease onset) and five control patients with minor glomerular abnormality were evaluated with respect to glomerular resolution. Apoptotic cells were assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labelling (TUNEL) as well as by immunostaining of single-stranded DNA (ssDNA).

RESULTS

The number of glomerular cells was high in the early-phase of APSGN and decreased over time. No TUNEL+ glomerular cells were found in control subjects, whereas prominent glomerular TUNEL+ cells were observed in APSGN patients, particularly in the early phase of the disease. The number of glomerular TUNEL+ cells decreased exponentially but was still prominent in renal tissue biopsied at 31 days after disease onset. Double staining for ssDNA and glomerular cell markers showed that glomerular apoptotic cells were predominantly mesangium and endothelial cells, with some neutrophils and macrophages.

CONCLUSIONS

These results suggest that apoptosis exists in the glomerulus in patients with APSGN from the early to the late stages of the disease and contributes to the resolution of glomerular hypercellularity.

Expression of the chemokine receptor CXCR1 in human glomerular diseases

Leukocyte infiltration, a hallmark of renal diseases, is orchestrated in part by the actions of chemokines. The chemokine CXCL8/interleukin (IL)-8 is expressed during renal diseases and allograft rejection, whereas the corresponding receptor CXCR1 has not been described previously. Expression of CXCR1 was characterized in peripheral blood using multicolor fluorescence-activated cell sorter analysis (FACS). CXCR1 was localized in 81 formalin-fixed, paraffin-embedded renal specimens by immunohistochemistry using a monoclonal antibody against human CXCR1. Included were biopsies with crescentic glomerulonephritis (CGN, n = 22), immunoglobulin (Ig) A nephropathy (n = 15), membranoproliferative glomerulonephritis (MPGN, n = 17), lupus nephritis (n = 12), membranous nephropathy (n = 11), and non-involved parts of tumor nephrectomies (n = 4). Consecutive tissue sections of human tonsils, allograft explants, and renal biopsies were stained for CD15- and CD68-positive cells. Expression of CXCR1 and CXCL8/IL-8 mRNA was quantified by real-time reverse transcriptase-polymerse chain reaction of microdissected renal biopsies (n = 35) of the same disease entities. By FACS CXCR1 expression was found on polymorphonuclear CXCR1 expression by polymorphonuclear leukocytes (PMNs), natural killer cells, and a subpopulation of monocytes. By immunohistochemistry, CXCR1 expression was found on infiltrating inflammatory cells (predominantly PMNs), as well as on intrinsic renal cells (arterial smooth muscle cells, endothelial cells of peritubular capillaries). The distribution pattern of CXCR1 differed between disease entities. The highest numbers of glomerular CXCR1-positive cells were present in biopsies with MPGN, followed by lupus nephritis, and CGN. CXCR1 might be involved in the recruitment of PMNs to the glomerular tuft, which could be targeted by CXCR1-blocking agents.

Platelet binding and phagocytosis by macrophages

BACKGROUND

Earlier it was reported that metabolic arrest followed by incubation at 4 degrees C reduces the platelet (PLT) storage defect. Here it is reported that this treatment also reduces binding and phagocytosis by macrophages.

STUDY DESIGN AND METHODS

Phagocytosis of mepacrine-labeled PLTs by macrophages changes the latter into bright fluorescent particles easily detected by fluorescence-activated cell sorting.

RESULTS

In combination with conventional binding analysis it was found that binding to phorbol 12-myristate 13-acetate-matured THP-1 cells is primarily regulated by PLT P-selectin expression and phagocytosis by combined phosphatidylserine (PS) exposure and glycoprotein (GP) Ibalpha clustering. It was found that trapping of PLT Ca2+ and raising cAMP reduces phagocytosis by lowering PS exposure. Chilling of PLTs leads to an increase in binding and PS- and GPIbalpha-mediated phagocytosis. Prior depletion of PLT energy stores prevents this increase by preserving low Ca2+ concentration, PS exposure, and PS-mediated phagocytosis.

CONCLUSION

These data characterize the individual factors that control PLT binding and phagocytosis and might help to define conditions that improve the survival of stored PLTs after transfusion.

Apoptosis and proliferation in childhood acute proliferative glomerulonephritis

Acute proliferative glomerulonephritis is characterized by glomerular hypercellularity that can be caused by many different etiologies and pathogenetic mechanisms. A balance between cell birth by mitosis and cell death by apoptosis is crucial. In this study, apoptosis and the regenerative activity (Ki67/apoptosis index) were investigated in acute proliferative glomerulonephritis. Thirty-five children with biopsy-proven acute proliferative glomerulonephritis and five controls with MCD were studied retrospectively. According to the clinical outcome, patients were divided into 2 groups: group 1 (n =21) were patients with normal renal functions at follow-up; group 2 (n =8) were patients with end-stage renal failure or those who died. Immunohistochemical staining of proliferating cells (Ki67) was done. In situ end labeling of DNA was used to evaluate apoptosis. Glomerular cell apoptosis was 45% in the patients with acute proliferative glomerulonephritis and 3% in controls ( p <0.001). Apoptotic cells were identified in the tubulointerstitial compartment with higher and heavier immunostaining in patients than controls (p =0.001). Tubular proliferative index (= tubular proliferation/tubular apoptosis ratio) was significantly higher in group 1 patients than in group 2 patients (2.03+/-2% versus 0.32+/-0.6%, p =0.002). Tubulointerstitial regenerative ratio (=tubular proliferation/interstitial proliferation ratio) was significantly higher in controls than in patients (3.4+/-1.9 versus 1.52+/-0.8, p =0.01). In addition, it was significantly increased in group 1 patients when compared with those in group 2 patients (1.89+/-0.8 versus 0.73+/-0.2, p =0.001). Since 17 patients presented with postinfectious proliferative glomerulonephritis, which is known to exhibit better course, we also evaluated those parameters in patients with postinfectious proliferative glomerulonephritis separately. We found statistically significant differences only in the tubulointerstitial regenerative ratio, which was higher in postinfectious cases when compared with those in other cases [1.60 interquartile range (IQR) 1.54 versus 1.22 IQR 1.26, respectively, p =0.003]. In conclusion, tubular proliferative index and tubulointerstitial regenerative ratio might be useful parameters for predicting final functional outcome in acute proliferative glomerulonephritis. Further studies, however, are still needed to clarify the importance of these histopathological parameters.

Epithelial cells as phagocytes: apoptotic epithelial cells are engulfed by mammary alveolar epithelial cells and repress inflammatory mediator release

Clearance of apoptotic cells is critical to tissue homeostasis and resolution of inflammatory lesions. Macrophages are known to remove dying cells and release anti-inflammatory mediators in response; however, many cells traditionally thought of as poor phagocytes can mediate this function as well. In the lactating mammary gland following weaning, alveolar epithelial cell death is massive, yet the gland involutes rapidly, attaining its prepregnancy state in a matter of days. We found histologic evidence of apoptotic cell phagocytosis by viable mammary epithelial cells (MEC) in the involuting mouse mammary gland. Cultured MEC were able to engulf apoptotic cells in vitro, utilizing many of the same receptors used by macrophages, including the phosphatidylserine receptor (PSR), CD36, the vitronectin receptor alpha(v)beta3, and CD91. In addition, MEC, like macrophages, produced TGFbeta in response to stimulation of the PSR by apoptotic cells or the anti-PSR ab 217G8E9, and downregulated endotoxin-stimulated proinflammatory cytokine production. These data support the hypothesis that amateur phagocytes play a significant role in apoptotic cell clearance and its regulation of inflammation.

Apoptosis in glomerulonephritis

PURPOSE OF REVIEW

Although glomerular cell apoptosis may be detrimental in acute and chronic inflammation, it is also a key component of the reparative glomerular remodelling that can follow injury. All glomerular cells are vulnerable to apoptosis although there are often differences in the nature of the initiating stimulus and the factors that are protective. The purpose of this review is to outline how modulation of this process may inhibit glomerular injury and promote tissue repair.

RECENT FINDINGS

In-vitro studies are providing more information on the factors that regulate apoptosis in individual glomerular cell types. It has now become apparent that growth factors such as vascular endothelial growth factor may have protective actions on several cell types and this may facilitate future treatments that promote the survival of multiple cell types within injured glomeruli. Work in this field has also emphasized that many current treatment strategies may exert a beneficial impact upon renal cell death.

SUMMARY

Although the advent of various antiapoptotic agents such as caspase inhibitors and recombinant growth factors does provide future opportunities to modulate apoptosis for therapeutic gain in patients with glomerulonephritis, there is still some way to go before such reagents are used to treat human disease. However, there is scope for optimism that such treatments will reach the clinic in due course.

Entamoeba histolytica and Entamoeba dispar utilize externalized phosphatidylserine for recognition and phagocytosis of erythrocytes

Amebic erythrophagocytosis is characteristic of invasive amebiasis, and mutants deficient in erythrocyte ingestion are avirulent. We sought to understand the molecular mechanisms underlying erythrocyte phagocytosis by Entamoeba histolytica. Following adherence to amebae, erythrocytes became round and crenulated, and phosphatidylserine (PS) was exposed on their outer membrane leaflets. These changes were similar to the effects of calcium treatment on erythrocytes, which we utilized to separate ameba-induced exposure of erythrocyte PS from the process of phagocytosis. The adherence and phagocytosis of calcium-treated erythrocytes were less inhibited by galactose than were those of healthy erythrocytes, suggesting the existence of an amebic coreceptor specific for PS. To test whether PS was recognized by amebae, calcium-treated cells were incubated with annexin V prior to adherence to or ingestion by E. histolytica. Annexin V blocked both adherence (50% +/- 12% inhibition; P < 0.05) and phagocytosis (65% +/- 10%; P < 0.05), providing evidence that at least one galactose-independent coreceptor was involved in the adherence and ingestion of red blood cells. The coreceptor was inhibited by phospho-l-serine and to a lesser extent by phospho-d-serine but not by phospho-l-threonine, which is consistent with the coreceptor functioning in the adherence and ingestion of erythrocytes via recognition of PS. We expanded our investigations to the highly related but noninvasive parasite Entamoeba dispar and demonstrated that it was deficient in red-blood-cell adherence, induction of PS exposure, and phagocytosis. These findings establish phosphatidylserine involvement in erythrophagocytosis by amebae and suggest the existence of a PS receptor on the surfaces of both E. histolytica and E. dispar.

Interaction between phosphatidylserine and the phosphatidylserine receptor inhibits immune responses in vivo

Phosphatidylserine (PS) on apoptotic cells promotes their uptake and induces anti-inflammatory responses in phagocytes, including TGF-beta release. Little is known regarding the effects of PS on adaptive immune responses. We therefore investigated the effects of PS-containing liposomes on immune responses in mice in vivo. PS liposomes specifically inhibited responses to Ags as determined by decreased draining lymph node tissue mass, with reduced numbers of total leukocytes and Ag-specific CD4(+) T cells. There was also a decrease in formation and size of germinal centers in spleen and lymph nodes, accompanied by decreased levels of Ag-specific IgG in blood. Many of these effects were mimicked by an agonistic Ab-specific for the PS receptor. TGF-beta appears to play a critical role in this inhibition, as the inhibitory effects of PS were reversed by in vivo administration of anti-TGF-beta Ab. PS-containing liposomes did not appear to directly inhibit dendritic cell maturation in vitro in response to a variety of stimuli, nor did it prevent their migration to regional lymph nodes in vivo, suggesting that the inhibitory effects may have resulted from complicated interactions between tissue cells and dendritic cells, subsequently inhibiting their ability to productively activate T lymphocytes.

Phagocytosis of apoptotic eosinophils but not neutrophils by bronchial epithelial cells

BACKGROUND

We have previously demonstrated that human bronchial epithelial cells engulf apoptotic eosinophils.

OBJECTIVES

To compare and contrast the phagocytic capabilities of monocyte-derived macrophage and primary airway epithelial cells for apoptotic granulocytes.

RESULTS

Here we compared phagocytosis of human apoptotic eosinophils and neutrophils by small and large airway epithelial cells (SAEC and LAEC) and monocyte-derived macrophages. Confocal microscopy of F-actin staining and scanning and transmission electron microscopy revealed phagocytic cup formation around apoptotic eosinophils by airway epithelial cells (AEC) membranes with evidence of their digestion. Resting and cytokine-stimulated AEC did not recognize and ingest apoptotic neutrophils. The latter were phagocytosed by macrophages that exhibited greater ingestion of and higher capacity for, apoptotic eosinophils over apoptotic neutrophils. Cytochalasin D completely abolished uptake of apoptotic eosinophils by SAEC, LAEC or macrophage monolayers. Ligation of epithelial cell CD44 receptors for 24 h increased phagocytosis of apoptotic eosinophils by SAEC and LAEC with a potency comparable with that of IL-1. Phagocytosis was a specific receptor-mediated process involving integrin- (alphavbeta3, alphavbeta5, CD36), phosphatidylserine receptor- and lectin-dependent mechanisms. No significant differences were observed in avarice for apoptotic eosinophils by SAEC or LAEC either resting, CD44 monoclonal antibodies- or cytokine- stimulated, or in their usage and expression of recognition receptors.

CONCLUSION

These findings further suggest and define an important role for the bronchial epithelium in the selective removal of apoptotic eosinophils from the airways in asthma.

Apoptosis in glomerulonephritis

Apoptosis is of fundamental importance and plays a key role in determining the outcome of glomerulonephritis. Under ideal circumstances,apoptosis deletes infiltrating leukocytes and excess numbers of resident cells that are surplus to requirements, thereby facilitating tissue remodeling and the restoration of normal tissue architecture. Apoptosis also has a darker side, however, and may be responsible for the deletion of critically important resident glomerular cells, resulting in hypocellular scarring and loss of renal function. Recent data indicate that glomerular cell apoptosis may be manipulated to improve outcome in experimental models of renal inflammation. It is hoped that further research will provide novel therapeutic strategies for patients with inflammatory glomerulonephritis.

Expression of Adhesion Molecules During Apoptosis of Circulating Neutrophils in COPD

STUDY OBJECTIVES

Neutrophil accumulation occurs in the lungs of patients with COPD. This can be due to increased recruitment and/or delayed tissue clearance. Previous studies have described alterations in circulating neutrophils in these patients that can facilitate the former. Dysregulation of neutrophil apoptosis may contribute to the latter. This study investigated the potential abnormalities of the apoptotic process in COPD patients.

DESIGN

Prospective study.

SETTINGS

Outpatient clinic in a urban, tertiary hospital.

PATIENTS

Fourteen stable patients with COPD, 8 smokers with normal lung function, and 8 healthy nonsmoking subjects.

MEASUREMENTS AND RESULTS

We cultured circulating neutrophils that had been harvested from the study subjects at 2, 6, and 24 h. Apoptosis was assessed using flow cytometry by annexin binding and CD16 expression. The surface expression of the adhesion molecules Mac-1 (CD11b) and L-selectin (CD62L) also was determined by flow cytometry. The percentage of apoptotic neutrophils increased with time similarly in all groups. However, the surface expression of Mac-1 (CD11b) was higher, and that of L-selectin (CD62L) was lower, during apoptosis in the neutrophils of patients with COPD.

CONCLUSIONS

These results show that, quantitatively, in vitro neutrophil apoptosis in COPD patients occurred at a rate similar to that found in healthy individuals and smokers with normal lung function. Qualitatively, however, the increased surface expression of Mac-1 (CD11b) and the decreased surface expression of L-selectin (CD62L) observed in the apoptotic neutrophils of COPD patients indicate increased activation during the apoptotic process. This may be relevant for the pathogenesis of COPD.

Essential contribution of monocyte chemoattractant protein-1/C-C chemokine ligand-2 to resolution and repair processes in acute bacterial pneumonia

Neutrophil infiltration is the first step in eradication of bacterial infection, but neutrophils rapidly die after killing bacteria. Subsequent accumulation of macrophage lineage cells, such as alveolar macrophages (AMs), is essential to remove dying neutrophils, which are a source of injurious substances. Macrophage lineage cells can promote tissue repair, by producing potential growth factors including hepatocyte growth factor (HGF). However, it remains elusive which factor activates macrophage in these processes. Intratracheal instillation of Pseudomonas aeruginosa caused neutrophil infiltration in the airspace; subsequently, the numbers of total AMs and neutrophil ingested AMs were increased. Bronchoalveolar lavage (BAL) fluid levels of monocyte chemoattractant protein (MCP)-1/CC chemokine ligand-2 (CCL2), a potent macrophage-activating factor, were increased before the increases in the number of AM ingesting neutrophils and HGF levels in BAL fluid. Immunoreactive MCP-1 proteins were detected in alveolar type II epithelial cells and AMs only after P. aeruginosa infection. The administration of anti-MCP-1/CCL2 Abs reduced the increases in the number of AM-ingesting neutrophils and HGF levels in BAL fluid, and eventually aggravated lung tissue injury. In contrast, the administration of MCP-1/CCL2 enhanced the increases in the number of AM ingesting neutrophils and HGF levels in BAL fluid, and eventually attenuated lung tissue injury. Furthermore, MCP-1/CCL2 enhanced the ingestion of apoptotic neutrophils and HGF production by a mouse macrophage cell line, RAW 267.4, in a dose-dependent manner. Collectively, MCP-1/CCL2 has a crucial role in the resolution and repair processes of acute bacterial pneumonia by enhancing the removal of dying neutrophils and HGF production by AMs.

Apoptotic neutrophils undergoing secondary necrosis induce human lung epithelial cell detachment

Clearance of apoptotic neutrophils by alveolar macrophages plays an important role in the resolution phase of lung inflammation. If not cleared, apoptotic neutrophils are postulated to release histotoxic granular contents. Since numerous cellular proteins are degraded during apoptosis, we sought to determine whether functional serine proteinases are indeed released by apoptosing neutrophils in vitro. In a coculture system, cytokine-activated neutrophils induced detachment in the human epithelial cell line, A549. This process was CD18- and serine proteinase-dependent. Early apoptotic neutrophils induced significant detachment, but live, senescent, resting neutrophils and terminal, secondary necrotic neutrophils had a different effect. This detachment process was CD18-independent but serine proteinase-dependent. Similarly, detachment occurred with primary human small airway epithelial cells. Notably, epithelial cell detachment correlated with the transition of early apoptotic neutrophils to secondary necrosis and with the accumulation of elastase in the supernatant. The membrane integrity of lung epithelial cells was damaged in advance of significant cell detachment. These observations suggest that not only live activated neutrophils but also apoptosing neutrophils can reveal functional elastase activities. Furthermore, the rapidity of the transition emphasizes the importance of the prompt clearance of apoptotic neutrophils before they progress to secondary necrosis at the site of lung inflammation.

Apoptotic neutrophils undergoing secondary necrosis induce human lung epithelial cell detachment

Clearance of apoptotic neutrophils by alveolar macrophages plays an important role in the resolution phase of lung inflammation. If not cleared, apoptotic neutrophils are postulated to release histotoxic granular contents. Since numerous cellular proteins are degraded during apoptosis, we sought to determine whether functional serine proteinases are indeed released by apoptosing neutrophils in vitro. In a coculture system, cytokine-activated neutrophils induced detachment in the human epithelial cell line, A549. This process was CD18- and serine proteinase-dependent. Early apoptotic neutrophils induced significant detachment, but live, senescent, resting neutrophils and terminal, secondary necrotic neutrophils had a different effect. This detachment process was CD18-independent but serine proteinase-dependent. Similarly, detachment occurred with primary human small airway epithelial cells. Notably, epithelial cell detachment correlated with the transition of early apoptotic neutrophils to secondary necrosis and with the accumulation of elastase in the supernatant. The membrane integrity of lung epithelial cells was damaged in advance of significant cell detachment. These observations suggest that not only live activated neutrophils but also apoptosing neutrophils can reveal functional elastase activities. Furthermore, the rapidity of the transition emphasizes the importance of the prompt clearance of apoptotic neutrophils before they progress to secondary necrosis at the site of lung inflammation.

Phagocytosis of apoptotic cells and the resolution of inflammation

Clearance of apoptotic cells by phagocytic cells plays a significant role in the resolution of inflammation, protecting tissue from harmful exposure to the inflammatory and immunogenic contents of dying cells. Apoptosis induces cell surface changes that are important for recognition and engulfment of cells by phagocytes. These changes include alterations in surface sugars, externalization of phosphatidylserine and qualitative changes in the adhesion molecule ICAM-3. Several studies have contributed to clarify the role of the receptors on the surface of phagocytes that are involved in apoptotic cell clearance. The phagocytic removal of apoptotic cells does not elicit pro-inflammatory responses; in contrast, apoptotic cell engulfment appears to activate signals that suppress release of pro-inflammatory cytokines. Therefore, clearance of apoptotic leucocytes is implicated in the resolution of inflammation and mounting evidence suggests that defective clearance of apoptotic cells contributes to inflammatory and autoimmune diseases. Defining the ligands on apoptotic cells and the corresponding receptors on phagocytes with which they engage, is likely to lead to the development of novel anti-inflammatory pro-resolution drugs. In this article, we will review the recognition and signaling mechanisms involved in the phagocytosis of apoptotic cells as well as the role of endogenous compounds that play a relevant role in the modulation of inflammation. We will also discuss what is currently known about diseases that may reflect impaired phagocytosis and the consequences on inflammation and immune responses.

Inducible cyclooxygenase-derived 15-deoxy(Delta)12-14PGJ2 brings about acute inflammatory resolution in rat pleurisy by inducing neutrophil and macrophage apoptosis

Failure of acute inflammation to resolve leads to persistence of the inflammatory response and may contribute to the development of chronic inflammation. Thus, an understanding of inflammatory resolution will provide insight into the etiology of chronic inflammation. In an acute pleurisy, polymorphonuclear leukocytes (PMNs) were found to predominate at the onset of the lesion but decreased in number by undergoing apoptosis, the principal mechanism by which PMNs died in this model. PMNs were progressively replaced by monocytes, which differentiated into macrophages. As with PMNs, macrophages also underwent programmed cell death leading to an abatement of the inflammatory response and eventual resolution. It was found that apoptosis of both these inflammatory cell types was mediated by pro-resolving cyclooxygenase 2-derived 15deoxyDelta12-14PGJ2, which is uniquely expressed during active resolution. Although PMN programmed cell death is well understood, the observation that macrophages apoptose during resolution of acute inflammation is less well described. These results provide insight into the mechanisms that switch off acute inflammation and prevent complications of wound healing and potentially the development of immune-mediated chronic inflammation.

Murine macrophages produce secretory leukocyte protease inhibitor during clearance of apoptotic cells: implications for resolution of the inflammatory response

Macrophage-derived secretory leukocyte protease inhibitor (SLPI) can be induced locally as well as systemically in response to microbial products such as LPS and lipotechoic acid. It is not known whether phagocytosis of apoptotic cells, an essential function of macrophages, can regulate expression and secretion of SLPI. In this study, we report that exposure of peritoneal macrophages of BALB/c mice or murine macrophage cell lines RAW264.7 and J774.1 to apoptotic target cells induced an elevation in SLPI secretion. Secreted SLPI retained its antichymotrypsin activity. SLPI expression in thymuses from BALB/c mice that had been injected with anti-CD3 Ab to induce apoptosis of thymocytes was also elevated both at the mRNA and protein levels. Colchicine, a microtubular inhibitor, blocked the internalization of apoptotic cells by macrophages but not SLPI secretion, suggesting that surface recognition of apoptotic cells is sufficient for the induction of SLPI. Exposure of RAW264.7 cells to apoptotic CTLL-2 cells induced both SLPI and TNF-alpha, and addition of IFN-gamma inhibited SLPI but augmented TNF-alpha production. Transfection of either the secreted or a nonsecreted form of SLPI into RAW264.7 cells led to suppression of TNF-alpha production in response to apoptotic cells. Thus, macrophages secrete an increased amount of SLPI when encountering apoptotic cells, which may help to attenuate potential inflammation during clearance of these cells.

Glomerular cell apoptosis in human lupus nephritis

Disturbed apoptosis is proposed to be involved in the pathogenesis of systemic lupus erythematosus. However, the role of renal cell apoptosis in the pathogenesis and progression of human lupus nephritis is still controversial. We have investigated glomerular cell apoptosis and the clinicopathological relationship between apoptosis and immunoserological or histological findings in 22 patients with lupus nephritis using electron microscopy and the TdT-mediated dUTP-biotin nick end labeling (TUNEL) method. Resident glomerular cells as well as infiltrating neutrophils undergoing apoptosis were observed in 12 of 20 patients with lupus nephritis using electron microscopy. TUNEL-positive cells were recognized in 93% of patients with diffuse proliferative lupus nephritis (class IV) in contrast to the 20% of patients with class V. The number of TUNEL-positive cells in glomeruli significantly correlated with the level of immunoserological activity of lupus, such as anti-double-stranded DNA autoantibody and consumption of plasma complement. There was a positive correlation between glomerular cell apoptosis and the degree of proliferation in lupus nephritis. These data suggest that apoptosis is increased, but not decreased in glomeruli from patients with lupus nephritis. The signals that could induce glomerular cell apoptosis in lupus nephritis will need to be identified.

Effects of leukocytosis and macrophage activation on anti-Thy 1.1 glomerulonephritis in the rat

OBJECTIVE

In anti-Thy 1.1 proliferative glomerulonephritis (GN), glomerular infiltration of polymorphonuclear leukocytes (PMNs) reaches a peak level after 1 h and that of macrophages does so 24 h after induction. However, the roles of PMNs and macrophages in the pathogenesis of anti-Thy 1.1 GN remain unclear. We examined the effects on this model of leukocytosis induced by granulocyte colony-stimulating factor (G-CSF) and of macrophages stimulated by macrophage colony-stimulating factor (M-CSF).

MATERIAL AND METHODS

Anti-Thy 1.1 GN was induced in male Wistar rats by intravenous injection of OX-7, a monoclonal antibody to the Thy 1 antigen. G-CSF (10 microg/kg/day), M-CSF (20 microg/kg/day) or vehicle was administered intraperitoneally for 7 days starting 24 h before the injection of OX-7. Histological examination of renal biopsy specimens was performed on Days 1, 5 and 14 after induction.

RESULTS

Circulating and glomerular-infiltrating PMNs (RP-3-positive cells) were increased at Day 5 in G-CSF-treated rats compared with controls receiving vehicle, and glomerular mesangiolysis continued at Day 5. The number of proliferating cells positive for proliferating cell nuclear antigen at Day 5 and matrix scores at Day 14 were smaller in G-CSF-treated rats than in control rats. The mesangiolysis score was significantly higher in the G-CSF group than in the control group at Days 5 and 14, but not at Day 1. ED-1-positive cells were increased in number at Day 5 and matrix accumulation decreased at Day 14 in M-CSF-treated rats compared with controls. Serum creatinine level at Day 14 was lower in the M-CSF group, but not in the G-CSF group, compared with the control group.

CONCLUSIONS

Activated macrophages may inhibit excess matrix accumulation and ameliorate the recovery of renal function, whereas leukocytosis inhibits the repair of mesangial cell injury in this model.

Oxidative stress-induced cell death of human oral neutrophils

Polymorphonuclear leukocytes (PMN) play crucial roles in protecting hosts against invading microbes and in the pathogenesis of inflammatory tissue injury. Although PMN migrate into mucosal layers of digestive and respiratory tracts, only limited information is available of their fate and function in situ. We previously reported that, unlike circulating PMN (CPMN), PMN in the oral cavity spontaneously generate superoxide radical and nitric oxide (NO) in the absence of any stimuli. When cultured for 12 h under physiological conditions, oral PMN (OPMN) showed morphological changes that are characteristic of those of apoptosis. Upon agarose gel electrophoresis, nuclear DNA samples isolated from OPMN revealed ladder-like profiles characteristic of nucleosomal fragmentation. l-cysteine, reduced glutathione (GSH), and herbimycin A, a protein tyrosine kinase inhibitor, suppressed the activation of caspase-3 and apoptosis of OPMN. Neither thiourea, superoxide dismutase (SOD), nor catalase inhibited the activation of caspase-3 and apoptosis. Moreover, N-acetyl-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-CHO), inhibitor for caspase-3, inhibited the fragmentation of DNA. These results suggested that oxidative stress and/or tyrosine-kinase-dependent pathway(s) activated caspase-3 in OPMN, thereby inducing their apoptosis.

Murine glomerular mesangial cell uptake of apoptotic cells is inefficient and involves serum-mediated but complement-independent mechanisms

An increased number of apoptotic bodies have been detected in glomeruli of non-nephritic kidneys of C1q-deficient mice. In these mice an in vivo impaired uptake of apoptotic cells by peritoneal macrophages was also demonstrated. Here we investigated whether C1q plays a role in the in vitro clearance of apoptotic cells by glomerular mesangial cells. Phagocytosis was assessed using a novel flow cytometric assay that was validated by immunofluorescence studies. The uptake of apoptotic cells by mesangial cells, measured as percentage of mesangial cells ingesting apoptotic cells, was approximately 25%, 10% and 10% for a T cell lymphoma line (RMA), thymocytes and neutrophils, respectively. The uptake reached a plateau phase after 3 h, was specific for apoptotic cells and was mediated by serum but not by complement components C1q or C3. The phagocytosis of apoptotic cells was significantly inhibited by Arg-Gly-Asp-Ser (RGDS), a peptide capable of blocking the interaction of thrombospondin with CD36 or the vitronectin receptor. Pretreatment of the mesangial cells with dexamethasone (200 nm) but not with LPS increased the uptake markedly. These findings indicate that murine mesangial cells are capable of taking up syngeneic apoptotic cells, although much less efficiently than professional phagocytic cells. They also show that serum proteins other than complement components mediate the removal of apoptotic cells by murine mesangial cells in vitro.

Lipoxins, aspirin-triggered epi-lipoxins, lipoxin stable analogues, and the resolution of inflammation: stimulation of macrophage phagocytosis of apoptotic neutrophils in vivo

Lipoxins (LX) are eicosanoids with antiinflammatory activity in glomerulonephritis (GN) and inflammatory diseases, hypersensitivity, and ischemia reperfusion injury. It has been demonstrated that LXA(4) stimulates non-phlogistic phagocytosis of apoptotic polymorphonuclear neutrophils (PMN) by monocyte-derived macrophages (Mphi) in vitro, suggesting a role for LX as endogenous pro-resolution lipid mediators. It is here reported that LXA(4), LXB(4), the aspirin-triggered LX (ATL) epimer, 15-epi-LXB(4), and a stable synthetic analogue 15(R/S)-methyl-LXA(4) stimulate phagocytosis of exogenously administered excess apoptotic PMN by macrophages (M phi) in vivo in a classic model of acute inflammation, namely thioglycollate-induced peritonitis. Significant enhancement of phagocytosis in vivo was observed with 15-min exposure to LX and with intraperitoneal doses of LXA(4), LXB(4), 15(R/S)-methyl-LXA(4), and 15-epi-LXB(4) of 2.5 to 10 micro g/kg. Non-phlogistic LX-stimulated phagocytosis by M phi was sensitive to inhibition of PKC and PI 3-kinase and associated with increased production of transforming growth factor-beta(1) (TGF-beta(1)). LX-stimulated phagocytosis was not inhibited by phosphatidylserine receptor (PSR) antisera and was abolished by prior exposure of M phi to beta 1,3-glucan, suggesting a novel M phi-PMN recognition mechanism. Interestingly, the recently described peptide agonists of the LXA(4) receptor (MYFINITL and LESIFRSLLFRVM) stimulated phagocytosis through a process associated with increased TGF-beta(1) release. These data provide the first demonstration that LXA(4), LXB(4), ATL, and LX stable analogues rapidly promote M phi phagocytosis of PMN in vivo and support a role for LX as rapidly acting, pro-resolution signals in inflammation. Engagement of the LXR by LX generated during cell-cell interactions in inflammation and by endogenous LXR peptide agonists released from distressed cells may be an important stimulus for clearance of apoptotic cells and may be amenable to pharmacologic mimicry for therapeutic gain.

Phagocytosis of apoptotic cells by macrophages induces novel signaling events leading to cytokine-independent survival and inhibition of proliferation: activation of Akt and inhibition of extracellular signal-regulated kinases 1 and 2

Recent evidence indicates that phagocytic clearance of apoptotic cells, initially thought to be a silent event, can modulate macrophage (M phi) function. We show in this work that phagocytic uptake of apoptotic cells or bodies, in the absence of serum or soluble survival factors, inhibits apoptosis and maintains viability of primary cultures of murine peritoneal and bone marrow M phi with a potency approaching that of serum-supplemented medium. Apoptotic uptake also profoundly inhibits the proliferation of bone marrow M phi stimulated to proliferate by M-CSF. While inhibition of proliferation is an unusual property for survival factors, the combination of increased survival and decreased proliferation may aid the M phi in its role as a scavenger during resolution of inflammation. The ability of apoptotic cells to promote survival and inhibit proliferation appears to be the result of simultaneous activation of Akt and inhibition of the mitogen-activated protein kinases extracellular signal-regulated kinase (ERK)1 and ERK2 (ERK1/2). While several activators of the innate immune system, or danger signals, also inhibit apoptosis and proliferation, danger signals and necrotic cells differ from apoptotic cells in that they activate, rather than inhibit, ERK1/2. These signaling differences may underlie the opposing tendencies of apoptotic cells and danger signals in promoting tolerance vs immunity.

The role of the macrophage in apoptosis: hunter, gatherer, and regulator

Clearance of cellular corpses is a critical feature of apoptosis in vivo during development, tissue homeostasis, and resolution of inflammation. As the professional phagocytes of the body, macrophages play a key role in this process. By recognizing emerging signals using several different receptors, macrophages engulf apoptotic cells swiftly and efficiently. In addition, the binding of apoptotic cells profoundly down-regulates the ability of the macrophage to produce inflammatory mediators by inducing the release of antiinflammatory mediators. Finally, macrophages may actually induce cell death in specific cells during embryogenesis. Abnormalities of apoptotic cell clearance may contribute to the pathogenesis of chronic inflammatory diseases, including those of autoimmune etiology. It is also possible that certain malignant tumor cells co-opt the mechanisms for apoptotic cell clearance to avoid immune surveillance by subverting macrophage and dendritic cell responses.

Caspase-3 and apoptosis in experimental chronic renal scarring

BACKGROUND

Caspase-3 is a member of the caspase enzyme family, having a central role in the execution of apoptosis. However, the significance of Caspase-3 in the inappropriate and excessive apoptosis that contributes to the progression of non-immune-mediated renal scarring has not been established.

METHODS

Kidneys from sham-operated and subtotal nephrectomized (SNx) rats were harvested on days 7, 15, 30, 60, 90 and 120 post-surgery. These were analyzed for apoptosis (in situ end labeling of DNA, light and electron microscopy), Caspase-3 activity (fluorometric substrate cleavage assay), protein and mRNA (Western and Northern blotting), as well as distribution (immunohistochemistry), inflammation (ED-1 immunohistochemistry) and fibrosis (Masson's Trichrome staining).

RESULTS

Apoptosis, inflammation and fibrosis gradually increased in glomeruli, tubules and interstitium of SNx rats. Caspase-3 was mainly located in damaged tubules, but also was found in some glomerular and interstitial cells. Little or no staining was noted in sham-operated kidneys. In SNx kidneys, Caspase-3 activity was significantly increased from day 30 and peaked on day 120 (2.5-fold). This resulted from increases in the 17 and 24 kD active protein subunits. The 32 kD precursor was increased at all time points (1861% on day 120, P < 0.01). Caspase-3 changes were transcription-dependent with the 2.7 kb caspase-3 mRNA significantly increased at all time points (287% on day 120). Caspase-3 activity was a better predictor of apoptosis (Std beta coefficient = 0.347, P < 0.05) than Caspase-3 proteins or mRNA; however, Caspase-3 at all levels correlated with apoptosis, inflammation and fibrosis (all P < 0.01).

CONCLUSIONS

Up-regulation of apoptosis in remnant kidneys is likely to be Caspase-3-dependent as it is associated with increases in Caspase-3 at the activity, protein and mRNA levels. Therefore, Caspase-3 is a potential therapeutic target for the modification of renal cell apoptosis and subsequently renal fibrosis.

Apoptosis: the quiet death silences the immune system

Apoptosis plays an essential role in maintaining cellular homeostasis during development, differentiation, and pathophysiological processes. In the immune system, recent investigations reveal that during the course of T-cell development in the thymus, negative selection of autoreactive immature T-cells is a typical apoptotic process. In addition, apoptosis is also involved in cytotoxic killing of target cells and the regulation of lymphocyte homeostasis during immune responses. Interestingly, recent evidence has suggested that cells dying by apoptosis are actively involved in immunosuppression in various circumstances. We have shown that apoptotic cells could inhibit the expression of CD69 during T-cell activation. Furthermore, apoptotic cells phagocytosed by macrophages and/or dendritic cells are immunosuppressive, a process likely mediated by the production of transforming growth factor-beta1. Since apoptosis is a common mechanism by which excessive cells in many tissues and organs are eliminated in various pathophysiological processes, we believe that further investigation into the mechanisms by which apoptotic cells affect the immune system will not only lead to a better understanding of the significance of apoptosis during immune responses, but will also provide novel strategies for the management of autoimmune diseases and transplantation.

Effects of 1,25(OH)2D3 in experimental mesangial proliferative nephritis in rats

BACKGROUND

1,25-Dihydroxyvitamin D3 [1,25(OH)2D3], the active form of vitamin D3, is a potent immunomodulatory agent on several cell types such as monocytes and mesangial cells. Recruitment of inflammatory cells, as well as stimulation of resident cells and mesangial matrix accumulation are key features of various experimental and human glomerular diseases. Here we show that 1,25(OH)2D3 attenuates the morphologic and functional alterations in anti-Thy-1.1. nephritis, an experimental model of mesangial proliferative glomerulonephritis.

METHODS

The anti-Thy-1.1 group (group I) comprised 24 rats that at day 0 received 0.5 mL of saline containing 400 microg of monoclonal antibodies (mAb) anti-Thy-1.1 IgG. The anti-Thy-1.1 treated with 1,25(OH)2D3 group (group II) were 24 rats given 1,25(OH)2D3 at the dose of 25 ng/100 g body wt/day, from day -3 to day 14. At day 0, the rats received 400 microg of anti-Thy-1.1 monoclonal IgG. The control group (group III) comprised 12 rats injected with vehicle alone; the control group treated with 1,25(OH)2D3 (group IV)-12 rats were given 1,25(OH)2D3 as in group II without mAb administration. Proteinuria and urinary interleukin-6 excretion were measured daily. Blood urea nitrogen and creatinine, creatinine clearance, calcium, and phosphate were measured at days 0, 4, 7, and 14. In addition to conventional periodic acid-Schiff staining, binding of anti-Thy-1.1 IgG and C3b complement fraction, His48- and ED1-positive cells were studied by immunofluorescence. Mesangial proliferation was studied by the proliferating cell nuclear antigen (PCNA) technique. Apoptosis was evaluated by the TUNEL assay.

RESULTS

The anti-Thy-1.1 treated with 1,25(OH)2D3 group versus the anti-Thy-1.1 alone group showed a significant reduction in urinary protein (at day 7, 424 +/- 228 vs. 66 +/- 30 mg/mg urinary creatinine, P = 0.02) and interleukin-6 excretion (at day 3, 537 +/- 360 pg/mL vs. 110 +/- 34 pg/mg urinary creatinine, P = 0.015), reduced glomerular diameters (at day 7, 283 +/- 38 vs. 261 +/- 48 microm, P < 0.01), decreased neutrophil (at day 4, 20 +/- 12 His48-positive cells/glomerulus vs. 3.7 +/- 1.3 His48-positive cells/glomerulus, P < 0.001), and monocyte accumulation (day 7, 4.9 +/- 2.9 ED1-positive cells/glomerulus vs. 2.8 +/- 2.9 ED1-positive cells/glomerulus, P < 0.05), and attenuated glomerular cells proliferation (day 7, 13 +/- 3.2 PCNA-positive cells/glomerulus vs. 9.4 +/- 3 PCNA-positive cells/glomerulus, P < 0.01). Apoptosis showed a biphasic behavior with an early peak at day 4 in the anti-Thy-1.1 group (2.3 +/- 2.2 TUNEL-positive cells/glom) related to cellular lysis and a late peak at day 14 related to the recovery phase.

CONCLUSIONS

1,25(OH)2D3 can reduce glomerular hypercellularity, inflammatory infiltration in anti-Thy-1.1 nephritis, preserving the apoptotic response of the reparative phase.

The trigger to cell death determines the efficiency with which dying cells are cleared by neighbours

Phagocytosis of apoptotic cells is required to prevent tissue injury. Professional phagocytes, such as monocyte-derived macrophages, are highly efficient scavengers of apoptotic cells but their presence cannot always be relied on; in that case, removal of effete cells is accomplished by helpful neighbours. This study describes differences in the efficiency with which apoptotic cells of the same type, but dying in response to different triggers, are engulfed; this varies from engulfment that is so proficient few or no unengulfed apoptotic cells are found, to engulfment that is so delayed apoptotic cells have become secondarily necrotic at the point of engulfment. In all cases the efficiency of engulfment is determined at least in part by the dying cells themselves. p53- and Bax-transfected kidney epithelial (293) cells (transiently transfected using a non-toxic method) were engulfed so proficiently by homotypic neighbours that cells did not show evidence of engagement of the apoptotic programme (chromatin condensation and TUNEL positivity) until engulfment had taken place. Engulfment nonetheless required activation of at least initiator caspases. 293 cells induced to apoptose by other means (etoposide and staurosporine treatment) were not so efficiently ingested: unengulfed apoptotic cells were consistently revealed at all doses and time points, even when treated cells were mixed with healthy, non-treated 293 cells. These data make it extremely unlikely that the fraction of viable, unaffected neighbours determines the efficiency with which engulfment proceeds. Furthermore, 293 cells treated with etoposide or staurosporine were differentially appealing both to homotypic neighbours and to cells in the professional phagocyte lineage (THP-1 cells). If different apoptotic stimuli programme cells to be recognised with different efficiencies, pathways to apoptosis may be injury limiting to greater or lesser degrees.

Neutrophil priming and apoptosis in anti-neutrophil cytoplasmic autoantibody-associated vasculitis

BACKGROUND

Interactions between anti-neutrophil cytoplasmic autoantibody (ANCA) and primed neutrophils (PMNs) may be central to the pathogenesis of primary small vessel vasculitis. PMNs from patients are primed, expressing proteinase 3 (PR3) on the cell surface, which permits interaction with ANCA. In vitro ANCA activates primed PMN to degranulate and generate a respiratory burst. Resultant reactive oxygen species are important in triggering apoptosis, but the fate of PMN in ANCA-associated vasculitis is unknown. Failure to remove apoptotic PMN in a nonphlogistic manner may sustain the inflammatory response.

METHODS

PMNs from patients or controls were isolated, and the basal production of superoxide was measured by the superoxide dismutase-inhibitable reduction of ferricytochrome C. ANCA antigen expression on apoptotic PMN was assessed at 0, 12, and 18 hours by flow cytometry using dual staining with FITC-conjugated annexin V and PE-conjugated anti-murine IgG against monoclonal ANCA. Apoptosis was also assessed by morphology. In further studies, apoptotic PMNs were opsonized with monoclonal anti-myeloperoxidase (MPO) or anti-proteinase-3 (PR3) or irrelevant isotype-matched IgG (N IgG) and phagocytosis by macrophages was measured using interaction assays. Cytokines interleukin-8 (IL-8) and interleukin-1 were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Proteinase-3 expression (active 63.04 +/- 5.6% of total number of cells, remission 51.47 +/- 7.9% of total number of cells, control 17.7 +/- 4.7% of total number of cells, P < 0.05) and basal superoxide production (active 6.9 +/- 0.8 nmol/L x 10(6) cells, remission 5.15 +/- 0.4 nmol/L/10(6) cells, control 3.63 +/- 0.3 nmol/L/10(6) cells, P < 0.001) were significantly greater with freshly isolated PMN from patients than controls. PR3 expression and superoxide generation were positively correlated. PMN from patients with active disease became apoptotic at a greater rate than those of controls (at 18 hours, patients 72.3 +/- 3.9% apoptosis, controls 53.2 +/- 2.7% apoptosis, P < 0.05). PR3 and MPO expression were significantly greater on PMN isolated from patients at 12 and 18 hours. Opsonization of apoptotic PMN with ANCA significantly enhanced recognition and phagocytosis by scavenger macrophages (anti-MPO 88.95 +/- 6.27, anti-PR3 93.98 +/- 4.90, N IgG 44.89 +/- 3.44, P < 0.01) with increased secretion of IL-1 (anti-PR3 34.73 +/- 6.8 pg/mL, anti-MPO 42.01 +/- 12.3 pg/mL, N IgG 8.04 +/- 6.3 pg/mL, P < 0.05) and IL-8 (anti-PR3 8.97 +/- 0.93 ng/mL, anti-MPO 8.45 +/- 1.46 ng/mL, N IgG 0.96 +/- 0.15 ng/mL, P < 0.01).

CONCLUSION

In vivo circulating PMNs are primed as assessed by PR3 expression and basal superoxide production, thereby enhancing their inflammatory potential. These PMNs undergo apoptosis more readily, at which times they express PR3 and MPO on their surface. These antigens may then provide targets for ANCA. Opsonization of apoptotic PMN will enhance clearance by macrophages but will also trigger the release of pro-inflammatory cytokines that may contribute to chronic inflammation.