Replicative senescence enhances apoptosis induced by pemphigus autoimmune antibodies in human keratinocytes

Immunosenescence and Skin: A State of Art of Its Etiopathogenetic Role and Crucial Watershed for Systemic Implications

Immunosenescence is a complex multifactorial phenomenon consisting of wide-ranging remodeling of the immune system during the life span, resulting in an age-related qualitative-quantitative decline of immune cells and cytokines. A growing body of evidence in the international literature is highlighting the etiopathogenetic role of skin immunosenescence in the onset of various dermatologic conditions. Skin immunosenescence also serves as an interesting watershed for the onset of system-wide conditions in the context of allergic inflammation. Moreover, in recent years, an increasingly emerging and fascinating etiopathogenetic parallelism has been observed between some mechanisms of immunosenescence, both at cutaneous and systemic sites. This would help to explain the occurrence of apparently unconnected comorbidities. Throughout our review, we aim to shed light on emerging immunosenescent mechanisms shared between dermatologic disorders and other organ-specific diseases in the context of a more extensive discussion on the etiopathogenetic role of skin immunosenescence. A promising future perspective would be to focus on better understanding the mutual influence between skin and host immunity, as well as the influence of high inter-individual variability on immunosenescence/inflammaging. This can lead to a more comprehensive "immunobiographic" definition of each individual.

Marked to Die-Cell Death Mechanisms for Keratinocyte Acantholysis in Pemphigus Diseases

Pemphigus is a group of blistering autoimmune diseases causing painful skin lesions, characterized by acantholysis and by the production of autoantibodies against, mainly, adhesion proteins. We reviewed the literature for molecules and/ or features involved in the 12 cell death pathways described by Nomenclature Committee on Cell Death, taking place in pemphigus patients, cell lines, or human skin organ cultures treated with sera or IgG from pemphigus patients or in pemphigus mouse models, and found 61 studies mentioning 97 molecules involved in cell death pathways. Among the molecules, most investigated were pleiotropic molecules such as TNF and CASP3, followed by FASL and CASP8, and then by FAS, BAX, BCL2, and TP53, all involved in more than one pathway but interpreted to function only within apoptosis. Most of these previous investigations focused only on apoptosis, but four recent studies, using TUNEL assays and/or electron microscopy, disqualified this pathway as a previous event of acantholysis. For PV, apoptolysis was suggested as a cell death mechanism based on pathogenic autoantibodies diversity, mitochondrial dysfunction, and p38 MAPK signaling. To answer those many questions that remain on cell death and pemphigus, we propose well-controlled, statistically relevant investigations on pemphigus and cell death pathways besides apoptosis, to overcome the challenges of understanding the etiopathology of pemphigus diseases.

Naringenin protects keratinocytes from oxidative stress injury via inhibition of the NOD2-mediated NF-κB pathway in pemphigus vulgaris

Naringenin is known to have anti-oxidative activity; however, the effect of naringenin on the progression of pemphigus vulgaris (PV) still remains unclear. This study aims to analyze the effect of naringenin on HaCaT cell apoptosis and oxidative damage under the treatment of PV serum. The results showed that PV serum significantly induced cell apoptosis compared with the control group; whereas, comparing with PV group, naringenin inhibited cell apoptosis. Moreover, PV serum increased the expression of bax and caspase-3, and decreased the expression of bcl-2; but naringenin significantly suppressed the expression of bax and caspase-3, induced the expression of bcl-2. Naringenin inhibited PV serum-induced disruption of cell-cell contacts. Naringenin also down-regulated the expression of Dsg1, Dsg3 and E-cadherin compared with the PV group. Additionally, naringenin noticeably decreased the PV serum-induced ROS production and alleviated PV serum induced the drop of mitochondrial membrane potential. Furthermore, naringenin increased the activity of SOD, GSH-Px and TAC under the treatment of PV serum. Naringenin also decreased the expression of NOD2, RIPK2 and NF-κB p-p65, but this effect could be reversed by muramyl dipeptide (MDP). In conclusion, these results suggested that naringenin protected keratinocytes from apoptosis and oxidative stress injury through inhibition of the NOD2-mediated NF-κB pathway.

Imaging of cellular aging in human retinal blood vessels

To date two main aging vascular lesions have been reported in elderly human retinas: acellular capillaries and microaneurysms. However, their exact mechanism of formation remains unclear. Using high resolution microscopy techniques we revise cellular alterations observed in aged human retinal vessels, such as lipofuscin accumulation, caveolae malfunction, blood basement membrane disruption and enhanced apoptosis that could trigger the development of these aging vascular lesions. Moreover, we have generated a set of original images comparing retinal vasculature between middle and old aged healthy humans to show in a comprehensive manner the main structural and ultrastructural alterations occurred during age in retinal blood vessels.

Studying of the expression of PERP protein in the skin of patients with pemphigus

The authors disclosed the participation of apoptosis proteins in the development of acantholysis in patients with pemphigus. In this connection, studies of the PERP protein passing apoptosis signals and regulating desmosomal functions in keratinocytes are of interest. There is no information about any studies aimed at the PERP protein expression in patients with pemphigus in available literature. Goal. To assess the PERP protein expression in the skin of patients with pemphigus. Materials and methods. There was a study of 22 patients with pemphigus, a patient with bullous pemphigoid and ten healthy people. The PERP protein expression was studied in the biopsy materials obtained from lesion foci and apparently healthy skin of the patients as well as healthy people using the indirect immunofluorescence method. Results. The PERP protein expression was revealed in patients with pemphigus on areas of apparently intact skin, in lesion foci in the patient with bullous pemphigoid and skin of healthy volunteers in the membrane of keratinocytes from all epidermal layers.The PERP protein expression in the blister operculum in lesion foci in patients with pemphigus was absent. Conclusion. Substantial differences in the PERP protein expression in the blister operculum and apparently intact skin of patients with pemphigus were revealed.

Pemphigus autoimmunity: hypotheses and realities

The goal of contemporary research in pemphigus vulgaris and pemphigus foliaceus is to achieve and maintain clinical remission without corticosteroids. Recent advances of knowledge on pemphigus autoimmunity scrutinize old dogmas, resolve controversies, and open novel perspectives for treatment. Elucidation of intimate mechanisms of keratinocyte detachment and death in pemphigus has challenged the monopathogenic explanation of disease immunopathology. Over 50 organ-specific and non-organ-specific antigens can be targeted by pemphigus autoimmunity, including desmosomal cadherins and other adhesion molecules, PERP cholinergic and other cell membrane (CM) receptors, and mitochondrial proteins. The initial insult is sustained by the autoantibodies to the cell membrane receptor antigens triggering the intracellular signaling by Src, epidermal growth factor receptor kinase, protein kinases A and C, phospholipase C, mTOR, p38 MAPK, JNK, other tyrosine kinases, and calmodulin that cause basal cell shrinkage and ripping desmosomes off the CM. Autoantibodies synergize with effectors of apoptotic and oncotic pathways, serine proteases, and inflammatory cytokines to overcome the natural resistance and activate the cell death program in keratinocytes. The process of keratinocyte shrinkage/detachment and death via apoptosis/oncosis has been termed apoptolysis to emphasize that it is triggered by the same signal effectors and mediated by the same cell death enzymes. The natural course of pemphigus has improved due to a substantial progress in developing of the steroid-sparing therapies combining the immunosuppressive and direct anti-acantholytic effects. Further elucidation of the molecular mechanisms mediating immune dysregulation and apoptolysis in pemphigus should improve our understanding of disease pathogenesis and facilitate development of steroid-free treatment of patients.

A hypothesis concerning a potential involvement of ceramide in apoptosis and acantholysis induced by pemphigus autoantibodies

Autoimmune diseases affect more than 50 million Americans, resulting in significant healthcare costs. Most autoimmune diseases occur sporadically; however, endemic pemphigus foliaceus (EPF) is an autoimmune skin disease localized to specific geographic loci. EPF, and the related diseases pemphigus vulgaris (PV) and pemphigus foliaceus (PF), are characterized by skin lesions and autoantibodies to molecules found on epidermal keratinocytes. A variant of EPF in patients from El Bagre, Colombia, South America, has recently been reported to be distinct from previously described loci in Brazil and Tunisia epidemiologically and immunologically. As in PF and EPF, El Bagre EPF patients exhibit autoantibodies towards desmoglein-1, a cell adhesion molecule critical for maintaining epidermal integrity. An association of El Bagre EPF with sun exposure has been detected, and ultraviolet irradiation also exacerbates symptoms in PV, PF and EPF. Our hypothesis is that: (1) the autoantibodies generate pathology through an alteration in ceramide metabolism in targeted keratinocytes, resulting in apoptosis and/or cell death and acantholysis, but only when the cell's ability to metabolize ceramide is exceeded, and (2) apoptosis in response to this altered ceramide metabolism is initiated and/or exacerbated by other agents that increase ceramide levels, such as cytokines, ultraviolet irradiation, and senescence.

Apoptotic pathways in pemphigus

Pemphigus is a group of human autoimmune blistering diseases of the skin in which autoantibodies to desmosome cadherins induce loss of cell-cell adhesion (acantholysis). In addition to steric hindrance and activation of intracellular signaling, apoptosis has been suggested to contribute to the mechanism by which pathogenic IgG induces acantholysis. We review the current literature examining the role of apoptosis in pemphigus. Current data suggest that apoptosis is not required for blister induction, but that activation of proapoptotic proteins, including caspase cysteine proteinases, may sensitize cells to the acantholytic effects of pemphigus IgG.

Experimental human cell and tissue models of pemphigus

Pemphigus is a chronic mucocutaneous autoimmune bullous disease that is characterized by loss of cell-cell contact in skin and/or mucous membranes. Past research has successfully identified desmosomes as immunological targets and has demonstrated that acantholysis is initiated through direct binding of IgG. The exact mechanisms of acantholysis, however, are still missing. Experimental model systems have contributed considerably to today's knowledge and are still a favourite tool of research. In this paper we will describe to what extent human cell and tissue models represent the in vivo situation, for example, organ cultures of human skin, keratinocyte cultures, and human skin grafted on mice and, furthermore, how suitable they are to study the pathogenesis of pemphigus. Organ cultures closely mimic the architecture of the epidermis but are less suitable to answer posed biochemical questions. Cultured keratinocyte monolayers are convenient in this respect, but their desmosomal make-up in terms of adhesion molecules does not exactly reflect the in vivo situation. Reconstituted skin is a relatively new model that approaches organ culture. In models of human skin grafted on mice, acantholysis can be studied in actual human skin but now with all the advantages of an animal model.

Antimitochondrial autoantibodies in pemphigus vulgaris: a missing link in disease pathophysiology

A loss of epidermal cohesion in pemphigus vulgaris (PV) results from autoantibody action on keratinocytes (KCs) activating the signaling kinases and executioner caspases that damage KCs, causing their shrinkage, detachment from neighboring cells, and rounding up (apoptolysis). In this study, we found that PV antibody binding leads to activation of epidermal growth factor receptor kinase, Src, p38 MAPK, and JNK in KCs with time pattern variations from patient to patient. Both extrinsic and intrinsic apoptotic pathways were also activated. Although Fas ligand neutralizing antibody could inhibit the former pathway, the mechanism of activation of the latter remained unknown. PV antibodies increased cytochrome c release, suggesting damage to mitochondria. The immunoblotting experiments revealed penetration of PVIgG into the subcellular mitochondrial fraction. The antimitochondrial antibodies from different PV patients recognized distinct combinations of antigens with apparent molecular sizes of 25, 30, 35, 57, 60, and 100 kDa. Antimitochondrial antibodies were pathogenic because their absorption abolished the ability of PVIgG to cause keratinocyte detachment both in vitro and in vivo. The downstream signaling of antimitochondrial antibodies involved JNK and late p38 MAPK activation, whereas the signaling of anti-desmoglein 3 (Dsg3) antibody involved JNK and biphasic p38 MAPK activation. Using KCs grown from Dsg3(-/-) mice, we determined that Dsg3 did not serve as a surrogate antigen allowing antimitochondrial antibodies to enter KCs. The PVIgG-induced activation of epidermal growth factor receptor and Src was affected neither in Dsg3(-/-) KCs nor due to absorption of antimitochondrial antibodies. These results demonstrated that apoptolysis in PV is a complex process initiated by at least three classes of autoantibodies directed against desmosomal, mitochondrial, and other keratinocyte self-antigens. These autoantibodies synergize with the proapoptotic serum and tissue factors to trigger both extrinsic and intrinsic pathways of cell death and break the epidermal cohesion, leading to blisters. Further elucidation of the primary signaling events downstream of PV autoantigens will be crucial for the development of a more successful therapy for PV patients.

Pemphigus in the XXI Century: New life to an old story

In this new century of pemphigus research, the search for novel treatments is switching from a monospecific approach, focused on immunosuppression, to a polyspecific approach that includes drugs acting on novel pathophysiologic pathways. Current research argues that acantholysis in pemphigus occurs as an active process resulting from intracellular signaling triggered as a result of IgG binding to the keratinocyte membrane antigens in a receptor-ligand fashion. Recent progress regarding the pathophysiology of pemphigus acantholysis led to, or was accompanied by, breakthrough discoveries of safer treatments. Both the identification of cell-surface receptors to acetylcholine among the nondesmoglein (Dsg) targets for pemphigus antibodies, and the elucidation of the cholinergic control of keratinocyte cell adhesion provide an explanation for the therapeutic efficacy of cholinomimetics in patients with pemphigus. In patients' skin, Fas-L, TNFalpha, and, probably, IL-1alpha act as autocrine/paracrine co-factors for anti-keratinocyte IgG. Thus, it appears that an array of interconnected signaling cascades is responsible for acantholysis and cell death in pemphigus. Future studies should define the signaling pathways mediating acantholysis that occur in individual pemphigus patients and identify the membrane proteins (receptors) triggering signaling along a specific pathway upon their ligation by autoantibodies. It will be important to determine which pathway 1) leads directly to a loss of cell-cell adhesion (primary pathway), 2) which is being activated due to cell shrinkage/detachment (secondary pathway), 3) which contributes to utilization of altered proteins and organelles (scavenging pathway), and 4) which represents the cell defense (protective pathway). To dissect out the signaling pathways originating from binding of pemphigus IgG to non-Dsg targets on the keratinocyte plasma membrane experiments should be performed in cultures of murine keratinocytes grown from the Dsg3-/- mice or human keratinocytes with the knocked-down expression of the Dsg1 and/or Dsg3 gene by the RNA interference.

Apoptolysis: a novel mechanism of skin blistering in pemphigus vulgaris linking the apoptotic pathways to basal cell shrinkage and suprabasal acantholysis

Understanding the acantholytic pathways leading to blistering in pemphigus vulgaris (PV) is a key to development of novel treatments. A novel paradigm of keratinocyte damage in PV, termed apoptolysis, links the suprabasal acantholytic and cell death pathways to basal cell shrinkage rendering a 'tombstone' appearance to PV lesions. In contrast to apoptolysis, the classic keratinocyte apoptosis mediating toxic epidermal necrolysis causes death and subsequent sloughing of the entire epidermis. Apoptolysis includes five consecutive steps. (1) Binding of autoantibodies to PV antigens. (2) Activation of EGF receptor, Src, mTOR, p38 MAPK and other signalling elements downstream of ligated antigens, elevation of intracellular calcium and launching of the cell death cascades. (3) Basal cell shrinkage due to: (i) collapse and retraction of the tonofilaments cleaved by executioner caspases; and (ii) dissociation of interdesmosomal adhesion complexes caused by phosphorylation of adhesion molecules. (4) Massive cleavage of cellular proteins by activated cell death enzymes leading to cell collapse, and tearing off desmosomes from the cell membrane stimulating secondary autoantibody production. (5) Rounding up and death of acantholytic cells. Thus, the structural damage (acantholysis) and death (apoptosis) of keratinocytes are mediated by the same cell death enzymes. Appreciation of the unifying concept of apoptolysis have several important implications: (i) linking together a number of seemingly unrelated events surrounding acantholysis; (ii) opening new avenues of investigation into the pathomechanism of pemphigus; and (iii) creating new approaches to the treatment of pemphigus based on blocking the signalling pathways and enzymatic processes that lead to blistering.

Biphasic activation of p38MAPK suggests that apoptosis is a downstream event in pemphigus acantholysis

In pemphigus vulgaris and pemphigus foliaceus (PF), autoantibodies against desmoglein-3 and desmoglein-1 induce epidermal cell detachment (acantholysis) and blistering. Activation of keratinocyte intracellular signaling pathways is emerging as an important component of pemphigus IgG-mediated acantholysis. We previously reported activation of p38 mitogen-activated protein kinase (MAPK) in response to pathogenic pemphigus vulgaris and PF IgG. Inhibition of p38MAPK blocked pemphigus IgG-induced cytoskeletal reorganization in tissue culture and blistering in pemphigus mouse models. We now extend these observations by demonstrating two peaks of p38MAPK activation in pemphigus tissue culture and mouse models. Administration of the p38MAPK inhibitor SB202190 before PF IgG injection blocked both peaks of p38MAPK phosphorylation and blister formation, consistent with our previous findings; however, administration of the inhibitor 4 h after PF IgG injection blocked only the later peak of p38MAPK activation but failed to block blistering. Examination of the temporal relationship of p38MAPK phosphorylation and apoptosis showed that apoptosis occurs at or after the second peak of p38MAPK activation. The time course of p38MAPK activation and apoptotic markers, as well as the ability of inhibitors of p38MAPK to block activation of the proapoptotic proteinase caspase-3, suggest that activation of apoptosis is downstream to, and a consequence of, p38MAPK activation in pemphigus acantholysis. Furthermore, these observations suggest that the earlier peak of p38MAPK activation is part of the mechanism leading to acantholysis, whereas the later peak of p38MAPK and apoptosis may not be essential for acantholysis.

Apoptosis is not required for acantholysis in pemphigus vulgaris

The autoimmune blistering skin disease pemphigus vulgaris (PV) is caused primarily by autoantibodies against desmosomal cadherins. It was reported that apoptosis can be detected in pemphigus skin lesions and that apoptosis can be induced by PV-IgG in cultured keratinocytes. However, the role of apoptosis in PV pathogenesis is unclear at present. In this study, we provide evidence that apoptosis is not required for acantholysis in PV. In skin lesions from two PV patients, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) positivity, but not cleaved caspase-3, was detected in single keratinocytes in some lesions but was completely absent in other lesions from the same patients. In cultures of human keratinocytes (HaCaT and normal human epidermal keratinocytes), PV-IgG from three different PV patients caused acantholysis, fragmented staining of Dsg 3 staining, and cytokeratin retraction in the absence of nuclear fragmentation, TUNEL positivity, and caspase-3 cleavage and hence in the absence of detectable apoptosis. To further rule out the contribution of apoptotic mechanisms, we used two different approaches that are effective to block apoptosis induced by various stimuli. Inhibition of caspases by z-VAD-fmk as well as overexpression of Fas-associated death domain-like interleukin-1β-converting enzyme (FLICE)-like inhibitory proteins FLIPL and FLIPS to inhibit receptor-mediated apoptosis did not block PV-IgG-induced effects, indicating that apoptosis was not required. Taken together, we conclude that apoptosis is not a prerequisite for skin blistering in PV but may occur secondary to acantholysis.

Inhibitors of cytochrome c release with therapeutic potential for Huntington's disease

Release of mitochondrial cytochrome c resulting in downstream activation of cell death pathways has been suggested to play a role in neurologic diseases featuring cell death. However, the specific biologic importance of cytochrome c release has not been demonstrated in Huntington's disease (HD). To evaluate the role of cytochrome c release, we screened a drug library to identify new inhibitors of cytochrome c release from mitochondria. Drugs effective at the level of purified mitochondria were evaluated in a cellular model of HD. As proof of principle, one drug was chosen for in depth evaluation in vitro and a transgenic mouse model of HD. Our findings demonstrate the utility of mitochondrial screening to identify inhibitors of cell death and provide further support for the important functional role of cytochrome c release in HD. Given that many of these compounds have been approved by the Food and Drug Administration for clinical usage and cross the blood-brain barrier, these drugs may lead to trials in patients.

The desmosome and pemphigus

Desmosomes are patch-like intercellular adhering junctions ("maculae adherentes"), which, in concert with the related adherens junctions, provide the mechanical strength to intercellular adhesion. Therefore, it is not surprising that desmosomes are abundant in tissues subjected to significant mechanical stress such as stratified epithelia and myocardium. Desmosomal adhesion is based on the Ca(2+)-dependent, homo- and heterophilic transinteraction of cadherin-type adhesion molecules. Desmosomal cadherins are anchored to the intermediate filament cytoskeleton by adaptor proteins of the armadillo and plakin families. Desmosomes are dynamic structures subjected to regulation and are therefore targets of signalling pathways, which control their molecular composition and adhesive properties. Moreover, evidence is emerging that desmosomal components themselves take part in outside-in signalling under physiologic and pathologic conditions. Disturbed desmosomal adhesion contributes to the pathogenesis of a number of diseases such as pemphigus, which is caused by autoantibodies against desmosomal cadherins. Beside pemphigus, desmosome-associated diseases are caused by other mechanisms such as genetic defects or bacterial toxins. Because most of these diseases affect the skin, desmosomes are interesting not only for cell biologists who are inspired by their complex structure and molecular composition, but also for clinical physicians who are confronted with patients suffering from severe blistering skin diseases such as pemphigus. To develop disease-specific therapeutic approaches, more insights into the molecular composition and regulation of desmosomes are required.

A perspective of pemphigus from bedside and laboratory-bench

Pemphigus represents a distinct organ-specific acquired autoimmune disease characterized by intra-epidermal blistering, which is induced by autoantibodies against desmosomal cadherins, desmoglein 1 (Dsg1), and Dsg3. Pemphigus is currently divided into three distinct varieties, i.e., pemphigus vulgaris (PV), pemphigus foliaceus (PF) and other variants of pemphigus (mostly associated with inflammation), depending on clinical features, the level of separation in the epidermis, and immunologic characteristics of auto-antigens. Blistering pathomechanisms differ for each of the types of pemphigus. Pemphigus, which results from autoantibodies against desmogleins and possibly to other proteins, binds to the cell surface antigens. This binding may cause steric hindrance to homophilic adhesion of desmogleins, and may, in turn, lead to internalization of desmogleins and inhibition of desmogleins' integration into desmosomes, resulting in the formation of Dsg3-depleted desmosomes in PV or Dsg1-depleted desmosomes in PF. Furthermore, PV-IgG activates an "outside-in" signaling pathway to induce disassembly of desmosomal components from the inside of the cells by phosphorylation of proteins, including Dsg3. On the other hand, Pemphigus-IgG-augmented signaling pathways may be linked to the secretion of cytokines such as in case of pemphigus herpetiformis and chemokines that initiate or activate inflammation. In this article, the classification of pemphigus and the characteristic pathomechanisms for acantholysis will be reviewed, with particular emphasis on the molecular and biochemical cell biology of these diseases.

No activation of urokinase plasminogen activator by anti-desmoglein 3 monoclonal IgG antibodies in cultured human keratinocytes

BACKGROUND

Although pemphigus vulgaris (PV)-IgG has been shown to activate urokinase plasminogen activator (uPA) in cultured keratinocytes, activation of uPA is thought to have no primary role in PV-acantholysis, because PV-IgG is still pathogenic in uPA- and tissue-PA-knockout mice.

OBJECTIVE

To determine if PV-IgG-induced uPA activation is due to specific antibody against Dsg3, we examined whether or not pathogenic monoclonal anti-Dsg3 antibody can activate uPA, because PV-IgG is thought to contain antibodies against unknown antigens besides Dsg3.

METHODS

We stimulated cultured normal human and DJM-1 keratinocytes with monoclonal anti-Dsg3 IgG1 antibodies (pathogenic AK23, AK19 and nonpathogenic AK18, AK20), negative control monoclonal mouse IgG1 and positive control PV-IgG. Cells were treated with IgGs over a time course of 24h, and uPA-protein content and activity in the culture medium were determined by enzyme-linked immunosorbent assay (ELISA) and chromogenic assay, respectively.

RESULTS

The uPA-protein content in samples treated with or without pathogenic, nonpathogenic, control monoclonal mouse IgG1s and PV-IgGs increased continuously up to 24h, with no differences between samples, suggesting a spontaneous secretion. In contrast, uPA activity in the culture medium of cells treated with PV-IgG increased dramatically, whereas that of cells treated with all AK-IgGs and control monoclonal mouse IgG1 did not increase at all.

CONCLUSION

These results suggest that PV-IgG-dependent uPA activation is not related to anti-Dsg3 antibody activity, which is an essential factor in PV-IgG acantholysis, and that it may be due to other antigens than Dsg3 or unknown factors contained in PV-IgG fraction.

Metalloproteinase 9 is the outer executioner of desmoglein 3 in apoptotic keratinocytes

OBJECTIVE

To investigate the specific matrix metalloproteinases (MMPs) targeting desmoglein 3 (Dsg3) in apoptotic keratinocytes.

METHOD

Inhibitor studies on cultured keratinocytes and Western blot analysis.

RESULTS

Blocking of MMP-9 activity strongly reduces shedding of Dsg3 from cell surface. MMP-2 has a less relevant role in the cleavage of Dsg3 while other MMPs, such as MMP-1, -3, and -8, do not target Dsg3.

CONCLUSION

Apoptic keratinocytes impair the extracellular domain of cell surface Dsg3 by MMP-9 activity. The discovery of a specific targeting of Dsg3 could be useful to understand the pathophysiology of diseases in which Dsg3 is affected.

Apoptotic mechanism in pemphigus autoimmunoglobulins-induced acantholysis--possible involvement of the EGF receptor

Pemphigus is an autoimmune cutaneous disease characterized by circulating autoantibodies that cause blistering and erosions on skin and mucous membranes. Circulating autoantibodies bind to epidermal cell membrane and cause cell-cell detachment (acantholysis), leading to epidermal tissue damage and cell death. The principal target of pemphigus vulgaris autoantibodies (PV-IgG) is desmosomal cadherin desmoglein 3 (Dsg3), a constituent of desmosomes, mediating cell-cell adhesion. Several hypotheses for the mechanisms of acantholysis induction by PV-IgG exist, but the actual mechanism is not clear as yet. We have previously reported on apoptosis induction in PV-IgG-mediated epidermal tissue and cell damage as a possible mechanism of acantholysis and cell death (Wang et al. 2004, Apoptosis, 9:131-143). In this study we investigated the involvement of the EGFR and intracellular signal transduction pathways in the PV-IgG-induced apoptosis. We show here that PV-IgG induced activation/autophosphorylation of EGFR in cultured keratinocytes in vitro. The specific tyrosine kinase inhibitor AG1478 abrogated EGFR autophosphorylation, cell death, FasL appearance and acantholysis, all induced by PV-IgG, in parallel, confirming the involvement of EGFR in this Fas apoptotic cascade. Activation of EGFR was followed by phosphorylation of its downstream substrates, MAP kinase ERK and transcription factor c-Jun, and internalization of EGFR. Pharmacological inactivation of the EGFR and ERK kinase activities, by use of specific inhibitors AG1478 and PD98059 respectively, blocked PV-IgG-induced phosphorylation of EGFR, ERK and c-Jun and cellular apoptosis, measured by flow cytometry and caspase 3 activity. Prolonged activation of EGFR by PV-IgG led to dramatic internalization of this receptor, possibly reducing the ability of the cell to perform survival signals. This suggests that activation of EGFR, followed by its internalization, is pivotal for intracellular apoptotic signal transduction via ERK/c-Jun pathways, leading to acantholysis. Our experimental data indicate that the EGFR is instrumental in transducing apoptotic/acantholytic signals in keratinocytes cultures in response to PV-IgG treatment. The acantholytic effect caused by PV-IgG binding to cell surface receptors begins with and depends on cell surface receptor (EGFR) activation of intracellular signaling pathways (ERK pathway) and apoptosis induction (FasR pathway), which later lead to major cell-cell separation (acantholysis) and cell death.

Apoptosis and immune response are responsible for the site-specific incidence of non-melanoma skin cancer

Generally, the cumulative UV exposure correlates with the site-specific incidence of skin cancer but more detailed analysis showed that the frequency of BCC of some facial regions cannot be explained with site-specific UV exposure. Apoptosis plays a central role in cancer development due to suppressed process of programmed cell death. Anatomic localization, UV and senescence can influence expression of apoptosis related molecules resulting in advantage of cancer cells development and tumor progression. Anti-tumor immune response, as an important factor in elimination of cancer cells, is also modified by UV radiation and aging, further contributing to cancer progression and its development.

HYPOTHESIS

UV radiation, senescence and proliferation intensity influence the expression of apoptosis related molecules in normal keratinocytes. Mutated cells express altered molecules with different degree of antigenicity. We propose that small differences in the expression of pro- and anti-apoptotic molecules in the keratinocytes in association with the local immune reaction (modulated also by UV radiation) determine the type of the non-melanoma skin cancer as well as their frequency (site-specific incidence). In vitro and in vivo models could explain how the modulation of UV can influence the apoptotic system and local immune reaction, while animal experiments could explain different site-specific incidence (frequency) of the same tumor. Better understanding of these mechanisms could lead to development of different therapeutic approaches for early elimination of cancer prone cells or cells in early stages of cancer development. The same model could be used to explain the site-specific localization of other types of cancer (i.e. melanoma) or benign tumors.

Novel mechanisms of target cell death and survival and of therapeutic action of IVIg in Pemphigus

Pemphigus vulgaris (PV) is a potentially lethal mucocutaneous blistering disease characterized by cell-cell detachment within the stratified epithelium (acantholysis) caused by IgG autoantibodies. Intravenous immunoglobulin (IVIg) therapy effectively treats PV, but the mechanism is not fully understood. To further understand acantholysis and the efficacy of IVIg, we measured effects of IgG fractions from PV patients on keratinocyte death processes. Using IgGs from representative PV patients who improved with IVIg, we identified apoptotic and oncotic signaling pathways in in vitro and in vivo PV models. We identified two groups of PV patients, each producing autoantibodies activating predominantly either apoptotic or oncotic cell death pathway. Experimental treatments with caspase 3 or calpain inhibitors demonstrated that PV IgGs induced acantholysis through both pathways. Upstream, the apoptotic signaling involved activation of caspases 8 and 3 and up-regulation of Fas ligand mRNA, whereas calpain-mediated cell death depended on elevated intracellular free Ca(2+). IVIg reduced PV IgG-mediated acantholysis and cell death and up-regulated the caspase inhibitor FLIP and the calpain inhibitor calpastatin. These results indicate that in different PV patients, IgG-induced acantholysis proceeds predominantly via distinct, yet complementary, pathways of programmed cell death differentially mediated by apoptosis and oncosis effectors, with IVIg protecting target cells by up-regulating endogenous caspase and calpain inhibitors.