Pemphigus vulgaris antibodies target the mitochondrial nicotinic acetylcholine receptors that protect keratinocytes from apoptolysis

Beyond the skin: B cells in pemphigus vulgaris, tolerance and treatment

Pemphigus vulgaris (PV) is a rare autoimmune bullous disease characterized by blistering of the skin and mucosa owing to the presence of autoantibodies against the desmosome proteins desmoglein 3 and occasionally in conjunction with desmoglein 1. Fundamental research into the pathogenesis of PV has revolutionized its treatment and outcome with rituximab, a B-cell-depleting therapy. The critical contribution of B cells to the pathogenesis of pemphigus is well accepted. However, the exact pathomechanism, mechanisms of onset, disease course and relapse remain unclear. In this narrative review, we provide an overview of the fundamental research progress that has unfolded over the past few centuries to give rise to current and emerging therapies. Furthermore, we summarize the multifaceted roles of B cells in PV, including their development, maturation and antibody activity. Finally, we explored how these various aspects of B-cell function contribute to disease pathogenesis and pave the way for innovative therapeutic interventions.

Multifaceted roles of mitochondria in wound healing and chronic wound pathogenesis

Mitochondria are intracellular organelles that play a critical role in numerous cellular processes including the regulation of metabolism, cellular stress response, and cell fate. Mitochondria themselves are subject to well-orchestrated regulation in order to maintain organelle and cellular homeostasis. Wound healing is a multifactorial process that involves the stringent regulation of several cell types and cellular processes. In the event of dysregulated wound healing, hard-to-heal chronic wounds form and can place a significant burden on healthcare systems. Importantly, treatment options remain limited owing to the multifactorial nature of chronic wound pathogenesis. One area that has received more attention in recent years is the role of mitochondria in wound healing. With regards to this, current literature has demonstrated an important role for mitochondria in several areas of wound healing and chronic wound pathogenesis including metabolism, apoptosis, and redox signalling. Additionally, the influence of mitochondrial dynamics and mitophagy has also been investigated. However, few studies have utilised patient tissue when studying mitochondria in wound healing, instead using various animal models. In this review we dissect the current knowledge of the role of mitochondria in wound healing and discuss how future research can potentially aid in the progression of wound healing research.

Contribution of the α5 nAChR Subunit and α5SNP to Nicotine-Induced Proliferation and Migration of Human Cancer Cells

Nicotine in tobacco is known to induce tumor-promoting effects and cause chemotherapy resistance through the activation of nicotinic acetylcholine receptors (nAChRs). Many studies have associated the α5 nicotinic receptor subunit (α5), and a specific polymorphism in this subunit, with (i) nicotine administration, (ii) nicotine dependence, and (iii) lung cancer. The α5 gene CHRNA5 mRNA is upregulated in several types of cancer, including lung, prostate, colorectal, and stomach cancer, and cancer severity is correlated with smoking. In this study, we investigate the contribution of α5 in the nicotine-induced cancer hallmark functions proliferation and migration, in breast, colon, and prostate cancer cells. Nine human cell lines from different origins were used to determine nAChR subunit expression levels. Then, selected breast (MCF7), colon (SW480), and prostate (DU145) cancer cell lines were used to investigate the nicotine-induced effects mediated by α5. Using pharmacological and siRNA-based experiments, we show that α5 is essential for nicotine-induced proliferation and migration. Additionally, upon downregulation of α5, nicotine-promoted expression of EMT markers and immune regulatory proteins was impaired. Moreover, the α5 polymorphism D398N (α5SNP) caused a basal increase in proliferation and migration in the DU145 cell line, and the effect was mediated through G-protein signaling. Taken together, our results indicate that nicotine-induced cancer cell proliferation and migration are mediated via α5, adding to the characterization of α5 as a putative therapeutical target.

Autoimmunity to Neuronal Nicotinic Acetylcholine Receptors

Nicotinic acetylcholine receptors (nAChRs) are widely expressed in many and diverse cell types, participating in various functions of cells, tissues and systems. In this review, we focus on the autoimmunity against neuronal nAChRs, the specific autoantibodies and their mechanisms of pathological action in selected autoimmune diseases. We summarize the current relevant knowledge from human diseases as well as from experimental models of autoimmune neurological disorders related to antibodies against neuronal nAChR subunits. Despite the well-studied high immunogenicity of the muscle nAChRs where autoantibodies are the main pathogen of myasthenia gravis, autoimmunity to neuronal nAChRs seems infrequent, except for the autoantibodies to the ganglionic receptor, the α3 subunit containing nAChR (α3-nAChR), which are detected and are likely pathogenic in Autoimmune Autonomic Ganglionopathy (AAG). We describe the detection, presence and function of these antibodies and especially the recent development of a cell-based assay (CBA) which, contrary to until recently available assays, is highly specific for AAG. Rare reports of autoantibodies to the other neuronal nAChR subtypes include a few cases of antibodies to α7 and/or α4β2 nAChRs in Rasmussen encephalitis, schizophrenia, autoimmune meningoencephalomyelitis, and in some myasthenia gravis patients with concurrent CNS symptoms. Neuronal-type nAChRs are also present in several non-excitable tissues, however the presence and possible role of antibodies against them needs further verification. It is likely that the future development of more sensitive and disease-specific assays would reveal that neuronal nAChR autoantibodies are much more frequent and may explain the mechanisms of some seronegative autoimmune diseases.

The Role of Non-Neuronal Acetylcholine in the Autoimmune Blistering Disease Pemphigus Vulgaris

The importance of acetylcholine (ACh) in keratinocyte adhesion and acantholysis has been investigated over the last three decades, particularly in the pathophysiology of autoimmune blistering dermatoses. Pemphigus vulgaris (PV) is an autoimmune blistering skin disease where autoantibody-mediated suprabasilar intraepidermal splitting causes flaccid blisters and non-healing erosions of the oral mucosa and sometimes also of the skin. Historically, acantholysis in PV was thought to be driven by anti-desmoglein (Dsg) antibodies. Herein, we describe the role of autoantibodies against keratinocyte muscarinic and nicotinic acetylcholine receptors, as well as the annexin-like molecule pemphaxin that also binds ACh, in the immunopathogenesis of PV. The identification of targets in this disease is important, as they may lead to novel diagnostic and therapeutic options in the future for this potentially deadly disease.

Mitochondrial Autoantibodies and the Role of Apoptosis in Pemphigus Vulgaris

Pemphigus vulgaris (PV) is an IgG autoantibody-mediated, potentially fatal mucocutaneous disease manifested by progressive non-healing erosions and blisters. Beyond acting to inhibit adhesion molecules, PVIgGs elicit a unique process of programmed cell death and detachment of epidermal keratinocytes termed apoptolysis. Mitochondrial damage by antimitochondrial antibodies (AMA) has proven to be a critical link in this process. AMA act synergistically with other autoantibodies in the pathogenesis of PV. Importantly, absorption of AMA inhibits the ability of PVIgGs to induce blisters. Pharmacologic agents that protect mitochondrial function offer a new targeted approach to treating this severe immunoblistering disease.

Chronic exposure to the anti-M3 muscarinic acetylcholine receptor autoantibody in pemphigus vulgaris contributes to disease pathophysiology

Pemphigus vulgaris (PV) is a potentially lethal autoimmune mucocutaneous blistering disease characterized by binding of IgG autoantibodies (AuAbs) to keratinocytes (KCs). In addition to AuAbs against adhesion molecules desmogleins 1 and 3, PV patients also produce an AuAb against the M3 muscarinic acetylcholine (ACh) receptor (M3AR) that plays an important role in regulation of vital functions of KCs upon binding endogenous ACh. This anti-M3AR AuAb is pathogenic because its adsorption eliminates the acantholytic activity of PV IgG; however, the molecular mechanism of its action is unclear. In the present study, we sought to elucidate the mode of immunopharmacologic action of the anti-M3AR AuAb in PV. Short-term exposures of cultured KCs to PV IgG or the muscarinic agonist muscarine both induced changes in the expression of keratins 5 and 10, consistent with the inhibition of proliferation and upregulated differentiation and in keeping with the biological function of M3AR. In contrast, long-term incubations induced a keratin expression pattern consistent with upregulated proliferation and decreased differentiation, in keeping with the hyperproliferative state of KCs in PV. This change could result from desensitization of the M3AR, representing the net antagonist-like effect of the AuAb. Therefore, chronic exposure of KCs to the anti-M3AR AuAb interrupts the physiological regulation of KCs by endogenous ACh, contributing to the onset of acantholysis. Since cholinergic agents have already demonstrated antiacantholytic activity in a mouse model of PV and in PV patients, our results have translational significance and can guide future development of therapies for PV patients employing cholinergic drugs.

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.

Autoimmune Pemphigus: Latest Advances and Emerging Therapies

Pemphigus represents a group of rare and severe autoimmune intra-epidermal blistering diseases affecting the skin and mucous membranes. These painful and debilitating diseases are driven by the production of autoantibodies that are mainly directed against the desmosomal adhesion proteins, desmoglein 3 (Dsg3) and desmoglein 1 (Dsg1). The search to define underlying triggers for anti-Dsg-antibody production has revealed genetic, environmental, and possible vaccine-driven factors, but our knowledge of the processes underlying disease initiation and pathology remains incomplete. Recent studies point to an important role of T cells in supporting auto-antibody production; yet the involvement of the myeloid compartment remains unexplored. Clinical management of pemphigus is beginning to move away from broad-spectrum immunosuppression and towards B-cell-targeted therapies, which reduce many patients’ symptoms but can have significant side effects. Here, we review the latest developments in our understanding of the predisposing factors/conditions of pemphigus, the underlying pathogenic mechanisms, and new and emerging therapies to treat these devastating diseases.

Nicotinic Acetylcholine Receptors in the Respiratory Tract

Nicotinic acetylcholine receptors (nAChR) are widely distributed in neuronal and non-neuronal tissues, where they play diverse physiological roles. In this review, we highlight the recent findings regarding the role of nAChR in the respiratory tract with a special focus on the involvement of nAChR in the regulation of multiple processes in health and disease. We discuss the role of nAChR in mucociliary clearance, inflammation, and infection and in airway diseases such as asthma, chronic obstructive pulmonary disease, and cancer. The subtype diversity of nAChR enables differential regulation, making them a suitable pharmaceutical target in many diseases. The stimulation of the α3β4 nAChR could be beneficial in diseases accompanied by impaired mucociliary clearance, and the anti-inflammatory effect due to an α7 nAChR stimulation could alleviate symptoms in diseases with chronic inflammation such as chronic obstructive pulmonary disease and asthma, while the inhibition of the α5 nAChR could potentially be applied in non-small cell lung cancer treatment. However, while clinical studies targeting nAChR in the airways are still lacking, we suggest that more detailed research into this topic and possible pharmaceutical applications could represent a valuable tool to alleviate the symptoms of diverse airway diseases.

Nicotinic acetylcholine receptors in chemotherapeutic drugs resistance: An emerging targeting candidate

There is no definitive cure for cancer, and most of the current chemotherapy drugs have limited effects due to the development of drug resistance and toxicity at high doses. Therefore, there is an ongoing need for identifying the causes of chemotherapeutic resistance, and it will be possible to develop innovative treatment approaches based on these novel targeting candidates. Cigarette smoking is known to be one of the main causes of resistance to chemotherapeutic agents. Nicotine as a component of cigarette smoke is an exogenous activator of nicotinic acetylcholine receptors (nAChRs). It can inhibit apoptosis, increase cell proliferation and cell survival, reducing the cytotoxic effects of chemotherapy drugs and cause a reduced therapeutic response. Recent studies have demonstrated that nAChRs and their downstream signaling pathways have considerable implications in different cancer's initiation, progression, and chemoresistance. In some previous studies, nAChRs have been targeted to obtain better efficacies for chemotherapeutics. Besides, nAChRs-based therapies have been used in combination with chemotherapy drugs to reduce the side effects. This strategy requires lower doses of chemotherapy drugs compared to the conditions that must be used alone. Here, we discussed the experimental and clinical studies that show the nAChRs involvement in response to chemotherapy agents. Also, controversies relating to the effects of nAChR on chemotherapy-induced apoptosis are in our focus in this review article. Delineating the complex influences of nAChRs would be of great interest in establishing new effective chemotherapy regimens.

Correlation of anti-γ/ε nicotinic acetylcholine receptor antibody levels with anti-desmoglein 1,3 antibody levels and disease severity in pemphigus vulgaris

BACKGROUND

A role for nondesmoglein antigens in the pathogenesis of pemphigus vulgaris (PV) has been suggested in several studies. Acetylcholine receptors (AchR), are one of the most important groups of these antigens. However, the exact role of both antimuscarinic (m) and nicotinic (n) AchR antibodies (Abs) is still controversial.

AIM

To evaluate anti-desmoglein (Dsg)1, Dsg 3 and anti-γ/ε nAchR Abs values in patients with PV before and 3 months after rituximab (RTX) treatment, and to assess their correlation with disease severity.

METHODS

In total, 75 patients with PV (26 men, 49 women) who were planned to receive RTX were enrolled. Disease activity was assessed by using the Pemphigus Disease Area Index (PDAI). Using ELISA, anti-Dsg1,3 and anti-γ/ε nAchR Abs were determined at baseline and 3 months after RTX treatment.

RESULTS

At baseline, 53.33% patients had positive values for anti-Dsg1, 89.33% for anti-Dsg3 and 13.33% for anti-γ/ε nAchR Abs. All patients with positive anti-γ/ε nAchR Abs had the mucocutaneous phenotype. PDAI, anti-Dsg1,3 and anti-γ/ε nAchR values were dramatically decreased 3 months after RTX infusion (P < 0.001). There was a significant positive correlation between disease activity and anti-γ/ε nAchR values at baseline (P = 0.04), whereas no significant correlation was observed between anti-Dsg1,3 and anti-γ/ε nAchR values at baseline and 3 months after RTX infusion.

CONCLUSION

The reduction in anti-γ/ε nAchR Abs with clinical improvement in this study may suggest a synergic role for anti-γ/ε nAchR Abs with anti-Dsg1,3 Abs, or it could be an epiphenomenon.

Intraepithelial autoimmune bullous dermatoses disease activity assessment and therapy

Intraepithelial autoimmune blistering dermatoses are a rare group of skin disorders characterized by disruptions of inter-keratinocyte connections within the epidermis through the action of autoantibodies. The second article in this continuing medical education series presents validated disease activity scoring systems, serologic parameters of disease, treatments, and clinical trials for pemphigus and its subtypes.

Mechanisms of Trx2/ASK1-Mediated Mitochondrial Injury in Pemphigus Vulgaris

Objective

Apoptotic events mediated by mitochondrial injury play an important role on the onset of Pemphigus vulgaris (PV). The thioredoxin-2 (Trx2)/apoptosis signal-regulating kinase 1 (ASK1) signaling pathway is considered a key cascade involved on the regulation of mitochondrial injury. Hence, we have investigated the regulatory mechanism of the Trx2/ASK1 signaling in PV-induced mitochondrial injury.

Methods

Serum and tissue samples were collected from clinical PV patients to detect the oxidative stress factors, cell apoptosis, and expression of members from Trx2/ASK1 signaling. HaCaT cells were cultured with the serum of PV patients and transfected with Trx2 overexpression or silencing vector. Changes in the levels of reactive oxygen species (ROS), mitochondrial membrane potential (△ψm), and apoptosis were further evaluated. A PV mouse model was established and administered with Trx2-overexpressing plasmid. The effect of ectopic Trx2 expression towards acantholysis in PV mice was observed.

Results

A series of cellular and molecular effects, including (i) increased levels of oxidative stress products, (ii) destruction of epithelial cells in the skin tissues, (iii) induction of apoptosis in keratinocytes, (iv) reduction of Trx2 protein levels, and (v) enhanced phosphorylation of ASK1, were detected in PV patients. In vitro experiments confirmed that Trx2 can inhibit ASK1 phosphorylation, alleviate ROS release, decrease △ψm, and lower the apoptotic rate. Injection of Trx2-overexpressing vectors in vivo could also relieve acantholysis and blister formation in PV mice.

Conclusion

The Trx2/ASK1 signaling pathway regulates the incidence of PV mediated by mitochondrial injury.

Correlation of IgG autoantibodies against acetylcholine receptors and desmogleins in patients with pemphigus treated with steroid sparing agents or rituximab

Introduction

Autoantibodies (autoAbs) against desmoglein-1 (DSG1) and desmoglein-3 (DSG3) have conventionally been studied and well accepted in the pathogenesis of pemphigus vulgaris (PV) and foliaceus (PF). Recent studies have suggested that non-DSG autoAbs may contribute to the pathogenesis of pemphigus, including autoAbs directed at acetylcholine receptors (AChR) and thyroid peroxidase (TPO). The purpose of this study is to retrospectively analyze PV and PF patient sera to better understand the relationship between anti-AChR and -TPO Abs to disease activity and DSG reactivity between patients treated with prednisone and steroid sparing agents (SSA; n = 22) or prednisone and rituximab (n = 21).

Methods

Patients were evaluated at 2 time points, T1 and T2, for disease activity using the Pemphigus Disease Area Index (PDAI), and sera were tested for the presence of TPO, DSG1, DSG3, muscarinic (M3) and nicotinic (n) AChR IgG autoAbs, as well as antibodies against Varicella Zoster Virus (VZV) by ELISA.

Results

Disease activity significantly decreased in patients from T1 to T2 (p < .0001). A significant difference was seen in IgG anti-DSG1 (p < .0001) and anti-DSG3 (p = .0049) levels when T1 was compared to T2 in both treatment groups. A significant increase was found between pemphigus patients and normal subjects with nAChR (p < .0001) at T1 but not with m3AChR, TPO or VZV Abs. No significant difference was seen between T1 and T2 values in patients with pemphigus for the non–desmoglein Abs TPO (p = .7559), M3AChR (p = .9003), nAChR (p = .5143) or VZV (p = .2454). These findings demonstrate that although an increase in IgG anti-nAChR autoAbs was found in PV and PF subjects, these Abs did not decrease with treatment. No other non-DSG Abs were increased or significantly changed over time in patients with pemphigus. This suggests that anti -AChR and -TPO Abs may not play a direct role in the pathogenesis of most patients with pemphigus, but does not rule out a role for non-DSG auto antibodies in distinct subsets of pemphigus patient.

Proton pump inhibitors act with unprecedented potencies as inhibitors of the acetylcholine biosynthesizing enzyme-A plausible missing link for their association with incidence of dementia

INTRODUCTION

Several pharmacoepidemiological studies indicate that proton pump inhibitors (PPIs) significantly increase the risk of dementia. Yet, the underlying mechanism is not known. Here, we report the discovery of an unprecedented mode of action of PPIs that explains how PPIs may increase the risk of dementia.

METHODS

Advanced in silico docking analyses and detailed enzymological assessments were performed on PPIs against the core-cholinergic enzyme, choline-acetyltransferase (ChAT), responsible for biosynthesis of acetylcholine (ACh).

RESULTS

This report shows compelling evidence that PPIs act as inhibitors of ChAT, with high selectivity and unprecedented potencies that lie far below their in vivo plasma and brain concentrations.

DISCUSSION

Given that accumulating evidence points at cholinergic dysfunction as a driving force of major dementia disorders, our findings mechanistically explain how prolonged use of PPIs may increase incidence of dementia. This call for restrictions for prolonged use of PPIs in elderly, and in patients with dementia or amyotrophic lateral sclerosis.

Rationale for including intravenous immunoglobulin in the multidrug protocol of curative treatment of pemphigus vulgaris and development of an assay predicting disease relapse

Analysis of reported outcomes of treatment of pemphigus vulgaris (PV) patients demonstrated that the multidrug approach offers a lower relapse rate compared to the FDA-approved prednisone/rituximab regimen. The multidrug protocol protects keratinocytes from autoantibody attack by systemic corticosteroids and mitochondrion-protecting drugs, selectively eliminates pathogenic autoantibodies by intravenous immunoglobulin (IVIg) and inhibits autoantibody production by cytotoxic immunosuppressors. Therefore, IVIg should be always added to the prednisone/rituximab regimen that does not eliminate circulating autoantibodies. To decrease risk for relapse to a minimum, PV should be maintained in full clinical remission until the critical mass of autoreactive plasma cells dies off. The two major factors that determine patient's risk for a relapse are the composition of the pool of pathogenic autoantibodies and the innate abilities of keratinocytes to sustain an autoantibody attack. As it is currently impossible to evaluate the risk for a relapse, development of a biomarker assay that could do so would be helpful in a long-term management of PV patients. We compared the magnitude of cytochrome c (CytC) release in keratinocytes by serum from PV patients in acute disease stage vs. remission and identified very strong positive correlation with disease severity. PV patients whose serum contained autoantibodies requiring higher amounts of normal IgG to neutralize their ability to release CytC were found to be at a higher risk for disease relapse. However, lack of very strong statistical correlation suggested that CytC is not an ideal biomarker to predict disease relapse, which should prompt a search for alternative candidates.

Nicotinic-nAChR signaling mediates drug resistance in lung cancer

Lung cancer is the leading cause of cancer death worldwide. Cigarette smoking is the most common risk factor for lung carcinoma; other risks include genetic factors and exposure to radon gas, asbestos, secondhand smoke, and air pollution. Nicotine, the primary addictive constituent of cigarettes, contributes to cancer progression through activation of nicotinic acetylcholine receptors (nAChRs), which are membrane ligand-gated ion channels. Activation of nicotine/nAChR signaling is associated with lung cancer risk and drug resistance. We focused on nAChR pathways activated by nicotine and its downstream signaling involved in regulating apoptotic factors of mitochondria and drug resistance in lung cancer. Increasing evidence suggests that several sirtuins play a critical role in multiple aspects of cancer drug resistance. Thus, understanding the consequences of crosstalk between nicotine/nAChRs and sirtuin signaling pathways in the regulation of drug resistance could be a critical implication for cancer therapy.

ST18 Enhances PV-IgG-Induced Loss of Keratinocyte Cohesion in Parallel to Increased ERK Activation

Pemphigus is an autoimmune blistering disease targeting the desmosomal proteins desmoglein (Dsg) 1 and Dsg3. Recently, a genetic variant of the Suppression of tumorigenicity 18 (ST18) promoter was reported to cause ST18 up-regulation, associated with pemphigus vulgaris (PV)-IgG-mediated increase in cytokine secretion and more prominent loss of keratinocyte cohesion. Here we tested the effects of PV-IgG and the pathogenic pemphigus mouse anti-Dsg3 antibody AK23 on cytokine secretion and ERK activity in human keratinocytes dependent on ST18 expression. Without ST18 overexpression, both PV-IgG and AK23 induced loss of keratinocyte cohesion which was accompanied by prominent fragmentation of Dsg3 immunostaining along cell borders. In contrast, release of pro-inflammatory cytokines such as IL-1α, IL-6, TNFα, and IFN-γ was not altered significantly in both HaCaT and primary NHEK cells. These experiments indicate that cytokine expression is not strictly required for loss of keratinocyte cohesion. Upon ST18 overexpression, fragmentation of cell monolayers increased significantly in response to autoantibody incubation. Furthermore, production of IL-1α and IL-6 was enhanced in some experiments but not in others whereas release of TNF-α dropped significantly upon PV-IgG application in both EV- and ST18-transfected HaCaT cells. Additionally, in NHEK, application of PV-IgG but not of AK23 significantly increased ERK activity. In contrast, ST18 overexpression in HaCaT cells augmented ERK activation in response to both c-IgG and AK23 but not PV-IgG. Because inhibition of ERK by U0126 abolished PV-IgG- and AK23-induced loss of cell cohesion in ST18-expressing cells, we conclude that autoantibody-induced ERK activation was relevant in this scenario. In summary, similar to the situation in PV patients carrying ST18 polymorphism, overexpression of ST18 enhanced keratinocyte susceptibility to autoantibody-induced loss of cell adhesion, which may be caused in part by enhanced ERK signaling.

Increased Active OMI/HTRA2 Serine Protease Displays a Positive Correlation with Cholinergic Alterations in the Alzheimer's Disease Brain

OMI/HTRA2 (high-temperature requirement serine protease A2) is a mitochondrial serine protease involved in several cellular processes, including autophagy, chaperone activity, and apoptosis. Few studies on the role of OMI/HTRA2 in Alzheimer's disease (AD) are available, but none on its relationship with the cholinergic system and neurotrophic factors as well as other AD-related proteins. In this study, immunohistochemical analyses revealed that AD patients had a higher cytosolic distribution of OMI/HTRA2 protein compared to controls. Quantitative analyses on brain extracts indicated a significant increase in the active form of OMI/HTRA2 in the AD brain. Activated OMI/HTRA2 protein positively correlated with stress-associated read-through acetylcholinesterase activity. In addition, α7 nicotinic acetylcholine receptor gene expression, a receptor also known to be localized on the outer membrane of mitochondria, showed a strong correlation with OMI/HTRA2 gene expression in three different brain regions. Interestingly, the activated OMI/HTRA2 levels also correlated with the activity of the acetylcholine-biosynthesizing enzyme, choline acetyltransferase (ChAT); with levels of the neurotrophic factors, NGF and BDNF; with levels of the soluble fragments of amyloid precursor protein (APP); and with gene expression of the microtubule-associated protein tau in the examined brain regions. Overall, the results demonstrate increased levels of the mitochondrial serine protease OMI/HTRA2, and a coherent pattern of association between the activated form of OMI/HTRA2 and several key proteins involved in AD pathology. In this paper, we propose a new hypothetical model to highlight the importance and needs of further investigation on the role of OMI/HTRA2 in the mitochondrial function and AD.

The Evolving Story of Autoantibodies in Pemphigus Vulgaris: Development of the "Super Compensation Hypothesis"

Emerging data and innovative technologies are re-shaping our understanding of the scope and specificity of the autoimmune response in Pemphigus vulgaris (PV), a prototypical humorally mediated autoimmune skin blistering disorder. Seminal studies identified the desmosomal proteins Desmoglein 3 and 1 (Dsg3 and Dsg1), cadherin family proteins which function to maintain cell adhesion, as the primary targets of pathogenic autoAbs. Consequently, pathogenesis in PV has primarily considered to be the result of anti-Dsg autoAbs alone. However, accumulating data suggesting that anti-Dsg autoAbs by themselves cannot adequately explain the loss of cell-cell adhesion seen in PV, nor account for the disease heterogeneity exhibited across PV patients has spurred the notion that additional autoAb specificities may contribute to disease. To investigate the role of non-Dsg autoAbs in PV, an increasing number of studies have attempted to characterize additional targets of PV autoAbs. The recent advent of protein microarray technology, which allows for the rapid, highly sensitive, and multiplexed assessment of autoAb specificity has facilitated the comprehensive classification of the scope and specificity of the autoAb response in PV. Such detailed deconstruction of the autoimmune response in PV, beyond simply tracking anti-Dsg autoAbs, has provided invaluable new insights concerning disease mechanisms and enhanced disease classification which could directly translate into superior tools for prognostics and clinical management, as well as the development of novel, disease specific treatments.

Non-Desmoglein Antibodies in Patients With Pemphigus Vulgaris

Pemphigus vulgaris (PV) is a potentially life-threatening mucocutaneous autoimmune blistering disease. Patients develop non-healing erosions and blisters due to cell–cell detachment of keratinocytes (acantholysis), with subsequent suprabasal intraepidermal splitting. Identified almost 30 years ago, desmoglein-3 (Dsg3), a Ca²⁺-dependent cell adhesion molecule belonging to the cadherin family, has been considered the “primary” autoantigen in PV. Proteomic studies have identified numerous autoantibodies in patients with PV that have known roles in the physiology and cell adhesion of keratinocytes. Antibodies to these autoantibodies include desmocollins 1 and 3, several muscarinic and nicotinic acetylcholine receptor subtypes, mitochondrial proteins, human leukocyte antigen molecules, thyroid peroxidase, and hSPCA1—the Ca²⁺/Mn²⁺-ATPase encoded by ATP2C1, which is mutated in Hailey–Hailey disease. Several studies have identified direct pathogenic roles of these proteins, or synergistic roles when combined with Dsg3. We review the role of these direct and indirect mechanisms of non-desmoglein autoantibodies in the pathogenesis of PV.

Molecular Determinants Conferring the Stoichiometric-Dependent Activity of α-Conotoxins at the Human α9α10 Nicotinic Acetylcholine Receptor Subtype

α9α10 nicotinic acetylcholine receptors (nAChRs) putatively exist at different stoichiometries. We systematically investigated the molecular determinants of α-conotoxins Vc1.1, RgIA#, and PeIA inhibition at hypothetical stoichiometries of the human α9α10 nAChR. Our results suggest that only Vc1.1 exhibits stoichiometric-dependent inhibition at the α9α10 nAChR. The hydrogen bond between N154 of α9 and D11 of Vc1.1 at the α9(+)-α9(-) interface is responsible for the stoichiometric-dependent potency of Vc1.1.

Autoantibody Signaling in Pemphigus Vulgaris: Development of an Integrated Model

Pemphigus vulgaris (PV) is an autoimmune skin blistering disease effecting both cutaneous and mucosal epithelia. Blister formation in PV is known to result from the binding of autoantibodies (autoAbs) to keratinocyte antigens. The primary antigenic targets of pathogenic autoAbs are known to be desmoglein 3, and to a lesser extent, desmoglein 1, cadherin family proteins that partially comprise the desmosome, a protein structure responsible for maintaining cell adhesion, although additional autoAbs, whose role in blister formation is still unclear, are also known to be present in PV patients. Nevertheless, there remain large gaps in knowledge concerning the precise mechanisms through which autoAb binding induces blister formation. Consequently, the primary therapeutic interventions for PV focus on systemic immunosuppression, whose side effects represent a significant health risk to patients. In an effort to identify novel, disease-specific therapeutic targets, a multitude of studies attempting to elucidate the pathogenic mechanisms downstream of autoAb binding, have led to significant advancements in the understanding of autoAb-mediated blister formation. Despite this enhanced characterization of disease processes, a satisfactory explanation of autoAb-induced acantholysis still does not exist. Here, we carefully review the literature investigating the pathogenic disease mechanisms in PV and, taking into account the full scope of results from these studies, provide a novel, comprehensive theory of blister formation in PV.

Monopathogenic vs multipathogenic explanations of pemphigus pathophysiology

This viewpoint highlights major, partly controversial concepts about the pathogenesis of pemphigus. The monopathogenic theory explains intra-epidermal blistering through the "desmoglein (Dsg) compensation" hypothesis, according to which an antibody-dependent disabling of Dsg 1- and/or Dsg 3-mediated cell-cell attachments of keratinocytes (KCs) is sufficient to disrupt epidermal integrity and cause blistering. The multipathogenic theory explains intra-epidermal blistering through the "multiple hit" hypothesis stating that a simultaneous and synchronized inactivation of the physiological mechanisms regulating and/or mediating intercellular adhesion of KCs is necessary to disrupt epidermal integrity. The major premise for a multipathogenic theory is that a single type of autoantibody induces only reversible changes, so that affected KCs can recover due to a self-repair. The damage, however, becomes irreversible when the salvage pathway and/or other cell functions are altered by a partnering autoantibody and/or other pathogenic factors. Future studies are needed to (i) corroborate these findings, (ii) characterize in detail patient populations with non-Dsg-specific autoantibodies, and (iii) determine the extent of the contribution of non-Dsg antibodies in disease pathophysiology.

DMSO: A Mixed-Competitive Inhibitor of Human Acetylcholinesterase

Dimethyl sulfoxide (DMSO) is the most common organic solvent used in biochemical and cellular assays during drug discovery programs. Despite its wide use, the effect of DMSO on several enzyme classes, which are crucial targets of the new therapeutic agents, are still unexplored. Here, we report the detailed biochemical analysis of the effects of DMSO on the human acetylcholine-degrading enzyme, acetylcholinesterase (AChE), the primary target of current Alzheimer's therapeutics. Our analysis showed that DMSO is a considerably potent and highly selective irreversible mixed-competitive inhibitor of human AChE with IC₅₀ values in the lower millimolar range, corresponding to 0.88% to 2.6% DMSO (v/v). Most importantly, 1-4% (v/v) DMSO, the commonly used experimental concentrations, showed ∼37-80% inhibition of human AChE activity. We believe that our results will assist in developing stringent protocols and help in the better interpretation of experimental outcomes during screening and biological evaluation of new drugs.

Nicotinic Acetylcholine Receptor α9 and α10 Subunits Are Expressed in the Brain of Mice

The α9 and α10 nicotinic acetylcholine receptor (nAChR) subunits are likely to be the evolutionary precursors to the entire cys-loop superfamily of ligand-gated ion channels, which includes acetylcholine, GABA, glycine and serotonin ionotropic receptors. nAChRs containing α9 and α10 subunits are found in the inner ear, dorsal root ganglia and many non-excitable tissues, but their expression in the central nervous system has not been definitely demonstrated. Here we show the presence of both α9 and α10 nAChR subunits in the mouse brain by RT-PCR and immunochemical approaches with a range of nAChR subunit-selective antibodies, which selectivity was demonstrated in the brain preparations of α7−/−, α9−/− and α10−/− mice. The α9 and α10 RNA transcripts were found in medulla oblongata (MO), cerebellum, midbrain (MB), thalamus and putamen (TP), somatosensory cortex (SC), frontal cortex (FC) and hippocampus. High α9-selective signal in ELISA was observed in the FC, SC, MO, TP and hippocampus and α10-selective signal was the highest in MO and FC. The α9 and α10 proteins were found in the brain mitochondria, while their presence on the plasma membrane has not been definitely confirmed The α7-, α9- and α10-selective antibodies stained mainly neurons and hypertrophied astrocytes, but not microglia. The α9- and α10-positive cells formed ordered structures or zones in cerebellum and superior olive (SO) and were randomly distributed among α7-positive cells in the FC; they were found in CA1, CA3 and CA4, but not in CA2 region of the hippocampus. The α9 and α10 subunits were up-regulated in α7−/− mice and both α7 and α9 subunits were down-regulated in α10−/− mice. We conclude that α9 and α10 nAChR subunits are expressed in distinct neurons of the mouse brain and in the brain mitochondria and are compensatory up-regulated in the absence of α7 subunits.

Molecular Mechanisms Regulating LPS-Induced Inflammation in the Brain

Neuro-inflammation, one of the pathogenic causes of neurodegenerative diseases, is regulated through the cholinergic anti-inflammatory pathway via the α7 nicotinic acetylcholine receptor (α7 nAChR). We previously showed that either bacterial lipopolysaccharide (LPS) or immunization with the α7(1-208) nAChR fragment decrease α7 nAChRs density in the mouse brain, exacerbating chronic inflammation, beta-amyloid accumulation and episodic memory decline, which mimic the early stages of Alzheimer's disease (AD). To study the molecular mechanisms underlying the LPS and antibody effects in the brain, we employed an in vivo model of acute LPS-induced inflammation and an in vitro model of cultured glioblastoma U373 cells. Here, we report that LPS challenge decreased the levels of α7 nAChR RNA and protein and of acetylcholinesterase (AChE) RNA and activity in distinct mouse brain regions, sensitized brain mitochondria to the apoptogenic effect of Ca(2+) and modified brain microRNA profiles, including the cholinergic-regulatory CholinomiRs-132/212, in favor of anti-inflammatory and pro-apoptotic ones. Adding α7(1-208)-specific antibodies to the LPS challenge prevented elevation of both the anti-inflammatory and pro-apoptotic miRNAs while supporting the resistance of brain mitochondria to Ca(2+) and maintaining α7 nAChR/AChE decreases. In U373 cells, α7-specific antibodies and LPS both stimulated interleukin-6 production through the p38/Src-dependent pathway. Our findings demonstrate that acute LPS-induced inflammation induces the cholinergic anti-inflammatory pathway in the brain, that α7 nAChR down-regulation limits this pathway, and that α7-specific antibodies aggravate neuroinflammation by inducing the pro-inflammatory interleukin-6 and dampening anti-inflammatory miRNAs; however, these antibodies may protect brain mitochondria and decrease the levels of pro-apoptotic miRNAs, preventing LPS-induced neurodegeneration.

Recent progress in revealing the biological and medical significance of the non-neuronal cholinergic system

This special issue of International Immunopharmacology is the proceedings of the Fourth International Symposium on Non-neuronal Acetylcholine that was held on August 28-30, 2014 at the Justus Liebig University of Giessen in Germany. It contains original contributions of meeting participants covering the significant progress in understanding of the biological and medical significance of the non-neuronal cholinergic system extending from exciting insights into molecular mechanisms regulating this system via miRNAs over the discovery of novel cholinergic cellular signaling circuitries to clinical implications in cancer, wound healing, immunity and inflammation, cardiovascular, respiratory and other diseases.

Critical Role of the Neonatal Fc Receptor (FcRn) in the Pathogenic Action of Antimitochondrial Autoantibodies Synergizing with Anti-desmoglein Autoantibodies in Pemphigus Vulgaris

Pemphigus vulgaris (PV) is a life-long, potentially fatal IgG autoantibody-mediated blistering disease targeting mucocutaneous keratinocytes (KCs). PV patients develop pathogenic anti-desmoglein (Dsg) 3 ± 1 and antimitochondrial antibodies (AMA), but it remained unknown whether and how AMA enter KCs and why other cell types are not affected in PV. Therefore, we sought to elucidate mechanisms of cell entry, trafficking, and pathogenic action of AMA in PV. We found that PVIgGs associated with neonatal Fc receptor (FcRn) on the cell membrane, and the PVIgG-FcRn complexes entered KCs and reached mitochondria where they dissociated. The liberated AMA altered mitochondrial membrane potential, respiration, and ATP production and induced cytochrome c release, although the lack or inactivation of FcRn abolished the ability of PVIgG to reach and damage mitochondria and to cause detachment of KCs. The assays of mitochondrial functions and keratinocyte adhesion demonstrated that although the pathobiological effects of AMA on KCs are reversible, they become irreversible, leading to epidermal blistering (acantholysis), when AMA synergize with anti-Dsg antibodies. Thus, it appears that AMA enter a keratinocyte in a complex with FcRn, become liberated from the endosome in the cytosol, and are trafficked to the mitochondria, wherein they trigger pro-apoptotic events leading to shrinkage of basal KCs uniquely expressing FcRn in epidermis. During recovery, KCs extend their cytoplasmic aprons toward neighboring cells, but anti-Dsg antibodies prevent assembly of nascent desmosomes due to steric hindrance, thus rendering acantholysis irreversible. In conclusion, FcRn is a common acceptor protein for internalization of AMA and, perhaps, for PV autoantibodies to other intracellular antigens, and PV is a novel disease paradigm for investigating and elucidating the role of FcRn in this autoimmune disease and possibly other autoimmune diseases.