Serum and IgG isolated from patients with the autoimmune blistering disease pemphigus vulgaris (PV) trigger complex intracellular pathways in keratinocytes, including alterations of the cell cycle and metabolism, which ultimately lead to cell-cell detachment (acantholysis). We have shown previously that one of the earliest pathogenic events in PV is the activation of protein kinases, including the PKR-like endoplasmic reticulum (ER) kinase PERK.
In the present study we investigated in more detail the role of PERK in the pathogenesis of PV.
PERK levels were assessed by Western blotting and in-cell enzyme-linked immunosorbent assay, and PERK expression was silenced by siRNA technology. The effects of PV sera/IgG on keratinocyte cultures were investigated by flow cytometry, MTT and adhesion assays.
We show that PERK is activated in keratinocytes exposed to PV serum, as demonstrated by an increase in phosphorylated PERK levels and phosphorylation of eIF2α. Decreased expression of PERK by siRNA reduced the effects of PV serum on the cell cycle and keratinocyte viability, two key events in PV pathophysiology. As impairment of metabolic activity in PV is partially due to non-IgG serum factors, we then investigated the activation of PERK in keratinocytes incubated with whole PV serum, purified PV IgG and IgG-depleted PV serum. The data demonstrated that PV sera depleted of IgG, but not PV IgG, triggered PERK phosphorylation and this correlated with a marked reduction of metabolic activity in keratinocytes exposed to IgG-free serum. Knockdown of PERK by siRNA abrogated the changes in the cell cycle and apoptosis induced by IgG-depleted PV serum. Finally, the reduction of metabolic activity observed in keratinocytes exposed to IgG-depleted PV serum was almost absent in PERK-deficient cells.
Taken together, the results demonstrate that activation of PERK participates in the reduction of metabolic activity and cell viability seen in PV and that this phenomenon depends on non-IgG factors. PERK activation may represent a novel signalling mechanism linking ER stress and acantholysis in PV.
"These results may be important for PV because EGFRK activation was observed following treatment with PVIgG (Frusic-Zlotkin et al, 2006; Chernyavsky et al, 2007). The presence of activated proteolytic enzymes in PV sera (Grando, 1992) may also explain why IgG-depleted PV sera were found to be pathogenic in culture (Cirillo et al, 2007c; Lanza et al, 2011). The fact that specific cleavage of Dsg1 by staphylococcal exfoliative toxin in bullous impetigo is sufficient to cause a histologic phenotype comparable to PF (Amagai et al, 2000a; Hanakawa et al, 2002) indicates that, in principle, specific proteolysis could be an effective mechanism in pemphigus. "
[Show abstract][Hide abstract] ABSTRACT: Oral Diseases (2012) 18, 442–458
Pemphigus vulgaris (PV) is the most common type of pemphigus. PV pathogenesis is still debated, and treatment remains challenging. We investigated five controversial topics: (1) What are the target antigens in PV? (2) Do desmogleins adequately address PV pathophysiology? (3) How does acantholysis occur in PV? (4) Is PV still a lethal disease? (5) What is the role of rituximab (RTX) in PV treatment? Results from extensive literature searches suggested the following: (1) Target antigens of PV include a variety of molecules and receptors that are not physically compartmentalized within the epidermis. (2) PV is caused by a variety of autoantibodies to keratinocyte self-antigens, which concur to cause blistering by acting synergistically. (3) The concept of apoptolysis distinguishes the unique mechanism of autoantibody-induced keratinocyte damage in PV from other known forms of cell death. (4) PV remains potentially life-threatening largely because of treatment side effects, but it is uncertain which therapies carry the highest likelihood of lethal risk. (5) RTX is a very promising treatment option in patients with widespread recalcitrant or life-threatening PV. RTX’s cost is an issue, its long-term side effects are still unknown, and randomized controlled trials are needed to establish the optimal dosing regimen.
[Show abstract][Hide abstract] ABSTRACT: Introduction:
Desmoglein 3 (Dsg3) is one of desmosomal cadherins and functions in epidermal keratinocyte adhesion. IgG anti-Dsg3 autoantibodies are detected in pemphigus vulgaris, an autoimmune bullous disease showing blisters and erosions on the skin and oral mucosa. Other types of pemphigus also show anti-Dsg3 antibodies. Genetic disease of Dsg3 has not been reported.
Many in vitro and in vivo studies have indicated pathogenic role of anti-Dsg3 antibodies. Blisters in pemphigus vulgaris are thought to be developed by loss of keratinocyte adhesions by binding of anti-Dsg3 antibodies to Dsg3 through steric hindrance, internalization of Dsg3, changes in molecular integrity or signal transduction. There are pathogenic and nonpathogenic anti-Dsg3 antibodies reactive with different epitopes. Recent studies of pemphigus vulgaris include existence of non-Dsg3 autoantibodies, B cells and T cells reactive with Dsg3, involvement of TNF-α and IL-1 and activation of intracellular signaling.
Although systemic corticosteroids and immunosuppressive agents are mainstays for treatment of pemphigus, intravenous immunoglobulin, plasmapheresis, immunoadsorption, rituximab and TNF-α inhibitors are emerging. Anti-Dsg3 antibody-targeting therapies are reported in mouse model, but they are not yet available clinically. Clarification of pathogenic role of anti-Dsg3 antibodies in pemphigus should provide us with safer and more effective therapies.
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