The mechanism of detachment and death of keratinocytes in
pemphigus vulgaris (PV) involves pro-apoptotic action of constellations of
autoantibodies determining disease severity and response to treatment. The presence of
antibodies to
nicotinic acetylcholine receptors (nAChRs) and the therapeutic efficacy of
cholinomimetics in PV is well-established. Recently, adsorption of anti-mitochondrial
antibodies abolished the ability of PVIgGs to cause
acantholysis, demonstrating their pathophysiological significance. Since, in addition to cell membrane, nAChRs are also present on the mitochondrial outer membrane, wherein they act to prevent activation of intrinsic (mitochondrial apoptosis), we hypothesized that mitochondrial (mt)-nAChRs might be targeted by PVIgGs. To test this hypothesis, we employed the immunoprecipitation-western blot assay of keratinocyte
mitochondrial proteins that visualized the α3, α5, α7, α9, α10, β2 and β4 mt-nAChR subunits precipitated by PV IgGs, suggesting that functions of mt-nAChRs are compromised in PV. To pharmacologically counteract the pro-apoptotic action of anti-mitochondrial
antibodies in PV, we exposed naked keratinocyte mitochondria to PVIgGs in the presence of the
nicotinic agonist nicotine ± antagonists, and measured
cytochrome c (CytC) release.
Nicotine abolished PVIgG-dependent CytC release, showing a dose-dependent effect, suggesting that protection of mitochondria can be a novel mechanism of therapeutic action of
nicotinic agonists in PV. The obtained results indicated that the mt-nAChRs targeted by anti-mitochondrial
antibodies produced by PV patients are coupled to inhibition of CytC release, and that nicotinergic stimulation can abolish PVIgG-dependent activation of intrinsic apoptosis in KCs. Future studies should determine if and how the distinct anti-mt-nAChR
antibodies penetrate KCs and correlate with disease severity.