Autoantibodies to Endothelial Cell Surface ATP Synthase, the Endogenous Receptor for Hsp60, Might Play a Pathogenic Role in Vasculatides

Abstract

BackgroundHeat shock protein (hsp) 60 that provides “danger signal” binds to the surface of resting endothelial cells (EC) but its receptor has not yet been characterized. In mitochondria, hsp60 specifically associates with adenosine triphosphate (ATP) synthase. We therefore examined the possible interaction between hsp60 and ATP synthase on EC surface.Methodology/Principal FindingsUsing Far Western blot approach, co-immunoprecipitation studies and surface plasmon resonance analyses, we demonstrated that hsp60 binds to the β-subunit of ATP synthase. As a cell surface-expressed molecule, ATP synthase is potentially targeted by anti-EC-antibodies (AECAs) found in the sera of patients suffering vasculitides. Based on enzyme-linked immunosorbent assay and Western blotting techniques with F1-ATP synthase as substrate, we established the presence of anti-ATP synthase antibodies at higher frequency in patients with primary vasculitides (group I) compared with secondary vasculitides (group II). Anti-ATP synthase reactivity from group I patients was restricted to the β-subunit of ATP synthase, whereas those from group II was directed to the α-, β- and γ-subunits. Cell surface ATP synthase regulates intracellular pH (pHi). In low extracellular pH medium, we detected abnormal decreased of EC pHi in the presence of anti-ATP synthase antibodies, irrespective of their fine reactivities. Interestingly, soluble hsp60 abrogated the anti-ATP synthase-induced pHi down-regulation.Conclusions/SignificanceOur results indicate that ATP synthase is targeted by AECAs on the surface of EC that induce intracellular acidification. Such pathogenic effect in vasculitides can be modulated by hsp60 binding on ATP synthase which preserves ATP synthase activity.

Bovine neonatal pancytopenia - Comparative proteomic characterization of two BVD vaccines and the producer cell surface proteome (MDBK)

“…myasthenia gravis [39]. ATP synthase (Table 1, proteins 17 and 18 and Table 2, proteins 10 and 17) catalyzes ATP from ADP at the mitochondrial membrane and is present on surface of various cells, including endothelial cells, where it is an autoantigen in immune-mediated vasculitides [40]. Although C3 and C4 (Table 1, proteins 19 and 20 and Table 2, proteins 1 and 23) play a significant role in the innate immune system [15] a mouse model demonstrated that deficiency in C3 can be compensated by thrombin [41] and a genetically determined deficiency of C4 increases the risk for developing systemic lupus erythematosus [42].…”

Heat Shock Protein Autoantibodies

“…Alarmin corresponds to all endogenous molecules that can act as danger signals recognized by the immune system. Our hypothesis is that HSPs may extend their chaperone and refolding functions outside of the cells to preserve the membrane-associated protein activities [3]. During inflammatory processes, they will be exposed or released outside of the cells and will be in contact with the immune system.…”

An Innovative Method to Identify Autoantigens Expressed on the Endothelial Cell Surface: Serological Identification System for Autoantigens Using a Retroviral Vector and Flow Cytometry (SARF)

“…Alard et al reported that recognition of cell-surface adenosine triphosphate (ATP) synthase in the low pH microenvironment contributes to intracellular acidification of ECs, which may induce cell death and trigger inflammation [43]. …”

“…The EC autoantigens may be either constitutively expressed or translocated from intracellular compartment to membrane by cytokines, such as IL-1 and tumor necrosis factor α (TNF α ), or physical effects [8, 47]. The reported autoantigens and their pathogenicities are summarized in Table 2 [7, 9, 22–24, 42, 43, 47–56]. …”

“…Proteomics analysis identified vimentin, Hsp60, voltage-dependent anion-selective channel 1 (VDAC-1), peroxiredoxin 2, and ATP synthase as targets for AECAs [41, 43, 48–50]. Expression libraries also identified tropomyosin, T-plastin, and RLIP76 [42, 56], and these technologies are therefore promising.…”