Background Functional autoantibodies to angiotensin II type 1 receptor (AT1R) and endothelin 1 type A receptor (ETAR) are found in elevated levels in systemic sclerosis (SSc) and they show an association to increased risk of SSc-related manifestations and reduced cumulative survival. Here, functional effects of these autoantibodies (anti-AT1R and anti-ETAR autoantibodies) were studied in vitro and in vivo.
Objectives To analyze anti-AT1R and anti-ETAR functions in vitro and in vivo.
Methods In vitro, autoantibody-mediated effects were studied on human microdermal endothelial cells-1 (HMEC-1), on healthy donor dermal fibroblasts and healthy donor neutrophils. In vivo, autoantibody-mediated effects were studied by passive autoantibody-transfer treatment into healthy C57Bl/6J mice. For each setting anti-AT1R and anti-ETAR autoantibody-positive IgG of SSc patients was used and IgG of healthy donors as a control. Angiotensin and endothelin receptor inhibitors were used in vitro to analyze receptor-mediated effects. In vitro effects were measured by endothelial cell activation (mRNA and protein levels), endothelial wound repair and trans-endothelial neutrophil migration. Fibroblast activation was measured by type I collagen protein expression. Systemic autoantibody-mediated effects were measured in mice by cellular BALF composition, lung histology and plasma chemokine levels after single and repeated autoantibody-transfer.
Results Treatment with anti-AT1R and anti-ETAR autoantibody-positive IgG of SSc patients resulted in several effects, both in vitro and in vivo. In vitro, endothelial cells showed an activation mediated by anti-AT1R and anti-ETAR autoantibodies reflected by enhanced expression of adhesion molecule VCAM-1, of IL-8 and by increased neutrophil trans-endothelial migration. Furthermore, endothelial cells displayed a reduced wound repair capacity, while fibroblasts showed increased type I collagen expression. Neutrophil migration, wound repair and collagen expression were induced in an anti-AT1R and anti-ETAR autoantibody-level dependent manner. Neutrophil counts were elevated in BALF of treated mice, accompanied by increased chemokine KC (functional homologue to human interleukin-8) plasma levels with a correlation between KC levels and neutrophil counts after a single transfer. Repeated transfer led to marked structural alterations in the lung architecture.
Conclusions Our findings demonstrate the potential to induce features of SSc pathogenesis on cellular and systemic level. The in vitro findings indicate direct receptor activation by anti-AT1R and anti-ETAR autoantibody-positive SSc-IgG, and activation of the angiotensin and endothelin receptors by these autoantibodies could account in part for effects seen here in animal experiments. These findings stress the autoimmunity aspect in the disease pathogenesis and provide further evidence for the significant involvement of the angiotensin and endothelin receptor activation in SSc. Therefore, receptor inactivation studies will be performed in vivo to assess a deeper knowledge of anti-AT1R and anti-ETAR autoantibody-mediated effects and to improve our current understanding of SSc pathogenesis.
Disclosure of Interest None declared