Antimitochondrial antibodies in systemic sclerosis target enteric neurons and are associated with GI dysmotility.

Objectives: Most patients with systemic sclerosis (SSc) experience gastrointestinal (GI) dysmotility. The enteric nervous system (ENS) regulates GI motility, and its dysfunction causes dysmotility. A subset of SSc patients harbour antimitochondrial M2 autoantibodies (AMA). Here, we investigate whether M2 is expressed by specific ENS cells, and if AMA are associated with GI dysmotility in SSc patients.

Methods: Sera from 154 well-characterised patients with SSc were screened for AMA by enzyme-linked immunosorbent assay. Clinical features and GI transit data were compared between AMA-positive and AMA-negative patients. Hepatocellular carcinoma cell line 2 (HepG2) cells were cultured with these sera and costained with AMA.

Results: Nineteen of 147 patients (12.9%) were AMA-positive. AMA positivity was significantly associated with slower transit in the oesophagus (β -14.4, 95%CI, -26.2, -2.6) and stomach (β -7.9, 95% CI, -14.1, -1.6). Immunostaining demonstrated pan-mitochondrial antigens TOM-20 and M2 enrichment in human ENS neurons, specifically in mesoderm-derived enteric neurons (MENS). Autoantibodies in SSc sera penetrated live adult murine MENs and HepG2 cells when adult murine longitudinal muscle containing myenteric plexus tissue and HepG2 cells were cultured in the presence of SSc sera. Upon penetrating live cells, AMA localised to mitochondria, and immunoprecipitation demonstrated binding to the M2 antigen. Seahorse assays show that penetration of HepG2 cells with SSc-AMA altered cellular respiration suggesting that penetrating AMA is pathogenic.

Conclusions: AMA in SSc patients are associated with slower GI transit. SSc autoantibodies penetrate live cells in vitro, and SSc-AM2A penetrates live cells to target the mitochondrial M2 antigen and cause functional deficits. Because a subset of enteric neurons (MENs) is enriched in mitochondria, which are similarly penetrated by SSc-AMA in vitro, the presence of GI dysmotility in SSc patients harbouring AMA suggests that SSc-AMA may penetrate MENs in vivo, driving ENS and GI dysfunction. Further studies are warranted to test how AMA alter ENS functions in vivo to contribute to GI dysmotility in SSc.