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

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 (AM2A). Here, we investigate whether M2 is expressed by specific ENS cells, and if AM2A are associated with GI dysmotility in SSc patients. Sera from 154 well-characterised patients with SSc were screened for AM2A by enzyme-linked immunosorbent assay. Clinical features and GI transit data were compared between AM2A-positive and AM2A-negative patients. Hepatocellular carcinoma cell line 2 (HepG2) cells were cultured with these sera and costained with AM2A. Nineteen of 147 patients (12.9%) were AM2A-positive. AM2A 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, AM2A localised to mitochondria, and immunoprecipitation demonstrated binding to the M2 antigen. Seahorse assays show that penetration of HepG2 cells with SSc-AM2A altered cellular respiration suggesting that penetrating AM2A is pathogenic. AM2A 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-AM2A in vitro, the presence of GI dysmotility in SSc patients harbouring AM2A suggests that SSc-AM2A may penetrate MENs in vivo, driving ENS and GI dysfunction. Further studies are warranted to test how AM2A alter ENS functions in vivo to contribute to GI dysmotility in SSc.