Anti-HuD-induced neuronal apoptosis underlying paraneoplastic gut dysmotility

Background & Aims: The role of autoimmunity underlying paraneoplastic gut dysmotility remains unsettled. Because anti-Hu antibodies may impair enteric neuronal function, we tested whether anti-HuD-positive sera from patients with paraneoplastic gut dysmotility or commercial anti-HuD antibodies activated the apoptotic cascade in a neuroblastoma cell line and cultured myenteric neurons. Methods: Anti-HuD antibodies from patients with severe paraneoplastic gut dysmotility were characterized by immunofluorescence and immunoblot. SH-Sy5Y neuroblasts and cultured myenteric neurons were exposed to sera containing anti-HuD antibodies or 2 commercial anti-HuD antibodies. Cells were processed for terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) technique to evaluate apoptosis. Immunofluorescence was used to identify activated caspase-3 and apaf-1, along with microtubule-associated protein 2. Results: In SH-Sy5Y cells, the percentage of TUNEL-positive nuclei observed after exposure to anti-HuD-positive sera (32% +/- 7%) or anti-HuD antibodies (23% +/- 2%) was significantly greater than that of control sera or fetal calf serum (P < 0.001). The time-course analysis showed a significantly greater number of apoptotic neuroblastoma cells evoked by the 2 commercial anti-HuD antibodies at 24, 48, and 72 hours versus controls. The number of TUNEL-positive myenteric neurons exposed to anti-HuD antibodies (60% +/- 14%) was significantly greater than that of fetal calf serum (7% +/- 2%; P < 0.001). Apaf-1 and caspase-3 immunolabeling showed intense cytoplasmic staining in a significantly greater proportion of cells exposed to anti-HuD-positive sera or to commercial anti-HuD antibodies compared with controls. Conclusions: Anti-HuD antibodies evoked neuronal apoptosis that may contribute to enteric nervous system impairment underlying paraneoplastic gut dysmotility. Apaf-1 activation suggests participation of a mitochondria-dependent apoptotic pathway.