Antibodies to the inositol 1,4,5-trisphosphate receptor type 1 (ITPR1) in cerebellar ataxia

Abstract

We report on a serum autoantibody associated with cerebellar ataxia. Immunohistochemical studies of sera from four patients referred for autoantibody testing revealed binding of high-titer (up to 1:5,000) IgG antibodies, mainly IgG1, to the molecular layer, Purkinje cell layer, and white matter on mouse, rat, porcine, and monkey cerebellum sections. The antibody bound to PC somata, dendrites, and axons, resulting in a binding pattern similar to that reported for anti-Ca/anti-ARHGAP26, but did not react with recombinant ARHGAP26. Extensive control studies were performed to rule out a broad panel of previously described paraneoplastic and non-paraneoplastic anti-neural autoantibodies. The characteristic binding pattern as well as double staining experiments suggested inositol 1,4,5-trisphosphate receptor type 1 (ITPR1) as the target antigen. Verification of the antigen included specific neutralization of the tissue reaction following preadsorption with ITPR1 (but not ARHGAP26) and a dot-blot assay with purified ITPR1 protein. By contrast, anti-ARHGAP26-positive sera did not bind to ITPR1. In a parallel approach, a combination of histoimmunoprecipitation and mass spectrometry also identified ITPR1 as the target antigen. Finally, a recombinant cell-based immunofluorescence assay using HEK293 cells expressing ITPR1 and ARHGAP26, respectively, confirmed the identification of ITPR1. Mutations of ITPR1 have previously been implicated in spinocerebellar ataxia with and without cognitive decline. Our findings suggest a role of autoimmunity against ITPR1 in the pathogenesis of autoimmune cerebellitis and extend the panel of diagnostic markers for this disease.

Responses to and Outcomes of Treatment of Autoimmune Cerebellar Ataxia in Adults

“…For example, patients with paraneoplastic chorea frequently have accompanying peripheral neuropathy. 26 Of additional note, we included patients who were seronegative for neural antibodies, and we did not reevaluate stored serum and CSF specimens of patients with seronegative ataxia for more recently reported neural autoantibodies pertinent to autoimmune ataxia, 19,20 although these autoantibodies are comparatively rare in our laboratory experience.…”

Inositol 1,4,5-trisphosphate receptor type 1 autoantibodies in paraneoplastic and non-paraneoplastic peripheral neuropathy

“…Testing for ITPR1-IgG, ITPR1-IgM and ITPR1-IgA by immunohistochemistry (IHC) was performed as previously described [1]. Briefly, 4-μm cryosections of mouse, rat and primate cerebellum and primate spinal cord (Euroimmun, Lübeck, Germany) and 10-μm cryosections of rat DRG tissue (Zyagen, San Diego, CA) as well as cryosections from an adenocarcinoma of the lung removed from a ITPR1-IgG-positive patient (patient 1) were carefully thawed and subsequently treated with formalin for 3 min, CHAPS for 3 min and 10 % goat serum for 1 h. Sections were then incubated for 1 h with diluted patient and control serum and with CSF samples.…”

“…The presence of ITPR1-specific IgG was confirmed using an immunoblot assay employing purified native ITPR1 from rat brain as previously described [1]. Briefly, Protran BA79 nitrocellulose membranes (Whatman) were spotted with increasing dilutions of full-length ITPR1 purified from rat cerebellum [6] and of ARHGAP26 (Abnova) in 0.1 % bovine serum albumin (BSA).…”

“…Recently, we described a new autoantibody (Ab) reactivity in patients with autoimmune cerebellar ataxia (ACA) which targets the inositol 1,4,5-trisphosphate receptor type 1 (ITPR1; also termed IP3RI) [1]. In the adult brain, ITPR1 is strongly expressed in Purkinje cells (PC) of the cerebellum, in hippocampal neurons (particularly in CA1 pyramidal cells) [2–4], and in the cerebral cortex (most pronounced in pyramidal layer V and in non-pyramidal layer II) [2, 3].…”

Inositol 1,4,5‐trisphosphate receptors and neurodegenerative disorders

“…Via different immunological methods, IP 3 R1 was identified as the target antigen of this reactivity. Thus, it was shown that IP 3 R1 represents a diagnostic serum marker of autoimmune cerebellar ataxia [71].…”