Muscarinic Acetylcholine Type-3 Receptor Desensitization Due to Chronic Exposure to Sjögren's Syndrome-Associated Autoantibodies

SEUNGHEE CHA, ERIC SINGSON, JANET CORNELIUS, JARAJAPU P. YAGNA, HARM J. KNOT, and AMMON B. PECK

ABSTRACT.

Objective. Sjögren's syndrome (SS) is an autoimmune disease characterized by salivary and lacrimal gland dysfunction leading to dry mouth (xerostomia) and dry eyes (xerophthalmia). Anti-muscarinic acetylcholine type-3 receptor (anti-M3R) autoantibodies have been shown to inhibit M3R-mediated responses by both in vitro contractility and fura-2 microfluorimetry analyses of intracellular calcium mobilization, suggesting an important role for anti-M3R autoantibody in secretory dysfunction. We investigated whether chronic stimulation of M3R by anti-M3R autoantibodies and/or the agonist pilocarpine results in a general M3R desensitization.

Methods. Carbachol-evoked responses of mouse-bladder smooth muscle strips were measured following exposure to anti-M3R-positive and/or anti-M3R-negative sera from either NOD/Lt mice, a model of SS-like disease, or human patients with primary SS.

Results. Bladder smooth muscle strips isolated from NOD/Lt mice with circulating anti-M3R autoantibodies exhibited lower carbachol-evoked responses than smooth muscle strips from anti-M3R autoantibody-negative NOD/Lt mice and control C57BL/6 mice. Repeated pilocarpine injections of NOD mice for 6 days also revealed M3R desensitization in the agonist-evoked contractile assay, whereas age and sex matched C57BL/6 mice injected with pilocarpine for the same period showed a 2-fold higher response. Incubation of smooth muscle strips with sera obtained from patients with primary SS resulted in both stimulated and inhibited responses.

Conclusion. These results support the hypothesis that chronic stimulation of membrane-bound M3R can result in receptor desensitization, and raise questions about repeated use of pilocarpine by patients positive for anti-M3R autoantibodies. (J Rheumatol 2006;33:296-306)

Key Indexing Terms:

SJÖGREN'S SYNDROME
NON-OBESE DIABETIC MOUSE
ANTI-MUSCARINIC ACETYLCHOLINE TYPE-3 RECEPTOR
AUTOANTIBODY
BLADDER STRIP CONTRACTILE ASSAY
SALIVARY GLAND DYSFUNCTION

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From the Department of Oral Biology, College of Dentistry; Department of Pathology, Immunology and Laboratory Medicine, College of Medicine; Department of Pharmacology, College of Medicine; and the Center for Orphaned Autoimmune Diseases, College of Dentistry, University of Florida, Gainesville, Florida, USA.

Supported by PHS grants DE55304, DE014344, and DE015152 from the National Institutes of Health. Dr. Cha was supported, in part, by the Sjögren's Syndrome Foundation and PHS grant U24 DE016509.

S. Cha, DDS, PhD, Research Assistant Professor; E. Singson, BS, Department of Oral Biology; J.G. Cornelius, MS, Department of Pathology, Immunology, and Laboratory Medicine; J.P. Yagna, MPharm, PhD; H.J. Knot, PhD, Department of Pharmacology; A.B. Peck, PhD, Professor, Departments of Oral Biology, Pathology, Immunology, and Laboratory Medicine; and Center for Orphaned Autoimmune Diseases.

Address reprint requests to A.B. Peck, Department of Oral Biology, PO Box 100424, University of Florida, Gainesville, FL 32610. E-mail: peck@pathology.ufl.edu

Accepted for publication September 29, 2005.

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