Increased degradation of extracellular matrix structures of lacrimal glands implicated in the pathogenesis of Sjögren's syndrome

Abstract

Lacrimal glands (LGs) of male non-obese diabetic (NOD) mice display many features of human LGs in patients afflicted with the autoimmune disease Sjögren's syndrome (SS), including the loss of secretory functions and a lymphocytic infiltration into the glands by 4 months of age. So far, research has mainly focused on the intracellular events that are involved in initiating LG dysfunction; however, the impact of SS on extracellular matrix (ECM) structures of the diseased LGs has not yet been determined. In this study we identified and compared LG ECM formation and integrity of age-matched male healthy (BALB/c) and diseased (NOD) mice. LG tissues were examined using routine histological, biochemical, immunohistochemical and gene expression analysis. Multiphoton imaging and second-harmonic generation (SHG) microscopy permitted the non-invasive analysis of major LG ECM structures including collagen- and elastin-containing fibers. Biochemical testing demonstrated a significant loss of collagen, glycosaminoglycans and desmosine in NOD LGs when compared to healthy BALB/c LGs. Immunohistochemical staining and gene expression analysis confirmed this disease-related alteration of LG ECM structures. Furthermore, laser-induced autofluorescence and SHG microscopy revealed dramatic changes in the structural organization of most collagenous and elastic fibers of the diseased LG tissues that were more pronounced than those displayed by histological analysis. Our results clearly show an enhanced degradation of ECM proteins accompanied by the severe disorganization and deformation of ECM structures of diseased LG tissues. These new insights into the involvement of ECM degradation in SS may lead to novel therapies for patients suffering from dry eye disease.