Characterization of apoptotic pathways in a salivary gland model

The pathogenesis of Sjögren's Syndrome (SS) is not clearly understood. It has been demonstrated that the expression of multiple apoptotic markers occur in vivo. It is now hypothesized that autoantigen conformation and different cell morphologic forms generated during apoptosis, may be pathway dependent and associated with distinctive differences in adhesion molecule expression. Objective: The objective is to induce apoptosis via two different pathways and evaluate cell morphology, antigen conformational changes and adhesion molecule expression resulting from this specific stimulation. Methods: Using a Human Salivary Gland cell line, apoptosis was activated separately with TNF-a and staurosporine. Apoptotic forms were visualized microscopically, photographed following Scanning Electron Microscopy (SEM). Antigen processing-associated gene expression and intercellular adhesion molecule gene expression in apoptotic cells, was detected using gene microarrays. Functional binding of apoptotic bodies to human Jurkat lymphocytes was evaluated in vitro using immunofluorescence. Results: SEM results show that human salivary ductal cells produce characteristic apoptotic bodies as a result of TNF-a stimulation compared with staurosporine as expected. Gene expression of Intercellular Adhesion Molecule-1 (ICAM-1) is markedly increased following TNF-a but not in the case of staurosporine stimulation. Conclusion: 1) that two different inducers of apoptosis resulted in different morphologic forms which had different biochemical and gene expression profiles; 2) TNF-a but not staurosporine treatment of HSG cells induced the expression of several genes known to be associated with an antigen presenting function in other cell types; 3) TNF-a treatment, but not staurosporine treatment of salivary gland cells, facilitated their binding to Jurkat cells; These results are consistant with a potential role for SG cells as antigen presenting cells when undergoing apoptosis stimulated by TNF-a. Apoptotic cell morphology, autoantigen conformation and adhesion molecule gene expression may be characteristic of the apoptotic pathway and relevant to pathogenesis of SS disease.