Sjogren's syndrome is an autoimmune disorder of poorly understood etiology that affects over 4,000,000 Americans every year. One of its hallmark symptoms is lacrimal gland dysfunction leading to dry eye. Aqueous tear production from the lacrimal gland occurs via acini which secret components of the fluids into the ducts of the glands. The acini are organized structures that contain specialized acinar epithelial cells. Acinar cells in the lacrimal glands from Sjogren's syndrome patients undergo apoptosis, while those from individuals with non-Sjogren's dry eye do not. This suggests that in Sjogren's Syndrome selective apoptosis of the acinar cells would reduce tear formation. ? ? The underlying mechanism for selective acinar cell apoptosis is not known. However, in the MRL/lpr mouse, a frequent model for Sjogren's Syndrome, lacrimal gland damage begins in the first month after birth. During this period, infiltration by Tlymphocytes occurs and interleukin (IL)-lp production increases. It has been observed that lymphocytic infiltration of the lacrimal gland of MRL/lpr mice triggers acinar cells to start IL-lp production and this production was limited to the acinar cells. ? ? We have previously shown that IL-l? can stimulate nitric oxide (NO) production in lacrimal gland acinar cells and this production could be blocked with the specific inducible nitric oxide synthase (iNOS) inhibitors. Excessive NO production could be toxic to the lacrimal gland. NO biosynthesis can lead to production of peroxynitrite which has been coupled to apoptosis. These observations allow us to propose the following Central Hypothesis: In Sjogren's Syndrome, pro-inflammatory cytokines from the lymphocytic infiltrate of the lacrimal gland stimulates supranormal IL-lp production in the acinar cells which leads to elevated NO levels with concomitantly increased peroxynitrite formation. Excessive peroxynitrite initiates apoptosis in the acinar cells. ? ? To test this hypothesis we will undertake the following three Aims. ? Levels of IL-lbeta, iNOS and peroxynitrite-modified proteins will be quantified in lacrimal glands from MRL/lpr mice and controls as a function of disease development.
This Aim will test for correlations between IL-lp, iNOS and peroxynitrite levels and apoptosis in lacrimal glands of MRL/lpr mice that are not found in controls. ? ? The ability of NO synthesis antagonists and peroxynitrite decomposition catalysts to prevent apoptotic lacrimal gland damage will be assessed.
This Aim will test whether NO and/or peroxynitrite are necessary for lacrimal gland acinar cell apoptosis or other ? lacrimal gland damage. ? ? MRL/lpr mice will be bred with mice containing homozygous knockouts of the IL-lbeta or iNOS genes to produce lines that do not produce these proteins and still have a defect in Fas. These hybrid animals will be tested for age-dependent damage to the lacrimal gland. This will test the Central hypothesis by genetically removing proteins we hypothesize to be necessary for lacrimal gland damage in Sjogren's Syndrome. ? ? This research is very significant because the outcome of these studies will lead the way to development of new methods for preventing or diminishing the development of dry eye in individuals afflicted Sjogren's Syndrome and perhaps related autoimmune disorders such as Systemic Lupus Erythematosus. ? ? ?
