The acinar cells of the lacrimal gland (LG) release proteins into tears that have nutrient, anti-infective and regulatory properties. Changes in the proteins released by these cells is associated with keratoconjunctivitis sicca (KCS), which can severely compromise visual acuity. KCS can occur with the systemic autoimmune disease, Sjogren's syndrome (SjS), or independently. In LG acinar cells (LGAC), the major source of tear proteins, packaging of materials destined for apically-targeted secretory vesicles (SV) occurs in the trans-Golgi network (TGN). Within acinar cells, the proteins destined for apical secretion via regulated exocytosis and the proteins destined to function in the lysosomes (Lys) follow the same biosynthetic pathway through the endoplasmic reticulum (ER) and Golgi complex to the TGN. The TGN is the cells'primary nexus for sorting both intraluminal, fluid phase proteins and membrane-embedded proteins. For the LG to sustain its primary secretory function, the TGN must sort proteins into the two pathways efficiently and accurately. Evidence from studies of SjS patients suggests profound changes in intracellular sorting at the TGN. Studies in non-obese diabetic (NOD) mice, a naturally occurring model of autoimmune dacryoadenitis which exhibit features of SjS, suggest that defects in the sorting of proteins from the TGN can promote imbalances in the normal distributions of secretory and Lys proteins, evoking a pathological cycle of disease. Our fundamental premise is that changes in the fidelity of sorting of SV and Lys proteins at the TGN may arise from diverse causal factors but, that once initiated, contribute to pathogenesis and maintenance of the diseased state. We specifically propose that the efflux of secretory proteins from TGN to Lys that may result when trafficking from TGN to SV is inhibited, and the efflux of Lys proteins from TGN to SV that may result when trafficking from TGN to Lys is inhibited each contribute uniquely to the cycle involved in initiation and progression of SjS. Here we use established in vitro systems and mouse models to explore the consequences of selected inhibition of key TGN trafficking effectors to SV and Lys, analyzing how these changes affect cell and organ health and ocular surface integrity. We also test the hypothesis that induction of autophagy protects against the pathological effects of TGN missorting in the NOD mouse model.
Our aims are:
Aim 1. To investigate the effects of targeted disruption of TGN to SV sorting on Lys.
Aim 2. To investigate the effects of targeted disruption of TGN to Lys sorting on SV.
Aim 3. To determine if autophagy can moderate the pathological effects associated with TGN missorting. Successful demonstration of the central role of TGN missorting in autoimmune dacryoadenitis will drive a paradigm shift from the current focus on causative factors (e.g., alterations in neurotransmitter, cytokine or hormonal stimulation) to the identification of precise molecular targets for treatment.
This project investigates whether changes in the fidelity of sorting of membrane cargo from the trans-Golgi network to secretory vesicles and/or lysosomes contribute to the pathological changes associated with development of tear-deficient keratoconjunctivitis sicca. Sjvgren's syndrome, responsible for the most severe cases of tear-deficient keratoconjunctivitis sicca, leads to corneal damage and loss of visual acuity. Successful completion of this application will result in a paradigm shift from our current understanding of the causal factors of Sjogren's syndrome to the identification of disease mechanisms and precise molecular targets for treatment.
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