The overall hypothesis guiding the proposed studies is based on observations that the expression and activity of the P2 nucleotide receptor subtypes in salivary glands change in response to tissue damage, including exocrine disease states, and during development. We posit that these changes are regulated through pathways involving mitogen-activated protein kinases (MAPK) and result in altered expression of P2 receptors that participate in regulating secretion and gene expression. In addition, we posit that the P2Y receptor subtypes found in salivary glands dimerize and that dimerization is an essential aspect of the pharmacological and signaling properties of these receptors.
Specific Aim 1 will determine the intracellular signaling pathways involved in regulating P2Y2 receptor expression, with a focus on the mitogen-activated protein kinase cascades. Furthermore, preliminary evidence indicates that up-regulation of P2Y2 receptors coincides with submandibular gland (SMG) dysfunction in a mouse model of Sjogren's syndrome. We propose to evaluate the ability of P2Y2 receptor agonists to enhance secretion in the affected glands as an initial assessment of the receptor as a potential therapeutic target.
Specific Aim 2 is to define the consequences of activation of the P2Y2 receptor following up-regulation, focusing on delineation of the signaling pathways utilized by the receptor to modulate secretion and gene expression.
Specific Aim 3 will determine if P2Y2 and P2Y1 receptors form homo- and hetero-dimers and how dimer formation contributes to receptor function in non-polarized and polarized model cell systems and in salivary gland cells.
Specific Aim 4 is based on observations that P2Y1 receptor activity is high in newborn rat SMG and declines as the gland matures, whereas receptor mRNA levels do not change.
This Aim will identify the point(s) in the signaling pathway responsible for the loss of P2Y1 receptor function during SMG development. These studies will initially emphasize prototypical P2 receptor subtypes in the rat and mouse submandibular gland, then will be expanded to address these issues as they relate to the known salivary gland P2 subtypes (P2Y1, P2Y2, P2X4, P2Xy) and to the parotid and sublingual glands, thereby establishing a relatively complete picture of P2 receptor expression and activity in salivary glands under various conditions.
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