Novel Role for the P2Y2 Receptor in the Autoimmune Disease Sjogren's Syndrome

Salivary gland dysfunction is symptomatic of Sjögren's syndrome (SS), an autoimmune disease associated with lymphocytic infiltration of the salivary gland. A commonality between many human autoimmune diseases, including SS, is chronic inflammation whereby sustained accumulation of immune cells promotes tissue degeneration and often leads to other damaging effects. A major focus of the parent grant for this supplement is to identify the functional relevance of extracellular nucleotide "alarmones" that are produced at the site of initial tissue damage. We have shown that G protein-coupled P2Y2 receptors (P2Y2R) for ATP and UTP are early responders to released nucleotide alarmones and that knockout of the P2Y2R in a mouse model of SS prevents infiltration of B and T lymphocytes into salivary glands, indicating a loss of the systemic immune response. We hypothesize that chronic inflammation in SS salivary glands is mediated by P2Y2Rs through activation of several signaling pathways through its distinct structural motifs. The Specific Aims of the parent grant are to investigate the cell mechanisms that initiate chronic inflammation at the level of P2Y2 receptors and to test the potential of targeting the P2Y2R in SS to prevent a systemic immune response. Directly relevant to this supplemental proposal, we have identified an Arg-Gly-Asp (RGD) sequence in the 1st extracellular loop of the P2Y2R and conclusively demonstrated its direct interaction with and activation of RGD-binding integrins. Corona Virus Disease 2019 (COVID-19) is a highly infectious disease caused by the novel Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). SARS-CoV-2 utilizes angiotensin-converting enzyme 2 (ACE2) to attach to cells via a receptor-binding domain (RBD) located on its Spike (S) protein. Interestingly, the S protein RBD also contains an RGD motif, suggesting that RGD-binding integrins may be co-receptors with ACE2 for S protein. Thus, considering the presence of an RGD motif in the SARS-CoV-2 S protein RBD and the established interaction between ACE2 and integrins, we hypothesize that P2Y2Rs and RGD-binding integrins modulate SARS-CoV-2 entry. In addition to lung tissues, ACE2 is also expressed in oral epithelial cells, particularly in the tongue. This finding suggests that the oral cavity is susceptible to SARS-CoV-2 infection, which presents a significant concern for potential infections associated with dental procedures. Thus, this supplement offers a unique opportunity to test the novel hypotheses that SARS-CoV-2 entry in oral epithelial cells is dependent on RGD-containing S protein association with RGD-binding integrins that act as a co-receptor with ACE2 and that this interaction underlying COVID-19 can be modulated by RGD-containing P2Y2Rs that bind to these same integrins. These studies potentially offer an innovative translational approach whereby patients undergoing dental procedures could be administered a P2Y2R or integrin modulator via mouthwash or mouth spray that would reduce SARS-CoV-2 entry into oral epithelial cells, thereby preventing viral transmission.