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Salivary gland damage and hypofunction result from various disorders, including autoimmune Sjögren's disease (SjD) and IgG4-related disease (IgG4-RD), as well as a side effect of radiotherapy for treating head and neck cancers. There are no therapeutic strategies to prevent the loss of salivary gland function in these disorders nor facilitate functional salivary gland regeneration. However, ongoing aquaporin-1 gene therapy trials to restore saliva flow show promise. To identify and develop novel therapeutic targets, we must better understand the cell-specific signaling processes involved in salivary gland regeneration. Transforming growth factor-β (TGF-β) signaling is essential to tissue fibrosis, a major endpoint in salivary gland degeneration, which develops in the salivary glands of patients with SjD, IgG4-RD, and radiation-induced damage. Though the deposition and remodeling of extracellular matrix proteins are essential to repair salivary gland damage, pathological fibrosis results in tissue hardening and chronic salivary gland dysfunction orchestrated by multiple cell types, including fibroblasts, myofibroblasts, endothelial cells, stromal cells, and lymphocytes, macrophages, and other immune cell populations. This review is focused on the role of TGF-β signaling in the development of salivary gland fibrosis and the potential for targeting TGF-β as a novel therapeutic approach to regenerate functional salivary glands. The studies presented highlight the divergent roles of TGF-β signaling in salivary gland development and dysfunction and illuminate specific cell populations in damaged or diseased salivary glands that mediate the effects of TGF-β. Overall, these studies strongly support the premise that blocking TGF-β signaling holds promise for the regeneration of functional salivary glands., (© 2024 The Authors.)

G protein-coupled receptors are the target of more than 30% of all FDA-approved drug therapies. Though the purinergic P2 receptors have been an attractive target for therapeutic intervention with successes such as the P2Y 12 receptor antagonist, clopidogrel, P2Y 2 receptor (P2Y 2 R) antagonism remains relatively unexplored as a therapeutic strategy. Due to a lack of selective antagonists to modify P2Y 2 R activity, studies using primarily genetic manipulation have revealed roles for P2Y 2 R in a multitude of diseases. These include inflammatory and autoimmune diseases, fibrotic diseases, renal diseases, cancer, and pathogenic infections. With the advent of AR-C118925, a selective and potent P2Y 2 R antagonist that became commercially available only a few years ago, new opportunities exist to gain a more robust understanding of P2Y 2 R function and assess therapeutic effects of P2Y 2 R antagonism. This review discusses the characteristics of P2Y 2 R that make it unique among P2 receptors, namely its involvement in five distinct signaling pathways including canonical Gα q protein signaling. We also discuss the effects of other P2Y 2 R antagonists and the pivotal development of AR-C118925. The remainder of this review concerns the mounting evidence implicating P2Y 2 Rs in disease pathogenesis, focusing on those studies that have evaluated AR-C118925 in pre-clinical disease models., (© 2022. The Author(s), under exclusive licence to Springer Nature B.V.)

Salivary glands sustain collateral damage following radiotherapy (RT) to treat cancers of the head and neck, leading to complications, including mucositis, xerostomia and hyposalivation. Despite salivary gland-sparing techniques and modified dosing strategies, long-term hypofunction remains a significant problem. Current therapeutic interventions provide temporary symptom relief, but do not address irreversible glandular damage. In this review, we summarize the current understanding of mechanisms involved in RT-induced hyposalivation and provide a framework for future mechanistic studies. One glaring gap in published studies investigating RT-induced mechanisms of salivary gland dysfunction concerns the effect of irradiation on adjacent non-irradiated tissue via paracrine, autocrine and direct cell-cell interactions, coined the bystander effect in other models of RT-induced damage. We hypothesize that purinergic receptor signaling involving P2 nucleotide receptors may play a key role in mediating the bystander effect. We also discuss promising new therapeutic approaches to prevent salivary gland damage due to RT.

Objectives: To assess functional expression of the P2Y 2 nucleotide receptor (P2Y 2 R) in head and neck squamous cell carcinoma (HNSCC) cell lines and define its role in nucleotide-induced epidermal growth factor receptor (EGFR) transactivation. The use of anti-EGFR therapeutics to treat HNSCC is hindered by intrinsic and acquired drug resistance. Defining novel pathways that modulate EGFR signaling could identify additional targets to treat HNSCC., Materials and Methods: In human HNSCC cell lines CAL27 and FaDu and the mouse oral cancer cell line MOC2, P2Y 2 R contributions to extracellular nucleotide-induced changes in intracellular free Ca 2+ concentration and EGFR and extracellular signal-regulated kinase (ERK1/2) phosphorylation were determined using the ratiometric Ca 2+ indicator fura-2 and immunoblot analysis, respectively. Genetic knockout of P2Y 2 Rs using CRISPR technology or pharmacological inhibition with P2Y 2 R-selective antagonist AR-C118925 defined P2Y 2 R contributions to in vivo tumor growth., Results: P2Y 2 R agonists UTP and ATP increased intracellular Ca 2+ levels and ERK1/2 and EGFR phosphorylation in CAL27 and FaDu cells, responses that were inhibited by AR-C118925 or P2Y 2 R knockout. P2Y 2 R-mediated EGFR phosphorylation was also attenuated by inhibition of the adamalysin family of metalloproteases or Src family kinases. P2Y 2 R knockout reduced UTP-induced CAL27 cell proliferation in vitro and significantly reduced CAL27 and FaDu tumor xenograft volume in vivo. In a syngeneic mouse model of oral cancer, AR-C118925 administration reduced MOC2 tumor volume., Conclusion: P2Y 2 Rs mediate HNSCC cell responses to extracellular nucleotides and genetic or pharmacological blockade of P2Y 2 R signaling attenuates tumor cell proliferation and tumorigenesis, suggesting that the P2Y 2 R represents a novel therapeutic target in HNSCC., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)