aPKCζ-dependent Repression of Yap is Necessary for Functional Restoration of Irradiated Salivary Glands with IGF-1

Abstract

Xerostomia and salivary hypofunction often result as a consequence of radiation therapy for head and neck cancers, which are diagnosed in roughly 60,000 individuals every year in the U.S. Due to the lack of effective treatments for radiation-induced salivary hypofunction, stem cell-based therapies have been suggested to regenerate the irradiated salivary glands. Pharmacologically, restoration of salivary gland function has been accomplished in mice by administering IGF-1 shortly after radiation treatment, but it is not known if salivary stem and progenitor cells play a role. We show that radiation inactivates aPKCζ and promotes nuclear redistribution of Yap in a population of label-retaining cells in the acinar compartment of the parotid gland (PG)– which comprises a heterogeneous pool of salivary progenitors. Administration of IGF-1 post-radiation maintains activation of aPKCζ and partially rescues Yap’s cellular localization in label retaining cells, while restoring salivary function. Finally, IGF-1 fails to restore saliva production in mice lacking aPKCζ, demonstrating the importance of the kinase as a potential therapeutic target.

P2 Receptors as Therapeutic Targets in the Salivary Gland: From Physiology to Dysfunction

“…While most current treatments for salivary gland dysfunction target expansion of residual salivary acinar cells to repair damaged tissue, regenerative therapy with stem cells is a novel and promising therapeutic approach to replace damaged salivary glands (Carpenter and Cotroneo, 2010;Lombaert et al, 2017;Ogawa and Tsuji, 2017). Several studies have identified and characterized subsets of endogenous salivary progenitor cells that can be exploited to promote tissue regeneration (Lombaert et al, 2008;Chibly et al, 2014Chibly et al, , 2018Pringle et al, 2016;Emmerson et al, 2018;Weng et al, 2018). The use of modified fibrin hydrogels (Nam et al, 2019a), layered sheets of isolated salivary gland cells released from thermoresponsive culture dishes (Nam et al, 2019b) and salivary organoid cultures generated from embryonic pluripotent stem cells (Tanaka et al, 2018) have been explored as regenerative therapies for damaged salivary glands.…”

Yap activation in irradiated parotid salivary glands is regulated by ROCK activity

“…Some prevailing theories in the field include damaged stem and progenitor cell (SPC) pools, defective secretory pathways, irregular inflammatory responses, and cell death [4][5][6][7][8][9]. Recent studies have shown that the structural integrity of the epithelium is altered and that these defects are associated with aberrant apical-basolateral polarity, loss of lateral junctions and disorganized cytoskeletal structure [10][11][12][13]. In particular, radiation damage reduces the activity of an apical polarity protein, atypical protein kinase zeta (aPKCz), in both SPCs and acinar cells resulting in hyperproliferation [11,12].…”

“…Recent studies have shown that the structural integrity of the epithelium is altered and that these defects are associated with aberrant apical-basolateral polarity, loss of lateral junctions and disorganized cytoskeletal structure [10][11][12][13]. In particular, radiation damage reduces the activity of an apical polarity protein, atypical protein kinase zeta (aPKCz), in both SPCs and acinar cells resulting in hyperproliferation [11,12]. Loss of aPKCz in the SPCs promoted nuclear translocation of Yes-associated protein (Yap), a transcriptional co-activator regulated by Hippo signaling [11].…”

Concise Review: A Critical Evaluation of Criteria Used to Define Salivary Gland Stem Cells

“…A caveat is that the DNA label will be retained by cells undergoing terminal differentiation, as well as by potential quiescent stem cells . Consistent with this, LRCs are found in all parenchymal compartments of the salivary glands , and can colocalize with markers of differentiated acinar or duct cells . Due to the low rate of cell turnover in the adult salivary gland, cells labeled during an earlier proliferative phase will be retained for long periods.…”

“…Labeling done during embryonic development identified LRCs after long‐term chase that had low proliferative potential in vitro and did not actively proliferate following injury . In contrast, labeling postnatally followed by a shorter chase identified LRCs that showed self‐renewal capacity in vitro and in vivo proliferation in response to injury . Labeling at embryonic or postnatal stages likely marked different populations of dividing cells.…”