SPM Receptor Expression and Localization in Irradiated Salivary Glands

Abstract

Radiation therapy-mediated salivary gland destruction is characterized by increased inflammatory cell infiltration and fibrosis, both of which ultimately lead to salivary gland hypofunction. However, current treatments (e.g., artificial saliva and sialagogues) only promote temporary relief of symptoms. As such, developing alternative measures against radiation damage is critical for restoring salivary gland structure and function. One promising option for managing radiation therapy-mediated damage in salivary glands is by activation of specialized proresolving lipid mediator receptors due to their demonstrated role in resolution of inflammation and fibrosis in many tissues. Nonetheless, little is known about the presence and function of these receptors in healthy and/or irradiated salivary glands. Therefore, the goal of this study was to detect whether these specialized proresolving lipid mediator receptors are expressed in healthy salivary glands and, if so, if they are maintained after radiation therapy-mediated damage. Our results indicate that specialized proresolving lipid mediator receptors are heterogeneously expressed in inflammatory as well as in acinar and ductal cells within human submandibular glands and that their expression persists after radiation therapy. These findings suggest that epithelial cells as well as resident immune cells represent potential targets for modulation of resolution of inflammation and fibrosis in irradiated salivary glands.

Keywords: fibrosis; inflammation; radiation therapy; specialized proresolving lipid mediators.

Figure 1.

Histological features of non-irradiated and irradiated human submandibular glands. (A) Non-irradiated human submandibular glands (hSMG) displayed lobular architecture. (B) Non-irradiated hSMG showed mixed serous and mucous units accompanied by ductal structures and thin connective strands. (C) Irradiated hSMG displayed disruption of lobular architecture. (D) Irradiated hSMG showed acinar vacuolization, ductal degeneration, nuclear atypia and alterations in the stroma. A representative image from n = 3 per experimental group is shown. Scale bars = 100 µm. Abbreviations: ID, intercalated duct; SA, serous acini; MA, mucous acini; SD, striated duct; AV, acinar vacuolization; DD, degenerated duct; NA, nuclear atypia; NE, nerve; IC, inflammatory cells; FI, fibrosis.

Figure 2.

Distribution of ALX/FPR2 in non-irradiated and irradiated human submandibular glands. Image shows the presence of ALX/FPR2 as cytoplasmic droplets in mucous acini, intercalated ducts, resident mononuclear cells, endothelial cells and adipocytes. White arrows indicate mucous cells, brown arrows indicate ductal cells, red arrow indicates a resident mononuclear cell, purple arrow indicates endothelial cells and blue arrows indicate adipocytes. Note that 20× and 63× images of each group were obtained to show parenchymal/stromal interface and detailed epithelial structures, respectively. A representative image from n = 3 per experimental group is shown. Scale bars in 20× and 63× magnifications represent 100 and 50 µm, respectively.

Figure 3.

Distribution of GPR32 in non-irradiated and irradiated human submandibular glands. Image shows the presence of GPR32 in serous acini and serous demilunes as well as in striated ducts, resident mononuclear cells, endothelial cells and adipocytes. White arrows indicate perinuclear expression in serous acinar cells, brown arrows indicate apical location in striated ducts, red arrow indicates resident mononuclear cells, purple arrow indicates endothelial cells and blue arrow indicates adipocytes. Note that 20× and 63× images of each group were obtained to show parenchymal/stromal interface and detailed epithelial structures, respectively. A representative image from n = 3 per experimental group is shown. Scale bars in 20× and 63× magnifications represent 100 and 50 µm, respectively.

Figure 4.

Distribution of CMKLR1 in non-irradiated and irradiated human submandibular glands. Image shows the presence of CMKLR1 in serous and mucous acini as well as in ducts, resident mononuclear cells and endothelial cells. White arrows indicate plasma membrane expression in acini, brown arrows indicate plasma membrane expression in ducts, red arrow indicates resident mononuclear cell and purple arrows indicate endothelial cells. Note that 20× and 63× images of each group were obtained to show parenchymal/stromal interface and detailed epithelial structures, respectively. A representative image from n = 3 per experimental group is shown. Scale bars in 20× and 63× magnifications represent 100 and 50 µm, respectively.

Figure 5.

Distribution of BLT1 in non-irradiated and irradiated human submandibular glands. Image shows the presence of BLT1 in acinar and ductal structures as well as in mononuclear cells and endothelial cells. Green arrows indicate cytoplasmic droplets expression in serous acini (inset), white arrow indicates basolateral expression in mucous acini, brown arrows indicate plasma membrane expression in intercalated and striated ducts, red arrow indicates a resident mononuclear cell and purple arrows indicate endothelial cells. Note that 20× and 63× images of each group were obtained to show parenchymal/stromal interface and detailed epithelial structures, respectively. A representative image from n = 3 per experimental group is shown. Scale bars in 20× and 63× magnifications represent 100 and 50 µm, respectively.