Diverse progenitor cells preserve salivary gland ductal architecture after radiation induced damage

Abstract

The ductal system of the salivary gland has long been postulated to be resistant to radiation-induced damage, a common side effect incurred by head and neck cancer patients receiving radiotherapy. Yet, whether the ducts are capable of regenerating after genotoxic injury, or whether damage to ductal cells induces lineage plasticity, as has been reported in other organ systems, remains unknown. Here, using the murine salivary gland, we show that two ductal progenitor populations, marked exclusively by KRT14 and KIT, maintain nonoverlapping ductal compartments after radiation exposure but do so through distinct cellular mechanisms. KRT14 + progenitor cells are fastcycling cells that proliferate in response to radiation-induced damage in a sustained manner and divide asymmetrically to produce differentiated cells of the larger granulated ducts. Conversely, KIT + intercalated duct cells are long-lived progenitors for the intercalated ducts that undergo few cell divisions either during homeostasis or after gamma radiation, thus maintaining ductal architecture with slow rates of cell turnover. Together, these data illustrate the regenerative capacity of the salivary ducts and highlight the heterogeneity in the damage responses used by salivary progenitor cells to maintain tissue architecture.

Immortalization of Salivary Gland Epithelial Cells of Xerostomic Patients: Establishment and Characterization of Novel Cell Lines

“…iSGEC-nSS1 exhibited the highest expression of both VIM and CST3, and the lowest expression of KRT19 (a ductal/epithelial cell maker of salivary glands) among iSGECs, indicating a heterologous mesenchymal phenotype ( Figure 3 B) [ 5 , 25 ]. KRT5 is a marker for progenitor and basal ductal cells of the salivary gland [ 26 , 27 ]. In agreement with the work by Jang et al on primary SGECs, KRT5 was the gene with highest expression in iSGECs by qRT-PCR among the characterization markers, which did not differ significantly among all three iSGEC lines [ 5 ].…”

“…KRT18 was the most uniform and ubiquitously expressed cytokeratin among iSGECs, whereas KRT8 exhibited focal protein expression in iSGEC-nSS2 ( Supplementary Figure S3 ). Heterogenous expression of KRT19 and KRT8 could indicate multiple stages of differentiation among cells [ 26 ]. Overall, the expression of KRT8, KRT18, and KRT19 indicates these cell lines to be of ductal origin and reflects other long-term cultures of SGECs in both mice and humans [ 5 , 30 , 31 ].…”

“…However, the expression of characterization marker KRT19 decreased while VIM expression increased in iSGEC-nSS2 cells cultured on matrigel. Higher VIM expression may indicate an increase in stemness properties by dedifferentiation, along with reduced KRT19 expression (differentiated ductal cell marker), which could also indicate an increase in stemness [ 26 , 44 ]. Similarly, changes in VIM and KRT19 expression were observed in long term 2D cultured (p-80) cells ( Figure 4 D).…”

“…Moreover, a spontaneously immortalized mouse cell line expressing mixed ductal and myoepithelial protein markers when cultured as a monolayer showed mRNA expression of acinar markers in monolayer and 3D culture [ 40 ]. Markers of differentiated ductal cells include KRT8 and KRT19 among others [ 26 ]. The lack of uniform expression by either KRT8 and KRT19 in monolayer cultures of iSGEC-nSS2 indicates a potential progenitor cell population, which is capable of differentiation into acinar-like and ductal-like cells when cultured on matrigel.…”

Lack of Conventional Acinar Cells in Parotid Salivary Gland of Patient Taking an Anti-PD-L1 Immune Checkpoint Inhibitor

“…The vast majority of saliva is produced by the major (parotid, submandibular, and sublingual) SGs, with small contributions from the minor SGs located in the lips and oral cavity. SGs are thought to be maintained by the proliferation and differentiation of tissue resident progenitor cells, largely located in the intercalated and striated ducts (6)(7)(8)(9). The observation that ICI-induced hyposalivation cannot be rescued by corticosteroid treatment to dampen inflammation suggests that inflammation is not causing SG hypofunction (3,10,11).…”