Collagen XVII in Human Salivary Glands: Influence on Dynamic Assembly

Objectives: An unbiased analysis of gene and protein expression data in two independent databases identified collagen XVII alpha 1 chain (COL17A1) as one of the most actively transcribed extracellular matrix-associated genes in human salivary glands and human stem/progenitor cells (hS/PCs) isolated from them. Previous studies on COL17A1 focused on the manifestations of COL17A1 in skin, where it functions as a structural component of the hemidesmosome in the dermo-epidermal anchoring complex. We aimed to study the tissue localization and potential structural/functional role(s) of COL17A1 in human salivary glands by examining fresh tissue and the stem/progenitor isolates.
Methods: COL17A1 localization was visualized in human salivary tissue sections by immunofluorescent confocal microscopy. Immunocytochemistry stains were performed on hS/PCs in culture. The relative abundance of COL17A1 in various patient samples was assessed by qPCR and COL17A1 by western blot. Scratch migration assays with control and knockdown cells were used to determine if COL17A1 influences hS/PC behavior. hS/PCs were encapsulated in three-dimensional (3D) hydrogel systems to examine COL17A1 localization during microtissue assembly.
Results: COL17A1 was found localized in cells adjacent to the basement membrane of salivary ductal cells consistent with its functions in hemidesmosomes. Immunocytochemistry stained hS/PCs in culture revealed high levels of COL17A1. Knockdown of COL17A1 slowed migration in scratch assays relative to controls. COL17A1 was deposited opposed to the basement membrane as hS/PCs assembled in 3D hydrogels.
Conclusions: These results indicate that COL17A1 is a key component of the salivary anchoring complex that could influence cell movement during ductal formation. This knowledge is useful both for understanding cell interactions with extracellular matrix during gland development and for tissue engineering endeavors to create replacement tissues for patients with hyposalivation disorders leading to xerostomia.