Reversible Conversion among Subtypes of Salivary Gland Duct Cells as Identified by Production of a Variety of Bioactive Polypeptides

Putative effect of chronic renal failure on granular convoluted tubule of submandibular gland in male rats: Immunohistochemical and ultrastructural study

Objective

This study aimed to investigate the ultrastructural and immunohistochemical changes in the granular convoluted tubule (GCT) of rodents' submandibular gland (SMG) upon theinduction of chronic renal failure.

Material and methods

Thirty young adult Sprague-Dawley rats were randomized into three groups: the Control group, rats received no intervention; the Sham group, rats underwent surgical incision without nephrectomy; the Experimental group, rats underwent surgical procedures to induce chronic renal failure. Afterward, SMG was examined for histological and ultrastructural changes and immunohistochemical staining for Renin.

Results

Histologically, the experimental group demonstrated cytoplasmic vacuolization within the seromucous acini and ducts. Several GCTs were proliferating, whereas others exhibited degenerative changes in the form of disturbed cytoplasmic architecture. On the ultrastructural level, both acini and ductal segments showed degenerative changes Interestingly, immunohistochemical examination of the lining cells of GCT and intralobular ducts of the experimental group revealed the presence of Renin.

Conclusion

Renal failure induced histological, immunohistochemical, and ultrastructural variations within GCTs of SMG.

IFT140+/K14+ cells function as stem/progenitor cells in salivary glands

Stem/progenitor cells are important for salivary gland development, homeostasis maintenance, and regeneration following injury. Keratin-14⁺ (K14⁺) cells have been recognized as bona fide salivary gland stem/progenitor cells. However, K14 is also expressed in terminally differentiated myoepithelial cells; therefore, more accurate molecular markers for identifying salivary stem/progenitor cells are required. The intraflagellar transport (IFT) protein IFT140 is a core component of the IFT system that functions in signaling transduction through the primary cilia. It is reportedly expressed in mesenchymal stem cells and plays a role in bone formation. In this study, we demonstrated that IFT140 was intensively expressed in K14⁺ stem/progenitor cells during the developmental period and early regeneration stage following ligation-induced injuries in murine submandibular glands. In addition, we demonstrated that IFT140⁺/ K14⁺ could self-renew and differentiate into granular duct cells at the developmental stage in vivo. The conditional deletion of Ift140 from K14⁺ cells caused abnormal epithelial structure and function during salivary gland development and inhibited regeneration. IFT140 partly coordinated the function of K14⁺ stem/progenitor cells by modulating ciliary membrane trafficking. Our investigation identified a combined marker, IFT140⁺/K14⁺, for salivary gland stem/progenitor cells and elucidated the essential role of IFT140 and cilia in regulating salivary stem/progenitor cell differentiation and gland regeneration.

A mesenchymal to epithelial switch in Fgf10 expression specifies an evolutionary-conserved population of ionocytes in salivary glands

Fibroblast growth factor 10 (FGF10) is well established as a mesenchyme-derived growth factor and a critical regulator of fetal organ development in mice and humans. Using a single-cell RNA sequencing (RNA-seq) atlas of salivary gland (SG) and a tamoxifen inducible Fgf10^CreERT2:R26-tdTomato mouse, we show that FGF10^pos cells are exclusively mesenchymal until postnatal day 5 (P5) but, after P7, there is a switch in expression and only epithelial FGF10^pos cells are observed after P15. Further RNA-seq analysis of sorted mesenchymal and epithelial FGF10^pos cells shows that the epithelial FGF10^pos population express the hallmarks of ancient ionocyte signature Forkhead box i1 and 2 (Foxi1, Foxi2), Achaete-scute homolog 3 (Ascl3), and the cystic fibrosis transmembrane conductance regulator (Cftr). We propose that epithelial FGF10^pos cells are specialized SG ionocytes located in ducts and important for the ionic modification of saliva. In addition, they maintain FGF10-dependent gland homeostasis via communication with FGFR2b^pos ductal and myoepithelial cells.

Mauduit et al. identified unique FGF10-expressing ionocytes in salivary glands. FGF10 expression shifts from fibroblasts to epithelial ionocytes during postnatal development. Ionocytes play a dual role in salivary gland homeostasis; they maintain specific ion composition in saliva and act as niche cells, providing growth factor support for other epithelial cells.