Transforming growth factor-β (TGF-β) is a multifunctional growth factor involved in many physiological processes including wound healing and inflammation. Excessive TGF-β signaling in the skin has been implicated in fibrotic skin disorders such as keloids and scleroderma. We previously identified CD109 as a TGF-β co-receptor and inhibitor of TGF-β signaling and have shown that transgenic mice overexpressing CD109 in the epidermis display decreased scarring. In certain cell types, in addition to the canonical type I receptor, ALK5, which activates Smad2/3, TGF-β can signal through another type I receptor, ALK1, which activates Smad1/5. Here we demonstrate that ALK1 is expressed and co-localizes with CD109 in mouse keratinocytes and that mice overexpressing CD109 in the epidermis display enhanced ALK1-Smad1/5 signaling but decreased ALK5-Smad2/3 signaling, TGF-β expression, and extracellular matrix production in the skin when compared with wild-type littermates. Furthermore, treatment with conditioned media from isolated keratinocytes or epidermal explants from CD109 transgenic mouse skin leads to a decrease in extracellular matrix production in mouse skin fibroblasts. Taken together, our findings suggest that CD109 differentially regulates TGF-β-induced ALK1-Smad1/5 versus ALK5-Smad2/3 pathways, leading to decreased extracellular matrix production in the skin and that epidermal CD109 expression regulates dermal function through a paracrine mechanism.

Saliva aids in digestion, lubrication, and protection of the oral cavity against dental caries and oropharyngeal infections. Reduced salivary secretion, below an adequate level to sustain normal oral functions, is unfortunately experienced by head and neck cancer patients treated with radiotherapy and by patients with Sjögren's syndrome. No disease‐modifying therapies exist to date to address salivary gland hypofunction (xerostomia, dry mouth) because pharmacotherapies are limited by the need for residual secretory acinar cells, which are lost at the time of diagnosis, whereas novel platforms such as cell therapies are yet immature for clinical applications. Autologous salivary gland primary cells have clinical utility as personalized cell therapies, if they could be cultured to a therapeutically useful mass while maintaining their in vivo phenotype. Here, we devised a serum‐free scalable suspension culture system that grows partially digested human salivary tissue filtrates composing of acinar and ductal cells attached to their native extracellular matrix components while retaining their 3D in vivo spatial organization; we have coined these salivary spheroids as salivary functional units (SFU). The proposed SFU culture system was sub‐optimal, but we have found that the cells could still survive and grow into larger salivary spheroids through cell proliferation and aggregation for 5 to 10 days within the oxygen diffusion rates in vitro. In summary, by using a less disruptive cell isolation procedure as the starting point for primary cell culture of human salivary epithelial cells, we demonstrated that aggregates of cells remained proliferative and continued to express acinar and ductal cell‐specific markers.