Salispheres from Different Major Salivary Glands for Glandular Regeneration

Abstract

Dysfunctional salivary glands (SGs) are a clinical challenge due to the lack of effective treatments. Cell therapy with stem/progenitor cells may improve this situation by providing promising therapeutic solutions. Therefore, exploring abundant cellular sources is important. Three major pairs of SGs are located in different anatomic regions: the parotid glands, the submandibular glands, and the sublingual glands. Although SG stem/progenitor cells can be isolated and cultivated from all major SGs as salispheres, the differences among SG origins remain unclear. In this study, salispheres were successfully isolated from all major SGs. The salispheres demonstrated unique cellular features that originated from their native tissues. The characteristic expression profiles and cellular features of SG stem cells were demonstrated in all salispheres. When they were transplanted into irradiated animals, the salispheres were all capable of improving the saliva secretion that was disrupted by irradiation. Typical histologic structures could be observed in most parts of the treated glands, and the fibrotic environments of irradiated submandibular glands were remodeled by all salispheres regardless of origins. This study characterized the cellular features and in vivo effects of salispheres that were derived from different anatomic origins. The results suggest the possibility of functional redundancy among distinct pairs of major SGs, which is useful for the design of cell therapy to treat dysfunctional glandular organs.

Emerging organoid-based platforms to study salivary gland hypofunction

“…After the successful generation of human SSp from the parotid gland (PG) and SMG using the same protocol applied to murine samples [25], researchers have tried to optimize culture conditions for long-term maintenance and functional maturation of SGOs. In general, floating culture and embedding into ECM material such as Matrigel are the most frequently utilized methods to generate SGOs and different culture conditions are required for SGSC expansion and induction of differentiation/ maturation (Table 1) [24][25][26][27][28][29][30][31][32]. Of note, Maimets et al [29] applied well-defined culture conditions for intestinal epithelial organoids to establish SGOs and revealed that the canonical Wnt/ β-catenin pathway is required for the maintenance of SGSC self-renewal in vitro.…”

“…Similar to other exocrine organs, the production of saliva is tightly regulated by the autonomous nervous system via interactive crosstalk between receptor signaling [54][55][56]. In these aspects, Lee et al [32] successfully generated region-specific SGOs with unique cellular composition, although their secretory functions were not determined. Therefore, it would be important to check the expression pattern of receptors (cholinergic and purinergic receptors) and to test the reactivity of differentiated SGOs to various stimuli for functional evaluation.…”

“…Considering that dissociated cells from the SG consist of differentiated mature cells as well as SGSCs and progenitors, many attempts have been reported to distinguish the SGSC population for SGO establishment. Based on the previous findings in other glandular-and epithelial tissue biology, several candidates such as c-kit, CD49f, CD24, CD29, CD133, and CD326 (EpCAM) have been suggested as SGSC markers (Table 1) [24][25][26][27][28][29][30][31][32]. Nanduri et al [27] classified the potential SGSC population among primary SS-dissociated cells into 4 groups according to their pattern of CD24/CD29 expression.…”

“…Furthermore, not only isolated SGSCs but also SGOs themselves are capable of tissue restoration. Several attempts have been conducted to test the therapeutic impact of reconstituted SGO-mesenchyme-biomaterial complex [4,32,52]. After the orthotopic engraftment of bioengineered SG structures in vivo, they were integrated into the recipient tissue properly with a differentiated structure.…”

Bioengineering in salivary gland regeneration

“…Indeed, clinical trials suggest stem cell therapy [ 16 , 17 , 19 ] combined with special cell culture methods such as spontaneous cell aggregation, hanging drop and rotating culture vessels [ 1 , 20 , 21 ] or scaffold material [ 22 – 25 ] to produce functional secretory epithelial organoids, and gene therapy [ 18 ] may offer new therapeutic options for radiation-induced xerostomia. Due to challenges related to keeping the functionality of SG cells, researchers have examined the potential benefit of using a combination of different biomaterials [ 26 , 27 ] and cell types to provide the optimal implant material for SG tissue engineering applications [ 28 – 30 ]. Nevertheless, fabricating a fully formed functional SG replacement in a controlled manner remains a challenge [ 11 ].…”