Salivary Gland Stem Cells and Tissue Regeneration: An Update on Possible Therapeutic Application

Saliva of persons with hemophilia A triggers coagulation via extrinsic tenase complexes

ABSTRACT

Human saliva contains extracellular vesicles (EVs). These EVs expose extrinsic tenase complexes of tissue factor (TF) and activated factor VII (FVIIa), and trigger blood coagulation. Here, we show that EVs exposing extrinsic tenase complexes are also present in saliva of persons with severe hemophilia A, that is, persons with FVIII deficiency. Addition of these salivary EVs to autologous FVIII-deficient blood results in FXa generation, thereby compensating for the lack of FXa generation via intrinsic tenase (FVIIIa/FIXa) complexes. Consistently, in our retrospective analysis of persons with severe hemophilia A who do not receive prophylactic FVIII substitution, oropharyngeal mucosal bleedings are infrequent and self-limited. Conversely, in saliva of persons with severe FVII deficiency, in whom oropharyngeal bleedings are prevalent, functional extrinsic tenase complexes are absent, because EVs lack FVII. Saliva of persons with severe FVII deficiency is unable to restore blood coagulation, which is because of the absence of FVII in both their saliva and blood. Picomolar levels of recombinant FVIIa can restore the coagulant potential of saliva of persons with FVII deficiency. Taken together, our findings may explain the paucity of oropharyngeal bleedings in persons with hemophilia A as well as the occurrence of such bleedings in persons with severe FVII deficiency.

Bioengineered Salivary Gland Microtissues─A Review of 3D Cellular Models and their Applications

Salivary glands (SGs) play a vital role in maintaining oral health through the production and release of saliva. Injury to SGs can lead to gland hypofunction and a decrease in saliva secretion manifesting as xerostomia. While symptomatic treatments for xerostomia exist, effective permanent solutions are still lacking, emphasizing the need for innovative approaches. Significant progress has been made in the field of three-dimensional (3D) SG bioengineering for applications in gland regeneration. This has been achieved through a major focus on cell culture techniques, including soluble cues and biomaterial components of the 3D niche. Cells derived from both adult and embryonic SGs have highlighted key in vitro characteristics of SG 3D models. While still in its first decade of exploration, SG spheroids and organoids have so far served as crucial tools to study SG pathophysiology. This review, based on a literature search over the past decade, covers the importance of SG cell types in the realm of their isolation, sourcing, and culture conditions that modulate the 3D microenvironment. We discuss different biomaterials employed for SG culture and the current advances made in bioengineering SG models using them. The success of these 3D cellular models are further evaluated in the context of their applications in organ transplantation and in vitro disease modeling.

Regeneration and anti-inflammatory effects of stem cells and their extracellular vesicles in gynecological diseases

There are many gynecological diseases, among which breast cancer (BC), cervical cancer (CC), endometriosis (EMs), and polycystic ovary syndrome (PCOS) are common and difficult to cure. Stem cells (SCs) are a focus of regenerative medicine. They are commonly used to treat organ damage and difficult diseases because of their potential for self-renewal and multidirectional differentiation. SCs are also commonly used for difficult-to-treat gynecological diseases because of their strong directional differentiation ability with unlimited possibilities, their tendency to adhere to the diseased tissue site, and their use as carriers for drug delivery. SCs can produce exosomes in a paracrine manner. Exosomes can be produced in large quantities and have the advantage of easy storage. Their safety and efficacy are superior to those of SCs, which have considerable potential in gynecological treatment, such as inhibiting endometrial senescence, promoting vascular reconstruction, and improving anti-inflammatory and immune functions. In this paper, we review the mechanisms of the regenerative and anti-inflammatory capacity of SCs and exosomes in incurable gynecological diseases and the current progress in their application in genetic engineering to provide a foundation for further research.

Minor salivary gland stem cells: a comparative study of the biological properties under clinical-grade culture conditions

Development of clinical-grade, cell preparations is central to cGMP (good manufacturing practice compliant) conditions. This study aimed to investigate the potential of two serum/xeno-free, cGMP (StemPro, StemMacs) culture media to maintain "stemness" of human minor salivary gland stem cell (mSG-SC) cultures compared to a complete culture medium (CCM). Overall, StemMacs resulted in higher proliferation rates after p.6 compared to the conventional serum-based medium, while StemPro showed substantial delays in cell proliferation after p.9. The mSG-SCs cultures exhibited two distinct cell populations at early passages a mesenchymal subpopulation and an epithelial-like subpopulation. Expression of several markers (CD146, STRO-1, SSEA-4, CD105, CD106, CD34, K 7/8, K14, K18) variably decreased with prolonged passaging (all three media). The percentage of SA-β-gal positive cells was initially higher for StemMacs compared to StemPro/CCM and increased with prolonged passaging in all cases. The telomere fragment length decreased with prolonged passaging in all three media but more pronouncedly for the CCM. Expansion under serum-free conditions caused pronounced upregulation of ALP and BMP-2, with parallel complete elimination of the baseline expressions of LPL (all three media) and ACAN (serum-free media), therefore, showing a preferential shift of the mSG-SCs towards osteogenic phenotypes. Finally, several markers (Nanog, SOX-2, PDX-1, OTX2, GSC, HCG) decreased with prolonged culture, indicating successive loss of "stemness". Based on the findings, it seems that StemPro preserve stemness of the mSG-SCs after prolonged culture. Nevertheless, there is still a vacant role for the ideal development of clinical-grade culture conditions.

Salivary stimulatory effect of novel low level transcutaneous electro neurostimulator in geriatric patients with xerostomia

BACKGROUND

Xerostomia (dryness of the mouth) is one of the most common long-term consequences of ageing, and it causes a tremendous impact on the function and morphology of the salivary ductal system. As a consequence, it leads to a decrease in the amount of salivary output and also affects the overall quality of life. The purpose of this study was to determine whether electrostimulation using a custom designed transcutaneous electrical nerve stimulation (TENS) device will help to improve the quality of secreted saliva following electrostimulation.

METHODS

One hundred thirty-five participants underwent the intervention for three months, twice daily (80 Hz). Pre-intervention and post-intervention unstimulated saliva were collected. Parameters such as salivary pH, cortisol level, salivary antioxidants, total protein, the viscosity of saliva, and microbial carriage were analysed.

RESULTS

Salivary pH, cortisol, microbial cultures, viscosity, and antioxidants showed a significant difference at the end of the 3rd month (p < 0.05). Irrespective of the patient's age, gender, and common underlying systemic illnesses (diabetes and hypertension), a significant change in the quality of the salivary analytes was observed.

CONCLUSION

The study emphasises the use of a custom designed TENS device in improving the quality of secreted saliva among old patients with oral dryness.

Bedside labial salivary gland biopsy (LSGBx: Lip biopsy): An update for rheumatologists

Retrieval of minor salivary glands from a labial submucosal site through a minimally invasive bedside procedure was first described nearly 60 years ago and remains an attractive alternative to more invasive surgical procedures to obtain salivary gland tissue for pathologic examination. Examination of glands for features of Sjögren's has constituted the primary use of this procedure but other systemic disorders can affect minor salivary glands and their diagnoses can be supported by biopsy. Performance of the procedure does not require specialized training in head and neck surgery or dentistry, only simple wound closure skills. Skill in performing the procedure enables the clinician to acquire potentially diagnostic material without the need for referral while offering immediate expert feedback to the patient being biopsied. Material obtained at biopsy can also be the focus of research investigations.

Bioengineering in salivary gland regeneration

Salivary gland (SG) dysfunction impairs the life quality of many patients, such as patients with radiation therapy for head and neck cancer and patients with Sjögren’s syndrome. Multiple SG engineering strategies have been considered for SG regeneration, repair, or whole organ replacement. An in-depth understanding of the development and differentiation of epithelial stem and progenitor cells niche during SG branching morphogenesis and signaling pathways involved in cell–cell communication constitute a prerequisite to the development of suitable bioengineering solutions. This review summarizes the essential bioengineering features to be considered to fabricate an engineered functional SG model using various cell types, biomaterials, active agents, and matrix fabrication methods. Furthermore, recent innovative and promising approaches to engineering SG models are described. Finally, this review discusses the different challenges and future perspectives in SG bioengineering.

Induction of Salivary Gland-Like Tissue by Induced Pluripotent Stem Cells In Vitro

BACKGROUND

To investigate the in vitro induction of salivary gland-like tissue by ips cells in an interferon regulatory factor 6 (IRF6) overexpression and parotid conditioned medium environment.

METHODS

Urine-derived ips cells were isolated, identified, transfected with IRF6 and cultured in parotid conditioned medium to induce ips cells into salivary gland differentiation, morphological changes of ips cells were observed, CCK-8 was used to determine the cell proliferation efficiency and transcriptome sequencing was used to detect the expression of genes related to parotid gland formation.

RESULTS

Immunofluorescence staining showed that the isolated ips cells were positive for NANOG, SSEA4 and OCT4 and had embryonic-like stem cell characteristics; CCK-8 showed that there was no statistical difference in the proliferation efficiency between the IRF6⁺ induced group and the simple induced group after induction of ips cells into salivary glands. The results of transcriptome sequencing showed that there were a total of 643 differentially expressed genes, including 365 up-regulated genes and 278 down-regulated genes in the IRF6⁺ induced group compared to the blank control group, and the salivary gland related genes HAPLN1, CCL2, MSX2, ANXA1, CYP11A1, HES1 and LUM were all highly expressed in the IRF6⁺ induced group.

CONCLUSION

IRF6 promotes salivary gland differentiation in urine-derived iPSCs, and its mechanism of promoting differentiation may be that IRF6 upregulates the expression of HAPLN1, CCL2, MSX2, ANXA1, CYP11A1, HES1 and LUM to promote epithelial differentiation.

Immunosuppressed Miniswine as a Model for Testing Cell Therapy Success: Experience With Implants of Human Salivary Stem/Progenitor Cell Constructs

An urgent need exists to develop large animal models for preclinical testing of new cell therapies designed to replace lost or damaged tissues. Patients receiving irradiation for treatment of head and neck cancers frequently develop xerostomia/dry mouth, a condition that could one day be treated by cell therapy to repopulate functional saliva-producing cells. Using immunosuppression protocols developed for patients receiving whole face transplants, we successfully used immunosuppressed miniswine as a suitable host animal to evaluate the long-term stability, biocompatibility, and fate of matrix-modified hyaluronate (HA) hydrogel/bioscaffold materials containing encapsulated salivary human stem/progenitor cells (hS/PCs). An initial biocompatibility test was conducted in parotids of untreated miniswine. Subsequent experiments using hS/PC-laden hydrogels were performed in animals, beginning an immunosuppression regimen on the day of surgery. Implant sites included the kidney capsule for viability testing and the parotid gland for biointegration time periods up to eight weeks. No transplant rejection was seen in any animal assessed by analysis of the tissues near the site of the implants. First-generation implants containing only cells in hydrogel proved difficult to handle in the surgical suite and were modified to adhere to a porcine small intestinal submucosa (SIS) membrane for improved handling and could be delivered through the da Vinci surgical system. Several different surgical techniques were assessed using the second-generation 3D-salivary tissue (3D-ST) for ease and stability both on the kidney capsule and in the capsule-less parotid gland. For the kidney, sliding the implant under the capsule membrane and quick stitching proved superior to other methods. For the parotid gland, creation of a tissue “pocket” for placement and immediate multilayer tissue closure were well tolerated with minimal tissue damage. Surgical clips were placed as fiduciary markers for tissue harvest. Some implant experiments were conducted with miniswine 90 days post-irradiation when salivation decreased significantly. Sufficient parotid tissue remained to allow implant placement, and animals tolerated immunosuppression. In all experiments, viability of implanted hS/PCs was high with clear signs of both vascular and nervous system integration in the parotid implants. We thus conclude that the immunosuppressed miniswine is a high-value emerging model for testing human implants prior to first-in-human trials.

Laminin-1 Peptides Conjugated to Fibrin Hydrogels Promote Salivary Gland Regeneration in Irradiated Mouse Submandibular Glands

Previous studies demonstrated that salivary gland morphogenesis and differentiation are enhanced by modification of fibrin hydrogels chemically conjugated to Laminin-1 peptides. Specifically, Laminin-1 peptides (A99: CGGALRGDN-amide and YIGSR: CGGADPGYIGSRGAA-amide) chemically conjugated to fibrin promoted formation of newly organized salivary epithelium both in vitro (e.g., using organoids) and in vivo (e.g., in a wounded mouse model). While these studies were successful, the model's usefulness for inducing regenerative patterns after radiation therapy remains unknown. Therefore, the goal of the current study was to determine whether transdermal injection with the Laminin-1 peptides A99 and YIGSR chemically conjugated to fibrin hydrogels promotes tissue regeneration in irradiated salivary glands. Results indicate that A99 and YIGSR chemically conjugated to fibrin hydrogels promote formation of functional salivary tissue when transdermally injected to irradiated salivary glands. In contrast, when left untreated, irradiated salivary glands display a loss in structure and functionality. Together, these studies indicate that fibrin hydrogel-based implantable scaffolds containing Laminin-1 peptides promote secretory function of irradiated salivary glands.

Regenerative Medicine of Epithelia: Lessons From the Past and Future Goals

This article explores examples of successful and unsuccessful regenerative medicine on human epithelia. To evaluate the applications of the first regenerated tissues, the analysis of the past successes and failures addresses some pending issues and lay the groundwork for developing new therapies. Research should still be encouraged to fill the gap between pathologies, clinical applications and what regenerative medicine can attain with current knowledge.