Transplantation of side population cells restores the function of damaged exocrine glands through clusterin

Retrospective study on the effect of adipose stem cell transplantation on jaw bone regeneration

PURPOSE

In patients with jaw bone atrophy, dental implant therapy requires bone augmentation on the alveolar ridge. Common methods are autologous bone transplantation or bone substitutes. The latter technique is less surgically invasive because it does not require bone harvesting; however, blood supply from the surrounding tissues and local differentiation of osteoblasts are not guaranteed, so adequate bone regeneration for dental implant therapy is often not achieved. Therefore, at our hospital we introduced a bone regenerative medicine technique that uses adipose stem cells (ASCs) from adipose tissue. The new approach is less surgically invasive and appears to have a better effect on bone regeneration. The current retrospective study aimed to demonstrate the efficacy of ASC transplantation in patients who underwent alveolar ridge bone augmentation at our hospital.

METHODS

We compared medical records, postoperative radiographic findings, and histological results from patients treated between January 2018 and March 2022 by augmentation of the jaw bone with bone substitutes (carbonate apatite) mixed with ASCs (ASCs+ group) and those treated with bone substitutes (carbonate apatite) alone (ASCs- group).

RESULTS

After 6 months, the survival rate of augmented bone and the gray scale value in dental cone beam computed tomography (a bone density index) were significantly higher in the ASCs+ group than in the ASCs- group. Histological analysis at 6 months showed more adequate bone tissue regeneration in the ASCs+ group.

CONCLUSIONS

The findings suggest the effectiveness of using ASCs in bone augmentation on the alveolar ridge in patients with jaw bone atrophy.

Complement C7 and clusterin form a complex in circulation

Introduction

The complement system is part of innate immunity and is comprised of an intricate network of proteins that are vital for host defense and host homeostasis. A distinct mechanism by which complement defends against invading pathogens is through the membrane attack complex (MAC), a lytic structure that forms on target surfaces. The MAC is made up of several complement components, and one indispensable component of the MAC is C7. The role of C7 in MAC assembly is well documented, however, inherent characteristics of C7 are yet to be investigated.

Methods

To shed light on the molecular characteristics of C7, we examined the properties of serum-purified C7 acquired using polyclonal and novel monoclonal antibodies. The properties of serum‑purified C7 were investigated through a series of proteolytic analyses, encompassing Western blot and mass spectrometry. The nature of C7 protein-protein interactions were further examined by a novel enzyme-linked immunosorbent assay (ELISA), as well as size‑exclusion chromatography.

Results

Protein analyses showcased an association between C7 and clusterin, an inhibitory complement regulator. The distinct association between C7 and clusterin was also demonstrated in serum-purified clusterin. Further assessment revealed that a complex between C7 and clusterin (C7-CLU) was detected. The C7-CLU complex was also identified in healthy serum and plasma donors, highlighting the presence of the complex in circulation.

Discussion

Clusterin is known to dissociate the MAC structure by binding to polymerized C9, nevertheless, here we show clusterin binding to the native form of a terminal complement protein in vivo. The presented data reveal that C7 exhibits characteristics beyond that of MAC assembly, instigating further investigation of the effector role that the C7-CLU complex plays in the complement cascade.

The Ins and Outs of Clusterin: Its Role in Cancer, Eye Diseases and Wound Healing

Clusterin (CLU) is a glycoprotein originally discovered in 1983 in ram testis fluid. Rapidly observed in other tissues, it was initially given various names based on its function in different tissues. In 1992, it was finally named CLU by consensus. Nearly omnipresent in human tissues, CLU is strongly expressed at fluid-tissue interfaces, including in the eye and in particular the cornea. Recent research has identified different forms of CLU, with the most prominent being a 75-80 kDa heterodimeric protein that is secreted. Another truncated version of CLU (55 kDa) is localized to the nucleus and exerts pro-apoptotic activities. CLU has been reported to be involved in various physiological processes such as sperm maturation, lipid transportation, complement inhibition and chaperone activity. CLU was also reported to exert important functions in tissue remodeling, cell-cell adhesion, cell-substratum interaction, cytoprotection, apoptotic cell death, cell proliferation and migration. Hence, this protein is sparking interest in tissue wound healing. Moreover, CLU gene expression is finely regulated by cytokines, growth factors and stress-inducing agents, leading to abnormally elevated levels of CLU in many states of cellular disturbance, including cancer and neurodegenerative conditions. In the eye, CLU expression has been reported as being severely increased in several pathologies, such as age-related macular degeneration and Fuch's corneal dystrophy, while it is depleted in others, such as pathologic keratinization. Nevertheless, the precise role of CLU in the development of ocular pathologies has yet to be deciphered. The question of whether CLU expression is influenced by these disorders or contributes to them remains open. In this article, we review the actual knowledge about CLU at both the protein and gene expression level in wound healing, and explore the possibility that CLU is a key factor in cancer and eye diseases. Understanding the expression and regulation of CLU could lead to the development of novel therapeutics for promoting wound healing.

Role of stem cells in regenerative treatment of dry eye disease caused by lacrimal gland dysfunction

An ageing population and increased screen use in younger people have contributed to a rise in incidence of dry eye disease (DED). Quality of life can be significantly affected by DED, with patients experiencing eye dryness, burning, pain and sensitivity to light. If left untreated, DED may progress to cause lasting damage to the delicate cell layers of the ocular surface. The aqueous-deficient form of DED is characterized by decreased tear volume. This can occur through underlying disease or damage to the lacrimal gland (LG), which results in increased inflammation at the ocular surface and decreased tear secretion. Regenerative therapy for treatment of aqueous-deficient DED would ideally restore LG function without causing adverse side effects and be feasible in terms of cost, production and practical application in the clinic. In this review, we evaluate research directed at the development of clinical procedures for regeneration of the LG using various stem cell types and their products. We also discuss work identifying potential therapeutic targets that may alter pathways to effect healing and ameliorate development of DED. Finally, we discuss shortcomings and recommend future avenues for research. These include determination of the best tissue of origin for mesenchymal cells and transference of knowledge gleaned from animal studies to clinical investigations.

Characterization of Transgenic NSG-SGM3 Mouse Model of Precision Radiation-Induced Chronic Hyposalivation

Regenerative medicine holds promise to cure radiation-induced salivary hypofunction, a chronic side effect in patients with head and neck cancers, therefore reliable preclinical models for salivary regenerative outcome will promote progress towards therapies. In this study, our objective was to develop a cone beam computed tomography-guided precision ionizing radiation-induced preclinical model of chronic hyposalivation using immunodeficient NSG-SGM3 mice. Using a Schirmer's test based sialagogue-stimulated saliva flow kinetic measurement method, we demonstrated significant differences in hyposalivation specific to age, sex, precision-radiation dose over a chronic (6 months) timeline. NSG-SMG3 mice tolerated doses from 2.5 Gy up to 7.5 Gy. Interestingly, 5-7.5 Gy had similar effects on stimulated-saliva flow (∼50% reduction in young female at 6 months after precision irradiation over sham-treated controls), however, >5 Gy led to chronic alopecia. Different groups demonstrated characteristic saliva fluctuations early on, but after 5 months all groups nearly stabilized stimulated-saliva flow with low-inter-mouse variation within each group. Further characterization revealed precision-radiation-induced glandular shrinkage, hypocellularization, gland-specific loss of functional acinar and glandular cells in all major salivary glands replicating features of human salivary hypofunction. This model will aid investigation of human cell-based salivary regenerative therapies.

Clusterin, other extracellular chaperones, and eye disease

Proteostasis refers to all the processes that maintain the correct expression level, location, folding and turnover of proteins, essential to organismal survival. Both inside cells and in body fluids, molecular chaperones play key roles in maintaining proteostasis. In this article, we focus on clusterin, the first-recognized extracellular mammalian chaperone, and its role in diseases of the eye. Clusterin binds to and inhibits the aggregation of proteins that are misfolded due to mutations or stresses, clears these aggregating proteins from extracellular spaces, and facilitates their degradation. Clusterin exhibits three main homeostatic activities: proteostasis, cytoprotection, and anti-inflammation. The so-called "protein misfolding diseases" are caused by aggregation of misfolded proteins that accumulate pathologically as deposits in tissues; we discuss several such diseases that occur in the eye. Clusterin is typically found in these deposits, which is interpreted to mean that its capacity as a molecular chaperone to maintain proteostasis is overwhelmed in the disease state. Nevertheless, the role of clusterin in diseases involving such deposits needs to be better defined before therapeutic approaches can be entertained. A more straightforward case can be made for therapeutic use of clusterin based on its proteostatic role as a proteinase inhibitor, as well as its cytoprotective and anti-inflammatory properties. It is likely that clusterin works together in this way with other extracellular chaperones to protect the eye from disease, and we discuss several examples. We end this article by predicting future steps that may lead to development of clusterin as a biological drug.

Mechanism, Prevention, and Treatment of Radiation-Induced Salivary Gland Injury Related to Oxidative Stress

Radiation therapy is a common treatment for head and neck cancers. However, because of the presence of nerve structures (brain stem, spinal cord, and brachial plexus), salivary glands (SGs), mucous membranes, and swallowing muscles in the head and neck regions, radiotherapy inevitably causes damage to these normal tissues. Among them, SG injury is a serious adverse event, and its clinical manifestations include changes in taste, difficulty chewing and swallowing, oral infections, and dental caries. These clinical symptoms seriously reduce a patient’s quality of life. Therefore, it is important to clarify the mechanism of SG injury caused by radiotherapy. Although the mechanism of radiation-induced SG injury has not yet been determined, recent studies have shown that the mechanisms of calcium signaling, microvascular injury, cellular senescence, and apoptosis are closely related to oxidative stress. In this article, we review the mechanism by which radiotherapy causes oxidative stress and damages the SGs. In addition, we discuss effective methods to prevent and treat radiation-induced SG damage.

Application of regenerative medicine to salivary gland hypofunction

Dry mouth results from hypofunction of the salivary glands due to Sjögren's syndrome (SS), various medications, and radiation therapy for head and neck cancer. In severe cases of salivary gland hypofunction, sialagogues are not always effective due to the loss of salivary parenchyma. Therefore, regenerative medicine using stem cell therapy is a promising treatment for severe cases. Stem cells are classified into three groups: tissue stem cells, embryonic stem cells, and induced pluripotent stem cells. Tissue stem cells, such as hematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs) and salivary stem/progenitor cells, could rescue irradiation-induced salivary gland hypofunction. Both HSCs and MSCs can rescue salivary gland hypofunction through soluble factors in a paracrine manner, while salivary stem/progenitor cells can reconstitute the damaged salivary glands. In fact, we clarified that CD133-positive cells in mouse submandibular glands showed stem cell features, which reconstituted the damaged salivary glands. Furthermore, we focused on the challenge of producing functional salivary glands that are three-dimensionally induced from mouse ES cells.

Pathology of salivary gland dysfunction and restoration of function

In this review, the author shows that simultaneous multiple disorders caused by reactivation of Epstein-Barr virus can lead to salivary gland disorders as part of Sjogren's syndrome (SS). Therefore, clinicians must differentiate SS from other diseases when diagnosing and treating salivary gland disorders. In particular, the author explains how microbial infection in SS overcomes immunological tolerance, leading to pathological changes, and how cytokine overexpression and endocrine disrupters contribute to glandular tissue injury. Also, the author suggests that involvement of reactive oxygen species is a common pathogenesis of salivary gland disorders and SS, so regulation of oxidative stress is an effective treatment for both. The results of clinical studies on restoring salivary gland function and regenerating salivary glands with tissue stem cells may provide clues on elucidating the cause of SS.

Mesenchymal stem cells enhance AQP1 expression in the sublingual salivary gland of ovariectomized menopausal rat model

BACKGROUND

Ovariectomized menopausal rat model was used to investigate the effects of menopause on the sublingual salivary gland (SSG) and the potential therapeutic effect of human umbilical cord blood mesenchymal stem cells (hUCB-MSCs).

METHODS

Thirty rats were equally divided into three groups: sham-operated (SHAM), ovariectomized (OVX), and ovariectomized stem cells injected (OVX+ hUCB-MSCs). Expressions of α-SMA, AQP1, Sca-1, PCNA, ssDNA, and caspase-3 were determined. Homing of hUCB-MSCs was detected by fluorescence microscopy and examination of immunostained sections for human CD105 and CD34 was performed. Morphometric data were statistically analyzed using the Kruskal-Wallis test followed by Scheffé's method. Correlation of AQP1 with Sca-1-positive sublingual stem cells was also analyzed.

RESULTS

In the SSGs of the OVX group, ballooned mucus acinar cells, atrophied serous cells, and a decreased number and height of duct lining cells were observed. The interstitial spaces were edematous, and the blood vessels were congested. The significant decrease in the positive area % of α-SMA and AQP1, the number of Sca-1-positive sublingual stem cells, and proliferating cells was associated with a significant increase in apoptotic cells. The OVX+hUCB-MSCs group showed significant structural improvement, manifested by the normal appearance of mucus and serous acini, as well as the number and height of striated duct cells. A significant increase in the positive area % of α-SMA and AQP1 and the number of proliferating and Sca-1-positive sublingual stem cells was observed. Interestingly, a significantly positive Pearson's correlation between the area % of AQP1 and the number of Sca-1-positive sublingual stem cells was also recorded.

CONCLUSION

Our results indicated a positive effect of hUCB-MSCs therapy for SSG pathology in a post ovariectomy rat model as evidenced by an improvement in the histologic architecture, upregulation of the immunostained area % of α-SMA and AQP1, increase in the number of Sca-1-positive sublingual stem cells and proliferating cells, and downregulation of apoptotic cells.

Brain clusterin protein isoforms and mitochondrial localization

Clusterin (CLU), or apolipoprotein J (ApoJ), is the third most predominant genetic risk factor associated with late-onset Alzheimer’s disease (LOAD). In this study, we use multiple rodent and human brain tissue and neural cell models to demonstrate that CLU is expressed as multiple isoforms that have distinct cellular or subcellular localizations in the brain. Of particular significance, we identify a non-glycosylated 45 kDa CLU isoform (mitoCLU) that is localized to the mitochondrial matrix and expressed in both rodent and human neurons and astrocytes. In addition, we show that rodent mitoCLU is translated from a non-canonical CUG (Leu) start site in Exon 3, a site that coincides with an AUG (Met) in human CLU. Last, we reveal that mitoCLU is present at the gene and protein level in the currently available CLU^–/– mouse model. Collectively, these data provide foundational knowledge that is integral in elucidating the relationship between CLU and the development of LOAD.

Towards Lacrimal Gland Regeneration: Current Concepts and Experimental Approaches

Dry eye disease (DED) is a complex and multifactorial disease resulting in a continual cycle of tear hyperosmolarity and inflammation. Patients suffering from DED experience severe pain and visual impairments leading to a reduced quality of life. Aqueous-deficient dry eye (ADDE), mainly caused through a loss of functional lacrimal gland tissue, results in the most severe forms of DED. Despite a high prevalence, the current treatments remain palliative and may be insufficient to alleviate the symptoms. Consequently, investigations on experimental approaches for in situ lacrimal gland regeneration are of great clinical interest. This article reviews the current knowledge about processes involved in lacrimal gland regeneration, about lacrimal gland resident stem cells, and offers deductions about possible concepts for in situ lacrimal gland regeneration. Promising starting points might be the utilization of therapeutic proteins, such as bone morphogenetic protein 7, mesenchymal stem cells (MSC) or MSC-based treatments such as conditioned medium, lyophilized cell extracts or adult acinar cells. This review further summarizes current experimental approaches for the treatment of ADDE in animal models and patients. Approaches investigating side population stem cells, epithelial progenitor cells and MSC showed that the transplantation of these cells had therapeutic effects on ADDE. However, the most promising and best-studied experimental approach is the use of MSC for induction/enhancement of in situ lacrimal gland regeneration. Their immunomodulatory effects, low immunogenicity, promotion of tissue regeneration and involvement during spontaneous lacrimal regeneration are favorable traits for clinical applications. In addition, the efficacy and safety of allogeneic MSC transplantation have already been demonstrated in a small patient cohort.

Sox9 regulates the luminal stem/progenitor cell properties of salivary glands

Exocrine glands share a common morphology consisting of ductal, acinar, and basal/myoepithelial cells, but their functions and mechanisms of homeostasis differ among tissues. Salivary glands are an example of exocrine glands, and they have been reported to contain multipotent stem cells that differentiate into other tissues. In this study, we purified the salivary gland stem/progenitor cells of adult mouse salivary glands using the cell surface marker CD133 by flow cytometry. CD133⁺ cells possessed stem cell capacity, and the transplantation of CD133⁺ cells into the submandibular gland reconstituted gland structures, including functional acinar. CD133⁺ cells were sparsely distributed in the intercalated and exocrine ducts and expressed Sox9 at higher levels than CD133^- cells. Moreover, we demonstrated that Sox9 was required for the stem cell properties CD133⁺ cells, including colony and sphere formation. Thus, the Sox9-related signaling may control the regeneration salivary glands.

Regeneration of Lacrimal Gland Function to Maintain the Health of the Ocular Surface

Dry eye is a multifactorial disease that is one of the most common diseases worldwide. A major cause of dry eye is the deficiency of aqueous tears, which are mainly secreted from the lacrimal gland. The lacrimal gland plays an important role in maintaining the health of the ocular surface and protecting it from environmental exposure. Dry eye can lead to ocular irritation and discomfort, as well as severe ocular surface diseases (e.g., ocular infections, corneal ulcerations, and ocular surface keratinization). These severe diseases can be induced by an atrophied or injured lacrimal gland; current therapies cannot completely restore the function of lacrimal gland. To develop more definitive therapies, it is important to understand lacrimal gland biology at the molecular level, as well as inflammatory processes affecting the function of the gland. During severe inflammation, the tissue structure of the lacrimal gland is destroyed; it is replaced by scar formation during wound healing, which leads to lacrimal gland dysfunction. Using an animal model of lacrimal gland dysfunction, many investigators have studied molecular mechanisms of inflammation in the lacrimal gland. To restore lacrimal gland function, the lacrimal acini must be restored in their niche. Notably, organ transplantation therapies have been reported to restore lacrimal gland function, directly or indirectly, in animal models. In this review, we describe the current understanding of the lacrimal gland as the therapeutic target for dry eye diseases, as well as recent advances in the field of lacrimal gland cell-based therapy to treat severe dry eye diseases.

Clusterin from human clinical tear samples: Positive correlation between tear concentration and Schirmer strip test results

PURPOSE

To investigate the relationship between tear concentration of the homeostatic protein clusterin (CLU) and dry eye signs and symptoms, and to characterize tear CLU protein.

METHODS

Two independent studies were conducted, one in Tucson (44 subjects), the other in Los Angeles (52 subjects). A cohort study design was employed to enroll patients without regard to dry eye diagnosis. Dry eye signs and symptoms were assessed using clinical tests. Tear samples were collected by Schirmer strip, and also by micropipette at slit lamp when possible. CLU from both sample types was quantified by immunoassay. The relationship between CLU concentration and clinical test scores was determined by Pearson's correlation coefficient (for individual eyes) and multiple linear regression analysis (including both eyes). CLU was also evaluated biochemically by western blotting.

RESULTS

In the Tucson cohort, a positive correlation was observed between tear CLU concentration and results of the Schirmer strip test, a measure of tear flow (p = 0.021 includes both eyes). This result was corroborated in the Los Angeles cohort (p = 0.013). The mean tear CLU concentration was 31 ± 14 μg/mL (n = 18 subjects, 33 eyes; range = 7-48 μg/mL). CLU from clinical tear samples appeared biochemically similar to CLU from a non-clinical tear sample and from blood plasma.

CONCLUSIONS

Results support the hypothesis that an optimal concentration of tear CLU is important for ocular surface health, and that this drops below the effective threshold in dry eye. Tear CLU measurement might identify patients that could benefit from supplementation. Information about concentration will aid development of therapeutic dosage parameters.

Mechanistic effect of human umbilical cord blood derived mesenchymal stem cells on the submandibular salivary gland in ovariectomized rats

We performed this study to understand the effect of human umbilical cord blood derived mesenchymal stem cells (hUCB-MSCs) on the submandibular gland after bilateral ovariectomy. For this, 21 adult female rats were distributed equally among 3 groups: the sham-operated group (SHAM); the ovariectomized group (OVX); and the OVX group that received repeated intravenous injections of the hUCB-MSCs (OVX + hUCB-MSCs). We used reverse transcription – PCR to analyze for the gene expression of AQPs 3, 4, 5, and BMP-6. The cellular localization and expression of human CD105, human CD34, proliferating nuclear antigen (PCNA), single-stranded DNA (ss-DNA), caspase 3, AQP1, and α smooth muscle actin (α-SMA) were determined immunohistochemically. In the OVX group, a significant decrease in the gene expression of AQP3, AQP4, and BMP6, as well as the acinar area % was detected, while area % of granular convoluted tubules (GCTs) showed a significant increase. A significant decrease in area % staining positively for AQP1 and α-SMA was noted. An obvious improvement in the structure of the submandibular gland was demonstrated in the group injected with hUCB-MSCs, as well as a significant increase in the gene expression of AQP3, AQP4, and BMP6. The acinar and GCT area %, as well as the different measured markers, were relatively normal. This demonstrates that E2-deficiency induces structural changes to the submandibular gland. Moreover, a definite amelioration of the structure and function of the submandibular gland was detected after the administration of hUCB-MSCs.

Clusterin in the eye: An old dog with new tricks at the ocular surface

The multifunctional protein clusterin (CLU) was first described in 1983 as a secreted glycoprotein present in ram rete testis fluid that enhanced aggregation ('clustering') of a variety of cells in vitro. It was also independently discovered in a number of other systems. By the early 1990s, CLU was known under many names and its expression had been demonstrated throughout the body, including in the eye. Its homeostatic activities in proteostasis, cytoprotection, and anti-inflammation have been well documented, however its roles in health and disease are still not well understood. CLU is prominent at fluid-tissue interfaces, and in 1996 it was demonstrated to be the most highly expressed transcript in the human cornea, the protein product being localized to the apical layers of the mucosal epithelia of the cornea and conjunctiva. CLU protein is also present in human tears. Using a preclinical mouse model for desiccating stress that mimics human dry eye disease, the authors recently demonstrated that CLU prevents and ameliorates ocular surface barrier disruption by a remarkable sealing mechanism dependent on attainment of a critical all-or-none concentration in the tears. When the CLU level drops below the critical all-or-none threshold, the barrier becomes vulnerable to desiccating stress. CLU binds selectively to the ocular surface subjected to desiccating stress in vivo, and in vitro to LGALS3 (galectin-3), a key barrier component. Positioned in this way, CLU not only physically seals the ocular surface barrier, but it also protects the barrier cells and prevents further damage to barrier structure. CLU depletion from the ocular surface epithelia is seen in a variety of inflammatory conditions in humans and mice that lead to squamous metaplasia and a keratinized epithelium. This suggests that CLU might have a specific role in maintaining mucosal epithelial differentiation, an idea that can now be tested using the mouse model for desiccating stress. Most excitingly, the new findings suggest that CLU could serve as a novel biotherapeutic for dry eye disease.

The role of stem cells in the prevention and treatment of radiation-induced xerostomia in patients with head and neck cancer

Xerostomia is an important complication following radiotherapy (RT) for head and neck cancer. Current treatment approaches are insufficient and can only temporarily relieve symptoms. New insights into the physiopathology of radiation‐induced xerostomia might help us in this regard. This review discusses the current knowledge of salivary gland stem cells in radiation‐induced xerostomia and their value in the prevention and treatment of this complication. Salivary gland stem cell transplantation, bone marrow‐derived cell mobilization, molecular regulation of parotid stem cells, stem cell sparing RT, and adaptive RT are promising techniques that are discussed in this study.

Characterization of Long-Term Cultured Murine Submandibular Gland Epithelial Cells

PURPOSE

Human and rat salivary gland cell lines derived from tumors or genetic modification are currently available for research. Here, we attempted to culture and characterize long-term cultured cells spontaneously derived from wild type murine submandibular glands (SGs).

METHODS

SGs were removed from 3-week-old C57B/6J female mice and dissociated by collagenase type 1 and hyaluronidase digestion. Isolated SG epithelial cells were cultured in low calcium, serum-free growth media in the presence of cholera toxin (CT) during early passages. Single-cell colonies were isolated by limiting dilution culture after 25 passages. Early- and late-stage cell cultures were characterized for keratin 14, keratin 18, α-smooth muscle actin, and p63 by immunostaining and quantitative real-time PCR analysis.

RESULTS

SG epithelial cells cultured in optimized media maintained their proliferative ability and morphology for over 80 passages. Long-term cultured cells expressed keratin 14, keratin 18, and p63, indicative of an epithelial phenotype.

CONCLUSIONS

Epithelial cells originating from wild type murine SGs could be cultured for longer periods of time and remain phenotypically similar to ductal basal epithelium.

A potential endophenotype for Alzheimer's disease: cerebrospinal fluid clusterin

Genome-wide association studies have associated clusterin (CLU) variants with Alzheimer's disease (AD). However, the role of CLU on AD pathogenesis is not totally understood. We used cerebrospinal fluid (CSF) and plasma CLU levels as endophenotypes for genetic studies to understand the role of CLU in AD. CSF, but not plasma, CLU levels were significantly associated with AD status and CSF tau/amyloid-beta ratio, and highly correlated with CSF apolipoprotein E (APOE) levels. Several loci showed almost genome-wide significant associations including LINC00917 (p = 3.98 × 10(-7)) and interleukin 6 (IL6, p = 9.94 × 10(-6), in the entire data set and in the APOE ε4- individuals p = 7.40 × 10(-8)). Gene ontology analyses suggest that CSF CLU levels may be associated with wound healing and immune response which supports previous functional studies that demonstrated an association between CLU and IL6. CLU may play a role in AD by influencing immune system changes that have been observed in AD or by disrupting healing after neurodegeneration.

Engineering of a Secretory Active Three-Dimensional Lacrimal Gland Construct on the Basis of Decellularized Lacrimal Gland Tissue

Lacrimal gland (LG) insufficiency is a main cause for severe dry eye leading to pain, visual impairment, and eventually loss of sight. Engineering of transplantable LG tissue with secretory capacity is a desirable goal. In this study, a three-dimensional decellularized LG (DC-LG) scaffold with preserved LG morphology was generated by treatment with 1% sodium deoxycholate and DNase solution using porcine LG tissue. To address clinical applicability, the primary in vitro culture of secretory active LG cells from a small tissue biopsy of 1.5 mm diameter was introduced and compared with an established isolation method by enzymatic digestion. Cells from both isolation methods depicted an epithelial phenotype, maintained their secretory capacity for up to 30 days, and exhibited progenitor cell capacity as measured by aldehyde dehydrogenase-1 activity, side population assay, and colony-forming units. Cells from passage 0 were reseeded into the DC-LG and secretory active cells migrated into the tissue. The cells resembled an LG-like morphology and the constructs showed secretory activity. These results demonstrate the possibility of engineering a secretory competent, three-dimensional LG construct using LG cells expanded from a small tissue biopsy and DC-LG as a matrix that provides the native structure and physiological niche for these cells.

Regenerating Salivary Glands in the Microenvironment of Induced Pluripotent Stem Cells

This report describes our initial attempt to regenerate salivary glands using induced pluripotent stem (iPS) cells in vivo and in vitro. Glandular tissues that were similar to the adult submandibular glands (SMGs) and sublingual glands could be partially produced by the transplantation of iPS cells into mouse salivary glands. However, the tumorigenicity of iPS cells has not been resolved yet. It is well known that stem cells affect their microenvironment, known as a stem cell niche. We focused on the niche and the interaction between iPS cells and salivary gland cells in our study on salivary gland regeneration. Coculture of embryonic SMG cells and iPS cells have better-developed epithelial structures and fewer undifferentiated specific markers than monoculture of embryonic SMG cells in vitro. These results suggest that iPS cells have a potential ability to accelerate differentiation for salivary gland development and regeneration.

Evaluation of the effects of quercetin on damaged salivary secretion

With the aim of discovering an effective method to treat dry mouth, we analyzed the effects of quercetin on salivary secretion and its mechanism of action. We created a mouse model with impaired salivary secretion by exposure to radiation and found that impaired secretion is suppressed by quercetin intake. Moreover, secretion levels were enhanced in quercetin-fed normal mice. To elucidate the mechanisms of these effects on salivary secretion, we conducted an analysis using mouse submandibular gland tissues, a human salivary gland epithelial cell line (HSY), and mouse aortic endothelial cells (MAECs). The results showed that quercetin augments aquaporin 5 (AQP5) expression and calcium uptake, and suppresses oxidative stress and inflammatory responses induced by radiation exposure, suggesting that quercetin intake may be an effective method to treat impaired salivary secretion.

Neurotrophic factor GDNF promotes survival of salivary stem cells

Stem cell-based regenerative therapy is a promising treatment for head and neck cancer patients that suffer from chronic dry mouth (xerostomia) due to salivary gland injury from radiation therapy. Current xerostomia therapies only provide temporary symptom relief, while permanent restoration of salivary function is not currently feasible. Here, we identified and characterized a stem cell population from adult murine submandibular glands. Of the different cells isolated from the submandibular gland, this specific population, Lin-CD24+c-Kit+Sca1+, possessed the highest capacity for proliferation, self renewal, and differentiation during serial passage in vitro. Serial transplantations of this stem cell population into the submandibular gland of irradiated mice successfully restored saliva secretion and increased the number of functional acini. Gene-expression analysis revealed that glial cell line-derived neurotrophic factor (Gdnf) is highly expressed in Lin-CD24+c-Kit+Sca1+ stem cells. Furthermore, GDNF expression was upregulated upon radiation therapy in submandibular glands of both mice and humans. Administration of GDNF improved saliva production and enriched the number of functional acini in submandibular glands of irradiated animals and enhanced salisphere formation in cultured salivary stem cells, but did not accelerate growth of head and neck cancer cells. These data indicate that modulation of the GDNF pathway may have potential therapeutic benefit for management of radiation-induced xerostomia.

Treatment of salivary gland hypofunction by transplantation with dental pulp cells

OBJECTIVE

This study aimed to establish a mouse model in which dental pulp cells (DPCs) could be used as a cell source for the treatment of salivary gland hypofunction.

DESIGN

DPCs were isolated from green fluorescent protein (GFP)-expressing mice and were differentiated into dental pulp endothelial cells (DPECs). DPEC behaviour was studied in vitro and in vivo to investigate their capacity to participate in neovascularisation. For in vivo assessment, a combination of DPECs and Matrigel was subcutaneously injected into nude mice. Two weeks after injection, Matrigel plugs were analysed for CD31 and GFP. Furthermore, both submandibular glands of the irradiated mice were injected with DPECs. Eight weeks after irradiation, the effect of DPECs on saliva secretion was evaluated by measuring amounts of saliva secretion.

RESULTS

DPECs showed typical endothelial morphology, including a cobblestone appearance. RT-PCR analysis of DPECs showed positive expression of CD31, foetal liver kinase-1, vascular-endothelial-cadherin, vascular endothelial growth factor-A and von Willebrand factor. DPECs reorganised into tube-like structures on Matrigel after 24h in vitro. Positive merged staining for both CD31 and GFP was observed in the tube-like structures, representative of the injected DPECs. The average saliva flow rate in mice treated with DPECs was significantly higher than that observed in mice treated with PBS (P=0.0452).

CONCLUSIONS

Our results show that radiation-induced salivary hypofunction is partially reverted following transplantation of DPECs. We established a mouse model in which DPCs could be used as a cell source for the treatment of salivary gland hypofunction.

Nanoparticle-mediated gene silencing confers radioprotection to salivary glands in vivo

Radiation treatment of head and neck cancers causes irreversible damage of the salivary glands (SG). Here, we introduce a preclinical mouse model for small-interfering RNA (siRNA)-based gene silencing to provide protection of SG from radiation-induced apoptosis. Novel, pH-responsive nanoparticles complexed with siRNAs were introduced into mouse submandibular glands (SMG) by retroductal injection to modulate gene expression in vivo. To validate this approach, we first targeted Nkcc1, an ion transporter that is essential for saliva secretion. Nkcc1 siRNA delivery resulted in efficient knockdown, as quantified at the mRNA and the protein levels, and the functional result of Nkcc1 knockdown phenocopied the severe decrease in saliva secretion, characteristic of the systemic Nkcc1 gene knockout. To establish a strategy to prevent apoptotic cell loss due to radiation damage, siRNAs targeting the proapoptotic Pkcδ gene were administered into SMG before ionizing radiation. Knockdown of Pkcδ not only reduced the number of apoptotic cells during the acute phase of radiation damage, but also markedly improved saliva secretion at 3 months in irradiated animals, indicating that this treatment confers protection from hyposalivation. These results demonstrate that nanoparticle delivery of siRNAs targeting a proapoptotic gene is a localized, nonviral, and effective means of conferring radioprotection to the SGs.

Lin28a is a putative factor in regulating cancer stem cell-like properties in side population cells of oral squamous cell carcinoma

Cancer stem cells (CSCs) are among the target cells of cancer therapy because they are uniquely involved in both cancer progression and sensitivity to chemotherapeutic agents. We identified side population (SP) cells, which are known to be an enriched population of CSC, in five oral squamous cell carcinoma (OSCC) cells (SCC9, SCC25, TOSCC7, TOSCC17, and TOSCC23). The percentages of SP cells ranged from 0% to 3.3%, with TOSCC23 cells showing the highest percentages of SP cells (3.3% of the total cell population). The SP cells isolated from TOSCC23 cells also showed greater cell proliferation and invasion compared to non-SP (MP) cells. Therefore, our initial findings suggested that SP cells were enriched for CSC-like cells. Furthermore, DNA microarray analysis revealed that the expression of cell proliferation-related and anti-apoptotic genes was greater in SP cells compared to MP cells. We focused on Lin28a, which showed the highest expression (approximately 22-fold) among the upregulated genes. The overexpression of Lin28a in TOSCC23 cells increased their proliferation, colony formation, and invasion. These findings suggest that Lin28a is an appropriate CSC target molecule for OSCC treatment.