Tissue Transplantation Therapy Research Articles

Salivary Gland Organ Regeneration for Oral Health

Salivary glands play essential roles in normal upper gastrointestinal tract function and oral health via saliva production. There are three types of salivary glands; the submandibular gland and parotid gland, which secrete serous saliva, and the sublingual gland secretes mucous saliva in mice [1]. Therefore, salivary gland dysfunction due to atrophy of acinar cells caused by Sjogren’s syndrome, radiation therapy for head and neck cancer, and aging and saliva reduction, and results in xerostomia (dry mouth syndrome), causes various clinical problems in oral health and influences overall bodily health [2]. Xerostomia induces various clinical problems in oral health, such as dental decay, bacterial infection, and disorders of mastication and swallowing, which result in a general reduction in the quality of life [3]. Current standard to cure xerostomia are symptomatic treatments, such as the administration of artificial saliva substitutes and sialogogues, and the administration of parasympathetic stimulation drugs, including pilocarpine and cevimeline [4]. In salivary gland regenerative therapy, stem cell transplantation, which expressed c-kit and Sca-1 as stem cell markers and exhibit high proliferative capacities [5,6], and gene modification for water channel aquaporin-1 (AQP1) and Interleukin-17 (IL-17) receptor antibody is performed to restore the damaged acinar tissue and recover the flow of saliva [7,8]. Salivary glands arise from the organ germ, which is induced by reciprocal epithelial and mesenchymal stem cell interactions during embryonic development [9]. In this two decades, advances in developmental biology have led to break-through in regeneration of functional bioengineered organ in vitro by using embryonic organ-inductive potential stem cells. Recently, regeneration of fully functional salivary gland as a next-generation organ regeneration has been reported after the transplantation of bioengineered salivary gland germ developed by using embryonic organ-inductive potential stem cells as well as iPS cells [10,11]. In 2013, we demonstrated the fully functional salivary gland regeneration by recapitulating the embryonic morphogenesis. The bioengineered salivary gland organ germ, which was reconstituted by our Organ Germ Method using organ-inductive potential stem cells derived from submandibular gland germs of ED 13.5 mice [12], showed reciprocal epithelial and mesenchymal interactions in in vitro organ culture. Following the orthotopic transplantation, the bioengineered germ develops into a mature salivary gland via acinar formations with a myoepithelium and innervation. The bioengineered salivary gland produces saliva in response to the pilocarpine administration and gustatory stimulation by citrate, protected against bacterial infection and restores normal swallowing function in a mouse model. This study provides a proofof- concept for bioengineered salivary gland regeneration. The next breakthrough first reported in 2008 was the emergence of an organoid as a mini-organ that was generated by inducing body patterning and a subsequent organ-forming field formation in pluripotent stem cells [13]. Organoids are useful to recapitulate the process of organogenesis, which are strictly regulated by morphogen signalling and transcriptional networks. To date, multiple types of organoids, including the retina, pituitary gland, liver, and lung have been successfully generated in vitro. Our colleagues identified a specific combination of two transcription factors, Sox9 and Foxc1, are responsible for the differentiation of mouse ES cells-derived oral ectodermal region into the salivary gland rudiment in a threedimensional organoid culture system [11]. The induced salivary gland rudiment showed a similar morphologies and gene expression profiles to those of the embryonic salivary gland rudiment of normal mice. Following orthotopic transplantation into salivary glands-defected mice, the induced salivary gland germ exhibited characteristics of mature salivary glands including histological morphologies, nerve innervation and saliva secretion. This study is the first report of the fully functional organ regeneration by using organoid, demonstrating the potential of salivary gland organ regeneration from pluripotent stem cells for an additional organ replacement regenerative therapy. As part of regenerative medicine, the autogenous transplantation of stem cells, including bone marrow, and tissue sheets such as skin, cornea, and cardiac muscle, has already been applied clinically through cell and tissue transplantation therapies. The progress made in the past two decades has been remarkable, paving the way for possible future organ replacement regenerative therapies. There remains a critical issue as to whether next-generation organ regenerative therapy can be adopted as a novel clinical therapy for patients of the loss of organ function. The bioengineered salivary gland organ germ by using both embryonic organ-inductive potential stem cells and pluripotent stem cells can grow where salivary grand should be in oral cavity and produce the saliva in response to various taste stimulations. These works indicate the potentials for clinical application of salivary gland organ regeneration. Applying knowledge of these basic research will enable the regeneration of salivary gland organ in the next decades.

Mouse Embryonic Stem Cell Derivation, and Mouse and Human Embryonic Stem Cell Culture and Differentiation as Embryoid Bodies

Embryonic stem (ES) cells are pluripotent cells derived from developing mouse blastocysts in vitro that maintain long-term self renewal and the capacity to give rise to all cell types in the adult body (including some extraembryonic cell types) when subjected to the appropriate conditions. It is envisaged that the development of methods enabling controlled differentiation of mouse ES cell counterparts from human blastocysts would enable the provision of an unlimited supply of tissue for cell and tissue transplantation therapies for the repair and replacement of diseased, injured, and senescent tissue. Furthermore, derivation of mouse ES cells has allowed for the generation of thousands of gene-targeted mouse mutants. Culture of mouse ES cells as embryoid bodies (EBs) has provided a convenient system for studying early mouse developmental processes, including several aspects of extraembryonic lineage and axis formation associated with the pre- and peri-gastrulating mouse embryo. Relatively little is known regarding the corresponding development of the early human embryo due to limitations associated with the acquisition of relevant tissue material for study. The transfer of methods such as EB formation to human systems should, by association, facilitate a more advanced understanding of similar processes associated with early human development. This unit describes protocols for isolating mouse embryonic stem cells and methods for propagating, freezing, and producing EBs from both mouse and human embryonic stem cells.

A few thoughts about the plasticity of stem cells

Over the last several years much attention has focused on the differentiation abilities of stem cells. In particular, it has been suggested that traditional concepts and dogmas regarding the developmental potential of somatic tissue resident stem cells need to be revisited. A number of reports have suggested that stem cells obtained from, for instance, bone marrow or the nervous system may be able to “transdifferentiate” or “dedifferentiate” [1–5]. That is, bone marrow stem cells can be “induced” to make neural tissue [6,7], and neural stem cells may be “induced” to produce blood and other tissues [8,9]. These are just two examples of numerous similar reports that include tissues such as muscle, liver, skin, gut, and lung [10–18]. The suggested “plasticity” of somatic tissue stem cells has a potential clinical impact and may revolutionize the way we think about tissue transplantation therapies and regenerative medicine [19]. Unlike most advances in the life sciences, the possibility of stem cell plasticity has been immediately put to use by various political and citizen's group forces.

Development-associated differences in integrative cartilage repair: roles of biosynthesis and matrix

A recurring problem in tissue transplantation therapies for articular cartilage defects is the lack of integration between the implant and the host cartilage. Previous studies have shown that in vitro integration between explants of calf cartilage is markedly higher than that between fetal cartilage, despite similarly high levels of deposition of newly synthesized collagen. The aim of this study was to determine if cellular biosynthesis and extracellular matrix each contribute to these development-associated differences in integrative repair in vitro. The approach taken was to examine integration between specific combinations of cartilage explants that were apposed for two weeks. The cartilage matrix showed different propensities for repair, as integration of calf live cartilage to calf devitalized cartilage was greater than that of calf live cartilage to fetal devitalized cartilage. An inhibiting factor appeared to be present in fetal cartilage matrix since guanidine treatment of fetal devitalized cartilage was able to enhance its integration. The difference between integration to living cartilage and integration to devitalized cartilage, for calf and fetal tissue, indicated that the biosynthetic contribution to integration by calf cartilage was greater than the biosynthetic contribution by fetal cartilage. Thus, the increasing level of integration between fetal and fetal cartilage, fetal and calf cartilage, and calf and calf cartilage appeared to reflect both biosynthetic and matrix differences. Therapeutic strategies to enhance integration to cartilage may thus target both the extracellular components and the cellular biosynthetic activities of implants and host cartilage.

Do brain tissue transplants alter personal identity? Inadequacies of some "standard" arguments.

Currently, brain tissue transplantations are being developed as a clinical-therapeutic tool in neurodegenerative diseases such as Parkinson's or Alzheimer's disease. From an ethical point of view, distinguishing between the preservation and an alteration of personal identity seems to be central to determining the scope for further application of brain tissue transplantation therapy. The purpose of this article is to review "standard" arguments which are used on the one hand by proponents to prove preservation of personal identity and by opponents on the other hand to prove that brain tissue transplantation results in an altered personal identity. Proponents and opponents are shown to use the same arguments, albeit with different presuppositions. These presuppositions concern the meaning of the term "identity", either numerical or qualitative, the definition of brain identity, either structurally or functionally, and the relationship between mental states, psychological functions and neurophysiological properties as criteria for personal identity. Furthermore the respective neurophysiological, clinical and philosophical evidence for the different presuppositions are discussed. It is concluded that evaluation of personal identity in brain tissue transplantation should not only rely on the "standard" arguments but, additionally, neurophysiological, clinical and philosophical implications should be discussed.