A role for chemistry in stem cell biology

Although stem cells hold considerable promise for the treatment of numerous diseases including cardiovascular disease, neurodegenerative disease, musculoskeletal disease, diabetes and cancer, obstacles such as the control of stem cell fate, allogenic rejection and limited cell availability must be overcome before their therapeutic potential can be realized. This requires an improved understanding of the signaling pathways that affect stem cell fate. Cell-based phenotypic and pathway-specific screens of natural products and synthetic compounds have recently provided a number of small molecules that can be used to selectively control stem cell proliferation and differentiation. Examples include the selective induction of neurogenesis and cardiomyogenesis in murine embryonic stem cells, osteogenesis in mesenchymal stem cells and dedifferentiation in skeletal muscle cells. Such molecules will likely provide new insights into stem cell biology, and may ultimately contribute to effective medicines for tissue repair and regeneration.     

Small extracellular vesicles from mesenchymal stromal cells: the next therapeutic paradigm for musculoskeletal disorders

Musculoskeletal disorders are one of the biggest contributors to morbidity and place an enormous burden on the health care system in an aging population. Owing to their immunomodulatory and regenerative properties, mesenchymal stromal/stem cells (MSCs) have demonstrated therapeutic efficacy for treatment of a wide variety of conditions, including musculoskeletal disorders. Although MSCs were originally thought to differentiate and replace injured/diseased tissues, it is now accepted that MSCs mediate tissue repair through secretion of trophic factors, particularly extracellular vesicles (EVs). Endowed with a diverse cargo of bioactive lipids, proteins, nucleic acids and metabolites, MSC-EVs have been shown to elicit diverse cellular responses and interact with many cell types needed in tissue repair. The present review aims to summarize the latest advances in the use of native MSC-EVs for musculoskeletal regeneration, examine the cargo molecules and mechanisms underlying their therapeutic effects, and discuss the progress and challenges in their translation to the clinic.     

Stem cells from umbilical cord and placenta for musculoskeletal tissue engineering

Mesenchymal stem cells isolated from amnion/amniotic fluid, umbilical cord blood, placental tissue, umbilical cord vein and the Wharton's Jelly are promising candidates for musculoskeletal tissue engineering of bone and cartilage tissues. The extracorporeal nature of this source avoids the ethical concerns that plague the isolation of embryonic stem cells. Moreover, the harvesting does not require the invasive and discomfort extraction procedures as well as patient risks that attend adult stem cell isolation. Current preclinical studies support the application of these cell-based therapies for the regeneration of musculoskeletal tissues. We performed a review of the literature to focus on actual knowledge and the future perspectives of the stem cells deriving from umbilical cord and placenta for musculoskeletal tissue engineering.     

Adipose-derived adult stem cells for cartilage tissue engineering

Tissue engineering is a promising therapeutic approach that uses combinations of implanted cells, biomaterial scaffolds, and biologically active molecules to repair or regenerate damaged or diseased tissues. Many diverse and increasingly complex approaches are being developed to repair articular cartilage, with the underlying premise that cells introduced exogenously play a necessary role in the success of engineered tissue replacements. A major consideration that remains in this field is the identification and characterization of appropriate sources of cells for tissue-engineered repair of cartilage. In particular, there has been significant emphasis on the use of undifferentiated progenitor cells, or "stem" cells that can be expanded in culture and differentiated into a variety of different cell types. Recent studies have identified the presence of an abundant source of stem cells in subcutaneous adipose tissue. These cells, termed adipose-derived adult stem (ADAS) cells, show characteristics of multipotent adult stem cells, similar to those of bone marrow derived mesenchymal stem cells (MSCs), and under appropriate culture conditions, synthesize cartilage-specific matrix proteins that are assembled in a cartilaginous extracellular matrix. The growth and chondrogenic differentiation of ADAS cells is strongly influenced by factors in the biochemical as well as biophysical environment of the cells. Furthermore, there is strong evidence that the interaction between the cells, the extracellular biomaterial substrate, and growth factors regulate ADAS cell differentiation and tissue growth. Overall, ADAS cells show significant promise for the development of functional tissue replacements for various tissues of the musculoskeletal system.     

Musculoskeletal mechanobiology: Interpretation by external force and engineered substratum

Mechanobiology aims to discover how the mechanical environment affects the biological activity of cells and how cells’ ability to sense these mechanical cues is converted into elicited cellular responses. Musculoskeletal mechanobiology is of particular interest given the high mechanical loads that musculoskeletal tissues experience on a daily basis. How do cells within these mechanically active tissues interpret external loads imposed on their extracellular environment, and, how are cell–substrate interactions converted into biochemical signals? This review outlines many of the main mechanotransduction mechanisms known to date, and describes recent literature examining effects of both external forces and cell–substrate interactions on musculoskeletal cells. Whether via application of external forces and/or cell–substrate interactions, our understanding and regulation of musculoskeletal mechanobiology can benefit by expanding upon traditional models, and shedding new light through novel investigative approaches. Current and future work in this field is focused on identifying specific forces, stresses, and strains at the cellular and tissue level through both experimental and computational approaches, and analyzing the role of specific proteins through fluorescence-based investigations and knockdown models.     

Musculoskeletal tissue engineering by endogenous stem/progenitor cells

From its inception, tissue engineering has had three tenets: cells, biomaterial scaffolds and signaling molecules. Among the triad, cells are the center piece, because cells are the building blocks of tissues. For decades, cell therapies have focused on the procurement, manipulation and delivery of healthy cells for the treatment of diseases or trauma. Given the complexity and potential high cost of cell delivery, there is recent and surging interest to orchestrate endogenous cells for tissue regeneration. Biomaterial scaffolds are vital for many but not all, tissue-engineering applications and serve to accommodate or promote multiple cellular functions. Signaling molecules can be produced by transplanted cells or endogenous cells, or delivered specifically to regulate cell functions. This review highlights recent work in tissue engineering and cell therapies, with a focus on harnessing the capacity of endogenous cells as an alternative or adjunctive approach for tissue regeneration.     

Endogenous musculoskeletal tissue engineering - a focused perspective

Two major difficulties facing widespread clinical implementation of existing Tissue Engineering (TE) strategies for the treatment of musculoskeletal disorders are (1) the cost, space and time required for ex vivo culture of a patient’s autologous cells prior to re-implantation as part of a TE construct, and (2) the potential risks and availability constraints associated with transplanting exogenous (foreign) cells. These hurdles have led to recent interest in endogenous TE strategies, in which the regenerative potential of a patient’s own cells is harnessed to promote tissue regrowth without ex vivo cell culture. This article provides a focused perspective on key issues in the development of endogenous TE strategies, progress to date, and suggested future research directions toward endogenous repair and regeneration of musculoskeletal tissues and organs.     

Role of molecular cell biology in understanding disease.

Molecular techniques have revolutionised our knowledge of cell and tissue function in both health and disease. We already have new and powerful treatments based on an understanding of communication between cells by messenger molecules called cytokines. Furthermore, there is great therapeutic promise in defining molecules which regulate cell adhesion, motility, proliferation, survival, and death. Rational manipulation of cell and tissue function for therapeutic ends may be much closer than you think.     

Inducible Expression of Neurotrophic Factors by Mesenchymal Progenitor Cells Derived from Traumatically Injured Human Muscle

Peripheral nerve damage frequently accompanies musculoskeletal trauma and repair of these nerves could be enhanced by the targeted application of neurotrophic factors (NTFs), which are typically expressed by endogenous cells that support nerve regeneration. Injured muscle tissues express NTFs to promote reinnervation as the tissue regenerates, but the source of these factors from within the muscles is not fully understood. We have previously identified a population of mesenchymal progenitor cells (MPCs) in traumatized muscle tissue with properties that support tissue regeneration, and our hypothesis was that MPCs also secrete the NTFs that are associated with muscle tissue reinnervation. We determined that MPCs express genes associated with neurogenic function and measured the protein-level expression of specific NTFs with known functions to support nerve regeneration. We also demonstrated the effectiveness of a neurotrophic induction protocol to enhance the expression of the NTFs, which suggests that the expression of these factors may be modulated by the cellular environment. Finally, neurotrophic induction affected the expression of cell surface markers and proliferation rate of the MPCs. Our findings indicate that traumatized muscle-derived MPCs may be useful as a therapeutic cell type to enhance peripheral nerve regeneration following musculoskeletal injury.     

In vivo tissue engineering of musculoskeletal tissues

Tissue engineering of musculoskeletal tissues often involves the in vitro manipulation and culture of progenitor cells, growth factors and biomaterial scaffolds. Though in vitro tissue engineering has greatly increased our understanding of cellular behavior and cell-material interactions, this methodology is often unable to recreate tissue with the hierarchical organization and vascularization found within native tissues. Accordingly, investigators have focused on alternative in vivo tissue engineering strategies, whereby the traditional triad (cells, growth factors, scaffolds) or a combination thereof are directly implanted at the damaged tissue site or within ectopic sites capable of supporting neo-tissue formation. In vivo tissue engineering may offer a preferential route for regeneration of musculoskeletal and other tissues with distinct advantages over in vitro methods based on the specific location of endogenous cultivation, recruitment of autologous cells, and patient-specific regenerated tissues.     

Differing cell surface distribution of human leukocyte antigen-DR molecules on epidermal Langerhans cells and eccrine duct cells.

Scanning electron microscopy (SEM) with immunogold labeling was employed to observe the undersurface of the human epidermis after it was split from dermal connective tissue, in an attempt to localize the molecules actually expressed on cell/tissue surfaces. We found that human leukocyte antigen-DR (HLA-DR) molecules were expressed on the surfaces of eccrine duct cells as well as those of epidermal Langerhans cells (LC) in normal skin. HLA-DR molecules, visualized by the deposition of gold particles, were distributed evenly on the LC surface but were present only along the interdigitating borders of the individual duct cells, thus producing a meshwork pattern on the duct surface. Transmission electron microscopy confirmed that the gold particles labeling cell surface HLA-DR molecules were seen only on the portions of duct cell membranes the interdigitated with neighboring duct cells. These findings suggest that the function of HLA-DR molecules may vary with their location and distribution. On the LC surface, the evenly distributed molecules seem to be well suited for promoting "accessory cell" functions. On duct cell surfaces, the HLA-DR molecules present along the intercellular spaces may be involved in trapping various peptide antigens that pass into the sweat gland filtrate and then are reabsorbed by the excretory duct, since these molecules have a highly permissive capacity for binding various peptides.     

Impact of Aging on the Regenerative Properties of Bone Marrow-, Muscle-, and Adipose-Derived Mesenchymal Stem/Stromal Cells

Mesenchymal stem/stromal cells (MSCs) are promising cell sources for regenerative therapies due to their multipotency and ready availability, but their application can be complicated by patient-specific factors like age or illness. MSCs have been investigated for the treatment of many musculoskeletal disorders, including osteoarthritis and osteoporosis. Due to the prevalence of these diseases in older populations, researchers have studied how aging affects MSC properties and have found that proliferation and differentiation potential are impaired. However, these effects have never been compared among MSCs isolated from multiple tissue sources in the same, healthy donor. Revealing differences in how MSCs are affected by age could help identify an optimal cell source for musculoskeletal therapies targeting older patients. MSCs were isolated from young and old rabbit bone marrow, muscle, and adipose tissue. Cell yield and viability were quantified after isolation procedures, and expansion properties were assessed using assays for proliferation, senescence, and colony formation. Multipotency was also examined using lineage-specific stains and spectrophotometry of metabolites. Results were compared between age groups and among MSC sources. Results showed that MSCs are differentially influenced by aging, with bone marrow-derived stem cells having impaired proliferation, senescence, and chondrogenic response, whereas muscle-derived stem cells and adipose-derived stem cells exhibited no negative effects. While age reduced overall cell yield and adipogenic potential of all MSC populations, osteogenesis and clonogenicity remained unchanged. These findings indicate the importance of age as a factor when designing cell-based therapies for older patients.     

Advances in single‐cell sequencing and its application to musculoskeletal system research

In recent years, single‐cell sequencing (SCS) technologies have continued to advance with improved operating procedures and reduced cost, leading to increasing practical adoption among researchers. These emerging technologies have superior abilities to analyse cell heterogeneity at a single‐cell level, which have elevated multi‐omics research to a higher level. In some fields of research, application of SCS has enabled many valuable discoveries, and musculoskeletal system offers typical examples. This article reviews some major scientific issues and recent advances in musculoskeletal system. In addition, combined with SCS technologies, the research of cell or tissue heterogeneity in limb development and various musculoskeletal system clinical diseases also provides new possibilities for treatment strategies. Finally, this article discusses the challenges and future development potential of SCS and recommends the direction of future applications of SCS to musculoskeletal medicine.     

Tissue engineering with muscle-derived stem cells

Tissue engineering and cell therapy approaches aim to take advantage of the repopulating ability and plasticity of multipotent stem cells to regenerate lost or diseased tissue. Researchers continue to investigate stem cells in mature tissues and demonstrate the potential ability of organ-specific cells to differentiate into multiple lineages. One stem cell that displays such promise is the muscle-derived stem cell (MDSC). Data supporting the existence of MDSCs have emerged as part of investigations to improve myoblast cell transplantation for the treatment of muscular dystrophies. As these efforts continue, the potential for MDSC-based therapy for other musculoskeletal injuries, as well as for cardiac and smooth muscle injuries, is currently being explored.     

组织工程中细胞与生物材料相互作用研究进展

种子细胞、生物材料和生长因子是组织工程三要素.生物材料模拟体内细胞外基质,为细胞提供良好的生长附着环境,维持细胞的活力和功能.材料表面的理化性质和表面改性分子直接影响细胞的粘附、增殖、迁移和分化等细胞行为,进而影响细胞功能和组织再生效果.材料表面修饰分子是细胞表面粘附和生长的直接接触位置,因此细胞与生物材料表面修饰分子...     

Molecular and cellular changes associated with the evolution of novel jaw muscles in parrots

Vertebrates have achieved great evolutionary success due in large part to the anatomical diversification of their jaw complex, which allows them to inhabit almost every ecological niche. While many studies have focused on mechanisms that pattern the jaw skeleton, much remains to be understood about the origins of novelty and diversity in the closely associated musculature. To address this issue, we focused on parrots, which have acquired two anatomically unique jaw muscles: the ethmomandibular and the pseudomasseter. In parrot embryos, we observe distinct and highly derived expression patterns for Scx, Bmp4, Tgfβ2 and Six2 in neural crest-derived mesenchyme destined to form jaw muscle connective tissues. Furthermore, immunohistochemical analysis reveals that cell proliferation is more active in the cells within the jaw muscle than in surrounding connective tissue cells. This biased and differentially regulated mode of cell proliferation in cranial musculoskeletal tissues may allow these unusual jaw muscles to extend towards their new attachment sites. We conclude that the alteration of neural crest-derived connective tissue distribution during development may underlie the spatial changes in jaw musculoskeletal architecture found only in parrots. Thus, parrots provide valuable insights into molecular and cellular mechanisms that may generate evolutionary novelties with functionally adaptive significance.     

Molecular complexity of vertebrate tight junctions (Review)

Separation of distinct body, organ and tissue compartments, and maintenance of epithelial cell polarity require tight junctions (TJ)--cell-cell junctions located in the apicolateral regions of epithelial and endothelial cells. Studies on the protein components of vertebrate TJ have revealed an intricate network of membrane, sub-membrane, cytoskeletal, and signalling molecules. How these molecules functionally interact to provide TJ with their functions, and what roles these molecules play in control of cell growth and differentiation is a fundamental problem in cell biology.     

Approaches in extracellular matrix engineering for determination of adhesion molecule mediated single cell function

The native extracellular matrix (ECM) and the cells that comprise human tissues are together engaged in a complex relationship; cells alter the composition and structure of the ECM to regulate the material and biologic properties of the surrounding environment while the composition and structure of the ECM modulates cellular processes that maintain healthy tissue and repair diseased tissue. This reciprocal relationship occurs via cell adhesion molecules (CAMs) such as integrins, selectins, cadherins and IgSF adhesion molecules. To study these cell-ECM interactions, researchers use two-dimensional substrates or three-dimensional matrices composed of native proteins or bioactive peptide sequences to study single cell function. While two-dimensional substrates provide valuable information about cell-ECM interactions, three-dimensional matrices more closely mimic the native ECM; cells cultured in three-dimensional matrices have demonstrated greater cell movement and increased integrin expression when compared to cells cultured on two-dimensional substrates. In this article we review a number of cellular processes (adhesion, motility, phagocytosis, differentiation and survival) and examine the cell adhesion molecules and ECM proteins (or bioactive peptide sequences) that mediate cell functionality.     

MiR-214 is an important regulator of the musculoskeletal metabolism and disease

MiR-214 belongs to a family of microRNA (small, highly conserved noncoding RNA molecules) precursors that play a pivotal role in biological functions, such as cellular function, tissue development, tissue homeostasis, and pathogenesis of diseases. Recently, miR-214 emerged as a critical regulator of musculoskeletal metabolism. Specifically, miR-214 can mediate skeletal muscle myogenesis and vascular smooth muscle cell proliferation, migration, and differentiation. MiR-214 also modulates osteoblast function by targeting specific molecular pathways and the expression of various osteoblast-related genes; promotes osteoclast activity by targeting phosphatase and tensin homolog (Pten); and mediates osteoclast-osteoblast intercellular crosstalk via an exosomal miRNA paracrine mechanism. Importantly, dysregulation in miR-214 expression is associated with pathological bone conditions such as osteoporosis, osteosarcoma, multiple myeloma, and osteolytic bone metastasis of breast cancer. This review discusses the cellular targets of miR-214 in bone, the molecular mechanisms governing the activities of miR-214 in the musculoskeletal system, and the putative role of miR-214 in skeletal diseases. Understanding the biology of miR-214 could potentially lead to the development of miR-214 as a possible biomarker and a therapeutic target for musculoskeletal diseases.     

Fluorescent inhibitors of a cell surface protease used to locate leukaemia cells in kidney sections

Guanidinobenzoatase is a trypsin-like protease on the surface of cells capable of migration, for example leukaemia cells. We have used a number of fluorescent probes that are competitive inhibitors of guanidinobenzoatase to locate leukaemia cells in resin sections of kidney tissue obtained from leukaemic rats. We have demonstrated how this competitive inhibition system can be used to direct desired molecules (such as cytotoxic drugs) to these cells and to monitor the arrival of such compounds at the active site of guanidinobenzoatase. The principles developed in this study could equally well be applied to other enzymes on other cells provided suitable competitive inhibitors were designed. The presence of an enzyme on the surface of a cell can be used to direct molecules to that cell provided that these molecules contain a functional group that acts as an inhibitor for the chosen enzyme.