Modulating the stem cell niche for tissue regeneration

Cell-Traction-Triggered On-Demand Electrical Stimulation for Neuron-Like Differentiation

Electromechanical interaction of cells and extracellular matrix are ubiquitous in biological systems. Understanding the fundamentals of this interaction and feedback is critical to design next-generation electroactive tissue engineering scaffold. Herein, based on elaborately modulating the dynamic mechanical forces in cell microenvironment, the design of a smart piezoelectric scaffold with suitable stiffness analogous to that of collagen for on-demand electrical stimulation is reported. Specifically, it generated a piezoelectric potential, namely a piezopotential, to stimulate stem cell differentiation with cell traction as a loop feedback signal, thereby avoiding the unfavorable effect of early electrical stimulation on cell spreading and adhesion. This is the first time to adapt to the dynamic microenvironment of cells and meet the electrical stimulation of cells in different states by a constant scaffold, diminishing the cumbersomeness of inducing material transformation or trigging by an external stimulus. This in situ on-demand electrical stimulation based on cell-traction-mediated piezopotential paves the way for smart scaffolds design and future bioelectronic therapies.

Synthetic liver fibrotic niche extracts achieve in vitro hepatoblasts phenotype enhancement and expansion

It is still a challenge for synthesizing ‘cellular niche-mimics’ in vitro with satisfactory reproducibility and fidelity to recreate the natural niche components (e.g., extracellular matrices and soluble factors) for stem cell cultivation. Inspired by the massive amplification of hepatic progenitor cells during liver fibrosis in vivo, here we optimized the in vitro liver fibrotic niches and subsequently harvested their bioactive ingredients as niche extracts (NEs). The fibrosis-relevant NE marginally outperformed Matrigel for phenotype maintenance of human embryonic stem cell (hESC)-derived hepatoblasts (HBs) and recapitulation of the pathological angiogenesis of hESC-derived endothelial cells both in 2D culture and 3D liver organoids. Finally, defined NE components (i.e., collagen III, IV, IL-17, IL-18 and M-CSF) were resolved by the quantitative proteomics which exhibited advantage over Matrigel for multi-passaged HB expansion. The pathology-relevant and tissue-specific NEs provide innovative and generalizable strategies for the discovery of optimal cellular niche and bioactive niche compositions.

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Fibrotic niches were constructed by 3 hepatic cell lines plus 4 profibrotic factors

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NE was produced by enzymatic digestion using pepsin and DNase

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Collagen III, IV, IL-17, IL-18, and M-CSF resolved from NE promoted HBs expansion

Combined administration of laminin-221 and prostacyclin agonist enhances endogenous cardiac repair in an acute infarct rat heart

Although endogenous cardiac repair by recruitment of stem cells may serve as a therapeutic approach to healing a damaged heart, how to effectively enhance the migration of stem cells to the damaged heart is unclear. Here, we examined whether the combined administration of prostacyclin agonist (ONO1301), a multiple-cytokine inducer, and stem cell niche laminin-221 (LM221), enhances regeneration through endogenous cardiac repair. We administered ONO1301- and LM221-immersed sheets, LM221-immersed sheets, ONO1301-immersed sheets, and PBS-immersed sheets (control) to an acute infarction rat model. Four weeks later, cardiac function, histology, and cytokine expression were analysed. The combined administration of LM221 and ONO1301 upregulated angiogenic and chemotactic factors in the myocardium after 4 weeks and enhanced the accumulation of ILB4 positive cells, SMA positive cells, and platelet-derived growth factor receptor alpha (PDGFRα) and CD90 double-positive cells, leading to the generation of mature microvascular networks. Interstitial fibrosis reduced and functional recovery was prominent in LM221- and ONO1301-administrated hearts as compared with those in ONO1301-administrated or control hearts. LM221 and ONO1301 combination enhanced recruitment of PDGFRα and CD90 double-positive cells, maturation of vessels, and functional recovery in rat acute myocardial infarction hearts, highlighting a new promising acellular approach for the failed heart.

Regulation of Limbal Epithelial Stem Cells: Importance of the Niche

Limbal epithelial stem/progenitor cells (LSCs) reside in a niche that contains finely tuned balances of various signaling pathways including Wnt, Notch, BMP, Shh, YAP, and TGFβ. The activation or inhibition of these pathways is frequently dependent on the interactions of LSCs with various niche cell types and extracellular substrates. In addition to receiving molecular signals from growth factors, cytokines, and other soluble molecules, LSCs also respond to their surrounding physical structure via mechanotransduction, interaction with the ECM, and interactions with other cell types. Damage to LSCs or their niche leads to limbal stem cell deficiency (LSCD). The field of LSCD treatment would greatly benefit from an understanding of the molecular regulation of LSCs in vitro and in vivo. This review synthesizes current literature around the niche factors and signaling pathways that influence LSC function. Future development of LSCD therapies should consider all these niche factors to achieve improved long-term restoration of the LSC population.

Advances in mesenchymal stem cell conditioned medium-mediated periodontal tissue regeneration

Periodontitis is a chronic inflammatory disease that leads to the destruction of both soft and hard periodontal tissues. Complete periodontal regeneration in clinics using the currently available treatment approaches is still a challenge. Mesenchymal stem cells (MSCs) have shown promising potential to regenerate periodontal tissue in various preclinical and clinical studies. The poor survival rate of MSCs during in vivo transplantation and host immunogenic reaction towards MSCs are the main drawbacks of direct use of MSCs in periodontal tissue regeneration. Autologous MSCs have limited sources and possess patient morbidity during harvesting. Direct use of allogenic MSCs could induce host immune reaction. Therefore, the MSC-based indirect treatment approach could be beneficial for periodontal regeneration in clinics. MSC culture conditioned medium (CM) contains secretomes that had shown immunomodulatory and tissue regenerative potential in pre-clinical and clinical studies. MSC-CM contains a cocktail of growth factors, cytokines, chemokines, enzymes, and exosomes, extracellular vesicles, etc. MSC-CM-based indirect treatment has the potential to eliminate the drawbacks of direct use of MSCs for periodontal tissue regeneration. MSC-CM holds the tremendous potential of bench-to-bed translation in periodontal regeneration applications. This review focuses on the accumulating evidence indicating the therapeutic potential of the MSC-CM in periodontal regeneration-related pre-clinical and clinical studies. Recent advances on MSC-CM-based periodontal regeneration, existing challenges, and prospects are well summarized as guidance to improve the effectiveness of MSC-CM on periodontal regeneration in clinics.

Generation of Skin Organoids: Potential Opportunities and Challenges

Although several types of human skin substitutes are currently available, they usually do not include important skin appendages such as hair follicles and sweat glands, or various skin-related cells, such as dermal adipocytes and sensory neurons. This highlights the need to improve the in vitro human skin generation model for use as a tool for investigating skin diseases and as a source of cells or tissues for skin regeneration. Skin organoids are generated from stem cells and are expected to possess the complexity and function of natural skin. Here, we summarize the current literatures relating to the "niches" of the local skin stem cell microenvironment and the formation of skin organoids, and then discuss the opportunities and challenges associated with multifunctional skin organoids.

Development of hierarchical porous bioceramic scaffolds with controlled micro/nano surface topography for accelerating bone regeneration

Mimicking hierarchical porous architecture of bone has been considered as a valid approach to promote bone regeneration. In this study, hierarchical porous β-tricalcium phosphate (β-TCP) scaffolds were constructed by combining digital light processing (DLP) printing technique and in situ growth crystal process. Macro/micro hierarchical scaffolds with designed macro pores for facilitating the ingrowth of bone tissue were fabricated by DLP printing. Three types of micro/nano surface topography were obtained by in situ growth crystal process to regulate stem cells behavior. The attachment and proliferation of rat bone marrow mesenchymal stem cells (rBMSCs) were strongly dependent on the surface roughness and the specific surface area. The micro/nano surface topography distinctly facilitated the differentiation of rBMSCs by targeting MAPK, STAT and AKT signaling pathways, in which the sodium hydroxide treatment group showed the highest promoting effect. Furthermore, in vivo results of skull defect repair model of rats indicated that hierarchical scaffolds with micro/nano topographies exhibited appealing bone regeneration capacity. The hierarchical porous bioceramic scaffolds constructed by integrating structural design and physical stimulation of the external surface topography have great potential for rapid bone repair via modulation of microenvironmental regulatory pathways at the bone defect site.

DNA Damage-Induced Inflammatory Microenvironment and Adult Stem Cell Response

Adult stem cells ensure tissue homeostasis and regeneration after injury. Due to their longevity and functional requirements, throughout their life stem cells are subject to a significant amount of DNA damage. Genotoxic stress has recently been shown to trigger a cascade of cell- and non-cell autonomous inflammatory signaling pathways, leading to the release of pro-inflammatory factors and an increase in the amount of infiltrating immune cells. In this review, we discuss recent evidence of how DNA damage by affecting the microenvironment of stem cells present in adult tissues and neoplasms can affect their maintenance and long-term function. We first focus on the importance of self-DNA sensing in immunity activation, inflammation and secretion of pro-inflammatory factors mediated by activation of the cGAS-STING pathway, the ZBP1 pathogen sensor, the AIM2 and NLRP3 inflammasomes. Alongside cytosolic DNA, the emerging roles of cytosolic double-stranded RNA and mitochondrial DNA are discussed. The DNA damage response can also initiate mechanisms to limit division of damaged stem/progenitor cells by inducing a permanent state of cell cycle arrest, known as senescence. Persistent DNA damage triggers senescent cells to secrete senescence-associated secretory phenotype (SASP) factors, which can act as strong immune modulators. Altogether these DNA damage-mediated immunomodulatory responses have been shown to affect the homeostasis of tissue-specific stem cells leading to degenerative conditions. Conversely, the release of specific cytokines can also positively impact tissue-specific stem cell plasticity and regeneration in addition to enhancing the activity of cancer stem cells thereby driving tumor progression. Further mechanistic understanding of the DNA damage-induced immunomodulatory response on the stem cell microenvironment might shed light on age-related diseases and cancer, and potentially inform novel treatment strategies.

The Importance of Mimicking Dermal-Epidermal Junction for Skin Tissue Engineering: A Review

There is a distinct boundary between the dermis and epidermis in the human skin called the basement membrane, a dense collagen network that creates undulations of the dermal-epidermal junction (DEJ). The DEJ plays multiple roles in skin homeostasis and function, namely, enhancing the adhesion and physical interlock of the layers, creating niches for epidermal stem cells, regulating the cellular microenvironment, and providing a physical boundary layer between fibroblasts and keratinocytes. However, the primary role of the DEJ has been determined as skin integrity; there are still aspects of it that are poorly investigated. Tissue engineering (TE) has evolved promising skin regeneration strategies and already developed TE scaffolds for clinical use. However, the currently available skin TE equivalents neglect to replicate the DEJ anatomical structures. The emergent ability to produce increasingly complex scaffolds for skin TE will enable the development of closer physical and physiological mimics to natural skin; it also allows researchers to study the DEJ effect on cell function. Few studies have created patterned substrates that could mimic the human DEJ to explore their significance. Here, we first review the DEJ roles and then critically discuss the TE strategies to create the DEJ undulating structure and their effects. New approaches in this field could be instrumental for improving bioengineered skin substitutes, creating 3D engineered skin, identifying pathological mechanisms, and producing and screening drugs.

Therapeutic Potential of Mesenchymal Stromal Cell-Derived Extracellular Vesicles in the Prevention of Organ Injuries Induced by Traumatic Hemorrhagic Shock

Severe trauma is the principal cause of death among young people worldwide. Hemorrhagic shock is the leading cause of death after severe trauma. Traumatic hemorrhagic shock (THS) is a complex phenomenon associating an absolute hypovolemia secondary to a sudden and significant extravascular blood loss, tissue injury, and, eventually, hypoxemia. These phenomena are responsible of secondary injuries such as coagulopathy, endotheliopathy, microcirculation failure, inflammation, and immune activation. Collectively, these dysfunctions lead to secondary organ failures and multi-organ failure (MOF). The development of MOF after severe trauma is one of the leading causes of morbidity and mortality, where immunological dysfunction plays a central role. Damage-associated molecular patterns induce an early and exaggerated activation of innate immunity and a suppression of adaptive immunity. Severe complications are associated with a prolonged and dysregulated immune–inflammatory state. The current challenge in the management of THS patients is preventing organ injury, which currently has no etiological treatment available. Modulating the immune response is a potential therapeutic strategy for preventing the complications of THS. Mesenchymal stromal cells (MSCs) are multipotent cells found in a large number of adult tissues and used in clinical practice as therapeutic agents for immunomodulation and tissue repair. There is growing evidence that their efficiency is mainly attributed to the secretion of a wide range of bioactive molecules and extracellular vesicles (EVs). Indeed, different experimental studies revealed that MSC-derived EVs (MSC-EVs) could modulate local and systemic deleterious immune response. Therefore, these new cell-free therapeutic products, easily stored and available immediately, represent a tremendous opportunity in the emergency context of shock. In this review, the pathophysiological environment of THS and, in particular, the crosstalk between the immune system and organ function are described. The potential therapeutic benefits of MSCs or their EVs in treating THS are discussed based on the current knowledge. Understanding the key mechanisms of immune deregulation leading to organ damage is a crucial element in order to optimize the preparation of EVs and potentiate their therapeutic effect.

Recent developments in mussel-inspired materials for biomedical applications

Over the decades, researchers have strived to synthesize and modify nature-inspired biomaterials, with the primary aim to address the challenges of designing functional biomaterials for regenerative medicine and tissue engineering. Among these challenges, biocompatibility and cellular interactions have been extensively investigated. Some of the most desirable characteristics for biomaterials in these applications are the loading of bioactive molecules, strong adhesion to moist areas, improvement of cellular adhesion, and self-healing properties. Mussel-inspired biomaterials have received growing interest mainly due to the changes in mechanical and biological functions of the scaffold due to catechol modification. Here, we summarize the chemical and biological principles and the latest advancements in production, as well as the use of mussel-inspired biomaterials. Our main focus is the polydopamine coating, the conjugation of catechol with other polymers, and the biomedical applications that polydopamine moieties are used for, such as matrices for drug delivery, tissue regeneration, and hemostatic control. We also present a critical conclusion and an inspired view on the prospects for the development and application of mussel-inspired materials.

Membrane-bound SCF and VCAM-1 synergistically regulate the morphology of hematopoietic stem cells

Membrane-bound factors expressed by niche stromal cells constitute a unique class of localized cues and regulate the long-term functions of adult stem cells, yet little is known about the underlying mechanisms. Here, we used a supported lipid bilayer (SLB) to recapitulate the membrane-bound interactions between hematopoietic stem cells (HSCs) and niche stromal cells. HSCs cluster membrane-bound stem cell factor (mSCF) at the HSC-SLB interface. They further form a polarized morphology with aggregated mSCF under a large protrusion through a synergy with VCAM-1 on the bilayer, which drastically enhances HSC adhesion. These features are unique to mSCF and HSCs among the factors and hematopoietic populations we examined. The mSCF-VCAM-1 synergy and the polarized HSC morphology require PI3K signaling and cytoskeletal reorganization. The synergy also enhances nuclear retention of FOXO3a, a crucial factor for HSC maintenance, and minimizes its loss induced by soluble SCF. Our work thus reveals a unique role and signaling mechanism of membrane-bound factors in regulating stem cell morphology and function.

Translational control of stem cell function

Stem cells are characterized by their ability to self-renew and differentiate into many different cell types. Research has focused primarily on how these processes are regulated at a transcriptional level. However, recent studies have indicated that stem cell behaviour is strongly coupled to the regulation of protein synthesis by the ribosome. In this Review, we discuss how different translation mechanisms control the function of adult and embryonic stem cells. Stem cells are characterized by low global translation rates despite high levels of ribosome biogenesis. The maintenance of pluripotency, the commitment to a specific cell fate and the switch to cell differentiation depend on the tight regulation of protein synthesis and ribosome biogenesis. Translation regulatory mechanisms that impact on stem cell function include mTOR signalling, ribosome levels, and mRNA and tRNA features and amounts. Understanding these mechanisms important for stem cell self-renewal and differentiation may also guide our understanding of cancer grade and metastasis.

Biofabrication of Artificial Stem Cell Niches in the Anterior Ocular Segment

The anterior segment of the eye is a complex set of structures that collectively act to maintain the integrity of the globe and direct light towards the posteriorly located retina. The eye is exposed to numerous physical and environmental insults such as infection, UV radiation, physical or chemical injuries. Loss of transparency to the cornea or lens (cataract) and dysfunctional regulation of intra ocular pressure (glaucoma) are leading causes of worldwide blindness. Whilst traditional therapeutic approaches can improve vision, their effect often fails to control the multiple pathological events that lead to long-term vision loss. Regenerative medicine approaches in the eye have already had success with ocular stem cell therapy and ex vivo production of cornea and conjunctival tissue for transplant recovering patients' vision. However, advancements are required to increase the efficacy of these as well as develop other ocular cell therapies. One of the most important challenges that determines the success of regenerative approaches is the preservation of the stem cell properties during expansion culture in vitro. To achieve this, the environment must provide the physical, chemical and biological factors that ensure the maintenance of their undifferentiated state, as well as their proliferative capacity. This is likely to be accomplished by replicating the natural stem cell niche in vitro. Due to the complex nature of the cell microenvironment, the creation of such artificial niches requires the use of bioengineering techniques which can replicate the physico-chemical properties and the dynamic cell-extracellular matrix interactions that maintain the stem cell phenotype. This review discusses the progress made in the replication of stem cell niches from the anterior ocular segment by using bioengineering approaches and their therapeutic implications.

Injectable silk nanofiber hydrogels as stem cell carriers to accelerate wound healing

Stem cells have potential utility in wound therapy, however the benefits are often limited due to cell injury from shear stress during injection and poor retention at the wound site. Here, shear-thinning silk nanofiber hydrogels were used to load bone marrow derived mesenchymal stem cells (BMSCs) and inject into wound sites to optimize cell retention and accelerate wound healing. The BMSCs in the silk nanofiber hydrogels maintained stemness better than the cells cultured on plates, and the expression of wound healing-related genes was significantly higher in the hydrogels with higher silk concentrations (2 wt%). The silk nanofibers physically prevented migration of BMSCs from the deposition site in the wound bed. In addition to faster wound healing, these BMSC-loaded hydrogels mediated angiogenesis and inflammation and improved collagen deposition and hair follicle regeneration in vivo in rats. Considering that these silk nanofiber hydrogels were successfully used here as carriers for stem cells to accelerate wound healing, further study for skin regeneration may be warranted.

Development and characterization of matrix-derived microcarriers from decellularized tissues using electrospraying techniques

Stirred bioreactor systems integrating microcarriers represent a promising approach for therapeutic cell manufacturing. While a variety of microcarriers are commercially available, current options do not integrate the tissue-specific composition of the extracellular matrix (ECM), which can play critical roles in directing cell function. The current study sought to generate microcarriers comprised exclusively of ECM from multiple tissue sources. More specifically, porcine decellularized dermis, porcine decellularized myocardium, and human decellularized adipose tissue were digested with α-amylase to obtain ECM suspensions that could be electrosprayed into liquid nitrogen to generate 3D microcarriers that were stable over a range of ECM concentrations without the need for chemical crosslinking or other additives. Characterization studies confirmed that all three microcarrier types had similar soft and compliant mechanical properties and were of a similar size range, but that their composition varied depending on the native tissue source. In vivo testing in immunocompetent mice revealed that the microcarriers integrated into the host tissues, supporting the infiltration of host cells including macrophages and endothelial cells at 2 weeks post-implantation. In vitro cell culture studies validated that the novel microcarriers supported the attachment of tissue-specific stromal cell populations under dynamic culture conditions within spinner flasks, with a significant increase in live cell numbers observed over 1 week on the dermal- and adipose-derived microcarriers. Overall, the findings demonstrate the versatility of the electrospraying methods and support the further development of the microcarriers as cell culture and delivery platforms.

Surface activation with oxygen plasma promotes osteogenesis with enhanced extracellular matrix formation in three-dimensional microporous scaffolds

Various types of synthetic polyesters have been developed as biomaterials for tissue engineering. These materials commonly possess biodegradability, biocompatibility, and formability, which are preferable properties for bone regeneration. The major challenge of using synthetic polyesters is the result of low cell affinity due to their hydrophobic nature, which hinders efficient cell seeding and active cell dynamics. To improve wettability, plasma treatment is widely used in industry. Here, we performed surface activation with oxygen plasma to hydrophobic copolymers, poly(l-lactide-co-trimethylene carbonate), which were shaped in 2D films and 3D microporous scaffolds, and then we evaluated the resulting surface properties and the cellular responses of rat bone marrow stem cells (rBMSC) to the material. Using scanning electron microscopy and Fourier-transform infrared spectroscopy, we demonstrated that short-term plasma treatment increased nanotopographical surface roughness and wettability with minimal change in surface chemistry. On treated surfaces, initial cell adhesion and elongation were significantly promoted, and seeding efficiency was improved. In an osteoinductive environment, rBMSC on plasma-treated scaffolds exhibited accelerated osteogenic differentiation with osteogenic markers including RUNX2, osterix, bone sialoprotein, and osteocalcin upregulated, and a greater amount of collagen matrix and mineral deposition were found. This study shows the utility of plasma surface activation for polymeric scaffolds in bone tissue engineering.

Identification of rare, transient post-mitotic cell states that are induced by injury and required for whole-body regeneration in Schmidtea mediterranea

Regeneration requires the coordination of stem cells, their progeny and distant differentiated tissues. Here, we present a comprehensive atlas of whole-body regeneration in Schmidtea mediterranea and identify wound-induced cell states. An analysis of 299,998 single-cell transcriptomes captured from regeneration-competent and regeneration-incompetent fragments identified transient regeneration-activated cell states (TRACS) in the muscle, epidermis and intestine. TRACS were independent of stem cell division with distinct spatiotemporal distributions, and RNAi depletion of TRACS-enriched genes produced regeneration defects. Muscle expression of notum, follistatin, evi/wls, glypican-1 and junctophilin-1 was required for tissue polarity. Epidermal expression of agat-1/2/3, cyp3142a1, zfhx3 and atp1a1 was important for stem cell proliferation. Finally, expression of spectrinβ and atp12a in intestinal basal cells, and lrrk2, cathepsinB, myosin1e, polybromo-1 and talin-1 in intestinal enterocytes regulated stem cell proliferation and tissue remodelling, respectively. Our results identify cell types and molecules that are important for regeneration, indicating that regenerative ability can emerge from coordinated transcriptional plasticity across all three germ layers.

2D biointerfaces to study stem cell-ligand interactions

Stem cells have great potential in the field of tissue engineering and regenerative medicine due to their inherent regenerative capabilities. However, an ongoing challenge within their clinical translation is to elicit or predict the desired stem cell behavior once transplanted. Stem cell behavior and function are regulated by their interaction with biophysical and biochemical signals present in their natural environment (i.e., stem cell niches). To increase our understanding about the interplay between stem cells and their resident microenvironments, biointerfaces have been developed as tools to study how these substrates can affect stem cell behaviors. This article aims to review recent developments on fabricating cell-instructive interfaces to control cell adhesion processes towards directing stem cell behavior. After an introduction on stem cells and their natural environment, static surfaces exhibiting predefined biochemical signals to probe the effect of chemical features on stem cell behaviors are discussed. In the third section, we discuss more complex dynamic platforms able to display biochemical cues with spatiotemporal control using on-off ligand display, reversible ligand display, and ligand mobility. In the last part of the review, we provide the reader with an outlook on future designs of biointerfaces. STATEMENT OF SIGNIFICANCE: Stem cells have great potential as treatments for many degenerative disorders prevalent in our aging societies. However, an ongoing challenge within their clinical translation is to promote stem cell mediated regeneration once they are transplanted in the body. Stem cells reside within our bodies where their behavior and function are regulated by interactions with their natural environment called the stem cell niche. To increase our understanding about the interplay between stem cells and their niche, 2D materials have been developed as tools to study how specific signals can affect stem cell behaviors. This article aims to review recent developments on fabricating cell-instructive interfaces to control cell adhesion processes towards directing stem cell behavior.

Mesenchymal stem cells plus bone repair materials as a therapeutic strategy for abnormal bone metabolism: Evidence of clinical efficacy and mechanisms of action implied

The regeneration process of human bones is very complicated, the management and treatment of bone damage caused by diseases are the main problems faced by clinicians worldwide. It is known that cell-based stem cell therapy together with biomaterials is a fast-developing method of tissue regeneration. This review focuses on the different types and main characteristics of scaffolds and stem cells suitable for bone regeneration, and aims to provide a state-of-the-art description of the current treatment of common bone metabolism related diseases such as osteoarthritis, osteoporosis and osteosarcoma and the strategies based on stem cell biological scaffolds used in bone tissue engineering. This method may provide a new treatment option for the treatment of common bone metabolism-related diseases that cannot be cured by ordinary and routine applications. Three databases (PubMed, CNKI and Web of Science) search terms used to write this review are: "arthritis", "osteoporosis", "osteosarcoma", "bone tissue engineering", "mesenchymal stem cells", "materials", "bioactive scaffolds" and their combinations, and the most relevant studies are selected. As a conclusion, it needs to be emphasized that despite the encouraging results, further development is needed due to the need for more in-depth research, standardization of stem cell manufacturing processes, large-scale development of clinical methods for bone tissue engineering, and market regulatory approval. Although the research and application of tissue regeneration technology and stem cells are still in their infancy, the application prospect is broad and it is expected to solve the current clinical problems.

Insight into Hypoxia Stemness Control

Recently, the research on stemness and multilineage differentiation mechanisms has greatly increased its value due to the potential therapeutic impact of stem cell-based approaches. Stem cells modulate their self-renewing and differentiation capacities in response to endogenous and/or extrinsic factors that can control stem cell fate. One key factor controlling stem cell phenotype is oxygen (O₂). Several pieces of evidence demonstrated that the complexity of reproducing O₂ physiological tensions and gradients in culture is responsible for defective stem cell behavior in vitro and after transplantation. This evidence is still worsened by considering that stem cells are conventionally incubated under non-physiological air O₂ tension (21%). Therefore, the study of mechanisms and signaling activated at lower O₂ tension, such as those existing under native microenvironments (referred to as hypoxia), represent an effective strategy to define if O₂ is essential in preserving naïve stemness potential as well as in modulating their differentiation. Starting from this premise, the goal of the present review is to report the status of the art about the link existing between hypoxia and stemness providing insight into the factors/molecules involved, to design targeted strategies that, recapitulating naïve O₂ signals, enable towards the therapeutic use of stem cell for tissue engineering and regenerative medicine.

The promise(s) of mesenchymal stem cell therapy in averting preclinical diabetes: lessons from in vivo and in vitro model systems

Obesity (Ob) poses a significant risk factor for the onset of metabolic syndrome with associated complications, wherein the Mesenchymal Stem Cell (MSC) therapy shows pre-clinical success. Here, we explore the therapeutic applications of human Placental MSCs (P-MSCs) to address Ob-associated Insulin Resistance (IR) and its complications. In the present study, we show that intramuscular injection of P-MSCs homed more towards the visceral site, restored HOMA-IR and glucose homeostasis in the WNIN/GR-Ob (Ob-T2D) rats. P-MSC therapy was effective in re-establishing the dysregulated cytokines. We report that the P-MSCs activates PI3K-Akt signaling and regulates the Glut4-dependant glucose uptake and its utilization in WNIN/GR-Ob (Ob-T2D) rats compared to its control. Our data reinstates P-MSC treatment's potent application to alleviate IR and restores peripheral blood glucose clearance evidenced in stromal vascular fraction (SVF) derived from white adipose tissue (WAT) of the WNIN/GR-Ob rats. Gaining insights, we show the activation of the PI3K-Akt pathway by P-MSCs both in vivo and in vitro (palmitate primed 3T3-L1 cells) to restore the insulin sensitivity dysregulated adipocytes. Our findings suggest a potent application of P-MSCs in  pre-clinical/Ob-T2D management.

Wnt signaling activation: targets and therapeutic opportunities for stem cell therapy and regenerative medicine

Wnt proteins are secreted morphogens that play critical roles in embryonic development, stem cell proliferation, self-renewal, tissue regeneration and remodeling in adults. While aberrant Wnt signaling contributes to diseases such as cancer, activation of Wnt/β-catenin signaling is a target of interest in stem cell therapy and regenerative medicine. Recent high throughput screenings from chemical and biological libraries, combined with improved gene expression reporter assays of Wnt/β-catenin activation together with rational drug design, led to the development of a myriad of Wnt activators, with different mechanisms of actions. Among them, Wnt mimics, antibodies targeting Wnt inhibitors, glycogen-synthase-3β inhibitors, and indirubins and other natural product derivatives are emerging modalities to treat bone, neurodegenerative, eye, and metabolic disorders, as well as prevent ageing. Nevertheless, the creation of Wnt-based therapies has been hampered by challenges in developing potent and selective Wnt activators without off-target effects, such as oncogenesis. On the other hand, to avoid these risks, their use to promote ex vivo expansion during tissue engineering is a promising application.

Stem Cell Niche Microenvironment: Review

The cornea comprises a pool of self-regenerating epithelial cells that are crucial to preserving clarity and visibility. Limbal epithelial stem cells (LESCs), which live in a specialized stem cell niche (SCN), are crucial for the survival of the human corneal epithelium. They live at the bottom of the limbal crypts, in a physically enclosed microenvironment with a number of neighboring niche cells. Scientists also simplified features of these diverse microenvironments for more analysis in situ by designing and recreating features of different SCNs. Recent methods for regenerating the corneal epithelium after serious trauma, including burns and allergic assaults, focus mainly on regenerating the LESCs. Mesenchymal stem cells, which can transform into self-renewing and skeletal tissues, hold immense interest for tissue engineering and innovative medicinal exploration. This review summarizes all types of LESCs, identity and location of the human epithelial stem cells (HESCs), reconstruction of LSCN and artificial stem cells for self-renewal.

SARS-CoV-2 infection in the mouse olfactory system

SARS-CoV-2 infection causes a wide spectrum of clinical manifestations in humans, and olfactory dysfunction is one of the most predictive and common symptoms in COVID-19 patients. However, the underlying mechanism by which SARS-CoV-2 infection leads to olfactory disorders remains elusive. Herein, we demonstrate that intranasal inoculation with SARS-CoV-2 induces robust viral replication in the olfactory epithelium (OE), not the olfactory bulb (OB), resulting in transient olfactory dysfunction in humanized ACE2 (hACE2) mice. The sustentacular cells and Bowman’s gland cells in the OE were identified as the major target cells of SARS-CoV-2 before invasion into olfactory sensory neurons (OSNs). Remarkably, SARS-CoV-2 infection triggers massive cell death and immune cell infiltration and directly impairs the uniformity of the OE structure. Combined transcriptomic and quantitative proteomic analyses revealed the induction of antiviral and inflammatory responses, as well as the downregulation of olfactory receptor (OR) genes in the OE from the infected animals. Overall, our mouse model recapitulates olfactory dysfunction in COVID-19 patients and provides critical clues for understanding the physiological basis for extrapulmonary manifestations of COVID-19.

Notch signaling in the dynamics of perivascular stem cells and their niches

The Notch signaling pathway is a fundamental regulator of cell fate determination in homeostasis and regeneration. In this work, we aimed to determine how Notch signaling mediates the interactions between perivascular stem cells and their niches in human dental mesenchymal tissues, both in homeostatic and regenerative conditions. By single cell RNA sequencing analysis, we showed that perivascular cells across the dental pulp and periodontal human tissues all express NOTCH3, and that these cells are important for the response to traumatic injuries in vivo in a transgenic mouse model. We further showed that the behavior of perivascular NOTCH3‐expressing stem cells could be modulated by cellular and molecular cues deriving from their microenvironments. Taken together, the present studies, reinforced by single‐cell analysis, reveal the pivotal importance of Notch signaling in the crosstalk between perivascular stem cells and their niches in tissue homeostasis and regeneration.

Transplantation Strategies for Spinal Cord Injury Based on Microenvironment Modulation

Spinal cord injury (SCI) is different from peripheral nerve injury; it results in devastating and permanent damage to the spine, leading to severe motor, sensory and autonomic dysfunction. SCI produces a complex microenvironment that can result in hemorrhage, inflammation and scar formation. Not only does it significantly limit regeneration, but it also challenges a multitude of transplantation strategies. In order to promote regeneration, researchers have recently begun to focus their attention on strategies that manipulate the complicated microenvironment produced by SCI. And some have achieved great therapeutic effects. Hence, reconstructing an appropriate microenvironment after transplantation could be a potential therapeutic solution for SCI. In this review, first, we aim to summarize the influential compositions of the microenvironment and their different effects on regeneration. Second, we highlight recent research that used various transplantation strategies to modulate different microenvironments produced by SCI in order to improve regeneration. Finally, we discuss future transplantation strategies regarding SCI.

Induction of Neurogenesis and Angiogenesis in a Rat Hemisection Spinal Cord Injury Model With Combined Neural Stem Cell, Endothelial Progenitor Cell, and Biomimetic Hydrogel Matrix Therapy

Acute spinal cord injury is a devastating injury that may lead to loss of independent function. Stem-cell therapies have shown promise; however, a clinically efficacious stem-cell therapy has yet to be developed. Functionally, endothelial progenitor cells induce angiogenesis, and neural stem cells induce neurogenesis. In this study, we explored using a multimodal therapy combining endothelial progenitor cells with neural stem cells encapsulated in a bioactive biomimetic hydrogel matrix to facilitate stem cell-induced neurogenesis and angiogenesis in a rat hemisection spinal cord injury model.

DESIGN

Laboratory experimentation.

SETTING

University laboratory.

SUBJECTS

Female Fischer 344 rats.

INTERVENTIONS

Three groups of rats: 1) control, 2) biomimetic hydrogel therapy, and 3) combined neural stem cell, endothelial progenitor cell, biomimetic hydrogel therapy underwent right-sided spinal cord hemisection at T9-T10. The blinded Basso, Beattie, and Bresnahan motor score was obtained weekly; after 4 weeks, observational histologic analysis of the injured spinal cords was completed.

MEASUREMENTS AND MAIN RESULTS

Blinded Basso, Beattie, and Bresnahan motor score of the hind limb revealed significantly improved motor function in rats treated with combined neural stem cell, endothelial progenitor cell, and biomimetic hydrogel therapy (p < 0.05) compared with the control group. The acellular biomimetic hydrogel group did not demonstrate a significant improvement in motor function compared with the control group. Immunohistochemistry evaluation of the injured spinal cords demonstrated de novo neurogenesis and angiogenesis in the combined neural stem cell, endothelial progenitor cell, and biomimetic hydrogel therapy group, whereas, in the control group, a gap or scar was found in the injured spinal cord.

CONCLUSIONS

This study demonstrates proof of concept that multimodal therapy with endothelial progenitor cells and neural stem cells combined with a bioactive biomimetic hydrogel can be used to induce de novo CNS tissue in an injured rat spinal cord.

TMT-Based Quantitative Proteomic Analysis Reveals the Effect of Bone Marrow Derived Mesenchymal Stem Cell on Hair Follicle Regeneration

Hair loss (HL) is a common chronic problem of poorly defined etiology. Herein, we explored the functionality of bone marrow-derived mesenchymal stem cell (BMSC) and conditioned medium (MSC-CM) as regulators of hair follicle proliferation and regeneration, and the mechanistic basis for such activity. BMSC were cultured and identified in vitro through the induction of multilineage differentiation and the use of a CCK-8 kit. The dorsal skin of mice was then injected with BMSC and MSC-CM, and the impact of these injections on hair cycle transition and hair follicle stem cell (HFSC) proliferation was then evaluated via hematoxylin and eosin (H&E) staining and immunofluorescent (IF) staining. We then conducted a tandem mass tags (TMT)-based quantitative proteomic analysis of control mice and mice treated with BMSC or MSC-CM to identify differentially expressed proteins (DEPs) associated with these treatments. Parallel reaction monitoring (PRM) was utilized as a means of verifying our proteomic analysis results. Herein, we found that BMSC and MSC-CM injection resulted in the transition of telogen hair follicles to anagen hair follicles, and we observed the enhanced proliferation of HFSCs positive for Krt15 and Sox9. Our TMT analyses identified 1,060 and 770 DEPs (fold change＞1.2 or＜0.83 and p ＜ 0.05) when comparing the BMSC vs. control and MSC-CM vs. control groups, respectively. Subsequent PRM validation of 14 selected DEPs confirmed these findings, and led to the identification of Stmn1, Ncapd2, Krt25, and Ctps1 as hub DEPs in a protein-protein interaction network. Together, these data suggest that BMSC and MSC-CM treatment can promote the proliferation of HFSCs, thereby facilitating hair follicle regeneration. Our proteomics analyses further indicate that Krt25, Cpm, Stmn1, and Mb may play central roles in hair follicle transition in this context and may represent viable clinical targets for the treatment of HL.

Adult stem cells in endometrial regeneration: Molecular insights and clinical applications

Endometrial damage is an important cause of female reproductive problems, manifested as menstrual abnormalities, infertility, recurrent pregnancy loss, and other complications. These conditions are collectively termed "Asherman syndrome" (AS) and are typically associated with recurrent induced pregnancy terminations, repeated diagnostic curettage and intrauterine infections. Cancer treatment also has unexpected detrimental side effects on endometrial function in survivors independently of ovarian effects. Endometrial stem cells act in the regeneration of the endometrium and in repair through direct differentiation or paracrine effects. Nonendometrial adult stem cells, such as bone marrow-derived mesenchymal stem cells and umbilical cord-derived mesenchymal stem cells, with autologous and allogenic applications, can also repair injured endometrial tissue in animal models of AS and in human studies. However, there remains a lack of research on the repair of the damaged endometrium after the reversal of tumors, especially endometrial cancers. Here, we review the biological mechanisms of endometrial regeneration, and research progress and challenges for adult stem cell therapy for damaged endometrium, and discuss the potential applications of their use for endometrial repair after cancer remission, especially in endometrial cancers. Successful application of such cells will improve reproductive parameters in patients with AS or cancer. Significance: The endometrium is the fertile ground for embryos, but damage to the endometrium will greatly impair female fertility. Adult stem cells combined with tissue engineering scaffold materials or not have made great progress in repairing the injured endometrium due to benign lesions. However, due to the lack of research on the repair of the damaged endometrium caused by malignant tumors or tumor therapies, the safety and effectiveness of such stem cell-based therapies need to be further explored. This review focuses on the molecular insights and clinical application potential of adult stem cells in endometrial regeneration and discusses the possible challenges or difficulties that need to be overcome in stem cell-based therapies for tumor survivors. The development of adult stem cell-related new programs will help repair damaged endometrium safely and effectively and meet fertility needs in tumor survivors.

Patient-Specific Organoid and Organ-on-a-Chip: 3D Cell-Culture Meets 3D Printing and Numerical Simulation

The last few decades have witnessed diversified in vitro models to recapitulate the architecture and function of living organs or tissues and contribute immensely to advances in life science. Two novel 3D cell culture models: 1) Organoid, promoted mainly by the developments of stem cell biology and 2) Organ-on-a-chip, enhanced primarily due to microfluidic technology, have emerged as two promising approaches to advance the understanding of basic biological principles and clinical treatments. This review describes the comparable distinct differences between these two models and provides more insights into their complementarity and integration to recognize their merits and limitations for applicable fields. The convergence of the two approaches to produce multi-organoid-on-a-chip or human organoid-on-a-chip is emerging as a new approach for building 3D models with higher physiological relevance. Furthermore, rapid advancements in 3D printing and numerical simulations, which facilitate the design, manufacture, and results-translation of 3D cell culture models, can also serve as novel tools to promote the development and propagation of organoid and organ-on-a-chip systems. Current technological challenges and limitations, as well as expert recommendations and future solutions to address the promising combinations by incorporating organoids, organ-on-a-chip, 3D printing, and numerical simulation, are also summarized.

Comparison of chondro-inductivity between collagen and hyaluronic acid hydrogel based on chemical/physical microenvironment

Achieving chondrogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) successfully is crucial for cartilage regeneration. To date, various hydrogels with different chemical microenvironment have been used to modulate chondrogenic differentiation of BMSCs, especially collagen and hyaluronic acid hydrogel. However, the chondro-inductive ability of collagen and hyaluronic acid hydrogel has not been evaluated yet and the different chemical and physical microenvironment of these two hydrogels increase the difficulty of comparison. In this study, three different hydrogels based on collagen and hyaluronic acid (self-assembled collagen hydrogel (Col), self-assembled collagen hydrogel cross-linked with genipin (Cgp), and methacrylated hyaluronic acid hydrogel (HA)) were prepared and their chondro-inductive ability on the encapsulated BMSCs was evaluated. Col and Cgp have the same chemical composition and similar microstructure, but are different from HA, while Cgp and HA hydrogels have the same mechanical strength. It was found that chemical and physical microenvironments of the hydrogels combined to influence cell condensation. Thanks to cell condensation was more likely to occur in collagen hydrogels in the early stage, the cartilage-induced ability was in the order of Col > Cgp > HA. However, the severe shrinkage of Col and Cgp resulted in no enough space for cell proliferation within hydrogels in the later stage. In contrast, relatively stable physical microenvironment of HA helped to maintain continuous production of cartilage-related matrix in the later stage. Overall, these results revealed that the chondro-inductive ability of collagen and hyaluronic acid hydrogel with different chemical and physical microenvironment cannot be evaluated by a particular time period. However, it provided important information for optimization and design of the future hydrogels towards successful repair of articular cartilage.

Silk-Reinforced Collagen Hydrogels with Raised Multiscale Stiffness for Mesenchymal Cells 3D Culture

Type I collagen hydrogels are of high interest in tissue engineering. With the evolution of 3D bioprinting technologies, a high number of collagen-based scaffolds have been reported for the development of 3D cell cultures. A recent proposal was to mix collagen with silk fibroin derived from Bombyx mori silkworm. Nevertheless, due to the difficulties in the preparation and the characteristics of the protein, several problems such as phase separation and collagen denaturation appear during the procedure. Therefore, the common solution is to diminish the concentration of collagen although in that way the most biologically relevant component is reduced. In this study, we present a new, simple, and effective method to develop a collagen-silk hybrid hydrogel with high collagen concentration and with increased stiffness approaching that of natural tissues, which could be of high interest for the development of cardiac patches for myocardial regeneration and for preconditioning of mesenchymal stem cells (MSCs) to improve their therapeutic potential. Sericin in the silk was preserved by using a physical solubilizing procedure that results in a preserved fibrous structure of type I collagen, as shown by ultrastructural imaging. The macro- and micromechanical properties of the hybrid hydrogels measured by tensile stretch and atomic force microscopy, respectively, showed a more than twofold stiffening than the collagen-only hydrogels. Rheological measurements showed improved printability properties for the developed biomaterial. The suitability of the hydrogels for 3D cell culture was assessed by 3D bioprinting bone marrow-derived MSCs cultured within the scaffolds. The result was a biomaterial with improved printability characteristics that better resembled the mechanical properties of natural soft tissues while preserving biocompatibility owing to the high concentration of collagen. Impact statement In this study, we report the development of silk microfiber-reinforced type I collagen hydrogels for 3D bioprinting and cell culture. In contrast with previously reported studies, a novel physical method allowed the preservation of the silk sericin protein. Hydrogels were stable, showed no phase separation between the biomaterials, and they presented improved printability. An increase between two- and threefold of the multiscale stiffness of the scaffolds was achieved with no need of using additional crosslinkers or complex methods, which could be of high relevance for cardiac patches development and for preconditioning mesenchymal stem cells (MSCs) for therapeutic applications. We demonstrate that bone marrow-derived MSCs can be effectively bioprinted and 3D cultured within the stiffened structures.

The regenerative mechanisms of platelet-rich plasma: A review

Orthobiologics continue to gain popularity in many areas of medical science, especially in the field of regenerative medicine. Platelet-rich plasma derivatives are orthobiologic tools of particular interest. These biologic products can be obtained via centrifugation of a patient's whole blood and the components can then be subsequently isolated, concentrated and ultimately administered into injured tissues, particularly in areas where standard healing is disrupted. The elevated concentration of platelets above the basal value enables accelerated growth of various tissues with minimal side effects. The application of autologous orthobiologics is a relatively new biotechnology undergoing expansion which continues to reveal optimistic results in the stimulation and enhanced healing of various sorts of tissue injuries. The local release of growth factors and cytokines contained in platelet alpha granules accelerates and ameliorates tissue repair processes, mimicking and supporting standard wound healing. This effect is greatly enhanced upon combination with the fibrinolytic system, which are essential for complete regeneration. Fibrinolytic reactions can dictate proper cellular recruitment of certain cell populations such as mesenchymal stem cells and other immunomodulatory agents. Additionally, these reactions also control proteolytic activity in areas of wound healing and regenerative processes of mesodermal tissues including bone, cartilage, and muscle, which makes it particularly valuable for musculoskeletal health, for instance. Although many investigations have demonstrated significant results with platelet-rich plasma derivatives, further studies are still warranted.

Regulation of tissue regeneration by the circadian clock

Circadian rhythms are regulated by a highly conserved transcriptional/translational feedback loop that maintains approximately 24-hr periodicity from cellular to organismal levels. Much research effort is being devoted to understanding how the outputs of the master clock affect peripheral oscillators, and in turn, numerous biological processes. Recent studies have revealed roles for circadian timing in the regulation of numerous cellular behaviours in support of complex tissue regeneration. One such role involves the interaction between the circadian clockwork and the cell cycle. The molecular mechanisms that control the cell cycle create a system of regulation that allows for high fidelity DNA synthesis, mitosis and apoptosis. In recent years, it has become clear that clock gene products are required for proper DNA synthesis and cell cycle progression, and conversely, elements of the cell cycle cascade feedback to influence molecular circadian timing mechanisms. It is through this crosstalk that the circadian system orchestrates stem cell proliferation, niche exit and control of the signalling pathways that govern differentiation and self-renewal. In this review, we discuss the evidence for circadian control of tissue homeostasis and repair and suggest new avenues for research.

Deep learning-based predictive identification of neural stem cell differentiation

The differentiation of neural stem cells (NSCs) into neurons is proposed to be critical in devising potential cell-based therapeutic strategies for central nervous system (CNS) diseases, however, the determination and prediction of differentiation is complex and not yet clearly established, especially at the early stage. We hypothesize that deep learning could extract minutiae from large-scale datasets, and present a deep neural network model for predictable reliable identification of NSCs fate. Remarkably, using only bright field images without artificial labelling, our model is surprisingly effective at identifying the differentiated cell types, even as early as 1 day of culture. Moreover, our approach showcases superior precision and robustness in designed independent test scenarios involving various inducers, including neurotrophins, hormones, small molecule compounds and even nanoparticles, suggesting excellent generalizability and applicability. We anticipate that our accurate and robust deep learning-based platform for NSCs differentiation identification will accelerate the progress of NSCs applications.

The differentiation of neural stem cells (NSCs) into neurons is a critical part in devising potential cell-based therapeutic strategies for central nervous system diseases but NSCs fate determination and prediction is problematic. Here, the authors present a deep neural network model for predictable reliable identification of NSCs fate.

A single-cell atlas of human teeth

Teeth exert fundamental functions related to mastication and speech. Despite their great biomedical importance, an overall picture of their cellular and molecular composition is still missing. In this study, we have mapped the transcriptional landscape of the various cell populations that compose human teeth at single-cell resolution, and we analyzed in deeper detail their stem cell populations and their microenvironment. Our study identified great cellular heterogeneity in the dental pulp and the periodontium. Unexpectedly, we found that the molecular signatures of the stem cell populations were very similar, while their respective microenvironments strongly diverged. Our findings suggest that the microenvironmental specificity is a potential source for functional differences between highly similar stem cells located in the various tooth compartments and open new perspectives toward cell-based dental therapeutic approaches.

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Dental atlas of the pulp and periodontal tissues of human teeth

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Identification of three common MSC subclusters between dental pulp and periodontium

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Dental pulp and periodontal MSCs are similar, and their niches diverge

Cryptic ligand on collagen matrix unveiled by MMP13 accelerates bone tissue regeneration via MMP13/Integrin α3/RUNX2 feedback loop

Extracellular matrix (ECM) remodeling is necessary for the development and self-healing of tissue, and the process is tissue specific. Matrix metalloproteinases (MMPs) play a role in ECM remodeling by unwinding and cleaving ECM. We hypothesized that ECM remodeling by MMPs is involved in the differentiation of stem cells into specific lineages during self-healing. To prove the hypothesis, we investigated which MMPs are involved in the osteogenic differentiation of human mesenchymal stem cells (hMSCs) grown on a type I collagen (Col I) matrix, and we found that specifically high expression of MMP13 in hMSCs grown on a Col I matirx during osteogenic differentiation. Moreover, knocking down of MMP13 decreased the osteogenic differentiation of hMSCs grown on a Col I matrix. In addition, pre-treatment of recombinant human MMP13 lead to remodeling of Col I matrix and increased the osteogenic differentiation of hMSCs and in vivo bone formation following the upregulation of the expression of runt-related transcription factor 2 (RUNX2), integrin α3 (ITGA3), and focal adhesion kinase. Furthermore, the transcription factor RUNX2 bound to the MMP13 promoter. These results suggest that growth on a remodeled Col I matrix by MMP13 stimulates osteogenic differentiation of hMSCs and self-healing of bone tissue via an MMP13/ITGA3/RUNX2 positive feedback loop. STATEMENT OF SIGNIFICANCE: Self-healing of tissue could be the key to treating diseases that cannot be overcome by present technology. We investigated the mechanism underlying the self-healing of tissue and we found that the osteogenic differentiation was increased in hMSCs grown on a remodeled Col I matrix by the optimized concentration of MMP13 not in hMSCs grown on a Col I fragments cleaved by a high concentration of MMP13. In addition, we found the remodeled Col I matrix by MMP13 increased the osteogenic capacity through a MMP13/integrin α3/RUNX2 positive feedback loop. This result would be able to not only provide a strategy for bone tissue-specific functional materials following strong evidence about the self-healing mechanism of bone through the interaction between stem cells and the ECM matrix. As such, we strongly believe our finding will be of interest to researchers studying biomaterials, stem cell biology and matrix interaction for regenerative medicine and therapy.

Pluripotent and Multipotent Stem Cells and Current Therapeutic Applications: Review

There is numerous evidence for the presence of stem cells, which is important for the treatment of a wide variety of disease conditions. Stem cells have a great therapeutic effect on different degenerative diseases through the development of specialized cells. Embryonic stem (ES) cells are derived from preimplantation embryos, which have a natural karyotype. This cell has the capacity of proliferation indefinitely and undifferentiated. Stem cells are very crucial for the treatment of different chronic and degenerative diseases. For instance, stem cell clinical trials have been done for ischemic heart disease. Also, the olfactory cells for spinal cord lesions and human fetal pancreatic cells for diabetes mellitus are the other clinical importance of stem cell therapy. Extracellular matrix (ECM) and other environmental factors influence the fate and activity of stem cells.

CDR1as regulated by hnRNPM maintains stemness of periodontal ligament stem cells via miR-7/KLF4

CDR1as is a well‐identified circular RNA with regulatory roles in a variety of physiological processes. However, the effects of CDR1as on stemness of periodontal ligament stem cells (PDLSCs) and the underlying mechanisms remain unclear. In this study, we detect CDR1as in human PDLSCs, and subsequently demonstrate that CDR1as maintains PDLSC stemness. Knockdown of CDR1as decreases the expression levels of stemness‐related genes and impairs the cell's multi‐differentiation and cell migration abilities, while overexpression of CDR1as increases the expression levels of stemness‐related genes and enhances these abilities. Furthermore, our results indicate that the RNA‐binding protein hnRNPM directly interacts with CDR1as and regulates its expression in PDLSCs. In addition, we show that CDR1as promotes the expression of stemness‐related genes in PDLSCs by inhibiting miR‐7‐mediated suppression of KLF4 expression. Collectively, our results demonstrate that CDR1as participates in the molecular circuitry that regulates PDLSC stemness.

Limbal stem cell diseases

The function of limbal stem/progenitor cells (LSCs) is critical to maintain corneal epithelial homeostasis. Many external insults and intrinsic defects can be deleterious to LSCs and their niche microenvironment, resulting in limbal stem cell dysfunction or deficiency (LSCD). Ocular comorbidities, frequent in eyes with LSCD, can exacerbate the dysfunction of residual LSCs, and limit the survival of transplanted LSCs. Clinical presentation and disease evolution vary among different etiologies of LSCD. New ocular imaging modalities and molecular markers are now available to standardize the diagnosis criteria and stage the severity of the disease. Medical therapies may be sufficient to reverse the disease if residual LSCs are present. A stepwise approach should be followed to optimize the ocular surface, eliminate the causative factors and treat comorbid conditions, before considering surgical interventions. Furthermore, surgical options are selected depending on the severity and laterality of the disease. The standardized diagnostic criteria to stage the disease is necessary to objectively evaluate and compare the efficacy of the emerging customized therapies.

Bioactive Molecular Discovery Using Deer Antlers as a Model of Mammalian Regeneration

The ability to activate and regulate stem cells during wound healing and tissue regeneration is a promising field that is resulting in innovative approaches in the field of regenerative medicine. The regenerative capacity of invertebrates has been well documented; however, in mammals, stem cells that drive organ regeneration are rare. Deer antlers are the only known mammalian structure that can annually regenerate to produce a tissue containing dermis, blood vessels, nerves, cartilage, and bone. The neural crest derived stem cells that drive this process result in antlers growing at up to 2 cm/day. Deer antlers thus provide superior attributes compared to lower-order animal models, when investigating the regulation of stem cell-based regeneration. Antler stem cells can therefore be used as a model to investigate the bioactive molecules, biological processes, and pathways involved in the maintenance of a stem cell niche, and their activation and differentiation during organ formation. This review examines stem cell-based regeneration with a focus on deer antlers, a neural crest stem cell-based mammalian regenerative structure. It then discusses the omics technical platforms highlighting the proteomics approaches used for investigating the molecular mechanisms underlying stem cell regulation in antler tissues.

Transplantation of 3D MSC/HUVEC spheroids with neuroprotective and proangiogenic potentials ameliorates ischemic stroke brain injury

Ischemic stroke, and the consequent brain cell death, is a common cause of death and disability worldwide. Current treatments that primarily aim to relieve symptoms are relatively inefficient in achieving brain tissue regeneration and functional recovery, and thus novel therapeutic options are urgently needed. Although cell-based therapies have shown promise for treating the infarcted brain, a recurring challenge is the inadequate retention and engraftment of transplanted cells at the target tissue, thereby limiting the ultimate therapeutic efficacy. Here, we show that transplantation of preassembled three-dimensional (3D) spheroids of mesenchymal stem cells (MSCs) and vascular endothelial cells (ECs) results in significantly improved cell retention and survival compared with conventional mixed-cell suspensions. The transplanted 3D spheroids exhibit notable neuroprotective, proneurogenic, proangiogenic and anti-scarring potential as evidenced by clear extracellular matrix structure formation and paracrine factor expression and secretion; this ultimately results in increased structural and motor function recovery in the brain of an ischemic stroke mouse model. Therefore, transplantation of MSCs and ECs using the 3D cell spheroid configuration not only reduces cell loss during cell harvesting/administration but also enhances the resultant therapeutic benefit, thus providing important proof-of-concept for future clinical translation.

Distinct Expression Patterns of Cxcl12 in Mesenchymal Stem Cell Niches of Intact and Injured Rodent Teeth

Specific stem cell populations within dental mesenchymal tissues guarantee tooth homeostasis and regeneration throughout life. The decision between renewal and differentiation of stem cells is greatly influenced by interactions with stromal cells and extracellular matrix molecules that form the tissue specific stem cell niches. The Cxcl12 chemokine is a general marker of stromal cells and plays fundamental roles in the maintenance, mobilization and migration of stem cells. The aim of this study was to exploit Cxcl12-GFP transgenic mice to study the expression patterns of Cxcl12 in putative dental niches of intact and injured teeth. We showed that endothelial and stromal cells expressed Cxcl12 in the dental pulp tissue of both intact molars and incisors. Isolated non-endothelial Cxcl12⁺ dental pulp cells cultured in different conditions in vitro exhibited expression of both adipogenic and osteogenic markers, thus suggesting that these cells possess multipotent fates. Taken together, our results show that Cxcl12 is widely expressed in intact and injured teeth and highlight its importance as a key component of the various dental mesenchymal stem cell niches.

Stem Cells and the Endometrium: From the Discovery of Adult Stem Cells to Pre-Clinical Models

Adult stem cells (ASCs) were long suspected to exist in the endometrium. Indeed, several types of endometrial ASCs were identified in rodents and humans through diverse isolation and characterization techniques. Putative stromal and epithelial stem cell niches were identified in murine models using label-retention techniques. In humans, functional methods (clonogenicity, long-term culture, and multi-lineage differentiation assays) and stem cell markers (CD146, SUSD2/W5C5, LGR5, NTPDase2, SSEA-1, or N-cadherin) facilitated the identification of three main types of endogenous endometrial ASCs: stromal, epithelial progenitor, and endothelial stem cells. Further, exogenous populations of stem cells derived from bone marrow may act as key effectors of the endometrial ASC niche. These findings are promoting the development of stem cell therapies for endometrial pathologies, with an evolution towards paracrine approaches. At the same time, promising therapeutic alternatives based on bioengineering have been proposed.

Towards uterus tissue engineering: a comparative study of sheep uterus decellularisation

Uterus tissue engineering may dismantle limitations in current uterus transplantation protocols. A uterine biomaterial populated with patient-derived cells could potentially serve as a graft to circumvent complicated surgery of live donors, immunosuppressive medication and rejection episodes. Repeated uterine bioengineering studies on rodents have shown promising results using decellularised scaffolds to restore fertility in a partially impaired uterus and now mandate experiments on larger and more human-like animal models. The aim of the presented studies was therefore to establish adequate protocols for scaffold generation and prepare for future in vivo sheep uterus bioengineering experiments. Three decellularisation protocols were developed using vascular perfusion through the uterine artery of whole sheep uteri obtained from slaughterhouse material. Decellularisation solutions used were based on 0.5% sodium dodecyl sulphate (Protocol 1) or 2% sodium deoxycholate (Protocol 2) or with a sequential perfusion of 2% sodium deoxycholate and 1% Triton X-100 (Protocol 3). The scaffolds were examined by histology, extracellular matrix quantification, evaluation of mechanical properties and the ability to support foetal sheep stem cells after recellularisation. We showed that a sheep uterus can successfully be decellularised while maintaining a high integrity of the extracellular components. Uteri perfused with sodium deoxycholate (Protocol 2) were the most favourable treatment in our study based on quantifications. However, all scaffolds supported stem cells for 2 weeks in vitro and showed no cytotoxicity signs. Cells continued to express markers for proliferation and maintained their undifferentiated phenotype. Hence, this study reports three valuable decellularisation protocols for future in vivo sheep uterus bioengineering experiments.