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Concept: Adult stem cell


Biological resurfacing of entire articular surfaces represents an important but challenging strategy for treatment of cartilage degeneration that occurs in osteoarthritis. Not only does this approach require anatomically sized and functional engineered cartilage, but the inflammatory environment within an arthritic joint may also inhibit chondrogenesis and induce degradation of native and engineered cartilage. The goal of this study was to use adult stem cells to engineer anatomically shaped, functional cartilage constructs capable of tunable and inducible expression of antiinflammatory molecules, specifically IL-1 receptor antagonist (IL-1Ra). Large (22-mm-diameter) hemispherical scaffolds were fabricated from 3D woven poly(ε-caprolactone) (PCL) fibers into two different configurations and seeded with human adipose-derived stem cells (ASCs). Doxycycline (dox)-inducible lentiviral vectors containing eGFP or IL-1Ra transgenes were immobilized to the PCL to transduce ASCs upon seeding, and constructs were cultured in chondrogenic conditions for 28 d. Constructs showed biomimetic cartilage properties and uniform tissue growth while maintaining their anatomic shape throughout culture. IL-1Ra-expressing constructs produced nearly 1 µg/mL of IL-1Ra upon controlled induction with dox. Treatment with IL-1 significantly increased matrix metalloprotease activity in the conditioned media of eGFP-expressing constructs but not in IL-1Ra-expressing constructs. Our findings show that advanced textile manufacturing combined with scaffold-mediated gene delivery can be used to tissue engineer large anatomically shaped cartilage constructs that possess controlled delivery of anticytokine therapy. Importantly, these cartilage constructs have the potential to provide mechanical functionality immediately upon implantation, as they will need to replace a majority, if not the entire joint surface to restore function.

Concepts: Biology, Extracellular matrix, Receptor, Cellular differentiation, Histology, Osteoarthritis, Engineering, Adult stem cell


Delineating the crosstalk between distinct signaling pathways is key to understanding the diverse and dynamic responses of adult stem cells during tissue regeneration. Here, we demonstrate that the Edn/EdnrB signaling pathway can interact with other signaling pathways to elicit distinct stem cell functions during tissue regeneration. EdnrB signaling promotes proliferation and differentiation of melanocyte stem cells (McSCs), dramatically enhancing the regeneration of hair and epidermal melanocytes. This effect is dependent upon active Wnt signaling that is initiated by Wnt ligand secretion from the hair follicle epithelial niche. Further, this Wnt-dependent EdnrB signaling can rescue the defects in melanocyte regeneration caused by Mc1R loss. This suggests that targeting Edn/EdnrB signaling in McSCs can be a therapeutic approach to promote photoprotective-melanocyte regeneration, which may be useful for those with increased risk of skin cancers due to Mc1R variants.

Concepts: Cell, Developmental biology, Stem cell, Secretion, Cell biology, Cellular differentiation, Skin, Adult stem cell


The shape of an animal body plan is constructed from protein components encoded by the genome. However, bioelectric networks composed of many cell types have their own intrinsic dynamics, and can drive distinct morphological outcomes during embryogenesis and regeneration. Planarian flatworms are a popular system for exploring body plan patterning due to their regenerative capacity, but despite considerable molecular information regarding stem cell differentiation and basic axial patterning, very little is known about how distinct head shapes are produced. Here, we show that after decapitation in G. dorotocephala, a transient perturbation of physiological connectivity among cells (using the gap junction blocker octanol) can result in regenerated heads with quite different shapes, stochastically matching other known species of planaria (S. mediterranea, D. japonica, and P. felina). We use morphometric analysis to quantify the ability of physiological network perturbations to induce different species-specific head shapes from the same genome. Moreover, we present a computational agent-based model of cell and physical dynamics during regeneration that quantitatively reproduces the observed shape changes. Morphological alterations induced in a genomically wild-type G. dorotocephala during regeneration include not only the shape of the head but also the morphology of the brain, the characteristic distribution of adult stem cells (neoblasts), and the bioelectric gradients of resting potential within the anterior tissues. Interestingly, the shape change is not permanent; after regeneration is complete, intact animals remodel back to G. dorotocephala-appropriate head shape within several weeks in a secondary phase of remodeling following initial complete regeneration. We present a conceptual model to guide future work to delineate the molecular mechanisms by which bioelectric networks stochastically select among a small set of discrete head morphologies. Taken together, these data and analyses shed light on important physiological modifiers of morphological information in dictating species-specific shape, and reveal them to be a novel instructive input into head patterning in regenerating planaria.

Concepts: DNA, Gene, Developmental biology, Stem cell, Cellular differentiation, Regeneration, Adult stem cell, Planarian


Following skeletal muscle injury, muscle stem cells (satellite cells) are activated, proliferate, and differentiate to form myofibers. We show that mRNA-decay protein AUF1 regulates satellite cell function through targeted degradation of specific mRNAs containing 3' AU-rich elements (AREs). auf1(-/-) mice undergo accelerated skeletal muscle wasting with age and impaired skeletal muscle repair following injury. Satellite cell mRNA analysis and regeneration studies demonstrate that auf1(-/-) satellite cell self-renewal is impaired due to increased stability and overexpression of ARE-mRNAs, including cell-autonomous overexpression of matrix metalloprotease MMP9. Secreted MMP9 degrades the skeletal muscle matrix, preventing satellite-cell-mediated regeneration and return to quiescence. Blocking MMP9 activity in auf1(-/-) mice restores skeletal muscle repair and maintenance of the satellite cell population. Control of ARE-mRNA decay by AUF1 represents a mechanism for adult stem cell regulation and is implicated in human skeletal muscle wasting diseases.

Concepts: DNA, Gene, Gene expression, Cell, Stem cell, Cell biology, Cellular differentiation, Adult stem cell


We present a new approach which aims to translate freeform biofabrication into the surgical field, while staying true to the practical constraints of the operating theatre. Herein we describe the development of a handheld biofabrication tool, dubbed the ‘biopen’, which enables the deposition of living cells and biomaterials in a manual, direct-write fashion. A gelatin-methacrylamide/hyaluronic acid-methacrylate (GelMa/HAMa) hydrogel was printed and UV crosslinked during the deposition process to generate surgically sculpted 3D structures. Custom titanium nozzles were fabricated to allow printing of multiple ink formulations in a collinear (side-by-side) geometry. Independently applied extrusion pressure for both chambers allows for geometric control of the printed structure and for the creation of compositional gradients. In vitro experiments demonstrated that human adipose stem cells maintain high viability (>97%) one week after biopen printing in GelMa/HAMa hydrogels. The biopen described in this study paves the way for the use of 3D bioprinting during the surgical process. The ability to directly control the deposition of regenerative scaffolds with or without the presence of live cells during the surgical process presents an exciting advance not only in the fields of cartilage and bone regeneration but also in other fields where tissue regeneration and replacement are critical.

Concepts: Human, Developmental biology, Stem cell, Surgery, Cellular differentiation, Field, Printing, Adult stem cell


Planarian neoblasts are pluripotent, adult somatic stem cells and lineage-primed progenitors required for production and maintenance of all differentiated cell types, including the germline. Neoblasts, originally defined as undifferentiated cells residing in the adult parenchyma, are frequently compared to embryonic stem cells yet their developmental origin remains obscure. We investigated the provenance of neoblasts during S. mediterranea embryogenesis, and report that neoblasts arise from an anarchic, cycling piwi-1+ population wholly responsible for production of all temporary and definitive organs during embryogenesis. Early embryonic piwi-1+ cells are molecularly and functionally distinct from neoblasts: they express unique cohorts of early embryo enriched transcripts and behave differently than neoblasts in cell transplantation assays. Neoblast lineages arise as organogenesis begins and are required for construction of all major organ systems during embryogenesis. These subpopulations are continuously generated during adulthood, where they act as agents of tissue homeostasis and regeneration.

Concepts: Cell, Developmental biology, Stem cell, Stem cells, Cellular differentiation, Organ, Embryonic stem cell, Adult stem cell


In musculoskeletal tissues like bone, chemotherapy can impair progenitor cell differentiation and proliferation, resulting in decreased bone growth and mineralization throughout a patient’s lifetime. In the current study, we investigated the effects of chemotherapeutics on adipose-derived stem cell (ASC) function to determine whether this cell source could be a candidate for repairing, or even preventing, chemotherapy-induced tissue damage. Dose-dependent proliferation rates of ASCs and normal human fibroblasts (NHFs) were quantified after treatment with cytarabine (CY), etoposide (ETO), methotrexate (MTX), and vincristine (VIN) using a fluorescence-based assay. The influence of MTX on the multipotency of ASCs and freshly isolated stromal vascular fraction (SVF) cells was also evaluated using lineage-specific stains and spectrophotometry. ASC and NHF proliferation were equally inhibited by exposure to CY and ETO; however, when treated with MTX and VIN, ASCs exhibited greater resistance. This was especially apparent for MTX-treated samples, with ASC proliferation showing no inhibition for clinically relevant MTX doses ranging from 0.1 to 50μM. Additional experiments revealed that the differentiation potential of ASCs was not affected by MTX treatment and that upregulation of dihydrofolate reductase possibly contributed to this response. Moreover, SVF cells, which include ASCs, exhibited similar resistance to MTX impairment, with respect to cellular proliferation, clonogenicity, and differentiation capability. Therefore, we have shown that the regenerative properties of ASCs resist the cytotoxicity of MTX, identifying these cells as a potential key for repairing musculoskeletal damage in patients undergoing chemotherapy.

Concepts: DNA, Developmental biology, Stem cell, Bone marrow, Cellular differentiation, Tissue, Adult stem cell, Meristem


Until recently, reliable markers for adult stem cells have been lacking for many regenerative mammalian tissues. Lgr5 (leucine-rich repeat-containing G-protein coupled receptor 5) has been identified as a marker for adult stem cells in intestine, stomach, and hair follicle; Lgr5-expressing cells give rise to all types of cells in these tissues. Taste epithelium also regenerates constantly, yet the identity of adult taste stem cells remains elusive. In this study, we found that Lgr5 is strongly expressed in cells at the bottom of trench areas at the base of circumvallate and foliate taste papillae and weakly expressed in the basal area of taste buds and that Lgr5-expressing cells in posterior tongue are a subset of K14-positive epithelial cells. Lineage-tracing experiments using an inducible Cre knock-in allele in combination with Rosa26-LacZ and Rosa26-tdTomato reporter strains showed that Lgr5-expressing cells gave rise to taste cells, perigemmal cells, along with self-renewing cells at the bottom of trench areas at the base of circumvallate and foliate papillae. Moreover, using subtype-specific taste markers, we found that Lgr5-expressing cell progeny include all three major types of adult taste cells. Our results indicate that Lgr5 may mark adult taste stem or progenitor cells in the posterior portion of the tongue.

Concepts: Signal transduction, Epithelium, Skin, Taste, Adult stem cell, Tongue, Gustatory system, Taste bud


: Adipose-derived stem cells have become the most studied adult stem cells. The authors examined the apoptosis and necrosis rates for adipocyte, stromal vascular fraction, and adipose-derived stem cells in fresh human lipoaspirates.

Concepts: Stem cell, Mesenchymal stem cell, Apoptosis, Cytoplasm, Adipose tissue, Adipocyte, Necrosis, Adult stem cell


Background: Acute kidney injury (AKI) is emerging as a public health problem in developing and developed countries. It affects up to 7% of hospitalized patients, with a higher prevalence in critical care units. Despite major advances in preventive strategies and support measures, the mortality rate among patients remains higher than 50%. Several pharmacological approaches to improve renal function and survival after an AKI episode have been largely unsuccessful in clinical practice. Summary: Stem cell-based therapy has provided new hopes of innovative interventions to enhance the limited capability of kidney regeneration in AKI. An important target for cell therapy is represented by tubular epithelial cells which after acute ischemic or toxic insults undergo dysfunction and detachment. Among adult stem cells, mesenchymal stromal/stem cells (MSC) are an attractive therapeutic tool by virtue of their unique biological properties, tropism for damaged tissues, and proregenerative capacity. In the present review, we discuss the mechanisms underlying the renoprotective effects of therapies with stem cells of different origins in preclinical models of AKI by evaluating new modalities by which MSC interact with damaged cells via the release of soluble factors and exosomes/microvesicles. Several biological effects, including antiapoptotic, promitogenic, immunomodulatory, and anti-inflammatory activities, have been analyzed in renal tissue of AKI animals receiving stem cell treatments. The mechanisms of stem cell homing and engraftment to sites of tissue damage have also been discussed. Key Messages: The translation of preclinical data on stem cells into effective and safe new modalities of care is still limited, and further studies are needed before their application in patients with AKI. © 2014 S. Karger AG, Basel.

Concepts: Renal failure, Cell division, Stem cell, Bone marrow, Stem cells, Cell biology, Cellular differentiation, Adult stem cell