Perivascular cells expressing annexin A5 define a novel mesenchymal stem cell-like population with the capacity to differentiate into multiple mesenchymal lineages

Signaling Pathways in Trans-differentiation of Mesenchymal Stem Cells: Recent Advances

Mesenchymal stem cells are a group of multipotent cells that can be induced to differentiate into other cell types. The cells fate is decided by various signaling pathways, growth factors, and transcription factors in differentiation. The proper coordination of these factors will result in cell specification. MSCs are capable of being differentiated into osteogenic, chondrogenic, and adipogenic lineages. Different conditions induces the MSCs into particular phenotypes. The MSC trans-differentiation ensues as a response to environmental factors or due to circumstances that prove to favor trans-differentiation. Depending on the stage at which they are expressed, and the genetic alterations they undergo prior to their expression, transcription factors can accelerate the process of trans-differentiation. Further research has been conducted on the challenging aspect of MSCs being developed into non-mesenchymal lineage. The cells that are differentiated in this way maintain their stability even after being induced in animals. The recent advancements in the trans-differentiation capacities of MSCs on induction with chemicals, growth inducers, improved differentiation mediums, growth factors from plant extracts, and electrical stimulation are discussed in this paper. Signaling pathways have a great effect on MSCs trans-differentiation and they need to be better understood for their applications in therapeutic techniques. So, this paper tends to review the major signaling pathways that play a vital role in the trans-differentiation of MSC.

The Role of Mesenchymal Stromal Cells in Tissue Repair and Fibrosis

Significance: The present review covers an overview of the current understanding of biology of mesenchymal stromal cells (MSCs) and suggests an important role of their differential potential for clinical approaches associated with tissue repair and fibrosis. Recent Advances: Genetic lineage tracing technology has enabled the delineation of cellular hierarchies and examination of MSC cellular origins and myofibroblast sources. This technique has led to the characterization of perivascular MSC populations and suggests that pericytes might provide a local source of tissue-specific MSCs, which can differentiate into tissue-specific cells for tissue repair and fibrosis. Autologous adipose tissue MSCs led to the advance in tissue engineering for regeneration of damaged tissues. Critical Issues: Recent investigation has revealed that perivascular MSCs might be the origin of myofibroblasts during fibrosis development, and perivascular MSCs might be the major source of myofibroblasts in fibrogenic disease. Adipose tissue MSCs combined with cytokines and biomaterials are available in the treatment of soft tissue defect and skin wound healing. Future Directions: Further investigation of the roles of perivascular MSCs may enable new approaches in the treatment of fibrogenic disease; moreover, perivascular MSCs might have potential as an antifibrotic target for fibrogenic disease. Autologous adipose tissue MSCs combined with cytokines and biomaterials will be an alternative method for the treatment of soft tissue defect and skin wound healing.

hiPSC-derived bone marrow milieu identifies a clinically actionable driver of niche-mediated treatment resistance in leukemia

Leukemia cells re-program their microenvironment to augment blast proliferation and enhance treatment resistance. Means of clinically targeting such niche-driven treatment resistance remain ambiguous. We develop human induced pluripotent stem cell (hiPSC)-engineered niches to reveal druggable cancer-niche dependencies. We reveal that mesenchymal (iMSC) and vascular niche-like (iANG) hiPSC-derived cells support ex vivo proliferation of patient-derived leukemia cells, affect dormancy, and mediate treatment resistance. iMSCs protect dormant and cycling blasts against dexamethasone, while iANGs protect only dormant blasts. Leukemia proliferation and protection from dexamethasone-induced apoptosis is dependent on cancer-niche interactions mediated by CDH2. Consequently, we test CDH2 antagonist ADH-1 (previously in Phase I/II trials for solid tumors) in a very aggressive patient-derived xenograft leukemia mouse model. ADH-1 shows high in vivo efficacy; ADH-1/dexamethasone combination is superior to dexamethasone alone, with no ADH-1-conferred additional toxicity. These findings provide a proof-of-concept starting point to develop improved, potentially safer therapeutics targeting niche-mediated cancer dependencies in blood cancers.

Annexin Animal Models-From Fundamental Principles to Translational Research

Routine manipulation of the mouse genome has become a landmark in biomedical research. Traits that are only associated with advanced developmental stages can now be investigated within a living organism, and the in vivo analysis of corresponding phenotypes and functions advances the translation into the clinical setting. The annexins, a family of closely related calcium (Ca²⁺)- and lipid-binding proteins, are found at various intra- and extracellular locations, and interact with a broad range of membrane lipids and proteins. Their impacts on cellular functions has been extensively assessed in vitro, yet annexin-deficient mouse models generally develop normally and do not display obvious phenotypes. Only in recent years, studies examining genetically modified annexin mouse models which were exposed to stress conditions mimicking human disease often revealed striking phenotypes. This review is the first comprehensive overview of annexin-related research using animal models and their exciting future use for relevant issues in biology and experimental medicine.

Calreticulin as a special marker to distinguish dental pulp stem cells from gingival mesenchymal stem cells

The construction of protein abundance profiles helps to interpret the clinical applications of stem cells. Dental pulp stem cells (DPSCs) and gingival mesenchymal stem cells (GMSCs) can be isolated from teeth and used as a highly convenient clinical potential material. Here, we aimed to explore commonalities and differences of DPSCs and GMSCs at the protein level. TMT-based quantitative proteomics and two-dimensional gel electrophoresis technology were used in combination to describe the protein profile of DPSCs and GMSCs extracted from the same donor. A total of 2821 proteins were identified by LC-MS/MS, of which 248 differentially abundant proteins (DAPs) were highly expressed in GMSCs while 782 proteins were highly expressed in DPSCs. The biological functions and molecular pathways of DAPs were annotated with GO enrichment and KEGG analysis. The relationship between molecular abundance and cell characteristics including source, proliferation, angiogenesis and inflammation were connected by WGCNA. Special markers, including Calreticulin (CALR), Annexin A5 (ANXA5) and Rho GDP dissociation inhibitor alpha (GDIR1), were proposed to distinguish DPSCs from GMSCs. Our results provide a molecular basis for in-depth understanding of the protein composition and special functions of dental stem cells, and promote the potential clinical application.

On the in vivo origin of human nasal mesenchymal stem cell cultures

OBJECTIVES

Mesenchymal stem cells (MSCs), classically expanded in culture from bone marrow, are of broad interest to the regenerative medicine community. Human nasal turbinate mesenchymal-like stem cell cultures have also been described, defined by an in vitro phenotype similar to bone marrow MSCs. Nonetheless, the identity in vivo of the cells that give rise to nasal MSC-like cultures remains unclear, and these cells are often suggested to be related to olfactory lineages. Here, we sought to define the in vivo phenotype of human nasal MSC-like cells.

METHODS

Human turbinate tissue samples were used for RNA and immunohistochemical analysis. We also analyzed a recently published single cell RNA-sequencing dataset from adult human olfactory and respiratory mucosa samples from our lab, to focus on cell populations expressing MSC markers. Immunochemistry was performed to stain turbinate sections and nasal MSC cultures for selected markers.

RESULTS

While there is no single MSC-specific gene, we identified a human nasal mucosal cell population in vivo that uniquely expressed transcripts characteristic of typical MSC cultures, including ENG (CD105), NES, and CD34, and lacked expression of other transcripts associated with surface epithelia. The expression of transcription factors such as SOX17, EBF1, and FOXP1 suggests cells in the MSC-like cluster maintain an ability to direct cell fate, consistent with the behavior of nasal MSC-like cells in vitro. SOX17 was found to be uniformly expressed by nasal MSC cultures, consistent with the in vivo data. Immunohistochemistry of human nasal tissue samples indicated that ENG, CD34, and SOX17 expression localized selectively to cells surrounding blood vessels in the lamina propria.

CONCLUSION

Our findings provide evidence that the in vivo origin of nasal MSC-like cultures is likely a vascular or pericyte population, rather than cells related to the olfactory neuronal lineage.

LEVEL OF EVIDENCE

NA.

Five Decades Later, Are Mesenchymal Stem Cells Still Relevant?

Mesenchymal stem cells are culture-derived mesodermal progenitors isolatable from all vascularized tissues. In spite of multiple fundamental, pre-clinical and clinical studies, the native identity and role in tissue repair of MSCs have long remained elusive, with MSC selection in vitro from total cell suspensions essentially unchanged as a mere primary culture for half a century. Recent investigations have helped understand the tissue origin of these progenitor cells, and uncover alternative effects of MSCs on tissue healing via growth factor secretion and interaction with the immune system. In this review, we describe current trends in MSC biology and discuss how these may improve the use of these therapeutic cells in tissue engineering and regenerative medicine.

Molecular Programming of Perivascular Stem Cell Precursors

Pericytes have been shown to act as precursors of resident adult stem cells in stromal tissues in vivo. When expanded in vitro these cells are capable of giving rise to multiple mesenchymal cell types, irrespective of their tissue of origin. This phenomenon of multi-lineage differentiation is only observed in culture, whereas in vivo, stromal stem cell differentiation is restricted to tissue-specific cell types. An important unanswered question is how a single, widely distributed cell type (a pericyte) gives rise to stem cells with tissue-specific functions and attributes. Using a combination of transcriptomics and epigenomics we have compared the molecular status of two populations of stromal stem cell precursors. Using a LacZ transgene insertion that is expressed in pericytes but not in stem cells, we were able to compare pericyte populations from two different tissues, mouse incisors and bone marrow. Pericytes, freshly isolated from mouse incisors and bone marrow, exhibited transcriptomes and epigenetic landscapes that were extensively different, reflecting their tissue of origin and future in vivo differentiation potential. Dspp, an odontoblast differentiation gene, as well as additional odontogenic genes, are shown to be expressed in dental pulp-derived pericytes. These genetic loci are also decorated with histone modifications indicative of a transcriptionally active chromatin state. In bone marrow pericytes, a major osteogenic differentiation gene, Runx2, is not expressed but is marked by both active and repressive histones and therefore primed to be expressed. Polycomb repressor complex 1 analysis showed that key genes involved in the induction of adipogenesis, chondrogenesis, and myogenesis are targeted by Ring1b and therefore stably repressed. This indicates that pericyte populations are molecularly obstructed from differentiating down certain lineages in vivo. Stem Cells 2018;36:1890-15.

The material and biological characteristics of osteoinductive calcium phosphate ceramics

The discovery of osteoinductivity of calcium phosphate (Ca-P) ceramics has set an enduring paradigm of conferring biological regenerative activity to materials with carefully designed structural characteristics. The unique phase composition and porous structural features of osteoinductive Ca-P ceramics allow it to interact with signaling molecules and extracellular matrices in the host system, creating a local environment conducive to new bone formation. Mounting evidence now indicate that the osteoinductive activity of Ca-P ceramics is linked to their physicochemical and three-dimensional structural properties. Inspired by this conceptual breakthrough, many laboratories have shown that other materials can be also enticed to join the rank of tissue-inducing biomaterials, and besides the bones, other tissues such as cartilage, nerves and blood vessels were also regenerated with the assistance of biomaterials. Here, we give a brief historical recount about the discovery of the osteoinductivity of Ca-P ceramics, summarize the underlying material factors and biological characteristics, and discuss the mechanism of osteoinduction concerning protein adsorption, and the interaction with different types of cells, and the involvement of the vascular and immune systems.

The NG2 Proteoglycan in Pericyte Biology

Studies of pericytes have been retarded by the lack of appropriate markers for identification of these perivascular mural cells. Use of antibodies against the NG2 proteoglycan as a pericyte marker has greatly facilitated recent studies of pericytes, emphasizing the intimate spatial relationship between pericytes and endothelial cells, allowing more accurate quantification of pericyte/endothelial cell ratios in different vascular beds, and revealing the participation of pericytes throughout all stages of blood vessel formation. The functional importance of NG2 in pericyte biology has been established via NG2 knockdown (in vitro) and knockout (in vivo) strategies that reveal significant deficits in blood vessel formation when NG2 is absent from pericytes. NG2 influences pericyte proliferation and motility by acting as an auxiliary receptor that enhances signaling through integrins and receptor tyrosine kinase growth factor receptors. By acting in a trans orientation, NG2 also activates integrin signaling in closely apposed endothelial cells, leading to enhanced maturation and formation of endothelial cell junctions. NG2 null mice exhibit reduced growth of both mammary and brain tumors that can be traced to deficits in tumor vascularization. Use of Cre-Lox technology to produce pericyte-specific NG2 null mice has revealed specific deficits in tumor vessels that include decreased pericyte ensheathment of endothelial cells, diminished assembly of the vascular basement membrane, reduced vessel patency, and increased vessel leakiness. Interestingly, myeloid-specific NG2 null mice exhibit even larger deficits in tumor vascularization, leading to correspondingly slower tumor growth. Myeloid-specific NG2 null mice are deficient in their ability to recruit macrophages to tumors and other sites of inflammation. This absence of macrophages deprives pericytes of a signal that is crucial for their ability to interact with endothelial cells. The interplay between pericytes, endothelial cells, and macrophages promises to be an extremely fertile area of future study.

Annexins - insights from knockout mice

Annexins are a highly conserved protein family that bind to phospholipids in a calcium (Ca2+) - dependent manner. Studies with purified annexins, as well as overexpression and knockdown approaches identified multiple functions predominantly linked to their dynamic and reversible membrane binding behavior. However, most annexins are found at multiple locations and interact with numerous proteins. Furthermore, similar membrane binding characteristics, overlapping localizations and shared interaction partners have complicated identification of their precise functions. To gain insight into annexin function in vivo, mouse models deficient of annexin A1 (AnxA1), A2, A4, A5, A6 and A7 have been generated. Interestingly, with the exception of one study, all mice strains lacking one or even two annexins are viable and develop normally. This suggested redundancy within annexins, but examining these knockout (KO) strains under stress conditions revealed striking phenotypes, identifying underlying mechanisms specific for individual annexins, often supporting Ca2+ homeostasis and membrane transport as central for annexin biology. Conversely, mice lacking AnxA1 or A2 show extracellular functions relevant in health and disease that appear independent of membrane trafficking or Ca2+ signaling. This review will summarize the mechanistic insights gained from studies utilizing mouse models lacking members of the annexin family.

Mimicking Angiogenesis in vitro: Three-dimensional Co-culture of Vascular Endothelial Cells and Perivascular Cells in Collagen Type I Gels

Angiogenesis defines the process of formation of new vascular structures form existing blood vessels, involved during development, repair processes like wound healing but also linked to pathological changes. During angiogenic processes, endothelial cells build a vascular network and recruit perivascular cells to form mature, stable vessels. Endothelial cells and perivascular cells secret and assemble a vascular basement membrane and interact via close cell-cell contacts. To mimic these processes in vitro we have developed a versatile three-dimensional culture system where perivascular cells (PVC) are co-cultured with human umbilical cord vascular endothelial cells (HUVEC) in a collagen type I gel. This co-culture system can be used to determine biochemical and cellular processes during neoangiogenic events with a wide range of analyses options.

Structural decoding of netrin-4 reveals a regulatory function towards mature basement membranes

Netrins, a family of laminin-related molecules, have been proposed to act as guidance cues either during nervous system development or the establishment of the vascular system. This was clearly demonstrated for netrin-1 via its interaction with the receptors DCC and UNC5s. However, mainly based on shared homologies with netrin-1, netrin-4 was also proposed to play a role in neuronal outgrowth and developmental/pathological angiogenesis via interactions with netrin-1 receptors. Here, we present the high-resolution structure of netrin-4, which shows unique features in comparison with netrin-1, and show that it does not bind directly to any of the known netrin-1 receptors. We show that netrin-4 disrupts laminin networks and basement membranes (BMs) through high-affinity binding to the laminin γ1 chain. We hypothesize that this laminin-related function is essential for the previously described effects on axon growth promotion and angiogenesis. Our study unveils netrin-4 as a non-enzymatic extracellular matrix protein actively disrupting pre-existing BMs.

Netrins are secreted guidance factors that promote axon outgrowth and orientation during nervous system development. Here the authors present structural and biological evidence that netrin-4 is not a guidance cue per se, but rather functions to modulate laminin-laminin interactions.

The gene expression profile of non-cultured, highly purified human adipose tissue pericytes: Transcriptomic evidence that pericytes are stem cells in human adipose tissue

Pericytes (PCs) are a subset of perivascular cells that can give rise to mesenchymal stromal cells (MSCs) when culture-expanded, and are postulated to give rise to MSC-like cells during tissue repair in vivo. PCs have been suggested to behave as stem cells (SCs) in situ in animal models, although evidence for this role in humans is lacking. Here, we analyzed the transcriptomes of highly purified, non-cultured adipose tissue (AT)-derived PCs (ATPCs) to detect gene expression changes that occur as they acquire MSC characteristics in vitro, and evaluated the hypothesis that human ATPCs exhibit a gene expression profile compatible with an AT SC phenotype. The results showed ATPCs are non-proliferative and express genes characteristic not only of PCs, but also of AT stem/progenitor cells. Additional analyses defined a gene expression signature for ATPCs, and revealed putative novel ATPC markers. Almost all AT stem/progenitor cell genes differentially expressed by ATPCs were not expressed by ATMSCs or culture-expanded ATPCs. Genes expressed by ATMSCs but not by ATPCs were also identified. These findings strengthen the hypothesis that PCs are SCs in vascularized tissues, highlight gene expression changes they undergo as they assume an MSC phenotype, and provide new insights into PC biology.

Detection of multiple annexin autoantibodies in a patient with recurrent miscarriages, fulminant stroke and seronegative antiphospholipid syndrome

Anti-phospholipid syndrome (APS) is one of the main causes for recurrent miscarriages. The diagnosis of APS is based on the occurrence of clinical symptoms such as thrombotic events or obstetric complications as well as the detection of antiphospholipid antibodies directed against β2-glycoprotein I and cardiolipin, or a positive lupus anticoagulant assay. However, there is a subpopulation of patients with clinical symptoms of APS, but the lack of serological markers (seronegative APS). In addition, a large proportion of patients with unexplained recurrent miscarriages exist. These cases may be attributed, at least in part, to a seronegative APS.
The presence of autoantibodies against annexins is potentially associated with APS. Here we used immunoassays and immunoblots to detect autoantibodies directed against annexin A1-5, and A8, respectively, in a patient with a seronegative APS and a history of six recurrent pregnancy losses and fulminant stroke. We found strong IgM isotype antibody reactivity directed against annexin A2 and annexin A8, and moderate to weak IgM isotype antibody reactivity directed against annexin A1, A3, and A5. Further studies will evaluate the diagnostic value of IgM isotype antibodies against annexin A1-A5, and A8 for seronegative APS and recurrent miscarriages.

Mesenchymal Stem and Progenitor Cells in Normal and Dysplastic Hematopoiesis-Masters of Survival and Clonality?

Myelodysplastic syndromes (MDS) are malignant hematopoietic stem cell disorders that have the capacity to progress to acute myeloid leukemia (AML). Accumulating evidence suggests that the altered bone marrow (BM) microenvironment in general, and in particular the components of the stem cell niche, including mesenchymal stem cells (MSCs) and their progeny, play a pivotal role in the evolution and propagation of MDS. We here present an overview of the role of MSCs in the pathogenesis of MDS, with emphasis on cellular interactions in the BM microenvironment and related stem cell niche concepts. MSCs have potent immunomodulatory capacities and communicate with diverse immune cells, but also interact with various other cellular components of the microenvironment as well as with normal and leukemic stem and progenitor cells. Moreover, compared to normal MSCs, MSCs in MDS and AML often exhibit altered gene expression profiles, an aberrant phenotype, and abnormal functional properties. These alterations supposedly contribute to the “reprogramming” of the stem cell niche into a disease-permissive microenvironment where an altered immune system, abnormal stem cell niche interactions, and an impaired growth control lead to disease progression. The current article also reviews molecular targets that play a role in such cellular interactions and possibilities to interfere with abnormal stem cell niche interactions by using specific targeted drugs.

Angiogenic and anti-inflammatory properties of mesenchymal stem cells from cord blood: soluble factors and extracellular vesicles for cell regeneration

In a recent work, our group showed the existence of two distinct mesenchymal stem cell (MSC) subsets within human umbilical cord blood. One less proliferative and short-living (SL-CBMSC), the other with higher growth rate and long-living (LL-CBMSC), and therefore better suited for regenerative medicine applications. We examined whether LL-CBMSC possess peculiar paracrine properties able to affect angiogenesis or inflammatory processes. It was shown for the first time that pro-angiogenic, proliferation-stimulating and tissue repairing factors were released at high level not only as soluble cytokines, but also as mRNA precursors embedded in membrane vesicles. The combination of this primary (proteic factors interacting with surface receptors) and delayed (mRNA transferred and translated via vesicle fusion and cargo release) interaction in endothelial target cells resulted in strong blood vessel induction with the development of capillary-like structures. In addition, LL-CBMSC dynamically modulated their release of pro-angiogenic and anti-inflammatory factors in an in vitro model of damage. In conclusion, LL-CBMSC synthesize and secrete multiple factors that may be attuned in response to the status of the target cell, a crucial requisite when paracrine mechanisms are needed at onset of tissue regeneration.

The Nervous System Orchestrates and Integrates Craniofacial Development: A Review

Development of a head is a dazzlingly complex process: a number of distinct cellular sources including cranial ecto- and endoderm, mesoderm and neural crest contribute to facial and other structures. In the head, an extremely fine-tuned developmental coordination of CNS, peripheral neural components, sensory organs and a musculo-skeletal apparatus occurs, which provides protection and functional integration. The face can to a large extent be considered as an assembly of sensory systems encased and functionally fused with appendages represented by jaws. Here we review how the developing brain, neurogenic placodes and peripheral nerves influence the morphogenesis of surrounding tissues as a part of various general integrative processes in the head. The mechanisms of this impact, as we understand it now, span from the targeted release of the morphogens necessary for shaping to providing a niche for cellular sources required in later development. In this review we also discuss the most recent findings and ideas related to how peripheral nerves and nerve-associated cells contribute to craniofacial development, including teeth, during the post- neural crest period and potentially in regeneration.

Induction of initial steps of angiogenic differentiation and maturation of endothelial cells by pericytes in vitro and the role of collagen IV

Activation of endothelial cells and recruitment of mural cells define critical steps during the formation of stable vascular elements. Both events are reflected by cocultures of endothelial cells and isolated murine pericyte-like cells and define a versatile platform for the analysis of distinct steps during the angiogenic process in vitro. Isolated pericyte-like cells promote the survival of endothelial cells, induce the assembly of endothelial cells as well as establish direct contacts with forming endothelial alignments. More importantly, they also induce characteristic steps of maturation including the assembly of stable cell-cell junctions, deposition of basement membrane-like matrices and local formation of a central lumen. The presence of pericyte-like cells induces the secretion of extracellular matrices enriched in collagen IV by endothelial cells, which improves endothelial tube formation and provides the adhesive substrate for mural cell recruitment. Collagen-binding integrins contribute differentially to the process, with α1β1 involved in the adhesion of pericyte-like cells to collagen IV and α2β1 mainly involved in endothelial cord formation. These data indicate that pericyte-like cells are essential for the survival of endothelial cells, the efficient formation of endothelial alignments as well as initial steps of maturation of capillary-like structures.

The Angiopoietin-1 Variant COMP-Ang1 Enhances BMP2-Induced Bone Regeneration with Recruiting Pericytes in Critical Sized Calvarial Defects

Craniofacial bone defects are observed in a variety of clinical situations, and their reconstructions require coordinated coupling between angiogenesis and osteogenesis. In this study, we explored the effects of cartilage oligomeric matrix protein-angiopoietin 1 (COMP-Ang1), a synthetic and soluble variant of angiopoietin 1, on bone morphogenetic protein 2 (BMP2)-induced cranial bone regeneration, and recruitment and osteogenic differentiation of perivascular pericytes. A critical-size calvarial defect was created in the C57BL/6 mouse and COMP-Ang1 and/or BMP2 proteins were delivered into the defects with absorbable collagen sponges. After 3 weeks, bone regeneration was evaluated using micro-computed tomography and histologic examination. Pericyte recruitment into the defects was examined using immunofluorescence staining with anti-NG2 and anti-CD31 antibodies. In vitro recruitment and osteoblastic differentiation of pericyte cells were assessed with Boyden chamber assay, staining of calcified nodules, RT-PCR and Western blot analyses. Combined administration of COMP-Ang1 and BMP2 synergistically enhanced bone repair along with the increased population of CD31 (an endothelial cell marker) and NG2 (a specific marker of pericyte) positive cells. In vitro cultures of pericytes consistently showed that pericyte infiltration into the membrane pore of Boyden chamber was more enhanced by the combination treatment. In addition, the combination further increased the osteoblast-specific gene expression, including bone sialoprotein (BSP), osteocalcin (OCN) and osterix (OSX), phosphorylation of Smad/1/5/8, and mineralized nodule formation. COMP-Ang1 can enhance BMP2-induced cranial bone regeneration with increased pericyte recruitment. Combined delivery of the proteins might be a therapeutic strategy to repair cranial bone damage.

Development of mRuby2-Transfected C3H10T1/2 Fibroblasts for Musculoskeletal Tissue Engineering

Mouse C3H10T1/2 fibroblasts are multipotent, mesenchymal stem cell (MSC)-like progenitor cells that are widely used in musculoskeletal research. In this study, we have established a clonal population of C3H10T1/2 cells stably-transfected with mRuby2, an orange-red fluorescence reporter gene. Flow cytometry analysis and fluorescence imaging confirmed successful transfection of these cells. Cell counting studies showed that untransfected C3H10T1/2 cells and mRuby2-transfected C3H10T1/2 cells proliferated at similar rates. Adipogenic differentiation experiments demonstrated that untransfected C3H10T1/2 cells and mRuby2-transfected C3H10T1/2 cells stained positive for Oil Red O and showed increased expression of adipogenic genes including adiponectin and lipoprotein lipase. Chondrogenic differentiation experiments demonstrated that untransfected C3H10T1/2 cells and mRuby2-transfected C3H10T1/2 cells stained positive for Alcian Blue and showed increased expression of chondrogenic genes including aggrecan. Osteogenic differentiation experiments demonstrated that untransfected C3H10T1/2 cells and mRuby2-transfected C3H10T1/2 cells stained positive for alkaline phosphatase (ALP) as well as Alizarin Red and showed increased expression of osteogenic genes including alp, ocn and osf-1. When seeded on calcium phosphate-based ceramic scaffolds, mRuby2-transfected C3H10T1/2 cells maintained even fluorescence labeling and osteogenic differentiation. In summary, mRuby2-transfected C3H10T1/2 cells exhibit mRuby2 fluorescence and showed little-to-no difference in terms of cell proliferation and differentiation as untransfected C3H10T1/2 cells. These cells will be available from American Type Culture Collection (ATCC; CRL-3268™) and may be a valuable tool for preclinical studies.

Lung mesenchymal stromal cells in development and disease: to serve and protect?

SIGNIFICANCE

Bronchopulmonary dysplasia (BPD) is a disease of the developing lung that afflicts extreme preterm infants in the neonatal intensive care unit. Follow-up studies into adulthood show that BPD is not merely a problem of the neonatal period, as it also may predispose to early-onset emphysema and poor lung function in later life.

RECENT ADVANCES

The increasing promise of bone marrow- or umbilical cord-derived mesenchymal stromal cells (MSCs) to repair neonatal and adult lung diseases may for the first time offer the chance to make substantial strides in improving the outcome of extreme premature infants at risk of developing BPD. As more knowledge has been obtained on MSCs over the past decades, it has become clear that each organ has its own reservoir of endogenous MSCs, including the lung.

CRITICAL ISSUES

We have only barely scratched the surface on what resident lung MSCs exactly are and what their role and function in lung development may be. Moreover, what happens to these putative repair cells in BPD when alveolar development goes awry and why do their counterparts from the bone marrow and umbilical cord succeed in restoring normal alveolar development when they themselves do not?

FUTURE DIRECTIONS

Much work remains to be carried out to validate lung MSCs, but with the high potential of MSC-based treatment for BPD and other lung diseases, a thorough understanding of the endogenous lung MSC will be pivotal to get to the bottom of these diseases.

Mesenchymal stem cells as cellular vectors for pediatric neurological disorders

Lysosomal storage diseases are a heterogeneous group of hereditary disorders characterized by a deficiency in lysosomal function. Although these disorders differ in their etiology and phenotype those that affect the nervous system generally manifest as a profound deterioration in neurologic function with age. Over the past several decades implementation of various treatment regimens including bone marrow and cord blood cell transplantation, enzyme replacement, and substrate reduction therapy have proved effective for managing some clinical manifestations of these diseases but their ability to ameliorate neurologic complications remains unclear. Consequently, there exists a need to develop alternative therapies that more effectively target the central nervous system. Recently, direct intracranial transplantation of tissue-specific stem and progenitor cells has been explored as a means to reconstitute metabolic deficiencies in the CNS. In this chapter we discuss the merits of bone marrow-derived mesenchymal stem cells (MSCs) for this purpose. Originally identified as progenitors of connective tissue cell lineages, recent findings have revealed several novel aspects of MSC biology that make them attractive as therapeutic agents in the CNS. We relate these advances in MSC biology to their utility as cellular vectors for treating neurologic sequelae associated with pediatric neurologic disorders.

Brain mesenchymal stem cells: The other stem cells of the brain?

Multipotent mesenchymal stromal cells (MSC), have the potential to differentiate into cells of the mesenchymal lineage and have non-progenitor functions including immunomodulation. The demonstration that MSCs are perivascular cells found in almost all adult tissues raises fascinating perspectives on their role in tissue maintenance and repair. However, some controversies about the physiological role of the perivascular MSCs residing outside the bone marrow and on their therapeutic potential in regenerative medicine exist. In brain, perivascular MSCs like pericytes and adventitial cells, could constitute another stem cell population distinct to the neural stem cell pool. The demonstration of the neuronal potential of MSCs requires stringent criteria including morphological changes, the demonstration of neural biomarkers expression, electrophysiological recordings, and the absence of cell fusion. The recent finding that brain cancer stem cells can transdifferentiate into pericytes is another facet of the plasticity of these cells. It suggests that the perversion of the stem cell potential of pericytes might play an even unsuspected role in cancer formation and tumor progression.

Natural history of mesenchymal stem cells, from vessel walls to culture vessels

Mesenchymal stem/stromal cells (MSCs) can regenerate tissues by direct differentiation or indirectly by stimulating angiogenesis, limiting inflammation, and recruiting tissue-specific progenitor cells. MSCs emerge and multiply in long-term cultures of total cells from the bone marrow or multiple other organs. Such a derivation in vitro is simple and convenient, hence popular, but has long precluded understanding of the native identity, tissue distribution, frequency, and natural role of MSCs, which have been defined and validated exclusively in terms of surface marker expression and developmental potential in culture into bone, cartilage, and fat. Such simple, widely accepted criteria uniformly typify MSCs, even though some differences in potential exist, depending on tissue sources. Combined immunohistochemistry, flow cytometry, and cell culture have allowed tracking the artifactual cultured mesenchymal stem/stromal cells back to perivascular anatomical regions. Presently, both pericytes enveloping microvessels and adventitial cells surrounding larger arteries and veins have been described as possible MSC forerunners. While such a vascular association would explain why MSCs have been isolated from virtually all tissues tested, the origin of the MSCs grown from umbilical cord blood remains unknown. In fact, most aspects of the biology of perivascular MSCs are still obscure, from the emergence of these cells in the embryo to the molecular control of their activity in adult tissues. Such dark areas have not compromised intents to use these cells in clinical settings though, in which purified perivascular cells already exhibit decisive advantages over conventional MSCs, including purity, thorough characterization and, principally, total independence from in vitro culture. A growing body of experimental data is currently paving the way to the medical usage of autologous sorted perivascular cells for indications in which MSCs have been previously contemplated or actually used, such as bone regeneration and cardiovascular tissue repair.

Pericytes and adaptive angioplasticity: the role of tumor necrosis factor-like weak inducer of apoptosis (TWEAK)

The TNF superfamily member TWEAK has emerged as a pleiotropic cytokine that regulates many cellular functions that include immune/inflammatory activity, angiogenesis, cell proliferation, and fate. TWEAK through its inducible receptor, FGF-inducible molecule 14 (Fn14), can induce both beneficial and deleterious activity that has a profound effect on cell survival. Thus it is highly likely that TWEAK and Fn14 expressed by cells of the neurovascular unit help regulate and maintain vascular and tissue homeostasis. In this chapter we discuss the expression of TWEAK and Fn14 signaling in the cerebral microvascular pericyte. Pericytes are a highly enigmatic population of microvascular cells that are important in regulatory pathways that modulate physiological angiogenesis in response to chronic mild hypoxic stress. A brief introduction will identify the microvascular pericyte. A more detailed discussion of pericyte TWEAK signaling during adaptive angioplasticity will follow.

Annexin A5 as a potential marker in tumors

Annexin A5 (Anxa5) promotes pancreatic adenocarcinoma, sarcoma, tumorigenesis and progression of breast cancer and prostate cancer stem cells. It is involved with metastasis, invasion and development of squamous cell carcinoma, and facilitates nodal progression of bladder cancer and angiogenesis and progression of glioma. Anxa5 de-regulation is associated with drug resistance in nasopharyngeal carcinoma and gastric cancer. Although Anxa5 protein up-regulation promotes cervical cancer progression, it is markedly suppressed in cervical carcinoma cells. Anxa5 is negatively correlated with thyroid cancer malignancy. In this review, we explore the mechanisms of Anxa5 action in tumors. Anxa5 could be a predictive biomarker for tumor development, metastasis and invasion, and be of diagnostic, prognostic and therapeutic significance in cancer.

The secretome of mesenchymal stem cells: potential implications for neuroregeneration

Mesenchymal stem cells have shown regenerative properties in many tissues. This feature had originally been ascribed to their multipotency and thus their ability to differentiate into tissue-specific cells. However, many researchers consider the secretome of mesenchymal stem cells the most important player in the observed reparative effects of these cells. In this review, we specifically focus on the potential neuroregenerative effect of mesenchymal stem cells, summarize several possible mechanisms of neuroregeneration and list key factors mediating this effect. We illustrate examples of mesenchymal stem cell treatment in central nervous system disorders including stroke, neurodegenerative disorders (such as Parkinson's disease, Huntington's disease, multiple system atrophy and cerebellar ataxia) and inflammatory disease (such as multiple sclerosis). We specifically highlight studies where mesenchymal stem cells have entered clinical trials.

Bidirectional myoblast-pericyte plasticity

Microvascular pericytes are able to generate multiple mesenchymal cell types, including skeletal muscle myoblasts. Cappellari et al. (2013) report in this issue of Developmental Cell that myoblasts can return the favor by generating pericytes via the action of Dll4 Notch ligand and PDGF-BB.

Expression profile of microRNAs regulating proliferation and differentiation in mouse adult cardiac stem cells

The identification of cardiac cells with stem cell properties changed the paradigm of the heart as a post mitotic organ. These cells proliferate and differentiate into cardiomyocytes, endothelial and vascular smooth muscle cells, providing for cardiac cell homeostasis and regeneration. microRNAs are master switches controlling proliferation and differentiation, in particular regulating stem cell biology and cardiac development. Modulation of microRNAs -regulated gene expression networks holds the potential to control cell fate and proliferation, with predictable biotechnologic and therapeutic applications. To obtain insights into the regulatory networks active in cardiac stem cells, we characterized the expression profile of 95 microRNAs with reported functions in stem cell and tissue differentiation in mouse cardiac stem cells, and compared it to that of mouse embryonic heart and mesenchymal stem cells. The most highly expressed microRNAs identified in cardiac stem cells are known to target key genes involved in the control of cell proliferation and adhesion, vascular function and cardiomyocyte differentiation. We report a subset of differentially expressed microRNAs that are proposed to act as regulators of differentiation and proliferation of adult cardiac stem cells, providing novel insights into active gene expression networks regulating their biological properties.

Immunological characterization of multipotent mesenchymal stromal cells--The International Society for Cellular Therapy (ISCT) working proposal

Cultured mesenchymal stromal cells (MSCs) possess immune regulatory properties and are already used for clinical purposes, although preclinical data (both in vitro and in vivo in animal models) are not always homogeneous and unequivocal. However, the various MSC-based clinical approaches to treat immunological diseases would be significantly validated and strengthened by using standardized immune assays aimed at obtaining shared, reproducible and consistent data. Thus, the MSC Committee of the International Society for Cellular Therapy has decided to put forward for general discussion a working proposal for a standardized approach based on a critical view of literature data.

Cell-based therapies for ocular inflammation

Since the plasticity and the potential for re-programming cells has become widely accepted, there has been great interest in cell-based therapies. These are being applied to a range of diseases, not least ocular diseases, where it is assumed that there is a reduced risk of immune rejection although this may be more perceived than real. There are two broad classes of cell-based therapies: those aimed at restoring structure and function of specific tissues and cells; and those directed towards restoring immunological homeostasis by controlling the damaging effects of inflammatory disease. Stem cells of all types represent the first group and prototypically have been used with the aim of regenerating failing cells. In contrast, immune cells have been suggested as potential modulators of inflammation. However, there is functional overlap in these two applications, with some types of stem cells, such as mesenchymal stem cells, demonstrating a potent immunomodulatory effect. This review summarises recent information on cell based therapies for ocular disease, with special emphasis on ocular inflammatory disease, and explores current uses, potential and limitations.

Therapeutic potential of perivascular cells from human pluripotent stem cells

Vascularization of injured tissues or artificial grafts is a major challenge in tissue engineering, stimulating a continued search for alternative sources for vasculogenic cells and the development of therapeutic strategies. Human pluripotent stem cells (hPSCs), either embryonic or induced, offer a plentiful platform for the derivation of large numbers of vasculogenic cells, as required for clinical transplantations. Various protocols for generation of vasculogenic smooth muscle cells (SMCs) from hPSCs have been described with considerably different SMC derivatives. In addition, we recently identified hPSC-derived pericytes, which are similar to their physiological counterparts, exhibiting unique features of blood vessel-residing perivascular cells, as well as multipotent mesenchymal precursors with therapeutic angiogenic potential. In this review we refer to methodologies for the development of a variety of perivascular cells from hPSCs with respect to developmental induction, differentiation capabilities, potency and their dual function as mesenchymal precursors. The therapeutic effect of hPSC-derived perivascular cells in experimental models of tissue engineering and regenerative medicine are described and compared to those of their native physiological counterparts.

PECAM1(+)/Sca1(+)/CD38(+) vascular cells transform into myofibroblast-like cells in skin wound repair

Skin injury induces the formation of new blood vessels by activating the vasculature in order to restore tissue homeostasis. Vascular cells may also differentiate into matrix-secreting contractile myofibroblasts to promote wound closure. Here, we characterize a PECAM1⁺/Sca1⁺ vascular cell population in mouse skin, which is highly enriched in wounds at the peak of neoangiogenesis and myofibroblast formation. These cells express endothelial and perivascular markers and present the receptor CD38 on their surface. PECAM1⁺/Sca1⁺/CD38⁺ cells proliferate upon wounding and could give rise to α-SMA⁺ myofibroblast-like cells. CD38 stimulation in immunodeficient mice reduced the wound size at the peak of neoangiogenesis and myofibroblast formation. In humans a corresponding cell population was identified, which was enriched in sprouting vessels of basal cell carcinoma biopsies. The results indicate that PECAM1⁺/Sca1⁺/CD38⁺ vascular cells could proliferate and differentiate into myofibroblast-like cells in wound repair. Moreover, CD38 signaling modulates PECAM1⁺/Sca1⁺/CD38⁺ cell activation in the healing process implying CD38 as a target for anti-angiogenic therapies in human basal cell carcinoma.

Adventitial pericyte progenitor/mesenchymal stem cells participate in the restenotic response to arterial injury

Restenosis is a major complication of coronary angioplasty, at least partly due to the fact that the origin and identity of contributing cell types are not well understood. In this study, we have investigated whether pericyte-like cells or mesenchymal stem cells (MSCs) from the adventitia contribute to restenosis. We demonstrate that while cells expressing the pericyte markers NG2, platelet-derived growth factor receptor β, and CD146 are rare in the adventitia of uninjured mouse femoral arteries, following injury their numbers strongly increase. Some of these adventitial pericyte-like cells acquire a more MSC-like phenotype (CD90+ and CD29+ are up-regulated) and also appear in the restenotic neointima. Via bone marrow transplantation and ex vivo artery culture approaches, we demonstrate that the pericyte-like MSCs of the injured femoral artery are not derived from the bone marrow, but originate in the adventitia itself mainly via the proliferation of resident pericyte-like cells. In summary, we have identified a population of resident adventitial pericyte-like cells or MSCs that contribute to restenosis following arterial injury. These cells are different from myofibroblasts, smooth muscle cells, and other progenitor populations that have been shown to participate in the restenotic process.

Perivascular mesenchymal stem cells in the adult human brain: a future target for neuroregeneration?

Perivascular adult stem cells have been isolated from several tissues, including the adult human brain. They have unique signatures resembling both pericytes and mesenchymal stem cells. Understanding the nature of these cells in their specific vascular niches is important to determine their clinical potential as a new adult stem cell source. Indeed, they have promising features in vitro in terms of multipotency, immunomodulation and secretion of growth factors and cytokines. However, their in vivo function is less known as yet. Recent emerging data show a crucial role of perivascular mesenchymal stem cells in tissue homeostasis and repair. Furthermore, these cells may play an important role in adult stem cell niche regulation and in neurodegeneration. Here we review the recent literature on perivascular mesenchymal stem cells, discuss their different in vitro functions and highlight especially the specific properties of brain-derived perivascular mesenchymal stem cells. We summarize current evidence that suggests an important in vivo function of these cells in terms of their regenerative potential that may indicate a new target cell for endogenous tissue regeneration and repair.

Loss of maternal annexin A5 increases the likelihood of placental platelet thrombosis and foetal loss

Antiphospholipid syndrome is associated with an increased risk of thrombosis and pregnancy loss. Annexin A5 (Anxa5) is a candidate autoantigen. It is not known, however, whether endogenous Anxa5 prevents foetal loss during normal pregnancy. We found significant reductions in litter size and foetal weight in Anxa5-null mice (Anxa5-KO). These changes occurred even when only the mother was Anxa5-KO. A small amount of placental fibrin deposition was observed in the decidual tissues, but did not noticeably differ between wild-type and Anxa5-KO mice. However, immunoreactivity for integrin beta 3/CD61, a platelet marker, was demonstrated within thrombi in the arterial canals only in Anxa5-KO mothers. Subcutaneous administration of the anticoagulant heparin to pregnant Anxa5-KO mice significantly reduced pregnancy loss, suggesting that maternal Anxa5 is crucial for maintaining intact placental circulation. Hence, the presence of maternal Anxa5 minimises the risk of thrombosis in the placental circulation and reduces the risk of foetal loss.

Depletion of annexin A5, annexin A6, and collagen X causes no gross changes in matrix vesicle-mediated mineralization, but lack of collagen X affects hematopoiesis and the Th1/Th2 response

Numerous biochemical studies have pointed to an essential role of annexin A5 (AnxA5), annexin A6 (AnxA6), and collagen X in matrix vesicle-mediated biomineralization during endochondral ossification and in osteoarthritis. By binding to the extracellular matrix protein collagen X and matrix vesicles, annexins were proposed to anchor matrix vesicles in the extracellular space of hypertrophic chondrocytes to initiate the calcification of cartilage. However, mineralization appears to be normal in mice lacking AnxA5 and AnxA6, whereas collagen X-deficient mice show only subtle alterations in the growth plate organization. We hypothesized that the simultaneous lack of AnxA5, AnxA6, and collagen X in vivo induces more pronounced changes in the growth plate development and the initiation of mineralization. In this study, we generated and analyzed mice deficient for AnxA5, AnxA6, and collagen X. Surprisingly, mice were viable, fertile, and showed no obvious abnormalities. Assessment of growth plate development indicated that the hypertrophic zone was expanded in Col10a1(-/-) and AnxA5(-/-) AnxA6(-/-) Col10a1(-/-) newborns, whereas endochondral ossification and mineralization were not affected in 13-day- and 1-month-old mutants. In peripheral quantitative computed tomography, no changes in the degree of biomineralization were found in femora of 1-month- and 1-year-old mutants even though the diaphyseal circumference was reduced in Col10a1(-/-) and AnxA5(-/-) AnxA6(-/-) Col10a1(-/-) mice. The percentage of naive immature IgM(+) /IgM(+) B cells and peripheral T-helper cells were increased in Col10a1(-/-) and AnxA5(-/-) AnxA6(-/-) Col10a1(-/-) mutants, and activated splenic T cells isolated from Col10a1(-/-) mice secreted elevated levels of IL-4 and GM-CSF. Hence, collagen X is needed for hematopoiesis during endochondral ossification and for the immune response, but the interaction of annexin A5, annexin A6, and collagen X is not essential for physiological calcification of growth plate cartilage. Therefore, annexins and collagen X may rather fulfill functions in growth plate cartilage not directly linked to the mineralization process.

Endothelial-mesenchymal transition and its contribution to the emergence of stem cell phenotype

Vascular endothelial cells can demonstrate considerable plasticity to generate other cell types during embryonic development and disease progression. This process occurs through a cell differentiation mechanism known as endothelial-mesenchymal transition (EndMT). The generation of mesenchymal cells from endothelium is a crucial step in endothelial cell differentiation to several lineages including fibroblasts, myofibroblasts, mural cells, osteoblasts, chondrocytes, and adipocytes. Such differentiation patterns have been observed in systems of cardiac development, fibrosis, diabetic nephropathy, heterotopic ossification and cancer. Here we describe the EndMT program and discuss the current evidence of EndMT-mediated acquisition of stem cell characteristics and multipotent differentiation capabilities.

The adult human brain harbors multipotent perivascular mesenchymal stem cells

Blood vessels and adjacent cells form perivascular stem cell niches in adult tissues. In this perivascular niche, a stem cell with mesenchymal characteristics was recently identified in some adult somatic tissues. These cells are pericytes that line the microvasculature, express mesenchymal markers and differentiate into mesodermal lineages but might even have the capacity to generate tissue-specific cell types. Here, we isolated, purified and characterized a previously unrecognized progenitor population from two different regions in the adult human brain, the ventricular wall and the neocortex. We show that these cells co-express markers for mesenchymal stem cells and pericytes in vivo and in vitro, but do not express glial, neuronal progenitor, hematopoietic, endothelial or microglial markers in their native state. Furthermore, we demonstrate at a clonal level that these progenitors have true multilineage potential towards both, the mesodermal and neuroectodermal phenotype. They can be epigenetically induced in vitro into adipocytes, chondroblasts and osteoblasts but also into glial cells and immature neurons. This progenitor population exhibits long-term proliferation, karyotype stability and retention of phenotype and multipotency following extensive propagation. Thus, we provide evidence that the vascular niche in the adult human brain harbors a novel progenitor with multilineage capacity that appears to represent mesenchymal stem cells and is different from any previously described human neural stem cell. Future studies will elucidate whether these cells may play a role for disease or may represent a reservoir that can be exploited in efforts to repair the diseased human brain.

A novel and simple method for culturing pericytes from mouse brain

Pericytes play critical roles in the development, maturation and remodeling of blood vessels, and in the central nervous system (CNS), evidence suggests that pericytes also regulate blood flow and form an integral part of the blood-brain barrier. The study of this important cell type has been hampered by the lack of any pericyte-specific marker and by the difficulty of culturing pericytes in adequate numbers to high purity. Here we present a novel yet simple approach to isolate and culture large numbers of pericytes from the mouse CNS that nevertheless leads to very pure pericyte cultures. In our method, vascular cells obtained from adult mice brains are cultured initially under conditions optimized for endothelial cells, but after two passages switched to a medium optimized for pericyte growth. After growing the cells for 1-2 additional passages we obtained a largely homogeneous population of cells that expressed the pericyte markers NG2, PDGFβ-receptor, and CD146, but were negative for markers of endothelial cells (CD31), microglia (Mac-1) and astrocytes (GFAP). Under these conditions, pericytes could be grown to high passage number, and were maintained highly pure and largely undifferentiated, as determined by antigen expression profile and low levels of α-SMA expression, a marker of pericyte differentiation. Furthermore, switching the cells from pericyte medium into DMEM containing 10% FBS promoted α-SMA expression, demonstrating that high passage pericytes could still differentiate. Thus, we provide an alternative approach to the culture of CNS pericytes that is easy to establish and provides large numbers of highly pure pericytes for extended periods of time. This system should provide others working in the pericyte field with a useful additional tool to study the behavior of this fascinating cell type.

Improved methods for detection of β-galactosidase (lacZ) activity in hard tissue

The β-galactosidase gene (lacZ) of Escherichia coli is widely used as a reporter gene. The expression of lacZ can be detected by enzyme-based histochemical staining using chromogenic substrates such as 5-bromo-4-chloro-3-indolyl-β-D: -galactoside (X-gal). Because the enzymatic activity of lacZ is vulnerable to high temperatures and acid treatment for demineralization, detection of lacZ on paraffinized sections is difficult, especially for hard tissues, which require demineralization before sectioning in paraffin. To circumvent this problem, whole-mount X-gal staining before sectioning is performed. However, detection of lacZ activity in the center of larger portions of hard whole adult tissues is challenging. In this study, focusing on fixation procedures, we determined the conditions conducive to improved detection of lacZ activity in deeper areas of whole tissues. We used an annexin a5 (Anxa5)-lacZ reporter mouse model in which the Anxa5 expression in hard tissue is indicated by lacZ activity. We found that lacZ activity could be detected throughout the periodontal ligament of adult mice when fixed in 100% acetone, whereas it was not detected in the periodontal ligament around the root apex fixed in glutaraldehyde and paraformaldehyde. This staining could not be detected in wild-type mice. Acetone maintains the lacZ activity within 48 h of fixation at both 4°C and at room temperature. In conclusion, acetone is the optimal fixative to improve permeability for staining of lacZ activity in large volumes of adult hard tissues.

Physiological cartilage tissue engineering effect of oxygen and biomechanics

In vitro engineering of cartilaginous tissues has been studied for many years, and tissue-engineered constructs are sought to be used clinically for treating articular cartilage defects. Even though there is a plethora of studies and data available, no breakthroughs have been achieved yet that allow for implanting in vivo cultured articular cartilaginous tissues in patients. A review of contributions to cartilage tissue engineering over the past decades emphasizes that most of the studies were performed under environmental conditions neglecting the physiological situation. This is specifically pronounced in the use of bioreactor systems which neither allow for application of near physiomechanical stimulations nor for controlling a hypoxic environment as it is experienced in synovial joints. It is suspected that the negligence of these important parameters has slowed down progress and prevented major breakthroughs in the field. This review focuses on the main aspects of cartilage tissue engineering with emphasis on the relation and understanding of employing physiological conditions.

Myopericytoma and arterial intimal thickening: the relationship between myopericytes and myointimal cells

BACKGROUND

Myopericytomas with intravascular growth have been reported and have been occasionally documented as intraarterial. In a retrospective study, we assessed intraarterial growth in myopericytomas, co-existence with arterial intimal thickening (IT) and the relationship between the two.

METHODS

This retrospective study was undertaken using 11 myopericytomas evaluated in serial microscopical sections. The results in light microscopy, electron microscopy and immunohistochemistry [including α-smooth muscle actin (SMA), desmin and h-caldesmon] were evaluated.

RESULTS

In four myopericytomas, we found intraarterial growth, with large areas of disrupted arterial wall and attachment of veins and venules, exhibiting angiogenic phenomena. Arterial IT was present and partially incorporated within the tumor (simulating medium-sized vessels). The neointimal (myointimal) cells shared morphological and immunohistochemical phenotype with the myopericytoma myoid cells, including α-SMA positivity and desmin negativity. Four of the remaining myopericytomas showed structures similar to arterial IT within the tumor.

CONCLUSIONS

The findings shown here, including the association between myopericytomas and arterial IT, the incorporation of the latter into the tumor and the similar phenotype of their respective myoid and myointimal cells, support a close relationship between these processes. Histogenically, the pericytes of the penetrating neovasculature originating from the attached venules and veins may contribute to both lesions.

Biphenotypic surface epithelial cells in the gastrointestinal tube with mixed epithelial-myofibroblastic differentiation: a paradigm

Epithelial cells and myofibroblasts are well-characterized histomorphological elements of tissues. They are distinguished from one another on the basis of topography and of differences in cytokeratin (CK) and α-smooth muscle actin (SMA) expression. Certain epithelial cells exhibit CK / SMA co-expression. This study aimed to define the immunophenotypical characteristics of these biphenotypic cells with respect to cytodifferentiation (broad spectrum of CKs, SMA), cell-cell interaction (E-cadherin, adenomatous polyposis coli - APC, β-catenin), and cell survival (cyclooxygenase-2 - Cox-2). At the routine gastrointestinal pathology service of the Department of Pathology, University of Szeged, tissue samples were identified from instances of cervical inlet patch (n = 5), Barrett's esophagus (n=5), gastritis (n=5), fundic gland polyp (n=2), gastric neoplastic polyp (n=1), inflammatory bowel disease (n=5), and colonic neoplastic polyp (n=3). that contained epithelial cells expressing SMA. These biphenotypic cells were further immunophenotyped. Foregut-derived biphenotypic cells expressed CKs 7 and 20, while hindgut-derived biphenotypic cells expressed only CK 20. Subepithelial myofibroblasts adjacent to biphenotypic epithelium expressed Cox-2, SMA, and β-catenin, as did biphenotypic cells. Myofibroblasts, however, did not express CKs. In neoplastic polyps, APC expression weakened as cytologic atypism increased, while intermingled biphenotypic cells in neoplastic glands overexpressed APC, as did myofibroblasts beneath. CK subspecies expression in biphenotypic cells reflects embryonic development of the gastrointestinal tract. The immunophenotyping analysis addresses bidirectional (via transdifferentiation from epithelia into myofibroblasts or vice versa) formation of biphenotypic cells within damaged epithelium, a phenomenon that must be further analysed.

Human hepatic stellate cell line (LX-2) exhibits characteristics of bone marrow-derived mesenchymal stem cells

The LX-2 cell line has characteristics of hepatic stellate cells (HSCs), which are considered pericytes of the hepatic microcirculatory system. Recent studies have suggested that HSCs might have mesenchymal origin. We have performed an extensive characterization of the LX-2 cells and have compared their features with those of mesenchymal cells. Our data show that LX-2 cells have a phenotype resembling activated HSCs as well as bone marrow-derived mesenchymal stem cells (BM-MSCs). Our immunophenotypic analysis showed that LX-2 cells are positive for activated HSC markers (αSMA, GFAP, nestin and CD271) and classical mesenchymal makers (CD105, CD44, CD29, CD13, CD90, HLA class-I, CD73, CD49e, CD166 and CD146) but negative for the endothelial marker CD31 and endothelial progenitor cell marker CD133 as well as hematopoietic markers (CD45 and CD34). LX-2 cells also express the same transcripts found in immortalized and primary BM-MSCs (vimentin, annexin 5, collagen 1A, NG2 and CD140b), although at different levels. We show that LX-2 cells are capable to differentiate into multilineage mesenchymal cells in vitro and can stimulate new blood vessel formation in vivo. LX-2 cells appear not to possess tumorigenic potential. Thus, the LX-2 cell line behaves as a multipotent cell line with similarity to BM-MSCs. This line should be useful for further studies to elucidate liver regeneration mechanisms and be the foundation for development of hepatic cell-based therapies.

Comprehensive transcriptome and immunophenotype analysis of renal and cardiac MSC-like populations supports strong congruence with bone marrow MSC despite maintenance of distinct identities

Cells resembling bone marrow mesenchymal stem cells (MSC) have been isolated from many organs but their functional relationships have not been thoroughly examined. Here we compared the immunophenotype, gene expression, multipotency and immunosuppressive potential of MSC-like colony-forming cells from adult murine bone marrow (bmMSC), kidney (kCFU-F) and heart (cCFU-F), cultured under uniform conditions. All populations showed classic MSC morphology and in vitro mesodermal multipotency. Of the two solid organ-specific CFU-F, only kCFU-F displayed suppression of T-cell alloreactivity in vitro, albeit to a lesser extent than bmMSC. Quantitative immunophenotyping using 81 phycoerythrin-conjugated CD antibodies demonstrated that all populations contained high percentages of cells expressing diagnostic MSC surface markers (Sca1, CD90.2, CD29, CD44), as well as others noted previously on murine MSC (CD24, CD49e, CD51, CD80, CD81, CD105). Illumina microarray expression profiling and bioinformatic analysis indicated a correlation of gene expression of 0.88-0.92 between pairwise comparisons. All populations expressed approximately 66% of genes in the pluripotency network (Plurinet), presumably reflecting their stem-like character. Furthermore, all populations expressed genes involved in immunomodulation, homing and tissue repair, suggesting these as conserved functions for MSC-like cells in solid organs. Despite this molecular congruence, strong biases in gene and protein expression and pathway activity were seen, suggesting organ-specific functions. Hence, tissue-derived MSC may also retain unique properties potentially rendering them more appropriate as cellular therapeutic agents for their organ of origin.