A role for pericytes as microenvironmental regulators of human skin tissue regeneration

Osteopontin activates mesenchymal stem cells to repair skin wound

Mesenchymal stem cells (MSCs) are promising candidates for skin wound repair due to their capabilities of accumulating at wounds and differentiating into multiple types of skin cells. However, the underlying mechanisms responsible for these processes remain unclear. In this study, we found that osteopontin (OPN) stimulated the migration of MSCs in vitro, and observed the recruitment of endogenous MSCs to a skin wound and their differentiation into keratinocytes and endothelial cells. In OPN knock-out mice, the recruitment of MSCs to the skin wound was significantly inhibited, and wound closure was hampered after an intradermal injection of exogenous MSCs compared to wild-type mice. Consistent with these observations, the expressions of adhesion molecule CD44 and its receptor E-selectin were significantly decreased in the lesions of OPN knock-out mice compared with wild-type mice suggesting that OPN may regulate the migration of MSCs through its interactions with CD44 during skin wound recovery. In summary, our data demonstrated that OPN played a critical role in activating the migration of MSCs to injured sites and their differentiation into specific skin cell types during skin wound healing.

The Importance of Pericytes in Healing: Wounds and other Pathologies

Much of current research investigates the beneficial properties of mesenchymal stem cells (MSCs) as a treatment for wounds and other forms of injury. In this review, we bring attention to and discuss the role of the pericyte, a cell type which shares much of the differentiation potential and regenerative properties of the MSC as well as specific roles in the regulation of angiogenesis, inflammation and fibrosis. Pericytes have been identified as dysfunctional or depleted in many disease states, and observing the outcomes of pericyte perturbation in models of disease and wound healing informs our understanding of overall pericyte function and identifies these cells as an important target in the development of therapies to encourage healing.

Disruption of lineage specification in adult pulmonary mesenchymal progenitor cells promotes microvascular dysfunction

Pulmonary vascular disease is characterized by remodeling and loss of microvessels and is typically attributed to pathological responses in vascular endothelium or abnormal smooth muscle cell phenotypes. We have challenged this understanding by defining an adult pulmonary mesenchymal progenitor cell (MPC) that regulates both microvascular function and angiogenesis. The current understanding of adult MPCs and their roles in homeostasis versus disease has been limited by a lack of genetic markers with which to lineage label multipotent mesenchyme and trace the differentiation of these MPCs into vascular lineages. Here, we have shown that lineage-labeled lung MPCs expressing the ATP-binding cassette protein ABCG2 (ABCG2+) are pericyte progenitors that participate in microvascular homeostasis as well as adaptive angiogenesis. Activation of Wnt/β-catenin signaling, either autonomously or downstream of decreased BMP receptor signaling, enhanced ABCG2+ MPC proliferation but suppressed MPC differentiation into a functional pericyte lineage. Thus, enhanced Wnt/β-catenin signaling in ABCG2+ MPCs drives a phenotype of persistent microvascular dysfunction, abnormal angiogenesis, and subsequent exacerbation of bleomycin-induced fibrosis. ABCG2+ MPCs may, therefore, account in part for the aberrant microvessel function and remodeling that are associated with chronic lung diseases.

A high-yield isolation and enrichment strategy for human lung microvascular endothelial cells

Vasculopathies, characterized by the formation of fragile and abnormal microvessels, are associated with the severity of many chronic lung diseases, including pulmonary fibrosis, emphysema/chronic obstructive pulmonary disease, systemic sclerosis, and hypertension. However, the study of human lung vasculature has been limited by the ability to isolate generous quantities of microvascular endothelial cells (MVEC) free from mesenchymal contamination. Expansion and passaging of primary human MVEC in vitro typically results in loss of a traditional phenotype in favor of an intermediate mesenchymal one, as early as passage five. Here we provide a detailed protocol for the selection of large quantities of enriched primary human lung MVEC based upon differential adherence from mesenchyme and simple magnetic separation, which decreases the need for excessive passaging, in order to obtain sufficient cell numbers to successfully freeze stock cultures. Additional protocols are provided for Ac-di-LDL selection, characterization, and a sandwich angiogenesis method of functional tube formation. The complete protocol including cell isolation and characterization takes approximately six weeks to complete.

Guanylate-binding protein 1 (GBP1) contributes to the immunity of human mesenchymal stromal cells against Toxoplasma gondii

Mesenchymal stromal cells (MSCs) have recently been shown to play important roles in mammalian host defenses against intracellular pathogens, but the molecular mechanism still needs to be clarified. We confirmed that human MSCs (hMSCs) prestimulated with IFN-γ showed a significant and dose-dependent ability to inhibit the growth of two types of Toxoplasma gondii [type I RH strain with green fluorescent proteins (RH/GFP) or type II PLK strain with red fluorescent proteins (PLK/RED)]. However, in contrast to previous reports, the anti-T. gondii activity of hMSCs was not mediated by indoleamine 2,3-dioxygenase (IDO). Genome-wide RNA sequencing (RNA-seq) analysis revealed that IFN-γ increased the expression of the p65 family of human guanylate-binding proteins (hGBPs) in hMSCs, especially hGBP1. To analyze the functional role of hGBPs, stable knockdowns of hGBP1, -2, and -5 in hMSCs were established using a lentiviral transfection system. hGBP1 knockdown in hMSCs resulted in a significant loss of the anti-T. gondii host defense property, compared with hMSCs infected with nontargeted control sequences. hGBP2 and -5 knockdowns had no effect. Moreover, the hGBP1 accumulation on the parasitophorous vacuole (PV) membranes of IFN-γ-stimulated hMSCs might protect against T. gondii infection. Taken together, our results suggest that hGBP1 plays a pivotal role in anti-T. gondii protection of hMSCs and may shed new light on clarifying the mechanism of host defense properties of hMSCs.

Pericytes, an overlooked player in vascular pathobiology

Pericytes are a heterogeneous population of cells located in the blood vessel wall. They were first identified in the 19th century by Rouget, however their biological role and potential for drug targeting have taken time to be recognised. Isolation of pericytes from several different tissues has allowed a better phenotypic and functional characterization. These findings revealed a tissue-specific, multi-functional group of cells with multilineage potential. Given this emerging evidence, pericytes have acquired specific roles in pathobiological events in vascular diseases. In this review article, we will provide a compelling overview of the main diseases in which pericytes are involved, from well-established mechanisms to the latest findings. Pericyte involvement in diabetes and cancer will be discussed extensively. In the last part of the article we will review therapeutic approaches for these diseases in light of the recently acquired knowledge. To unravel pericyte-related vascular pathobiological events is pivotal not only for more tailored treatments of disease but also to establish pericytes as a therapeutic tool.

End Sequence Analysis Toolkit (ESAT) expands the extractable information from single-cell RNA-seq data

RNA-seq protocols that focus on transcript termini are well suited for applications in which template quantity is limiting. Here we show that, when applied to end-sequencing data, analytical methods designed for global RNA-seq produce computational artifacts. To remedy this, we created the End Sequence Analysis Toolkit (ESAT). As a test, we first compared end-sequencing and bulk RNA-seq using RNA from dendritic cells stimulated with lipopolysaccharide (LPS). As predicted by the telescripting model for transcriptional bursts, ESAT detected an LPS-stimulated shift to shorter 3′-isoforms that was not evident by conventional computational methods. Then, droplet-based microfluidics was used to generate 1000 cDNA libraries, each from an individual pancreatic islet cell. ESAT identified nine distinct cell types, three distinct β-cell types, and a complex interplay between hormone secretion and vascularization. ESAT, then, offers a much-needed and generally applicable computational pipeline for either bulk or single-cell RNA end-sequencing.

Defining the cellular lineage hierarchy in the interfollicular epidermis of adult skin

The interfollicular epidermis regenerates from heterogeneous basal skin cell populations that divide at different rates. It has previously been presumed that infrequently dividing basal cells known as label-retaining cells (LRCs) are stem cells, whereas non-LRCs are short-lived progenitors. Here we employ the H2B-GFP pulse-chase system in adult mouse skin and find that epidermal LRCs and non-LRCs are molecularly distinct and can be differentiated by Dlx1(CreER) and Slc1a3(CreER) genetic marking, respectively. Long-term lineage tracing and mathematical modelling of H2B-GFP dilution data show that LRCs and non-LRCs constitute two distinct stem cell populations with different patterns of proliferation, differentiation and upward cellular transport. During homeostasis, these populations are enriched in spatially distinct skin territories and can preferentially produce unique differentiated lineages. On wounding or selective killing, they can temporarily replenish each other's territory. These two discrete interfollicular stem cell populations are functionally interchangeable and intrinsically well adapted to thrive in distinct skin environments.

Pericytes: A newly recognized player in wound healing

Pericytes have generally been considered in the context of stabilizing vessels, ensuring the blood barriers, and regulating the flow through capillaries. However, new reports suggest that pericytes may function at critical times to either drive healing with minimal scarring or, perversely, contribute to fibrosis and ongoing scar formation. Beneficially, pericytes probably drive much of the vascular involution that occurs during the transition from the regenerative to the resolution phases of healing. Pathologically, pericytes can assume a fibrotic phenotype and promote scarring. This perspective will discuss pericyte involvement in wound repair and the relationship pericytes form with the parenchymal cells of the skin. We will further evaluate the role pericytes may have in disease progression in relation to chronic wounds and fibrosis.

Mesenchymal Stromal Cells as Cell-Based Therapeutics for Wound Healing

Chronic wounds are a source of substantial morbidity for patients and are a major financial burden for the healthcare system. There are no current therapies that reliably improve nonhealing wounds or reverse pathological scarring. Mesenchymal stromal cells (MSCs) are a promising source of novel cell-based therapies due to the ease of their harvest and their integral role in the native wound repair process. Recent work has addressed the problems of loss of plasticity and off-target delivery through use of modern bioengineering techniques. Here we describe the applications of MSCs harvested from different sources to the wound healing process and recent advances in delivery of MSCs to targeted sites of injury.

Dermal Contributions to Human Interfollicular Epidermal Architecture and Self-Renewal

The human interfollicular epidermis is renewed throughout life by populations of proliferating basal keratinocytes. Though interfollicular keratinocyte stem cells have been identified, it is not known how self-renewal in this compartment is spatially organized. At the epidermal-dermal junction, keratinocytes sit atop a heterogeneous mix of dermal cells that may regulate keratinocyte self-renewal by influencing local tissue architecture and signalling microenvironments. Focusing on the rete ridges and complementary dermal papillae in human skin, we review the identity and organisation of abundant dermal cells types and present evidence for interactions between the dermal microenvironment and the interfollicular keratinocytes.

Concise Review: Human Dermis as an Autologous Source of Stem Cells for Tissue Engineering and Regenerative Medicine

The exciting potential for regenerating organs from autologous stem cells is on the near horizon, and adult dermis stem cells (DSCs) are particularly appealing because of the ease and relative minimal invasiveness of skin collection. A substantial number of reports have described DSCs and their potential for regenerating tissues from mesenchymal, ectodermal, and endodermal lineages; however, the exact niches of these stem cells in various skin types and their antigenic surface makeup are not yet clearly defined. The multilineage potential of DSCs appears to be similar, despite great variability in isolation and in vitro propagation methods. Despite this great potential, only limited amounts of tissues and clinical applications for organ regeneration have been developed from DSCs. This review summarizes the literature on DSCs regarding their niches and the specific markers they express. The concept of the niches and the differentiation capacity of cells residing in them along particular lineages is discussed. Furthermore, the advantages and disadvantages of widely used methods to demonstrate lineage differentiation are considered. In addition, safety considerations and the most recent advancements in the field of tissue engineering and regeneration using DSCs are discussed. This review concludes with thoughts on how to prospectively approach engineering of tissues and organ regeneration using DSCs. Our expectation is that implementation of the major points highlighted in this review will lead to major advancements in the fields of regenerative medicine and tissue engineering.

SIGNIFICANCE

Autologous dermis-derived stem cells are generating great excitement and efforts in the field of regenerative medicine and tissue engineering. The substantial impact of this review lies in its critical coverage of the available literature and in providing insight regarding niches, characteristics, and isolation methods of stem cells derived from the human dermis. Furthermore, it provides analysis of the current state-of-the-art regenerative approaches using human-derived dermal stem cells, with consideration of current guidelines, to assist translation toward therapeutic use.

The potential of mesenchymal stem cells in the management of radiation enteropathy

Although radiotherapy is effective in managing abdominal and pelvic malignant tumors, radiation enteropathy is still unavoidable. This disease severely affects the quality of life of cancer patients due to some refractory lesions, such as intestinal ischemia, mucositis, ulcer, necrosis or even perforation. Current drugs or prevailing therapies are committed to alleviating the symptoms induced by above lesions. But the efficacies achieved by these interventions are still not satisfactory, because the milieus for tissue regeneration are not distinctly improved. In recent years, regenerative therapy for radiation enteropathy by using mesenchymal stem cells is of public interests. Relevant results of preclinical and clinical studies suggest that this regenerative therapy will become an attractive tool in managing radiation enteropathy, because mesenchymal stem cells exhibit their pro-regenerative potentials for healing the injuries in both epithelium and endothelium, minimizing inflammation and protecting irradiated intestine against fibrogenesis through activating intrinsic repair actions. In spite of these encouraging results, whether mesenchymal stem cells promote tumor growth is still an issue of debate. On this basis, we will discuss the advances in anticancer therapy by using mesenchymal stem cells in this review after analyzing the pathogenesis of radiation enteropathy, introducing the advances in managing radiation enteropathy using regenerative therapy and exploring the putative actions by which mesenchymal stem cells repair intestinal injuries. At last, insights gained from the potential risks of mesenchymal stem cell-based therapy for radiation enteropathy patients may provide clinicians with an improved awareness in carrying out their studies.

Regenerative Translation of Human Blood-Vessel-Derived MSC Precursors

Mesenchymal stem/stromal cells (MSCs) represent a promising adult progenitor cell source for tissue repair and regeneration. Their mysterious identity in situ has gradually been unveiled by the accumulating evidence indicating an association between adult multipotent stem/progenitor cells and vascular/perivascular niches. Using immunohistochemistry and fluorescence-activated cell sorting, we and other groups have prospectively identified and purified subpopulations of multipotent precursor cells associated with the blood vessels within multiple human organs. The three precursor subsets, myogenic endothelial cells (MECs), pericytes (PCs), and adventitial cells (ACs), are located, respectively, in the three structural tiers of typical blood vessels: intima, media, and adventitia. MECs, PCs, and ACs have been extensively characterized in prior studies and are currently under investigation for their therapeutic potentials in preclinical animal models. In this review, we will briefly discuss the identification, isolation, and characterization of these human blood-vessel-derived stem cells (hBVSCs) and summarize the current status of regenerative applications of hBVSC subsets.

Pericytes in sarcomas of bone

Pericytes are mesenchymal cells that closely enwrap small blood vessels, lying in intimate association with the endothelium. Pericytes have recently gained attention as an important mediator of vascular biology and angiogenesis in cancer. Although better studied in carcinoma, pericytes have known interaction with sarcomas of bone, including Ewing's sarcoma, osteosarcoma, and chondrosarcoma. Best studied is Ewing's sarcoma (ES), which displays a prominent perivascular growth pattern. Signaling pathways of known importance in intratumoral pericytes in ES include Notch, PDGF/PDGFR-β, and VEGF signaling. In summary, pericytes serve important functions in the tumor microenvironment. Improved understanding of pericyte biology may hold significant implications for the development of new therapies in sarcoma.

Response of endothelial cells and pericytes to hypoxia and erythropoietin in a co-culture assay dedicated to soft tissue repair

The increasing mean life expectancy of the citizens of the western world countries leads to an increase of the age-related diseases, among them soft tissue defects exhibiting inadequate healing. In order to develop new therapeutic strategies to support disturbed soft tissue repair, there is a strong need of sophisticated in vitro assays. A new assay combining scratch wounding with co-cultures of primary human microvascular endothelial cells (HDMEC) and pericytes (HPC) focuses on basic characteristics of cell interaction against the background of soft tissue repair. The cell parameters proliferation, migration and differentiation, and the release of monocyte chemoattractant protein-1 (MCP-1) were analysed in response to hypoxia (pO2 < 5 mmHg) and to erythropoietin (EPO; 50 IU/ml), a glycoprotein hormone having shown promising effects in soft tissue repair. As basic characteristics of the assay, direct cell contact in co-culture led to a weakened proliferation of both cell types, an increase of the percentage of myofibroblast-like pericytes and to a higher release of MCP-1. Hypoxia caused a proliferation decrease of HPC in co-culture, which was slightly attenuated by EPO. Hypoxia also reduced the MCP-1 release of co-cultured cells, when EPO had been added. In addition, EPO had a rather positive effect on HPC migration under hypoxia. These in vitro results allow new insights into the interaction of pericytes with endothelial cells in the context of soft tissue repair.

Laminins: Roles and Utility in Wound Repair

Significance: Laminins are complex extracellular macromolecules that are major players in the control of a variety of core cell processes, including regulating rates of cell proliferation, differentiation, adhesion, and migration. Laminins, and related extracellular matrix components, have essential roles in tissue homeostasis; however, during wound healing, the same proteins are critical players in re-epithelialization and angiogenesis. Understanding how these proteins influence cell behavior in these different conditions holds great potential in identifying new strategies to enhance normal wound closure or to treat chronic/nonhealing wounds. Recent Advances: Laminin-derived bioactive peptides and, more recently, laminin-peptide conjugated scaffolds, have been designed to improve tissue regeneration after injuries. These peptides have been shown to be effective in decreasing inflammation and granulation tissue, and in promoting re-epithelialization, angiogenesis, and cell migration. Critical Issues: Although there is now a wealth of knowledge concerning laminin form and function, there are still areas of some controversy. These include the relative contribution of two laminin-based adhesive devices (focal contacts and hemidesmosomes) to the re-epithelialization process, the impact and implications of laminin proteolytic processing, and the importance of laminin polymer formation on cell behavior. In addition, the roles in wound healing of the laminin-related proteins, netrins, and LaNts are still to be fully defined. Future Directions: The future of laminin-based therapeutics potentially lies in the bioengineering of specific substrates to support laminin deposition for ex vivo expansion of autologous cells for graft formation and transplantation. Significant recent advances suggest that this goal is within sight.

Pericytes at the intersection between tissue regeneration and pathology

Perivascular multipotent cells, pericytes, contribute to the generation and repair of various tissues in response to injury. They are heterogeneous in their morphology, distribution, origin and markers, and elucidating their molecular and cellular differences may inform novel treatments for disorders in which tissue regeneration is either impaired or excessive. Moreover, these discoveries offer novel cellular targets for therapeutic approaches to many diseases. This review discusses recent studies that support the concept that pericyte subtypes play a distinctive role in myogenesis, neurogenesis, adipogenesis, fibrogenesis and angiogenesis.

Neural-competent cells of adult human dermis belong to the Schwann lineage

Resident neural precursor cells (NPCs) have been reported for a number of adult tissues. Understanding their physiological function or, alternatively, their activation after tissue damage or in vitro manipulation remains an unsolved issue. Here, we investigated the source of human dermal NPCs in adult tissue. By following an unbiased, comprehensive approach employing cell-surface marker screening, cell separation, transcriptomic characterization, and in vivo fate analyses, we found that p75NTR⁺ precursors of human foreskin can be ascribed to the Schwann (CD56⁺) and perivascular (CD56⁻) cell lineages. Moreover, neural differentiation potential was restricted to the p75NTR⁺CD56⁺ Schwann cells and mediated by SOX2 expression levels. Double-positive NPCs were similarly obtained from human cardiospheres, indicating that this phenomenon might be widespread.

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Human dermis-derived cultures show two types of SOX2⁺ cells: Schwann and perivascular

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p75NTR⁺CD56⁺ Schwann cells are responsible for neural progeny

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SOX2 expression levels regulate the neural competence of dermal precursors

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p75NTR⁺CD56⁺ neural precursor cells similarly arise from human cardiospheres

Vasculogenesis and Angiogenesis in Modular Collagen-Fibrin Microtissues

The process of new blood vessel formation is critical in tissue development, remodeling and regeneration. Modular tissue engineering approaches have been developed to enable the bottom-up assembly of more complex tissues, including vascular networks. In this study, collagen-fibrin composite microbeads (100-300 μm in diameter) were fabricated using a water-in-oil emulsion technique. Human endothelial cells and human fibroblasts were embedded directly in the microbead matrix at the time of fabrication. Microbead populations were characterized and cultured for 14 days either as free-floating populations or embedded in a surrounding fibrin gel. The collagen-fibrin matrix efficiently entrapped cells and supported their viability and spreading. By 7 days in culture, endothelial cell networks were evident within microbeads, and these structures became more prominent by day 14. Fibroblasts co-localized with endothelial cells, suggesting a pericyte-like function, and laminin deposition indicated maturation of the vessel networks over time. Microbeads embedded in a fibrin gel immediately after fabrication showed the emergence of cells and the coalescence of vessel structures in the surrounding matrix by day 7. By day 14, inosculation of neighboring cords and prominent vessel structures were observed. Microbeads pre-cultured for 7 days prior to embedding in fibrin gave rise to vessel networks that emanated radially from the microbead by day 7, and developed into connected networks by day 14. Lumen formation in endothelial cell networks was confirmed using confocal sectioning. These data show that collagen-fibrin composite microbeads support vascular network formation. Microbeads embedded directly after fabrication emulated the process of vasculogenesis, while the branching and joining of vessels from pre-cultured microbeads resembled angiogenesis. This modular microtissue system has utility in studying the processes involved in new vessel formation, and may be developed into a therapy for the treatment of ischemic conditions.

Pericytes: multitasking cells in the regeneration of injured, diseased, and aged skeletal muscle

Pericytes are perivascular cells that envelop and make intimate connections with adjacent capillary endothelial cells. Recent studies show that they may have a profound impact in skeletal muscle regeneration, innervation, vessel formation, fibrosis, fat accumulation, and ectopic bone formation throughout life. In this review, we summarize and evaluate recent advances in our understanding of pericytes' influence on adult skeletal muscle pathophysiology. We also discuss how further elucidating their biology may offer new approaches to the treatment of conditions characterized by muscle wasting.

SLIT3-ROBO4 activation promotes vascular network formation in human engineered tissue and angiogenesis in vivo

Successful implantation and long-term survival of engineered tissue grafts hinges on adequate vascularization of the implant. Endothelial cells are essential for patterning vascular structures, but they require supportive mural cells such as pericytes/mesenchymal stem cells (MSCs) to generate stable, functional blood vessels. While there is evidence that the angiogenic effect of MSCs is mediated via the secretion of paracrine signals, the identity of these signals is unknown. By utilizing two functionally distinct human MSC clones, we found that so-called "pericytic" MSCs secrete the pro-angiogenic vascular guidance molecule SLIT3, which guides vascular development by directing ROBO4-positive endothelial cells to form networks in engineered tissue. In contrast, "non-pericytic" MSCs exhibit reduced activation of the SLIT3/ROBO4 pathway and do not support vascular networks. Using live cell imaging of organizing 3D vascular networks, we show that siRNA knockdown of SLIT3 in MSCs leads to disorganized clustering of ECs. Knockdown of its receptor ROBO4 in ECs abolishes the generation of functional human blood vessels in an in vivo xenogenic implant. These data suggest that the SLIT3/ROBO4 pathway is required for MSC-guided vascularization in engineered tissues. Heterogeneity of SLIT3 expression may underlie the variable clinical success of MSCs for tissue repair applications.

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.

Lipopolysaccharide activates Toll-like receptor 4 (TLR4)-mediated NF-κB signaling pathway and proinflammatory response in human pericytes

Pericytes and mesenchymal stem cells (MSCs) are ontogenically related, and in fact, no significant phenotypic differences could be observed by flow cytometry. Transcriptome analysis of human pericytes and MSCs revealed that 43 genes were up-regulated more than 10-fold in pericytes compared with MSCs. Identification of Toll-like receptor 4 (TLR4) as one of the most abundant RNA species in pericytes with respect to MSCs and confirmation of TLR4 expression on the cell surface led us to obtain a comprehensive overview of the expression program of lipopolysaccharide (LPS)-stimulated pericytes. Transcriptional profiling of LPS-treated cells revealed that 22 genes were up-regulated more than 5-fold. Of them, 10 genes encoded chemokines and cytokines (CXCL10, CCL20, IL8, CXCL1, IL6, CCL2, IL1B, CXCL2, IL1A, and CXCL6), and three genes encoded adhesion molecules (ICAM1, VCAM1, and SELE). LPS induced nuclear translocation of the transcription factor NF-κB in stimulated pericytes. Moreover, inhibition of NF-κB activation by SC-514 blocked LPS-induced up-regulation of a subset of chemokine genes, confirming the key role of NF-κB in LPS signaling in pericytes. At the protein level, we assessed the secretion of the proinflammatory cytokines and chemokines IL-6, IL-8, CXCL1, CXCL2, CXCL3, and CCL2 not only after LPS treatment but also in HMGB1-stimulated pericytes. Up-regulation of the adhesion molecules ICAM-1 and VCAM-1 resulted in an increased adhesion of peripheral blood leukocytes to an LPS-treated pericyte monolayer. The role of pericytes in the inflammatory context has been scarcely addressed; according to these results, pericytes should be considered as active players in the inflammatory cascade with potential physiopathological implications.

Pericytes, mesenchymal stem cells and the wound healing process

Pericytes are cells that reside on the wall of the blood vessels and their primary function is to maintain the vessel integrity. Recently, it has been realized that pericytes have a much greater role than just the maintenance of vessel integrity essential for the development and formation of a vascular network. Pericytes also have stem cell-like properties and are seemingly able to differentiate into adipocytes, chondrocytes, osteoblasts and granulocytes, leading them to be identified as mesenchymal stem cells (MSCs). More recently it has been suggested that pericytes play a key role in wound healing, whereas the beneficial effects of MSCs in accelerating the wound healing response has been recognized for some time. In this review, we collate the most recent data on pericytes, particularly their role in vessel formation and how they can affect the wound healing process.

Human skin cells that express stage-specific embryonic antigen 3 associate with dermal tissue regeneration

Stage-specific embryonic antigen 3 (SSEA3) is a glycosphingolipid that has previously been used to identify cells with stem cell-like, multipotent, and pluripotent characteristics. A rare subpopulation of SSEA3-expressing cells exists in the dermis of adult human skin. These SSEA3-expressing cells undergo a significant increase in cell number in response to injury, suggesting a possible role in regeneration. These SSEA3-expressing regeneration-associated (SERA) cells were derived through primary cell culture, purified by fluorescence-activated cell sorting (FACS), and characterized. Longer in vitro culture of the primary skin cells led to lower SSEA3 expression stability after FACS-based purification, suggesting that the current culture conditions may need to be optimized to permit the large-scale expansion of SERA cells. The SERA cells demonstrated a global transcriptional state that was most similar to bone marrow- and fat-derived mesenchymal stem cells (MSCs), and the highest expressing SSEA3-expressing cells co-expressed CD105 (clone 35). However, while a rare population of MSCs was observed in primary human skin cell cultures that could differentiate into adipocytes, osteoblasts, or chondrocytes, SERA cells did not possess this differentiation capacity, suggesting that there are at least two different rare subpopulations in adult human skin primary cultures. The identification, efficient purification, and large-scale expansion of these rare subpopulations (SERA cells and MSCs) from heterogeneous adult human skin primary cell cultures may have applications for future patient-specific cellular therapies.

Skin basement membrane: the foundation of epidermal integrity--BM functions and diverse roles of bridging molecules nidogen and perlecan

The epidermis functions in skin as first defense line or barrier against environmental impacts, resting on extracellular matrix (ECM) of the dermis underneath. Both compartments are connected by the basement membrane (BM), composed of a set of distinct glycoproteins and proteoglycans. Herein we are reviewing molecular aspects of BM structure, composition, and function regarding not only (i) the dermoepidermal interface but also (ii) the resident microvasculature, primarily focusing on the per se nonscaffold forming components perlecan and nidogen-1 and nidogen-2. Depletion or functional deficiencies of any BM component are lethal at some stage of development or around birth, though BM defects vary between organs and tissues. Lethality problems were overcome by developmental stage- and skin-specific gene targeting or by cell grafting and organotypic (3D) cocultures of normal or defective cells, which allows recapitulating BM formation de novo. Thus, evidence is accumulating that BM assembly and turnover rely on mechanical properties and composition of the adjacent ECM and the dynamics of molecular assembly, including further "minor" local components, nidogens largely functioning as catalysts or molecular adaptors and perlecan as bridging stabilizer. Collectively, orchestration of BM assembly, remodeling, and the role of individual players herein are determined by the developmental, tissue-specific, or functional context.

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.

Laminin α5 guides tissue patterning and organogenesis

Laminins (LM) are extracellular matrix molecules that contribute to and are required for the formation of basement membranes. They participate in the modulation of epithelial/mesenchymal interactions and are implicated in organogenesis and maintenance of organ homeostasis. Among the LM molecules, the LM α5 chain (LMα5) is one of the most widely distributed LM in the developing and mature organism. Its presence in some basement membranes during embryogenesis is absolutely required for maintenance of basement membrane integrity and thus for proper organogenesis. LMα5 also regulates the expression of genes important for major biological processes, in part by repressing or activating signaling pathways, depending upon the physiological context.

The pro-metastatic role of bone marrow-derived cells: a focus on MSCs and regulatory T cells

Several bone marrow-derived cells have been shown to promote tumour growth and progression. These cells can home to the primary tumour and become active components of the tumour microenvironment. Recent studies have also identified bone marrow-derived cells—such as mesenchymal stem cells and regulatory T cells—as contributors to cancer metastasis. The innate versatility of these cells provides diverse functional aid to promote malignancy, ranging from structural support to signal-mediated suppression of the host immune response. Here, we review the role of mesenchymal stem cells and regulatory T cells in cancer metastasis. A better understanding of the bipolar nature of these bone marrow-derived cells in physiological and malignant contexts could pave the way for new therapeutics against metastatic disease.

Extracellular matrix and the neural stem cell niche

Basal lamina is present in many stem cell niches, but we still have a poor understanding of the role of this and other extracellular matrix (ECM) components. Here, we review current knowledge regarding ECM expression and function in the neural stem cell niche, focusing on the subependymal zone of the adult CNS. An increasing complexity of ECM molecules has been described, and a number of receptors expressed on the stem cells identified. Experiments perturbing the niche using genetics or cytotoxic ablation of the rapidly dividing precursors, or using explant culture models to examine specific growth factors, have been influential in showing how changes in these ECM receptors might regulate neural stem cell behavior. However the role of changes in the matrix itself remains to be determined. The answers will be important, as they will point to the molecules required to engineer niches ex-vivo so as to provide tools for regenerative neuroscience.

Perivascular-like cells contribute to the stability of the vascular network of osteogenic tissue formed from cell sheet-based constructs

In recent years several studies have been supporting the existence of a close relationship in terms of function and progeny between Mesenchymal Stem Cells (MSCs) and Pericytes. This concept has opened new perspectives for the application of MSCs in Tissue Engineering (TE), with special interest for the pre-vascularization of cell dense constructs. In this work, cell sheet technology was used to create a scaffold-free construct composed of osteogenic, endothelial and perivascular-like (CD146⁺) cells for improved in vivo vessel formation, maturation and stability. The CD146 pericyte-associated phenotype was induced from human bone marrow mesenchymal stem cells (hBMSCs) by the supplementation of standard culture medium with TGF-β1. Co-cultured cell sheets were obtained by culturing perivascular-like (CD146⁺) cells and human umbilical vein endothelial cells (HUVECs) on an hBMSCs monolayer maintained in osteogenic medium for 7 days. The perivascular-like (CD146⁺) cells and the HUVECs migrated and organized over the collagen-rich osteogenic cell sheet, suggesting the existence of cross-talk involving the co-cultured cell types. Furthermore the presence of that particular ECM produced by the osteoblastic cells was shown to be the key regulator for the singular observed organization. The osteogenic and angiogenic character of the proposed constructs was assessed in vivo. Immunohistochemistry analysis of the explants revealed the integration of HUVECs with the host vasculature as well as the osteogenic potential of the created construct, by the expression of osteocalcin. Additionally, the analysis of the diameter of human CD146 positive blood vessels showed a higher mean vessel diameter for the co-cultured cell sheet condition, reinforcing the advantage of the proposed model regarding blood vessels maturation and stability and for the in vitro pre-vascularization of TE constructs.

Angiogenesis potential of human limbal stromal niche cells

PURPOSE

The perivascular localization of stem cell (SC) niches suggests the presence of a vascular niche. We aimed to determine the angiogenesis potential of limbal niche cells (NCs).

METHODS

Human limbal NCs were isolated and serially passaged on plastic or coated Matrigel in embryonic SC medium containing BFGF and leukemia inhibitory factor before being reseeded in 3D Matrigel. Expression of angiogenesis markers was assessed by RT-qPCR and immunofluorescence staining. Their angiogenesis potential was measured by differentiation into vascular endothelial cells and by supporting vascular tube network formed by human umbilical vein endothelial cells (HUVEC) on Matrigel. Their support of limbal epithelial progenitor cells (LEPC) was examined in sphere growth formed by reunion in 3D Matrigel.

RESULTS

On plastic, limbal NC could be cultured only up to four passages before turning into myofibroblasts. In contrast, on coated Matrigel, they could be expanded for up to 12 passages with upregulation of markers suggestive of angiogenesis progenitors when reseeded in 3D Matrigel because they could differentiate into vascular endothelial cells and pericytes stabilizing the tube network formed by HUVEC. Although both expanded limbal NCs and HUVEC rejoined with LEPC to form spheres to upregulate expression of ΔNp63α, CK15, and CEBPδ, the former but not the latter abolished expression of CK12 keratin.

CONCLUSIONS

Human limbal NCs continuously expanded on the basement membrane differentiate into angiogenesis progenitors that prevent differentiation of LEPC/SCs. They may partake in formation of the vascular niche and contribute to angiogenesis during wound healing.

SIV-induced impairment of neurovascular repair: a potential role for VEGF

Peripheral nerves and blood vessels travel together closely during development but little is known about their interactions post-injury. The SIV-infected pigtailed macaque model of human immunodeficiency virus (HIV) recapitulates peripheral nervous system pathology of HIV infection. In this study, we assessed the effect of SIV infection on neurovascular regrowth using a validated excisional axotomy model. Six uninfected and five SIV-infected macaques were studied 14 and 70 days after axotomy to characterize regenerating vessels and axons. Blood vessel extension preceded the appearance of regenerating nerve fibers suggesting that vessels serve as scaffolding to guide regenerating axons through extracellular matrix. Vascular endothelial growth factor (VEGF) was expressed along vascular silhouettes by endothelial cells, pericytes, and perivascular cells. VEGF expression correlated with dermal nerve (r=0.68, p=0.01) and epidermal nerve fiber regrowth (r=0.63, p=0.02). No difference in blood vessel growth was observed between SIV-infected and control macaques. In contrast, SIV-infected animals demonstrated altered length, pruning and arborization of nerve fibers as well as alteration of VEGF expression. These results reinforce earlier human primate findings that vessel growth precedes and influences axonal regeneration. The consistency of these observations across human and non-human primates validates the use of the pigtailed-macaque as a preclinical model.

The role of the myofibroblast in tumor stroma remodeling

Since its first description in wound granulation tissue, the myofibroblast has been recognized to be a key actor in the epithelial-mesenchymal cross-talk that plays a crucial role in many physiological and pathological situations, such as regulation of prostate development, ventilation-perfusion in lung alveoli or organ fibrosis. The presence of myofibroblasts in the stroma reaction to epithelial tumors is well established and many data are accumulating which suggest that the stroma compartment is an active participant in tumor onset and/or evolution. In this review we summarize the evidence in favor of this concept, the main mechanisms that regulate myofibroblast differentiation and function, as well as the biophysical and biochemical factors possibly involved in epithelial-stroma interactions, using liver carcinoma as main model, in view of achieving a better understanding of tumor progression mechanisms and of tools directed toward stroma as eventual therapeutic target.

Concise review: role of mesenchymal stem cells in wound repair

Wound healing requires a coordinated interplay among cells, growth factors, and extracellular matrix proteins. Central to this process is the endogenous mesenchymal stem cell (MSC), which coordinates the repair response by recruiting other host cells and secreting growth factors and matrix proteins. MSCs are self-renewing multipotent stem cells that can differentiate into various lineages of mesenchymal origin such as bone, cartilage, tendon, and fat. In addition to multilineage differentiation capacity, MSCs regulate immune response and inflammation and possess powerful tissue protective and reparative mechanisms, making these cells attractive for treatment of different diseases. The beneficial effect of exogenous MSCs on wound healing was observed in a variety of animal models and in reported clinical cases. Specifically, they have been successfully used to treat chronic wounds and stimulate stalled healing processes. Recent studies revealed that human placental membranes are a rich source of MSCs for tissue regeneration and repair. This review provides a concise summary of current knowledge of biological properties of MSCs and describes the use of MSCs for wound healing. In particular, the scope of this review focuses on the role MSCs have in each phase of the wound-healing process. In addition, characterization of MSCs containing skin substitutes is described, demonstrating the presence of key growth factors and cytokines uniquely suited to aid in wound repair.

Emerging roles for multipotent, bone marrow-derived stromal cells in host defense

Multipotent, bone marrow-derived stromal cells (BMSCs, also known as mesenchymal stem cells [MSCs]), are culture-expanded, nonhematopoietic cells with immunomodulatory effects currently being investigated as novel cellular therapy to prevent and to treat clinical disease associated with aberrant immune response. Emerging preclinical studies suggest that BMSCs may protect against infectious challenge either by direct effects on the pathogen or through indirect effects on the host. BMSCs may reduce pathogen burden by inhibiting growth through soluble factors or by enhancing immune cell antimicrobial function. In the host, BMSCs may attenuate pro-inflammatory cytokine and chemokine induction, reduce pro-inflammatory cell migration into sites of injury and infection, and induce immunoregulatory soluble and cellular factors to preserve organ function. These preclinical studies provide provocative hints into the direction MSC therapeutics may take in the future. Notably, BMSCs appear to function as a critical fulcrum, providing balance by promoting pathogen clearance during the initial inflammatory response while suppressing inflammation to preserve host integrity and facilitate tissue repair. Such exquisite balance in BMSC function appears intrinsically linked to Toll-like receptor signaling and immune crosstalk.

Brain pericytes: emerging concepts and functional roles in brain homeostasis

Brain pericytes are an important constituent of neurovascular unit. They encircle endothelial cells and contribute to the maturation and stabilization of the capillaries in the brain. Recent studies have revealed that brain pericytes play pivotal roles in a variety of brain functions, such as regulation of capillary flow, angiogenesis, blood brain barrier, immune responses, and hemostasis. In addition, brain pericytes are pluripotent and can differentiate into different lineages similar to mesenchymal stem cells. The brain pericytes are revisited as a key player to maintain brain function and repair brain damage.

Immortalized CNS pericytes are quiescent smooth muscle actin-negative and pluripotent

Despite their identification more than 100 years ago by the French scientist Charles-Marie Benjamin Rouget, microvascular pericytes have proven difficult to functionally characterize, due in part to their relatively low numbers and the lack of specific cell markers. However, recent progress is beginning to shed light on the diverse biological functions of these cells. Pericytes are thought to be involved in regulating vascular homeostasis and hemostasis as well as serving as a local source of adult stem cells. To further define the properties of these intriguing cells, we have isolated pericytes from transgenic mice (Immortomouse®) harboring a temperature-sensitive mutant of the SV40 virus target T-gene. This Immortopericyte (IMP) conditional cell line is stable for long periods of time and, at 33°C in the presence of interferon gamma, does not differentiate. Under these conditions IMPs are alpha muscle actin-negative and exhibit a pluripotent phenotype, but can be induced to differentiate along both mesenchymal and neuronal lineages at 37°C. Alternatively, differentiation of wild type pericytes and IMPs can be induced directly from capillaries in culture. Finally, the addition of endothelial cells to purified IMP cultures augments their rate of self-renewal and differentiation, possibly in a cell-to-cell contact dependent manner.

Integrated genomic analysis of nodular tissue in macronodular adrenocortical hyperplasia: progression of tumorigenesis in a disorder associated with multiple benign lesions

CONTEXT

Massive macronodular adrenocortical disease or ACTH-independent macronodular adrenal hyperplasia (AIMAH) is a clinically and genetically heterogeneous disorder.

OBJECTIVE AND DESIGN

Whole-genome expression profiling and oligonucleotide array comparative genomic hybridization changes were analyzed in samples of different nodules from the same patients with AIMAH. Quantitative RT-PCR and staining were employed to validate the mRNA array data.

RESULTS

Chromosomal gains were more frequent in larger nodules when compared with smaller nodules from the same patients. Among the 50 most overexpressed genes, 50% had a chromosomal locus that was amplified in the comparative genomic hybridization data. Although the list of most over- and underexpressed genes was similar between the nodules of different size, the gene set enrichment analysis identified different pathways associated with AIMAH that corresponded to the size; the smaller nodules were mainly enriched for metabolic pathways, whereas p53 signaling and cancer genes were enriched in larger nodules. Confirmatory studies demonstrated that BCL2, E2F1, EGF, c-KIT, MYB, PRKCA, and CTNNB1 were overexpressed in the larger nodules at messenger and/or protein levels. Chromosomal enrichment analysis showed that chromosomes 20q13 and 14q23 might be involved in progression of AIMAH from smaller to larger tumors.

CONCLUSION

Integrated transcriptomic and genomic data for AIMAH provides supporting evidence to the hypothesis that larger adrenal lesions, in the context of this chronic, polyclonal hyperplasia, accumulate an increased number of genomic and, subsequently, transcript abnormalities. The latter shows that the disease appears to start with mainly tissue metabolic derangements, as suggested by the study of the smaller nodules, but larger lesions showed aberrant expression of oncogenic pathways.

Multilineage stem cells in the adult: a perivascular legacy?

Mesenchymal stem cells proliferate extensively in cultures of unselected, total cell isolates from multiple fetal and adult organs. Perivascular cells, principally pericytes surrounding capillaries and microvessels, but also adventitial cells located around larger arteries and veins, have been recently identified as possible originators of mesenchymal stem cells, first by phenotypic analogies and eventually following stringent cell sorting. While it is clear that purified perivascular cells exhibit multiple mesodermal developmental potentials and become indistinguishable from conventionally derived mesenchymal stem cells after in vitro culture, the possible roles played by these blood vessel-bound cells in organogenesis and adult tissue repair remain elusive. Unsolved questions regarding the identity of mesenchymal stem cells have not compromised the consideration of these cells as outstanding candidates for cell therapies. Better knowledge of the lineage affiliation, tissue distribution and molecular identity of mesenchymal stem cells will contribute to the development of more efficient, safer therapeutic cells.

Nicotinic acetylcholine receptor α1 promotes calpain-1 activation and macrophage inflammation in hypercholesterolemic nephropathy

The nicotinic acetylcholine receptor α1 (nAChRα1) was investigated as a potential proinflammatory molecule in the kidney, given a recent report that it is an alternative urokinase plasminogen activator (uPA) receptor, in addition to the classical receptor uPAR. Two animal models and in vitro monocyte studies were involved: (1) In an ApoE(-/-) mouse model of chronic kidney disease, glomerular-resident cells and monocytes/macrophages were identified as the primary cell types that express nAChRα1 during hypercholesterolemia/uninephrectomy-induced nephropathy. Silencing of the nAChRα1 gene for 4 months (6 months on Western diet) prevented the increases in renal monocyte chemoattractant protein-1 and osteopontin expression levels and F4/80+ macrophage infiltration compared with the nonsilenced mice. These changes were associated with significantly reduced transforming growth factor-β1 mRNA (50% decrease) and α smooth muscle actin-positive (αSMA+) myofibroblasts (90% decrease), better glomerular and tubular basement membranes (GBM/TBM) preservation (threefold less disintegration), and better renal function preservation (serum creatinine 40% lower) in the nAChRα1-silenced mice. The nAChRα1 silencing was also associated with significantly reduced renal tissue calcium deposition (78% decrease) and calpain-1 (but not calpain-2) activation (70% decrease). (2) The nAChRα1 was expressed in vitro by mouse monocyte cell line WEHI-274.1. The silencing of nAChRα1 significantly reduced both calpain-1 and -2 activities, and reduced the degradation of the calpain substrate talin. (3) To further explore the role of calpain-1 activity in hypercholesterolemic nephropathy, disease severities were compared in CAST(-/-)ApoE(-/-) (calpain overactive) mice and ApoE(-/-) mice fed with Western diet for 10 months (n=12). Macrophages were the main cell type of renal calpain-1 production in the model. The number of renal F4/80+ macrophages was 10-fold higher in the CAST(-/-)ApoE(-/-) mice (P<0.05), and was associated with a significantly higher level of αSMA+ cells, increased GBM/TBM destruction, and higher serum creatinine levels. Our studies suggest that the receptor nAChRα1 is an important regulator of calpain-1 activation and inflammation in the chronic hypercholesterolemic nephropathy. This new proinflammatory pathway may also be relevant to other disorders beyond hyperlipidemic nephropathy.

Emerging roles of the host defense peptide LL-37 in human cancer and its potential therapeutic applications

Human cathelicidin LL-37, a host defense peptide derived from leukocytes and epithelial cells, plays a crucial role in innate and adaptive immunity. Not only does LL-37 eliminate pathogenic microbes directly but also modulates host immune responses. Emerging evidence from tumor biology studies indicates that LL-37 plays a prominent and complex role in carcinogenesis. Although overexpression of LL-37 has been implicated in the development or progression of many human malignancies, including breast, ovarian and lung cancers, LL-37 suppresses tumorigenesis in gastric cancer. These data are beginning to unveil the intricate and contradictory functions of LL-37. The reasons for the tissue-specific function of LL-37 in carcinogenesis remain to be elucidated. Here, we review the relationship between LL-37, its fragments and cancer progression as well as discuss the potential therapeutic implications of targeting this peptide.

Basement membrane components are key players in specialized extracellular matrices

More than three decades ago, basement membranes (BMs) were described as membrane-like structures capable of isolating a cell from and connecting a cell to its environment. Since this time, it has been revealed that BMs are specialized extracellular matrices (sECMs) with unique components that support important functions including differentiation, proliferation, migration, and chemotaxis of cells during development. The composition of these sECM is as unique as the tissues to which they are localized, opening the possibility that such matrices can fulfill distinct functions. Changes in BM composition play significant roles in facilitating the development of various diseases. Furthermore, tissues have to provide sECM for their stem cells during development and for their adult life. Here, we briefly review the latest research on these unique sECM and their components with a special emphasis on embryonic and adult stem cells and their niches.

Quiescence and activation of stem and precursor cell populations in the subependymal zone of the mammalian brain are associated with distinct cellular and extracellular matrix signals

The subependymal zone (SEZ) of the lateral ventricles is one of the areas of the adult brain where new neurons are continuously generated from neural stem cells (NSCs), via rapidly dividing precursors. This neurogenic niche is a complex cellular and extracellular microenvironment, highly vascularized compared to non-neurogenic periventricular areas, within which NSCs and precursors exhibit distinct behavior. Here, we investigate the possible mechanisms by which extracellular matrix molecules and their receptors might regulate this differential behavior. We show that NSCs and precursors proceed through mitosis in the same domains within the SEZ of adult male mice--albeit with NSCs nearer ependymal cells--and that distance from the ventricle is a stronger limiting factor for neurogenic activity than distance from blood vessels. Furthermore, we show that NSCs and precursors are embedded in a laminin-rich extracellular matrix, to which they can both contribute. Importantly, they express differential levels of extracellular matrix receptors, with NSCs expressing low levels of alpha6beta1 integrin, syndecan-1, and lutheran, and in vivo blocking of beta1 integrin selectively induced the proliferation and ectopic migration of precursors. Finally, when NSCs are activated to reconstitute the niche after depletion of precursors, expression of laminin receptors is upregulated. These results indicate that the distinct behavior of adult NSCs and precursors is not necessarily regulated via exposure to differential extracellular signals, but rather via intrinsic regulation of their interaction with their microenvironment.

Morphological and proteomic analysis of early stage of osteoblast differentiation in osteoblastic progenitor cells

Bone remodeling relies on a dynamic balance between bone formation and resorption, mediated by osteoblasts and osteoclasts, respectively. Under certain stimuli, osteoprogenitor cells may differentiate into premature osteoblasts and further into mature osteoblasts. This process is marked by increased alkaline phosphatase (ALP) activity and mineralized nodule formation. In this study, we induced osteoblast differentiation in mouse osteoprogenitor MC3T3-E1 cells and divided the process into three stages. In the first stage (day 3), the MC3T3-E1 cell under osteoblast differentiation did not express ALP or deposit a mineralized nodule. In the second stage, the MC3T3-E1 cell expressed ALP but did not form a mineralized nodule. In the third stage, the MC3T3-E1 cell had ALP activity and formed mineralized nodules. In the present study, we focused on morphological and proteomic changes of MC3T3-E1 cells in the early stage of osteoblast differentiation - a period when premature osteoblasts transform into mature osteoblasts. We found that mean cell area and mean stress fiber density were increased in this stage due to enhanced cell spreading and decreased cell proliferation. We further analyzed the proteins in the signaling pathway of regulation of the cytoskeleton using a proteomic approach and found upregulation of IQGAP1, gelsolin, moesin, radixin, and Cfl1. After analyzing the focal adhesion signaling pathway, we found the upregulation of FLNA, LAMA1, LAMA5, COL1A1, COL3A1, COL4A6, and COL5A2 as well as the downregulation of COL4A1, COL4A2, and COL4A4. In conclusion, the signaling pathway of regulation of the cytoskeleton and focal adhesion play critical roles in regulating cell spreading and actin skeleton formation in the early stage of osteoblast differentiation.