Platelet-derived growth factor-beta receptor activation is essential for fibroblast and pericyte recruitment during cutaneous wound healing

Endothelial smoothened-dependent hedgehog signaling is not required for sonic hedgehog induced angiogenesis or ischemic tissue repair

Sonic Hedgehog (Shh) signaling induces neovascularization and angiogenesis. It is not known whether the hedgehog signaling pathway in endothelial cells is essential to angiogenesis. Smoothened (Smo) transduces hedgehog signaling across the cell membrane. This study assessed whether endothelial Smoothened-dependent Shh signaling is required for Shh-mediated angiogenesis and ischemic tissue repair. Endothelial-specific smoothened knockout mice, eSmo^Null were created using Cre-lox recombination system. eSmo^Null mice had no observable phenotype at baseline and showed normal cardiac function. Smoothened in CD31+ cells isolated from eSmo^Null hearts was significantly reduced compared to CD31+ cells from eSmo^WT littermate control hearts. Fluorescence immunostaining of eSmo^Null heart sections showed Smo expression in endothelial cells was abolished. The hind-limb ischemia (HLI) model was used to assess the response to ischemic injury. Perfusion ratio, limb motor function, and limb necrosis were not significantly different after HLI between eSmo^Null mice and eSmo^WT. Capillary densities in the ischemic limb in eSmo^Null mice were also similar to eSmo^WT at 4 weeks after HLI. Next, response to exogenous Shh was assessed in the corneal angiogenesis model. There was no significant difference in corneal angiogenesis induced by administration of Shh pellets between eSmo^WT and eSmo^Null mice. Furthermore, in vitro experiments demonstrated that direct Shh had limited effects on endothelial cell proliferation and migration. However, conditioned media from Shh-treated fibroblasts had a more potent effect on endothelial cell proliferation and migration than non-treated conditioned media. Furthermore, Shh treatment of fibroblasts dramatically stimulated angiogenic growth factor expression, including PDGF-B, VEGF-A, HGF and IGF. PDGF-B was the most upregulated and may contribute to the large neo-vessels associated with Shh-induced angiogenesis. Taken together, these data demonstrate that Shh signaling via Smoothened in endothelial cells is not required for angiogenesis and ischemic tissue repair. Shh signaling via stromal cells likely mediates its angiogenic effects.

Role and regulation of growth plate vascularization during coupling with osteogenesis in tibial dyschondroplasia of chickens

Tibial dyschondroplasia (TD) is the most-prevalent leg disorder in fast-growing chickens; it is intractable and characterized by abnormal endochondral bone formation of proximal tibial growth-plates (TGPs). Previous studies have shown that bone is a highly vascularized tissue dependent on the coordinated coupling between angiogenesis and osteogenesis, but the underlying mechanisms of bone formation and bone remodeling are poorly defined in TD chickens. Here, we observed that inhibition of vasculogenesis and angiogenesis remarkably impaired vascular invasion in the hypertrophic chondrocyte zone of the TGPs, resulting in the massive death of chondrocytes due to a shortage of blood vessels and nutrients. Moreover, the balance of the OPG (osteoprotegerin)/RANKL (receptor activator of nuclear factor-kB ligand) system is also severely disrupted during the osteogenesis process while coupling with angiogenesis, both of which eventually lead to abnormal endochondral bone formation in TD chickens. Thus, the process of vascular formation in endochondral bone appears to initiate the pathological changes in TD, and improvement of this process during coupling with osteogenesis may be a potential therapeutic approach to treat this intractable disease.

Platelet-derived growth factor receptor beta identifies mesenchymal stem cells with enhanced engraftment to tissue injury and pro-angiogenic property

Mesenchymal stem cells (MSCs) are heterogeneous likely consisting of subpopulations with various therapeutic potentials. Here we attempted to acquire a subset of MSCs with enhanced effect in wound healing. We found that human placental MSCs expressing platelet-derived growth factor (PDGF) receptor (PDGFR)-β exhibited greater proliferation rates and generated more colony-forming unit-fibroblast (CFU-F), compared to PDGFR-β- MSCs. Notably, PDGFR-β+ MSCs expressed higher levels of pro-angiogenic factors such as Ang1, Ang2, VEGF, bFGF and PDGF. When 106 GFP-expressing MSCs were topically applied into excisional wounds in mice, PDGFR-β+ MSCs actively incorporated into the wound tissue, resulting in enhanced engraftment (3.92 ± 0.31 × 105 remained in wound by 7 days) and accelerated wound closure; meanwhile, PDGFR-β- MSCs tended to remain on the top of the wound bed with significantly fewer cells (2.46 ± 0.26 × 105) engrafted into the wound, suggesting enhanced chemotactic migration and engraftment of PDGFR-β+ MSCs into the wound. Real-Time PCR and immunostain analyses revealed that the expression of PDGF-B was upregulated after wounding; transwell migration assay showed that PDGFR-β+ MSCs migrated eightfold more than PDGFR-β- MSCs toward PDGF-BB. Intriguingly, PDGFR-β+ MSC-treated wounds showed significantly enhanced angiogenesis compared to PDGFR-β- MSC- or vehicle-treated wounds. Thus, our results indicate that PDGFR-β identifies a subset of MSCs with enhanced chemotactic migration to wound injury and effect in promoting angiogenesis and wound healing, implying a greater therapeutic potential for certain diseases.

Pericytes in Tissue Engineering

Pericytes have crucial roles in blood-brain barrier function, blood vessel function/stability, angiogenesis, endothelial cell proliferation/differentiation, wound healing, and hematopoietic stem cells maintenance. They can be isolated from fetal and adult tissues and have multipotential differentiation capacity as mesenchymal stem cells (MSCs). All of these properties make pericytes as preferred cells in the field of tissue engineering. Current developments have shown that tissue-engineered three-dimensional (3D) systems including multiple cell layers (or types) and a supporting biological matrix represent the in vivo environment better than those monolayers on plastic dishes. Tissue-engineered models are also more ethical and cheaper systems than animal models. This chapter describes the role of pericytes in tissue engineering for regenerative medicine.

4-Hydroxybenzaldehyde accelerates acute wound healing through activation of focal adhesion signalling in keratinocytes

4-Hydroxybenzaldehyde (4-HBA) is a naturally occurring benzaldehyde and the major active constituent of Gastrodia elata. While recent studies have demonstrated metabolic effects of 4-HBA, little is known about the physiological role of 4-HBA in acute wound healing. Here, we investigated the effects and mechanisms of 4-HBA on acute wound healing. Using an in vitro approach, we found that 4-HBA significantly promoted keratinocyte cell migration and invasion by increasing focal adhesion kinase and Src activity. In addition, 4-HBA treatment also promoted wound healing and re-epithelialization in an in vivo excision wound animal model. Combination treatment with 4-HBA and platelet-derived growth factor subunit B homodimer showed synergistic effects in promoting wound healing. Taken together, our results demonstrated that treatment with 4-HBA promoted keratinocyte migration and wound healing in mouse skin through the Src/mitogen-activated protein kinase pathway. Therefore, 4-HBA could be a candidate therapeutic agent with the potential to promote acute wound healing.

Therapeutic efficiency of platelet gel for the treatment of oral ulcers related to chronic graft versus host disease after allogeneic haematopoietic stem cell transplantation

BACKGROUND

Platelet (PLT) gel has been successfully used in tissue regeneration of diabetic and surgical wounds through the releasing of growth factors such as basic fibroblast and PLT-derived growth factors. Based on this background, our previous clinical trial have assessed the feasibility and efficacy of PLT gel for the treatment of muco-cutaneous lesions related to graft versus host disease (GvHD) after allogeneic haematopoietic stem cell transplantion (HSCT). The promising results reported in a small series of 6 patients, of whom 1 with oral ulcers, represent the rationale of the present study.

MATERIALS AND METHODS

The aim of this study was to verify the efficacy and safety of PLT gel for treating oral ulcers due to chronic GvHD. Allogeneic hemocomponents were used to obtain PLT gel with an automated system for the on-site preparation and application of patient (autologous) or healthy blood donor (allogeneic)-derived fibrin sealant or PLT-rich fibrin (Vivostat system, Vivostat A/S). Ten patients with multiple oral lesions related to chronic GvHD underwent allogeneic PLT gel as local therapy alone or in combination with systemic therapy in half of the cases.

RESULTS

After the second PLT gel application, all patients resumed the feeding and a significant improvement of the oral pain was observed. After a median of five PLT gel applications (range, 2-15), 7 out of 10 patients showed a complete response. No side effects were documented.

CONCLUSION

These data confirm that the PLT gel may be used as a safe and effective tool, alone or in combination with systemic therapy, for the treatment of mucosal lesions of mouth related to cGvHD.

Diabetes and Wound Angiogenesis

Diabetes Mellitus Type II (DM2) is a growing international health concern with no end in sight. Complications of DM2 involve a myriad of comorbidities including the serious complications of poor wound healing, chronic ulceration, and resultant limb amputation. In skin wound healing, which has definite, orderly phases, diabetes leads to improper function at all stages. While the etiology of chronic, non-healing diabetic wounds is multi-faceted, the progression to a non-healing phenotype is closely linked to poor vascular networks. This review focuses on diabetic wound healing, paying special attention to the aberrations that have been described in the proliferative, remodeling, and maturation phases of wound angiogenesis. Additionally, this review considers therapeutics that may offer promise to better wound healing outcomes.

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.

Concise Review: Wharton's Jelly: The Rich, but Enigmatic, Source of Mesenchymal Stromal Cells

The umbilical cord has become an increasingly used source of mesenchymal stromal cells for preclinical and, more recently, clinical studies. Despite the increased activity, several aspects of this cell population have been under‐appreciated. Key issues are that consensus on the anatomical structures within the cord is lacking, and potentially different populations are identified as arising from a single source. To help address these points, we propose a histologically based nomenclature for cord structures and provide an analysis of their developmental origins and composition. Methods of cell isolation from Wharton's jelly are discussed and the immunophenotypic and clonal characteristics of the cells are evaluated. The perivascular origin of the cells is also addressed. Finally, clinical trials with umbilical cord cells are briefly reviewed. Interpreting the outcomes of the many clinical studies that have been undertaken with mesenchymal stromal cells from different tissue sources has been challenging, for many reasons. It is, therefore, particularly important that as umbilical cord cells are increasingly deployed therapeutically, we strive to better understand the derivation and functional characteristics of the cells from this important tissue source. Stem Cells Translational Medicine2017;6:1620–1630

Pericytes: The Role of Multipotent Stem Cells in Vascular Maintenance and Regenerative Medicine

Blood vessels consist of an inner endothelial cell layer lining the vessel wall and perivascular pericytes, also known as mural cells, which envelop the vascular tube surface. Pericytes have recently been recognized for their central role in blood vessel formation. Pericytes are multipotent cells that are heterogeneous in their origin, function, morphology and surface markers. Similar to other types of stem cells, pericytes act as a repair system in response to injury by maintaining the structural integrity of blood vessels. Several studies have shown that blood vessels lacking pericytes become hyperdilated and haemorrhagic, leading to vascular complications ranging from diabetic retinopathy to embryonic death. The role of pericytes is not restricted to the formation and development of the vasculature: they have been shown to possess stem cell-like characteristics and may differentiate into cell types from different lineages. Recent discoveries regarding the contribution of pericytes to tumour metastasis and the maintenance of tumour vascular supply and angiogenesis have led researchers to propose targeting pericytes with anti-angiogenic therapies. In this review, we will examine the different physiological roles of pericytes, their differentiation potential, and how they interact with surrounding cells to ensure the integrity of blood vessel formation and maintenance.

The role of myofibroblasts in wound healing

The importance of proper skin wound healing becomes evident when our body's repair mechanisms fail, leading to either non-healing (chronic) wounds or excessive repair (fibrosis). Chronic wounds are a tremendous burden for patients and global healthcare systems and are on the rise due to their increasing incidence with age and diabetes. Curiously, these same risk factors also sign responsible for the development of hypertrophic scarring and organ fibrosis. Activated repair cells - myofibroblasts - are the main producers and organizers of extracellular matrix which is needed to restore tissue integrity after injury. Too many myofibroblasts working for too long cause tissue contractures that ultimately obstruct organ function. Insufficient myofibroblast activation and activities, in turn, prevents normal wound healing. This short review puts a spotlight on the myofibroblast for those who seek therapeutic targets in the context of dysregulated tissue repair. "Keep your myofibroblasts in balance" is the message.

Growth factor pathways in hypertrophic scars: Molecular pathogenesis and therapeutic implications

Hypertrophic scars represent the most common complication of skin injury and are caused by excessive cutaneous wound healing characterized by hypervascularity and pathological deposition of extracellular matrix (ECM) components. To date, the optimal and specific treatment methods for hypertrophic scars have not been available in the clinic. Current paradigm has established fibroblasts and myofibroblasts as pivotal effector cells in the pathophysiology of wound healing. Their biological properties including origin, proliferation, migration, contraction and ECM regulation have profound impacts on the progression and regression of hypertrophic scars. These complex processes are executed and modulated by a signaling network involving a number of growth factors and cytokines. Of particular importance is transforming growth factor-β, platelet-derived growth factor, connective tissue growth factor, epidermal growth factor, and vascular endothelial growth factor. This review article briefly describes the biological functions of fibroblasts and myofibroblasts during hypertrophic scars, and thereafter examines the up-to-date molecular knowledge on the roles of key growth factor pathways in the pathophysiology of hypertrophic scars. Importantly, the therapeutic implications and future challenges of these molecular discoveries are critically discussed in the hope of advancing therapeutic approaches to limit pathological scar formation.

Mesenchymal stem cell subpopulations: phenotype, property and therapeutic potential

Mesenchymal stem cells (MSC) are capable of differentiating into cells of multiple cell lineages and have potent paracrine effects. Due to their easy preparation and low immunogenicity, MSC have emerged as an extremely promising therapeutic agent in regenerative medicine for diverse diseases. However, MSC are heterogeneous with respect to phenotype and function in current isolation and cultivation regimes, which often lead to incomparable experimental results. In addition, there may be specific stem cell subpopulations with definite differentiation capacity toward certain lineages in addition to stem cells with multi-differentiation potential. Recent studies have identified several subsets of MSC which exhibit distinct features and biological activities, and enhanced therapeutic potentials for certain diseases. In this review, we give an overview of these subsets for their phenotypic, biological and functional properties.

Pericyte-targeting drug delivery and tissue engineering

Pericytes are contractile mural cells that wrap around the endothelial cells of capillaries and venules. Depending on the triggers by cellular signals, pericytes have specific functionality in tumor microenvironments, properties of potent stem cells, and plasticity in cellular pathology. These features of pericytes can be activated for the promotion or reduction of angiogenesis. Frontier studies have exploited pericyte-targeting drug delivery, using pericyte-specific peptides, small molecules, and DNA in tumor therapy. Moreover, the communication between pericytes and endothelial cells has been applied to the induction of vessel neoformation in tissue engineering. Pericytes may prove to be a novel target for tumor therapy and tissue engineering. The present paper specifically reviews pericyte-specific drug delivery and tissue engineering, allowing insight into the emerging research targeting pericytes.

Effects of the eukaryotic initiation factor 6 gene on expression levels of inflammatory mediators in M2 macrophages during scar repair

The aim of the present study was to evaluate the effects of the eukaryotic initiation factor 6 (eIF6) gene on the secretion of M2 macrophage fibrosis‑associated factors and the expression levels of key proteases during scar repair. Male eIF6 wild‑type (eIF6+/+) and knockout (eIF6+/‑) C57BL/6 mice were intraperitoneally lavaged to obtain macrophages, which were induced to the M2 type using interleukin‑4. Differences between the gene expression profiles of these macrophages were compared with gene microarrays, and the results were validated using reverse transcription-quantitative polymerase chain reaction analysis and ELISA. Compared with the eIF6+/‑ mice, the mRNA and protein expression levels of vascular endothelial growth factor (VEGF) and tissue inhibitor of metalloproteinase‑2 (TIMP‑2) in the M2 macrophages of the eIF6+/+ mice were significantly downregulated (P<0.05), whereas the mRNA and protein expression levels of matrix metalloproteinase‑2 (MMP‑2) were significantly upregulated (P<0.05). Therefore, the results indicated that eIF6 alleviated cicatrization, possibly by inhibiting the generation of VEGF, in order to prevent overgrowth of blood vessels and granulation tissues, and to regulate the MMP-2/TIMP-2 ratio to balance the degradation and deposition of the extracellular matrix.

Pericytes: Properties, Functions and Applications in Tissue Engineering

Mesenchymal stem cells (MSCs) are one of the most studied adult stem cells and in recent years. They have become attractive agents/cell source for cellular therapy and regenerative medicine applications. During investigations about their origin, researchers hypothesized that perivascular regions are the common anatomical regions where MSCs come from and perivascular cells like pericytes (PCs) (Rouget cells, mural cells) are in vivo counterparts of MSCs. Beside capillaries and microvessels as their most common locations, PCs are also found in large vessels (arteries and veins). They can be isolated from several tissues and organs particularly from retina and brain. There are different approaches about their isolation, characterization and culture but there has been no common protocol yet because of the lack of defined PC-specific marker. They make special contact with endothelial cells in the basement membrane and have very important functions in several tissues and organs. They participate in vascular development, stabilization, maturation, and remodeling, blood pressure control, endothelial cell proliferation and differentiation, contractility of vascular smooth muscle cells, wound healing, vasculogenesis and angiogenesis, long-term maintenance of hematopoietic stem cells in bone marrow niche. Their multipotential differentiation capacity and participation in many events in the body make PCs preferred cells in tissue engineering applications including 3D blood-brain barrier models, skeletal muscle constructs, bone tissue engineering and tissue-engineered vascular grafts.

Distinct protein signature of hypertension-induced damage in the renal proteome of the two-kidney, one-clip rat model

BACKGROUND

Hypertensive nephrosclerosis is one of the most frequent causes of chronic kidney failure. Proteome analysis potentially improves the pathophysiological understanding and diagnostic precision of this disorder. In the present exploratory study, we investigated experimental nephrosclerosis in the two-kidney, one-clip (2K1C) hypertensive rat model.

METHODS

The renal cortex proteome from juxtamedullary cortex and outer cortex of 2K1C male Wistar-Hannover rats (n = 4) was compared with the sham-operated controls (n = 6), using mass spectrometry-based quantitative proteomics. We combined a high abundant plasma protein depletion strategy with an extended liquid chromatographic gradient to improve peptide and protein identification. Immunohistology was used for independent confirmation of abundance.

RESULTS

We identified 1724 proteins, of which 1434 were quantified with at least two unique peptides. Comparative proteomics revealed 608 proteins, including the platelet-derived growth factor receptor-β signalling pathway, with different abundances between the non-clipped kidney of hypertensive 2K1C rats and the corresponding kidney of the normotensive controls (P < 0.05, absolute fold change ≥1.5). Among the most significantly altered proteins in the whole cortex were periostin, transgelin, and creatine kinase B-type. Relative abundance of periostin alone allowed clear classification of 2K1C and controls. Enrichment of periostin in 2K1C rats was verified by immunohistology, showing positivity especially around the fibrotic vessels.

CONCLUSION

The proteome is altered in hypertension-induced kidney damage. We propose periostin, especially in combination with transgelin and creatine kinase B-type, as possible proteomic classifier to distinguish hypertensive nephrosclerosis from the normal tissue. This classifier needs to be further validated with respect to early diagnosis of fibrosis, prognosis, and its potential as a novel molecular target for pharmacological interventions.

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.

PDGFRα plays a crucial role in connective tissue remodeling

Platelet derived growth factor (PDGF) plays a pivotal role in the remodeling of connective tissues. Emerging data indicate the distinctive role of PDGF receptor-α (PDGFRα) in this process. In the present study, the Pdgfra gene was systemically inactivated in adult mouse (α-KO mouse), and the role of PDGFRα was examined in the subcutaneously implanted sponge matrices. PDGFRα expressed in the fibroblasts of Pdgfra-preserving control mice (Flox mice), was significantly reduced in the sponges in α-KO mice. Neovascularized areas were largely suppressed in the α-KO mice than in the Flox mice, whereas the other parameters related to the blood vessels and endothelial cells were similar. The deposition of collagen and fibronectin and the expression of collagen 1a1 and 3a1 genes were significantly reduced in α-KO mice. There was a significantly decrease in the number and dividing fibroblasts in the α-KO mice, and those of macrophages were similar between the two genotypes. Hepatocyte growth factor (Hgf) gene expression was suppressed in Pdgfra-inactivated fibroblasts and connective tissue. The findings implicate the role of PDGFRα-dependent ECM and HGF production in fibroblasts that promotes the remodeling of connective tissue and suggest that PDGFRα may be a relevant target to regulate connective tissue remodeling.

Hyaluronan's Role in Fibrosis: A Pathogenic Factor or a Passive Player?

Fibrosis is a debilitating condition that can lead to impairment of the affected organ's function. Excessive deposition of extracellular matrix (ECM) molecules is characteristic of most fibrotic tissues. Fibroblasts activated by cytokines or growth factors differentiate into myofibroblasts that drive fibrosis by depositing ECM molecules, such as collagen, fibronectin, and connective tissue growth factor. Transforming growth factor-β (TGF-β) is one of the major profibrotic cytokines which promotes fibrosis by signaling abnormal ECM regulation. Hyaluronan (HA) is a major ECM glycosaminoglycan that is regulated by TGF-β and whose role in fibrosis is emerging. Aside from its role as a hydrating, space filling polymer, HA regulates different cellular functions and is known to have a role in wound healing and inflammation. Importantly, HA deposition is increased in multiple fibrotic diseases. In this review we highlight studies that link HA to fibrosis and discuss what is known about the role of HA, its receptors, and its anabolic and catabolic enzymes in different fibrotic diseases.

Mesenchymal stromal cells for sphincter regeneration

Stress urinary incontinence (SUI), defined as the involuntary loss of considerable amounts of urine during increased abdominal pressure (exertion, effort, sneezing, coughing, etc.), is a severe problem to the individuals affected and a significant medical, social and economic challenge. SUI is associated with pelvic floor debility, absence of detrusor contraction, or a loss of control over the sphincter muscle apparatus. The pathology includes an increasing loss of muscle cells, replacement of muscular tissue with fibrous tissue, and general aging associated processes of the sphincter complex. When current therapies fail to cure or improve SUI, application of regeneration-competent cells may be an alternative therapeutic option. Here we discuss different aspects of the biology of mesenchymal stromal cells, which are relevant to their clinical applications and for regenerating the sphincter complex. However, there are reports in favor of and against cell-based therapies. We therefore summarize the potential and the risks of cell-based therapies for the treatment of SUI.

Involvement of platelet-derived growth factor receptor β in fibrosis through extracellular matrix protein production after ischemic stroke

Fibrosis is concomitant with repair processes following injuries in the central nervous system (CNS). Pericytes are considered as an origin of fibrosis-forming cells in the CNS. Here, we examined whether platelet-derived growth factor receptor β (PDGFRβ), a well-known indispensable molecule for migration, proliferation, and survival of pericytes, was involved in the production of extracellular matrix proteins, fibronectin and collagen type I, which is crucial for fibrosis after ischemic stroke. Immunohistochemistry demonstrated induction of PDGFRβ expression in vascular cells of peri-infarct areas at 3-7days in a mouse stroke model. The PDGFRβ-expressing cells extended from peri-infarct areas toward the ischemic core after day 7 while expressing fibronectin and collagen type I in the infarct areas. In contrast, desmin and α-smooth muscle actin, markers of pericytes, were only expressed in vascular cells. In PDGFRβ heterozygous knockout mice, the expression of fibronectin and collagen type I was attenuated at both mRNA and protein levels with an enlargement of the infarct volume after ischemic stroke compared with that in wild-type littermates. In cultured brain pericytes, the expression of PDGF-B, PDGFRβ, fibronectin, and collagen type I, but not desmin, was significantly increased by serum depletion (SD). The SD-induced upregulation of fibronectin and collagen type I was suppressed by SU11652, an inhibitor of PDGFRβ, while PDGF-B further increased the SD-induced upregulation. In conclusion, the expression level of PDGFRβ may be a crucial determinant of fibrosis after ischemic stroke. Moreover, PDGFRβ signaling participates in the production of fibronectin and collagen type I after ischemic stroke.

Fibroblasts and myofibroblasts in wound healing

(Myo)fibroblasts are key players for maintaining skin homeostasis and for orchestrating physiological tissue repair. (Myo)fibroblasts are embedded in a sophisticated extracellular matrix (ECM) that they secrete, and a complex and interactive dialogue exists between (myo)fibroblasts and their microenvironment. In addition to the secretion of the ECM, (myo)fibroblasts, by secreting matrix metalloproteinases and tissue inhibitors of metalloproteinases, are able to remodel this ECM. (Myo)fibroblasts and their microenvironment form an evolving network during tissue repair, with reciprocal actions leading to cell differentiation, proliferation, quiescence, or apoptosis, and actions on growth factor bioavailability by binding, sequestration, and activation. In addition, the (myo)fibroblast phenotype is regulated by mechanical stresses to which they are subjected and thus by mechanical signaling. In pathological situations (excessive scarring or fibrosis), or during aging, this dialogue between the (myo)fibroblasts and their microenvironment may be altered or disrupted, leading to repair defects or to injuries with damaged and/or cosmetic skin alterations such as wrinkle development. The intimate dialogue between the (myo)fibroblasts and their microenvironment therefore represents a fascinating domain that must be better understood in order not only to characterize new therapeutic targets and drugs able to prevent or treat pathological developments but also to interfere with skin alterations observed during normal aging or premature aging induced by a deleterious environment.

MFG-E8 regulates angiogenesis in cutaneous wound healing

Our research group recently demonstrated that pericytes are major sources of the secreted glycoprotein and integrin ligand lactadherin (MFG-E8) in B16 melanoma tumors, and that MFG-E8 promotes angiogenesis via enhanced PDGF-PDGFRβ signaling mediated by integrin-growth factor receptor crosstalk. However, sources of MFG-E8 and its possible roles in skin physiology are not well characterized. The objective of this study was to characterize the involvement of MFG-E8 in skin wound healing. In the dermis of normal murine and human skin, accumulations of MFG-E8 were found around CD31(+) blood vessels, and MFG-E8 colocalized with PDGFRβ(+), αSMA(+), and NG2(+) pericytes. MFG-E8 protein and mRNA levels were elevated in the dermis during full-thickness wound healing in mice. MFG-E8 was diffusely present in granulation tissue and was localized around blood vessels. Wound healing was delayed in MFG-E8 knockout mice, compared with the wild type, and myofibroblast and vessel numbers in wound areas were significantly reduced in knockout mice. Inhibition of MFG-E8 production with siRNA attenuated the formation of capillary-like structures in vitro. Expression of MFG-E8 in fibrous human granulation tissue with scant blood vessels was less than that in granulation tissue with many blood vessels. These findings suggest that MFG-E8 promotes cutaneous wound healing by enhancing angiogenesis.

Image analysis of platelet derived growth factor receptor-beta (PDGFRβ) expression to determine the grade and dynamics of myelofibrosis in bone marrow biopsy samples

BACKGROUND

Myelofibrosis (MF) is characterized by accumulation of stromal cells and extracellular matrix. Progression of fibrosis is an important clinical issue and monitoring is required for new therapeutic approaches. Currently, the quantification is based on semiquantitative evaluation of reticulin silver stained slides. We recently reported that platelet derived growth factor receptor beta (PDGFRβ) expression in fibroblasts is a useful marker of stromal activation. PDGFRβ expression based scores represent significant differences in different MF grade which provides optimal source of quantification. In this study, slide-based measurements were performed to support correlations of PDGFRβ expression with MF grade.

METHODS

Scanned image tiles from 79 bone marrow samples (BM) with different MF grades were evaluated for PDGFRβ-related IHC parameters. Following the determination of immunopositive (brown component) and total area (region of interest) of the BM, PDGFRβ related image parameters were defined and evaluated in comparison with the classical reticulin based grading.

RESULTS

Eight PDGFRβ expression related image parameters showed excellent correlation with the MF grade (correlation coefficient ranging between 0.79 and 0.83) and with PDGFRβ score (0.76-0.87). Despite the significant sample heterogeneity, the parameters showed significant differences between fibrotic and nonfibrotic cases and between mild and advanced fibrosis. Distribution of values within a particular specimen emphasizes the heterogeneity of bone marrow involvement which may cause difficulties in semiquantitative methods.

CONCLUSIONS

Our results clearly demonstrated the correlation between MF and PDGFRβ expression considering all relevant areas in BM samples. This method provides good basis for follow-up comparison of the fibrotic samples.

The role of the extracellular matrix components in cutaneous wound healing

Wound healing is the physiologic response to tissue trauma proceeding as a complex pathway of biochemical reactions and cellular events, secreted growth factors, and cytokines. Extracellular matrix constituents are essential components of the wound repair phenomenon. Firstly, they create a provisional matrix, providing a structural integrity of matrix during each stage of healing process. Secondly, matrix molecules regulate cellular functions, mediate the cell-cell and cell-matrix interactions, and serve as a reservoir and modulator of cytokines and growth factors' action. Currently known mechanisms, by which extracellular matrix components modulate each stage of the process of soft tissue remodeling after injury, have been discussed.

Understanding the origin, activation and regulation of matrix-producing myofibroblasts for treatment of fibrotic disease

Fibrosis and scar formation results from chronic progressive injury in virtually every tissue and affects a growing number of people around the world. Myofibroblasts drive fibrosis, and recent work has demonstrated that mesenchymal cells, including pericytes and perivascular fibroblasts, are their main progenitors. Understanding the cellular mechanisms of pericyte/fibroblast-to-myofibroblast transition, myofibroblast proliferation and the key signalling pathways that regulate these processes is essential to develop novel targeted therapeutics for the growing patient population suffering from solid organ fibrosis. In this review, we summarize the current knowledge about different progenitor cells of myofibroblasts, discuss major pathways that regulate their transdifferentiation and discuss the current status of novel targeted anti-fibrotic therapeutics in development.

Pulsed estrogen therapy prevents post-OVX porcine dura mater microvascular network weakening via a PDGF-BB-dependent mechanism

In postmenopausal women, estrogen (E2) deficiencies are frequently associated with higher risk of intracranial hemorrhage, increased incidence of stroke, cerebral aneurysm, and decline in cognitive abilities. In younger postpartum women and those using oral contraceptives, perturbations in E2 are associated with higher risk of cerebral venous thrombosis. A number of serious intracranial pathologic conditions linked to E2 deficiencies, such as dural sinus thrombosis, dural fistulae, non-parenchymal intracranial hemorrhages, migraines, and spontaneous cerebrospinal fluid leaks, involve the vessels not of the brain itself, but of the outer fibrous membrane of the brain, the dura mater (DM). The pathogenesis of these disorders remains mysterious and how estrogen regulates structural and functional integrity of DM vasculature is largely unknown. Here, we demonstrate that post ovariectomy (OVX) DM vascular remodeling is manifested by microvessel destabilization, capillary rarefaction, increased vascular permeability, and aberrant angio-architecture, and is the result of disrupted E2-regulated PDGF-BB signaling within dura microvasculature. These changes, associated with the reduction in systemic PDGF-BB levels, are not corrected by a flat-dose E2 hormone replacement therapy (HRT), but are largely prevented using HRT schedules mimicking physiological E2 fluctuations. We demonstrate that 1) E2 regulates PDGF-BB production by endothelial cells in a dose-dependent manner and 2) optimization of PDGF-BB levels and induction of robust PDGF-mediated endothelial cell-vascular pericyte interactions require high (estrous) E2 concentrations. We conclude that high (estrous) levels of E2 are important in controlling PDGF-mediated crosstalk between endothelial cells and pericytes, a fundamental mechanism governing microvessel stability and essential for preserving intracranial homeostasis.

Tyrosine kinases inhibition by Imatinib slows progression in chronic anti-thy1 glomerulosclerosis of the rat

Background

Chronic progressive mesangioproliferative nephropathy represents a major cause of end-stage renal disease worldwide. Until now, effective approaches to stop or even slow its progression are limited. We tested the effects of an inhibitor of PDGF receptor, abl and c-kit tyrosine kinases, Imatinib, in a chronic progressive model of mesangioproliferative glomerulosclerosis.

Methods

Anti-thy1 glomerulosclerosis was induced by injection of anti-thy1 antibody into uninephrectomized Wistar rats. One week after disease induction, according to the degree of proteinuria, animals were stratified and assigned to chronic glomerulosclerosis (cGS) and cGS plus Imatinib (10 mg/kg body weight/day). In week 20, renoprotective actions of Imatinib were analyzed by a set of functional, histological and molecular biological parameters.

Results

Untreated cGS rats showed elevation of systolic blood pressure and marked progression in proteinuria, renal fibrosis, cell infiltration, cell proliferation and function lost. Administration of Imatinib went along significantly with lower systolic blood pressure (−10 mmHg) and proteinuria (−33%). Imatinib administration was paralled by significant reductions in tubulointerstitial accumulation of matrix proteins (−44%), collagen I deposition (−86%), expression of TGF-beta1 (−30%), production of fibronectin (−23%), myofibroblast differentiation (−87%), macrophage infiltration (−36%) and cell proliferation (−45%), respectively. In comparison with untreated cGS animals, Imatinib therapy lowered also blood creatinine (−41%) and blood urea concentrations (−36%) and improved creatinine clearance (+25%). Glomerular fibrotic changes were lowered moderately by Imatinib.

Conclusions

Therapy with Imatinib limits the progressive course of chronic anti-thy1 glomerulosclerosis towards tubulointerstitial fibrosis and renal insufficiency. This was paralleled by direct and indirect sign of TGF-β1 and PDGF inhibition. The findings suggest that the pharmacological principal of inhibition of tyrosine kinases with drugs such as Imatinib might serve as approach for limiting progression of human mesangioproliferative glomerulosclerosis.

Serial transplantation and long-term engraftment of intra-arterially delivered clonally derived mesenchymal stem cells to injured bone marrow

It has been hypothesized that mesenchymal stem cells (MSCs) home to sites of injury. Nevertheless, efficient delivery of MSCs to target organs and description of their ultimate fate remain major challenges. We provide evidence that intra-arterially (IA) injected MSCs selectively engraft from the circulation as perivascular cells in the bone marrow (BM) after a localized radiation injury. Luciferase-expressing MSCs, derived from a conditionally immortalized clone (BMC-9) representing a pure population of cells, were arterially delivered into mice irradiated in one leg. Cell distribution was measured by bioluminescent imaging and final destination assessed by luciferase immunolocalization. IA injections resulted in engraftment only in the irradiated leg where cells localize and proliferate abluminal to the BM vasculature, a phenomenon not replicated with intravenous injections or with IA injections of kidney cells harvested from the same donor used for MSCs. Furthermore, MSCs harvested from the engrafted marrow and serially transplanted retain the ability to selectively engraft at sites of injury. This study demonstrates that MSCs can serially engraft at sites of injury from the circulation, that they reside in the perivascular space, and that arterial delivery is more efficient than venous delivery for cell engraftment.

Extracellular matrix synthesis in vascular disease: hypertension, and atherosclerosis

Extracellular matrix (ECM) within the vascular network provides both a structural and regulatory role. The ECM is a dynamic composite of multiple proteins that form structures connecting cells within the network. Blood vessels are distended by blood pressure and, therefore, require ECM components with elasticity yet with enough tensile strength to resist rupture. The ECM is involved in conducting mechanical signals to cells. Most importantly, ECM regulates cellular function through chemical signaling by controlling activation and bioavailability of the growth factors. Cells respond to ECM by remodeling their microenvironment which becomes dysregulated in vascular diseases such hypertension, restenosis and atherosclerosis. This review examines the cellular and ECM components of vessels, with specific emphasis on the regulation of collagen type I and implications in vascular disease.

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.

Platelet derived growth factor receptor-beta (PDGFRβ) expression is limited to activated stromal cells in the bone marrow and shows a strong correlation with the grade of myelofibrosis

Platelet derived growth factor receptor (PDGFR) is a membrane tyrosine-kinase receptor required for fibroblast activation in stromal proliferations. In order to assess the role of PDGFR in myelofibrosis (MF) we determined in 60 bone marrow biopsies the occurrence and distribution of its α and β subunits in normal and fibrotic bone marrow stroma using immunohistochemistry, and compared this with the grade of MF determined by Gömöri's silver impregnation. PDGF receptor subunits were found to be differentially expressed in the marrow parenchyma. PDGFRα expression identified megakaryocytes, endosteal and endothelial cells while PDGFRβ was virtually absent from inter-trabecular spaces in normal marrow. Activated fibroblasts characteristic for MF intensely expressed PDGFRβ but only a moderate increase in PDGFRα expression was seen. Semi-quantitative PDGFRβ immunoreactivity scores correlated well with the grade of MF in the vast majority of the MF cases (Spearman r= 0.83). Altogether, 21/60 (35.0%) cases showed a relative increase of PDGFRβ expression, compared to the MF grade, suggesting that increased stromal PDGFRβ expression occurs early and precedes reticulin and collagen fiber production during fibroblast activation. In conclusion, bone marrow PDGFRβ expression closely correlates with the grade of MF. Increased immunoreactivity for PDGFRβ occurs already in the prefibrotic stage of the disease and might allow a functional classification of the bone marrow stromal reaction.

Not all MSCs can act as pericytes: functional in vitro assays to distinguish pericytes from other mesenchymal stem cells in angiogenesis

Pericytes play a crucial role in angiogenesis and vascular maintenance. They can be readily identified in vivo and isolated as CD146(+)CD34(-) cells from various tissues. Whether these and other markers reliably identify pericytes in vitro is unclear. CD146(+)CD34(-) selected cells exhibit multilineage potential. Thus, their perivascular location might represent a stem cell niche. This has spurred assumptions that not only all pericytes are mesenchymal stromal cells (MSCs), but also that all MSCs can act as pericytes. Considering this hypothesis, we developed functional assays by confronting test cells with endothelial cultures based on matrigel assay, spheroid sprouting, and cord formation. We calibrated these assays first with commercial cell lines [CD146(+)CD34(-) placenta-derived pericytes (Pl-Prc), bone marrow (bm)MSCs and fibroblasts]. We then functionally compared the angiogenic abilities of CD146(+)CD34(-)selected bmMSCs with CD146(-) selected bmMSCs from fresh human bm aspirates. We show here that only CD146(+)CD34(-) selected Pl-Prc and CD146(+)CD34(-) selected bmMSCs maintain endothelial tubular networks on matrigel and improve endothelial sprout morphology. CD146(-) selected bmMSCs neither showed these abilities, nor did they attain pericyte function despite progressive CD146 expression once passaged. Thus, cell culture conditions appear to influence expression of this and other reported pericyte markers significantly without correlation to function. The newly developed assays, therefore, promise to close a gap in the in vitro identification of pericytes via function. Indeed, our functional data suggest that pericytes represent a subpopulation of MSCs in bm with a specialized role in vascular biology. However, these functions are not inherent to all MSCs.

Targeted therapies for systemic sclerosis

Pathogenic processes that underlie the development and progression of systemic sclerosis (SSc) are being defined in preclinical, clinical and genetic studies. Important evidence of interplay between the vasculature, connective tissue and specialized epithelial structures is emerging, and abnormalities of both the innate and adaptive immune systems have been identified. In this context, information regarding pivotal mediators, pathways or cell types that could be targets for therapeutic intervention, and that might offer potential for true disease modification, is accruing. Precedent for the regression of some aspects of the pathology has been set in clinical studies showing that potential exists to improve tissue structure and function as well as to prevent disease progression. This article reviews the concept of targeted therapies and considers potential pathways and processes that might be attenuated by therapeutic intervention in SSc. As well as improving outcomes, such approaches will undoubtedly provide information about pathogenesis. The concept of translational medicine is especially relevant in SSc, and we anticipate that the elusive goal of an effective antifibrotic treatment will emerge from one of the several clinical trials currently underway or planned in this disease. Therapeutic advances in SSc would have implications and potential beyond autoimmune rheumatic diseases.

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.

Ontological differences in first compared to third trimester human fetal placental chorionic stem cells

Human mesenchymal stromal/stem cells (MSC) isolated from fetal tissues hold promise for use in tissue engineering applications and cell-based therapies, but their collection is restricted ethically and technically. In contrast, the placenta is a potential source of readily-obtainable stem cells throughout pregnancy. In fetal tissues, early gestational stem cells are known to have advantageous characteristics over neonatal and adult stem cells. Accordingly, we investigated whether early fetal placental chorionic stem cells (e-CSC) were physiologically superior to their late gestation fetal chorionic counterparts (l-CSC). We showed that e-CSC shared a common phenotype with l-CSC, differentiating down the osteogenic, adipogenic and neurogenic pathways, and containing a subset of cells endogenously expressing NANOG, SOX2, c-MYC, and KLF4, as well as an array of genes expressed in pluripotent stem cells and primordial germ cells, including CD24, NANOG, SSEA4, SSEA3, TRA-1-60, TRA-1-81, STELLA, FRAGILIS, NANOS3, DAZL and SSEA1. However, we showed that e-CSC have characteristics of an earlier state of stemness compared to l-CSC, such as smaller size, faster kinetics, uniquely expressing OCT4A variant 1 and showing higher levels of expression of NANOG, SOX2, c-MYC and KLF4 than l-CSC. Furthermore e-CSC, but not l-CSC, formed embryoid bodies containing cells from the three germ layer lineages. Finally, we showed that e-CSC demonstrate higher tissue repair in vivo; when transplanted in the osteogenesis imperfecta mice, e-CSC, but not l-CSC increased bone quality and plasticity; and when applied to a skin wound, e-CSC, but not l-CSC, accelerated healing compared to controls. Our results provide insight into the ontogeny of the stemness phenotype during fetal development and suggest that the more primitive characteristics of early compared to late gestation fetal chorionic stem cells may be translationally advantageous.

New cellular and molecular mechanisms of lung injury and fibrosis in idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis is a serious and progressive chronic lung disease that is characterised by altered cellular composition and homoeostasis in the peripheral lung, leading to excessive accumulation of extracellular matrix and, ultimately, loss of lung function. It is the interstitial pneumonia with the worst prognosis--mortality 3-5 years after diagnosis is 50%. During the past decade, researchers have described several novel cellular and molecular mechanisms and signalling pathways implicated in the pathogenesis of idiopathic pulmonary fibrosis, resulting in the identification of new therapeutic targets. These advances will hopefully result in increased survival rates and improved quality of life for patients with this disorder in future.

A comparison of epithelial-to-mesenchymal transition and re-epithelialization

Wound healing and cancer metastasis share a common starting point, namely, a change in the phenotype of some cells from stationary to motile. The term, epithelial-to-mesenchymal transition (EMT) describes the changes in molecular biology and cellular physiology that allow a cell to transition from a sedentary cell to a motile cell, a process that is relevant not only for cancer and regeneration, but also for normal development of multicellular organisms. The present review compares the similarities and differences in cellular response at the molecular level as tumor cells enter EMT or as keratinocytes begin the process of re-epithelialization of a wound. Looking toward clinical interventions that might modulate these processes, the mechanisms and outcomes of current and potential therapies are reviewed for both anti-cancer and pro-wound healing treatments related to the pathways that are central to EMT. Taken together, the comparison of re-epithelialization and tumor EMT serves as a starting point for the development of therapies that can selectively modulate different forms of EMT.

Fingolimod inhibits PDGF-B-induced migration of vascular smooth muscle cell by down-regulating the S1PR1/S1PR3 pathway

Platelet Derived Growth Factor (PDGF) and sphingosine-1-phosphate (S1P) pathways play a key role in mural cell recruitment during tumor growth and angiogenesis. Fingolimod, a S1P analogue, has been shown to exert antitumor and antiangiogenic properties. However, molecular targets and modes of action of fingolimod remain unclear. In this study, we confirmed the antagonizing action of S1P and PDGF-B on rat vascular smooth muscle cell (VSMCs) growth and migration. We then compared siRNA and/or fingolimod (100 nM) treatments on PDGFR-β, S1PR1 S1PR2 and S1PR3 expression. Fingolimod induced a 50% reduction in S1PR3 protein expression which was cumulative with that obtained with anti-S1PR3 siRNA. We found that siRNA-induced inhibition of both PDGFR-β and S1PR3 was the most effective means to block VSMC migration induced by PDGF-B. Finally, we observed that fingolimod treatment associated with anti-S1PR1 siRNA principally inhibited VSMC growth while in combination with anti-S1PR3 siRNA it strongly inhibited VSMC migration. These results suggest that for rat VSMCs, the PDGFR-S1PR1 pathway is predominantly dedicated to cell growth while PDGFR-S1PR3 stimulates cell migration. As an S1P analogue, fingolimod is considered a potent activator of S1PR1 and S1PR3. However, its action on the PDGFR-S1PR platform appears to be dependent on S1PR1 and S1PR3 specific downregulation. Considering that the S1P pathway has already been shown to exert various crosstalks with tyrosine kinase pathways, it seems of great interest to evaluate fingolimod potential in combination with the numerous tyrosine kinase inhibitors used in oncology.

Microvascular remodeling and wound healing: a role for pericytes

Physiologic wound healing is highly dependent on the coordinated functions of vascular and non-vascular cells. Resolution of tissue injury involves coagulation, inflammation, formation of granulation tissue, remodeling and scarring. Angiogenesis, the growth of microvessels the size of capillaries, is crucial for these processes, delivering blood-borne cells, nutrients and oxygen to actively remodeling areas. Central to angiogenic induction and regulation is microvascular remodeling, which is dependent upon capillary endothelial cell and pericyte interactions. Despite our growing knowledge of pericyte-endothelial cell crosstalk, it is unclear how the interplay among pericytes, inflammatory cells, glia and connective tissue elements shape microvascular injury response. Here, we consider the relationships that pericytes form with the cellular effectors of healing in normal and diabetic environments, including repair following injury and vascular complications of diabetes, such as diabetic macular edema and proliferative diabetic retinopathy. In addition, pericytes and stem cells possessing "pericyte-like" characteristics are gaining considerable attention in experimental and clinical efforts aimed at promoting healing or eradicating ocular vascular proliferative disorders. As the origin, identification and characterization of microvascular pericyte progenitor populations remains somewhat ambiguous, the molecular markers, structural and functional characteristics of pericytes will be briefly reviewed.