All MSCs are pericytes?

Learning from Mother Nature: Innovative Tools to Boost Endogenous Repair of Critical or Difficult-to-Heal Large Tissue Defects

For repair of chronic or difficult-to-heal tissue lesions and defects, major constraints exist to a broad application of cell therapy and tissue engineering approaches, i.e., transplantation of “ex vivo” expanded autologous stem/progenitor cells, alone or associated with carrier biomaterials. To enable a large number of patients to benefit, new strategies should be considered. One of the main goals of contemporary regenerative medicine is to develop new regenerative therapies, inspired from Mother Nature. In all injured tissues, when platelets are activated by tissue contact, their released factors promote innate immune cell migration to the wound site. Platelet-derived factors and factors secreted by migrating immune cells create an inflammatory microenvironment, in turn, causing the activation of angiogenesis and vasculogenesis processes. Eventually, repair or regeneration of the injured tissue occurs via paracrine signals activating, mobilizing or recruiting to the wound site cells with healing potential, such as stem cells, progenitors, or undifferentiated cells derived from the reprogramming of tissue differentiated cells. This review, largely based on our studies, discusses the identification of new tools, inspired by cellular and molecular mechanisms overseeing physiological tissue healing, that could reactivate dormant endogenous regeneration mechanisms lost during evolution and ontogenesis.

Mesenchymal Stem Cells: Time to Change the Name!

Mesenchymal stem cells (MSCs) were officially named more than 25 years ago to represent a class of cells from human and mammalian bone marrow and periosteum that could be isolated and expanded in culture while maintaining their in vitro capacity to be induced to form a variety of mesodermal phenotypes and tissues. The in vitro capacity to form bone, cartilage, fat, etc., became an assay for identifying this class of multipotent cells and around which several companies were formed in the 1990s to medically exploit the regenerative capabilities of MSCs. Today, there are hundreds of clinics and hundreds of clinical trials using human MSCs with very few, if any, focusing on the in vitro multipotential capacities of these cells. Unfortunately, the fact that MSCs are called “stem cells” is being used to infer that patients will receive direct medical benefit, because they imagine that these cells will differentiate into regenerating tissue‐producing cells. Such a stem cell treatment will presumably cure the patient of their medically relevant difficulties ranging from osteoarthritic (bone‐on‐bone) knees to various neurological maladies including dementia. I now urge that we change the name of MSCs to Medicinal Signaling Cells to more accurately reflect the fact that these cells home in on sites of injury or disease and secrete bioactive factors that are immunomodulatory and trophic (regenerative) meaning that these cells make therapeutic drugs in situ that are medicinal. It is, indeed, the patient's own site‐specific and tissue‐specific resident stem cells that construct the new tissue as stimulated by the bioactive factors secreted by the exogenously supplied MSCs. Stem Cells Translational Medicine2017;6:1445–1451

Identification of Multipotent Stem Cells in Human Brain Tissue Following Stroke

Perivascular regions of the brain harbor multipotent stem cells. We previously demonstrated that brain pericytes near blood vessels also develop multipotency following experimental ischemia in mice and these ischemia-induced multipotent stem cells (iSCs) can contribute to neurogenesis. However, it is essential to understand the traits of iSCs in the poststroke human brain for possible applications in stem cell-based therapies for stroke patients. In this study, we report for the first time that iSCs can be isolated from the poststroke human brain. Putative iSCs were derived from poststroke brain tissue obtained from elderly stroke patients requiring decompressive craniectomy and partial lobectomy for diffuse cerebral infarction. Immunohistochemistry showed that these iSCs were localized near blood vessels within poststroke areas containing apoptotic/necrotic neurons and expressed both the stem cell marker nestin and several pericytic markers. Isolated iSCs expressed these same markers and demonstrated high proliferative potential without loss of stemness. Furthermore, isolated iSCs expressed other stem cell markers, such as Sox2, c-myc, and Klf4, and differentiated into multiple cells in vitro, including neurons. These results show that iSCs, which are likely brain pericyte derivatives, are present within the poststroke human brain. This study suggests that iSCs can contribute to neural repair in patients with stroke.

Role of mesenchymal stem cells in osteoarthritis treatment

As the most common form of joint disorder, osteoarthritis (OA) imposes a tremendous burden on health care systems worldwide. Without effective cure, OA represents a unique opportunity for innovation in therapeutic development. In contrast to traditional treatments based on drugs, proteins, or antibodies, stem cells are poised to revolutionize medicine as they possess the capacity to replace and repair tissues and organs such as osteoarthritic joints. Among different types of stem cells, mesenchymal stem cells (MSCs) are of mesoderm origin and have been shown to generate cells for tissues of the mesoderm lineage, thus, raising the hope for them being used to treat diseases such as OA. However, given their ability to differentiate into other cell types, MSCs have also been tested in treating a myriad of conditions from diabetes to Parkinson's disease, apparently of the ectoderm and endoderm lineages. There are ongoing debates whether MSCs can differentiate into lineages outside of the mesoderm and consequently their effectiveness in treating conditions from the ectoderm and endoderm lineages. In this review, we discuss the developmental origin of MSCs, their differentiation potential and immunomodulatory effects, as well as their applications in treating OA. We suggest further investigations into new therapies or combination therapies that may provide more effective treatment for bone and joint diseases. Furthermore, cell-based therapy and its associated safety and effectiveness should be carefully evaluated before clinical translation. This review provides updated information on recent approval of clinical trials and related applications of MSCs, and discusses additional efforts on cell-based therapy for treating OA and other joint and bone diseases.

Efficacy of a Cellular Bone Allograft for Foot and Ankle Arthrodesis and Revision Nonunion Procedures

BACKGROUND

Bone graft substitutes are often required in patients at risk for nonunion, and therefore, an allograft that most closely mimics an autograft is highly sought after. This study explored the utility and efficacy of a cellular bone allograft used for foot and ankle arthrodesis and revision nonunion procedures in a patient population at risk for nonunion.

METHODS

An institutional review board-approved retrospective review of consecutive patients who underwent arthrodesis and revision nonunion procedures with a cellular bone allograft was performed at a single academic institution. No external sources of funding were provided for this study. Inclusion criteria included patients who were more than 1 year after surgery or less than 1 year after surgery if they had undergone a second operative procedure for nonunion or if they had computed tomography-documented union. Forty operative procedures in 36 patients with a mean follow-up of 13 months (range, 6-25 months) were included for data analysis. All patients had at least one of the following risk factors associated with nonunion: current smoker, diabetes, avascular necrosis (AVN) of the involved bone, active same-site operative infection, history of nonunion, previous same-site surgery, or gap of 5 mm or greater after joint preparation. The primary outcome was radiographic union.

RESULTS

The union rate in this high-risk population was 83% (33/40). Univariate analysis demonstrated that the use of a cellular bone allograft helped mitigate the presence of risk factors known to cause nonunion. There was no significant difference in fusion rates among groups with current smoking, AVN of the involved bone, active same-site operative infections, history of nonunion, rheumatoid arthritis on medication, previous same-site operative procedures or infections, or a gap of 5 mm or greater after joint preparation. However, in this population, diabetic and female patients remained at a high risk of recurrent nonunion ( P = .0015), despite the use of a cellular bone allograft. Chi-square analysis of patients with increasing numbers of risk factors directly correlated with an increased risk of nonunion ( P = .025). Four wound complications were reported in this cohort that required irrigation and debridement (10%).

CONCLUSION

These data demonstrated a union rate of 83% in patients with risk factors known to cause nonunion. The benefits of the use of a cellular bone allograft allowed for the avoidance of morbidity associated with autograft harvesting while still improving the local biology to facilitate fusion in a difficult patient population to attain a successful fusion mass.

LEVEL OF EVIDENCE

Level IV, retrospective case series.

Administration of multipotent mesenchymal stromal cells restores liver regeneration and improves liver function in obese mice with hepatic steatosis after partial hepatectomy

Background

The liver has the remarkable capacity to regenerate in order to compensate for lost or damaged hepatic tissue. However, pre-existing pathological abnormalities, such as hepatic steatosis (HS), inhibits the endogenous regenerative process, becoming an obstacle for liver surgery and living donor transplantation.

Recent evidence indicates that multipotent mesenchymal stromal cells (MSCs) administration can improve hepatic function and increase the potential for liver regeneration in patients with liver damage. Since HS is the most common form of chronic hepatic illness, in this study we evaluated the role of MSCs in liver regeneration in an animal model of severe HS with impaired liver regeneration.

Methods

C57BL/6 mice were fed with a regular diet (normal mice) or with a high-fat diet (obese mice) to induce HS. After 30 weeks of diet exposure, 70% hepatectomy (Hpx) was performed and normal and obese mice were divided into two groups that received 5 × 10⁵ MSCs or vehicle via the tail vein immediately after Hpx.

Results

We confirmed a significant inhibition of hepatic regeneration when liver steatosis was present, while the hepatic regenerative response was promoted by infusion of MSCs. Specifically, MSC administration improved the hepatocyte proliferative response, PCNA-labeling index, DNA synthesis, liver function, and also reduced the number of apoptotic hepatocytes.

These effects may be associated to the paracrine secretion of trophic factors by MSCs and the hepatic upregulation of key cytokines and growth factors relevant for cell proliferation, which ultimately improves the survival rate of the mice.

Conclusions

MSCs represent a promising therapeutic strategy to improve liver regeneration in patients with HS as well as for increasing the number of donor organs available for transplantation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0469-y) contains supplementary material, which is available to authorized users.

Biologic Approaches for the Treatment of Partial Tears of the Anterior Cruciate Ligament: A Current Concepts Review

BACKGROUND

Anterior cruciate ligament reconstruction (ACLR) has been established as the gold standard for treatment of complete ruptures of the anterior cruciate ligament (ACL) in active, symptomatic individuals. In contrast, treatment of partial tears of the ACL remains controversial. Biologically augmented ACL-repair techniques are expanding in an attempt to regenerate and improve healing and outcomes of both the native ACL and the reconstructed graft tissue.

PURPOSE

To review the biologic treatment options for partial tears of the ACL.

STUDY DESIGN

Review.

METHODS

A literature review was performed that included searches of PubMed, Medline, and Cochrane databases using the following keywords: partial tear of the ACL, ACL repair, bone marrow concentrate, growth factors/healing enhancement, platelet-rich plasma (PRP), stem cell therapy.

RESULTS

The use of novel biologic ACL repair techniques, including growth factors, PRP, stem cells, and bioscaffolds, have been reported to result in promising preclinical and short-term clinical outcomes.

CONCLUSION

The potential benefits of these biological augmentation approaches for partial ACL tears are improved healing, better proprioception, and a faster return to sport and activities of daily living when compared with standard reconstruction procedures. However, long-term studies with larger cohorts of patients and with technique validation are necessary to assess the real effect of these approaches.

Pericytes from Mesenchymal Stem Cells as a model for the blood-brain barrier

Blood brain-barrier (BBB) in vitro models have been widely reported in studies of the BBB phenotype. However, established co-culture systems involve brain endothelial cells, astrocytes, neurons and pericytes, and therefore are often consuming and technically challenging. Here we use mesenchymal system cells (MSC) as a potential substitute for pericytes in a BBB model. Both MSC and pericyte markers in 2D culture environment were evaluated on different extracellular matrix compositions. Further experiments indicated that MSC contributed in a similar manner to pericytes in a co-cultured 3D model on increasing trans-endothelial electric resistance (TEER) and decreasing permeability against macromolecules.

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.

Adipose, Bone Marrow and Synovial Joint-Derived Mesenchymal Stem Cells for Cartilage Repair

Current cell-based repair strategies have proven unsuccessful for treating cartilage defects and osteoarthritic lesions, consequently advances in innovative therapeutics are required and mesenchymal stem cell-based (MSC) therapies are an expanding area of investigation. MSCs are capable of differentiating into multiple cell lineages and exerting paracrine effects. Due to their easy isolation, expansion, and low immunogenicity, MSCs are an attractive option for regenerative medicine for joint repair. Recent studies have identified several MSC tissue reservoirs including in adipose tissue, bone marrow, cartilage, periosteum, and muscle. MSCs isolated from these discrete tissue niches exhibit distinct biological activities, and have enhanced regenerative potentials for different tissue types. Each MSC type has advantages and disadvantages for cartilage repair and their use in a clinical setting is a balance between expediency and effectiveness. In this review we explore the challenges associated with cartilage repair and regeneration using MSC-based cell therapies and provide an overview of phenotype, biological activities, and functional properties for each MSC population. This paper also specifically explores the therapeutic potential of each type of MSC, particularly focusing on which cells are capable of producing stratified hyaline-like articular cartilage regeneration. Finally we highlight areas for future investigation. Given that patients present with a variety of problems it is unlikely that cartilage regeneration will be a simple "one size fits all," but more likely an array of solutions that need to be applied systematically to achieve regeneration of a biomechanically competent repair tissue.

Biologic Treatments for Sports Injuries II Think Tank-Current Concepts, Future Research, and Barriers to Advancement, Part 1: Biologics Overview, Ligament Injury, Tendinopathy

Biologic therapies, including stem cells, platelet-rich plasma, growth factors, and other biologically active adjuncts, have recently received increased attention in the basic science and clinical literature. At the 2015 AOSSM Biologics II Think Tank held in Colorado Springs, Colorado, a group of orthopaedic surgeons, basic scientists, veterinarians, and other investigators gathered to review the state of the science for biologics and barriers to implementation of biologics for the treatment of sports medicine injuries. This series of current concepts reviews reports the summary of the scientific presentations, roundtable discussions, and recommendations from this think tank.

Microvascular Fragment Transplantation Improves Rat Dorsal Skin Flap Survival

BACKGROUND

The development of flap necrosis distally remains a concern during microsurgical flap transfers because, at least in part, of decreased perfusion. Microvascular fragments (MVFs) are microvessels isolated from adipose tissue that are capable of improving tissue perfusion in a variety of tissue defects. The aim of this study was to determine whether the transplantation of MVFs in a dorsal rat skin flap model can improve flap survival.

METHODS

A 10 × 3 cm flap was raised in a cranial to caudal fashion on the dorsal side of 16 Lewis rats, with the caudal side remaining intact. The rats were equally divided into a treatment group (MVFs) and a control group (sterile saline). At the time of surgery, sterile saline with or without MVFs was injected directly into the flap. Microvessel density was determined after harvesting flap tissue by counting vessels that positively stained for Griffonia simplicifolia lectin I-isolectin B4. Laser Doppler was used to measure blood flow before and after surgery and 7 and 14 days later. Flap survival was evaluated 7 and 14 days after surgery by evaluating the percentage of viable tissue of the flap with photodigital planimetry.

RESULTS

Despite the lack of a significant difference in microvessel density and tissue perfusion, flap survival increased 6.4% (P < 0.05) in MVF-treated animals compared with controls.

CONCLUSIONS

The use of MVFs may be a means to improve flap survival. Future studies are required to delineate mechanisms whereby this occurs and to further optimize their application.

In Vivo Angiogenic Capacity of Stem Cells from Human Exfoliated Deciduous Teeth with Human Umbilical Vein Endothelial Cells

Dental pulp is a highly vascularized tissue requiring adequate blood supply for successful regeneration. In this study, we investigated the functional role of stem cells from human exfoliated deciduous teeth (SHEDs) as a perivascular source for in vivo formation of vessel-like structures. Primarily isolated SHEDs showed mesenchymal stem cell (MSC)-like characteristics including the expression of surface antigens and in vitro osteogenic and adipogenic differentiation potentials. Moreover, SHEDs were positive for NG2, α-smooth muscle actin (SMA), platelet-derived growth factor receptor beta (PDGFRβ), and CD146 as pericyte markers. To prove feasibility of SHEDs as perivascular source, SHEDs were transplanted into immunodeficient mouse using Matrigel with or without human umbilical vein endothelial cells (HUVECs). Transplantation of SHEDs alone or HUVECs alone resulted in no formation of vessel-like structures with enough red blood cells. However, when SHEDs and HUVECs were transplanted together, extensive vessel-like structures were formed. The presence of murine erythrocytes within lumens suggested the formation of anastomoses between newly formed vessel-like structures in Matrigel plug and the host circulatory system. To understand underlying mechanisms of in vivo angiogenesis, the expression of angiogenic cytokine and chemokine, their receptors, and MMPs was compared between SHEDs and HUVECs. SHEDs showed higher expression of VEGF, SDF-1α, and PDGFRβ than HUVECs. On the contrary, HUVECs showed higher expression of VEGF receptors, CXCR4, and PDGF-BB than SHEDs. This differential expression pattern suggested reciprocal interactions between SHEDs and HUVECs and their involvement during in vivo angiogenesis. In conclusion, SHEDs could be a feasible source of perivascular cells for in vivo angiogenesis.

The bone marrow pericyte: an orchestrator of vascular niche

The concept of pericyte has been changing over years. This cell type was believed to possess only a function of trophic support to endothelial cells and to maintain vasculature stabilization. In the last years, the discovery of multipotent ability of perivascular populations led to the concept of vessel/wall niche. Likewise, several perivascular populations have been identified in animal and human bone marrow. In this review, we provide an overview on bone marrow perivascular population, their cross-talk with other niche components, relationship with bone marrow stromal stem cells, and similarities and differences with the perivascular population of the vessel/wall niche. Finally, we focus on the regenerative potential of these cells and the forthcoming challenges related to their use as cell therapy products.

Mesenchymal Stem Cells and Pericytes: To What Extent Are They Related?

Mesenchymal stem cells (MSCs) were initially identified as progenitors of skeletal tissues within mammalian bone marrow and cells with similar properties were also obtained from other tissues such as adipose and dental pulp. Although MSCs have been extensively investigated, their native behavior and in vivo identity remain poorly defined. Uncovering the in vivo identity of MSCs has been challenging due to the lack of exclusive cell markers, cellular alterations caused by culture methods, and extensive focus on in vitro properties for characterization. Although MSC site of origin influences their functional properties, these mesenchymal progenitors can be found in the perivascular space in virtually all organs from where they were obtained. However, the precise identity of MSCs within the vascular wall is highly controversial. The recurrent concept that MSCs correspond to pericytes in vivo has been supported mainly by their perivascular localization and expression of some molecular markers. However, this view has been a subject of controversy, in part, due to the application of loose criteria to define pericytes and due to the lack of a marker able to unequivocally identify these cells. Furthermore, recent evidences indicate that subpopulations of MSCs can be found at extravascular sites such as the endosteum. In this opinion review, we bring together the advances and pitfalls on the search for the in vivo identity of MSCs and highlight the recent evidences that suggest that perivascular MSCs are adventitial cells, acting as precursors of pericytes and other stromal cells during tissue homeostasis.

Stem Cells of Dental Origin: Current Research Trends and Key Milestones towards Clinical Application

Dental Mesenchymal Stem Cells (MSCs), including Dental Pulp Stem Cells (DPSCs), Stem Cells from Human Exfoliated Deciduous teeth (SHED), and Stem Cells From Apical Papilla (SCAP), have been extensively studied using highly sophisticated in vitro and in vivo systems, yielding substantially improved understanding of their intriguing biological properties. Their capacity to reconstitute various dental and nondental tissues and the inherent angiogenic, neurogenic, and immunomodulatory properties of their secretome have been a subject of meticulous and costly research by various groups over the past decade. Key milestone achievements have exemplified their clinical utility in Regenerative Dentistry, as surrogate therapeutic modules for conventional biomaterial-based approaches, offering regeneration of damaged oral tissues instead of simply “filling the gaps.” Thus, the essential next step to validate these immense advances is the implementation of well-designed clinical trials paving the way for exploiting these fascinating research achievements for patient well-being: the ultimate aim of this ground breaking technology. This review paper presents a concise overview of the major biological properties of the human dental MSCs, critical for the translational pathway “from bench to clinic.”

The double life of cardiac mesenchymal cells: Epimetabolic sensors and therapeutic assets for heart regeneration

Organ-specific mesenchymal cells naturally reside in the stroma, where they are exposed to some environmental variables affecting their biology and functions. Risk factors such as diabetes or aging influence their adaptive response. In these cases, permanent epigenetic modifications may be introduced in the cells with important consequences on their local homeostatic activity and therapeutic potential. Numerous results suggest that mesenchymal cells, virtually present in every organ, may contribute to tissue regeneration mostly by paracrine mechanisms. Intriguingly, the heart is emerging as a source of different cells, including pericytes, cardiac progenitors, and cardiac fibroblasts. According to phenotypic, functional, and molecular criteria, these should be classified as mesenchymal cells. Not surprisingly, in recent years, the attention on these cells as therapeutic tools has grown exponentially, although only very preliminary data have been obtained in clinical trials to date. In this review, we summarized the state of the art about the phenotypic features, functions, regenerative properties, and clinical applicability of mesenchymal cells, with a particular focus on those of cardiac origin.

Strategies in regenerative medicine for intervertebral disc repair using mesenchymal stem cells and bioscaffolds

The intervertebral disc (IVD) is a major weight bearing structure that undergoes degenerative changes with aging limiting its ability to dissipate axial spinal loading in an efficient manner resulting in the generation of low back pain. Low back pain is a number one global musculoskeletal disorder with massive socioeconomic impact. The WHO has nominated development of mesenchymal stem cells and bioscaffolds to promote IVD repair as primary research objectives. There is a clear imperative for the development of strategies to effectively treat IVD defects. Early preclinical studies with mesenchymal stem cells in canine and ovine models have yielded impressive results in IVD repair. Combinatorial therapeutic approaches encompassing biomaterial and cell-based therapies promise significant breakthroughs in IVD repair in the near future.

Semaphorin 3A Shifts Adipose Mesenchymal Stem Cells towards Osteogenic Phenotype and Promotes Bone Regeneration In Vivo

Adipose mesenchymal stem cells (ASCs) are considered as the promising seed cells for bone regeneration. However, the lower osteogenic differentiation capacity limits its therapeutic efficacy. Identification of the key molecules governing the differences between ASCs and BMSCs would shed light on manipulation of ASCs towards osteogenic phenotype. In this study, we screened semaphorin family members in ASCs and BMSCs and identified Sema3A as an osteogenic semaphorin that was significantly and predominantly expressed in BMSCs. The analyses in vitro showed that the overexpression of Sema3A in ASCs significantly enhanced the expression of bone-related genes and extracellular matrix calcium deposition, while decreasing the expression of adipose-related genes and thus lipid droplet formation, resembling a BMSCs phenotype. Furthermore, Sema3A modified ASCs were then engrafted into poly(lactic-co-glycolic acid) (PLGA) scaffolds to repair the critical-sized calvarial defects in rat model. As expected, Sema3A modified ASCs encapsulation significantly promoted new bone formation with higher bone volume fraction and bone mineral density. Additionally, Sema3A was found to simultaneously increase multiple Wnt related genes and thus activating Wnt pathway. Taken together, our study here identifies Sema3A as a critical gene for osteogenic phenotype and reveals that Sema3A-modified ASCs would serve as a promising candidate for bettering bone defect repair.

Periodontal Tissue Regeneration Using Syngeneic Adipose-Derived Stromal Cells in a Mouse Model

Current treatment of periodontitis is still associated with a high degree of variability in clinical outcomes. Recent advances in regenerative medicine by mesenchymal cells, including adipose stromal cells (ASC) have paved the way to improved periodontal regeneration (PD) but little is known about the biological processes involved. Here, we aimed to use syngeneic ASCs for periodontal regeneration in a new, relevant, bacteria‐induced periodontitis model in mice. Periodontal defects were induced in female C57BL6/J mice by oral gavage with periodontal pathogens. We grafted 2 × 10⁵ syngeneic mouse ASCs expressing green fluorescent protein (GFP) (GFP+/ASC) within a collagen vehicle in the lingual part of the first lower molar periodontium (experimental) while carrier alone was implanted in the contralateral side (control). Animals were sacrificed 0, 1, 6, and 12 weeks after treatment by GFP+/ASC or vehicle graft, and microscopic examination, immunofluorescence, and innovative bio‐informatics histomorphometry methods were used to reveal deep periodontium changes. From 1 to 6 weeks after surgery, GFP+ cells were identified in the periodontal ligament (PDL), in experimental sites only. After 12 weeks, cementum regeneration, the organization of PDL fibers, the number of PD vessels, and bone morphogenetic protein‐2 and osteopontin expression were greater in experimental sites than in controls. Specific stromal cell subsets were recruited in the newly formed tissue in ASC‐implanted periodontium only. These data suggest that ASC grafting in diseased deep periodontium, relevant to human pathology, induces a significant improvement of the PDL microenvironment, leading to a recovery of tooth‐supporting tissue homeostasis. Stem Cells Translational Medicine2017;6:656–665

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.

Not All Pericytes Are Born Equal: Pericytes from Human Adult Tissues Present Different Differentiation Properties

Pericytes (PCs) have been recognized for a long time only as structural cells of the blood vessels. The identification of tight contacts with endothelial cells and the ability to interact with surrounding cells through paracrine signaling revealed additional functions of PCs in maintaining the homeostasis of the perivascular environment. PCs got the front page, in the late 1990s, after the identification and characterization of a new embryonic cell population, the mesoangioblasts, from which PCs present in the adult organism are thought to derive. From these studies, it was clear that PCs were also endowed with multipotent mesodermal abilities. Furthermore, their ability to cross the vascular wall and to reconstitute skeletal muscle tissue after systemic injection opened the way to a number of studies aimed to develop therapeutic protocols for a cell therapy of muscular dystrophy. This has resulted in a major effort to characterize pericytic cell populations from skeletal muscle and other adult tissues. Additional studies also addressed their relationship with other cells of the perivascular compartment and with mesenchymal stem cells. These data have provided initial evidence that PCs from different adult tissues might be endowed with distinctive differentiation abilities. This would suggest that the multipotent mesenchymal ability of PCs might be restrained within different tissues, likely depending on the specific cell renewal and repair requirements of each tissue. This review presents current knowledge on human PCs and highlights recent data on the differentiation properties of PCs isolated from different adult tissues.

Angiogenic and anti-inflammatory properties of micro-fragmented fat tissue and its derived mesenchymal stromal cells

BACKGROUND

Adipose-derived mesenchymal stromal cells (Ad-MSCs) are a promising tool for advanced cell-based therapies. They are routinely obtained enzymatically from fat lipoaspirate (LP) as SVF, and may undergo prolonged ex vivo expansion, with significant senescence and decline in multipotency. Besides, these techniques have complex regulatory issues, thus incurring in the compelling requirements of GMP guidelines. Hence, availability of a minimally manipulated, autologous adipose tissue would have remarkable biomedical and clinical relevance. For this reason, a new device, named Lipogems® (LG), has been developed. This ready-to-use adipose tissue cell derivate has been shown to have in vivo efficacy upon transplantation for ischemic and inflammatory diseases. To broaden our knowledge, we here investigated the angiogenic and anti-inflammatory properties of LG and its derived MSC (LG-MSCs) population.

METHODS

Human LG samples and their LG-MSCs were analyzed by immunohistochemistry for pericyte, endothelial and mesenchymal stromal cell marker expression. Angiogenesis was investigated testing the conditioned media (CM) of LG (LG-CM) and LG-MSCs (LG-MSCs-CM) on cultured endothelial cells (HUVECs), evaluating proliferation, cord formation, and the expression of the adhesion molecules (AM) VCAM-1 and ICAM-1. The macrophage cell line U937 was used to evaluate the anti-inflammatory properties, such as migration, adhesion on HUVECs, and release of RANTES and MCP-1.

RESULTS

Our results indicate that LG contained a very high number of mesenchymal cells expressing NG2 and CD146 (both pericyte markers) together with an abundant microvascular endothelial cell (mEC) population. Substantially, both LG-CM and LG-MSC-CM increased cord formation, inhibited endothelial ICAM-1 and VCAM-1 expression following TNFα stimulation, and slightly improved HUVEC proliferation. The addition of LG-CM and LG-MSC-CM strongly inhibited U937 migration upon stimulation with the chemokine MCP-1, reduced their adhesion on HUVECs and significantly suppressed the release of RANTES and MCP-1.

CONCLUSIONS

Our data indicate that LG micro-fragmented adipose tissue retains either per se, or in its embedded MSCs content, the capacity to induce vascular stabilization and to inhibit several macrophage functions involved in inflammation.

The 3Rs of Cell Therapy

The 3Rs for a good education are “reading, 'riting, and 'rithmetic.” The basis for good health care solutions for the emergent field of cell therapy in the future will also involve 3Rs: regulation, reimbursement, and realization of value. The business models in this new field of cell therapy will involve these 3Rs. This article brings forth realities facing this new industry for its approaches to provide curative health care solutions. Stem Cells Translational Medicine2017;6:17–21

The dental pulp stem cell niche based on aldehyde dehydrogenase 1 expression

AIM

To detect cells expressing the stem cell marker ALDH1 (aldehyde dehydrogenase1) in the pulp of human permanent teeth and to investigate the expression of ALDH1 in isolated dental pulp cells.

METHODOLOGY

Pulp tissue was collected and processed for immunohistochemistry to detect ALDH1-, STRO-1- and CD90-positive cells. In addition, cells were isolated and analysed by flow cytometry for ALDH1 activity and for the cell surface markers CD44, CD73, CD90, STRO-1 and CD45. Cells were also examined for multidifferentiation capacity. Within these cells, an ALDH1(+) cell subpopulation was selected and evaluated for multidifferentiation capacity.

RESULTS

The immunohistochemistry analyses showed that ALDH1-, CD90- and STRO-1-positive cells were located mainly in the perivascular areas and nerve fibres of dental pulps. Cells on the fifth passage had high expression for CD44, CD73 and CD90, whereas moderate labelling was observed for STRO-1 and ALDH1 in flow cytometry analysis. On the same passages, cells were able to differentiate into osteogenic, adipogenic and chondrogenic lineages. The ALDH1(+) cell subpopulation also demonstrated multilineage differentiation ability.

CONCLUSIONS

Dental pulp stem cells reside in the vicinity of blood vessels and nerve fibres, indicating the possible existence of more than one stem cell niche in dental pulps. Furthermore, ALDH1 was expressed by isolated dental pulp cells, which had mesenchymal stem cell characteristics. Thus, it can be suggested that ALDH1 may be used as a DPSC marker.

Adipose Tissue and Mesenchymal Stem Cells: State of the Art and Lipogems® Technology Development

In the past few years, interest in adipose tissue as an ideal source of mesenchymal stem cells (MSCs) has increased. These cells are multipotent and may differentiate in vitro into several cellular lineages, such as adipocytes, chondrocytes, osteoblasts, and myoblasts. In addition, they secrete many bioactive molecules and thus are considered “mini-drugstores.” MSCs are being used increasingly for many clinical applications, such as orthopedic, plastic, and reconstructive surgery. Adipose-derived MSCs are routinely obtained enzymatically from fat lipoaspirate as SVF and/or may undergo prolonged ex vivo expansion, with significant senescence and a decrease in multipotency, leading to unsatisfactory clinical results. Moreover, these techniques are hampered by complex regulatory issues. Therefore, an innovative technique (Lipogems®; Lipogems International SpA, Milan, Italy) was developed to obtain microfragmented adipose tissue with an intact stromal vascular niche and MSCs with a high regenerative capacity. The Lipogems® technology, patented in 2010 and clinically available since 2013, is an easy-to-use system designed to harvest, process, and inject refined fat tissue and is characterized by optimal handling ability and a great regenerative potential based on adipose-derived MSCs. In this novel technology, the adipose tissue is washed, emulsified, and rinsed and adipose cluster dimensions gradually are reduced to about 0.3 to 0.8 mm. In the resulting Lipogems® product, pericytes are retained within an intact stromal vascular niche and are ready to interact with the recipient tissue after transplantation, thereby becoming MSCs and starting the regenerative process. Lipogems® has been used in more than 7000 patients worldwide in aesthetic medicine and surgery, as well as in orthopedic and general surgery, with remarkable and promising results and seemingly no drawbacks. Now, several clinical trials are under way to support the initial encouraging outcomes. Lipogems® technology is emerging as a valid intraoperative system to obtain an optimal final product that may be used immediately for regenerative purposes.

View from the heart: cardiac fibroblasts in development, scarring and regeneration

In the adult, tissue repair after injury is generally compromised by fibrosis, which maintains tissue integrity with scar formation but does not restore normal architecture and function. The process of regeneration is necessary to replace the scar and rebuild normal functioning tissue. Here, we address this problem in the context of heart disease, and discuss the origins and characteristics of cardiac fibroblasts, as well as the crucial role that they play in cardiac development and disease. We discuss the dual nature of cardiac fibroblasts, which can lead to scarring, pathological remodelling and functional deficit, but can also promote heart function in some contexts. Finally, we review current and proposed approaches whereby regeneration could be fostered by interventions that limit scar formation.

Perivascular Progenitor Cells Derived From Human Embryonic Stem Cells Exhibit Functional Characteristics of Pericytes and Improve the Retinal Vasculature in a Rodent Model of Diabetic Retinopathy

: Diabetic retinopathy (DR) is the leading cause of blindness in working-age people. Pericyte loss is one of the pathologic cellular events in DR, which weakens the retinal microvessels. Damage to the microvascular networks is irreversible and permanent; thus further progression of DR is inevitable. In this study, we hypothesize that multipotent perivascular progenitor cells derived from human embryonic stem cells (hESC-PVPCs) improve the damaged retinal vasculature in the streptozotocin-induced diabetic rodent models. We describe a highly efficient and feasible protocol to derive such cells with a natural selection method without cell-sorting processes. As a cellular model of pericytes, hESC-PVPCs exhibited marker expressions such as CD140B, CD146, NG2, and functional characteristics of pericytes. Following a single intravitreal injection into diabetic Brown Norway rats, we demonstrate that the cells localized alongside typical perivascular regions of the retinal vasculature and stabilized the blood-retinal barrier breakdown. Findings in this study highlight a therapeutic potential of hESC-PVPCs in DR by mimicking the role of pericytes in vascular stabilization.

SIGNIFICANCE

This study provides a simple and feasible method to generate perivascular progenitor cells from human embryonic stem cells. These cells share functional characteristics with pericytes, which are irreversibly lost at the onset of diabetic retinopathy. Animal studies demonstrated that replenishing the damaged pericytes with perivascular progenitor cells could restore retinal vascular integrity and prevent fluid leakage. This provides promising and compelling evidence that perivascular progenitor cells can be used as a novel therapeutic agent to treat diabetic retinopathy patients.

Rebuilding the Damaged Heart: Mesenchymal Stem Cells, Cell-Based Therapy, and Engineered Heart Tissue

Mesenchymal stem cells (MSCs) are broadly distributed cells that retain postnatal capacity for self-renewal and multilineage differentiation. MSCs evade immune detection, secrete an array of anti-inflammatory and anti-fibrotic mediators, and very importantly activate resident precursors. These properties form the basis for the strategy of clinical application of cell-based therapeutics for inflammatory and fibrotic conditions. In cardiovascular medicine, administration of autologous or allogeneic MSCs in patients with ischemic and nonischemic cardiomyopathy holds significant promise. Numerous preclinical studies of ischemic and nonischemic cardiomyopathy employing MSC-based therapy have demonstrated that the properties of reducing fibrosis, stimulating angiogenesis, and cardiomyogenesis have led to improvements in the structure and function of remodeled ventricles. Further attempts have been made to augment MSCs' effects through genetic modification and cell preconditioning. Progression of MSC therapy to early clinical trials has supported their role in improving cardiac structure and function, functional capacity, and patient quality of life. Emerging data have supported larger clinical trials that have been either completed or are currently underway. Mechanistically, MSC therapy is thought to benefit the heart by stimulating innate anti-fibrotic and regenerative responses. The mechanisms of action involve paracrine signaling, cell-cell interactions, and fusion with resident cells. Trans-differentiation of MSCs to bona fide cardiomyocytes and coronary vessels is also thought to occur, although at a nonphysiological level. Recently, MSC-based tissue engineering for cardiovascular disease has been examined with quite encouraging results. This review discusses MSCs from their basic biological characteristics to their role as a promising therapeutic strategy for clinical cardiovascular disease.

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

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

Tumor-associated fibroblasts predominantly come from local and not circulating precursors

Fibroblasts are common cell types in cancer stroma and lay down collagen required for survival and growth of cancer cells. Although some cancer therapy strategies target tumor fibroblasts, their origin remains controversial. Multiple publications suggest circulating mesenchymal precursors as a source of tumor-associated fibroblasts. However, we show by three independent approaches that tumor fibroblasts derive primarily from local, sessile precursors. First, transplantable tumors developing in a mouse expressing green fluorescent reporter protein (EGFP) under control of the type I collagen (Col-I) promoter (COL-EGFP) had green stroma, whereas we could not find COL-EGFP(+) cells in tumors developing in the parabiotic partner lacking the fluorescent reporter. Lack of incorporation of COL-EGFP(+) cells from the circulation into tumors was confirmed in parabiotic pairs of COL-EGFP mice and transgenic mice developing autochthonous intestinal adenomas. Second, transplantable tumors developing in chimeric mice reconstituted with bone marrow cells from COL-EGFP mice very rarely showed stromal fibroblasts expressing EGFP. Finally, cancer cells injected under full-thickness COL-EGFP skin grafts transplanted in nonreporter mice developed into tumors containing green stromal cells. Using multicolor in vivo confocal microscopy, we found that Col-I-expressing fibroblasts constituted approximately one-third of the stromal mass and formed a continuous sheet wrapping the tumor vessels. In summary, tumors form their fibroblastic stroma predominantly from precursors present in the local tumor microenvironment, whereas the contribution of bone marrow-derived circulating precursors is rare.

Isolation of CD146+ Resident Lung Mesenchymal Stromal Cells from Rat Lungs

Mesenchymal stromal cells (MSCs) are increasingly recognized for their therapeutic potential in a wide range of diseases, including lung diseases. Besides the use of bone marrow and umbilical cord MSCs for exogenous cell therapy, there is also increasing interest in the repair and regenerative potential of resident tissue MSCs. Moreover, they likely have a role in normal organ development, and have been attributed roles in disease, particularly those with a fibrotic nature. The main hurdle for the study of these resident tissue MSCs is the lack of a clear marker for the isolation and identification of these cells. The isolation technique described here applies multiple characteristics of lung resident MSCs (L-MSCs). Upon sacrifice of the rats, lungs are removed and rinsed multiple times to remove blood. Following mechanical dissociation by scalpel, the lungs are digested for 2-3 hr using a mix of collagenase type I, neutral protease and DNase type I. The obtained single cell suspension is subsequently washed and layered over density gradient medium (density 1.073 g/ml). After centrifugation, cells from the interphase are washed and plated in culture-treated flasks. Cells are cultured for 4-7 days in physiological 5% O2, 5% CO2 conditions. To deplete fibroblasts (CD146(-)) and to ensure a population of only L-MSCs (CD146(+)), positive selection for CD146(+) cells is performed through magnetic bead selection. In summary, this procedure reliably produces a population of primary L-MSCs for further in vitro study and manipulation. Because of the nature of the protocol, it can easily be translated to other experimental animal models.

Mesenchymal Stem Cells from Human Extra Ocular Muscle Harbor Neuroectodermal Differentiation Potential

Mesenchymal stem cells (MSC) have been proposed as suitable candidates for cell therapy for neurological disorderssince they exhibit good neuronal differentiation capacity. However, for better therapeutic outcomes, it is necessary to isolate MSC from a suitable tissue sourcethat posses high neuronal differentiation. In this context, we isolated MSC from extra ocular muscle (EOM) tissue and tested the in vitro neuronal differentiation potential. In the current study, EOM tissue derived MSC were characterized and compared with bone marrow derived MSC. We found that EOM derived MSC proliferated as a monolayer and showed similarities in morphology, growth properties and cell surface marker expression with bone marrow derived MSC and expressed high levels of NES, OCT4, NANOG and SOX2 in its undifferentiated state. They also expressed embryonic cell surface marker SSEA4 and their intracellular mitochondrial distribution pattern was similar to that of multipotent stem cells. Although EOM derived MSC differentiated readily into adipocytes, osteocytes and chondrocytes, they differentiated more efficiently into neuroectodermal cells. The differentiation into neuroectodermal cellswas confirmed by the expression of neuronal markers NGFR and MAP2B. Thus, EOM derived MSC might be good candidates for stem cell based therapies for treating neurodegenerative diseases.

Stem cells sources for intervertebral disc regeneration

Intervertebral disc regeneration field is rapidly growing since disc disorders represent a major health problem in industrialized countries with very few possible treatments. Indeed, current available therapies are symptomatic, and surgical procedures consist in disc removal and spinal fusion, which is not immune to regardable concerns about possible comorbidities, cost-effectiveness, secondary risks and long-lasting outcomes. This review paper aims to share recent advances in stem cell therapy for the treatment of intervertebral disc degeneration. In literature the potential use of different adult stem cells for intervertebral disc regeneration has already been reported. Bone marrow mesenchymal stromal/stem cells, adipose tissue derived stem cells, synovial stem cells, muscle-derived stem cells, olfactory neural stem cells, induced pluripotent stem cells, hematopoietic stem cells, disc stem cells, and embryonic stem cells have been studied for this purpose either in vitro or in vivo. Moreover, several engineered carriers (e.g., hydrogels), characterized by full biocompatibility and prompt biodegradation, have been designed and combined with different stem cell types in order to optimize the local and controlled delivery of cellular substrates in situ. The paper overviews the literature discussing the current status of our knowledge of the different stem cells types used as a cell-based therapy for disc regeneration.

A Naturally Derived, Growth Factor-Binding Polysaccharide for Therapeutic Angiogenesis

We herein report the discovery of a naturally derived carbohydrate with binding affinities for two pro-angiogenic growth factors-fibroblast growth factor-2 (FGF-2) and platelet-derived growth factor-BB (PDGF-BB). This galacturonic acid-containing polysaccharide (EUP3) sequestered endogenous FGF-2 and PDGF-BB in vivo and promoted in situ formation and maturation of new blood vessels. Our findings suggest EUP3 as the first nonglycosaminoglycan, nonanimal-originated carbohydrate molecule that binds two pro-angiogenic growth factors to stimulate angiogenesis. Further investigations into this carbohydrate may lead to the development of new tools for therapeutic angiogenesis.

The CS Sulfation Motifs 4C3, 7D4, 3B3[-]; and Perlecan Identify Stem Cell Populations and Their Niches, Activated Progenitor Cells and Transitional Areas of Tissue Development in the Fetal Human Elbow

We compared the immunohistochemical distribution of (1) the novel chondroitin sulfate (CS) sulfation motifs 7D4, 4C3, and 3B3[-], (2) native heparan sulfate (HS) and Δ-HS "stubs" generated by heparitinase III digestion and (3) the HS-proteoglycan (PG), perlecan, in the fetal human elbow joint. Putative stem cell populations associated with hair bulbs, humeral perichondrium, humeral and ulnar rudiment stromal/perivascular tissues expressed the CS motifs 4C3, 7D4, and 3B3[-] along with perlecan in close association but not colocalized. Chondrocytes in the presumptive articular cartilage of the fetal elbow expressed the 4C3 and 7D4 CS sulfation motifs consistent with earlier studies on the expression of these motifs in knee cartilage following joint cavitation. This study also indicated that hair bulbs, skin, perichondrium, and rudiment stroma were all perlecan-rich progenitor cell niches that contributed to the organization and development of the human fetal elbow joint and associated connective tissues. One of the difficulties in determining the precise role of stem cells in tissue development and repair processes is their short engraftment period and the lack of specific markers, which differentiate the activated stem cell lineages from the resident cells. The CS sulfation motifs 7D4, 4C3, and 3B3[-] decorate cell surface PGs on activated stem/progenitor cells and thus can be used to identify these cells in transitional areas of tissue development and in repair tissues and may be applicable to determining a more precise mode of action of stem cells in these processes. Isolation of perlecan from 12 to 14 week gestational age fetal knee rudiments demonstrated that perlecan in these fetal tissues was a HS-CS hybrid PG further supporting roles for CS in tissue development.

The cast of clasts: catabolism and vascular invasion during bone growth, repair, and disease by osteoclasts, chondroclasts, and septoclasts

Three named cell types degrade and remove skeletal tissues during growth, repair, or disease: osteoclasts, chondroclasts, and septoclasts. A fourth type, unnamed and less understood, removes nonmineralized cartilage during development of secondary ossification centers. "Osteoclasts," best known and studied, are polykaryons formed by fusion of monocyte precursors under the influence of colony stimulating factor 1 (CSF)-1 (M-CSF) and RANKL. They resorb bone during growth, remodeling, repair, and disease. "Chondroclasts," originally described as highly similar in cytological detail to osteoclasts, reside on and degrade mineralized cartilage. They may be identical to osteoclasts since to date there are no distinguishing markers for them. Because osteoclasts also consume cartilage cores along with bone during growth, the term "chondroclast" might best be reserved for cells attached only to cartilage. "Septoclasts" are less studied and appreciated. They are mononuclear perivascular cells rich in cathepsin B. They extend a cytoplasmic projection with a ruffled membrane and degrade the last transverse septum of hypertrophic cartilage in the growth plate, permitting capillaries to bud into it. To do this, antiangiogenic signals in cartilage must give way to vascular trophic factors, mainly vascular endothelial growth factor (VEGF). The final cell type excavates cartilage canals for vascular invasion of articular cartilage during development of secondary ossification centers. The "clasts" are considered in the context of fracture repair and diseases such as arthritis and tumor metastasis. Many observations support an essential role for hypertrophic chondrocytes in recruiting septoclasts and osteoclasts/chondroclasts by supplying VEGF and RANKL. The intimate relationship between blood vessels and skeletal turnover and repair is also examined.

Stem cells in articular cartilage regeneration

Mesenchymal stem cells (MSCs) have emerged as a promising option to treat articular defects and early osteoarthritis (OA) stages. However, both their potential and limitations for a clinical use remain controversial. Thus, the aim of this systematic review was to examine MSCs treatment strategies in clinical settings, in order to summarize the current evidence of their efficacy for the treatment of cartilage lesions and OA.Among the 60 selected studies, 7 were randomized, 13 comparative, 31 case series, and 9 case reports; 26 studies reported the results after injective administration, whereas 33 used surgical implantation. One study compared the two different modalities. With regard to the cell source, 20 studies concerned BMSCs, 17 ADSCs, 16 BMC, 5 PBSCs, 1 SDSCs, and 1 compared BMC versus PBSCs. Overall, despite the increasing literature on this topic, the evidence is still limited, in particular for high-level studies. On the other hand, the available studies allow to draw some indications. First, no major adverse events related to the treatment or to the cell harvest have been reported. Second, a clinical benefit of using MSCs therapies has been reported in most of the studies, regardless of cell source, indication, or administration method. This effectiveness has been reflected by clinical improvements and also positive MRI and macroscopic findings, whereas histologic features gave more controversial results among different studies. Third, young age, lower BMI, smaller lesion size for focal lesions, and earlier stages of OA joints have been shown to correlate with better outcomes, even though the available data strength does not allow to define clear cutoff values. Finally, definite trends can be observed with regard to the delivery method: currently cultured cells are mostly being administered by i.a. injection, while one-step surgical implantation is preferred for cell concentrates. In conclusion, while promising results have been shown, the potential of these treatments should be confirmed by reliable clinical data through double-blind, controlled, prospective and multicenter studies with longer follow-up, and specific studies should be designed to identify the best cell sources, manipulation, and delivery techniques, as well as pathology and disease phase indications.

The Placenta as an Organ and a Source of Stem Cells and Extracellular Matrix: A Review

The placenta is a temporal, dynamic and diverse organ with important immunological features that facilitate embryonic and fetal development and survival, notwithstanding the fact that several aspects of its formation and function closely resemble tumor progression. Placentation in mammals is commonly used to characterize the evolution of species, including insights into human evolution. Although most placentas are discarded after birth, they are a high-yield source for the isolation of stem/progenitor cells and are rich in extracellular matrix (ECM), representing an important resource for regenerative medicine purposes. Interactions among cells, ECM and bioactive molecules regulate tissue and organ generation and comprise the foundation of tissue engineering. In the present article, differences among several mammalian species regarding the placental types and classifications, phenotypes and potency of placenta-derived stem/progenitor cells, placental ECM components and current placental ECM applications were reviewed to highlight their potential clinical and biomedical relevance.

Minicircle DNA-mediated endothelial nitric oxide synthase gene transfer enhances angiogenic responses of bone marrow-derived mesenchymal stem cells

Background

Non-viral-based gene modification of adult stem cells with endothelial nitric oxide synthase (eNOS) may enhance production of nitric oxide and promote angiogenesis. Nitric oxide (NO) derived from endothelial cells is a pleiotropic diffusible gas with positive effects on maintaining vascular tone and promoting wound healing and angiogenesis. Adult stem cells may enhance angiogenesis through expression of bioactive molecules, and their genetic modification to express eNOS may promote NO production and subsequent cellular responses.

Methods

Rat bone marrow-derived mesenchymal stem cells (rBMSCs) were transfected with a minicircle DNA vector expressing either green fluorescent protein (GFP) or eNOS. Transfected cells were analysed for eNOS expression and NO production and for their ability to form in vitro capillary tubules and cell migration. Transcriptional activity of angiogenesis-associated genes, CD31, VEGF-A, PDGFRα, FGF2, and FGFR2, were analysed by quantitative polymerase chain reaction.

Results

Minicircle vectors expressing GFP (MC-GFP) were used to transfect HEK293T cells and rBMSCs, and were compared to a larger parental vector (P-GFP). MC-GFP showed significantly higher transfection in HEK293T cells (55.51 ± 3.3 %) and in rBMSC (18.65 ± 1.05 %) compared to P-GFP in HEK293T cells (43.4 ± 4.9 %) and rBMSC (15.21 ± 0.22 %). MC-eNOS vectors showed higher transfection efficiency (21 ± 3 %) compared to P-eNOS (9 ± 1 %) and also generated higher NO levels. In vitro capillary tubule formation assays showed both MC-eNOS and P-eNOS gene-modified rBMSCs formed longer (14.66 ± 0.55 mm and 13.58 ± 0.68 mm, respectively) and a greater number of tubules (56.33 ± 3.51 and 51 ± 4, respectively) compared to controls, which was reduced with the NOS inhibitor L-NAME. In an in vitro wound healing assay, MC-eNOS transfected cells showed greater migration which was also reversed by L-NAME treatment. Finally, gene expression analysis in MC-eNOS transfected cells showed significant upregulation of the endothelial-specific marker CD31 and enhanced expression of VEGFA and FGF-2 and their corresponding receptors PDGFRα and FGFR2, respectively.

Conclusions

A novel eNOS-expressing minicircle vector can efficiently transfect rBMSCs and produce sufficient NO to enhance in vitro models of capillary formation and cell migration with an accompanying upregulation of CD31, angiogenic growth factor, and receptor gene expression.

MSC Therapeutics in Chronic Inflammation

The utilization of mesenchymal stem cells (also known as mesenchymal stromal cells, or MSCs) as a cell-based therapy for diseases that have ongoing inflammatory damage has become increasingly available. Our understanding of the cell biology of MSCs is still incomplete. However, as a result of increasing numbers of pre-clinical and clinical studies, general themes are emerging. The capacity of MSCs to reduce disease burden is largely associated with their ability to modulate the activity of the host immune responses rather than to contribute directly to tissue regeneration. As a result, they have significant potential in the treatment of chronic inflammatory disease regardless of the affected tissue. For example, MSC based therapies have been developed in the context of diseases as diverse as rheumatoid arthritis and multiple sclerosis. Here we discuss some of the principles that link these conditions, and the aspects of MSC biology that contribute to their use as a therapy for chronic inflammatory conditions.

Adipose derived pericytes rescue fractures from a failure of healing--non-union

Atrophic non-union is attributed to biological failure of the fracture repair process. It occurs in up to 10% of fractures, results in significant morbidity to patients, and treatment often requires complex reconstructive procedures. We tested the ability of human bone derived marrow mesenchymal stem cells (MSC), and human adipose derived pericytes (the native ancestor of the MSC) delivered percutaneously to the fracture gap to prevent the formation of atrophic non-union in a rat model. At eight weeks, 80% of animals in the cell treatment groups showed evidence of bone healing compared to only 14% of those in the control group. Radiographic parameters showed significant improvement over the eight-week period in the cell treatment groups, and histology confirmed bone bridges at the fracture gap in the both treatment groups. The quality of bone produced and its biomechanical properties were significantly enhanced in both treatment groups. The results from this study demonstrate that MSC and pericytes have significant bone regeneration potential in an atrophic non-union model. These cells may have a role in the prevention of atrophic non-union and could enable a paradigm shift in the treatment of fractures at high risk of failing to heal and developing non-union.