Effective Regenerative Therapies Research Articles

Glucose metabolism: key endogenous regulator of β‐cell replication and survival

Recent studies in mice have shown that pancreatic β-cells have a significant potential for regeneration, suggesting that regenerative therapy for diabetes is feasible. Genetic lineage tracing studies indicate that β-cell regeneration is based on the replication of fully differentiated, insulin-positive β-cells. Thus, a major challenge for this field is to identify and enhance the molecular pathways that control β-cell replication and mass. We review evidence, from human genetics and mouse models, that glucose is a major signal for β-cell replication. The mitogenic effect of blood glucose is transmitted via glucose metabolism within β-cells, and through a signalling cascade that resembles the pathway for glucose-stimulated insulin secretion. We introduce the concept that the individual β-cell workload, defined as the amount of insulin that an individual β-cell must secrete to maintain euglycaemia, is the primary determinant of replication, survival and mass. We also propose that a cell-autonomous pathway, similar to that regulating replication, appears to be responsible for at least some of the toxic effects of glucose on β-cells. Understanding and uncoupling the mitogenic and toxic effects of glucose metabolism on β-cells may allow for the development of effective regenerative therapies for diabetes.

Support for Cardiovascular Cell Therapy Research at the National Heart, Lung, and Blood Institute

Heart failure (HF) exerts an enormous burden both in the United States and worldwide, compounded by the lack of effective therapies for patients with end-stage HF. Current options other than medical management are limited to cardiac transplantation, severely limited by the lack of donor availability, and ventricular assist device (VAD) implantation. Although the introduction of newer VADs has reduced complications such as thrombosis and infection, mortality in patients with VADs is still significant (≈25% in the first year1). Since the capacity of the heart to repair itself after myocardial infarction (MI) is very limited, effective regenerative therapies for patients with large acute MI to prevent progression to HF would be highly beneficial in decreasing the morbidity and mortality associated with end-stage HF. Regenerative therapies to repair failing hearts have the potential to provide new options for patients with advanced HF who currently face low quality of life as well as poor prognosis. ### National Heart, Lung, and Blood Institute Cardiovascular Cell Therapy Research Network Clinical trials to test the ability of cell therapy to treat patients after MI were initiated a decade ago in Europe with injection of autologous skeletal myoblasts in patients undergoing coronary artery bypass surgery,2 followed rapidly by trials using other cell types and delivery routes. In response to the proliferation of non-US cell therapy trials, the National Heart, Lung, and Blood Institute (NHLBI) held a working group in August 2004 to assess the status of clinical studies of cell-based therapies for cardiovascular disease, to determine the gaps in knowledge and barriers that prevent the implementation of well-designed and safe clinical studies. Another charge to the working group was to identify the areas of opportunity to apply cell-based therapies for cardiovascular disease.3 The primary recommendation of the working group was the formation of a cardiovascular cell therapy research network, consisting of a clinical research network component …

Regenerating functional heart tissue for myocardial repair

Heart disease is one of the leading causes of death worldwide and the number of patients with the disease is likely to grow with the continual decline in health for most of the developed world. Heart transplantation is one of the only treatment options for heart failure due to an acute myocardial infarction, but limited donor supply and organ rejection limit its widespread use. Cellular cardiomyoplasty, or cellular implantation, combined with various tissue-engineering methods aims to regenerate functional heart tissue. This review highlights the numerous cell sources that have been used to regenerate the heart as well as cover the wide range of tissue-engineering strategies that have been devised to optimize the delivery of these cells. It will probably be a long time before an effective regenerative therapy can make a serious impact at the bedside.

Endogenous musculoskeletal tissue regeneration

Damaged musculoskeletal tissues collectively represent the most common cause of pain and functional disability worldwide (Mason 2007). Clinical efforts to restore structural integrity and function to non-healing musculoskeletal tissues are often complicated by challenging biomechanical conditions, advanced age, adjacent tissue trauma, infection risks, ischemia conditions, or the general disease status of the patient (Lysaght et al. 2008). With this special issue, we aim at reviewing recent scientific developments in the field of musculoskeletal regeneration and at identifying clinical challenges associated with augmenting or stimulating endogenous repair processes and restoring function to musculoskeletal tissues. In parallel with discussions among the authors of this special issue, an International Workshop on Endogenous Musculoskeletal Tissue Regeneration was held on March 16, 2011 in Hilton Head, South Carolina, USA. Contributors to the special issue were invited to speak at the workshop and over 80 participants from North America, Europe and Asia were in attendance. Several recurring concepts and unresolved questions emerged from the workshop presentations and discussion. There was a clear consensus that effective regenerative therapies must take into consideration the biological constraints specific to the individual patient and clinical problem. Advanced age, radiation therapy, composite tissue trauma, or accompanying diseases such as diabetes, for example, present special challenges in the functional regeneration of damaged tissues. For some of these clinical scenarios, the endogenous progenitor cell supply might be critically diminished. The creation of extracellular matrix niches either in vitro or in vivo appears as an emerging strategy to enhance the viability and function of exogenously delivered cells. As has become evident, the direct synthesis of extracellular matrix might be only one role that progenitor cells play in regeneration and other aspects such as paracrine effects on adjacent cells might also be relevant to enable endogenous regeneration cascades. The potential for delivered cells to be used as tissue-inductive drugdelivery vehicles needs further investigation, as does the potential effects of the local host cells and environment on delivered stromal cell function and survival. Another important new strategy to promote endogenous regeneration is to increase the supply of circulating progenitor cells and their homing to sites of injury. Factors that stimulate the mobilization of stromal cells into the blood or provide signals to enhance site-specific recruitment could overcome the poor endogenous repair capacity in aged or otherwise impaired patients in order to heal challenging defects. A question that remains widely unanswered in regenerative medicine is whether healing deficits are a direct cause of a lack of responding progenitor cells or other factors. An alternative strategy to enhance regeneration D. W. Hutmacher (*) Institute of Health and Biomedical Innovation, Queensland University of Technology & George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology, Atlanta, Ga., USA e-mail: dietmar.hutmacher@qut.edu.au

Amniotic Stem Cells: Potential in Regenerative Medicine

Amniotic Stem Cells: Potential in Regenerative Medicine

Roles for MSI2 and PROX1 in hematopoietic stem cell activity

The MSI2 and PROX1 proteins are increasingly recognized for their critical roles in the biology of primitive hematopoietic cells and for their potential contributions to leukemic pathogenesis. Here we summarize the studies that have shed light on the hematopoietic-specific roles of MSI2 and PROX1 and give an overview of the molecular mechanisms underlying their function. In addition to a likely role in cell cycle restraint, the hematopoietic stem cell agonist MSI2 is essential for the maintenance of primitive cell fate through ensuring appropriate balance between self-renewal and differentiation. Overexpression of Msi2 can contribute to the progression of murine myeloid leukemia and in the human setting is associated with poor prognosis. Regulatory control imposed by MSI2 may be achieved partly through regulation of the Notch signaling pathway. Prox1 behaves in an opposing manner to Msi2, resulting in elevated stem cell numbers when depleted. It has a potential role in cell cycle control and may act at the level of primitive hematopoietic stem and progenitor cells as it does in other systems by directly promoting commitment and differentiation. PROX1 functions as a tumor suppressor in numerous tissue types and has been found mutated in hematopoietic cell lines and primary blood malignancies. Deciphering the molecular mechanisms through which MSI2 and PROX1 affect primitive hematopoietic cell fate will provide insight into the regulation of normal hematopoiesis and facilitate better understanding of the leukemic transformation process. This will be directly applicable to the development of effective regenerative therapies and targeted leukemia treatments.

Bone Marrow Stem Cell Derived Paracrine Factors for Regenerative Medicine: Current Perspectives and Therapeutic Potential

During the past several years, there has been intense research in the field of bone marrow-derived stem cell (BMSC) therapy to facilitate its translation into clinical setting. Although a lot has been accomplished, plenty of challenges lie ahead. Furthermore, there is a growing body of evidence showing that administration of BMSC-derived conditioned media (BMSC-CM) can recapitulate the beneficial effects observed after stem cell therapy. BMSCs produce a wide range of cytokines and chemokines that have, until now, shown extensive therapeutic potential. These paracrine mechanisms could be as diverse as stimulating receptor-mediated survival pathways, inducing stem cell homing and differentiation or regulating the anti-inflammatory effects in wounded areas. The current review reflects the rapid shift of interest from BMSC to BMSC-CM to alleviate many logistical and technical issues regarding cell therapy and evaluates its future potential as an effective regenerative therapy.

Human Vascular Progenitor Cells Can Guide Mesodermal Lineage Choice of Mesenchymal Stem and Progenitor Cells After Co-Transplantation In Vivo.

AbstractAbstract 939 Background:Multilineage differentiation potential of mesenchymal stem and progenitor cells (MSPCs) make them attractive candidates for tissue regeneration purposes. Guiding the differentiation of MSPCs towards single lineages would facilitate their application for targeted therapies in vivo. We have previously shown that MSPCs are essential for endothelial colony-forming progenitor cell (ECFC)-derived patent vessel formation in vivo* [Blood 2009; 113 (26):6716-25]. Preliminary data indicate that the ratio of co-applied cells can change mesenchymal lineage differentiation from vascular support towards either osteogenesis with subsequent bone marrow (BM) ingrowth or chondrogenesis. We hypothesized that environmental conditioning by ECFCs plays an instructive role during the developmental fate decision of MSPCs in vivo. Methods:MSPCs as well as ECFCs were isolated from adult BM, white adipose tissue (WAT), umbilical cord blood (UCB) and perivascular cord tissue**[J Vis Exp. 2009;(32) pii: 1525]. Proliferation potential and clonogenicity were monitored. Phenotype was analyzed by flow cytometry and immune cytochemistry. Cell function was studied in differentiation assays and during vascular network assembly in vitro. Models for in vivo human vessel as compared to bone, BM or cartilage formation were established in immune-deficient NSG mice (NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ). Non-invasive imaging was performed using computed tomography (CT), magnetic resonance (MRI) and near-infrared fluorescence imaging to elucidate the time course of heterotopic tissue development. Immune histochemistry was applied for morphologic studies of organogenesis. Results:Baseline analysis confirmed MSPC and ECFC purity, immune phenotype and sustained proliferation potential. We could show that human BM-derived MSPCs are capable of forming bone in vivo. Osteogenic differentiation and heterotopic ossicle formation was followed by attraction of mouse hematopoiesis and the establishment of entire murine BM including red and white blood cells and megakaryocytes within a human endosteal niche. Co-transplanted human ECFCs could instruct the MSPCs to differentiate also into pericytes or chondrocytes in vivo, depending on the applied MSPC/ECFC cell ratio. Non-invasive imaging and histological staining revealed that ectopic organogenesis had already started after 2–4 weeks and was stable during the observation period of 20 weeks. Non-BM-derived populations, although phenotypically identical, invariably lacked the capacity to build bone and marrow environment in this model in vivo. Conclusion:These data indicate that human ECFCs can instruct MSPCs and induce developmental fate decisions early in the time course of organ regeneration after transplantation. We suppose that effective regenerative stem cell therapy in vivo requires more than the injection of one single cell population. For vascular repair as compared to bone and marrow environment reconstitution our model is a promising tool to study the therapeutic applicability and risk profile of such ECFC/MSPC-based transplantation strategies. Disclosures:No relevant conflicts of interest to declare.

Periodontal Regeneration in Class III Furcation Defects of Beagle Dogs Using Guided Tissue Regenerative Therapy With Platelet‐Derived Growth Factor

We developed an effective regenerative therapy, referred to as platelet-derived growth factor-BB (PDGF-BB)-modulated guided tissue regenerative (GTR) therapy (P-GTR), capable of achieving periodontal regeneration of horizontal (Class III) furcation defects in the beagle dog. To determine its efficacy, repair and regeneration of horizontal furcation defects by P-GTR therapy and GTR therapy were compared. Chronically inflamed horizontal furcation defects were created around the second (P2) and fourth mandibular premolars (P4). After demineralization of the root surfaces with citric acid, the surfaces of left P2 and P4 were treated with PDGF-BB (P-GTR therapy) and those of contralateral teeth were treated with vehicle only (GTR therapy). Periodontal membranes were placed and retained 0.5 mm above the cemento-enamel junction for both groups. The mucoperiosteal flap was sutured in a coronal position and plaque control was achieved by daily irrigation with 2% chlorhexidine gluconate. At 5, 8, and 11 weeks, two animals each were sacrificed by perfusion with 2.5% glutaraldehyde through the carotid arteries, and the lesions were sliced mesio-distally, demineralized, dehydrated, and embedded. Periodontal healing and regeneration after GTR and P-GTR therapy were compared by histomorphometric as well as morphological analysis. Morphometric analysis for each time period was performed on the pooled samples of P2 and P4. Five weeks after both therapies, the lesions were filled primarily by tissue-free area, epithelium, inflamed tissue, and a small amount of newly formed fibrous connective tissue. At 8 and 11 weeks after P-GTR therapy, there was a statistically greater amount of bone and periodontal ligament formed in the lesions. The newly formed bone filled 80% of the lesion at 8 weeks and 87% at 11 weeks with P-GTR therapy, compared to 14% of the lesion at 8 weeks and 60% at 11 weeks with GTR therapy. Also, with P-GTR therapy there was less epithelium and tissue-free area, less inflamed tissue, and less connective tissue. Morphological analysis indicated that the defects around P2 revealed faster periodontal repair and regeneration than those around P4. While the lesions around P2 were effectively regenerated by 11 weeks even after GTR therapy, those around P4 failed to regenerate. On the other hand, P-GTR therapy further promoted periodontal repair and regeneration so that at 8 weeks the lesions around P2 and P4 demonstrated complete and nearly complete regeneration, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Platelet-derived growth factor-modulated guided tissue regenerative therapy.

The goal of this study was to develop an effective regenerative therapy capable of achieving periodontal regeneration of Class III furcation defects. We attempted to achieve this goal by combining three therapeutic approaches. First, the lesion was protected by an expanded polytetrafluoroethylene barrier membrane that prevents migration of gingival fibroblasts as well as osteogenic cells from the mucoperiosteal flaps. Second, platelet-derived growth factor-BB (PDGF-BB), which has potent chemotactic and mitogenic effects on periodontal ligament fibroblasts (PDL), was used to promote migration of fibroblasts and their proliferation on the root surface. Third, the root surface, demineralized by citric acid conditioning, was chosen as the primary site for PDGF-BB application. The demineralized root surface appeared to have the capability of providing a sustained release of the applied growth factor. This seemed to facilitate rapid repopulation of PDL fibroblasts on the root surface and new PDL formation in the early stages of repair, which contributed to complete periodontal regeneration without root resorption and ankylosis in later stages. Combining these approaches, we developed a therapy referred to as "PDGF-modulated guided tissue regenerative therapy." Unlike guided tissue regenerative therapy alone (without PDGF-BB), this therapy effectively promoted periodontal regeneration of Class III furcation defects in the beagle dog without significant ankylosis or root resorption.