Preconditioning mesenchymal stem cells with transforming growth factor-alpha improves mesenchymal stem cell-mediated cardioprotection. Shock. 2010;33:24-30. [PMID: 19996917 DOI: 10.1097/shk.0b013e3181b7d137]

Empowering adult stem cells for myocardial regeneration

Treatment strategies for heart failure remain a high priority for ongoing research due to the profound unmet need in clinical disease coupled with lack of significant translational progress. The underlying issue is the same whether the cause is acute damage, chronic stress from disease, or aging: progressive loss of functional cardiomyocytes and diminished hemodynamic output. To stave off cardiomyocyte losses, a number of strategic approaches have been embraced in recent years involving both molecular and cellular approaches to augment myocardial structure and performance. Resultant excitement surrounding regenerative medicine in the heart has been tempered by realizations that reparative processes in the heart are insufficient to restore damaged myocardium to normal functional capacity and that cellular cardiomyoplasty is hampered by poor survival, proliferation, engraftment, and differentiation of the donated population. To overcome these limitations, a combination of molecular and cellular approaches must be adopted involving use of genetic engineering to enhance resistance to cell death and increase regenerative capacity. This review highlights biological properties of approached to potentiate stem cell-mediated regeneration to promote enhanced myocardial regeneration, persistence of donated cells, and long-lasting tissue repair. Optimizing cell delivery and harnessing the power of survival signaling cascades for ex vivo genetic modification of stem cells before reintroduction into the patient will be critical to enhance the efficacy of cellular cardiomyoplasty. Once this goal is achieved, then cell-based therapy has great promise for treatment of heart failure to combat the loss of cardiac structure and function associated with acute damage, chronic disease, or aging.

Preconditioning approach in stem cell therapy for the treatment of infarcted heart

Nearly two decades of research in regenerative medicine have been focused on the development of stem cells as a therapeutic option for treatment of the ischemic heart. Given the ability of stem cells to regenerate the damaged tissue, stem-cell-based therapy is an ideal approach for cardiovascular disorders. Preclinical studies in experimental animal models and clinical trials to determine the safety and efficacy of stem cell therapy have produced encouraging results that promise angiomyogenic repair of the ischemically damaged heart. Despite these promising results, stem cell therapy is still confronted with issues ranging from uncertainty about the as-yet-undetermined "ideal" donor cell type to the nonoptimized cell delivery strategies to harness optimal clinical benefits. Moreover, these lacunae have significantly hampered the progress of the heart cell therapy approach from bench to bedside for routine clinical applications. Massive death of donor cells in the infarcted myocardium during acute phase postengraftment is one of the areas of prime concern, which immensely lowers the efficacy of the procedure. An overview of the published data relevant to stem cell therapy is provided here and the various strategies that have been adopted to develop and optimize the protocols to enhance donor stem cell survival posttransplantation are discussed, with special focus on the preconditioning approach.

Cardiac cell therapy: pre-conditioning effects in cell-delivery strategies

Stem-cell therapy holds great promise for the treatment of ischemic heart disease. However, the benefit of cardiac cell therapy has not yet been proven in long-term clinical trials. Poor engraftment and survival of transplanted cells is one of the major concerns for the successful application of stem cells in cardiac cell therapy. Cell and cardiac pre-conditioning are now being explored as new approaches to support cell survival and enhance the therapeutic efficacy. In this paper, we summarize the state-of-the-art methods of cell delivery and cell survival post-delivery, with a focus on the pre-conditioning approaches that have been attempted to support the survival of transplanted cells.

Advances in mesenchymal stem cell research in sepsis

BACKGROUND

Sepsis remains a source of morbidity and mortality in the postoperative patient despite appropriate resuscitative and antimicrobial approaches. Recent research has focused upon additional interventions such as exogenous cell-based therapy. Mesenchymal stem cells (MSCs) exhibit multiple beneficial properties through their capacity for homing, attenuating the inflammatory response, modulating immune cells, and promoting tissue healing. Recent animal trials have provided evidence that MSCs may be useful therapeutic adjuncts.

MATERIALS AND METHODS

A directed search of recent medical literature was performed utilizing PubMed to examine the pathophysiology of sepsis, mechanisms of mesenchymal stem cell interaction with host cells, sepsis animal models, and recent trials utilizing stem cells in sepsis.

RESULTS

MSCs continue to show promise in the treatment of sepsis by their intrinsic ability to home to injured tissue, secrete paracrine signals to limit systemic and local inflammation, decrease apoptosis in threatened tissues, stimulate neoangiogenesis, activate resident stem cells, beneficially modulate immune cells, and exhibit direct antimicrobial activity. These effects are associated with reduced organ dysfunction and improved survival in animal models.

CONCLUSION

Research utilizing animal models of sepsis has provided a greater understanding of the beneficial properties of MSCs. Their capacity to home to sites of injury and use paracrine mechanisms to change the local environment to ultimately improve organ function and survival make MSCs attractive in the treatment of sepsis. Future studies are needed to further evaluate the complex interactions between MSCs and host tissues.

IL-6 and TGF-α costimulate mesenchymal stem cell vascular endothelial growth factor production by ERK-, JNK-, and PI3K-mediated mechanisms

Mesenchymal stem cells (MSCs) protect ischemic tissues in part through paracrine growth factor production. IL-6, which is upregulated in the heart during ischemia, has been shown to enhance stem cell proliferation and migration. The effect of IL-6 on MSC paracrine function, however, remains unknown. In addition, TGF-α increases MSC vascular endothelial growth factor (VEGF) production and may share downstream signaling pathways with IL-6 involving ERK, JNK, and PI3K. We hypothesize that cotreatment with IL-6 and TGF-α will result in greater MSC VEGF production than by either treatment alone via these signaling pathways. Murine MSCs were treated with IL-6 (0.05 ng/mL) with or without TGF-α (250 ng/mL) and in combination with inhibitors of ERKI/II, JNK, and PI3K for 24 h. Vascular endothelial growth factor concentrations in the supernatants were measured using enzyme-linked immunosorbent assay. Phosphorylation of ERK, JNK, and PI3K was measured using Western blot analysis. IL-6 increased MSC VEGF production at a dose of 0.05 ng/mL, and the combination of IL-6 and TGF-α (250 ng/mL) increased VEGF production to a greater extent than IL-6 or TGF-α alone. IL-6 induced phosphorylation of ERK, JNK, and PI3K, and inhibition of each suppressed IL-6-induced VEGF production. TGF-α cotreatment overcame VEGF suppression after ERK2 inhibition but not ERK1, JNK, or PI3K. These data suggest that IL-6 stimulates MSC VEGF production alone and additively with TGF-α via ERK-, JNK-, and PI3K-mediated mechanisms. IL-6 and TGF-α cotreatment may be a useful strategy for enhancing MSC VEGF production and cardioprotection during myocardial ischemia.

Amniotic fluid stem cells are cardioprotective following acute myocardial infarction

In recent years, various types of stem cells have been characterized and their potential for cardiac regeneration has been investigated. We have previously described the isolation of broadly multipotent cells from amniotic fluid, defined as amniotic fluid stem (AFS) cells. The aim of this study was to investigate the therapeutic potential of human AFS cells (hAFS) in a model of acute myocardial infarction. Wistar rats underwent 30 min of ischemia by ligation of the left anterior descending coronary artery, followed by administration of hAFS cells and 2 h of reperfusion. Infarct size was assessed by 2,3,5-triphenyltetrazolium chloride staining and planimetry. hAFS cells were also analyzed by enzyme-linked immunosorbent assay to detect secretion of putative paracrine factors, such as the actin monomer-binding protein thymosin β4 (Tβ4). The systemic injection of hAFS cells and their conditioned medium (hAFS-CM) was cardioprotective, improving myocardial cell survival and decreasing the infarct size from 53.9%±2.3% (control animals receiving phosphate-buffered saline injection) to 40.0%±3.0% (hAFS cells) and 39.7%±2.5% (hAFS-CM, P<0.01). In addition, hAFS cells were demonstrated to secrete Tβ4, previously shown to be both cardioprotective and proangiogenic. Our results suggest that AFS cells have therapeutic potential in the setting of acute myocardial infarction, which may be mediated through paracrine effectors such as Tβ4. Therefore, AFS cells might represent a novel source for cell therapy and cell transplantation strategies in repair following ischemic heart disease, with a possible paracrine mechanism of action and a potential molecular candidate for acute cardioprotection.

Mesenchymal stem cells for cardiac cell therapy

Despite refinements of medical and surgical therapies, heart failure remains a fatal disease. Myocardial infarction is the most common cause of heart failure, and only palliative measures are available to relieve symptoms and prolong the patient's life span. Because mammalian cardiomyocytes irreversibly exit the cell cycle at about the time of birth, the heart has traditionally been considered to lack any regenerative capacity. This paradigm, however, is currently shifting, and the cellular composition of the myocardium is being targeted by various regeneration strategies. Adult progenitor and stem cell treatment of diseased human myocardium has been carried out for more than 10 years (Menasche et al., 2001; Stamm et al., 2003), and it has become clear that, in humans, the regenerative capacity of hematopoietic stem cells and endothelial progenitor cells, despite potent proangiogenic effects, is limited (Stamm et al., 2009). More recently, mesenchymal stem cells (MSCs) and related cell types are being evaluated in preclinical models of heart disease as well as in clinical trials (see Published Clinical Trials, below). MSCs have the capacity to self-renew and to differentiate into lineages that normally originate from the embryonic mesenchyme (connective tissues, blood vessels, blood-related organs) (Caplan, 1991; Prockop, 1997; Pittenger et al., 1999). The current definition of MSCs includes plastic adherence in cell culture, specific surface antigen expression (CD105(+)/CD90(+)/CD73(+), CD34(-)/CD45(-)/CD11b(-) or CD14(-)/CD19(-) or CD79α(-)/HLA-DR1(-)), and multilineage in vitro differentiation potential (osteogenic, chondrogenic, and adipogenic) (Dominici et al., 2006 ). If those criteria are not met completely, the term "mesenchymal stromal cells" should be used for marrow-derived adherent cells, or other terms for MSC-like cells of different origin. For the purpose of this review, MSCs and related cells are discussed in general, and cell type-specific properties are indicated when appropriate. We first summarize the preclinical data on MSCs in models of heart disease, and then appraise the clinical experience with MSCs for cardiac cell therapy.

Ablation of TNF-alpha receptors influences mesenchymal stem cell-mediated cardiac protection against ischemia

Mesenchymal stem cell (MSC) infusion may reduce myocardial ischemic injury. TNF-alpha is a proinflammatory cytokine produced in large quantities during myocardial ischemia that can exert beneficial or detrimental effects on MSC function by binding to a 55-kd receptor (TNFR1) or a 75-kd receptor (TNFR2) on MSCs. We investigated whether genetic modification with ablation of TNFR1 and/or TNFR2 affects MSC-mediated protection against myocardial ischemic injury. The MSCs were harvested from wild-type mice (WT-MSCs) and knockout mice with ablation of TNFR1 and/or TNFR2 (TNFR1KO, TNFR2KO, and TNFR1/R2KO MSCs). After anesthesia was initiated via inhalation of isoflurane, myocardial ischemia was induced in rats via coronary artery ligation. Hearts were then injected with vehicle or MSCs (1 x 10 cells/mL). Myocardial function was assessed 28 days postsurgery with 2-dimensional echocardiograms and isolated heart perfusion. Myocardial tissue was collected for cytokine analysis and infarct measurements. We found that MSC treatment offered significant protection against myocardial ischemia, namely by decreasing infarct size, improving heart function, and decreasing ventricular remodeling compared with vehicle. Compared with WT-MSCs, TNFR1KO MSCs conferred increased cardiac protection, although TNFR2KO and TNFR1/R2KO MSCs conferred less cardiac protection. In addition, treatment with TNFR1KO MSCs was associated with decreased levels of proinflammatory cytokines and an increased level of vascular endothelial growth factor in the myocardium, whereas treatment with TNFR2KO or TNFR1/R2KO MSCs was associated with increased levels of proinflammatory cytokines and a decreased level of vascular endothelial growth factor compared with treatment with WT-MSCs. We conclude that MSC TNFR1 and TNFR2 play important roles in MSC-mediated cardiac protection after myocardial ischemia.

Growth factor regulation of proliferation and survival of multipotential stromal cells

Multipotential stromal cells (MSCs) have been touted to provide an alternative to conservative procedures of therapy, be it heart transplants, bone reconstruction, kidney grafts, or skin, neuronal and cartilage repair. A wide gap exists, however, between the number of MSCs that can be obtained from the donor site and the number of MSCs needed for implantation to regenerate tissue. Standard methods of MSC expansion being followed in laboratories are not fully suitable due to time and age-related constraints for autologous therapies, and transplant issues leave questions for allogenic therapies. Beyond these issues of sufficient numbers, there also exists a problem of MSC survival at the graft. Experiments in small animals have shown that MSCs do not persist well in the graft environment. Either there is no incorporation into the host tissue, or, if there is incorporation, most of the cells are lost within a month. The use of growth and other trophic factors may be helpful in counteracting these twin issues of MSC expansion and death. Growth factors are known to influence cell proliferation, motility, survival and morphogenesis. In the case of MSCs, it would be beneficial that the growth factor does not induce differentiation at an early stage since the number of early-differentiating progenitors would be very low. The present review looks at the effect of and downstream signaling of various growth factors on proliferation and survival in MSCs.

Hypoxic preconditioning induces the expression of prosurvival and proangiogenic markers in mesenchymal stem cells

Stem cells transplanted to the ischemic myocardium usually encounter massive cell death within a few days of therapy. Hypoxic preconditioning (HPC) is currently employed as a strategy to prepare stem cells for increased survival and engraftment in the heart. However, HPC of stem cells has provided varying results, supposedly due to the differences in the oxygen concentration, duration of exposure, and passage conditions. In the present study, we determined the effect of HPC on rat mesenchymal stem cells (MSCs) exposed to 0.5% oxygen concentration for 24, 48, or 72 h. We evaluated the expression of prosurvival, proangiogenic, and functional markers such as hypoxia-inducible factor-1α, VEGF, phosphorylated Akt, survivin, p21, cytochrome c, caspase-3, caspase-7, CXCR4, and c-Met. MSCs exposed to 24-h hypoxia showed reduced apoptosis on being subjected to severe hypoxic conditions. They also had significantly higher levels of prosurvival, proangiogenic, and prodifferentiation proteins when compared with longer exposure (72 h). Cells taken directly from the cryopreserved state did not respond effectively to the 24-h HPC as those that were cultured under normoxia before HPC. Cells cultured under normoxia before HPC showed decreased apoptosis, enhanced expression of connexin-43, cardiac myosin heavy chain, and CD31. The preconditioned cells were able to differentiate into the cardiovascular lineage. The results suggest that MSCs cultured under normoxia before 24-h HPC are in a state of optimal expression of prosurvival, proangiogenic, and functional proteins that may increase the survival and engraftment in the infarct heart. These results could provide further insights into optimal preparation of MSCs which would greatly influence the effectiveness of cell therapy in vivo.

Paracrine mechanisms of stem cell reparative and regenerative actions in the heart

Stem cells play an important role in restoring cardiac function in the damaged heart. In order to mediate repair, stem cells need to replace injured tissue by differentiating into specialized cardiac cell lineages and/or manipulating the cell and molecular mechanisms governing repair. Despite early reports describing engraftment and successful regeneration of cardiac tissue in animal models of heart failure, these events appear to be infrequent and yield too few new cardiomyocytes to account for the degree of improved cardiac function observed. Instead, mounting evidence suggests that stem cell mediated repair takes place via the release of paracrine factors into the surrounding tissue that subsequently direct a number of restorative processes including myocardial protection, neovascularization, cardiac remodeling, and differentiation. The potential for diverse stem cell populations to moderate many of the same processes as well as key paracrine factors and molecular pathways involved in stem cell-mediated cardiac repair will be discussed in this review. This article is part of a special issue entitled, "Cardiovascular Stem Cells Revisited".

Mesenchymal stem cells attenuate myocardial functional depression and reduce systemic and myocardial inflammation during endotoxemia

BACKGROUND

Endotoxemia is associated with depressed cardiac function during sepsis. Mesenchymal stem cells (MSCs) possess an ability to modulate the inflammatory response during sepsis, but it is unknown whether MSCs possess the ability to reduce endotoxemia-induced myocardial injury and dysfunction.

METHODS

Endotoxemia was induced in rats via injection of lipopolysaccharide (LPS). Animals were divided into the following groups: (1) saline + saline; (2) LPS + saline; (3) LPS + MSCs; and (4) LPS + LLC-PK1 renal epithelial cells (differentiated control). At 6 hours, animals were anesthetized, serum was collected, and hearts were extracted and perfused via the isolated heart system. Hearts and serum were analyzed for tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-6, and IL-10.

RESULTS

The administration of LPS depressed myocardial function. Treatment with MSCs ameliorated this depression. Serum TNF-alpha, IL-1beta, and IL-6 were elevated in LPS-treated groups. Treatment with MSCs was associated with reduced levels of these cytokines. A trend toward reduced myocardial TNF-alpha and significant reductions in myocardial IL-1beta and IL-6 were observed in the MSC-treated group. IL-10 levels were increased after the LPS administration in both serum and myocardium. Serum levels were increased further after treatment with MSCs.

CONCLUSION

Treatment with MSCs during endotoxemia reduces systemic and myocardial inflammation and is associated with a reduction in LPS-induced myocardial functional depression.

Optimizing stem cell function for the treatment of ischemic heart disease

BACKGROUND

Stem cell-based therapies for myocardial ischemia have demonstrated promising early clinical results, but their benefits have been limited in duration due to impaired donor cell engraftment and function. Several strategies have emerged for enhancing stem cell function prior to their therapeutic use particularly with regard to stem cell homing, paracrine function, and survival. This review discusses current understandings of stem cell-mediated cardioprotection as well as methods of enhancing post-transplantation stem cell function and survival through hypoxic preconditioning, genetic manipulation, and pharmacologic pretreatment.

MATERIALS AND METHODS

A literature search was performed using the MEDLINE and PubMed databases using the keywords "stem cell therapy," "myocardial ischemia," "hypoxic preconditioning," "paracrine function," and "stem cell pretreatment." Studies published in English since January 1990 were selected. In addition, studies were identified from references cited in publications found using the search terms.

RESULTS

All included studies utilized animal studies and/or in vitro techniques. Stem cell modifications generally targeted stem cell homing (SDF-1, CXCR4), paracrine function (VEGF, angiogenin, Ang-1, HGF, IL-18 binding protein, TNFR1/2), or survival (Akt, Bcl-2, Hsp20, HO-1, FGF-2). However, individual modifications commonly exhibited pleiotropic effects involving some or all of these general categories.

CONCLUSION

These strategies for optimizing stem cell-mediated cardioprotection present unique potential sets of advantages and disadvantages for clinical application. Additional questions remain including those that are most efficacious in terms of magnitude and duration of benefit as well as whether combinations may yield greater benefits in both the preclinical and clinical settings.

Postinfarct intramyocardial injection of mesenchymal stem cells pretreated with TGF-alpha improves acute myocardial function

Stem cell-based therapies offer promising potential for myocardial infarction (MI), but endogenous molecules released in response to injury likely impair posttransplantation stem cell function. Stem cell-mediated cardioprotection occurs in part via paracrine effects, and transforming growth factor-alpha (TGF-alpha) has been shown to enhance paracrine function. However, it is unknown whether pretreating stem cells with TGF-alpha increases stem cell-mediated cardioprotection after acute MI. Mesenchymal stem cells (MSCs) were treated with TGF-alpha (250 ng/ml) for 24 h. Adult male Sprague-Dawley rat hearts were isolated and perfused using the Langendorff method. MI was induced by ligating the left anterior descending coronary artery. Postligation (30 min), vehicle or 1 x 10(6) MSCs with or without pretreatment were injected in the infarct border zones, and the hearts were perfused for an additional 60 min. Left ventricular function was continuously measured, and infarct size was assessed with Evans blue dye and 2,3,5-triphenyltetrazolium chloride staining. Myocardial production of interleukin (IL)-1beta and IL-6 and caspase 3 activation was also measured. Left ventricular function decreased significantly following coronary artery ligation but improved following injection of untreated MSCs and to a greater extent after injection of pretreated MSCs. In addition, the infarct area, myocardial caspase 3 activation, and IL-6 production were lowest in hearts injected with pretreated cells. Intramyocardial injection of TGF-alpha-pretreated MSCs after acute MI is associated with increased myocardial function and decreased myocardial injury. This strategy may be useful for optimizing the therapeutic efficacy of stem cells for the treatment of acute MI.