Ralf Gaebel

Is the intravascular administration of mesenchymal stem cells safe?: Mesenchymal stem cells and intravital microscopy

We investigated the kinetics of human mesenchymal stem cells (MSCs) after intravascular administration into SCID mouse cremaster vasculature by intravital microscopy. MSCs were injected into abdominal aorta through left femoral artery at two different concentrations (1 x 10(6) or 0.2 x 10(6) cell). Arterial blood velocity decrease by 60 and 18% 1 min after high/low dose MSCs injection respectively. The blood microcirculation was interrupted after 174+/-71 and 485+/-81 s. Intravital microscopy observation and histopathologic analysis of cremaster muscles indicated MSCs were entrapped in capillaries in both groups. 40 and 25% animals died of pulmonary embolism respectively in both high and low MSCs dose groups, which was detected by histopathologic analysis of the lungs. Intraarterial MSCs administration may lead to occlusion in the distal vasculature due to their relatively large cell size. Pulmonary sequestration may cause death in small laboratory animals. MSCs should be used cautiously for intravascular transplantation.

Cell Origin of Human Mesenchymal Stem Cells Determines a Different Healing Performance in Cardiac Regeneration

The possible different therapeutic efficacy of human mesenchymal stem cells (hMSC) derived from umbilical cord blood (CB), adipose tissue (AT) or bone marrow (BM) for the treatment of myocardial infarction (MI) remains unexplored. This study was to assess the regenerative potential of hMSC from different origins and to evaluate the role of CD105 in cardiac regeneration. Male SCID mice underwent LAD-ligation and received the respective cell type (400.000/per animal) intramyocardially. Six weeks post infarction, cardiac catheterization showed significant preservation of left ventricular functions in BM and CD105+-CB treated groups compared to CB and nontreated MI group (MI-C). Cell survival analyzed by quantitative real time PCR for human GAPDH and capillary density measured by immunostaining showed consistent results. Furthermore, cardiac remodeling can be significantly attenuated by BM-hMSC compared to MI-C. Under hypoxic conditions in vitro, remarkably increased extracellular acidification and apoptosis has been detected from CB-hMSC compared to BM and CD105 purified CB-derived hMSC. Our findings suggests that hMSC originating from different sources showed a different healing performance in cardiac regeneration and CD105+ hMSC exhibited a favorable survival pattern in infarcted hearts, which translates into a more robust preservation of cardiac function.

Human Mesenchymal Stem Cells Display Reduced Expression of CD105 after Culture in Serum-Free Medium

Human Mesenchymal Stem Cells (hMSCs) present a promising tool for regenerative medicine. However, ex vivo expansion is necessary to obtain sufficient cells for clinical therapy. Conventional growth media usually contain the critical component fetal bovine serum. For clinical use, chemically defined media will be required. In this study, the capability of two commercial, chemically defined, serum-free hMSC growth media (MSCGM-CD and PowerStem) for hMSC proliferation was examined and compared to serum-containing medium (MSCGM). Immunophenotyping of hMSCs was performed using flow cytometry, and they were tested for their ability to differentiate into a variety of cell types. Although the morphology of hMSCs cultured in the different media differed, immunophenotyping displayed similar marker patterns (high expression of CD29, CD44, CD73, and CD90 cell surface markers and absence of CD45). Interestingly, the expression of CD105 was significantly lower for hMSCs cultured in MSCGM-CD compared to MSCGM. Both groups maintained mesenchymal multilineage differentiation potential. In conclusion, the serum-free growth medium is suitable for hMSC culture and comparable to its serum-containing counterpart. As the expression of CD105 has been shown to positively influence hMSC cardiac regenerative potential, the impact of CD105 expression onto clinical use after expansion in MSCGM-CD will have to be tested.

The CD4(+)AT2R(+) T cell subpopulation improves post-infarction remodelling and restores cardiac function

Myocardial infarction (MI) is a major condition causing heart failure (HF). After MI, the renin angiotensin system (RAS) and its signalling octapeptide angiotensin II (Ang II) interferes with cardiac injury/repair via the AT1 and AT2 receptors (AT1R, AT2R). Our study aimed at deciphering the mechanisms underlying the link between RAS and cellular components of the immune response relying on a rodent model of HF as well as HF patients. Flow cytometric analyses showed an increase in the expression of CD4+ AT2R+ cells in the rat heart and spleen post‐infarction, but a reduction in the peripheral blood. The latter was also observed in HF patients. The frequency of rat CD4+ AT2R+ T cells in circulating blood, post‐infarcted heart and spleen represented 3.8 ± 0.4%, 23.2 ± 2.7% and 22.6 ± 2.6% of the CD4+ cells. CD4+ AT2R+ T cells within blood CD4+ T cells were reduced from 2.6 ± 0.2% in healthy controls to 1.7 ± 0.4% in patients. Moreover, we characterized CD4+ AT2R+ T cells which expressed regulatory FoxP3, secreted interleukin‐10 and other inflammatory‐related cytokines. Furthermore, intramyocardial injection of MI‐induced splenic CD4+ AT2R+ T cells into recipient rats with MI led to reduced infarct size and improved cardiac performance. We defined CD4+ AT2R+ cells as a T cell subset improving heart function post‐MI corresponding with reduced infarction size in a rat MI‐model. Our results indicate CD4+ AT2R+ cells as a promising population for regenerative therapy, via myocardial transplantation, pharmacological AT2R activation or a combination thereof.

Mechanisms of stem cell based cardiac repair-gap junctional signaling promotes the cardiac lineage specification of mesenchymal stem cells

Different subtypes of bone marrow-derived stem cells are characterized by varying functionality and activity after transplantation into the infarcted heart. Improvement of stem cell therapeutics requires deep knowledge about the mechanisms that mediate the benefits of stem cell treatment. Here, we demonstrated that co-transplantation of mesenchymal stem cells (MSCs) and hematopoietic stem cells (HSCs) led to enhanced synergistic effects on cardiac remodeling. While HSCs were associated with blood vessel formation, MSCs were found to possess transdifferentiation capacity. This cardiomyogenic plasticity of MSCs was strongly promoted by a gap junction-dependent crosstalk between myocytes and stem cells. The inhibition of cell-cell coupling significantly reduced the expression of the cardiac specific transcription factors NKX2.5 and GATA4. Interestingly, we observed that small non-coding RNAs are exchanged between MSCs and cardiomyocytes in a GJ-dependent manner that might contribute to the transdifferentiation process of MSCs within a cardiac environment. Our results suggest that the predominant mechanism of HSCs contribution to cardiac regeneration is based on their ability to regulate angiogenesis. In contrast, transplanted MSCs have the capability for intercellular communication with surrounding cardiomyocytes, which triggers the intrinsic program of cardiogenic lineage specification of MSCs by providing cardiomyocyte-derived cues.

Data on the fate of MACS® MicroBeads intramyocardially co-injected with stem cell products

The data presented in this article are related to the research article “Intramyocardial Fate and Effect of Iron Nanoparticles co-injected with MACS® purified Stem Cell Products” (Müller et al., 2017) [1]. This article complements the cellular localization of superparamagnetic iron dextran particles (MACS® MicroBeads) used for magnetic activated cell sorting (MACS®). Data evaluate the time-dependent detachment of these nanoparticles from CD133+ haematopoietic stem cells (HSCs) and CD271+ mesenchymal stem cells (MSCs). Furthermore, the influence of these stem cells as well as of nanoparticles on cardiac remodeling processes after myocardial infarction (MI) was investigated.

Exploiting AT2R to Improve CD117 Stem Cell Function In Vitro and In Vivo - Perspectives for Cardiac Stem Cell Therapy

Background/Aims: CD117+ stem cell (SC) based therapy is considered an alternative therapeutic option for terminal heart disease. However, controversies exist on the effects of CD117+ SC implantation. In particular, the link between CD117+ SC function and angiotensin-II-type-2 receptor (AT2R) after MI is continuously discussed. We therefore asked whether 1) AT2R stimulation influences CD117+ SC properties in vitro and, 2) which effects can be ascribed to AT2R stimulation in vivo. Methods: We approached AT2R stimulation with Angiotensin II while simultaneously blocking its opponent receptor AT1 with Losartan. CD117 effects were dissected using a 2D-Matrigel assay and HL-1 co-culture in vitro. A model of myocardial infarction, in which we implanted EGFP+ CD117 SC, was further applied. Results: While we found indications for AT2R driven vasculogenesis in vitro, co-culture experiments revealed that CD117+ SC improve vitality of cardiomyocytes independently of AT2R function. Likewise, untreated CD117+ SC had a positive effect on cardiac function and acted cardioprotective in vivo. Conclusions: Therefore, our data show that transient AT2R stimulation does not significantly add to the beneficial actions of CD117+ SC in vivo. Yet, exploiting AT2R driven vasculogenis via an optimized AT2R stimulation protocol may become a promising tool for cardiac SC therapy.

Cardiac Mesenchymal Stem Cells Proliferate Early in the Ischemic Heart

Background/Purpose: Cardiac mesenchymal stem cells (MSCs) could stimulate cell-specific regenerative mechanisms after myocardial infarction (MI) depending on spatial origin, distribution, and niche regulation. We aimed at identifying and isolating tissue-specific cardiac MSCs that could contribute to regeneration. Methods: Following permanent ligation of the left anterior descending coronary artery in rats (n = 16), early cardiac tissues and cardiac mononuclear cells (MNCs) were analyzed by immunohistology, confocal laser scanning microscopy, and flow cytometry, respectively. Early postischemic specific MSCs were purified by fluorescence-activated cell sorting, cultivated under standardized culture conditions, and tested for multipotent differentiation in functional identification kits. Results: Cardiac MSC niches were detected intramyocardially in cell clusters after MI and characterized by positive expression for vimentin, CD29, CD44, CD90, CD105, PDGFRα, and DDR2. Following myocardial ischemia, proliferation was induced early and proliferation density was approximately 11% in intramyocardial MSC clusters of the peri-infarction border zone. Cluster sizes increased by 157 and 64% in the peri-infarction and noninfarcted areas of infarcted hearts compared with noninfarcted hearts 24 h following MI, respectively. Coincidentally, flow cytometry analyses illustrated postischemic moderate enrichments of CD45–CD44+ and CD45–DDR2+ cardiac MNCs. We enabled isolation of early postischemic culturable cardiac CD45–CD44+DDR2+ MSCs that demonstrated typical clonogenicity with colony-forming unit-fibroblast formation as well as adipogenic, chondrogenic, and osteogenic differentiation. Conclusions: MI triggered early proliferation in specific cardiac MSC niches that were organized in intramyocardial clusters. Following targeted isolation, early postischemic cardiac CD45–CD44+DDR2+ MSCs exhibited typical characteristics with multipotent differentiation capacity and clonogenic expansion.

Intramyocardial angiogenetic stem cells and epicardial erythropoietin save the acute ischemic heart

ABSTRACT Ischemic heart failure is the leading cause of mortality worldwide. An early boost of intracardiac regenerative key mechanisms and angiogenetic niche signaling in cardiac mesenchymal stem cells (MSCs) could improve myocardial infarction (MI) healing. Epicardial erythropoietin (EPO; 300 U kg−1) was compared with intraperitoneal and intramyocardial EPO treatments after acute MI in rats (n=156). Real-time PCR and confocal microscopy revealed that epicardial EPO treatment enhanced levels of intracardiac regenerative key indicators (SDF-1, CXCR4, CD34, Bcl-2, cyclin D1, Cdc2 and MMP2), induced transforming growth factor β (TGF-β)/WNT signaling in intramyocardial MSC niches through the direct activation of AKT and upregulation of upstream signals FOS and Fzd7, and augmented intracardiac mesenchymal proliferation 24 h after MI. Cardiac catheterization and tissue analysis showed superior cardiac functions, beneficial remodeling and increased capillary density 6 weeks after MI. Concomitant fluorescence-activated cell sorting, co-cultures with neonatal cardiomyocytes, angiogenesis assays, ELISA, western blotting and RAMAN spectroscopy demonstrated that EPO could promote cardiomyogenic differentiation that was specific of tissue origin and enhance paracrine angiogenetic activity in cardiac CD45−CD44+DDR2+ MSCs. Epicardial EPO delivery might be the optimal route for efficient upregulation of regenerative key signals after acute MI. Early EPO-mediated stimulation of mesenchymal proliferation, synergistic angiogenesis with cardiac MSCs and direct induction of TGF-β/WNT signaling in intramyocardial cardiac MSCs could initiate an accelerated healing process that enhances cardiac recovery. Summary: Cardiac mesenchymal stem cells respond early to myocardial infarction. Their regenerative capacity is directly upregulated by optimized stimulation of the heart through epicardial erythropoietin delivery.

Direct sprayed endothelialization, basement membrane and cell junction development on biological and artificial products are highly substrate-dependent and require optimized biofunctionalization

Abstract Background: Optimizing endothelialization of medical implants requires deep mechanistic insight into cellular adhesion, cell junction and physiological basement membrane development at the endothelial cell-to-scaffold substrate interface. Methods and results: We employed and standardized endothelial cells and fibrin hydrogel for simultaneous cell-plus-fibrin (EC-Fib) spray application using the Maslanka® spray pen. Quality assessment illustrated excellent structural integrity of EC-Fib. Acellular SynerGraft® showed improved intimal endothelial recellularization after short-term physical and chemical preconditionings including dry-freezing, sodium desoxycholate, Triton-X, acetic acid and collagenase treatments. Artificial substrates poly-L-lactic acid (PLLA), and polyamide-6 (PA-6) were tested regarding their mechanical appropriateness, revealed complete endothelialization following EC-Fib application and showed partially physiological basement membrane development. Additional laminin 1 biofunctionalization on PA-6 moderately enhanced basement membrane gene and protein expression. However, scanning electron microscopy, immunohistology and PCR analyses underlined immature endothelialization, basement membrane and cell junction development on all substrates with clear substrate-dependent differences. Conclusions: Direct sprayed endothelialization outlined the necessity for preconditioning acellular SynerGraft® prostheses for adequate recellularization. Laminin 1 biofunctionalization could slightly improve endothelialization of PA-6 substrates whereas physiological organization of the microenvironment remained immature and seemed highly substrate dependent.