Hendrik Gremmels

Cellular stress conditions are reflected in the protein and RNA content of endothelial cell-derived exosomes.

Background: The healthy vascular endothelium, which forms the barrier between blood and the surrounding tissues, is known to efficiently respond to stress signals like hypoxia and inflammation by adaptation of cellular physiology and the secretion of (soluble) growth factors and cytokines. Exosomes are potent mediators of intercellular communication. Their content consists of RNA and proteins from the cell of origin, and thus depends on the condition of these cells at the time of exosome biogenesis. It has been suggested that exosomes protect their target cells from cellular stress through the transfer of RNA and proteins. We hypothesized that endothelium-derived exosomes are involved in the endothelial response to cellular stress, and that exosome RNA and protein content reflect the effects of cellular stress induced by hypoxia, inflammation or hyperglycemia. Methods: We exposed cultured endothelial cells to different types of cellular stress (hypoxia, TNF-α-induced activation, high glucose and mannose concentrations) and compared mRNA and protein content of exosomes produced by these cells by microarray analysis and a quantitative proteomics approach. Results: We identified 1,354 proteins and 1,992 mRNAs in endothelial cell-derived exosomes. Several proteins and mRNAs showed altered abundances after exposure of their producing cells to cellular stress, which were confirmed by immunoblot or qPCR analysis. Conclusion: Our data show that hypoxia and endothelial activation are reflected in RNA and protein exosome composition, and that exposure to high sugar concentrations alters exosome protein composition only to a minor extend, and does not affect exosome RNA composition. To access the supplementary material to this article: Tables SI-SIV and Figures S1-2, please see Supplementary files under Article Tools online.

Prolonged presence of VEGF promotes vascularization in 3D bioprinted scaffolds with defined architecture

Timely vascularization is essential for optimal performance of bone regenerative constructs. Vascularization is efficiently stimulated by vascular endothelial growth factor (VEGF), a substance with a short half-life time. This study investigates the controlled release of VEGF from gelatin microparticles (GMPs) as a means to prolong VEGF activity at the preferred location within 3D bioprinted scaffolds, and the effects on subsequent vascularization. The release of VEGF from GMPs was continuous for 3 weeks during in vitro studies, and bioactivity was confirmed using human endothelial progenitor cells (EPCs) in migration assays. Traditional and real-time migration assays showed immediate and efficient EPC migration in the presence of GMP-released VEGF, indistinguishable from VEGF-solution that was added to the medium. Matrigel scaffolds containing EPCs and VEGF, which was released either in a fast or sustained fashion by application of GMPs, were investigated for their in vivo vasculogenic capacity. Implantation in subcutaneous pockets in nude mice for one week demonstrated that vessel formation was significantly higher in the VEGF sustained-release group compared to the fast release group. In addition, regional differences with respect to VEGF release were introduced in 3D bioprinted EPC-laden scaffolds and their influence on vasculogenesis was investigated in vivo. The different regions were retained and vessel formation occurred analogous with the results seen in the Matrigel plugs. We conclude that GMPs are suitable to generate sustained release profiles of bioactive VEGF, and that they can be used to create defined differentiation regions in 3D bioprinted heterogeneous constructs, allowing a new generation of smart scaffold design. The prolonged presence of VEGF led to a significant increase in scaffold vascularization when applied in vivo.

Cardiac Stem Cell Treatment in Myocardial Infarction: A Systematic Review and Meta-Analysis of Preclinical Studies

RATIONALE Cardiac stem cells (CSC) therapy has been clinically introduced for cardiac repair after myocardial infarction (MI). To date, there has been no systematic overview and meta-analysis of studies using CSC therapy for MI. OBJECTIVE Here, we used meta-analysis to establish the overall effect of CSCs in preclinical studies and assessed translational differences between and within large and small animals in the CSC therapy field. In addition, we explored the effect of CSC type and other clinically relevant parameters on functional outcome to better predict and design future (pre)clinical studies using CSCs for MI. METHODS AND RESULTS A systematic search was performed, yielding 80 studies. We determined the overall effect of CSC therapy on left ventricular ejection fraction and performed meta-regression to investigate clinically relevant parameters. We also assessed the quality of included studies and possible bias. The overall effect observed in CSC-treated animals was 10.7% (95% confidence interval 9.4-12.1; P<0.001) improvement in ejection fraction compared with placebo controls. Interestingly, CSC therapy had a greater effect in small animals compared with large animals (P<0.001). Meta-regression indicated that cell type was a significant predictor for ejection fraction improvement in small animals. Minor publication bias was observed in small animal studies. CONCLUSIONS CSC treatment resulted in significant improvement of ejection fraction in preclinical animal models of MI compared with placebo. There was a reduction in the magnitude of effect in large compared with small animal models. Although different CSC types have overlapping culture characteristics, we observed a significant difference in their effect in post-MI animal studies.Rationale: Cardiac stem cells (CSC) therapy has been clinically introduced for cardiac repair after myocardial infarction (MI). To date, there has been no systematic overview and meta-analysis of studies using CSC therapy for MI. Objective: Here, we used meta-analysis to establish the overall effect of CSCs in preclinical studies and assessed translational differences between and within large and small animals in the CSC therapy field. In addition, we explored the effect of CSC type and other clinically relevant parameters on functional outcome to better predict and design future (pre)clinical studies using CSCs for MI. Methods and Results: A systematic search was performed, yielding 80 studies. We determined the overall effect of CSC therapy on left ventricular ejection fraction and performed meta-regression to investigate clinically relevant parameters. We also assessed the quality of included studies and possible bias. The overall effect observed in CSC-treated animals was 10.7% (95% confidence interval 9.4–12.1; P <0.001) improvement in ejection fraction compared with placebo controls. Interestingly, CSC therapy had a greater effect in small animals compared with large animals ( P <0.001). Meta-regression indicated that cell type was a significant predictor for ejection fraction improvement in small animals. Minor publication bias was observed in small animal studies. Conclusions: CSC treatment resulted in significant improvement of ejection fraction in preclinical animal models of MI compared with placebo. There was a reduction in the magnitude of effect in large compared with small animal models. Although different CSC types have overlapping culture characteristics, we observed a significant difference in their effect in post-MI animal studies. # Novelty and Significance {#article-title-50}

Deoxynivalenol: a trigger for intestinal integrity breakdown

Disintegration of the colonic epithelial barrier is considered a key event in the initiation and progression of inflammatory bowel and celiac disease. As the primary etiology of these diseases remains unknown, we hypothesized that the trichothecene deoxynivalenol (DON), a fungal metabolite found in grain‐based human diets, might be one of the triggers resulting in an impairment of the intestinal tight junction network preceding an inflammatory response. Using horizontal impedance measurements, we demonstrate that DON disintegrates a human Caco‐2 cell monolayer within <1 h after exposure to concentrations as low as 1.39 μM. This initial trigger is followed by a decrease in transepithelial resistance and an increased permeability of marker molecules, such as lucifer yellow and FITC‐labeled dextran. In parallel, the increase in paracellular transport of FITC‐dextran is demonstrated in vivo in B6C3F1 mice, challenged orally with DON. In vitro claudin protein levels are decreased and correlated with a displacement within the cells in vitro and in vivo, accompanied by a compensatory up‐regulation of mRNA levels of claudins and their binding partner ZO‐1. In treated mice, alterations in villus architecture in the entire intestinal tract resemble the disintegration of the epithelial barrier, a characteristic of chronic inflammatory bowel disease.—Akbari, P., Braber, S., Gremmels, H., Koelink, P. J., Verheijden, K. A. T., Garssen, J., Fink‐Gremmels, J. Deoxynivalenol: a trigger for intestinal integrity breakdown. FASEB J. 28, 2414–2429 (2014). www.fasebj.org

Bone Marrow Alterations and Lower Endothelial Progenitor Cell Numbers in Critical Limb Ischemia Patients

Background Critical limb ischemia (CLI) is characterized by lower extremity artery obstruction and a largely unexplained impaired ischemic neovascularization response. Bone marrow (BM) derived endothelial progenitor cells (EPC) contribute to neovascularization. We hypothesize that reduced levels and function of circulating progenitor cells and alterations in the BM contribute to impaired neovascularization in CLI. Methods Levels of primitive (CD34+ and CD133+) progenitors and CD34+KDR+ EPC were analyzed using flow cytometry in blood and BM from 101 CLI patients in the JUVENTAS-trial (NCT00371371) and healthy controls. Blood levels of markers for endothelial injury (sE-selectin, sICAM-1, sVCAM-1, and thrombomodulin), and progenitor cell mobilizing and inflammatory factors were assessed by conventional and multiplex ELISA. BM levels and activity of the EPC mobilizing protease MMP-9 were assessed by ELISA and zymography. Circulating angiogenic cells (CAC) were cultured and their paracrine function was assessed. Results Endothelial injury markers were higher in CLI (P<0.01). CLI patients had higher levels of VEGF, SDF-1α, SCF, G-CSF (P<0.05) and of IL-6, IL-8 and IP-10 (P<0.05). Circulating EPC and BM CD34+ cells (P<0.05), lymphocytic expression of CXCR4 and CD26 in BM (P<0.05), and BM levels and activity of MMP-9 (P<0.01) were lower in CLI. Multivariate regression analysis showed an inverse association between IL-6 and BM CD34+ cell levels (P = 0.007). CAC from CLI patients had reduced paracrine function (P<0.0001). Conclusion CLI patients have reduced levels of circulating EPC, despite profound endothelial injury and an EPC mobilizing response. Moreover, CLI patients have lower BM CD34+-cell levels, which were inversely associated with the inflammatory marker IL-6, and lower BM MMP-9 levels and activity. The results of this study suggest that inflammation-induced BM exhaustion and a disturbed progenitor cell mobilization response due to reduced levels and activity of MMP-9 in the BM and alterations in the SDF-1α/CXCR4 interaction contribute to the attenuated neovascularization in CLI patients.

Neovascularization Capacity of Mesenchymal Stromal Cells From Critical Limb Ischemia Patients Is Equivalent to Healthy Controls

Critical limb ischemia (CLI) is often poorly treatable by conventional management and alternatives such as autologous cell therapy are increasingly investigated. Whereas previous studies showed a substantial impairment of neovascularization capacity in primary bone-marrow (BM) isolates from patients, little is known about dysfunction in patient-derived BM mesenchymal stromal cells (MSCs). In this study, we have compared CLI-MSCs to healthy controls using gene expression profiling and functional assays for differentiation, senescence and in vitro and in vivo pro-angiogenic ability. Whereas no differentially expressed genes were found and adipogenic and osteogenic differentiation did not significantly differ between groups, chondrogenic differentiation was impaired in CLI-MSCs, potentially as a consequence of increased senescence. Migration experiments showed no differences in growth factor sensitivity and secretion between CLI- and control MSCs. In a murine hind-limb ischemia model, recovery of perfusion was enhanced in MSC-treated mice compared to vehicle controls (71 ± 24% versus 44 ± 11%; P < 1 × 10(-6)). CLI-MSC- and control-MSC-treated animals showed nearly identical amounts of reperfusion (ratio CLI:Control = 0.98, 95% CI = 0.82-1.14), meeting our criteria for statistical equivalence. The neovascularization capacity of MSCs derived from CLI-patients is not compromised and equivalent to that of control MSCs, suggesting that autologous MSCs are suitable for cell therapy in CLI patients.

Cell-based therapies for experimental chronic kidney disease: a systematic review and meta-analysis.

Cell-based therapy is a promising strategy for treating chronic kidney disease (CKD) and is currently the focus of preclinical studies. We performed a systematic review and meta-analysis to evaluate the efficacy of cell-based therapy in preclinical (animal) studies of CKD, and determined factors affecting cell-based therapy efficacy in order to guide future clinical trials. In total, 71 articles met the inclusion criteria. Standardised mean differences (SMD) and 95% confidence intervals (CI) were calculated for outcome parameters including plasma urea, plasma creatinine, urinary protein, blood pressure, glomerular filtration rate, glomerulosclerosis and interstitial fibrosis. Sub-analysis for each outcome measure was performed for model-related factors (species, gender, model and timing of therapy) and cell-related factors (cell type, condition and origin, administration route and regime of therapy). Overall, meta-analysis showed that cell-based therapy reduced the development and progression of CKD. This was most prominent for urinary protein (SMD, 1.34; 95% CI, 1.00–1.68) and urea (1.09; 0.66–1.51), both P<0.001. Changes in plasma urea were associated with changes in both glomerulosclerosis and interstitial fibrosis. Sub-analysis showed that cell type (bone-marrow-derived progenitors and mesenchymal stromal cells being most effective) and administration route (intravenous or renal artery injection) were significant predictors of therapeutic efficacy. The timing of therapy in relation to clinical manifestation of disease, and cell origin and dose, were not associated with efficacy. Our meta-analysis confirms that cell-based therapies improve impaired renal function and morphology in preclinical models of CKD. Our analyses can be used to optimise experimental interventions and thus support both improved preclinical research and development of cell-based therapeutic interventions in a clinical setting.

Different types of cultured human adult cardiac progenitor cells have a high degree of transcriptome similarity.

The discovery and isolation of different resident cardiac progenitor cells (CPCs) a decade ago, as described by several research groups, stimulated the use of these cells for cardiac regeneration. Human CPCs are moving towards the clinic as one of the most promising cell types for cardiac repair, but the extent to which their molecular profiles vary as a result of donor heterogeneity or different isolation methods remain unclear. Defining a common molecular profile that defines CPC’s is therefore an important goal. Similarly, identifying robust and multilaboratory isolation and culture protocols that generate reproducible cell populations from genetically diverse donors is critical for their translational success. In this respect, we collected human auricle biopsy samples anonymously from 20 different adult patients that underwent bypass surgery and generated a total number of 33 different cardiac derived progenitor cell (CPC) lines (Table S1). Human CPCs were isolated according the original published protocol, based on c-kit 1 or Sca-1 2 expression or auricles were cut in 1 mm3 parts and cultured as explants to obtain Cardiospheres (CSps) 3 and Cardiosphere Derived Cells (CDCs) 4. CPCs were subsequently propagated in a panel of different media formulations, either in their originally described culture media or switched to media and culture coatings of the other CPC subsets (Figure S1, Table S7). When comparing individual CPC cell-lines, isolated with different methodologies, they shared a high degree of similarities and correlation in gene expression patterns (Fig. ​(Fig.1B).1B). By averaging expression profiles of individual CPC conditions, thereby reducing donor variability, similarities increased even more, ranging from 0.92 to 0.96 (Fig. ​(Fig.1C;1C; Table S2). These results suggest that individual donor differences were larger than influences of isolation and medium conditions. Moreover, the strongest correlations between the different CPC lines were observed when cells were isolated and cultured in the same conditions. Among the different CPCs, spheres-growing CSps showed the least correlation (0.91–0.96), while monolayer-growing CPCs shared higher correlations among them (0.96–0.98). We performed a moderated t-test to evaluate significant differentially expressed genes between the individual samples (Tables S3 and S4). Out of the 13,073 analysd genes, we found only few genes differentially expressed in 5 of 20 different monolayer-cultured CPC cell-lines comparisons. Only when the 3D-cultured CSps were compared with the other CPCs more differently expressed genes could be identified. Although only limited genes were different, we further explored if we could identify differences in gene patterns between the different CPC populations, based on selected genes important for stem cell-maintenance, their growth and biology. In particular, we evaluated genes involved in the regulation of different stem cell pathways like TGF-β, Wnt, NFkB, p53, JAK/STAT, Notch and Hedgehog (Fig. S2A), cell cycle (Fig. S2B), stem cell transcription factors (Fig. S2C), and growth factors, cytokines and chemokines (Fig. S2D). Detailed heat map analysis showed again; however, a very similar profile among all samples, with small differences mainly related to individual donors and not to different cell types or conditions (Fig. S2). Since CSps and monolayer growing CPCs have differently expressed patterns, we selected all the significantly differentially expressed genes that displayed a two fold or more difference and compared them with CDCs, and c-Kit and Sca-1+ CPCs monolayer-cultures (Table S6). Ingenuity pathway analysis identified a gene network in CSps that is enriched in genes encoding for growth factor production and signalling molecules involved in the development of cardiac muscle, vasculogenesis and angiogenesis (Fig. ​(Fig.2).2). Among them BMP-2, HGF, LIF, PTGS-2, VEGFA and PDGFRB are known to play an important role during cardiac development. Moreover, having a protective effect on a developing heart failure. Figure 1 Experimental design of the project (A) and hierarchical clustering of CPCs samples (B and C). Sca-1+ cells were isolated from human auricle biopsy and cultured in gelatin coated flask and Sca-1 medium (Sca GEL S-MED) (2) (d). After expansion cells were ... Figure 2 Ingenuity molecular networks analysis of the differentially expressed genes. Fold difference ≥2; p<0.05. (A) Differentially regulated genes between CSps and Sca GEL SP++ in Cardiovascular System Development and Function, Embryonic Development, ... Taken together, our data suggest that human CPCs can be isolated from patient heart biopsies using different markers, such as c-kit or Sca-1- like, and alternative methodologies, via direct cell isolation or via explant culture, such as CSps and CDCs. For the first time, however, we showed that upon culture expansion, these cell populations have a very similar gene expression profile, even more pronounced when cultured in comparable culture conditions and even transcended by donor differences. Among the different CPCs analysed, CSps are the most different, probably because of the unselected cell populations and containing more supporting cell population that form CSps and their particular 3D culture structure and thereby different interactions and growing conditions. Surprisingly CDCs, which is a cell population derived from CSps, are more similar with other antigen selected CPCs rather than with CSps, confirming the idea that monolayer and high proliferative culture condition might play an important role in minimizing the differences among the different CPCs analysed. Recently, Dey et al. isolated murine CPCs, based on different surface markers 5, and showed that these, non-cultured cells, represent progenitor cell populations at different stages of cardiac commitment 5. In our study, we did not observe such differences between the different human monolayer CPCs population upon culture propagation. A similar stage difference, however, might be present in situ in humans as well but lost upon culture expansion. The expression of these different stem cell markers and their co-expression probably represent different developmental and/or physiological stages of CPCs, rather than intrinsic different CPC populations. For future translation for cardiac cell therapy, our results suggest that we need to take into account the cell donor variability between patients more than the isolation methodology, and further study the correlation between CPC characteristics and e.g. the diseased status of a patient. Our findings are of fundamental importance to create a consensus among different scientists in the field of myocardial regeneration, which should help align future clinical approaches to improve the reported beneficial effects of cell therapy for heart disease by using cardiac derived progenitor cell populations.

Transcriptome Analysis in Endothelial Progenitor Cell Biology

The use of endothelial progenitor cells (EPCs) is a promising new treatment option for cardiovascular diseases. Many of the underlying mechanisms that result in an improvement of endothelial function in vivo remain poorly elucidated to this date, however. We summarize the current positions and potential applications of gene-expression profiling in the field of EPC biology. Based on our own and published gene-expression data, we demonstrate that gene-expression profiling can efficiently be used to characterize different EPC types. Furthermore, we highlight the potential of gene-expression profiling for the analysis of changes that EPCs undergo during culture and examine changes in gene transcription in diseased patients. Transcriptome profiling is a powerful tool for the characterization and functional analysis of EPCs in health and disease.

Exosomes from hypoxic endothelial cells have increased collagen crosslinking activity through up-regulation of lysyl oxidase-like 2

Exosomes are important mediators of intercellular communication. Additionally, they contain a variety of components capable of interacting with the extracellular matrix (ECM), including integrins, matrix metalloproteinases and members of the immunoglobin superfamily. Despite these observations, research on exosome‐ECM interactions is limited. Here, we investigate whether the exosome‐associated lysyl oxidase family member lysyl oxidase‐like 2 (LOXL2) is involved in ECM remodelling. We found that LOXL2 is present on the exterior of endothelial cell (EC)‐derived exosomes, placing it in direct vicinity of the ECM. It is up‐regulated twofold in EC‐derived exosomes cultured under hypoxic conditions. Intact exosomes from hypoxic EC and LOXL2 overexpressing EC show increased activity in a fluorometric lysyl oxidase enzymatic activity assay as well as in a collagen gel contraction assay. Concordantly, knockdown of LOXL2 in exosome‐producing EC in both normal and hypoxic conditions reduces activity of exosomes in both assays. Our findings show for the first time that ECM crosslinking by EC‐derived exosomes is mediated by LOXL2 under the regulation of hypoxia, and implicate a role for exosomes in hypoxia‐regulated focal ECM remodelling, a key process in both fibrosis and wound healing.