Merle M. Krebber

Bio: Merle M. Krebber is an academic researcher from Utrecht University. The author has contributed to research in topics: Medicine & Kidney disease. The author has an hindex of 6, co-authored 12 publications receiving 95 citations.

A new microfluidic model that allows monitoring of complex vascular structures and cell interactions in a 3D biological matrix

Abstract: Microfluidic organ-on-a-chip designs are used to mimic human tissues, including the vasculature. Here we present a novel microfluidic device that allows the interaction of endothelial cells (ECs) with pericytes and the extracellular matrix (ECM) in full bio-matrix encased 3D vessel structures (neovessels) that can be subjected to continuous, unidirectional flow and perfusion with circulating immune cells. We designed a polydimethylsiloxane (PDMS) device with a reservoir for a 3D fibrinogen gel with pericytes. Open channels were created for ECs to form a monolayer. Controlled, continuous, and unidirectional flow was introduced via a pump system while the design facilitated 3D confocal imaging. In this vessel-on-a-chip system, ECs interact with pericytes to create a human cell derived blood vessel which maintains a perfusable lumen for up to 7 days. Dextran diffusion verified endothelial barrier function while demonstrating the beneficial role of supporting pericytes. Increased permeability after thrombin stimulation showed the capacity of the neovessels to show natural vascular response. Perfusion of neovessels with circulating THP-1 cells demonstrated this system as a valuable platform for assessing interaction between the endothelium and immune cells in response to TNFα. In conclusion: we created a novel vascular microfluidic device that facilitates the fabrication of an array of parallel soft-channel structures in ECM gel that develop into biologically functional neovessels without hard-scaffold support. This model provides a unique tool to conduct live in vitro imaging of the human vasculature during perfusion with circulating cells to mimic (disease) environments in a highly systematic but freely configurable manner.

Matrix Metalloproteinases and Tissue Inhibitors of Metalloproteinases in Extracellular Matrix Remodeling during Left Ventricular Diastolic Dysfunction and Heart Failure with Preserved Ejection Fraction: A Systematic Review and Meta-Analysis

Abstract: Matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) are pivotal regulators of extracellular matrix (ECM) composition and could, due to their dynamic activity, function as prognostic tools for fibrosis and cardiac function in left ventricular diastolic dysfunction (LVDD) and heart failure with preserved ejection fraction (HFpEF). We conducted a systematic review on experimental animal models of LVDD and HFpEF published in MEDLINE or Embase. Twenty-three studies were included with a total of 36 comparisons that reported established LVDD, quantification of cardiac fibrosis and cardiac MMP or TIMP expression or activity. LVDD/HFpEF models were divided based on underlying pathology: hemodynamic overload (17 comparisons), metabolic alteration (16 comparisons) or ageing (3 comparisons). Meta-analysis showed that echocardiographic parameters were not consistently altered in LVDD/HFpEF with invasive hemodynamic measurements better representing LVDD. Increased myocardial fibrotic area indicated comparable characteristics between hemodynamic and metabolic models. Regarding MMPs and TIMPs; MMP2 and MMP9 activity and protein and TIMP1 protein levels were mainly enhanced in hemodynamic models. In most cases only mRNA was assessed and there were no correlations between cardiac tissue and plasma levels. Female gender, a known risk factor for LVDD and HFpEF, was underrepresented. Novel studies should detail relevant model characteristics and focus on MMP and TIMP protein expression and activity to identify predictive circulating markers in cardiac ECM remodeling.

H3K27ac acetylome signatures reveal the epigenomic reorganization in remodeled non-failing human hearts

Abstract: H3K27ac histone acetylome changes contribute to the phenotypic response in heart diseases, particularly in end-stage heart failure. However, such epigenetic alterations have not been systematically investigated in remodeled non-failing human hearts. Therefore, valuable insight into cardiac dysfunction in early remodeling is lacking. This study aimed to reveal the acetylation changes of chromatin regions in response to myocardial remodeling and their correlations to transcriptional changes of neighboring genes. We detected chromatin regions with differential acetylation activity (DARs; Padj. < 0.05) between remodeled non-failing patient hearts and healthy donor hearts. The acetylation level of the chromatin region correlated with its RNA polymerase II occupancy level and the mRNA expression level of its adjacent gene per sample. Annotated genes from DARs were enriched in disease-related pathways, including fibrosis and cell metabolism regulation. DARs that change in the same direction have a tendency to cluster together, suggesting the well-reorganized chromatin architecture that facilitates the interactions of regulatory domains in response to myocardial remodeling. We further show the differences between the acetylation level and the mRNA expression level of cell-type-specific markers for cardiomyocytes and 11 non-myocyte cell types. Notably, we identified transcriptome factor (TF) binding motifs that were enriched in DARs and defined TFs that were predicted to bind to these motifs. We further showed 64 genes coding for these TFs that were differentially expressed in remodeled myocardium when compared with controls. Our study reveals extensive novel insight on myocardial remodeling at the DNA regulatory level. Differences between the acetylation level and the transcriptional level of cell-type-specific markers suggest additional mechanism(s) between acetylome and transcriptome. By integrating these two layers of epigenetic profiles, we further provide promising TF-encoding genes that could serve as master regulators of myocardial remodeling. Combined, our findings highlight the important role of chromatin regulatory signatures in understanding disease etiology.

The therapeutic potential of three-dimensional multipotent mesenchymal stromal cell spheroids.

Abstract: The efficiency of clinical trials involving transplantation of multipotent mesenchymal stromal cells (MSCs) is often insufficient due to harsh conditions present within the target tissue including hypoxia, low nutrient supply as well as inflammatory reactions. This indicates the necessity for optimization of cell-based therapy approaches which might include either modification of the cell manufacturing process or specific cell pretreatment procedures prior to transplantation. Recent reports confirm evidence that the aggregation of MSCs into three-dimensional (3D) multicellular spheroids results in enhancement of the overall therapeutic potential of cells, by improving the anti-inflammatory and angiogenic properties, stemness and survival of MSCs after transplantation. Such an MSCs spheroid generation approach may open new opportunities for the enlargement of MSCs applications in clinical research and therapy. However, the unification and optimization of 3D spheroid generation techniques, including the selection of appropriate clinical-grade culture conditions and methods for their large-scale production, are still of great importance. The current review addresses questions regarding therapeutic-associated properties of 3D multicellular MSCs spheroids in vitro and during preclinical animal studies, with special attention to the possibilities of translating these research achievements toward further clinical manufacturing and applications.

Novel Immune-Related Gene Signature for Risk Stratification and Prognosis of Survival in Lower-Grade Glioma

Abstract: Objective Despite several clinicopathological factors being integrated as prognostic biomarkers, the individual variants and risk stratification have not been fully elucidated in lower grade glioma (LGG). With the prevalence of gene expression profiling in LGG, and based on the critical role of the immune microenvironment, the aim of our study was to develop an immune-related signature for risk stratification and prognosis prediction in LGG.

Vascularization strategies for skin tissue engineering

Abstract: A number of challenges in skin grafting for wound healing have drawn researchers to focus on skin tissue engineering as an alternative solution. The core idea of tissue engineering is to use scaffolds, cells, and/or bioactive molecules to help the skin to properly recover from injuries. Over the past decades, the field has significantly evolved, developing various strategies to accelerate and improve skin regeneration. However, there are still several concerns that should be addressed. Among these limitations, vascularization is known as a critical challenge that needs thorough consideration. Delayed wound healing of large defects results in an insufficient vascular network and ultimately ischemia. Recent advances in the field of tissue engineering paved the way to improve vascularization of skin substitutes. Broadly, these solutions can be classified into two categories as (1) use of growth factors, reactive oxygen species-inducing nanoparticles, and stem cells to promote angiogenesis, and (2) in vitro or in vivo prevascularization of skin grafts. This review summarizes the state-of-the-art approaches, their limitations, and highlights the latest advances in therapeutic vascularization strategies for skin tissue engineering.

Lymphatic Tissue Engineering and Regeneration.

Abstract: The lymphatic system is a major circulatory system within the body, responsible for the transport of interstitial fluid, waste products, immune cells, and proteins. Compared to other physiological systems, the molecular mechanisms and underlying disease pathology largely remain to be understood which has hindered advancements in therapeutic options for lymphatic disorders. Dysfunction of the lymphatic system is associated with a wide range of disease phenotypes and has also been speculated as a route to rescue healthy phenotypes in areas including cardiovascular disease, metabolic syndrome, and neurological conditions. This review will discuss lymphatic system functions and structure, cell sources for regenerating lymphatic vessels, current approaches for engineering lymphatic vessels, and specific therapeutic areas that would benefit from advances in lymphatic tissue engineering and regeneration.