Journal of Stem Cells Research Development & Therapy Category: Medical Type: Short Commentary
Using Transcriptome Analysis for Redefining the in vivo Relevance of in vitro Cultured Circulating Angiogenic Cells (CACiv)
- Bert R Everaert1*, Steven J Van Laere2, Jean-Pierre Timmermans1, Christiaan J Vrints3
- 1 Laboratory Of Cell Biology And Histology, Department Of Veterinary Sciences, University Of Antwerp, Antwerp, Belgium
- 2 Translational Cancer Research Unit, Oncology Center, St-Augustinus Hospital, Wilrijk, Belgium
- 3 Laboratory Of Cellular And Molecular Cardiology, Antwerp University Hospital, Edegem, Belgium
*Corresponding Author:Bert R Everaert
Laboratory Of Cell Biology And Histology, Department Of Veterinary Sciences, University Of Antwerp, Antwerp, Belgium
Received Date: Jul 23, 2019 Accepted Date: Aug 19, 2019 Published Date: Aug 26, 2019
inflammatory; macrophage phenotype; Angiogenic Cells
However, still considerable debate about the origin and function of EPCs remains and much of this uncertainty is caused by a high degree of confusion about the definition of EPCs. Over the years, different culture protocols have emerged, all claiming to produce EPCs from Bone Marrow (BM) or peripheral blood-derived mononuclear cells. Furthermore, a variety of molecular marker combinations have been utilized for their characterization. Obviously, the ambiguity that surrounds the term ‘EPC’ has not facilitated the understanding of EPC biology.
This lack of phenotypical characterization and the limited knowledge of the underlying EPC biology have, however, not hindered the early use of Bone Marrow-Derived Stem Cells (BMSCs) in clinical indications. Not surprisingly, a Cochrane Review investigating the effects of BMSC therapy in the setting of Acute Myocardial Infarction (AMI) reported a marked heterogeneity between trials and concluded that larger study populations and more reliable outcome measures would be needed to evaluate the benefits of BMSC therapy .
Originally, the concept of EPCs dates back to a landmark study published in 1997 by Asahara et al. , who isolated a ‘putative progenitor endothelial cell’ that was found within the CD34+ mononuclear blood cell fraction. These EPCs were able to differentiate in vitro into an endothelial phenotype and incorporated into sites of neovascularization in vivo. After more than a decade of vigorous research, the exact function of these cells is still uncertain. Therefore, we investigated the phenotype and biological function of a particular EPC subtype that has been extensively studied and was renamed as circulating angiogenic cell (CAC) , early EPC  or Early Pro-angiogenic Cell (EPC) .
TRANSCRIPTOME ANALYSIS REVEALS THE TRUE NATURE OF IN VITRO CULTURED CAC
Using Ingenuity Pathway Analysis (IPA) software, we disclosed previously unrecognized biological processes in CACiv, such as riboflavin metabolism and liver X receptor (LXR)/retinoid X receptor (RXR) and farnesoid X receptor (FXR)/RXR pathways. Both LXRs and FXRs are cholesterol-sensing nuclear receptors regulating cholesterol homeostasis through upregulation of cholesterol efflux transporters. Moreover, both pathways are capable of down regulating inflammatory gene expression by repression of nuclear factor κB (NFκB) in macrophages, which would endow CACiv with anti-inflammatory properties. Therefore, CACiv therapy might be a convenient treatment strategy to selectively target cholesterol metabolism in atherosclerotic disease and induce reverse plaque remodeling. The finding that riboflavin metabolism is actively upregulated in CACiv, suggests that CACiv could have therapeutic potential under conditions of increased oxidative damage and endothelial dysfunction. Riboflavin or vitamin B2 is the central element of the cofactors Flavin Mononucleotide (FMN) and Flavin Adenine Dinucleotide (FAD). FMN and FAD play important roles in cellular oxidoreductase reactions. They are essential cofactors in cellular energy metabolism and cellular resistance to oxidative damage and in the enzymatic reaction catalysed by Nitric Oxide Synthase (NOS) isoforms.
Together, the biological pathways we found to be upregulated in the CACiv profile, relate to reverse cholesterol transport, immunomodulation, energy metabolism and NO bioavailability. These findings could indicate new treatment options with these in vitro cultured CAC, being in nature immune-modulatory macrophages, with interesting pleiotropic effects in the treatment of atherosclerotic and cardiovascular disease. Alternatively, pathophysiological conditions leading to the impaired in vivofunction of these immune-modulatory macrophages would be able to promoteendothelial dysfunction and atherosclerotic plaque formation and progression. However, future experimental studies are required to confirm these hypotheses.
TRANSCRIPTOME ANALYSIS REVEALS CACIV SIGNATURE AS AN IN VIVO RELEVANT GENE EXPRESSION ENTITY
Finally, we correlated the monocyte and macrophage profiles to the AMI transcriptome (Figure 2B, 2C). We observed an influx of a monocyte-associated profile in the first hours after AMI and found evidence of accumulation of macrophage-related gene expression in the subacute phase of AMI. As far as macrophage differentiation is concerned, a temporal down regulation of M1-associated gene expression and a switch towards a predominant M2 expression profile during the remodeling phase of AMI was evident (Figure 2D).
Rather than indicating active progenitor cell homing, the influx of the CACiv signature most probably results from the in situ transformation of the inflammatory cell population toward a more regulatory M2 macrophage phenotype that actively promotes immunomodulation, tissue remodeling and angiogenesis in the later stages of the post-myocardial infarction healing phase. This finding validates the CACivtranscriptome as a biologically, in vivo relevant gene expression entity, more specifically in the late post-myocardial infarction healing phase. This could have important clinical implications towards the optimal timing of future stem cell or CACiv therapy in the setting of myocardial infarction and other ischemia-related conditions.
- Everaert BR, Van Craenenbroeck EM, Hoymans VY, Haine SE, Van Nassauw L, et al. (2010) Current perspective of pathophysiological and interventional effects on endothelial progenitor cell biology: Focus on Pi3K/AKT/eNOS pathway. Int J Cardiol 144: 350-366.
- Martin-Rendon E, Brunskill S, Doree C, Hyde C, Watt S, et al. (2008) Stem cell treatment for acute myocardial infarction. Cochrane Database Syst Rev CD006536.
- Asahara T, Murohara T, Sullivan A, Silver M, van der Zee R, et al. (1997) Isolation of putative progenitor endothelial cells for angiogenesis. Science 275: 964-967.
- Rehman J, Li J, Orschell CM, March KL (2003) Peripheral blood "endothelial progenitor cells" are derived from monocyte/macrophages and secrete angiogenic growth factors. Circulation 107: 1164-1169.
- Hur J, Yoon CH, Kim HS, Choi JH, Kang HJ, et al. (2004) Characterization of two types of endothelial progenitor cells and their different contributions to neovasculogenesis. Arterioscler Thromb Vasc Biol 24: 288-293.
- Urbich C, De Souza AI, Rossig L, Yin X, Xing Q, et al. (2011) Proteomic characterization of human early pro-angiogenic cells. J Mol Cell Cardiol 50: 333-336.
- Everaert BR, Van Laere SJ, Lembrechts R, Hoymans VY, Timmermans JP, et al. (2019) Identification of Macrophage Genotype and Key Biological Pathways in Circulating Angiogenic Cell Transcriptome. Stem Cells Int 2019: 9545261.
- Van Ginderachter JA, Movahedi K, Hassanzadeh Ghassabeh G, Meerschaut S, Beschin A, et al. (2006) Classical and alternative activation of mononuclear phagocytes: picking the best of both worlds for tumor promotion. Immunobiology 211: 487-501.
- Mosser DM, Edwards JP (2008) Exploring the full spectrum of macrophage activation. Nat Rev Immunol 8: 958-969.
- Sica A, Schioppa T, Mantovani A, Allavena P (2006) Tumour-associated macrophages are a distinct M2 polarised population promoting tumour progression: potential targets of anti-cancer therapy. Eur J Cancer 42: 717-727.
Citation:Everaert BR, Laere SJV, Timmermans J-P, Vrints CJ (2019) Using Transcriptome Analysis for Redefining the in vivo Relevance of in vitro Cultured Circulating Angiogenic Cells (CACiv). J Stem Cell Res Dev Ther 5: 015.
Copyright: © 2019 Bert R Everaert, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.