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EMBRYONIC STEM CELLS

CXCR4⁺/FLK-1⁺ Biomarkers Select a Cardiopoietic Lineage from Embryonic Stem Cells

Marriott Heart Disease Research Program, Division of Cardiovascular Diseases, Departments of Medicine, Molecular Pharmacology and Experimental Therapeutics, and Medical Genetics, Mayo Clinic, Rochester, Minnesota, USA

Key Words. Biomarker • Cardiopoiesis • Cardiac differentiation • Network • Transcriptome

Correspondence: Andre Terzic, M.D., Ph.D., Mayo Clinic, 200 First Street SW, Rochester, Minnesota 55905, USA. Telephone: 507-284-2747; Fax: 507-266-9936; e-mail: terzic.andre{at}mayo.edu

Received September 23, 2007; accepted for publication March 14, 2008.
First published online in STEM CELLS EXPRESS   March 27, 2008.



Pluripotent stem cells demonstrate an inherent propensity for unrestricted multi-lineage differentiation. Translation into regenerative applications requires identification and isolation of tissue-specified progenitor cells. From a comprehensive pool of 11,272 quality-filtered genes, profiling embryonic stem cells at discrete stages of cardiopoiesis revealed 736 transcripts encoding membrane-associated proteins, where 306 were specifically upregulated with cardiogenic differentiation. Bioinformatic dissection of exposed surface biomarkers prioritized the chemokine receptor cluster as the most significantly over-represented gene receptor family during pre cardiac induction, with CXCR4 uniquely associated with mesendoderm formation. CXCR4⁺ progenitors were sorted from the embryonic stem cell pool into mesoderm-restricted progeny according to co-expression with the early mesoderm marker Flk-1. In contrast to CXCR4^–/Flk-1^– cells, the CXCR4⁺/Flk-1⁺ subpopulation demonstrated overexpressed cardiac lineage transcription factors (Mef2C, Myocardin, Nkx2.5), whereas pluripotent genes (Oct4, Fgf4, Sox2) as well as neuroectoderm (Sox1) and endoderm alpha-fetoprotein markers were all depleted. In fact, the CXCR4⁺/Flk-1⁺ biomarker combination identified embryonic stem cell progeny significantly enriched with Mesp-1, GATA-4, and Tbx5, indicative of pre cardiac mesoderm and the primary heart field. Although the CXCR4⁺/Flk-1⁺ transcriptome shared 97% identity with the CXCR4^–/Flk-1^– counterpart, the 818 divergent gene set represented predominantly cardiovascular developmental functions and formed a primitive cardiac network. Differentiation of CXCR4⁺/Flk-1⁺ progenitors yielded nuclear translocation of myocardial transcription factors and robust sarcomerogenesis with nascent cardiac tissue demonstrating beating activity and calcium transients. Thus, the CXCR4/Flk-1 biomarker pair predicts the emergence of cardiogenic specification within a pluripotent stem cell pool, enabling targeted selection of cardiopoietic lineage.

Disclosure of potential conflicts of interest is found at the end of this article.