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INTRODUCTION: IFATS COLLECTION: TISSUE-SPECIFIC STEM CELLS

IFATS Collection: Combinatorial Peptides Identify 5β1 Integrin as a Receptor for the Matricellular Protein SPARC on Adipose Stromal Cells

^aHope Heart Program, Benaroya Research Institute at Virginia Mason, Seattle, Washington, USA;
^bDepartment of Medicine, Baylor College of Medicine, Houston, Texas, USA;
^cIndiana Center for Vascular Biology and Medicine, Indiana University, Indianapolis, Indiana, USA;
^dThe University of Texas M.D. Anderson Cancer Center, Houston, Texas, USA;
^eThe Brown Foundation Institute of Molecular Medicine for the Prevention of Human Disease, University of Texas Health Science Center at Houston, Houston, Texas, USA

Key Words. Adipose stromal cells • Extracellular matrix • Mobilization • Peptide phage display

Correspondence: Correspondence: Mikhail G. Kolonin, Ph.D.,The Brown Foundation Institute of Molecular Medicine, Center for Stem Cell Research, University of Texas Health Science Center at Houston, 1825 Pressler St., Rm. 630-F, Houston, Texas 77030, USA. Telephone: 713-500-3146; Fax: 713-500-2424; e-mail: Mikhail.G.Kolonin{at}uth.tmc.edu

Received on March 4, 2008; accepted for publication on June 11, 2008.

First published online in STEM CELLS EXPRESS  June 26, 2008.

The biological features of adipose stromal (stem) cells (ASC), which serve as progenitors for differentiated cells of white adipose tissue (WAT), are still largely undefined. In an initiative to identify functional ASC surface receptors, we screened a combinatorial library for peptide ligands binding to patient-derived ASC. We demonstrate that both primary and cultured human and mouse stromal cells express a conserved receptor targeted by peptides found to mimic SPARC, a matricellular protein that is required for normal WAT development. A signaling receptor for SPARC has not as yet been determined. By using the SPARC-mimicking peptides CMLAGWIPC (termed hPep) and CWLGEWLGC (termed mPep), isolated by panning on human and mouse cells, respectively, we identified the 5β1 integrin complex as a candidate receptor for SPARC. On the basis of these results, we evaluated ASC responses to SPARC or SPARC-mimicking peptide exposure. Our results suggest that extracellular SPARC binds to 5β1 integrin at sites of focal adhesions, an interaction disrupting firm attachment of ASC to extracellular matrix. We propose that SPARC-mediated mobilization of ASC through its effect on 5β1 integrin complex provides a functional basis for the regulation of WAT body composition by SPARC. We also show that 5β1 integrin is a potential target for ASC-selective intracellular delivery of bioactive peptides and gene therapy vectors directed by the SPARC-mimicking peptides.

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

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