Delivery of bioactive lipids from composite microgel-microsphere injectable scaffolds enhances stem cell recruitment and skeletal repair.

Edward A Botchwey,Daniel A Barker,Cheryl M Lau,Anusuya Das,Tiffany Wang,Yong Lin

doi:10.1371/journal.pone.0101276

Edward A Botchwey, Daniel A Barker + Show 4 more

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https://doi.org/10.1371/journal.pone.0101276

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Journal: PloS one	Publication Date: Jul 31, 2014
Citations: 58	License type: CC BY 4.0

Affiliation: Georgia Institute of Technology, University of Virginia

Abstract

In this study, a microgel composed of chitosan and inorganic phosphates was used to deliver poly(lactic-co-glycolic acid) (PLAGA) microspheres loaded with sphingolipid growth factor FTY720 to critical size cranial defects in Sprague Dawley rats. We show that sustained release of FTY720 from injected microspheres used alone or in combination with recombinant human bone morphogenic protein-2 (rhBMP2) improves defect vascularization and bone formation in the presence and absence of rhBMP2 as evaluated by quantitative microCT and histological measurements. Moreover, sustained delivery of FTY720 from PLAGA and local targeting of sphingosine 1-phosphate (S1P) receptors reduces CD45+ inflammatory cell infiltration, promotes endogenous recruitment of CD29+CD90+ bone progenitor cells and enhances the efficacy of rhBMP2 from chitosan microgels. Companion in vitro studies suggest that selective activation of sphingosine receptor subtype-3 (S1P3) via FTY720 treatment induces smad-1 phosphorylation in bone-marrow stromal cells. Additionally, FTY720 enhances stromal cell-derived factor-1 (SDF-1) mediated chemotaxis of CD90+CD11B-CD45- bone progenitor cells in vitro after stimulation with rhBMP2. We believe that use of such small molecule delivery formulations to recruit endogenous bone progenitors may be an attractive alternative to exogenous cell-based therapy.

Highlights

Injury of bone and supporting vasculature induces a wound healing cascade marked by an initial inflammatory response and the subsequent recruitment and differentiation of progenitor cells
Mesenchymal stem cells (MSCs) release a multitude of cytokines, and can differentiate into osteoblasts in vivo, and many studies have shown that co-administration of bone marrow derived mesenchymal stem cells (BMSCs) and osteoinductive factors such as bone morphogenic protein-2 (BMP-2) accelerates the process of cranial defect healing [2,7]
Transwell migration assays conducted on whole bone marrow pretreated with BMP-2, FTY720 or their combination were used to assess the effect of these factors on cell migration via stromal cell-derived factor-1 (SDF-1) and sphingosine 1-phosphate (S1P) dependent pathways (Figure 1a–c)

Summary

Introduction

Injury of bone and supporting vasculature induces a wound healing cascade marked by an initial inflammatory response (complement activation, recruitment of monocytes/macrophages, clearance of damaged tissue) and the subsequent recruitment and differentiation of progenitor cells. Many challenges involved with healing critical size defects (CSD) such as the need to accelerate bone formation and enhance defect site vascularization may not be overcome through delivery of growth factors alone, and numerous studies have explored adjunct delivery of exogenous stem and progenitor cell sources [1,2,3,4]. MSCs release a multitude of cytokines, and can differentiate into osteoblasts in vivo, and many studies have shown that co-administration of bone marrow derived mesenchymal stem cells (BMSCs) and osteoinductive factors such as BMP-2 accelerates the process of cranial defect healing [2,7]. Enhancing endogenous stem cell contributions to bone repair through the use novel small molecules to increase their recruitment to the injury site via enhanced defect site vascularization and migration may provide a safe and cost effective alternative to conventional exogenous cell-based therapy [11,12,13]

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