title: A prosurvival and proangiogenic stem cell delivery system to promote ischemic limb regeneration.
abstract: Stem cell therapy is one of the most promising strategies to restore blood perfusion and promote muscle regeneration in ischemic limbs. Yet its therapeutic efficacy remains low owing to the inferior cell survival under the low oxygen and nutrient environment of the injured limbs. To increase therapeutic efficacy, high rates of both short- and long-term cell survival are essential, which current approaches do not support. In this work, we hypothesized that a high rate of short-term cell survival can be achieved by introducing a prosurvival environment into the stem cell delivery system to enhance cell survival before vascularization is established; and that a high rate of long-term cell survival can be attained by building a proangiogenic environment in the system to quickly vascularize the limbs. The system was based on a biodegradable and thermosensitive poly(N-Isopropylacrylamide)-based hydrogel, a prosurvival and proangiogenic growth factor bFGF, and bone marrow-derived mesenchymal stem cells (MSCs). bFGF can be continuously released from the system for 4weeks. The released bFGF significantly improved MSC survival and paracrine effects under low nutrient and oxygen conditions (0% FBS and 1% O2) in vitro. The prosurvival effect of the bFGF on MSCs was resulted from activating cell Kruppel-like factor 4 (KLF4) pathway. When transplanted into the ischemic limbs, the system dramatically improved MSC survival. Some of the engrafted cells were differentiated into skeletal muscle and endothelial cells, respectively. The system also promoted the proliferation of host cells. After only 2weeks of implantation, tissue blood perfusion was completely recovered; and after 4weeks, the muscle fiber diameter was restored similarly to that of the normal limbs. These pronounced results demonstrate that the developed stem cell delivery system has a potential for ischemic limb regeneration.
  
  
  CONCLUSIONS
  Stem cell therapy is a promising strategy to restore blood perfusion and promote muscle regeneration in ischemic limbs. Yet its therapeutic efficacy remains low owing to the inferior cell survival under the ischemic environment of the injured limbs. To increase therapeutic efficacy, high rate of cell survival is essential, which current approaches do not support. In this work, we tested the hypothesis that a stem cell delivery system that can continuously release a prosurvival and proangiogenic growth factor will promote high rates of cell survival in the ischemic limbs. The prosurvival effect could augment cell survival before vascularization is established, while the proangiogenic effect could stimulate quick angiogenesis to achieve long-term cell survival. Meanwhile, the differentiation of stem cells into endothelial and myogenic lineages, and cell paracrine effects will enhance vascularization and muscle regeneration.
authors.affiliation: Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210, United States.
authors.forename: Yanyi
authors.initials: Y
authors.lastname: Xu
authors.affiliation: Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210, United States; Department of Gerontology, Sichuan Academy of Medical Sciences & Sichuan Provincial People's Hospital, Chengdu, Sichuan 610072, China.
authors.forename: Minghuan
authors.initials: M
authors.lastname: Fu
authors.affiliation: Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210, United States; Division of General Surgery, Shanghai Pudong New District Zhoupu Hospital, Shanghai 201200, China.
authors.forename: Zhihong
authors.initials: Z
authors.lastname: Li
authors.affiliation: Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210, United States.
authors.forename: Zhaobo
authors.initials: Z
authors.lastname: Fan
authors.affiliation: Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210, United States.
authors.forename: Xiaofei
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Gerontology, Tongji Hospital, Tongji University, Shanghai, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210, United States.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Anderson
authors.affiliation: Department of Gerontology, Tongji Hospital, Tongji University, Shanghai, China.
authors.forename: Xiaoyun
authors.initials: X
authors.lastname: Xie
authors.affiliation: Davis Heart and Lung Research Institute, The Ohio State University, OH 43210, United States.
authors.forename: Zhenguo
authors.initials: Z
authors.lastname: Liu
authors.affiliation: Department of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210, United States; Tongji Hospital, Tongji University, Shanghai, China. Electronic address: guan.21@osu.edu.
authors.forename: Jianjun
authors.initials: J
authors.lastname: Guan
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D049109:Cell Proliferation; D002470:Cell Survival; D005121:Extremities / Q000473:pathology*; D016222:Fibroblast Growth Factor 2 / Q000378:metabolism; D020100:Hydrogels / Q000737:chemistry; D007511:Ischemia / Q000473:pathology*; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors / Q000378:metabolism; D008297:Male; D059630:Mesenchymal Stem Cells / Q000166:cytology; D051379:Mice; D008810:Mice, Inbred C57BL; D018482:Muscle, Skeletal / Q000378:metabolism / Q000473:pathology; D018919:Neovascularization, Physiologic; D010100:Oxygen / Q000737:chemistry; D010477:Perfusion; D012038:Regeneration; D013234:Stem Cells / Q000166:cytology*
chemical_list: D020100:Hydrogels; C000715468:Klf4 protein, mouse; D000090062:Kruppel-Like Factor 4; D051741:Kruppel-Like Transcription Factors; D016222:Fibroblast Growth Factor 2; D010100:Oxygen
keywords: Angiogenesis; Growth factors; Hydrogel; Injectable; Myogenic differentiation; Skeletal muscle regeneration; Stem cells