title: Endothelial cells direct human mesenchymal stem cells for osteo- and chondro-lineage differentiation through endothelin-1 and AKT signaling.
abstract: BACKGROUND
  Human mesenchymal stem cells (hMSCs) reside in a perivascular niche of the body, suggesting that they interact closely with vascular endothelial cells (ECs) through cell-cell interaction or paracrine signaling to maintain cell functions. Endothelin-1 (ET1) is a paracrine factor mainly secreted by ECs. We thus hypothesize that ECs can regulate cellular activities of hMSCs and direct their stem cell fate.
  
  
  METHODS
  We investigated whether co-cultured human aortic endothelial cells (HAECs) were able to regulate expression of potency- and lineage-related markers in bone marrow-derived hMSCs. We further explored the regulatory effects of ET1 on cell proliferation, expression of surface antigens and pluripotency-related markers, and multilineage differentiation in hMSCs. Activation of the AKT signaling pathway in hMSCs was also analyzed to identify its mechanistic role in the ET1-induced regulation.
  
  
  RESULTS
  Co-cultured HAECs enhanced expression of mesenchymal lineage-related markers in hMSCs. Treatment of ET receptor antagonist downregulated the increased expression of CBFA1 in hMSCs cultured with HAEC-conditioned medium. hMSCs treated with ET1 showed cell proliferation and expression of surface antigens, CD73, CD90, and CD105, comparable with those without ET1 treatment. ET1-treated hMSCs also expressed upregulated mRNA transcript levels of OCT3/4, NANOG, CBFA1 and SOX9. When induced for lineage-specific differentiation, hMSCs pre-treated with ET1 showed enhanced osteogenesis and chondrogenesis. However, adipogenic differentiation of hMSCs was not affected by ET1 pretreatment. We further showed that the ET1-induced regulation was mediated by activation of AKT signaling.
  
  
  CONCLUSIONS
  Our results demonstrate that ET1 secreted by HAECs can direct bone marrow-derived hMSCs for osteo- and chondro-lineage differentiation through activation of the AKT signaling pathway, suggesting that ET1 plays a crucial role in regulation of hMSC activity. Our findings may help understand how hMSCs interact with ECs in a perivascular niche.
authors.affiliation: Department of Orthopedics and Rehabilitation, Laboratory of Musculoskeletal Biology and Regenerative Medicine, University of Wisconsin-Madison, 1111 Highland Ave, WIMR 5051, Madison, WI, 53705, USA. tsai@ortho.wisc.edu.|Department of Biomedical Engineering, University of Wisconsin-Madison, 1111 Highland Ave, WIMR 5051, Madison, WI 53705, USA. tsai@ortho.wisc.edu.
authors.forename: Tsung-Lin
authors.initials: TL
authors.lastname: Tsai
authors.affiliation: Department of Surgery, University of Wisconsin-Madison, 1111 Highland Ave, WIMR 5151, Madison, WI 53705, USA. WANGB@surgery.wisc.edu.
authors.forename: Bowen
authors.initials: B
authors.lastname: Wang
authors.affiliation: Department of Orthopedics and Rehabilitation, Laboratory of Musculoskeletal Biology and Regenerative Medicine, University of Wisconsin-Madison, 1111 Highland Ave, WIMR 5051, Madison, WI, 53705, USA. Squire@ortho.wisc.edu.
authors.forename: Matthew W
authors.initials: MW
authors.lastname: Squire
authors.affiliation: Department of Surgery, University of Wisconsin-Madison, 1111 Highland Ave, WIMR 5151, Madison, WI 53705, USA. GUO@surgery.wisc.edu.
authors.forename: Lian-Wang
authors.initials: LW
authors.lastname: Guo
authors.affiliation: Department of Orthopedics and Rehabilitation, Laboratory of Musculoskeletal Biology and Regenerative Medicine, University of Wisconsin-Madison, 1111 Highland Ave, WIMR 5051, Madison, WI, 53705, USA. li@ortho.wisc.edu.|Department of Biomedical Engineering, University of Wisconsin-Madison, 1111 Highland Ave, WIMR 5051, Madison, WI 53705, USA. li@ortho.wisc.edu.
authors.forename: Wan-Ju
authors.initials: WJ
authors.lastname: Li
mesh_terms: D015703:Antigens, CD / Q000378:metabolism; D001011:Aorta / Q000166:cytology; D001854:Bone Marrow Cells / Q000166:cytology; D002454:Cell Differentiation / Q000187:drug effects; D019070:Cell Lineage; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D020219:Chondrogenesis / Q000187:drug effects; D018920:Coculture Techniques; D050659:Core Binding Factor Alpha 1 Subunit / Q000378:metabolism; D017077:Culture Media, Conditioned / Q000494:pharmacology; D015536:Down-Regulation / Q000187:drug effects; D042783:Endothelial Cells / Q000166:cytology* / Q000378:metabolism; D019332:Endothelin-1 / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D059630:Mesenchymal Stem Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D010012:Osteogenesis / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D015703:Antigens, CD; D050659:Core Binding Factor Alpha 1 Subunit; D017077:Culture Media, Conditioned; D019332:Endothelin-1; D014157:Transcription Factors; D051057:Proto-Oncogene Proteins c-akt