title: Mesenchymal stroma cells trigger early attraction of M1 macrophages and endothelial cells into fibrin hydrogels, stimulating long bone healing without long-term engraftment.
abstract: Implantation of mesenchymal stroma cells (MSCs) is an attractive approach to stimulate closure of large bone defects but an optimal carrier has yet to be defined. MSCs may display trophic and/or immunomodulatory features or stimulate bone healing by their osteogenic activity. The aim of this study was to unravel whether fibrin hydrogel supports early actions of implanted MSCs, such as host cell recruitment, immunomodulation and tissue regeneration, in long bone defects. Female rats received cell-free fibrin or male MSCs embedded in a fibrin carrier into plate-stabilized femoral bone defects. Removed callus was analyzed for host cell invasion (day 6), local cytokine expression (days 3 and 6) and persistence of male MSCs (days 3, 6, 14 and 28). Fibrin-MSC composites triggered fast attraction of host cells into the hydrogel while cell-free fibrin implants were not invaded. A migration front dominated by M1 macrophages and endothelial progenitor cells formed while M2 macrophages remained sparse. Only MSC-seeded fibrin hydrogel stimulated early tissue maturation and primitive vessel formation at day 6 in line with significantly higher VEGF mRNA levels recorded at day 3. Local TNF-α, IL-1β and IL-10 expression indicated a balanced immune cell activity independent of MSC implantation. Implanted MSCs persisted until day 14 but not day 28. Our results demonstrate that fibrin hydrogel is an attractive carrier for MSC implantation into long bone defects, supporting host cell attraction and pro-angiogenic activity. By this angiogenesis, implant integration and tissue maturation was stimulated in long bone healing independent of long-term engraftment of implanted MSCs.
authors: Research Centre for Experimental Orthopaedics, Orthopaedic University Hospital Heidelberg, Schlierbacher Landstrasse 200a, 69118 Heidelberg, Germany.
authors: Elisabeth
authors: E
authors: Seebach
authors: Research Centre for Experimental Orthopaedics, Orthopaedic University Hospital Heidelberg, Schlierbacher Landstrasse 200a, 69118 Heidelberg, Germany.
authors: Holger
authors: H
authors: Freischmidt
authors: Research Centre for Experimental Orthopaedics, Orthopaedic University Hospital Heidelberg, Schlierbacher Landstrasse 200a, 69118 Heidelberg, Germany.
authors: Jeannine
authors: J
authors: Holschbach
authors: Research Centre for Experimental Orthopaedics, Orthopaedic University Hospital Heidelberg, Schlierbacher Landstrasse 200a, 69118 Heidelberg, Germany.
authors: Jörg
authors: J
authors: Fellenberg
authors: Research Centre for Experimental Orthopaedics, Orthopaedic University Hospital Heidelberg, Schlierbacher Landstrasse 200a, 69118 Heidelberg, Germany. Electronic address: wiltrud.richter@med.uni-heidelberg.de.
authors: Wiltrud
authors: W
authors: Richter
mesh_terms: D000818:Animals; D001861:Bone Regeneration / Q000187:drug effects; D002146:Bony Callus / Q000187:drug effects / Q000473:pathology; D016207:Cytokines / Q000378:metabolism; D042783:Endothelial Cells / Q000166:cytology* / Q000187:drug effects; D005260:Female; D005269:Femur / Q000187:drug effects / Q000473:pathology; D005337:Fibrin / Q000494:pharmacology*; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate / Q000494:pharmacology*; D007155:Immunologic Factors / Q000378:metabolism; D008264:Macrophages / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D008297:Male; D045164:Mesenchymal Stem Cell Transplantation; D059630:Mesenchymal Stem Cells / Q000166:cytology* / Q000187:drug effects; D019919:Prosthesis Implantation; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D014945:Wound Healing / Q000187:drug effects*
chemical_list: D016207:Cytokines; D007155:Immunologic Factors; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D005337:Fibrin
keywords: Bone healing; Fibrin hydrogel; Host cell recruitment; Macrophage; Mesenchymal stroma cells