Hypertrophic differentiation during chondrogenic differentiation of progenitor cells is stimulated by BMP-2 but suppressed by BMP-7.
OBJECTIVE
Bone morphogenic protein (BMP)-2 and BMP-7 are clinically approved and their recombinant proteins are used for bone tissue regenerative purposes and widely evaluated for cartilage regeneration. Previous comparison of the in vitro chondrogenic characteristics of BMP-2 vs BMP-7 did not address hypertrophic differentiation and characterizing their chondrogenic properties with a focus in on chondrocyte hypertrophy was topic of investigation in this study.


METHODS
Equimolar concentrations of BMP-2 or BMP-7 were added to chondrogenic differentiating ATDC5, human bone marrow stem cells or rabbit periosteal explants. Expression of Col2a1, Sox9, Acan, Col10a1, Runx2, ALP, Mmp13, Mef2c and Bapx1/Nkx3.2 was determined by reverse transcription-quantitative PCR (RT-qPCR) and immunoblotting. Glycosaminoglycan content, cell proliferation capacity and ALP activity were analysed by colourimetric analyses. Expression of Bapx1/Nkx3.2 and Sox9 was targeted by transfection of target specific siRNA duplexes.


RESULTS
BMP-2 dose-dependently increased chondrocyte hypertrophy during chondrogenic differentiation of progenitor cells, whereas BMP-7 acted hypertrophy-suppressive and chondro-promotive. Both BMPs did not influence cell proliferation, but they did increase total glycosaminoglycan content. In a candidate approach Bapx1/Nkx3.2 was found to be involved in the BMP-7 mediated suppression of chondrocyte hypertrophy in ATDC5 cells.


CONCLUSIONS
BMP-2 and BMP-7 display opposing actions on the chondrogenic outcome of differentiating progenitor cells: BMP-2 acts a specific inducer of chondrocyte hypertrophy, while BMP-7 appears to increase or maintain chondrogenic potential and prevent chondrocyte hypertrophy. Our results pave the way for an application-dependent differential use of BMP-2 or BMP-7.
Department of Orthopaedic Surgery, Caphri School for Public Health and Primary Care, Maastricht University Medical Center, PO Box 5800, 6202 AZ, Maastricht, The Netherlands. marjolein.caron@maastrichtuniversity.nl
M M J
MM
Caron
P J
PJ
Emans
A
A
Cremers
D A M
DA
Surtel
M M E
MM
Coolsen
L W
LW
van Rhijn
T J M
TJ
Welting
D000818:Animals; D001854:Bone Marrow Cells / Q000187:drug effects; D055396:Bone Morphogenetic Protein 2 / Q000494:pharmacology*; D055419:Bone Morphogenetic Protein 7 / Q000494:pharmacology*; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D049108:Cell Enlargement / Q000187:drug effects; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology / Q000187:drug effects* / Q000473:pathology; D020219:Chondrogenesis / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D018398:Homeodomain Proteins / Q000502:physiology; D006801:Humans; D006984:Hypertrophy; D011817:Rabbits; D013234:Stem Cells / Q000166:cytology / Q000187:drug effects*; D014157:Transcription Factors / Q000502:physiology
D055396:Bone Morphogenetic Protein 2; D055419:Bone Morphogenetic Protein 7; D018398:Homeodomain Proteins; C491536:NKX3-2 protein, human; D014157:Transcription Factors