Expression and activation of the BMP-signaling components in human fracture nonunions.
BACKGROUND
The potential use of bone morphogenetic proteins (BMPs) to promote bone-healing is of great interest to orthopaedic surgeons. Although the complex mechanism leading from the local presence of BMP (whether endogenous or exogenous) to bone formation is increasingly understood, limited information is available as to whether endogenous BMPs, their receptors, or other molecules involved in their signal transduction, such as Smad1, are present or disappear during the development of fracture nonunions. The purpose of the present study was to determine, by immunohistochemical analysis, whether BMPs, BMP receptors, or Smad1 disappear from tissues during the development of a fracture nonunion.


METHODS
Twenty-one patients (average age, sixty-one years; range, thirty to eighty-five years) with a delayed union (four patients) or a nonunion (seventeen patients) were included. The average duration of the delayed union or nonunion was twenty-two months (range, 3.5 to 120 months). With use of immunohistochemical analysis, we studied the localization of BMP-2, BMP-4, and BMP-7 and their receptors BMPR-IA, BMPR-IB, and BMPR-II as well as pSmad1. With use of a pSmad1 antibody, we also studied whether the BMP receptors that were expressed were activated.


RESULTS
The immunohistochemical localization of all seven BMP-signaling components was demonstrated in seventeen (81%) of the twenty-one patients. The remaining four patients lacked one or more of the components. Areas of newly formed bone had the highest percentage of positively staining cells, with the staining generally decreasing in areas remote from bone formation. However, even in areas of dense fibrous tissue and in specimens that lacked newly formed bone, immunostaining was still present. The staining patterns showed co-localization of the BMP-2, BMP-4, and BMP-7 proteins with the BMP receptors. The presence of pSmad1 signified the activated state of the BMP receptors, which implies that the BMP signal is transduced inside the cell.
Kloen
Peter
P
The Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021, USA.
Doty
Steven B
SB
Gordon
Eric
E
Rubel
Iván F
IF
Goumans
Marie-José
MJ
Helfet
David L
DL
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D055396:Bone Morphogenetic Protein 2; D055415:Bone Morphogenetic Protein 4; D055419:Bone Morphogenetic Protein 7; D052005:Bone Morphogenetic Protein Receptors, Type I; D052006:Bone Morphogenetic Protein Receptors, Type II; D019485:Bone Morphogenetic Proteins / Q000378:metabolism*; D002968:Clavicle / Q000293:injuries; D004268:DNA-Binding Proteins / Q000378:metabolism; D005260:Female; D017102:Fracture Healing / Q000502:physiology*; D005599:Fractures, Ununited / Q000503:physiopathology*; D006801:Humans; D006810:Humeral Fractures / Q000378:metabolism*; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011885:Radius Fractures / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism; D017978:Receptors, Growth Factor / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D051785:Smad Proteins; D051898:Smad1 Protein; D013978:Tibial Fractures / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism; D016212:Transforming Growth Factor beta
C525718:BMP2 protein, human; C525809:BMP4 protein, human; C525819:BMP7 protein, human; D055396:Bone Morphogenetic Protein 2; D055415:Bone Morphogenetic Protein 4; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins; D004268:DNA-Binding Proteins; D011956:Receptors, Cell Surface; D017978:Receptors, Growth Factor; C497399:SMAD1 protein, human; D051785:Smad Proteins; D051898:Smad1 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases; C498211:BMPR1A protein, human; C498214:BMPR1B protein, human; C498218:BMPR2 protein, human; D052005:Bone Morphogenetic Protein Receptors, Type I; D052006:Bone Morphogenetic Protein Receptors, Type II