It is increasingly appreciated that coordinated regulation of angiogenesis and osteogenesis is needed for bone formation. How this regulation is achieved during peri-implant bone healing, such as osseointegration, is largely unclear. This study examined the relationship between angiogenesis and osteogenesis in a unique model of osseointegration of a mouse tibial implant by pharmacologically blocking the vascular endothelial growth factor (VEGF) pathway. An implant was inserted into the right tibia of 16-week-old female C57BL/6 mice (n = 38). Mice received anti-VEGF receptor-1 (VEGFR-1) antibody (25 mg/kg) and VEGF receptor-2 (VEGFR-2) antibody (25 mg/kg; n = 19) or an isotype control antibody (n = 19). Flow cytometric (n = 4/group) and immunofluorescent (n = 3/group) analyses were performed at two weeks post-implantation to detect the distribution and density of CD31hiEMCNhi endothelium. RNA sequencing analysis was performed using sorted CD31hiEMCNhi endothelial cells (n = 2/group). Osteoblast lineage cells expressing osterix (OSX) and osteopontin (OPN) were also detected with immunofluorescence. Mechanical pull-out testing (n = 12/group) was used at four weeks post-implantation to determine the strength of the bone-implant interface. After pull-out testing, the tissue attached to the implant surface was harvested. Whole mount immunofluorescent staining of OSX and OPN was performed to determine the amount of osteoblast lineage cells.Aims
Materials and Methods
Previous studies support the important role of
vascular endothelial growth factor (VEGF) and syndecan-4 in the pathogenesis
of osteoarthritis (OA). Both VEGF and syndecan-4 are expressed by
chondrocytes and both are involved in the regulation of matrix metalloproteinase-3,
resulting in the activation of aggrecanase II (ADAMTS-5), which
is essential in the pathogenesis of OA. However, the relationship
between VEGF and syndecan-4 has not been established. As a pilot
study, we assayed the expression of VEGF and syndecan-4 in cartilage
samples and cultured chondrocytes from osteoarthritic knee joints
and analysed the relationship between these two factors. Specimens were collected from 21 female patients (29 knees) who
underwent total knee replacement due to severe medial OA of the
knee (Kellgren–Lawrence grade 4). Articular cartilage samples, obtained
from bone and cartilage excised during surgery, were analysed and
used for chondrocyte culture. We found that the levels of expression
of VEGF and syndecan-4 mRNA did not differ significantly between
medial femoral cartilage with severe degenerative changes and lateral
femoral cartilage that appeared grossly normal (p = 0.443 and 0.622,
respectively). Likewise, the levels of expression of VEGF and syndecan-4
mRNA were similar in cultured chondrocytes from medial and lateral
femoral cartilage. The levels of expression of VEGF and syndecan-4
mRNAs were significantly and positively correlated in cartilage
explant (r = 0.601, p = 0.003) but not in cultured chondrocytes.
These results suggest that there is a close relationship between
VEGF and syndecan-4 in the cartilage of patients with OA. Further
studies are needed to determine the exact pathway by which these
two factors interact in the pathogenesis of OA. Cite this article:
