Although cancer chemotherapy is one of the best methods for eliminating malignancies, its skeletal side effects such as bone loss and fractures, osteonecrosis, bone marrow adiposity and bone vascular damage, have increased among cancer survivors. However, the mechanisms by which chemotherapy affects bone integrity remain unclear.
Notch signalling plays a central role in skeletal development and homeostasis, controlling osteogenesis and angiogenesis [2]. Our previous studies demonstrated that treatment with methotrexate (MTX) in rats decreases bone volume, elevates bone resorption, increases marrow adiposity, and damages bone vasculature [3]. However, whether these bone damages are associated with alteration in Notch signalling needs to be investigated.
In the current study, using bone specimens from a rat model of MTX treatment (5 consecutive days of SC. injections at 0.75mg/kg), we performed PCR array for screening mRNA expression levels of osteogenic-angiogenic factors.
Based on PCR array results, we focused on investigating the roles of Notch signalling in disrupting osteogenesis and angiogenesis balance after MTX treatment. We found that one day after the 5 doses of MTX, there was a significant increase in mRNA expression of Notch2 and Notch targeting genes (Hes1, Hey1 and HeyL) [1] in tibial metaphysis that suggests over activation of Notch signalling may be accompanying with bone loss and bone vascular damage.
in co-culture osteoblasts induced tube formation and migration abilities of endothelial cells which were significantly diminished after exposing to MTX. PCR array results illustrated that the most significantly altered factor after MTX treatment was a notch2.
IHC staining of bone sections with anti-Notch2 antibody confirmed that osteoblasts are the cells with high Notch2 expression levels.
These data suggest that MTX upregulate Notch signalling via Notch2 that might be associated with bone damages. We will investigate roles of Notch2 in MTX-induced bone damages and its potential as a therapeutic target.