Ph.D Thesis

Ph.D StudentBen-David Dror
SubjectThe Involvement of Oxidants and NF-kB in Cytokines Induced
MMP-2,-9 Synthesis by Bone Marrow-Derived
Osteoprogenitor Cells
DepartmentDepartment of Medicine
Supervisors MRS Erella Livne (Deceased)
ASSOCIATE PROF. Abraham Reznick
Full Thesis textFull thesis text - English Version


An intimate interplay exists between bone and the immune system which has been recently termed osteoimmunology. The activity of immune cells affect the intrinsic balance of bone mineralization and resorption carried out by the opposing actions of osteoblasts and osteoclasts. These processes are regulated by combined effects of growth factors and cytokines, however the fine tuning of these actions in various conditions in not yet fully understood.

This study was aimed on determining the possible interaction between inflammatory -induced conditions and synthesis and secretion of matrix metalloproteinases (MMPs) capable of degrading collagen type I. The study was performed using a culture system of rat bone marrow-derived mesenchymal stem cells (MSCs) during advanced stages of osteogenesis.

Rat bone marrow-derived MSCs were directed towards osteogenic differentiation. Upon osteogenic commitment, cultures were exposed to pro-inflammatory cytokines: TNF- and IL-1. Different techniques were used to discern the influence of pro-inflammatory cytokines on MMP-1, -2, -8, -9, -13 synthesis and secretion.

Results indicated that synthesis and secretion of all MMPs checked were significantly induced after exposure to the cytokines treatments, except MMP-2, which its levels remained unchanged. Most interestingly, MMP-9 which was not accounted under control conditions was highly induced to be synthesized and secreted under the inflammatory conditions.

In order to understand better the mechanism that stands behind MMP-9 induction, we chose to determine the possible involvement of NF-B transcription factor in regulation of MMP-2, -9 induction by pro-inflammatory cytokines in rat MSCs.

Results showed that induced MMP-9 secretion under the effects of inflammatory cytokines was mediated by activation of NF-B classical pathway and that oxidants play a significant role in this signal transduction pathway. No such effect was observed for synthesis of MMP-2. Moreover, by performing collagen type I degradation assays we showed that indeed pro-inflammatory cytokines induction caused increased collagen degradation in osteoprogenitor cell culture at the close vicinity of the cells and inhibition of NF-B negated this increase substantially.

In light of these results we suggest that during inflammation processes osteoblasts may contribute to bone resorption by secreting elevated levels of collagen type I degrading MMPs, mostly MMP-9. Moreover, NF-B is the dominant signal transduction pathway involved in the induced synthesis of MMP-9. It thus provides additional possible route for bone resorption not reported previously. Our results also demonstrate that NF-B inhibitors may be used to diminish increased resumption that may be caused due to inflammation induced MMP-9 secretion.