Strategies for Understanding and Treating Osteoarthritis.
Gibson, Averi.
2016
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Abstract:
Osteoarthritis (OA) is a disease characterized by articular cartilage degeneration. It
causes chronic, debilitating pain, and as it is associated with aging and obesity, it is
a continually expanding issue. Under OA conditions, mechanical stress and an increase in
inflammatory cytokines such as IL-1β cause a disruption in joint homeostasis. As a
result, metabolic and structural ... read morechanges occur in multiple joint tissues, including the
induction of catabolic enzymes that degrade articular cartilage matrix (such as MMPs)
and the formation of ectopic bone spurs. Ultimately these changes lead to progressive
and irreversible joint degeneration. However, current therapies are mostly focused on
pain relief, rather than slowing down joint destruction. This thesis presents two
independent but inter-related projects that aim to identify and facilitate the
investigation of novel disease-modifying therapeutic targets for OA. A major hurdle in
OA research is the lack of sensitive detection and monitoring methods, which hampers the
evaluation of potential therapeutics. The aim of my first study was to investigate if
metabolic imaging of the joint using a near infrared fluorescence (NIRF) probe activated
by MMPs (MMPSense680) could visualize in vivo OA progression. Using MMPSense680, I
assessed the IL-1β induced upregulation of MMP activity in human chondrocytes in
vitro. MMP activity was then evaluated in vivo in the destabilization of the medial
meniscus (DMM) OA mouse model. The in vitro studies confirmed that NIRF imaging could
identify enhanced MMP activity in IL-1β-treated human chondrocytes. In vivo
imaging showed significantly higher fluorescence in OA knees compared to sham (control)
knees of the same mice and the emitted fluorescence intensity steadily increased over
the entire course of OA examined. Therefore, imaging of MMP activity in vivo provided
sensitive and consistent visualization of OA progression, beginning from early time
points post OA inducing surgery. The aim of my second study was to examine Wnt7a as a
potential disease-modifying reagent for OA development, as Wnt signaling has been
implicated in OA pathogenesis, but with unclear and controversial results. I first
examined Wnt7a gene expression in cartilage samples from healthy subjects and OA
patients. The effect of lentiviral Wnt7a ectopic expression was then investigated in
vitro using human articular chondrocytes under pro-inflammatory cytokine IL-1β
treatment and in vivo using the DMM OA mouse model. Wnt7a mRNA expression was reduced in
human OA cartilage and displayed an inverse correlation with MMP and IL-1β
expression. In vitro, lentiviral Wnt7a ectopic expression inhibited IL-1β-induced
gene expression in human chondrocytes. In vivo, lentiviral Wnt7a strongly attenuated
articular cartilage damage and chondrocyte cell loss induced by DMM surgery. In
addition, joint Wnt7a ectopic expression inhibited the progressive upregulation of NIRF
MMPSense680 signals in the DMM animals. I also found that Wnt7a induced mediators of
multiple Wnt pathways in chondrocytes. An NFAT inhibitor impaired Wnt7a's activity in
inhibiting MMPs, and blockage of Wnt canonical signaling with NFAT inhibition further
increased IL-1β-induced MMP expression. These results indicate that Wnt7a
signaling inhibits inflammatory-induced catabolic gene expression in human chondrocytes
and requires NFAT for this activity. In experimental OA, Wnt7a is sufficient to
attenuate MMP activities in the joint and promote joint cartilage
integrity.
Thesis (Ph.D.)--Tufts University, 2016.
Submitted to the Dept. of Cell, Molecular & Developmental Biology.
Advisor: Li Zeng.
Committee: James Schwob, Pamela Yelick, Alexander Poltorak, and Vicki Rosen.
Keyword: Cellular biology.read less - ID:
- 7s75dr31v
- Component ID:
- tufts:20344
- To Cite:
- TARC Citation Guide EndNote
