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|Title: ||C-type Natriuretic Peptide Over Expression in Chondrocytes Prevents Growth Delay in Murine Arthritis|
|Authors: ||Bükülmez, H.|
L Warman, M.
|Keywords: ||C-type Natriuretic Peptide, Chondrocytes, Murine Arthritis|
|Issue Date: ||2012 |
|Citation: ||In process|
C-type natriuretic peptide (CNP) signaling pathway is a major contributor to post-natal skeletal growth in humans. CNP signaling pathway controls the endochondral bone growth by its inhibitory effects over FGFR3-induced mitogen-activated protein kinase (MAPK) Erk1/2 activity at the Raf-1 level. It is unknown whether this pathway is affected during chronic inflammatory diseases or whether its excess may rescue the growth delay secondary to the inflammatory arthritis. In this study, using a mouse model for arthritis and a transgenic mouse that over express CNP in cartilage with longitudinal overgrowth we investigated the potential therapeutic role of CNP signaling in growth delay due to chronic inflammatory arthritis.
We developed a transgenic mouse that over expressed CNP in chondrocytes and analyzed its longitudinal bone growth pattern. Then we analyzed and the mouse model of rheumatoid arthritis that develop arthritis at a juvenile age (K/BxN TCR mice) for its longitudinal bone growth. By crossing the two transgenic mice we obtained mice that developed arthritis and over expressed CNP in cartilage. Both arthritic and CNP over expressing mice growth patterns were characterized using in vivo/ex vivo anatomic and histologic measurements. The degree of arthritis was analyzed using a scoring system. Using primary chondrocytes isolated from the newborn mice gene and protein expression of molecules CNP signaling pathway were analyzed by RT-PCR and western blotting. Primary chondrocytes were treated with proinflammatory cytokines in order to check the response of CNP signaling system to inflammatory stimuli. Statistical analysis was performed between transgenic and non-transgenic mice and chondrocyte cultures using student’s t-test. Correlations between the measurements were performed using Pearson’s correlation matrices.
K/BxN TCR mice with arthritis shows that significant longitudinal growth delay by 13 weeks (n=88, females, p=0.001, males, p=0.001). Growth delay of K/BxN TCR mice correlate with severity of arthritis. Histologic evaluation of proximal tibia growth plates in K/BxN TCR mice showed diminished chondrocyte proliferation (BrDU percent uptake) and decreased matrix synthesis (evidenced by narrowed hypertrophic chondrocyte zone and decreased proteoglycan staining) starting with significantly narrow growth plates by 6-week-age (p<0.01). Mice that over expressed CNP in cartilage developed significant longitudinal overgrowth after 6 weeks (n=24, p<0.01). We then mated K/BxN TCR mice with and transgenic mice that over express CNP. Offspring transgenic for CNP and developed arthritis with K/BxN TCR background (n=11) showed no evidence for histopathologic or anatomic growth delay (n=14) (p<0.01). Clinical and histopathologic findings of arthritis were found to be less severe in K/BxN TCR mouse with CNP over expression. Expression of matrix molecules, collagen II, X, aggrecan and NPR2 (receptor to CNP) genes and matrix metalloproteinases (MMP) -3, -9, -13 gene and protein were found significantly higher in the primary chondrocyte cultures isolated from CNP transgenic mice in vitro. Exposure of these chondrocyte cultures to TNF-α, and IL-1β in vitro further enhanced both gene and protein expression of MMP-3, -9, -13, NPR2 and phopshorylation of MAPK p38..
Our results demonstrate that CNP over expression can prevent the endochondral growth delay in K/BxN TCR mice with arthritis. The cartilage protective effect of CNP signaling is due to its effects of chondrocyte proliferation and matrix synthesis. CNP or its downstream effecting molecules may represent novel therapeutic agents to prevent growth retardation and may protect joint cartilage homeostasis during systemic inflammatory diseases such as that noted in juvenile idiopathic arthritis (JIA).|
|Appears in Collections:||College of Applied Medical Sciences|
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