. The biologic effect of one cytokine is often modified or augmented by another, but the exact mechanisms are still unclear. It is generally accepted that progressive tissue destruction in IVD degeneration results from over-expression of various proteolytic enzymes and other catabolic agents. Action of MMPs is a crucial event in IVD degeneration by initiating matrix catabolism and then IVD degeneration. In our study, MMP-1 and MMP-13 levels in CECs increased significantly in response to ET-1 in a dose-dependent manner, whereas TIMP-1 correspondingly decreased. MMP-1 and MMP-13 are collagenolytic enzymes that play an important role in the alteration of collagen in degenerated discs; especially MMP-13, which cleaves extracellular matrix order KU55933 proteins including type II collagen. The results demonstrate that the effect of ET-1 was greater on MMP-13 production than on MMP-1. Generally, MMP enzymes are maintained in an inactive form by tissue inhibitors. Our results show that ET-1 significantly increased MMP-1 and MMP-13 release in CECs, affecting the balance of MMP/TIMP and presumably assisting in the degradation of the extracellular matrix. In addition, NO has been shown to mediate changes in proteoglycan synthesis in human IVDs as well as pain-related behavior in a rat model of radiculopathy, so excess NO is harmful to cells. Our results showed that NO levels significantly increased in a dose-dependent manner with ET-1 treatment. Therefore, the action of ET-1 seems to depend on increases in both MMP and NO production. In the study, CECs derived from human degenerated disc samples, may be subject to TNFa induction in vivo, and thus may release a certain amount of ET-1 in the absence of any exogenous stimulation. During the process of CEP degeneration seen in our tissue samples, blood vessels from bone marrow of the vertebral body invaded the degenerated endplate tissue, which is also known to secrete ET-1. We suggest that ET-1 
may not only be secreted by 8 ET-1 in Cartilaginous Endplate Degeneration CECs but also be released by invasive blood vessels. They may act synergistically in CEP degradation. Wang et al. reported that the vertebral endplate degeneration was related to endplate cell apoptosis. We found that 22286128 ET-1 did not act on IVD degeneration through induction of apoptosis. Others have reported similar results of ET-1 on articular chondrocytes without apoptosis. In conclusion, our results showed associations between ET-1 protein levels and a number of changes in cultured CECs from degenerated endplates suggesting that ET-1 functions as a medi- ator in the etiology of disc degeneration. Future biologic treatments including inhibitors or blockers of ET-1 or various intracellular signaling molecules may potentially help replenish the matrix content by decreasing catabolic processes. ~~ ~~ The fruit fly Drosophila melanogaster has various characteristics that make 11121575 it a useful model for medical and fundamental research. For example, more than 75% of human disease genes have a homologue in flies, and the bipartite UAS-GAL4 system developed by Perrimon and collegues offers an extremely flexible tool to control, in space and time, the expression of transgenes. Also, the numerous mutant and transgenic flies available, and the associated databases, are powerful tools for both large output screening and basic research. For these reasons and despite obvious morphological, size and neuronal circuitry differences between human and fly brains, Drosophil
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