The role of cathepsin E in osteoclast and the research for substrate molecule binding with cathepsin E

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An axis of RANK(Receptor Activator of NF-kB)/ RANKL(RANK Ligand), OPG(Osteoprotegerin) and Macrophage colony stimulating factor(M-CSF)/ c-fms is one of the most important signal pathways in differentiation and activation of osteoclast. In previous study, we reported that number of osteoclast significantly decreased in cathepsin E(CE) knockout mice. In this time, real time PCR analyses showed that mRNA expression levels of M-CSF, c-fms, RANK, c-fos and osteoclast specific marker, cathepsin K and TRAP tended to decrease in CE KO mice, although no statistical differences were recognized. Moreover, mRNA of fusion-related protein such as DC-STAMP and OC-STAMP also decreased. Therefore, we examined mRNA profile with wild(C57BL/ 6) and CE KO mice using DNA microarray. Then, lots of factors related with oxidative stress significantly increased in CE KO mice compared with wild type mice. Furthermore, hydrogen peroxide also increased in CE KO mice after adding RANKL. Studies of autophagy related molecules such as p62, LC3 and ubiquitin showed that they migrated toward non soluble fraction from soluble fraction. These results suggest that CE deficiency causes impairment of autophagy, a degradation system for aggregated proteins and damaged organelles, and increase of oxidative stress. Finally, number of osteoclast significantly decrease in CE KO mice.