Antagonism of cysteinyl leukot-riene receptor 1 (cysLT1R) by montelukast regulates differentiation of MC3T3-E1 cells under overloaded mechanical environment.

Long-term exposure to overloaded mechanical environment induces bone fatigue damage symptoms and osteoblast damages. Montelukast is a selective cysteinyl leukot-riene receptor 1 (cysLT1R) antagonist, which has been used for the treatment of bronchial asthma in clinics. In the current study, we have identified a novel pharmacological role of montelukast by finding that it has protective properties against overload damage in osteoblastic MC3T3-E1 cells. Firstly, our results show that CysLT1R is expressed in MC3T3-E1 cells. Mechanical tensile strain of 5000-7000 µÎµ resulted in a significant upregulation of CysLT1R in osteoblastic MC3T3-E1 cells in an intensity dependent manner. Secondly, MTT assay indicates that loading with 5000 µÎµ mechanical strain inhibited cell proliferation, which was suppressed by montelukast treatment. Furthermore, montelukast promotes cell differentiation by increasing the expression of ALP and RUNX2. Alizarin Red S staining assay showed that montelukast abolished the inhibitory effects of overload mechanics on osteoblast mineralization. Mechanistically, the effect of montelukast on osteoblastic differentiation acted by activating the extracellular regulated protein kinases (ERK) pathway. The obtained results suggested that montelukast promotes proliferation and differentiation in osteoblasts exposed to overload mechanics.

The cysteinyl leukotriene receptor 1 (CysLT1R) antagonist montelukast suppresses matrix metalloproteinase-13 expression induced by lipopolysaccharide.

Bacterial products such as LPS are critical factors responsible for bone destruction. MMP-13, a member of the matrix metalloproteinase family, plays a critical role in the proteolytic degradation of extracellular matrix components, which includes collagen fibrils in the bone matrix. Montelukast is a selective cysteinyl leukotrienes receptor 1 (cysLT1R) antagonist used clinically for the treatment of asthma, as it reduces eosinophilic inflammation in airways. This study aims to explore the role of montelukast in regulating MMP-13 expression induced by LPS in osteoblasts. Our results indicate that LPS stimulated cysLT1R expression in mouse MC3T3-E1 osteoblasts in a dose- and time-dependent manner. Notably, LPS-induced up-regulation of MMP-13 was ameliorated by treatment with montelukast in a dose-dependent manner. Furthermore, treatment with montelukast stimulated the expression of SOCS3, an inhibitor of MMP-13. Silencing of SOCS3 abolished the inhibitory effects of montelukast on MMP-13 expression. Mechanistically, we found that montelukast suppressed LPS-induced nuclear translocation of NF-κB p65 as well as NF-κB transcriptional activity by inhibiting the phosphorylation and degradation of IκBα. These data suggest that montelukast can modulate inflammatory events in bone diseases.

Leukotriene D4 induces cellular senescence in osteoblasts.

Aging is associated with the development of osteoporosis, in which cellular senescence in osteoblasts plays a key role. Leukotriene D4 (LTD4), an important cysteinyl leukotriene (cysLT), is a powerful pro-inflammatory mediator formed from arachidonic acid. However, little information regarding the effects of LTD4 on the pathogenesis of osteoporosis has been reported before. In the present study, we defined the physiological roles of LTD4 in cellular senescence in osteoblasts. Our results indicate that LTD4 treatment decreased the expression of SIRT1 in a dose-dependent manner in MC3T3-E1 osteoblastic cells. Additionally, LTD4 significantly increased the expression of p53, p21 and plasminogen activator inhibitor-1 (PAI-1). LTD4 was also found to elevate the activity of ß-galactosidase (SA-ß-Gal) but to prevent BrdU incorporation. Our results indicate that cysteinyl leukotriene receptor 1 (cysLT1R) could be detected in MC3T3-E1 osteoblastic cells at both the mRNA and protein levels. However, cysLT2R was not expressed in these cells. Interestingly, we found that knockdown of cysLT1R or use of the selective cysLT1R antagonist montelukast abolished the LTD4-induced reduction in SIRT1 and increase in p53, p21, and PAI-1. Notably, knockdown of cysLT1R by transfection with cysLT1R siRNA or treatment with montelukast attenuated the LTD4-induced increase in SA-ß-Gal activity. Our study shows for the first time that LTD4 has a significant impact on cellular senescence in osteoblasts.