Induction of bovine articular chondrocyte senescence with oxidized low-density lipoprotein through lectin-like oxidized low-density lipoprotein receptor 1.
OBJECTIVE
Findings of recent in vivo and in vitro studies suggest that oxidized low-density lipoprotein (ox-LDL) plays a role in the degeneration of cartilage. The purpose of this study was to determine whether ox-LDL induces chondrocyte senescence through binding to lectin-like ox-LDL receptor 1 (LOX-1).


METHODS
The effects of ox-LDL on senescence of cultured bovine articular chondrocytes (BACs) were investigated by observing senescence-associated (SA) beta-galactosidase (beta-gal) activity, cell proliferation activity, and telomerase activity. Telomerase activity was measured after adding LY294002 (a specific inhibitor of phosphatidylinositol 3-kinase [PI3K]) or after adding insulin-like growth factor 1 (IGF-1; an activator of PI3K) plus ox-LDL to the culture medium to elucidate the involvement of the PI3K/Akt pathway. Immunoblot analysis was used to investigate whether ox-LDL affects the phosphorylation of Akt. To ascertain whether these effects were attributable to ox-LDL binding to LOX-1, BACs were preincubated with TS-20, an anti-bovine LOX-1 blocking antibody.


RESULTS
The activity of SA beta-gal was increased and the incorporation of bromodeoxyuridine into BACs was decreased by ox-LDL in a dose-dependent manner. The telomerase activity of BACs was suppressed by the addition of ox-LDL in a time- and dose-dependent manner. LY294002 suppressed the telomerase activity of BACs, and IGF-1 reversed the ox-LDL-induced suppression of telomerase activity. In addition, ox-LDL rapidly decreased the amount of phosphorylated Akt in BACs. Pretreatment of cultured BACs with TS-20 recovered these effects.


CONCLUSIONS
These data show that ox-LDL binding to LOX-1 induces stress-induced premature senescence of chondrocytes and results in suppression of telomerase activity by inactivating the PI3K/Akt pathway. Oxidized LDL may play an important role in the pathogenesis of osteoarthritis by inducing chondrocyte senescence.
Zushi
Satoshi
S
Kinki University School of Medicine, Osaka-Sayama City, Osaka, Japan.
Akagi
Masao
M
Kishimoto
Hideki
H
Teramura
Takeshi
T
Sawamura
Tatsuya
T
Hamanishi
Chiaki
C
D000818:Animals; D000888:Antibodies, Anti-Idiotypic / Q000494:pharmacology; D002358:Cartilage, Articular / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology*; D002417:Cattle; D049109:Cell Proliferation; D002478:Cells, Cultured; D016922:Cellular Senescence / Q000502:physiology*; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology*; D002867:Chromones / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D008077:Lipoproteins, LDL / Q000378:metabolism*; D023421:Models, Animal; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051127:Scavenger Receptors, Class E / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D019098:Telomerase / Q000037:antagonists & inhibitors / Q000378:metabolism; D001616:beta-Galactosidase / Q000378:metabolism
D000888:Antibodies, Anti-Idiotypic; D002867:Chromones; D004791:Enzyme Inhibitors; D008077:Lipoproteins, LDL; D009025:Morpholines; D051127:Scavenger Receptors, Class E; C099252:oxidized low density lipoprotein; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D019098:Telomerase; D001616:beta-Galactosidase