RESUMO
Jun is essential for fetal development, as fetuses lacking Jun die at mid-gestation with multiple cellular defects in liver and heart. Embryos expressing JunD in place of Jun (Jun(d/d)) can develop to term with normal fetal livers, but display cardiac defects as observed in fetuses lacking Jun. Jun(d/d) mouse embryonic fibroblasts (MEFs) exhibit early senescence, which can be rescued by EGF and HB-EGF stimulation, probably through activation of Akt signaling. Thus, JunD cannot functionally replace Jun in regulating fibroblast proliferation. In Jun(-/-) fetal livers, increased hydrogen peroxide levels are detected and expression of Nrf1 and Nrf2 (nuclear erythroid 2-related transcription factors) is downregulated. Importantly, increased oxidative stress as well as expression of Nrf1 and Nrf2 is rescued by JunD in Jun(d/d) fetal livers. These data show that Jun is of critical importance for cellular protection against oxidative stress in fetal livers and fibroblasts, and Jun-dependent cellular senescence can be restored by activation of the epidermal growth factor receptor pathway.
Assuntos
Proliferação de Células , Estresse Oxidativo , Proteínas Proto-Oncogênicas c-jun/metabolismo , Proteínas Proto-Oncogênicas/metabolismo , Transdução de Sinais/fisiologia , Estruturas Animais/anormalidades , Estruturas Animais/metabolismo , Estruturas Animais/patologia , Animais , Antioxidantes/farmacologia , Proliferação de Células/efeitos dos fármacos , Senescência Celular/efeitos dos fármacos , Senescência Celular/genética , Ciclina D1/genética , Ciclina D1/metabolismo , Inibidor de Quinase Dependente de Ciclina p21/metabolismo , Embrião de Mamíferos/anormalidades , Embrião de Mamíferos/metabolismo , Embrião de Mamíferos/patologia , Fator de Crescimento Epidérmico/farmacologia , Receptores ErbB/genética , Fibroblastos/metabolismo , Fibroblastos/patologia , Expressão Gênica/efeitos dos fármacos , Expressão Gênica/genética , Cardiopatias Congênitas/genética , Cardiopatias Congênitas/patologia , Hepatócitos/citologia , Hepatócitos/metabolismo , Peróxido de Hidrogênio/metabolismo , Fígado/metabolismo , Fígado/patologia , Camundongos , Camundongos da Linhagem 129 , Camundongos Endogâmicos C57BL , Camundongos Knockout , Camundongos Transgênicos , Fator 2 Relacionado a NF-E2/genética , Fator 1 Nuclear Respiratório/genética , Estresse Oxidativo/genética , Proteínas Proto-Oncogênicas/genética , Proteínas Proto-Oncogênicas c-akt/metabolismo , Proteínas Proto-Oncogênicas c-jun/genética , Transdução de Sinais/efeitos dos fármacos , Proteína Supressora de Tumor p53/genética , Proteína Supressora de Tumor p53/metabolismoRESUMO
Platelets are activated at fracture sites or upon the insertion of implants as a consequence of vascular disruption and secrete the contents of their granules into the developing hematoma. The regeneration of injured tissue requires bone remodeling and the resorbing activity of osteoclasts. To test our hypothesis that platelets can stimulate osteoclastogenesis, we examined the effects of supernatants released from thrombin-activated platelets on osteoclast-like cell formation in murine bone marrow cultures. Histochemical analysis indicated the presence of bone-resorbing, tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells. Transcripts that are characteristically expressed in native osteoclasts were increased in these cultures, as determined by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis. The inhibition of both cyclooxygenases with indomethacin, as well as the addition of the cyclooxygenase-2 (COX-2)-selective antagonist, NS398, completely blocked osteoclast-like cell formation and decreased endogenous prostaglandin E(2) production. Platelet-released supernatants stimulated the expression of receptor activator of NF-kappaB ligand (RANKL), whereas mRNA levels of osteoprotegerin (OPG) were decreased. The formation of osteoclast-like cells was prevented by recombinant OPG. Our results suggest that COX-2 activity is necessary for osteoclast-like cell formation in response to platelet-released supernatants, and that endogenously produced prostaglandin E(2) can, in turn, increase the RANKL:OPG ratio, indicating that platelets can contribute to bone remodeling by stimulation of osteoclastogenesis.