RESUMEN
When platelets are strongly stimulated, a procoagulant platelet subpopulation is formed that is characterized by phosphatidylserine (PS) exposure and epitope modulation of integrin αIIbß3 or a loss of binding of activation-dependent antibodies. Mitochondrial permeability transition pore (mPTP) formation, which is essential for the formation of procoagulant platelets, is impaired in the absence of cyclophilin D (CypD). Here we investigate the mechanisms responsible for these procoagulant platelet-associated changes in integrin αIIbß3 and the physiologic role of procoagulant platelet formation in the regulation of platelet aggregation. Among strongly stimulated adherent platelets, integrin αIIbß3 epitope changes, mPTP formation, PS exposure, and platelet rounding were closely associated. Furthermore, platelet mPTP formation resulted in a decreased ability to recruit additional platelets. In the absence of CypD, integrin αIIbß3 function was accentuated in both static and flow conditions, and, in vivo, a prothrombotic phenotype occurred in mice with a platelet-specific deficiency of CypD. CypD-dependent proteolytic events, including cleavage of the integrin ß3 cytoplasmic domain, coincided closely with integrin αIIbß3 inactivation. Calpain inhibition blocked integrin ß3 cleavage and inactivation but not mPTP formation or PS exposure, indicating that integrin inactivation and PS exposure are mediated by distinct pathways subsequent to mPTP formation. mPTP-dependent alkalinization occurred in procoagulant platelets, suggesting a possible alternative mechanism for enhancement of calpain activity in procoagulant platelets. Together, these results indicate that, in strongly stimulated platelets, mPTP formation initiates the calpain-dependent cleavage of integrin ß3 and associated regulatory proteins, resulting in integrin αIIbß3 inactivation, and demonstrate a novel CypD-dependent negative feedback mechanism that limits platelet aggregation and thrombotic occlusion.
Asunto(s)
Plaquetas/metabolismo , Mitocondrias/metabolismo , Agregación Plaquetaria , Complejo GPIIb-IIIa de Glicoproteína Plaquetaria/metabolismo , Proteolisis , Trombosis/metabolismo , Animales , Plaquetas/patología , Calpaína/genética , Calpaína/metabolismo , Peptidil-Prolil Isomerasa F , Ciclofilinas/genética , Ciclofilinas/metabolismo , Ratones , Ratones Noqueados , Mitocondrias/genética , Mitocondrias/patología , Proteínas de Transporte de Membrana Mitocondrial/genética , Proteínas de Transporte de Membrana Mitocondrial/metabolismo , Poro de Transición de la Permeabilidad Mitocondrial , Complejo GPIIb-IIIa de Glicoproteína Plaquetaria/genética , Trombosis/genética , Trombosis/patologíaRESUMEN
All animals, including humans, show differential susceptibility to infection with viruses. Study of the genetics of susceptibility or resistance to specific pathogens is most easily studied in inbred mice. We have been using mouse mammary tumor virus (MMTV), a retrovirus that causes mammary tumors in mice, to study virus/host interactions. These studies have focused on understanding the mechanisms that determine genetic susceptibility to MMTV-induced mammary tumors, the regulation of virus gene expression in vivo and how the virus is transmitted between different cell types. We have found that some endogenous MMTVs are only expressed in lymphoid tissue and that a single base pair change in the long terminal repeat of MMTV determines whether the virus is expressed in mammary gland. This expression in lymphoid cells is necessary for the infectious cycle of MMTV, and both T and B cells express and shed MMTV. Infected lymphocytes are required not only for the initial introduction of MMTV to the mammary gland, but also for virus spread at later times. Without this virus spread, mammary tumorigenesis is dramatically reduced. Mammary tumor incidence is also affected by the genetic background of the mouse and at least one gene that affects infection of both lymphocytes and mammary cells has not yet been identified. The results obtained from these studies will greatly increase our understanding of the genetic mechanisms that viruses use to infect their hosts and how genetic resistance to such viruses in the hosts occurs.(Au)
Asunto(s)
Animales , Ratones , Predisposición Genética a la Enfermedad , Virus del Tumor Mamario del Ratón/genética , Nucleótidos/genética , Infecciones por Retroviridae/genética , Infecciones Tumorales por Virus/genética , Gammaretrovirus/genética , Linfocitos B/inmunología , Secuencia de Carbohidratos/genética , Virus del Tumor Mamario del Ratón/inmunología , Ratones Endogámicos C57BL , Infecciones por Retroviridae/inmunología , Linfocitos T/inmunología , Infecciones Tumorales por Virus/inmunología , Gammaretrovirus/inmunología , Integración Viral/genética , Integración Viral/inmunologíaRESUMEN
All animals, including humans, show differential susceptibility to infection with viruses. Study of the genetics of susceptibility or resistance to specific pathogens is most easily studied in inbred mice. We have been using mouse mammary tumor virus (MMTV), a retrovirus that causes mammary tumors in mice, to study virus/host interactions. These studies have focused on understanding the mechanisms that determine genetic susceptibility to MMTV-induced mammary tumors, the regulation of virus gene expression in vivo and how the virus is transmitted between different cell types. We have found that some endogenous MMTVs are only expressed in lymphoid tissue and that a single base pair change in the long terminal repeat of MMTV determines whether the virus is expressed in mammary gland. This expression in lymphoid cells is necessary for the infectious cycle of MMTV, and both T and B cells express and shed MMTV. Infected lymphocytes are required not only for the initial introduction of MMTV to the mammary gland, but also for virus spread at later times. Without this virus spread, mammary tumorigenesis is dramatically reduced. Mammary tumor incidence is also affected by the genetic background of the mouse and at least one gene that affects infection of both lymphocytes and mammary cells has not yet been identified. The results obtained from these studies will greatly increase our understanding of the genetic mechanisms that viruses use to infect their hosts and how genetic resistance to such viruses in the hosts occurs.
Asunto(s)
Animales , Ratones , Predisposición Genética a la Enfermedad , Infecciones por Retroviridae/genética , Infecciones Tumorales por Virus/genética , Nucleótidos/genética , Virus del Tumor Mamario del Ratón/genética , Gammaretrovirus/genética , Linfocitos B , Infecciones por Retroviridae/inmunología , Infecciones Tumorales por Virus/inmunología , Integración Viral/genética , Integración Viral/inmunología , Secuencia de Carbohidratos/genética , Linfocitos T , Virus del Tumor Mamario del Ratón/inmunología , Gammaretrovirus/inmunologíaRESUMEN
All animals, including humans, show differential susceptibility to infection with viruses. Study of the genetics of susceptibility or resistance to specific pathogens is most easily studied in inbred mice. We have been using mouse mammary tumor virus (MMTV), a retrovirus that causes mammary tumors in mice, to study virus/host interactions. These studies have focused on understanding the mechanisms that determine genetic susceptibility to MMTV-induced mammary tumors, the regulation of virus gene expression in vivo and how the virus is transmitted between different cell types. We have found that some endogenous MMTVs are only expressed in lymphoid tissue and that a single base pair change in the long terminal repeat of MMTV determines whether the virus is expressed in mammary gland. This expression in lymphoid cells is necessary for the infectious cycle of MMTV, and both T and B cells express and shed MMTV. Infected lymphocytes are required not only for the initial introduction of MMTV to the mammary gland, but also for virus spread at later times. Without this virus spread, mammary tumorigenesis is dramatically reduced. Mammary tumor incidence is also affected by the genetic background of the mouse and at least one gene that affects infection of both lymphocytes and mammary cells has not yet been identified. The results obtained from these studies will greatly increase our understanding of the genetic mechanisms that viruses use to infect their hosts and how genetic resistance to such viruses in the hosts occurs.
