RESUMO
Alveolar growth abnormalities and severe respiratory dysfunction are often fatal. Identifying mechanisms that control epithelial proliferation and enlarged, poorly septated airspaces is essential in developing new therapies for lung disease. The membrane-bound ligand ephrin-B2 is strongly expressed in lung epithelium, and yet in contrast to its known requirement for arteriogenesis, considerably less is known regarding the function of this protein in the epithelium. We hypothesize that the vascular mediator ephrin-B2 governs alveolar growth and mechanics beyond the confines of the endothelium. We used the in vivo manipulation of ephrin-B2 reverse signaling to determine the role of this vascular mediator in the pulmonary epithelium and distal lung mechanics. We determined that the ephrin-B2 gene (EfnB2) is strongly expressed in alveolar Type 2 cells throughout development and into adulthood. The role of ephrin-B2 reverse signaling in the lung was assessed in Efnb2(LacZ/6YFΔV) mutants that coexpress the intracellular truncated ephrin-B2-ß-galactosidase fusion and an intracellular point mutant ephrin-B2 protein that is unable to become tyrosine-phosphorylated or to interact with either the SH2 or PDZ domain-containing downstream signaling proteins. In these viable mice, we observed pulmonary hypoplasia and altered pulmonary mechanics, as evidenced by a marked reduction in lung compliance. Associated with the reduction in lung compliance was a significant increase in insoluble fibronectin (FN) basement membrane matrix assembly with FN deposition, and a corresponding increase in the α5 integrin receptor required for FN fibrillogenesis. These experiments indicate that ephrin-B2 reverse signaling mediates distal alveolar formation, fibrillogenesis, and pulmonary compliance.
Assuntos
Efrina-B2/metabolismo , Fibronectinas/metabolismo , Integrina alfa5beta1/metabolismo , Complacência Pulmonar/fisiologia , Transdução de Sinais/fisiologia , Anormalidades Múltiplas/genética , Anormalidades Múltiplas/metabolismo , Anormalidades Múltiplas/fisiopatologia , Animais , Citoplasma/genética , Citoplasma/metabolismo , Citoplasma/fisiologia , Efrina-B2/genética , Células Epiteliais/metabolismo , Células Epiteliais/fisiologia , Fibronectinas/genética , Integrina alfa5beta1/genética , Pulmão/anormalidades , Pulmão/metabolismo , Pulmão/fisiopatologia , Complacência Pulmonar/genética , Pneumopatias/genética , Pneumopatias/metabolismo , Pneumopatias/fisiopatologia , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Camundongos , Domínios PDZ/genética , Fosforilação/genética , Mutação Puntual/genética , Alvéolos Pulmonares/metabolismo , Alvéolos Pulmonares/fisiologia , Mucosa Respiratória/metabolismo , Mucosa Respiratória/fisiologia , Transdução de Sinais/genética , beta-Galactosidase/genética , beta-Galactosidase/metabolismoRESUMO
Aging alters many aspects of circadian rhythmicity, including responsivity to phase-shifting stimuli and the amplitude of the rhythm of melatonin secretion. As melatonin is both an output from and an input to the circadian clock, we hypothesized that the decreased melatonin levels exhibited by old hamsters may adversely impact the circadian system as a whole. We enhanced the diurnal rhythm of melatonin by feeding melatonin to young and old hamsters. Animals of both age groups on the melatonin diet showed larger phase shifts than control-fed animals in response to an injection with the benzodiazepine triazolam at a circadian time known to induce phase advances in the activity rhythm of young animals. Thus melatonin treatment can increase the sensitivity of the circadian timing system of young animals to a nonphotic stimulus, and the ability to increase this sensitivity persists into old age, indicating exogenous melatonin might be useful in reversing at least some age-related changes in circadian clock function.