RESUMO
Hepatic stellate cells (HSC) are critical effector cells of liver fibrosis. In the injured liver, HSC differentiate into a myofibrobastic phenotype. A critical feature distinguishing myofibroblastic from quiescent HSC is cytoskeletal reorganization. Soluble NSF attachment receptor (SNARE) proteins are important in trafficking of newly synthesized proteins to the plasma membrane for release into the extracellular environment. The goals of this project were to determine the expression of specific SNARE proteins in myofibroblastic HSC and to test whether their alteration changed the HSC phenotype in vitro and progression of liver fibrosis in vivo. We found that HSC lack the t-SNARE protein, SNAP-25, but express a homologous protein, SNAP-23. Downregulation of SNAP-23 in HSC induced reduction in polymerization and disorganization of the actin cytoskeleton associated with loss of cell movement. In contrast, reduction in SNAP-23 in mice by monogenic deletion delayed but did not prevent progression of liver fibrosis to cirrhosis. Taken together, these findings suggest that SNAP-23 is an important regular of actin dynamics in myofibroblastic HSC, but that the role of SNAP-23 in the progression of liver fibrosis in vivo is unclear.
Assuntos
Citoesqueleto de Actina/ultraestrutura , Células Estreladas do Fígado/ultraestrutura , Miofibroblastos/ultraestrutura , Proteínas Qb-SNARE/deficiência , Proteínas Qc-SNARE/deficiência , Citoesqueleto de Actina/química , Fatores de Despolimerização de Actina/biossíntese , Actinas/análise , Animais , Tetracloreto de Carbono/toxicidade , Linhagem Celular , Movimento Celular , Separação Celular , Técnicas de Silenciamento de Genes , Células Estreladas do Fígado/metabolismo , Humanos , Fígado/citologia , Cirrose Hepática/induzido quimicamente , Cirrose Hepática/patologia , Camundongos , Proteínas Qb-SNARE/antagonistas & inibidores , Proteínas Qb-SNARE/genética , Proteínas Qb-SNARE/fisiologia , Proteínas Qc-SNARE/antagonistas & inibidores , Proteínas Qc-SNARE/genética , Proteínas Qc-SNARE/fisiologia , Interferência de RNA , RNA Interferente Pequeno/genética , RNA Interferente Pequeno/farmacologia , Transdução de Sinais , Fibras de Estresse/química , Fibras de Estresse/ultraestrutura , Cicatrização , Quinases Associadas a rho/fisiologiaRESUMO
Abdominal pumping in caterpillars has only been documented during molting. Using synchrotron X-ray imaging in conjunction with high-speed flow-through respirometry, we show that Manduca sexta caterpillars cyclically contract their bodies in response to hypoxia, resulting in significant compressions of the tracheal system. Compression of tracheae induced by abdominal pumping drives external gas exchange, as evidenced by the high correlation between CO2 emission peaks and body movements. During abdominal pumping, both the compression frequency and fractional change in diameter of tracheae increased with body mass. However, abdominal pumping and tracheal compression were only observed in larger, older caterpillars (>0.2 g body mass), suggesting that this hypoxic response increases during ontogeny. The diameters of major tracheae in the thorax increased isometrically with body mass. However, tracheae in the head did not scale with mass, suggesting that there is a large safety margin for oxygen delivery in the head in the youngest animals. Together, these results highlight the need for more studies of tracheal system scaling and suggest that patterns of tracheal investment vary regionally in the body.
