RESUMEN
Principal cells of the epididymis are the most prominent cell type and are noted for an apical cell surface studded with microvilli. The latter contain channel proteins that condition the microenvironment of epididymal lumen and promote sperm maturation; however, the regulation of the structure and integrity of microvilli is not well known. Espins are a family of proteins implicated in microvillar growth. The objectives of this study were to assess the regulation of espin in epididymal principal cells both in vitro and in vivo. Treatment of immortalized rat caput epididymal (RCE) cells with increasing doses of a homogenized testicular extract revealed a dose-dependent increase in the size of microvilli. Reverse transcriptase-polymerase chain reaction (RT-PCR) of adult rat epididymal RNA using espin-specific primers indicated the presence of a band at about 290 base pairs (bp) in all regions. Western blot analysis using affinity-purified espin antibody confirmed the presence of an approximately 110-kDa band in the epididymis, corresponding to espin isoform 1. In adult rats, immunocytochemistry revealed espin expression over principal cells. In orchidectomized rats, espin expression was significantly reduced, whereas ligation of the efferent ducts resulted in a decrease of espin expression but not to the extent of orchidectomy. The fact that espin expression was restored to control levels in orchidectomized rats supplemented with high levels of testosterone indicated that its expression was dependent on androgens and not on other lumicrine factors derived from the testis. Taken together, these data indicate that espin is expressed in the epididymis and is regulated by androgens.
Asunto(s)
Andrógenos/fisiología , Epidídimo/ultraestructura , Proteínas de Microfilamentos/metabolismo , Testículo/metabolismo , Animales , Línea Celular , Epidídimo/metabolismo , Epidídimo/fisiología , Expresión Génica , Masculino , Microvellosidades/metabolismo , Microvellosidades/fisiología , Microvellosidades/ultraestructura , Isoformas de Proteínas , Ratas , Ratas Sprague-DawleyRESUMEN
Both GH and IGF-I stimulate islet cell growth, inhibit cell apoptosis, and regulate insulin biosynthesis and secretion. GH receptor gene deficiency (GHR(-/-)) caused diminished pancreatic islet cell mass and serum insulin level and elevated insulin sensitivity. Because IGF-I gene expression was nearly abolished in these mice, we sought to determine whether that had caused the islet defects. To restore IGF-I level, we have generated transgenic mice that express rat IGF-I cDNA under the direction of rat insulin promoter 1 (RIP-IGF). Using RNase protection assay and immunohistochemistry, the IGF-I transgene expression was revealed specifically in pancreatic islets of the RIP-IGF mice, which exhibited normal growth and development and possess no abnormalities in glucose homeostasis, insulin production, and islet cell mass. GHR(-/-) mice exhibited 50% reduction in the ratio of islet cell mass to body weight and increased insulin sensitivity but impaired glucose tolerance. Compared with GHR(-/-) alone, IGF-I overexpression on a GHR(-/-) background caused no change in the diminished blood glucose and serum insulin levels, pancreatic insulin contents, and insulin tolerance but improved glucose tolerance and insulin secretion. Remarkably, islet-specific overexpression of IGF-I gene in GHR(-/-) mice restored islet cell mass, at least partially through cell hypertrophy. Interestingly, double-transgenic male mice demonstrated a transient rescue in growth rates vs. GHR(-/-) alone, at 2-3 months of age. Our results suggest that IGF-I deficiency is part of the underlying mechanism of diminished islet growth in GHR(-/-) mice and are consistent with the notion that IGF-I mediates GH-induced islet cell growth.
Asunto(s)
Proteínas de Homeodominio/genética , Factor I del Crecimiento Similar a la Insulina/genética , Islotes Pancreáticos/citología , Islotes Pancreáticos/fisiología , Receptores de Somatotropina/genética , Transactivadores/genética , Animales , Glucemia/metabolismo , División Celular/fisiología , Expresión Génica/fisiología , Glucagón/sangre , Glucagón/metabolismo , Intolerancia a la Glucosa/fisiopatología , Insulina/sangre , Insulina/metabolismo , Secreción de Insulina , Factor I del Crecimiento Similar a la Insulina/fisiología , Islotes Pancreáticos/metabolismo , Ratones , Ratones Endogámicos C3H , Ratones Endogámicos C57BL , Ratones Transgénicos , Transgenes/fisiologíaRESUMEN
Growth hormone, acting through its receptor (GHR), plays an important role in carbohydrate metabolism and in promoting postnatal growth. GHR gene-deficient (GHR(-/-)) mice exhibit severe growth retardation and proportionate dwarfism. To assess the physiological relevance of growth hormone actions, GHR(-/-) mice were used to investigate their phenotype in glucose metabolism and pancreatic islet function. Adult GHR(-/-) mice exhibited significant reductions in the levels of blood glucose and insulin, as well as insulin mRNA accumulation. Immunohistochemical analysis of pancreatic sections revealed normal distribution of the islets despite a significantly smaller size. The average size of the islets found in GHR(-/-) mice was only one-third of that in wild-type littermates. Total beta-cell mass was reduced 4.5-fold in GHR(-/-) mice, significantly more than their body size reduction. This reduction in pancreatic islet mass appears to be related to decreases in proliferation and cell growth. GHR(-/-) mice were different from the human Laron syndrome in serum insulin level, insulin responsiveness, and obesity. We conclude that growth hormone signaling is essential for maintaining pancreatic islet size, stimulating islet hormone production, and maintaining normal insulin sensitivity and glucose homeostasis.
Asunto(s)
Hormona del Crecimiento/fisiología , Insulina/fisiología , Islotes Pancreáticos/anatomía & histología , Receptores de Somatotropina/fisiología , Animales , Glucemia/metabolismo , División Celular , Glucagón/sangre , Glucosa/metabolismo , Homeostasis , Insulina/sangre , Islotes Pancreáticos/crecimiento & desarrollo , Ratones , Ratones Noqueados/genética , Obesidad/genética , Receptores de Somatotropina/genéticaRESUMEN
Liver-specific IGF-I gene deficient (LID) mice exhibit pancreatic islet hyperplasia and insulin resistance. To clarify their causal relationship, we studied age-dependent changes in these two aspects and the response to beta-cell damage caused by streptozotocin in adult mice. As a result, the onset of insulin resistance in LID mice was detectable as early as 1-month of age, while hyperinsulinemia was developed after a significant delay at 2.5-month. Upon streptozotocin administration, control mice exhibited significant hyperglycemia after 9 days, and glucose levels continued to rise at 12-15 days. LID mice developed diabetes much more rapidly, with hyperglycemia after 6 days and higher glucose levels up to 15 days. They also exhibited significant weight loss and 6/19 died. Serum insulin assay, insulin mRNA analysis and immunohistochemistry revealed that the more severe diabetes in LID mice was not due to more damage to their beta-cells. Thus LID mice are more sensitive to streptozotocin-induced beta-cell damage, due to a primary defect in insulin responsiveness. The pancreatic islet hyperplasia observed in these mice seems to represent a compensatory response to insulin resistance, therefore, offers no protection against beta-cell damage.
Asunto(s)
Diabetes Mellitus Experimental/genética , Resistencia a la Insulina/genética , Factor I del Crecimiento Similar a la Insulina/genética , Islotes Pancreáticos/patología , Edad de Inicio , Animales , Glucemia , Diabetes Mellitus Experimental/etiología , Progresión de la Enfermedad , Femenino , Hiperglucemia , Hiperinsulinismo , Hiperplasia/etiología , Factor I del Crecimiento Similar a la Insulina/deficiencia , Hígado , Masculino , Ratones , Ratones Noqueados , Estreptozocina , Factores de TiempoRESUMEN
Ghrelin activates GH release and is implicated in growth and metabolic regulation. The regulation of its biosynthesis has not been well studied. The current investigation was designed to examine some of the factors that may influence ghrelin gene expression in the stomach. Thus, in C57BL/6 mice, ghrelin mRNA was detectable by Northern blots throughout the age groups studied, but the levels changed markedly over time. Levels were low at E18.5 and increased rapidly after birth to 6-fold at P14 before peaking to 8-fold at P21. The levels then exhibited a gradual decline at P60 (75% of the peak level) and at 6 months (67%) and a drastic decrease as the animals aged to 19 months (only 5%). Furthermore, sexual dimorphic gene expression, the effect of liver-derived IGF-I deficiency, as well as ghrelin secretion were studied. Our results support a role of ghrelin in growth/metabolism in juvenile and young adult mice of both sexes and in sexually dimorphic regulation of GH secretion in aged mice.