ABSTRACT
Objetivos. Describir la presencia de receptores de leptina (OBR) en el testículo en la llegada de la pubertad en terneros y estudiar la posible asociación entre la expresión de éstos y los niveles de leptina (L) y de testosterona. Materiales y métodos. Se utilizaron 6 terneros Holstein x Cebú a los cuales se les midió quincenalmente y durante 7 meses concentraciones de testosterona y de L por RIA. Fueron castrados unilateralmente según períodos peripuberales para estudiar por RT-PCR la expresión de isoformas del receptor de L. El análisis estadístico se realizó con el programa Statistica®. Resultados. La testosterona presentó niveles desde menores a 1ng/mL a los 6 y 6.5 meses de edad, hasta concentraciones de 5.3 ng/ml a los 12.5 meses antes de la llegada a pubertad, momento en el cual los animales tuvieron niveles de 4.01±1.8 ng/ml. Las concentraciones de L variaron entre 0.61 y 0.98 ng/ml, con una concentración en pubertad de 0.91±0.05 ng/ml. Dos isoformas, OBRi y OBRb, fueron encontradas y se correlacionaron significativamente entre ellas en la pubertad. Se hallaron correlaciones negativas entre OBRi-OBRb y niveles de testosterona y de L (p=0.08). Los niveles de testosterona y de L mostraron una correlación directa significativa. Conclusiones. Se sugiere un posible efecto directo de la leptina en gónadas de terneros hasta la llegada a pubertad. La correlación entre las isoformas de OBR y su asociación con las concentraciones de leptina y testosterona también sugiere la acción complementaria o conjunta de ambos receptores OBR en testículos de terneros peripuberales.
Subject(s)
Cattle , Infant , Genes , Hormones , Obesity , Sexual MaturationABSTRACT
Cells of the ovarian follicle undergo extensive proliferation and differentiation from the time that the follicle escapes from the primordial state to its acquisition of ovulatory capacity. We examined the dynamic modification of the phosphorylation state of the histone H3 N-terminal tail in granulosa cells during follicular development. In rodent follicles, the granulosa cell H3 phosphorylation on Ser10 peaks during proestrus. This epigenetic mark is induced by both FSH and 17beta-estradiol (E2), acting independently. E2-induced H3 phosphorylation fails to occur in mice with inactivated alpha-isoform of the nuclear estrogen receptor. E2 induction of histone phosphorylation is attenuated by cell cycle inhibition. Further, E2 induces the activity of the mitotic kinase, Aurora B, in a mammary tumor cell model where mitosis is estrogen receptor-alpha dependent. These results provide evidence for mitotic regulation in follicle development by estrogen and demonstrate a previously undiscovered mechanism for induction of cell proliferation in ovarian and mammary gland cells.
Subject(s)
Breast Neoplasms/enzymology , Estradiol/pharmacology , Histones/metabolism , Ovarian Follicle/enzymology , Protein Serine-Threonine Kinases/metabolism , Animals , Aurora Kinase B , Aurora Kinases , Cell Cycle/drug effects , Epithelial Cells/drug effects , Epithelial Cells/enzymology , Estrogen Receptor alpha/agonists , Estrogen Receptor alpha/antagonists & inhibitors , Estrogen Receptor alpha/genetics , Estrogen Receptor beta/agonists , Estrogen Receptor beta/antagonists & inhibitors , Estrogen Receptor beta/genetics , Female , Follicle Stimulating Hormone/pharmacology , Humans , Mice , Mice, Knockout , Mitosis/drug effects , Ovarian Follicle/chemistry , Ovarian Follicle/drug effects , Phosphorylation , Proestrus/metabolism , Protein Serine-Threonine Kinases/analysis , Protein Serine-Threonine Kinases/antagonists & inhibitors , Rats , Rats, Wistar , Tumor Cells, CulturedABSTRACT
The direct effects of recombinant porcine leptin on porcine granulosa cells were studied to test the hypothesis that leptin, acting through the nuclear transcription factor signal transducer and activator of transcription 3 (STAT-3), modulates sterol regulatory element-binding protein 1 (SREBP1) thereby increasing steroidogenesis. In porcine granulosa cells in culture over 48 h, leptin at 10 ng/ml increased progesterone accumulation 3-fold while it was reduced by leptin at 1000 ng/ml. Leptin had no effect on progression of granulosa cells through the cell cycle nor on the frequency of cell death. Leptin treatment at 24 or 48 h of culture resulted in dose-dependent 2- to 4-fold increases in tyrosine phosphorylation of STAT-3. Leptin had a biphasic effect on the abundance of membrane-bound and transcriptionally active forms of SREBP1. In transient transfection of primary porcine granulosa cells, the plasmid expressing the transcriptionally active form of SREPB-1 induced transcription of the key regulator of steroidogenesis, the steroidogenic acute regulatory protein (StAR). StAR transcription was also increased by the low dose of leptin and was further upregulated in the presence of the SREBP plasmid. Leptin at 1000 ng/ml inhibited SREBP1-induced StAR expression. Thus, leptin, acting through STAT-3, modulates steroidogenesis in a biphasic and dose-dependent manner, and SREBP1 induction of StAR expression may be in the cascade of regulatory events.
