Insulin-like growth factor I gene expression by primary cultures of ovarian cells: insulin and dexamethasone dependence.
A growing body of information now supports the existence of a complete intraovarian insulin-like growth Factor I (IGF-I) system replete with ligands, receptors, and binding protein(s). However, studies concerned with the regulation of ovarian IGF-I gene expression remain scarce. It was thus the objective of this communication to evaluate the expression of the IGF-I gene in the immature rat ovary under in vitro conditions. Whole ovarian dispersates or isolated granulosa cells were cultured for up to 96 h under serum-free conditions in the absence or presence of the indicated experimental agents. Extracted total RNA was subjected to a sensitive solution hybridization/RNase protection assay using 32P-labeled rat IGF-I and/or type I IGF receptor antisense RNA probes. Cultured in the absence or presence of FSH (100 ng/ml), whole ovarian dispersates (or isolated granulosa cells) displayed time-dependent (FSH-independent) decrements in the relative abundance of IGF-I transcripts apparent as early as 3 h after the onset of culture. No evidence of recovery was apparent by 96 h of culture. The apparent lack of an FSH effect did not reflect diminished biopotency as attested to by the ability of the hormone to promote time-dependent increments in the accumulation of progesterone. Importantly, the apparent decrease in ovarian IGF-I gene expression proved to be IGF-I specific in that type I IGF receptor transcripts displayed a substantial and sustained (for up to 96 h) FSH-independent increase beginning at the 24-h time point. At no point were IGF-II transcripts detected. The apparent decrease in the expression of IGF-I did not reflect the lack of extracellular matrix support in that neither laminin, collagen, nor whole serum supported sustained ovarian IGF-I gene expression. Treatment of whole ovarian dispersates with pharmacological concentrations of either insulin (1 micrograms/ml) or dexamethasone (10(-7) M) did not reverse the decline in IGF-I gene expression. Importantly, however, the combined application of both insulin and dexamethasone resulted in virtually complete preservation of IGF-I gene expression, the relative abundance of the corresponding transcripts proving uniform throughout. Taken together, these in vitro observations reveal irreversible (FSH-independent) decrements in ovarian IGF-I (but not type I IGF receptor) gene expression, the preservation of which required the concurrent provision of both insulin and dexamethasone.
Division of Reproductive Endocrinology, University of Maryland School of Medicine, Baltimore 21201.
L F
LF
Botero
C T
CT
Roberts
D
D
LeRoith
E Y
EY
Adashi
E R
ER
Hernandez
D000818:Animals; D002470:Cell Survival; D002478:Cells, Cultured; D003907:Dexamethasone / Q000494:pharmacology*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects*; D007328:Insulin / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D010053:Ovary / Q000166:cytology / Q000502:physiology*; D051381:Rats; D013997:Time Factors
D007328:Insulin; D007334:Insulin-Like Growth Factor I; D003907:Dexamethasone; D005640:Follicle Stimulating Hormone