Cholesterol uptake/trafficking, steroid biosynthesis and gonadotropin responsiveness in young women with poor ovarian response

Poor ovarian response to stimulation is one of the most challenging conditions for clinicians that substantially decreases IVF success rates. It is characterized by suboptimal ovarian response to gonadotropin stimulation, low oocyte yield and live birth rates. Poor response is usually associated with advanced age as ovarian response declines with age-related loss in the ovarian follicle pool. It is not known whether poor response in young IVF patients is simply fewer follicle growth due to an early loss in ovarian reserve, or there are specific intrinsic perturbations in the functions of the GCs. The purpose of this study was to analyze and compare steroidogenic function and gonadotropin responsiveness of luteal GCs obtained from poor versus normal responding IVF patients younger than 35 years of age. The study group comprised 20 women who were diagnosed as poor responders based on a collection of ≤ 3 oocytes in the current ovarian stimulation cycle and an abnormal ovarian reserve test. The control group included 20 women with normal ovarian response. While the mean ages of the patients were comparable between two groups, peak E2 and P4 levels, oocyte yield and clinical pregnancy rates were significantly lower in the poor responders compared to the normal responders. The steroidogenic enzymes (StAR, 3HSD, aromatase) as well as FSH and LH receptors were expressed at significantly lower levels in the GCs of the poor responders in the qRT-PCR and immunoblot analyses. In-vitro E2 and P4 production of the GCs of the poor responders were significantly lower than those of the normal responders. Furthermore, these cells poorly responded to exogenously administered FSH and hCG. Confocal imaging showed that the GCs of the poor responders have weaker signal intensities of the steroidogenic enzymes, reduced mitochondrial content, smaller intracytoplasmic lipid accumulation defective co-localization of the mitochondria with steroidogenic enzymes and lipids compared to the normal responders. Confocal time-lapse live cell imaging revealed that the uptake of cholesterol and its cytoplasmic accumulation, transportation, and eventual co-localization with mitochondria were significantly delayed and reduced in the poor responders. The expression of LDL receptor was also reduced in the poor responders in the immunoblot analysis. Taken together, these findings demonstrate intrinsic defects in the LDL receptor expression, uptake/trafficking of cholesterol, gonadotropin receptor expression, and basal and gonadotropin-stimulated steroidogenesis in the GCs of young poor ovarian responders. From the clinical perspective, poor ovarian response in young individuals should not simply be regarded as fewer follicle growth due to diminished ovarian reserve and the underlying pathogenic mechanisms appear to be more complex. It is likely that observed defects in steroidogenesis and gonadotropin responsiveness impair not only luteal function but also follicular phase growth characteristics of the poor responders.