Weightlessness leads to an increase granulosa cells in the growing follicle

Abstract

The participation of women in space programs of increasing flight duration requires research of their reproductive system from the perspective of subsequent childbearing and healthy aging. For the first time, we present hormonal and structural data on the dynamics of recovery after a 157-day space flight in a woman of reproductive age. There were no clinically significant changes in the reproductive system, but detailed analysis shows that weightlessness leads to an increase in the proportion of early antral follicles and granulosa cells in large antral follicles. Returning to Earth's gravity reduces the number and diameter of early antral follicles.

Fig. 1. Experimental design and the menstrual cycle characteristic: its duration and luteinizing hormone at the ovulatory phase.

Panel (A) shows time points of the data collection during the study. Baseline (green)—period before launch, space flight (blue) – from launch to landing, early post-flight (pink)—during 200 days after landing, late post-flight period (orange)—from 200 days after landing up to 325 days. Hormone concentration in blood samples was determined on the 3rd day of menstrual cycle (dmc). MRI was provided usually on the 2nd dmc, expect just after the space flight—the first MRI in the early post-flight period was on the 29 dmc. Ovulation tests were made from the 12 dmc to the 16 dmc over 3 months in each data collection period. Panel (B) shows the menstrual cycle duration, with median values derived from 5 to 6 cycles in each period of the data collection, for the baseline data—it was during 13 cycles. Panel (C) shows relative concentration of the luteinizing hormone according to ovulation tests at the ovulatory phase of menstrual cycle. * – p < 0.05—significant difference between the space flight period and the early post-flight period, ^# – p = 0.1—tendency between the space flight period and the late post-flight period. Due to the technical limitations and considerable variability of this method we have provided the exact meaning of the probability for comparisons as well as primary images in the supplementary materials (Supplementary Fig. 2).

Fig. 2. Diameter and number of the antral follicles according to MRI.

Baseline data (88 days before space flight) are green, early post-flight (19 days and 135 days after space flight)—pink, late post-flight (225 days after space flight)—orange. * – p < 0.05 in comparison with the baseline data. # – p < 0.1 in comparison with baseline data. All MRI scans were made on the 2nd dmc—early follicular phase, except the early post-flight MRI (12 days after landing)—it was on the 29th dmc (marked as x) – late luteal phase. For early and mid-size antral follicles second MRI data were suitable for relevant comparison with baseline data. Growing antral follicles are recruited to the FSH-dependent growth within the current menstrual cycle. Hence, the second MRI data are not relevant due to a different phase of the menstrual cycle. To prevent any confusion, we did not provide statistical analysis for both the entire cohort of antral follicles and the sub-cohort of growing antral follicles. Panel (A) shows the diameters of follicles from the cohort of all antral follicles throughout the post-flight period. Panel (B) shows the number of measured follicles (means are near the colored circles). Panel (C, D) show diameters and number, respectively, of follicles from sub-cohorts (early, mid-size and growing), separated by gray dotted lines.