Circadian effects of ionizing radiation on reproductive function and clock genes expression in male mouse

Abstract

Background: Exposure to the ionizing radiation (IR) encountered outside the magnetic field of the Earth poses a persistent threat to the reproductive functions of astronauts. The potential effects of space IR on the circadian rhythms of male reproductive functions have not been well characterized so far.

Methods: Here, we investigated the circadian effects of IR exposure (3 Gy X-rays) on reproductive functional markers in mouse testicular tissue and epididymis at regular intervals over a 24-h day. For each animal, epididymis was tested for sperm motility, and the testis tissue was used for daily sperm production (DSP), testosterone levels, and activities of testicular enzymes (glucose-6-phosphate dehydrogenase (G6PDH), sorbitol dehydrogenase (SDH), lactic dehydrogenase (LDH), and acid phosphatase (ACP)), and the clock genes mRNA expression such as Clock, Bmal1, Ror-α, Ror-β, or Ror-γ.

Results: Mice exposed to IR exhibited a disruption in circadian rhythms of reproductive markers, as indicated by decreased sperm motility, increased daily sperm production (DSP), and reduced activities of testis enzymes such as G6PDH, SDH, LDH, and ACP. Moreover, IR exposure also decreased mRNA expression of five clock genes (Clock, Bmal1, Ror-α, Ror-β, or Ror-γ) in testis, with alteration in the rhythm parameters.

Conclusion: These findings suggested potential health effects of IR exposure on reproductive functions of male astronauts, in terms of both the daily overall level as well as the circadian rhythmicity.

Keywords: Circadian rhythm; Clock genes; Ionizing radiation; Reproductive marker.

Fig. 1

Procedure of ionizing radiation for mice

Fig. 2

Zero-amplitude test results for circadian rhythms in unirradiated control mice. a DSP, sperm motility, and testosterone; b G6PDH, SDH, ACP, and LDH; c Clock and Bmal1; and d Ror-α, Ror-β, and Ror-γ. The circles represent the 95% joint confidence intervals of amplitude and acrophase. The pole (zero-point) of the polar coordinate was not overlapped by the circles, namely, the zero amplitude hypothesis was rejected because of p < 0.05, which indicates a distinct circadian rhythmicity of these reproductive markers and five clock genes expression

Fig. 3

Circadian rhythm of reproductive markers of Control and IR mice. The best-fitting curves (means ± standard error) determined for DSP (a), sperm motility (b), and testosterone (c); Y-axis represents DSP, sperm motility and testosterone levels; x-axis represents the time during the 24-h light-dark cycle; M and A represents the median and the amplitude of the rhythm, respectively. Mice were exposed to X-ray (3 Gy) at CT 3:00, CT 7:00, CT 11:00, CT 15:00, CT 19:00, and CT 23:00 in a 24-h CT period. Control mice were in the same experimental circumstances without being exposed to X-ray. The white and dark boxes on the x-axis represent light and dark

Fig. 4

Circadian rhythm of testis mark enzymes activities of Control and IR mice. The best-fitting curves (means ± standard error) determined for G6PDH (a), SDH (b), ACP (c), and LDH (d); Y-axis represents testis mark enzymes activities; x-axis represents the time during the 24-h light-dark cycle; M and A represents the median and the amplitude of the rhythm, respectively. Mice were exposed to X-ray (3 Gy) at CT 3:00, CT 7:00, CT 11:00, CT 15:00, CT 19:00, and CT 23:00 in a 24-h CT period. Control mice were in the same experimental circumstances without being exposed to X-ray. The white and dark boxes on the x-axis represent light and dark

Fig. 5

Circadian rhythm of testis clock genes expression levels of Control and IR mice. The best-fitting curves (means ± standard error) determined for Clock (a), Bmal1 (b), Ror-α (c), Ror-β (d), and Ror-γ (e); Y-axis represents mRNA expression level of clock genes; x-axis represents the time during the 24-h light-dark cycle; M and A represents the median and the amplitude of the rhythm, respectively. Mice were exposed to X-ray (3 Gy) at CT 3:00, CT 7:00, CT 11:00, CT 15:00, CT 19:00, and CT 23:00 in a 24-h CT period. Control mice were in the same experimental circumstances without being exposed to X-ray. The white and dark boxes on the x-axis represent light and dark