The Circadian Clock Protein BMAL1 Is Necessary for Fertility and Proper Testosterone Production in Mice

Abstract

Although it is well established that the circadian clock regulates mammalian reproductive physiology, the molecular mechanisms by which this regulation occurs are not clear. The authors investigated the reproductive capacity of mice lacking Bmal1 (Arntl, Mop3), one of the central circadian clock genes. They found that both male and female Bmal1 knockout (KO) mice are infertile. Gross and microscopic inspection of the reproductive anatomy of both sexes suggested deficiencies in steroidogenesis. Male Bmal1 KO mice had low testosterone and high luteinizing hormone serum concentrations, suggesting a defect in testicular Leydig cells. Importantly, Leydig cells rhythmically express BMAL1 protein, suggesting peripheral control of testosterone production by this clock protein. Expression of steroidogenic genes was reduced in testes and other steroidogenic tissues of Bmal1 KO mice. In particular, expression of the steroidogenic acute regulatory protein (StAR) gene and protein, which regulates the rate-limiting step of steroidogenesis, was decreased in testes from Bmal1 KO mice. A direct effect of BMAL1 on StAR expression in Leydig cells was indicated by in vitro experiments showing enhancement of StAR transcription by BMAL1. Other hormonal defects in male Bmal1 KO mice suggest that BMAL1 also has functions in reproductive physiology outside of the testis. These results enhance understanding of how the circadian clock regulates reproduction.Keywords circadian rhythms; fertility; testosterone; testes; sperm; StAR; mice Disruption of circadian rhythms results in a variety of pathophysiologic states (Hastings et al., 2003). Reproductive physiology, in particular, is profoundly influenced by circadian rhythms (Boden and Kennaway, 2006). In various insect species, the circadian clock is necessary for proper ovulation, sperm production, and fertility (Giebultowicz et al., 1989;Beaver et al., 2002;Beaver et al., 2003;Beaver and Giebultowicz, 2004 (Lucas and Eleftheriou, 1980;Clair et al., 1985;Chappell et al., 2003;Miller et al., 2004). For example, the surge of luteinizing hormone (LH) necessary for ovulation in rodents, which occurs at the same time of day during each estrous cycle, requires a functional circadian clock (Barbacka-Surowiak et al., 2003). In addition, at the onset of puberty, a clear diurnal rhythm of gonadotropin serum levels is established in both mice and humans (Andrews and Ojeda, 1981;Jean-Faucher et al., 1986;Dunkel et al., 1992;Apter et al., 1993). It is unclear whether this diurnal rhythm continues into adulthood, but testosterone serum concentration shows daily oscillations in adult male mice and humans (Lucas and Eleftheriou, 1980;Clair et al., 1985). Although the association between circadian rhythms and testosterone is a long-established phenomenon, the molecular mechanisms by which the circadian clock regulates testosterone production are unknown.The circadian clock is based on a transcription translation feedback loop that results in the cyclic expression of genes and proteins over a 24-h p...

The Circadian Clock Components CRY1 and CRY2 Are Necessary to Sustain Sex Dimorphism in Mouse Liver Metabolism

“…Ϫ/Ϫ males are fertile 4 and exhibit normal levels of circulating testosterone (3784 Ϯ 1099 pg/ml, n ϭ 8, and 2996 Ϯ 860 pg/ml, n ϭ 6, in wild type and Cry Ϫ/Ϫ males, respectively, p Ͼ 0.05, Mann-Whitney U test), which is in contrast with another mutant mouse line lacking the circadian clock protein BMAL1 (21). These observations suggest that the feminization of the liver of Cry Ϫ/Ϫ mutant males is not driven by impaired gonadic function.…”

FSH induces the development of circadian clockwork in rat granulosa cells via a gap junction protein Cx43-dependent pathway

“…As for the specific mechanism, Star expression is involved with many transcription factors, such as SF-1, CCAAT/enhancer-binding proteins, Sp1, DAX-1, and other transcription factors (49). Several reports described that Star transcription is implicated with the circadian clock system (1,8,43,60). Specifically, Star promoter contains E-box enhancers that bind to CLOCK/BMAL1 heterodimers to activate gene transcription.…”

Reproductive biology of female Bmal1 null mice

“…Of particular interest, only Star mRNA expression was reduced in Bmal1 null mice. The protein product of this gene, which is the rate-limiting enzyme in steroid hormone synthesis (which was low in Bmal1 null mice), has been shown to be rhythmically expressed in the dominant follicle of the quail (Nakao et al 2007) and to be impaired in both male (Alvarez et al 2008) and female (Ratajczak et al 2009) Bmal1 null mice.…”