Summary: Circadian rhythms are modulated in a variety of peripheral tissues including the prostate, in which the mesenchyme and epithelium cells are controlled under androgens. Here, we investigated the testosterone regulation of core clock genes such as Bmal1, Clock, Per2 and Nr1d1 under a deficient state of testosterone. In vivo studies showed that the Bmal1 mRNA expression in the prostates displayed a peak at ZT 20 and a trough at ZT 12. Both Bmal1 and Clock transcripts decreased after castration. Conversely, the expression of Per2 that is promoted by binding of Bmal1 and Clock heterodimers to the E-box, enhanced or did not decease at least within 1 week after castration. The clock gene transcripts were recovered to the intact levels, when 1 mg testosterone was administered daily for 5 days. Fluorescent immunohistochemical studies revealed the increased staining of caspase 3 in the epithelium and Per2 in both the mesenchyme and epithelium after 1-week castration. In the mesenchyme cells prepared from castrated rats, the Per2 oscillation was generated in response to dexamethasone. The circadian rhythms of Bmal1 and Nr1d1 transcripts were obviously antiphase in the cells. However, the mesenchyme cells displayed the different profiles in the presence or absence of testosterone; the amplitude of the first phase was significantly decreased by testosterone. Addition of testosterone significantly increased the transcripts of Bmal1, Clock and Casp3 in cultured cells, whereas the Per2 and Nr1d1 transcripts were significantly inhibited. Collectively, the present results demonstrated that Bmal1 and Clock, but not Per2 and Nr1d1, are down-regulated in mesenchyme cells by testosterone deficiency. In addition to the conservative interlocked transcriptional-translational feedback loop, it is strongly suggested that the prostate clock system is controlled under androgen.
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