The circadian clock, regulating hormonal secretion and metabolisms

The circadian clock is responsible for the generation of circadian rhythms in hormonal secretion and metabolism. These peripheral clocks could be reset by various cues in order to adapt to environmental variations. The ovary can be characterized as having highly dynamic physiology regulated by gonadotropins. Here, we aimed to address the status of circadian clock in the ovary, and to explore how gonadotropins could regulate clockwork in granulosa cells (GCs). To this end, we mainly utilized the immunohistochemistry, RT-PCR, and real-time monitoring of gene expression methods. PER1 protein was constantly abundant across the daily cycle in the GCs of immature ovaries. In contrast, PER1 protein level was obviously cyclic through the circadian cycle in the luteal cells of pubertal ovaries. In addition, both FSH and LH induced Per1 expression in cultured immature and mature GCs, respectively. The promoter analysis revealed that the Per1 expression was mediated by the cAMP response element binding protein. In cultured transgenic GCs, both FSH and LH also induced the circadian oscillation of Per2. However, the Per2 oscillation promoted by FSH quickly dampened within only one cycle, whereas the Per2 oscillation promoted by LH was persistently maintained. Collectively, these findings strongly suggest that both FSH and LH play an important role in regulating circadian clock in the ovary; however, they might exert differential actions on the clockwork in vivo due to each specific role within ovarian physiology.

Background: It is considered that the increasing intramyocellular lipid (IMCL) affects health risks and muscle attenuation. Though body fat increases significantly with age in lean humans, it is not known whether IMCL increases or not. In this study, we investigated the changes with age in IMCL concentrations in skeletal muscles using ¹H-MR spectroscopy and studied them in relation to body fat percentage, waist-hip ratio, and blood components. Methods: Twenty-four lean young (age 21.2 ± 1.9, BMI 21.5 ± 1.8) and 23 lean old (age 70.9 ± 2.4, BMI 21.7 ± 1.3) subjects took part in the study. Subjects were grouped by gender into age- and BMI-matched young and old groups. The ¹H-MRS was obtained from the tibialis anterior (TA), medial gastrocnemius (MG) and soleus (SOL) muscles. Results: The IMCL content in SOL and MG in the old was found to be higher (p < 0.01) than that in the young. No age difference in IMCL content in TA was found. IMCL concentrations in SOL were higher than those in MG and TA in the order of SOL > MG > TA (p < 0.01). IMCL content correlated significantly with waist-hip ratio in all skeletal muscles. A significant relationship was observed between percent body fat and IMCL in TA and MG (p < 0.05). However, no correlation was found between IMCL content in each muscle and BMI. The IMCL content in all skeletal muscles significantly correlated with HbA1c, triglyceride, total cholesterol and LDL cholesterol concentrations. Conclusion: These results suggest that increased IMCL in both lean older men and women might be related to body composition, blood lipids and lipoprotein profiles, and that this might affect muscle attenuation.

Ovarian circadian oscillators have been implicated in the reproductive processes of mammals. However, there are few reports regarding the detection of ovarian clock-controlled genes (CCGs). The present study was designed to unravel the mechanisms through which CCG ovarian circadian oscillators regulate fertility, primarily using quantitative RT-PCR and RNA interference against Bmal1 in rat granulosa cells. Mature granulosa cells were prepared from mouse Per2-destabilized luciferase (dLuc) reporter gene transgenic rats. A real-time monitoring system of Per2 promoter activity was employed to detect Per2-dLuc oscillations. The cells exposed to luteinizing hormone (LH) displayed clear Per2-dLuc oscillations and a rhythmic expression of clock genes (Bmal1, Per1, Per2, Rev-erbα, and Dbp). Meanwhile, the examined ovarian genes (Star, Cyp19a1, Cyp11a1, Ptgs2, Lhcgr, and p53) showed rhythmic transcript profiles except for Hsd3b2, indicating that these rhythmic expression genes may be CCGs. Notably, Bmal1 small interfering (si)RNA treatment significantly decreased both the amplitude of Per2-dLuc oscillations and Bmal1 mRNA levels compared with nonsilencing RNA treatment in luteinizing granulosa cells. Depletion of Bmal1 by siRNA decreased the transcript levels of clock genes (Per1, Per2, Rev-erbα, and Dbp) and examined ovarian genes (Star, Cyp19a1, Cyp11a1, Ptgs2, Hsd3b2, and Lhcgr). Accordingly, knockdown of Bmal1 also inhibited the synthesis of progesterone and prostaglandin E2, which are associated with crucial reproductive processes. Collectively, these data suggest that ovarian circadian oscillators regulate the synthesis of steroid hormones and prostaglandins through ovarian-specific CCGs in response to LH stimuli. The present study provides new insights into the physiologic significance of Bmal1 related to fertility in ovarian circadian oscillators.

Four kinds of cultured clonal cell line were established from estrogen-induced mammotropic pituitary tumor. These clones showed differences of hormone secretion, morphology, and response to estrogen. One clone tentatively designated MtT/E, consisted of spindle-shaped epithelial cells and showed the strongest adhesion to the culture dish, but did not secrete any pituitary hormone. The second cell line, designated MtT/S, secreted only GH, showed very weak contact with the culture dish, and proliferated almost anchorage independently. the MtT/S cells were mainly spherical and formed floating or weakly adherent clusters. Some of them had very long dendrite- or neurite-like cell processes. Electron microscopic examination of the MtT/S cells showed a normal somatotrope-like appearance, i.e. the presence in the cytoplasm of many GH-containing secretory granules, well developed rough endoplasmic reticulum, and Golgi apparatus. Furthermore, these cells secreted GH in response to stimulation with GRF. The third cell line with an ovoid cell appearance tentatively designated MtT/SM, secreted both PRL and GH, and showed anchorage-dependent proliferation. The fourth cell line designated MtT/Se secreted only a small amount of GH. Among these newly established cell lines, MtT/Se was the smallest in size and showed estrogen-dependent proliferation. The many small secretory-like granules present in the cytoplasm of MtT/Se cells showed no immunocytochemically positive reaction for anterior pituitary hormone. MtT/S and MtT/SM cell lines were also sensitive to estrogen.