First Department of Pediatrics, University of Athens Medical School, "Aghia Sophia" Children's Hospital, Athens, Greece.
PLoS One. 2011;6(9):e25612. doi: 10.1371/journal.pone.0025612. Epub 2011 Sep 28.
Circulating cortisol fluctuates diurnally under the control of the "master" circadian CLOCK, while the peripheral "slave" counterpart of the latter regulates the transcriptional activity of the glucocorticoid receptor (GR) at local glucocorticoid target tissues through acetylation. In this manuscript, we studied the effect of CLOCK-mediated GR acetylation on the sensitivity of peripheral tissues to glucocorticoids in humans.
We examined GR acetylation and mRNA expression of GR, CLOCK-related and glucocorticoid-responsive genes in peripheral blood mononuclear cells (PBMCs) obtained at 8 am and 8 pm from 10 healthy subjects, as well as in PBMCs obtained in the morning and cultured for 24 hours with exposure to 3-hour hydrocortisone pulses every 6 hours. We used EBV-transformed lymphocytes (EBVLs) as non-synchronized controls.
GR acetylation was higher in the morning than in the evening in PBMCs, mirroring the fluctuations of circulating cortisol in reverse phase. All known glucocorticoid-responsive genes tested responded as expected to hydrocortisone in non-synchronized EBVLs, however, some of these genes did not show the expected diurnal mRNA fluctuations in PBMCs in vivo. Instead, their mRNA oscillated in a Clock- and a GR acetylation-dependent fashion in naturally synchronized PBMCs cultured ex vivo in the absence of the endogenous glucocorticoid, suggesting that circulating cortisol might prevent circadian GR acetylation-dependent effects in some glucocorticoid-responsive genes in vivo.
Peripheral CLOCK-mediated circadian acetylation of the human GR may function as a target-tissue, gene-specific counter regulatory mechanism to the actions of diurnally fluctuating cortisol, effectively decreasing tissue sensitivity to glucocorticoids in the morning and increasing it at night.
在“主”生物钟的控制下，循环皮质醇呈昼夜波动，而后者的外周“从属”对应物通过乙酰化调节局部糖皮质激素靶组织中糖皮质激素受体（GR）的转录活性。在本文中，我们研究了 CLOCK 介导的 GR 乙酰化对人体外周组织对糖皮质激素敏感性的影响。
我们检查了 10 名健康受试者在上午 8 点和晚上 8 点从外周血单核细胞（PBMCs）中获得的 GR 乙酰化和 GR、CLOCK 相关和糖皮质激素反应基因的 mRNA 表达，以及在上午获得并在暴露于每 6 小时 3 小时氢化可的松脉冲的情况下培养 24 小时的 PBMCs。我们使用 EBV 转化的淋巴细胞（EBVLs）作为非同步对照。
PBMCs 中的 GR 乙酰化在上午高于晚上，与循环皮质醇的相反相位波动相吻合。所有测试的已知糖皮质激素反应基因在非同步 EBVLs 中对氢化可的松的反应都如预期的那样，但其中一些基因在体内 PBMCs 中没有表现出预期的昼夜 mRNA 波动。相反，它们的 mRNA 在自然同步的 PBMCs 中以时钟和 GR 乙酰化依赖的方式振荡，在没有内源性糖皮质激素的情况下体外培养，表明循环皮质醇可能会防止某些糖皮质激素反应基因在体内的昼夜 GR 乙酰化依赖性作用。
外周 CLOCK 介导的人类 GR 昼夜乙酰化可能作为一种组织特异性、基因特异性的反调节机制，作用于昼夜波动的皮质醇，有效降低早晨组织对糖皮质激素的敏感性，夜间增加。
