Physiologie de la Reproduction et des Comportements UMR85, INRA, Nouzilly F-37380, France.
BMC Neurosci. 2011 Jul 29;12:76. doi: 10.1186/1471-2202-12-76.
It is now widely accepted that AMP-activated protein kinase (AMPK) is a critical regulator of energy homeostasis. Recently, it has been shown to regulate circadian clocks. In seasonal breeding species such as sheep, the circadian clock controls the secretion of an endogenous rhythm of melatonin and, as a consequence, is probably involved in the generation of seasonal rhythms of reproduction. Considering this, we identified the presence of the subunits of AMPK in different hypothalamic nuclei involved in the pre- and post-pineal pathways that control seasonality of reproduction in the ewe and we investigated if the intracerebroventricular (i.c.v.) injection of two activators of AMPK, metformin and AICAR, affected the circadian rhythm of melatonin in ewes that were housed in constant darkness. In parallel the secretion of insulin was monitored as a peripheral metabolic marker. We also investigated the effects of i.c.v. AICAR on the phosphorylation of AMPK and acetyl-CoA carboxylase (ACC), a downstream target of AMPK, in brain structures along the photoneuroendocrine pathway to the pineal gland.
All the subunits of AMPK that we studied were identified in all brain areas that were dissected but with some differences in their level of expression among structures. Metformin and AICAR both reduced (p < 0.001 and p < 0.01 respectively) the amplitude of the circadian rhythm of melatonin secretion independently of insulin secretion. The i.c.v. injection of AICAR only tended (p = 0.1) to increase the levels of phosphorylated AMPK in the paraventricular nucleus but significantly increased the levels of phosphorylated ACC in the paraventricular nucleus (p < 0.001) and in the pineal gland (p < 0.05).
Taken together, these results suggest a potential role for AMPK on the secretion of melatonin probably acting trough the paraventricular nucleus and/or directly in the pineal gland. We conclude that AMPK may act as a metabolic cue to modulate the rhythm of melatonin secretion.
现在人们普遍认为，AMP 激活的蛋白激酶（AMPK）是能量平衡的关键调节因子。最近，它被证明可以调节生物钟。在绵羊等季节性繁殖物种中，生物钟控制着内源性褪黑素节律的分泌，因此可能参与了繁殖的季节性节律的产生。考虑到这一点，我们在参与控制母羊繁殖季节性的松果腺前和后导途径的不同下丘脑核中鉴定出 AMPK 的亚基的存在，并研究了向母羊脑室内（i.c.v.）注射两种 AMPK 激活剂二甲双胍和 AICAR 是否会影响处于持续黑暗环境中的母羊的褪黑素的昼夜节律。同时监测胰岛素的分泌作为外周代谢标志物。我们还研究了向脑室内注射 AICAR 对沿光神经内分泌途径至松果腺的脑结构中 AMPK 的磷酸化和乙酰辅酶 A 羧化酶（ACC）的影响，ACC 是 AMPK 的下游靶点。
我们研究的 AMPK 的所有亚基都在所有被解剖的脑区中被鉴定出来，但在结构之间的表达水平存在一些差异。二甲双胍和 AICAR 均独立于胰岛素分泌降低（p < 0.001 和 p < 0.01 分别）褪黑素分泌的昼夜节律振幅。脑室内注射 AICAR 仅倾向于增加（p = 0.1）室旁核中磷酸化 AMPK 的水平，但显著增加了室旁核（p < 0.001）和松果腺（p < 0.05）中磷酸化 ACC 的水平。
综上所述，这些结果表明 AMPK 可能在褪黑素的分泌中发挥作用，可能通过室旁核起作用，或直接在松果腺中起作用。我们得出结论，AMPK 可能作为代谢线索调节褪黑素分泌的节律。
