Alteration of circadian rhythm and sleep by HIV protein Tat

描述（由申请人提供）：昼夜节律是24小时周期的生理功能，包括睡眠-觉醒周期、体温、神经内分泌和神经免疫相互作用。健康个体的循环淋巴细胞具有强大的昼夜节律振荡，在夜间达到峰值，但这种昼夜节律在hiv感染患者中减弱。事实上，在艾滋病毒感染的早期阶段，睡眠模式和昼夜节律紊乱是最常见的疾病之一。位于下丘脑视交叉上核（SCN）的生物钟调节所有器官系统的昼夜节律。我们假设艾滋病毒感染患者的睡眠模式和昼夜节律的改变可能是由破坏这种中央昼夜节律引起的。HIV-1感染与多种神经系统疾病有关。尽管HIV-1的神经发病机制很复杂，但病毒蛋白Tat似乎起着重要作用。SCN位于第三脑室底部，周围是下丘脑室周器官（CVO）。CVOs是大脑中最具渗透性的结构之一。由于Tat可以从受感染的细胞分泌到循环中，并且Tat可以很容易地穿过血脑屏障，我们假设SCN可能是Tat最早的靶点之一。尽管HIV-1感染影响神经元功能的确切机制尚不清楚，但它可能在HIV感染期间昼夜节律和睡眠的改变中发挥关键作用。我们之前的研究表明，在体外和体内将Tat直接急性应用于SCN可以重置生物钟（Clark et al, 2005）。为了评估Tat对睡眠和昼夜节律系统的长期影响，我们使用了四环素依赖和脑（GFAP）特异性Tat转基因小鼠。RT-PCR证实了强力霉素饮食后SCN中Tat的表达。在表达tat的小鼠中，昼夜节律和睡眠模式的改变与临床结果相当，其特征是运动活动减少，与环境光暗周期的同步受损。脑电图分析显示，Tat小鼠的δ功率发生了改变。从Tat小鼠记录的脑电图数据与艾滋病患者的发现相似（Darko et al . 1995; Polich et al . 2000）。由于在细胞和分子水平上对病毒诱导的昼夜节律和睡眠的改变知之甚少，这项研究可能会对病毒神经发病机制产生新的认识，并可能导致hiv感染患者经历昼夜节律障碍的治疗方法。

DESCRIPTION (provided by applicant): Circadian rhythms are physiological functions that manifest a 24-hr period, including sleep-wake cycle, body temperature, neuroendocrine and neuroimmune interactions. Healthy individuals have a robust circadian oscillation of circulating lymphocytes with the peak at night, but this circadian rhythm is diminished in HIV-infected patients. In fact, disruption of sleep patterns and circadian rhythms are among the most common disorders in the early stages of HIV infection. A circadian clock located in the suprachiasmaticnucleus (SCN) of the hypothalamus regulates the circadian rhythms of all organ systems. We hypothesize that the alteration of sleep patterns and circadian rhythms in HIV infected patients may be caused by disrupting this central circadian clock. HIV-1 infection has been associated with a variety of neurological disorders. Although the neuropathogenesis of HIV-1 is complex, the viral protein Tat appears to play an important role. The SCN is located in the base on the third cerebral ventricle surrounded by the hypothalamic circumventricular organs (CVO). The CVOs are among the most permeable structures in the brain. Since Tat can be secreted to the circulation from infected cells and Tat can readily cross the blood brain barrier, we hypothesize that the SCN may be among the earliest target of Tat. Although the exact mechanism by which HIV-1 infection affects neuronal function remains unknown, Tat may play a pivotal role in the alteration of circadian rhythms and sleep during HIV infection. Our previous study showed that acute application of Tat directly to the SCN both in vitro and in vivo could reset the circadian clock (Clark et al 2005). To assess the long term effect of Tat to the sleep and circadian timing system, we used the tetracycline-dependent and brain (GFAP) specific Tat transgenic mice. RT-PCR confirmed Tat expression in the SCN following doxycycline diet. The alteration of circadian rhythm and sleep pattern in the Tat-expressing mouse is comparable to clinical findings, characterized with reduced motor activity and impaired synchronization to the environmental light dark cycle. EEG analysis showed altered delta power in the Tat mice. The EEG data recorded from the Tat mice are similar to findings in AIDS patients (Darko et al 1995; Polich et al 2000). Since little is known about viral- induced alteration of circadian rhythm and sleep at a cellular and molecular level, this research may yield novel understanding of viral neuropathogenesis and potentially lead to therapeutic approaches to circadian rhythm disorders experienced by HIV-infected patients. PUBLIC HEALTH RELEVANCE: Alteration of circadian rhythm and sleep occurs in AIDS patients with different disease stages and with a wide range of CD4 counts. Although the exact mechanism of HIV-1 neuropathogenesis remains poorly understood, viral proteins (gp41, gp120, and Tat) are thought to play a major role in the neural AIDS. Among these viral proteins, Tat is important because it can be secreted from infected cells to the extracellular space, subsequently affecting nearby neurons. Since our previous study demonstrated that Tat could reset the circadian clock in the brain, the suprachiasmatic nucleus (SCN), we hypothesize that the disruption of circadian rhythm and sleep during HIV infection could be a consequence of Tat on the SCN. To test our hypothesis, we used a transgenic mouse model that can selectively induce the expression of Tat in the brain when doxycycline is administered to the animals. RT-PCR confirmed Tat expression in the mouse SCN two weeks after feeding the animals with the doxycycline diet. Interestingly, the alteration of circadian rhythm in the Tat-expressing mouse is comparable to that found in the HIV-infected patients, characterized with reduced motor activity and impaired synchronization to the environmental light dark cycle. EEG analysis showed decreased delta power in the Tat transgenic mice compared to wild type mice.