Phosphodiesterase 8 Synergies: Regulation of Brown Fat, and Cardiac Functions

描述（由申请人提供）：众所周知，cAMP在许多不同细胞类型的发育和功能中具有重要的多种调节作用。还已知cAMP主要通过激活cAMP依赖性蛋白激酶（PKA）和/或鸟嘌呤核苷酸交换蛋白Epac来发挥其作用。重要的是，由cAMP/PKA/Epac调节的许多不同过程高度受控于一系列环AMP降解磷酸二酯酶（PDE）。此外，通过选择性和特异性抑制剂抑制单个环核苷酸降解PDE已成为对抗许多病理学的最佳方法。例如，药物伟哥（R）以这种方式工作。然而，在最近的资助期间，我们发现至少在两种不同的组织中，抑制单一PDE不足以调节该组织中的某些生理过程。例如，我们已经证明，经典的PDE 4抑制剂在控制Leydig细胞中的类固醇产生方面是完全无效的，除非这些细胞的PDE 8活性也被抑制。这是协同作用过程的一个主要例子- 几种途径调节剂一起作用比单独作用更有效。如果这一概念在多种组织中普遍有效，那么它对未来PDE抑制剂设计策略具有重大影响。因此，我们计划研究是否同样的原则适用于两个不同的组织，高度调节cAMP和高度表达cAMP特异性PDE 8样类固醇产生Leydig细胞。我们打算解决这个问题，是否需要一个以上的PDE被抑制，以有效地调节cAMP依赖的过程中，这些组织。我们将研究多种PDE抑制剂治疗（包括一种新的PDE 8抑制剂）对棕色脂肪组织（BAT）/棕色脂肪细胞产热的影响，以及对心肌细胞钙信号传导和心脏功能参数的影响。这些过程中的每一个都是高度cAMP依赖性的，并且每种细胞类型都表达高水平的PDE 8A。然而，据我们所知，没有一种细胞检测了其cAMP依赖性过程中单独抑制PDE 8的作用，特别是不与抑制这些细胞中表达的其他PDE联合作用。此外，我们将研究多种PDE在各种细胞类型（包括Leydig细胞和肝细胞）中协同作用的分子机制，我们已经证明了PDE协同作用的发生。在过去的20年里，许多制药公司已经花费了数亿美元寻找选择性PDE抑制剂来治疗各种疾病，包括炎症，癌症和肥胖。除了勃起功能障碍和肺动脉高压（由cGMP调节的过程），这些努力只取得了轻微的成功。如果拟议的研究结果符合预期，它们将大大有助于解释为什么这些选择性抑制剂方法中的许多方法只显示出很小的疗效。此外，这些数据可能会建议通过使用靶向一种以上PDE的药物来使用PDE抑制剂治疗各种疾病的替代方法。

DESCRIPTION (provided by applicant): It is well recognized that cAMP has important and multiple regulatory roles in the development and function of many different cell types. It is also known that cAMP exerts its effects largely through activation of cAMP- dependent protein kinases (PKAs) and/or the guanine nucleotide exchange protein, Epac. Importantly, the many different processes regulated by cAMP/PKA/Epac are highly controlled by a series of cyclic AMP- degrading phosphodiesterases (PDEs). Moreover, inhibition of individual cyclic nucleotide degrading PDEs by selective and specific inhibitors has been a favorite approach for pharmacologically counteracting a number of pathologies. For example, the drug Viagra(R) works in this manner. However, during the recent grant period we have made the discovery that in at least in two different tissues, inhibition of a single PDE is NOT sufficient to regulate certin physiological processes in that tissue. We have shown, for example, that a classic PDE4 inhibitor is completely ineffective in controlling steroid production in Leydig cells unless the PDE8 activity of these cells is also inhibited. This is a prime example of the process of synergy - several pathway modulators acting together to have a greater effect than either one alone. If this concept turns out to be generally valid in several tissues, it has GREAT implications for the strategies of PDE inhibitor design in the future. Therefore, we plan to investigate whether the same principle holds true in two different tissues that are highly regulated by cAMP and highly express the cAMP-specific PDE8 like steroid producing Leydig cells. We intend to address the question, does more than one PDE need to be inhibited in order to effectively regulate cAMP-dependent processes in these tissues. We will study the effects of multiple PDE inhibitor treatment, including a new PDE8 inhibitor, on thermogenesis in brown adipose tissue (BAT)/brown adipocytes, and on calcium signaling in cardiomyocytes and functional parameters of the heart. Each of these processes is highly cAMP-dependent and each cell type expresses high levels of PDE8A. However, none of them to our knowledge have had their cAMP-dependent processes examined for the effects of PDE8 inhibition alone and particularly not in conjunction with inhibition of other PDEs expressed in these cells. Moreover, we will investigate the molecular mechanisms underlying the synergistic action of multiple PDEs in a variety of cell types including Leydig cells and hepatocytes, for which we have already shown the occurrence of PDE synergies. Over the last 20 years, many drug companies have spent hundreds and hundreds of millions of dollars searching for selective PDE inhibitors to treat various disorders including inflammation, cancer, and obesity. With the exception of erectile dysfunction and pulmonary hypertension (processes regulated by cGMP) these efforts have been only marginally successful. If the proposed studies turnout as expected, they will contribute substantially to explaining why many of these selective inhibitor approaches have shown only minor efficacy. Moreover, the data will likely suggest an alternate approach for the treatment of various diseases with PDE inhibitors by using drugs that target more than one PDE.