Beta-adrenergic regulation of adipose tissue function by PKA and MAP kinases

摘要 肥胖症现在已成为流行病，是导致II型糖尿病等多种衰弱疾病的危险因素， 高血压和心血管疾病。 肾上腺素能受体（AR）是脂肪组织代谢的关键调节因子，以控制（i）脂肪分解， 动员储存的能量和（ii）适应性产热棕色脂肪。所有3种已知的AR亚型均在 脂肪细胞和AR与细胞内cAMP的增加和cAMP依赖性蛋白激酶的激活偶联 (PKA)然而，除了这个经典的途径，我们已经表明，额外的信号级联从AR发出 在脂肪细胞中，这些包括ERK和p38 MAP激酶途径。 本研究的目的是鉴定PKA和/p38 MAP激酶之间的信号传导成分， 白色和棕色脂肪细胞中AR介导的信号传导，并确定白色细胞中p38 MAPK的功能。 脂肪细胞为了实现这些目标，我们已经（i）确定MKK 3和p38 MAPK是这一过程的必要组成部分。 级联;（ii）建立p38的转录靶点;（iii）产生p38 <$MAPK的脂肪特异性缺失 (p38¿/).尽管缺乏p38 â，棕色脂肪的产热在p38 â中仍被保留或略有升高/ 老鼠，在 是在p38缺失的情况下选择性激活JNK，/ 动物即使吃高脂肪的食物也很瘦。 在这个新的项目期间，提出了三个目标： 目的1：建立PKA到MKK 3/p38 α信号转导机制的剩余组分 MAPK。实验通过候选MKKK的层次结构进行，以识别负责激活的MKKK。 棕色和白色脂肪细胞中的MKK 3和p38 MAPK。这些实验也验证了小G 蛋白质如Rac 1是这一途径的组成部分，我们将确定协调这一途径的支架蛋白。 MAPK、MKK和MKKK整合成一个功能单位。 目的2：确定缺乏p38 <$（p38 <$）的脂肪细胞中的<$AR信号通路/）已成为“重新布线”， 利用JNK作为“补偿性”激酶。实验将确定p38中的信号元件。/ 现在允许JNK被激活的脂肪细胞。它评估了MKKK的灵活性和其他元素， 目的1，以及它们的参与是否在p38中保守？/ 老鼠.这些实验也决定了 已知的转录因子靶向脂肪细胞中的p38 <$（ATF-2和PGC-1 <$），以及它们现在是否受到 JNK假设p38 <$在脂肪细胞中的一个关键靶点是一种双特异性MAPK磷酸酶， 在非活性的、去磷酸化的状态下，也被探索。 目的3：检验p38基因中的瘦型/ 老鼠是由于增加的能量消耗。的 在这个目的的实验测试是否在p38的情况下，JNK现在是一个更强大的棕色脂肪适应性激活剂 产热和能量消耗，导致较小的白色脂肪细胞和瘦型，以及几种特定的 提出了机制。我们还研究了瘦表型和较小的脂肪库存在的可能性， 脂肪酸储存能力不足的代价，矛盾地导致胰岛素抵抗和脂肪变性。 PHS 398/2590（2004年9月修订，2006年4月重新印发）

ABSTRACT Obesity is now at epidemic proportions and is a risk factor for several debilitating illnesses such as Type II diabetes, hypertension and cardiovascular disease. The ¿-adrenergic receptors (¿ARs) are key regulators of adipose tissue metabolism to control (i) lipolysis for mobilization of stored energy and (ii) adaptive thermogenesis in brown fat. All 3 known ¿AR subtypes are expressed in adipocytes, and ¿ARs are coupled to increases in intracellular cAMP and activation of cAMP-dependent protein kinase (PKA) However, besides this classic pathway, we have shown that additional signaling cascades emanate from ¿ARs in adipocytes, and these include the ERK and p38 MAP kinase pathways. The goals of this proposal are to identity the signaling components between PKA and /p38 MAP kinase that convey the ¿AR-mediated signaling in white and brown adipocytes, and determine the function of p38 MAPK in white adipocytes. Toward achieving these goals we have (i) identified MKK3 and p38¿ MAPK as necessary components of this cascade; (ii) established the transcription targets of p38; (iii) generated an adipose-specific deletion of p38¿ MAPK (p38¿/). Despite the absence of p38¿, thermogenesis in brown fat is preserved or slightly elevated in p38¿/ mice, there is selective activation of JNK in the absence of p38¿, and p38¿/ animals are lean even on a high-fat diet. Three Aims are proposed for this new project period: Aim 1: Establish the remaining components of the signal transduction mechanism from PKA to MKK3/p38alpha MAPK. The experiments proceed through a hierarchy of candidate MKKKs to identify the one responsible for activating MKK3 and p38¿ MAPK in brown and white adipocytes. These experiments also test the hypotheses that a small G protein such as Rac1 is a component of this pathway, and we will identify the scaffolding protein that coordinates the MAPK, the MKK and the MKKK into a functioning unit. Aim 2: Determine how the ¿AR signaling pathway in adipocytes lacking p38¿ (p38¿/) has become "re-wired" to utilize JNK as the "compensatory" kinase. The experiments will determine the signaling elements in p38¿/ adipocytes that now allow JNK to be activated. It assesses the flexibility of the MKKK and other elements identified in Aim 1, and whether their participation is conserved in the p38¿/ mouse. These experiments also determine the status of the known transcription factor targets of p38¿ in adipocytes (ATF-2 and PGC-1¿), and whether they are now regulated by JNK The hypothesis that a key target of p38¿ in adipocytes is a dual-specificity MAPK phosphatases, that maintains JNK in an inactive, dephosphorylated state, is also explored. Aim 3: Test the hypothesis that the lean phenotype in p38¿/ mice is due to increased energy expenditure. The experiments in this Aim test whether in the absence of p38¿, JNK is now a more powerful activator of brown fat adaptive thermogenesis and energy expenditure, resulting in smaller white adipocytes and a lean phenotype, and several specific mechanisms are proposed. We also examine the possibility that the lean phenotype and smaller adipose depots exists at the expense of an insufficient storage capacity for fatty acids, paradoxically resulting in insulin resistance and steatosis. PHS 398/2590 (Rev. 09/04, Reissued 4/2006) Page Continuation Format Page