Developmental genes, miRNAs and adipose tissue

描述（由申请人提供）：这是NIH拨款DK082659题为“发育基因，miRNAs和脂肪组织”的竞争性更新。在过去的十年里，人们已经清楚地认识到，脂肪组织比原先认为的要复杂得多。除了白色脂肪和棕色脂肪外，这两种脂肪都是异质的。内脏WAT的积累与胰岛素抵抗和代谢性疾病有关，而皮下WAT的积累则没有这种风险，甚至可能具有保护作用。这至少部分是由于这些储存库中脂肪细胞之间的细胞自主功能差异。在过去的研究期间，我们发现来自不同脂肪库的白色脂肪细胞和前脂肪细胞表现出明显不同的发育/模式基因表达水平，这表明WAT的发育异质性。我们重点研究了其中的三个基因（Shox2， Tbx15和Glypican-4），因为在人类中，这些基因的表达与BMI和脂肪分布密切相关。我们已经证明这些基因的过表达或敲低可以改变脂肪细胞的分化和功能。例如，Shox2调节脂肪细胞的脂溶反应，而Tbx15可以调节线粒体代谢以及脂肪细胞糖酵解和氧化代谢的平衡。另一方面，Glypican-4 （Gpc4）调节胰岛素受体的结合和作用，并从脂肪细胞释放到循环中，在循环中它可以作用于其他靶细胞。我们发现不同的WAT储存库的mirna表达也不同，并且在肥胖和衰老中存在mirna的改变。后者是由于miRNA加工酶Dicer的表达减少。在令人兴奋的新数据中，我们还表明脂肪组织是循环mirna的主要来源。这些数据导致了两个相互关联的假设。首先，我们假设，与骨骼肌细胞或淋巴细胞相似，但具有不同的功能，白色脂肪细胞在本质上是异质的，并且发育/模式基因促成了脂肪组织发育和功能的异质性和程序差异。其次，脂肪细胞的功能和异质性被miRNA表达的差异进一步改变。此外，这些mirna被释放到循环中，在那里它们作为脂肪对其他组织影响的新介质。未来的具体目标是：1)确定发育基因ethx15如何促进WAT的异质性并影响脂肪细胞的决定和功能。2)进一步表征Gpc4作为脂肪细胞功能和胰岛素信号传导调节剂的作用，以及Gpc4如何从脂肪细胞释放到循环中并参与胰岛素敏感性的改变。3)确定不同储存库脂肪细胞和前脂肪细胞之间miRNA表达的差异，以及miRNA表达变化对不同储存库脂肪细胞功能的影响。我们还将探讨我们的初步发现，即脂肪组织是循环mirna的主要来源，这些循环mirna可能作为脂肪对其他组织影响的介质。

DESCRIPTION (provided by applicant): This is a competitive renewal of NIH grant DK082659 entitled "Developmental Genes, miRNAs and Adipose Tissue". Over the past decade it has become clear that adipose tissue is more complex than originally believed. In addition to both white and brown fat, both types of fat are heterogeneous. Accumulation of visceral WAT is associated with insulin resistance and metabolic disease, whereas accumulation of subcutaneous WAT does not have such a risk and may even be protective. This is due, at least in part, to cell-autonomous, functional differences between adipocytes in these depots. During the past grant period, we have shown that white adipocytes and preadipocytes from different fat depots exhibit markedly different levels of expression of developmental/patterning genes, suggesting developmental heterogeneity of WAT. We have focused on three of these genes (Shox2, Tbx15 and Glypican-4), since in humans, the expression of these genes strongly correlates with BMI and fat distribution. We have shown that overexpression or knockdown of these genes can alter adipocyte differentiation and function. For example, Shox2 regulates the lipolytic response of adipocytes, whereas Tbx15 can modulate mitochondrial metabolism and the balance between glycolytic and oxidative metabolism in fat cells. Glypican-4 (Gpc4), on the other hand, modulates insulin receptor binding and action, and is released from fat cells into the circulation where is can act on other target cells. We have found that different WAT depots also differ in their expression of miRNAs and that there are alterations in miRNAs in obesity and aging. The latter is due to a decrease in the expression of the miRNA processing enzyme Dicer. In exciting new data, we also show that adipose tissue is a major source of circulating miRNAs. These data have led to two inter-related hypotheses. First, we hypothesize that, in analogy to skeletal muscle cells or lymphocytes which look alike but have different functions, white adipocytes are heterogeneous in nature and that development/patterning genes contribute to this heterogeneity and program differences in adipose tissue development and function. Secondly, adipocyte function and heterogeneity is further modified by differences in miRNA expression. In addition these miRNAs are released into the circulation where they act as novel mediators of the effects of fat on other tissues. The specific aims going forward are to: 1) Determine how the developmental geneTbx15 contributes to heterogeneity of WAT and affects adipocyte determination and function. 2) Further characterize the role of Gpc4 as a modifier of adipocyte function and insulin signaling, and how Gpc4 is released from adipocytes into the circulation and contributes to changes in insulin sensitivity. 3) Determine how miRNA expression differs between adipocytes and preadipocytes from different depots, and how changes in miRNA expression affect function of adipocytes in different depots. We will also explore our preliminary findings that adipose tissue is a major source of circulating miRNAs and that these circulating miRNAs may serve as mediators of adipose effects on other tissues.