The role of delta-6 desaturase on omega-3 fatty acid regulation of adipose tissue function

Omega-3多不饱和脂肪酸(N3PUFA)是白色脂肪组织(WAT)中调节多种信号通路的重要分子，包括脂肪生成、脂代谢、炎症和脂肪因子的产生。体内发现的三种最丰富的N3PUFA是α-亚麻酸(ALA)、二十碳五烯酸(EPA)和二十二碳六烯酸(DHA)。值得注意的是，人们对不同N3PUFA的单独作用知之甚少，因为ALA在体内通过Delta-6去饱和酶(D6D)不断转化为EPA/DHA。为了解决这一现有的知识差距，我的NSERC资助的研究计划使用了无法将ALA转化为EPA/DHA的D6D基因敲除(D6D-KO)小鼠，以促进我们对不同的N3PUFA如何调节Wat代谢的基本理解。 我们最近发现，喂食含ALA(但不含EPA/DHA)的D6D-KO小鼠的Wat脂肪垫和脂肪细胞比喂食相同食物的野生型小鼠小，或喂食含EPA/DHA的D6D-KO小鼠的Wat脂肪垫和脂肪细胞小。这一新的发现揭示了D6D介导的ALA向EPA/DHA的转化对WAT生理学具有比先前认识的更重要的意义。因此，我提出的NSERC研究计划的目标是揭示ALA独立于EPA/DHA影响WAT脂肪垫和脂肪细胞大小的机制。首先，我们将确定在只喂饲ALA的D6D-KO小鼠中，控制脂肪形成的关键转录因子的表达和活性是否受到损害。其次，我们将确定在只喂食ALA的D6D-KO小鼠中看到的较小的脂肪细胞是源于脂肪酸摄取和三酰甘油储存途径受损，还是源于脂解和氧化途径活性增加。最后，我们将确定只喂ALA的D6D-KO小鼠是否比喂EPA/DHA的小鼠表现出更高的炎症信号活性。我们建议在功能和功能失调的脂肪组织以及雄性和雌性小鼠中进行所有研究，以进一步促进我们对不同N3PUFA在WAT中的独立影响的理解。用单独的N3PUFA和D6D抑制剂处理培养的小鼠脂肪细胞的互补实验将被用来验证我们的小鼠研究中确定的信号通路中的关键调节点。我们假设，在只喂食ALA的D6D-KO小鼠中看到的较小的脂肪垫/较小的脂肪细胞是脂肪生成受损、脂肪酸摄取减少和三酰甘油储存途径减少的结果。此外，我们预计，给D6D-KO小鼠喂食含有EPA/DHA的饲料将防止WAT中的这些损害。 拟议的研究具有原创性和创新性，建立在我们最近工作的基础上，并将极大地促进我们对不同的N3PUFA如何调节WAT功能的理解。此外，拟议的研究计划将为对整合营养生物化学、生理学和生物信息学感兴趣的HQP提供一个出色的培训环境。

Omega-3 polyunsaturated fatty acids (N3PUFA) are important molecules that regulate numerous signaling pathways in white adipose tissue (WAT), including adipogenesis, lipid metabolism, inflammation, and adipokine production. The three most abundant N3PUFA found in the body are alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Remarkably little is known about the individual roles of different N3PUFA because ALA is continuously converted into EPA/DHA in the body by the delta-6 desaturase (D6D) enzyme. To address this existing gap in knowledge, my NSERC-funded research program uses D6D knock-out (D6D-KO) mice that are unable to convert ALA into EPA/DHA to advance our fundamental understanding of how different N3PUFA regulate WAT metabolism. We recently discovered that D6D-KO mice fed a diet containing ALA (but no EPA/DHA) have smaller WAT fat pads and smaller adipocytes compared to wild-type mice fed the same diet, or D6D-KO mice fed a diet containing EPA/DHA. This novel discovery revealed that D6D-mediated conversion of ALA to EPA/DHA is of greater importance for WAT physiology than previously appreciated. Therefore, the objective of my proposed NSERC research program is to uncover the mechanisms by which ALA influences WAT fat pad and adipocyte size independent of EPA/DHA. First, we will establish if the expression and activity of key transcription factors that control adipogenesis are impaired in D6D-KO mice fed only ALA. Second, we will determine if the smaller adipocytes seen in D6D-KO mice fed only ALA stems from impaired fatty acid uptake and triacylglycerol storage pathways, or from increased activity of lipolysis and oxidation pathways. Finally, we will determine if D6D-KO mice fed only ALA show higher inflammatory signalling activity compared to mice fed EPA/DHA. We propose to run all studies in functional and dysfunctional adipose tissue, as well as in male and female mice, to further advance our understanding of the independent effects of different N3PUFA in WAT. Complementary experiments in cultured mouse adipocyte cells treated with individual N3PUFA and a D6D inhibitor will be used to validate key regulatory points in signalling pathways that were identified in our mouse studies. We hypothesize that the smaller fat pads / smaller adipocytes seen in D6D-KO mice fed only ALA is a result of both impaired adipogenesis, and reduced fatty acid uptake and triacylglycerol storage pathways. Further, we anticipate that feeding D6D-KO mice a diet containing EPA/DHA will prevent these impairments in WAT. The proposed studies are original and innovative, build upon our recent work, and will significantly advance our understanding of how different N3PUFA regulate WAT function. Further, the proposed research program will provide an outstanding training environment for HQP interested in integrating nutritional biochemistry, physiology, and bioinformatics.