Studies on the mechanism by which MMP-7 modulates cholesterol metabolism

背景资料：胆固醇生物合成受到细胞内胆固醇的抑制，这通过阻断转录因子的固醇调节元件结合蛋白家族的成员SREBP-2的活化而导致胆固醇生物合成酶的转录下调。 基质金属蛋白酶（MMP）共同负责组织重塑，但通常不被视为主要的代谢调节剂。这项NSERC发现资助将通过针对MMP家族最小成员MMP-7的原始研究来挑战这一概念，MMP-7也被称为基质溶解素，我们建议通过一种新的生理途径调节肝脏SREBP依赖性对胆固醇的反应。 基本原理：在初步研究中，我们发现MMP-7的缺乏损害了小鼠肝脏SREBP-2靶基因对膳食胆固醇补充剂的转录反应。此外，我们确定了一种致病性释放的促炎性磷脂酶A2（sPLA 2）从器官进入循环，导致肝脏炎症Mmp 7-/-小鼠。虽然我们尚未全面研究Mmp 7-/-小鼠的生理学，但我们知道，抑制全身循环sPLA 2可部分恢复Mmp 2-/-和Mmp 9-/-小鼠肝脏炎症和SREBP-2途径中基因对膳食胆固醇的肝脏转录反应。MMP-7可通过与sPLA 2类似的机制调节肝脏胆固醇代谢。 具体假设：MMP-7通过新的sPLA 2/肝脏炎症/SREBP-2轴的负调节来调节胆固醇代谢。 目的1在分子水平上研究MMP-7对sPLA 2（s）的调控作用。 目的2定位MMP-7/sPLA 2轴调控SREBP-2通路的生物学通路。 总体战略：我们将在两个互补的小鼠模型中解决我们的假设：Mmp 7-/-小鼠（全身MMP-7缺陷）和Mmp 7（flox/flox）x Alb-cre小鼠（肝脏特异性MMP-7敲低）。第一个模型将允许我们检验外周器官通过作为代谢信号的sPLA 2影响肝脏代谢的假设。第二个模型将使我们能够描述肝脏MMP-7在肝脏SREBP-2通路调节中的特定作用。两名研究生将推动这项研究。我们将与加拿大、法国、美国和日本的长期合作伙伴一起开展这些项目。 重要性：假设的MMP-7/sPLA 2/肝脏炎症/SREBP-2轴是胆固醇稳态的系统调节的新生化机制，在健康和疾病中具有潜在意义。

Background: Cholesterol biosynthesis is inhibited by intracellular cholesterol, which leads to transcriptional down-regulation of cholesterol biosynthetic enzymes through blockade of the activation of SREBP-2, a member of the sterol regulatory element-binding protein family of transcription factors. Matrix metalloproteinases (MMPs) are collectively responsible for tissue remodeling but not typically viewed as major metabolic modulators. This NSERC Discovery Grant will challenge this notion through original studies targeting the smallest member of the MMP family, MMP-7 also known as matrilysin, which we propose modulates hepatic SREBP-dependent responses to cholesterol via a novel physiological pathway. Rationale: In preliminary studies, we discovered that the lack of MMP-7 impairs the transcriptional responses of hepatic SREBP-2 target genes to dietary cholesterol supplementation in mice. Furthermore, we identified a pathogenic release of a pro-inflammatory phospholipase A2 (sPLA2) from organs into circulation resulting in hepatic inflammation in Mmp7-/- mice. Although we have not yet comprehensively investigated the physiology of Mmp7-/- mice, we know that the inhibition of systemic circulating sPLA2 partially normalizes hepatic inflammation and the hepatic transcriptional responses of genes in the SREBP-2 pathway to dietary cholesterol in Mmp2-/- and Mmp9-/- mice. MMP-7 could modulate hepatic cholesterol metabolism through a similar mechanism involving sPLA2. Specific hypothesis: MMP-7 modulates cholesterol metabolism through the negative regulation of a novel sPLA2/hepatic inflammation/SREBP-2 axis. Aim 1 Characterize the sPLA2(s) regulated by MMP-7 at the molecular level. Aim 2 Map the biological pathways by which the MMP-7/sPLA2 axis modulates the SREBP-2 pathway. Overall strategy: We will address our hypothesis in two complementary mouse models: Mmp7-/- mice (with full body MMP-7 deficiency) and Mmp7(flox/flox) x Alb-cre mice (with liver-specific MMP-7 knockdown). The 1st model will allow us to test the hypothesis that peripheral organs influence the metabolism of the liver through sPLA2, which serves as a metabolic signal. The 2nd model will allow us to delineate the specific role of hepatic MMP-7 in modulation of the hepatic SREBP-2 pathway. Two graduate students will drive this research. We will pursue these projects with long-standing collaborators in Canada, France, USA and Japan. Significance: The postulated MMP-7/sPLA2/hepatic inflammation/SREBP-2 axis is a novel biochemical mechanism of systemic modulation of cholesterol homeostasis with potential significance in health and disease.