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

背景：细胞内胆固醇抑制胆固醇的生物合成，通过阻断转录因子中固醇调节元件结合蛋白家族成员SREBP-2的激活，导致胆固醇生物合成酶的转录下调。 基质金属蛋白酶(MMPs)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发现拨款将通过针对基质金属蛋白酶家族中最小的成员-基质分解素-7的原创性研究来挑战这一概念，我们建议通过一种新的生理途径调节肝脏SREBP对胆固醇的依赖反应。 理论基础：在初步研究中，我们发现，在小鼠中，缺乏基质金属蛋白酶-7会损害肝脏SREBP-2靶基因对饮食中胆固醇补充的转录反应。此外，我们还发现致病性促炎症磷脂酶A2(SPLA2)从器官释放到循环中，导致Mmp7-/-小鼠的肝脏炎症。虽然我们还没有全面研究MMP7-/-小鼠的生理学，但我们知道，抑制系统循环sPLA2可以部分恢复MMP2-/-和MMP9-/-小鼠的肝脏炎症和SREBP-2途径中基因对饮食胆固醇的转录反应。基质金属蛋白酶-7可能通过与sPLA2类似的机制调节肝脏胆固醇代谢。 具体假设：基质金属蛋白酶-7通过负调控新的sPLA2/肝脏炎症/SREBP-2轴来调节胆固醇代谢。 目的1从分子水平研究基质金属蛋白酶-7(MMP7)对小分子磷脂酶A2(S)的调控。 目的2绘制基质金属蛋白酶-7/sPLA2轴调控SREBP-2途径的生物学途径。 总体策略：我们将在两个互补的小鼠模型中解决我们的假设：Mmp7-/-小鼠(全身MMP7缺乏)和Mmp7(FLOX/FLOX)x Alb-cre小鼠(肝脏特异性MMP7基因敲除)。第一个模型将允许我们检验这一假设，即外围器官通过sPLA2影响肝脏的新陈代谢，sPLA2作为代谢信号。第二个模型将使我们能够描述肝脏基质金属蛋白酶-7在调节肝脏SREBP-2途径中的特定作用。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推进这些项目。 意义：推测的MMP-7/sPLA2/肝脏炎症/SREBP-2轴是一种新的系统调节胆固醇稳态的生化机制，具有潜在的健康和疾病意义。

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.