Impaired bile acid synthesis due to CYP7A1 and CYP7B1 suppression in malnutrition

营养不良时 CYP7A1 和 CYP7B1 抑制导致胆汁酸合成受损

基本信息

批准号：
10445334
负责人：
Geoffrey A Preidis
金额：
$ 12.04万
依托单位：
BAYLOR COLLEGE OF MEDICINE
依托单位国家：
美国
项目类别：
财政年份：
2021
资助国家：
美国
起止时间：
2021-07-15 至 2023-06-30
项目状态：
已结题

来源：
https://reporter.nih.gov/project-details/10445334
关键词：
Acute Address Adolescent Affect Anorexia Nervosa Back Bile Acid Biosynthesis Pathway Bile Acids Binding Binding Sites Blood Coagulation Disorders Blood Coagulation Factor Body Weight decreased CYP7A1 gene Cell Line Cessation of life Child Child Malnutrition Cholesterol Coagulation Process Cytochrome P450 DNA Data Digestive System Disorders Drug Kinetics Enteral Enzymes Family Fat-Soluble Vitamin Female Genes Genetic Transcription Goals Growth Heme Hepatic Hepatocyte Homeostasis Impairment In Vitro Individual Infant Intestines Investigation Label Life Ligands Link Liver Malabsorption Syndromes Malnutrition Measures Mediator of activation protein Membrane Metabolism Mus Nuclear Nuclear Receptors Nutrient Nutritional status Outcome PPAR alpha Pathology Pathway interactions Pharmacology Process Production Promoter Regions Prosthesis Publishing Receptor Activation Regulation Research Response Elements Role SRE-1 binding protein Signal Transduction Small Interfering RNA Small for Gestational Age Infant Testing Transcription Repressor Vitamin K Weight Gain Western Blotting antagonist base dietary drug metabolism experimental study feeding gene repression genetic corepressor improved outcome in vivo inhibitor innovation insight liver function male member mouse model novel novel therapeutic intervention novel therapeutics nutrition oxidation oxysterol 7-alpha-hydroxylase peroxisome predicting response promoter receptor recruit therapeutic candidate therapy outcome transcription factor

项目摘要

Malnutrition contributes to half of all global child deaths. Liver function abnormalities, including decreased bile acid synthesis, are common in severe malnutrition. In the intestine, bile acid deficiency leads to nutrient malabsorption and impaired growth. In the liver, bile acids signal through nuclear receptors including farnesoid- X-receptor (FXR) to regulate a wide range of processes from energy homeostasis to coagulation. We discovered that decreased bile acid synthesis in malnutrition causes decreased FXR activation and decreased expression of FXR target genes, including coagulation factors. The resulting malnutrition-induced coagulopathy can be fatal. It is not known why bile acid synthesis is impaired in malnutrition. My ongoing K08 project uses a unique mouse model of early-life malnutrition, revealing loss of expression of peroxisome proliferator-activated receptor- α (PPARα) and subsequent loss of peroxisomes, which are required for an essential β-oxidation step to generate mature bile acids. Our published data and new preliminary data indicate that suppression of two key cytochrome P450 (CYP) enzymes upstream of peroxisomal β-oxidation also contributes to decreased bile acid synthesis in malnutrition, independently of PPARα. Hepatocytes synthesize bile acids from cholesterol in two parallel pathways. Our data suggest that the classic pathway of bile acid synthesis is suppressed through decreased activity of CYP7A1, the rate-determining enzyme. We predict that decreased CYP7A1 activity occurs because malnourished hepatocytes are depleted of heme, the essential prosthetic group for CYP7A1. Similarly, we have evidence that the alternative pathway of bile acid synthesis is suppressed through decreased expression of CYP7B1, the key enzyme in this pathway. We predict that decreased expression of CYP7B1 occurs because malnutrition upregulates its potent transcriptional repressor, the sterol regulatory element-binding protein-1 (SREBP-1). Thus, we hypothesize that, in addition to PPARα-dependent peroxisome loss, malnutrition impairs bile acid synthesis also by suppressing CYP7A1 and CYP7B1 to impair both the classic and the alternative pathways of synthesis. The Specific Aims are 1) to characterize altered heme metabolism in malnutrition and its role in decreased CYP7A1 activity by quantifying flux of labeled cholesterol, measuring expression levels of heme synthesizing enzymes, and treating hepatocytes and mice with heme; and 2) to determine the role of SREBP-1 in the transcriptional repression of CYP7B1 and its relative contribution to decreased bile acid synthesis in malnutrition by defining the corepressors recruited to the CYP7B1 promoter, and by inhibiting SREBP-1 with siRNA and pharmacologic antagonists in vitro and in vivo. Expected outcomes include a deeper understanding of how nutritional status influences bile acid homeostasis. This approach is innovative because it will explore CYP suppression as a novel link between malnutrition and impaired bile acid synthesis. The proposed research is significant because of the potential to develop new strategies to restore liver synthetic function in severe malnutrition and in other digestive diseases characterized by acquired bile acid deficiency.

营养不良造成了全球儿童死亡的一半。肝功能异常，包括胆汁降低酸合成在严重营养不良中很常见。在肠道中，胆汁酸缺乏导致营养吸收不良和增长受损。在肝脏中，胆汁酸通过包括Farnesoid-的核接收器信号 X受体（FXR），以调节从能量稳态到凝结的广泛过程。我们发现了减少营养不良中的胆汁酸合成会导致FXR激活降低，表达降低 FXR靶基因，包括凝血因子。产生的营养不良诱导的凝血病可能是致命的。尚不清楚为什么营养不良中胆汁酸合成受损。我正在进行的K08项目使用了独特的早期营养不良的小鼠模型，揭示了过氧化物体增生剂激活受体表达的丧失 α（PPARα）和随后的过氧化物损失，这是生成必需β氧化步骤所必需的成熟的胆汁酸。我们发布的数据和新的初步数据，表明抑制了两个关键的细胞色素过氧化物体β氧化上游的P450（CYP）酶也有助于减少胆汁酸合成营养不良，独立于PPARα。肝细胞在两个平行的胆固醇中合成胆汁酸途径。我们的数据表明，胆汁酸合成的经典途径通过减少而抑制 CYP7A1的活性，速率确定的酶。我们预测CYP7A1活性降低是因为营养不良的肝细胞耗尽了CYP7A1基本假体的血红素。同样，我们也有通过降低的表达抑制了胆汁酸合成的替代途径的证据 CYP7B1，该途径中的关键酶。我们预测CYP7B1的表达降低是因为营养不良可以上调其潜在的转录表示，即立体调节元件结合蛋白1 （SREBP-1）。这是我们假设的，除了依赖PPARα的过氧化物体损失外，营养不良会损害胆汁酸合成也通过抑制CYP7A1和CYP7B1来损害经典和替代方案合成途径。具体目的是1）表征营养不良中血红素代谢的改变通过量化标记胆固醇的通量，它在改善CYP7A1活性中的作用，测量表达水平血红素合成酶，并用血红素治疗肝细胞和小鼠； 2）确定 CYP7B1转录表示中的SREBP-1及其对胆汁酸下降的相对贡献通过定义募集到CYP7B1启动子并抑制营养不良者的合成营养不良。 SREBP-1在体外和体内与siRNA和药物拮抗剂。预期的结果包括更深的了解营养状况如何影响胆汁酸稳态。这种方法是创新的，因为它将探索CYP抑制作用，作为营养不良与胆汁酸合成受损之间的新联系。这拟议的研究很重要，因为有可能制定新策略来恢复肝脏合成在严重营养不良和其他以获得胆汁酸缺乏为特征的消化疾病中的功能。