NPC1L1 and Metabolic Diseases

描述（由申请人提供）：Niemann-Pick C1-Like 1 （NPC1L1）最初被认为是肠道胆固醇吸收的必需蛋白。它是ezetmibe的靶标，ezetmibe是一种胆固醇吸收抑制剂，被广泛用于降低人类血液中的胆固醇。令人惊讶的是，最近发现小鼠NPC1L1的基因失活或依折替米贝抑制可以预防高脂肪饮食（HFD）诱导的肥胖（DIO）和相关的代谢紊乱。这些新发现背后的分子机制尚不清楚。拟议研究的总体目标是确定NPC1L1缺乏如何影响DIO。在初步研究中，我们发现野生型（WT）和NPC1L1敲除（L1KO）小鼠的食物摄入量相同，但L1KO小鼠对DIO和脂肪肝有保护作用，这与促进棕色脂肪组织（BAT）和骨骼肌中能量消耗的基因表达增加有关。因此，我们假设NPC1L1缺乏通过增加能量消耗来保护小鼠免受DIO。我们将直接测量能量消耗，并通过测量WT和L1KO小鼠在饮食过量、依zetimibe治疗或禁食条件下的生化和基因表达水平的代谢变化，从分子上定义NPC1L1缺乏如何刺激能量消耗。在小鼠中，NPC1L1在小肠中高表达，而在非肠道组织中只能检测到低水平的NPC1L1 mRNA。我们假设肠道NPC1L1的缺失是DIO耐药的原因。为了直接验证这一假设，我们将新建立的小肠特异性表达人类NPC1L1的转基因小鼠与L1KO小鼠杂交，从而重建肠道NPC1L1的表达，并确定这是否会挽救L1KO小鼠的体重增加。我们还将确定NPC1L1缺乏是否需要甲状腺激素激活酶2型碘甲状腺原氨酸脱碘酶（D2）来预防DIO，因为我们发现D2在L1KO小鼠的BAT和肌肉中的表达显著升高，并且D2激活已知可促进能量消耗。为了探索NPC1L1缺乏和D2激活之间的分子联系，我们将研究WT和L1KO小鼠在HFD上的胆汁酸代谢是否不同，因为我们发现L1KO小鼠回肠中许多胆汁酸敏感基因上调，胆汁酸可以作为信号分子通过D2依赖机制刺激能量消耗。综上所述，这些研究将为NPC1L1在代谢性疾病中的作用提供重要的新见解，并有可能揭示预防和治疗肥胖及相关代谢危险因素的新方法，这些因素是导致疾病发病率和死亡率的重要因素。

DESCRIPTION (provided by applicant): Niemann-Pick C1-Like 1 (NPC1L1) was originally identified as an essential protein for intestinal cholesterol absorption. It is the target of ezetmibe, a cholesterol absorption inhibitor that is widely used to lower blood cholesterol in humans. Surprisingly, genetic inactivation or ezetimibe inhibition of NPC1L1 in mice was recently found to protect against high fat diet (HFD)-induced obesity (DIO) and associated metabolic disorders. The molecular mechanisms underlying these novel findings remain unknown. The overall goal of the proposed studies is to define how NPC1L1 deficiency affects DIO. In preliminary studies, we found that food intake was identical between wild-type (WT) and NPC1L1 knockout (L1KO) mice, yet L1KO mice were protected against DIO and fatty liver, which was associated with increased expression of genes promoting energy expenditure in brown adipose tissue (BAT) and skeletal muscle. Thus, we hypothesize that NPC1L1 deficiency protects mice from DIO by increasing energy expenditure. We will directly measure energy expenditure, and molecularly define how NPC1L1 deficiency stimulates energy dissipation by measuring metabolic changes at biochemical and gene expression levels in WT and L1KO mice under dietary excess, ezetimibe treatment or fasting conditions. In mice, NPC1L1 is highly expressed in small intestine and only low levels of NPC1L1 mRNA can be detected in non-intestinal tissues. We hypothesize that loss of intestinal NPC1L1 is responsible for resistance to DIO. To directly test this hypothesis, we will cross our newly-created transgenic mice specifically expressing human NPC1L1 in small intestine to L1KO mice, thereby re-establishing intestinal NPC1L1 expression, and determine if this will rescue weight gain in L1KO mice. We will also determine if NPC1L1 deficiency requires a thyroid hormone activating enzyme type 2 iodothyronine deiodinase (D2) to prevent DIO since we found that D2 expression was substantially elevated in BAT and muscle in L1KO mice, and D2 activation is known to promote energy expenditure. To probe the molecular link between NPC1L1 deficiency and D2 activation, we will examine if bile acid metabolism differs between WT and L1KO mice on HFD because we found that many bile acid sensitive genes were upregulated in the ileum of L1KO mice and bile acids can function as signaling molecules to stimulate energy expenditure via a D2- dependent mechanism. Taken together, these studies will provide important new insight into the role of NPC1L1 in metabolic diseases, and have the potential to reveal new approaches for the prevention and treatment of obesity and associated metabolic risk factors, which contribute substantially to disease morbidity and mortality.