Hypoxia-controlled sterol and fatty acid synthesis with immune-modulatory consequences in myeloid cells

缺氧唤起适应性细胞反应，通过规范和非规范信号传递。对氧可用性降低的经典反应使用缺氧诱导因子（HIF）作为转录激活因子。有几种非典型转导系统，其中包括直接抑制耗氧反应。我们假设这也适用于胆固醇代谢。在THP-1单核细胞中使用SLAM-Seq（用于RNA代谢测序的巯基烷基化）方法的试点数据表明，参与胆固醇合成的几个基因的从头转录。我们假设这是hif独立的，并建议直接抑制羊毛甾醇去甲基化酶，这是一种氧依赖性酶，属于细胞色素P450家族。因此，我们提出改变胆固醇代谢产物，胆固醇本身减少，而甾醇中间体，如羊毛甾醇和二氢羊毛甾醇积累。作为分子解释，我们设想SREBP（甾醇调节元件结合蛋白）的激活负责全球转录变化。由于我们认为这是一种普遍的调节现象，我们想了解胆固醇代谢物的变化如何影响单核细胞和巨噬细胞的生物学功能。我们认为这些细胞是终末分化细胞和高度增殖细胞之间的极端，通过胆固醇途径的通量可能决定细胞的敏感性。SREBP的激活可能改变胆固醇代谢物，从而引发I型干扰素反应，或者SREBP可能直接激活干扰素刺激基因（ISG）。无论哪种方式，我们认为这最终导致干扰素产生水平的增加。作为一个功能性读数，我们想要确定干扰素产生的增加是否会增强巨噬细胞的抗肿瘤功能。这一假设是基于我们的SLAM-Seq方法已经表明了缺氧驱动的I型干扰素基因特征。此外，我们认为缺氧也会改变不饱和脂肪酸的水平，这一反应也是由SERBP驱动的。在这些实验中，我们主要关注SCD（甾醇-辅酶a -去饱和酶）和FADS2（脂肪酸去饱和酶2），因为它们是高度缺氧诱导的。关于它们的表达，调控和功能对单核/巨噬细胞的活力和生物学的细节将被探索。我们的目标是了解缺氧如何调节胆固醇代谢的分子细节，以及这些改变如何影响骨髓细胞的生物学。

Hypoxia evokes adaptive cell responses that are transmitted via canonical and non-canonical signals. Classical responses towards decreased oxygen availability use hypoxia-inducible factors (HIF) as transcriptional activators. There are several non-canonical transducing systems that comprise among others direct inhibition of oxygen consuming reactions. We postulate that this also applies to cholesterol metabolism. Pilot data using a SLAM-Seq (thiol-linked alkylation for the metabolic sequencing of RNA) approach in THP-1 monocytes indicates de novo transcription of several genes involved in cholesterol synthesis. We assume that this is HIF-independent and suggest direct inhibition of lanosterol demethylases, which are oxygen-dependent enzymes, belonging to the cytochrome P450 family. As a consequence we propose altered cholesterol metabolites, with cholesterol itself being decreased, while sterol intermediates such as lanosterol and dihydrolanosterol accumulate. As a molecular explanation we envision activation of SREBP (sterol regulatory element-binding protein) being responsible for global transcriptional changes. As we assume this to be a universal regulatory phenomenon we would like to understand how changes in cholesterol metabolites affect biological functions of monocytes and macrophages. We consider these cells being extremes between terminally differentiated vs. highly proliferating cells with notion that the flux through the cholesterol pathway may determine cellular sensitivity. Activation of SREBP may either alter cholesterol metabolites that in turn elicit a type I interferon response or SREBP may directly activate interferon-stimulated genes (ISG). Either way, we propose that this culminates in increased levels of interferon production. As a functional readout we like to determine whether increased interferon production enhances the anti-tumor function of macrophages. This assumption is based on the notion that our SLAM-Seq approach already indicated a hypoxia-driven type I interferon gene signature. In addition, we propose that hypoxia also alters the level of unsaturated fatty acids, a response also being SERBP driven. For these experiments we focus on SCD (sterol-CoA-desaturase) and FADS2 (fatty acid desaturase 2) as they are highly hypoxia inducible. Details concerning their expression, regulation, and function towards the viability and biology of monocytes/macrophages will be explored. We aim at understanding molecular details how hypoxia regulates cholesterol metabolism and how these alterations affect the biology of myeloid cells.