Pon3, a natural antioxidant protein: its role in development and disease.

氧在维持生命方面发挥着关键作用，但由于它具有高度的反应性，细胞有多种防御系统来保护自己免受氧化应激和损伤。氧化应激的有害影响随着年龄的增长而增加，氧化应激是几种常见主要疾病的公认特征，包括糖尿病、代谢综合征、神经退行性疾病和年龄相关性黄斑变性。在出生时，胎儿在开始呼吸时会暴露在氧气的快速和大量增加中，许多防御系统在这个时候被上调。因此，我们寻找以前未被认识到的或新的内源性抗氧化剂，这些抗氧化剂在怀孕后期胎儿中上调。这些分子可能对早产儿有治疗作用，但也可能是成人抗氧化防御系统的重要组成部分。他们也可能在一些以氧化应激为特征的病理过程中受到干扰。我们进行了这项研究，并确定了对氧磷酶3(Pon3)。这种蛋白质在大鼠、小鼠、绵羊和人类出生前在肺和肠道中强烈诱导，至少在绵羊中是如此，这是由糖皮质激素控制的。对氧磷酶家族由3种密切相关的酶组成，它们分解来自几个不同生物重要家族的广泛的分子。这些物质包括类激素分子、过氧化脂质、花生四烯酸和雌激素酯的氧化产物。因此，桥脑具有调节由这些分子介导的信号通路的潜力。这些酶还有效地分解细菌在许多细菌存在的情况下(例如肠道中的情况)用来调节其生长的分子。它们还可以分解有毒的杀虫剂。在血液中，PON1与含脂颗粒有关，它可以减少氧化脂质的有害炎症作用。人为增加小鼠体内PON3水平可抑制动脉粥样硬化病变的形成，体内脂肪和脑桥通常具有抗氧化剂和抗炎作用。在人类中，PON1基因的突变会改变心脏病发作和中风的风险。因此，除了它们被推定为有效的循环抗氧化剂外，这些酶还具有抗动脉粥样硬化和抗炎的特性；能够代谢重要调节激素的衍生物；可以降解杀虫剂，并有可能改变宿主/微生物的相互作用。因此，它们与多种重要的生物学过程有关，并引起了人们的极大关注。尽管如此，这个保守的酶家族的生理功能仍然不清楚。为了了解Pon3的正常作用，我们使用了一只基因工程小鼠，其中Pon3基因已经被敲除。当我们一起饲养杂合子小鼠时，Pon3/-动物的数量比预期的要少得多(25%的预期数量，但只有9%发现)。突变的小鼠在怀孕早期死亡，因此我们得出结论，Pon3在早期胚胎发育中具有必要的和非多余的生物学作用。我们预测Pon3的缺失或减少将导致氧化应激增加，从而导致胚胎死亡或胚胎生长减少。我们将在正常和Pon3基因敲除小鼠中使用详细的组织学、生化和分子方法来研究这一点。此外，这种Pon3的减少可能会加剧成年生活中的氧化应激和疾病敏感性。我们将改造条件性基因敲除小鼠，并研究Pon3基因的缺失对小鼠衰老和高脂肪饮食的影响。这些研究将确定Pon3是否在保护小鼠免受年龄和不良饮食的有害影响方面发挥作用。生化研究将确定在人类中可能类似的途径，使我们能够在未来的研究中确定Pon3是否可能在人类疾病中起重要作用。

Oxygen plays a critical role in maintaining life but because it is highly reactive, cells have multiple defences to protect themselves from oxidative stress and damage. The detrimental effects of oxidative stress are increased with age and oxidative stress is a well-recognised feature of several common major conditions including diabetes, metabolic syndrome, neurodegenerative diseases and age-related macular degeneration. At birth the fetus is exposed to a rapid and substantial increase in oxygen as it begins to breathe and many defence systems are up-regulated at this time. We therefore searched for previously unrecognised or novel endogenous antioxidants which are up-regulated in late gestation in the fetus. Such molecules may be useful therapeutically in the pre-term infant but may also be important components of the adult anti-oxidant defence system. They may also be perturbed in some of the pathologies characterised by oxidative stress.We carried out this search and identified paraoxonase 3 (Pon3). This protein is strongly induced in the lung and gut prior to birth in rats, mice, sheep and humans and at least in the sheep, this is controlled by glucocorticoid hormones. We conclude that this may be a systemic preparative process for birth.The paraoxonase family consists of 3 closely related enzymes which break down a wide range of molecules from several different biologically important families. These include hormone-like molecules, lipid peroxides, the oxidation products of arachidonic acid and estrogen esters. Thus, the Pons have the potential to modulate the signalling pathways mediated by such molecules. These enzymes also effectively break down molecules that bacteria use to regulate their growth in situations where many bacteria are present (as may be the case in the intestine for example). They also break down toxic pesticides.In blood, PON1 is associated with lipid-containing particles and it can reduce the harmful inflammatory action of oxidized lipid. Artificially increasing PON3 levels in mice inhibited atherosclerotic lesion formation and body fat and Pons in general are antioxidants and anti-inflammatory. In humans mutations in the PON1 gene alter the risk of heart attack and stroke. Thus, in addition to their presumed role as potent circulating antioxidants, these enzymes have anti-atherogenic and anti-inflammatory properties; are capable of metabolising derivatives of important regulatory hormones; can degrade pesticides and have the potential to alter host/microbe interaction. As such, they are implicated in diverse and important biological processes and have attracted considerable attention. Despite this, the physiological function of this family of well-conserved enzymes remains unclear.To understand the normal role of Pon3 we have used a genetically engineered mice in which the Pon3 gene has been knocked-out. When we bred heterozygous mice together there were significantly fewer Pon3-/- animals than expected (25% expected but only 9% found). The mutant mice die early in pregnancy so we conclude that Pon3 has an essential and non-redundant biological role in early embryonic development.We predict that loss of or a reduction in Pon3 will lead to increased oxidative stress hence embryonic lethality or reduced embryonic growth. We will investigate this using detailed histological, biochemical and molecular methods in normal and Pon3 knockout mice. Furthermore, this reduction of Pon3 may exacerbate oxidative stress and disease sensitivity in adult life. We will engineer conditional knockout mice and study how loss of Pon3 effects mice as they age and are fed a high fat diet.These studies will determine whether Pon3 plays a role in protecting mice from the detrimental effects of age and a poor diet. The biochemical studies will identify pathways that are likely to be similar in humans allowing us in future studies to determine whether Pon3 may be important in human disease.