ICF: Neutrophils and cellular senescence: A vicious circle promoting age-related disease.

慢性肝病(CLD)是一个全球性的医疗保健问题，有超过15亿人面临发展为肝硬化和/或原发性肝癌的风险。老龄化和肥胖是肝病发生和发展的主要危险因素。尤其值得关注的是非酒精性脂肪性肝炎(NASH)，这是一种与肥胖和II型糖尿病相关的代谢性肝病。随着年龄的增长，NASH的发病率急剧增加，NASH进展为肝硬变的风险也随之增加，这表明衰老与NASH之间存在联系。此外，在NASH背景下发生的肝癌中，高达25%是在没有肝硬变的情况下发生的。NASH的特征是肝脏中的脂肪沉积(脂肪变性)、炎症、瘢痕(纤维化)以及受损(气球)和衰老的肝细胞(主要是肝细胞)的存在。细胞衰老是一种细胞失去增殖能力的状态，也是一种促进伤口修复和再生的生物活性分子汤，被称为衰老相关分泌表型(SASP)。在年轻人中，衰老的细胞被免疫系统清除。然而，衰老伴随着免疫功能的下降和衰老细胞清除效率的降低，导致它们积累并持续存在SASP。这可能导致SASP促进衰老扩散到旁观者细胞的病理过程，并刺激慢性炎症和不适应伤口修复。这些病理是NASH和脂肪变性的典型特征。2014-2015年，我们在小鼠中报告了富含中性粒细胞的持续性低度炎症导致肝细胞衰老、脂肪变性、纤维化、癌症和早期死亡。2021年，我们发现中性粒细胞可以通过氧化DNA损伤直接引发肝细胞衰老。此外，我们发现中性粒细胞在衰老的肝脏中积聚的程度更大，并被衰老的肝细胞所吸引。由于中性粒细胞是NASH的典型组织病理学特征，这是一个非常重要的发现。在早期的一项研究中，肝细胞衰老被证明是脂肪变性的必要条件和充分条件。这些观察表明，中性粒细胞炎症、衰老和脂肪变性在机制上是有联系的。我们假设，它们通过正前馈信号通路结合在一起，促进与年龄相关的NASH、CLD和癌症。为了验证我们的假设，我们将首先进行实验，确定衰老的肝细胞和中性粒细胞相互作用对这两种细胞的表型和功能的双向前馈效应，我们预测这两种细胞的表型和功能是高度动态的。这些实验将使用定制的人类肝脏切片技术，并在诱导肥胖、脂肪变性和NASH的小鼠模型上进行遗传学实验。我们希望做出一些发现，阐明中性粒细胞和衰老的肝细胞如何相互协作，促进炎症驱动的组织老化和CLD。我们还将包括一些实验，探讨与感染相关的急性中性粒细胞炎症如何加剧NASH，这与新冠肺炎有关，据报道，NASH会加剧CLD。其次，我们将询问是否可以利用我们的发现，即中性粒细胞被衰老细胞吸引来刺激免疫系统，清除衰老的肝细胞。我们将改造中性粒细胞在其表面表达抗体，选择性地锁定在衰老细胞表面表达的蛋白质，这旨在加强它们的物理相互作用，并在这样做的同时鼓励中性粒细胞介导的衰老细胞的清除。通过实施这项为期3年的项目，我们将(1)大幅增加对炎症和衰老如何结合起来促进CLD的知识，(2)发现生物学家和免疫学家广泛感兴趣的新的机制生物学，以及(3)了解中性粒细胞是否可以被操纵用于衰老和肥胖相关疾病的免疫治疗目的。

Chronic liver disease (CLD) is a global health care problem affecting in excess of 1.5 billion people who are at risk of developing cirrhosis and/or a primary liver cancer. Ageing and obesity are major risk factors for the development and progression of liver disease. Of particular concern is non-alcoholic steatohepatitis (NASH) which is a metabolic liver disease associated with obesity and type II diabetes. NASH incidence increases dramatically with ageing, as does the risk of progression of NASH to cirrhosis, indicating a link between ageing and NASH. Moreover, up to 25% of liver cancers that develop on the background of NASH do so in the absence of cirrhosis. NASH is characterised by fatty deposits (steatosis) in the liver, inflammation, scaring (fibrosis) and the presence of damaged (ballooned) and aged (senescent) hepatocytes (predominant liver cell).Cellular senescence is a state in which cells lose their ability to proliferate and also secrete a soup of bioactive molecules that promote wound repair and regeneration, termed the senescence-associated secretory phenotype (SASP). In a young person senescent cells are cleared by the immune system. However, ageing is accompanied by immune decline and reduced efficiency of senescent cell clearance, leading to their accumulation and persistence of the SASP. This can lead to a pathological process where the SASP promotes spread of senescence to bystander cells and stimulates chronic inflammation and maladaptive wound repair. These pathologies being typical features of NASH alongside steatosis.In 2014-2015 we reported in mice that a neutrophil rich persistent low-grade inflammation drives hepatocyte senescence, steatosis, fibrosis, cancer and early death. In 2021 we showed that neutrophils can directly trigger senescence in hepatocytes via oxidative DNA damage. Moreover, we discovered that neutrophils accumulate to a greater extent in the ageing liver and are attracted to senescent hepatocytes. As neutrophils are a classic histopathological characteristic of NASH this is a very significant discovery. In an earlier study, hepatocyte senescence was shown to be necessary and sufficient for steatosis. These observations suggest that neutrophilic inflammation, senescence and steatosis are mechanistically linked. We hypothesise that they combine through positive feedforward signalling pathways to promote age-related NASH, CLD and cancer. To test our hypothesis, we will first carry out experiments that determine the bidirectional feedforward effects of interactions of senescent hepatocytes and neutrophils on the phenotype and function of these two cell types which we predict to be highly dynamic. These experiments will use a bespoke human liver slice technology and genetic experiments carried out in mouse models of induced obesity, steatosis and NASH. We expect to make discoveries that will illuminate how neutrophils and senescent hepatocytes collude to promote inflammation-driven tissue ageing and CLD. We will also include experiments that ask how acute neutrophilic inflammation associated with infections exacerbates NASH, this being relevant to Covid-19 which is reported to aggravate CLD.Secondly, we will ask if our discovery that neutrophils are attracted to senescent cells can be exploited to stimulate the immune system to clear senescent hepatocytes. We will engineer neutrophils to express antibodies at their surface that selectively lock onto proteins expressed at the surface of senescent cells, this aimed at enhancing their physical interaction and in doing so encouraging neutrophil-mediated clearance of senescent cells.By carrying out this 3-year project we will (1) substantially increase knowledge of how inflammation and ageing combine to promote CLD, (2) discover new mechanistic biology of broad interest to biologists and immunologists and (3) learn if neutrophils can be manipulated for immunotherapeutic purposes in ageing- and obesity-related diseases.