Acute senescence: a novel host defence counteracting typhoidal Salmonella

伤寒是一种由伤寒沙门氏菌引起的传染病，每年造成1400万例病例，14万人死亡，800万人因健康状况不佳而损失每日调整生命年。由于缺乏合适的生物标志物，抗菌素耐药性和诊断不佳加剧了这一问题。我们必须增进对伤寒的了解，以加快开发治疗性干预措施，这是世卫组织和联合国可持续发展目标的重点。伤寒在感染血液（菌血症）并扩散到身体不同器官之前，在我们的肠道细胞内生存，导致伤寒。我的UKRI FLF是在我们发现伤寒沙门氏菌通过释放一种毒素导致人体细胞过早衰老后获得的。伤寒毒素会在我们的细胞中造成DNA损伤，就像紫外线一样，这会在细胞中引发一种类似衰老的过程，称为急性衰老。随着年龄的增长，人们更容易受到感染。因此，我们最初假设毒素导致衰老，使人类细胞更容易受到感染。令我们惊讶的是，在我的FLF期间的发现表明，相反的情况可能是正确的，急性衰老是一种新的免疫防御途径，它可以通过抗菌活性攻击伤寒杆菌，并有助于预防伤寒。这是出乎意料的，然而，在生命早期，已知急性衰老可以预防癌症，因此，我们假设急性衰老可能共同进化以对抗传染病，如伤寒。FLF的更新旨在引领研究急性衰老抗微生物反应（ASAR）的新领域。我们对培养细胞和临床样本的实验表明，当伤寒毒素引起DNA损伤时，细胞通过(i)通过人类基因p21进入衰老状态，以及（ii）分泌抗菌蛋白进入细胞外环境来表达它们的痛苦。在癌细胞中，p21阻止细胞长成肿瘤，并分泌吸引免疫细胞的蛋白质来摧毁癌细胞。因此，我们将确定p21是否启动ASAR:(i)通过抑制生活在衰老细胞内的伤寒沙门氏菌的生长，以及（ii）通过分泌抗菌剂和免疫细胞引诱剂来抑制细胞外伤寒沙门氏菌的生长。这就是我们将如何研究ASAR：目标1：提前发现伤寒患者体内分泌的抗菌素。一项临床研究显示，携带伤寒毒素的野生型（WT）伤寒沙门氏菌感染人类伤寒菌血症的持续时间比毒素阴性（TN）伤寒沙门氏菌短（WT 48小时，TN 96小时）。这表明未知因素正在攻击WT而不是TN S.Typhi。因此，我们将确定来自WT感染参与者的临床样本是否含有响应伤寒毒素释放的抗菌生物标志物。目的2：确定抗微生物反应是否受衰老调节。我们将验证通过目的1鉴定的抗菌生物标志物是否依赖于p21介导的衰老。这将通过在人体组织培养实验和感染小鼠中检查受沙门氏菌感染的细胞衰老来实现。我们将从目标2开始，阐明分泌的衰老相关抗菌生物标志物是否会攻击细胞外的伤寒沙门氏菌，以及被感染的衰老细胞中的p21是否通过激活细胞内对伤寒沙门氏菌的防御来抑制感染。通过揭示ASAR作为一种抑制沙门氏菌感染的新型先天防御，我的团队将发现一种对抗伤寒的新免疫途径。在全球重要的相关病原体感染期间，这将是重要的。通过引领ASAR研究的新领域，此次更新将促进增强ASAR的方法，并发现具有诊断潜力的可翻译的抗菌生物标志物。

Typhoid fever is an infectious disease caused by Salmonella Typhi resulting in 14 million cases, 140,000 deaths and 8 million daily-adjusted life years lost to ill health per annum. The problem is exacerbated by antimicrobial-resistance and poor diagnostics due to a lack of suitable biomarkers. We must advance understanding of typhoid to accelerate development of therapeutic interventions, which represent priorities for the WHO and UN Sustainable Development Goals.S.Typhi lives inside our gut cells before infecting the bloodstream (bacteraemia) and spreading to different organs in the body resulting in typhoid fever. My UKRI FLF was awarded upon our discovery that S.Typhi causes premature ageing in human cells by releasing a toxin. The typhoid toxin causes DNA damage in our cells, in much the same way as UV light, and this elicits an ageing-like process in cells called acute senescence. Ageing comes with increased susceptibility to infection. Thus, we initially hypothesised that the toxin causes senescence to make human cells more vulnerable to infection. To our surprise, discoveries during my FLF indicate the opposite may be true and that acute senescence is a novel immune defence pathway, which can attack S.Typhi through antimicrobial activities and help prevent typhoid. This is unexpected yet, in early life, acute senescence is known to prevent cancer, thus, we hypothesise that acute senescence may have co-evolved to counteract infectious diseases such as typhoid. The FLF renewal aims to lead a new area of research investigating Acute Senescence Antimicrobial Responses (ASAR).Our experiments with cultured cells and clinical samples indicate that when typhoid toxin causes DNA damage, cells signal their distress by(i) entering into a senescent state through the human gene p21, and by(ii) secreting antimicrobial proteins into the extracellular environment.In cancerous cells, p21 stops the cells from growing into tumours and secrete proteins that attracts immune cells to destroy the cancer cells. Thus, we will determine whether p21 launches ASAR: (i) by suppressing the growth of S.Typhi living inside senescent cells, and (ii) by suppressing the growth of extracellular S.Typhi via secretion of antimicrobials and immune cell attractants. This is how we will investigate ASAR:Objective 1: Advance discovery of antimicrobials secreted in human participants with typhoid.A clinical study revealed that the duration of bacteraemia in human participants with typhoid was shorter with wild-type (WT) S.Typhi carrying typhoid toxin than toxin-negative (TN) S.Typhi (WT 48 hours; TN 96 hours). This indicates that unknown factors are attacking WT but not TN S.Typhi. Thus, we will determine whether clinical samples from participants infected with WT contain antimicrobial biomarkers released in response to typhoid toxin.Objective 2: Determine whether antimicrobial responses are regulated by senescence. We will validate whether antimicrobial biomarkers identified through objective 1 rely upon p21-mediated senescence. This will be achieved by examining Salmonella-infected cells undergoing senescence in human tissue culture experiments and infected miceObjective 3: Establish antimicrobial activities of the Acute Senescence Antimicrobial Response We will progress from objective 2 by elucidating whether secreted senescent-associated antimicrobial biomarkers attack extracellular S.Typhi and whether p21 in the infected senescent cells suppress infection by activating intracellular defences against S.Typhi.By revealing ASAR as a novel innate defence suppressing Salmonella infection, my team will discover a new immune pathway that combats typhoid fever, which will be significant during infections by related pathogens of global importance. By leading a new area of research on ASAR, the renewal will facilitate ways to enhance ASAR and discover of translatable antimicrobial biomarkers with diagnostic potential.