Disruption of tRNA biogenesis enhances proteostatic resilience, improves later-life health, and promotes longevity

tRNAs are evolutionarily ancient molecular decoders essential for protein translation. In eukaryotes, tRNAs and other short, noncoding RNAs are transcribed by RNA polymerase (Pol) III, an enzyme that promotes ageing in yeast, worms, and flies. Here, we show that a partial reduction in Pol III activity specifically disrupts tRNA levels. This effect is conserved across worms, flies, and mice, where computational models indicate that it impacts mRNA decoding. In all 3 species, reduced Pol III activity increases proteostatic resilience. In worms, it activates the unfolded protein response (UPR) and direct disruption of tRNA metabolism is sufficient to recapitulate this. In flies, decreasing Pol III’s transcriptional initiation on tRNA genes by a loss-of-function in the TFIIIC transcription factor robustly extends lifespan, improves proteostatic resilience and recapitulates the broad-spectrum benefits to late-life health seen following partial Pol III inhibition. We provide evidence that a partial reduction in Pol III activity impacts translation, quantitatively or qualitatively, in both worms and flies, indicating a potential mode of action. Our work demonstrates a conserved and previously unappreciated role of tRNAs in animal ageing

Longevity is determined by ETS transcription factors in multiple tissues and diverse species

Ageing populations pose one of the main public health crises of our time. Reprogramming gene expression by altering the activities of sequence-specific transcription factors (TFs) can ameliorate deleterious effects of age. Here we explore how a circuit of TFs coordinates pro-longevity transcriptional outcomes, which reveals a multi-tissue and multi-species role for an entire protein family: the E-twenty-six (ETS) TFs. In Drosophila, reduced insulin/IGF signalling (IIS) extends lifespan by coordinating activation of Aop, an ETS transcriptional repressor, and Foxo, a Forkhead transcriptional activator. Aop and Foxo bind the same genomic loci, and we show that, individually, they effect similar transcriptional programmes in vivo. In combination, Aop can both moderate or synergise with Foxo, dependent on promoter context. Moreover, Foxo and Aop oppose the gene-regulatory activity of Pnt, an ETS transcriptional activator. Directly knocking down Pnt recapitulates aspects of the Aop/Foxo transcriptional programme and is sufficient to extend lifespan. The lifespan-limiting role of Pnt appears to be balanced by a requirement for metabolic regulation in young flies, in which the Aop-Pnt-Foxo circuit determines expression of metabolic genes, and Pnt regulates lipolysis and responses to nutrient stress. Molecular functions are often conserved amongst ETS TFs, prompting us to examine whether other Drosophila ETS-coding genes may also affect ageing. We show that five out of eight Drosophila ETS TFs play a role in fly ageing, acting from a range of organs and cells including the intestine, adipose and neurons. We expand the repertoire of lifespan-limiting ETS TFs in C. elegans, confirming their conserved function in ageing and revealing that the roles of ETS TFs in physiology and lifespan are conserved throughout the family, both within and between species

Roundabout receptor 4 and its role in endothelial barrier dysfunction following cardiac surgery

Endothelial barrier dysfunction contributes to the systemic inflammatory response in patients undergoing cardiac surgery with surgery necessitating cardiopulmonary bypass. The bypass enables to perform complicated operations on static heart, but it comes with risks such as a damage to the endothelium which causes inflammation. Activation of endothelial cells by inflammatory mediators leads to changes in endothelial function. These changes include up-regulation of adhesion molecules, production and secretion of inflammatory mediators and chemo-attractant agents, as well as vasoactive compounds. These changes are central to the pathological processes leading to sepsis syndrome. The exaggerated release of pro- and anti-inflammatory cytokines leads to development of septic and vasoplegic syndromes which complicate recovery and can even cause a death. Currently, there are no specific therapies that target the endothelium, but greater insight into the pathogenesis of endothelial barrier dysfunction could lead to new biomarkers and therapies. Roundabout receptor 4 could be a novel biomarker and target for specific pharmacological intervention. Roundabout receptor 4 was originally identified as an axon guidance molecule but is now known to mediate various endothelial processes including cell migration and proliferation. At the outset of this thesis a role for Roundabout receptor 4 and its Slit 2 glycoprotein ligand as regulators of endothelial barrier function were also beginning to emerge; but there was little evidence of how Roundabout receptor 4 expression profiles and function might differ between endothelial cells; or of implications of Roundabout receptor 4 detected in human plasma. In patients (n=48) undergoing cardiac surgery, standard biomarkers of endothelial activation significantly increased 24h after surgery; by contrast, Roundabout receptor 4 increased immediately post-operatively, as did another novel biomarker of endothelial dysfunction - Syndecan-1. Roundabout receptor 4 could be a useful early marker of endothelial dysfunction in this patient group. There were significant associations between Roundabout receptor 4 plasma levels and prolonged length of stay in intensive care and hospital. Higher pre-operative plasma levels of Roundabout receptor 4 were also associated with the development of vasoplegia, a post-operative complication. Vasoplegia is caused by an imbalance of vasodilator and vasopressor mechanisms in the body, but the exact pathophysiology is not known. Vasoplegic patients are treated with high and prolonged doses of vasoconstrictor medications. This treatment can cause peripheral vasoconstriction and ischemia of limbs that can lead to metabolic acidosis and tissue necrosis. In vitro, Robo4 external expression decreased in endothelial cells treated with inflammatory cytokines. Robo4 plasma levels increased after cardiac surgery with snCPB. These results suggest that Robo4 might be cleaved or secreted by endothelial cells exposed to inflammation and released into the bloodstream. Roundabout receptor 4 expression was greater on human umbilical vein endothelial cells than on human pulmonary artery endothelial cells; and decreased following stimulation with tumour necrosis factor-alpha. In parallel, Slit2 increased barrier integrity in human umbilical vein endothelial cells but not in human pulmonary artery endothelial cells; difference could relate to differences in Roundabout receptor 4 expression levels, as Slit2 effects were inhibited with Roundabout receptor 4 short interfering RNA. The finding from these investigations inform greater understanding of the important role of Robo4 as an endothelial biomarker and its role in barrier function.Open Acces

Xbp1 targets canonical UPRER and non-canonical pathways in separate tissues to promote longevity

Summary: Transcription factors can reprogram gene expression to promote longevity. Here, we investigate the role of Drosophila Xbp1. Xbp1 is activated by splicing of its primary transcript, Xbp1u, to generate Xbp1s, a key activator of the endoplasmic reticulum unfolded protein response (UPRER). We show that Xbp1s induces the conical UPRER in the gut, promoting longevity from the resident stem cells. In contrast, in the fat body, Xbp1s does not appear to trigger UPRER but alters metabolic gene expression and is still able to extend lifespan. In the fat body, Xbp1s and dFOXO impinge on the same target genes, including the PGC-1α orthologue Srl, and dfoxo requires Xbp1 to extend lifespan. Interestingly, unspliceable version of the Xbp1 mRNA, Xbp1u can also extend lifespan, hinting at roles in longevity for the poorly characterized Xbp1u transcription factor. These findings reveal the diverse functions of Xbp1 in longevity in the fruit fly

Transcriptional memory of dFOXO activation in youth curtails later-life mortality through chromatin remodelling and Xbp1

A transient, homeostatic transcriptional response can result in transcriptional memory, programming subsequent transcriptional outputs. Transcriptional memory has great but unappreciated potential to alter animal ageing as animals encounter a multitude of diverse stimuli throughout their lifespan. Here we show that activating an evolutionarily conserved, longevity-promoting transcription factor, dFOXO, solely in early adulthood of female fruit flies is sufficient to improve their subsequent health and survival in mid- and late life. This youth-restricted dFOXO activation causes persistent changes to chromatin landscape in the fat body and requires chromatin remodellers such as the SWI/SNF and ISWI complexes to program health and longevity. Chromatin remodelling is accompanied by a long-lasting transcriptional programme that is distinct from that observed during acute dFOXO activation and includes induction of We show that this later-life induction of is sufficient to curtail later-life mortality. Our study demonstrates that transcriptional memory can profoundly alter how animals age

Indices of systemic inflammation^a.

a<p>n = 32 patients undergoing cardiac surgery requiring cardiopulmonary bypass.</p><p>CRP, c-reactive protein; WCC, white cell count; IL-6, -8,-10, interleukin-6, -8,-10; IQR = interquartile range, SD = standard deviation.</p><p><b>*</b>p = 0.0378, <b>**</b>p<0.01, <b>***</b>p<0.001, <b>^†</b>p<0.0001, compared with pre-op levels.</p>#<p>p<0.05, compared with 2 h.</p><p>Indices of systemic inflammation^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0111459#nt103" target="_blank">a</a>}.</p

Clinical and biochemical characteristics, operative variables and post-operative outcomes of study patients^a.

a<p>n = 32 patients undergoing cardiac surgery requiring cardiopulmonary bypass.</p><p>IQR = interquartile range; SD = standard deviation; CABG = Coronary artery bypass grafting; ICU = intensive care unit.</p><p>Clinical and biochemical characteristics, operative variables and post-operative outcomes of study patients^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0111459#nt101" target="_blank">a</a>}.</p

Indices of organ dysfunction/injury^a.

a<p>n = 32 patients undergoing cardiac surgery requiring cardiopulmonary bypass; ^bn = 31.</p><p>NGAL, neutrophil gelatinase-associated lipocalin; vWF, von Willibrand Factor; Ang-2, Angiopoeitin-2; IQR = interquartile range, SD = standard deviation.</p><p>***p<0.001, compared with pre-op levels; ^###p<0.001 compared with 2 h.</p><p>Indices of organ dysfunction/injury^{<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0111459#nt107" target="_blank">a</a>}.</p

Plasma Robo4 levels in patients with or without AKI based on NGAL levels.

<p>Plasma levels of Robo4 in patients, 2 h post-cardiac surgery requiring cardiopulmonary bypass with or without acute kidney injury (AKI); assigned using plasma NGAL cut-off levels of 150 ng/ml. Data presented as bar graphs with mean and SD concentrations (pg/ml) of Robo4; n = 16 (AKI), n = 16 (non-AKI).</p

Plasma levels of Robo4 before and after cardiac surgery.

<p>Plasma levels of Robo4 increased 2 h post-cardiac surgery requiring cardiopulmonary bypass compared with pre-operative levels and those 24 h post-surgery. Data are presented as bar graphs with mean and SD concentrations (pg/ml) of Robo4; n = 32, ***p<0.001 compared with pre- and 24 h levels.</p