Aging
Abstract
The β-secretase BACE1 is a central drug target for Alzheimer’s disease. Clinically tested, BACE1-directed inhibitors also block the homologous protease BACE2. Yet, little is known about physiological BACE2 substrates and functions in vivo. Here, we identify BACE2 as the protease shedding the lymphangiogenic vascular endothelial growth factor receptor 3 (VEGFR3). Inactivation of BACE2, but not BACE1, inhibited shedding of VEGFR3 from primary human lymphatic endothelial cells (LECs) and reduced release of the shed, soluble VEGFR3 (sVEGFR3) ectodomain into the blood of mice, non-human primates and humans. Functionally, BACE2 inactivation increased full-length VEGFR3 and enhanced VEGFR3 signaling in LECs and also in vivo in zebrafish, where enhanced migration of LECs was observed. Thus, this study identifies BACE2 as a modulator of lymphangiogenic VEGFR3 signaling and demonstrates the utility of sVEGFR3 as a pharmacodynamic plasma marker for BACE2 activity in vivo, a prerequisite for developing BACE1-selective inhibitors for a safer prevention of Alzheimer’s disease.
Authors
Andree Schmidt, Brian Hrupka, Frauke van Bebber, Sanjay Sunil Kumar, Xiao Feng, Sarah K. Tschirner, Marlene Aßfalg, Stephan A. Müller, Laura Sophie Hilger, Laura I. Hofmann, Martina Pigoni, Georg Jocher, Iryna Voytyuk, Emily L. Self, Mana Ito, Kana Hyakkoku, Akimasa Yoshimura, Naotaka Horiguchi, Regina Feederle, Bart De Strooper, Stefan Schulte-Merker, Eckhard Lammert, Dieder Moechars, Bettina Schmid, Stefan F. Lichtenthaler
Abstract
The identification of genes that confer either extension of lifespan or accelerate age-related decline was a step forward in understanding the mechanisms of ageing and revealed that it is partially controlled by genetics and transcriptional programs. Here we discovered that the human DNA sequence C16ORF70 encoded for a protein, named MYTHO (Macroautophagy and YouTH Optimizer), which controls life- and health-span. MYTHO protein is conserved from C. elegans to humans and its mRNA was upregulated in aged mice and elderly people. Deletion of the ortholog myt-1 gene in C. elegans dramatically shortened lifespan and decreased animal survival upon exposure to oxidative stress. Mechanistically, MYTHO is required for autophagy likely because it acts as a scaffold that binds WIPI2 and BCAS3 to recruit and assemble the conjugation system at the phagophore, the nascent autophagosome. We conclude that MYTHO is a transcriptionally regulated initiator of autophagy that is central in promoting stress resistance and healthy ageing.
Authors
Anais Franco-Romero, Valeria Morbidoni, Giulia Milan, Roberta Sartori, Jesper Wulff, Vanina Romanello, Andrea Armani, Leonardo Salviati, Maria Conte, Stefano Salvioli, Claudio Franceschi, Viviana Buonomo, Casey O. Swoboda, Paolo Grumati, Luca Pannone, Simone Martinelli, Harold B.J. Jefferies, Ivan Dikic, Jennifer van der Laan, Filipe Cabreiro, Douglas P. Millay, Sharon A. Tooze, Eva Trevisson, Marco Sandri
Abstract
Cells expressing features of senescence, including upregulation of p21 and p16, appear transiently following tissue injury, yet the properties of these cells or how they contrast with age-induced senescent cells remains unclear. Here, we used skeletal injury as a model and identified the rapid appearance following fracture of p21+ cells expressing senescence markers, mainly as osteochondroprogenitors (OCHs) and neutrophils. Targeted genetic clearance of p21+ cells suppressed senescence-associated signatures within the fracture callus and accelerated fracture healing. By contrast, p21+ cell clearance did not alter bone loss due to aging; conversely, p16+ cell clearance, known to alleviate skeletal aging, did not affect fracture healing. Following fracture, p21+ neutrophils were enriched in signaling pathways known to induce paracrine stromal senescence, while p21+ OCHs were highly enriched in senescence-associated secretory phenotype factors known to impair bone formation. Further analysis revealed an injury-specific stem cell-like OCH subset that was p21+ and highly inflammatory, with a similar inflammatory mesenchymal population (fibro-adipogenic progenitors) evident following muscle injury. Thus, intercommunicating senescent-like neutrophils and mesenchymal progenitor cells were key regulators of tissue repair in bone and potentially across tissues. Moreover, our findings established contextual roles of p21+ vs p16+ senescent/senescent-like cells that may be leveraged for therapeutic opportunities.
Authors
Dominik Saul, Madison L. Doolittle, Jennifer L. Rowsey, Mitchell N. Froemming, Robyn L. Kosinsky, Stephanie J. Vos, Ming Ruan, Nathan K. LeBrasseur, Abhishek Chandra, Robert J. Pignolo, João F. Passos, Joshua N. Farr, David G. Monroe, Sundeep Khosla
Abstract
Sarcopenia burdens the elderly population through loss of muscle energy and mass, yet treatments to functionally rescue both parameters are missing. The glucocorticoid prednisone remodels muscle metabolism based on frequency of intake, but its mechanisms in sarcopenia are unknown. We found that once-weekly intermittent prednisone rescued muscle quality in aged 24-month-old mice to levels comparable to young 4-month-old mice. We discovered an age- and sex-independent glucocorticoid receptor transactivation program in muscle encompassing PGC1α and its co-factor Lipin1. Treatment coordinately improved mitochondrial abundance through isoform 1 and muscle mass through isoform 4 of the myocyte-specific PGC1α, which was required for the treatment-driven increase in carbon shuttling from glucose to amino acid biogenesis. We also probed the myocyte-specific Lipin1 as non-redundant factor coaxing PGC1α upregulation to the stimulation of both oxidative and anabolic effects. Our study unveils an aging-resistant druggable program in myocytes to coordinately rescue energy and mass in sarcopenia.
Authors
Ashok Daniel Prabakaran, Kevin McFarland, Karen Miz, Hima Bindu Durumutla, Kevin Piczer, Fadoua El Abdellaoui-Soussi, Hannah Latimer, Cole Werbrich, Hyun-Jy Chung, N. Scott Blair, Douglas P. Millay, Andrew J. Morris, Brendan Prideaux, Brian N. Finck, Mattia Quattrocelli
Abstract
The appearance of senescent cells in age-related diseases has spurred the search for compounds that can target senescent cells in tissues (“senolytics”). However, a major caveat with current senolytic screens is the use of cell lines as targets where senescence is induced in vitro, which does not necessarily reflect the identity and function of pathogenic senescent cells in vivo. Here, we developed a new pipeline leveraging a fluorescent murine reporter that allows for isolation and quantification of p16Ink4a+ cells in diseased tissues. By high-throughput screening in vitro, precision cut lung slice (PCLS) screening ex vivo, and phenotypic screening in vivo, we identified a HSP90 inhibitor (XL888) as a potent senolytic in tissue fibrosis. XL888 treatment eliminated pathogenic p16Ink4a+ fibroblasts in a murine model of lung fibrosis and reduced fibrotic burden. Finally, XL888 preferentially targeted p16INK4a-high human lung fibroblasts isolated from patients with idiopathic pulmonary fibrosis (IPF), and reduced p16INK4a+ fibroblasts from IPF PCLS ex vivo. This study provides proof of concept for a platform where p16INK4a+ cells are directly isolated from diseased tissues to identify compounds with in vivo and ex vivo efficacy in mouse and human respectively and provides a senolytic screening platform for other age-related diseases.
Authors
Jin Young Lee, Nabora S. Reyes, Supriya Ravishankar, Minqi Zhou, Maria Krasilnikov, Christian Ringler, Grace Pohan, Chris Wilson, Kenny Kean-Hooi Ang, Paul J. Wolters, Tatsuya Tsukui, Dean Sheppard, Michelle R. Arkin, Tien Peng
Abstract
Senescent vascular smooth muscle cells (VSMCs) accumulate in the vasculature with age and tissue damage, and secrete factors that promote atherosclerotic plaque vulnerability and disease. Here, we report increased levels and activity of dipeptidyl peptidase 4 (DPP4), a serine protease, in senescent VSMCs. Analysis of the conditioned media from senescent VSMCs revealed a unique senescence-associated secretory phenotype (SASP) signature comprising many complement and coagulation factors; silencing or inhibiting DPP4 reduced these factors and increased cell death. Serum samples from persons with high risk for cardiovascular disease contained high levels of DPP4-regulated complement and coagulation factors. Importantly, DPP4 inhibition reduced senescent cell burden and coagulation and improved plaque stability, while single-cell resolution of senescent VSMCs reflected the senomorphic and senolytic effects of DPP4 inhibition in murine atherosclerosis. We propose that DPP4-regulated factors could be exploited therapeutically to reduce senescent cell function, reverse senohemostasis, and improve vascular disease.
Authors
Allison B. Herman, Dimitrios Tsitsipatis, Carlos Anerillas, Krystyna Mazan-Mamczarz, Angelica E. Carr, Jordan M. Gregg, Mingyi Wang, Jing Zhang, Marc Michel, Charnae' Henry-Smith, Sophia C. Harris, Rachel Munk, Jennifer L Martindale, Yulan Piao, Jinshui Fan, Julie A. Mattison, Supriyo De, Kotb Abdelmohsen, Robert W. Maul, Toshiko Tanaka, Ann Z. Moore, Megan E. DeMouth, Simone Sidoli, Luigi Ferrucci, Yie Liu, Rafael de Cabo, Edward G. Lakatta, Myriam Gorospe
Abstract
Clearance of senescent cells (SnCs) can prevent several age-related pathologies, including bone loss. However, the local versus systemic roles of SnCs in mediating tissue dysfunction remain unclear. Thus, we developed a mouse model (p16-LOX-ATTAC) that allows for inducible SnC elimination (senolysis) in a cell-specific manner and compared the effects of local versus systemic senolysis during aging using bone as a prototype tissue. Specific removal of Sn osteocytes prevented age-related bone loss at the spine, but not the femur, by improving bone formation without affecting osteoclasts or marrow adipocytes. By contrast, systemic senolysis prevented bone loss at the spine and femur and not only improved bone formation, but also reduced osteoclasts and marrow adipocytes. Transplantation of SnCs into the peritoneal cavity of young mice caused bone loss and also induced senescence in distant host osteocytes. Collectively, our findings provide the first proof-of-concept evidence that local senolysis has health benefits in the context of aging, but importantly, local senolysis only partially replicates the benefits of systemic senolysis. Further, we establish that SnCs, through their SASP, lead to senescence in distant cells. Therefore, our study indicates that optimizing senolytic drugs may require systemic instead of local SnC targeting to extend healthy aging.
Authors
Joshua N. Farr, Dominik Saul, Madison L. Doolittle, Japneet Kaur, Jennifer L. Rowsey, Stephanie J. Vos, Mitchell N. Froemming, Anthony B. Lagnado, Yi Zhu, Megan M. Weivoda, Yuji Ikeno, Robert J. Pignolo, Laura J. Niedernhofer, Paul D. Robbins, Diana Jurk, João F. Passos, Nathan K. LeBrasseur, Tamara Tchkonia, James L. Kirkland, David G. Monroe, Sundeep Khosla
Abstract
Obesity is a risk factor for neurodegenerative disease associated with cognitive dysfunction, including Alzheimer’s disease. Low-grade inflammation is common in obesity, but the mechanism between inflammation and cognitive impairment in obesity is unclear. Accumulative evidence shows that quinolinic acid (QA), a neuroinflammatory neurotoxin, is involved in the pathogenesis of neurodegenerative processes. We investigated the role of QA in obesity-induced cognitive impairment and the beneficial effect of butyrate in counteracting impairments of cognition, neural morphology, and signaling. We show that in human obesity, there was a negative relationship between serum QA levels and cognitive function and decreased cortical gray matter. Diet-induced obese mice had increased QA levels in the cortex associated with cognitive impairment. At single-cell resolution, we confirmed that QA impaired neurons, altered the dendritic spine’s intracellular signal, and reduced brain-derived neurotrophic factor (BDNF) levels. Using Caenorhabditis elegans models, QA induced dopaminergic and glutamatergic neuron lesions. Importantly, the gut microbiota metabolite butyrate was able to counteract those alterations, including cognitive impairment, neuronal spine loss, and BDNF reduction in both in vivo and in vitro studies. Finally, we show that butyrate prevented QA-induced BDNF reductions by epigenetic enhancement of H3K18ac at BDNF promoters. These findings suggest that increased QA is associated with cognitive decline in obesity and that butyrate alleviates neurodegeneration.
Authors
Xing Ge, Mingxuan Zheng, Minmin Hu, Xiaoli Fang, Deqin Geng, Sha Liu, Li Wang, Jun Zhang, Li Guan, Peng Zheng, Yuanyi Xie, Wei Pan, Menglu Zhou, Limian Zhou, Renxian Tang, Kuiyang Zheng, Yinghua Yu, Xu-Feng Huang
Abstract
As representatives for our entire team, we thank Jhaveri et al. (1) for their insightful comments on our recent study investigating the increased expression of programmed cell death protein-1 (PD1) in kidneys during aging and FSGS.(2) In our manuscript we showed that PD1 was predominantly increased in podocytes and kidney tubular epithelial cells in both mice and humans. Moreover, in humans, age-elevated glomerular PCDC1 (gene encoding human PD1) levels were associated with a lower eGFR, increased segmental glomerulosclerosis, and reduced arterial intima-to-lumen ratio. We also demonstrated a mechanistic link between increased PD1 levels in podocytes and their shortened lifespan. Finally, specifically antagonizing the PD1 pathway with a specific anti-PD1 antibody (similar to humanized Pembrolizumab or Nivolumab) in aged mice and mice with experimental FSGS had major benefits on kidney histology, podocyte life- and health-span, and tubular epithelial injury.(2) In their response, Jhaveri and colleagues, experts in onco-nephrology, eloquently discuss the clinical kidney-specific adverse events (AEs) when using immune checkpoint inhibitors (ICI) in cancer patients.(1) They provide important clinical insights and an up-to-date summary of the incidence and types of glomerular lesions, acute kidney injury and acute interstitial nephritis observed in patients receiving ICI for cancer treatment.(3,4) Importantly, complete or partial remission of kidney-specific AEs upon discontinuation of ICI treatment in a subset of patients suggests a causal link.(3, 4) We unreservedly agree with Jhaveri et al. that caution is warranted when using ICI clinically. In fact, we have not advocated the clinical use of anti-PD1 treatment to limit or reverse kidney aging, nor to be used as a therapy for FSGS. The clinical data highlighted by Jhaveri et al. underscore the importance of gaining a better understanding of the mechanism(s) underlying kidney complications in patients. While T cell activation, proliferation and subsequent kidney infiltration is the leading hypothesis,(3, 4) how this cumulates into kidney dysfunction is unknown. ICIs block the CTLA-4 and/or PD1 pathways. CTLA-4 acts early in tolerance induction, stopping potentially autoreactive T cells at the initial stage of naive T-cell activation, while PD1 acts late to maintain long-term tolerance, primarily in peripheral tissues.(5) Typically a lower incidence of AEs is associated with PD1 blockade compared with CTLA-4 blockade.(3, 4) Interestingly, in our study mice Ctla4 mRNA levels in contrast to PD1 were not elevated in podocytes with age. There are also several differences between humans and mice that may influence the response to anti-PD1 treatments. To reconcile these, one needs to experimentally align the animal studies with the therapeutic scenario in human cancer patients. Possible considerations include: (i) the duration of therapy - in our study mice received 8 weeks of treatment, while human patients typically receive a 13-week median drug exposure before glomerular disease is first detected; (ii) the presence of comorbid conditions is oftentimes present in humans (e.g., patients receiving additional medications or already exhibiting altered kidney function before receiving ICI agents), but was absent in our mice; (iii) sex and age – the median age of patients developing glomerular disease after ICI treatment is 63 years and 75% thereof are male,(4) while our mouse study was based on males only; (iv) drug dosing – the therapeutic doses of ICIs used in humans might be much higher than the doses of the mouse-specific anti-PD1 antibody yielding beneficial effects in mouse podocytes; (v) finally, genetic variation in humans may influence the response to anti-PD1 treatments, while mice strains are genetically very homogenous. We believe that our study has provided some exciting new considerations that has moved us ahead scientifically. First, the PD1 signaling is a new pathway contributing to the aging of podocytes and other kidney epithelial cells, as well as the response of podocytes in disease. Second, podocyte aging and diseased-induced podocyte injury share a new common pathway – PD1. This raises the possibility that PD1 signaling is one of the pathways responsible for the more severe kidney injury when FSGS is superimposed on an aged kidney. Third, the effects of the anti-PD1 antibody treatment are not restricted to the kidney, but also reduced some aspects of liver aging. This suggests that it might be a common aging pathway, that needs to be studied further. Fourth, the unexpected discovery of PD1 signaling in aging leads us to predict that there will be additional surprises in new pathways contributing to kidney aging and disease that will translate into new druggable targets.
Authors
Stuart J. Shankland, Jeffrey W. Pippin, Oliver Wessely
Abstract
With an aging population, kidney health becomes an important medical and socioeconomic factor. Kidney aging mechanisms are not well understood. We previously showed that podocytes isolated from aged mice exhibit increased expression of programmed cell death protein 1 (PD-1) surface receptor and its 2 ligands (PD-L1 and PD-L2). PDCD1 transcript increased with age in microdissected human glomeruli, which correlated with lower estimated glomerular filtration rate and higher segmental glomerulosclerosis and vascular arterial intima-to-lumen ratio. In vitro studies in podocytes demonstrated a critical role for PD-1 signaling in cell survival and in the induction of a senescence-associated secretory phenotype. To prove PD-1 signaling was critical to podocyte aging, aged mice were injected with anti–PD-1 antibody. Treatment significantly improved the aging phenotype in both kidney and liver. In the glomerulus, it increased the life span of podocytes, but not that of parietal epithelial, mesangial, or endothelial cells. Transcriptomic and immunohistochemistry studies demonstrated that anti–PD-1 antibody treatment improved the health span of podocytes. Administering the same anti–PD-1 antibody to young mice with experimental focal segmental glomerulosclerosis (FSGS) lowered proteinuria and improved podocyte number. These results suggest a critical contribution of increased PD-1 signaling toward both kidney and liver aging and in FSGS.
Authors
Jeffrey W. Pippin, Natalya Kaverina, Yuliang Wang, Diana G. Eng, Yuting Zeng, Uyen Tran, Carol J. Loretz, Anthony Chang, Shreeram Akilesh, Chetan Poudel, Hannah S. Perry, Christopher O’Connor, Joshua C. Vaughan, Markus Bitzer, Oliver Wessely, Stuart J. Shankland
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ISSN: 0021-9738 (print), 1558-8238 (online)