Every major cause of death and disability in the developed world shares a greatest risk factor, and it is probably not what most people would think. Smoking, obesity, a sedentary lifestyle and drinking too much alcohol all contribute to disease: however, their contributions are small in comparison to the physiological changes that result from aging. Whether biological aging causes the many functional declines that occur with age, or just permits them, is perhaps open for debate, but there is no question that, for most of us, biological aging determines how and when we and our loved ones will get sick and die.
This connection between aging and disease has become particularly consequential during the COVID-19 pandemic, with the vast majority of severe cases and deaths occurring among the elderly. Given this obvious relationship, it is somewhat surprising how slowly the biomedical research community has come to appreciate the importance of biological aging in many of the disease processes under study. It is our hope that the articles in the eLife special issue on aging, geroscience and longevity will contribute to a greater appreciation and understanding of aging biology among the broader scientific community. A number of the authors of these articles also spoke at a recent eLife symposium on this topic.
Today, unfortunately, too many scientists study individual diseases without recognizing the impact of aging biology. It is still common, for example, to see research studies in cancer, neuroscience, metabolism and other fields where young animal models (such as 4–6 month old mice) are used to study disease processes that almost exclusively occur in old people. ‘Mice are not people’ is a standard refrain when explaining why so many preclinical therapies fail in human trials. Perhaps the mouse isn’t the problem. Failing to account for the physiological changes that occur during aging, both in mice and in people, may be a much bigger reason why so much preclinical research fails to translate to the clinic.
It is still common to see research studies in cancer, neuroscience, metabolism and other fields where young animal models are used to study disease processes that almost exclusively occur in old people.
Thinking about certain conserved molecular mechanisms as 'hallmarks' or 'pillars' of aging (Kennedy et al., 2014; López-Otín et al., 2013) has benefitted researchers within the field, and has also allowed scientists outside the field to begin to recognize how aging biology impacts on their own research. Many of these conserved mechanisms are studied in the papers in this special issue, including telomere attrition, mitochondrial dysfunction, cellular senescence, epigenetic alterations, stem cell exhaustion, genomic instability, and loss of proteostasis.
Another important advance in aging research has been the development of a concept called geroscience: researchers in this area seek to understand mechanistically how the hallmarks of aging cause age-related disease and functional decline (Sierra and Kohanski, 2017). The growth of the geroscience concept also reflects a recognition that aging research is much closer to clinical application than it was twenty years ago. Numerous interventions have been developed that target one or more of the hallmarks of aging in order to delay, or even reverse, age-related functional declines. In rodents, for example, it has been shown that the drug rapamycin can prevent age-related diseases and improve function in multiple aged tissues and organs. Now, in the eLife special issue on aging, An et al. report that rapamycin also works in the oral cavity and can reverse periodontal disease in mice (An et al., 2020). Other articles suggest translational strategies to target specific hallmarks of aging for intervertebral disc degeneration (Cherif et al., 2020) and age-related heart disease (Chiao et al., 2020). At the time of writing there are two review articles and more than 20 research articles in the special issue, and more will be added over time.
The future of aging research is brighter than ever before, and the pace of discovery is only increasing. We look forward to major breakthroughs over the next few years that will revolutionize the way we think about aging biology and have the potential to significantly impact human healthspan and longevity.
The development of haematopoietic stem cells into mature erythrocytes – erythropoiesis – is a controlled process characterized by cellular reorganization and drastic reshaping of the proteome landscape. Failure of ordered erythropoiesis is associated with anaemias and haematological malignancies. Although the ubiquitin system is a known crucial post-translational regulator in erythropoiesis, how the erythrocyte is reshaped by the ubiquitin system is poorly understood. By measuring the proteomic landscape of in vitro human erythropoiesis models, we found dynamic differential expression of subunits of the CTLH E3 ubiquitin ligase complex that formed maturation stage-dependent assemblies of topologically homologous RANBP9- and RANBP10-CTLH complexes. Moreover, protein abundance of CTLH’s cognate E2 ubiquitin conjugating enzyme UBE2H increased during terminal differentiation, and UBE2H expression depended on catalytically active CTLH E3 complexes. CRISPR-Cas9-mediated inactivation of CTLH E3 assemblies or UBE2H in erythroid progenitors revealed defects, including spontaneous and accelerated erythroid maturation as well as inefficient enucleation. Thus, we propose that dynamic maturation stage-specific changes of UBE2H-CTLH E2-E3 modules control the orderly progression of human erythropoiesis.
Different organelles traveling through neurons exhibit distinct properties in vitro, but this has not been investigated in the intact mammalian brain. We established simultaneous dual color two-photon microscopy to visualize the trafficking of Neuropeptide Y (NPY)-, LAMP1-, and RAB7-tagged organelles in thalamocortical axons imaged in mouse cortex in vivo. This revealed that LAMP1- and RAB7-tagged organelles move significantly faster than NPY-tagged organelles in both anterograde and retrograde direction. NPY traveled more selectively in anterograde direction than LAMP1 and RAB7. By using a synapse marker and a calcium sensor, we further investigated the transport dynamics of NPY-tagged organelles. We found that these organelles slow down and pause at synapses. In contrast to previous in vitro studies, a significant increase of transport speed was observed after spontaneous activity and elevated calcium levels in vivo as well as electrically stimulated activity in acute brain slices. Together, we show a remarkable diversity in speeds and properties of three axonal organelle marker in vivo that differ from properties previously observed in vitro.