Impairment of an Endothelial NAD+-H2S Signaling Network Is a Reversible Cause of Vascular Aging.

A decline in capillary density and blood flow with age is a major cause of mortality and morbidity. Understanding why this occurs is key to future gains in human health. NAD precursors reverse aspects of aging, in part, by activating sirtuin deacylases (SIRT1-SIRT7) that mediate the benefits of exercise and dietary restriction (DR). We show that SIRT1 in endothelial cells is a key mediator of pro-angiogenic signals secreted from myocytes. Treatment of mice with the NAD+ booster nicotinamide mononucleotide (NMN) improves blood flow and increases endurance in elderly mice by promoting SIRT1-dependent increases in capillary density, an effect augmented by exercise or increasing the levels of hydrogen sulfide (H2S), a DR mimetic and regulator of endothelial NAD+ levels. These findings have implications for improving blood flow to organs and tissues, increasing human performance, and reestablishing a virtuous cycle of mobility in the elderly.

Reprogramming to recover youthful epigenetic information and restore vision.

Ageing is a degenerative process that leads to tissue dysfunction and death. A proposed cause of ageing is the accumulation of epigenetic noise that disrupts gene expression patterns, leading to decreases in tissue function and regenerative capacity1-3. Changes to DNA methylation patterns over time form the basis of ageing clocks4, but whether older individuals retain the information needed to restore these patterns-and, if so, whether this could improve tissue function-is not known. Over time, the central nervous system (CNS) loses function and regenerative capacity5-7. Using the eye as a model CNS tissue, here we show that ectopic expression of Oct4 (also known as Pou5f1), Sox2 and Klf4 genes (OSK) in mouse retinal ganglion cells restores youthful DNA methylation patterns and transcriptomes, promotes axon regeneration after injury, and reverses vision loss in a mouse model of glaucoma and in aged mice. The beneficial effects of OSK-induced reprogramming in axon regeneration and vision require the DNA demethylases TET1 and TET2. These data indicate that mammalian tissues retain a record of youthful epigenetic information-encoded in part by DNA methylation-that can be accessed to improve tissue function and promote regeneration in vivo.

NAD+ in COVID-19 and viral infections.

NAD+, as an emerging regulator of immune responses during viral infections, may be a promising therapeutic target for coronavirus disease 2019 (COVID-19). In this Opinion, we suggest that interventions that boost NAD+ levels might promote antiviral defense and suppress uncontrolled inflammation. We discuss the association between low NAD+ concentrations and risk factors for poor COVID-19 outcomes, including aging and common comorbidities. Mechanistically, we outline how viral infections can further deplete NAD+ and its roles in antiviral defense and inflammation. We also describe how coronaviruses can subvert NAD+-mediated actions via genes that remove NAD+ modifications and activate the NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome. Finally, we explore ongoing approaches to boost NAD+ concentrations in the clinic to putatively increase antiviral responses while curtailing hyperinflammation.

When stem cells grow old: phenotypes and mechanisms of stem cell aging.

All multicellular organisms undergo a decline in tissue and organ function as they age. An attractive theory is that a loss in stem cell number and/or activity over time causes this decline. In accordance with this theory, aging phenotypes have been described for stem cells of multiple tissues, including those of the hematopoietic system, intestine, muscle, brain, skin and germline. Here, we discuss recent advances in our understanding of why adult stem cells age and how this aging impacts diseases and lifespan. With this increased understanding, it is feasible to design and test interventions that delay stem cell aging and improve both health and lifespan.

Reduced Levels of NAD in Skeletal Muscle and Increased Physiologic Frailty Are Associated With Viral Coinfection in Asymptomatic Middle-Aged Adults.

BACKGROUND: People living with HIV (PLWH) are disproportionately burdened with multimorbidity and decline in physiologic function compared with their uninfected counterparts, but biological mechanisms that differentially contribute to the decline in muscle function in PLWH compared with uninfected people remain understudied. SETTING: The study site was Brigham and Women's Hospital, Harvard Medical School, Boston, MA. METHODS: We evaluated skeletal muscle tissue for levels of total nicotinamide adenine dinucleotide (NAD), NAD+, and nicotinamide adenine dinucleotide (NADH) in middle-aged asymptomatic PLWH, coinfected with hepatitis C virus and/or cytomegalovirus and compared them with uninfected control participants. RESULTS: Of the 54 persons with muscle biopsy data, the mean age was 57 years with 33% women. Total NAD levels declined in skeletal muscle in association with HIV infection and was exacerbated by hepatitis C virus and cytomegalovirus coinfection, with lowest levels of total NAD, NAD+, and NADH among persons who were coinfected with all 3 viruses (P = 0.015, P = 0.014, and P = 0.076, respectively). Levels of total NAD, NAD+, and NADH in skeletal muscle were inversely associated with inflammation (P = 0.014, P = 0.013, and P = 0.055, respectively). Coinfections were also associated with measures of inflammation (CD4/CD8 ratio: P < 0.001 and sCD163: P < 0.001) and immune activation (CD38 and human leukocyte antigen-DR expression on CD8 T cells: P < 0.001). In addition, coinfection was associated with increased physiologic frailty based on the Veteran Aging Cohort Study 1.0 index assessment (P = 0.001). CONCLUSIONS: Further research is warranted to determine the clinical relevance of preclinical deficits in NAD metabolites in skeletal muscle in association with viral coinfection and inflammation, as well as the observed association between viral coinfection and physiologic frailty.

Can artificial intelligence identify effective COVID-19 therapies?

In this issue of EMBO Molecular Medicine, Stebbing et al (2020b) validate an artificial intelligence-assisted prediction that a drug used to treat rheumatoid arthritis could be a potent weapon against COVID-19. Using liver organoids infected with SARS-CoV-2, they confirm dual antiviral and anti-inflammatory activities and show that its administration in four COVID-19 patients is correlated with disease improvement, paving the way for more rigorous placebo-controlled trials.

Feeding During Infancy: Interpersonal Behavior, Physiology, and Obesity Risk.

Infancy is a sensitive developmental period that presents both opportunities and challenges for caregivers to feed their infants in ways that support healthy growth and development. The capacity to eat in a way that supports energy (caloric) intake aligned with the body's physiologic need for growth and development appear to diminish in the years following infancy, but the reasons for this and whether this is developmentally typical are unclear. Feeding interactions that undermine infants' ability to regulate their intake in response to hunger and satiety are thought to confer risk for obesity in infancy and beyond. In this integrative review, we consider what we know about the emergence of self-regulation of behavior and emotion from both a behavioral and a physiological perspective. Then, we apply this information to our emerging understanding of how self-regulation of energy intake may be derailed through feeding interactions between caregivers and infants.

Age and life expectancy clocks based on machine learning analysis of mouse frailty.

The identification of genes and interventions that slow or reverse aging is hampered by the lack of non-invasive metrics that can predict the life expectancy of pre-clinical models. Frailty Indices (FIs) in mice are composite measures of health that are cost-effective and non-invasive, but whether they can accurately predict health and lifespan is not known. Here, mouse FIs are scored longitudinally until death and machine learning is employed to develop two clocks. A random forest regression is trained on FI components for chronological age to generate the FRIGHT (Frailty Inferred Geriatric Health Timeline) clock, a strong predictor of chronological age. A second model is trained on remaining lifespan to generate the AFRAID (Analysis of Frailty and Death) clock, which accurately predicts life expectancy and the efficacy of a lifespan-extending intervention up to a year in advance. Adoption of these clocks should accelerate the identification of longevity genes and aging interventions.

Publisher Correction: Age and life expectancy clocks based on machine learning analysis of mouse frailty.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Molecular and Cellular Characterization of SIRT1 Allosteric Activators.

SIRT1 is an NAD+-dependent lysine deacetylase that promotes healthy aging and longevity in diverse organisms. Small molecule allosteric activators of SIRT1 such as resveratrol and SRT2104 directly bind to the N-terminus of SIRT1 and lower the Km for the protein substrate. In rodents, sirtuin-activating compounds (STACs) protect from age-related diseases and extend life span. In human clinical trials, STACs have a high safety profile and anti-inflammatory activities. Here, we describe methods for identifying and characterizing STACs, including production of recombinant protein, in vitro assays with recombinant protein, and cellular assays based on mitochondrial dynamics. The methods described in this chapter will facilitate this discovery of improved STACs, natural and synthetic, in the pursuit of interventions to treat age-related diseases.

Harvard HIV and Aging Workshop: Perspectives and Priorities from Claude D. Pepper Centers and Centers for AIDS Research.

People aging with HIV (PAWH) infection experience greater impairments in physical and cognitive function, in addition to higher rates of peripheral comorbid conditions (e.g., renal failure, diabetes, bone fracture, hypertension, cardiovascular disease, polypharmacy, and multimorbidity). While multifactorial drivers, including HIV infection itself, antiretroviral therapy-related toxicities, disparities in care, and biobehavioral factors, likely contribute, there remains an overarching question as to what are the relevant age-related mechanisms and models that could inform interventions that promote health span and life span in PAWH? This workshop was convened to hear from experts on the biology of aging and HIV researchers studying PAWH to focus on advancing investigations at the interface of HIV and Aging. In this study, we summarize the discussions from the Harvard Center for AIDS Research and Boston Claude D. Pepper cosponsored workshop on HIV and Aging, which took place in October 2018.

Conceptual Congruence in Mindfulness-Based Weight Loss Intervention Studies.

Whether one kind of mindfulness applies to all situations or only some (i.e., scope) is controversial. Eating may not be an everyday behavior subsumed under everyday mindfulness. To rigorously test the efficacy of mindfulness-based weight loss interventions, researchers must use scales that measure the type of mindfulness manipulated by the intervention. The mixed findings of mindfulness-based weight loss intervention studies may be related to the lack of conceptual congruence (i.e., the pairing of interventions and measures of the same scope). The aims of this systematic review were to: (a) describe the scopes of the mindfulness interventions and measures used in mindfulness-based weight loss intervention studies; and (b) compare conceptual congruence to the statistical significance of mindfulness and weight outcomes of each study. All articles published prior to December 31, 2016 were retrieved from PubMed, CINAHL, PsycINFO, and Embase. After screening and full-text review, eight articles were included in the review. Five studies paired mindfulness-based eating interventions with general mindfulness measures; two studies paired mindfulness-based eating interventions with eating-specific mindfulness measures; and one study paired a general mindfulness intervention with a general mindfulness measure. There was no apparent relationship between conceptual congruence and the statistical significance of the mindfulness and weight outcomes. However, given other findings and the limitations of this review, further investigation is needed. In particular, future studies should include mediation analyses using both general and eating-specific mindfulness measures.

Assays for NAD+-Dependent Reactions and NAD+ Metabolites.

Nicotinamide adenine dinucleotide (NAD+) is an essential redox cofactor and signaling molecule that controls the activity of enzymes involved in metabolism, DNA repair, and cellular survival, such as the PARPs, CD38, and the sirtuins. Here, we describe three methods for measuring the activity of these enzymes: the etheno-NAD+ assay measures NAD+ hydrolase activity using an NAD+ analog to produce a fluorescent product that is measured in real time; the PNC1 assay converts a native product of NAD+ hydrolysis, nicotinamide, into a quantitative fluorescent readout; and liquid chromatography tandem mass spectrometry (LC-MS/MS) is used to characterize the entire NAD+ metabolome in a sample. These methods will enable new insights into the roles that NAD+ and the enzymes that utilize it play in health and disease.

Why NAD(+) Declines during Aging: It's Destroyed.

NAD(+) is required not only for life but for a long life. In this issue, Camacho-Pereira et al. (2016) implicate CD38 in the decline of NAD(+) during aging, with implications for combating age-related diseases.