Elena Katsyuba

Mitonuclear protein imbalance as a conserved longevity mechanism

Longevity is regulated by a network of closely linked metabolic systems. We used a combination of mouse population genetics and RNA interference in Caenorhabditis elegans to identify mitochondrial ribosomal protein S5 (Mrps5) and other mitochondrial ribosomal proteins as metabolic and longevity regulators. MRP knockdown triggers mitonuclear protein imbalance, reducing mitochondrial respiration and activating the mitochondrial unfolded protein response. Specific antibiotics targeting mitochondrial translation and ethidium bromide (which impairs mitochondrial DNA transcription) pharmacologically mimic mrp knockdown and extend worm lifespan by inducing mitonuclear protein imbalance, a stoichiometric imbalance between nuclear and mitochondrially encoded proteins. This mechanism was also conserved in mammalian cells. In addition, resveratrol and rapamycin, longevity compounds acting on different molecular targets, similarly induced mitonuclear protein imbalance, the mitochondrial unfolded protein response and lifespan extension in C. elegans. Collectively these data demonstrate that MRPs represent an evolutionarily conserved protein family that ties the mitochondrial ribosome and mitonuclear protein imbalance to the mitochondrial unfolded protein response, an overarching longevity pathway across many species.

The NAD(+)/Sirtuin Pathway Modulates Longevity through Activation of Mitochondrial UPR and FOXO Signaling.

NAD(+) is an important cofactor regulating metabolic homeostasis and a rate-limiting substrate for sirtuin deacylases. We show that NAD(+) levels are reduced in aged mice and Caenorhabditis elegans and that decreasing NAD(+) levels results in a further reduction in worm lifespan. Conversely, genetic or pharmacological restoration of NAD(+) prevents age-associated metabolic decline and promotes longevity in worms. These effects are dependent upon the protein deacetylase sir-2.1 and involve the induction of mitonuclear protein imbalance as well as activation of stress signaling via the mitochondrial unfolded protein response (UPR(mt)) and the nuclear translocation and activation of FOXO transcription factor DAF-16. Our data suggest that augmenting mitochondrial stress signaling through the modulation of NAD(+) levels may be a target to improve mitochondrial function and prevent or treat age-associated decline.

Urolithin A induces mitophagy and prolongs lifespan in C. elegans and increases muscle function in rodents

The biological effects of urolithins remain poorly characterized, despite wide-spread human exposure via the dietary consumption of their metabolic precursors, the ellagitannins, which are found in the pomegranate fruit, as well as in nuts and berries. We identified urolithin A (UA) as a first-in-class natural compound that induces mitophagy both in vitro and in vivo following oral consumption. In C. elegans, UA prevented the accumulation of dysfunctional mitochondria with age and extended lifespan. Likewise, UA prolonged normal activity during aging in C. elegans, including mobility and pharyngeal pumping, while maintaining mitochondrial respiratory capacity. These effects translated to rodents, where UA improved exercise capacity in two different mouse models of age-related decline of muscle function, as well as in young rats. Our findings highlight the health benefits of urolithin A and its potential application in strategies to improve mitochondrial and muscle function.

Protein acetylation in metabolism - metabolites and cofactors.

Reversible acetylation was initially described as an epigenetic mechanism regulating DNA accessibility. Since then, this process has emerged as a controller of histone and nonhistone acetylation that integrates key physiological processes such as metabolism, circadian rhythm and cell cycle, along with gene regulation in various organisms. The widespread and reversible nature of acetylation also revitalized interest in the mechanisms that regulate lysine acetyltransferases (KATs) and deacetylases (KDACs) in health and disease. Changes in protein or histone acetylation are especially relevant for many common diseases including obesity, diabetes mellitus, neurodegenerative diseases and cancer, as well as for some rare diseases such as mitochondrial diseases and lipodystrophies. In this Review, we examine the role of reversible acetylation in metabolic control and how changes in levels of metabolites or cofactors, including nicotinamide adenine dinucleotide, nicotinamide, coenzyme A, acetyl coenzyme A, zinc and butyrate and/or β-hydroxybutyrate, directly alter KAT or KDAC activity to link energy status to adaptive cellular and organismal homeostasis.

Inhibiting poly ADP-ribosylation increases fatty acid oxidation and protects against fatty liver disease

BACKGROUND & AIMS To date, no pharmacological therapy has been approved for non-alcoholic fatty liver disease (NAFLD). The aim of the present study was to evaluate the therapeutic potential of poly ADP-ribose polymerase (PARP) inhibitors in mouse models of NAFLD. METHODS As poly ADP-ribosylation (PARylation) of proteins by PARPs consumes nicotinamide adenine dinucleotide (NAD+), we hypothesized that overactivation of PARPs drives NAD+ depletion in NAFLD. Therefore, we assessed the effectiveness of PARP inhibition to replenish NAD+ and activate NAD+-dependent sirtuins, hence improving hepatic fatty acid oxidation. To do this, we examined the preventive and therapeutic benefits of the PARP inhibitor (PARPi), olaparib, in different models of NAFLD. RESULTS The induction of NAFLD in C57BL/6J mice using a high-fat high-sucrose (HFHS)-diet increased PARylation of proteins by PARPs. As such, increased PARylation was associated with reduced NAD+ levels and mitochondrial function and content, which was concurrent with elevated hepatic lipid content. HFHS diet supplemented with PARPi reversed NAFLD through repletion of NAD+, increasing mitochondrial biogenesis and β-oxidation in liver. Furthermore, PARPi reduced reactive oxygen species, endoplasmic reticulum stress and fibrosis. The benefits of PARPi treatment were confirmed in mice fed with a methionine- and choline-deficient diet and in mice with lipopolysaccharide-induced hepatitis; PARP activation was attenuated and the development of hepatic injury was delayed in both models. Using Sirt1hep-/- mice, the beneficial effects of a PARPi-supplemented HFHS diet were found to be Sirt1-dependent. CONCLUSIONS Our study provides a novel and practical pharmacological approach for treating NAFLD, fueling optimism for potential clinical studies. LAY SUMMARY Non-alcoholic fatty liver disease (NAFLD) is now considered to be the most common liver disease in the Western world and has no approved pharmacological therapy. PARP inhibitors given as a treatment in two different mouse models of NAFLD confer a protection against its development. PARP inhibitors may therefore represent a novel and practical pharmacological approach for treating NAFLD.

Modulating NAD+ metabolism, from bench to bedside

Discovered in the beginning of the 20th century, nicotinamide adenine dinucleotide (NAD+) has evolved from a simple oxidoreductase cofactor to being an essential cosubstrate for a wide range of regulatory proteins that include the sirtuin family of NAD+‐dependent protein deacylases, widely recognized regulators of metabolic function and longevity. Altered NAD+ metabolism is associated with aging and many pathological conditions, such as metabolic diseases and disorders of the muscular and neuronal systems. Conversely, increased NAD+ levels have shown to be beneficial in a broad spectrum of diseases. Here, we review the fundamental aspects of NAD+ biochemistry and metabolism and discuss how boosting NAD+ content can help ameliorate mitochondrial homeostasis and as such improve healthspan and lifespan.

Loss of Sirt1 function improves intestinal anti-bacterial defense and protects from colitis-induced colorectal cancer.

Dysfunction of Paneth and goblet cells in the intestine contributes to inflammatory bowel disease (IBD) and colitis-associated colorectal cancer (CAC). Here, we report a role for the NAD+-dependent histone deacetylase SIRT1 in the control of anti-bacterial defense. Mice with an intestinal specific Sirt1 deficiency (Sirt1int−/−) have more Paneth and goblet cells with a consequent rearrangement of the gut microbiota. From a mechanistic point of view, the effects on mouse intestinal cell maturation are mediated by SIRT1-dependent changes in the acetylation status of SPDEF, a master regulator of Paneth and goblet cells. Our results suggest that targeting SIRT1 may be of interest in the management of IBD and CAC.

α-Amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSD) Inhibitors as Novel Modulators of de novo Nicotinamide Adenine Dinucleotide (NAD+) Biosynthesis

NAD+ has a central function in linking cellular metabolism to major cell-signaling and gene-regulation pathways. Defects in NAD+ homeostasis underpin a wide range of diseases, including cancer, metabolic disorders, and aging. Although the beneficial effects of boosting NAD+ on mitochondrial fitness, metabolism, and lifespan are well established, to date, no therapeutic enhancers of de novo NAD+ biosynthesis have been reported. Herein we report the discovery of 3-[[[5-cyano-1,6-dihydro-6-oxo-4-(2-thienyl)-2-pyrimidinyl]thio]methyl]phenylacetic acid (TES-1025, 22), the first potent and selective inhibitor of human ACMSD (IC50 = 0.013 μM) that increases NAD+ levels in cellular systems. The results of physicochemical-property, ADME, and safety profiling, coupled with in vivo target-engagement studies, support the hypothesis that ACMSD inhibition increases de novo NAD+ biosynthesis and position 22 as a first-class molecule for the evaluation of the therapeutic potential of ACMSD inhibition in treating disorders with perturbed NAD+ supply or homeostasis.

De novo NAD+ synthesis enhances mitochondrial function and improves health.

Nicotinamide adenine dinucleotide (NAD+) is a co-substrate for several enzymes, including the sirtuin family of NAD+-dependent protein deacylases. Beneficial effects of increased NAD+ levels and sirtuin activation on mitochondrial homeostasis, organismal metabolism and lifespan have been established across species. Here we show that α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSD), the enzyme that limits spontaneous cyclization of α-amino-β-carboxymuconate-ε-semialdehyde in the de novo NAD+ synthesis pathway, controls cellular NAD+ levels via an evolutionarily conserved mechanism in Caenorhabditis elegans and mouse. Genetic and pharmacological inhibition of ACMSD boosts de novo NAD+ synthesis and sirtuin 1 activity, ultimately enhancing mitochondrial function. We also characterize two potent and selective inhibitors of ACMSD. Because expression of ACMSD is largely restricted to kidney and liver, these inhibitors may have therapeutic potential for protection of these tissues from injury. In summary, we identify ACMSD as a key modulator of cellular NAD+ levels, sirtuin activity and mitochondrial homeostasis in kidney and liver.Genetic or pharmacological inhibition of α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase increases NAD+ and improves mitochondrial function in nematodes and mice, and may have therapeutic potential in kidney and liver disease.

NAD+ Modulation: Biology and Therapy

Abstract The capacity of nicotinamide adenine dinucleotide (NAD+) to control the activity of sirtuins was reported for the first time in 2000. Since then, the number of studies exploring the NAD+–SIRT connection and their coordinated regulation of different aspects of metabolism has been increasing exponentially. In this chapter we discuss the main points of NAD+ metabolism, including different aspects of its synthesis, the factors affecting NAD+ homeostasis and the enzymes consuming NAD+ for their catalytic activity. We also provide an overview of the physiological impact of NAD+ boosting strategies on sirtuin activity, which can be employed as a treatment for a wide range of different disease states.