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 alpha-amino-beta-carboxymuconate-epsilon-semialdehyde decarboxylase (ACMSD), the enzyme that limits spontaneous cyclization of alpha-amino-beta-carboxymuconate-epsilon-semialdehyde in the de novo NAD(+) synthesis pathway, controls cellular NAD(+) levels via an evolutionarily conserved mechanism in Cuenorhabditis eleguns 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.

Role of ACMSD in regulation of NAD+ metabolism and mitochondrial function

Elena Katsyuba

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 most notoriously the sirtuin family of NAD+-dependent protein deacylases. Altered NAD+ metabolism is associated with many pathological conditions, including aging and obesity, while beneficial effects of increased NAD+ levels and subsequent sirtuin activation have been established across many different species. Due to their capacity to ameliorate mitochondrial homeostasis, organismal metabolism and lifespan, strategies aiming to boost NAD+ content possess a high therapeutic potential. This thesis describes a novel approach to increase NAD+ levels by stimulating its de novo biosynthesis from the amino acid tryptophan. The enzyme Aminocarboxymuconate Semialdehyde Decarboxylase (ACMSD) converts its substrate, ACMS, into the side branch of the pathway leading to its complete oxidation, consequently limiting the proportion of ACMS capable to generate NAD+. Since reducing ACMSD activity would prevent the flux of metabolites into the side branch and channel them towards NAD+ formation instead, the ultimate goal of this thesis was to establish the role of ACMSD in the control of the intracellular NAD+ content. First, by using genetic tools I found that reduction of ACMSD activity indeed boosts de novo NAD+ synthesis through a mechanism that is conserved from the worm C. elegans to the mouse. Beneficial effects associated with the observed increase in cellular NAD+ levels promoted mitochondrial biogenesis involving sirtuin activation. Secondly, I participated in the development of a panel of potent and selective ACMSD inhibitors. Given the restricted expression of ACMSD in the kidney and liver, its pharmacological inhibition can be a valuable strategy to increase NAD+ content in these tissues and to protect them from injury. After primary characterisation of the ACMSD inhibitors in cell models, I explored the therapeutic potential of the lead compounds to protect from non-alcoholic fatty liver disease and acute kidney injury in mice. Collectively, the data reported in this thesis describe ACMSD as an evolutionary conserved modulator of cellular NAD+ levels, sirtuin activity and mitochondrial homeostasis. Through its impact on cellular NAD+ levels ACMSD inhibition is able to preserve the hepatic and renal function from injury.

EPFL2017

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

Johan Auwerx, Karim Laurent Gariani, Pooja Jha, Elena Katsyuba, Jun Yong Kim, Vera Monica Lemos Da Silva, Keir Joe Menzies, Alessia Perino, Dongryeol Ryu, Kristina Schoonjans, Matthias Alexander Sokrates Stein, Hongbo Zhang

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 beta-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 Sirt1(heP-/-) 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. (C) 2016 European Association for the Study of the Liver. Published by Elsevier B.V.

Elsevier Science Bv2017

Protein deacetylation by SIRT1: An emerging key post- translational modification in metabolic regulation

Johan Auwerx, Jiujiu Yu

The biological function of most proteins relies on reversible post-translational modifications, among which phosphorylation is most prominently studied and well recognized. Recently, a growing amount of evidence indicates that acetylation-deacetylation reactions, when applied to crucial mediators, can also robustly affect the function of target proteins and thereby have wide-ranging physiological impacts. Sirtuin 1 (SIRT1), which functions as a nicotinamide adenine dinucleotide (NAD(+))-dependent protein deacetylase, deacetylates a wide variety of metabolic molecules in response to the cellular energy and redox status and as such causes significant changes in metabolic homeostasis. This review surveys the evidence for the emerging role of SIRT1-mediated deacetylation in the control of metabolic homeostasis.

Elsevier2010

Role of ACMSD in regulation of NAD+ metabolism and mitochondrial function

Elena Katsyuba

EPFL2017

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

Elsevier Science Bv2017