Increased cardiac fatty acid oxidation in a mouse model with decreased malonyl-CoA sensitivity of CPT1B

Aims

Mitochondrial fatty acid oxidation (FAO) is an important energy provider for cardiac work and changes in cardiac substrate preference are associated with different heart diseases. Carnitine palmitoyltransferase 1B (CPT1B) is thought to perform the rate limiting enzyme step in FAO and is inhibited by malonyl-CoA. The role of CPT1B in cardiac metabolism has been addressed by inhibiting or decreasing CPT1B protein or after modulation of tissue malonyl-CoA metabolism. We assessed the role of CPT1B malonyl-CoA sensitivity in cardiac metabolism.

Methods and results

We generated and characterized a knock in mouse model expressing the CPT1BE3A mutant enzyme, which has reduced sensitivity to malonyl-CoA. In isolated perfused hearts, FAO was 1.9-fold higher in Cpt1bE3A/E3A hearts compared with Cpt1bWT/WT hearts. Metabolomic, proteomic and transcriptomic analysis showed increased levels of malonylcarnitine, decreased concentration of CPT1B protein and a small but coordinated downregulation of the mRNA expression of genes involved in FAO in Cpt1bE3A/E3A hearts, all of which aim to limit FAO. In vivo assessment of cardiac function revealed only minor changes, cardiac hypertrophy was absent and histological analysis did not reveal fibrosis.

Conclusions

Malonyl-CoA-dependent inhibition of CPT1B plays a crucial role in regulating FAO rate in the heart. Chronic elevation of FAO has a relatively subtle impact on cardiac function at least under baseline conditions.

Cross-species functional modules link proteostasis to human normal aging

The evolutionarily conserved nature of the few well-known anti-aging interventions that affect lifespan, such as caloric restriction, suggests that aging-related research in model organisms is directly relevant to human aging. Since human lifespan is a complex trait, a systems-level approach will contribute to a more comprehensive understanding of the underlying aging landscape. Here, we integrate evolutionary and functional information of normal aging across human and model organisms at three levels: gene-level, process-level, and network-level. We identify evolutionarily conserved modules of normal aging across diverse taxa, and notably show proteostasis to be conserved in normal aging. Additionally, we find that mechanisms related to protein quality control network are enriched for genes harboring genetic variants associated with 22 age-related human traits and associated to caloric restriction. These results demonstrate that a systems-level approach, combined with evolutionary conservation, allows the detection of candidate aging genes and pathways relevant to human normal aging.

The mitophagy activator urolithin A is safe and induces a molecular signature of improved mitochondrial and cellular health in humans

Urolithin A (UA) is a natural dietary, microflora-derived metabolite shown to stimulate mitophagy and improve muscle health in old animals and in preclinical models of aging¹. Here, we report the results of a first-in-human clinical trial in which we administered UA, either as a single dose or as multiple doses over a 4-week period, to healthy, sedentary elderly individuals. We show that UA has a favourable safety profile (primary outcome). UA was bioavailable in plasma at all doses tested, and 4 weeks of treatment with UA at doses of 500 mg and 1,000 mg modulated plasma acylcarnitines and skeletal muscle mitochondrial gene expression in elderly individuals (secondary outcomes). These observed effects on mitochondrial biomarkers show that UA induces a molecular signature of improved mitochondrial and cellular health following regular oral consumption in humans.

Autophagy regulates lipid metabolism through selective turnover of NCoR1

Selective autophagy ensures the removal of specific soluble proteins, protein aggregates, damaged mitochondria, and invasive bacteria from cells. Defective autophagy has been directly linked to metabolic disorders. However how selective autophagy regulates metabolism remains largely uncharacterized. Here we show that a deficiency in selective autophagy is associated with suppression of lipid oxidation. Hepatic loss of Atg7 or Atg5 significantly impairs the production of ketone bodies upon fasting, due to decreased expression of enzymes involved in β-oxidation following suppression of transactivation by PPARα. Mechanistically, nuclear receptor co-repressor 1 (NCoR1), which interacts with PPARα to suppress its transactivation, binds to the autophagosomal GABARAP family proteins and is degraded by autophagy. Consequently, loss of autophagy causes accumulation of NCoR1, suppressing PPARα activity and resulting in impaired lipid oxidation. These results suggest that autophagy contributes to PPARα activation upon fasting by promoting degradation of NCoR1 and thus regulates β-oxidation and ketone bodies production.

Defective autophagy has been associated with metabolic disorders. Here Saito et al. show that autophagy promotes the selective degradation of NCoR1, a repressor of lipid metabolism regulator PPARα, in response to starvation, and thus induces the expression of enzymes involved in lipid oxidation and the production of ketone bodies.

Niacin: an old lipid drug in a new NAD+ dress

Niacin, the first antidyslipidemic drug, has been at the center stage of lipid research for many decades before the discovery of statins. However, to date, despite its remarkable effects on lipid profiles, the clinical outcomes of niacin treatment on cardiac events is still debated. In addition to its historically well-defined interactions with central players of lipid metabolism, niacin can be processed by eukaryotic cells to synthesize a crucial cofactor, NAD+ NAD+ acts as a cofactor in key cellular processes, including oxidative phosphorylation, glycolysis, and DNA repair. More recently, evidence has emerged that NAD+ also is an essential cosubstrate for the sirtuin family of protein deacylases and thereby has an impact on a wide range of cellular processes, most notably mitochondrial homeostasis, energy homeostasis, and lipid metabolism. NAD+ achieves these remarkable effects through sirtuin-mediated deacetylation of key transcriptional regulators, such as peroxisome proliferator-activated receptor gamma coactivator 1-α, LXR, and SREBPs, that control these cellular processes. Here, we present an alternative point of view to explain niacin's mechanism of action, with a strong focus on the importance of how this old drug acts as a control switch of NAD+/sirtuin-mediated control of metabolism.

Mild inborn errors of metabolism in commonly used inbred mouse strains

Inbred mouse strains are a cornerstone of translational research but paradoxically many strains carry mild inborn errors of metabolism. For example, α-aminoadipic acidemia and branched-chain ketoacid dehydrogenase deficiency are known in C57BL/6J mice. Using RNA sequencing, we now reveal the causal variants in Dhtkd1 and Bckdhb, and the molecular mechanism underlying these metabolic defects. C57BL/6J mice have decreased Dhtkd1 mRNA expression due to a solitary long terminal repeat (LTR) in intron 4 of Dhtkd1. This LTR harbors an alternate splice donor site leading to a partial splicing defect and as a consequence decreased total and functional Dhtkd1 mRNA, decreased DHTKD1 protein and α-aminoadipic acidemia. Similarly, C57BL/6J mice have decreased Bckdhb mRNA expression due to an LTR retrotransposon in intron 1 of Bckdhb. This transposable element encodes an alternative exon 1 causing aberrant splicing, decreased total and functional Bckdhb mRNA and decreased BCKDHB protein. Using a targeted metabolomics screen, we also reveal elevated plasma C5-carnitine in 129 substrains. This biochemical phenotype resembles isovaleric acidemia and is caused by an exonic splice mutation in Ivd leading to partial skipping of exon 10 and IVD protein deficiency. In summary, this study identifies three causal variants underlying mild inborn errors of metabolism in commonly used inbred mouse strains.

The RNA-Binding Protein PUM2 Impairs Mitochondrial Dynamics and Mitophagy During Aging

Little information is available about how post-transcriptional mechanisms regulate the aging process. Here, we show that the RNA-binding protein Pumilio2 (PUM2), which is a translation repressor, is induced upon aging and acts as a negative regulator of lifespan and mitochondrial homeostasis. Multi-omics and cross-species analyses of PUM2 function show that it inhibits the translation of the mRNA encoding for the mitochondrial fission factor (Mff), thereby impairing mitochondrial fission and mitophagy. This mechanism is conserved in C. elegans by the PUM2 ortholog PUF-8. puf-8 knock-down in old nematodes and Pum2 CRISPR/Cas9-mediated knockout in the muscles of elderly mice enhances mitochondrial fission and mitophagy in both models, hence improving mitochondrial quality control and tissue homeostasis. Our data reveal how a PUM2-mediated layer of post-transcriptional regulation links altered Mff translation to mitochondrial dynamics and mitophagy, thereby mediating age-related mitochondrial dysfunctions.

Automated high-content phenotyping from the first larval stage till the onset of adulthood of the nematode Caenorhabditis elegans

The nematode Caenorhabditis elegans is increasingly used as a model for human biology. However, in vivo culturing platforms for C. elegans allowing high-content phenotyping during their life cycle in an automated fashion are lacking so far. Here, a multiplexed microfluidic platform for the rapid high-content phenotyping of populations of C. elegans down to single animal resolution is presented. Nematodes are (i) reversibly and regularly confined during their life inside tapered channels for imaging fluorescence signal expression and to measure their growth parameters, and (ii) allowed to freely move in microfluidic chambers, during which the swimming behavior was video-recorded. The obtained data sets are analyzed in an automated way and 19 phenotypic parameters are extracted. Our platform is employed for studying the effect of bacteria dilution, a form of dietary restriction (DR) in nematodes, on a worm model of Huntington's disease and demonstrates the influence of DR on disease regression.

MicroRNA-382 silencing induces a mitonuclear protein imbalance and activates the mitochondrial unfolded protein response in muscle cells

Proper mitochondrial function plays a central role in cellular metabolism. Various diseases as well as aging are associated with diminished mitochondrial function. Previously, we identified 19 miRNAs putatively involved in the regulation of mitochondrial metabolism in skeletal muscle, a highly metabolically active tissue. In the current study, these 19 miRNAs were individually silenced in C2C12 myotubes using antisense oligonucleotides, followed by measurement of the expression of 27 genes known to play a major role in regulating mitochondrial metabolism. Based on the outcomes, we then focused on miR‐382‐5p and identified pathways affected by its silencing using microarrays, investigated protein expression, and studied cellular respiration. Silencing of miRNA‐382‐5p significantly increased the expression of several genes involved in mitochondrial dynamics and biogenesis. Conventional microarray analysis in C2C12 myotubes silenced for miRNA‐382‐5p revealed a collective downregulation of mitochondrial ribosomal proteins and respiratory chain proteins. This effect was accompanied by an imbalance between mitochondrial proteins encoded by the nuclear and mitochondrial DNA (1.35‐fold, p < 0.01) and an induction of HSP60 protein (1.31‐fold, p < 0.05), indicating activation of the mitochondrial unfolded protein response (mtUPR). Furthermore, silencing of miR‐382‐5p reduced basal oxygen consumption rate by 14% ( p < 0.05) without affecting mitochondrial content, pointing towards a more efficient mitochondrial function as a result of improved mitochondrial quality control. Taken together, silencing of miR‐382‐5p induces a mitonuclear protein imbalance and activates the mtUPR in skeletal muscle, a phenomenon that was previously associated with improved longevity.

Multimodal imaging and high-throughput image-processing for drug screening on living organisms on-chip

A major step for the validation of medical drugs is the screening on whole organisms, which gives the systemic information that is missing when using cellular models. Caenorhabditis elegans is a soil worm that catches the interest of researchers who study systemic physiopathology (e.g., metabolic and neurodegenerative diseases) because: (1) its large genetic homology with humans supports translational analysis; (2) worms are much easier to handle and grow in large amounts compared with rodents, for which (3) the costs and (4) the ethical concerns are substantial. Here, we demonstrate how multimodal optical imaging on such an organism can provide high-content information relevant to the drug development pipeline (e.g., mode-of-action identification, dose-response analysis), especially when combined with on-chip multiplexing capability. After designing a microfluidic array to select small separated populations of C. elegans, we combine fluorescence and bright-field imaging along with high-throughput feature recognition and signal detection to enable the identification of the mode-of-action of an antibiotic. For this purpose, we use a genetically encoded fluorescence reporter of mitochondrial stress, which we studied in living specimens during their entire development. Furthermore, we demonstrate real-time, very large field-of-view capability on multiplexed motility assays for the assessment of the dose-response relation of an anesthetic.

De novo NAD+ synthesis enhances mitochondrial function and improves health

Nicotinamide adenine dinucleotide (NAD⁺) is a cosubstrate 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 the proportion of ACMS able to undergo spontaneous cyclisation in the de novo NAD⁺ synthesis pathway, controls cellular NAD⁺ levels via an evolutionary conserved mechanism from C. elegans to the mouse. Genetic and pharmacological inhibition of ACMSD boosts de novo NAD⁺ synthesis and SIRT1 activity, ultimately enhancing mitochondrial function. We furthermore characterized a series of potent and selective ACMSD inhibitors, which, given the restricted ACMSD expression in kidney and liver, are of high therapeutic interest to protect these tissues from injury. ACMSD hence is a key modulator of cellular NAD⁺ levels, sirtuin activity, and mitochondrial homeostasis in kidney and liver.

Abstract 060: Mitochondrial Deacetylase Sirt3 in Endothelial and Smooth Muscle Cells Protects From Vascular Dysfunction and Attenuates Hypertension

Vascular dysfunction plays a key role in the development of hypertension and heart disease which causes one-third of deaths worldwide. Cardiovascular disease risk factors reduce mitochondrial deacetylase Sirt3 and Sirt3 declines with age paralleling the increased incidence of cardiovascular disease and hypertension; however, the role of Sirt3 was largely ignored. We hypothesized that Sirt3 plays critical role in vascular dysfunction and hypertension. To test this hypothesis we have developed novel tamoxifen-inducible endothelium specific Sirt3 knockout (Ec Sirt3KO ), endothelial Sirt3 overexpressing (Ec Sirt3OX ), smooth muscle Sirt3 knockout (Smc Sirt3KO ), smooth muscle Sirt3 overexpressing (Smc Sirt3OX ) and global Sirt3 overexpressing (Sirt3OX) mice on C57Bl/6J background, and examined the effect of Sirt3 expression on vascular dysfunction and angiotensin II-induced hypertension. It was found that cell-specific Sirt3 depletion in endothelial and smooth muscle in Ec Sirt3KO and Smc Sirt3KO mice increases vascular permeability by 2-fold, raises T cell and monocyte vascular accumulation, diminishes endothelial NO and increases blood pressure by 10 mm Hg compared with wild-type Sham mice. Angiotensin II infusion in Ec Sirt3KO and Smc Sirt3KO mice caused vascular hyperpermeability, increased vascular hypertrophy, exacerbated endothelial dysfunction and hypertension. Meanwhile, Sirt3 overexpression reduced vascular permeability and diminished vascular inflammation compared to Sham wild-type mice. Sirt3 overexpression in endothelial and smooth muscle prevents angiotensin II-induced vascular hyperpermeability, inhibits vascular oxidative stress, preserves endothelial-dependent relaxation, diminishes vascular hypertrophy and attenuates hypertension by 20 mm Hg in angiotensin II-infused Ec Sirt3OX and Smc Sirt3OX mice compared with the wild-type littermates. Interestingly, Sirt3 depletion in human aortic endothelial cells and human vascular smooth muscle cells reduces expression of differentiation markers. We suggest that Sirt3 is central in redox and metabolic regulations of smooth muscle and endothelial cells. Our data support a therapeutic potential of targeting Sirt3 in vascular dysfunction and hypertension.

Genetic cartography of longevity in humans and mice: Current landscape and horizons

Aging is a complex and highly variable process. Heritability of longevity among humans and other species is low, and this finding has given rise to the idea that it may be futile to search for DNA variants that modulate aging. We argue that the problem in mapping longevity genes is mainly one of low power and the genetic and environmental complexity of aging. In this review we highlight progress made in mapping genes and molecular networks associated with longevity, paying special attention to work in mice and humans. We summarize 40 years of linkage studies using murine cohorts and 15 years of studies in human populations that have exploited candidate gene and genome-wide association methods. A small but growing number of gene variants contribute to known longevity mechanisms, but a much larger set have unknown functions. We outline these and other challenges and suggest some possible solutions, including more intense collaboration between research communities that use model organisms and human cohorts. Once hundreds of gene variants have been linked to differences in longevity in mammals, it will become feasible to systematically explore gene-by-environmental interactions, dissect mechanisms with more assurance, and evaluate the roles of epistasis and epigenetics in aging. A deeper understanding of complex networks-genetic, cellular, physiological, and social-should position us well to improve healthspan.

Enhanced longevity and metabolism by brown adipose tissue with disruption of the regulator of G protein signaling 14

Disruption of the regulator for G protein signaling 14 (RGS14) knockout (KO) in mice extends their lifespan and has multiple beneficial effects related to healthful aging, that is, protection from obesity, as reflected by reduced white adipose tissue, protection against cold exposure, and improved metabolism. The observed beneficial effects were mediated by improved mitochondrial function. But most importantly, the main mechanism responsible for the salutary properties of the RGS14 KO involved an increase in brown adipose tissue (BAT), which was confirmed by surgical BAT removal and transplantation to wild-type (WT) mice, a surgical simulation of a molecular knockout. This technique reversed the phenotype of the RGS14 KO and WT, resulting in loss of the improved metabolism and protection against cold exposure in RGS14 KO and conferring this protection to the WT BAT recipients. Another mechanism mediating the salutary features in the RGS14 KO was increased SIRT3. This mechanism was confirmed in the RGS14 X SIRT3 double KO, which no longer demonstrated improved metabolism and protection against cold exposure. Loss of function of the Caenorhabditis elegans RGS-14 homolog confirmed the evolutionary conservation of this mechanism. Thus, disruption of RGS14 is a model of healthful aging, as it not only enhances lifespan, but also protects against obesity and cold exposure and improves metabolism with a key mechanism of increased BAT, which, when removed, eliminates the features of healthful aging.

Loss of Sirt3 accelerates arterial thrombosis by increasing formation of neutrophil extracellular traps and plasma tissue factor activity

Aims

Sirtuin 3 (Sirt3) is a mitochondrial, nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase that reduces oxidative stress by activation of superoxide dismutase 2 (SOD2). Oxidative stress enhances arterial thrombosis. This study investigated the effects of genetic Sirt3 deletion on arterial thrombosis in mice in an inflammatory setting and assessed the clinical relevance of these findings in patients with ST-elevation myocardial infarction (STEMI).

Methods and results

Using a laser-induced carotid thrombosis model with lipopolysaccharide (LPS) challenge, in vivo time to thrombotic occlusion in Sirt3-/- mice (n = 6) was reduced by half compared to Sirt3+/+ wild-type (n = 8, P < 0.01) controls. Ex vivo analyses of whole blood using rotational thromboelastometry revealed accelerated clot formation and increased clot stability in Sirt3-/- compared to wild-type blood. rotational thromboelastometry of cell-depleted plasma showed accelerated clotting initiation in Sirt3-/- mice, whereas overall clot formation and firmness remained unaffected. Ex vivo LPS-induced neutrophil extracellular trap formation was increased in Sirt3-/- bone marrow-derived neutrophils. Plasma tissue factor (TF) levels and activity were elevated in Sirt3-/- mice, whereas plasma levels of other coagulation factors and TF expression in arterial walls remained unchanged. SOD2 expression in bone marrow -derived Sirt3-/- neutrophils was reduced. In STEMI patients, transcriptional levels of Sirt3 and its target SOD2 were lower in CD14+ leukocytes compared with healthy donors (n = 10 each, P < 0.01).

Conclusions

Sirt3 loss-of-function enhances experimental thrombosis in vivo via an increase of neutrophil extracellular traps and elevation of TF suggesting thrombo-protective effects of endogenous Sirt3. Acute coronary thrombosis in STEMI patients is associated with lower expression levels of SIRT3 and SOD2 in CD14+ leukocytes. Therefore, enhancing SIRT3 activity by pan-sirtuin activating NAD+-boosters may provide a novel therapeutic target to prevent or treat thrombotic arterial occlusion in myocardial infarction or stroke.

Increased Hepatic PDGF-AA Signaling Mediates Liver Insulin Resistance in Obesity-Associated Type 2 Diabetes

In type 2 diabetes (T2D), hepatic insulin resistance is strongly associated with nonalcoholic fatty liver disease (NAFLD). In this study, we hypothesized that the DNA methylome of livers from patients with T2D compared with livers of individuals with normal plasma glucose levels can unveil some mechanism of hepatic insulin resistance that could link to NAFLD. Using DNA methylome and transcriptome analyses of livers from obese individuals, we found that hypomethylation at a CpG site in PDGFA (encoding platelet-derived growth factor α) and PDGFA overexpression are both associated with increased T2D risk, hyperinsulinemia, increased insulin resistance, and increased steatohepatitis risk. Genetic risk score studies and human cell modeling pointed to a causative effect of high insulin levels on PDGFA CpG site hypomethylation, PDGFA overexpression, and increased PDGF-AA secretion from the liver. We found that PDGF-AA secretion further stimulates its own expression through protein kinase C activity and contributes to insulin resistance through decreased expression of insulin receptor substrate 1 and of insulin receptor. Importantly, hepatocyte insulin sensitivity can be restored by PDGF-AA-blocking antibodies, PDGF receptor inhibitors, and by metformin, opening therapeutic avenues. Therefore, in the liver of obese patients with T2D, the increased PDGF-AA signaling contributes to insulin resistance, opening new therapeutic avenues against T2D and possibly NAFLD.

Quantifying and Localizing the Mitochondrial Proteome Across Five Tissues in A Mouse Population

We have used SWATH mass spectrometry to quantify 3648 proteins across 76 proteomes collected from genetically diverse BXD mouse strains in two fractions (mitochondria and total cell) from five tissues: liver, quadriceps, heart, brain, and brown adipose (BAT). Across tissues, expression covariation between genes' proteins and transcripts-measured in the same individuals-broadly aligned. Covariation was however far stronger in certain subsets than others: only 8% of transcripts in the lowest expression and variance quintile covaried with their protein, in contrast to 65% of transcripts in the highest quintiles. Key functional differences among the 3648 genes were also observed across tissues, with electron transport chain (ETC) genes particularly investigated. ETC complex proteins covary and form strong gene networks according to tissue, but their equivalent transcripts do not. Certain physiological consequences, such as the depletion of ATP synthase in BAT, are thus obscured in transcript data. Lastly, we compared the quantitative proteomic measurements between the total cell and mitochondrial fractions for the five tissues. The resulting enrichment score highlighted several hundred proteins which were strongly enriched in mitochondria, which included several dozen proteins were not reported in literature to be mitochondrially localized. Four of these candidates were selected for biochemical validation, where we found MTAP, SOAT2, and IMPDH2 to be localized inside the mitochondria, whereas ABCC6 was in the mitochondria-associated membrane. These findings demonstrate the synergies of a multi-omics approach to study complex metabolic processes, and this provides a resource for further discovery and analysis of proteoforms, modified proteins, and protein localization.

Genetic Regulation of Plasma Lipid Species and Their Association with Metabolic Phenotypes

The genetic regulation and physiological impact of most lipid species are unexplored. Here, we profiled 129 plasma lipid species across 49 strains of the BXD mouse genetic reference population fed either chow or a high-fat diet. By integrating these data with genomics and phenomics datasets, we elucidated genes by environment (diet) interactions that regulate systemic metabolism. We found quantitative trait loci (QTLs) for ~94% of the lipids measured. Several QTLs harbored genes associated with blood lipid levels and abnormal lipid metabolism in human genome-wide association studies. Lipid species from different classes provided signatures of metabolic health, including seven plasma triglyceride species that associated with either healthy or fatty liver. This observation was further validated in an independent mouse model of non-alcoholic fatty liver disease (NAFLD) and in plasma from NAFLD patients. This work provides a resource to identify plausible genes regulating the measured lipid species and their association with metabolic traits.

Jha et al. provide a resource of genetic loci regulating individual plasma lipid species identified by studying a large mouse population and demonstrate the potential of lipid species to reflect metabolic health status of individuals. Several lipid-regulating loci in the mouse population harbor genes associated with abnormal lipid metabolism in human GWAS. The potential of lipid species to reflect health status was validated in dietary and therapeutic models of NAFLD in mice and human NAFLD patients.

Microfluidics-enabled phenotyping of a whole population of C. elegans worms over their embryonic and post-embryonic development at single-organism resolution

The organism Caenorhabditis elegans is a performant model system for studying human biological processes and diseases, but until now all phenome data are produced as population-averaged read-outs. Monitoring of individual responses to drug treatments would however be more informative. Here, a new strategy to track different phenotypic traits of individual C. elegans nematodes throughout their full life-cycle-i.e., embryonic and post-embryonic development, until adulthood onset, differently from life-span-is presented. In an automated fashion, single worms were synchronized, isolated, and cultured from egg to adulthood in a microfluidic device, where their identity was preserved during their whole development. Several phenotypes were monitored and quantified for each animal, resulting in high-content phenome data. Specifically, the method was validated by analyzing the response of C. elegans to doxycycline, an antibiotic fairly well-known to prolong the development and activate mitochondrial stress-response pathways in different species. Interestingly, the obtained extensive single-worm phenome not only confirmed the dramatic doxycycline effect on the worm developmental delay, but more importantly revealed subtle yet severe treatment-dependent phenotypes that are representative of minority subgroups and would have otherwise stayed hidden in an averaged dataset. Such heterogeneous response started during the embryonic development, which makes essential having a dedicated chip that allows including this early developmental stage in the drug assay. Our approach would therefore allow elucidating pharmaceutical or therapeutic responses that so far were still being overlooked.

Reduced oxidative capacity in macrophages results in systemic insulin resistance

Oxidative functions of adipose tissue macrophages control the polarization of M1-like and M2-like phenotypes, but whether reduced macrophage oxidative function causes systemic insulin resistance in vivo is not clear. Here, we show that mice with reduced mitochondrial oxidative phosphorylation (OxPhos) due to myeloid-specific deletion of CR6-interacting factor 1 (Crif1), an essential mitoribosomal factor involved in biogenesis of OxPhos subunits, have M1-like polarization of macrophages and systemic insulin resistance with adipose inflammation. Macrophage GDF15 expression is reduced in mice with impaired oxidative function, but induced upon stimulation with rosiglitazone and IL-4. GDF15 upregulates the oxidative function of macrophages, leading to M2-like polarization, and reverses insulin resistance in ob/ob mice and HFD-fed mice with myeloid-specific deletion of Crif1. Thus, reduced macrophage oxidative function controls systemic insulin resistance and adipose inflammation, which can be reversed with GDF15 and leads to improved oxidative function of macrophages.

M1-like polarization of macrophages is thought to control adipose inflammation and associated insulin resistance and metabolic syndrome. Here the authors show that macrophage-specific deletion of the OxPhos-related gene Crif1 results in an M1-like phenotype in mice, and that the effects can be reversed by recombinant GDF15.