Pten knockout in mouse preosteoblasts leads to changes in bone turnover and strength

Bone development and remodeling are controlled by the phosphoinositide-3-kinase (Pi3k) signaling pathway. We investigated the effects of downregulation of phosphatase and tensin homolog (Pten), a negative regulator of Pi3k signaling, in a mouse model of Pten deficiency in preosteoblasts. We aimed to identify mechanisms that are involved in the regulation of bone turnover and are linked to bone disorders. Femora, tibiae, and bone marrow stromal cells (BMSCs) isolated from mice with a conditional deletion of Pten (Pten cKO) in Osterix/Sp7-expressing osteoprogenitor cells were compared to Cre-negative controls. Bone phenotyping was performed by μCT measurements, bone histomorphometry, quantification of bone turnover markers CTX and procollagen type 1 N propeptide (P1NP), and three-point bending test. Proliferation of BMSCs was measured by counting nuclei and Ki-67-stained cells. In vitro, osteogenic differentiation capacity was determined by ALP staining, as well as by detecting gene expression of osteogenic markers. BMSCs from Pten cKO mice were functionally different from control BMSCs. Osteogenic markers were increased in BMSCs derived from Pten cKO mice, while Pten protein expression was lower and Akt phosphorylation was increased. We detected a higher trabecular bone volume and an altered cortical bone morphology in Pten cKO bones with a progressive decrease in bone and tissue mineral density. Pten cKO bones displayed fewer osteoclasts and more osteoblasts (P = .00095) per trabecular bone surface and a higher trabecular bone formation rate. Biomechanical analysis revealed a significantly higher bone strength (P = .00012 for males) and elasticity of Pten cKO femora. On the cellular level, both proliferation and osteogenic differentiation capacity of Pten cKO BMSCs were significantly increased compared to controls. Our findings suggest that Pten knockout in osteoprogenitor cells increases bone stability and elasticity by increasing trabecular bone mass and leads to increased proliferation and osteogenic differentiation of BMSCs.

Epilepsies of presumed genetic etiology show enrichment of rare variants that occur in the general population

Previous studies suggested that severe epilepsies, e.g., developmental and epileptic encephalopathies (DEEs), are mainly caused by ultra-rare de novo genetic variants. For milder disease, rare genetic variants could contribute to the phenotype. To determine the importance of rare variants for different epilepsy types, we analyzed a whole-exome sequencing cohort of 9,170 epilepsy-affected individuals and 8,436 control individuals. Here, we separately analyzed three different groups of epilepsies: severe DEEs, genetic generalized epilepsy (GGE), and non-acquired focal epilepsy (NAFE). We required qualifying rare variants (QRVs) to occur in control individuals with an allele count ≥ 1 and a minor allele frequency ≤ 1:1,000, to be predicted as deleterious (CADD ≥ 20), and to have an odds ratio in individuals with epilepsy ≥ 2. We identified genes enriched with QRVs primarily in NAFE (n = 72), followed by GGE (n = 32) and DEE (n = 21). This suggests that rare variants may play a more important role for causality of NAFE than for DEE. Moreover, we found that genes harboring QRVs, e.g., HSGP2, FLNA, or TNC, encode proteins that are involved in structuring the brain extracellular matrix. The present study confirms an involvement of rare variants for NAFE that occur also in the general population, while in DEE and GGE, the contribution of such variants appears more limited.

The role of rare genetic variants enrichment in epilepsies of presumed genetic etiology

Previous studies suggested that severe epilepsies e.g., developmental and epileptic encephalopathies (DEE) are mainly caused by ultra-rare de novo genetic variants. For milder phenotypes, rare genetic variants could contribute to the phenotype. To determine the importance of rare variants for different epilepsy types, we analyzed a whole-exome sequencing cohort of 9,170 epilepsy-affected individuals and 8,436 controls. Here, we separately analyzed three different groups of epilepsies : severe DEEs, genetic generalized epilepsy (GGE), and non-acquired focal epilepsy (NAFE). We required qualifying rare variants (QRVs) to occur in controls at a minor allele frequency ≤ 1:1,000, to be predicted as deleterious (CADD≥20), and to have an odds ratio in epilepsy cases ≥2. We identified genes enriched with QRVs in DEE (n=21), NAFE (n=72), and GGE (n=32) - the number of enriched genes are found greatest in NAFE and least in DEE. This suggests that rare variants may play a more important role for causality of NAFE than in DEE. Moreover, we found that QRV-carrying genes e.g., HSGP2, FLNA or TNC are involved in structuring the brain extracellular matrix. The present study confirms an involvement of rare variants for NAFE, while in DEE and GGE, the contribution of such variants appears more limited.

Phospholipid Scramblase 4 (PLSCR4) Regulates Adipocyte Differentiation via PIP3-Mediated AKT Activation

Phospholipid scramblase 4 (PLSCR4) is a member of a conserved enzyme family with high relevance for the remodeling of phospholipid distribution in the plasma membrane and the regulation of cellular signaling. While PLSCR1 and -3 are involved in the regulation of adipose-tissue expansion, the role of PLSCR4 is so far unknown. PLSCR4 is significantly downregulated in an adipose-progenitor-cell model of deficiency for phosphatase and tensin homolog (PTEN). PTEN acts as a tumor suppressor and antagonist of the growth and survival signaling phosphoinositide 3-kinase (PI3K)/AKT cascade by dephosphorylating phosphatidylinositol-3,4,5-trisphosphate (PIP3). Patients with PTEN germline deletion frequently develop lipomas. The underlying mechanism for this aberrant adipose-tissue growth is incompletely understood. PLSCR4 is most highly expressed in human adipose tissue, compared with other phospholipid scramblases, suggesting a specific role of PLSCR4 in adipose-tissue biology. In cell and mouse models of lipid accumulation, we found PLSCR4 to be downregulated. We observed increased adipogenesis in PLSCR4-knockdown adipose progenitor cells, while PLSCR4 overexpression attenuated lipid accumulation. PLSCR4 knockdown was associated with increased PIP3 levels and the activation of AKT. Our results indicated that PLSCR4 is a regulator of PI3K/AKT signaling and adipogenesis and may play a role in PTEN-associated adipose-tissue overgrowth and lipoma formation.

Altered gene expression profiles impair the nervous system development in individuals with 15q13.3 microdeletion

The 15q13.3 microdeletion has pleiotropic effects ranging from apparently healthy to severely affected individuals. The underlying basis of the variable phenotype remains elusive. We analyzed gene expression using blood from three individuals with 15q13.3 microdeletion and brain cortex tissue from ten mice Df[h15q13]/+. We assessed differentially expressed genes (DEGs), protein–protein interaction (PPI) functional modules, and gene expression in brain developmental stages. The deleted genes’ haploinsufficiency was not transcriptionally compensated, suggesting a dosage effect may contribute to the pathomechanism. DEGs shared between tested individuals and a corresponding mouse model show a significant overlap including genes involved in monogenic neurodevelopmental disorders. Yet, network-wide dysregulatory effects suggest the phenotype is not caused by a single critical gene. A significant proportion of blood DEGs, silenced in adult brain, have maximum expression during the prenatal brain development. Based on DEGs and their PPI partners we identified altered functional modules related to developmental processes, including nervous system development. We show that the 15q13.3 microdeletion has a ubiquitous impact on the transcriptome pattern, especially dysregulation of genes involved in brain development. The high phenotypic variability seen in 15q13.3 microdeletion could stem from an increased vulnerability during brain development, instead of a specific pathomechanism.

Small integral membrane protein 10 like 1 downregulation enhances differentiation of adipose progenitor cells

Small integral membrane protein 10 like 1 (SMIM10L1) was identified by RNA sequencing as the most significantly downregulated gene in Phosphatase and Tensin Homologue (PTEN) knockdown adipose progenitor cells (APCs). PTEN is a tumor suppressor that antagonizes the growth promoting Phosphoinositide 3-kinase (PI3K)/AKT/mechanistic Target of Rapamycin (mTOR) cascade. Diseases caused by germline pathogenic variants in PTEN are summarized as PTEN Hamartoma Tumor Syndrome (PHTS). This overgrowth syndrome is associated with lipoma formation, especially in pediatric patients. The mechanisms underlying this adipose tissue dysfunction remain elusive. We observed that SMIM10L1 downregulation in APCs led to an enhanced adipocyte differentiation in two- and three-dimensional cell culture and increased expression of adipogenesis markers. Furthermore, SMIM10L1 knockdown cells showed a decreased expression of PTEN, pointing to a mutual crosstalk between PTEN and SMIM10L1. In line with these observations, SMIM10L1 knockdown cells showed increased activation of PI3K/AKT/mTOR signaling and concomitantly increased expression of the adipogenic transcription factor SREBP1. We computationally predicted an α-helical structure and membrane association of SMIM10L1. These results support a specific role for SMIM10L1 in regulating adipogenesis, potentially by increasing PI3K/AKT/mTOR signaling, which might be conducive to lipoma formation in pediatric patients with PHTS.

Pediatric percentiles for transient elastography measurements - effects of age, sex, weight status and pubertal stage

BACKGROUND AND AIMS

Transient Elastography is a non-invasive, cost-efficient, non-ionizing, observer-independent and reliable method to detect liver fibrosis using Liver Stiffness Measurement (LSM) and the degree of fat accumulation in the liver using Controlled Attenuation Parameter (CAP). This study aims to derive reference values for both measures from healthy children and adolescents. Further, we aim to assess the potential influence of age, sex, puberty, and BMI-SDS on CAP and LSM.

METHODS

Within the LIFE Child study, amongst others, anthropometric data and pubertal status were assessed. Transient Elastography (TE) was performed using the FibroScan^® device in a population-based cohort at 982 study visits of 482 healthy children aged between 10 and 18 years. Percentiles for LSM and CAP were estimated, and the effects of age, sex, puberty and weight status were assessed through hierarchical regression models.

RESULTS

There was a strong age dependency for LSM with higher values for older children, most pronounced in the upper percentiles in boys. Contrarily, CAP was relatively stable across the age span without considerable difference between boys and girls. We found a significant positive correlation between BMI-SDS and both CAP and LSM for BMI-SDS >1.28. For BMI-SDS < 1.28, the association was also positive but reached statistical significance only for CAP. Further, the association between BMI-SDS and CAP was significantly stronger in younger than in older children. There was no association between pubertal status and CAP. For LSM, we found that children with a high BMI-SDS but not children with normal weight had significantly higher LSM values in Tanner stage 4.

CONCLUSIONS

Age, sex, pubertal status and weight status should be considered when interpreting LSM and CAP in pediatric patients to facilitate and improve early detection of abnormal liver function, which is associated with common pathologies, such as NAFLD.

Phenotype-tissue expression and exploration (PTEE) resource facilitates the choice of tissue for RNA-seq-based clinical genetics studies

BACKGROUND

RNA-seq emerges as a valuable method for clinical genetics. The transcriptome is "dynamic" and tissue-specific, but typically the probed tissues to analyze (TA) are different from the tissue of interest (TI) based on pathophysiology.

RESULTS

We developed Phenotype-Tissue Expression and Exploration (PTEE), a tool to facilitate the decision about the most suitable TA for RNA-seq. We integrated phenotype-annotated genes, used 54 tissues from GTEx to perform correlation analyses and identify expressed genes and transcripts between TAs and TIs. We identified skeletal muscle as the most appropriate TA to inquire for cardiac arrhythmia genes and skin as a good proxy to study neurodevelopmental disorders. We also explored RNA-seq limitations and show that on-off switching of gene expression during ontogenesis or circadian rhythm can cause blind spots for RNA-seq-based analyses.

CONCLUSIONS

PTEE aids the identification of tissues suitable for RNA-seq for a given pathology to increase the success rate of diagnosis and gene discovery. PTEE is freely available at https://bioinf.eva.mpg.de/PTEE/.

Obesity-An Update on the Basic Pathophysiology and Review of Recent Therapeutic Advances

Obesity represents a major public health problem with a prevalence increasing at an alarming rate worldwide. Continuous intensive efforts to elucidate the complex pathophysiology and improve clinical management have led to a better understanding of biomolecules like gut hormones, antagonists of orexigenic signals, stimulants of fat utilization, and/or inhibitors of fat absorption. In this article, we will review the pathophysiology and pharmacotherapy of obesity including intersection points to the new generation of antidiabetic drugs. We provide insight into the effectiveness of currently approved anti-obesity drugs and other therapeutic avenues that can be explored.

Nicotinamide riboside has minimal impact on energy metabolism in mouse models of mild obesity

Supplementation with precursors of NAD has been shown to prevent and reverse insulin resistance, mitochondrial dysfunction, and liver damage in mouse models of diet-induced obesity. We asked whether the beneficial effects of supplementation with the NAD precursor nicotinamide riboside (NR) are dependent on mouse strain. We compared the effects of NR supplementation on whole-body energy metabolism and mitochondrial function in mildly obese C57BL/6N and C57BL/6J mice, two commonly used strains to investigate metabolism. Male C57BL/6N and C57BL/6J mice were fed a high-fat diet (HFD) or standard chow with or without NR supplementation for 8 weeks. Body and organ weights, glucose tolerance, and metabolic parameters as well as mitochondrial O2 flux in liver and muscle fibers were assessed. We found that NR supplementation had no influence on body or organ weight, glucose metabolism or hepatic lipid accumulation, energy expenditure, or metabolic flexibility but increased mitochondrial respiration in soleus muscle in both mouse strains. Strain-dependent differences were detected for body and fat depot weight, fasting blood glucose, hepatic lipid accumulation, and energy expenditure. We conclude that, in mild obesity, NR supplementation does not alter metabolic phenotype in two commonly used laboratory mouse strains.

PTEN regulates adipose progenitor cell growth, differentiation, and replicative aging

The tumor suppressor phosphatase and tensin homolog (PTEN) negatively regulates the insulin signaling pathway. Germline PTEN pathogenic variants cause PTEN hamartoma tumor syndrome (PHTS), associated with lipoma development in children. Adipose progenitor cells (APCs) lose their capacity to differentiate into adipocytes during continuous culture, whereas APCs from lipomas of patients with PHTS retain their adipogenic potential over a prolonged period. It remains unclear which mechanisms trigger this aberrant adipose tissue growth. To investigate the role of PTEN in adipose tissue development, we performed functional assays and RNA-Seq of control and PTEN knockdown APCs. Reduction of PTEN levels using siRNA or CRISPR led to enhanced proliferation and differentiation of APCs. Forkhead box protein O1 (FOXO1) transcriptional activity is known to be regulated by insulin signaling, and FOXO1 was downregulated at the mRNA level while its inactivation through phosphorylation increased. FOXO1 phosphorylation initiates the expression of the lipogenesis-activating transcription factor sterol regulatory element-binding protein 1 (SREBP1). SREBP1 levels were higher after PTEN knockdown and may account for the observed enhanced adipogenesis. To validate this, we overexpressed constitutively active FOXO1 in PTEN CRISPR cells and found reduced adipogenesis, accompanied by SREBP1 downregulation. We observed that PTEN CRISPR cells showed less senescence compared with controls and the senescence marker CDKN1A (p21) was downregulated in PTEN knockdown cells. Cellular senescence was the most significantly enriched pathway found in RNA-Seq of PTEN knockdown versus control cells. These results provide evidence that PTEN is involved in the regulation of APC proliferation, differentiation, and senescence, thereby contributing to aberrant adipose tissue growth in patients with PHTS.

Tolerogenic effects of 1,25-dihydroxyvitamin D on dendritic cells involve induction of fatty acid synthesis

The active form of vitamin D, 1,25-dihydroxyvitamin D (1,25D) is a potent regulator of immune function, promoting anti-inflammatory, tolerogenic T cell responses by modulating antigen presentation by dendritic cells (DC). Transcriptomic analyses indicate that DC responses to 1,25D involve changes in glycolysis, oxidative phosphorylation, electron transport and the TCA cycle. To determine the functional impact of 1,25D-mediated metabolic remodelling, human monocyte-derived DC were differentiated to immature (+vehicle, iDC), mature (+LPS, mDC), and immature tolerogenic DC (+1,25D, itolDC) and characterised for metabolic function. In contrast to mDC which showed no change in respiration, itolDC showed increased basal and ATP-linked respiration relative to iDC. Tracer metabolite analyses using 13C -labeled glucose showed increased lactate and TCA cycle metabolites. Analysis of lipophilic metabolites of 13C-glucose revealed significant incorporation of label in palmitate and palmitoleate, indicating that 1,25D promotes metabolic fatty acid synthesis in itolDC. Inhibition of fatty acid synthesis in itolDC altered itolDC morphology and suppressed expression of CD14 and IL-10 by these cells. These data indicate that the ability of 1,25D to induce tolerogenic DC involves metabolic remodelling leading to synthesis of fatty acids.

A new human adipocyte model with PTEN haploinsufficiency

Few human cell strains are suitable and readily available as in vitro adipocyte models. We used resected lipoma tissue from a patient with germline phosphatase and tensin homolog (PTEN) haploinsufficiency to establish a preadipocyte cell strain termed LipPD1 and aimed to characterize cellular functions and signalling pathway alterations in comparison to the established adipocyte model Simpson-Golabi-Behmel-Syndrome (SGBS) and to primary stromal-vascular fraction cells. We found that both cellular life span and the capacity for adipocyte differentiation as well as adipocyte-specific functions were preserved in LipPD1 and comparable to SGBS adipocytes. Basal and growth factor-stimulated activation of the PI3 K/AKT signalling pathway was increased in LipPD1 preadipocytes, corresponding to reduced PTEN levels in comparison to SGBS cells. Altogether, LipPD1 cells are a novel primary cell model with a defined genetic lesion suitable for the study of adipocyte biology.

How Reliable are Commercially Available Glypican4 ELISA Kits?

OBJECTIVE

Glypican4 is an interesting new adipokine, which seems to play an important role in developmental processes and is potentially associated with metabolic changes in obesity and type 2 diabetes mellitus. Currently, only a few studies examined glypican4 in human blood, mainly in adults.

DESIGN, PATIENTS AND MEASUREMENTS

The aim of our study was to investigate glypican4 serum levels in lean, overweight, and obese children and adolescents, to unravel a possible association between glypican4 serum levels and parameters of obesity and insulin resistance. In order to determine a suitable method for investigating glypican4 serum levels, we validated two commercially available human glypican4 ELISA kits, using serum and plasma samples of an obese, insulin-resistant patient, and a healthy control subject, a human recombinant glypican4 protein fragment and glypican4-overexpressing cell lysate.

RESULTS

Using ELISA kit #1 we were not able to detect values above background level, apart from standard curve values. ELISA kit #2 initially seemed suitable to measure glypican4, but further validation experiments showed non-linearity of serial dilutions, no recognition of a human recombinant glypican4 protein fragment and non-linearity in the recovery of glypican4-overexpressing cell lysate. In addition, there was a considerable decrease (approx. 68%) of measured values between two experiments, performed at different time points with aliquots of the same serum sample. Contrary to that, further experiments found sample stability not to be compromised.

CONCLUSIONS

Extensive evaluation of the performance of two commercially available ELISA kits led to the conclusion that none of them is applicable for the measurement of glypican4 in human blood samples.

Nicotinamide Riboside Augments the Aged Human Skeletal Muscle NAD+ Metabolome and Induces Transcriptomic and Anti-inflammatory Signatures

Nicotinamide adenine dinucleotide (NAD⁺) is modulated by conditions of metabolic stress and has been reported to decline with aging in preclinical models, but human data are sparse. Nicotinamide riboside (NR) supplementation ameliorates metabolic dysfunction in rodents. We aimed to establish whether oral NR supplementation in aged participants can increase the skeletal muscle NAD⁺ metabolome and if it can alter muscle mitochondrial bioenergetics. We supplemented 12 aged men with 1 g NR per day for 21 days in a placebo-controlled, randomized, double-blind, crossover trial. Targeted metabolomics showed that NR elevated the muscle NAD⁺ metabolome, evident by increased nicotinic acid adenine dinucleotide and nicotinamide clearance products. Muscle RNA sequencing revealed NR-mediated downregulation of energy metabolism and mitochondria pathways, without altering mitochondrial bioenergetics. NR also depressed levels of circulating inflammatory cytokines. Our data establish that oral NR is available to aged human muscle and identify anti-inflammatory effects of NR.

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NR supplementation in aged subjects augments the skeletal muscle NAD⁺ metabolome

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NR supplementation does not affect skeletal muscle mitochondrial bioenergetics

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NR supplementation reduces levels of circulating inflammatory cytokines

OR03-06 NAD+ Availability Modulates 11β-HSD1-Mediated Glucocorticoid Regeneration in Mouse Skeletal Muscle

11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) is an NADPH-dependant reductase located in the sarcoplasmic reticulum (SR) lumen of skeletal muscle. It generates active glucocorticoids to regulate permissive and adaptive metabolism and contributes to the development of the Cushing’s syndrome phenotype in mice receiving oral corticosterone. The SR enzyme hexose-6-phosphate dehydrogenase (H6PDH) generates NADPH which supports 11β-HSD1 activity. H6PDH depletion disrupts the SR NADPH/NADP ratio leading 11β-HSD1 to assume glucocorticoid-inactivating dehydrogenase activity. Little is understood regarding routes to NAD(P)(H) biosynthesis and metabolism in the SR. Here we asked whether modulating cellular nicotinamide adenine dinucleotide (NAD+) availability (the parent molecule of NAD(P)(H)) would influence muscle 11β-HSD1 activity given its sensitivity to the SR NADPH/NADP ratio. We used FK866 to inhibit nicotinamide phospho-ribosyltransferase (NAMPT, rate-limiting enzyme in NAD+ biosynthesis) to deplete NAD(P)(H) in wild type mouse primary myotubes. FK866 treatment for 48h impaired cellular energetic status, reducing NAD+ (>90%), NADP+ (>50%) and ATP (>30%) without limiting cell viability. 11β-HSD1 reductase activity was decreased to 30% that of untreated cells (152±18 vs. 512±44 pmol/mg protein/h respectively, p<0.005). Employing H6PD knockout myotubes, NADP+-dependent 11β-HSD1 dehydrogenase activity was also impaired following NAMPT inhibition. The NAD+ precursor nicotinamide riboside (NR, 0.5mM), which bypasses NAMPT inhibition through the NR kinase pathway restored NAD+ levels and rapidly rescued 11β-HSD1 reductase activity in wild type and dehydrogenase activity in H6PD knockout myotubes. To assess this in vivo, we examined 11β-HSD1 reductase activity in muscle explants of inducible muscle-specific NAMPT knockout mice in which NAD+ levels are reduced by 90%, and show 40% lower activity compared to wild type explants (114±14 vs. 67±10 pmol/mg protein/h, p=0.04). These data suggest a novel level of redox-regulated 11β-HSD1-mediated glucocorticoid metabolism in skeletal muscle. These data also imply a pathway by which NAD+ status is communicated between the cytosol and the SR, which is contrary to the current belief that the pyridine nucleotide pool in these compartments is separate. NAMPT inhibition is being studied as a potential anti-cancer therapy and these data reveal hitherto unanticipated effects this therapy may have in a range of tissues.

Relation of Whole Blood Amino Acid and Acylcarnitine Metabolome to Age, Sex, BMI, Puberty, and Metabolic Markers in Children and Adolescents

Background: Changes in the metabolic fingerprint of blood during child growth and development are a largely under-investigated area of research. The examination of such aspects requires a cohort of healthy children and adolescents who have been subjected to deep phenotyping, including collection of biospecimens for metabolomic analysis. The present study considered whether amino acid (AA) and acylcarnitine (AC) concentrations are associated with age, sex, body mass index (BMI), and puberty during childhood and adolescence. It also investigated whether there are associations between amino acids (AAs) and acylcarnitines (ACs) and laboratory parameters of glucose and lipid metabolism, as well as liver, kidney, and thyroid parameters. Methods: A total of 3989 dried whole blood samples collected from 2191 healthy participants, aged 3 months to 18 years, from the LIFE Child cohort (Leipzig, Germany) were analyzed using liquid chromatography tandem mass spectrometry to detect levels of 23 AAs, 6 ACs, and free carnitine (C0). Age- and sex-related percentiles were estimated for each metabolite. In addition, correlations between laboratory parameters and levels of the selected AAs and ACs were calculated using hierarchical models. Results: Four different age-dependent profile types were identified for AAs and ACs. Investigating the association with puberty, we mainly identified peak metabolite levels at Tanner stages 2 to 3 in girls and stages 3 to 5 in boys. Significant correlations were observed between BMI standard deviation score (BMI-SDS) and certain metabolites, among them, branched-chain (leucine/isoleucine, valine) and aromatic (phenylalanine, tyrosine) amino acids. Most of the metabolites correlated significantly with absolute concentrations of glucose, glycated hemoglobin (HbA1c), triglycerides, cystatin C (CysC), and creatinine. After age adjustment, significant correlations were observed between most metabolites and CysC, as well as HbA1c. Conclusions: During childhood, several AA and AC levels are related to age, sex, BMI, and puberty. Moreover, our data verified known associations but also revealed new correlations between AAs/ACs and specific key markers of metabolic function.

Induction of the nicotinamide riboside kinase NAD+ salvage pathway in a model of sarcoplasmic reticulum dysfunction

Background

Hexose-6-Phosphate Dehydrogenase (H6PD) is a generator of NADPH in the Endoplasmic/Sarcoplasmic Reticulum (ER/SR). Interaction of H6PD with 11β-hydroxysteroid dehydrogenase type 1 provides NADPH to support oxo-reduction of inactive to active glucocorticoids, but the wider understanding of H6PD in ER/SR NAD(P)(H) homeostasis is incomplete. Lack of H6PD results in a deteriorating skeletal myopathy, altered glucose homeostasis, ER stress and activation of the unfolded protein response. Here we further assess muscle responses to H6PD deficiency to delineate pathways that may underpin myopathy and link SR redox status to muscle wide metabolic adaptation.

Methods

We analysed skeletal muscle from H6PD knockout (H6PDKO), H6PD and NRK2 double knockout (DKO) and wild-type (WT) mice. H6PDKO mice were supplemented with the NAD⁺ precursor nicotinamide riboside. Skeletal muscle samples were subjected to biochemical analysis including NAD(H) measurement, LC-MS based metabolomics, Western blotting, and high resolution mitochondrial respirometry. Genetic and supplement models were assessed for degree of myopathy compared to H6PDKO.

Results

H6PDKO skeletal muscle showed adaptations in the routes regulating nicotinamide and NAD⁺ biosynthesis, with significant activation of the Nicotinamide Riboside Kinase 2 (NRK2) pathway. Associated with changes in NAD⁺ biosynthesis, H6PDKO muscle had impaired mitochondrial respiratory capacity with altered mitochondrial acylcarnitine and acetyl-CoA metabolism. Boosting NAD⁺ levels through the NRK2 pathway using the precursor nicotinamide riboside elevated NAD⁺/NADH but had no effect to mitigate ER stress and dysfunctional mitochondrial respiratory capacity or acetyl-CoA metabolism. Similarly, H6PDKO/NRK2 double KO mice did not display an exaggerated timing or severity of myopathy or overt change in mitochondrial metabolism despite depression of NAD⁺ availability.

Conclusions

These findings suggest a complex metabolic response to changes in muscle SR NADP(H) redox status that result in impaired mitochondrial energy metabolism and activation of cellular NAD⁺ salvage pathways. It is possible that SR can sense and signal perturbation in NAD(P)(H) that cannot be rectified in the absence of H6PD. Whether NRK2 pathway activation is a direct response to changes in SR NAD(P)(H) availability or adaptation to deficits in metabolic energy availability remains to be resolved.

Direct physical interaction of active Ras with mSIN1 regulates mTORC2 signaling

Background

The mechanistic (or mammalian) target of rapamycin (mTOR), a Ser/Thr kinase, associates with different subunits forming two functionally distinct complexes, mTORC1 and mTORC2, regulating a diverse set of cellular functions in response to growth factors, cellular energy levels, and nutrients. The mechanisms regulating mTORC1 activity are well characterized; regulation of mTORC2 activity, however, remains obscure. While studies conducted in Dictyostelium suggest a possible role of Ras protein as a potential upstream regulator of mTORC2, definitive studies delineating the underlying molecular mechanisms, particularly in mammalian cells, are still lacking.

Methods

Protein levels were measured by Western blotting and kinase activity of mTORC2 was analyzed by in vitro kinase assay. In situ Proximity ligation assay (PLA) and co-immunoprecipitation assay was performed to detect protein-protein interaction. Protein localization was investigated by immunofluorescence and subcellular fractionation while cellular function of mTORC2 was assessed by assaying extent of cell migration and invasion.

Results

Here, we present experimental evidence in support of the role of Ras activation as an upstream regulatory switch governing mTORC2 signaling in mammalian cancer cells. We report that active Ras through its interaction with mSIN1 accounts for mTORC2 activation, while disruption of this interaction by genetic means or via peptide-based competitive hindrance, impedes mTORC2 signaling.

Conclusions

Our study defines the regulatory role played by Ras during mTORC2 signaling in mammalian cells and highlights the importance of Ras-mSIN1 interaction in the assembly of functionally intact mTORC2.

The Novel Phosphatidylinositol-3-Kinase (PI3K) Inhibitor Alpelisib Effectively Inhibits Growth of PTEN-Haploinsufficient Lipoma Cells

Germline mutations in the tumor suppressor gene PTEN cause PTEN Hamartoma Tumor Syndrome (PHTS). Pediatric patients with PHTS frequently develop lipomas. Treatment attempts with the mTORC1 inhibitor rapamycin were unable to reverse lipoma growth. Recently, lipomas associated with PIK3CA-related overgrowth syndrome were successfully treated with the novel PI3K inhibitor alpelisib. Here, we tested whether alpelisib has growth-restrictive effects and induces cell death in lipoma cells. We used PTEN-haploinsufficient lipoma cells from three patients and treated them with alpelisib alone or in combination with rapamycin. We tested the effect of alpelisib on viability, proliferation, cell death, induction of senescence, adipocyte differentiation, and signaling at 1-100 µM alpelisib. Alpelisib alone or in combination with rapamycin reduced proliferation in a concentration- and time-dependent manner. No cell death but an induction of senescence was detected after alpelisib incubation for 72 h. Alpelisib treatment led to a reduced phosphorylation of AKT, mTOR, and ribosomal protein S6. Rapamycin treatment alone led to increased AKT phosphorylation. This effect could be reversed by combining rapamycin with alpelisib. Alpelisib reduced the size of lipoma spheroids by attenuating adipocyte differentiation. Since alpelisib was well tolerated in first clinical trials, this drug alone or in combination with rapamycin is a potential new treatment option for PHTS-related adipose tissue overgrowth.

Metabolic tracing reveals novel adaptations to skeletal muscle cell energy production pathways in response to NAD + depletion

Background: Skeletal muscle is central to whole body metabolic homeostasis, with age and disease impairing its ability to function appropriately to maintain health. Inadequate NAD + availability is proposed to contribute to pathophysiology by impairing metabolic energy pathway use. Despite the importance of NAD + as a vital redox cofactor in energy production pathways being well-established, the wider impact of disrupted NAD + homeostasis on these pathways is unknown. Methods: We utilised skeletal muscle myotube models to induce NAD + depletion, repletion and excess and conducted metabolic tracing to provide comprehensive and detailed analysis of the consequences of altered NAD + metabolism on central carbon metabolic pathways. We used stable isotope tracers, [1,2-13C] D-glucose and [U- 13C] glutamine, and conducted combined 2D-1H,13C-heteronuclear single quantum coherence (HSQC) NMR spectroscopy and GC-MS analysis. Results: NAD + excess driven by nicotinamide riboside (NR) supplementation within skeletal muscle cells resulted in enhanced nicotinamide clearance, but had no effect on energy homeostasis or central carbon metabolism. Nicotinamide phosphoribosyltransferase (NAMPT) inhibition induced NAD + depletion and resulted in equilibration of metabolites upstream of glyceraldehyde phosphate dehydrogenase (GAPDH). Aspartate production through glycolysis and TCA cycle activity was increased in response to low NAD +, which was rapidly reversed with repletion of the NAD + pool using NR. NAD + depletion reversibly inhibits cytosolic GAPDH activity, but retains mitochondrial oxidative metabolism, suggesting differential effects of this treatment on sub-cellular pyridine pools. When supplemented, NR efficiently reversed these metabolic consequences. However, the functional relevance of increased aspartate levels after NAD + depletion remains unclear, and requires further investigation. Conclusions: These data highlight the need to consider carbon metabolism and clearance pathways when investigating NAD + precursor usage in models of skeletal muscle physiology.

Sorafenib-Induced Apoptosis in Hepatocellular Carcinoma Is Reversed by SIRT1

Sorafenib is a multi-kinase inhibitor and one of the few systemic treatment options for patients with advanced hepatocellular carcinomas (HCCs). Resistance to sorafenib develops frequently and could be mediated by the nicotinamide adenine dinucleotide (NAD)-dependent deacetylase sirtuin (SIRT)1. We aimed to test whether sorafenib efficacy is influenced by cellular NAD levels and NAD-dependent SIRT1 function. We analyzed sorafenib effects on apoptosis induction, NAD salvage, mitochondrial function, and related signaling pathways in HCC cell lines (HepG2, Hep3B, und HUH7) overexpressing SIRT1 or supplemented with the NAD metabolite nicotinamide mononucleotide (NMN) compared to controls. Treatment of HCC cell lines with sorafenib dose-dependently induced apoptosis and a significant decrease in cellular NAD concentrations. The SIRT1 protein was downregulated in HUH7 cells but not in Hep3B cells. After sorafenib treatment, mitochondrial respiration in permeabilized cells was lower, citrate synthase activity was attenuated, and cellular adenosine triphosphate (ATP) levels were decreased. Concomitant to increased phosphorylation of adenosine monophosphate (AMP)-activated protein kinase (AMPK), sorafenib treatment led to decreased activity of the mechanistic target of rapamycin (mTOR), indicative of energy deprivation. Transient overexpression of SIRT1, as well as NAD repletion by NMN, decreased sorafenib-induced apoptosis. We can, therefore, conclude that sorafenib influences the NAD/SIRT1/AMPK axis. Overexpression of SIRT1 could be an underlying mechanism of resistance to sorafenib treatment in HCC.

NAD metabolites interfere with proliferation and functional properties of THP-1 cells

Over the past few years the NAD-related compounds nicotinamide (NAM), nicotinamide riboside (NR) and 1-methylnicotinamide (MNA) have been established as important molecules in signalling pathways that contribute to metabolic functions of many cells, including those of the immune system. Among immune cells, monocytes/macrophages, which are the major players of inflammatory processes, are especially susceptible to the anti-inflammatory action of NAM. Here we asked whether NAM and the two other compounds have the potential to regulate differentiation and LPS-induced biological answers of the monocytic cell line THP-1. We show that treatment of THP-1 cells with NAM, NR and MNA resulted in growth retardation accompanied by enrichment of cells in the G0/G1-phase independent of p21 and p53. NAM and NR caused an increase in intracellular NAD concentrations and SIRT1 and PARP1 mRNA expression was found to be enhanced. The compounds failed to up-regulate the expression of the cell surface differentiation markers CD38, CD11b and CD14. They modulated the reactive oxygen species production and primed the cells to respond less effectively to the LPS induced TNF-α production. Our data show that the NAD metabolites interfere with early events associated with differentiation of THP-1 cells along the monocytic path and that they affect LPS-induced biological responses of the cell line.

SUN-109 PTEN Regulates Differentiation and Proliferation of Aging Preadipocytes

Background: The tumor suppressor gene phosphatase and tensin homologe (PTEN) is one of the most frequently altered genes in human cancer. It antagonizes the PI3K/AKT/mTOR pathway, which is activated by various factors like IGF-1 or insulin and promotes cell growth and proliferation. Germline PTEN mutations cause the PTEN hamartoma tumor syndrome, characterized by an overgrowth of different soft tissues. This includes the formation of lipomas. To understand these adipose tissue malformations we aim to assess the function of PTEN in the context of preadipocyte proliferation, differentiation and senescence. Methods: We used preadipocytes obtained from healthy individuals and reduced the PTEN levels either transiently by siRNA mediated PTEN knock-down or stably using the CRISPR/Cas9 system. Results: Reduced PTEN levels (0.59 ± 0.03 fold) led to an increased proliferation of the preadipocytes as measured by nuclei counting (1.5 ± 0.2 fold after 7 days) and staining of the proliferation marker Ki-67 (1,09 ± 0.01 fold). Moreover, the adipocyte differentiation capacity of low passage preadipocytes was increased after PTEN knock-down (1.14 ± 0.04 fold lipid accumulation) compared to control transfected cells. Differentiation capacity could even be restored in high passage presenescent cells that had already lost their ability to differentiate (1.41 ± 0.14 fold lipid accumulation). This corresponded with an increase in the adipocyte differentiation marker PPARy, as analyzed via qPCR (1.8 ± 0.4 fold). We not only observed an activation of AKT signaling (enhanced AKT and ribosomal protein S6 phosphorylation) in PTEN knock-down cells, but noticed a decrease of the senescence marker p21 (0.4 ± 0.09 fold) and an increase in the NAD-synthesis enzyme NAMPT (visfatin) (1.28 ± 0.06 fold) suggesting a role of PTEN in regulating cellular lifespan. To address the question, if PTEN plays a role not only in disease but also in normal preadipocyte function, we measured PTEN protein levels in cells of different passages. During long-term culture PTEN levels increased (3.7 ± 0.7 fold after 25 days), resulting in a decreased AKT phosphorylation (0.4 ± 0.3 fold). Levels of NAMPT decreased during long-term culture (0.04 ± 0.02 fold). Conclusion: Considering the observations in normal preadipocytes during cellular aging and the findings in PTEN knock-down cells, our results provide strong evidence that PTEN is involved in regulation of preadipocyte aging.

SIRT6 deacetylase activity regulates NAMPT activity and NAD(P)(H) pools in cancer cells

Nicotinamide phosphoribosyltransferase (NAMPT) is the rate-limiting enzyme in the NAD⁺ salvage pathway from nicotinamide. By controlling the biosynthesis of NAD⁺, NAMPT regulates the activity of NAD⁺-converting enzymes, such as CD38, poly-ADP-ribose polymerases, and sirtuins (SIRTs). SIRT6 is involved in the regulation of a wide number of metabolic processes. In this study, we investigated the ability of SIRT6 to regulate intracellular NAMPT activity and NAD(P)(H) levels. BxPC-3 cells and MCF-7 cells were engineered to overexpress a catalytically active or a catalytically inactive SIRT6 form or were engineered to silence endogenous SIRT6 expression. In SIRT6-overexpressing cells, NAD(H) levels were up-regulated, as a consequence of NAMPT activation. By immunopurification and incubation with recombinant SIRT6, NAMPT was found to be a direct substrate of SIRT6 deacetylation, with a mechanism that up-regulates NAMPT enzymatic activity. Extracellular NAMPT release was enhanced in SIRT6-silenced cells. Also glucose-6-phosphate dehydrogenase activity and NADPH levels were increased in SIRT6-overexpressing cells. Accordingly, increased SIRT6 levels reduced cancer cell susceptibility to H₂O₂-induced oxidative stress and to doxorubicin. Our data demonstrate that SIRT6 affects intracellular NAMPT activity, boosts NAD(P)(H) levels, and protects against oxidative stress. The use of SIRT6 inhibitors, together with agents inducing oxidative stress, may represent a promising treatment strategy in cancer.-Sociali, G., Grozio, A., Caffa, I., Schuster, S., Becherini, P., Damonte, P., Sturla, L., Fresia, C., Passalacqua, M., Mazzola, F., Raffaelli, N., Garten, A., Kiess, W., Cea, M., Nencioni, A., Bruzzone, S. SIRT6 deacetylase activity regulates NAMPT activity and NAD(P)(H) pools in cancer cells.

Metabolic tracing reveals novel adaptations to skeletal muscle cell energy production pathways in response to NAD + depletion

Background: Skeletal muscle is central to whole body metabolic homeostasis, with age and disease impairing its ability to function appropriately to maintain health. Inadequate NAD + availability is proposed to contribute to pathophysiology by impairing metabolic energy pathway use. Despite the importance of NAD + as a vital redox cofactor in energy production pathways being well-established, the wider impact of disrupted NAD + homeostasis on these pathways is unknown. Methods: We utilised skeletal muscle myotube models to induce NAD + depletion, repletion and excess and conducted metabolic tracing to provide comprehensive and detailed analysis of the consequences of altered NAD + metabolism on central carbon metabolic pathways. We used stable isotope tracers, [1,2-13C] D-glucose and [U- 13C] glutamine, and conducted combined 2D-1H,13C-heteronuclear single quantum coherence (HSQC) NMR spectroscopy and GC-MS analysis. Results: NAD + excess driven by nicotinamide riboside (NR) supplementation within skeletal muscle cells results in enhanced nicotinamide clearance, but had no effect on energy homeostasis or central carbon metabolism. Nicotinamide phosphoribosyltransferase (NAMPT) inhibition induced NAD + depletion and resulted in equilibration of metabolites upstream of glyceraldehyde phosphate dehydrogenase (GAPDH). Aspartate production through glycolysis and TCA cycle activity is increased in response to low NAD +, which is rapidly reversed with repletion of the NAD + pool using NR. NAD + depletion reversibly inhibits cytosolic GAPDH activity, but retains mitochondrial oxidative metabolism, suggesting differential effects of this treatment on sub-cellular pyridine pools. When supplemented, NR efficiently reverses these metabolic consequences. However, the functional relevance of increased aspartate levels after NAD + depletion remains unclear, and requires further investigation. Conclusions: These data highlight the need to consider carbon metabolism and clearance pathways when investigating NAD + precursor usage in models of skeletal muscle physiology.

Omentin-1 and NAMPT serum concentrations are higher and CK-18 levels are lower in children and adolescents with type 1 diabetes when compared to healthy age, sex and BMI matched controls

Background Adipokines were shown to affect glucose homeostasis and β-cell function in patients with pancreatic dysfunction which is associated with changes in the adipose tissue secretory profile. However, information about adipokines associated with β-cell dysfunction is lacking in pediatric patients with type 1 diabetes. Methods (1) We compared serum concentrations of nicotinamide phosphoribosyltransferase (NAMPT), omentin-1 and caspase-cleaved cytokeratin 18 fragment M30 (CK-18) in pediatric type 1 diabetes patients (n=245) and healthy age, sex and body mass index standard deviation score (BMI-SDS) matched controls (n=243). (2) We investigated the influence of insulin treatment on serum concentrations of NAMPT, omentin-1 and CK-18 in groups of patients with type 1 diabetes stratified according to the duration of their disease: at onset (n=50), ≥6 months and <5 years (n=185), ≥5 and <10 years (n=98), and ≥10 years (n=52). Results Patients at onset compared with healthy controls demonstrated no significant differences in NAMPT levels (p=0.129), whereas omentin-1 levels were elevated (p<0.001) and CK-18 levels were lowered (p=0.034). In contrast, NAMPT and omentin-1 were elevated and CK-18 serum levels were lower in longstanding patients compared to healthy controls (p<0.001). NAMPT serum levels did not change significantly during the duration of type 1 diabetes (p=0.546). At onset, omentin-1 and CK-18 levels were higher than in any group of longstanding type 1 diabetes (p<0.025). Conclusions Altered serum levels of NAMPT, omentin-1 and CK-18 in pediatric type 1 diabetes patients indicate metabolic changes caused by adipose tissue dysregulation which do not normalize during insulin therapy.

Hepatic NAD+ levels and NAMPT abundance are unaffected during prolonged high-fat diet consumption in C57BL/6JBomTac mice

Dietary supplementation of nicotinamide adenine dinucleotide (NAD⁺) precursors has been suggested as a treatment for non-alcoholic fatty liver disease and obesity. In the liver, NAD⁺ is primarily generated by nicotinamide phosphoribosyltransferase (NAMPT), and hepatic levels of NAMPT and NAD⁺ have been reported to be dependent on age and body composition. The aim of the present study was to identify time course-dependent changes in hepatic NAD content and NAD⁺ salvage capacity in mice challenged with a high-fat diet (HFD). We fed 7-week-old C57BL/6JBomTac male mice either regular chow or a 60% HFD for 6, 12, 24, and 48 weeks, and we evaluated time course-dependent changes in whole body metabolism, liver steatosis, and abundance of hepatic NAD-associated metabolites and enzymes. Mice fed a 60% HFD rapidly accumulated fat and hepatic triglycerides with associated changes in respiratory exchange ratio (RER) and a disruption of the circadian feeding pattern. The HFD did not alter hepatic NAD⁺ levels, but caused a decrease in NADP⁺ and NADPH levels. Decreased NADP⁺ content was not accompanied by alterations in NAD kinase (NADK) abundance in HFD-fed mice, but NADK levels increased with age regardless of diet. NAMPT protein abundance did not change with age or diet. HFD consumption caused a severe decrease in protein lysine malonylation after six weeks, which persisted throughout the experiment. This decrease was not associated with changes in SIRT5 abundance. In conclusion, hepatic NAD⁺ salvage capacity is resistant to long-term HFD feeding, and hepatic lipid accumulation does not compromise the hepatic NAD⁺ pool in HFD-challenged C57BL/6JBomTac male mice.

Inhibition of NAMPT sensitizes MOLT4 leukemia cells for etoposide treatment through the SIRT2-p53 pathway

NAMPT (Nicotinamide phosphoribosyltransferase) catalyses the rate-limiting step in the NAD biosynthesis from nicotinamide and thereby regulates the activity of NAD-dependent enzymes. Cancer cells are highly dependent on NAD for energy and DNA repair processes and are assumed to be more susceptible to an inhibition of NAD synthesis than non-transformed cells. We aimed to investigate whether or not inhibition of NAMPT with its specific inhibitor FK866 can sensitize leukemia cells for chemotherapeutic agents. NAMPT protein abundance, enzymatic activity and NAD concentrations were significantly higher in Jurkat and Molt-4 leukemia cell lines compared to normal peripheral blood mononuclear cells. Combination of etoposide and FK866 caused increased cell death in leukemia cell lines compared to etoposide alone. Etoposide decreased protein abundance of NAD-dependent deacetylases SIRTUIN1. After combining etoposide and FK866 treatment SIRTUIN2 was further decreased and accumulation and acetylation of the downstream target p53 was further enhanced in MOLT4 cells. Concomitantly, protein abundance of p21 and cleaved BAX was increased. Targeting NAMPT could be a novel therapeutic strategy to enhance the efficacy of chemotherapeutic agents such as etoposide against leukemia.

EWS-FLI1 confers exquisite sensitivity to NAMPT inhibition in Ewing sarcoma cells

Ewing sarcoma (EwS) is the second most common bone cancer in children and adolescents with a high metastatic potential. EwS development is driven by a specific chromosomal translocation resulting in the generation of a chimeric EWS-ETS transcription factor, most frequently EWS-FLI1.

Nicotinamide adenine dinucleotide (NAD) is a key metabolite of energy metabolism involved in cellular redox reactions, DNA repair, and in the maintenance of genomic stability. This study describes targeting nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme of NAD synthesis, by FK866 in EwS cells. Here we report that blocking NAMPT leads to exhaustive NAD depletion in EwS cells, followed by a metabolic collapse and cell death. Using conditional EWS-FLI1 knockdown by doxycycline-inducible shRNA revealed that EWS-FLI1 depletion significantly reduces the sensitivity of EwS cells to NAMPT inhibition. Consistent with this finding, a comparison of 7 EwS cell lines of different genotypes with 5 Non-EwS cell lines and mesenchymal stem cells revealed significantly higher FK866 sensitivity of EWS-ETS positive EwS cells, with IC₅₀ values mostly below 1nM.

Taken together, our data reveal evidence of an important role of the NAMPT-mediated NAD salvage pathway in the energy homeostasis of EwS cells and suggest NAMPT inhibition as a potential new treatment approach for Ewing sarcoma.

Simvastatin induces apoptosis in PTEN‑haploinsufficient lipoma cells

Adipose tissue tumors (lipomas) frequently develop in patients with heterozygous germ line phosphatase and tensin homolog (PTEN) mutations. simvastatin has been demonstrated to exhibit antitumor effects, and so the aim of the present study was to assess the effects of simvastatin on the growth of human PTEN haploinsufficient lipoma cells. Whether the effects of simvastatin in lipomas are mediated via PTEN upregulation was also assessed. The results of the present study revealed that simvastatin treatment reduced cell viability and induced apoptosis in human lipoma cells. Furthermore, it was demonstrated that the expression of cellular PTEN mRNA and protein was increased following simvastatin stimulation. In addition, the phosphorylation of protein kinase B and downstream targets of mammalian target of rapamycin and 4E‑binding protein (4E‑BP)‑1 was attenuated. It was also demonstrated that simvastatin induced PTEN transcriptional upregulation by increasing peroxisome proliferator‑activated receptor (PPAR)γ expression. The small interfering RNA‑mediated knockdown of PPARγ abrogated the stimulatory effect of simvastatin on the PTEN protein, but did not influence apoptosis. The results of the present study suggest that simvastatin may be beneficial for patients with inoperable PTEN haploinsufficient lipomas.

Oleate ameliorates palmitate-induced reduction of NAMPT activity and NAD levels in primary human hepatocytes and hepatocarcinoma cells

BACKGROUND

Nicotinamide phosphoribosyltransferase (NAMPT) and nicotinamide adenine dinucleotide (NAD) levels are crucial for liver function. The saturated fatty acid palmitate and the unsaturated fatty acid oleate are the main free fatty acids in adipose tissue and human diet. We asked how these fatty acids affect cell survival, NAMPT and NAD levels in HepG2 cells and primary human hepatocytes.

METHODS

HepG2 cells were stimulated with palmitate (0.5mM), oleate (1mM) or a combination of both (0.5mM/1mM) as well as nicotinamide mononucleotide (NMN) (0.5 mM) or the specific NAMPT inhibitor FK866 (10nM). Cell survival was measured by WST-1 assay and Annexin V/propidium iodide staining. NAD levels were determined by NAD/NADH Assay or HPLC. Protein and mRNA levels were analysed by Western blot analyses and qPCR, respectively. NAMPT enzyme activity was measured using radiolabelled 14C-nicotinamide. Lipids were stained by Oil red O staining.

RESULTS

Palmitate significantly reduced cell survival and induced apoptosis at physiological doses. NAMPT activity and NAD levels significantly declined after 48h of palmitate. In addition, NAMPT mRNA expression was enhanced which was associated with increased NAMPT release into the supernatant, while intracellular NAMPT protein levels remained stable. Oleate alone did not influence cell viability and NAMPT activity but ameliorated the negative impact of palmitate on cell survival, NAMPT activity and NAD levels, as well as the increased NAMPT mRNA expression and secretion. NMN was able to normalize intracellular NAD levels but did not ameliorate cell viability after co-stimulation with palmitate. FK866, a specific NAMPT inhibitor did not influence lipid accumulation after oleate-treatment.

CONCLUSIONS

Palmitate targets NAMPT activity with a consequent cellular depletion of NAD. Oleate protects from palmitate-induced apoptosis and variation of NAMPT and NAD levels. Palmitate-induced cell stress leads to an increase of NAMPT mRNA and accumulation in the supernatant. However, the proapoptotic action of palmitate seems not to be mediated by decreased NAD levels.

Nicotinamide riboside kinases display redundancy in mediating nicotinamide mononucleotide and nicotinamide riboside metabolism in skeletal muscle cells

Objective

Augmenting nicotinamide adenine dinucleotide (NAD⁺) availability may protect skeletal muscle from age-related metabolic decline. Dietary supplementation of NAD⁺ precursors nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR) appear efficacious in elevating muscle NAD⁺. Here we sought to identify the pathways skeletal muscle cells utilize to synthesize NAD⁺ from NMN and NR and provide insight into mechanisms of muscle metabolic homeostasis.

Methods

We exploited expression profiling of muscle NAD⁺ biosynthetic pathways, single and double nicotinamide riboside kinase 1/2 (NRK1/2) loss-of-function mice, and pharmacological inhibition of muscle NAD⁺ recycling to evaluate NMN and NR utilization.

Results

Skeletal muscle cells primarily rely on nicotinamide phosphoribosyltransferase (NAMPT), NRK1, and NRK2 for salvage biosynthesis of NAD⁺. NAMPT inhibition depletes muscle NAD⁺ availability and can be rescued by NR and NMN as the preferred precursors for elevating muscle cell NAD⁺ in a pathway that depends on NRK1 and NRK2. Nrk2 knockout mice develop normally and show subtle alterations to their NAD+ metabolome and expression of related genes. NRK1, NRK2, and double KO myotubes revealed redundancy in the NRK dependent metabolism of NR to NAD⁺. Significantly, these models revealed that NMN supplementation is also dependent upon NRK activity to enhance NAD⁺ availability.

Conclusions

These results identify skeletal muscle cells as requiring NAMPT to maintain NAD⁺ availability and reveal that NRK1 and 2 display overlapping function in salvage of exogenous NR and NMN to augment intracellular NAD⁺ availability.

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NRK1 and NRK2 are expressed in skeletal muscle and display redundancy in converting NR and NMN to NAD⁺.

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NRK1 and NRK2 are dispensable for maintaining basal skeletal muscle cell NAD⁺.

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Exogenous NMN salvage to NAD⁺ is NRK dependent.

Short-term overfeeding of zebrafish with normal or high-fat diet as a model for the development of metabolically healthy versus unhealthy obesity

BACKGROUND

Obese individuals differ in their risk of developing metabolic and cardiovascular complications depending on fat distribution (subcutaneous versus visceral) and adipose tissue (AT) phenotype (hyperplasic versus hypertrophic). However, the exact mechanisms which determine whether an obese individual is metabolically healthy or unhealthy are not clear, and analyses of the underlying pathomechanisms are limited by the lack of suitable in vivo models in which metabolically healthy versus metabolically unhealthy AT accumulation can be specifically induced. In the current study, we aimed to establish a protocol for the use of zebrafish as a model for obesity-related metabolically healthy versus metabolically unhealthy AT accumulation.

METHODS

We overfed adult male zebrafish of the AB strain with normal fat diet (NFD) or high fat diet (HFD) for 8 weeks and compared parameters related to obesity, i.e. body weight, body mass index, condition index and body fat percentage, to control zebrafish fed under physiological conditions. In addition, we investigated the presence of early obesity-related metabolic alterations by quantifying blood glucose levels, plasma triglyceride and cholesterol levels, and by assessing ectopic lipid accumulation in the liver of zebrafish. Finally, we determined gene expression levels of marker genes related to lipid metabolism, inflammation and fibrosis in visceral AT and liver.

RESULTS

We show that 8-weeks overfeeding with either NFD or HFD leads to a significant increase in body weight and AT mass compared to controls. In contrast to NFD-overfed zebrafish, HFD-overfed zebrafish additionally present metabolic alterations, e.g. hyperglycemia and ectopic lipid accumulation in the liver, and a metabolically unhealthy AT phenotype with adipocyte hypertrophy especially in the visceral AT depot, which is accompanied by changes in the expression of marker genes for lipid metabolism, inflammation and fibrosis.

CONCLUSIONS

In summary, we have established a method for the specific induction of metabolically distinct obesity phenotypes in zebrafish. Our results indicate that zebrafish represents an attractive model to study regulatory mechanisms involved in the determination of AT phenotype during development of metabolically healthy versus metabolically unhealthy obesity.

Altered hepatic lipid metabolism in mice lacking both the melanocortin type 4 receptor and low density lipoprotein receptor

Obesity is often associated with dyslipidemia and hepatosteatosis. A number of animal models of non-alcoholic fatty liver disease (NAFLD) are established but they significantly differ in the molecular and biochemical changes depending on the genetic modification and diet used. Mice deficient for melanocortin type 4 receptor (Mc4r^mut) develop hyperphagia, obesity, and subsequently NAFLD already under regular chow and resemble more closely the energy supply-driven obesity found in humans. This animal model was used to assess the molecular and biochemical consequences of hyperphagia-induced obesity on hepatic lipid metabolism. We analyzed transcriptome changes in Mc4r^mut mice by RNA sequencing and used high resolution ¹H magic angle spinning NMR spectroscopy and MALDI-TOF mass spectrometry to assess changes in the lipid composition. On the transcriptomic level we found significant changes in components of the triacylglycerol metabolism, unsaturated fatty acids biosynthesis, peroxisome proliferator-activated receptor signaling pathways, and lipid transport and storage compared to the wild-type. These findings were supported by increases in triacylglycerol, monounsaturated fatty acid, and arachidonic acid levels. The transcriptome signatures significantly differ from those of other NAFLD mouse models supporting the concept of hepatic subphenotypes depending on the genetic background and diet. Comparative analyses of our data with previous studies allowed for the identification of common changes and genotype-specific components and pathways involved in obesity-associated NAFLD.

Resveratrol Potentiates Growth Inhibitory Effects of Rapamycin in PTEN-deficient Lipoma Cells by Suppressing p70S6 Kinase Activity

Patients with phosphatase and tensin homolog (PTEN) hamartoma tumor syndrome and germline mutations in PTEN frequently develop lipomatosis, for which there is no standard treatment. Rapamycin was shown to reduce the growth of lipoma cells with heterozygous PTEN deficiency in vitro, but concomitantly induced an upregulation of AKT phosphorylation. Since it was shown that resveratrol stabilizes PTEN, we asked whether co-incubation with resveratrol could suppress the rapamycin-induced AKT phosphorylation in PTEN-deficient lipoma cells. Resveratrol incubation resulted in decreased lipoma cell viability by inducing G1-phase cell cycle arrest and apoptosis. PTEN expression and AKT phosphorylation were not significantly changed, whereas p70S6 kinase (p70S6K) phosphorylation was reduced in PTEN-deficient lipoma cells after resveratrol incubation. Rapamycin/resveratrol co-incubation significantly decreased viability further at lower doses of resveratrol and resulted in decreased p70S6K phosphorylation compared to rapamycin incubation alone, suggesting that resveratrol potentiated the growth inhibitory effects of rapamycin by reducing p70S6K activation. Both viability and p70S6K phosphorylation of primary PTEN wild-type preadipocytes were less affected compared to PTEN-deficient lipoma cells by equimolar concentrations of resveratrol. These results support the concept of combining chemopreventive natural compounds with mammalian target of rapamycin (mTOR) inhibitors to increase the efficacy of chemotherapeutic drugs for patients suffering from overgrowth syndromes.

Hepatic NAD salvage pathway is enhanced in mice on a high-fat diet

Nicotinamide phosphoribosyltransferase (Nampt) is the rate-limiting enzyme for NAD salvage and the abundance of Nampt has been shown to be altered in non-alcoholic fatty liver disease. It is, however, unknown how hepatic Nampt is regulated in response to accumulation of lipids in the liver of mice fed a high-fat diet (HFD). HFD mice gained more weight, stored more hepatic lipids and had an impaired glucose tolerance compared with control mice. NAD levels as well as Nampt mRNA expression, protein abundance and activity were significantly increased in HFD mice. Enhanced NAD levels were associated with deacetylation of p53 and Nfκb indicating increased activation of Sirt1. Despite impaired glucose tolerance and increased hepatic lipid levels in HFD mice, NAD metabolism was significantly enhanced. Thus, improved NAD metabolism may be a compensatory mechanism to protect against negative impact of hepatic lipid accumulation.

Physiological and pathophysiological roles of NAMPT and NAD metabolism

Nicotinamide phosphoribosyltransferase (NAMPT) is a regulator of the intracellular nicotinamide adenine dinucleotide (NAD) pool. NAD is an essential coenzyme involved in cellular redox reactions and is a substrate for NAD-dependent enzymes. In various metabolic disorders and during ageing, levels of NAD are decreased. Through its NAD-biosynthetic activity, NAMPT influences the activity of NAD-dependent enzymes, thereby regulating cellular metabolism. In addition to its enzymatic function, extracellular NAMPT (eNAMPT) has cytokine-like activity. Abnormal levels of eNAMPT are associated with various metabolic disorders. NAMPT is able to modulate processes involved in the pathogenesis of obesity and related disorders such as nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes mellitus (T2DM) by influencing the oxidative stress response, apoptosis, lipid and glucose metabolism, inflammation and insulin resistance. NAMPT also has a crucial role in cancer cell metabolism, is often overexpressed in tumour tissues and is an experimental target for antitumour therapies. In this Review, we discuss current understanding of the functions of NAMPT and highlight progress made in identifying the physiological role of NAMPT and its relevance in various human diseases and conditions, such as obesity, NAFLD, T2DM, cancer and ageing.

Phosphatidylinositol 3-kinase (PI3K) signalling regulates insulin-like-growth factor binding protein-2 (IGFBP-2) production in human adipocytes

OBJECTIVE

Insulin-like-growth factor binding protein 2 (IGFBP-2) is thought to be a marker for the phosphatase and tensin homolog (PTEN) status and activity of the phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway. We aimed to evaluate whether or not lipoma cells of a patient with a heterozygous deletion in the PTEN gene would produce more IGFBP-2 than PTEN non deficient control cells. Moreover, we analysed the influence of pharmacological inhibitors of the PI3K/AKT/mTOR pathway on IGFBP-2 production.

DESIGN

PTEN deficient preadipocytes and control PTEN non deficient preadipocytes were differentiated in vitro and treated with the respective inhibitors. PTEN was transiently down regulated by siRNA in human preadipocytes. IGFBP-2 mRNA and protein expression and IGFBP-2 in culture supernatant were measured.

RESULTS

PTEN deficient lipoma cells were found to produce IGFBP-2 during in vitro differentiation in comparable amounts to PTEN non deficient cells. In contrast, acute down regulation of PTEN in preadipocytes resulted in enhanced production of IGFBP-2. Incubation with the PI3K inhibitors LY294002 and wortmannin decreased IGFBP-2 mRNA and protein. Neither the mTOR complex 1 inhibitor rapamycin nor PD98059, an inhibitor of MEK (mitogen-activated protein kinase kinase), showed a significant effect on IGFBP-2 production.

CONCLUSION

IGFBP-2 production in PTEN deficient preadipocytes was not influenced by PTEN deficiency or by inhibition of mTORC1 and MAPK. In contrast, inhibition of PI3K decreased IGFBP-2 expression and secretion.

FK866-induced NAMPT inhibition activates AMPK and downregulates mTOR signaling in hepatocarcinoma cells

BACKGROUND

Nicotinamide phosphoribosyltransferase (NAMPT) is the key enzyme of the NAD salvage pathway starting from nicotinamide. Cancer cells have an increased demand for NAD due to their high proliferation and DNA repair rate. Consequently, NAMPT is considered as a putative target for anti-cancer therapies. There is evidence that AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) become dysregulated during the development of hepatocellular carcinoma (HCC). Here, we investigated the effects of NAMPT inhibition by its specific inhibitor FK866 on the viability of hepatocarcinoma cells and analyzed the effects of FK866 on the nutrient sensor AMPK and mTOR complex1 (mTORC1) signaling.

RESULTS

FK866 markedly decreased NAMPT activity and NAD content in hepatocarcinoma cells (Huh7 cells, Hep3B cells) and led to delayed ATP reduction which was associated with increased cell death. These effects could be abrogated by administration of nicotinamide mononucleotide (NMN), the enzyme product of NAMPT. Our results demonstrated a dysregulation of the AMPK/mTOR pathway in hepatocarcinoma cells compared to non-cancerous hepatocytes with a higher expression of mTOR and a lower AMPKα activation in hepatocarcinoma cells. We found that NAMPT inhibition by FK866 significantly activated AMPKα and inhibited the activation of mTOR and its downstream targets p70S6 kinase and 4E-BP1 in hepatocarcinoma cells. Non-cancerous hepatocytes were less sensitive to FK866 and did not show changes in AMPK/mTOR signaling after FK866 treatment.

CONCLUSION

Taken together, these findings reveal an important role of the NAMPT-mediated NAD salvage pathway in the energy homeostasis of hepatocarcinoma cells and suggest NAMPT inhibition as a potential treatment option for HCC.

Sirolimus treatment of severe PTEN hamartoma tumor syndrome: case report and in vitro studies

BACKGROUND

Phosphatase and tensin homolog (PTEN) hamartoma tumor syndrome (PHTS) is caused by germ line mutations in the PTEN gene. Symptoms include cancer predisposition, immune deviations, and lipomas/lipomatosis. No causal standard therapy is available. We describe a therapeutic attempt with the mammalian target of rapamycin (mTOR) inhibitor sirolimus for a PHTS patient suffering from thymus hyperplasia and lipomatosis. We furthermore assessed the in vitro effects of sirolimus and other inhibitors on lipoma cells of the patient.

METHODS

The patient underwent clinical and blood examinations and whole-body magnetic resonance imaging to assess tumor sizes. Lipoma cells of the patient were incubated with inhibitors of the phosphoinositide-3-kinase (PI3K)/AKT/mTOR signaling pathway to analyze the effects on proliferation, adipocyte differentiation, and survival in vitro.

RESULTS

Sirolimus treatment improved somatic growth and reduced thymus volume. These effects diminished over the treatment period of 19 mo. Sirolimus decreased lipoma cell proliferation and adipocyte differentiation in vitro but did not cause apoptosis. PI3K and AKT inhibitors induced apoptosis significantly.

CONCLUSION

Sirolimus treatment led to an improvement of the patient's clinical status and a transient reduction of the thymus. Our in vitro findings point to PI3K and AKT inhibitors as potential treatment options for patients with severe forms of PHTS.

Resveratrol differentially regulates NAMPT and SIRT1 in Hepatocarcinoma cells and primary human hepatocytes

Resveratrol is reported to possess chemotherapeutic properties in several cancers. In this study, we wanted to investigate the molecular mechanisms of resveratrol-induced cell cycle arrest and apoptosis as well as the impact of resveratrol on NAMPT and SIRT1 protein function and asked whether there are differences in hepatocarcinoma cells (HepG2, Hep3B cells) and non-cancerous primary human hepatocytes. We found a lower basal NAMPT mRNA and protein expression in hepatocarcinoma cells compared to primary hepatocytes. In contrast, SIRT1 was significantly higher expressed in hepatocarcinoma cells than in primary hepatocytes. Resveratrol induced cell cycle arrest in the S- and G2/M- phase and apoptosis was mediated by activation of p53 and caspase-3 in HepG2 cells. In contrast to primary hepatocytes, resveratrol treated HepG2 cells showed a reduction of NAMPT enzymatic activity and increased p53 acetylation (K382). Resveratrol induced NAMPT release from HepG2 cells which was associated with increased NAMPT mRNA expression. This effect was absent in primary hepatocytes where resveratrol was shown to function as NAMPT and SIRT1 activator. SIRT1 inhibition by EX527 resembled resveratrol effects on HepG2 cells. Furthermore, a SIRT1 overexpression significantly decreased both p53 hyperacetylation and resveratrol-induced NAMPT release as well as S-phase arrest in HepG2 cells. We could show that NAMPT and SIRT1 are differentially regulated by resveratrol in hepatocarcinoma cells and primary hepatocytes and that resveratrol did not act as a SIRT1 activator in hepatocarcinoma cells.

Nicotinamide phosphoribosyltransferase inhibitors, design, preparation, and structure-activity relationship

Existing pharmacological inhibitors for nicotinamide phosphoribosyltransferase (NAMPT) are promising therapeutics for treating cancer. By using medicinal and computational chemistry methods, the structure-activity relationship for novel classes of NAMPT inhibitors is described, and the compounds are optimized. Compounds are designed inspired by the NAMPT inhibitor APO866 and cyanoguanidine inhibitor scaffolds. In comparison with recently published derivatives, the new analogues exhibit an equally potent antiproliferative activity in vitro and comparable activity in vivo. The best performing compounds from these series showed subnanomolar antiproliferative activity toward a series of cancer cell lines (compound 15: IC50 0.025 and 0.33 nM, in A2780 (ovarian carcinoma) and MCF-7 (breast), respectively) and potent antitumor in vivo activity in well-tolerated doses in a xenograft model. In an A2780 xenograft mouse model with large tumors (500 mm(3)), compound 15 reduced the tumor volume to one-fifth of the starting volume at a dose of 3 mg/kg administered ip, bid, days 1-9. Thus, compounds found in this study compared favorably with compounds already in the clinic and warrant further investigation as promising lead molecules for the inhibition of NAMPT.

Oleate rescues INS-1E β-cells from palmitate-induced apoptosis by preventing activation of the unfolded protein response

BACKGROUND

Saturated free fatty acids (FFAs), such as palmitate, cause β-cell apoptosis whereas unsaturated FFAs, e.g. oleate, are not harmful. The toxicity of palmitate could be mediated through endoplasmic reticulum (ER) stress which triggers the activation of a signal responding cascade also called unfolded protein response (UPR). We investigated whether or not palmitate induced β-cell apoptosis through UPR activation and whether or not oleate as a monounsaturated fatty acid could counteract these effects.

METHODS

INS-1E β-cells were incubated with palmitate [0.5mM], oleate [1mM] or the combination [0.5/1mM] for 1, 6 and 24h. Viability and induction of apoptosis were measured by WST-1 assay and FITC-Annexin/PI-staining, respectively. Western blot analyses were performed for UPR specific proteins and mRNA expression of target molecules was determined by qPCR.

RESULTS

Palmitate significantly decreased viability (29±8.8%) of INS-1E β-cells compared to controls after 24h. Stimulation with oleate showed no effect on viability but the combination of oleate and palmitate improved viability compared to palmitate treated cells (55±9.3%) or controls (26±5.3%). The number of apoptotic cells was increased 2-fold after 24h incubation with palmitate compared to controls. Again, oleate showed no effect but in combination ameliorated the effect of palmitate to control level. Phosphorylation of eIF2α was increased after 6 and 24h incubation with palmitate. In contrast, oleate had no effect and in combination prevented phosphorylation of eIF2α. Increased Xbp1 splicing was visible already 6h after palmitate treatment and remained elevated at 24h. The combination with oleate abolished Xbp1 splicing. Interestingly, mRNA expression of the chaperones Bip, Pdi, Calnexin and Grp94 was not altered by FFA treatment. Only the proapoptotic transcription factor Chop was significantly enhanced by palmitate incubation. In accordance with sustained cell survival the combination as well as oleate alone, did not result in increased Chop levels compared to controls. In summary, we showed that oleate protects INS-1E β-cells from palmitate-induced apoptosis by the suppression of ER stress which was independent of chaperone activation.