Cancer cells frequently show elevated glucose consumption to support proliferation and survival. This led to the assumption that glycolytic inhibitors could be effective in cancer treatment. However, barriers to clinical implementation remain. Adaptive strategies, such as metabolizing alternative nutrients, may play a role. Here, we investigated the use of an understudied sugar, mannose, in lung cancer cells and xenografts. Stable isotope tracing reveals enhanced contribution of mannose to GDP-mannose and GDP-fucose, key glycosylation precursors, upon treatment with the glycolytic inhibitor 2-deoxyglucose (2-DG) or glucose starvation in vitro. Mannose restores the glucose-withdrawal-induced decrease of GDP-mannose and GDP-fucose pools, and partially rescues proliferation upon 2-DG treatment or glucose deprivation. 13C6-mannose infusion in patient-derived xenograft mice reveals a considerable contribution of mannose to GDP-mannose and GDP-fucose in tumors, which is further enhanced by 2-DG. In normal lungs, the pathway is only partially active. Mannose is also shuttled towards glycolysis in lung tumors in vivo and glucose-deprived cells in vitro. In conclusion, mannose utilization for glycosylation precursor synthesis represents an adaptive strategy in lung cancer cells under metabolic stress. Alternative nutrients might limit the efficacy of glycolytic intervention in cancer treatment. This study highlights the importance of mannose utilization for glycosylation precursors upon inhibition of glycolysis or glucose starvation. Alternative nutrients might limit the efficacy of glycolytic intervention in cancer treatment. This study highlights the importance of mannose utilization for glycosylation precursors upon inhibition of glycolysis or glucose starvation.

BACKGROUND:New biomarkers are needed to improve risk prediction in patients with acute heart failure. We aimed to identify serum lipids with prognostic value and clinical utility in patients hospitalized due to acute heart failure. METHODS:Targeted mass spectrometry-based lipidomics was performed on serum samples from 315 (discovery) and 139 (validation) patients prospectively enrolled in 2 observational acute heart failure studies. Prognostic lipids were identified by consolidating orthogonal partial least squares discriminant analysis, least absolute shrinkage and selection operator regression, and random forest (Boruta) results into a single ranking using TopKSignal. RESULTS:In the discovery cohort, lysophosphatidylethanolamine 20:4, lysophosphatidylcholine 20:4, lysophosphatidylcholine 14:0, and lysophosphatidylethanolamine 18:1 were most strongly associated with in-hospital mortality. Serum concentrations were significantly lower in nonsurvivors, and these inverse associations remained significant after adjustment in both cohorts, except for lysophosphatidylethanolamine 18:1 after adjustment for OPTIMIZE-HF (Organized Program to Initiate Lifesaving Treatment in Hospitalized Patients With Heart Failure) in the validation cohort. These lipids demonstrated moderate discriminative performance (area under the curve, 0.72-0.76 in the discovery and 0.71-0.77 in the validation cohort) and provided additional prognostic value beyond ADHERE (Acute Decompensated Heart Failure National Registry), GWTG-HF (Get With The Guidelines Heart Failure), and OPTIMIZE-HF (Δarea under the curve, 0.04-0.17) scores. Decision curve analyses showed improved net clinical benefit for mortality prediction across threshold probabilities of 12% to 35% in the discovery and 15% to 28% in the validation cohort. CONCLUSIONS:Low serum levels of lysophosphatidylethanolamine 20:4, lysophosphatidylcholine 20:4, lysophosphatidylcholine 14:0, and lysophosphatidylethanolamine 18:1 were independently associated with in-hospital mortality in acute heart failure. These findings suggest that specific lysophospholipids may serve as novel prognostic biomarkers, warranting validation in larger studies to confirm their clinical applicability.

BACKGROUND: Glucose is an important fuel in cancer cells, however, its availability may be limited in solid tumors. Cell-autonomous, metabolic adaptations of cancer cells and non-malignant cells to glucose deprivation are still incompletely understood. METHODS: Here, we addressed the changes in central carbon metabolism in lung cancer cells and normal lung cells facing glucose limitation using stable isotopic labeling followed by nuclear magnetic resonance spectroscopy and mass spectrometry. RESULTS: Elevated levels and the release of newly synthesized aspartate were among the most prominent changes in low compared to high glucose conditions. The low glucose-induced export of aspartate occurred in different lung cancer cell lines, but also bronchial epithelial cells and cancer-associated fibroblasts. It was accompanied by a reduced use of aspartate in purine synthesis and suppressed by hypoxia. A knockout of the malate-aspartate shuttle (MAS) enzyme mitochondrial aspartate aminotransferase (GOT2) decreased aspartate release. Low glucose conditions diminished reduced nicotinamide adenine dinucleotide (NADH) and restoring NADH reversed aspartate synthesis, suggesting that the distal, NADH-dependent arm of the MAS is compromised under glucose deprivation. CONCLUSIONS: Cells accumulate and release aspartate, a biosynthetic precursor and signaling molecule, under low glucose conditions, largely due to a truncated MAS, as part of their adaptive metabolic response.

Mitochondrial diseases are highly complex and heterogeneous, and nearly 20% of cases involve severe liver pathology. MIC13-mediated hepato-encephalopathy is a rare mitochondrial hepatopathy with profound liver dysfunction, yet the mechanism by which MIC13 deficiency leads to severe hepatic dysfunction remains poorly understood. Here, we describe an affected individual carrying a pathogenic MIC13 variant (c.260-2A > G) that results in severe multisystem disease, including hepatopathy. To investigate hepatocyte-specific consequences of MIC13 variant, we generated iPSCs carrying this disease-causing variant and differentiated them into induced hepatocytes (iHeps). MIC13, a key component of the MICOS complex required for cristae formation, was disrupted in these cells, and the resultant iHeps exhibited the same cristae defects observed in clinical samples. Integrated multi-omics and biochemical analyses revealed extensive metabolic rewiring, including disrupted amino acid turnover, accumulation of tricarboxylic acid (TCA) and urea cycle intermediates. Additionally, profound alterations in methionine cycle and transsulfuration pathways, along with enhanced bile acid synthesis, collectively affect methylation potential, redox homeostasis, and detoxification. Lipid metabolism was also impaired, with incomplete beta-oxidation, increased ketogenesis, and diminished lipid storage. At the cellular level, extensive extracellular matrix (ECM) remodelling, increased intracellular collagen accumulation and enhanced cell migration indicated an early fibrotic phenotype. Overall, this clinically relevant model uncovers how cristae defects drive metabolic imbalance and hepatocyte dysfunction, ultimately leading to early fibrotic changes in mitochondrial liver disease. These findings provide the first mechanistic link between MIC13-dependent cristae disruption and hepatic metabolic failure and offer a foundation for identifying therapeutic strategies for mitochondrial hepatopathies. ### Competing Interest Statement The authors have declared no competing interest. Heinrich Heine University Düsseldorf, https://ror.org/024z2rq82, FoKo-2020-71 Deutsche Forschungsgemeinschaft, https://ror.org/018mejw64, AN 1440/3-1, AN 1440/4-1 Boehringer Ingelheim (Germany), https://ror.org/00q32j219, Exploration grant Walter and Monika Neupert foundation

Spinal muscular atrophy (SMA) is a rare neuromuscular disease caused by biallelic mutations in the SMN1 gene, leading to progressive muscle weakness due to degeneration of the anterior horn cells. Since 2017, SMA patients can be treated with the anti-sense oligonucleotide Nusinersen, which promotes alternative splicing of the SMN2 gene, by regular intrathecal injections. In this prospective study, we applied metabolomic, lipidomic, and proteomic analysis to examine sequential CSF samples from 13 SMA patients and controls. This multi-omic approach identified over 800 proteins and 400 small molecules including lipids. Multivariate analysis of multi-omic data successfully discriminated between the CSF derived from SMA patients and control subjects. Lipidomic analysis revealed increased levels of cholesteryl esters and lyso-phospholipids, along with reduced levels of cholesterol and phospholipids in the CSF of SMA patients as compared to healthy controls. These data, combined with results from functional assays, led us to conclude that SMA patients exhibit altered levels and function of high-density-lipoprotein (HDL)-like particles in the CSF. Notably, Nusinersen therapy was observed to reverse disease-specific profile changes toward a physiological state, potentially explicable by restoring HDL function.

ABHD5-syndromic epidermal differentiation disorder (ABHD5-sEDD; also known as Chanarin-Dorfman syndrome) is a rare autosomal recessive disorder caused by mutations in the α/β-hydrolase domain-containing 5 (ABHD5) gene, leading to systemic accumulation of neutral lipids and ichthyosis due to impaired activation of patatin-like phospholipase domain-containing (PNPLAs) proteins. While ABHD5 is a well-known co-activator of adipose triglyceride lipase (ATGL, also referred to as PNPLA2), its role in epidermal lipid metabolism is incompletely understood. Here, we identify ABHD5 as a key regulator of PNPLA1, an enzyme essential for ω-O-acylceramide (acylCer) synthesis and skin barrier formation. We analyzed seven disease-associated ABHD5 missense mutations and found that they disrupt PNPLA1 localization and function by distinct mechanisms: (i) mutations affecting the PNPLA1 binding region of ABHD5 impair PNPLA1 recruitment to intracellular lipid droplets (LDs), thus reducing acylCer synthesis; (ii) mutations in potential perilipin-binding domains of ABHD5 prevent ABHD5 association with LDs, thereby disrupting PNPLA1-LD localization. Despite these defects, restoring co-localization of ABHD5 mutants with PNPLA1 in proteoliposomes rescued full PNPLA1 enzyme activity, indicating that spatial proximity rather than direct protein binding is sufficient to facilitate acylCer formation. In summary, our findings establish a co-localization-driven model of PNPLA1 regulation, in which ABHD5 ensures proper PNPLA1 targeting to LDs and simultaneously enables its enzymatic activation. This model suggests that pharmacological strategies aimed at restoring PNPLA1 localization to LDs may represent a potential therapeutic approach for ichthyosis in ABHD5-sEDD. By elucidating the molecular mechanisms underlying disease pathogenesis, our study provides important new insights into epidermal lipid metabolism and therapeutic targeting.

Macrophages are recruited to sites of infection contributing to the killing of bacteria, but also to malignant tumors, where they promote angiogenesis and suppress antitumor immune responses. The metabolic microenvironment in tumors is frequently depleted of important nutrients such as glucose. Here, we investigated metabolic adaptation strategies of macrophages to glucose deprivation using stable isotopic tracing. Lactate production was decreased, potentially indicating a reduction of glycolysis. In contrast, the contribution of glutamine to the tricarboxylic acid cycle via α-ketoglutarate and reductive carboxylation were increased. Moreover, gluconeogenesis, the reverse pathway of glycolysis, was activated in glucose-deprived macrophages, proceeding partially to the generation of glycolytic intermediates and glycerol-3-phosphate. The partial gluconeogenesis pathway was abrogated in human and murine macrophages lacking the initial gluconeogenic enzyme phosphoenolpyruvate carboxykinase (PCK2, mitochondrial isoform). Partial gluconeogenesis was higher in anti-inflammatory, interleukin-4-stimulated compared to proinflammatory, interferon-γ/lipopolysaccharide-stimulated macrophages. Single-cell analysis and immunostaining revealed expression of PCK2 in macrophages from both lung cancer and normal lung. Low glucose conditions only partially modulated macrophage phenotypes, leading to reduced CD80 surface marker levels in proinflammatory, and enhanced vascular endothelial growth factor expression in anti-inflammatory macrophages. Our study reveals partial gluconeogenesis in glucose-deprived macrophages and shows that this versatile type of immune cells exhibits remarkable metabolic flexibility.

Serine and glycine give rise to important building blocks in proliferating cells. Both amino acids are either synthesized de novo or taken up from the extracellular space. In lung cancer, serine synthesis gene expression is variable, yet, expression of the initial enzyme, phosphoglycerate dehydrogenase (PHGDH), was found to be associated with poor prognosis. While the contribution of de novo synthesis to serine pools has been shown to be enhanced by serine starvation, the impact of glucose deprivation, a commonly found condition in solid cancers is poorly understood. Here, we utilized a stable isotopic tracing approach to assess serine and glycine de novo synthesis and uptake in different lung cancer cell lines and normal bronchial epithelial cells in variable serine, glycine, and glucose conditions. Under low glucose supplementation (0.2 mM, 3–5% of normal plasma levels), serine de novo synthesis was maintained or even activated. As previously reported, also gluconeogenesis supplied carbons from glutamine to serine and glycine under these conditions. Unexpectedly, low glucose treatment consistently enhanced serine to glycine conversion, along with an up-regulation of the mitochondrial one-carbon metabolism enzymes, serine hydroxymethyltransferase (SHMT2) and methylenetetrahydrofolate dehydrogenase (MTHFD2). The relative contribution of de novo synthesis greatly increased in low serine/glycine conditions. In bronchial epithelial cells, adaptations occurred in a similar fashion as in cancer cells, but serine synthesis and serine to glycine conversion, as assessed by label enrichments and gene expression levels, were generally lower than in (PHGDH positive) cancer cells. In summary, we found a variable contribution of glucose or non-glucose carbon sources to serine and glycine and a high adaptability of the downstream one-carbon metabolism pathway to variable glucose supply.

Monoglyceride lipase (MGL) hydrolyzes monoacylglycerols (MG) to glycerol and one fatty acid. Among the various MG species, MGL also degrades 2-arachidonoylglycerol, the most abundant endocannabinoid and potent activator of the cannabinoid receptors 1 and 2. We investigated the consequences of MGL deficiency on platelet function using systemic (Mgl−/−) and platelet-specific Mgl-deficient (platMgl−/−) mice. Despite comparable platelet morphology, loss of MGL was associated with decreased platelet aggregation and reduced response to collagen activation. This was reflected by reduced thrombus formation in vitro, accompanied by a longer bleeding time and a higher blood volume loss. Occlusion time after FeCl3-induced injury was markedly reduced in Mgl−/− mice, which is consistent with contraction of large aggregates and fewer small aggregates in vitro. The absence of any functional changes in platelets from platMgl−/− mice is in accordance with lipid degradation products or other molecules in the circulation, rather than platelet-specific effects, being responsible for the observed alterations in Mgl−/− mice. We conclude that genetic deletion of MGL is associated with altered thrombogenesis.

OBJECTIVE:Lysosomal acid lipase (LAL) is the only enzyme known to hydrolyze cholesteryl esters (CE) and triacylglycerols in lysosomes at an acidic pH. Despite the importance of lysosomal hydrolysis in skeletal muscle (SM), research in this area is limited. We hypothesized that LAL may play an important role in SM development, function, and metabolism as a result of lipid and/or carbohydrate metabolism disruptions. RESULTS:Mice with systemic LAL deficiency (Lal-/-) had markedly lower SM mass, cross-sectional area, and Feret diameter despite unchanged proteolysis or protein synthesis markers in all SM examined. In addition, Lal-/- SM showed increased total cholesterol and CE concentrations, especially during fasting and maturation. Regardless of increased glucose uptake, expression of the slow oxidative fiber marker MYH7 was markedly increased in Lal-/-SM, indicating a fiber switch from glycolytic, fast-twitch fibers to oxidative, slow-twitch fibers. Proteomic analysis of the oxidative and glycolytic parts of the SM confirmed the transition between fast- and slow-twitch fibers, consistent with the decreased Lal-/- muscle size due to the "fiber paradox". Decreased oxidative capacity and ATP concentration were associated with reduced mitochondrial function of Lal-/- SM, particularly affecting oxidative phosphorylation, despite unchanged structure and number of mitochondria. Impairment in muscle function was reflected by increased exhaustion in the treadmill peak effort test in vivo. CONCLUSION:We conclude that whole-body loss of LAL is associated with a profound remodeling of the muscular phenotype, manifested by fiber type switch and a decline in muscle mass, most likely due to dysfunctional mitochondria and impaired energy metabolism, at least in mice.

OBJECTIVE:In brown adipose tissue (iBAT), the balance between lipid/glucose uptake and lipolysis is tightly regulated by insulin signaling. Downstream of the insulin receptor, PDK1 and mTORC2 phosphorylate AKT, which activates glucose uptake and lysosomal mTORC1 signaling. The latter requires the late endosomal/lysosomal adaptor and MAPK and mTOR activator (LAMTOR/Ragulator) complex, which serves to translate the nutrient status of the cell to the respective kinase. However, the role of LAMTOR in metabolically active iBAT has been elusive. METHODS:Using an AdipoqCRE-transgenic mouse line, we deleted LAMTOR2 (and thereby the entire LAMTOR complex) in adipose tissue (LT2 AKO). To examine the metabolic consequences, we performed metabolic and biochemical studies in iBAT isolated from mice housed at different temperatures (30 °C, room temperature and 5 °C), after insulin treatment, or in fasted and refed condition. For mechanistic studies, mouse embryonic fibroblasts (MEFs) lacking LAMTOR 2 were analyzed. RESULTS:Deletion of the LAMTOR complex in mouse adipocytes resulted in insulin-independent AKT hyperphosphorylation in iBAT, causing increased glucose and fatty acid uptake, which led to massively enlarged lipid droplets. As LAMTOR2 was essential for the upregulation of de novo lipogenesis, LAMTOR2 deficiency triggered exogenous glucose storage as glycogen in iBAT. These effects are cell autonomous, since AKT hyperphosphorylation was abrogated by PI3K inhibition or by deletion of the mTORC2 component Rictor in LAMTOR2-deficient MEFs. CONCLUSIONS:We identified a homeostatic circuit for the maintenance of iBAT metabolism that links the LAMTOR-mTORC1 pathway to PI3K-mTORC2-AKT signaling downstream of the insulin receptor.

Polyunsaturated fatty acids (PUFAs) are components of membrane phospholipids and precursors of bioactive lipid mediators. Here, we investigated the crosstalk of three pathways providing PUFAs for lipid mediator production: (i) secreted group X phospholipase A2 (GX sPLA2) and (ii) cytosolic group IVA PLA2 (cPLA2α), which both mobilize PUFAs from phospholipids, and (iii) adipose triglyceride lipase (ATGL), which breaks down triacylglycerols (TAGs) stored in lipid droplets (LDs). Combining lipidomic and functional analyses, we demonstrate that lipid mediator production depends on TAG turnover. GX sPLA2 directs PUFAs into TAGs and ATGL is required for their entry into lipid mediator biosynthetic pathways. ATGL also promotes the incorporation of LD-derived PUFAs into phospholipids representing substrates for cPLA2α. Additionally, inhibition of TAG synthesis mediated by acyl-CoA:diacylglycerol acyltransferase 1 (DGAT1) reduces the levels of mitogenic lipid signals and compromises tumour growth. This study expands the paradigm of PLA2-driven lipid mediator signalling and identifies LDs as central lipid mediator production hubs.

Introduction Lipids and fatty acids are key components in metabolic processes of the human placenta, thereby contributing to the development of the fetus. Placental dyslipidemia and aberrant activity of lipases have been linked to diverse pregnancy associated complications, such as preeclampsia and preterm birth. The serine hydrolases, diacylglycerol lipase α and β (DAGLα, DAGLβ) catalyze the degradation of diacylglycerols, leading to the formation of monoacylglycerols (MAG), including one main endocannabinoid 2-arachidonoylglycerol (2-AG). The major role of DAGL in the biosynthesis of 2-AG is evident from various studies in mice but has not been investigated in the human placenta. Here, we report the use of the small molecule inhibitor DH376, in combination with the ex vivo placental perfusion system, activity-based protein profiling (ABPP) and lipidomics, to determine the impact of acute DAGL inhibition on placental lipid networks. Methods DAGLα and DAGLβ mRNA expression was detected by RT-qPCR and in situ hybridization in term placentas. Immunohistochemistry staining for CK7, CD163 and VWF was applied to localize DAGLβ transcripts to different cell types of the placenta. DAGLβ activity was determined by in- gel and MS-based activity-based protein profiling (ABPP) and validated by addition of the enzyme inhibitors LEI-105 and DH376. Enzyme kinetics were measured by EnzChek™ lipase substrate assay. Ex vivo placental perfusion experiments were performed +/- DH376 [1 µM] and changes in tissue lipid and fatty acid profiles were measured by LC-MS. Additionally, free fatty acid levels of the maternal and fetal circulations were determined. Results We demonstrate that mRNA expression of DAGLβ prevails in placental tissue, compared to DAGLα (p ≤ 0.0001) and that DAGLβ is mainly located to CK7 positive trophoblasts (p ≤ 0.0001). Although few DAGLα transcripts were identified, no active enzyme was detected applying in-gel or MS-based ABPP, which underlined that DAGLβ is the principal DAGL in the placenta. DAGLβ dependent substrate hydrolysis in placental membrane lysates was determined by the application of LEI-105 and DH376. Ex vivo pharmacological inhibition of DAGLβ by DH376 led to reduced MAG tissue levels (p ≤ 0.01), including 2-AG (p≤0.0001). We further provide an activity landscape of serine hydrolases, showing a broad spectrum of metabolically active enzymes in the human placenta. Discussion Our results emphasize the role of DAGLβ activity in the human placenta by determining the biosynthesis of 2-AG. Thus, this study highlights the special importance of intra-cellular lipases in lipid network regulation. Together, the activity of these specific enzymes may contribute to the lipid signaling at the maternal-fetal interface, with implications for function of the placenta in normal and compromised pregnancies.

Hormone-sensitive lipase (HSL) plays a crucial role in intracellular lipolysis, and loss of HSL leads to diacylglycerol (DAG) accumulation, reduced FA mobilization, and impaired PPARγ signaling. Hsl knockout mice exhibit adipose tissue inflammation, but the underlying mechanisms are still not clear. Here, we investigated if and to what extent HSL loss contributes to endoplasmic reticulum (ER) stress and adipose tissue inflammation in Hsl knockout mice. Furthermore, we were interested in how impaired PPARγ signaling affects the development of inflammation in epididymal white adipose tissue (eWAT) and inguinal white adipose tissue (iWAT) of Hsl knockout mice and if DAG and ceramide accumulation contribute to adipose tissue inflammation and ER stress. Ultrastructural analysis showed a markedly dilated ER in both eWAT and iWAT upon loss of HSL. In addition, Hsl knockout mice exhibited macrophage infiltration and increased F4/80 mRNA expression, a marker of macrophage activation, in eWAT, but not in iWAT. We show that treatment with rosiglitazone, a PPARγ agonist, attenuated macrophage infiltration and ameliorated inflammation of eWAT, but expression of ER stress markers remained unchanged, as did DAG and ceramide levels in eWAT. Taken together, we show that HSL loss promoted ER stress in both eWAT and iWAT of Hsl knockout mice, but inflammation and macrophage infiltration occurred mainly in eWAT. Also, PPARγ activation reversed inflammation but not ER stress and DAG accumulation. These data indicate that neither reduction of DAG levels nor ER stress contribute to the reversal of eWAT inflammation in Hsl knockout mice.

According to genome-wide RNA sequencing data from human and mouse platelets, adipose triglyceride lipase (ATGL), the main lipase catalyzing triglyceride (TG) hydrolysis in cytosolic lipid droplets (LD) at neutral pH, is expressed in platelets. Currently, it is elusive to whether common lipolytic enzymes are involved in the degradation of TG in platelets. Since the consequences of ATGL deficiency in platelets are unknown, we used whole-body and platelet-specific (plat)Atgl-deficient (−/−) mice to investigate the loss of ATGL on platelet function. Our results showed that platelets accumulate only a few LD due to lack of ATGL. Stimulation with platelet-activating agonists resulted in comparable platelet activation in Atgl−/−, platAtgl−/−, and wild-type mice. Measurement of mitochondrial respiration revealed a decreased oxygen consumption rate in platelets from Atgl−/− but not from platAtgl−/− mice. Of note, global loss of ATGL was associated with an anti-thrombogenic phenotype, which was evident by reduced thrombus formation in collagen-coated channels in vitro despite unchanged bleeding and occlusion times in vivo. We conclude that genetic deletion of ATGL affects collagen-induced thrombosis without pathological bleeding and platelet activation.

The lung airways are constantly exposed to inhaled toxic substances, resulting in cellular damage that is repaired by local expansion of resident bronchiolar epithelial club cells. Disturbed bronchiolar epithelial damage repair lies at the core of many prevalent lung diseases, including chronic obstructive pulmonary disease, asthma, pulmonary fibrosis, and lung cancer. However, it is still not known how bronchiolar club cell energy metabolism contributes to this process. Here, we show that adipose triglyceride lipase (ATGL), the rate-limiting enzyme for intracellular lipolysis, is critical for normal club cell function in mice. Deletion of the gene encoding ATGL, Pnpla2 (also known as Atgl), induced substantial triglyceride accumulation, decreased mitochondrial numbers, and decreased mitochondrial respiration in club cells. This defect manifested as bronchiolar epithelial thickening and increased airway resistance under baseline conditions. After naphthalene‑induced epithelial denudation, a regenerative defect was apparent. Mechanistically, dysfunctional PPARα lipid-signaling underlies this phenotype because (a) ATGL was needed for PPARα lipid-signaling in regenerating bronchioles and (b) administration of the specific PPARα agonist WY14643 restored normal bronchiolar club cell ultrastructure and regenerative potential. Our data emphasize the importance of the cellular energy metabolism for lung epithelial regeneration and highlight the significance of ATGL-mediated lipid catabolism for lung health.

In brown adipose tissue (iBAT), the balance of lipid/glucose uptake and lipolysis is regulated by insulin signaling. Downstream of the insulin receptor, PDK1 and mTORC2 phosphorylate AKT, which activates glucose uptake and lysosomal mTORC1 signaling. The latter requires the late endosomal/lysosomal adaptor and MAPK and mTOR activator (LAMTOR/Ragulator). Deletion of LAMTOR2 (and thereby loss of the LAMTOR complex) in mouse adipocytes resulted in insulin-independent AKT hyperphosphorylation in iBAT, causing increased glucose and fatty acid uptake as evidenced by massively enlarged lipid droplets. As LAMTOR2 was essential for the upregulation of de novo lipogenesis, LAMTOR2 deficiency triggered exogenous glucose storage as glycogen in iBAT. These effects are cell autonomous, since AKT hyperphosphorylation was reversed by PI3K inhibition or by deletion of the mTORC2 component Rictor in LAMTOR2-deficient mouse embryonic fibroblasts. We identified a homeostatic circuit connecting LAMTOR-mTORC1 signaling with PI3K-mTORC2-AKT signaling downstream of the insulin receptor to maintain iBAT metabolism.

Age-related muscle dysfunction and sarcopenia are major causes of physical incapacitation in older adults and currently lack viable treatment strategies. Here we find that sphingolipids accumulate in mouse skeletal muscle upon aging and that both genetic and pharmacological inhibition of sphingolipid synthesis prevent age-related decline in muscle mass while enhancing strength and exercise capacity. Inhibition of sphingolipid synthesis confers increased myogenic potential and promotes protein synthesis. Within the sphingolipid pathway, we show that accumulation of dihydroceramides is the culprit disturbing myofibrillar homeostasis. The relevance of sphingolipid pathways in human aging is demonstrated in two cohorts, the UK Biobank and Helsinki Birth Cohort Study in which gene expression-reducing variants of SPTLC1 and DEGS1 are associated with improved and reduced fitness of older individuals, respectively. These findings identify sphingolipid synthesis inhibition as an attractive therapeutic strategy for age-related sarcopenia and co-occurring pathologies.