Sphingolipids function as membrane constituents and signaling molecules, with crucial roles in human diseases, from neurodevelopmental to cancer, best exemplified in the inborn errors of sphingolipid metabolism in lysosomes. The dihydroceramide desaturase DEGS1 acts in the last step of a sector of the sphingolipid pathway, de novo ceramide biosynthesis. Defects in DEGS1 cause the recently described hypomyelinating leukodystrophy-18 (HLD18, OMIM #618404). Here, we reveal that DEGS1 is a mitochondria-associated endoplasmic reticulum membrane (MAM)-resident enzyme, refining previous reports locating DEGS1 at the endoplasmic reticulum only. Using patient fibroblasts, multi-omics and enzymatic assays, we show that DEGS1 deficiency disrupts the main core functions of the MAM: i) mitochondrial dynamics, with a hyperfused mitochondrial network associated with decreased activation of dynamin-related protein 1; ii) cholesterol metabolism, with impaired sterol O-acyltransferase activity and decreased cholesteryl esters; iii) phospholipid metabolism, with increased phosphatidic acid and phosphatidylserine and decreased phosphatidylethanolamine; iv) biogenesis of lipid droplets, with increased size and numbers. Moreover, we detected increased mitochondrial superoxide species production in fibroblasts and mitochondrial respiration impairment in patient muscle biopsy tissues. Our findings shed light on the pathophysiology of HLD18 and broaden our understanding of the role of sphingolipid metabolism in MAMs function.
Laura Planas-Serra, Nathalie Launay, Leire Goicoechea, Bénédicte Heron, Cristina Jou, Natalia Juliá-Palacios, Montserrat Ruiz, Stéphane Fourcade, Carlos Casasnovas, Carolina De La Torre, Antoinette Gelot, Maria Marsal, Pablo Loza-Alvarez, Àngels García-Cazorla, Ali Fatemi, Isidre Ferrer, Manuel Portero-Otin, Estela Area-Gómez, Aurora Pujol
Pathogens and inflammatory conditions rapidly induce the expression of immune-responsive gene 1 (IRG1) in cells of myeloid lineage. IRG1 encodes an aconitate decarboxylase (ACOD1) that produces the immunomodulatory metabolite itaconate (ITA). In addition to rapid intracellular accumulation, ITA is also secreted from the cell, but whether secreted ITA functions as a signaling molecule is unclear. Here, we identified ITA as an orthosteric agonist of the GPCR OXGR1, with an EC50 of approximately 0.3 mM, which was in the same range as the physiological concentration of extracellular ITA upon macrophage activation. ITA activated OXGR1 to induce Ca2+ mobilization, ERK phosphorylation, and endocytosis of the receptor. In a mouse model of pulmonary infection with bacterial Pseudomonas aeruginosa, ITA stimulated Oxgr1-dependent mucus secretion and transport in respiratory epithelium, the primary innate defense mechanism of the airway. Our study thus identifies ITA as a bona fide ligand for OXGR1 and the ITA/OXGR1 paracrine signaling pathway during the pulmonary innate immune response.
Yi-Rong Zeng, Jun-Bin Song, Dezheng Wang, Zi-Xuan Huang, Cheng Zhang, Yi-Ping Sun, Gang Shu, Yue Xiong, Kun-Liang Guan, Dan Ye, Pu Wang
Activation of STING signaling in dendritic cells (DCs) promotes antitumor immunity. Aerobic glycolysis is a metabolic hallmark of activated DCs, but how the glycolytic pathway intersects with STING signaling in tumor-infiltrating DCs remains elusive. Here, we show that glycolysis drives STING signaling to facilitate DC-mediated antitumor immune responses. Tumor-infiltrating DCs exhibited elevated glycolysis, and blockade of glycolysis by DC-specific Ldha/Ldhb double deletion resulted in defective antitumor immunity. Mechanistically, glycolysis augmented ATP production to boost STING activation and STING-dependent DC antitumor functions. Moreover, DC-intrinsic STING activation accelerated HIF-1a–mediated glycolysis and established a positive feedback loop. Importantly, glycolysis facilitated STING-dependent DC activity in tissue samples from non-small cell lung cancer patients. Our results provide mechanistic insight into how the crosstalk of glycolytic metabolism and STING signaling enhances DC antitumor activity and can be harnessed to improve cancer therapies.
Zhilin Hu, Xiaoyan Yu, Rui Ding, Ben Liu, Chuanjia Gu, Xiu-Wu Pan, Qiaoqiao Han, Yuerong Zhang, Jie Wan, Xin-gang Cui, Jiayuan Sun, Qiang Zou
Adaptation of the islet β-cell insulin secretory response to changing insulin demand is critical for blood glucose homeostasis, yet the mechanisms underlying this adaptation are unknown. Here, we have shown that nutrient-stimulated histone acetylation plays a key role in adapting insulin secretion through regulation of genes involved in β-cell nutrient sensing and metabolism. Nutrient regulation of the epigenome occurred at sites occupied by the chromatin-modifying enzyme Lysine-specific demethylase 1 (Lsd1) in islets. β-cell-specific deletion of Lsd1 led to insulin hypersecretion, aberrant expression of nutrient response genes, and histone hyperacetylation. Islets from mice adapted to chronically increased insulin demand exhibited shared epigenetic and transcriptional changes. Moreover, we found that genetic variants associated with type 2 diabetes were enriched at LSD1-bound sites in human islets, suggesting that interpretation of nutrient signals is genetically determined and clinically relevant. Overall, these studies revealed that adaptive insulin secretion involves Lsd1-mediated coupling of nutrient state to regulation of the islet epigenome.
Matthew Wortham, Fenfen Liu, Austin R. Harrington, Johanna Y. Fleischman, Martina Wallace, Francesca Mulas, Medhavi Mallick, Nicholas K. Vinckier, Benjamin R. Cross, Joshua Chiou, Nisha A. Patel, Yinghui Sui, Carolyn McGrail, Yesl Jun, Gaowei Wang, Ulupi S. Jhala, Roland Schüle, Orian S. Shirihai, Mark O. Huising, Kyle J. Gaulton, Christian M. Metallo, Maike Sander
YunZu Michele Wang, Cynthia B. Taggart, John F. Huber, Stella M. Davies, David F. Smith, John B. Hogenesch, Christopher E. Dandoy
Obesity is a risk factor for neurodegenerative disease associated with cognitive dysfunction, including Alzheimer’s disease. Low-grade inflammation is common in obesity, but the mechanism between inflammation and cognitive impairment in obesity is unclear. Accumulative evidence shows that quinolinic acid (QA), a neuroinflammatory neurotoxin, is involved in the pathogenesis of neurodegenerative processes. We investigated the role of QA in obesity-induced cognitive impairment and the beneficial effect of butyrate in counteracting impairments of cognition, neural morphology, and signaling. We show that in human obesity, there was a negative relationship between serum QA levels and cognitive function and decreased cortical gray matter. Diet-induced obese mice had increased QA levels in the cortex associated with cognitive impairment. At single-cell resolution, we confirmed that QA impaired neurons, altered the dendritic spine’s intracellular signal, and reduced brain-derived neurotrophic factor (BDNF) levels. Using Caenorhabditis elegans models, QA induced dopaminergic and glutamatergic neuron lesions. Importantly, the gut microbiota metabolite butyrate was able to counteract those alterations, including cognitive impairment, neuronal spine loss, and BDNF reduction in both in vivo and in vitro studies. Finally, we show that butyrate prevented QA-induced BDNF reductions by epigenetic enhancement of H3K18ac at BDNF promoters. These findings suggest that increased QA is associated with cognitive decline in obesity and that butyrate alleviates neurodegeneration.
Xing Ge, Mingxuan Zheng, Minmin Hu, Xiaoli Fang, Deqin Geng, Sha Liu, Li Wang, Jun Zhang, Li Guan, Peng Zheng, Yuanyi Xie, Wei Pan, Menglu Zhou, Limian Zhou, Renxian Tang, Kuiyang Zheng, Yinghua Yu, Xu-Feng Huang
Glucose homeostasis can be improved after bariatric surgery that alters bile flow and stimulate gut hormone secretion, in particular FGF15/19. FGFR1 expression in AGRP expressing cells is required for bile acids's ability to improve glucose control. We show that the mouse Agrp gene has 3 promoter/enhancer regions that direct transcription of each of their own AGRP transcripts. One of these Agrp promoters/enhancers, Agrp B, is regulated by bile acids. We generated an Agrp B knock-in FLP/knockout allele. AGRP B expressing cells are found in endocrine cells the pars tuberalis (PT) and co-expressDAGLB (an endocannabinoid biosynthetic enzyme), distinct from PT thyrotropes. AGRP B expression is also found in the folliculostellate cells of the pituitary's anterior lobe. Mice without AGRP B are protected from high fat feeding induced glucose intolerance but not excess weight gain. Chemogenetic inhibition of AGRP B cells improves glucose tolerance by enhancing glucose stimulated insulin secretion. Inhibition of the AGRP B cells also caused weight loss. The improved glucose tolerance and reduced body weight persisted up to 6 weeks after cessation of the DREADD mediated inhibition, suggesting the presence of a biological switch for glucose homeostasis that is regulated by long term stability of food availability.
Shun-Mei Liu, Bruno Ifebi, Fred Johnson III, Alison Xu, Jacquelin Ho, Yunlei Yang, Gary J. Schwartz, Young-Hwan Jo, Streamson Chua
The non-essential amino acid asparagine can only be synthesized de novo by the enzymatic activity of asparagine synthetase (ASNS). While ASNS and asparagine have been implicated in the response to numerous metabolic stressors in cultured cells, the in vivo relevance of this enzyme in stress-related pathways remains unexplored. Here, we found ASNS to be expressed in pericentral hepatocytes, a population of hepatic cells specialized in xenobiotic detoxification. ASNS expression was strongly enhanced in two models of acute liver injury: carbon tetrachloride (CCl4) and acetaminophen (APAP). We found that mice with hepatocyte-specific Asns deletion (Asnshep-/-) were more prone to pericentral liver damage than their control (Asnshep+/+) littermates after toxin exposure. This phenotype could be reverted by intravenous administration of asparagine. Unexpectedly, the stress-induced upregulation of ASNS involved an ATF4-independent, non-canonical pathway mediated by the nuclear receptor, liver receptor homolog 1 (LRH-1; NR5A2). Altogether, our data indicate that the induction of the asparagine-producing enzyme ASNS acts as an adaptive mechanism to constrain the necrotic wave that follows toxin administration and provide proof of concept that intravenous delivery of asparagine can dampen hepatotoxin-induced pericentral hepatocellular death.
Yu Sun, Hadrien Demagny, Adrien Faure, Francesca Pontanari, Antoine Jalil, Nadia Bresciani, Ece Yildiz, Melanie Korbelius, Alessia Perino, Kristina Schoonjans
Type 2 diabetes (T2D) is caused by insufficient insulin secretion from pancreatic β-cells. To identify candidates contributing to T2D pathophysiology, we studied human pancreatic islets from ~300 individuals. We found 395 differentially expressed genes (DEGs) in islets from individuals with T2D, including, to our knowledge, novel (OPRD1, PAX5, TET1) and previously identified (CHL1, GLRA1, IAPP) candidates. A third of the identified islet expression changes may predispose to diabetes, as they associated with HbA1c in individuals not previously diagnosed with T2D. Most DEGs were expressed in human β-cells based on single-cell RNA-sequencing data. Additionally, DEGs displayed alterations in open chromatin and associated with T2D-SNPs. Mouse knock-out strains demonstrated that T2D-associated candidates regulate glucose homeostasis and body composition in vivo. Functional validation showed that mimicking T2D-associated changes for OPRD1, PAX5, and SLC2A2 impaired insulin secretion. Impairments in Pax5-overexpressing β-cells were due to severe mitochondrial dysfunction. Finally, we discovered PAX5 as a potential transcriptional regulator of many T2D-associated DEGs in human islets. Overall, we identified molecular alterations in human pancreatic islets contributing to β-cell dysfunction in T2D pathophysiology.
Karl Bacos, Alexander Perfilyev, Alexandros Karagiannopoulos, Elaine Cowan, Jones K. Ofori, Ludivine Bertonnier-Brouty, Tina Rönn, Andreas Lindqvist, Cheng Luan, Sabrina Ruhrmann, Mtakai Ngara, Åsa Nilsson, Sevda Gheibi, Claire L. Lyons, Jens O. Lagerstedt, Mohammad Barghouth, Jonathan L.S. Esguerra, Petr Volkov, Malin Fex, Hindrik Mulder, Nils Wierup, Ulrika Krus, Isabella Artner, Lena Eliasson, Rashmi B. Prasad, Luis Rodrigo Cataldo, Charlotte Ling
The molecular mechanisms of sodium-glucose cotransporter-2 (SGLT2) inhibitors (SGLT2i) remain incompletely understood. Single-cell RNA sequencing and morphometric data were collected from research kidney biopsies donated by young persons with type 2 diabetes (T2D), aged 12-21 years, and healthy controls (HC). Participants with T2D were obese, had higher estimated glomerular filtration rates, mesangial and glomerular volumes than HC. Ten T2D participants had been prescribed SGLT2i (T2Di(+)) and 6 not (T2Di(-)). Transcriptional profiles showed SGLT2 expression exclusively in the proximal tubular (PT) cluster with highest expression in T2Di(-). However, transcriptional alterations with SGLT2i treatment were seen across nephron segments, particularly in the distal nephron. SGLT2i treatment was associated with suppression of transcripts in the glycolysis, gluconeogenesis, tricarboxylic acid cycle pathways in PT, but enhanced in thick ascending limb. Transcripts in the energy sensitive mammalian target of rapamycin complex1 (mTORC1) signaling pathway returned towards HC levels in all tubular segments in T2Di(+), consistent with a diabetes mouse model treated with SGLT2i. Decreased levels of phosphorylated S6 protein in proximal and distal tubules in T2Di(+) confirmed changes in mTORC1 pathway activity. We propose that SGLT2i treatment benefits the kidneys by mitigating diabetes-induced metabolic perturbations via suppression of mTORC1 signaling in kidney tubules.
Jennifer A. Schaub, Fadhl M. AlAkwaa, Phillip J. McCown, Abhijit S. Naik, Viji Nair, Sean Eddy, Rajasree Menon, Edgar A. Otto, Dawit Demeke, John Hartman, Damian Fermin, Christopher O'Connor, Lalita Subramanian, Markus Bitzer, Roger Harned, Patricia Ladd, Laura Pyle, Subramaniam Pennathur, Ken Inoki, Jeffrey B. Hodgin, Frank C. Brosius, Robert G. Nelson, Matthias Kretzler, Petter Bjornstad