Excessive lipolysis in white adipose tissues (WAT) leads to insulin resistance (IR) and ectopic fat accumulation in insulin-sensitive tissues. However, the impact of Gi-coupled receptors in restraining adipocyte lipolysis through inhibition of cAMP production remained poorly elucidated. Given that the Gi-coupled P2Y13 receptor (P2Y13-R) is a purinergic receptor expressed in WAT, we investigated its role in adipocyte lipolysis and its effect on IR and metabolic dysfunction-associated steatotic liver disease (MASLD). In human, mRNA expression of P2Y13-R in WAT was negatively correlated to adipocytes lipolysis. In mice, adipocytes lacking P2Y13-R displayed higher intracellular cAMP levels, indicating impaired Gi signaling. Consistently, the absence of P2Y13-R was linked to increased lipolysis in adipocytes and WAT explants via hormone-sensitive lipase activation. Metabolic studies indicate that mice lacking P2Y13-R show a greater susceptibility to diet-induced IR, systemic inflammation, and MASLD compared to their wild-type counterparts. Assays conducted on precision-cut liver slices exposed to WAT conditioned medium and on liver-specific P2Y13-R knockdown mice suggested that P2Y13-R activity in WAT protects from hepatic steatosis, independently of liver P2Y13-R expression. In conclusion, our findings support the idea that targeting adipose P2Y13-R activity may represent a pharmacological strategy to prevent obesity-associated disorders, including type 2 diabetes and MASLD.
Thibaut Duparc, Emilia Gore, Guillaume Combes, Diane Beuzelin, Julie Pires Da Silva, Vanessa Bouguetoch, Marie-Adeline Marquès, Ana Velazquez, Nathalie Viguerie, Geneviève Tavernier, Peter Arner, Mikael Rydén, Dominique Langin, Nabil Sioufi, Mohamad Nasser, Cendrine Cabou, Souad Najib, Laurent O. Martinez
Accumulation of sphingolipids, especially sphingosines, in the lysosomes is a key driver of several lysosomal storage diseases. The transport mechanism for sphingolipids from the lysosome remains unclear. Here, we identified SPNS1, which shares the highest homology to SPNS2 - a sphingosine-1-phosphate (S1P) transporter, functions as a transporter for lysolipids from the lysosome. We generated Spns1 knockout cells and mice and employed lipidomic and metabolomic approaches to reveal SPNS1 ligand identity. Global knockout of Spns1 caused embryonic lethality between E12.5-E13.5 and an accumulation of sphingosine, lysophosphatidylcholines (LPC) and lysophosphatidylethanolamines (LPE) in the fetal livers. Similarly, metabolomic analysis of livers from postnatal Spns1 knockout (Spns1-KO) mice presented an accumulation of sphingosines and lysoglycerophospholipids including LPC and LPE. Subsequently, biochemical assays showed that SPNS1 is required for LPC and sphingosine release from lysosomes. The accumulation of these lysolipids in the lysosomes of Spns1-KO mice affected liver functions and altered the PI3K-AKT signaling pathway. Furthermore, we identified three human siblings with a homozygous variant in the SPNS1 gene. These patients suffer from developmental delay, neurological impairment, intellectual disability, and exhibiting cerebellar hypoplasia. These results reveal a critical role of SPNS1 as a promiscuous lysolipid transporter in the lysosomes and link its physiological functions with lysosomal storage diseases.
Hoa T.T. Ha, SiYi Liu, Xuan T.A. Nguyen, Linh K. Vo, Nancy C.P. Leong, Dat T. Nguyen, Shivaranjani Balamurugan, Pei Yen Lim, YaJun Wu, Eunju Seong, Toan Q. Nguyen, Jeongah Oh, Markus R. Wenk, Amaury Cazenave-Gassiot, Zuhal Yapici, Wei-Yi Ong, Margit Burmeister, Long N. Nguyen
Connexin43 (Cx43) is the most abundant gap junction protein present in the mesenchymal lineage. In mature adipocytes, Cx43 mediates white adipose tissue (WAT) “beiging” in response to cold exposure and maintains the mitochondrial integrity of brown adipose tissue (BAT). We found that genetic deletion of Gja1 (Cx43 gene) in cells that give rise to chondro-osteogenic and adipogenic precursors driven by the Dermo1/Twist2 promoter led to lower body adiposity and partial protection against the weight gain and metabolic syndrome induced by a high fat diet (HFD) in both sexes. These protective effects from obesogenic diet were related to increased locomotion, fuel utilization, energy expenditure, non-shivering thermogenesis, and better glucose tolerance in conditionally Gja1 ablated mice. Accordingly, Gja1 mutant mice exhibited reduced adipocyte hypertrophy, partially preserved insulin sensitivity, increased BAT lipolysis and decreased whitening under HFD. This metabolic phenotype was not reproduced with more restricted Gja1 ablation in differentiated adipocytes, suggesting that Cx43 in adipocyte progenitors or other targeted cells restrains energy expenditures and promotes fat accumulation. These results disclose an hitherto unknown action of Cx43 in adiposity, and offer a promising new pharmacologic target for improving metabolic balance in diabetes and obesity.
Seung-Yon Lee, Francesca Fontana, Toshifumi Sugatani, Ignacio Portales Castillo, Giulia Leanza, Ariella Coler-Reilly, Roberto Civitelli
Glucose homeostasis is achieved via complex interactions between the endocrine pancreas and other peripheral tissues and glucoregulatory neurocircuits in the brain that remain incompletely defined. Within the brain, neurons in the hypothalamus appear to play a particularly important role. Consistent with this notion, we report evidence that (pro)renin receptor (PRR) signaling within a subset of tyrosine hydroxylase (TH) neurons located in the hypothalamic paraventricular nucleus (PVNTH neurons) is a physiological determinant of the defended blood glucose level. Specifically, we demonstrate that PRR deletion from PVNTH neurons restores normal glucose homeostasis in mice with diet-induced obesity (DIO). Conversely, chemogenetic inhibition of PVNTH neurons mimics the deleterious effect of DIO on glucose. Combined with our finding that PRR activation inhibits PVNTH neurons, these findings suggest that in mice, (a) PVNTH neurons play a physiological role in glucose homeostasis, (b) PRR activation impairs glucose homeostasis by inhibiting these neurons, and (c) this mechanism plays a causal role in obesity-associated metabolic impairment.
Shiyue Pan, Lucas A.C. Souza, Caleb J. Worker, Miriam E. Reyes Mendez, Ariana Julia B. Gayban, Silvana G. Cooper, Alfredo Sanchez Solano, Richard N. Bergman, Darko Stefanovski, Gregory J. Morton, Michael W. Schwartz, Yumei Feng Earley
AMP-activated protein kinase (AMPK) plays a crucial role in maintaining ATP homeostasis in photoreceptor neurons. AMPK is a heterotrimeric protein consisting of alpha, beta, and gamma subunits. The independent functions of the two isoforms of the catalytic alpha subunit, PRKAA1 and PRKAA2, are uncharacterized in specialized neurons such as photoreceptors. Here we demonstrate in mice that rod photoreceptors lacking PRKAA2, but not PRKAA1, show altered levels of cGMP, GTP, and ATP, suggesting isoform-specific regulation of photoreceptor metabolism. Furthermore, PRKAA2 deficient mice display visual functional deficits on electroretinography and photoreceptor outer segment structural abnormalities on transmission electron microscopy consistent with neuronal dysfunction, but not neurodegeneration. Phosphoproteomics identified inosine monophosphate dehydrogenase (IMPDH) as a molecular driver of PRKAA2-specific photoreceptor dysfunction, and inhibition of IMPDH improved visual function in Prkaa2 rod photoreceptor knockout mice. These findings highlight a novel, therapeutically targetable PRKAA2 isoform-specific function of AMPK in regulating photoreceptor metabolism and function through a previously uncharacterized mechanism affecting IMPDH activity.
Tae Jun Lee, Yo Sasaki, Philip A. Ruzycki, Norimitsu Ban, Joseph B. Lin, Hung-Ting Wu, Andrea Santeford, Rajendra S. Apte
BACKGROUND. Obesity is a multi-factorial disease with adverse health implications including insulin resistance (IR). In patients with obesity, the presence of high circulating levels of leptin, deemed hyperleptinemia, is associated with IR. Recent data in mice with diet-induced-obesity (DIO) shows a partial reduction in leptin levels improves IR. Additional animal studies demonstrate IL-4 decreases leptin levels. In rodents, resident adipose tissue (AT) eosinophils (EOS) are the main source of IL-4 and are instrumental in maintaining metabolic homeostasis. A marked reduction in AT-EOS content is observed in animal models of DIO. These observations have not been explored in humans. METHODS. We analyzed AT from individuals with obesity and age-matched lean counterparts for AT-EOS content, IL-4, circulating leptin levels and measures of IR. RESULTS. Our results showed that individuals with obesity (n=15) had a significant reduction in AT-EOS content (P<0.01), decreased AT-IL-4 gene expression (P=0.02), and decreased IL-4 plasma levels (P<0.05) in addition to expected IR (P<0.001) and hyperleptinemia (P<0.01) compared to lean subjects (n=15). AT-EOS content inversely correlated with BMI (P=0.002) and IR (P=0.005). Ex vivo AT explants and in vitro cell culture of primary, human mature adipocytes exposed to either IL-4 or EOS conditioned media produced less leptin (P<0.05). CONCLUSIONS. Our results suggested for IL-4 to act as a link between EOS, AT, and leptin production. Future studies exploring this interaction may identify a new avenue for the treatment of obesity and its complications through amelioration of hyperleptinemia. TRIAL REGISTRATION. Clinicaltrials.gov NCT02378077 & NCT04234295. FUNDING. Dr. Eleanna De Filippis received support by Arizona Department of Health Services, Arizona Biomedical Research Commission (ABRC) (ADHS14-00003606), the Katryn H. and Roger Penske Career Development Award in Endocrinology in Honor of Dr. Ian Hay, and Mayo Foundation, KL2 TR002379-02-01 CTSA UL1 TR002377 NCATS/NIH. Dr. Elizabeth A. Jacobsen received support from NIAID AI132840 and Mayo Foundation
James D. Hernandez, Ting Li, Hamza Ghannam, Cassandra M. Rau, Mia Y. Masuda, James A. Madura, Elizabeth A. Jacobsen, Eleanna De Filippis
Depletion of torsinA from hepatocytes leads to reduced liver triglyceride secretion and marked hepatic steatosis. TorsinA is an atypical ATPase that lacks intrinsic activity unless it is bound to its activators lamina-associated polypeptide 1 (LAP1) or luminal domain-like LAP1 (LULL1). We previously demonstrated that depletion of LAP1 from hepatocytes has more modest effects on liver triglyceride secretion and steatosis development than depletion of torsinA. We now show that depletion of LULL1 alone does not significantly decrease triglyceride secretion or cause steatosis. However, simultaneous depletion of both LAP1 and LULL1 leads to defective triglyceride secretion and marked steatosis similar to that observed with depletion of torsinA. Depletion of both LAP1 and torsinA from hepatocytes generated phenotypes similar to those observed with only torsinA depletion, implying that the two proteins act in the same pathway in liver lipid metabolism. Our results demonstrate that torsinA and its activators dynamically regulate hepatic lipid metabolism.
Antonio Hernandez-Ono, Yi Peng Zhao, John W. Murray, Cecilia Östlund, Michael J. Lee, Angsi Shi, William T. Dauer, Howard J. Worman, Henry N. Ginsberg, Ji-Yeon Shin
Hyperuricemia is implicated in numerous pathologies but the mechanisms underlying uric acid production are poorly understood. Using a combination of mouse studies, cultured cell studies, and human serum samples, we sought to determine the cellular source of uric acid. In mice, fasting and glucocorticoid treatment increased serum uric acid and uric acid release from ex vivo incubated skeletal muscle. In vitro, glucocorticoids and the transcription factor FoxO3 increased purine nucleotide degradation and purine release from differentiated muscle cells, which coincided with the transcriptional upregulation of AMP deaminase 3, a rate-limiting enzyme in adenine nucleotide degradation. Heavy isotope tracing during co-culture experiments revealed that oxidation of muscle purines to uric acid required their transfer from muscle cells to a cell type that expresses xanthine oxidoreductase, such as endothelial cells. Lastly, in healthy women, matched for age and body composition, serum uric acid was greater in individuals scoring below average on standard physical function assessments. Together, these studies reveal skeletal muscle purine degradation is an underlying driver of uric acid production, with the final step of uric acid production occurring primarily in a non-muscle cell type. This suggests that skeletal muscle fiber purine degradation may represent a therapeutic target to reduce serum uric acid and treat numerous pathologies.
Spencer G. Miller, Catalina Matias, Paul S. Hafen, Andrew S. Law, Carol A. Witczak, Jeffrey J. Brault
Interorgan crosstalk via secreted hormones and metabolites is a fundamental aspect of mammalian metabolic physiology. Beyond the highly specialized endocrine cells, peripheral tissues are emerging as an important source of metabolic hormones that influence energy and nutrient metabolism and contribute to disease pathogenesis. Neuregulin 4 (Nrg4) is a fat-derived hormone that protects mice from nonalcoholic steatohepatitis (NASH) and NASH-associated liver cancer by shaping hepatic lipid metabolism and the liver immune microenvironment. Despite its enriched expression in brown fat, whether NRG4 plays a role in thermogenic response and mediates the metabolic benefits of cold exposure remain unexplored. Here we show that Nrg4 expression in inguinal white adipose tissue (iWAT) is highly responsive to chronic cold exposure. Nrg4 deficiency impairs beige fat induction and renders mice more susceptible to diet-induced metabolic disorders under mild cold conditions. Using mice with adipocyte and hepatocyte-specific Nrg4 deletion, we reveal that adipose tissue-derived NRG4, but not hepatic NRG4, is essential for beige fat induction following cold acclimation. Furthermore, treatment with recombinant NRG4-Fc fusion protein promotes beige fat induction in iWAT and improves metabolic health in diet-induced obese mice. These findings highlight a critical role of NRG4 in mediating beige fat induction and preserving metabolic health under mild cold conditions.
Zhimin Chen, Peng Zhang, Tongyu Liu, Xiaoxue Qiu, Siming Li, Jiandie D. Lin
Increased mitochondrial function may render some cancers vulnerable to mitochondrial inhibitors. Since mitochondrial function is regulated partly by mitochondrial DNA copy number (mtDNAcn), accurate measurements of mtDNAcn could help reveal which cancers are driven by increased mitochondrial function and may be candidates for mitochondrial inhibition. However, prior studies have employed bulk macrodissections that fail to account for cell type-specific or tumor cell heterogeneity in mtDNAcn. These studies have often produced unclear results, particularly in prostate cancer. Herein, we developed a multiplex in situ method to spatially quantify cell type specific mtDNAcn. We show that mtDNAcn is increased in luminal cells of high-grade prostatic intraepithelial neoplasia (HGPIN), is increased in prostatic adenocarcinomas (PCa), and is further elevated in metastatic castration-resistant prostate cancer. Increased PCa mtDNAcn was validated by two orthogonal methods and is accompanied by increases in mtRNAs and enzymatic activity. Mechanistically, MYC inhibition in prostate cancer cells decreases mtDNA replication and expression of several mtDNA replication genes, and MYC activation in the mouse prostate leads to increased mtDNA levels in the neoplastic prostate cells. Our in situ approach also revealed elevated mtDNAcn in precancerous lesions of the pancreas and colon/rectum, demonstrating generalization across cancer types using clinical tissue samples.
Jiayu Chen, Qizhi Zheng, Jessica L. Hicks, Levent Trabzonlu, Busra Ozbek, Tracy Jones, Ajay M. Vaghasia, Tatianna C. Larman, Rulin Wang, Mark C. Markowski, Samuel R. Denmeade, Kenneth J. Pienta, Ralph H. Hruban, Emmanuel S. Antonarakis, Anuj Gupta, Chi V. Dang, Srinivasan Yegnasubramanian, Angelo M. De Marzo
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