Adipocyte lipolysis-stimulated interleukin-6 production requires sphingosine kinase 1 activity

Antioxidant, Antiinflammation, and Antifibrotic Activity of Ciplukan (Physalis angulata L). Extract

Purpose

Physalis angulata Linn. (Ciplukan) is a plant widely used in traditional medicine in subtropical and tropical regions. Most studies focus on its antioxidant and anti-inflammatory activity. Many studies also reported its therapeutic potential for treating cancer, malaria, hepatitis, rheumatism, liver problems, and tumors, but few studies have reported its anti-fibrosis activity. Here, we aimed to investigate the potential of P. angulata as an antioxidant and anti-inflammatory that may be correlated with its anti-fibrosis action.

Methods

In our study, we treated 3T3-L1 and TGF-β-induced 3T3-L1 cells with an ethanol extract of P. angulata. We then monitored the cell's response, evaluated the antioxidant activity using an MTT assay, and observed the cells' migration using the cell scratch assay. We used RT-PCR to determine the expression of HIF-1α and IL-6 on TGF-β-induced 3T3-L1 cells.

Results

The ethanol extract of P. angulata showed antioxidant activity and promoted cell proliferation on 3T3-L1 cells. Interestingly, the extract inhibited the migration of TGF-β-induced 3T3-L1 cells. Further analysis revealed that the extract could inhibit HIF-1α expression and suppress IL-6 expression on TGF-β-induced 3T3-L1 cells.

Conclusion

The ethanol extract of P. angulata showed antioxidant and anti-inflammation activities in 3T3-L1 cells. Both activities are associated with the antifibrotic activity of P. angulata's ethanol extract.

Analyzing the expression of the transcriptome in adipose tissue of fat- and thin-tailed sheep

Significant efforts have been made to understand how fat deposition in sheep tail is regulated in genetic, transcriptomic, physiologic, biochemical, and metabolic levels in order to elucidate the complex mechanisms underlying the energy storage, lipid metabolism in adipose tissue, adaptability to harsh environments, and evolutionary domestication. Through RNA-seq data analysis, we are able to compare the gene expression of fat-tailed sheep versus thin-tailed sheep breeds in an acceptable resolution at transcriptome level. The purpose of this study was to compare the transcriptomes of Ghezel (fat-tailed) and Zel (thin-tailed) sheep. Total RNA from subcutaneous and tail tissue samples from healthy lambs was sequenced (150b PE) to identify differentially expressed genes (DEGs) between the two mentioned tissues and between the Ghezel and Zel sheep breeds. Further downstream pathway and network analyses were conducted afterwards. The results uncovered the association of the most important DEGs such as CAV1, ALB, and SOCS3 with cellular signaling pathways of lipids metabolism. It seems that the SOCS3 gene plays an important role in the differential deposition of lipid in the tails of two phenotypically different sheep breeds. Although the detail of gene expression in the tail and subcutaneous tissues of two morphologically different breeds was decoded here, to fully understand how differential expression of the SOCS3 gene affects the fat synthesis, further studies are needed.

Lipid Droplets and Neurodegeneration

Energy metabolism in the brain has been considered one of the critical research areas of neuroscience for ages. One of the most vital parts of brain metabolism cascades is lipid metabolism, and fatty acid plays a crucial role in this process. The fatty acid breakdown process in mitochondria undergoes through a conserved pathway known as β-oxidation where acetyl-CoA and shorter fatty acid chains are produced along with a significant amount of energy molecule. Further, the complete breakdown of fatty acids occurs when they enter the mitochondrial oxidative phosphorylation. Cells store energy as neutral lipids in organelles known as Lipid Droplets (LDs) to prepare for variations in the availability of nutrients. Fatty acids are liberated by lipid droplets and are transported to various cellular compartments for membrane biogenesis or as an energy source. Current research shows that LDs are important in inflammation, metabolic illness, and cellular communication. Lipid droplet biology in peripheral organs like the liver and heart has been well investigated, while the brain's LDs have received less attention. Recently, there has been increased awareness of the existence and role of these dynamic organelles in the central nervous system, mainly connected to neurodegeneration. In this review, we discussed the role of beta-oxidation and lipid droplet formation in the oxidative phosphorylation process, which directly affects neurodegeneration through various pathways.

Pharmacological Upregulation of Microglial Lipid Droplet Alleviates Neuroinflammation and Acute Ischemic Brain Injury

Lipid droplets (LDs) were reported to play an important role in the modulation of inflammation and various cellular processes among multiple cell types. However, LDs accumulation, its function and mechanisms of its formation during ischemic stroke remained poorly-identified. In this study, we observed increased LDs accumulation in microglia at the acute stage of ischemic stroke by immunofluorescence and flow cytometry. Transcriptomic analysis indicated that microglia accumulated with LDs were associated with inflammation and phagocytosis. Both inflammatory activation and phagocytosis of tissue debris in microglia could contribute to LDs formation. Moreover, through specific LDs depletion and overload experiments by pharmacological approaches, we proposed that LDs was critical for the maintenance of anti-inflammatory properties of microglia. Furthermore, Atglistatin, a specific adipose triglyceride lipase (ATGL) inhibitor, was shown to prevent proinflammatory cytokines production in primary microglia through decreased LDs lipolysis. After Atglistatin treatment, middle cerebral artery occlusion (MCAO) mice showed decreased infarct volume and improved neurobehavioral performance at the acute stage of stroke. Our findings provided a biological basis for microglial LDs regulation as a potential therapeutic strategy for acute ischemic stroke and uncovered the neuroprotective role of Atglistatin in the treatment of MCAO mice.

Adipokines in obesity and metabolic-related-diseases

The discovery of leptin in the 1990s led to a reconsideration of adipose tissue (AT) as not only a fatty acid storage organ, but also a proper endocrine tissue. AT is indeed capable of secreting bioactive molecules called adipokines for white AT or batokines for brown/beige AT, which allow communication with numerous organs, especially brain, heart, liver, pancreas, and/or the vascular system. Adipokines exert pro or anti-inflammatory activities. An equilibrated balance between these two sets ensures homeostasis of numerous tissues and organs. During the development of obesity, AT remodelling leads to an alteration of its endocrine activity, with increased secretion of pro-inflammatory adipokines relative to the anti-inflammatory ones, as shown in the graphical abstract. Pro-inflammatory adipokines take part in the initiation of local and systemic inflammation during obesity and contribute to comorbidities associated to obesity, as detailed in the present review.

Geniposide augments apoptosis in fibroblast-like synoviocytes by restoring hypoxia-enhanced JNK-BNIP3-mediated autophagy

BACKGROUND

As the main effector cells of chronic inflammation and hyperplasia of synovium, fibroblast-like synoviocytes (FLSs) show abnormal proliferation and insufficient apoptosis in the hypoxic microenvironment, which is due to the increase of BNIP3-mediated autophagy. This study aimed to explore the mechanism of geniposide (GE) on hypoxia-induced hyper-proliferative FLSs with a focus on autophagy and the JNK-BNIP3 pathway.

METHODS

The dynamic changes of autophagy, apoptosis, and hypoxia-related proteins in adjuvant arthritis (AA) rats were detected by immunohistochemistry and Western blot. The proliferation, autophagy, apoptosis, and mitochondrial state of FLSs were detected by CCK-8, flow cytometry, immunofluorescence, and transmission electron microscopy, respectively. Western blot, qRT-PCR, and co-immunoprecipitation were used to detect the expression of the JNK-BNIP3 pathway.

RESULTS

The excessive accumulation of BNIP3 in the synovium of AA rats was accompanied by inhibition of apoptosis and an increase in autophagy. GE inhibited the expression of BNIP3, enhanced apoptosis, decreased autophagy, and improved chronic inflammation and hyperplasia of synovium. The amount of autophagy under different oxygen concentrations was the key to mediating the different survival rates of FLSs, and the inhibition of autophagy triggered apoptosis. GE suppressed the proliferation of FLSs and down-regulated autophagy, leading to the accumulation of ROS and the decrease of mitochondrial membrane potential, induced the increase of apoptosis, and suppressed the accumulation of BNIP3 and the hyperphosphorylation of JNK.

CONCLUSION

GE inhibited autophagy by restoring the hypoxia-induced activated JNK-BNIP3 pathway, inducing mitochondrial oxidative damage, augmented apoptosis, and decreased survival rate of FLSs.

Clinical pharmacology of β-3 adrenergic receptor agonists for cardiovascular diseases

INTRODUCTION

Few agonists of the third isotype of beta-adrenergic receptors, the β3-adrenoreceptor, are currently used clinically, and new agonists are under development for the treatment of overactive bladder disease. As the receptor is expressed in human cardiac and vascular tissues, it is important to understand their beneficial (or adverse) effect(s) on these targets.

AREAS COVERED

We discuss the most recent results of clinical trials testing the benefit and safety of β3-adrenoreceptor activation on cardiovascular outcomes in light of current knowledge on the receptor biology, genetic polymorphisms, and agonist pharmacology.

EXPERT OPINION

While evidence from small clinical trials is limited so far, the β3-agonist, mirabegron seems to be safe in patients at high cardiovascular risk but produces benefits on selected cardiovascular outcomes only at higher than standard doses. Activation of cardiovascular β3-adrenoreceptors deserves to be tested with more potent agonists, such as vibegron.

Phillyrin restores metabolic disorders in mice fed with high-fat diet through inhibition of interleukin-6-mediated basal lipolysis

The function of white adipose tissue as an energy reservoir is impaired in obesity, leading to lipid spillover and ectopic lipid deposition. Adipose tissue inflammation can reduce the efficacy of lipid storage in adipocytes by augmenting basal lipolysis through producing interleukin-6 (IL-6). Therefore, pharmacological compounds targeting adipose tissue inflammation or IL-6 signaling might have the potential to combat obesity. This study aims to investigate the impact of Phillyrin, which is frequently used for treating respiratory infections in clinics in China, on obesity-related metabolic dysfunctions. Firstly, a mouse model of diet-induced obesity is used to assess the pharmacological applications of Phillyrin on obesity in vivo. Secondly, ex vivo culture of adipose tissue explants is utilized to investigate actions of Phillyrin on IL-6-linked basal lipolysis. Thirdly, a mouse model of IL-6 injection into visceral adipose tissue is explored to confirm the anti-basal lipolytic effect of Phillyrin against IL-6 in vivo. The results show that Phillyrin treatment reduces circulating level of glycerol, decreases hepatic steatosis and improves insulin sensitivity in obese mice. Meanwhile, Phillyrin attenuates obesity-related inflammation and IL-6 production in adipose tissue in obese mice. Furthermore, Phillyrin treatment results in resistance to IL-6-induced basal lipolysis in adipose tissue through suppressing expression of adipose triglyceride lipase (ATGL) both in vivo and in vitro. Collectively, these findings suggest that Phillyrin can restrain lipid efflux from inflamed adipose tissue in obesity by inhibiting IL-6-initiated basal lipolysis and ATGL expression, and thus is a potential candidate in the treatment of obesity-associated complications.

IL-6: The Link Between Inflammation, Immunity and Breast Cancer

Breast cancer is one of the leading causes of mortality in females. Over the past decades, intensive efforts have been made to uncover the pathogenesis of breast cancer. Interleukin-6 (IL-6) is a pleiotropic factor which has a vital role in host defense immunity and acute stress. Moreover, a wide range of studies have identified the physiological and pathological roles of IL-6 in inflammation, immune and cancer. Recently, several IL-6 signaling pathway-targeted monoclonal antibodies have been developed for cancer and immune therapy. Combination of IL-6 inhibitory antibody with other pathways blockage drugs have demonstrated promising outcome in both preclinical and clinical trials. This review focuses on emerging studies on the strong linkages of IL-6/IL-6R mediated regulation of inflammation and immunity in cancer, especially in breast cancer.

Sphingolipids in Adipose: Kin or Foe?

Obesity research has shifted in recent years to address not only the total amount of adipose tissue present in an individual but also to include adipose tissue functions such as endocrine function and thermogenesis. Data suggest that sphingolipids are critical regulators of metabolic homeostasis, and that disruption of their levels is associated with metabolic disease. Abundant data from mouse models has revealed both beneficial and deleterious roles for sphingolipids in adipose function, and numerous human studies have shown that obesity alters circulating sphingolipid profiles. Sphingolipids comprise a large family of interrelated metabolites, and pinpointing specific functions for specific lipids will be required to fully exploit the therapeutic potential of targeting sphingolipids to treat obesity and related disorders.

Adipocyte CAMK2 deficiency improves obesity-associated glucose intolerance

OBJECTIVE

Obesity-related adipose tissue dysfunction has been linked to the development of insulin resistance, type 2 diabetes, and cardiovascular disease. Impaired calcium homeostasis is associated with altered adipose tissue metabolism; however, the molecular mechanisms that link disrupted calcium signaling to metabolic regulation are largely unknown. Here, we investigated the contribution of a calcium-sensing enzyme, calcium/calmodulin-dependent protein kinase II (CAMK2), to adipocyte function, obesity-associated insulin resistance, and glucose intolerance.

METHODS

To determine the impact of adipocyte CAMK2 deficiency on metabolic regulation, we generated a conditional knockout mouse model and acutely deleted CAMK2 in mature adipocytes. We further used in vitro differentiated adipocytes to dissect the mechanisms by which CAMK2 regulates adipocyte function.

RESULTS

CAMK2 activity was increased in obese adipose tissue, and depletion of adipocyte CAMK2 in adult mice improved glucose intolerance and insulin resistance without an effect on body weight. Mechanistically, we found that activation of CAMK2 disrupted adipocyte insulin signaling and lowered the amount of insulin receptor. Further, our results revealed that CAMK2 contributed to adipocyte lipolysis, tumor necrosis factor alpha (TNFα)-induced inflammation, and insulin resistance.

CONCLUSIONS

These results identify a new link between adipocyte CAMK2 activity, metabolic regulation, and whole-body glucose homeostasis.

Remodeling of Macrophages in White Adipose Tissue under the Conditions of Obesity as well as Lipolysis

Adipose tissue macrophages (ATM) are a major source of low-grade inflammation in obesity, and yet reasons driving ATM accumulation in white adipose tissue (WAT) are not fully understood. Emerging evidence suggested that ATM underwent extensive remodeling in obesity. In addition to abundance, ATM in obesity were lipid-laden and metabolically reprogrammed, which in turn was tightly related to their functional alterations and persistence in obesity. Herein, we aimed to discuss that activation of lipid sensing signaling associated with metabolic reprogramming in ATM was indispensible for their migration, retention, or proliferation in obesity. Likewise, lipolysis also induced similar but transient ATM remodeling. Therefore, we assumed that obesity might share overlapping mechanisms with lipolysis in remodeling ATM. Formation of crown-like structures (CLS) in WAT was presumably a common event initiating ATM remodeling, with a spectrum of lipid metabolites released from adipocytes being potential signaling molecules. Moreover, adipose interlerkin-6 (IL-6) exhibited homologous alterations by obesity and lipolysis. Thus, we postulated a positive feedback loop between ATM and adipocytes via IL-6 signaling backing ATM persistence by comparison of ATM remodeling under obesity and lipolysis. An elucidation of ATM persistence could help to provide novel therapeutic targets for obesity-associated inflammation.

4-Phenylbutyric acid improves free fatty acid-induced hepatic insulin resistance in vivo

Plasma free fatty acids (FFAs) are elevated in obesity and can induce insulin resistance via endoplasmic reticulum (ER) stress. However, it is unknown whether hepatic insulin resistance caused by the elevation of plasma FFAs is alleviated by chemical chaperones. Rats received one of the following i.v. treatments for 48 h: saline, intralipid plus heparin (IH), IH plus the chemical chaperone 4-phenylbutyric acid (PBA), or PBA alone and a hyperinsulinemic-euglycemic clamp was performed during the last 2 h. PBA co-infusion normalized IH-induced peripheral insulin resistance, similar to our previous findings with an antioxidant and an IκBα kinase β (IKKβ) inhibitor. Different from our previous results with the antioxidant and IKKβ inhibitor, PBA also improved IH-induced hepatic insulin resistance in parallel with activation of Akt. Unexpectedly, IH did not induce markers of ER stress in the liver, but PBA prevented IH-induced elevation of phosphorylated eukaryotic initiation factor-2α protein in adipose tissue. PBA tended to decrease circulating fetuin-A and significantly increased circulating fibroblast growth factor 21 (FGF21) without affecting markers of activation of hepatic protein kinase C-δ or p38 mitogen-activated protein kinase that we have previously involved in hepatic insulin resistance in this model. In conclusion: (i) PBA prevented hepatic insulin resistance caused by prolonged plasma FFA elevation without affecting hepatic ER stress markers; (ii) the PBA effect is likely due to increased FGF21 and/or decreased fetuin-A, which directly signal to upregulate Akt activation.

Elevated S-adenosylhomocysteine induces adipocyte dysfunction to promote alcohol-associated liver steatosis

It has been previously shown that chronic ethanol administration-induced increase in adipose tissue lipolysis and reduction in the secretion of protective adipokines collectively contribute to alcohol-associated liver disease (ALD) pathogenesis. Further studies have revealed that increased adipose S-adenosylhomocysteine (SAH) levels generate methylation defects that promote lipolysis. Here, we hypothesized that increased intracellular SAH alone causes additional related pathological changes in adipose tissue as seen with alcohol administration. To test this, we used 3-deazaadenosine (DZA), which selectively elevates intracellular SAH levels by blocking its hydrolysis. Fully differentiated 3T3-L1 adipocytes were treated in vitro for 48 h with DZA and analysed for lipolysis, adipokine release and differentiation status. DZA treatment enhanced adipocyte lipolysis, as judged by lower levels of intracellular triglycerides, reduced lipid droplet sizes and higher levels of glycerol and free fatty acids released into the culture medium. These findings coincided with activation of both adipose triglyceride lipase and hormone sensitive lipase. DZA treatment also significantly reduced adipocyte differentiation factors, impaired adiponectin and leptin secretion but increased release of pro-inflammatory cytokines, IL-6, TNF and MCP-1. Together, our results demonstrate that elevation of intracellular SAH alone by DZA treatment of 3T3-L1 adipocytes induces lipolysis and dysregulates adipokine secretion. Selective elevation of intracellular SAH by DZA treatment mimics ethanol's effects and induces adipose dysfunction. We conclude that alcohol-induced elevations in adipose SAH levels contribute to the pathogenesis and progression of ALD.

Hepatic Igf1-Deficiency Protects Against Atherosclerosis in Female Mice

Atherosclerosis is the leading cause of cardiovascular disease (CVD), with distinct sex-specific pathogenic mechanisms that are poorly understood. Aging, a major independent risk factor for atherosclerosis, correlates with a decline in circulating insulin-like growth factor-1 (IGF-1). However, the precise effects of Igf1 on atherosclerosis remain unclear. In the present study, we assessed the essential role of hepatic Igf1, the major source of circulating IGF-1, in atherogenesis. We generated hepatic Igf1-deficient atherosclerosis-prone apolipoprotein E (ApoE)-null mice (L-Igf1-/-ApoE-/-) using the Cre-loxP system driven by the Albumin promoter. Starting at 6 weeks of age, these mice and their littermate controls, separated into male and female groups, were placed on an atherogenic diet for 18 to 19 weeks. We show that hepatic Igf1-deficiency led to atheroprotection with reduced plaque macrophages in females, without significant effects in males. This protection from atherosclerosis in females was associated with increased subcutaneous adiposity and with impaired lipolysis. Moreover, this impaired lipid homeostasis was associated with disrupted adipokine secretion with reduced circulating interleukin-6 (IL-6) levels. Together, our data show that endogenous hepatic Igf1 plays a sex-specific regulatory role in atherogenesis, potentially through athero-promoting effects of adipose tissue-derived IL-6 secretion. These data provide potential novel sex-specific mechanisms in the pathogenesis of atherosclerosis.

Sphingosine 1-phosphate metabolism and insulin signaling

Insulin is the main anabolic hormone secreted by β-cells of the pancreas stimulating the assimilation and storage of glucose in muscle and fat cells. It modulates the postprandial balance of carbohydrates, lipids and proteins via enhancing lipogenesis, glycogen and protein synthesis and suppressing glucose generation and its release from the liver. Resistance to insulin is a severe metabolic disorder related to a diminished response of peripheral tissues to the insulin action and signaling. This leads to a disturbed glucose homeostasis that precedes the onset of type 2 diabetes (T2D), a disease reaching epidemic proportions. A large number of studies reported an association between elevated circulating fatty acids and the development of insulin resistance. The increased fatty acid lipid flux results in the accumulation of lipid droplets in a variety of tissues. However, lipid intermediates such as diacylglycerols and ceramides are also formed in response to elevated fatty acid levels. These bioactive lipids have been associated with the pathogenesis of insulin resistance. More recently, sphingosine 1-phosphate (S1P), another bioactive sphingolipid derivative, has also been shown to increase in T2D and obesity. Although many studies propose a protective role of S1P metabolism on insulin signaling in peripheral tissues, other studies suggest a causal role of S1P on insulin resistance. In this review, we critically summarize the current state of knowledge of S1P metabolism and its modulating role on insulin resistance. A particular emphasis is placed on S1P and insulin signaling in hepatocytes, skeletal muscle cells, adipocytes and pancreatic β-cells. In particular, modulation of receptors and enzymes that regulate S1P metabolism can be considered as a new therapeutic option for the treatment of insulin resistance and T2D.

Molecular mechanisms of fat deposition: IL-6 is a hub gene in fat lipolysis, comparing thin-tailed with fat-tailed sheep breeds

Tail fat content affects meat quality and varies significantly among different breeds of sheep. Ghezel (fat-tailed) and Zel (thin-tailed) are two important Iranian local sheep breeds with different patterns of fat storage. The current study presents the transcriptome characterization of tail fat using RNA sequencing in order to get a better comprehension of the molecular mechanism of lipid storage in the two mentioned sheep breeds. Seven (Zel  =  4 and Ghezel  =  3) 7-month-old male lambs were used for this experiment. The results of sequencing were analyzed with bioinformatics methods, including differentially expressed genes (DEGs) identification, functional enrichment analysis, structural classification of proteins, protein-protein interaction (PPI) and network and module analyses. Some of the DEGs, such as LIPG, SAA1, SOCS3, HIF-1 α , and especially IL-6, had a close association with lipid metabolism. Furthermore, functional enrichment analysis revealed pathways associated with fat deposition, including "fatty acid metabolism", "fatty acid biosynthesis" and "HIF-1 signaling pathway". The structural classification of proteins showed that major down-regulated DEGs in the Zel (thin-tailed) breed were classified under transporter class and that most of them belonged to the solute carrier transporter (SLC) families. In addition, DEGs under the transcription factor class with an important role in lipolysis were up-regulated in the Zel (thin-tailed) breed. Also, network analysis revealed that IL-6 and JUNB were hub genes for up-regulated PPI networks, and HMGCS1, VPS35 and VPS26A were hub genes for down-regulated PPI networks. Among the up-regulated DEGs, the IL-6 gene seems to play an important role in lipolysis of tail fat in thin-tailed sheep breeds via various pathways such as tumor necrosis factor (TNF) signaling and mitogen-activated protein kinase (MAPK) signaling pathways. Due to the probable role of the IL-6 gene in fat lipolysis and also due to the strong interaction of IL-6 with the other up-regulated DEGs, it seems that IL-6 accelerates the degradation of lipids in tail fat cells.

Role of Sphingosine Kinase in Type 2 Diabetes Mellitus

Sphingolipids are a class of essential lipids, functioning as both cell membrane constituents and signaling messengers. In the sphingolipid metabolic network, ceramides serve as the central hub that is hydrolyzed to sphingosine, followed by phosphorylation to sphingosine 1-phosphate (S1P) by sphingosine kinase (SphK). SphK is regarded as a "switch" of the sphingolipid rheostat, as it catalyzes the conversion of ceramide/sphingosine to S1P, which often exhibit opposing biological roles in the cell. Besides, SphK is an important signaling enzyme that has been implicated in the regulation of a wide variety of biological functions. In recent years, an increasing body of evidence has suggested a critical role of SphK in type 2 diabetes mellitus (T2D), although a certain level of controversy remains. Herein, we review recent findings related to SphK in the field of T2D research with a focus on peripheral insulin resistance and pancreatic β-cell failure. It is expected that a comprehensive understanding of the role of SphK and the associated sphingolipids in T2D will help to identify druggable targets for future anti-diabetes therapy.

Targeting sphingosine kinase 1 (SK1) enhances oncogene-induced senescence through ceramide synthase 2 (CerS2)-mediated generation of very-long-chain ceramides

Senescence is an antiproliferative mechanism that can suppress tumor development and can be induced by oncogenes such as genes of the Ras family. Although studies have implicated bioactive sphingolipids (SL) in senescence, the specific mechanisms remain unclear. Here, using MCF10A mammary epithelial cells, we demonstrate that oncogenic K-Ras (Kirsten rat sarcoma viral oncogene homolog) is sufficient to induce cell transformation as well as cell senescence-as revealed by increases in the percentage of cells in the G1 phase of the cell cycle, p21WAF1/Cip1/CDKN1A (p21) expression, and senescence-associated β-galactosidase activity (SA-β-gal). Furthermore, oncogenic K-Ras altered SL metabolism, with an increase of long-chain (LC) C18, C20 ceramides (Cer), and very-long-chain (VLC) C22:1, C24 Cer, and an increase of sphingosine kinase 1 (SK1) expression. Since Cer and sphingosine-1-phosphate have been shown to exert opposite effects on cellular senescence, we hypothesized that targeting SK1 could enhance oncogenic K-Ras-induced senescence. Indeed, SK1 downregulation or inhibition enhanced p21 expression and SA-β-gal in cells expressing oncogenic K-Ras and impeded cell growth. Moreover, SK1 knockdown further increased LC and VLC Cer species (C18, C20, C22:1, C24, C24:1, C26:1), especially the ones increased by oncogenic K-Ras. Fumonisin B1 (FB1), an inhibitor of ceramide synthases (CerS), reduced p21 expression induced by oncogenic K-Ras both with and without SK1 knockdown. Functionally, FB1 reversed the growth defect induced by oncogenic K-Ras, confirming the importance of Cer generation in the senescent phenotype. More specifically, downregulation of CerS2 by siRNA blocked the increase of VLC Cer (C24, C24:1, and C26:1) induced by SK1 knockdown and phenocopied the effects of FB1 on p21 expression. Taken together, these data show that targeting SK1 is a potential therapeutic strategy in cancer, enhancing oncogene-induced senescence through an increase of VLC Cer downstream of CerS2.

Transcriptomic profiling of adipose tissue inflammation, remodeling, and lipid metabolism in periparturient dairy cows (Bos taurus)

Background

Periparturient cows release fatty acid reserves from adipose tissue (AT) through lipolysis in response to the negative energy balance induced by physiological changes related to parturition and the onset of lactation. However, lipolysis causes inflammation and structural remodeling in AT that in excess predisposes cows to disease. The objective of this study was to determine the effects of the periparturient period on the transcriptomic profile of AT using NGS RNAseq.

Results

Subcutaneous AT samples were collected from Holstein cows (n = 12) at 11 ± 3.6 d before calving date (PreP) and at 6 ± 1d (PP1) and 13 ± 1.4d (PP2) after parturition. Differential expression analyses showed 1946 and 1524 DEG at PP1 and PP2, respectively, compared to PreP. Functional Enrichment Analysis revealed functions grouped in categories such as lipid metabolism, molecular transport, energy production, inflammation, and free radical scavenging to be affected by parturition and the onset of lactation (FDR < 0.05). Inflammation related genes such as TLR4 and IL6 were categorized as upstream lipolysis triggers. In contrast, FASN, ELOVL6, ACLS1, and THRSP were identified as upstream inhibitors of lipid synthesis. Complement (C3), CXCL2, and HMOX1 were defined as links between inflammatory pathways and those involved in the generation of reactive oxygen species.

Conclusions

Results offer a comprehensive characterization of gene expression dynamics in periparturient AT, identify upstream regulators of AT function, and demonstrate complex interactions between lipid mobilization, inflammation, extracellular matrix remodeling, and redox signaling in the adipose organ.

Supplementary Information

Supplementary information accompanies this paper at 10.1186/s12864-020-07235-0.

Biochemical adaptations in white adipose tissue following aerobic exercise: from mitochondrial biogenesis to browning

Our understanding of white adipose tissue (WAT) biochemistry has evolved over the last few decades and it is now clear that WAT is not simply a site of energy storage, but rather a pliable endocrine organ demonstrating dynamic responsiveness to the effects of aerobic exercise. Similar to its established effects in skeletal muscle, aerobic exercise induces many biochemical adaptations in WAT including mitochondrial biogenesis and browning. While past research has focused on the regulation of these biochemical processes, there has been renewed interest as of late given the potential of harnessing WAT mitochondrial biogenesis and browning to treat obesity and type II diabetes. Unfortunately, despite increasing evidence that innumerable factors, both exercise induced and pharmacological, can elicit these biochemical adaptations in WAT, the underlying mechanisms remain poorly defined. Here, we begin with a historical account of our understanding of WAT exercise biochemistry before presenting detailed evidence in favour of an up-to-date model by which aerobic exercise induces mitochondrial biogenesis and browning in WAT. Specifically, we discuss how aerobic exercise induces increases in WAT lipolysis and re-esterification and how this could be a trigger that activates the cellular energy sensor 5' AMP-activated protein kinase to mediate the induction of mitochondrial biogenesis and browning via the transcriptional co-activator peroxisome proliferator-activated receptor gamma co-activator-1 alpha. While this review primarily focuses on mechanistic results from rodent studies special attention is given to the translation of these results, or lack thereof, to human physiology.

Generation of mice with hepatocyte-specific conditional deletion of sphingosine kinase 1

SphK1 gene has different roles in various types of cells in liver diseases, but most studies are based on global knockout mice, which hampers the study on the cellular and molecular mechanisms of SphK1. In order to further study the role of SphK1 in liver, SphK1 conditional knockout mice were constructed. A liver-specific SphK1 gene knockout mouse model was constructed by the Cre/Loxp recombinant enzyme system. PCR technologies and western blotting were used to identified the elimination of SphK1 gene in hepatocytes. SphK1^flox/flox mice were used as a control group to verify the effectiveness of SphK1 liver-specific knockout mice from the profile, pathology, and serology of mice. The ablation of SphK1 in hepatic parenchymal cells was demonstrated by fluorescent in situ hybridization and the contents of S1P and Sph were measured by ELISA kit. The genotypes of liver in SphK1 conditional knockout mice were different from that of other organs. The mRNA and protein levels of SphK1 in liver tissue of SphK1 conditional knockout mice were almost depleted by compared with SphK1^flox/flox mice. Physiology and pathology showed no significant difference between SphK1 liver conditional knockout mice and SphK1^flox/flox mice. Additionally, SphK1 was eliminated in hepatocytes, leading to the reduce of S1P content in hepatocytes and liver tissues and the increase of Sph content in hepatocytes. The model of SphK1 gene liver conditional knockout mice was successfully constructed, providing a tool for the study of the roles of SphK1 in hepatocyte and liver diseases.

Bioactive lipids, inflammation and chronic diseases

Endogenous bioactive lipids are part of a complex network that modulates a plethora of cellular and molecular processes involved in health and disease, of which inflammation represents one of the most prominent examples. Inflammation serves as a well-conserved defence mechanism, triggered in the event of chemical, mechanical or microbial damage, that is meant to eradicate the source of damage and restore tissue function. However, excessive inflammatory signals, or impairment of pro-resolving/anti-inflammatory pathways leads to chronic inflammation, which is a hallmark of chronic pathologies. All main classes of endogenous bioactive lipids - namely eicosanoids, specialized pro-resolving lipid mediators, lysoglycerophopsholipids and endocannabinoids - have been consistently involved in the chronic inflammation that characterises pathologies such as cancer, diabetes, atherosclerosis, asthma, as well as autoimmune and neurodegenerative disorders and inflammatory bowel diseases. This review gathers the current knowledge concerning the involvement of endogenous bioactive lipids in the pathogenic processes of chronic inflammatory pathologies.

Origin and Function of Stress-Induced IL-6 in Murine Models

Acute psychological stress has long been known to decrease host fitness to inflammation in a wide variety of diseases, but how this occurs is incompletely understood. Using mouse models, we show that interleukin-6 (IL-6) is the dominant cytokine inducible upon acute stress alone. Stress-inducible IL-6 is produced from brown adipocytes in a beta-3-adrenergic-receptor-dependent fashion. During stress, endocrine IL-6 is the required instructive signal for mediating hyperglycemia through hepatic gluconeogenesis, which is necessary for anticipating and fueling "fight or flight" responses. This adaptation comes at the cost of enhancing mortality to a subsequent inflammatory challenge. These findings provide a mechanistic understanding of the ontogeny and adaptive purpose of IL-6 as a bona fide stress hormone coordinating systemic immunometabolic reprogramming. This brain-brown fat-liver axis might provide new insights into brown adipose tissue as a stress-responsive endocrine organ and mechanistic insight into targeting this axis in the treatment of inflammatory and neuropsychiatric diseases.

Obesity, Bioactive Lipids, and Adipose Tissue Inflammation in Insulin Resistance

Obesity is a major risk factor for the development of insulin resistance and type 2 diabetes. The exact mechanism by which adipose tissue induces insulin resistance is still unclear. It has been demonstrated that obesity is associated with the adipocyte dysfunction, macrophage infiltration, and low-grade inflammation, which probably contributes to the induction of insulin resistance. Adipose tissue synthesizes and secretes numerous bioactive molecules, namely adipokines and cytokines, which affect the metabolism of both lipids and glucose. Disorders in the synthesis of adipokines and cytokines that occur in obesity lead to changes in lipid and carbohydrates metabolism and, as a consequence, may lead to insulin resistance and type 2 diabetes. Obesity is also associated with the accumulation of lipids. A special group of lipids that are able to regulate the activity of intracellular enzymes are biologically active lipids: long-chain acyl-CoAs, ceramides, and diacylglycerols. According to the latest data, the accumulation of these lipids in adipocytes is probably related to the development of insulin resistance. Recent studies indicate that the accumulation of biologically active lipids in adipose tissue may regulate the synthesis/secretion of adipokines and proinflammatory cytokines. Although studies have revealed that inflammation caused by excessive fat accumulation and abnormalities in lipid metabolism can contribute to the development of obesity-related insulin resistance, further research is needed to determine the exact mechanism by which obesity-related insulin resistance is induced.

Adipose Tissue Distribution, Inflammation and Its Metabolic Consequences, Including Diabetes and Cardiovascular Disease

Adipose tissue plays essential roles in maintaining lipid and glucose homeostasis. To date several types of adipose tissue have been identified, namely white, brown, and beige, that reside in various specific anatomical locations throughout the body. The cellular composition, secretome, and location of these adipose depots define their function in health and metabolic disease. In obesity, adipose tissue becomes dysfunctional, promoting a pro-inflammatory, hyperlipidemic and insulin resistant environment that contributes to type 2 diabetes mellitus (T2DM). Concurrently, similar features that result from adipose tissue dysfunction also promote cardiovascular disease (CVD) by mechanisms that can be augmented by T2DM. The mechanisms by which dysfunctional adipose tissue simultaneously promote T2DM and CVD, focusing on adipose tissue depot-specific adipokines, inflammatory profiles, and metabolism, will be the focus of this review. The impact that various T2DM and CVD treatment strategies have on adipose tissue function and body weight also will be discussed.

β3-adrenoreceptor blockade reduces tumor growth and increases neuronal differentiation in neuroblastoma via SK2/S1P2 modulation

Neuroblastoma (NB) is the most frequently observed among extracranial pediatric solid tumors. It displays an extreme clinical heterogeneity, in particular for the presentation at diagnosis and response to treatment, often depending on cancer cell differentiation/stemness. The frequent presence of elevated hematic and urinary levels of catecholamines in patients affected by NB suggests that the dissection of adrenergic system is crucial for a better understanding of this cancer. β3-adrenoreceptor (β3-AR) is the last identified member of adrenergic receptors, involved in different tumor conditions, such as melanoma. Multiple studies have shown that the dysregulation of the bioactive lipid sphingosine 1-phosphate (S1P) metabolism and signaling is involved in many pathological diseases including cancer. However, whether S1P is crucial for NB progression and aggressiveness is still under investigation. Here we provide experimental evidence that β3-AR is expressed in NB, both human specimens and cell lines, where it is critically involved in the activation of proliferation and the regulation between stemness/differentiation, via its functional cross-talk with sphingosine kinase 2 (SK2)/S1P receptor 2 (S1P₂) axis. The specific antagonism of β3-AR by SR59230A inhibits NB growth and tumor progression, by switching from stemness to cell differentiation both in vivo and in vitro through the specific blockade of SK2/S1P₂ signaling.

The endocrine function of adipose tissues in health and cardiometabolic disease

In addition to their role in glucose and lipid metabolism, adipocytes respond differentially to physiological cues or metabolic stress by releasing endocrine factors that regulate diverse processes, such as energy expenditure, appetite control, glucose homeostasis, insulin sensitivity, inflammation and tissue repair. Both energy-storing white adipocytes and thermogenic brown and beige adipocytes secrete hormones, which can be peptides (adipokines), lipids (lipokines) and exosomal microRNAs. Some of these factors have defined targets; for example, adiponectin and leptin signal through their respective receptors that are expressed in multiple organs. For other adipocyte hormones, receptors are more promiscuous or remain to be identified. Furthermore, many of these hormones are also produced by other organs and tissues, which makes defining the endocrine contribution of adipose tissues a challenge. In this Review, we discuss the functional role of adipose tissue-derived endocrine hormones for metabolic adaptations to the environment and we highlight how these factors contribute to the development of cardiometabolic diseases. We also cover how this knowledge can be translated into human therapies. In addition, we discuss recent findings that emphasize the endocrine role of white versus thermogenic adipocytes in conditions of health and disease.

Ceramide and sphingosine 1-phosphate in adipose dysfunction

The increased adipose tissue mass of obese individuals enhances the risk of metabolic syndrome, type 2 diabetes and cardiovascular diseases. During pathological expansion of adipose tissue, multiple molecular controls of lipid storage, adipocyte turn-over and endocrine secretion are perturbed and abnormal lipid metabolism results in a distinct lipid profile. There is a role for ceramides and sphingosine 1-phosphate (S1P) in inducing adipose dysfunction. For instance, the alteration of ceramide biosynthesis, through the de-regulation of key enzymes, results in aberrant formation of ceramides (e.g. C_16:0 and C_18:0) which block insulin signaling and promote adipose inflammation. Furthermore, S1P can induce defective adipose tissue phenotypes by promoting chronic inflammation and inhibiting adipogenesis. These abnormal changes are discussed in the context of possible therapeutic approaches to re-establish normal adipose function and to, thereby, increase insulin sensitivity in type 2 diabetes. Such novel approaches include blockade of ceramide biosynthesis using inhibitors of sphingomyelinase or dihydroceramide desaturase and by antagonism of S1P receptors, such as S1P₂.

Inflammation and Immunity: From an Adipocyte's Perspective

Comprehension of adipocyte function has evolved beyond a long-held belief of their inert nature, as simple energy storing and releasing cells. Adipocytes, including white, brown, and beige, are capable mediators of global metabolic health, but their intersection with inflammation is a budding field of exploration. Evidence hints at a reciprocal relationship adipocytes share with immune cells. Adipocyte's capacity to behave in an "immune-like" manner and ability to sense inflammatory cues that subsequently alter core adipocyte function might play an important role in shaping immune responses. Clarifying this intricate relationship could uncover previously underappreciated contribution of adipocytes to inflammation-driven human health and disease. In this review, we highlight the potential of largely underappreciated adipocyte "immune-like" function and how it may contribute to inflammation, immunity, and pathology of various diseases.

Regulation of the bi-directional cross-talk between ovarian cancer cells and adipocytes by SPARC

Ovarian cancer (OvCa) exhibits a specific predilection for metastasis to the omentum. Our earlier studies highlighted the tumour-suppressor effect of secreted protein acidic and rich in cysteine (SPARC) in OvCa through multi-faceted roles inhibiting cancer cell interactions within the peritoneal milieu. The goal of this study is to investigate the role of SPARC in OvCa interactions with omental adipocytes and its role in OvCa colonization in the omentum. We employed multi-pronged approach using primary omental adipocytes from Sparc knockout mice, genetically engineered human omental adipocytes in 3D co-cultures with OvCa cells, as well as treatment with recombinant SPARC protein. We show that SPARC suppresses multistep cascade in OvCa omental metastasis. SPARC inhibited in vivo and adipocyte-induced homing, proliferation, and invasion of OvCa cells. SPARC suppressed metabolic programming of both adipocytes and OvCa cells and exerted an inhibitory effect of adipocyte differentiation and their phenotypic switch to cancer-associated phenotype. Mechanistic studies revealed that this effect is mediated through inhibition of cEBPβ-NFkB-AP-1 transcription machinery. These findings define a novel and functionally important role of SPARC in OvCa and not only bridge the knowledge gap but highlight the need to consider SPARC protein expression in therapeutic development.

Sex Differences in Inflammatory Responses to Adipose Tissue Lipolysis in Diet-Induced Obesity

Males are known to have profound adipose tissue macrophage (ATM) accumulation in gonadal white adipose tissue (GWAT) during obesity, whereas females are protected from such an inflammatory response even with increased adiposity. The inflammatory tone in males is linked to insulin resistance and might be the underlying cause for sex differences in metabolic disease. Factors regulating the meta-inflammatory response remain unclear but enhanced lipid storage in females may explain the reduced inflammatory response to high-fat diets. In this study, we evaluated lean and obese females with stimulated lipolysis to understand whether a stress release of free fatty acids (FFAs) could induce female ATMs. We demonstrate that in both lean and obese females, GWAT CD11c- resident ATMs accumulate with β-3 adrenergic receptor-stimulated lipolysis. Lipolysis elevated serum FFA, triglyceride, and IL-6 levels in females that corresponded to significant phosphorylated hormone-sensitive lipase and adipose triglyceride lipase protein expression in obese female GWAT compared with males. Increased lipolytic response in obese females was associated with crown-like structures and induced Il6, Mcp1, Arg1, and Mgl1 expression in obese female GWAT, suggesting an environment of lipid clearance and adipose remodeling. With this finding we next investigated whether lipid storage and lipolytic mediators differed by sex. Diacylglycerol, ceramides, phospholipids, and certain fatty acid species associated with inflammation were elevated in male GWAT compared with obese female GWAT. Overall, our data demonstrate a role for GWAT lipid storage and lipolytic metabolites to induce inflammation in males and induce remodeling in females that might explain sex differences in overall metabolic health.

Neurogenic obesity and systemic inflammation following spinal cord injury: A review

CONTENT

Spinal Cord Injury (SCI) results in physiological changes that markedly reduces whole-body metabolism, resulting in neurogenic obesity via adipose tissue accumulation. Adipose tissue has been implicated in the release of proinflammatory adipokines that lead to chronic, systemic inflammation, and evidence suggests these adipokines contribute to the pathogeneses of metabolic diseases that often accompany obesity. In this review, we propose the concept of neurogenic obesity through paralysis-induced adiposity as the primary source of systemic inflammation and metabolic dysfunction reported in chronic SCI. We also briefly discuss how exercise in SCI can attenuate the negative consequences of obesity-induced inflammation and its comorbidities.

METHODS

A MEDLINE, PubMed, Google Scholar, and ClinicalKey search was performed using the following search terms: obesity, adiposity, adipose tissue, proinflammatory adipokines, proinflammatory cytokines, metabolic dysfunction, exercise, physical activity, and spinal cord injury. All papers identified were full-text, English language papers. The reference list of identified papers was also searched for additional papers.

RESULTS

Research suggests that obesity in SCI results in a state of chronic, systemic inflammation primarily through proinflammatory adipokines secreted from excess adipose tissue. The reduction of adipose tissue through the use of diet and exercise demonstrates promise to combat neurogenic obesity, inflammation, and cardiometabolic dysfunction in SCI.

CONCLUSION

Proinflammatory adipokines may serve as biomarkers for the development of obesity-related complication in SCI. Mechanistic and interventional studies on neurogenic obesity-induced inflammation in chronic SCI are warranted.

Adipose-specific lipin1 overexpression in mice protects against alcohol-induced liver injury

Excessive fatty acid release from the white adipose tissue (WAT) contributes to the development of alcoholic liver disease (ALD). Lipin1 (LPIN1), as a co-regulator of DNA-bound transcription factors and a phosphatidic acid (PA) phosphatase (PAP) enzyme that dephosphorylates PA to form diacylglycerol (DAG), is dramatically reduced by alcohol in the WAT. This study aimed at determining the role of adipose LPIN1 in alcohol-induced lipodystrophy and the development of ALD. Transgenic mice overexpressing LPIN1 in adipose tissue (LPIN1-Tg) and wild type (WT) mice were fed a Lieber-DeCarli alcohol or isocaloric maltose dextrin control liquid diet for 8 weeks. Alcohol feeding to WT mice resulted in significant liver damage, which was significantly alleviated in the LPIN1-Tg mice. Alcohol feeding significantly reduced epididymal WAT (EWAT) mass, inhibited lipogenesis, and increased lipolysis in WT mice, which were attenuated in the LPIN1-Tg mice. LPIN1 overexpression also partially reversed alcohol-reduced plasma leptin levels. In WT mice, alcohol feeding induced hepatic lipid accumulation and down-regulation of beta-oxidation genes, which were dramatically alleviated in the LPIN1-Tg mice. LPIN1 overexpression also significantly attenuated alcohol-induced hepatic ER stress. These results suggest that overexpression of LPIN1 in adipose tissue restores WAT lipid storage function and secretive function to alleviate alcohol-induced liver injury.

Micro-RNA-1 is decreased by hypoxia and contributes to the development of pulmonary vascular remodeling via regulation of sphingosine kinase 1

Sphingosine kinase 1 (SphK1) upregulation is associated with pathologic pulmonary vascular remodeling in pulmonary arterial hypertension (PAH), but the mechanisms controlling its expression are undefined. In this study, we sought to characterize the regulation of SphK1 expression by micro-RNAs (miRs). In silico analysis of the SphK1 3'-untranslated region identified several putative miR binding sites, with miR-1-3p (miR-1) being the most highly predicted target. Therefore we further investigated the role of miR-1 in modulating SphK1 expression and characterized its effects on the phenotype of pulmonary artery smooth muscle cells (PASMCs) and the development of experimental pulmonary hypertension in vivo. Our results demonstrate that miR-1 is downregulated by hypoxia in PASMCs and can directly inhibit SphK1 expression. Overexpression of miR-1 in human PASMCs inhibits basal and hypoxia-induced proliferation and migration. Human PASMCs isolated from PAH patients exhibit reduced miR-1 expression. We also demonstrate that miR-1 is downregulated in mouse lung tissues during experimental hypoxia-mediated pulmonary hypertension (HPH), consistent with upregulation of SphK1. Furthermore, administration of miR-1 mimics in vivo prevented the development of HPH in mice and attenuated induction of SphK1 in PASMCs. These data reveal the importance of miR-1 in regulating SphK1 expression during hypoxia in PASMCs. A pivotal role is played by miR-1 in pulmonary vascular remodeling, including PASMC proliferation and migration, and its overexpression protects from the development of HPH in vivo. These studies improve our understanding of the molecular mechanisms underlying the pathogenesis of pulmonary hypertension.

Ginsenoside Rb1 inhibits free fatty acids‑induced oxidative stress and inflammation in 3T3‑L1 adipocytes

Free fatty acids (FFAs) increase in visceral fat and are inferred to be one of the underlying inducers of adipose tissue inflammation. In our previous study, it was demonstrated that ginsenoside Rb1 stimulates endothelial nitric oxide synthase (eNOS) and Sirtuin 1 to protect against endothelial cell senescence. In the present study, 3T3‑L1 adipocytes were exposed to 0.5 mM FFAs with or without Rb1 (10‑40 µM). Monocyte chemotactic protein‑1 (MCP‑1) and interleukin‑6 (IL‑6) secretion was measured using ELISA. Tumor necrosis factor‑α (TNF‑α) expression and nuclear factor‑κB (NF‑κB) p65 phosphorylation were detected using western blot analysis. Oxidative stress was determined via measuring intracellular reactive oxygen species (ROS) and nitric oxide (NO) production. The results demonstrated that MCP‑1 and IL‑6 secretion, as well as TNF‑α expression, were significantly increased following FFA treatment, which was attenuated by Rb1 in a dose‑dependent manner. Furthermore, Rb1 attenuated FFA‑induced NF‑κB phosphorylation, suggesting that the inhibitory effect of Rb1 on inflammatory cytokines was partially mediated through blockade of NF‑κB phosphorylation. Further experiments demonstrated that Rb1 ameliorated FFA‑induced ROS generation and NO reduction through upregulation of superoxide dismutase 2 and eNOS expression. Taken together, these results demonstrate proinflammatory and pro‑oxidant effects of FFA on 3T3‑L1 adipocytes, which are effectively ameliorated by Rb1. Suppression of inflammatory responses and oxidative stress may be a novel mechanism for attenuating the effect of Rb1 on adipocyte dysfunction.

Sphingosine Kinases and Sphingosine 1-Phosphate Receptors: Signaling and Actions in the Cardiovascular System

The sphingosine kinases 1 and 2 (SphK1 and 2) catalyze the phosphorylation of the lipid, sphingosine, generating the signal transmitter, sphingosine 1-phosphate (S1P). The activation of such kinases and the subsequent S1P generation and secretion in the blood serum of mammals represent a major checkpoint in many cellular signaling cascades. In fact, activating the SphK/S1P system is critical for cell motility and proliferation, cytoskeletal organization, cell growth, survival, and response to stress. In the cardiovascular system, the physiological effects of S1P intervene through the binding and activation of a family of five highly selective G protein-coupled receptors, called S1PR_1-5. Importantly, SphK/S1P signal is present on both vascular and myocardial cells. S1P is a well-recognized survival factor in many tissues. Therefore, it is not surprising that the last two decades have seen a flourishing of interest and investigative efforts directed to obtain additional mechanistic insights into the signaling, as well as the biological activity of this phospholipid, and of its receptors, especially in the cardiovascular system. Here, we will provide an up-to-date account on the structure and function of sphingosine kinases, discussing the generation, release, and function of S1P. Keeping the bull's eye on the cardiovascular system, we will review the structure and signaling cascades and biological actions emanating from the stimulation of different S1P receptors. We will end this article with a summary of the most recent, experimental and clinical observations targeting S1PRs and SphKs as possible new therapeutic avenues for cardiovascular disorders, such as heart failure.

β1-Blockade Prevents Post-Ischemic Myocardial Decompensation Via β3AR-Dependent Protective Sphingosine-1 Phosphate Signaling

BACKGROUND

Although β-blockers increase survival in patients with heart failure (HF), the mechanisms behind this protection are not fully understood, and not all patients with HF respond favorably to them. We recently showed that, in cardiomyocytes, a reciprocal down-regulation occurs between β₁-adrenergic receptors (ARs) and the cardioprotective sphingosine-1-phosphate (S1P) receptor-₁ (S1PR₁).

OBJECTIVES

The authors hypothesized that, in addition to salutary actions due to direct β₁AR-blockade, agents such as metoprolol (Meto) may improve post-myocardial infarction (MI) structural and functional outcomes via restored S1PR₁ signaling, and sought to determine mechanisms accounting for this effect.

METHODS

We tested the in vitro effects of Meto in HEK293 cells and in ventricular cardiomyocytes isolated from neonatal rats. In vivo, we assessed the effects of Meto in MI wild-type and β₃AR knockout mice.

RESULTS

Here we report that, in vitro, Meto prevents catecholamine-induced down-regulation of S1PR₁, a major cardiac protective signaling pathway. In vivo, we show that Meto arrests post-MI HF progression in mice as much as chronic S1P treatment. Importantly, human HF subjects receiving β₁AR-blockers display elevated circulating S1P levels, confirming that Meto promotes S1P secretion/signaling. Mechanistically, we found that Meto-induced S1P secretion is β₃AR-dependent because Meto infusion in β₃AR knockout mice does not elevate circulating S1P levels, nor does it ameliorate post-MI dysfunction, as in wild-type mice.

CONCLUSIONS

Our study uncovers a previously unrecognized mechanism by which β₁-blockers prevent HF progression in patients with ischemia, suggesting that β₃AR dysfunction may account for limited/null efficacy in β₁AR-blocker-insensitive HF subjects.

Pharmacological inhibition of adipose triglyceride lipase corrects high-fat diet-induced insulin resistance and hepatosteatosis in mice

Elevated circulating fatty acids (FAs) contribute to the development of obesity-associated metabolic complications such as insulin resistance (IR) and non-alcoholic fatty liver disease (NAFLD). Hence, reducing adipose tissue lipolysis to diminish the mobilization of FAs and lower their respective plasma concentrations represents a potential treatment strategy to counteract obesity-associated disorders. Here we show that specific inhibition of adipose triglyceride lipase (Atgl) with the chemical inhibitor, Atglistatin, effectively reduces adipose tissue lipolysis, weight gain, IR and NAFLD in mice fed a high-fat diet. Importantly, even long-term treatment does not lead to lipid accumulation in ectopic tissues such as the skeletal muscle or heart. Thus, the severe cardiac steatosis and cardiomyopathy that is observed in genetic models of Atgl deficiency does not occur in Atglistatin-treated mice. Our data validate the pharmacological inhibition of Atgl as a potentially powerful therapeutic strategy to treat obesity and associated metabolic disorders.

The enzyme Atgl participates in the breakdown of lipids in adipose tissue. Here the authors show that pharmacological inhibition of Atgl reduces weight gain and improves metabolic health in mice fed a high-fat diet, without causing adverse effects in cardiac muscle associated with genetic depletion of Atgl.

The role of sphingolipid signalling in diabetes‑associated pathologies (Review)

Sphingosine kinase (SphK) is an important signalling enzyme that catalyses the phosphorylation of sphingosine (Sph) to form sphingosine‑1‑phosphate (S1P). The multifunctional lipid, S1P binds to a family of five G protein-coupled receptors (GPCRs). As an intracellular second messenger, S1P activates key signalling cascades responsible for the maintenance of sphingolipid metabolism, and has been implicated in the progression of cancer, and the development of other inflammatory and metabolic diseases. SphK and S1P are critical molecules involved in the regulation of various cellular metabolic processes, such as cell proliferation, survival, apoptosis, adhesion and migration. There is strong evidence supporting the critical roles of SphK and S1P in the progression of diabetes mellitus, including insulin sensitivity and insulin secretion, pancreatic β‑cell apoptosis, and the development of diabetic inflammatory state. In this review, we summarise the current state of knowledge for SphK/S1P signalling effects, associated with the development of insulin resistance, pancreatic β‑cell death and the vascular complications of diabetes mellitus.

Fasting rapidly increases fatty acid oxidation in white adipose tissue of young broiler chickens

Upregulating the fatty acid oxidation capacity of white adipose tissue in mice protects against diet-induced obesity, inflammation and insulin resistance. Part of this capacity results from induction of brown-like adipocytes within classical white depots, making it difficult to determine the oxidative contribution of the more abundant white adipocytes. Avian genomes lack a gene for uncoupling protein 1 and are devoid of brown adipose cells, making them a useful model in which to study white adipocyte metabolism in vivo. We recently reported that a brief (5 hour) period of fasting significantly upregulated many genes involved in mitochondrial and peroxisomal fatty acid oxidation pathways in white adipose tissue of young broiler chickens. The objective of this study was to determine if the effects on gene expression manifested in increased rates of fatty acid oxidation. Abdominal adipose tissue was collected from 21 day-old broiler chicks that were fasted for 3, 5 or 7 hours or fed ad libitum (controls). Fatty acid oxidation was determined by measuring and summing ¹⁴CO₂ production and ¹⁴C-labeled acid-soluble metabolites from the oxidation of [1-¹⁴C] palmitic acid. Fasting induced a progressive increase in complete fatty acid oxidation and citrate synthase activity relative to controls. These results confirm that fatty acid oxidation in white adipose tissue is dynamically controlled by nutritional status. Identifying the underlying mechanism may provide new therapeutic targets through which to increase fatty acid oxidation in situ and protect against the detrimental effects of excess free fatty acids on adipocyte insulin sensitivity.

Sphingosine Kinases and Sphingosine 1-Phosphate Receptors: Signaling and Actions in the Cardiovascular System

The sphingosine kinases 1 and 2 (SphK1 and 2) catalyze the phosphorylation of the lipid, sphingosine, generating the signal transmitter, sphingosine 1-phosphate (S1P). The activation of such kinases and the subsequent S1P generation and secretion in the blood serum of mammals represent a major checkpoint in many cellular signaling cascades. In fact, activating the SphK/S1P system is critical for cell motility and proliferation, cytoskeletal organization, cell growth, survival, and response to stress. In the cardiovascular system, the physiological effects of S1P intervene through the binding and activation of a family of five highly selective G protein-coupled receptors, called S1PR_1-5. Importantly, SphK/S1P signal is present on both vascular and myocardial cells. S1P is a well-recognized survival factor in many tissues. Therefore, it is not surprising that the last two decades have seen a flourishing of interest and investigative efforts directed to obtain additional mechanistic insights into the signaling, as well as the biological activity of this phospholipid, and of its receptors, especially in the cardiovascular system. Here, we will provide an up-to-date account on the structure and function of sphingosine kinases, discussing the generation, release, and function of S1P. Keeping the bull's eye on the cardiovascular system, we will review the structure and signaling cascades and biological actions emanating from the stimulation of different S1P receptors. We will end this article with a summary of the most recent, experimental and clinical observations targeting S1PRs and SphKs as possible new therapeutic avenues for cardiovascular disorders, such as heart failure.

C5a/C5aR pathway is essential for up-regulating SphK1 expression through p38-MAPK activation in acute liver failure

AIM

To investigate the role of the complement 5a (C5a)/C5a receptor (C5aR) pathway in the pathogenesis of acute liver failure (ALF) in a mouse model.

METHODS

BALB/c mice were randomly assigned to different groups, and intraperitoneal injections of lipopolysaccharide (LPS)/D-galactosamine (D-GalN) (600 mg/kg and 10 μg/kg) were used to induce ALF. The Kaplan-Meier method was used for survival analysis. Serum alanine aminotransferase (ALT) levels, at different time points within a 1-wk period, were detected with a biochemistry analyzer. Pathological examination of liver tissue was performed 36 h after ALF induction. Serum complement 5 (C5), C5a, tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6, high-mobility group protein B1 (HMGB1) and sphingosine-1-phosphate levels were detected by enzyme-linked immunosorbant assay. Hepatic morphological changes at 36 h after ALF induction were assessed by hematoxylin and eosin staining. Expression of C5aR, sphingosine kinase 1 (SphK1), p38-MAPK and p-p38-MAPK in liver tissue, peripheral blood mononuclear cells (PBMCs) and peritoneal exudative macrophages (PEMs) of mice or RAW 264.7 cells was analyzed by western blotting. C5aR mRNA levels were detected by quantitative real-time PCR.

RESULTS

Activation of C5 and up-regulation of C5aR were observed in liver tissue and PBMCs of mice with ALF. Blockade of C5aR with a C5aR antagonist (C5aRa C5aRa) significantly reduced the levels of serum ALT, inflammatory cytokines (TNF-α, IL-1β and IL-6) and HMGB1, as well as the liver tissue damage, but increased the survival rates (P < 0.01 for all). Blockade of C5aR decreased SphK1 expression in both liver tissue and PBMCs significantly at 0.5 h after ALF induction. C5aRa pretreatment significantly down-regulated the phosphorylation of p38-MAPK in liver tissues of ALF mice and C5a stimulated PEMs or RAW 264.7 cells. Moreover, inhibition of p38-MAPK activity with SB203580 reduced SphK1 protein production significantly in PEMs after C5a stimulation.

CONCLUSION

The C5a/C5aR pathway is essential for up-regulating SphK1 expression through p38 MAPK activation in ALF in mice, which provides a potential immunotherapeutic strategy for ALF in patients.

TGF-β/SMAD3 Pathway Stimulates Sphingosine-1 Phosphate Receptor 3 Expression: IMPLICATION OF SPHINGOSINE-1 PHOSPHATE RECEPTOR 3 IN LUNG ADENOCARCINOMA PROGRESSION

Previously, we showed that levels of sphingosine-1 phosphate receptor 3 (S1PR3) are increased in a panel of cultured human lung adenocarcinoma cell lines, and that S1PR3-mediated signaling pathways regulate proliferation, soft agar growth, and invasion of human lung adenocarcinoma cells in vitro In the present study, we examine S1PR3 levels in human lung adenocarcinoma specimens. cDNA array and tumor microarray analysis shows that mRNA and protein levels of S1PR3 are significantly increased in human lung adenocarcinomas when compared with normal lung epithelial cells. Promoter analysis shows 16 candidate SMAD3 binding sites in the promoter region of S1PR3. ChIP indicates that TGF-β treatment stimulates the binding of SMAD3 to the promoter region of S1PR3. Luciferase reporter assay demonstrates that SMAD3 transactivates S1PR3 promoter. TGF-β stimulation or ectopic expression of TGF-β up-regulates S1PR3 levels in vitro and ex vivo Pharmacologic inhibition of TGF-β receptor or SMAD3 abrogates the TGF-β-stimulated S1PR3 up-regulation. Moreover, S1PR3 knockdown dramatically inhibits tumor growth and lung metastasis, whereas ectopic expression of S1PR3 promotes the growth of human lung adenocarcinoma cells in animals. Pharmacological inhibition of S1PR3 profoundly inhibits the growth of lung carcinoma in mice. Our studies suggest that levels of S1PR3 are up-regulated in human lung adenocarcinomas, at least in part due to the TGF-β/SMAD3 signaling axis. Furthermore, S1PR3 activity promotes the progression of human lung adenocarcinomas. Therefore, S1PR3 may represent a novel therapeutic target for the treatment of deadly lung adenocarcinomas.

Inhibition of sphingosine kinase 1 ameliorates acute liver failure by reducing high-mobility group box 1 cytoplasmic translocation in liver cells

AIM

To determine the therapeutic potential of sphingosine kinase 1 (Sphk1) inhibition and its underlying mechanism in a well-characterized mouse model of D-galactosamine (D-GalN)/lipopolysaccharide (LPS)-induced acute liver failure (ALF).

METHODS

Balb/c mice were randomly assigned to different groups, with ALF induced by intraperitoneal injection of D-GaIN (600 mg/kg) and LPS (10 μg/kg). The Kaplan-Meier method was used for survival analysis. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels at different time points within one week were determined using a multi-parametric analyzer. Serum high-mobility group box 1 (HMGB1), tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6, IL-10, and sphingosine-1-phosphate were detected by enzyme-linked immunosorbent assay. Hepatic morphological changes at 36 h after acute liver injury induction were assessed by hematoxylin and eosin staining. HMGB1 expression in hepatocytes and cytoplasmic translocation were detected by immunohistochemistry. Expression of Sphk1 in liver tissue and peripheral blood mononuclear cells (PBMCs) was analyzed by Western blot.

RESULTS

The expression of Sphk1 in liver tissue and PBMCs was upregulated in GalN/LPS-induced ALF. Upregulated Sphk1 expression in liver tissue was mainly caused by Kupffer cells, the resident macrophages of the liver. The survival rates of mice in the N,N-dimethylsphingosine (DMS, a specific inhibitor of SphK1) treatment group were significantly higher than that of the control group (P < 0.001). DMS treatment significantly decreased the levels of serum ALT and AST at 6, 12, and 24 h compared with that of the control group (P < 0.01 for all). Serum HMGB1 levels at 6, 12, and 24 h, as well as serum TNF-α, IL-6, and IL-1β levels at 12 h, were significantly lower in the DMS treatment group than in the control group (P < 0.01 for all). Furthermore, hepatic inflammation, necrosis, and HMGB1 cytoplasm translocation in liver cells were significantly decreased in the DMS treatment group compared to the control group (43.72% ± 5.51% vs 3.57% ± 0.83%, χ(2) = 12.81, P < 0.01).

CONCLUSION

Inhibition of SphK1 ameliorates ALF by reducing HMGB1 cytoplasmic translocation in liver cells, and so might be a potential therapeutic strategy for this disease.