Role of S6K1 in regulation of SREBP1c expression in the liver

The PI3K/Akt signaling axis and type 2 diabetes mellitus (T2DM): From mechanistic insights into possible therapeutic targets

Type 2 diabetes mellitus (T2DM) is an immensely debilitating chronic disease that progressively undermines the well-being of various bodily organs and, indeed, most patients succumb to the disease due to post-T2DM complications. Although there is evidence supporting the activation of the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway by insulin, which is essential in regulating glucose metabolism and insulin resistance, the significance of this pathway in T2DM has only been explored in a few studies. The current review aims to unravel the mechanisms by which different classes of PI3Ks control the metabolism of glucose; and also to discuss the original data obtained from international research laboratories on this topic. We also summarized the role of the PI3K/Akt signaling axis in target tissues spanning from the skeletal muscle to the adipose tissue and liver. Furthermore, inquiries regarding the impact of disrupting this axis on insulin function and the development of insulin resistance have been addressed. We also provide a general overview of the association of impaired PI3K/Akt signaling pathways in the pathogenesis of the most prevalent diabetes-related complications. The last section provides a special focus on the therapeutic potential of this axis by outlining the latest advances in active compounds that alleviate diabetes via modulation of the PI3K/Akt pathway. Finally, we comment on the future research aspects in which the field of T2DM therapies using PI3K modulators might be developed.

Tri-ortho-cresyl phosphate induces hepatic steatosis by mTOR activation and ER stress induction

Tri-ortho-cresyl phosphate (TOCP), an organophosphorus compound (OP), which is widely used as plasticizer, flame retardant and other industrial products, has been reported to cause multiple toxicities including neurotoxicity and reproductive toxicity. However, it remains to be elusive whether TOCP induces hepatotoxicity. The purpose of this study was to investigate the effect of TOCP on hepatocytes and the lipid metabolism in particular. The adult mice were given a single dose of TOCP (800 mg/kg, p.o.) and the histological changes in liver tissue and lipid content in serum were determined. The results showed that more vacuoles and lipid droplets were observed in the liver of the mice exposed to TOCP. And triglyceride concentrations in serum and liver tissue significantly increased. However, the histopathological changes of the liver and the elevated triglyceride levels in the exposed mice can be reversed by endoplasmic reticulum (ER) stress inhibitor 4-phenylbutyric acid and mTOR signal inhibitor rapamycin. It was also found that the changes of expression levels of the biomarkers of ER stress and mTOR signaling pathway, such as GRP78, CHOP, and p-mTOR, in the exposed mice were consistent with those observed in the cultured primary hepatocytes treated with the same chemicals. These results showed that TOCP activated mTOR signal and ER stress to induce de novo lipid synthesis, which led to the hepatic steatosis in mouse.

Roles of immune dysregulation in MASLD

Metabolic dysfunction-associated steatotic liver disease (MASLD) is the most common chronic liver disease worldwide. Its occurrence and progression involve the process from simple hepatic steatosis to metabolic dysfunction associated steatohepatitis (MASH), which could develop into advanced liver fibrosis, cirrhosis, or hepatocellular carcinoma (HCC). Growing evidences support that the pathogenesis and progression of MASLD are closely related to immune system dysfunction. This review aims to summarize the association of MASLD with immune disorders and the prospect of using immunotherapy for MASLD.

Lipidomic landscape of lipokines in adipose tissue derived extracellular vesicles

Introduction: Adipose tissue-derived extracellular vesicles (EVs-AT) are recognized as critical mediators of metabolic alterations in obesity-related diseases. However, few studies have focused on the role of lipids within EVs-AT in the development of obesity-related diseases. Methods: In this study, we performed a targeted lipidomic analysis to compare the lipidome of EVs secreted by inguinal white adipose tissue (EVs-iWAT), epididymal white adipose tissue (EVs-eWAT), and interscapular brown adipose tissue (EVs-BAT) in lean and obese mice. Results: We uncovered a comprehensive lipidomic map, revealing the diversity and specific lipid sorting in EVs-iWAT, EVs-eWAT, and EVs-BAT in obesity. Biological function analyses suggested that lipids encapsulated within EVs-AT of obese individuals might correlate with metabolism, pro-inflammatory response, and insulin resistance. These effects were particularly pronounced in EVs-eWAT and EVs-BAT. Conclusion: Our findings indicated that EVs-AT serves as novel carriers for lipokines, thereby mediating the biological functions of EVs-AT. This study holds promise for the identification of new biomarkers for obesity-related diseases and the development of new strategies to combat metabolic diseases.

An atlas of genome-wide gene expression and metabolite associations and possible mediation effects towards body mass index

Investigating the cross talk of different omics layers is crucial to understand molecular pathomechanisms of metabolic diseases like obesity. Here, we present a large-scale association meta-analysis of genome-wide whole blood and peripheral blood mononuclear cell (PBMC) gene expressions profiled with Illumina HT12v4 microarrays and metabolite measurements from dried blood spots (DBS) characterized by targeted liquid chromatography tandem mass spectrometry (LC-MS/MS) in three large German cohort studies with up to 7706 samples. We found 37,295 associations comprising 72 amino acids (AA) and acylcarnitine (AC) metabolites (including ratios) and 8579 transcripts. We applied this catalogue of associations to investigate the impact of associating transcript-metabolite pairs on body mass index (BMI) as an example metabolic trait. This is achieved by conducting a comprehensive mediation analysis considering metabolites as mediators of gene expression effects and vice versa. We discovered large mediation networks comprising 27,023 potential mediation effects within 20,507 transcript-metabolite pairs. Resulting networks of highly connected (hub) transcripts and metabolites were leveraged to gain mechanistic insights into metabolic signaling pathways. In conclusion, here, we present the largest available multi-omics integration of genome-wide transcriptome data and metabolite data of amino acid and fatty acid metabolism and further leverage these findings to characterize potential mediation effects towards BMI proposing candidate mechanisms of obesity and related metabolic diseases. KEY MESSAGES: Thousands of associations of 72 amino acid and acylcarnitine metabolites and 8579 genes expand the knowledge of metabolome-transcriptome associations. A mediation analysis of effects on body mass index revealed large mediation networks of thousands of obesity-related gene-metabolite pairs. Highly connected, potentially mediating hub genes and metabolites enabled insight into obesity and related metabolic disease pathomechanisms.

Emerging role of aging in the progression of NAFLD to HCC

With the aging of global population, the incidence of nonalcoholic fatty liver disease (NAFLD) has surged in recent decades. NAFLD is a multifactorial disease that follows a progressive course, ranging from simple fatty liver, nonalcoholic steatohepatitis (NASH) to liver cirrhosis and hepatocellular carcinoma (HCC). It is well established that aging induces pathological changes in liver and potentiates the occurrence and progression of NAFLD, HCC and other age-related liver diseases. Studies of senescent cells also indicate a pivotal engagement in the development of NAFLD via diverse mechanisms. Moreover, nicotinamide adenine dinucleotide (NAD⁺), silence information regulator protein family (sirtuins), and mechanistic target of rapamycin (mTOR) are three vital and broadly studied targets involved in aging process and NAFLD. Nevertheless, the crucial role of these aging-associated factors in aging-related NAFLD remains underestimated. Here, we reviewed the current research on the roles of aging, cellular senescence and three aging-related factors in the evolution of NAFLD to HCC, aiming at inspiring promising therapeutic targets for aging-related NAFLD and its progression.

Look who's TORking: mTOR-mediated integration of cell status and external signals during limb development and endochondral bone growth

The balance of cell proliferation and size is key for the control of organ development and repair. Moreover, this balance has to be coordinated within tissues and between tissues to achieve robustness in the organ's pattern and size. The tetrapod limb has been used to study these topics during development and repair, and several conserved pathways have emerged. Among them, mechanistic target of rapamycin (mTOR) signaling, despite being active in several cell types and developmental stages, is one of the least understood in limb development, perhaps because of its multiple potential roles and interactions with other pathways. In the body of this review, we have collated and integrated what is known about the role of mTOR signaling in three aspects of tetrapod limb development: 1) limb outgrowth; 2) chondrocyte differentiation after mesenchymal condensation and 3) endochondral ossification-driven longitudinal bone growth. We conclude that, given its ability to interact with the most common signaling pathways, its presence in multiple cell types, and its ability to influence cell proliferation, size and differentiation, the mTOR pathway is a critical integrator of external stimuli and internal status, coordinating developmental transitions as complex as those taking place during limb development. This suggests that the study of the signaling pathways and transcription factors involved in limb patterning, morphogenesis and growth could benefit from probing the interaction of these pathways with mTOR components.

Kidney Proximal Tubule GLUT2-More than Meets the Eye

Tubulopathy plays a central role in the pathophysiology of diabetic kidney disease (DKD). Under diabetic conditions, the kidney proximal tubule cells (KPTCs) are exposed to an extensive amount of nutrients, most notably glucose; these nutrients deteriorate KPTCs function and promote the development and progression of DKD. Recently, the facilitative glucose transporter 2 (GLUT2) in KPTCs has emerged as a central regulator in the pathogenesis of DKD. This has been demonstrated by identifying its specific role in enhancing glucose reabsorption and glucotoxicity, and by deciphering its effect in regulating the expression of the sodium-glucose transporter 2 (SGLT2) in KPTCs. Moreover, reduction/deletion of KPTC-GLUT2 has been recently found to ameliorate DKD, raising the plausible idea of considering it as a therapeutic target against DKD. However, the underlying molecular mechanisms by which GLUT2 exerts its deleterious effects in KPTCs remain vague. Herein, we review the current findings on the proximal tubule GLUT2 biology and function under physiologic conditions, and its involvement in the pathophysiology of DKD. Furthermore, we shed new light on its cellular regulation during diabetic conditions.

Stress-Induced Premature Senescence Related to Oxidative Stress in the Developmental Programming of Nonalcoholic Fatty Liver Disease in a Rat Model of Intrauterine Growth Restriction

Metabolic syndrome (MetS) refers to cardiometabolic risk factors, such as visceral obesity, dyslipidemia, hyperglycemia/insulin resistance, arterial hypertension and non-alcoholic fatty liver disease (NAFLD). Individuals born after intrauterine growth restriction (IUGR) are particularly at risk of developing metabolic/hepatic disorders later in life. Oxidative stress and cellular senescence have been associated with MetS and are observed in infants born following IUGR. However, whether these mechanisms could be particularly associated with the development of NAFLD in these individuals is still unknown. IUGR was induced in rats by a maternal low-protein diet during gestation versus. a control (CTRL) diet. In six-month-old offspring, we observed an increased visceral fat mass, glucose intolerance, and hepatic alterations (increased transaminase levels, triglyceride and neutral lipid deposit) in male rats with induced IUGR compared with the CTRL males; no differences were found in females. In IUGR male livers, we identified some markers of stress-induced premature senescence (SIPS) (lipofuscin deposit, increased protein expression of p21WAF, p16INK4a and Acp53, but decreased pRb/Rb ratio, foxo-1 and sirtuin-1 protein and mRNA expression) associated with oxidative stress (higher superoxide anion levels, DNA damages, decreased Cu/Zn SOD, increased catalase protein expression, increased nfe2 and decreased keap1 mRNA expression). Impaired lipogenesis pathways (decreased pAMPK/AMPK ratio, increased pAKT/AKT ratio, SREBP1 and PPARγ protein expression) were also observed in IUGR male livers. At birth, no differences were observed in liver histology, markers of SIPS and oxidative stress between CTRL and IUGR males. These data demonstrate that the livers of IUGR males at adulthood display SIPS and impaired liver structure and function related to oxidative stress and allow the identification of specific therapeutic strategies to limit or prevent adverse consequences of IUGR, particularly metabolic and hepatic disorders.

Activation of Liver mTORC1 Protects Against NASH via Dual Regulation of VLDL-TAG Secretion and De Novo Lipogenesis

BACKGROUND & AIMS

Dysregulation of liver lipid metabolism is associated with the development and progression of nonalcoholic fatty liver disease, a spectrum of liver diseases including nonalcoholic steatohepatitis (NASH). In the liver, insulin controls lipid homeostasis by increasing triglyceride (TAG) synthesis, suppressing fatty acid oxidation, and enhancing TAG export via very low-density lipoproteins. Downstream of insulin signaling, the mechanistic target of rapamycin complex 1 (mTORC1), is a key regulator of lipid metabolism. Here, we define the role of hepatic mTORC1 activity in mouse models of NASH and investigate the mTORC1-dependent mechanisms responsible for protection against liver damage in NASH.

METHODS

Utilizing 2 rodent NASH-promoting diets, we demonstrate that hepatic mTORC1 activity was reduced in mice with NASH, whereas under conditions of insulin resistance and benign fatty liver, mTORC1 activity was elevated. To test the beneficial effects of hepatic mTORC1 activation in mouse models of NASH, we employed an acute, liver-specific knockout model of TSC1 (L-TSC-KO), a negative regulator of mTORC1.

RESULTS

L-TSC-KO mice are protected from and have improved markers of NASH including reduced steatosis, decreased circulating transaminases, and reduced expression of inflammation and fibrosis genes. Mechanistically, protection from hepatic inflammation and fibrosis by constitutive mTORC1 activity occurred via promotion of the phosphatidylcholine synthesizing enzyme, CCTα, and enhanced very low-density lipoprotein-triglyceride export. Additionally, activation of mTORC1 protected from hepatic steatosis via negative feedback of the mTORC2-AKT-FOXO-SREBP1c lipogenesis axis.

CONCLUSIONS

Collectively, this study identifies a protective role for liver mTORC1 signaling in the initiation and progression of NASH in mice via dual control of lipid export and synthesis.

Viruses and Metabolism: The Effects of Viral Infections and Viral Insulins on Host Metabolism

Over the past decades, there have been tremendous efforts to understand the cross-talk between viruses and host metabolism. Several studies have elucidated the mechanisms through which viral infections manipulate metabolic pathways including glucose, fatty acid, protein, and nucleotide metabolism. These pathways are evolutionarily conserved across the tree of life and extremely important for the host's nutrient utilization and energy production. In this review, we focus on host glucose, glutamine, and fatty acid metabolism and highlight the pathways manipulated by the different classes of viruses to increase their replication. We also explore a new system of viral hormones in which viruses mimic host hormones to manipulate the host endocrine system. We discuss viral insulin/IGF-1-like peptides and their potential effects on host metabolism. Together, these pathogenesis mechanisms targeting cellular signaling pathways create a multidimensional network of interactions between host and viral proteins. Defining and better understanding these mechanisms will help us to develop new therapeutic tools to prevent and treat viral infections.

Lamin regulates the dietary restriction response via the mTOR pathway in Caenorhabditis elegans

Animals subjected to dietary restriction (DR) have reduced body size, low fecundity, slower development, lower fat content and longer life span. We identified lamin as a regulator of multiple dietary restriction phenotypes. Downregulation of lmn-1, the single Caenorhabditis elegans lamin gene, increased animal size and fat content specifically in DR animals. The LMN-1 protein acts in the mTOR pathway, upstream of RAPTOR and S6 kinase β1 (S6K), a key component of and target of the mechanistic target of rapamycin (mTOR) complex 1 (mTORC1), respectively. DR excludes the mTORC1 activator RAGC-1 from the nucleus. Downregulation of lmn-1 restores RAGC-1 to the nucleus, a necessary step for the activation of the mTOR pathway. These findings further link lamin to metabolic regulation.

Summary: Downregulation of the single C. elegans lamin gene increases animal size and fat content specifically in dietary restricted animals. The lamin protein acts in the mTOR pathway to regulate these phenotypes.

Adaptive immunity at the crossroads of autophagy and metabolism

The function of lymphocytes is dependent on their plasticity, particularly their adaptation to energy availability and environmental stress, and their protein synthesis machinery. Lymphocytes are constantly under metabolic stress, and macroautophagy/autophagy is the primary metabolic pathway that helps cells overcome stressors. The intrinsic role of autophagy in regulating the metabolism of adaptive immune cells has recently gained increasing attention. In this review, we summarize and discuss the versatile roles of autophagy in regulating cellular metabolism and the implications of autophagy for immune cell function and fate, especially for T and B lymphocytes.

Genome-wide miRNA expression profiling in potato (Solanum tuberosum L.) reveals TOR-dependent post-transcriptional gene regulatory networks in diverse metabolic pathway

Target of rapamycin (TOR) operates as a hub of the signal transduction that integrates nutrient and energy signaling to promote cell proliferation and growth through mediating the transcriptional and post- transcriptional regulator networks in all eukaryotic species. MicroRNAs (miRNAs) are widespread classes of small, single-stranded, non-coding endogenous RNAs and are widely found in eukaryotes, which play a vital role in regulating gene expression by degrading targeted mRNAs or translational repression at post-transcriptional level. Recent studies found that there were necessarily close connections between miRNA and TOR pathways in mammals. However, there is little information about the interplay between the miRNA and TOR in plants. Thus, the aim of this study was to identify potential TOR-miRNA-mRNA regulatory networks in TOR signaling through global mRNA and microRNA expression profiling in potato. Based on the previous high-throughput transcriptome sequencing and filtering, a total of 2,899 genes were significantly differentially expressed in potato under TOR inhibitors treatment. Pathway analysis revealed that these genes were significantly enriched in multiple metabolic processes. Similarly, in the present study, suppression of TOR resulted in 41 miRNAs up-regulated and 45 down-regulated, revealing that TOR plays a crucial role in the regulation of miRNA regulatory network. Furthermore, integrated mRNA and miRNA expression profiling uncovered that these miRNAs participated in large-scale metabolic process in the TOR signal pathway in potato, such as regulation of autophagy and ubiquitination, and biosynthesis of secondary metabolites. Overall, the results shed new insight into TOR related post-transcriptional gene regulatory networks in potato and suggesting TOR-miRNA-targeting genes relevant networks as a potential genetic resource for potato improvement.

Ilexgenin A restrains CRTC2 in the cytoplasm to prevent SREBP1 maturation via AMP kinase activation in the liver

BACKGROUND AND PURPOSE

Ilexgenin A is a triterpenoid from ShanLv Cha with beneficial effects on metabolic homeostasis. We investigated whether ilexgenin A could inhibit hepatic de novo fatty acid synthesis via the interfering with SREBP1 maturation.

EXPERIMENTAL APPROACH

The effects of Ilexgenin A on CRTC2 translocation and SREBP1 maturation were investigated in the liver of fasted mice and hepatocytes exposed to saturated fatty acids. The effect of Iilexgenin A on hepatic lipid accumulation was also observed in high-fat diet fed mice.

KEY RESULTS

Sec23A and Sec31A are two subunits of COPII complex and their interaction is essential for the processing of SREBP1 maturation. Ilexgenin A activates AMPK by reducing cellular energy and preventing cytoplasmic CRTC2 to compete with Sec23A for binding to Sec31A under nutrient-rich conditions. Consequently, ilexgenin A impaired COPII-dependent SREBP1 maturation via disrupting Sec31A-Sec23A interaction, leading to the inhibition of de novo fatty acid synthesis in the liver. In contrast, mTORC1 phosphorylated Ser136 of CRTC2, facilitating the formation of Sec31A-Sec23A interaction to promote SREBP1 maturation, whereas this action was reversed by ilexgenin A in an AMPK-dependent manner. Ilexgenin A protected CRTC2 function and restrained hepatic lipogenic response in high fat diet-fed mice, providing in vivo evidence to support the beneficial effects of ilexgenin A on lipid metabolism.

CONCLUSIONS AND IMPLICATIONS

Ilexgenin A activated AMPK and restrained CRTC2 to the cytoplasm to prevent SREBP1 maturation via impairing COPII function in the liver. This suggests that CRTC2 might be a potential target for pharmacological intervention to prevent hepatic lipid deposition.

Postnatal overfeeding induces hepatic microRNA-221 expression and impairs the PI3K/AKT pathway in adult male rats

BACKGROUND

Increasing evidence suggests that postnatal overfeeding induces childhood obesity, which is strongly associated with metabolic syndrome. Insulin resistance is a risk factor for metabolic syndrome. MicroRNA-221 (miR-221) is involved in the development of obesity and has been reported to negatively regulate insulin sensitivity. However, the underlying mechanism remains unclear.

METHODS

Rats raised in small litters (SLs, three pups/dam, n = 10) and normal litters (NLs, 10 pups/dam, n = 10) were used to model early postnatal overfeeding and act as controls, respectively. miR-221 and proteins related to the phosphoinositide 3-kinases (PI3K)/protein kinase B (AKT) pathway were assessed in the liver.

RESULTS

Early postnatal overfeeding significantly increased body weight, visceral fat index, blood glucose, serum triglycerides, and the homeostasis model assessment of insulin resistance at 9 weeks. Real-time polymerase chain reaction (PCR) and western blot analysis revealed that postnatal overfeeding induced insulin receptor and insulin receptor substrate 2 expression, but decreased PI3K and AKT phosphorylation in the liver. Quantitative real-time PCR showed that hepatic miR-221 was significantly overexpressed in the SL group.

CONCLUSIONS

These results indicate that postnatal overfeeding induces hepatic miR-221 overexpression and impairs the PI3K/AKT signal pathway, which may cause insulin resistance.

IMPACT

We first report postnatal overfeeding induces hepatic miR-221 expression. Postnatal overfeeding impairs PI3K/AKT pathway in the liver of adult rats. Postnatal overfeeding induces obesity and high blood glucose. Avoidance of overfeeding during early postnatal life may prevent obesity and T2DM.

Differential Gene Expression and Biological Analyses of Primary Hepatocytes Following D-Chiro-Inositol Supplement

Dietary supplements have improved the prevention of insulin resistance and metabolic diseases, which became a research hotspot in food science and nutrition. Obesity and insulin resistance, caused by a high-fat diet, eventually result in severe metabolic diseases, can be prevented with the dietary supplement D-chiro-inositol (DCI). In this work, we isolated mice primary hepatocytes with palmitic acid stimulation and DCI was applied to compare and contrast its effects of in primary hepatocyte biology. Before and after intervention with DCI, we used RNA-Seq technology to establish a primary hepatocyte transcriptome gene profile. We found that both PA and DCI cause a wide variation in gene expression. Particularly, we found that DCI plays critical role in this model by acting on glycolysis and gluconeogenesis. Overall, we generated extensive transcripts from primary hepatocytes and uncovered new functions and gene targets for DCI.

Insight on Transcriptional Regulation of the Energy Sensing AMPK and Biosynthetic mTOR Pathway Genes

The Adenosine Monophosphate-activated Protein Kinase (AMPK) and the Mechanistic Target of Rapamycin (mTOR) are two evolutionarily conserved kinases that together regulate nearly every aspect of cellular and systemic metabolism. These two kinases sense cellular energy and nutrient levels that in turn are determined by environmental nutrient availability. Because AMPK and mTOR are kinases, the large majority of studies remained focused on downstream substrate phosphorylation by these two proteins, and how AMPK and mTOR regulate signaling and metabolism in normal and disease physiology through phosphorylation of their substrates. Compared to the wealth of information known about the signaling and metabolic pathways modulated by these two kinases, much less is known about how the transcription of AMPK and mTOR pathway genes themselves are regulated, and the extent to which AMPK and mTOR regulate gene expression to cause durable changes in phenotype. Acute modification of cellular systems can be achieved through phosphorylation, however, induction of chronic changes requires modulation of gene expression. In this review we will assemble evidence from published studies on transcriptional regulation by AMPK and mTOR and discuss about the putative transcription factors that regulate expression of AMPK and mTOR complex genes.

Role of Pro-inflammatory Cytokines in Regulation of Skeletal Muscle Metabolism: A Systematic Review

Background:

Metabolic pathways perturbations lead to skeletal muscular atrophy in the cachexia and sarcopenia due to increased catabolism. Pro-inflammatory cytokines induce the catabolic pathways that impair the muscle integrity and function. Hence, this review primarily concentrates on the effects of pro-inflammatory cytokines in regulation of skeletal muscle metabolism.

Objective:

This review will discuss the role of pro-inflammatory cytokines in skeletal muscles during muscle wasting conditions. Moreover, the coordination among the pro-inflammatory cytokines and their regulated molecular signaling pathways which increase the protein degradation will be discussed.

Results:

During normal conditions, pro-inflammatory cytokines are required to balance anabolism and catabolism and to maintain normal myogenesis process. However, during muscle wasting their enhanced expression leads to marked destructive metabolism in the skeletal muscles. Proinflammatory cytokines primarily exert their effects by increasing the expression of calpains and E3 ligases as well as of Nf-κB, required for protein breakdown and local inflammation. Proinflammatory cytokines also locally suppress the IGF-1and insulin functions, hence increase the FoxO activation and decrease the Akt function, the central point of carbohydrates lipid and protein metabolism.

Conclusion:

Current advancements have revealed that the muscle mass loss during skeletal muscular atrophy is multifactorial. Despite great efforts, not even a single FDA approved drug is available in the market. It indicates the well-organized coordination among the pro-inflammatory cytokines that need to be further understood and explored.

GRP78 regulates milk biosynthesis and the proliferation of bovinemammaryepithelial cells through the mTOR signaling pathway

Background

Glucose-regulated protein 78 (GRP78) is a member of the HSP70 protein family and a key endoplasmic reticulum chaperone. It has been revealed to play important roles both in the maturation, folding and transport of proteins and in cellproliferation. However, its involvement in milk biosynthesis or the proliferation of bovine primary mammary epithelial cells (BMECs) has yet to be established.

Methods

The expressions of GRP78 in BMECs stimulated with methionine, leucine, estrogen and prolactin were determined using western blotting and immunofluorescence assays. To explore the function of GRP78 in BMECs, the protein was overexpressed or knocked down, respectively using an overexpression vector or an siRNA mixture transfected into cells cultured in vitro. Flow cytometry was used to analyze cell proliferation and cell activity. The contents of lactose and triglyceride (TG) secreted from the treated BMECs were measured using lactose and TG assay kits, respectively. Western blotting analysis was used to measure the β-casein content and the protein levels of the signaling molecules known to be involved in milk biosynthesis and cell proliferation.

Results

GRP78overexpression significantly stimulated milk protein and milk fat synthesis, enhanced cell proliferation, positively regulated the phosphorylation of mammalian target of rapamycin (mTOR), and increased the amount of protein of cyclinD1andsterol regulatory element-binding protein 1c (SREBP-1c). GRP78 knockdown after siRNA transfection had the opposite effects. We further found that GRP78 was located in the cytoplasm of BMECs, and that stimulating methionine, leucine, estrogen and prolactin expression led to a significant increase in the protein expression of GRP78 in BMECs.

Conclusions

These data reveal that GRP78 is an important regulator of milk biosynthesis and the proliferation of BMECs through the mTOR signaling pathway.

Rapamycin attenuates liver injury caused by vinyl chloride metabolite chloroethanol and lipopolysaccharide in mice

Vinyl chloride (VC) is a prevalent environmental toxicant that is rapidly metabolized within the liver. Its metabolites have been shown to directly cause hepatic injury at high exposure levels. We have previously reported that VC metabolite, chloroethanol (CE), potentiates liver injury caused by lipopolysaccharide (LPS). Importantly, that study showed that CE alone, while not causing damage per se, was sufficient to alter hepatic metabolism and increase mTOR phosphorylation in mice, suggesting a possible role for the mTOR pathway. Here, we explored the effect of an mTOR inhibitor, rapamycin, in this model. C57BL/6 J mice were administered CE, followed by rapamycin 1 h and LPS 24 h later. As observed previously, the combination of CE and LPS significantly enhanced liver injury, inflammation, oxidative stress, and metabolic dysregulation. Rapamycin attenuated not only inflammation, but also restored the metabolic phenotype and protected against CE + LPS-induced oxidative stress. Importantly, rapamycin protected against mitochondrial damage and subsequent production of reactive oxygen species (ROS). The protective effect on mitochondrial function by rapamycin was mediated, by restoring the integrity of the electron transport chain at least in part, by blunting the deactivation of mitochondrial c-src, which is involved mitochondrial ROS production by electron transport chain leakage. Taken together, these results further demonstrate a significant role of mTOR-mediated pathways in VC-metabolite induced liver injury and provide further insight into VC-associated hepatic damage. As mTOR mediated pathways are very complex and rapamycin is a more global inhibitor, more specific mTOR (i.e. mTORC1) inhibitors should be considered in future studies.

LRG ameliorates steatohepatitis by activating the AMPK/mTOR/SREBP1 signaling pathway in C57BL/6J mice fed a high‑fat diet

The pathogenesis of nonalcoholic fatty liver disease non‑alcoholic steatohepatitis (NASH) has not been fully elucidated, and there are currently no effective treatments for NASH. The aim of the present study was to explore the therapeutic effects of the glucagon‑like peptide‑1 (GLP‑1) receptor agonist liraglutide (LRG) on NASH and the underlying mechanisms. C57BL6J mice were fed a high‑fat diet (HFD) for 8 weeks to induce hepatic steatosis, and then LRG was injected subcutaneously for 4 weeks. The expression of sterol regulatory element‑binding protein 1 (SREBP1) and adenosine monophosphate‑activated protein kinase (AMPK) as well as the phosphorylation of mechanistic target of rapamycin (mTOR) and p70 ribosomal S6 kinase (p70S6K) were determined by western blot analysis. The intracellular distribution of SREBP1 was assessed by immunofluorescence staining. The results revealed that LRG treatment ameliorated HFD‑induced hepatic lipid accumulation and inhibited body weight gain. In addition, LRG treatment significantly suppressed the expression of hepatic SREBP1 as well as the phosphorylation of mTOR and p70S6K; it also increased the phosphorylation of AMPK and acetyl coenzyme A carboxylase. Furthermore, LRG treatment inhibited the hepatic nuclear translocation of SREBP1. It was suggested that the GLP‑1 receptor agonist LRG may have ameliorated hepatic steatosis by activating the AMPK/mTOR/SREBP1 signaling pathway as opposed to inhibiting body weight gain.

mTOR is a Key Protein Involved in the Metabolic Effects of Simple Sugars

One of the most important threats to global human health is the increasing incidences of metabolic pathologies (including obesity, type 2 diabetes and non-alcoholic fatty liver disease), which is paralleled by increasing consumptions of hypercaloric diets enriched in simple sugars. The challenge is to identify the metabolic pathways affected by the excessive consumption of these dietary components when they are consumed in excess, to unravel the molecular mechanisms leading to metabolic pathologies and identify novel therapeutic targets to manage them. Mechanistic (mammalian) target of rapamycin (mTOR) has emerged as one of the key molecular nodes that integrate extracellular signals, such as energy status and nutrient availability, to trigger cell responses that could lead to the above-mentioned diseases through the regulation of lipid and glucose metabolism. By activating mTOR signalling, excessive consumption of simple sugars (such as fructose and glucose), could modulate hepatic gluconeogenesis, lipogenesis and fatty acid uptake and catabolism and thus lipid deposition in the liver. In the present review we will discuss some of the most recent studies showing the central role of mTOR in the metabolic effects of excessive simple sugar consumption.

The PI3K/AKT pathway in obesity and type 2 diabetes

Obesity and type 2 diabetes mellitus are complicated metabolic diseases that affect multiple organs and are characterized by hyperglycaemia. Currently, stable and effective treatments for obesity and type 2 diabetes mellitus are not available. Therefore, the mechanisms leading to obesity and diabetes and more effective ways to treat obesity and diabetes should be identified. Based on accumulated evidences, the PI3K/AKT signalling pathway is required for normal metabolism due to its characteristics, and its imbalance leads to the development of obesity and type 2 diabetes mellitus. This review focuses on the role of PI3K/AKT signalling in the skeletal muscle, adipose tissue, liver, brain and pancreas, and discusses how this signalling pathway affects the development of the aforementioned diseases. We also summarize evidences for recently identified therapeutic targets of the PI3K/AKT pathway as treatments for obesity and type 2 diabetes mellitus. PI3K/AKT pathway damaged in various tissues of the body leads to obesity and type 2 diabetes as the result of insulin resistance, and in turn, insulin resistance exacerbates the PI3K/AKT pathway, forming a vicious circle.

LXRɑ participates in the mTOR/S6K1/SREBP-1c signaling pathway during sodium palmitate-induced lipogenesis in HepG2 cells

Background

The aim of this study was to investigate how the signaling pathway downstream of mTOR/S6K1 contributes to the regulation of SREBP-1c expression during lipogenesis in HepG2 cells.

Methods

The model of steatosis was established using human hepatocytes HepG2 and inducting them with sodium palmitate. mTOR, S6K1 and LXRα were inhibited by rapamycin, PF-4708671 and siRNA-LXRα, respectively. After a variety of different treatment, the levels of intracellular triglycerides, the accumulation of lipid droplets and the expression levels of related genes were detected.

Results

Rapamycin, PF-4708671 and siRNA-LXRα treatment could decrease the accumulation of triglycerides and lipid droplets induced by sodium palmitate in HepG2 cells, and the inhibitory effect could be enhanced by the combination of them. Sodium palmitate stimulated the expression of genes encoding mTOR, S6K1, LXRα, SREBP-1c and SREBP-1c target enzymes (FAS and ACC1) in HepG2 cells. Moreover, these genes were sensitive to rapamycin. PF-4708671 also decreased the expression of these genes, except for the mTOR gene, and the extent of reduction could be enhanced by combination with rapamycin. Knockdown of LXRα decreased the expression of SREBP-1c, FAS and ACC1, but it had no effect on the expression of mTOR or S6K1. Furthermore, rapamycin and PF-4708671 enhanced the inhibitory effect of siRNA-LXRα.

Conclusions

mTOR/S6K1 regulates the SREBP-1c signaling pathway through LXRα in sodium palmitate-induced HepG2 cells, suggesting LXRα might be a potential therapeutic target for NAFLD.

The Role of mTOR in Neuroendocrine Tumors: Future Cornerstone of a Winning Strategy?

The mechanistic target of rapamycin (mTOR) is part of the phosphoinositide-3-kinase (PI3K)/protein kinase B (AkT)/mTOR pathway and owes its name to the inhibitory effect of rapamycin. The mTOR has a central converging role for many cell functions, serving as a sensor for extracellular signals from energy status and nutrients availability, growth factors, oxygen and stress. Thus, it also modulates switch to anabolic processes (protein and lipid synthesis) and autophagy, in order to regulate cell growth and proliferation. Given its functions in the cell, its deregulation is implicated in many human diseases, including cancer. Its predominant role in tumorigenesis and progression of neuroendocrine tumors (NETs), in particular, has been demonstrated in preclinical studies and late clinical trials. mTOR inhibition by everolimus is an established therapeutic target in NETs, but there are no identified predictive or prognostic factors. This review is focused on the role of mTOR and everolimus in NETs, from preclinical studies to major clinical trials, and future perspectives involving mTOR in the treatment of NETs.

Serum Lipid and Protein Changes in Healthy Dyslipidemic Subjects Given a Selective Inhibitor of p70 S6 Kinase-1

The safety, pharmacokinetic, and pharmacodynamic effects of LY2584702, a selective inhibitor for p70 S6 serine/threonine protein kinase-1, were evaluated in healthy dyslipidemic volunteers. LY2584702 was tolerated well as a monotherapy and dose-dependently reduced low-density lipoprotein cholesterol and triglycerides by up to 60% and 50%, respectively, without significantly changing high-density lipoprotein cholesterol levels in plasma. LY2584702 also dose-dependently decreased factor V activity. Alanine aminotransferase elevations were noted in 2 subjects when LY2584702 was given with atorvastatin. We suspect that the formation of 4-aminopyrazolo[3,4-d]pyrimidine (4-APP) during metabolism may have contributed to some of the adverse effects of LY2584702, and the contribution of 4-APP to the pharmacology merits further investigation. Although clinical investigation of LY2584702 has been terminated because of hepatotoxicity risk, we suggest that a selective inhibitor of p70 S6 serine/threonine protein kinase-1 with a larger margin of safety and without the possibility of being metabolized to 4-APP may be useful in the treatment of dyslipidemia.

The Role of Mammalian Target of Rapamycin (mTOR) in Insulin Signaling

The mammalian target of rapamycin (mTOR) is a serine/threonine kinase that controls a wide spectrum of cellular processes, including cell growth, differentiation, and metabolism. mTOR forms two distinct multiprotein complexes known as mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2), which are characterized by the presence of raptor and rictor, respectively. mTOR controls insulin signaling by regulating several downstream components such as growth factor receptor-bound protein 10 (Grb10), insulin receptor substrate (IRS-1), F-box/WD repeat-containing protein 8 (Fbw8), and insulin like growth factor 1 receptor/insulin receptor (IGF-IR/IR). In addition, mTORC1 and mTORC2 regulate each other through a feedback loop to control cell growth. This review outlines the current understanding of mTOR regulation in insulin signaling in the context of whole body metabolism.

Identification of 4-Aminopyrazolopyrimidine Metabolite That May Contribute to the Hypolipidemic Effects of LY2584702 in Long Evans Diet-Induced Obese Rats

LY2584702 is an inhibitor of p70 S6 kinase-1 previously developed for the treatment of cancer. In two phase 1 trials in oncology patients, significant reductions of total cholesterol, low-density lipoprotein cholesterol (LDL-C), and triglyceride were observed. In the current study, we sought to understand the potential mechanism of action of this compound in regulating lipid metabolism. In Long Evans diet-induced obese (DIO) rats, oral administration of LY2584702 for 3-4 weeks led to robust reduction of LDL-C up to 60%. An unexpected finding of liver triglyceride (TG) increase implicated a metabolite of LY2584702, 4-aminopyrazolo[3,4-day]pyrimidine (4-APP), in modulation of lipid metabolism in these rats. We showed that low-dose 4-APP, when administered orally for 3-4 weeks to Long Evans DIO rats, produced lipoprotein profile changes that were strikingly similar to LY2584702. Kinetic studies suggested that both LY2584702 and 4-APP had no effect on chylomicron-TG secretion and only exerted a modest effect on hepatic very low-density lipoprotein (VLDL)-TG secretion. In human hepatoma HepG2 cells, 4-APP, but not LY2584702, increased LDL uptake. We hypothesize that generation of the 4-APP metabolite may contribute to the efficacy of LY2584702 in lowering LDL-C in rats and potentially in humans as well. This mechanism of LDL-C lowering may include inhibition of VLDL production and increase in LDL clearance.

mTORC1 signaling and the metabolic control of cell growth

mTOR [mechanistic target of rapamycin] is a serine/threonine protein kinase that, as part of mTORC1 (mTOR complex 1), acts as an important molecular connection between nutrient signals and the metabolic processes indispensable for cell growth. While there has been pronounced interest in the upstream mechanisms regulating mTORC1, the full range of downstream molecular targets through which mTORC1 signaling stimulates cell growth is only recently emerging. It is now evident that mTORC1 promotes cell growth primarily through the activation of key anabolic processes. Through a diverse set of downstream targets, mTORC1 promotes the biosynthesis of macromolecules, including proteins, lipids, and nucleotides to build the biomass underlying cell, tissue, and organismal growth. Here, we focus on the metabolic functions of mTORC1 as they relate to the control of cell growth. As dysregulated mTORC1 underlies a variety of human diseases, including cancer, diabetes, autoimmune diseases, and neurological disorders, understanding the metabolic program downstream of mTORC1 provides insights into its role in these pathological states.

RKIP phosphorylation-dependent ERK1 activation stimulates adipogenic lipid accumulation in 3T3-L1 preadipocytes overexpressing LC3

3T3-L1 preadipocytes undergo adipogenesis in response to treatment with dexamethaxone, 1-methyl-3-isobutylxanthine, and insulin (DMI) through activation of several adipogenic transcription factors. Many autophagy-related proteins are also highly activated in the earlier stages of adipogenesis, and the LC3 conjugation system is required for formation of lipid droplets. Here, we investigated the effect of overexpression of green fluorescent protein (GFP)-LC3 fusion protein on adipogenesis. Overexpression of GFP-LC3 in 3T3-L1 preadipocytes using poly-l-lysine-assisted adenoviral GFP-LC3 transduction was sufficient to produce intracellular lipid droplets. Indeed, GFP-LC3 overexpression stimulated expression of some adipogenic transcription factors (e.g., C/EBPα or β, PPARγ, SREBP2). In particular, SREBP2 was highly activated in preadipocytes transfected with adenoviral GFP-LC3. Also, phosphorylation of Raf kinase inhibitory protein (RKIP) at serine 153, consequently stimulating extracellular-signal regulated kinase (ERK)1 activity, was significantly increased during adipogenesis induced by either poly-l-lysine-assisted adenoviral GFP-LC3 transduction or culture in the presence of dexamethasone, 1-methyl-3-isobutylxanthine, and insulin. Furthermore, RKIP knockdown promoted ERK1 and PPARγ activation, and significantly increased the intracellular accumulation of triacylglycerides in DMI-induced adipogenesis. In conclusion, GFP-LC3 overexpression in 3T3-L1 preadipocytes stimulates adipocyte differentiation via direct modulation of RKIP-dependent ERK1 activity.

The Roles of mTOR Complexes in Lipid Metabolism

The synthesis of lipids in response to food intake represents a key advantage that allows organisms to survive when energy availability is limited. In mammals, circulating levels of insulin and nutrients, which fluctuate between fasting and feeding, dictate whether lipids are synthesized or catabolized by tissues. The mechanistic target of rapamycin (mTOR), a kinase that is activated by anabolic signals, plays fundamental roles in regulating lipid biosynthesis and metabolism in response to nutrition. The mTOR kinase nucleates two large protein complexes named mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). Following their activation, these complexes facilitate the accumulation of triglycerides by promoting adipogenesis and lipogenesis and by shutting down catabolic processes such as lipolysis and β-oxidation. Here, we review and discuss the roles of mTOR complexes in various aspects of lipid metabolism in mammals. We also use this opportunity to discuss the implication of these relations to the maintenance of systemic lipid homeostasis.

The effect of isorhamnetin glycosides extracted from Opuntia ficus-indica in a mouse model of diet induced obesity

A diet rich in polyphenols can ameliorate some metabolic alterations associated with obesity and type 2 diabetes. Opuntia ficus-indica (OFI) is a plant rich in isorhamnetin glycosides and is highly consumed in Mexico. The purpose of this research was to determine the metabolic effect of an OFI extract on a mouse model of diet-induced obesity and in isolated pancreatic islets. OFI extract was added to a high fat (HF) diet at a low (0.3%) or high (0.6%) dose and administered to C57BL/6 mice for 12 weeks. Mice fed the HF diet supplemented with the OFI extract gained less body weight and exhibited significantly lower circulating total cholesterol, LDL cholesterol and HDL cholesterol compared to those fed the HF diet alone. The HF-OFI diet fed mice presented lower glucose and insulin concentration than the HF diet fed mice. However, the HF-OFI diet fed mice tended to have higher insulin concentration than control mice. The OFI extract stimulated insulin secretion in vitro, associated with increased glucose transporter 2 (GLUT2) and peroxisome proliferator-activated receptor gamma (PPARγ) mRNA content. Furthermore, the OFI extract improved glucose tolerance, and additionally increased energy expenditure. These metabolic improvements were associated with reduced adipocyte size, increased hepatic IRS1 tyr-608 and S6 K thr-389 phosphorylation. OFI isorhamnetin glycosides also diminished the hepatic lipid content associated with reduced mRNA expression of the endoplasmic reticulum stress markers and lipogenic enzymes and increased mRNA expression of genes related to fatty acid oxidation. Overall, the OFI extract prevented the development of metabolic abnormalities associated with diet-induced obesity.

Non-alcoholic steatohepatitis: emerging molecular targets and therapeutic strategies

Non-alcoholic fatty liver disease - the most common chronic liver disease - encompasses a histological spectrum ranging from simple steatosis to non-alcoholic steatohepatitis (NASH). Over the next decade, NASH is projected to be the most common indication for liver transplantation. The absence of an effective pharmacological therapy for NASH is a major incentive for research into novel therapeutic approaches for this condition. The current focus areas for research include the modulation of nuclear transcription factors; agents that target lipotoxicity and oxidative stress; and the modulation of cellular energy homeostasis, metabolism and the inflammatory response. Strategies to enhance resolution of inflammation and fibrosis also show promise to reverse the advanced stages of liver disease.

Anti-obesity and anti-diabetic effects of flavonoid derivative (Fla-CN) via microRNA in high fat diet induced obesity mice

3-O-[(E)-4-(4-cyanophenyl)-2-oxobut-3-en-1-yl]kaempferol (Fla-CN), a semi-synthesized flavonoid derivative of tiliroside, reduces whole-body adiposity, ameliorates metabolic lipid disorder, improves insulin sensitivity and benefits other disorders characterized by insulin resistance in high fat diet induced obesity mice. The improvement of insulin sensitivity and the reduction of weight gain are correlated with the changes of leptin and adiponectin levels. As a result, Fla-CN treatment could increase the expressions of pAMPK and miR-27 in the liver and adipose tissues. Meanwhile, we discovered that the expressions of various adipogenesis genes were downregulated, which were target genes of miR-27. This is the first report for the action of miR-27 by flavonoid derivative in rodents. The action of Fla-CN might be through multiple approaches including AMPK activation and enhancement in miR-27 expression.

Cellular and molecular effects of the mTOR inhibitor everolimus

mTOR (mechanistic target of rapamycin) functions as the central regulator for cell proliferation, growth and survival. Up-regulation of proteins regulating mTOR, as well as its downstream targets, has been reported in various cancers. This has promoted the development of anti-cancer therapies targeting mTOR, namely fungal macrolide rapamycin, a naturally occurring mTOR inhibitor, and its analogues (rapalogues). One such rapalogue, everolimus, has been approved in the clinical treatment of renal and breast cancers. Although results have demonstrated that these mTOR inhibitors are effective in attenuating cell growth of cancer cells under in vitro and in vivo conditions, subsequent sporadic response to rapalogues therapy in clinical trials has promoted researchers to look further into the complex understanding of the dynamics of mTOR regulation in the tumour environment. Limitations of these rapalogues include the sensitivity of tumour subsets to mTOR inhibition. Additionally, it is well known that rapamycin and its rapalogues mediate their effects by inhibiting mTORC (mTOR complex) 1, with limited or no effect on mTORC2 activity. The present review summarizes the pre-clinical, clinical and recent discoveries, with emphasis on the cellular and molecular effects of everolimus in cancer therapy.

A hepatic amino acid/mTOR/S6K-dependent signalling pathway modulates systemic lipid metabolism via neuronal signals

Metabolism is coordinated among tissues and organs via neuronal signals. Levels of circulating amino acids (AAs), which are elevated in obesity, activate the intracellular target of rapamycin complex-1 (mTORC1)/S6kinase (S6K) pathway in the liver. Here we demonstrate that hepatic AA/mTORC1/S6K signalling modulates systemic lipid metabolism via a mechanism involving neuronal inter-tissue communication. Hepatic expression of an AA transporter, SNAT2, activates the mTORC1/S6K pathway, and markedly elevates serum triglycerides (TGs), while downregulating adipose lipoprotein lipase (LPL). Hepatic Rheb or active-S6K expression have similar metabolic effects, whereas hepatic expression of dominant-negative-S6K inhibits TG elevation in SNAT2 mice. Denervation, pharmacological deafferentation and β-blocker administration suppress obesity-related hypertriglyceridemia with adipose LPL upregulation, suggesting that signals are transduced between liver and adipose tissue via a neuronal pathway consisting of afferent vagal and efferent sympathetic nerves. Thus, the neuronal mechanism uncovered here serves to coordinate amino acid and lipid levels and contributes to the development of obesity-related hypertriglyceridemia.

The Human Blood Metabolome-Transcriptome Interface

Biological systems consist of multiple organizational levels all densely interacting with each other to ensure function and flexibility of the system. Simultaneous analysis of cross-sectional multi-omics data from large population studies is a powerful tool to comprehensively characterize the underlying molecular mechanisms on a physiological scale. In this study, we systematically analyzed the relationship between fasting serum metabolomics and whole blood transcriptomics data from 712 individuals of the German KORA F4 cohort. Correlation-based analysis identified 1,109 significant associations between 522 transcripts and 114 metabolites summarized in an integrated network, the 'human blood metabolome-transcriptome interface' (BMTI). Bidirectional causality analysis using Mendelian randomization did not yield any statistically significant causal associations between transcripts and metabolites. A knowledge-based interpretation and integration with a genome-scale human metabolic reconstruction revealed systematic signatures of signaling, transport and metabolic processes, i.e. metabolic reactions mainly belonging to lipid, energy and amino acid metabolism. Moreover, the construction of a network based on functional categories illustrated the cross-talk between the biological layers at a pathway level. Using a transcription factor binding site enrichment analysis, this pathway cross-talk was further confirmed at a regulatory level. Finally, we demonstrated how the constructed networks can be used to gain novel insights into molecular mechanisms associated to intermediate clinical traits. Overall, our results demonstrate the utility of a multi-omics integrative approach to understand the molecular mechanisms underlying both normal physiology and disease.

Oncogenic PI3K and K-Ras stimulate de novo lipid synthesis through mTORC1 and SREBP

An enhanced capacity for de novo lipid synthesis is a metabolic feature of most cancer cells that distinguishes them from their cells of origin. However, the mechanisms through which oncogenes alter lipid metabolism are poorly understood. We find that expression of oncogenic PI3K (H1047R) or K-Ras (G12V) in breast epithelial cells is sufficient to induce de novo lipogenesis, and this occurs through the convergent activation of the mechanistic target of rapamycin complex 1 (mTORC1) downstream of these common oncogenes. Oncogenic stimulation of mTORC1 signaling in this isogenic setting or a panel of eight breast cancer cell lines leads to activation of the sterol regulatory element-binding proteins (SREBP1 and SREBP2) that are required for oncogene-induced lipid synthesis. The SREBPs are also required for the growth factor-independent growth and proliferation of oncogene-expressing cells. Finally, we find that elevated mTORC1 signaling is associated with increased mRNA and protein levels of canonical SREBP targets in primary human breast cancer samples. These data suggest that the mTORC1/SREBP pathway is a major mechanism through which common oncogenic signaling events induce de novo lipid synthesis to promote aberrant growth and proliferation of cancer cells.

Branched-chain amino acids modulate the expression of hepatic fatty acid metabolism-related genes in female broiler chickens

SCOPE

The effects and roles of branched-chain amino acids (BCAAs) in hepatic fat metabolism are still unknown.

METHODS AND RESULTS

Here, we used broiler chickens, in which lipogenesis occurs essentially in the liver as in human, to investigate the effects of three levels of BCAAs (control "C," low "L" and exogenous supplemented diet "L+S") on growth, carcass traits, immunity, and hepatic fat metabolism. Despite the same productive performance, immunity, and plasma BCAA levels between all groups, low BCAA levels significantly downregulated the hepatic expression of lipogenic genes particularly acetyl-CoA carboxylase alpha (ACCα) and stearoyl-coA desaturase 1 (p = 0.0036 and p = 0.0008, respectively) and upregulated the hepatic expression of mitochondrial β-oxidation- (uncoupling protein and NRF-1, p < 0.05) and dynamic-related genes (DNM1, p < 0.05). Concomitant with these changes, low BCAA levels increased the phosphorylation of AMP-activated protein kinase (AMPK)α(Thr172), ACCα(Ser79), and forkhead box protein O1 (FoxO1(Ser256)) and decreased the phosphorylation of mTOR(Ser2481) and P70 S6 kinase (Thr389). The mRNA abundance of the transcription factors SREBP1/2, peroxisome proliferator activated receptor alpha/beta, and FoxO1 were also increased in the liver of L group compared to the control.

CONCLUSION

Together our data indicate that low BCAA levels inhibit fatty acid synthesis and enhanced fatty acid β-oxidation in the liver of female broiler chickens and these effects were probably mediated through AMPK-mTOR-FoxO1 pathway.

Fructose leads to hepatic steatosis in zebrafish that is reversed by mechanistic target of rapamycin (mTOR) inhibition

Nonalcoholic fatty liver disease (NAFLD), the accumulation of lipid within hepatocytes, is increasing in prevalence. Increasing fructose consumption correlates with this increased prevalence, and rodent studies directly support fructose leading to NAFLD. The mechanisms of NAFLD and in particular fructose-induced lipid accumulation remain unclear, although there is evidence for a role for endoplasmic reticulum (ER) stress and oxidative stress. We have evidence that NAFLD models demonstrate activation of the target of rapamycin complex 1 (Torc1) pathway. We set out to assess the contribution of ER stress, oxidative stress, and Torc1 up-regulation in the development of steatohepatitis in fructose-treated larval zebrafish. Zebrafish were treated with fructose or glucose as a calorie-matched control. We also treated larvae with rapamycin, tunicamycin (ER stress), or valinomycin (oxidative stress). Fish were stained with oil red O to assess hepatic lipid accumulation, and we also performed quantitative polymerase chain reaction (qPCR)and western blot analysis. We performed immunostaining on samples from patients with NAFLD and nonalcoholic steatohepatitis (NASH). Treatment with fructose induced hepatic lipid accumulation, mitochondrial abnormalities, and ER defects. In addition, fructose-treated fish showed activation of inflammatory and lipogenic genes. Treatment with tunicamycin or valinomycin also induced hepatic lipid accumulation. Expression microarray studies of zebrafish NAFLD models showed an elevation of genes downstream of Torc1 signaling. Rapamycin treatment of fructose-treated fish prevented development of hepatic steatosis, as did treatment of tunicamycin- or valinomycin-treated fish. Examination of liver samples from patients with hepatic steatosis demonstrated activation of Torc1 signaling.

CONCLUSION

Fructose treatment of larval zebrafish induces hepatic lipid accumulation, inflammation, and oxidative stress. Our results indicate that Torc1 activation is required for hepatic lipid accumulation across models of NAFLD, and in patients.

Function of SREBP1 in the milk fat synthesis of dairy cow mammary epithelial cells

Sterol regulatory element-binding proteins (SREBPs) belong to a family of nuclear transcription factors. The question of which is the most important positive regulator in milk fat synthesis in dairy cow mammary epithelial cells (DCMECs) between SREBPs or other nuclear transcription factors, such as peroxisome proliferator-activated receptor γ (PPARγ), remains a controversial one. Recent studies have found that mTORC1 (the mammalian target of rapamycin C1) regulates SREBP1 to promote fat synthesis. Thus far, however, the interaction between the SREBP1 and mTOR (the mammalian target of rapamycin) pathways in the regulation of milk fat synthesis remains poorly understood. This study aimed to identify the function of SREBP1 in milk fat synthesis and to characterize the relationship between SREBP1 and mTOR in DCMECs. The effects of SREBP1 overexpression and gene silencing on milk fat synthesis and the effects of stearic acid and serum on SREBP1 expression in the upregulation of milk fat synthesis were investigated in DCMECs using immunostaining, Western blotting, real-time quantitative PCR, lipid droplet staining, and detection kits for triglyceride content. SREBP1 was found to be a positive regulator of milk fat synthesis and was shown to be regulated by stearic acid and serum. These findings indicate that SREBP1 is the key positive regulator in milk fat synthesis.

Ribosomal proteins and human diseases: pathogenesis, molecular mechanisms, and therapeutic implications

Ribosomes are essential components of the protein synthesis machinery. The process of ribosome biogenesis is well organized and tightly regulated. Recent studies have shown that ribosomal proteins (RPs) have extraribosomal functions that are involved in cell proliferation, differentiation, apoptosis, DNA repair, and other cellular processes. The dysfunction of RPs has been linked to the development and progression of hematological, metabolic, and cardiovascular diseases and cancer. Perturbation of ribosome biogenesis results in ribosomal stress, which triggers activation of the p53 signaling pathway through RPs-MDM2 interactions, resulting in p53-dependent cell cycle arrest and apoptosis. RPs also regulate cellular functions through p53-independent mechanisms. We herein review the recent advances in several forefronts of RP research, including the understanding of their biological features and roles in regulating cellular functions, maintaining cell homeostasis, and their involvement in the pathogenesis of human diseases. We also highlight the translational potential of this research for the identification of molecular biomarkers, and in the discovery and development of novel treatments for human diseases.

Tissue-specific insulin signaling in the regulation of metabolism and aging

In mammals, insulin signaling regulates glucose homeostasis and plays an essential role in metabolism, organ growth, development, fertility, and lifespan. The defects in this signaling pathway contribute to various metabolic diseases such as type 2 diabetes, polycystic ovarian disease, hypertension, hyperlipidemia, and atherosclerosis. However, reducing the insulin signaling pathway has been found to increase longevity and delay the aging-associated diseases in various animals, ranging from nematodes to mice. These seemly paradoxical findings raise an interesting question as to how modulation of the insulin signaling pathway could be an effective approach to improve metabolism and aging. In this review, we summarize current understanding on tissue-specific functions of insulin signaling in the regulation of metabolism and lifespan. We also discuss the potential benefits and limitations in modulating tissue-specific insulin signaling pathway to improve metabolism and healthspan.

Molecular Characterization and Expression Analysis of S6K1 in Cashmere Goats (Capra hircus)

p70 ribosomal S6 kinase (p70S6K) can integrate nutrient and growth factor signals to promote cell growth and survival. We report our molecular characterization of the complementary DNA (cDNA) that encodes the goat p70S6K gene 40S ribosomal S6 kinase 1 (S6K1) (GenBank accession GU144017) and its 3′ noncoding sequence in Inner Mongolia Cashmere goats (Capra hircus). Goat S6K1 cDNA was 2,272 bp and include an open reading frame (ORF) of 1,578 bp, corresponding to a polypeptide of 525 amino acids, and a 694-residue 3′ noncoding sequence with a polyadenylation signal at nucleotides 2,218 to 2,223. The relative abundance of S6K1 mRNA was measured by real-time PCR in 6 tissues, and p70S6K expression was examined by immunohistochemistry in heart and testis. The phosphorylation of p70S6K is regulated by mitogen-activated protein kinase (MAPK) signaling in fetal fibroblasts.