Srebp-1c/Fgf21/Pgc-1α Axis Regulated by Leptin Signaling in Adipocytes-Possible Mechanism of Caloric Restriction-Associated Metabolic Remodeling of White Adipose Tissue

The Roles of White Adipose Tissue and Liver NADPH in Dietary Restriction-Induced Longevity

Dietary restriction (DR) protocols frequently employ intermittent fasting. Following a period of fasting, meal consumption increases lipogenic gene expression, including that of NADPH-generating enzymes that fuel lipogenesis in white adipose tissue (WAT) through the induction of transcriptional regulators SREBP-1c and CHREBP. SREBP-1c knockout mice, unlike controls, did not show an extended lifespan on the DR diet. WAT cytoplasmic NADPH is generated by both malic enzyme 1 (ME1) and the pentose phosphate pathway (PPP), while liver cytoplasmic NADPH is primarily synthesized by folate cycle enzymes provided one-carbon units through serine catabolism. During the daily fasting period of the DR diet, fatty acids are released from WAT and are transported to peripheral tissues, where they are used for beta-oxidation and for phospholipid and lipid droplet synthesis, where monounsaturated fatty acids (MUFAs) may activate Nrf1 and inhibit ferroptosis to promote longevity. Decreased WAT NADPH from PPP gene knockout stimulated the browning of WAT and protected from a high-fat diet, while high levels of NADPH-generating enzymes in WAT and macrophages are linked to obesity. But oscillations in WAT [NADPH]/[NADP+] from feeding and fasting cycles may play an important role in maintaining metabolic plasticity to drive longevity. Studies measuring the WAT malate/pyruvate as a proxy for the cytoplasmic [NADPH]/[NADP+], as well as studies using fluorescent biosensors expressed in the WAT of animal models to monitor the changes in cytoplasmic [NADPH]/[NADP+], are needed during ad libitum and DR diets to determine the changes that are associated with longevity.

Fibroblast growth factor 21: An emerging pleiotropic regulator of lipid metabolism and the metabolic network

Fibroblast growth factor 21 (FGF21) was originally identified as an important metabolic regulator which plays a crucial physiological role in regulating a variety of metabolic parameters through the metabolic network. As a novel multifunctional endocrine growth factor, the role of FGF21 in the metabolic network warrants extensive exploration. This insight was obtained from the observation that the FGF21-dependent mechanism that regulates lipid metabolism, glycogen transformation, and biological effectiveness occurs through the coordinated participation of the liver, adipose tissue, central nervous system, and sympathetic nerves. This review focuses on the role of FGF21-uncoupling protein 1 (UCP1) signaling in lipid metabolism and how FGF21 alleviates non-alcoholic fatty liver disease (NAFLD). Additionally, this review reveals the mechanism by which FGF21 governs glucolipid metabolism. Recent research on the role of FGF21 in the metabolic network has mostly focused on the crucial pathway of glucolipid metabolism. FGF21 has been shown to have multiple regulatory roles in the metabolic network. Since an adequate understanding of the concrete regulatory pathways of FGF21 in the metabolic network has not been attained, this review sheds new light on the metabolic mechanisms of FGF21, explores how FGF21 engages different tissues and organs, and lays a theoretical foundation for future in-depth research on FGF21-targeted treatment of metabolic diseases.

Sulforaphane Mitigates High-Fat Diet-Induced Obesity by Enhancing Mitochondrial Biogenesis in Skeletal Muscle via the HDAC8-PGC1α Axis

SCOPE

Histone deacetylases (HDACs) play a crucial role in the transcriptional regulation of various genes which can contribute to metabolic disorders. Although sulforaphane (SFN), a natural HDAC inhibitor, has been reported to alleviate obesity in humans and mice, the specific mechanisms and how HDACs contribute to SFN's anti-obesity effects remain unclear.

METHODS AND RESULTS

Oral administration of SFN in mice fed high-fat diet increases peroxisome proliferator activating receptor γ coactivator (PGC1α)-induced mitochondrial biogenesis in skeletal muscle. Among HDACs, SFN specifically inhibits HDAC8 activity. SFN enhances mitochondrial DNA and adenosine triphosphate (ATP) production in C2C12 myotubes, similar to the action of PCI34051, a synthetic HDAC8-specific inhibitor. These effects are mediated by increased expression of PGC1α via upregulation of cAMP response element binding (CREB, Ser133 ) phosphorylation and p53 (Lys379 ) acetylation. These SFN-induced effects are not observed in cells with a genetic deletion of HDAC8, suggesting the existence of a regulatory loop between HDAC8 and PGC1α in SFN's action.

CONCLUSION

SFN prevents obesity-related metabolic dysregulation by enhancing mitochondrial biogenesis and function via targeting the HDAC8-PGCα axis. These results suggest SFN as a beneficial anti-obesity agent providing new insight into the role of HDAC8 in the PGC1α-mediated mitochondrial biogenesis, which may be a novel and promising drug target for metabolic diseases.

Asperosaponin VI protects alcohol-induced hepatic steatosis and injury via regulating lipid metabolism and ER stress

BACKGROUND

Asperosaponin VI (AVI) is a natural triterpenoid saponin isolated from Dipsacus asper Wall with documented anti-inflammatory and bone protective effects. Our previous work reported that AVI protects the liver of septic mice from acute inflammatory damage. In this paper, we further explored the protective effect and the potential mechanisms of AVI in alcoholic fatty liver disease (AFLD).

METHODS

The Lieber-Decarli model was constructed to evaluate the effect of AVI on AFLD in C57BL/6 J mice. Additional in vitro work was performed to investigate HepG2 cells exposed to alcohol, then analyzed the degree of liver injury by detecting the ALT and AST levels both in the liver and serum. H&E staining and Sirius red staining were used to evaluate the histopathology variations in the liver. Further, observe lipid droplets in the cytoplasm by Oil Red O staining. We detected the expression of inflammatory cytokines with qualitative PCR; ROS, MDA, SOD, and GSH-px levels were analyzed to observe oxidative stress. Finally, exploring the activation of AMPK signaling pathway by real-time PCR and Western blotting.

RESULTS

Histological examination of liver tissue combined with serum ALT and AST levels showed a significant protective effect of AVI against alcoholic liver injury in AFLD mice. Compared with the model group, AVI evidently improved antioxidant capacity, reduced inflammatory response and lipid accumulation both in vitro and in vivo. For mechanically, it was found that AVI up-regulated phosphorylation level of AMP-activated protein kinase (AMPK) and inhibited the endoplasmic reticulum stress (ER) pathway in AFLD.

CONCLUSION

AVI protects mice from alcohol-induced hepatic steatosis and liver injury through activating AMPK signaling and repress ER stress, suggesting that it might be a potential therapeutic agent for AFLD.

Effect of mitochondrial quantity and quality controls in white adipose tissue on healthy lifespan: Essential roles of GH/IGF-1-independent pathways in caloric restriction-mediated metabolic remodeling

Long-term caloric restriction is a conventional and reproducible dietary intervention to improve whole body metabolism, suppress age-related pathophysiology, and extend lifespan. The beneficial actions of caloric restriction are widely accepted to be regulated in both growth hormone/insulin-like growth factor 1-dependent and -independent manners. Although growth hormone/insulin-like growth factor 1-dependent regulatory mechanisms are well described, those occurring independent of growth hormone/insulin-like growth factor 1 are poorly understood. In this review, we focus on molecular mechanisms of caloric restriction regulated in a growth hormone/insulin-like growth factor 1-independent manner. Caloric restriction increases mitochondrial quantity and improves mitochondrial quality by activating an axis involving sterol regulatory element binding protein-c/peroxisome proliferator-activated receptor γ coactivator-1α/mitochondrial intermediate peptidase in a growth hormone/insulin-like growth factor 1-independent manner, particularly in white adipose tissue. Fibroblast growth factor 21 is also involved in this axis. Moreover, the axis may be regulated by lower leptin signaling. Thus, caloric restriction appears to induce beneficial actions partially by regulating mitochondrial quantity and quality in white adipose tissue in a growth hormone/insulin-like growth factor 1-independent manner.

Unraveling the Role of Hepatic PGC1α in Breast Cancer Invasion: A New Target for Therapeutic Intervention?

Breast cancer (BC) is the most common cancer among women worldwide and the main cause of cancer deaths in women. Metabolic components are key risk factors for the development of non-alcoholic fatty liver disease (NAFLD), which may promote BC. Studies have reported that increasing PGC1α levels increases mitochondrial biogenesis, thereby increasing cell proliferation and metastasis. Moreover, the PGC1α/ERRα axis is a crucial regulator of cellular metabolism in various tissues, including BC. However, it remains unclear whether NAFLD is closely associated with the risk of BC. Therefore, the present study aimed to determine whether hepatic PGC1α promotes BC cell invasion via ERRα. Various assays, including ELISA, western blotting, and immunoprecipitation, have been employed to explore these mechanisms. According to the KM plot and TCGA data, elevated PGC1α expression was highly associated with a shorter overall survival time in patients with BC. High concentrations of palmitic acid (PA) promoted PGC1α expression, lipogenesis, and inflammatory processes in hepatocytes. Conditioned medium obtained from PA-treated hepatocytes significantly increased BC cell proliferation. Similarly, recombinant PGC1α in E0771 and MCF7 cells promoted cell proliferation, migration, and invasion in vitro. However, silencing PGC1α in both BC cell lines resulted in a decrease in this trend. As determined by immunoprecipitation assay, PCG1a interacted with ERRα, thereby facilitating the proliferation of BC cells. This outcome recognizes the importance of further investigations in exploring the full potential of hepatic PGC1α as a prognostic marker for BC development.

Decreased FGF19 and FGF21: possible underlying common pathogenic mechanism of metabolic and cognitive dysregulation in depression

Background

Accumulating studies suggested that major depressive disorder (MDD) was closely related to metabolic syndrome (MetS). Important endogenous regulators fibroblast growth factors (FGFs) 19 and 21 were also reported to participate in psychiatric disorders. This study aimed to investigate the role of FGF19 and FGF21 in MDD and to explore the possible pathogenic mechanism of metabolic and cognitive dysregulation in depression.

Methods

A total of 59 MDD patients and 55 healthy control participants were recruited. The serum levels of FGF19 and FGF21 and lipid profiles were measured by means of enzymatic methods. Cognitive function was measured by repeatable battery for the assessment of neuropsychological status (RBANS) scores. The gene expression of PGC-1α and FNDC5 was determined by quantitative polymerase chain reaction (PCR).

Results

We found that plasma FGF19 and FGF21 levels were significantly decreased in patients with MDD. Meanwhile, triglyceride (TG) was significantly elevated and PGC-1α was significantly downregulated in MDD patients. Correlation analyses showed negative associations between TG and FGF19 levels. As for cognitive performance, both FGF19 and FGF21 levels were positively correlated with immediate memory. However, FGF19 levels were negatively correlated with language, and FGF21 levels were also negatively correlated with attention and delayed memory. Additionally, negative associations were found between FGF19 levels and PGC-1α. FGF21 levels were positively associated with PGC-1α and negatively associated with FNDC5.

Conclusion

This study elucidated the role of FGF19 and FGF21 in MDD. MDD patients were confirmed to have metabolic and cognitive dysregulation, and this abnormality was linked to the decreased concentrations of FGF19 and FGF21 through the PGC-1α/FNDC5 pathway. Our results showed that the alterations of FGF19 and FGF21 levels may be a common pathogenic mechanism of metabolic and cognitive disturbances in patients with MDD.

Early-onset caloric restriction alleviates ageing-associated steatohepatitis in male mice via restoring mitochondrial homeostasis

Non-alcoholic fatty liver disease is associated with ageing, and impaired mitochondrial homeostasis is the main cause for hepatic ageing. Caloric restriction (CR) is a promising therapeutic approach for fatty liver. The purpose of the present study was to investigate the possibility of early-onset CR in decelerating the progression of ageing-related steatohepatitis. The putative mechanism associated with mitochondria was further determined. C57BL/6 male mice at 8 weeks of age were randomly assigned to one of three treatments: Young-AL (AL, ad libitum), Aged-AL, or Aged-CR (60% intake of AL). Mice were sacrificed when they were 7 months old (Young) or 20 months old (Aged). Aged-AL mice displayed the greatest body weight, liver weight, and liver relative weight among treatments. Steatosis, lipid peroxidation, inflammation, and fibrosis coexisted in the aged liver. Mega mitochondria with short, randomly organized crista were noticed in the aged liver. The CR ameliorated these unfavourable outcomes. The level of hepatic ATP decreased with ageing, but this was reversed by CR. Ageing caused a decrease in mitochondrial-related protein expressions of respiratory chain complexes (NDUFB8 and SDHB) and fission (DRP1), but an increase in proteins related to mitochondrial biogenesis (TFAM), and fusion (MFN2). CR reversed the expression of these proteins in the aged liver. Both Aged-CR and Young-AL revealed a comparable pattern of protein expression. To summarize, this study demonstrated the potential of early-onset CR in preventing ageing-associated steatohepatitis, and maintaining mitochondrial functions may contribute to CR's protection during hepatic ageing.

An IGF-1R-mTORC1-SRPK2 signaling Axis contributes to FASN regulation in breast cancer

Background

Fatty acid synthase (FASN) expression is associated with a more aggressive breast cancer phenotype and is regulated downstream of receptor tyrosine kinase (RTK) signaling pathways. Recently, post transcriptional regulation of lipogenic transcripts have been demonstrated as being mediated downstream of serine-arginine rich protein kinase 2 (SRPK2), which acts to phosphorylate serine-arginine rich splicing factors (SRSFs), resulting in RNA binding and various RNA regulatory processes. Though post-transcriptional regulation of FASN has been studied previously, the upstream mediators of these pathways have not been elucidated.

Methods

Western blotting and RT-qPCR were utilized to demonstrate alterations in FASN and mRNA expression upon modulation of the IGF-1-mTORC1-SRPK2 pathway by small molecule inhibitors or RNAi mediated silencing. RNA stability was accessed by using the transcriptional inhibitor actinomycin-D followed by RT-qPCR. Further, we employed RNA-immunoprecipitation to demonstrate the direct binding of SRSF-1 to FASN transcripts.

Results

In the current study, we demonstrated an IGF-1 induced increase in FASN mRNA and protein expression that was attenuated by mTORC1 inhibition. This mTORC1 inhibition also resulted in decreases in total and nuclear p-SRPK2 in response to IGF-1 exposure. Upon SRPK2 knockdown and inhibition, we observed a decrease in FASN protein and mRNA stability, respectively, in response to IGF-1 exposure that was specific to triple negative and HER2+ breast cancer cell lines. As we explored further, IGF-1 exposure resulted in an altered localization of eGFP expressed SRSF-1, pEGFP-SRSF-1 that was rescued upon both SRPK2 knockdown and mTORC1 inhibition. Further, we observed an increase binding of SRSF-1 to FASN RNA upon IGF-1 exposure, which was abrogated by SRPK2 knockdown.

Conclusion

These current findings establish a potential IGF-1-mTORC1-SRPK2-FASN axis in breast cancer, which could be a potential therapeutic target for cancers that overexpress FASN and components of the IGF-1R pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-10062-z.

Long-term adjustment of hepatic lipid metabolism after chronic stress and the role of FGF21

Chronic stress leads to post-traumatic stress disorder (PTSD) and metabolic disorders including fatty liver. We hypothesized that stress-induced molecular mechanisms alter energy metabolism, thereby promoting hepatic lipid accumulation even after a stress-free recovery period. In this context, we investigated fibroblast growth factor-21 (FGF21) as protective for energy and glucose homeostasis. FGF21 knockout mice (B6.129S6(SJL)-Fgf21tm1.2Djm; FGF21KO) and control mice (C57BL6; WT) were subjected to chronic variable stress. Mice were examined directly after acute intervention (Cvs) and long-term after 3 months of recovery (3mCvs). In WT, Cvs reduced insulin sensitivity and hepatic lipid accumulation, whilst fatty acid uptake increased. FGF21KO mice responded to Cvs with improved glucose tolerance, insulin resistance but liver triglycerides and plasma lipids were unaltered. Hepatic gene expression was specifically altered by genotype and stress e.g. by PPARa and SREBP-1 regulated genes. The stress-induced alteration of hepatic metabolism persisted after stress recovery. In hepatocytes at 3mCvs, differential gene regulation and secreted proteins indicated a genotype specific progression of liver dysfunction. Overall, at 3mCvs FGF21 was involved in maintaining mitochondrial activity, attenuating de novo lipogenesis, increased fatty acid uptake and histone acetyltransferase activity. Glucocorticoid release and binding to the FGF21 promoter may contribute to prolonged FGF21 release and protection against hepatic lipid accumulation. In conclusion, we showed that stress favors fatty liver disease and FGF21 protected against hepatic lipid accumulation after previous chronic stress loading by i) restored physiological function, ii) modulated gene expression via DNA-modifying enzymes, and iii) maintained energy metabolism.

Mitochondrial regulation and white adipose tissue homeostasis

The important role of mitochondria in the regulation of white adipose tissue (WAT) remodeling and energy balance is increasingly appreciated. The remarkable heterogeneity of the adipose tissue stroma provides a cellular basis to enable adipose tissue plasticity in response to various metabolic stimuli. Regulating mitochondrial function at the cellular level in adipocytes, in adipose progenitor cells (APCs), and in adipose tissue macrophages (ATMs) has a profound impact on adipose homeostasis. Moreover, mitochondria facilitate the cell-to-cell communication within WAT, as well as the crosstalk with other organs, such as the liver, the heart, and the pancreas. A better understanding of mitochondrial regulation in the diverse adipose tissue cell types allows us to develop more specific and efficient approaches to improve adipose function and achieve improvements in overall metabolic health.

Astaxanthin from Haematococcus pluvialis alleviates obesity by modulating lipid metabolism and gut microbiota in mice fed a high-fat diet

Obesity is a global chronic disease epidemic that is attributed to the abnormal accumulation of lipids in adipose tissue. Astaxanthin (AST) from Haematococcus pluvialis, a natural carotenoid, exhibits antioxidant, anti-lipogenic, anti-diabetic and other potent effects. Herein, we evaluated the effect of AST to illuminate its efficacy and mechanisms in high-fat diet-fed mice. AST supplementation not only significantly decreased body weight and lipid droplet accumulation in the liver but also modulated liver function and serum lipid levels. Lipidomic analysis revealed that 13 lipids might be potential biomarkers responsible for the effects of AST in lipid reduction, such as total free fatty acids (FFAs), triacylglycerols (TGs) and cholesterol esters (CEs). The gut microbiota sequencing results indicated that AST alleviated HFD-induced gut microbiota dysbiosis by optimizing the ratio of Firmicutes to Bacteroides and inhibiting the abundance of obesity-related pathogenic microbiota while promoting the abundance of probiotics related to glucose and lipid metabolism. In addition, qRT-PCR demonstrated that AST could regulate the gene expressions of the AMPK/SREBP1c pathway by downregulating lipogenesis correlated-genes and upregulating the lipid oxidant related-gene. The present study revealed the new function of AST in regulating lipid metabolism, which provided a theoretical basis for the development of high-quality AST functional food and the application of diet active substances in obesity, as demonstrated in mice.

Contribution of PGC-1α to Obesity- and Caloric Restriction-Related Physiological Changes in White Adipose Tissue

Peroxisome proliferator-activated receptor γ coactivator-1 α (PGC-1α) regulates mitochondrial DNA replication and mitochondrial gene expression by interacting with several transcription factors. White adipose tissue (WAT) mainly comprises adipocytes that store triglycerides as an energy resource and secrete adipokines. The characteristics of WAT vary in response to systemic and chronic metabolic alterations, including obesity or caloric restriction. Despite a small amount of mitochondria in white adipocytes, accumulated evidence suggests that mitochondria are strongly related to adipocyte-specific functions, such as adipogenesis and lipogenesis, as well as oxidative metabolism for energy supply. Therefore, PGC-1α is expected to play an important role in WAT. In this review, we provide an overview of the involvement of mitochondria and PGC-1α with obesity- and caloric restriction-related physiological changes in adipocytes and WAT.

Natural Extracts to Augment Energy Expenditure as a Complementary Approach to Tackle Obesity and Associated Metabolic Alterations

Obesity is the epidemic of the 21st century. In developing countries, the prevalence of obesity continues to rise, and obesity is occurring at younger ages. Obesity and associated metabolic stress disrupt the whole-body physiology. Adipocytes are critical components of the systemic metabolic control, functioning as an endocrine organ. The enlarged adipocytes during obesity recruit macrophages promoting chronic inflammation and insulin resistance. Together with the genetic susceptibility (single nucleotide polymorphisms, SNP) and metabolic alterations at the molecular level, it has been highlighted that key modifiable risk factors, such as those related to lifestyle, contribute to the development of obesity. In this scenario, urgent therapeutic options are needed, including not only pharmacotherapy but also nutrients, bioactive compounds, and natural extracts to reverse the metabolic alterations associated with obesity. Herein, we first summarize the main targetable processes to tackle obesity, including activation of thermogenesis in brown adipose tissue (BAT) and in white adipose tissue (WAT-browning), and the promotion of energy expenditure and/or fatty acid oxidation (FAO) in muscles. Then, we perform a screening of 20 natural extracts (EFSA approved) to determine their potential in the activation of FAO and/or thermogenesis, as well as the increase in respiratory capacity. By means of innovative technologies, such as the study of their effects on cell bioenergetics (Seahorse bioanalyzer), we end up with the selection of four extracts with potential application to ameliorate the deleterious effects of obesity and the chronic associated inflammation.