Mapping the response of human fibroblast growth factor 21 (FGF21) promoter to serum availability and lipoic acid in HepG2 hepatoma cells

Alpha lipoic acid-loaded electrospun fibrous patch films protect heart in acute myocardial infarction mice by inhibiting oxidative stress

Oxidative stress, characterized by excessive accumulation of reactive oxygen species (ROS), is involved in acute myocardial infarction (AMI)-related pathological processes and vascular reperfusion therapy injury. Alpha lipoic acid (LA) exhibits excellent antioxidant properties, however, its application is limited by inherent characteristics, including rapid clearance and extensive volume distribution. In this study, we hypothesized that scavenging cardiac ROS using adequately delivered LA could promote heart repair. Here, we report a new strategy for dynamic-release LA to treat AMI disease. In particular, this involves using poly(lactic-co-glycolic) (PLGA) copolymers as carriers to form a thin film (LA@PLGA) via electrospinning technology to achieve controlled release of LA, which essentially blocking local ROS production in damaged hearts. The drug-loading capacity and capsulation efficiency of this compound film could be regulated by determining the dose proportions of LA and PLGA. The incubation of LA@PLGA showed strong anti-oxidative activity and anti-apoptosis effect in hydrogen peroxide-administered primary cardiomyocytes. Patching LA@PLGA on the infarcted cardiac surfaces of AMI mice dramatically improved heart functions and reduced cardiac fibrosis throughout ventricular remodeling process. Importantly, the attenuation of detrimental pathologies was observed, including oxidative stress, senescence, DNA damage, cytokine-related processes, apoptosis, and ferroptosis. These results suggest that PLGA-carried LA can reduce ROS damage and restore heart function after myocardial damage, demonstrating a great potential for LA drugs in treating AMI disease.

α-Lipoic acid upregulates gene expression but reduces protein levels of fibroblast growth factor 21 in HepG2 Cells

Fibroblast growth factor 21 (FGF21) is a metabolism-regulating hepatokine, and its expression is finely controlled by the nutrients and cellular stressors. α-Lipoic acid (ALA) regulates fuel metabolism as a nutrient, but it also arouses mitochondrial and endoplasmic reticulum (ER) stress as well as oxidative stress in hepatocytes. However, the role of cellular stress in ALA-regulated FGF21 expression has not been demonstrated as yet. The present study found that ALA upregulated FGF21 gene expression while it reduced FGF21 protein levels in HepG2 cells, which was accompanied by mitochondrial damage that was shown by ATP reduction and ROS elevation. ALA led to mitochondrial stress and ER stress as shown by the increased expression of HSP60, ATF6 and ATF4. Inhibition of ER stress by 4-PBA significantly attenuated ALA-stimulated FGF21 gene expression while it did not influence the reduction of FGF21 protein levels. H₂ O₂ -induced oxidative stress reduced FGF21 protein levels in HepG2 cells, and anti-oxidation by Tempol blocked ALA-induced reduction of FGF21 proteins. In conclusion, ALA upregulates FGF21 gene expression through the stimulation of mitochondrial and ER stress while it reduces FGF21 protein levels through the induction of oxidative stress in HepG2 cells. Further studies are needed to demonstrate the in vivo effect of ALA on hepatic FGF21 expression.

The Jun-dependent axon regeneration gene program: Jun promotes regeneration over plasticity

The regeneration-associated gene (RAG) expression program is activated in injured peripheral neurons after axotomy and enables long-distance axon re-growth. Over 1000 genes are regulated, and many transcription factors are upregulated or activated as part of this response. However, a detailed picture of how RAG expression is regulated is lacking. In particular, the transcriptional targets and specific functions of the various transcription factors are unclear. Jun was the first-regeneration-associated transcription factor identified and the first shown to be functionally important. Here we fully define the role of Jun in the RAG expression program in regenerating facial motor neurons. At 1, 4 and 14 days after axotomy, Jun upregulates 11, 23 and 44% of the RAG program, respectively. Jun functions relevant to regeneration include cytoskeleton production, metabolic functions and cell activation, and the downregulation of neurotransmission machinery. In silico analysis of promoter regions of Jun targets identifies stronger over-representation of AP1-like sites than CRE-like sites, although CRE sites were also over-represented in regions flanking AP1 sites. Strikingly, in motor neurons lacking Jun, an alternative SRF-dependent gene expression program is initiated after axotomy. The promoters of these newly expressed genes exhibit over-representation of CRE sites in regions near to SRF target sites. This alternative gene expression program includes plasticity-associated transcription factors and leads to an aberrant early increase in synapse density on motor neurons. Jun thus has the important function in the early phase after axotomy of pushing the injured neuron away from a plasticity response and towards a regenerative phenotype.

R-α-Lipoic Acid and 4-Phenylbutyric Acid Have Distinct Hypolipidemic Mechanisms in Hepatic Cells

The constitutive activation of the mechanistic target of rapamycin complex 1 (mTORC1) leads to the overproduction of apoB-containing triacylglycerol-rich lipoproteins in HepG2 cells. R-α-lipoic acid (LA) and 4-phenylbutyric acid (PBA) have hypolipidemic function but their mechanisms of action are not well understood. Here, we reported that LA and PBA regulate hepatocellular lipid metabolism via distinct mechanisms. The use of SQ22536, an inhibitor of adenylyl cyclase, revealed cAMP’s involvement in the upregulation of CPT1A expression by LA but not by PBA. LA decreased the secretion of proprotein convertase subtilisin/kexin type 9 (PCSK9) in the culture media of hepatic cells and increased the abundance of LDL receptor (LDLR) in cellular extracts in part through transcriptional upregulation. Although PBA induced LDLR gene expression, it did not translate into more LDLR proteins. PBA regulated cellular lipid homeostasis through the induction of CPT1A and INSIG2 expression via an epigenetic mechanism involving the acetylation of histone H3, histone H4, and CBP-p300 at the CPT1A and INSIG2 promoters.

Fibroblast Growth Factor 21 and the Adaptive Response to Nutritional Challenges

The Fibroblast Growth Factor 21 (FGF21) is considered an attractive therapeutic target for obesity and obesity-related disorders due to its beneficial effects in lipid and carbohydrate metabolism. FGF21 response is essential under stressful conditions and its metabolic effects depend on the inducer factor or stress condition. FGF21 seems to be the key signal which communicates and coordinates the metabolic response to reverse different nutritional stresses and restores the metabolic homeostasis. This review is focused on describing individually the FGF21-dependent metabolic response activated by some of the most common nutritional challenges, the signal pathways triggering this response, and the impact of this response on global homeostasis. We consider that this is essential knowledge to identify the potential role of FGF21 in the onset and progression of some of the most prevalent metabolic pathologies and to understand the potential of FGF21 as a target for these diseases. After this review, we conclude that more research is needed to understand the mechanisms underlying the role of FGF21 in macronutrient preference and food intake behavior, but also in β-klotho regulation and the activity of the fibroblast activation protein (FAP) to uncover its therapeutic potential as a way to increase the FGF21 signaling.

Effects of EPA and lipoic acid supplementation on circulating FGF21 and the fatty acid profile in overweight/obese women following a hypocaloric diet

FGF21 has emerged as a key metabolism and energy homeostasis regulator. Dietary supplementation with eicosapentaenoic acid (EPA) and/or α-lipoic acid (LIP) has shown beneficial effects on obesity. In this study, we evaluated EPA and/or LIP effects on plasma FGF21 and the fatty acid (FA) profile in overweight/obese women following hypocaloric diets. At the baseline, FGF21 levels were negatively related to the AST/ALT ratio and HMW adiponectin. The weight loss did not cause any significant changes in FGF21 levels, but after the intervention FGF21 increased in EPA-supplemented groups compared to non-EPA-supplemented groups. EPA supplementation decreased the plasma n-6-PUFA content and increased n-3-PUFAs, mainly EPA and DPA, but not DHA. In the LIP-alone supplemented group a decrease in the total SFA and n-6-PUFA content was observed after the supplementation. Furthermore, EPA affected the desaturase activity, lowering Δ4D and raising Δ5/6D. These effects were not observed in the LIP-supplemented groups. Besides, the changes in FGF21 levels were associated with the changes in EPA, n-3-PUFAs, Δ5/6D, and n-6/n-3 PUFA ratio. Altogether, our study suggests that n-3-PUFAs influence FGF21 levels in obesity, although the specific mechanisms implicated remain to be elucidated.

Nutritional regulation of fibroblast growth factor 21: from macronutrients to bioactive dietary compounds

Obesity is a worldwide health problem mainly due to its associated comorbidities. Fibroblast growth factor 21 (FGF21) is a peptide hormone involved in metabolic homeostasis in healthy individuals and considered a promising therapeutic candidate for the treatment of obesity. FGF21 is predominantly produced by the liver but also by other tissues, such as white adipose tissue (WAT), brown adipose tissue (BAT), skeletal muscle, and pancreas in response to different stimuli such as cold and different nutritional challenges that include fasting, high-fat diets (HFDs), ketogenic diets, some amino acid-deficient diets, low protein diets, high carbohydrate diets or specific dietary bioactive compounds. Its target tissues are essentially WAT, BAT, skeletal muscle, heart and brain. The effects of FGF21 in extra hepatic tissues occur through the fibroblast growth factor receptor (FGFR)-1c together with the co-receptor β-klotho (KLB). Mechanistically, FGF21 interacts directly with the extracellular domain of the membrane bound cofactor KLB in the FGF21- KLB-FGFR complex to activate FGFR substrate 2α and ERK1/2 phosphorylation. Mice lacking KLB are resistant to both acute and chronic effects of FGF21. Moreover, the acute insulin sensitizing effects of FGF21 are also absent in mice with specific deletion of adipose KLB or FGFR1. Most of the data show that pharmacological administration of FGF21 has metabolic beneficial effects. The objective of this review is to compile existing information about the mechanisms that could allow the control of endogenous FGF21 levels in order to obtain the beneficial metabolic effects of FGF21 by inducing its production instead of doing it by pharmacological administration.

The regulation of FGF21 gene expression by metabolic factors and nutrients

Fibroblast growth factor 21 (FGF21) gene expression is altered by a wide array of physiological, metabolic, and environmental factors. Among dietary factors, high dextrose, low protein, methionine restriction, short-chain fatty acids (butyric acid and lipoic acid), and all-trans-retinoic acid were repeatedly shown to induce FGF21 expression and circulating levels. These effects are usually more pronounced in liver or isolated hepatocytes than in adipose tissue or isolated fat cells. Although peroxisome proliferator-activated receptor α (PPARα) is a key mediator of hepatic FGF21 expression and function, including the regulation of gluconeogenesis, ketogenesis, torpor, and growth inhibition, there is increasing evidence of PPARα-independent transactivation of the FGF21 gene by dietary molecules. FGF21 expression is believed to follow the circadian rhythm and be placed under the control of first order clock-controlled transcription factors, retinoic acid receptor-related orphan receptors (RORs) and nuclear receptors subfamily 1 group D (REV-ERBs), with FGF21 rhythm being anti-phase to REV-ERBs. Key metabolic hormones such as glucagon, insulin, and thyroid hormone have presumed or clearly demonstrated roles in regulating FGF21 transcription and secretion. The control of the FGF21 gene by glucagon and insulin appears more complex than first anticipated. Some discrepancies are noted and will need continued studies. The complexity in assessing the significance of FGF21 gene expression resides in the difficulty to ascertain (i) when transcription results in local or systemic increase of FGF21 protein; (ii) if FGF21 is among the first or second order genes upregulated by physiological, metabolic, and environmental stimuli, or merely an epiphenomenon; and (iii) whether FGF21 may have some adverse effects alongside beneficial outcomes.