Cytoplasmic SIRT6-mediated ACSL5 deacetylation impedes nonalcoholic fatty liver disease by facilitating hepatic fatty acid oxidation.

Nonalcoholic fatty liver disease (NAFLD) is characterized by excessive hepatic lipid accumulation, which can progress to nonalcoholic steatohepatitis (NASH). Histone deacetylase Sirtuin 6 (SIRT6) regulates NAFLD by regulating metabolism-related gene expression, but an extrachromosomal role for SIRT6 in NAFLD development remains elusive. We investigated whether SIRT6 functions on NAFLD in the cytoplasm. We found that SIRT6 binds saturated fatty acids, especially palmitic acid. This binding leads to its nuclear export, where it deacetylates long-chain acyl-CoA synthase 5 (ACSL5), thereby facilitating fatty acid oxidation. High-fat diet-induced NAFLD is suppressed by ACSL5 hepatic overexpression but is exacerbated by its depletion. As confirmation, overexpression of a deacetylated ACSL5 mimic attenuated NAFLD in Sirt6 liver-specific knockout mice. Moreover, NASH-hepatic tissues from both patients and diet-fed mice exhibited significantly reduced cytoplasmic SIRT6 levels and increased ACSL5 acetylation. The SIRT6/ACSL5 signaling pathway has a critical role in NAFLD progression and might constitute an avenue for therapeutic intervention.

Regulation of membrane fluidity by RNF145-triggered degradation of the lipid hydrolase ADIPOR2.

The regulation of membrane lipid composition is critical for cellular homeostasis. Cells are particularly sensitive to phospholipid saturation, with increased saturation causing membrane rigidification and lipotoxicity. How mammalian cells sense membrane lipid composition and reverse fatty acid (FA)-induced membrane rigidification is poorly understood. Here we systematically identify proteins that differ between mammalian cells fed saturated versus unsaturated FAs. The most differentially expressed proteins were two ER-resident polytopic membrane proteins: the E3 ubiquitin ligase RNF145 and the lipid hydrolase ADIPOR2. In unsaturated lipid membranes, RNF145 is stable, promoting its lipid-sensitive interaction, ubiquitination and degradation of ADIPOR2. When membranes become enriched in saturated FAs, RNF145 is rapidly auto-ubiquitinated and degraded, stabilising ADIPOR2, whose hydrolase activity restores lipid homeostasis and prevents lipotoxicity. We therefore identify RNF145 as a FA-responsive ubiquitin ligase which, together with ADIPOR2, defines an autoregulatory pathway that controls cellular membrane lipid homeostasis and prevents acute lipotoxic stress.

Fatty acid preference for beta-oxidation in mitochondria of murine cultured astrocytes.

The brain utilizes glucose as a primary energy substrate but also fatty acids for the ß-oxidation in mitochondria. The ß-oxidation is reported to occur mainly in astrocytes, but its capacity and efficacy against different fatty acids remain unknown. Here, we show the fatty acid preference for the ß-oxidation in mitochondria of murine cultured astrocytes. Fatty acid oxidation assay using an extracellular flux analyzer showed that saturated or monosaturated fatty acids, palmitic acid and oleic acid, are preferred substrates over polyunsaturated fatty acids like arachidonic acid and docosahexaenoic acid. We also report that fatty acid binding proteins expressed in the astrocytes contribute less to fatty acid transport to mitochondria for ß-oxidation. Our results could give insight into understanding energy metabolism through fatty acid consumption in the brain.

Palmitic acid induces ß-cell ferroptosis by activating ceramide signaling pathway.

Individuals with type 2 diabetes mellitus frequently display heightened levels of palmitic acid (PA) in their serum, which may lead to ß-cell damage. The involvement of ferroptosis, a form of oxidative cell death in lipotoxic ß-cell injury remains uncertain. Here, we have shown that PA induces intracellular lipid peroxidation, increases intracellular Fe2+ content and decreases intracellular glutathione peroxidase 4 (GPX4) expression. Furthermore, PA causes distinct changes in pancreatic islets and INS-1 cells, such as mitochondrial atrophy and increased membrane density. Furthermore, the presence of the ferroptosis inhibitor has a significant mitigating effect on PA-induced ß-cell damage. Mechanistically, PA increased ceramide content and c-Jun N-terminal kinase (JNK) phosphorylation. The ceramide synthase inhibitor effectively attenuated PA-induced ß-cell damage and GPX4/Fe2+ abnormalities, while inhibiting JNK phosphorylation. Additionally, the JNK inhibitor SP600125 improved PA-induced cell damage. In conclusion, by promoting ceramide synthesis, PA inhibited GPX4 expression and increased intracellular Fe2+ to induce ß-cell ferroptosis. Moreover, JNK may be a downstream mechanism of ceramide-triggered lipotoxic ferroptosis in ß-cells.

Protein phosphatase 4 mediates palmitic acid-induced endothelial dysfunction by decreasing eNOS phosphorylation at serine 633 in HUVECs.

Plasma saturated free fatty acid (FFA)-induced endothelial dysfunction (ED) contributes to the pathogenesis of atherosclerosis and cardiovascular diseases. However, the mechanism underlying saturated FFA-induced ED remains unclear. This study demonstrated that palmitic acid (PA) induced ED by activating the NADPH oxidase (NOX)/ROS signaling pathway to activate protein phosphatase 4 (PP4) and protein phosphatase 2A (PP2A), thereby reducing endothelial nitric oxide synthase (eNOS) phosphorylation at Ser633 and Ser1177, respectively. Okadaic acid (OA) and fostriecin (FST), which are inhibitors of PP2A, inhibited the PA-induced decreases in eNOS phosphorylation at Ser633 and Ser1177. The antioxidants N-acetylcysteine (NAC) and apocynin (APO) or knockdown of gp91phox or p67phox (NOX subunits) restored PA-mediated downregulation of PP4R2 protein expression and eNOS Ser633 phosphorylation. Knockdown of the PP4 catalytic subunit (PP4c) specifically increased eNOS Ser633 phosphorylation, while silencing the PP2A catalytic subunit (PP2Ac) restored only eNOS Ser1177 phosphorylation. Furthermore, PA dramatically decreased the protein expression of the PP4 regulatory subunit R2 (PP4R2) but not the other regulatory subunits. PP4R2 overexpression increased eNOS Ser633 phosphorylation, nitric oxide (NO) production, cell migration and tube formation but did not change eNOS Ser1177 phosphorylation levels. Coimmunoprecipitation (Co-IP) suggested that PP4R2 and PP4c interacted with the PP4R3α and eNOS proteins. In summary, PA decreases PP4R2 protein expression through the Nox/ROS pathway to activate PP4, which contributes to ED by dephosphorylating eNOS at Ser633. The results of this study suggest that PP4 is a novel therapeutic target for ED and ED-associated vascular diseases.

Dysregulated palmitic acid metabolism promotes the formation of renal calcium-oxalate stones through ferroptosis induced by polyunsaturated fatty acids/phosphatidic acid.

The pathogenesis of renal calcium-oxalate (CaOx) stones is complex and influenced by various metabolic factors. In parallel, palmitic acid (PA) has been identified as an upregulated lipid metabolite in the urine and serum of patients with renal CaOx stones via untargeted metabolomics. Thus, this study aimed to mechanistically assess whether PA is involved in stone formation. Lipidomics analysis of PA-treated renal tubular epithelial cells compared with the control samples revealed that α-linoleic acid and α-linolenic acid were desaturated and elongated, resulting in the formation of downstream polyunsaturated fatty acids (PUFAs). In correlation, the levels of fatty acid desaturase 1 and 2 (FADS1 and FADS2) and peroxisome proliferator-activated receptor α (PPARα) in these cells treated with PA were increased relative to the control levels, suggesting that PA-induced upregulation of PPARα, which in turn upregulated these two enzymes, forming the observed PUFAs. Lipid peroxidation occurred in these downstream PUFAs under oxidative stress and Fenton Reaction. Furthermore, transcriptomics analysis revealed significant changes in the expression levels of ferroptosis-related genes in PA-treated renal tubular epithelial cells, induced by PUFA peroxides. In addition, phosphatidyl ethanolamine binding protein 1 (PEBP1) formed a complex with 15-lipoxygenase (15-LO) to exacerbate PUFA peroxidation under protein kinase C ζ (PKC ζ) phosphorylation, and PKC ζ was activated by phosphatidic acid derived from PA. In conclusion, this study found that the formation of renal CaOx stones is promoted by ferroptosis of renal tubular epithelial cells resulting from PA-induced dysregulation of PUFA and phosphatidic acid metabolism, and PA can promote the renal adhesion and deposition of CaOx crystals by injuring renal tubular epithelial cells, consequently upregulating adhesion molecules. Accordingly, this study provides a new theoretical basis for understanding the correlation between fatty acid metabolism and the formation of renal CaOx stones, offering potential targets for clinical applications.

Dysregulation of mitochondrial dynamics and mitophagy are involved in high-fat diet-induced steroidogenesis inhibition.

Male obesity is a pandemic health issue and can disrupt testicular steroidogenesis. Here, we explored the mechanism by which a high-fat diet (HFD) induced steroidogenic inhibition. As expected, HFD induced lipid droplet accumulation and reduced the expression of StAR, P450scc, and 3ß-HSD, three steroidogenic enzymes, in mouse testes. Palmitic acid (PA), a saturated fatty acid usually used to trigger lipotoxicity in vitro, induced greater accumulation of lipid droplets and the downregulation of steroidogenic enzymes in TM3 cells. Mechanistically, both HFD and PA disturbed mitochondrial fusion/fission dynamics and then induced mitochondrial dysfunction and mitophagy inhibition in mouse Leydig cells. Additionally, mitochondrial fusion promoter M1 attenuated PA-induced imbalance of mitochondrial dynamics, mitophagy inhibition, mitochondrial reactive oxygen species (ROS) production, and mitochondrial dysfunction in TM3 cells. Mitofusin 2 (Mfn2) knock-down further aggravated the PA-induced imbalance of mitochondrial dynamics, mitochondrial ROS production, and mitochondrial dysfunction in TM3 cells. Importantly, M1 rescued PA-induced downregulation of steroidogenic enzymes, whereas Mfn2 knock-down further aggravated PA-induced downregulation of steroidogenic enzymes in TM3 cells. Overall, our results provide laboratory evidence that mitochondrial dysfunction and mitophagy inhibition caused by dysregulation of mitochondrial fusion may be involved in HFD-induced steroidogenesis inhibition in mouse Leydig cells.

4EBP2-regulated protein translation has a critical role in high-fat diet-induced insulin resistance in hepatocytes.

A high-fat diet (HFD) plays a critical role in hepatocyte insulin resistance. Numerous models and factors have been proposed to elucidate the mechanism of palmitic acid (PA)-induced insulin resistance. However, proteomic studies of insulin resistance by HFD stimulation are usually performed under insulin conditions, leading to an unclear understanding of how a HFD alone affects hepatocytes. Here, we mapped the phosphorylation rewiring events in PA-stimulated HepG2 cells and found PA decreased the phosphorylation level of the eukaryotic translation initiation factor 4E-binding protein 2 (4EBP2) at S65/T70. Further experiments identified 4EBP2 as a key node of insulin resistance in either HFD mice or PA-treated cells. Reduced 4EBP2 levels increased glucose uptake and insulin sensitivity, whereas the 4EBP2_S65A/T70A mutation exacerbated PA-induced insulin resistance. Additionally, the nascent proteome revealed many glycolysis-related proteins translationally regulated by 4EBP2 such as hexokinase-2, pyruvate kinase PKM, TBC1 domain family member 4, and glucose-6-phosphate 1-dehydrogenase. In summary, we report the critical role of 4EBP2 in regulating HFD-stimulated insulin resistance in hepatocytes.

Sex-specific vulnerabilities in human astrocytes underpin the differential impact of palmitic acid.

Obesity and neurometabolic diseases have been linked to neurodegenerative diseases. Our hypothesis is that the endogenous estrogenic component of human astrocytes plays a critical role in cell response during lipotoxic damage, given that obesity can disrupt hormonal homeostasis and cause brain inflammation. Our findings showed that high concentrations of palmitic acid (PA) significantly reduced cell viability more in male astrocytes, indicating sex-specific vulnerabilities. PA induced a greater increase in cytosolic reactive oxygen species (ROS) production in males, while female astrocytes exhibited higher superoxide ion levels in mitochondria. In addition, female astrocytes treated with PA showed increased expression of antioxidant proteins, including catalase, Gpx-1 and Nrf2 suggesting a stronger cellular defence mechanism. Interestingly, there was a difference in the expression of estrogenic components, such as estrogen, androgens, and progesterone receptors, as well as aromatase and 5α-reductase enzymes, between males and females. PA induced their expression mainly in females, indicating a potential protective mechanism mediated by endogenous hormones. In summary, our findings highlight the impact of sex on the response of human astrocytes to lipotoxicity. Male astrocytes appear to be more susceptible to cellular damage when exposed to high concentrations of fatty acids.

The fadXDEBA locus of Staphylococcus aureus is required for metabolism of exogenous palmitic acid and in vivo growth.

In Staphylococcus aureus, genes that should confer the capacity to metabolize fatty acids by ß-oxidation occur in the fadXDEBA locus, but their function has not been elucidated. Previously, incorporation into phospholipid through the fatty acid kinase FakA pathway was thought to be the only option available for S. aureus to metabolize exogenous saturated fatty acids. We now find that in S. aureus USA300, a fadX::lux reporter was repressed by glucose and induced by palmitic acid but not stearic acid, while in USA300ΔfakA basal expression was significantly elevated, and enhanced in response to both fatty acids. When cultures were supplemented with palmitic acid, palmitoyl-CoA representing the first metabolite in the ß-oxidation pathway was detected in USA300, but not in a fadXDEBA deletion mutant USA300Δfad, which relative to USA300 exhibited increased incorporation of palmitic acid into phospholipid accompanied by a rapid loss of viability. USA300Δfad also exhibited significantly reduced viability in a murine tissue abscess infection model. Our data are consistent with FakA-mediated incorporation of fatty acids into phospholipid as a preferred pathway for metabolism of exogenous fatty acids, while the fad locus is critical for metabolism of palmitic acid, which is the most abundant free fatty acid in human plasma.

Regulation of genes involved in the metabolic adaptation of murine microglial cells in response to elevated HIF-1α mediated activation.

Microglia cells are activated in response to different stress signals. Several metabolic adaptations underlie microglia activation in the brain. Among these, in conditions like ischemic stroke and, hypoxic stress stimuli activate microglia cells. Hypoxic stress is mediated by HIF-1α. Although HIF-1α has been implicated in the alteration of metabolic pathways, changes in microglia lipid metabolism during M1 activation of microglia induced by elevated HIF-1α levels are yet to be understood. This can also merit interest in the development of novel targets to mitigate chronic inflammation. Our study aims to elucidate the transcriptional regulation of metabolic pathways in microglia cells during HIF-1α mediated activation. To study the adaptations in the metabolic pathways we induced microglia activation, by activating HIF-1α. Here, we show that microglia cells activated in response to elevated HIF-1α require ongoing lipogenesis and fatty acid breakdown. Notably, autophagy is activated during the initial stages of microglia activation. Inhibition of autophagy in activated microglia affects their viability and phagocytic activity. Collectively, our study expands the understanding of the molecular link between autophagy, lipid metabolism, and inflammation during HIF-1α mediated microglial activation that can lead to the development of promising strategies for controlling maladaptive activation states of microglia responsible for neuroinflammation. Together, our findings suggest that the role of HIF-1α in regulating metabolic pathways during hypoxia in microglia is beyond optimization of glucose utilization and distinctly regulates lipid metabolism during pro-inflammatory activation.

Role of TFEB-autophagy lysosomal pathway in palmitic acid induced renal tubular epithelial cell injury.

Lysosomal dysfunction and impaired autophagic flux are involved in the pathogenesis of lipotoxicity in the kidney. Here, we investigated the role of transcription factor EB (TFEB), a master regulator of autophagy-lysosomal pathway, in palmitic acid induced renal tubular epithelial cells injury. We examined lipid accumulation, autophagic flux, expression of Ps211-TFEB, and nuclear translocation of TFEB in HK-2 cells overloaded with palmitic acid (PA). By utilizing immunohistochemistry, we detected TFEB expression in renal biopsy tissues from patients with diabetic nephropathy and normal renal tissue adjacent to surgically removed renal carcinoma (controls), as well as kidney tissues from rat fed with high-fat diet (HFD) and low-fat diet (LFD). We found significant lipid accumulation, increased apoptosis, accompanied with elevated Ps211-TFEB, decreased nuclear TFEB, reduced lysosome biogenesis and insufficient autophagy in HK-2 cells treated with PA. Kidney tissues from patients with diabetic nephropathy had lower nuclear and total levels of TFEB than that in control kidney tissues. Level of renal nuclear TFEB in HFD rats was also lower than that in LFD rats. Exogenous overexpression of TFEB increased the nuclear TFEB level in HK-2 cells treated with PA, promoted lysosomal biogenesis, improved autophagic flux, reduced lipid accumulation and apoptosis. Our results collectively indicate that PA is a strong inducer for TFEB phosphorylation modification at ser211 accompanied with lower nuclear translocation of TFEB. Impairment of TFEB-mediated lysosomal biogenesis and function by palmitic acid may lead to insufficient autophagy and promote HK-2 cells injury.

Thermal effects and drugs competition on the palmitate binding capacity of human serum albumin.

Human serum albumin (HSA) is the most abundant plasma protein of the circulatory system. It is a multidomain, multifunctional protein that, combining diverse affinities and wide specificity, binds, stores, and transports a variety of biological compounds, pharmacores, and fatty acids. HSA is finding increasing uses in drug-delivery due to its ability to carry functionalized ligands and prodrugs. All this raises the question of competition for binding sites occupancy in case of multiple ligands, which in turn influences the protein structure/dynamic/function relationship and also has an impact on the biomedical applications. In this work, the effects of interactive binding of palmitic acid (PA), warfarin (War) and ibuprofen (Ibu) on the thermal stability of HSA were studied using DSC, ATR-FTIR, and EPR. PA is a high-affinity physiological ligand, while the two drugs are widely used for their anticoagulant (War) and anti-inflammatory (Ibu) efficacy, and are exogenous compounds that accommodate in the deputed drug site DS1 and DS2, respectively overlapping with some of the fatty acid binding sites. The results indicate that HSA acquires the highest thermal stability when it is fully saturated with PA. The binding of this physiological ligand does not hamper the binding of War or Ibu to the native state of the protein. In addition, the three ligands bind simultaneously, suggesting a synergic cooperative influence due to allosteric effects. The increased thermal stability subsequent to binary and multiple ligands binding moderates protein aggregation propensity and restricts protein dynamics. The biophysics findings provide interesting features about protein stability, aggregation, and dynamics in interaction with multiple ligands and are relevant in drug-delivery.

The differential effects of palmitic acid and oleic acid on the metabolic response of hypothalamic astrocytes from male and female mice.

Diets rich in saturated fats are more detrimental to health than those containing mono- or unsaturated fats. Fatty acids are an important source of energy, but they also relay information regarding nutritional status to hypothalamic metabolic circuits and when in excess can be detrimental to these circuits. Astrocytes are the main site of central fatty acid ß-oxidation, and hypothalamic astrocytes participate in energy homeostasis, in part by modulating hormonal and nutritional signals reaching metabolic neurons, as well as in the inflammatory response to high-fat diets. Thus, we hypothesized that how hypothalamic astrocytes process-specific fatty acids participates in determining the differential metabolic response and that this is sex dependent as males and females respond differently to high-fat diets. Male and female primary hypothalamic astrocyte cultures were treated with oleic acid (OA) or palmitic acid (PA) for 24 h, and an untargeted metabolomics study was performed. A clear predictive model for PA exposure was obtained, while the metabolome after OA exposure was not different from controls. The observed modifications in metabolites, as well as the expression levels of key metabolic enzymes, indicate a reduction in the activity of the Krebs and glutamate/glutamine cycles in response to PA. In addition, there were specific differences between the response of astrocytes from male and female mice, as well as between hypothalamic and cerebral cortical astrocytes. Thus, the response of hypothalamic astrocytes to specific fatty acids could result in differential impacts on surrounding metabolic neurons and resulting in varied systemic metabolic outcomes.

Palmitic acid impairs human and mouse placental function by inhibiting trophoblast autophagy through induction of acyl-coenzyme A-binding protein (ACBP) upregulation.

STUDY QUESTION: Can exposure to palmitic acid (PA), a common saturated fatty acid, modulate autophagy in both human and mouse trophoblast cells through the regulation of acyl-coenzyme A-binding protein (ACBP)? SUMMARY ANSWER: PA exposure before and during pregnancy impairs placental development through mechanisms involving placental autophagy and ACBP expression. WHAT IS KNOWN ALREADY: High-fat diets, including PA, have been implicated in adverse effects on human placental and fetal development. Despite this recognition, the precise molecular mechanisms underlying these effects are not fully understood. STUDY DESIGN, SIZE, DURATION: Extravillous trophoblast (EVT) cell line HTR-8/SVneo and human trophoblast stem cell (hTSC)-derived EVT (hTSCs-EVT) were exposed to PA or vehicle control for 24 h. Female wild-type C57BL/6 mice were divided into PA and control groups (n = 10 per group) and subjected to a 12-week dietary intervention. Afterward, they were mated with male wild-type C57BL/6 mice and euthanized on Day 14 of gestation. Female ACBPflox/flox mice were also randomly assigned to control and PA-exposed groups (each with 10 mice), undergoing the same dietary intervention and mating with ACBPflox/floxELF5-Cre male mice, followed by euthanasia on Day 14 of gestation. The study assessed the effects of PA on mouse embryonic development and placental autophagy. Additionally, the role of ACBP in the pathogenesis of PA-induced placental toxicity was investigated. PARTICIPANTS/MATERIALS, SETTING, METHODS: The findings were validated using real-time PCR, Western blot, immunofluorescence, transmission electron microscopy, and shRNA knockdown approaches. MAIN RESULTS AND THE ROLE OF CHANCE: Exposure to PA-upregulated ACBP expression in both human HTR-8/SVneo cells and hTSCs-EVT, as well as in mouse placenta. PA exposure also induced autophagic dysfunction in HTR-8/SVneo cells, hTSCs-EVT, and mouse placenta. Through studies on ACBP placental conditional knockout mice and ACBP knockdown human trophoblast cells, it was revealed that reduced ACBP expression led to trophoblast malfunction and affected the expression of autophagy-related proteins LC3B-II and P62, thereby impacting embryonic development. Conversely, ACBP knockdown partially mitigated PA-induced impairment of placental trophoblast autophagy, observed both in vitro in human trophoblast cells and in vivo in mice. LARGE SCALE DATA: N/A. LIMITATIONS, REASONS FOR CAUTION: Primary EVT cells from early pregnancy are fragile, limiting research use. Maintaining their viability is tough, affecting data reliability. The study lacks depth to explore PA diet cessation effects after 12 weeks. Without follow-up, understanding postdiet impacts on pregnancy stages is incomplete. Placental abnormalities linked to elevated PA diet in embryos lack confirmation due to absence of control groups. Clarifying if issues stem solely from PA exposure is difficult without proper controls. WIDER IMPLICATIONS OF THE FINDINGS: Consuming a high-fat diet before and during pregnancy may result in complications or challenges in successfully carrying the pregnancy to term. It suggests that such dietary habits can have detrimental effects on the health of both the mother and the developing fetus. STUDY FUNDING/COMPETING INTEREST(S): This work was supported in part by the National Natural Science Foundation of China (82171664, 82301909) and the Natural Science Foundation of Chongqing Municipality of China (CSTB2022NS·CQ-LZX0062, cstc2019jcyj-msxmX0749, and cstc2021jcyj-msxmX0236). The authors declare that they have no conflict of interest. TRIAL REGISTRATION NUMBER: N/A.

BDNF mimetics recover palmitic acid-induced injury in cardiomyocytes by ameliorating Akt-dependent mitochondrial impairments.

Cardiac lipotoxicity is a prevalent consequence of lipid metabolism disorders occurring in cardiomyocytes, which in turn precipitates the onset of heart failure. Mimetics of brain-derived neurotrophic factor (BDNF), such as 7,8-dihydroxyflavone (DHF) and 7,8,3'-trihydroxyflavone (THF), have demonstrated significant cardioprotective effects. However, it remains unclear whether these mimetics can protect cardiomyocytes against lipotoxicity. The aim of this study was to examine the impact of DHF and THF on the lipotoxic effects induced by palmitic acid (PA), as well as the concurrent mitochondrial dysfunction. H9c2 cells were subjected to treatment with PA alone or in conjunction with DHF or THF. Various factors such as cell viability, lactate dehydrogenase (LDH) release, death ratio, and mitochondrial function including mitochondrial membrane potential (MMP), mitochondrial-derived reactive oxygen species (mito-SOX) production, and mitochondrial respiration were assessed. PA dose-dependently reduced cell viability, which was restored by DHF or THF. Additionally, both DHF and THF decreased LDH content, death ratio, and mito-SOX production, while increasing MMP and regulating mitochondrial oxidative phosphorylation in cardiomyocytes. Moreover, DHF and THF specifically activated Akt signaling. The protective effects of DHF and THF were abolished when an Akt inhibitor was used. In conclusion, BDNF mimetics attenuate PA-induced injury in cardiomyocytes by alleviating mitochondrial impairments through the activation of Akt signaling.

The presence of free palmitic acid modulates the effects of lutein on structural and dynamic properties of lipid membranes.

Free fatty acids, like palmitic acid (PA), and xanthophyll pigments, like lutein (LUT) are the natural membrane compounds in plants. To study the effect of PA on LUT and their organization, a model membrane of 1,2-dimyristoyl-sn-glycerol-3-phosphocholine (DMPC) enriched with 2 mol% PA and 1 mol% LUT was formed. Molecular mechanisms underlying the interaction between these two compounds were examined with application of molecular spectroscopy techniques, e.g., visible spectroscopy, electron paramagnetic resonance and Fourier transform infrared. We determined the monomeric/dimeric organization of LUT in the membrane. We proved that the presence of PA in the lipid phase facilitated and stabilized the formation of LUT structures in the membrane. Lutein with PA did not form strong molecular aggregates like H- and J-structures. We presented the simplified model membrane that could be a suitable representation of the physiological process of de-esterification of PA from LUT appearing in natural biomembranes in humans.

Palmitic acid-activated GPRs/KLF7/CCL2 pathway is involved in the crosstalk between bone marrow adipocytes and prostate cancer.

BACKGROUND: Obesity-induced abnormal bone marrow microenvironment is one of the important risk element for bone metastasis in prostate cancer (PCa). The present study aimed to determine whether obesity-induced elevation in palmitic acid (PA), which is the most abundant of the free fatty acids (FFAs), increased CCL2 via the GPRs/KLF7 pathway in bone marrow adipocytes (BMA) to facilitate PCa growth and metastasis. METHODS: We constructed a bone-tumor bearing mouse model with obesity through high-fat diet, and observed the tumor formation ability of PCa cells. In vitro, observe the effect of PA on the expression level of CCL2 in BMA through GPRs/KLF7 signaling pathway. After co-culture of BMA and PCa cells, CCK8 assay and transwell experiment were used to detect the changes in biological behavior of PCa cells stimulated by BMA. RESULTS: The BMA distribution in the bone marrow cavity of BALB/c nude mice fed with the high-fat diet (HFD) was evidently higher than that in the mice fed with the normal diet (ND). Moreover, HFD-induced obesity promoted KLF7/CCL2 expression in BMA and PCa cell growth in the bone marrow cavity of the mice. In the vitro experiment, a conditioned medium with increased CCL2 obtained from the BMA cultured with PA (CM-BMA-PA) was used for culturing the PCa cell lines, which evidently enhanced the proliferation, invasion, and migration ability. KLF7 significantly increased the CCL2 expression and secretion levels in BMA by targeting the promoter region of the CCL2 gene. In addition, GPR40/120 engaged in the PA-induced high KLF7/CCL2 levels in BMA to facilitate the malignant progression of PC-3 cells. CONCLUSIONS: PA-activated GPRs/KLF7/CCL2 pathway in BMA facilitates prostate cancer growth and metastasis.

GPAT1 Activity and Abundant Palmitic Acid Impair Insulin Suppression of Hepatic Glucose Production in Primary Mouse Hepatocytes.

BACKGROUND: Glycerol-3-phosphate acyltransferase (GPAT) activity is correlated with obesity and insulin resistance in mice and humans. However, insulin resistance exists in people with normal body weight, and individuals with obesity may be metabolically healthy, implying the presence of complex pathophysiologic mechanisms underpinning insulin resistance. OBJECTIVE: We asked what conditions related to GPAT1 must be met concurrently for hepatic insulin resistance to occur. METHODS: Mouse hepatocytes were overexpressed with GPATs via adenoviral infection or exposed to high or low concentrations of glucose. Glucose production by the cells and phosphatidic acid (PA) content in the cells were assayed, GPAT activity was measured, relative messenger RNA expressions of sterol-regulatory element-binding protein 1c (SREBP1c), carbohydrate response element-binding protein (ChREBP), and GPAT1 were analyzed, and insulin signaling transduction was examined. RESULTS: Overexpressing GPAT1 in mouse hepatocytes impaired insulin's suppression of glucose production, together with an increase in both N-ethylmaleimide-resistant GPAT activity and the content of di-16:0 PA. Akt-mediated insulin signaling was inhibited in hepatocytes that overexpressed GPAT1. When the cells were exposed to high-glucose concentrations, insulin suppression of glucose production was impaired, and adding palmitic acid exacerbated this impairment. High-glucose exposure increased the expression of SREBP1c, ChREBP, and GPAT1 by ∼2-, 5-, and 5.7-fold, respectively. The addition of 200 mM palmitic acid or linoleic acid to the culture media did not change the upregulation of expression of these genes by high glucose. High-glucose exposure increased di-16:0 PA content in the cells, and adding palmitic acid further increased di-16:0 PA content. The effect was specific to palmitic acid because linoleic acid did not show these effects. CONCLUSION: These data demonstrate that high-GPAT1 activity, whether induced by glucose exposure or acquired by transfection, and abundant palmitic acid can impair insulin's ability to suppress hepatic glucose production in primary mouse hepatocytes.

Palmitic Acid Modulation of the Insulin-Like Growth Factor System in Hypothalamic Astrocytes and Neurons.

INTRODUCTION: Insulin-like growth factor (IGF)1 and IGF2 have neuroprotective effects, but less is known regarding how other members of the IGF system, including IGF binding proteins (IGFBPs) and the regulatory proteinase pappalysin-1 (PAPP-A) and its endogenous inhibitor stanniocalcin-2 (STC2) participate in this process. Here, we analyzed whether these members of the IGF system are modified in neurons and astrocytes in response to palmitic acid (PA), a fatty acid that induces cell stress when increased centrally. METHODS: Primary hypothalamic astrocyte cultures from male and female PND2 rats and the pro-opiomelanocortin (POMC) neuronal cell line, mHypoA-POMC/GFP-2, were treated with PA, IGF1 or both. To analyze the role of STC2 in astrocytes, siRNA assays were employed. RESULTS: In astrocytes of both sexes, PA rapidly increased cell stress factors followed by increased Pappa and Stc2 mRNA levels and then a decrease in Igf1, Igf2, and Igfbp2 expression and cell number. Exogenous IGF1 did not revert these effects. In mHypoA-POMC/GFP-2 neurons, PA reduced cell number and Pomc and Igf1 mRNA levels, and increased Igfbp2 and Stc2, again with no effect of exogenous IGF1. PA increased STC2 expression, but no effects of decreasing its levels by interference assays or exogenous STC2 treatment in astrocytes were found. CONCLUSIONS: The response of the IGF system to PA was cell and sex specific, but no protective effects of the IGFs were found. However, the modifications in hypothalamic PAPP-A and STC2 indicate that further studies are required to determine their role in the response to fatty acids and possibly in metabolic control.