Fatty Acid-induced Apoptosis Research Articles

SIRT1 activation attenuates palmitate induced apoptosis in C2C12 muscle cells.

Type 2 diabetes is characterized by insulin resistance, which manifests mainly in skeletal muscles. SIRT1 has been found to play a role in the insulin signaling pathway. However, the molecular underpinnings of SIRT1's function in palmitate fatty acid-induced apoptosis still need to be better understood. In this research, skeletal muscle cells are treated with palmitate to be insulin resistant. It is approached that SIRT1 is downregulated in C2C12 muscle cells during palmitate-induced apoptosis and that activating SIRT1 mitigates this effect. Based on these findings, palmitate-induced apoptosis suppressed mitochondrial biogenesis by lowering PGC-1 expression, while SIRT1 overexpression boosted. The SIRT1 inhibitor sirtinol, on the other hand, decreased mitochondrial biogenesis under the same conditions. This research also shows that ROS levels rise in the conditions necessary for apoptosis induction by palmitate, and ROS inhibitors can mitigate this effect. This work demonstrated that lowering ROS levels by boosting SIRT1 expression inhibited apoptotic induction in skeletal muscle cells. This study's findings suggested that SIRT1 can improve insulin resistance in type 2 diabetes by slowing the rate of lipo-apoptosis and boosting mitochondrial biogenesis, among other benefits.

Protective effect of oleic acid against very long-chain fatty acid-induced apoptosis in peroxisome-deficient CHO cells

Very long-chain fatty acids (VLCFAs) are degraded exclusively in peroxisomes, as evidenced by the accumulation of VLCFAs in patients with certain peroxisomal disorders. Although accumulation of VLCFAs is considered to be associated with health issues, including neuronal degeneration, the mechanisms underlying VLCFAs-induced tissue degeneration remain unclear. Here, we report the toxic effect of VLCFA and protective effect of C18: 1 FA in peroxisome-deficient CHO cells. We examined the cytotoxicity of saturated and monounsaturated VLCFAs with chain-length at C20–C26, and found that longer and saturated VLCFA showed potent cytotoxicity at lower accumulation levels. Furthermore, the extent of VLCFA-induced toxicity was found to be associated with a decrease in cellular C18:1 FA levels. Notably, supplementation with C18:1 FA effectively rescued the cells from VLCFA-induced apoptosis without reducing the cellular VLCFAs levels, implying that peroxisome-deficient cells can survive in the presence of accumulated VLCFA, as long as the cells keep sufficient levels of cellular C18:1 FA. These results suggest a therapeutic potential of C18:1 FA in peroxisome disease and may provide new insights into the pharmacological effect of Lorenzo's oil, a 4:1 mixture of C18:1 and C22:1 FA.

Fenofibrate Attenuates Renal Tubular Cell Apoptosis by Up-Regulating MCAD in Diabetic Kidney Disease.

Diabetic kidney disease (DKD) is a major diabetic microvascular complication. Fatty acid-induced lipotoxicity and apoptosis were associated with the exacerbation of DKD. However, the association of lipotoxicity with renal tubular apoptosis and the effects of fenofibrate on DKD are not fully understood. Eight-week-old db/db mice were given fenofibrate or saline by gavage for 8 weeks. Human kidney proximal tubular epithelial (HK2) cells stimulated with palmitic acid (PA) and high glucose (HG) were used as a model of lipid metabolism disorders. Apoptosis was assessed with or without fenofibrate. The AMP-activated protein kinase (AMPK) activator 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) and AMPK inhibitor Compound C were used to determine the involvement of AMPK and Medium-chain acyl-CoA dehydrogenase (MCAD) in the regulation of lipid accumulation by fenofibrate. MCAD silencingwasachievedbysmall interfering RNA (siRNA)transfection. Fenofibrate reduced triglyceride (TG) content and lipid accumulation in DKD. Importantly, renalfunction and tubularcellapoptosis weresignificantlyimproved by fenofibrate. Fenofibrate reduced apoptosis, accompanied by increased activation of the AMPK/FOXA2/MCAD pathway. MCAD silencing resulted in apoptosis and lipid accumulation despite fenofibrate treatment. Fenofibrate improves lipid accumulation and apoptosis through the AMPK/FOXA2/MCAD pathway. MCAD may be a potential therapeutic target of DKD, and the use of fenofibrate as a treatment for DKD warrants further study.

Non-Esterified Fatty Acid-Induced Apoptosis in Bovine Granulosa Cells via ROS-Activated PI3K/AKT/FoxO1 Pathway

Non-esterified fatty acid (NEFA), one of negative energy balance (NEB)'s most well-known products, has a significant impact on cows' reproductive potential. Our study used an in vitro model to investigate the deleterious effects of NEFA on bovine granulosa cells (BGCs) and its underlying molecular mechanism. The results showed that high levels of NEFA led to the accumulation of reactive oxygen species (ROS), increased the expression of apoptosis-related factors such as Bcl2-Associated X/B-cell lymphoma-2 (Bax/Bcl-2) and Caspase-3, and down-regulated steroid synthesis-related genes such as sterol regulatory element binding protein 1 (SREBP-1), cytochrome P450c17 (CYP17), and cytochrome P450 aromatase (CYP19), to promote oxidative stress, cell apoptosis, and steroid hormone synthesis disorders in BGCs. In addition, NEFA significantly inhibited phosphatidylinositol 3-kinase (PI3K) and phosphorylated protein kinase B (p-AKT) activity and increased forkhead box O1 (FoxO1) expression. To further explore the role of the PI3K/AKT/FoxO1 signaling pathway in NEFA, we found that pretreatment with AKT-specific activator SC79 (5 mg/mL) for 2 h or transfection with FoxO1 knockdown siRNA in BGCs could alleviate the negative effects of NEFA treatment by decreasing Bax/Bcl-2 ratio and Caspase-3 expression, and upregulating SREBP-1, CYP17, and CYP19 expression. Meanwhile, SC79 significantly inhibited NEFA-induced dephosphorylation and massive nuclear translocation of FoxO1. Taken together, the NEFA induced oxidative stress, apoptosis, and steroid hormone synthesis disorders in BGCs by inhibiting the PI3K/AKT pathway that regulates FoxO1 phosphorylation and nuclear translocation. Our findings help to clarify the molecular mechanisms underlying the negative effects of high levels of NEFA on BGCs.

Nuciferine Ameliorates Nonesterified Fatty Acid-Induced Bovine Mammary Epithelial Cell Lipid Accumulation, Apoptosis, and Impaired Migration via Activating LKB1/AMPK Signaling Pathway.

High blood concentrations of nonesterified fatty acids (NEFAs) provoke various metabolic disorders and are associated with mammary tissue injury and decreased milk production in dairy cows. Nuciferine, an alkaloid found in Nelumbo nucifera leaves, has great potential for correcting lipid metabolism derangements and lipotoxicity. In this study, we evaluated the lipotoxicity induced by excessive NEFA in bovine mammary epithelial cells (bMECs) and investigated whether nuciferine alleviates NEFA-induced lipotoxicity and the underlying molecular mechanisms. We found that excessive NEFA (1.2 and 2.4 mM) induced lipid accumulation, apoptosis, and migration ability impairment in bMECs, whereas nuciferine could ameliorate these disarrangements, as indicated by decreasing triglyceride content, protein abundance of SREBP-1c, cytoplasmic cytochrome c, and cleaved caspase-3 and increasing protein abundance of PPARα and migration ability. Moreover, nuciferine could reverse NEFA-induced LKB1/AMPK signaling inhibition, and the protective effect of nuciferine on lipotoxicity caused by NEFA was abrogated by AMPK inhibitor dorsomorphin. Furthermore, transfection with LKB1 siRNA (si-LKB1) largely abolished the activation effect of nuciferine on AMPK. Overall, nuciferine can protect bMECs from excessive NEFA-induced lipid accumulation, apoptosis, and impaired migration by activating LKB1/AMPK signaling pathway.

Free Fatty Acids Induce Lipid Accumulation, Autophagy, and Apoptosis in Human Sebocytes

Background: A disruption of sebocyte differentiation and lipogenesis has fatal consequences and can cause a wide spectrum of skin diseases, from acne vulgaris to sebaceous carcinoma, however, the relevant molecular mechanisms have not been fully clarified. Objectives: The induction of autophagy and apoptosis in human sebocytes in response to biologically relevant fatty acids was investigated. Methods: Free fatty acids (arachidonic acid, linoleic acid, palmitic acid, and palmitoleic acid) and the pan-caspase inhibitor QVD-Oph were added to the supernatant of cultured human SZ95 sebocytes. Individual relevant proteins were analyzed by Western blotting. Apoptosis and cell viability were determined, and typical autophagy structures were detected through electron microscopy. To obtain cell growth curves, cell confluence was continuously monitored by real-time cell analysis. Results: Fatty acids induced the development of intracellular lipid droplets with subsequent apoptosis, whereas arachidonic acid caused the most rapid effect. Cleavage products of caspase-3 were only detected in arachidonic acid-induced apoptosis. The high basal apoptotic rate of cultured SZ95 sebocytes was strongly suppressed by QVD-Oph. Fatty acid-induced apoptosis was also markedly inhibited by QVD-Oph, whereas intracellular lipid droplets further accumulated. While cell viability after incubation with linoleic acid, palmitic acid, or palmitoleic acid and QVD-Oph was comparable with that of non-treated controls, arachidonic acid significantly reduced cell viability and cell density despite the concomitant pan-caspase inhibitor treatment. Using electron microscopy, typical autophagy structures were detected, such as autophagosomes and autolysosomes, at the basal level, which became more pronounced after treatment with fatty acids. Conclusions: Our findings contribute to a better understanding of the inflammation-associated mechanisms of lipogenesis and cell death induction in human sebocytes and may help to unveil the effects of fatty acid-rich human nutrition.

MiR-141-3p regulates saturated fatty acid-induced cardiomyocyte apoptosis through Notch1/PTEN/AKT pathway via targeting PSEN1.

It has been reported that miR-141-3p levels are markedly upregulated in the cardiomyocytes of obese rats induced by a high-fat diet. However, the role of miR-141-3p in myocardial lipotoxicity remains elusive. In the present study, the role of miR-141-3p in lipotoxic injury of H9c2 cells induced by palmitic acid (PA) and its possible mechanisms were assessed. The results indicated that miR-141-3p was significantly upregulated in PA-induced cardiomyocytes. miR-141-3p inhibitor enhanced the cell viability, reduced the release of lactate dehydrogenase (LDH), creatine kinase-MB (CK-MB), and troponin I (CTN-I), decreased cell apoptosis rate, and repressed the activation of mitochondrial apoptosis pathway in PA-treated H9c2, whereas treatment with miR-141-3p mimics resulted in the opposite effects. Mechanistically, it was further revealed that miR-141-3p could specifically bind to presenilin 1 (PSEN1) 3'UTR, and upregulating miR-141-3p levels reduced the expression of PSEN1, thereby inhibiting the activation of the Notch1/PTEN/AKT pathway. Additionally, inhibition of Notch1/AKT signaling pathway by its inhibitor could abrogate the effect of miR-141-3p on mitochondrial-mediated apoptosis induced by PA. In conclusion, the present study demonstrates that miR-141-3p regulates saturated fatty acid-induced cardiomyocyte apoptosis through Notch1/PTEN/AKT pathway via targeting PSEN1, which gains a new insight into the mechanisms of myocardial lipotoxic injury.

Protein Kinases Signaling in Pancreatic Beta-cells Death and Type 2 Diabetes.

Type 2 diabetes (T2D) is a worldwide serious public health problem. Insulin resistance and β-cell failure are the two major components of T2D pathology. In addition to defective endoplasmic reticulum (ER) stress signaling due to glucolipotoxicity, β-cell dysfunction or β-cell death initiates the deleterious vicious cycle observed in T2D. Although the primary cause is still unknown, overnutrition that contributes to the induction of the state of low-grade inflammation, and the activation of various protein kinases-related metabolic pathways are main factors leading to T2D. In this chapter following subjects, which have critical checkpoints regarding β-cell fate and protein kinases pathways are discussed; hyperglycemia-induced β-cell failure, chronic accumulation of unfolded protein in β-cells, the effect of intracellular reactive oxygen species (ROS) signaling to insulin secretion, excessive saturated free fatty acid-induced β-cell apoptosis, mitophagy dysfunction, proinflammatory responses and insulin resistance, and the reprogramming of β-cell for differentiation or dedifferentiation in T2D. There is much debate about selecting proposed therapeutic strategies to maintain or enhance optimal β-cell viability for adequate insulin secretion in T2D. However, in order to achieve an effective solution in the treatment of T2D, more intensive clinical trials are required on newer therapeutic options based on protein kinases signaling pathways.

Correction: Toyocamycin attenuates free fatty acid-induced hepatic steatosis and apoptosis in cultured hepatocytes and ameliorates nonalcoholic fatty liver disease in mice.

[This corrects the article DOI: 10.1371/journal.pone.0170591.].

Non-Esterified Fatty Acid-Induced Reactive Oxygen Species Mediated Granulosa Cells Apoptosis Is Regulated by Nrf2/p53 Signaling Pathway.

Negative energy balance (NEB) during the perinatal period can affect dairy cow follicular development and reduce the fecundity. Non-esterified fatty acid (NEFA) concentration is elevated during NEB, and is known to be toxic for multiple cell types. In the ovary, NEB increased NEFA, and may influences follicular growth and development. However, the effect and mechanism of NEFA on granulosa cells (GCs) in vitro remains unknown. In this study, we found that NEFA dose-dependently induced apoptosis in primary cultured granulosa cells. Mechanistically, our data showed that NEFA significantly increased reactive oxygen species (ROS) levels, resulting in the activation of endoplasmic reticulum stress (ERS) and eventually cell apoptosis in GCs. Moreover, NEFA also increased the phosphorylation levels of ERK1/2 and p38MAPK pathways, upregulated the expression of p53 and potentially promoted its translocation to the nuclear, thus transcriptionally activated Bax, a downstream gene of this pathway. NEFA also promoted nuclear factor E2 (Nrf2) expression and its level in the nuclear. To elucidate the mechanism of NEFA action, N-acetyl-l-cysteine (NAC), a ROS scavenger was used to verify the role of ROS in NEFA induced apoptosis of GCs. NAC pretreatment reversed the NEFA-induced ERS-related protein and apoptosis-related protein levels. Meanwhile, NAC pretreatment also blocked the phosphorylation of ERK1/2 and p38 induced by NEFA, and the nucleation of Nrf2 and p53, suggesting that ROS plays a crucial role in regulating the NEFA-induced apoptosis of GCs. Together, these findings provide an improved understanding of the mechanisms underlying GCs apoptosis, which could potentially be useful for improving ovarian function.

High-density lipoprotein ameliorates palmitic acid-induced lipotoxicity and oxidative dysfunction in H9c2 cardiomyoblast cells via ROS suppression

BackgroundHigh levels circulating saturated fatty acids are associated with diabetes, obesity and hyperlipidemia. In heart, the accumulation of saturated fatty acids has been determined to play a role in the development of heart failure and diabetic cardiomyopathy. High-density lipoprotein (HDL) has been reported to possess key atheroprotective biological properties, including cellular cholesterol efflux capacity, anti-oxidative and anti-inflammatory activities. However, the underlying mechanisms are still largely unknown. Therefore, the aim of the present study is to test whether HDL could protect palmitic acid (PA)-induced cardiomyocyte injury and explore the possible mechanisms.ResultsH9c2 cells were pretreated with HDL (50–100 μg/ml) for 2 h followed by PA (0.5 mM) for indicated time period. Our results showed that HDL inhibited PA-induced cell death in a dose-dependent manner. Moreover, HDL rescued PA-induced ROS generation and the phosphorylation of JNK which in turn activated NF-κB-mediated inflammatory proteins expressions. We also found that PA impaired the balance of BCL2 family proteins, destabilized mitochondrial membrane potential, and triggered subsequent cytochrome c release into the cytosol and activation of caspase 3. These detrimental effects were ameliorated by HDL treatment.ConclusionPA-induced ROS accumulation and results in cardiomyocyte apoptosis and inflammation. However, HDL attenuated PA-induced lipotoxicity and oxidative dysfunction via ROS suppression. These results may provide insight into a possible molecular mechanism underlying HDL suppression of the free fatty acid-induced cardiomyocyte apoptosis.

Effect of selenium nanoparticles against abnormal fatty acid metabolism induced by hexavalent chromium in chicken's liver.

The effect of selenium on excessive fatty acid-induced apoptosis and abnormal amino acid metabolism in the liver is well known, because it is an important site in the fatty acid metabolism pathway. However, the protective role of nano-elemental selenium (nano-Se) supplementation against hexavalent chromium (K2Cr2O7)-induced abnormal fatty acid metabolism has not been evaluated yet. Therefore, we conducted chicken experiments with different nano-Se supplementation doses to investigate the role of nano-Se against Cr(VI)-induced adverse effects. For this purpose, a total of 120 1-day-old chicks were randomly divided into control group, Cr(VI)-exposed group, protection group, treatment group, prevention group, and nano-Se control group. The results of RT-qPCR showed that the nano-Se supplementation notably downregulated (P < 0.01) the messenger RNA (mRNA) expression levels of fatty acid synthase (FASN), whereas nano-Se supplementation significantly upregulated (P < 0.01) the mRNA expression level of acyl-coenzyme A oxidase 1 (ACOX1) in chicken's liver at day 35 of the experiment. Similar results were further verified by western blot analysis. Moreover, nano-Se supplementation significantly enhanced and reduced the antibody expression levels of ACOX1 and FASN in immunohistochemical analysis, respectively. Thus, finally, it was concluded that nano-Se can alleviate K2Cr2O7-induced abnormal fatty acid metabolism in chicken's liver.

20(S)-Protopanaxatriol Promotes Fatty Acid-Induced ER Stress and Apoptosis in Multiple Myeloma By Down-Regulating SCD1 Expression

Multiple myeloma (MM), is a hematological malignancy characterized by the accumulation of clonal malignant plasma cells. Nowadays more and more studies concern that alert metabolism including glycolysis, glutaminolysis and lipid metabolism has potent in vivo anticancer activity in multiple myeloma. While glycolysis and glutaminolysis was well established, lipid metabolism of MM is poorly understood and there is a need for a new low-toxic therapy that selectively target MM.Lipid metabolism studies such as on the use of inhibitors of fatty acid synthesis and their effects on MM cell survival have been reported. Our study showed the increase of the expression of stearoyl CoA desaturase 1 (SCD1) and the elevated fatty acid biosynthesis in MM cells (Fig.1A, p<0.001). We found that SCD1 is overexpression in MM patients' samples and associated with clinical stage of myeloma (Fig 1B, p<0.05). Then we examined the level of lipid droplets(LDs) in MM cells, and the high level of LDs detected in MM cells demonstrated the lipid accumulation in MM (Fig.1C). Stable depletion of SCD1 inhibited fatty acid biosynthesis and decreased LDs levels and this reduction of LDs remained at low levels in MM cells (Fig.1D, E). These results suggest that MM cell growth party relies on SCD1-mediated fatty acid metabolism.The finding that 20(S)-protopanaxatriol(PPT) has significant effect on inhibiting the transcription of lipogenic genes have reported. Western blotting analysis shows that PPT decreased SCD1 protein levels in RPMI-8226, ARH-77 cell lines. In addition, PPT treatment decreased fatty acid biosynthesis and blocked lipid storage in lipid droplets(LDs) (Fig.1F). The proportion of saturated and monounsaturated was also decreased after treatment (Fig. 1G). Given that 20(S)-protopanaxatriol(PPT) has lipid-lowering effect in MM, we hypothesized that PPT exerts anti-myeloma effects by disrupting lipogenesis. In vitro experiments demonstrate the significant effect of PPT on decreasing proliferation and inducing apoptosis in multiple myeloma (Fig.1H). Supplementation with the SCD1 enzymatic product, oleic acid, rescued MM cells from PPT cell killing and SCD1 silencing, decreasing levels of SCD1 inhibition induced apoptosis and proliferation inhibition (Fig.1I). The results of Western Blot Analysis show a positive correlation between SCD1 inhibition and endoplasmic reticulum stress (ER stress) (Fig.1J). In addition, PPT can obviously induce ER stress after inhibiting SCD1, while ER-stress inhibitor TUDCA can significantly reverse the induced apoptosis of PPT treatment in MM cells (Fig.1K, p<0.05). These results suggest that excessive endoplasmic reticulum stress is the main cause of PPT induced apoptosis.In summary, our studies reveal that regulation of fatty acid metabolism in MM cells is an essential target. We show that the redeployed drug PPT killed MM cells by decreasing SCD1 protein levels and promoting fatty acid-induced ER stress. This study is relevant to the wider context of multiple myeloma therapeutics that developing therapeutics which can disrupt fatty acid biosynthesis. To our knowledge, this is the first study to describe the aglycone of ginsenosides 20(S)-protopanaxatriol with demonstrable anti-myeloma activity that target fatty acid biosynthesis [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

The endocrine pancreas: Endoplasmic reticulum stress in the beta cell

The heterogeneity in clinical presentation of type 2 diabetes points to a complex pathophysiology, with diverse routes leading to beta cell failure. Genetic variants, epigenetic factors and environmental stresses, such as Western diets rich in saturated fats, play essential roles. Our work has focused on the role of saturated free fatty acids in beta cell failure. We have used RNA sequencing to map the human islet transcriptome and uncover mechanisms of fatty acid-induced beta cell dysfunction and death. We identified endoplasmic reticulum stress as an important cellular response contributing to free fatty acid-induced beta cell dysfunction and apoptosis. In particular, signaling in the PERK branch of the endoplasmic reticulum stress response leads to lipotoxic beta cell demise. Monogenic forms of diabetes provide strong human genetic evidence for the importance of PERK signaling in maintaining beta cell integrity. Loss-of-function mutations in several genes in the PERK branch of the endoplasmic reticulum stress response have been described as a cause of monogenic young-onset diabetes. A better understanding of the mechanisms of beta cell failure will enable to identify therapeutic targets for beta cell protection in monogenic and polygenic diabetes.

1389 Caspase controls the free fatty acid-induced sebocyte apoptosis

1389 Caspase controls the free fatty acid-induced sebocyte apoptosis

Euodia daniellii Hemsl. (Bee-Bee Tree) Oil Attenuates Palmitate-Induced Lipid Accumulation and Apoptosis in Hepatocytes

Hepatic lipid accumulation and apoptosis is elevated in patients with non-alcoholic steatohepatitis and is closely associated with severity. Saturated fatty acid palmitate stimulates lipid accumulation and apoptosis in hepatocytes. In the present study, we examined bee-bee tree oil (BO)-mediated protective effects on palmitate-induced lipid accumulation and apoptosis in mouse primary hepatocytes. Cells were cultured in a control media or the same media containing 150 or 300 µmol/L of albumin-bound palmitate for 24 h. BO concentrations used were 0, 0.1, 0.2, or 0.5%. Palmitate induced lipid accumulation and mRNA expression of lipogenic genes such as SREBP1c and SCD1. However, BO prevented these changes. Furthermore, palmitate stimulated caspase-3 activity and decreased cell viability in the absence of BO. BO reduced palmitate-induced activation of caspase-3 and cell death in a dose-dependent manner. AMP-activated protein kinase inhibitors abolished the effects of BO. Furthermore, BO suppressed palmitate-induced c-Jun N-terminal kinase (JNK) phosphorylation through the 5' adenosine monophosphate-activated protein kinase (AMPK)-dependent pathway. In conclusion, BO attenuated palmitate-induced hepatic steatosis and apoptosis through AMPK-mediated suppression of JNK signaling. These data suggest that BO is an important determinant of saturated fatty acid-induced lipid accumulation and apoptosis, and may be an effective therapeutic strategy for treatment of obesity-mediated liver diseases.

WITHDRAWN: Parkin-mediated mitophagy ameliorates fatty acid-induced mitochondrial injury and apoptosis in tubular epithelial cells by reducing oxidative stress

// Yue Wu 1,* , Jiangmin Wan 1,2,* , Xuemei Chen 3,* , Wei Hua 4 , Haibo Gui 3 , Xushun Jiang 1 , Huizhe Huang 5 , Xiongzhong Ruan 6,7 and Xiaogang Du 1,8 1 Department of Nephrology, The First Affiliated Hospital of Chongqing Medical University, Chongqing, China 2 Department of Nephrology, People&rsquo;s Hospital of Qijiang Distract, Chongqing, China 3 Emergency Department, The First Affiliated Hospital of Chongqing Medical University, Chongqing, China 4 Department of Nephrology, The Sixth People&rsquo;s Hospital of Chongqing, Chongqing, China 5 The second Affiliated Hospital of Chongqing Medical University, Chongqing, China 6 Centre for Nephrology, Royal Free and University College Medical School, University College London, Royal Free Campus, London, United Kingdom 7 Centre for Lipid Research, Key Laboratory of Molecular Biology on Infectious Diseases, Ministry of Education, Chongqing Medical University, Chongqing, China 8 The Chongqing Key Laboratory of Translational Medicine in Major Metabolic Disease, Chongqing, China * These authors contributed equally to this work Correspondence: Xiaogang Du, email: dxgcxm@163.com Keywords : parkin; mitophagy; palmitic acid; tubular epithelial cells; apoptosis Received: October 07, 2016&nbsp;&nbsp;&nbsp;&nbsp; Accepted: December 18, 2017&nbsp;&nbsp;&nbsp;&nbsp; Epub: December 26, 2017 Abstract Chronic kidney disease (CKD) is often accompanied by dyslipidemia. Excessive lipid accumulation in renal tubular epithelial cells (HK-2 cells) triggers mitochondrial dysfunction and overproduction of reactive oxygen species (ROS). Mitophagy reportedly plays a crucial protective role by selectively degrading dysfunctional or damaged mitochondria. This is largely regulated by Parkin, an E3 ubiquitin ligase. In this study, we found increased Parkin, Beclin1 and LC3 expression in the renal tissues of CKD patients and rats fed a high-fat diet (HFD), and in HK-2 cells stimulated by palmitic acid (PA). We also found that PA induced upregulation and translocation of Parkin to mitochondria and increased the colocalization of Parkin and GFP-LC3 puncta, Parkin siRNA reversed this increase, indicating that Parkin participated in PA-induced mitophagy in HK-2 cells. Furthermore, our study demonstrated that PA stimulation decreased MitoTracker Red fluorescence and mitochondrial membrane potential and increased apoptosis and mitochondrial ROS generation in HK-2 cells. However, Parkin deficiency further reduced mitochondrial membrane potential, enhanced apoptosis and production of mitochondrial ROS. These data provide evidence that Parkin-mediated mitophagy plays a protective role against fatty acid-induced renal tubular epithelial cells apoptosis by reducing oxidative stress.

Fenofibrate attenuates fatty acid-induced islet β-cell dysfunction and apoptosis via inhibiting the NF-κB/MIF dependent inflammatory pathway

BackgroundFatty acid-induced lipotoxicity and macrophage migration inhibitory factor (MIF) affect pancreatic β-cell function, and may promote the development of diabetes mellitus. However, the association of lipotoxicity with MIF and the effect of Fenofibrate on β-cell function remain unknown. MethodsLPL+/− mice and MIN6 cells stimulated with palmitic acid (PA) were utilized as models of lipid metabolism disorders. Factors associated with insulin secretion and apoptosis were assessed in the presence or absence of Fenofibrate. The possible mechanisms of lipotoxicity-induced β-cell dysfunction were also explored. ResultsFenofibrate effectively improved lipid accumulation in pancreatic β-cells, increased glucose-stimulated insulin secretion and β-cell mass, and significantly downregulated pro-apoptotic molecules, at the gene and protein levels, both in vivo and in vitro. Additionally, elevated MIF levels in serum from LPL+/− mice and PA-treated MIN6 cells were starkly decreased after Fenofibrate administration. Mechanistic analysis indicated that NF-κB signaling was remarkably triggered, which could further activate MIF transcription. Furthermore, Fenofibrate exerted beneficial effects on fatty acid-induced β-cell dysfunction likely by inhibiting the NF-κB/MIF dependent inflammatory response. ConclusionsFenofibrate ameliorates lipotoxicity-induced β-cell dysfunction and apoptosis by inhibiting the NF-κB/MIF inflammatory pathway. These findings provide novel insights into the treatment of lipotoxicity-induced metabolic disorders.

High-throughput screening and bioinformatic analysis to ascertain compounds that prevent saturated fatty acid-induced β-cell apoptosis

Pancreatic β-cell lipotoxicity is a central feature of the pathogenesis of type 2 diabetes. To study the mechanism by which fatty acids cause β-cell death and develop novel approaches to prevent it, a high-throughput screen on the β-cell line INS1 was carried out. The cells were exposed to palmitate to induce cell death and compounds that reversed palmitate-induced cytotoxicity were ascertained. Hits from the screen were analyzed by an increasingly more stringent testing funnel, ending with studies on primary human islets treated with palmitate. MAP4K4 inhibitors, which were not part of the screening libraries but were ascertained by a bioinformatics analysis, and the endocannabinoid anandamide were effective at inhibiting palmitate-induced apoptosis in INS1 cells as well as primary rat and human islets. These targets could serve as the starting point for the development of therapeutics for type 2 diabetes.

Toyocamycin attenuates free fatty acid-induced hepatic steatosis and apoptosis in cultured hepatocytes and ameliorates nonalcoholic fatty liver disease in mice.

Background and aimsA high serum level of saturated free fatty acids (FFAs) is associated with the development of nonalcoholic fatty liver disease (NAFLD). X-box binding protein-1 (XBP-1) is activated by FFA treatment upon splicing. XBP-1 is a transcription factor induced by the endoplasmic reticulum (ER) stress sensor endoribonuclease inositol-requiring enzyme 1 alpha (IRE1α). However, the role of XBP-1 in NAFLD remains relatively unexplored. Toyocamycin was recently reported to attenuate the activation of XBP-1, possibly by inducing a conformational change in IRE1α. In this study, we examined the effect of toyocamycin on hepatocyte lipoapoptosis and steatosis. We also explored the effects of toyocamycin in a mouse model of NAFLD.MethodsHuh-7 cells and isolated rat primary hepatocytes were treated with palmitic acid (PA), which is a saturated FFA, in the presence or absence of toyocamycin. In addition, male C57BL/6J mice were fed a diet rich in saturated fat, fructose, and cholesterol (FFC) for 4 months, after which the effect of toyocamycin was assessed.ResultsToyocamycin attenuated FFA-induced steatosis. It also significantly reduced PA-induced hepatocyte lipoapoptosis. In addition, toyocamycin reduced the expression of cytosine-cytosine-adenosine-adenosine-thymidine enhancer-binding protein homologous protein (CHOP), which is a key player in ER stress-mediated apoptosis, as well as its downstream cell death modulator, death receptor 5. In the in vivo study, toyocamycin ameliorated the liver injury caused by FFC-induced NAFLD. It also reduced hepatic steatosis and the expression of lipogenic genes.ConclusionsThe data we obtained suggest that toyocamycin attenuates hepatocyte lipogenesis and ameliorates NAFLD in vivo and may therefore be beneficial in the treatment of NAFLD in humans.