小檗碱对游离脂肪酸损伤的胰岛βTC3细胞的保护作用

目的:观察小檗碱对棕榈酸损伤的胰岛βTC3细胞是否具有保护作用,并筛查出小檗碱起保护作用的有效浓度及合适的作用时间。方法:以胰岛βTC3细胞为研究对象,用棕榈酸构建脂毒性模型,MTT法筛选小檗碱起保护作用的有效浓度及时间;流式细胞技术检测胰岛βTC3细胞凋亡情况。结果:10.001-1μmol/L小檗碱作用βTC3细胞24、48、72 h,对细胞增殖有不同程度促进作用(与对照组比较P0.05);随着作用时间的延长,低浓度小檗碱对βTC3细胞的保护作用增加,而1μmol/L浓度保护作用下降,10μmol/L及以上浓度出现细胞毒性作用(与对照组相比P0.01),并呈浓度依赖性。2棕榈酸(0.2-1.0 mmol/L)对βTC3细胞的损伤作用具有浓度及时间依赖性(与对照组比较P0.05)。3棕榈酸处理βTC3细胞不同时间后,小檗碱治疗组较模型组的细胞凋亡率显著降低(P0.01)。结论:小檗碱对脂毒性损伤的胰岛βTC3细胞具有保护作用,且脂毒性作用时间越短,小檗碱的保护作用越好,随着脂毒性作用时间的延长,小檗碱的保护作用明显减弱。因此,建议临床上在脂代谢紊乱早期给予小檗碱干预以减轻甚至逆转游离脂肪酸导致的胰岛β细胞凋亡。     

小檗碱对游离脂肪酸损伤的胰岛betaTC3 细胞的保护作用*

目的：观察小檗碱对棕榈酸损伤的胰岛betaTC3 细胞是否具有保护作用,并筛查出小檗碱起保护作用的有效浓度及合适的作 用时间。方法：以胰岛betaTC3 细胞为研究对象,用棕榈酸构建脂毒性模型,MTT 法筛选小檗碱起保护作用的有效浓度及时间;流式 细胞技术检测胰岛betaTC3 细胞凋亡情况。结果：①0.001-1 umol/L小檗碱作用茁TC3细胞24、48、72 h,对细胞增殖有不同程度促进 作用（与对照组比较P＜ 0.05）;随着作用时间的延长,低浓度小檗碱对betaTC3细胞的保护作用增加,而1 umol/L浓度保护作用下 降,10 umol/L及以上浓度出现细胞毒性作用（与对照组相比P＜0.01）,并呈浓度依赖性。②棕榈酸（0.2 -1.0 mmol/L)对betaTC3细胞 的损伤作用具有浓度及时间依赖性（与对照组比较P＜0.05）。③棕榈酸处理betaTC3细胞不同时间后,小檗碱治疗组较模型组的细 胞凋亡率显著降低（P<0.01)。结论：小檗碱对脂毒性损伤的胰岛betaTC3 细胞具有保护作用,且脂毒性作用时间越短,小檗碱的保护 作用越好,随着脂毒性作用时间的延长,小檗碱的保护作用明显减弱。因此,建议临床上在脂代谢紊乱早期给予小檗碱干预以减 轻甚至逆转游离脂肪酸导致的胰岛茁细胞凋亡。     

PTEN参与小檗碱保护脂毒性损伤的胰岛βTC3细胞

目的:探讨小檗碱保护棕榈酸诱导的胰岛βTC3细胞的可能机制,观察PTEN是否参与该过程,以及小檗碱对胰岛素分泌的影响。方法:用1.0 mmol/L棕榈酸制作胰岛βTC3细胞脂毒性损伤模型,给予小檗碱干预;放射免疫法检测胰岛素分泌,West-ern blot法进行PTEN、p-AKT、AKT、Bcl-2、Bax、活性Caspase3蛋白的检测。实验分3大组(对照组、棕榈酸组、棕榈酸+小檗碱治疗组),棕榈酸分别作用3个时间段(24、48、72 h)。结果:(1)放射免疫法胰岛素分泌测定结果显示:β细胞暴露于棕榈酸24 h后,5.6、16.7 mmol/L葡萄糖刺激的胰岛素分泌均较正常对照组显著减少(P0.01);添加小檗碱干预后胰岛素分泌较棕榈酸组回升,但较对照组减少(P均0.01)。(2)在棕榈酸处理的3个时间段内,与对照组相比,棕榈酸组的PTEN、Bax、Active-Caspase3蛋白表达水平显著升高,p-AKT、Bcl-2蛋白水平下降;小檗碱干预后PTEN、Bax蛋白表达水平下降,p-AKT、Bcl-2蛋白水平提高(P均0.01)。结论:小檗碱可改善棕榈酸引起的胰岛素分泌减少,抑制脂毒性诱导的PTEN表达增加,减少促凋亡基因Bax、Active-Caspase3表达,并增加抑凋亡基因Bcl-2基因表达及AKT的活化,从而拮抗棕榈酸诱导的β细胞凋亡,保护β细胞功能。     

中性神经酰胺酶在胰岛β细胞脂毒性中的变化及作用

目的:探讨中性神经酰胺酶(NCDase)在胰岛β细胞脂毒性中的变化及作用。方法:采用0.5 mM棕榈酸作用INS-1细胞不同时间,用MTT法检测细胞活力;细胞内分别建立NCDase基因过表达和干扰后,用MTT法检测细胞的增殖活力;棕榈酸刺激细胞24 h,HPLC法和Western Blot法检测NCDase活性和蛋白表达;重组质粒pEGFP-C3-NCDase过表达NCDase基因和NCDase siRNA干扰NCDase基因分别建立后,棕榈酸刺激24 h,用流式细胞术检测细胞凋亡。结果:与对照组相比,棕榈酸刺激24 h时细胞抑制率显著降低(52±3.2)%(P0.01);与BSA对照相比,棕榈酸刺激24 h NCDase活性显著被抑制(P0.01),NCDase蛋白水平也被显著下调(P0.001);与BSA对照组相比,过表达NCDase显著促进细胞的增殖,然而NCDase干扰显著抑制细胞的增殖(P0.05);与p EGFP-C3+棕榈酸组相比,pEGFP-C3-NCDase显著缓解棕榈酸诱导的细胞凋亡(P0.01);与con.siRNA+棕榈酸组相比,NCDase siRNA显著促进了棕榈酸诱导的细胞凋亡(P0.01)。结论:棕榈酸刺激后抑制β细胞NCDase活性和蛋白表达,NCDase过表达促进β细胞增殖并且在β细胞脂毒性中起着保护作用。     

雷诺嗪对高糖高脂诱导的NIT-1细胞凋亡的保护作用

目的 研究雷诺嗪对高糖高脂诱导的NIT-1胰岛β细胞凋亡的保护作用及Cleaved caspase-3表达的影响,探讨雷诺嗪保护胰岛β细胞的机制.方法 采用CCK-8法测定不同浓度的雷诺嗪对体外培养及高糖高脂诱导的NIT-1胰岛β细胞的增殖能力的影响,同时应用流式细胞术检测NIT-1细胞凋亡,Western blot检测凋亡因子Caspase-3活化片段Cleaved caspase-3蛋白的表达.结果 不同浓度的雷诺嗪对NIT-1胰岛β细胞保护作用呈剂量依赖性:低浓度雷诺嗪对细胞凋亡无明显保护作用,随浓度升高保护作用明显.在培养基中加入高脂高糖及高浓度的雷诺嗪(5μmol/L)共同培养24h,雷诺嗪组细胞凋亡率明显低于高脂高糖单独作用组(P＜0.01),同时相对于高糖高脂组,激活型Caspase3表达明显降低(P＜0.05).结论 雷诺嗪能抑制高糖高脂诱导的NIT-1胰岛β细胞凋亡,其分子机制可能是雷诺嗪对Caspase-3的激活作用.     

小檗碱对损伤胰岛βTC6细胞相关信号分子表达的影响

目的:探讨小檗碱在棕榈酸(palmic acid, PA)诱导的胰岛β细胞发生凋亡时PTEN及AMPK的变化及其作用机制。方法:采用1.0 mmol/L PA诱导胰岛βTC6细胞损伤模型,然后给予小檗碱干预。采用流式细胞术检测βTC6细胞凋亡率,RT-q PCR法及免疫荧光法检测在PA及小檗碱作用下信号转导通路分子PTEN及AMPK表达的变化。结果:PA抑制βTC6细胞的生长并诱导其凋亡,小檗碱可缓解PA引起的βTC6的凋亡,对氧化应激具有保护作用;伴随着凋亡的发生,AMPK的表达显著降低,而PTEN的表达显著升高,表明细胞氧化损伤严重时抑制了AMPK的表达及转录,而PTEN在βTC6细胞的凋亡中具有促进作用;小檗碱治疗后,AMPK的表达增多,而PTEN的表达下降,暗示着小檗碱通过激活AMPK并抑制PTEN的表达来增强βTC6细胞的抗氧化能力。结论:小檗碱对PA引起的细胞凋亡有保护作用,同时小檗碱可能通过调节AMPK及PTEN的表达来发挥抗氧化作用。     

小檗碱通过PTEN/Nrf2途径抑制胰岛βTC6氧化应激及细胞凋亡

摘要 目的：探讨小檗碱（Berberine,BBR）在棕榈酸（palmitic acid,PA）诱导的胰岛β细胞氧化应激及凋亡中的角色及分子机制。方法：BBR和PA单独或联合处理敲低PTEN的βTC6细胞,利用MTT、Caspase-3活性检测、流式细胞术、ROS含量检测、硝基酪氨酸定量等测定各实验分组的细胞凋亡程度并比较彼此氧化应激水平,利用定量PCR以及Western blotting检测PTEN、AMPK、Nrf2的表达变化。此外,我们还评估了BBR是否可以缓解糖尿病小鼠全身炎症状态和胰岛细胞凋亡,并再次验证了BBR对糖尿病小鼠的治疗效果。结果：BBR通过降低PTEN同时升高Nrf2的表达,进而减轻PA诱导胰岛βTC6细胞ROS以及硝基酪氨酸积累,降低PA诱导性Caspase-3升高。干扰PTEN表达可以与BBR发生协同效应,即协同降低氧化应激性凋亡。经动物实验发现BBR可明显降低糖尿病小鼠血糖以及血清IL-6水平,同时在转录水平降低小鼠胰腺PTEN并上调Nrf2,TUNEL实验发现BBR可以明显抑制糖尿病小鼠胰岛细胞凋亡,而二甲双胍（Metformin, Met）未发现抑制效应。结论：BBR通过下调PTEN并上调Nrf2的表达来发挥对PA引起的βTC6细胞氧化应激以及凋亡的保护作用,而沉默PTEN可反过来与BBR形成协同保护作用。BBR与MET治疗2型糖尿病的降糖效果没有差异性,但BBR可以额外地通过PTEN/Nrf2途径发挥抗炎及抗氧化应激作用。     

滇结香花改善糖尿病胰岛损伤及机制研究

本文旨在评价滇结香花正己烷提取物(EGH)降糖及保护胰岛作用,并通过胰岛损伤细胞模型探究其作用机制。采用链脲佐菌素(STZ)联合高脂饲料诱导小鼠2型糖尿病模型,通过检测小鼠空腹血糖、糖化血红蛋白和胰岛素分泌,评价EGH的降糖和保护胰岛作用。并采用棕榈酸联合葡萄糖诱导胰岛RIN-m5F细胞损伤模型,对ROS生成量、caspase-3基因水平、AKT、FOXO1和JNK蛋白水平进行检测,探究EGH改善糖尿病胰岛损伤作用机制。结果表明EGH可以减少ROS生成量、降低caspase-3基因转录水平、激活AKT抑制FOXO1,同时抑制JNK的激活,从而改善β细胞的损伤。     

依法克生对大鼠胰岛细胞损伤的保护作用

目的探讨炎症因子对体外培养大鼠胰岛细胞的损伤情况及依法克生可能的保护作用。方法将分离、纯化的SD大鼠胰岛细胞置于体外培养,观察炎症因子IL-1β不同浓度(0.1~10 ng/ml)和不同作用时间(0~48 h)下对胰岛细胞分泌功能影响。胰岛细胞分为对照组、IL-1β组和依法克生组,用单因素方差分析比较各组在低糖和高糖环境下的胰岛素分泌,观察依法克生对胰岛素分泌的影响,对胰岛功能IL-1β损伤的保护作用,并比较三组间胰岛细胞凋亡率。结果高糖浓度下,随IL-1β浓度升高,胰岛素分泌下降(P0.001),随作用时间延长,胰岛素分泌亦减少(P0.001),IL-1β浓度超过5.0 ng/ml、时间超过24 h抑制作用较为明显。依法克生组胰岛素分泌较IL-1β组明显升高(P0.001),与对照组无差异。胰岛细胞凋亡在IL-1β组(49.7±15.5)﹪高于对照组(9.7±2.5)﹪(P0.01),在依法克生组(15.7±5.5)﹪低于IL-1β组(P0.01),提示干预后胰岛细胞凋亡明显减少。结论 IL-1β抑制高糖环境下胰岛素的分泌,并存在剂量和时间依赖关系。依法克生加入体外培养的胰岛细胞中,可有效防止IL-1β诱导胰岛细胞损伤,逆转被抑制的胰岛分泌功能,并减少胰岛细胞凋亡。     

棕榈酸诱导胰岛β细胞氧化应激和内质网应激的研究进展

2型糖尿病（T2DM）主要由胰岛β细胞的胰岛素分泌缺陷和胰岛素抵抗引起。棕榈酸作为人体内最丰富的游离脂肪酸之一，其体内含量过高易造成脂代谢紊乱，诱导胰岛β细胞功能障碍及胰岛素抵抗。这与T2DM的发生发展密切相关，但具体机制尚未完全明确。棕榈酸诱导胰岛β细胞发生的氧化应激和内质网应激（ERS）是影响胰岛β细胞功能以及破坏胰岛素信号传导的关键应激途径。棕榈酸通过增加线粒体氧化、二酰基甘油-蛋白质激酶C-还原型辅酶Ⅱ途径、改变线粒体呼吸链正常功能和炎症刺激加重氧化应激，通过影响内质网折叠能力、破坏胞内蛋白运输途径、上调未折叠蛋白反应相关转录因子、棕榈酰化、降解羧肽酶E和减少内质网中Ca2+促进ERS，加剧胰岛β细胞功能障碍和凋亡，最终导致T2DM的发生与发展。本文综述了棕榈酸与胰岛β细胞内氧化应激和ERS的关联性，介绍了蛋白激酶R抑制剂、人参皂苷Rg1和三黄汤等具有潜力的中、西医靶向干预药物，为T2DM的临床治疗提供新思路。     

利拉鲁肽下调游离脂肪酸作用下βTC3 细胞PERK 的表达

目的:探讨游离脂肪酸(FFA)作用下胰岛βTC3细胞双链RNA依赖性蛋白样内质网激酶(PERK)的表达以及利拉鲁肽(Lira)对其表达的干预作用。方法:以βTC3细胞为研究对象,分为对照组和FFA组(0.125,0.25,0.5及1 mmol/L)孵育24 h,Westernblot方法检测PERK的表达。然后,分为对照组,FFA组,和FFA+Lira组(0.5 mg/L和1 mg/L),Lira预孵育6 h后,1 mmol/L FFA继续孵育24 h,Western blot检测PERK的表达。结果:①不同浓度FFA孵育24 h后,与对照组相比,1 mmol/L FFA组PERK表达增加(P<0.05)。②与1 mmol/L FFA组相比,0.5mg/L Lira+1 mmol/L FFA和1 mg/L Lira+1 mmol/L FFA组PERK表达减少(P<0.05),两组之间有统计学差异(P<0.05)。结论:FFA作用能够上调βTC3细胞PERK的表达,而Lira在一定程度上逆转FFA水平异常导致的βTC3细胞PERK表达上调,减轻内质网应激反应。     

Role of ERp46 in β-cell lipoapoptosis through endoplasmic reticulum stress pathway as well as the protective effect of exendin-4

Endoplasmic reticulum (ER) stress is considered as a key factor in free fatty acid (FFA)-induced apoptosis. ERp46, a new member of the thioredoxin family, is highly expressed in pancreatic β-cells and plays an important role in glucose toxicity. In this study we examined the potential role of ERp46 in palmitic acid (PA)-induced cell apoptosis and the protective role of exendin-4, a long-acting agonist of the hormone glucagon-like peptide-1 (GLP-1) receptor. The glucose-sensitive mouse β-pancreatic cell line, βTC6, was used to investigate the mechanisms of PA-induced apoptosis. Our results showed that ERp46 expression was reduced in a dose- and time-dependent manner after PA treatment. Furthermore, inhibition of ERp46 expression by small interfering (si)RNA-mediated silencing enhanced the ER stress response via three separate pathways and increased βTC6 cell apoptosis rates. Moreover, exendin-4 reduced the ER stress response and levels of apoptosis in NC transfected cells after PA treatment, but not in cells transfected with ERp46siRNA. In conclusion, ERp46 plays a protective role in PA-induced cell apoptosis by decreasing the ER stress response and might be a novel target for anti-diabetic drugs. Exendin-4 might protect against βTC6 cell lipoapoptosis in part by activating ERp46 signaling pathway.     

Chronic palmitic acid-induced lipotoxicity correlates with defective trafficking of ATP sensitive potassium channels in pancreatic β cells

Lipotoxicity is associated with a high level of fatty acid accumulation in pancreatic β-cells. An overload of free fatty acids contributes to pancreatic β-cell apoptosis and dysfunction. Insulin secretion involves sequential ionic events upon glucose stimulation. ATP sensitive potassium (K_ATP) channels serve as glucose sensors and effectively initiate glucose-stimulated insulin secretion. This study investigated the effects of lipotoxicity on the trafficking of K_ATP channels in pancreatic β cells using chronic palmitic acid –injected mice and treated insulinoma cells. The chronic palmitic acid -injected mice displayed type II diabetic characteristics. The pancreatic sections of these mice exhibited a decrease in the expression of K_ATP channels. We then tested the time and dose effects of palmitic acid on the cell viability of INS-1 cells. We observed a significant decrease in the surface expression of K_ATP channels after 72 h of treatment with 0.4 mM palmitic acid. In addition, this treatment induced pancreatic β-cell apoptosis by increasing cleaved caspase 3 protein level. Our results demonstrated cotreatment with glibenclamide, the sulfonylurea compounds for type II diabetes mellitus, in palmitic acid -treated cells reduces cell death and recovers the glucose stimulated insulin secretion through increasing the surface expression of K_ATP channels. Importantly, glibenclamide also improved glucose tolerance, triglyceride concentration, and insulin sensitivity in the palmitic acid-injected mice. In conclusion, an increase in the surface expression of K_ATP channels restores insulin secretion, reduces pancreatic β-cell’s apoptosis, highlighting correct trafficking of K_ATP channels is important in survival of β-cells during lipotoxicity.     

Saturated free fatty acids and apoptosis in microvascular mesangial cells: palmitate activates pro-apoptotic signaling involving caspase 9 and mitochondrial release of endonuclease G

Background

In type 2 diabetes, free fatty acids (FFA) accumulate in microvascular cells, but the phenotypic consequences of FFA accumulation in the microvasculature are incompletely understood. Here we investigated whether saturated FFA induce apoptosis in human microvascular mesangial cells and analyzed the signaling pathways involved.

Methods

Saturated and unsaturated FFA-albumin complexes were added to cultured human mesangial cells, after which the number of apoptotic cells were quantified and the signal transduction pathways involved were delineated.

Results

The saturated FFA palmitate and stearate were apoptotic unlike equivalent concentrations of the unsaturated FFA oleate and linoleate. Palmitate-induced apoptosis was potentiated by etomoxir, an inhibitor of mitochondrial β-oxidation, but was prevented by an activator of AMP-kinase, which increases fatty acid β-oxidation. Palmitate stimulated an intrinsic pathway of pro-apoptotic signaling as evidenced by increased mitochondrial release of cytochrome-c and activation of caspase 9. A caspase 9-selective inhibitor blocked caspase 3 activation but incompletely blocked apoptosis in response to palmitate, suggesting an additional caspase 9-independent pathway. Palmitate stimulated mitochondrial release of endonuclease G by a caspase 9-independent mechanism, thereby implicating endonuclease G in caspase 9-indpendent regulation of apoptosis by saturated FFA. We also observed that the unsaturated FFA oleate and linoleate prevented palmitate-induced mitochondrial release of both cytochrome-c and endonuclease G, which resulted in complete protection from palmitate-induced apoptosis.

Conclusions

Taken together, these results demonstrate that palmitate stimulates apoptosis by evoking an intrinsic pathway of proapoptotic signaling and identify mitochondrial release of endonuclease G as a key step in proapoptotic signaling by saturated FFA and in the anti-apoptotic actions of unsaturated FFA.     

No in vitro effects of fatty acids on glucose uptake, lipolysis or insulin signaling in rat adipocytes.

Elevated plasma levels of free fatty acids (FFA) can produce insulin resistance in skeletal muscle tissue and liver and, together with alterations in beta-cell function, this has been referred to as lipotoxicity. This study explores the effects of FFAs on insulin action in rat adipocytes. Cells were incubated 4 or 24 h with or without an unsaturated FFA, oleate or a saturated FFA, palmitate (0.6 and 1.5 mM, respectively). After the culture period, cells were washed and insulin effects on glucose uptake and lipolysis as well as cellular content of insulin signaling proteins (IRS-1, PI3-kinase, PKB and phosphorylated PKB) and the insulin regulated glucose transporter GLUT4 were measured. No significant differences were found in basal or insulin-stimulated glucose uptake in FFA-treated cells compared to control cells, regardless of fatty acid concentration or incubation period. Moreover, there were no significant alterations in the expression of IRS-1, PI3-kinase, PKB and GLUT4 following FFA exposure. Insulin's ability to stimulate PKB phosphorylation was also left intact. Nor did we find any alterations following FFA exposure in basal or cAMP-stimulated lipolysis or in the ability of insulin to inhibit lipolysis. The results indicate that oleate or palmitate does not directly influence insulin action to stimulate glucose uptake and inhibit lipolysis in rat fat cells. Thus, lipotoxicity does not seem to occur in the fat tissue itself.     

Exendin-4, a glucagon-like peptide-1 receptor agonist, inhibits cell apoptosis induced by lipotoxicity in pancreatic β-cell line

Lipotoxicity plays an important role in the underlying mechanism of type 2 diabetes mellitus. Prolonged exposure of pancreatic β-cells to elevated concentrations of fatty acid is associated with β-cell apoptosis. Recently, glucagon-like peptide-1 (GLP-1) receptor agonists have been reported to have direct beneficial effects on β-cells, such as anti-apoptotic effects, increased β-cell mass, and improvement of β-cell function. The mechanism of GLP-1 receptor agonists' protection of pancreatic β-cells against lipotoxicity is not completely understood. We investigated whether the GLP-1 receptor agonist exendin-4 promoted cell survival and attenuated palmitate-induced apoptosis in murine pancreatic β-cells (MIN6). Exposure of MIN6 cells to palmitate (0.4mM) for 24h caused a significant increase in cell apoptosis, which was inhibited by exendin-4. Exposure of MIN6 cells to exendin-4 caused rapid activation of protein kinase B (PKB) under lipotoxic conditions. Furthermore, LY294002, a PI3K inhibitor, abolished the anti-lipotoxic effect of exendin-4 on MIN6 cells. Exendin-4 also inhibited the mitochondrial pathway of apoptosis and down-regulated Bax in MIN6 cells. Exendin-4 enhanced glucose-stimulated insulin secretion in the presence of palmitate. Our findings suggest that exendin-4 may prevent lipotoxicity-induced apoptosis in MIN6 cells through activation of PKB and inhibition of the mitochondrial pathway.     

Inhibition of GPR40 protects MIN6 β cells from palmitate-induced ER stress and apoptosis

Chronic exposure to elevated concentration of free fatty acids (FFA) has been verified to induce endoplasmic reticulum (ER) stress, which leads to pancreatic β-cell apoptosis. As one of the medium and long chain FFA receptors, GPR40 is highly expressed in pancreatic β cells, mediates both acute and chronic effects of FFA on β-cell function, but the role of GPR40 in FFA-induced β-cell apoptosis remains unclear. In this study, we investigated the possible effects of GPR40 in palmitate-induced MIN6 β-cell apoptosis, and found that DC260126, a novel small molecular antagonist of GPR40, could protect MIN6 β cells from palmitate-induced ER stress and apoptosis. Similar results were observed in GPR40-deficient MIN6 cells, indicating that palmitate-induced β-cell apoptosis is at least partially dependent on ER stress pathway via GRP40.     

Modulation of lipid-induced ER stress by fatty acid shape

Exposure of pancreatic β cells to long-chain saturated fatty acids (SFA) induces a so-called endoplasmic reticulum (ER) stress that can ultimately lead to cell death. This process is believed to participate in insulin deficiency associated with type 2 diabetes, via a decrease in β-cell mass. By contrast, some unsaturated fatty acid species appear less toxic to the cells and can even alleviate SFA-induced ER stress. In the present study, we took advantage of a simple yeast-based model, which brings together most of the trademarks of lipotoxicity in human cells, to screen fatty acids of various structures for their capacity to counter ER stress. Here we demonstrate that the tendency of a free fatty acid (FFA) to reduce SFA toxicity depends on a complex conjunction of parameters, including chain length, level of unsaturation, position of the double bonds and nature of the isomers (cis or trans). Interestingly, potent FFA act as building blocks for phospholipid synthesis and help to restore an optimal membrane organization, compatible with ER function and normal protein trafficking.     

Drak2 overexpression results in increased beta-cell apoptosis after free fatty acid stimulation

Drak2 is a serine threonine kinase in the death-associated protein family. In this study, we investigated its role in free fatty acid (FFA)-induced islet apoptosis. Drak2 mRNA and protein were rapidly induced in islet beta-cells after FFA stimulation. Such Drak2 upregulation was accompanied by increased beta-cell apoptosis, which was inhibited by Drak2 knockdown using siRNA. Conversely, transgenic (Tg) Drak2 overexpression led to aggravated beta-cell apoptosis triggered by FFA. Drak2 overexpression in islets compromised the increase of anti-apoptotic factors, such as Bcl-2, Bcl-xL and Flip, upon FFA assault. Further in vivo experiments demonstrated that Drak2 Tg mice presented compromised glucose tolerance in a diet-induced obesity model. Our data show that Drak2 is detrimental to islet survival in the presence of excessive lipid.