Effect of Endoplasmic Reticulum Stress in VEGF-Induced Neuroprotection

Researchers suggest that endoplasmic reticulum (ER) stress cause apoptosis after ischemia. Caspase-12 has been localized to the ER and is a signal for apoptosis. We sought to clarify the role of caspase-12 in the vascular endothelial growth factor (VEGF) induced neuroprotective effect. Transient focal cerebral ischemia was produced by occluding left middle cerebral artery in rabbit. The expressions of caspase-12 and caspase-3 were detected by immunohistochemistry. Neuronal apoptosis was detected by TUNEL staining. We confirmed that the number of apoptotic cells and the expressions of caspase-12 and caspase-3 significantly increased during reperfusion. VEGF inhibited the cell apoptosis and the expressions of caspase-12 and caspase-3. These results suggest that VEGF may protect neurons from apoptosis by inhibiting ER stress pathway.     

Duodenal-Jejunal Bypass Surgery Ameliorates Glucose Homeostasis and Reduces Endoplasmic Reticulum Stress in the Liver Tissue in a Diabetic Rat Model

Background

Duodenal-jejunal bypass (DJB) has been shown to be an effective surgical treatment for type 2 diabetes mellitus (T2DM). However, the underlying mechanisms are poorly understood. Recently, accumulating evidences suggest that endoplasmic reticulum (ER) stress plays an important role in the development of insulin resistance in T2DM. The present study was designed to investigate the effect of DJB on glucose homeostasis, the ER stress state in the liver tissue, and the involving signaling independently of weight loss.

Methods

Thirty adult male T2DM Sprague-Dawley (SD) rats induced by high-fat diet and low dose of streptozotocin (STZ) were randomly divided into DJB and sham groups. Ten age-matched male SD rats were assigned as the control group. The parameters of body weight and calorie intake were measured at indicated time points. The glucose tolerance and insulin resistance were detected to evaluate the glucose homeostasis. Serum insulin was determined by enzyme-linked immunosorbent assay (ELISA). The markers of ER stress, the activity of c-Jun N-terminal kinase (JNK) and serine phosphorylation of insulin receptor substrate 1 (IRS-1) in the liver tissue, were determined by Western blotting.

Results

DJB induced significant improvements in glucose homeostasis and insulin sensitivity, but without weight loss. DJB improved the ER stress state indicated by decreased protein kinase RNA (PKR)-like ER protein kinase (PERK) and inositol-requiring enzyme 1 (IRE-1) phosphorylation in the liver tissue. The JNK activity and serine phosphorylation of IRS-1 in the liver tissue were significantly reduced after DJB.

Conclusions

DJB ameliorates glucose homeostasis. Meanwhile, our study helps to reveal that the reduced hepatic ER stress and the decreased JNK activity may contribute to the improved glucose homeostasis after DJB.

     

Insulin Resistance Is Associated With Diminished Endoplasmic Reticulum Stress Responses in Adipose Tissue of Healthy and Diabetic Subjects

We recently showed that insulin increased ER stress in human adipose tissue. The effect of insulin resistance on ER stress is not known. It could be decreased, unchanged, or increased, depending on whether insulin regulates ER stress via the metabolic/phosphoinositide 3-kinase (PI3K) or alternate signaling pathways. To address this question, we examined effects of lipid-induced insulin resistance on insulin stimulation of ER stress. mRNAs of several ER stress markers were determined in fat biopsies obtained before and after 8-h hyperglycemic-hyperinsulinemic clamping in 13 normal subjects and in 6 chronically insulin-resistant patients with type 2 diabetes mellitus (T2DM). In normal subjects, hyperglycemia-hyperinsulinemia increased after/before mRNA ratios of several ER stress markers (determined by ER stress pathway array and by individual RT-PCR). Lipid infusion was associated with inhibition of the PI3K insulin-signaling pathway and with a decrease of hyperinsulinemia-induced ER stress responses. In chronically insulin-resistant patients with T2DM, hyperglycemic-hyperinsulinemia did not increase ER stress response marker mRNAs. In summary, insulin resistance, either produced by lipid infusions in normal subjects or chronically present in T2DM patients, was associated with decreased hyperinsulinemia-induced ER stress responses. This suggests, but does not prove, that these two phenomena were causally related.     

Proteasome Dysfunction Mediates Obesity-Induced Endoplasmic Reticulum Stress and Insulin Resistance in the Liver

Chronic endoplasmic reticulum (ER) stress is a major contributor to obesity-induced insulin resistance in the liver. However, the molecular link between obesity and ER stress remains to be identified. Proteasomes are important multicatalytic enzyme complexes that degrade misfolded and oxidized proteins. Here, we report that both mouse models of obesity and diabetes and proteasome activator (PA)28-null mice showed 30–40% reduction in proteasome activity and accumulation of polyubiquitinated proteins in the liver. PA28-null mice also showed hepatic steatosis, decreased hepatic insulin signaling, and increased hepatic glucose production. The link between proteasome dysfunction and hepatic insulin resistance involves ER stress leading to hyperactivation of c-Jun NH₂-terminal kinase in the liver. Administration of a chemical chaperone, phenylbutyric acid (PBA), partially rescued the phenotypes of PA28-null mice. To confirm part of the results obtained from in vivo experiments, we pretreated rat hepatoma-derived H4IIEC3 cells with bortezomib, a selective inhibitor of the 26S proteasome. Bortezomib causes ER stress and insulin resistance in vitro—responses that are partly blocked by PBA. Taken together, our data suggest that proteasome dysfunction mediates obesity-induced ER stress, leading to insulin resistance in the liver.Obesity is a major cause of insulin resistance and contributes to the development of type 2 diabetes (1). Growing evidence suggests that chronic endoplasmic reticulum (ER) stress in the liver is a major contributor to obesity-induced insulin resistance (2–4). However, the molecular mechanisms linking obesity and ER stress are not fully understood.We previously identified metabolic pathways that are significantly altered by obesity in the livers of people with type 2 diabetes by analyzing comprehensive gene expression profiles using DNA chips (5). We found that genes involved in ubiquitin-proteasome pathways were coordinately upregulated in obese individuals. Proteasomes play fundamental roles in processes that are essential for cell viability (6).Eukaryotic cells contain several types of proteasomes. Core 20S proteasomes (20S) have binding sites for the regulatory particles proteasome activator (PA)700 and PA28 (7). PA700–20S-PA700 complexes are known as 26S proteasomes and are ATP-dependent machines that degrade cell proteins (7). PA28 is found in both previously described PA28–20S-PA28 complexes and PA700–20S-PA28 complexes, which also contain PA700 (8). The PA28 family comprises three members: α, β, and γ. PA28α encoded by the PSME1 gene and PA28β encoded by the PSME2 gene form a heteropolymer, which is mainly located in the cytoplasm, whereas PA28γ encoded by the PSME3 gene forms a homopolymer that predominantly occurs in the nucleus (9). The association of the PA28 with the 20S may play a role in antigen processing by modulating peptide cleavage in the 20S (10,11), but it appears that the PA28 may play a greater role in intracellular protein degradation than in antigen processing (12). Recently, it was reported that PA28α overexpression enhances ubiquitin-proteasome system–mediated degradation of abnormal proteins (13).It has been reported that fatty acids, insulin (14), and oxidative stress (15) inhibit proteasome activity in cultured hepatocellular carcinoma (Hep)G2 cells. However, it remains to be determined whether liver proteasome function is dysregulated in obesity and type 2 diabetes.Based on these findings, we hypothesized that proteasome dysregulation in the liver is involved in the development of hepatic insulin resistance in obesity and type 2 diabetes. To test this hypothesis, we generated PA28α-PA28β-PA28γ triple-knockout (PA28 KO) mice as a model of impaired proteasome function and investigated their metabolic phenotypes.     

Epidermal Growth Factor Receptor Inhibition Slows Progression of Diabetic Nephropathy in Association With a Decrease in Endoplasmic Reticulum Stress and an Increase in Autophagy

Previous studies by us and others have reported renal epidermal growth factor receptors (EGFRs) are activated in models of diabetic nephropathy. In the present study, we examined the effect of treatment with erlotinib, an inhibitor of EGFR tyrosine kinase activity, on the progression of diabetic nephropathy in a type 1 diabetic mouse model. Inhibition of renal EGFR activation by erlotinib was confirmed by decreased phosphorylation of EGFR and extracellular signal–related kinase 1/2. Increased albumin/creatinine ratio in diabetic mice was markedly attenuated by erlotinib treatment. Erlotinib-treated animals had less histological glomerular injury as well as decreased renal expression of connective tissue growth factor and collagens I and IV. Autophagy plays an important role in the pathophysiology of diabetes mellitus, and impaired autophagy may lead to increased endoplasmic reticulum (ER) stress and subsequent tissue injury. In diabetic mice, erlotinib-treated mice had evidence of increased renal autophagy, as indicated by altered expression and activity of ATG12, beclin, p62, and LC3A II, hallmarks of autophagy, and had decreased ER stress, as indicated by decreased expression of C/EBP homologous protein, binding immunoglobulin protein, and protein kinase RNA-like ER kinase. The mammalian target of rapamycin (mTOR) pathway, a key factor in the development of diabetic nephropathy and an inhibitor of autophagy, is inhibited by AMP-activated protein kinase (AMPK) activation. Erlotinib-treated mice had activated AMPK and inhibition of the mTOR pathway, as evidenced by decreased phosphorylation of raptor and mTOR and the downstream targets S6 kinase and eukaryotic initiation factor 4B. Erlotinib also led to AMPK-dependent phosphorylation of Ulk1, an initiator of mammalian autophagy. These studies demonstrate that inhibition of EGFR with erlotinib attenuates the development of diabetic nephropathy in type 1 diabetes, which is mediated at least in part by inhibition of mTOR and activation of AMPK, with increased autophagy and inhibition of ER stress.In the industrialized world, diabetes mellitus represents the leading cause of end-stage renal disease (ESRD). Diabetic nephropathy is one of the major microvascular complications of diabetes and a major source of morbidity and mortality. The renal lesions are similar in type 1 and 2 diabetes (1). Both the incidence and prevalence of ESRD secondary to diabetes continue to rise. In the United States, >30% of patients receiving either dialytic therapy or renal transplantation have ESRD as a result of diabetic nephropathy, and >40% of the incident cases of ESRD are attributable to diabetes. Given the global epidemic of obesity in developed countries, an increasing incidence of diabetic nephropathy is being widely reported.The underlying mechanisms predisposing to development and progression of diabetic nephropathy are an area of active investigation. Inadequate control of blood glucose and blood pressure undoubtedly contributes, and there is evidence for a genetic predisposition, although the modifier genes involved have yet to be conclusively identified. Studies in experimental animals have implicated a number of cytokines, hormones, and intracellular signaling pathways in either development or progression of diabetic nephropathy. Angiotensin II and transforming growth factor-β have been posited to play central roles in mediating the progressive glomerulopathy and tubulointerstitial fibrosis that characterize diabetic nephropathy. Blockade of angiotensin II production or signaling is the only specific intervention currently available for treatment of patients with diabetic nephropathy, and given that renin-angiotensin system inhibition can slow but usually not prevent progressive injury in diabetic nephropathy, it is imperative that additional, complementary therapeutic targets be identified. In previous studies, we reported that epidermal growth factor receptor (EGFR) phosphorylation increased in murine kidneys within 2 weeks of induction of diabetes by streptozotocin (STZ), which was inhibited by the EGFR tyrosine kinase inhibitor erlotinib. Erlotinib also inhibited renal extracellular signal–related kinase (ERK) activation and transforming growth factor-β expression and signaling in these animals (2). The current studies investigated whether prolonged EGFR signaling plays a role in mediating progressive glomerular and tubulointerstitial injury in diabetic nephropathy.     

Brain Death Is Associated With Endoplasmic Reticulum Stress and Apoptosis in Rat Liver

Cell death pathways initiated by stress on the endoplasmic reticulum (ER) have been implicated in a variety of common diseases, such as ischemia/reperfusion injury, diabetes, heart disease, and neurodegenerative disorders. However, the contribution of ER stress to apoptosis and liver injury after brain death is not known. In the present study, we found that brain death induces a variety of signature ER stress markers, including ER stress–specific X box–binding protein 1 and up-regulation of glucose-regulated protein 78. Furthermore, brain death causes up-regulation of C/EBP homologous protein and caspase-12. Consistent with this, terminal deoxynucleotidyl transferase–mediated 2′-deoxyuridine 5′-triphosphate nick-end labeling assay and transmission electron microscopy confirmed apoptosis in the liver after brain death. Taken together, the present study provides strong evidence supporting the presence and importance of ER stress and response in mediating brain death–induced apoptosis and liver injury.     

疏血通治疗糖尿病周围神经病变的疗效观察

目的 观察疏血通对糖尿病周围神经病变的治疗效果,探讨护理方法.方法 对70例糖尿病周围神经病变患者均给予疏血通6 ml加入0.9%氯化钠注射液250 ml静脉输注,1次/d,10 d为1个疗程.治疗期间严密观察患者的症状、体征及不良反应,及时对症处理.结果 治疗2个疗程总有效率为94.3%.结论 用药过程中,严密药物观察及护理是保证疏血通治疗顺利完成的关键.     

穴位按摩辅助治疗糖尿病伴周围神经病变疗效观察

随机将 90例糖尿病伴周围神经病变的病人分为治疗组 (4 7例 )与对照组 (4 3例 ) ,对照组采用常规药物治疗 ;治疗组在药物治疗基础上采用点法、按法、压法、掐法、揉法穴位按摩治疗。结果治疗组效果明显好于对照组 (χ2 =2 3.2 1,P <0 .0 5 )。提示穴位按摩对糖尿病伴周围神经病变是一种简便有效的治疗方法     

肾小管上皮细胞内质网应激时NGAL表达改变的调控机制研究

目的:探讨人肾小管上皮细胞(HK-2细胞)发生内质网应激时,NGAL表达增加的上游调控机制。方法:将HK-2细胞分为对照组(正常HK-2细胞),TG(毒胡萝卜素,thapsigargin)组(5μmol/L TG处理8 h),单纯转染组(siRNAATF4试剂转染24 h),转染+TG组(siRNA-ATF4试剂转染24 h后,5μmol/L TG处理8 h),阴性对照组(siRNA-阴性对照物转染24 h),DMSO组(5μmol/L DMSO处理8 h)。采用Western blot检测各组细胞内质网源性转录因子(CHOP)、内质网分子伴侣葡萄糖调节蛋白78(GRP78)、中性粒细胞明胶酶相关性载脂蛋白(NGAL)、激活转录因子4(ATF4)的表达,采用Real-time PCR方法测得ATF4mRNA、NGALmRNA表达量。结果:与对照组相比,TG组细胞NGAL、ATF4、ATF4mRNA、NGALmRNA表达量显著提高(P <0. 05),而转染+TG组、单纯转染组、阴性对照组、DMSO组中ATF4及NGAL差异无统计学意义(P> 0. 05)。与TG组相比,转染+TG组ATF4、NGAL、ATF4mRNA及NGALmRNA表达量呈显著降低趋势(P <0. 05)。在TG组与转染+TG组细胞中,CHOP和GRP78呈过表达状态(P <0. 05),而转染+TG组细胞CHOP和GRP78提升趋势明显低于TG组细胞(P <0. 05)。结论:(1) TG可诱导人肾小管上皮HK-2细胞发生内质网应激反应。(2) HK-2细胞发生内质网应激反应时,抑制ATF4表达会引起NGAL降低,提示ATF4是NGAL表达的上游调控因子。(3) HK-2细胞发生内质网应激反应时,抑制ATF4不能阻止CHOP和GRP78发生过表达,但可降低其升高程度,提示ATF4及NGAL降低可能对内质网应激反应介导HK-2细胞损伤起到一定的缓解作用。     

疏血通治疗糖尿病周围神经病变的疗效观察

目的 观察疏血通对糖尿病周围神经病变的治疗效果．探讨护理方法。方法 对70例糖尿病周围神经病变患者均给予疏血通6ml加入0．9%氯化钠注射液250ml静脉输注．1次d．10d为1个疗程。治疗期间严密观察患者的症状、体征及不良反应，及时对症处理。结果 治疗2个疗程总有效率为94．3％。结论 用药过程中．严密药物观察及护理是保证疏血通治疗顺利完成的关键。     

Activation of AMP-Activated Protein Kinase Inhibits Oxidized LDL-Triggered Endoplasmic Reticulum Stress In Vivo

OBJECTIVE

The oxidation of LDLs is considered a key step in the development of atherosclerosis. How LDL oxidation contributes to atherosclerosis remains poorly defined. Here we report that oxidized and glycated LDL (HOG-LDL) causes aberrant endoplasmic reticulum (ER) stress and that the AMP-activated protein kinase (AMPK) suppressed HOG-LDL–triggered ER stress in vivo.

RESEARCH DESIGN AND METHODS

ER stress markers, sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase (SERCA) activity and oxidation, and AMPK activity were monitored in cultured bovine aortic endothelial cells (BAECs) exposed to HOG-LDL or in isolated aortae from mice fed an atherogenic diet.

RESULTS

Exposure of BAECs to clinically relevant concentrations of HOG-LDL induced prolonged ER stress and reduced SERCA activity but increased SERCA oxidation. Chronic administration of Tempol (a potent antioxidant) attenuated both SERCA oxidation and aberrant ER stress in mice fed a high-fat diet in vivo. Likewise, AMPK activation by pharmacological (5′-aminoimidazole-4-carboxymide-1-β-d-ribofuranoside, metformin, and statin) or genetic means (adenoviral overexpression of constitutively active AMPK mutants) significantly mitigated ER stress and SERCA oxidation and improved the endothelium-dependent relaxation in isolated mouse aortae. Finally, Tempol administration markedly attenuated impaired endothelium-dependent vasorelaxation, SERCA oxidation, ER stress, and atherosclerosis in ApoE^−/− and ApoE^−/−/AMPKα2^−/− fed a high-fat diet.

CONCLUSION

We conclude that HOG-LDL, via enhanced SERCA oxidation, causes aberrant ER stress, endothelial dysfunction, and atherosclerosis in vivo, all of which are inhibited by AMPK activation.LDL oxidation and glycation are known to promote atherosclerosis through several mechanisms that include promoting vascular proinflammatory responses, intracellular oxidative stress, and apoptosis associated with endothelial dysfunction (1,2). In addition, LDL oxidation is greatly enhanced by LDL glycation (3,4). For example, glycation of LDL slows the clearance of these particles from the circulation (5), increases their susceptibility to oxidative damage (6), enhances entrapment of extravasated particles in the vascular subintimal space, and increases chemotactic activity of monocytes (7). The presence of both glycated LDL and glycoxidized LDL in human atherosclerotic plaques has been confirmed by immunochemical methods both in vivo and in vitro (8–10). Increasing evidence suggests that glycation and oxidation of LDL induces apoptosis in arterial wall cells (11,12), and glycoxidized LDL triggers apoptosis in vascular smooth muscle cells (13,14). Overall, glycation of LDL promotes the formation of oxidized LDL, and this phenomenon contributes to accelerated atherosclerosis, an important pathologic corollary of diabetes.Endoplasmic reticulum (ER) stress has been linked to a wide range of human pathologies including diabetes (15–17), obesity (16,17), atherosclerosis (18), cancer, neurodegenerative disorders, and inflammatory conditions. ER stress may be triggered by high glucose, oxidative stress, Ca²⁺ overload, ischemia, and hypoxia. In addition, it causes the accumulation of unfolded and misfolded proteins, leading to an “unfolded protein response” (19). The normal ER is the principal site of protein synthesis, folding, and maturation. In unfolded protein response, unfolded or misfolded proteins are sent to the cytoplasm by a “retro-translocation mechanism” to be degraded by the ubiquitin proteasome system (20).AMP-activated protein kinase (AMPK), a sensor of cellular energy status, plays a critical role in controlling the cell''s energy balance and metabolism (21), and activation of AMPK is an important defensive response to stress (22). AMPK activation is neuroprotective (23), and also mediates at least some cardiovascular protective effects of drugs such as hydroxymethylglutaryl-CoA reductase inhibitors (e.g., the statins such as pravastatin and atorvastatin) and metformin (a biguanide that activates AMPK) (24,25). Activation of AMPK protects cardiomyocytes against hypoxic injury through attenuation of ER stress (26). However, whether AMPK alters oxidized LDL-induced ER stress in endothelial cells has not been investigated to date. In this study, we report that oxidized, glycated-LDL (HOG-LDL) via the oxidation and inhibition of sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase (SERCA), triggers ER stress in endothelial cells in vivo. In addition, we have uncovered evidence suggesting that AMPK activation attenuates ER stress by inhibiting SERCA oxidation caused by HOG-LDL.     

调节内质网应激反应抑制肿瘤细胞自噬的研究进展

目的了解调节内质网应激反应抑制肿瘤细胞自噬的研究进展。方法对国内外有关内质网应激反应抑制肿瘤细胞自噬的文献进行综述。结果在Ca2+释放及未折叠蛋白聚集而诱发的内质网应激反应中,自噬可被多种通路激活,并调节生理及病理过程。结论在肿瘤细胞内质网应激反应中,调节其反应通路因子进而抑制自噬的发生仍需进一步研究。     

环形嵌顿痔分段切除剥离加压术与外剥内扎术后并发症的护理

目的 探讨环形嵌顿痔分段切除剥离加压术与外剥内扎术术后不同并发症的护理。方法 将84例环形嵌顿痔患者按手术方式分为两组，A组43例，行分段切除剥离加压术。B组41例，行外剥内扎术。结果 手术均顺利完成，患者均痊愈出院。两组术后并发症发生率比较，差异有显著性意义（P〈0．05）；A组发生6例肛缘水肿、1例排尿困难，B组3例肛门狭窄、2例肛缘水肿、5例排尿困难，但两组并发症构成情况比较，差异无显著性意义（P〉0．05）。结论 采用分段切除剥离加压术治疗环形嵌顿痔患者术后多发生肛缘水肿，而采用外剥内扎术治疗者术后多发生肛门狭窄和排尿困难，因此应针对不同术式采取护理措施预防并发症。     

毫米波联合甲钴胺治疗糖尿病周围神经病变的护理

目的 观察毫米波脉冲刺激联合甲钴胺治疗糖尿病周围神经病变患者的疗效.方法 将86例糖尿病周围神经病变患者随机分为观察组与对照组各43例.两组患者在饮食和降糖治疗不变的前提下进入治疗期.对照组应用甲钴胺0.5mg肌内注射,1次/d.观察组在对照组基础上采用糖尿病治疗仪进行治疗.两组均观察4周评价疗效.结果 观察组总有效率90.7%,对照组67.4%,观察组显著高于对照组(P＜0.01),且观察组神经传导速度显著优于对照组(均P＜0.05)).结论 毫米波脉冲刺激穴位可改善神经细胞的代谢,促进神经修复再生,联合甲钴胺治疗糖尿病周围神经病变疗效显著.治疗中需掌握糖尿病治疗仪的操作方法,密切观察治疗效果及不良反应,做好健康教育及心理护理.     

Intracellular Accumulation of Advanced Glycation End Products Induces Osteoblast Apoptosis Via Endoplasmic Reticulum Stress

Osteoporosis is an aging-associated disease that is attributed to excessive osteoblast apoptosis. It is known that the accumulation of advanced glycation end products (AGEs) in bone extracellular matrix deteriorates osteoblast functions. However, little is known about the interaction between intracellular AGE accumulation and the induction of osteoblast apoptosis. In this study, we investigated the effect of intracellular AGE accumulation on osteoblast apoptosis in vitro and in vivo. In vitro, murine osteoblastic MC3T3-E1 cells were treated with glycolaldehyde (GA), an AGE precursor. GA-induced intracellular AGE accumulation progressed in time- and dose-dependent manners, followed by apoptosis induction. Intracellular AGE formation also activated endoplasmic reticulum (ER) stress-related proteins (such as glucose-regulated protein 78, inositol-requiring protein-1α (IRE1α), and c-Jun N-terminal kinase) and induced apoptosis. In agreement, treatment with the ER stress inhibitor 4-phenylbutyric acid and knocking down IRE1α expression ameliorated osteoblast apoptosis. Furthermore, the ratio between AGE- and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-positive osteoblasts in human vertebral bodies was significantly higher in an elderly group than in a younger group. A positive linear correlation between the ratio of AGE-positive and TUNEL-positive osteoblasts (r = 0.72) was also observed. Collectively, these results indicate that AGEs accumulated in osteoblasts with age and that intracellular AGE accumulation induces apoptosis via ER stress. These findings offer new insight into the mechanisms of osteoblast apoptosis and age-related osteoporosis. © 2020 American Society for Bone and Mineral Research.     

Imatinib Mesylate Reduces Endoplasmic Reticulum Stress and Induces Remission of Diabetes in db/db Mice

OBJECTIVE—Imatinib has been reported to induce regression of type 2 diabetes in chronic leukemia patients. However, the mechanism of diabetes amelioration by imatinib is unknown, and it is uncertain whether imatinib has effects on type 2 diabetes itself without other confounding diseases like leukemia. We studied the effect of imatinib on diabetes in db/db mice and investigated possible mechanism''s underlying improved glycemic control by imatinib.RESEARCH DESIGN AND METHODS—Glucose tolerance and insulin tolerance tests were done after daily intraperitoneal injection of 25 mg/kg imatinib into db/db and C57BL/6 mice for 4 weeks. Insulin signaling and endoplasmic reticulum stress responses were studied by Western blotting. β-Cell mass and apoptotic β-cell number were determined by combined terminal deoxynucleotidyl transferase–mediated dUTP nick-end labeling (TUNEL) staining and insulin immunohistochemistry. The in vitro effect of imatinib was studied using HepG2 cells.RESULTS—Imatinib induced remission of diabetes in db/db mice and amelioration of insulin resistance. Expression of endoplasmic reticulum stress markers in the liver and adipose tissues of db/db mice, such as phospho-PERK, phospho-eIF2α, TRB3, CHOP, and phospho–c-Jun NH₂-terminal kinase, was reduced by imatinib. Insulin receptor substrate-1 tyrosine phosphorylation and Akt phosphorylation after insulin administration were improved by imatinib. Serum aminotransferase levels and hepatic triglyceride contents were decreased by imatinib. Pancreatic β-cell mass was increased by imatinib, accompanied by decreased TUNEL⁺ β-cell and increased BrdU⁺ β-cell numbers. Imatinib attenuated endoplasmic reticulum stress in hepatoma cells in vitro.CONCLUSIONS—Imatinib ameliorated endoplasmic reticulum stress and induced remission of diabetes in db/db mice. Imatinib or related compounds could be used as therapeutic agents against type 2 diabetes and metabolic syndrome.Type 2 diabetes is a metabolic disease that affects 2.8% of all age-groups worldwide, and this proportion is expected to increase to 4.4% by 2030 (1). The two major components of the pathogenesis of type 2 diabetes are insulin resistance and β-cell failure. However, the biochemical mechanisms underlying these two phenomena are incompletely understood.Regarding the mechanism of insulin resistance, several hypotheses have been proposed, for example, increased circulating free fatty acid level, mitochondrial dysfunction, elevated reactive oxygen species production, and increased levels of proinflammatory mediators (2–4). Downstream of these molecules or events, disturbance in intracellular signaling, such as c-Jun NH₂-terminal kinase (JNK) phosphorylation, IKKβ activation, or endoplasmic reticulum stress responses, may play a role in the development of insulin resistance (5–7).Imatinib mesylate (Gleevec) is a well-known anticancer agent that has a dramatic effect on chronic myelogenous leukemia (CML) and gastrointestinal stromal tumor by specifically inhibiting Bcr-Abl or Kit kinase (8,9). Recently, it was reported that imatinib induced remission of type 2 diabetes in patients having both CML and type 2 diabetes (10,11). The effect of imatinib on animal models of type 1 diabetes resulting from islet injury has also been studied (12,13). However, the effect of imatinib on type 2 diabetes itself in patients or experimental animals without other confounding diseases has not been explored. Furthermore, the mechanism of the improvement of type 2 diabetes by imatinib is unknown. In fact, the possibility that improved glucose tolerance in type 2 diabetic patients with CML by imatinib is due to a positive side effect of leukemic responses leading to the nonspecific generalized improvement of health status cannot be eliminated (11). Thus, it is uncertain whether imatinib could improve glycemic control in type 2 diabetic patients or animals without other confounding diseases. To address this question, we investigated whether imatinib could improve glycemic control in diabetic db/db mice.