Suppressive effects of 4-phenylbutyrate on the aggregation of Pael receptors and endoplasmic reticulum stress

Endoplasmic reticulum (ER) stress is defined as an accumulation of unfolded proteins in the endoplasmic reticulum. 4-phenylbutyrate (4-PBA) has been demonstrated to promote the normal trafficking of the DeltaF508 cystic fibrosis transmembrane conductance regulator (CFTR) mutant from the ER to the plasma membrane and to restore activity. We have reported that 4-PBA protected against cerebral ischemic injury and ER stress-induced neuronal cell death. In this study, we revealed that 4-PBA possesses chemical chaperone activity in vitro, which prevents the aggregation of denatured alpha-lactalbumin and bovine serum albumin (BSA). Furthermore, we investigated the effects of 4-PBA on the accumulation of Parkin-associated endothelin receptor-like receptor (Pael-R) pathologically relevant to the loss of dopaminergic neurons in autosomal recessive juvenile parkinsonism (AR-JP). Interestingly, 4-PBA restored the normal expression of Pael-R protein and suppressed ER stress induced by the overexpression of Pael-R. In addition, we showed that 4-PBA attenuated the activation of ER stress-induced signal transduction pathways and subsequent neuronal cell death. Moreover, 4-PBA restored the viability of yeasts that fail to induce an ER stress response under ER stress conditions. These results suggest that 4-PBA suppresses ER stress by directly reducing the amount of misfolded protein, including Pael-R accumulated in the ER.     

4-Phenylbutyric acid protects against neuronal cell death by primarily acting as a chemical chaperone rather than histone deacetylase inhibitor

This letter describes the mechanism behind the protective effect of 4-phenylbutyric acid (4-PBA) against endoplasmic reticulum (ER) stress-induced neuronal cell death using three simple 4-(p-substituted phenyl) butyric acids (4-PBA derivatives). Their relative human histone deacetylase (HDAC) inhibitory activities were consistent with a structural model of their binding to HDAC7, and their ability to suppress neuronal cell death and activity of chemical chaperone in vitro. These data suggest that 4-PBA protects against neuronal cell death mediated by the chemical chaperone activity rather than by inhibition of histone deacetylase.     

Altered ubiquitin-proteasome system leads to neuronal cell death in a spontaneous obese rat model

Background

Obesity is associated with various progressive age-related diseases, including neurological disorders. However, underlying molecular basis for increased risk of neurodegeneration in obesity is unknown. A suitable animal model would immensely help in understanding the obesity-linked neurological problems.

Methods

A spontaneously developed obese rat (WNIN/Ob) which is highly vulnerable for a variety of degenerative diseases was isolated from the existing WNIN stock rats. Ultrastructure of neurons in the cerebral cortex of 12-month old obese rats was evaluated by transmission electron microscopy. qRT-PCR and immunoblotting of ubiquitin C-terminal hydrolases (UCHs), ubiquitin, proteasomal sub-units, markers of ER stress and apoptosis were performed in the cerebral cortex. Proteasome activity was assayed by fluorometric method. Immunohistochemistry was performed for mediators of apoptosis, which was further confirmed by TUNEL assay. These investigations were also carried in high-fat diet-induced obese rat model.

Results

Neurons in the cerebral cortex of 12-month obese rats showed swollen mitochondria, disrupted ER and degenerating axons, nucleus and finally neurons. Results showed altered UPS, existence of ER stress, up-regulation of apoptotic markers and apoptosis in the cerebral cortex of obese rats. It appears that UCHL-1 mediated apoptosis through stabilizing p53 might play a role in neuronal cell death in obese rat. Similar changes were observed in the brain of diet-induced obese WNIN rats.

Conclusion

Altered UPS could be one of the underlying mechanisms for the neuronal cell death in obese conditions.

General significance

This is the first report to highlight the role of altered UPS in neurodegeneration due to obesity.     

The unfolded protein response to endoplasmic reticulum stress in cultured astrocytes and rat brain during experimental diabetes

Oxidative-nitrosative stress and inflammatory responses are associated with endoplasmic reticulum (ER) stress in diabetic retinopathy, raising the possibility that disturbances in ER protein processing may contribute to CNS dysfunction in diabetics. Upregulation of the unfolded protein response (UPR) is a homeostatic response to accumulation of abnormal proteins in the ER, and the present study tested the hypothesis that the UPR is upregulated in two models for diabetes, cultured astrocytes grown in 25 mmol/L glucose for up to 4 weeks and brain of streptozotocin (STZ)-treated rats with diabetes for 1–7 months. Markers associated with translational blockade (phospho-eIF2α and apoptosis (CHOP), inflammatory response (inducible nitric oxide synthase, iNOS), and nitrosative stress (nuclear translocation of glyceraldehyde-3-phosphate dehydrogenase, GAPDH) were not detected in either model. Nrf2 was present in nuclei of low- and high-glucose cultures, consistent with oxidative stress. Astrocytic ATF4 expression was not altered by culture glucose concentration, whereas phospho-IRE and ATF6 levels were higher in low- compared with high-glucose cultures. The glucose-regulated chaperones, GRP78 and GRP94, were also expressed at higher levels in low- than high-glucose cultures, probably due to recurrent glucose depletion between feeding cycles. In STZ-rat cerebral cortex, ATF4 level was transiently reduced at 4 months, and p-IRE levels were transiently elevated at 3 months. However, GRP78 and GRP94 expression was not upregulated, and iNOS, amyloid-β, and nuclear accumulation of GAPDH were not evident in STZ-diabetic brain. High-glucose cultured astrocytes and STZ-diabetic brain are relatively resistant to diabetes-induced ER stress, in sharp contrast with cultured retinal Müller cells and diabetic rodent retina.     

Amelioration of neuronal cell death in a spontaneous obese rat model by dietary restriction through modulation of ubiquitin proteasome system

Dietary restriction (DR) has been shown to increase longevity, delay onset of aging, reduce DNA damage and oxidative stress and prevent age-related decline of neuronal activity. We previously reported the role of altered ubiquitin proteasome system (UPS) in the neuronal cell death in a spontaneous obese rat model (WNIN/Ob rat). In this study, we investigated the effect of DR on obesity-induced neuronal cell death in a rat model. Two groups of 40-day-old WNIN/Ob rats were either fed ad libitum (Ob) or pair-fed with lean. The lean phenotype of WNIN/Ob rats served as ad libitum control. These animals were maintained for 6.5 months on their respective diet regime. At the end of the study, cerebral cortex was collected and markers of UPS, endoplasmic reticulum (ER) stress and autophagy were analyzed by quantitative real-time polymerase chain reaction, immunoblotting and immunohistochemistry. Chymotrypsin-like activity of proteasome was assayed by the fluorimetric method. Apoptotic cells were analyzed by TUNEL assay. DR improved metabolic abnormalities in obese rats. Alterations in UPS (up-regulation of UCHL1, down-regulation of UCHL5, declined proteasomal activity), increased ER stress, declined autophagy and increased expression of α-synuclein, p53 and BAX were observed in obese rats and DR alleviated these changes in obese rats. Further, DR decreased TUNEL-positive cells. In conclusion, DR in obese rats could not only restore the metabolic abnormalities but also preserved neuronal health in the cerebral cortex by preventing alterations in the UPS.     

Differential proteomic profiling identifies novel molecular targets of pterostilbene against experimental diabetes

Pterostilbene (PTS), a naturally occurring stilbene, confers protection against oxidative and cytokine stress induced pancreatic β-cell apoptosis in vitro and in vivo. To provide insights into the molecular mechanism, we performed a proteomic study on the pancreas of PTS-treated diabetic mice using electrospray ionization tandem–mass spectrometry (LC–MS/MS). A total of 1,260 proteins were detected in triplicate samples. Of which, 359 proteins were found to be differentially regulated in streptozotocin-induced diabetic mice pancreas with two fold difference ( P < 0.05, two or more peptides) and on PTS treatment 315 proteins were normalized to control levels. Gene ontology (GO) indicated that majority of the differentially regulated proteins are involved in cellular functions such as metabolism, cellular structure, oxidative stress, endoplasmic-reticulum-associated protein degradation (ERAD) pathway and several stress sensors. Protein–protein interaction network analysis of these differentially expressed proteins showed clustering of proteins involved in protein processing in endoplasmic reticulum (protein synthesis machinery and protein folding), oxidative phosphorylation/oxidative stress proteins, oligosaccharide metabolic process, and antioxidant activity. Our results highlighted that PTS administration rehabilitated the defective metabolic process and redox imbalance, and also suppressed the unfolded protein response and ERAD pathways. The effects on targeting ER machinery and suppressing oxidative stress suggest the great potential of PTS for diabetes management.     

ω-Hydroxyundec-9-enoic acid induces apoptosis through ROS-mediated endoplasmic reticulum stress in non-small cell lung cancer cells

ω-Hydroxyundec-9-enoic acid (ω-HUA), a hydroxyl unsaturated fatty acid derivative, is involved in the antifungal activity of wild rice (Oryza officinalis). Here, we investigated the anti-cancer activity of ω-HUA on a non-small cell lung cancer (NSCLC) cell line. ω-HUA increased apoptosis and induced cleavages of caspase-6, caspase-9, and poly (ADP-ribose) polymerase (PARP). ω-HUA treatment significantly induced endoplasmic reticulum (ER) stress response. Suppression of CHOP expression and inhibiting ER stress by 4-phenylbutyrate (4-PBA) significantly attenuated the ω-HUA treatment-induced activation of caspase-6, caspase-9, and PARP, and subsequent apoptotic cell death, indicating a role for ER stress in ω-HUA-induced apoptosis. In addition, cells subjected to ω-HUA exhibited significantly increased quantity of reactive oxygen species (ROS), and the ROS scavenger N-acetyl-l-cysteine (NAC) inhibited ω-HUA-induced apoptotic cell death and ER stress signals, indicating a role for ROS in ER stress-mediated apoptosis in ω-HUA-treated cells. Taken together, these results suggest that sequential ROS generation and ER stress activation are critical in ω-HUA treatment-induced apoptosis and that ω-HUA represents a promising candidate for NSCLC treatment.     

4-苯基丁酸钠通过抑制内质网应激减轻皮层神经元氧糖剥夺/再灌注损伤

4-苯基丁酸钠（4-phenylbutyric acid,4-PBA）是协助内质网中蛋白质转录后修饰和折叠的分子伴侣,故可减轻非折叠蛋白反应（unfolded protein response,UPR）及其介导的细胞凋亡。既往研究表明,4-PBA可以减轻脑组织的缺血性损伤,但采用原代皮层神经元构建氧糖剥夺/再灌注（oxygen glucose deprivation/reoxygenation, OGD/R）损伤模型,来研究4-PBA对神经元损伤的保护作用及其机制尚未见报道。本文采用原代培养的皮层神经元OGD/R损伤模型,同时给予4-PBA处理,探讨4-PBA对OGD/R诱导的神经元内质网应激（endoplasmic reticulum stress,ERS）的作用及其机制。分别采用MTT、LDH和Hoechst 33342染色法检测神经元存活率、细胞膜完整性和细胞凋亡情况。Western印迹检测ERS标志物葡萄糖调节蛋白78 (glucose regulated protein 78,GRP78),以及肌醇必需酶1（inositol requiring enzyme 1, IRE1）通路相关蛋白质的表达。Western印迹结果显示,在OGD/R后0～48 h,GRP78的表达较对照组明显升高。MTT、LDH漏出率和Hoechst 33342染色法检测显示,4-PBA显著改善OGD/R所导致的神经元存活率下降、LDH漏出率升高和细胞凋亡增加,且具有明显的剂量依赖性。通过Western印迹检测发现,4-PBA显著逆转OGD/R所致GRP78蛋白表达水平的上调。此外,对肌醇必需酶1通路相关蛋白质的检测显示,4-PBA下调氧糖剥夺/再灌注组神经元p IRE1和p JNK的表达,增加抗凋亡蛋白Bcl 2表达。上述研究结果表明,4-PBA在氧糖剥夺/再灌注情况下对神经元具有保护作用,该保护作用可能是通过抑制肌醇必需酶1信号通路介导的非折叠蛋白反应和内质网应激实现的。     

4-Phenylbutyrate Inhibits Tunicamycin-Induced Acute Kidney Injury via CHOP/GADD153 Repression

Different forms of acute kidney injury (AKI) have been associated with endoplasmic reticulum (ER) stress; these include AKI caused by acetaminophen, antibiotics, cisplatin, and radiocontrast. Tunicamycin (TM) is a nucleoside antibiotic known to induce ER stress and is a commonly used inducer of AKI. 4-phenylbutyrate (4-PBA) is an FDA approved substance used in children who suffer from urea cycle disorders. 4-PBA acts as an ER stress inhibitor by aiding in protein folding at the molecular level and preventing misfolded protein aggregation. The main objective of this study was to determine if 4-PBA could protect from AKI induced by ER stress, as typified by the TM-model, and what mechanism(s) of 4-PBA''s action were responsible for protection. C57BL/6 mice were treated with saline, TM or TM plus 4-PBA. 4-PBA partially protected the anatomic segment most susceptible to damage, the outer medullary stripe, from TM-induced AKI. In vitro work showed that 4-PBA protected human proximal tubular cells from apoptosis and TM-induced CHOP expression, an ER stress inducible proapoptotic gene. Further, immunofluorescent staining in the animal model found similar protection by 4-PBA from CHOP nuclear translocation in the tubular epithelium of the medulla. This was accompanied by a reduction in apoptosis and GRP78 expression. CHOP^−/− mice were protected from TM-induced AKI. The protective effects of 4-PBA extended to the ultrastructural integrity of proximal tubule cells in the outer medulla. When taken together, these results indicate that 4-PBA acts as an ER stress inhibitor, to partially protect the kidney from TM-induced AKI through the repression of ER stress-induced CHOP expression.     

3-Bromo-7-nitroindazole attenuates brain ischemic injury in diabetic stroke via inhibition of endoplasmic reticulum stress pathway involving CHOP

AimsThe role of nitric oxide (NO) and endoplasmic reticulum (ER) stress has been implicated in the pathogenesis of cerebral ischemic/reperfusion (I/R) injury and diabetes. The aim of the study was to investigate the neuroprotective potential of 3-bromo-7-nitroindazole (3-BNI), a potent and selective neuronal nitric oxide synthase (nNOS) inhibitor against ER stress and focal cerebral I/R injury associated with comorbid type 2 diabetes in-vivo.Main methodsType 2 diabetes was induced by feeding high-fat diet and streptozotocin (35 mg/kg) treatment in rats. Focal cerebral ischemia was induced by 2 h middle cerebral artery occlusion (MCAO) followed by 22 h of reperfusion. Immunohistochemistry and western blotting methods were employed for the detection and expression of ER stress/apoptosis markers [78 kDa glucose regulated protein (GRP78) and CCAAT/enhancer binding protein homologous protein (CHOP)]. TUNEL assay for DNA fragmentation was also performed.Key findingsThe diabetic rats subjected to cerebral I/R had prominent neurological damage and functional deficits compared with sham-operated rats. Massive DNA fragmentation was observed in ischemic penumbral region of diabetic brains. Concomitantly, the enhanced immunoreactivity and expression of ER stress/apoptosis markers were noticed. 3-BNI (30 mg/kg, i.p.) treatment significantly inhibited the cerebral infarct, edema volume and improved functional recovery of neurological deficits. The neuroprotection was further evident by lesser DNA fragmentation with a concomitant reduction of GRP78 and CHOP.SignificanceThe study demonstrates the neuroprotective potential of 3-BNI in diabetic stroke model which may be partly due to inhibition of ER stress pathway involving CHOP.     

Exercise protects against diabetic cardiomyopathy by the inhibition of the endoplasmic reticulum stress pathway in rats

To explore the protective effect of exercise training on the injury of myocardium tissues induced by streptozotocin (STZ) in diabetic rats and the relationship with endoplasmic reticulum stress (ERS), the male sprague-dawley (SD) rats were fed with high-fat and high-sugar diet for 4 weeks, followed by intraperitoneal injection of STZ, 40 mg/kg, to establish a diabetes model, and then 10 rats were randomly selected as diabetes mellitus (DM) controls and 20 eligible diabetic rats were randomized into two groups: low-intensity exercise training (n = 10) and high-intensity exercise training (n = 10). After 12 weeks of exercise training, rats were killed and serum samples were used to determine cardiac troponin-I (cTn-I). Myocardial tissues were sampled for morphological analysis to detect myocardial cell apoptosis, and to analyze protein expression of glucose-regulated protein 78 (GRP78), C/EBP homologous protein (CHOP), and caspase-12. Different intensities (low and high) significantly reduced serum cTn-I levels compared with the DCM group (p < 0.01), and significantly reduced the percentage of apoptotic myocardial cells and improved the parameters of cardiac function. Hematoxylin and eosin and Masson staining indicated that exercise training could attenuate myocardial apoptosis. Additionally, exercise training significantly reduced GRP78, CHOP, and cleaved caspase-12 protein expression in an intensity-dependent manner. These findings suggest that exercise appeared to ameliorate diabetic cardiomyopathy by inhibiting endoplasmic reticulum stress-induced apoptosis in diabetic rats.     

内质网应激反应分子机理研究进展

内质网应激是导致心脑组织缺血梗塞、神经退行性疾病等发生的重要环节 .目前发现同型半胱氨酸、氧化应激、钙代谢紊乱等都能引起内质网应激级联反应 ,表现为蛋白质合成暂停、内质网应激蛋白表达和细胞凋亡等 .这些表现包括在未折叠蛋白反应 (UPR)、整合应激反应 (ISR)和内质网相关性死亡 (ERAD)三个相互关联的动态过程中 ,每一过程的分子机理现已逐步被揭示 .作为细胞保护性应对机制的内质网应激体系一旦遭到破坏 ,细胞将不能合成应有的蛋白质 ,亦不能发挥正常的生理功能 ,甚至会出现细胞凋亡 .掌握内质网应激过程对进一步理解多种疾病的发生机理有十分重要的理论意义     

Diabetes- and angiotensin II-induced cardiac endoplasmic reticulum stress and cell death: metallothionein protection

We have shown cardiac protection by metallothionein (MT) in the development of diabetic cardiomyopathy (DCM) via suppression of cardiac cell death in cardiac-specific MT-overexpressing transgenic (MT-TG) mice. The present study was undertaken to define whether diabetes can induce cardiac endoplasmic reticulum (ER) stress and whether MT can prevent cardiac cell death via attenuating ER stress. Diabetes was induced by streptozotocin in both MT-TG and wild-type (WT) mice. Two weeks, and 2 and 5 months after diabetes onset, cardiac ER stress was detected by expression of ER chaperones, and apoptosis was detected by CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) and cleaved caspase-3 and caspase-12. Cardiac apoptosis in the WT diabetic mice, but not in MT-TG diabetic mice, was significantly increased 2 weeks after diabetes onset. In parallel with apoptotic effect, significant up-regulation of the ER chaperones, including glucose-regulated protein (GRP)78 and GRP94, cleaved ATF6 and phosporylated eIF2α, in the hearts of WT, but not MT-TG diabetic mice. Infusion of angiotensin II (Ang II) also significantly induced ER stress and apoptosis in the hearts of WT, but not in MT-TG mice. Direct administration of chemical ER stress activator tunicamycin significantly increased cardiac cell death only in WT mice. Pre-treatment with antioxidants completely prevented Ang II-induced ER stress and apoptosis in the cultured cardiac cells. These results suggest that ER stress exists in the diabetic heart, which may cause the cardiac cell death. MT prevents both diabetes- and Ang II-induced cardiac ER stress and associated cell death most likely via its antioxidant action, which may be responsible for MT's prevention of DCM.     

Nephroprotective potential of Quercus infectoria galls against experimentally induced diabetic nephropathy in rats through inhibition of renal oxidative stress and TGF-β

Diabetic nephropathy (DN) is the leading cause of death in diabetic patients and the current treatment options available have a limited significance. The insect galls of Quercus infectoria are traditionally important in the treatment of numerous diseases including diabetes. Hence, the present study was undertaken to evaluate the effect of Q. infectoria gall extract (QIGE) against experimental DN. Type 2 diabetes was induced by feeding rats with a high-fat diet (HFD) initially for 5 weeks, followed by a single intraperitoneal injection of streptozotocin (STZ, 35?mg/kg?bw/day). QIGE was administered to the rats orally at doses of 100 and 200?mg/kg?bw/day, respectively. At the end of the experimental period, various glycemic and renal function parameters were evaluated in the serum, urine and kidney tissues. The QIGE treatment significantly (p?p?via the inhibition of hyperglycemia-induced oxidative stress and renal TGF-β expression and is, therefore, a potential therapeutic agent in the treatment of diabetic complications, especially DN.     

Selenoprotein S-dependent Selenoprotein K Binding to p97(VCP) Protein Is Essential for Endoplasmic Reticulum-associated Degradation

Cytosolic valosin-containing protein (p97(VCP)) is translocated to the ER membrane by binding to selenoprotein S (SelS), which is an ER membrane protein, during endoplasmic reticulum-associated degradation (ERAD). Selenoprotein K (SelK) is another known p97(VCP)-binding selenoprotein, and the expression of both SelS and SelK is increased under ER stress. To understand the regulatory mechanisms of SelS, SelK, and p97(VCP) during ERAD, the interaction of the selenoproteins with p97(VCP) was investigated using N2a cells and HEK293 cells. Both SelS and SelK co-precipitated with p97(VCP). However, the association between SelS and SelK did not occur in the absence of p97(VCP). SelS had the ability to recruit p97(VCP) to the ER membrane but SelK did not. The interaction between SelK and p97(VCP) did not occur in SelS knockdown cells, whereas SelS interacted with p97(VCP) in the presence or absence of SelK. These results suggest that p97(VCP) is first translocated to the ER membrane via its interaction with SelS, and then SelK associates with the complex on the ER membrane. Therefore, the interaction between SelK and p97(VCP) is SelS-dependent, and the resulting ERAD complex (SelS-p97(VCP)-SelK) plays an important role in ERAD and ER stress.     

A rat model of human FENIB (familial encephalopathy with neuroserpin inclusion bodies)

FENIB (familial encephalopathy with neuroserpin inclusion bodies) is caused by intracellular accumulation/polymerization of mutant neuroserpins in the endoplasmic reticulum (ER). Transgenic rats overexpressing megsin (Tg meg), a newly identified serine protease inhibitor (serpin), demonstrated intraneuronal periodic-acid Schiff (PAS)-positive inclusions distributed throughout deeper layers of cerebral cortex, CA1 of the hippocampus, and substantia nigra. Hippocampal extracts from Tg meg rats showed increased expression of ER stress proteins, and activation of caspases-12 and -3, associated with decreased neuronal density. Enhanced ER stress was also observed in dopaminergic neurons in the substantia nigra, in parallel with decreased neuronal viability and motor coordination. In each case, PAS-positive inclusions were also positive for megsin. These data suggest that overexpression of megsin results in ER stress, eventuating in the formation of PAS-positive inclusions. Tg meg rats provide a novel model of FENIB, where accumulation of serpins in the ER induces selective dysfunction/loss of specific neuronal populations.     

Naringenin alleviates hyperglycemia-induced renal toxicity by regulating activating transcription factor 4–C/EBP homologous protein mediated apoptosis

Endoplasmic reticulum (ER) dysfunction plays a prominent role in the pathophysiology of diabetic nephropathy (DN). This study aimed to investigate the novel role of Naringenin (a flavanone mainly found in citrus fruits) in modulating ER stress in hyperglycemic NRK 52E cells and STZ/nicotinamide induced diabetes in Wistar rats. The results demonstrated that Naringenin supplementation downregulated the expression of ER stress marker proteins, including p-PERK, p-eIF2α, XBP1s, ATF4 and CHOP during hyperglycemic renal toxicity in vitro and in vivo. Naringenin abrogated hyperglycemia-induced ultrastructural changes in ER, evidencing its anti-ER stress effects. Interestingly, treatment of Naringenin prevented nuclear translocation of ATF4 and CHOP in hyperglycemic renal cells and diabetic kidneys. Naringenin prevented apoptosis in hyperglycemic renal cells and diabetic kidney tissues by downregulating expression of apoptotic marker proteins. Further, photomicrographs of TEM confirmed anti-apoptotic potential of Naringenin as it prevented membrane blebbing and formation of apoptotic bodies in hyperglycemic renal cells. Naringenin improved glucose tolerance, restored serum insulin level and reduced serum glucose level in diabetic rats evidencing its anti-hyperglycemic effects. Histopathological examination of kidney tissues also confirmed prevention of damage after 28 days of Naringenin treatment in diabetic rats. Additionally, Naringenin diminished oxidative stress and improved antioxidant defense response during hyperglycemic renal toxicity. Taken together, our study revealed a novel role of Naringenin in ameliorating ER stress during hyperglycemic renal toxicity along with prevention of apoptosis, cellular and tissue damage. The findings suggest that prevention of ER stress can be exploited as a novel approach for the management of hyperglycemic nephrotoxicity. Supplementary InformationThe online version contains supplementary material available at 10.1007/s12079-021-00644-0.     

Ginsenoside Rg1 ameliorates diabetic cardiomyopathy by inhibiting endoplasmic reticulum stress‐induced apoptosis in a streptozotocin‐induced diabetes rat model

Ginsenoside Rg1 has been demonstrated to have cardiovascular protective effects. However, whether the cardioprotective effects of ginsenoside Rg1 are mediated by endoplasmic reticulum (ER) stress‐induced apoptosis remain unclear. In this study, among 80 male Wistar rats, 15 rats were randomly selected as controls; the remaining 65 rats received a diet rich in fat and sugar content for 4 weeks, followed by intraperitoneal injection of streptozotocin (STZ, 40 mg/kg) to establish a diabetes model. Seven days after STZ injection, 10 rats were randomly selected as diabetic model (DM) controls, 45 eligible diabetic rats were randomized to three treatment groups and administered ginsenoside Rg1 in a dosage of 10, 15 or 20 mg/kg/day, respectively. After 12 weeks of treatment, rats were killed and serum samples obtained to determine cardiac troponin (cTn)‐I. Myocardial tissues were harvested for morphological analysis to detect myocardial cell apoptosis, and to analyse protein expression of glucose‐regulated protein 78 (GRP78), C/EBP homologous protein (CHOP), and Caspase‐12. Treatment with ginsenoside Rg1 (10–20 mg/kg) significantly reduced serum cTnI levels compared with DM control group (all P < 0.01). Ginsenoside Rg1 (15 and 20 mg/kg) significantly reduced the percentage of apoptotic myocardial cells and improved the parameters of cardiac function. Haematoxylin and eosin and Masson staining indicated that ginsenoside Rg1 could attenuate myocardial lesions and myocardial collagen volume fraction. Additionally, ginsenoside Rg1 significantly reduced GRP78, CHOP, and cleaved Caspase‐12 protein expression in a dose‐dependent manner. These findings suggest that ginsenoside Rg1 appeared to ameliorate diabetic cardiomyopathy by inhibiting ER stress‐induced apoptosis in diabetic rats.     

Modulation of palmitate-induced endoplasmic reticulum stress and apoptosis in pancreatic β-cells by stearoyl-CoA desaturase and Elovl6

Induction of endoplasmic reticulum (ER) stress and apoptosis by elevated exogenous saturated fatty acids (FAs) plays a role in the pathogenesis of β-cell dysfunction and loss of islet mass in type 2 diabetes. Regulation of monounsaturated FA (MUFA) synthesis through FA desaturases and elongases may alter the susceptibility of β-cells to saturated FA-induced ER stress and apoptosis. Herein, stearoyl-CoA desaturase (SCD)1 and SCD2 mRNA expression were shown to be induced in islets from prediabetic hyperinsulinemic Zucker diabetic fatty (ZDF) rats, whereas SCD1, SCD2, and fatty acid elongase 6 (Elovl6) mRNA levels were markedly reduced in diabetic ZDF rat islets. Knockdown of SCD in INS-1 β-cells decreased desaturation of palmitate to MUFA, lowered FA partitioning into complex neutral lipids, and increased palmitate-induced ER stress and apoptosis. Overexpression of SCD2 increased desaturation of palmitate to MUFA and attenuated palmitate-induced ER stress and apoptosis. Knockdown of Elovl6 limited palmitate elongation to stearate, increasing palmitoleate production and attenuating palmitate-induced ER stress and apoptosis, whereas overexpression of Elovl6 increased palmitate elongation to stearate and palmitate-induced ER stress and apoptosis. Overall, these data support the hypothesis that enhanced MUFA synthesis via upregulation of SCD2 activity can protect β-cells from elevated saturated FAs, as occurs in prediabetic states. Overt type 2 diabetes is associated with diminished islet expression of SCD and Elovl6, and this can disrupt desaturation of saturated FAs to MUFAs, rendering β-cells more susceptible to saturated FA-induced ER stress and apoptosis.