Type 2 diabetes mellitus is characterized by insulin resistance and failure of pancreatic beta-cells producing insulin. Autophagy plays a crucial role in cellular homeostasis through degradation and recycling of organelles such as mitochondria or endoplasmic reticulum (ER). Here we discussed the role of beta-cell autophagy in development of diabetes, based on our own studies using mice with beta-cell-specific deletion of Atg7 (autophagy-related 7), an important autophagy gene, and studies by others. beta-cell-specific Atg7-null mice showed reduction in beta-cell mass and pancreatic insulin content. Insulin secretory function ex vivo was also impaired, which might be related to organelle dysfunction associated with autophagy deficiency. As a result, beta-cell-specific Atg7-null mice showed hypoinsulinemia and hyperglycemia. However, diabetes never developed in those mice. Obesity and/or lipid are physiological ER stresses that can precipitate beta-cell dysfunction. Our recent studies showed that beta-cell-specific Atg7-null mice, when bred with ob/ob mice, indeed become diabetic. Thus, autophagy deficiency in beta-cells could be a precipitating factor in the progression from obesity to diabetes due to inappropriate response to obesity-induced ER stress.
Animals ; Autophagy/genetics/*physiology ; Diabetes Mellitus/genetics/*metabolism ; Endoplasmic Reticulum Stress/genetics/*physiology ; Humans ; Insulin-Secreting Cells/*metabolism

BACKGROUNDCalreticulin (CRT) is major Ca 2+ -binding chaperone mainly resident in the endoplasmic reticulum (ER) lumen. Recently, it has been shown that non-ER CRT regulates a wide array of cellular responses. We previously found that CRT was up-regulated during hypoxia/reoxygenation (H/R) and this study was aimed to investigate whether CRT nuclear translocation aggravates ER stress (ERS)-associated apoptosis during H/R injury in neonatal rat cardiomyocytes.

METHODSApoptosis rate and lactate dehydrogenase (LDH) leakage in culture medium were measured as indices of cell injury. Immunofluorescence staining showed the morphological changes of ER and intracellular translocation of CRT. Western blotting or reverse transcription polymerase chain reaction was used to detect the expression of target molecules.

RESULTSCompared with control, H/R increased apoptosis rate and LDH activity. The ER became condensed and bubbled, and CRT translocated to the nucleus. Western blotting showed up-regulation of CRT, Nrf2, activating transcription factor 4 (ATF4), CHOP and caspase-12 expression after H/R. Exogenous CRT overexpression induced by plasmid transfection before H/R increased cell apoptosis, LDH leakage, ER disorder, CRT nuclear translocation and the expression of ERS-associated molecules. However, administration of the ERS inhibitor, taurine, or CRT siRNA alleviated cell injury, ER disorder, and inhibited ERS-associated apoptosis.

CONCLUSIONSOur results indicated that during H/R stress, CRT translocation increases cell apoptosis and LDH leakage, aggravates ER disorder, up-regulates expression of nuclear transcription factors, Nrf2 and ATF4, and activates ERS-associated apoptosis.

Animals ; Apoptosis ; genetics ; physiology ; Calreticulin ; genetics ; metabolism ; Cell Hypoxia ; genetics ; physiology ; Cell Survival ; genetics ; physiology ; Cells, Cultured ; Endoplasmic Reticulum Stress ; physiology ; Myocytes, Cardiac ; cytology ; metabolism ; RNA Interference ; Rats

BACKGROUNDVanishing white matter disease (VWM), a human autosomal recessive inherited leukoencephalopathy, is due to mutations in eukaryotic initiation factor 2B (eIF2B). eIF2B is responsible for the initiation of protein synthesis by its guanine nucleotide exchange factor (GEF) activity. Mutations of eIF2B impair GEF activity at different degree. Previous studies implied improperly activated unfolded protein response (UPR) and endoplasmic reticulum stress (ERS) participated in the pathogenesis of VWM. Autophagy relieves endoplasmic reticulum load by eliminating the unfolded protein. It is still unknown the effects of genotypes on the pathogenesis. In this work, UPR and autophagy flux were analyzed with different mutational types.

METHODSERS tolerance, reflected by apoptosis and cell viability, was detected in human oligodendrocyte cell line transfected with the wild type, or different mutations of p. Arg113His, p. Arg269FNx01 or p. Ser610-Asp613del in eIF2Bε. A representative UPR-PERK component of activating transcription factor 4 (ATF4) was measured under the basal condition and ERS induction. Autophagy was analyzed the flux in the presence of lysosomal inhibitors.

RESULTSThe degree of ERS tolerance varied in different genotypes. The truncated or deletion mutant showed prominent apoptosis cell viability declination after ERS induction. The most seriously damaged GEF activity of p. Arg269FNx01 group underwent spontaneous apoptosis. The truncated or deletion mutant showed elevated ATF4 under basal as well as ERS condition. Decreased expression of LC3-I and LC3-II in the mutants reflected an impaired autophagy flux, which was more obvious in the truncated or deletion mutants after ERS induction.

CONCLUSIONSGEF activities in different genotypes could influence the cell ERS tolerance as well as compensatory pathways of UPR and autophagy. Oligodendrocytes with truncated or deletion mutants showed less tolerable to ERS.

Cell Line ; Endoplasmic Reticulum Stress ; genetics ; physiology ; Eukaryotic Initiation Factor-2B ; genetics ; Humans ; Mutation ; genetics ; Oligodendroglia ; metabolism ; Unfolded Protein Response ; genetics ; physiology

BACKGROUNDOur previous study has confirmed that one bout of exhaustion (Ex) can cause hippocampus neurocyte damage, excessive apoptosis, and dysfunction. Its initial reason is intracellular calcium overload in hippocampus triggered by N-methyl-D-aspartic acid receptor (NMDAR) over-activation. NMDAR activation can be suppressed by γ-aminobutyric acid (A) receptor (GABAAR). Whether GABAAR can prevent intense exercise-induced hippocampus apoptosis, damage, or dysfunction will be studied in this study.

METHODSAccording to dose test, rats were randomly divided into control (Con), Ex, muscimol (MUS, 0.1 mg/kg) and bicuculline (BIC, 0.5 mg/kg) groups, then all rats underwent once swimming Ex except ones in Con group only underwent training. Intracellular free calcium concentration ([Ca2+]i) was measured by Fura-2-acetoxymethyl ester; glial librillary acidic protein (GFAP) and synaptophysin (SYP) immunofluorescence were also performed; apoptosis were displayed by dUTP nick end labeling (TUNEL) stain; endoplasmic reticulum stress-induced apoptosis pathway was detected by Western blotting analysis; Morris water maze was used to detect learning ability and spatial memory.

RESULTSThe appropriate dose was 0.1 mg/kg for MUS and 0.5 mg/kg for BIC. Ex group showed significantly increased [Ca2+]i and astrogliosis; TUNEL positive cells and levels of GFAP, B cell lymphoma-2 (Bcl-2) associated X protein (Bax), caspase-3, caspase-12 cleavage, CCAAT/enhancer binding protein homologous protein (CHOP), and p-Jun amino-terminal kinase (p-JNK) in Ex group also raised significantly compared to Con group, while SYP, synapse plasticity, and Bcl-2 levels in Ex group were significantly lower than those in Con group. These indexes were back to normal in MUS group. BIC group had the highest levels of [Ca2+]i, astrogliosis, TUNEL positive cell, GFAP, Bax, caspase-3, caspase-12 cleavage, CHOP, and p-JNK, it also gained the lowest SYP, synapse plasticity, and Bcl-2 levels among all groups. Water maze test showed that Ex group had longer escape latency (EL) and less quadrant dwell time than Con group; all indexes between MUS and Con groups had no significant differences; BIC had the longest EL and least quadrant dwell time among all groups.

CONCLUSIONSActivation of GABAA R could prevent intense exercise-induced synapses damage, excessive apoptosis, and dysfunction of hippocampus.

Animals ; Apoptosis ; physiology ; Body Weight ; physiology ; Endoplasmic Reticulum Stress ; physiology ; Hippocampus ; metabolism ; Male ; Physical Exertion ; physiology ; Rats ; Rats, Sprague-Dawley ; Receptors, GABA ; genetics ; metabolism ; Synapses ; pathology

Hearing impairment (HI) affects 1/1000 children and over 2% of the aged population. We have previously reported that mutations in the gene encoding gap junction protein connexin-31 (C×31) are associated with HI. The pathological mechanism of the disease mutations remains unknown. Here, we show that expression of C×31 in the mouse inner ear is developmentally regulated with a high level in adult inner hair cells and spiral ganglion neurons that are critical for the hearing process. In transfected cells, wild type C×31 protein (C×31wt) forms functional gap junction at cell-cell-contacts. In contrast, two HI-associated C×31 mutants, C×31R180X and C×31E183K resided primarily in the ER and Golgi-like intracellular punctate structures, respectively, and failed to mediate lucifer yellow transfer. Expression of C×31 mutants but not C×31wt leads to upregulation of and increased association with the ER chaperone BiP indicating ER stress induction. Together, the HI-associated C×31 mutants are impaired in trafficking, promote ER stress, and hence lose the ability to assemble functional gap junctions. The study reveals a potential pathological mechanism of HI-associated C×31 mutations.
Animals ; Connexins ; genetics ; Ear, Inner ; metabolism ; Endoplasmic Reticulum ; physiology ; Gap Junctions ; genetics ; metabolism ; physiology ; Golgi Apparatus ; genetics ; metabolism ; Hearing Loss ; genetics ; metabolism ; pathology ; Mice ; Mutation ; Neurons ; metabolism ; Protein Transport ; genetics ; Stress, Physiological

Endoplasmic reticulum (ER) stress occurs in macrophage-rich areas of advanced atherosclerotic lesions and contributes to macrophage apoptosis and subsequent plaque necrosis. The purpose of the present study was to investigate the effects of caveolin-1 (Cav-1) on ER stress-induced apoptosis in cultured macrophages and the underlying mechanisms. RAW264.7 cells were incubated with thapsigargin (TG) to establish ER stress model. And Cav-1 expression was detected by Western blot. After being pretreated with filipin(III), a caveolae inhibitor, RAW264.7 cells were assayed with flow cytometry and confocal laser scanning microscopy to detect cell apoptosis. Moreover, p38 mitogen-activated protein kinase (MAPK) phosphorylation and C/EBP homologous protein (CHOP) expression were detected with Western blot. The results showed that Cav-1 expression was markedly increased at early stage of TG treatment (P < 0.05) and then decreased with prolonged or high dose TG treatments. The increasing of Cav-1 expression induced by TG in RAW264.7 cells was abolished under inhibition of caveolae by filipin(III) (P < 0.05). The effect of TG on apoptosis of RAW264.7 cells was further augmented after pretreatment with filipin(III) (P < 0.05). Western blotting showed that MAPK phosphorylation induced by TG was inhibited by filipin(III) in RAW264.7 cells (P < 0.05), whereas CHOP remained unchanged (P > 0.05). These results suggest that Cav-1 may play a critical role in suppressing ER stress-induced macrophages apoptosis in vitro, and one of the mechanisms may be correlated with the activation of p38 MAPK prosurvival pathway.
Animals ; Apoptosis ; drug effects ; Caveolin 1 ; genetics ; metabolism ; Cell Line ; Endoplasmic Reticulum Stress ; physiology ; Filipin ; pharmacology ; MAP Kinase Signaling System ; Macrophages ; cytology ; drug effects ; Mice ; Thapsigargin ; pharmacology ; Transcription Factor CHOP ; metabolism ; p38 Mitogen-Activated Protein Kinases ; metabolism

BACKGROUNDAccumulated evidence shows that hypoxia can induce endothelial apoptosis, however the mechanism is still unknown. We hypothesized whether intermittent or persistent hypoxia could induce endoplasmic reticular stress, leading to endothelial apoptosis.

METHODSTwenty-four 8-week male Sprague Dawley (SD) rats were divided into three groups: normoxia (NC) group, intermittent hypoxia (IH) group and persistent hypoxia (PH) group. TUNEL staining was performed to detect aortic arch endotheliar apoptosis, and immunohistochemistry for BIP, CHOP and caspase12 to test protein expression; human umbilical vein endothelial cells (HUVECs) of the line ECV304 were cultured (with or without taurodeoxycholic acid (TUDCA) 10 mmol/L, 100 mmol/L) and divided into four groups: NC group (20.8% O2 for 4 hours), PH1 group (5% O2 for 4 hours), PH2 group (5% O2 for 12 hours) and IH group (20.8% O2 and 5% O2 alternatively for 8 hours). Annexin V-fluorescein-isothiocyanate/propidium iodide flow cytometry was used to assess apoptosis in each group. The expressions of GRP78, CHOP and caspase12 were detected by real-time quantitative reverse-transcription PCR. Result Intermittent and persistent hypoxia could increase the rate of endothelium apoptosis and the expressions of GRP78, CHOP and caspase12 compared with the control, induction by intermittent hypoxia was slightly higher than persistent hypoxia. In the HUVEC experiment, TUDCA significantly reduced apoptosis and the expressions of GRP78, CHOP and caspase12.

CONCLUSIONHypoxia, especially intermittent, can induce endothelial cell apoptosis possibly through endoplasmic reticulum stress pathway, which can be attenuated by taurodeoxycholic acid.

Animals ; Apoptosis ; drug effects ; genetics ; physiology ; Caspase 12 ; genetics ; Endoplasmic Reticulum Stress ; drug effects ; genetics ; physiology ; Heat-Shock Proteins ; genetics ; Human Umbilical Vein Endothelial Cells ; Humans ; Hypoxia ; genetics ; physiopathology ; Male ; Rats ; Rats, Sprague-Dawley ; Taurodeoxycholic Acid ; pharmacology ; Transcription Factor CHOP ; genetics