Browsing by Subject "endoplasmic reticulum stress"

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    Effects of knee loading on obesity‐related nonalcoholic fatty liver disease in an ovariectomized mouse model with high fat diet
    (Wiley, 2018) Tan, Nian; Li, Xinle; Zhai, Lidong; Liu, Daquan; Li, Jie; Yokota, Hiroki; Zhang, Ping; Anatomy and Cell Biology, School of Medicine
    Aim Hormonal and nutritional disorders are the main causes of obesity and nonalcoholic fatty liver disease, especially in the elderly and postmenopausal women. Although physical activity may alleviate these disorders, the elderly may often have difficulty in conducting physical exercise. The purpose of this study was to investigate the therapeutic effect of knee loading, a new form of physical stimulation, on the symptom of obesity and fatty liver. Methods Using ovariectomized mice with high fat diet, we evaluated the effect of knee loading that applies gentle cyclic loads to the knee. Female C57BL/6 mice were divided into five groups: control (SCD), high fat diet (HF), HF with loading (HF+L), HF with ovariectomy (HF+OVX), and HF+OVX with loading (HF+OVX+L). Except for SCD, mice underwent sham operation or ovariectomy and maintained on high fat diet. After 6 weeks, the mice in HF+L and HF+OVX+L were treated with 6‐week knee loading. Results Compared to the obesity groups (HF and HF+OVX), knee loading significantly decreased a gain in body weight, liver weight, and white adipose tissue (all P<0.01). It also reduced the lipid level in the serum (P<0.01) and histological severity of hepatic steatosis (P<0.01). Furthermore, knee loading downregulated biomarkers related to the endoplasmic reticulum stress (GRP78, p‐eIF2α and ATF4) and altered biomarkers in autophagy (LC3 and p62). Conclusions Knee loading suppressed obesity‐associated metabolic alterations and hepatic steatosis, the effect with knee loading might be associated with suppression of the ER stress and promotion of autophagy.
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    Prevention of glucocorticoid induced-apoptosis of osteoblasts and osteocytes by protecting against endoplasmic reticulum (ER) stress
    (Office of the Vice Chancellor for Research, 2014-04-11) Sato, A; Plotkin, L; Bellido, T
    Increased oxidative stress, such as with excess of glucocorticoids (GC) or during aging, has been associated with endoplasmic reticulum (ER) stress, due to accumulation of misfolded or unfolded proteins, leading to cellular apoptosis. The double-stranded RNA-activated protein kinase-like ER kinase (PERK) is activated to alleviate ER stress and phosphorylates the eukaryotic translation initiation factor 2 alpha subunit (eIF2α). Phosphorylated eIF2α in turn inhibits global protein translation to provide time to the ER to recover from the unfolded protein load, promoting cell viability. We hypothesized that the pro-apoptotic effect of GC on osteoblasts and osteocytes are at least in part due to induction of ER stress. To test this hypothesis, we used MLO-Y4 osteocytic cells, OB-6 osteoblastic cells, and primary osteoblastic cells derived from neonatal murine calvaria. We found that the synthetic GC dexamethasone (DEX) significantly increased the percentage of apoptotic cells in cultures of MLO-Y4, OB-6, and primary osteoblastic cells. Similarly, the specific ER-stress inducing agents brefeldin A, an inhibitor of ER-golgi apparatus vesicle transport, and tunicamycin, a protein glycosylation inhibitor, significantly increased OB-6 cell apoptosis. We then tested the effect of salubrinal, an agent that protects against ER stress by inhibiting the dephosphorylation of eIF2α, on bone cell apoptosis. Salubrinal blocked apoptosis induced by the ER stressors brefeldin A and tunicamycin in OB-6 cells. Salubrinal was also effective in blocking apoptosis induced by DEX in MLO-Y4, OB-6 and primary osteoblastic cells. Optimal responses were found at 10 μM salubrinal, after either 6 or 24 h. Guanabenz, another inhibitor of eIF2α dephosphorylation, also blocked DEX and tunicamycin-induced apoptosis of primary osteoblastic cells. Furthermore, addition of DEX to mineralizing OB-6 or primary osteoblastic cells markedly decreased mineral deposition and hydroxyapatite formation. In contrast, treatment with guanabenz increased mineralization of OB-6 cell cultures and prevented the inhibitory effect of DEX. We conclude that part of the pro-apoptotic actions of GC on osteoblastic cells are mediated through ER stress and that interventions that prevent dephosphorylation of eIF2α could potentially prevent the deleterious effects of GC on bone.
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    Role of endoplasmic reticulum stress in disuse osteoporosis
    (Elsevier, 2017-04) Li, Jie; Yang, Shuang; Li, Xinle; Liu, Daquan; Gao, Zhe; Zhao, Xiaoyu; Zhang, Jiuguo; Gou, Fanglin; Yokota, Hiroki; Zhang, Ping; Department of Biomedical and Applied Sciences, School of Dentistry
    Osteoporosis is a major skeletal disease with low bone mineral density, which leads to an increased risk of bone fracture. Salubrinal is a synthetic chemical that inhibits dephosphorylation of eukaryotic translation initiation factor 2 alpha (eIF2α) in response to endoplasmic reticulum (ER) stress. To understand possible linkage of osteoporosis to ER stress, we employed an unloading mouse model and examined the effects of salubrinal in the pathogenesis of disuse osteoporosis. The results presented several lines of evidence that osteoclastogenesis in the development of osteoporosis was associated with ER stress, and salubrinal suppressed unloading-induced bone loss. Compared to the age-matched control, unloaded mice reduced the trabecular bone area/total area (B.Ar/T.Ar) as well as the number of osteoblasts, and they increased the osteoclasts number on the trabecular bone surface in a time-dependent way. Unloading-induced disuse osteoporosis significantly increased the expression of Bip, p-eIF2α and ATF4 in short-term within 6 h of tail suspension, but time-dependent decreased in HU2d to HU14d. Furthermore, a significant correlation of ER stress with the differentiation of osteoblasts and osteoclasts was observed. Administration of salubrinal suppressed the unloading-induced decrease in bone mineral density, B.Ar/T.Ar and mature osteoclast formation. Salubrinal also increased the colony-forming unit-fibroblasts and colony-forming unit-osteoblasts. It reduced the formation of mature osteoclasts, suppressed their migration and adhesion, and increased the expression of Bip, p-eIF2α and ATF4. Electron microscopy showed that rough endoplasmic reticulum expansion and a decreased number of ribosomes on ER membrane were observed in osteoblast of unloading mice, and the abnormal ER expansion was significantly improved by salubrinal treatment. A TUNEL assay together with CCAAT/enhancer binding protein homologous protein (CHOP) expression indicated that ER stress-induced osteoblast apoptosis was rescued by salubrinal. Collectively, the results support the notion that ER stress plays a key role in the pathogenesis of disuse osteoporosis, and salubrinal attenuates unloading-induced bone loss by altering proliferation and differentiation of osteoblasts and osteoclasts via eIF2α signaling.