NGF-induced phosphatidylinositol 3-kinase signaling pathway prevents thapsigargin-triggered ER stress-mediated apoptosis in PC12 cells

Heterogeneous enhancer states orchestrate β cell responses to metabolic stress

Obesity-induced β cell dysfunction contributes to the onset of type 2 diabetes. Nevertheless, elucidating epigenetic mechanisms underlying islet dysfunction at single cell level remains challenging. Here we profile single-nuclei RNA along with enhancer marks H3K4me1 or H3K27ac in islets from lean or obese mice. Our study identifies distinct gene signatures and enhancer states correlating with β cell dysfunction trajectory. Intriguingly, while many metabolic stress-induced genes exhibit concordant changes in both H3K4me1 and H3K27ac at their enhancers, expression changes of specific subsets are solely attributable to either H3K4me1 or H3K27ac dynamics. Remarkably, a subset of H3K4me1+H3K27ac- primed enhancers prevalent in lean β cells and occupied by FoxA2 are largely absent after metabolic stress. Lastly, cell-cell communication analysis identified the nerve growth factor (NGF) as protective paracrine signaling for β cells through repressing ER stress. In summary, our findings define the heterogeneous enhancer responses to metabolic challenges in individual β cells.

Neuroprotective Effects of Physical Activity via the Adaptation of Astrocytes

The multifold benefits of regular physical exercise have been largely demonstrated in human and animal models. Several studies have reported the beneficial effects of physical activity, both in peripheral tissues and in the central nervous system (CNS). Regular exercise improves cognition, brain plasticity, neurogenesis and reduces the symptoms of neurodegenerative diseases, making timeless the principle of “mens sana in corpore sano” (i.e., a healthy mind in a healthy body). Physical exercise promotes morphological and functional changes in the brain, acting not only in neurons but also in astrocytes, which represent the most numerous glial cells in the brain. The multiple effects of exercise on astrocytes comprise the increased number of new astrocytes, the maintenance of basal levels of catecholamine, the increase in glutamate uptake, the major release of trophic factors and better astrocytic coverage of cerebral blood vessels. The purpose of this review is to highlight the effects of exercise on brain function, emphasize the role of astrocytes in the healthy CNS, and provide an update for a better understanding of the effects of physical exercise in the modulation of astrocyte function.

Cerebrolysin enhances spinal cord conduction and reduces blood-spinal cord barrier breakdown, edema formation, immediate early gene expression and cord pathology after injury

Spinal cord evoked potentials (SCEP) are good indicators of spinal cord function in health and disease. Disturbances in SCEP amplitudes and latencies during spinal cord monitoring predict spinal cord pathology following trauma. Treatment with neuroprotective agents preserves SCEP and reduces cord pathology after injury. The possibility that cerebrolysin, a balanced composition of neurotrophic factors improves spinal cord conduction, attenuates blood-spinal cord barrier (BSCB) disruption, edema formation, and cord pathology was examined in spinal cord injury (SCI). SCEP is recorded from epidural space over rat spinal cord T9 and T12 segments after peripheral nerves stimulation. SCEP consists of a small positive peak (MPP), followed by a prominent negative peak (MNP) that is stable before SCI. A longitudinal incision (2mm deep and 5mm long) into the right dorsal horn (T10 and T11 segments) resulted in an immediate long-lasting depression of the rostral MNP with an increase in the latencies. Pretreatment with either cerebrolysin (CBL 5mL/kg, i.v. 30min before) alone or TiO₂ nanowired delivery of cerebrolysin (NWCBL 2.5mL/kg, i.v.) prevented the loss of MNP amplitude and even enhanced further from the pre-injury level after SCI without affecting latencies. At 5h, SCI induced edema, BSCB breakdown, and cell injuries were significantly reduced by CBL and NWCBL pretreatment. Interestingly this effect on SCEP and cord pathology was still prominent when the NWCBL was delivered 2min after SCI. Moreover, expressions of c-fos and c-jun genes that are prominent at 5h in untreated SCI are also considerably reduced by CBL and NWCBL treatment. These results are the first to show that CBL and NWCBL enhanced SCEP activity and thwarted the development of cord pathology after SCI. Furthermore, NWCBL in low doses has superior neuroprotective effects on SCEP and cord pathology, not reported earlier. The functional significance and future clinical potential of CBL and NWCBL in SCI are discussed.

Molecular mechanism of nur77 gene expression and downstream target genes in the early stage of forskolin-induced differentiation in PC12 cells

Forskolin promotes neuronal differentiation of PC12 cells via the PKA-CREB-dependent signaling pathway. Activation of PKA by forskolin phosphorylates CREB, which then binds to CRE sites in numerous gene promoters. However, it is unclear which gene contains the CRE sites responsible for forskolin-induced neuronal differentiation. In this study, we investigated how an immediate early gene, nur77, which has CRE sites in the promoter region, contributes to the early stage of differentiation of forskolin-treated PC12 cells. After treatment with forskolin, expression of Nur77 was upregulated within 1 hr. In addition, knockdown of nur77 inhibited neurite outgrowth induced by forskolin. We also revealed that the specific four CRE sites near the transcriptional start site (TSS) of nur77 were strongly associated with phosphorylated CREB within 1 hr after treatment with forskolin. To analyze the roles of these four sites, reporter assays using the nur77 promoter region were performed. The results showed that nur77 expression was mediated through three of the CRE sites, -242, -222, and -78, and that -78, the nearest of the three to the TSS of nur77, was particularly important. An analysis of neuronal markers controlled by Nur77 after A-CREB-Nur77-Synapsin1 signaling pathway plays a pivotal role in differentiation of forskolin-induced PC12 cells.

Nerve Growth Factor Induces Proliferation and Aggressiveness In Prostate Cancer Cells

Resistance to hormone therapy and disease progression is the major challenge in clinical management of prostate cancer (PC). Drugs currently used in PC therapy initially show a potent antitumor effects, but PC gradually develops resistance, relapses and spreads. Most patients who fail primary therapy and have recurrences eventually develop castration-resistant prostate cancer (CRPC), which is almost incurable. The nerve growth factor (NGF) acts on a variety of non-neuronal cells by activating the NGF tyrosine-kinase receptor, tropomyosin receptor kinase A (TrkA). NGF signaling is deregulated in PC. In androgen-dependent PC cells, TrkA mediates the proliferative action of NGF through its crosstalk with the androgen receptor (AR). Epithelial PC cells, however, acquire the ability to express NGF and TrkA, as the disease progresses, indicating a role for NGF/TrkA axis in PC progression and androgen-resistance. We here report that once activated by NGF, TrkA mediates proliferation, invasiveness and epithelial-mesenchymal transition (EMT) in various CRPC cells. NGF promotes organoid growth in 3D models of CRPC cells, and specific inhibition of TrkA impairs all these responses. Thus TrkA represents a new biomarker to target in CRPC.

2,5-Hexanedione mediates neuronal apoptosis through suppression of NGF via PI3K/Akt signaling in the rat sciatic nerve

Because precise mechanism for 2,5-hexanedione (HD)-induced neuronal apoptosis largely remains unknown, we explored the potential mechanisms both in vivo and in vitro Rats were intraperitoneally exposed to HD at different doses for 5 weeks, following which the expression levels of nerve growth factor (NGF), phosphorylation of Akt and Bad, dimerization of Bad and Bcl-xL, as well as the release of cytochrome c and the caspase-3 activity were measured. Moreover, these variables were also examined in vitro in HD-exposed VSC4.1 cells with or without a PI3K-specific agonist (IGF-1), and in HD-exposed VSC4.1 cells with or without a PI3K-specific inhibitor (LY294002) in the presence or absence of NGF. The data indicate that, as the concentration of HD increased, rats exhibited progressive gait abnormalities, and enhanced neuronal apoptosis in the rat sciatic nerve, compared with the results observed in the control group. Furthermore, HD significantly down-regulated NGF expression in the rat sciatic nerve. Moreover, suppression of NGF expression inhibited the phosphorylation of Akt and Bad. Meanwhile, an increase in the dimerization of Bad and Bcl-xL in mitochondria resulted in cytochrome c release and caspase-3 activation. In contrast, HD-induced apoptosis was eliminated by IGF-1. Additionally, NGF supplementation reversed the decrease in phosphorylation of Akt and Bad, as well as reversing the neuronal apoptosis in HD-exposed VSC4.1 cells. However, LY294002 blocked these effects of NGF. Collectively, our results demonstrate that mitochondrial-dependent apoptosis is induced by HD through NGF suppression via the PI3K/Akt pathway both in vivo and in vitro.

2,5-hexanedione downregulates nerve growth factor and induces neuron apoptosis in the spinal cord of rats via inhibition of the PI3K/Akt signaling pathway

2,5-hexanedione (2,5-HD) is the main active metabolite of n-hexane and induces apoptosis in nerve tissue, however, the mechanism of which remains unclear. In the present study, neuropathic animal models were successfully constructed in rats by injecting 100, 200 and 400 mg/kg 2,5-HD intraperitoneally for 5 weeks. Rats exposed to 2,5-HD exhibited progressive gait abnormalities and slower motor neural response in a dose-dependent manner. TUNEL analysis and immunofluorescence dual labeling revealed that the spinal cord of the 2,5-HD treated rats underwent significantly more apoptosis in the cells of spinal cord than that of the control group. The neuron apoptosis index in spinal cord was 4.1%, 6.7%, 9.8% respectively in rats exposed to 100, 200 and 400 mg/kg 2,5-HD, compared with 1.1% in the control group (p < 0.05). Biochemical analysis showed that 2,5-HD exposure downregulated NGF expression in the spinal cord of the intoxicated rats; inhibited the phosphorylation of Akt and Bad, two key players in PI3K/Akt pathway downstream of NGF; increased the dimerization of Bad with Bcl-xL in the mitochondrial fraction, followed by the release of cytochrome c and activation of caspase-3 in the spinal cord of rats. In vitro study showed that the NGF expression decreased significantly in VSC4.1 cells dosed with 5.0, 10.0 mM 2,5-HD in comparison with the control group. It was also found that NGF supplement repressed the induced apoptosis, and increased p-Akt and p-Bad level in 2,5-HD treated VSC4.1 cells, which could be antagonized by PI3K kinase (the upstream member of Akt) inhibitor LY294002. Taken together, our experimental results indicate that 2,5-HD may induce apoptosis in the spinal cord of rats via downregulating NGF expression and subsequently repressing PI3K/Akt signaling pathway.

Calpain-1 induces endoplasmic reticulum stress in promoting cardiomyocyte apoptosis following hypoxia/reoxygenation

Both calpain activation and endoplasmic reticulum (ER) stress are implicated in ischemic heart injury. However, the role of calpain in ER stress remains largely elusive. This study investigated whether calpain activation causes ER stress, thereby mediating cardiomyocyte apoptosis in an in vitro model of hypoxia/re-oxygenation (H/R). In neonatal mouse cardiomyocytes and rat cardiomyocyte-like H9c2 cells, up-regulation of calpain-1 sufficiently induced ER stress, c-Jun N-terminal protein kinase1/2 (JNK1/2) activation and apoptosis. Inhibition of ER stress or JNK1/2 prevented apoptosis induced by calpain-1. In an in vitro model of H/R-induced injury in cardiomyocytes, H/R was induced by a 24-hour hypoxia followed by a 24-hour re-oxygenation. H/R activated calpain-1, induced ER stress and JNK1/2 activation, and triggered apoptosis. Inhibition of calpain and ER stress blocked JNK1/2 activation and prevented H/R-induced apoptosis. Furthermore, blockade of JNK1/2 signaling inhibited apoptosis following H/R. The role of calpain in ER stress was also demonstrated in an in vivo model of ischemia/reperfusion using transgenic mice over-expressing calpastatin. In summary, calpain-1 induces ER stress and JNK1/2 activation, thereby mediating apoptosis in cardiomyocytes. Accordingly, inhibition of calpain prevents ER stress, JNK1/2 activation and apoptosis in H/R-induced cardiomyocytes. Thus, ER stress/JNK1/2 activation may represent an important mechanism linking calpain-1 to ischemic injury.

Nerve growth factor protects the ischemic heart via attenuation of the endoplasmic reticulum stress induced apoptosis by activation of phosphatidylinositol 3-kinase

BACKGROUND

Increased expression of nerve growth factor (NGF) has been found in the myocardium suffered from ischemia and reperfusion (I/R). The pro-survival activity of NGF on ischemic heart has been supposed to be mediated by phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling pathway. Endoplasmic reticulum (ER) stress, which is activated initially as a defensive response to eliminate the accumulated unfolded proteins, has shown a critical involvement in the ischemia induced myocardial apoptosis. This study was aimed to investigate whether NGF induced heart protection against I/R injury includes a mechanism of attenuation of ER stress-induced myocardial apoptosis by activation of PI3K/Akt pathway.

METHODS

Isolated adult rat hearts were perfused with a Langendörff perfusion system. Hearts in the Sham group were subjected to 225 min of continuous Krebs-Henseleit buffer (KHB) perfusion without ischemia. Hearts in I/R group were perfused with KHB for a 75-min of equilibration period followed by 30 min of global ischemia and 120 min of KHB reperfusion. Hearts in the NGF group accepted 45 min of euilibration perfusion and 30 min of NGF pretreatment (with a final concentration of 100 ng/ml in the KHB) before 30 min of global ischemia and 120 min of reperfusion. Hearts in K252a and LY294002 groups were pretreated with either a TrkA inhibitor, K252a or a phosphatidyl inositol 3-kinase inhibitor, LY294002 for 30 min before NGF (100 ng/ml) administration. Cardiac hemodynamics were measured from the beginning of the perfusion. Cardiac enzymes and cardiac troponin I (cTnI) were assayed before ischemia and at the end of reperfusion. Myocardial apoptosis rate was measured by TUNEL staining, and expression of glucose-related protein 78 (GRP78), CCAAT/enhancer-binding protein homologous protein (CHOP), caspase-12, total- and phospho-(Ser473)-Akt were assessed by Western blot analyses.

RESULTS

NGF pretreatment significantly improved the recovery of post-ischemia cardiac hemodynamics. Reduced creatine kinase-MB (CK-MB), lactate dehydrogenase (LDH) activity and cTnI levels, as well as decreased myocardial apoptosis ratio were observed in the NGF group. The improvement of NGF on recovery of cardiac function and alleviation of myocardial injury were completely abolished by K252a or LY294002. GRP78, caspase-12 and CHOP were highly expressed in ischemic myocardium, while NGF significantly inhibited the overexpression of these proteins which were involved in ER stress-induced myocardial apoptosis. NGF pretreatment also induced phosphorylation of Akt. When the activation of PI3K/Akt pathway is blocked by LY294002, the NGF induced suppression of the apoptosis-related proteins expression was reversed.

CONCLUSIONS

NGF pretreatment may protect the ischemic heart via inhibition of the ER stress-induced apoptosis; this pro-survival effect is mediated by PI3K/Akt pathway.

The histone deacetylase inhibitor trichostatin A induces neurite outgrowth in PC12 cells via the epigenetically regulated expression of the nur77 gene

Histone deacetylase (HDAC) inhibitors induce histone acetylation and gene expression by changing local chromatin structures. They can thereby influence various cells to proliferate or differentiate. It has been reported that trichostatin A (TSA) or valproic acid (VPA) can induce the neuronal differentiation of mouse embryonic neural stem cells and rat cerebellar granule cells. It is unclear however which gene is responsible for the neuronal differentiation induced by HDAC inhibitors. In this study, we investigated the contribution of immediate early gene (IEG) nur77 to the neuronal differentiation induced by TSA. We report that TSA induces neurite outgrowth in PC12 cells, and C646, an inhibitor of HAT (histone acetyl transferase) (p300), prevents TSA-induced neurite formation. The acetylation of the Lys14 residue of histone H3, and mRNA and protein expression of nur77 gene were found to be stimulated after treatment with TSA, but not in the presence of C646. A knock-down of nur77 inhibits the neurite outgrowth induced by TSA. Furthermore, the ectopic expression of nur77 significantly elicits neurite formation in PC12 cells. These results suggest that the expression of nur77, which is up-regulated via the TSA-induced acetylation of Lys14 on histone H3, is essential for the neuronal differentiation in TSA-induced PC12 cells.

Nerve growth factor improves functional recovery by inhibiting endoplasmic reticulum stress-induced neuronal apoptosis in rats with spinal cord injury

Background

Endoplasmic reticulum (ER) stress-induced apoptosis plays a major role in various diseases, including spinal cord injury (SCI). Nerve growth factor (NGF) show neuroprotective effect and improve the recovery of SCI, but the relations of ER stress-induced apoptosis and the NGF therapeutic effect in SCI still unclear.

Methods

Young adult female Sprague-Dawley rats’s vertebral column was exposed and a laminectomy was done at T9 vertebrae and moderate contusion injuries were performed using a vascular clip. NGF stock solution was diluted with 0.9% NaCl and administered intravenously at a dose of 20 μg/kg/day after SCI and then once per day until they were executed. Subsequently, the rats were executed at 1d, 3 d, 7d and 14d. The locomotor activities of SCI model rats were tested by the 21-point Basso-Beattie-Bresnahan (BBB) locomotion scale, inclined plane test and footprint analysis. In addition, Western blot analysis was performed to identify the expression of ER-stress related proteins including CHOP, GRP78 and caspase-12 both in vivo and in vitro. The level of cell apoptosis was determined by TUNEL in vivo and Flow cytometry in vitro. Relative downstream signals Akt/GSK-3β and ERK1/2were also analyzed with or without inhibitors in vitro.

Results

Our results demonstrated that ER stress-induced apoptosis was involved in the injury of SCI model rats. NGF administration improved the motor function recovery and increased the neurons survival in the spinal cord lesions of the model rats. NGF decreases neuron apoptosis which measured by TUNEL and inhibits the activation of caspase-3 cascade. The ER stress-induced apoptosis response proteins CHOP, GRP78 and caspase-12 are inhibited by NGF treatment. Meanwhile, NGF administration also increased expression of growth-associated protein 43 (GAP43). The administration of NGF activated downstream signals Akt/GSK-3β and ERK1/2 in ER stress cell model in vitro.

Conclusion

The neuroprotective role of NGF in the recovery of SCI is related to the inhibition of ER stress-induced cell death via the activation of downstream signals, also suggested a new trend of NGF translational drug development in the central neural system injuries which involved in the regulation of chronic ER stress.

Combined effects of multiple endoplasmic reticulum stresses on cytokine secretion in macrophage

Cells show various stress signs when they are challenged with severe physiological problems. Majority of such cellular stresses are conveyed to endoplasmic reticulum (ER) and unfolded protein response (UPR) serves as typical defense mechanism against ER stress. This study investigated an interaction between ER stress agents using macropage cell line Raw 264.7. When activated by lipopolysaccharide (LPS), the cell lines showed typical indicators of ER stress. Along with molecular chaperones, the activation process leads to the production of additional infl ammatory mediators. Following activation, the macrophage cell line was further treated with TUN and characterized in terms of chaperone expression and cytokine secretion. When treated with TUN, the activated macrophage cell leads to increased secretion of IL-6 although expression of ER stress markers, GRP94 and GRP78 increased. The secretion of cytokines continued until the addition of BFA which inhibits protein targeting from ER to Golgi. However, secretion of cytokines was ceased upon dual treatments with BFA and TG. This result strongly implies that cells may differently deal with various polypeptides depending on the urgency in cellular function under ER stress. Considering IL-6 is one of the most important signal molecules in macrophage, the molecule might be able to circumvent ER stress and UPR to reach its targeting site.

FGF-2 prevents cancer cells from ER stress-mediated apoptosis via enhancing proteasome-mediated Nck degradation

Induction of ER (endoplasmic reticulum) stress-mediated apoptosis in cancer cells represents an alternative approach for cancer therapy. Whether FGF-2 (fibroblast growth factor 2)-induced survival signals may interact with ER stress signalling in cancer cells remains elusive. In the present study, we showed that pretreatment with FGF-2 decreased the inhibition of DNA synthesis and induction of apoptosis by two different ER stress inducers, TM (tunicamycin) and TG (thapsigargin), in both human hepatoblastoma HepG2 cells and breast cancer MCF-7 cells. Pretreatment with FGF-2 prevented ER stress-mediated apoptosis by decreasing ER stress-induced CHOP [C/EBP (CCAAT/enhancer-binding protein)-homologous protein] expression. We further demonstrated that pretreatment with FGF-2 mediated the decrease in TM-induced CHOP expression and apoptosis through ERK1/2 (extracellular-signal-regulated kinases 1 and 2) pathway. Finally, we demonstrated that FGF-2 promoted proteasome-mediated degradation of Nck (non-catalytic region of tyrosine kinase adaptor protein), an SH (Src homology) 2/SH3-containing adaptor protein. Whereas overexpression of Nck1 decreased FGF-2-induced ERK1/2 phosphorylation to inhibit the effect of FGF-2 on TM-induced CHOP expression and apoptosis, a decrease in Nck expression prevented TM-induced CHOP expression and apoptosis. Taken together, the findings of the present study provide the first evidence that Nck plays a pivotal role in integrating FGF-2 and ER stress signals to counteract the ER stress deleterious effect on cancer cell survival.

Exogenous basic fibroblast growth factor inhibits ER stress-induced apoptosis and improves recovery from spinal cord injury

AIM

To investigate the mechanism of endoplasmic reticulum (ER) stress-induced apoptosis as well as the protective action of basic fibroblast growth factor (bFGF) both in vivo and in vitro.

METHODS AND RESULTS

ER stress-induced apoptosis was involved in the injuries of spinal cord injury (SCI) model rat. bFGF administration improved the recovery and increased the survival of neurons in spinal cord lesions in model rat. The protective effect of bFGF is related to the inhibition of CHOP, GRP78 and caspase-12, which are ER stress-induced apoptosis response proteins. bFGF administration also increased the survival of neurons and the expression of growth-associated protein 43 (GAP43), which is related to neural regeneration. The protective effect of bFGF is related to the activation of downstream signals, PI3K/Akt/GSK-3β and ERK1/2, especially in the ER stress cell model.

CONCLUSIONS

This is the first study to illustrate that the role of bFGF in SCI recovery is related to the inhibition of ER stress-induced cell death via the activation of downstream signals. Our work also suggested a new trend for bFGF drug development in central neural system injuries, which are involved in chronic ER stress-induced apoptosis.

Appearance of nuclear-sorted caspase-12 fragments in cerebral cortical and hippocampal neurons in rats damaged by autologous blood clot embolic brain infarctions

Following endoplasmic reticulum (ER) stress, cerebral infarctions have been reported to involve an apoptotic process, including the activation of the caspase cascade. To confirm whether fragmented caspase-12, which is activated by cleavage and is detectable during ER stress, is also involved in embolic cerebral infarctions in rats, we adopted an autologous blood clot model for the analysis of cerebral infarctions. We performed experiments in rats with brain infarctions, which are closely related to embolic cerebral infarctions. We utilized a homologous blood clot, i.e., natural materials, to form the infarct area. Our findings reveal that caspase-12 is fragmented when infarct areas form in cerebral cortical neurons. Interestingly, we observed that these fragments translocated to the nuclei of not only cerebral cortical neurons but hippocampal neurons. We further found that glucose-regulated protein 78 (GRP78), a marker of ER stress, is up-regulated in both cerebral cortical and hippocampal neurons during cerebral infarction. This result suggests that the fragmentation of caspase-12 and the subsequent nuclear translocation of these fragments are involved in the brain infarction process in rats.

Analysis of the role of nerve growth factor in promoting cell survival during endoplasmic reticulum stress in PC12 cells

Nerve growth factor (NGF) was first described by Rita Levi-Montalcini in the early 1960s from her studies of peripheral neurons. It has since been reported that NGF has the potential to elongate neurites or to prevent apoptosis via specific intracellular mechanisms. It has further been reported that as a component of these mechanisms, NGF binds to a specific receptor, TrkA, and thereby contributes to peripheral nerve cell functions or neuronal functions. It is noteworthy in this regard that pheochromocytoma 12 (PC12) cells express TrkA and respond to neurite outgrowth or anti-apoptotic signals by binding to NGF. Hence, PC12 cells have been used as an in vitro model system for the study of neuronal functions. It has been reported that endoplasmic reticulum (ER) stress is involved in neurodegenerative disorders, including Alzheimer's, Parkinson's, and Huntington's disease. The common link with regard to ER stress is that the neuronal cells die in these pathologies via specific intracellular mechanisms. This type of cell death, if it is apoptotic in nature, is termed ER stress-mediated apoptosis. In the process of ER stress-mediated apoptosis, the cleavage of pro-caspase-12 residing on the ER and the expression of glucose-regulated protein 78 (GRP78) can be observed. The expression of GRP78 protein is a characteristic of an unfolded protein response (UPR) via specific signal transduction pathways mediated by the unfolded protein response element (UPRE) in the upstream region of the grp78 gene so on. In ER stress-mediated apoptosis, a caspase cascade is also observed. To further clarify the mechanisms underlying ER stress-mediated apoptosis, a better understanding of the UPR is therefore important. In our current study, we describe a method for detecting gene induction via the UPR, focusing on GRP78 and caspase activities as the measurement end-points. The information generated by our method will accelerate our understanding of the pathophysiological processes leading to ER stress-mediated apoptosis.

Calpain and caspase processing of caspase-12 contribute to the ER stress-induced cell death pathway in differentiated PC12 cells

Neuronal cell death after traumatic brain injury, Alzheimer's disease and ischemic stroke may in part be mediated through endoplasmic reticulum (ER) stress and unfolded protein response (UPR). UPR results in induction of molecular chaperone GRP78 and the ER-resident caspase-12, whose activation has been proposed to be mediated by calpain and caspase processing, although their relative contribution remains unclear. In this study we induced ER stress with thapsigargin (TG), and determined the activation profile of calpain-2, caspase-3, caspase-7, and caspase-12 by analyses of protein levels, corresponding substrates and breakdown products (BDP). Specific calpain and caspase activity was assessed by analysis of αII-spectrin BDP of 145 kDa (SBDP145), BDP of 150 kDa (SBDP150) and BDP of 120 kDa (SBDP120). Decrease in pro-calpain-2 protein and increased SBDP145 levels by 3 h after TG treatment indicated early calpain activity. Active caspase-7 (p20) increase occurred after 8 h, followed by concomitant up-regulation of active caspase-3 and SBDP120 after 24 h. In vitro digestion experiments supported that SBDP120 was exclusively generated by active caspase-3 and validated that kinectin and co-chaperone p23 were calpain and caspase-7 substrates, respectively. Pro-caspase-12 protein processing by the specific action of calpain and caspase-3/7 was observed in a time-dependent manner. N-terminal pro-domain processing of pro-caspase-12 by calpain generated a 38 kDa fragment, while caspase-3/7 generated a 35 kDa fragment. Antibody developed specifically against the caspase-3/7 C-terminal cleavage site D(341) detected the presence of large subunit (p20) containing 23 kDa fragment that increased after 24 h of TG treatment. Significant caspase-12 enzyme activity was only detected after 24 h of TG treatment and was completely inhibited by caspase 3/7 inhibitor DEVD-fmk and partially by calpain inhibitor SNJ-1945. ER-stress-induced cell death pathway in TG-treated PC12 cells was characterized by up-regulation of GRP-78 and processing and activation of caspase-12 by the orchestrated proteolytic activity of calpain-2 and caspase-3/7.

Treadmill exercise suppresses muscle cell apoptosis by increasing nerve growth factor levels and stimulating p-phosphatidylinositol 3-kinase activation in the soleus of diabetic rats

We investigated the effects of treadmill exercise performed regularly for 6 weeks on the levels of nerve growth factor (NGF), tyrosine kinase A and p75 receptors, phosphatidylinositol 3-kinase (PI3-K), mitogen-activated protein kinase/extracellular signal-regulated kinase (Erk) 1,2, cyclic AMP response element-binding protein (CREB), and caspase-3 in the soleus of rats with streptozotocin (STZ)-induced diabetes. Thirty-two male Sprague-Dawley rats were divided into the following four groups: (1) normal control group (NCG; n = 8), (2) normal exercise group (NEG; n = 8), (3) diabetes control group (DCG; n = 8), and (4) diabetes exercise group (DEG; n = 8). Diabetes was induced by intraperitoneal injection of STZ (55 mg/kg dissolved in 0.05 M citrate buffer, pH 4.5). Rats were subjected to treadmill exercise 5 days a week for 6 weeks. The protein level of NGF significantly increased in the NEG and DEG (p < 0.001), whereas the levels of tyrosine kinase A and p75 receptors significantly increased in the NEG (p < 0.001). The levels of t-PI3-K, p-PI3-K, and p-CREB, and the p-CREB/t-CREB ratio significantly increased in the NEG (p < 0.001, respectively). The p-PI3-K/t-PI3-K ratio significantly increased in the DEG (p < 0.001). The p-Erk1/t-Erk1 ratio significantly increased in the NEG (p < 0.001), whereas the p-Erk2/t-Erk2 ratio significantly decreased in the DCG and DEG (p < 0.001). The caspase-3 level significantly increased in the DCG compared with that in the DEG (p < 0.001). These results suggest that treadmill exercise increases NGF levels and accelerates p-PI3-K activation in order to suppress apoptotic cell death in the soleus muscle of diabetic rats.

Dibutyryl-cAMP up-regulates nur77 expression via histone modification during neurite outgrowth in PC12 cells

An elevated level of cyclic AMP (cAMP) within cells activates gene expression through the cAMP-PKA-CREB pathway. Among the CREB target genes, some immediate early genes exist that are responsive to cAMP including the nur77 and c-fos genes. Treatment with dibutyryl-cAMP (dbcAMP) as well as nerve growth factor (NGF) induces neurite outgrowth in PC12 cells. Here, we report that acetylation of histone H3 was gradually stimulated after treatment with dbcAMP in PC12 cells and peaked 1 h after treatment. As the result of reverse transcription-polymerase chain reaction (RT-PCR) and quantitative real-time PCR (qPCR) experiments, both nur77 and c-fos gene expression were found to have peak 1 h after treatment. Knock-down with siRNA against nur77 mRNA inhibited the neurite outgrowth induced by dbcAMP, whereas knock-down with siRNA against c-fos mRNA did not inhibit the dbcAMP-induced neurite outgrowth. A chromatin immunoprecipitation (ChIP) assay revealed that the nur77 gene was associated with the acetylated Lys14 of histone H3 after treatment with dbcAMP. However, the amount of c-fos gene associated with acetylated histone H3 was not changed after treatment with dbcAMP. These results suggest that the expression of nur77, which is essential for the neuronal differentiation induced by dbcAMP, is up-regulated via dbcAMP-induced acetylation of the Lys14 of histone H3 in PC12 cells.

Nerve growth factor attenuates 2-deoxy-d-glucose-triggered endoplasmic reticulum stress-mediated apoptosis via enhanced expression of GRP78

The glucose analog 2-deoxy-d-glucose (2DG) depletes cells of glucose. Inhibition of glycosylation caused by glucose depletion induces endoplasmic reticulum (ER) stress with subsequent apoptosis. Glucose-regulated protein 78 (GRP78) is a molecular chaperone that acts within the ER. During ER stress, GRP78 expression is induced as part of the unfolded protein response (UPR). We found that nerve growth factor (NGF) prevented 2DG-triggered ER stress-mediated apoptosis, but not the induction of GRP78 expression, in PC12 cells. Surprisingly, GRP78 expression was further up-regulated when NGF was added to 2DG-treated PC12 cells. When a specific inhibitor of phosphatidylinositol 3-kinase (PI3-K), LY294002, was added to 2DG plus NGF-treated cells, both the effects of NGF on 2DG-induced apoptosis and GRP78 expression were significantly diminished. In addition, versipelostatin (VST), a specific inhibitor of GRP78 expression, and small interfering RNA (siRNA) against GRP78 mRNA also decreased both the effects of NGF on 2DG-induced apoptosis and GRP78 expression. RT-PCR and Western blot analyses revealed that enhanced production of nuclear p50 ATF6, but not spliced XBP1, mainly contributed to the NGF-induced enhancement of GRP78 expression in 2DG-treated cells. These results suggest that the NGF-activated PI3-K/Akt signaling pathway plays a protective role against ER stress-mediated apoptosis via enhanced expression of GRP78 in PC12 cells.

Forced, moderate-intensity treadmill exercise suppresses apoptosis by increasing the level of NGF and stimulating phosphatidylinositol 3-kinase signaling in the hippocampus of induced aging rats

While nerve growth factor (NGF) activates various signaling cascades, the phosphatidylinositol 3-kinase (PI3-K)/Akt pathway plays a pivotal role in controlling the survival of neurons, although this activity declines during the aging process. We investigated the effect of forced moderate-intensity treadmill exercise on the level of NGF and the PI3-K/Akt signaling pathway in the hippocampus of induced aging rats. Forty-five male Sprague-Dawley rats were divided into the following three groups: (1) control group, in which aging was not induced (CON: n=15), (2) aging-control group, in which aging was induced but the rats were not subjected to exercise (ACON: n=15), and (3) the aging-exercise group, in which aging was induced and the rats were subjected to treadmill exercise (AEX: n=15). d-Galactose (50mg/kg) was injected into the abdominal cavity for 8 weeks to induce aging. Rats were subjected to treadmill exercise 5 days a week for 8 weeks, and the speed of the treadmill was gradually increased. The protein levels of NGF, P-PI3-K, and P-Akt were significantly high in the AEX group (p<0.01, p<0.01, and p<0.001, respectively). Tyrosine kinase A (Trk A) receptor level was significantly higher in the CON and AEX groups than in the ACON group (p<0.01). TUNEL assay showed a significant reduction in apoptosis in the AEX group (p<0.001). Caspase-3 activation was significantly decreased in the AEX and CON groups (p<0.05). These results show that forced moderate-intensity treadmill exercise increases the level of NGF and activates P-PI3-K to induce P-Akt in order to suppress apoptotic cell death in the hippocampus of induced aging rats.

Nicotine suppresses tunicamycin-induced, but not thapsigargin-induced, expression of GRP78 during ER stress-mediated apoptosis in PC12 cells

We previously reported that nicotine protected against tunicamycin (Tm)-induced ER stress-mediated apoptosis, but not thapsigargin (Tg)-induced apoptosis in PC12 cells. In the present study, we report that the expression of glucose-regulated protein 78 (GRP78) was suppressed by nicotine in Tm-treated PC12 cells. Interestingly, the GRP78 expression was not changed by nicotine in Tg-treated cells. Moreover, nicotine reduced the activation of caspase-12 in Tm-treated cells, but not in Tg-treated cells. These results suggest that nicotine prevented Tm-induced ER stress-mediated apoptosis by attenuating an early stage of Tm-induced ER stress. It was possible that the suppression of GRP78 expression by nicotine was achieved through the suppression of the Ire1-XBP1 and/or ATF6 pathways. We observed that nicotine suppressed the Tm-induced, but not Tg-induced, splicing of XBP1 mRNA, and also suppressed the Tm-induced, but not Tg-induced, production of cleaved ATF6 in PC12 cells. These results indicate that the suppression of Ire1-XBP1 and ATF6 pathways contributes to the suppression of GRP78 expression by nicotine in Tm-treated PC12 cells, suggesting that nicotine suppresses a common step upstream of both the Ire1-XBP1 and ATF6 pathways which are required for the expression of GRP78 during Tm-induced ER stress.

Nerve growth factor blocks thapsigargin-induced apoptosis at the level of the mitochondrion via regulation of Bim

This study examined how the neurotrophin, nerve growth factor (NGF), protects PC12 cells against endoplasmic reticulum (ER) stress-induced apoptosis. ER stress was induced using thapsigargin (TG) that inhibits the sarcoplasmic/ER Ca2+-ATPase pump (SERCA) and depletes ER Ca2+ stores. NGF pre-treatment inhibited translocation of Bax to the mitochondria, loss of mitochondrial transmembrane potential, cytochrome c release, activation of caspases (-3, -7 and -9) and apoptosis induction by TG. Notably, TG also caused a marked induction of BimEL mRNA and protein, and knockdown of Bim with siRNA protected cells against TG-induced apoptosis. NGF delayed the induction and increased the phosphorylation of BimEL. NGF-mediated protection was dependent on phosphatidylinositol-3 kinase (PI3K) signalling since all above apoptotic events, including expression and phosphorylation status of BimEL protein, could be reverted by the PI3K inhibitor LY294002. In contrast, NGF had no effect on the TG-mediated induction of the unfolded protein response (increased expression of Grp78, GADD34, splicing of XBP1 mRNA) or ER stress-associated pro-apoptotic responses (induction of C/EBP homologous protein [CHOP], induction and processing of caspase-12). These data indicate that NGF-mediated protection against ER stress-induced apoptosis occurs at the level of the mitochondria by regulating induction and activation of Bim and mitochondrial translocation of Bax.

Thapsigargin-induced apoptosis was prevented by glycogen synthase kinase-3 inhibitors in PC12 cells

Uncontrolled calcium stress has been linked causally to a variety of neurodegenerative diseases, including ischemia, excitotoxicity and Alzheimer's disease. Thapsigargin, which increases [Ca2+]i, induces apoptotic cell death (chromatin condensation and DNA fragmentation) accompanied by caspase-3 activation in PC12 cells. We examined whether GSK-3 is involved in thapsigargin-induced cell death by using GSK-3 inhibitors in PC12 cells. Cells treated with 0.1 microM thapsigargin for 24h shrank. The injured cells underwent chromatin condensation and nuclear fragmentation, indicating apoptotic cell death. We assayed the effects of selective GSK-3 inhibitors, SB216763, azakenpaullone and alsteropaullone on thapsigargin-induced apoptosis. These inhibitors completely protected cells from thapsigargin-induced apoptosis. Alsterpaullone did not reduce the GRP78 protein expression induced by thapsigargin, suggesting that GSK-3 activation is not involved in induction of GRP78. In addition, GSK-3 inhibitors inhibited caspase-3 activation accompanied by thapsigargin-induced apoptosis. We showed in this report that thapsigargin-induced apoptosis is prevented by GSK-3 inhibitors, suggesting that thapsigargin induces caspase-dependent apoptosis mediated through GSK-3 activation in PC12 cells.