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At least 217 records · Page 12Linked to original sources
PubMed2006

Astroglial activation of extracellular-regulated kinase in early stages of Alzheimer disease.

Characterization of the earliest neuropathologic features of Alzheimer disease (AD) indicates that synaptic degeneration accompanied by tau hyperphosphorylation and amyloid deposition might be an important feature. The mechanisms involved are unclear; however, dysregulation of signaling cascades such as the extracellular signal-regulated kinase (ERK) pathway might play a role. In this context, the main objective of this study was to determine whether ERK hyperactivation occurs in early stages of AD. We compared the patterns of total and phosphorylated ERK (pERK) expression in the midfrontal cortex of patients clinically and neuropathologically characterized with early, intermediate, or advanced AD. Immunocytochemical and Western blot analysis showed that in early AD, there was extensive activation of ERK in astroglial cells in the white matter accompanied by intense astrogliosis. In contrast, in patients with more advanced AD, pERK immunoreactivity was associated with neuronal cell bodies and dystrophic neurites around plaques. Levels of astroglial pERK immunoreactivity in the white matter were strongly correlated with scores of cognitive performance (Blessed, Mini-Mental Status Examination, and Clinical Dementia Rating) and with the severity of AD neuropathology (Braak stage). These findings suggest that astroglial ERK activation may be an important early response to the onset of AD pathology. Identification of cell signaling events unique to early AD may provide therapeutic targets for the prevention or delay of dementia.

Aged↗
PubMed2003

Oxidative damage to the endoplasmic reticulum is implicated in ischemic neuronal cell death.

The endoplasmic reticulum (ER), which plays important roles in apoptosis, is susceptible to oxidative stress. Because reactive oxygen species (ROS) are robustly produced in the ischemic brain, ER damage by ROS may be implicated in ischemic neuronal cell death. We induced global brain ischemia on wild-type and copper/zinc superoxide dismutase (SOD1) transgenic rats and compared ER stress and neuronal damage. Phosphorylated forms of eukaryotic initiation factor 2 alpha (eIF2 alpha) and RNA-dependent protein kinase-like ER eIF2 alpha kinase (PERK), both of which play active roles in apoptosis, were increased in hippocampal CA1 neurons after ischemia but to a lesser degree in the transgenic animals. This finding, together with the finding that the transgenic animals showed decreased neuronal degeneration, indicates that oxidative ER damage is involved in ischemic neuronal cell death. To elucidate the mechanisms of ER damage by ROS, we analyzed glucose-regulated protein 78 (GRP78) binding with PERK and oxidative ER protein modification. The proteins were oxidatively modified and stagnated in the ER lumen, and GRP78 was detached from PERK by ischemia, all of which were attenuated by SOD1 overexpression. We propose that ROS attack and modify ER proteins and elicit ER stress response, which results in neuronal cell death.

Animals↗
PubMed2004

Cerebral ischemia and the unfolded protein response.

We review studies of endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) following cerebral ischemia and reperfusion (I/R). The UPR is a cell stress program activated when misfolded proteins accumulate in the ER lumen. UPR activation causes: (i) a PERK-mediated phosphorylation of eIF2alpha, inhibiting protein synthesis to prevent further accumulation of unfolded proteins in the ER and (ii) upregulation of genes coding for ER-resident enzymes and chaperones and others, via eIF2alpha(p), and ATF6 and IRE1 activation. UPR-induced transcription increases capacity of the ER to process misfolded proteins. If ER stress and the UPR are prolonged, apoptosis ensues. Multiple forms of ER stress have been observed following brain I/R. The UPR following brain I/R is not isomorphic between in vivo I/R models and in vitro cell culture systems with pharmacological UPR induction. Although PERK and IRE1 are activated in the initial hours of reperfusion, total PERK decreases, ATF6 is not activated, and there is delayed appearance of UPR-induced mRNAs. Thus, multiple damage mechanisms associated with brain I/R alter UPR expression and contribute to a pro-apoptotic phenotype in neurons. Insights resulting from these studies will be important for the development of therapies to halt neuronal death following brain I/R.

Animals↗
PubMed2005

OSBP is a cholesterol-regulated scaffolding protein in control of ERK 1/2 activation.

Oxysterol-binding protein (OSBP) is the founding member of a family of sterol-binding proteins implicated in vesicle transport, lipid metabolism, and signal transduction. Here, OSBP was found to function as a cholesterol-binding scaffolding protein coordinating the activity of two phosphatases to control the extracellular signal-regulated kinase (ERK) signaling pathway. Cytosolic OSBP formed a approximately 440-kilodalton oligomer with a member of the PTPPBS family of tyrosine phosphatases, the serine/threonine phosphatase PP2A, and cholesterol. This oligomer had dual specific phosphatase activity for phosphorylated ERK (pERK). When cell cholesterol was lowered, the oligomer disassembled and the level of pERK rose. The oligomer also disassembled when exposed to oxysterols. Increasing the amount of OSBP oligomer rendered cells resistant to the effects of cholesterol depletion and decreased the basal level of pERK. Thus, cholesterol functions through its interaction with OSBP outside of membranes to regulate the assembly of an oligomeric phosphatase that controls a key signaling pathway in the cell.

Binding Sites↗
PubMed2004

Activating transcription factor 4 is translationally regulated by hypoxic stress.

Hypoxic stress results in a rapid and sustained inhibition of protein synthesis that is at least partially mediated by eukaryotic initiation factor 2alpha (eIF2alpha) phosphorylation by the endoplasmic reticulum (ER) kinase PERK. Here we show through microarray analysis of polysome-bound RNA in aerobic and hypoxic HeLa cells that a subset of transcripts are preferentially translated during hypoxia, including activating transcription factor 4 (ATF4), an important mediator of the unfolded protein response. Changes in mRNA translation during the unfolded protein response are mediated by PERK phosphorylation of the translation initiation factor eIF2alpha at Ser-51. Similarly, PERK is activated and is responsible for translational regulation under hypoxic conditions, while inducing the translation of ATF4. The overexpression of a C-terminal fragment of GADD34 that constitutively dephosphorylates eIF2alpha was able to attenuate the phosphorylation of eIF2alpha and severely inhibit the induction of ATF4 in response to hypoxic stress. These studies demonstrate the essential role of ATF4 in the response to hypoxic stress, define the pathway for its induction, and reveal that GADD34, a target of ATF4 activation, negatively regulates the eIF2alpha-mediated inhibition of translation. Taken with the concomitant induction of additional ER-resident proteins identified by our microarray analysis, this study suggests an important integrated response between ER signaling and the cellular adaptation to hypoxic stress.

Activating Transcription Factor 4↗
PubMed2006

Functional coupling of p38-induced up-regulation of BiP and activation of RNA-dependent protein kinase-like endoplasmic reticulum kinase to drug resistance of dormant carcinoma cells.

It has been proposed that occult, disseminated metastatic cells are refractory to chemotherapy due to lack of proliferation. We have shown that p38 activation induces dormancy of squamous carcinoma cells. We now show that p38 signaling in these cells activates a prosurvival mechanism via the up-regulation of the endoplasmic reticulum (ER) chaperone BiP and increased activation of the ER stress-activated eukaryotic translation initiator factor 2alpha kinase RNA-dependent protein kinase-like ER kinase (PERK) allowing dormant tumor cells to resist drug toxicity. RNA interference and dominant-negative expression studies revealed that both BiP and PERK signaling promote survival and drug resistance of dormant cells, and that BiP up-regulation prevents Bax activation. We propose that stress-dependent activation of p38 via BiP up-regulation and PERK activation protects dormant tumor cells from stress insults, such as chemotherapy.

Apoptosis↗
PubMed2002

Pituitary adenylate cyclase activating polypeptide and neuropeptide Y regulation of gonadotropin subunit gene expression in tilapia: role of PKC, PKA and ERK.

There is ample information on the hypophysiotropic function of pituitary adenylate cyclase-activating polypeptide (PACAP) and neuropeptide Y (NPY) in fish as in mammals, although evidence as to their direct effects on gonadotropic cells is scarce. We have previously reported that NPY and PACAP38 augment gonadotropin-releasing hormone (GnRH)-induced expression of glycoprotein alpha (alpha) subunit gene in the teleost fish, tilapia. The aim of the present study was to elucidate possible direct effects of these peptides on gonadotropin subunit gene expression in culture of tilapia pituitary cells, as well as the transduction pathways involved. Both NPY and PACAP38 (0.001-10 nM) increased the level of phosphorylated extracellular signal-regulated kinase (pERK) dose-dependently, reaching a peak at 0.1 and 0.01 nM, respectively. Inhibition of protein kinase C (PKC) by GF109203X (GF; 0.01-10 nM) suppressed NPY-stimulated pERK levels and its effect on alpha and luteinizing hormone (LH) beta subunit mRNA levels. However, NPY had no effect on follicle stimulating hormone (FSH) beta mRNA levels. NPY-elevated alpha, LHbeta mRNA and pERK levels were also attenuated by inhibition of protein kinase A (PKA) with H89 (0.01-10 nM). Exposure of the cells to the MAPK kinase (MEK) inhibitor (PD98059; PD 10, 25 and 50 microM) completely blocked NPY-induced ERK activity. In addition, this inhibitor abated the alpha and LHbeta mRNA responses to NPY. Similar experiments conducted to elucidate PACAP38 signaling revealed that PACAP38 (0.01 nM) elevated all three-gonadotropin subunit gene expression via both PKC-ERK and PKA-ERK cascades. It is suggested that both NPY and PACAP38 act directly on gonadotropes to elevate gonadotropin subunit gene expression. Whereas the expression of alpha and LHbeta subunit genes is regulated by both NPY and PACAP, the effect on the FSHbeta transcript is elicited only by PACAP38. NPY and PACAP38 stimulatory actions are mediated via protein kinase C (PKC) and protein kinase A (PKA), converging at the MEK-ERK cascade. These findings represent one of the fine tuning levels that differentially regulates gonadotropin subunit gene expression.

Animals↗
PubMedDate not supplied

Diet restriction impairs extracellular signal-regulated kinase activation of peritoneal exudative cells after N-formyl-methionyl-leucyl-phenylalanine stimulation in a murine peritonitis model.

BACKGROUND: Phosphorylation of extracellular signal-regulated kinase (ERK) enhances various inflammatory responses in immune cells. It is unknown whether dysfunction of immune cells during malnutrition is attributed to derangement of ERK activation. METHODS: Male Institute of Cancer Research (ICR) mice received chow (146 g/kg per day, ad libitum or 36.5 g/kg per day, diet-restricted) for 7 days. Mice (n = 55) were given 6.5 mg/kg of an ERK inhibitor (PD98059) or vehicle intraperitoneally (IP), at 2 hours before cecal ligation and puncture (CLP). Survival was observed up to 60 hours. Detection of phosphorylated ERK (pERK) in the peritoneal exudative cells (PECs) was done as follows. In a separate study, PECs were harvested by peritoneal lavage 2 hours after an IP injection of 1% glycogen. PECs were incubated with or without 100 nmol/L N-formyl-methionyl-leucyl-phenylalanine (fMLP) for 1 minute. PEC ERK activation was detected with Western blot analysis (n = 38), by densitometric quantification, and with a laser scanning cytometer (LSC; n = 13). Subpopulations of PECs were determined by Wright-Giemsa staining. Unstimulated pERK expression was normalized to 100% for Western blot analysis. RESULTS: Diet restriction reduced survival after CLP compared with the ad libitum mice. ERK inhibition showed no effect on survival in diet-restricted mice but reduced survival in ad libitum mice. There were no differences in subpopulations of PECs 2 hours after glycogen injection between the groups. Western blot analysis revealed that fMLP stimulation significantly increased the phosphorylation of ERK1/2 in PECs from the ad libitum group (ERK1, 199 +/- 41%; ERK2, 211 +/- 49%; p < .03) but not in those from diet-restricted mice (ERK1, 98 +/- 10%; ERK2, 91 +/- 9%). Mean fluorescence intensity (MFI) of pERK in PECs obtained by LSC was significantly elevated after fMLP in the ad libitum group (from 19.4 +/- 1.5 MFI to 22.4 +/- 1.2 MFI; p < .05) but did not change in the diet-restricted group (from 19.4 +/- 1.8 MFI to 19.1 +/- 1.5 MFI). CONCLUSIONS: ERK activation is essential for survival in this murine sepsis model. Impaired ERK activation of PECs may, at least in part, impair host defense during malnutrition.

Animals↗
PubMed2005

Up-regulation of GRP78 and antiapoptotic signaling in murine peritoneal macrophages exposed to insulin.

The unfolded protein response pathway (UPR) compensates for excessive protein accumulation in the endoplasmic reticulum (ER). As insulin induces global protein synthesis, it may cause accumulation of unfolded proteins in the ER, thus triggering UPR. We assessed UPR activation in insulin-treated murine peritoneal macrophages using a number of markers including 78 kDa glucose response protein (GRP78), X-box-binding protein (XBP)-1, pancreatic ER kinase (PERK), eukaryotic initiation factor 2 (eIF2)alpha, and growth arrest and DNA damage (GADD)34. Exposure of cells to insulin activated UPR, as evidenced by an increased expression of GRP78, XBP-1, phosphorylated PERK (p-PERK), and p-eIF2alpha. The insulin-induced, elevated expression of GRP78 was comparable with that observed with tunicamycin, a classical inducer of ER stress. Concomitantly, insulin also up-regulated prosurvival mechanisms by elevating GADD34 and elements of the antiapoptotic pathway including Bcl-2, X-linked inhibitor of apoptosis, and phosphorylated forkhead transcription factor. In conclusion, we show here that insulin treatment does cause ER stress in macrophages, but insulin-dependent mechanisms overcome this ER stress by up-regulating UPR and the antiapoptotic pathway to promote cell survival.

Animals↗
PubMed2025

Matrine alleviates coronary microvascular dysfunction in ischemia with non-obstructive coronary artery disease mice induced by advanced glycation end products inhibition of the reactive oxygen species-mediated endoplasmic reticulum stress in cardiac microvascular endothelial cells.

OBJECTIVE: To investigate the protective effect of matrine on coronary microvascular dysfunction (CMD) induced by advanced glycation end products (AGEs) in a mouse model of ischemia with non-obstructive coronary artery disease (INOCA), with a focus on the underlying mechanisms, particularly the endoplasmic reticulum (ER) stress protein kinase R-like ER kinase (PERK)/ nuclear factor of activated T-cells (NFAT) signaling pathway. METHODS: An INOCA model was established in mice, and CMD was induced by peritoneal injections of AGEs. Matrine was administered daily via intraperitoneal injections. Coronary microcirculation was evaluated using coronary flow velocity reserve (CFVR), and cardiac microvascular endothelial cells (CMECs) were isolated for assessment of apoptosis, inflammation, oxidative stress, and microthrombosis. Markers of ER stress and the PERK/NFAT pathway were examined through immunoblotting, immunofluorescence, and enzymatic assays. The effect of matrine were further evaluated in CMECs treated with AGEs and the PERK agonist. RESULTS: Matrine treatment significantly improved CFVR and reduced CMD in AGEs-exposed INOCA mice. In CMECs, matrine attenuated AGEs-induced apoptosis, inflammation, and microthrombosis. It also suppressed intracellular reactive oxygen species (ROS) generation, ER stress markers, and PERK/NFAT signaling. Matrine's effects were concentration-dependent and partially reversed by the PERK agonist, confirming its action through the ER stress pathway. No significant toxicities were observed with matrine administration. CONCLUSION: Matrine attenuates AGEs-induced CMD in INOCA by suppressing the ROS-mediated ER stress PERK/NFAT signaling pathway in CMECs. This study highlights matrine's potential as a therapeutic agent for CMD in diabetic cardiovascular complications.

Animals↗
PubMed2002

Endoplasmic reticulum stress and the development of diabetes: a review.

The early steps of insulin biosynthesis occur in the endoplasmic reticulum (ER), and the beta-cell has a highly developed and active ER. All cells regulate the capacity of their ER to fold and process client proteins and they adapt to an imbalance between client protein load and folding capacity (so-called ER stress). Mutations affecting the ER stress-activated pancreatic ER kinase (PERK) and its downstream effector, the translation initiation complex eukaryotic initiation factor 2 (eIF2), have a profound impact on islet cell development, function, and survival. PERK mutations are associated with the Wolcott-Rallison syndrome of infantile diabetes and mutations that prevent the alpha-subunit of eIF2 from being phosphorylated by PERK, block beta-cell development, and impair gluconeogenesis. We will review this and other rare forms of clinical and experimental diabetes and consider the role of ER stress in the development of more common forms of the disease.

Animals↗
PubMed2006

The PERK/eIF2alpha/ATF4 module of the UPR in hypoxia resistance and tumor growth.

Hypoxia is a dynamic feature of the tumor microenvironment that contributes to cancer progression. In order to adapt and overcome hypoxic stress, tumor cells activate survival pathways that attempt to couple metabolic processes to reduced energy availability due to oxygen deprivation. While the hypoxia-inducible factors HIF-1 and HIF-2 are critical to the cellular response to hypoxia, HIF-independent processes are known to contribute to this adaptation. Recent evidence demonstrates that hypoxia activates components of the Unfolded Protein Response (UPR), a coordinated program that regulates cellular adaptation to increased levels of unfolded proteins in the endoplasmic reticulum (ER). Here we review the evidence implicating the ER kinase PERK, its downstream target translation initiation factor eIF2alpha, and the subsequent translational upregulation of the transcription factor ATF4 in this response. Not only are cells with compromised PERK-eIF2alpha-ATF4 signaling more sensitive to hypoxic stress in vitro but they also form tumors that grow slower in vivo with smaller hypoxic areas, indicating that the PERK-eIF2alpha-ATF4 pathway confers a survival advantage for tumor cells under hypoxia. These results, together with evidence for an involvement of other UPR pathways and ER stress proteins in hypoxia tolerance and tumor maintenance, point to a central role for UPR activation in tumor progression and suggest that this response may offer an attractive target for new anti-tumor modalities.

Activating Transcription Factor 4↗
PubMed2003

[Involvement of unfolded protein responses in neurodegeneration].

Various stresses cause the accumulation of unfolded proteins in the endoplasmic reticulum (ER). To manage the state, cells have the unfolded protein responses (UPR). If the UPR is unsuccessful, ER-mediated apoptosis occurs. To date, three types of UPR, i.e. the induction of chaperones, the translation block, and ER-associated degradation (ERAD) have been reported. To sense the accumulation of unfolded proteins, the ER has IRE1, PERK, and ATF6. The pathways mediated by IRE1 and ATF6 cause the induction of chaperones. The pathway mediated by PERK causes a translation block. The induction of caspase 12, the activation of the JNK pathway, and the induction of CHOP have been reported as apoptosis caused by ER stress. The stability of the cell is based on the balance between UPR and ER-mediated apoptosis. Recently several diseases have been reported to be related to ER stress. We reported that mutant presenilin 1 causes a vulnerability to ER stress because it attenuates the activation of IRE1, PERK, and ATF6. Recent reports have also shown that Parkinson disease and polyglutamine diseases are relevant to ER stress. Therefore it is suggested that the ER stress story is the common mechanism for neurodegerative disorders.

Activating Transcription Factor 6↗
PubMed2006

Growth and activation of PI-3K/PKB and Akt by stromal cell-derived factor 1alpha in endometrial carcinoma cells with expression of suppressor endoprotein PTEN.

BACKGROUND: Mutation or deletion in the phosphatase and tensin homologue deleted on chromosome ten (PTEN) gene has been identified as an important cause of endometrial carcinoma; stromal cell derived factor-1alpha (SDF-1alpha) exerts growth-promoting effects on endometrial cancer cells through activation of the PI-3 kinase/Akt pathway and downstream effectors such as extracellular-responsive kinase (ERK). In this study, a plasmid containing the PTEN gene was transfected into Ishikawa cells to investigate the difference in growth and signal transduction between Ishikawa-PTEN and Ishikawa cells after SDF-1alpha stimulation, and to study mechanisms of the involvement of PTEN protein in endometrial carcinoma development. METHODS: Ishikawa cells were transfected with a plasmid (pLXSN-PTEN) containing the PTEN gene and a plasmid (pLXSN-EGFP) with enhanced green fluorescent protein (EGFP). Cells were then screened to obtain Ishikawa-PTEN cells and Ishikawa-neo cells that can both stably express PTEN protein and EGFP. Expression of PTEN protein, phosphorylation levels of AKT and ERK (pAKT and pERK) and growth differences in Ishikawa-PTEN, Ishikawa-neo and Ishikawa cells before and after SDF-1alpha stimulation were then determined by Western blots and MTT assays. RESULTS: Western blot analysis showed that Ishikawa cells produced PTEN after transfection with the PTEN gene. At 15 minutes after SDF-1alpha stimulation, the pAKT level of Ishikawa-PTEN cells was lower than that of Ishikawa-neo cells and Ishikawa cells. There was no significant difference in pERK levels among the three cell lines. The positive effect of SDF-1alpha on Ishikawa-PTEN cells growth was markedly less than the effect on Ishikawa-neo and Ishikawa cells. However, in the absence of SDF-1alpha stimulation (baseline), the pAKT level in Ishikawa-PTEN cells was less than that in Ishikawa cells. There was a significant difference in growth between the Ishikawa-PTEN cells and the Ishikawa-neo cells. CONCLUSIONS: PTEN gene transfection can regulate the level of pAKT but not pERK in Ishikawa-PTEN cells. PTEN protein may suppress the growth-promoting effect of SDF-1alpha on endometrial carcinoma by inhibiting the PI-3K/AKT signal transduction pathway.

Cell Line, Tumor↗
PubMed2005

Photoreceptor synapses degenerate early in experimental choroidal neovascularization.

Severe visual loss in patients with age-related macular degeneration is associated with the development of choroidal neovascularization (CNV). The pathogenic mechanisms for CNV formation have been extensively investigated, but remarkably little research has addressed the mechanisms for dysfunction of the retina in CNV. Using laser-induced CNV in mice, we evaluated the mechanisms of retinal dysfunction. At 3 days, 1 week, 2 weeks, and 4 weeks after laser application, retinas under experimental CNV were characterized physiologically (ERG recordings, synaptic uptake of the exocytotic marker FM1-43, and light-induced translocation of transducin), histologically, and immunohistochemically. ERG amplitudes were reduced by 20% at 1 week after CNV. Depolarization-induced FM1-43 uptake in photoreceptor synapses was selectively reduced by 45% at 1 week after CNV. Although photoreceptor outer segments were shortened by 36%, light adaptation as measured by transducin translocation was mostly preserved. Early in CNV (3 days to 1 week), Muller cells demonstrated induction of c-fos and pERK expression. Also, the density of macrophage-like, F4/80 immunoreactive cells increased approximately 3-fold. Minimal photoreceptor death occurred during the first week, and was variable thereafter. At later times in CNV formation (> or =2 weeks), expression of photoreceptor synaptic markers was reduced in the outer plexiform layer, indicating loss of photoreceptor synaptic terminals. ERG amplitudes, synaptic uptake of FM1-43, and the induction of c-fos and pERK in Muller cells were altered within 1 week of experimental CNV, suggesting that during CNV formation, deficits in retinal function, in particular photoreceptor synaptic function, precede degeneration of photoreceptor terminals and photoreceptor cell death.

Adaptation, Ocular↗
PubMed2005

Divergent stress responses to IL-1beta, nitric oxide, and tunicamycin by chondrocytes.

As the only cell in cartilage responsible for matrix synthesis, the chondrocyte's viability is crucial to healthy tissue. It must tolerate stresses from both mechanical and cellular sources. This study examines the endoplasmic reticulum (ER) stress response in chondrocytes after exposure to IL-1beta, nitric oxide, or tunicamycin in order to determine whether this form of stress causes cell death. Cultures of the immortalized human juvenile costal chondrocyte cell line, C-28/I2, were treated with IL-1beta, S-nitroso-N-acetylpenicillamine (SNAP), and tunicamycin. Increasing intracellular nitric oxide levels by SNAP treatment or inhibiting protein folding in the ER lumen by tunicamycin induced the ER stress response as evidenced by increased protein and gene expression of GADD153 as well as PERK and eIF2-alpha phosphorylation, and resulted in apoptosis. IL-1beta treatment induced PERK and eIF2-alpha phosphorylation, but not GADD153 expression or apoptosis. The ER stress signaling pathway of IL-1beta involved iNOS because blocking its expression, inhibited ER stress gene expression. Therefore, inducing the ER stress response in chondrocytes results in divergent responses depending on the agent used. Even though IL-1beta, a common proinflammatory cytokine, induces the ER stress response, it is not proapoptotic to chondrocytes. On the other hand, exposure to high levels of intracellular nitric oxide induce chondrocyte apoptosis as part of the ER stress response.

Activating Transcription Factor 4↗
PubMed2004

Acute and persistent protein synthesis inhibition following cerebral reperfusion.

Lack of recovery from protein synthesis inhibition (PSI) closely correlates with neuronal death following brain ischemia and reperfusion. It has therefore been suggested that understanding the mechanisms of PSI will shed light on the mechanisms of selective neuronal death following ischemia and reperfusion. It is now known that the PKR-like ER kinase (PERK)-mediated phosphorylation of eukaryotic initiation factor 2alpha (eIF2alpha) causes translation inhibition at initial reperfusion. Activation of PERK, in turn, indicates endoplasmic reticulum stress and activation of the unfolded protein response. However, phosphorylation of eIF2alpha is a transient event and can account for PSI only in the initial hours of reperfusion. Although a number of other regulators of protein synthesis, such as eIF4F, 4EBP-1, eEF-2, and S6 kinase, have been assessed following cerebral ischemia and reperfusion, the causes of prolonged PSI have yet to be fully elucidated. The purpose of the present article is to bring together the evidence indicating that, at minimum, postischemic PSI should be conceptualized as consisting of two components: an acute, transient component mediated by unfolded protein response-induced eIF2alpha phosphorylation and a longer term component that correlates with neuronal death. Ischemic tolerance appears to separate the acute and persistent components of reperfusion-induced translation inhibition. Specific models of the relationship among acute PSI, persistent PSI, and neuronal death are presented to clarify issues that have emerged from ongoing work in this area.

Animals↗
PubMed2005

A group of neurokinin-1 receptor-immunoreactive neurons expressing phospho-extracellular signal-regulated protein kinases in the pre-Bötzinger complex of rats.

Extracellular-signal-regulated kinases (ERKs) were described originally as critical regulators of cell growth and differentiation. ERKs have received increasing attention as important regulators of neuronal function, especially in synaptic plasticity and memory. We found a group of phospho-ERK1/2 (pERK1/2)-immunoreactive (ir) neurons in the ventrolateral medulla oblongata of adult rats. In the pre-Botzinger complex (pre-BotC) region, identified by neurokinin-1 receptor (NK1R) immunoreactivity, the distribution of pERK1/2-ir neurons seemed to overlap with that of NK1R-ir neurons. A detailed study combining immunofluorescence and immunogold-silver staining was designed to determine whether ERK-ir neurons were NK1R-ir and related to respiratory function in the pre-BotC. The pERK1/2 immunoreactivity was present mainly in somas and processes of small- to medium-sized neurons. Of pERK1/2-ir neurons in the pre-BotC, 19.7% were NK1R-ir. Some of the small, fusiform, NK1R-ir neurons, the putative rhythmogenic neurons, were also pERK1/2-ir. Under the electron microscope, immunogold particles indicative of pERK1/2 immunoreactivity were found in somas and dendrites in pre-BotC neurons. They were associated mainly with rough endoplasmic reticula and ribosomes. Immunogold particles could also be found in nuclei, but were absent from nucleoli. The existence of pERK1/2 in a subtype of NK1R-ir pre-BotC neurons implies that the pERK cascade may play a role in normal respiratory activity in adult rats. The pERK cascade may also participate in sympathoexcitatory activity, given that 42.2% of pERK1/2-ir neurons expressed tyrosine hydroxylase, a marker of C1 adrenergic neurons in the ventrolateral medulla oblongata.

Animals↗