Identification of an axotomy-induced glycosylated protein, AIGP1, possibly involved in cell death triggered by endoplasmic reticulum-Golgi stress

SERINC5 as a New Restriction Factor for Human Immunodeficiency Virus and Murine Leukemia Virus

SERINC genes encode for homologous multipass transmembrane proteins with unknown cellular function, despite being highly conserved across eukaryotes. Among the five SERINC genes found in humans, SERINC5 was shown to act as a powerful inhibitor of retroviruses. It is efficiently incorporated into virions and blocks the penetration of the viral core into target cells, by impairing the fusion process with a yet unclear mechanism. SERINC5 was also found to promote human immunodeficiency virus 1 (HIV-1) virion neutralization by antibodies, indicating a pleiotropic activity, which remains mostly unexplored. Counteracting factors have emerged independently in at least three retrovirus lineages, underscoring their fundamental importance during retrovirus evolution. Nef and S2 of primate and equine lentiviruses, and glycoGag of gammaretroviruses, act similarly by targeting SERINC5 to endosomes and excluding it from virions. Here, we discuss the features that distinguish SERINC5 from other known restriction factors, delineating a yet unique class of antiviral inhibitors.

cAMP-induced activation of protein kinase A and p190B RhoGAP mediates down-regulation of TC10 activity at the plasma membrane and neurite outgrowth

Cyclic AMP plays a pivotal role in neurite growth. During outgrowth, a trafficking system supplies membrane at growth cones. However, the cAMP-induced signaling leading to the regulation of membrane trafficking remains unknown. TC10 is a Rho family GTPase that is essential for specific types of vesicular trafficking. Recent studies have shown a role of TC10 in neurite growth in NGF-treated PC12 cells. Here, we investigated a mechanical linkage between cAMP and TC10 in neuritogenesis. Plasmalemmal TC10 activity decreased abruptly after cAMP addition in neuronal cells. TC10 was locally inactivated at extending neurite tips in cAMP-treated PC12 cells. TC10 depletion led to a decrease in cAMP-induced neurite outgrowth. Constitutively active TC10 could not rescue this growth reduction, supporting our model for a role of GTP hydrolysis of TC10 in neuritogenesis by accelerating vesicle fusion. The cAMP-induced TC10 inactivation was mediated by PKA. Considering cAMP-induced RhoA inactivation, we found that p190B, but not p190A, mediated inactivation of TC10 and RhoA. Upon cAMP treatment, p190B was recruited to the plasma membrane. STEF depletion and Rac1-N17 expression reduced cAMP-induced TC10 inactivation. Together, the PKA-STEF-Rac1-p190B pathway leading to inactivation of TC10 and RhoA at the plasma membrane plays an important role in cAMP-induced neurite outgrowth.

Efficient labeling in vitro with non-ionic gadolinium magnetic resonance imaging contrast agent and fluorescent transfection agent in bone marrow stromal cells of neonatal rats

Although studies have been undertaken on gadolinium labeling-based molecular imaging in magnetic resonance imaging (MRI), the use of non-ionic gadolinium in the tracking of stem cells remains uncommon. To investigate the efficiency in tracking of stem cells with non-ionic gadolinium as an MRI contrast agent, a rhodamine-conjugated fluorescent reagent was used to label bone marrow stromal cells (BMSCs) of neonatal rats in vitro, and MRI scanning was undertaken. The fluorescent-conjugated cell uptake reagents were able to deliver gadodiamide into BMSCs, and cell uptake was verified using flow cytometry. In addition, the labeled stem cells with paramagnetic contrast medium remained detectable by an MRI monitor for a minimum of 28 days. The present study suggested that this method can be applied efficiently and safely for the labeling and tracking of bone marrow stromal cells in neonatal rats.

ATF4 orchestrates a program of BH3-only protein expression in severe hypoxia

Intratumoral hypoxia is associated with poor prognosis, regardless of the mode of therapy. Cancer cells survive this condition through activating several adaptive signaling pathways, including the integrated stress response (ISR) and autophagy. Activating transcription factor 4 (ATF4) is the major transcriptional mediator of the ISR, which we have shown to be involved in autophagy regulation to protect cells from severe hypoxia. Here we demonstrate that ATF4 orchestrates a program of BH3-only protein expression in severe hypoxia. We find that the BH3-only proteins HRK, PUMA, and NOXA are transcriptionally induced in severe hypoxia and that their expression is abrogated by RNA interference against ATF4. In particular, we show that the BH3-only protein harakiri (HRK) is transactivated by ATF4 in severe hypoxia through direct binding of ATF4 to the promoter region. Furthermore, we demonstrate through siRNA knockdown that HRK induces autophagy and promotes cancer cell survival in severe hypoxia.

Differential effects of unfolded protein response pathways on axon injury-induced death of retinal ganglion cells

Loss of retinal ganglion cells (RGCs) accounts for visual function deficits after optic nerve injury, but how axonal insults lead to neuronal death remains elusive. By using an optic nerve crush model that results in the death of the majority of RGCs, we demonstrate that axotomy induces differential activation of distinct pathways of the unfolded protein response in axotomized RGCs. Optic nerve injury provokes a sustained CCAAT/enhancer binding homologous protein (CHOP) upregulation, and deletion of CHOP promotes RGC survival. In contrast, IRE/XBP-1 is only transiently activated, and forced XBP-1 activation dramatically protects RGCs from axon injury-induced death. Importantly, such differential activations of CHOP and XBP-1 and their distinct effects on neuronal cell death are also observed in RGCs with other types of axonal insults, such as vincristine treatment and intraocular pressure elevation, suggesting a new protective strategy for neurodegeneration associated with axonal damage.

C12 derivatives of the hydroperoxide lyase pathway are produced by product recycling through lipoxygenase-2 in Nicotiana attenuata leaves

In response to diverse stresses, the hydroperoxide lyase (HPL) pathway produces C(6) aldehydes and 12-oxo-(9Z )-dodecenoic acid ((9Z )-traumatin). Since the original characterization of (10E )-traumatin and traumatic acid, little has been added to our knowledge of the metabolism and fluxes associated with the conversion of (9Z )-traumatin into diverse products in response to wounding and herbivory. A liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) method was developed to quantify C(12) derivatives of the HPL pathway and to determine their metabolism after wounding and simulated herbivory in Nicotiana attenuata leaves. Ninety-eight per cent of the (9Z )-traumatin produced was converted to 9-hydroxy-(10E )-traumatin (9-OH-traumatin); two-thirds by product recycling through lipoxygenase-2 (NaLOX2) activity and one-third by nonenzymatic oxidation. Thirty-eight per cent of the de novo produced 9-OH-traumatin was conjugated to glutathione, consistent with this oxylipin being a reactive electrophile species. 12-OH-(9Z )-dodecenoic and dodecenedioic acids also showed rapid increases after wounding and simulated herbivory and a role for C(12) derivatives as signals in these processes was consistent with their ability to elicit substantial changes in gene expression. These results underscore the importance of metabolite reflux through LOX2, an insight which creates new opportunities for a functional understanding of C(12) derivatives of the HPL pathway in the regulation of stress responses.

Endothelin/endothelin-B receptor signals regulate ventricle-directed interkinetic nuclear migration of cerebral cortical neural progenitors

We determined the expression profile of ∼300 G protein-coupled receptors (GPCRs) in embryonic cortical neural progenitor cells (NPCs) and identified a number of highly expressed GPCRs, among which endothelin-B receptor (ET(B)-R) was expressed at the highest level. We also revealed that endothelins (ETs) were predominantly expressed in CD31-positive endothelial cells of the embryonic cerebral cortex. Activation of ET(B)-R induced NPC assembly in vitro by promoting fibronectin-dependent-motility and N-cadherin-associated cell contact. NPC assembly also required a Rho-family GTPase(s) and phosphatidylinositol-3-kinase. In the embryonic cerebral cortex, a specific ET(B)-R agonist, IRL-1620, accelerated interkinetic nuclear migration (INM) of NPCs toward the ventricular wall (VW) ex vivo. Conversely, a specific ET(B)-R antagonist, BQ788, slowed INM, thereby inducing mislocalization of phospho-histone H3-positive M-phase nuclei in the ventricular zone (VZ) and decreasing the number of Tuj1-positive newborn neurons. Our results suggest that ET(B)-R-mediated assembly signals drive INM that precedes neurogenesis.

Kinin B1 receptor enhances the oxidative stress in a rat model of insulin resistance: outcome in hypertension, allodynia and metabolic complications

Background

Kinin B₁ receptor (B₁R) is induced by the oxidative stress in models of diabetes mellitus. This study aims at determining whether B₁R activation could perpetuate the oxidative stress which leads to diabetic complications.

Methods and Findings

Young Sprague-Dawley rats were fed with 10% D-Glucose or tap water (controls) for 8–12 weeks. A selective B₁R antagonist (SSR240612) was administered acutely (3–30 mg/kg) or daily for a period of 7 days (10 mg/kg) and the impact was measured on systolic blood pressure, allodynia, protein and/or mRNA B₁R expression, aortic superoxide anion (O₂^•−) production and expression of superoxide dismutase (MnSOD) and catalase. SSR240612 reduced dose-dependently (3–30 mg/kg) high blood pressure in 12-week glucose-fed rats, but had no effect in controls. Eight-week glucose-fed rats exhibited insulin resistance (HOMA index), hypertension, tactile and cold allodynia and significant increases of plasma levels of glucose and insulin. This was associated with higher aortic levels of O₂^•−, NADPH oxidase activity, MnSOD and catalase expression. All these abnormalities including B₁R overexpression (spinal cord, aorta, liver and gastrocnemius muscle) were normalized by the prolonged treatment with SSR240612. The production of O₂^•− in the aorta of glucose-fed rats was also measured in the presence and absence of inhibitors (10–100 µM) of NADPH oxidase (apocynin), xanthine oxidase (allopurinol) or nitric oxide synthase (L-NAME) with and without Sar[D-Phe⁸]des-Arg⁹-BK (20 µM; B₁R agonist). Data show that the greater aortic O₂^•− production induced by the B₁R agonist was blocked only by apocynin.

Conclusions

Activation of kinin B₁R increased O₂^•− through the activation of NADPH oxidase in the vasculature. Prolonged blockade of B₁R restored cardiovascular, sensory and metabolic abnormalities by reducing oxidative stress and B₁R gene expression in this model.

Microarray analysis of somatostatin receptor 5-regulated gene expression profiles in murine pancreas

BACKGROUND

We previously demonstrated that somatostatin receptor type 5 (SSTR5) gene ablation results in alterations in insulin secretion and glucose metabolism, accompanied by morphologic alterations in the islets of Langerhans. The underlying mechanism(s) by which SSTR5 exerts its cellular functions remain(s) unknown. We hypothesized that SSTR5 mediates the inhibitory effect of somatostatin (SST) on insulin secretion and islet proliferation by regulating a specific set of pancreatic genes.

METHODS

To identify SSTR5-regulated pancreatic genes, gene expression microarray analysis was performed on the whole pancreas of 1- and 3-month-old wild-type (WT) and SSTR5 knockout (SSTR5-/-) male mice. Real-time RT-PCR and immunofluorescence were performed to validate selected differentially expressed genes.

RESULTS

A set of 143 probes were identified to be differentially expressed in the pancreas of 1-month-old SSTR5-/- mice, 72 of which were downregulated and 71 upregulated. At 3 months of age, SSTR5 gene ablation resulted in downregulation of a set of 30 probes and upregulation of a set of 37 probes. Among these differentially expressed genes, there were 15 and 5 genes that were upregulated and downregulated, respectively, in mice at both 1 and 3 months of age. Three genes, PAP/INGAP, ANG, and TDE1, were selected to be validated by real-time RT-PCR and immunofluorescence.

CONCLUSIONS

A specific set of genes linked to a wide range of cellular functions such as islet proliferation, apoptosis, angiogenesis, and tumorigenesis were either upregulated or downregulated in SSTR5-deficient male mice compared with their expression in wild-type mice. Therefore, these genes are potential SSTR5-regulated genes during normal pancreatic development and functional maintenance.

Clock genes regulate neurogenic transcription factors, including NeuroD1, and the neuronal differentiation of adult neural stem/progenitor cells

The circadian clock system plays multiple roles in our bodies, and clock genes are expressed in various brain regions, including the lateral subventricular zone (SVZ) where neural stem/progenitor cells (NSPCs) persist and postnatal neurogenesis continues. However, the functions of clock genes in adult NSPCs are not well understood. Here, we first investigated the expression patterns of Clock and Bmal1 in the SVZ by immunohistochemistry and then verified how the expression levels of 17 clock and clock-related genes changed during differentiation of cultured adult NSPCs using quantitative RT-PCR. Finally, we used RNAi to observe the effects of Clock and Bmal1 on neuronal differentiation. Our results revealed that Clock and Bmal1 were expressed in the SVZ and double-stained with the neural progenitor marker Nestin and neural stem marker GFAP. In cultured adult NSPCs, the clock genes changed their expression patterns during differentiation, and interestingly, Bmal1 started endogenous oscillation. Moreover, gene silencing of Clock or Bmal1 by RNAi decreased the percentages of neuronal marker Map2-positive cells and expression levels of NeuroD1 mRNA. These findings suggest that clock genes are involved in the neuronal differentiation of adult NSPCs and may extend our understanding of various neurological/psychological disorders linked to adult neurogenesis and circadian rhythm.

Cellular localization of kinin B1 receptor in the spinal cord of streptozotocin-diabetic rats with a fluorescent [Nalpha-Bodipy]-des-Arg9-bradykinin

Background

The kinin B₁ receptor (B₁R) is upregulated by pro-inflammatory cytokines, bacterial endotoxins and hyperglycaemia-induced oxidative stress. In animal models of diabetes, it contributes to pain polyneuropathy. This study aims at defining the cellular localization of B₁R in thoracic spinal cord of type 1 diabetic rats by confocal microscopy with the use of a fluorescent agonist, [Nα-Bodipy]-des-Arg⁹-BK (BdABK) and selective antibodies.

Methods

Diabetes was induced by streptozotocin (STZ; 65 mg/kg, i.p.). Four days post-STZ treatment, B₁R expression was confirmed by quantitative real-time PCR and autoradiography. The B₁R selectivity of BdABK was determined by assessing its ability to displace B₁R [¹²⁵I]-HPP-desArg¹⁰-Hoe140 and B₂R [¹²⁵I]-HPP-Hoe 140 radioligands. The in vivo activity of BdABK was also evaluated on thermal hyperalgesia.

Results

B₁R was increased by 18-fold (mRNA) and 2.7-fold (binding sites) in the thoracic spinal cord of STZ-treated rats when compared to control. BdABK failed to displace the B₂R radioligand but displaced the B₁R radioligand (IC₅₀ = 5.3 nM). In comparison, IC₅₀ values of B₁R selective antagonist R-715 and B₁R agonist des-Arg⁹-BK were 4.3 nM and 19 nM, respectively. Intraperitoneal BdABK and des-Arg⁹-BK elicited dose-dependent thermal hyperalgesia in STZ-treated rats but not in control rats. The B₁R fluorescent agonist was co-localized with immunomarkers of microglia, astrocytes and sensory C fibers in the spinal cord of STZ-treated rats.

Conclusion

The induction and up-regulation of B₁R in glial and sensory cells of the spinal cord in STZ-diabetic rats reinforce the idea that kinin B₁R is an important target for drug development in pain processes.

Alterations of Fc gamma receptor I and Toll-like receptor 4 mediate the antiinflammatory actions of microglia and astrocytes after adrenaline-induced blood-brain barrier opening in rats

Blood-brain barrier (BBB) opening occurs under many physiological and pathological conditions. BBB opening will lead to the leakage of large circulating molecules into the brain parenchyma. These invasive molecules will induce immune responses. Microglia and astrocytes are the two major cell types responsible for immune responses in the brain, and Fc gamma receptor I (FcgammaRI) and Toll-like receptor 4 (TLR4) are the two important receptors mediating these processes. Data suggest that activation of the FcgammaRI pathway mediates antiinflammatory processes, whereas activation of TLR4 pathway leads to proinflammatory activities. In the present study, we tested the hypothesis that BBB opening could lead to alterations in FcgammaRI and TLR4 pathways in microglia and astrocytes, thus limiting excessive inflammation in the brain. The transient BBB opening was induced by adrenaline injection through a caudal vein in Sprague-Dawley rats. We found that the FcgammaRI pathway was significantly activated in both microglia and astrocytes, as exhibited by the up-regulation of FcgammaRI and its key downstream molecule Syk, as well as the increased production of the effector cytokines, interleukin (IL)-10 and IL-4. Interestingly, after transient BBB opening, TLR4 expression was also increased. However, the expression of MyD88, the central adapter of the TLR4 pathway, was significantly inhibited, with decreased production of the effector cytokines IL-12a and IL-1beta. These results indicate that, after transient BBB opening, FcgammaRI-mediated antiinflammatory processes were activated, whereas TLR4-mediated proinflammatory activities were inhibited in microglia and astrocytes. This may represent an important neuroprotective mechanism of microglia and astrocytes that limits excessive inflammation after BBB opening.

Blockade of sensory abnormalities and kinin B(1) receptor expression by N-acetyl-L-cysteine and ramipril in a rat model of insulin resistance

Glucose-fed rat is a model of insulin resistance that displays sensory polyneuropathy and hypertension. This study aimed at comparing the beneficial effects of N-acetyl-L-cysteine (NAC, antioxidant) and ramipril (angiotensin-1 converting enzyme inhibitor) on tactile and cold allodynia induced by chronic glucose feeding. Impact of these treatments was also assessed on hypertension, plasma glucose and insulin concentrations, insulin resistance and kinin B(1) receptor expression. Male Wistar rats (50-75 g) were given 10% d-glucose in their drinking water for 11 weeks or tap water (controls). Glucose-fed rats were treated either with NAC (1 g/kg/day, gavage), ramipril (1 mg/kg/day in drinking water) or no drug during the last 5 weeks. Glucose feeding for 6 weeks induced a significant increase in systolic blood pressure and hyperglycaemia which was accompanied by tactile and cold allodynia. At 11 weeks, plasma insulin, insulin resistance (HOMA index), kinin B(1) receptor mRNA in spinal cord and renal cortex and B(1) receptor binding sites in spinal cord were enhanced in glucose-fed rats. NAC and ramipril caused a progressive to complete inhibition of tactile and cold allodynia from 6 to 11 weeks. High systolic blood pressure, hyperinsulinemia, insulin resistance and kinin B(1) receptor expression were also normalized or attenuated in glucose-fed rats by either treatment. Results suggest that chronic treatment with an antioxidant or an ACE inhibitor provides similar beneficial effects on sensory polyneuropathy, hypertension and insulin resistance in glucose-fed rats. Both therapies were associated with a reduction of the expression of the pro-nociceptive kinin B(1) receptor.

Retinal plasma extravasation in streptozotocin-diabetic rats mediated by kinin B(1) and B(2) receptors

BACKGROUND AND PURPOSE

We investigated whether or not kinin receptors play a role in diabetic blood-retinal barrier breakdown, which is a leading cause of vision loss.

EXPERIMENTAL APPROACH

Blood-retinal barrier breakdown was quantified using Evans blue, and expression of kinin B(1) receptor mRNA was measured using quantitative reverse transcrition-PCR. Diabetic rats (streptozotocin (STZ), 65 mg kg(-1)) received a single intraocular injection of bradykinin (BK) or des-Arg(9)-BK, alone, or in combination with antagonists for B(1) (des-Arg(10)-Hoe140, R-715) and/or B(2) (Hoe140) receptors, given intraocularly or intravenously (i.v.).

KEY RESULTS

In control rats, BK (0.1-10 nmol) dose-dependently increased plasma extravasation, which was inhibited by Hoe140 (0.2 nmol), whereas des-Arg(9)-BK (0.1 and 1 nmol) was without effect. B(1) receptor mRNA was markedly increased in retinas of diabetic rats, and this was prevented by N-acetyl-L-cysteine (1 g kg(-1) day(-1) for 7 days). Plasma extravasation in retinas of STZ-diabetic rats was higher than in controls and enhanced by des-Arg(9)-BK. Response to des-Arg(9)-BK was inhibited by intraocular or i.v. injection of B(1) receptor antagonists. Diabetes-induced plasma extravasation was inhibited only by a combination of des-Arg(10)-Hoe140 and Hoe 140 (100 nmol kg(-1), i.v. 15 min earlier) or by R-715 (1 micromol kg(-1), i.v.) injected daily for 7 days.

CONCLUSIONS AND IMPLICATIONS

Kinin B(1) receptors are upregulated in retinas of STZ-diabetic rats through a mechanism involving oxidative stress. Both kinin B(1) and B(2) receptors contribute to increased plasma extravasation in diabetic retinopathy. Chronic inhibition of both kinin receptors, possibly with antioxidant adjuvants, may be a novel therapeutic strategy for diabetic retinopathy.

A novel 165-kDa Golgin protein induced by brain ischemia and phosphorylated by Akt protects against apoptosis

A cDNA encoding a novel protein was cloned from ischemic rat brain and found to be homologous to testis Mea-2 Golgi-associated protein (Golga3). The sequence predicted a 165-kDa protein, and in vitro translated protein exhibited a molecular mass of 165-170 kDa. Because brain ischemia induced the mRNA, and the protein localized to the Golgi apparatus, this protein was designated Ischemia-Inducible Golgin Protein 165 (IIGP165). In HeLa cells, serum and glucose deprivation-induced caspase-dependent cleavage of the IIGP165 protein, after which the IIGP165 fragments translocated to the nucleus. The C-terminus of IIGP165, which contains a LXXLL motif, appears to function as a transcriptional co-regulator. Akt co-localizes with IIGP165 protein in the Golgi in vivo, and phosphorylates IIGP165 on serine residues 345 and 134. Though transfection of IIGP165 cDNA alone does not protect HeLa cells from serum deprivation or Brefeldin-A-triggered cell death, co-transfection of both Akt and IIGP165 cDNA or combined IIGP165-transfection with PDGF treatment significantly protects HeLa cells better than either treatment alone. These data show that Akt phosphorylation of IIGP165 protects against apoptotic cell death, and add to evidence that the Golgi apparatus also plays a role in regulating apoptosis.

Alpha 1-adrenoceptor agonists protect against stress-induced death of neural progenitor cells

Here, we show that alpha(1)-adrenoceptor agonists suppress stress-induced death of mouse embryonic brain-derived neural progenitor cells (NPCs). NPCs highly expressed both alpha(1A)- and alpha(1B)-adrenoceptor genes, whereas the gene encoding alpha(1D)-adrenoceptor was expressed at low levels. Application of the alpha(1)-adrenoceptor agonists phenylephrine and cirazoline significantly promoted cell survival of embryonic NPCs that had been exposed to stress, as measured by a lactate dehydrogenase release assay, but had no remarkable effect on differentiation of the NPCs. Both phenylephrine and cirazoline protected NPCs from death induced by growth factor deprivation, N2 nutrient deprivation, tunicamycin treatment or staurosporine treatment. Phenylephrine and cirazoline treatments both maximally reduced stress-induced cell death by approximately 60% but did not change the percentage of undifferentiated cells as measured by nestin staining. Moreover, phenylephrine and cirazoline treatments did not affect the cellular activities of caspase-3 and caspase-7 but markedly reduced propidium iodide penetration into the cytoplasm, suggesting that alpha(1)-adrenoceptor agonists inhibit caspase-3/7-independent death of the embryonic NPCs.

ER stress and diseases

Proteins synthesized in the endoplasmic reticulum (ER) are properly folded with the assistance of ER chaperones. Malfolded proteins are disposed of by ER-associated protein degradation (ERAD). When the amount of unfolded protein exceeds the folding capacity of the ER, human cells activate a defense mechanism called the ER stress response, which induces expression of ER chaperones and ERAD components and transiently attenuates protein synthesis to decrease the burden on the ER. It has been revealed that three independent response pathways separately regulate induction of the expression of chaperones, ERAD components, and translational attenuation. A malfunction of the ER stress response caused by aging, genetic mutations, or environmental factors can result in various diseases such as diabetes, inflammation, and neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, and bipolar disorder, which are collectively known as 'conformational diseases'. In this review, I will summarize recent progress in this field. Molecules that regulate the ER stress response would be potential candidates for drug targets in various conformational diseases.

Neuroprotective role of bradykinin because of the attenuation of pro-inflammatory cytokine release from activated microglia

Bradykinin (BK) has been reported to be a mediator of brain damage in acute insults. Receptors for BK have been identified on microglia, the pathologic sensors of the brain. Here, we report that BK attenuated lipopolysaccharide (LPS)-induced release of tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta from microglial cells, thus acting as an anti-inflammatory mediator in the brain. This effect was mimicked by raising intracellular cAMP or stimulating the prostanoid receptors EP2 and EP4, while it was abolished by a cAMP antagonist, a prostanoid receptor antagonist, or by an inhibitor of the inducible cyclooxygenase (cyclooxygenase-2). BK also enhanced formation of prostaglandin E(2) and expression of microsomal prostaglandin E synthase. Expression of BK receptors and EP2/EP4 receptors were also enhanced. Using physiological techniques, we identified functional BK receptors not only in culture, but also in microglia from acute brain slices. BK reduced LPS-induced neuronal death in neuron-microglia co-cultures. This was probably mediated via microglia as it did not affect TNF-alpha-induced neuronal death in pure neuronal cultures. Our data imply that BK has anti-inflammatory and neuroprotective effects in the central nervous system by modulating microglial function.

Role of p53 in neurotoxicity induced by the endoplasmic reticulum stress agent tunicamycin in organotypic slice cultures of rat spinal cord

The endoplasmic reticulum (ER) is important for maintaining the quality of cellular proteins. Various stimuli can disrupt ER homeostasis and cause the accumulation of unfolded or misfolded proteins, i.e., a state of ER stress. Recently, ER stress has been reported to play an important role in the pathogenesis of neurological disorders such as cerebral ischemia and neurodegenerative diseases, but its involvement in the spinal cord diseases has not been fully discussed. We conducted this study using tunicamycin (Tm) as an ER stress inducer for rat spinal cord in organotypic slice culture, a system that we have recently established. Tm was shown to induce ER stress by increased expression of GRP78. The viability rate of spinal cord neurons decreased in a dose-dependent manner with Tm treatment, and dorsal horn interneurons were more vulnerable to Tm-induced neurotoxicity. A p53 inhibitor significantly increased the viability of dorsal horn interneurons, and immunofluorescence studies showed nuclear accumulation of p53 in the dorsal horns of Tm-treated spinal cord slices. These findings suggest that p53 plays an important role in the killing of dorsal horn interneurons by Tm. In contrast, motor neurons were not protected by the p53 inhibitor, suggesting that the role of p53 may vary between different cell types. This difference might be a clue to the mechanism of the stress-response pathway and might also contribute to the potential application of p53 inhibitors for the treatment of spinal cord diseases, including amyotrophic lateral sclerosis.

Ubiquitin C-terminal hydrolase L1 regulates the morphology of neural progenitor cells and modulates their differentiation

Ubiquitin C-terminal hydrolase L1 (UCH-L1) is a component of the ubiquitin system, which has a fundamental role in regulating various biological activities. However, the functional role of the ubiquitin system in neurogenesis is not known. Here we show that UCH-L1 regulates the morphology of neural progenitor cells (NPCs) and mediates neurogenesis. UCH-L1 was expressed in cultured NPCs as well as in embryonic brain. Its expression pattern in the ventricular zone (VZ) changed between embryonic day (E) 14 and E16, which corresponds to the transition from neurogenesis to gliogenesis. At E14, UCH-L1 was highly expressed in the ventricular zone, where neurogenesis actively occurs; whereas its expression was prominent in the cortical plate at E16. UCH-L1 was very weakly detected in the VZ at E16, which corresponds to the start of gliogenesis. In cultured proliferating NPCs, UCH-L1 was co-expressed with nestin, a marker of undifferentiated cells. In differentiating cells, UCH-L1 was highly co-expressed with the early neuronal marker TuJ1. Furthermore, when UCH-L1 was induced in nestin-positive progenitor cells, the number and length of cellular processes of the progenitors decreased, suggesting that the progenitor cells were differentiating. In addition, NPCs derived from gad (UCH-L1-deficient) mice had longer processes compared with controls. The ability of UCH-L1 to regulate the morphology of nestin-positive progenitors was dependent on its binding affinity for ubiquitin but not on hydrolase activity; this result was also confirmed using gad-mouse-derived NPCs. These results suggest that UCH-L1 spatially mediates and enhances neurogenesis in the embryonic brain by regulating progenitor cell morphology.

Solo/Trio8, a membrane-associated short isoform of Trio, modulates endosome dynamics and neurite elongation

With DNA microarrays, we identified a gene, termed Solo, that is downregulated in the cerebellum of Purkinje cell degeneration mutant mice. Solo is a mouse homologue of rat Trio8-one of multiple Trio isoforms recently identified in rat brain. Solo/Trio8 contains N-terminal sec14-like and spectrin-like repeat domains followed by a single guanine nucleotide exchange factor 1 (GEF1) domain, but it lacks the C-terminal GEF2, immunoglobulin-like, and kinase domains that are typical of Trio. Solo/Trio8 is predominantly expressed in Purkinje neurons of the mouse brain, and expression begins following birth and increases during Purkinje neuron maturation. We identified a novel C-terminal membrane-anchoring domain in Solo/Trio8 that is required for enhanced green fluorescent protein-Solo/Trio8 localization to early endosomes (positive for both early-endosome antigen 1 [EEA1] and Rab5) in COS-7 cells and primary cultured neurons. Solo/Trio8 overexpression in COS-7 cells augmented the EEA1-positive early-endosome pool, and this effect was abolished via mutation and inactivation of the GEF domain or deletion of the C-terminal membrane-anchoring domain. Moreover, primary cultured neurons transfected with Solo/Trio8 showed increased neurite elongation that was dependent on these domains. These results suggest that Solo/Trio8 acts as an early-endosome-specific upstream activator of Rho family GTPases for neurite elongation of developing Purkinje neurons.

Dopaminergic neuronal loss in transgenic mice expressing the Parkinson's disease-associated UCH-L1 I93M mutant

The I93M mutation in ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1) was reported in one German family with autosomal dominant Parkinson's disease (PD). The causative role of the mutation has, however, been questioned. We generated transgenic (Tg) mice carrying human UCHL1 under control of the PDGF-B promoter; two independent lines were generated with the I93M mutation (a high- and low-expressing line) and one line with wild-type human UCH-L1. We found a significant reduction in the dopaminergic neurons in the substantia nigra and the dopamine content in the striatum in the high-expressing I93M Tg mice as compared with non-Tg mice at 20 weeks of age. Although these changes were absent in the low-expressing I93M Tg mice, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment profoundly reduced dopaminergic neurons in this line as compared with wild-type Tg or non-Tg mice. Abnormal neuropathologies were also observed, such as silver staining-positive argyrophilic grains in the perikarya of degenerating dopaminergic neurons, in I93M Tg mice. The midbrains of I93M Tg mice contained increased amounts of insoluble UCH-L1 as compared with those of non-Tg mice, perhaps resulting in a toxic gain of function. Collectively, our data represent in vivo evidence that expression of UCHL1(I93M) leads to the degeneration of dopaminergic neurons.

Human TDE1, a TDE1/TMS family member, inhibits apoptosis in vitro and stimulates in vivo tumorigenesis

We have previously described hTDE1, the human homologue of the recently described TDE1/TMS family of proteins whose members have been identified in several species. Although a defined biochemical activity has yet to be assigned to TDE1/TMS family members, previous results point to the overexpression of family members in tumor cell lines or tissues. To define whether hTDE1 may directly impact on neoplastic transformation, we derived and characterized stable Rat-1 transfectants that constitutively express hTDE1 at the plasma membrane. Expression of hTDE1 in Rat-1 transfectants had a significant effect on cell contact inhibition in vitro as judged by a focus formation assay. In addition, by monitoring caspase-3 activity and Hoechst staining, we determined that hTDE1 overexpression partially protects cells from serum starvation- and etoposide-induced apoptosis. Finally, hTDE1 Rat-1-expressing clones accelerated the formation of tumors in a nude mouse assay. Our results suggest that hTDE1 contributes directly to oncogenesis in vivo that may in part be explained by its effect on apoptosis in vitro.

Identification and functional characterization of mouse TPO1 as a myelin membrane protein

TPO1 is a member of the AIGP family, a unique group of proteins that contains 11 putative transmembrane domains. Expression of the rat TPO1 gene is upregulated in cultured oligodendrocytes (OLs) during development from pro-oligodendroblasts to postmitotic OLs. However, the distribution of native TPO1 protein in cultured OLs and in the brain has not been elucidated. We investigated the distribution and cellular function of TPO1 in myelinating cells of the nervous system. In mice, TPO1 gene expression was detected in the central (CNS) and peripheral (PNS) nervous systems and was markedly upregulated at postnatal days 10-20, an early phase of myelination in the mouse brain. To investigate TPO1 localization, we generated affinity-purified antibodies to synthetic peptides derived from mouse TPO1. Immunohistochemical analysis showed that TPO1 was expressed in OLs and Schwann cells but not in neurons and astrocytes. Schwann cells from trembler mice, which lack PNS myelin, had significantly decreased TPO1 expression and an altered localization pattern, suggesting that TPO1 is a functional myelin membrane protein. In OL lineage cell cultures, TPO1 was detected in A2B5+ bipolar early progenitors, A2B5+ multipolar Pro-OLs, GalC+ immature OLs and MBP+ mature OLs. The subcellular localization of TPO1 in OL lineage cells was mapped to the GM130+ Golgi in cell bodies and Fyn+ cell processes and myelin-like sheets. Furthermore, TPO1 selectively colocalized with non-phosphorylated Fyn and promoted Fyn autophosphorylation in COS7 cells, suggesting that TPO1 may play a role in myelin formation via Fyn kinase activation in the PNS and CNS.

JNK inhibitory kinase is up-regulated in retinal ganglion cells after axotomy and enhances BimEL expression level in neuronal cells

Optic nerve transection results in retinal ganglion cell (RGC) death in adult mammals, after the alteration of gene expression of RGCs. To elucidate the molecular mechanism by which axotomy induces RGC death, we isolated the molecules up-regulated after optic nerve transection. One of these, axotomy-related [corrected] gene (ARG)357, an 898-amino-acid [corrected] protein containing a complete serine-threonine kinase domain, was isolated from a subtraction library of the rat retina. The sequence showed that this gene was a rat homolog of human c-Jun N-terminal kinase (JNK) inhibitory kinase and so belonged to the germinal center kinase-VIII subfamily of Sterile20s protein kinase. We designated ARG357 as rat JNK inhibitory kinase (JIK). Rat JIK was expressed ubiquitously in various tissues and was highly expressed in the retina, with selective expression in RGCs. After axotomy, BimEL and Hrk, which are BH3-only proteins, and rat JIK were up-regulated in RGCs. Overexpression of rat JIK in neuronal cells up-regulated the expression of BimEL, but not that of Hrk. These results indicate that JIK may contribute to axotomy-induced RGC death by up-regulating the expression of BH3-only protein.

Ischemic neuronal cell death and organellae damage

The brain is an organ that consumes much energy. This is partially due to the character of neurons; they possess excitable plasma membrane and a large amount of ATP is indispensable for maintaining ion gradient. Once neurons experience energy failure, calcium accumulates in the intracellular space as a result of disturbed ion homeostasis. This, in turn, activates many cellular processes, which culminate in cell death. In this cellular catastrophic cascade, many organelles play important roles. In addition to the plasma membrane, cytosol is the 'organelle' that first becomes exposed to the increased level of calcium. Many proteases, kinases and lipases are localized here, and are activated directly or indirectly by the ischemic insult. Some enzymes are pro-apoptotic ones, while others are anti-apoptotic. It was reported that neurons that would die later showed activated pro-apoptotic enzymes, but ones that would survive possessed activated anti-apoptotic molecules. Mitochondria is the organelle that plays the central role for intrinsic pathways of apoptosis. The release of cytochrome c from this organelle is the key step in apoptotic cascade in the ischemic neurons. However, the exact molecular mechanism of cytochrome c release remains uncertain. In addition, expression of genes essential for mitochondrial function changes in neurons after ischemia, which further indicates the crucial role of this organelle in cell death. Endoplasmic reticulum (ER) not only mediates proteins processing, but also regulates intracellular calcium homeostasis and cell death signal activation. Recent reports indicate that dysfunction of this organelle occurs at an early stage after ischemia and might be the initial step of apoptotic cascades in neurons. Golgi apparatus and lysosomes are organelles that are involved in apoptotic cell death in some situations. There have been no reports that demonstrated active role of these organelles in ischemic neuronal cell death. Further investigation would be desired about this issue. Nucleus is the organelle that contains genomic DNA. Many studies demonstrated DNA breakage in the neurons that would die later, but whether this is the cause or merely the result of the insult remains uncertain. If the more precise role of each organelle in neuronal cell death are disclosed, we should be able to think about new means of therapy for ischemic stroke.

Overexpression of ubiquitin carboxyl-terminal hydrolase L1 arrests spermatogenesis in transgenic mice

Ubiquitin carboxyl-terminal hydrolase 1 (UCH-L1) can be detected in mouse testicular germ cells, mainly spermatogonia and somatic Sertoli cells, but its physiological role is unknown. We show that transgenic (Tg) mice overexpressing EF1alpha promoter-driven UCH-L1 in the testis are sterile due to a block during spermatogenesis at an early stage (pachytene) of meiosis. Interestingly, almost all spermatogonia and Sertoli cells expressing excess UCH-L1, but little PCNA (proliferating cell nuclear antigen), showed no morphological signs of apoptosis or TUNEL-positive staining. Rather, germ cell apoptosis was mainly detected in primary spermatocytes having weak or negative UCH-L1 expression but strong PCNA expression. These data suggest that overexpression of UCH-L1 affects spermatogenesis during meiosis and, in particular, induces apoptosis in primary spermatocytes. In addition to results of caspases-3 upregulation and Bcl-2 downregulation, excess UCH-L1 influenced the distribution of PCNA, suggesting a specific role for UCH-L1 in the processes of mitotic proliferation and differentiation of spermatogonial stem cells during spermatogenesis.

Developmental Regulation of Ubiquitin C-Terminal Hydrolase Isozyme Expression During Spermatogenesis in Mice

The ubiquitin pathway functions in the process of protein turnover in eukaryotic cells. This pathway comprises the enzymes that ubiquitinate/deubiquitinate target proteins and the proteasome that degrades ubiquitin-conjugated proteins. Ubiquitin C-terminal hydrolases (UCHs) are thought to be essential for maintaining ubiquitination activity by releasing ubiquitin (Ub) from its substrates. Mammalian UCH-L1 and UCH-L3 are small proteins that share considerable homology at the amino acid level. Both of these UCHs are highly expressed in the testis/ ovary and neuronal cells. Our previous work demonstrated that UCH-L1-deficient gracile axonal dystrophy (gad) mice exhibit progressively decreasing spermatogonial stem cell proliferation, suggesting that UCH isozymes in the testis function during spermatogenesis. To analyze the expression patterns of UCH isozymes during spermatogenesis, we isolated nearly homogeneous populations of spermatogonia, spermatocytes, spermatids, and Sertoli cells from mouse testes. Western blot analysis detected UCH-L1 in spermatogonia and Sertoli cells, whereas UCH-L3 was detected in spermatocytes and spermatids. Moreover, reverse transcription-polymerase chain reaction analysis of UCH isozymes showed that UCH-L1 and UCH-L4 mRNAs are expressed in spermatogonia, whereas UCH-L3 and UCH-L5 mRNAs are expressed mainly in spermatocytes and spermatids. These results suggest that UCH-L1 and UCH-L3 have distinct functions during spermatogenesis, namely, that UCH-L1 may act during mitotic proliferation of spermatogonial stem cells whereas UCH-L3 may function in the meiotic differentiation of spermatocytes into spermatids.

Comparison of mice deficient in the high- or low-affinity neurotensin receptors, Ntsr1 or Ntsr2, reveals a novel function for Ntsr2 in thermal nociception

Neurotensin (NT) is a neuropeptide that induces a wide range of biological activities including hypothermia and analgesia. Such effects are mediated by the NT receptors Ntsr1, Ntsr2 and Ntsr3, although the involvement of each receptor in specific NT functions remains unknown. To address nociceptive function in vivo, we generated both Ntsr1-deficient and Ntsr2-deficient mice. In addition, histochemical analyses of both Ntsr1 and Ntsr2 mRNAs were performed in the mouse brain regions involved in NT-related nociception. The expression of Ntsr2 mRNA was greater than that of Ntsr1 in the periaqueductal gray (PAG) and the rostral ventral medulla (RVM). The mutant and control mice were subjected to the examination of thermal nociception, and in the hot plate test, a significant alteration in jump latency was observed in Ntsr2-deficient mice compared to Ntsr1-deficient or wild-type control mice. Latencies of tail flick and hind paw licking of the mutant mice were not affected compared to control mice. These results suggest that Ntsr2 has an important role in thermal nociception compared to Ntsr1, and that these mutant mice may represent a useful tool for the development of analgesic drugs.