Possible involvement of convergent nociceptive input to medullary dorsal horn neurons in intraoral hyperalgesia following peripheral nerve injury.

Previous studies demonstrated that the number of c-Fos protein-like immunoreactive (c-Fos-IR) neurons in the medullary dorsal horn (MDH) evoked by noxious stimulation was increased after peripheral nerve injury, and such increase has been proposed to reflect the development of neuropathic pain state. The aim of this study was to examine the MDH for convergent collateral primary afferent input to second order neurons deafferented by peripheral nerve injury, and to explore a possibility of its contribution to the c-Fos hyperinducibility. Double immunofluorescence labeling for c-Fos and phosphorylated extracellular signal-regulated kinase (p-ERK) was performed to detect convergent synaptic input. c-Fos expression and the phosphorylation of ERK were induced by the intraoral application of capsaicin and by electrical stimulation of the inferior alveolar nerve (IAN), respectively. The number of c-Fos-IR neurons in the MDH induced by the intraoral application of capsaicin was increased after IAN injury, whereas the number of p-ERK immunoreactive neurons remained unchanged. The number of double-labeled neurons, that presumably received convergent primary afferent input from the lingual nerve and the IAN, was significantly increased after IAN injury. These results indicated that convergent primary nociceptive input through neighboring intact nerves may contribute to the c-Fos hyperinducibility in the MDH and the pathogenesis of neuropathic pain following trigeminal nerve injury.

Effect of adenosine A1 receptor agonist on the enhanced excitability of spinal dorsal horn neurons after peripheral nerve injury.

Neuronal hyperactivity has been implicated in abnormal pain sensation following peripheral nerve injuries. Previous studies have indicated that the activation of adenosine A1 receptors (A1R) in the central and peripheral nervous systems produces an antinociceptive effect. However, the mechanisms involved in the peripheral effect are still not fully understood. The effects of the local application of the selective A1R agonist, 2-chloro-N(6)-cyclopentyladenosine (CCPA) on neuronal hyperactivity were examined in this study using a neuropathic pain model induced by a tibial nerve injury. We utilized Fos protein-like immunoreactivity induced by noxious heat stimulation to examine changes in the number of Fos protein like immunoreactive (Fos-LI) neuron profiles in the spinal dorsal horn, and behavioral analysis for mechanical and thermal sensitivities. The nerve injury induced an exaggerated Fos response to noxious heat stimulation. The number of Fos-LI neuron profiles was significantly decreased and their distribution was restricted to the central terminal field of the spared peroneal nerve 3 days after the injury. The number of Fos-LI neuron profiles returned to control levels and a large number of these profiles were observed in the central terminal field of the injured tibial nerve 14 days after the injury. These enhanced Fos responses were attenuated by the local application of CCPA. The nerve injury also resulted in mechanical allodynia and thermal hyperalgesia. The local application of CCPA inhibited thermal hyperalgesia, but was less effective against mechanical allodynia. These results indicated that activation of peripheral A1R plays a role in the regulation of nerve injury-induced hyperalgesia.

Fos protein-like immunoreactive neurons induced by electrical stimulation in the trigeminal sensory nuclear complex of rats with chronically injured peripheral nerve.

The rat trigeminal sensory nuclear complex (TSNC) was examined for Fos protein-like immunoreactive (Fos-LI) neurons induced by electrical stimulation (ES) of the lingual nerve (LN) at 2 weeks after injury to the LN or the inferior alveolar nerve (IAN). Intensity-dependent increase in the number of Fos-LI neurons was observed in the subnucleus oralis (Vo) and caudalis (Vc) of the spinal trigeminal tract nucleus irrespective of nerve injury. The number of Fos-LI neurons induced by ES of the chronically injured LN at A-fiber intensity (0.1 mA) was significantly increased in the Vo but not the Vc. On the other hand, in rats with chronically injured IAN, the number of Fos-LI neurons induced by ES of the LN at C-fiber intensity (10 mA) was significantly increased in the Vc but not the Vo. These results indicated that injury of a nerve innervating intraoral structures increased the c-Fos response of Vo neurons to A-fiber intensity ES of the injured nerve. A similar nerve injury enhanced the c-Fos response of Vc neurons to C-fiber intensity ES of a spared uninjured nerve innervating an intraoral territory neighboring that of the injured nerve. The present result show that nerve injury causes differential effects on c-Fos expression in the Vo and Vc, which may explain complexity of neuropathic pain symptoms in clinical cases.

Differential activation of mitogen-activated protein kinases and glial cells in the trigeminal sensory nuclear complex following lingual nerve injury.

Mitogen-activated protein kinases (MAPKs) play a pivotal role in the mediation of cellular responses to a variety of signaling molecules. The current study demonstrates phosphorylation of extracellular signal-regulated kinase (ERK) and p38 MAPK in each subdivision of the trigeminal sensory nuclear complex (TSNC) following lingual nerve injury. Immunohistochemical labeling for phosphorylated ERK (p-ERK) or phosphorylated p38 (p-p38) MAPK was performed in histological sections of the brainstem. A transient increase in the immunoreactivity for p-ERK was found in each subdivision of the TSNC followed by a prolonged increase in the immunoreactivity for p-p38 MAPK after nerve injury. Double immunofluorescence labeling with cell-specific markers revealed that ERK and p38 MAPK were phosphorylated predominantly by OX-42-positive microglia or GFAP-positive astrocytes. Increased immunofluorescence labeling for OX-42 and GFAP indicated that microglia and astrocytes were activated by nerve injury in the TSNC. Activation of MAPKs and glial cells in the rostral subdivisions of the TSNC was comparable with that in the subnucleus caudalis of the trigeminal spinal tract nucleus (Vc). We conclude that differential activation of MAPKs and glial cells in the rostral subdivisions of the TSNC as well as the Vc may have a substantial role in the pathogenesis of neuropathic pain following trigeminal nerve injury.

Bach1 inhibits oxidative stress-induced cellular senescence by impeding p53 function on chromatin.

Cellular senescence is one of the key strategies to suppress expansion of cells with mutations. Senescence is induced in response to genotoxic and oxidative stress. Here we show that the transcription factor Bach1 (BTB and CNC homology 1, basic leucine zipper transcription factor 1), which inhibits oxidative stress-inducible genes, is a crucial negative regulator of oxidative stress-induced cellular senescence. Bach1-deficient murine embryonic fibroblasts showed a propensity to undergo more rapid and profound p53-dependent premature senescence than control wild-type cells in response to oxidative stress. Bach1 formed a complex that contained p53, histone deacetylase 1 and nuclear co-repressor N-coR. Bach1 was recruited to a subset of p53 target genes and contributed to impeding p53 action by promoting histone deacetylation. Because Bach1 is regulated by oxidative stress and heme, our data show that Bach1 connects oxygen metabolism and cellular senescence as a negative regulator of p53.

Upregulation of heme oxygenase-1 combined with increased adiponectin lowers blood pressure in diabetic spontaneously hypertensive rats through a reduction in endothelial cell dysfunction, apoptosis and oxidative stress.

This study was designed to investigate the effect of increased levels of HO-1 on hypertension exacerbated by diabetes. Diabetic spontaneously hypertensive rat (SHR) and WKY (control) animals were treated with streptozotocin (STZ) to induce diabetes and stannous chloride (SnCl(2)) to upregulate HO-1. Treatment with SnCl(2) not only attenuated the increase of blood pressure (p<0.01), but also increased HO-1 protein content, HO activity and plasma adiponectin levels, decreased the levels of superoxide and 3-nitrotyrosine (NT), respectively. Reduction in oxidative stress resulted in the increased expression of Bcl-2 and AKT with a concomitant reduction in circulating endothelial cells (CEC) in the peripheral blood (p<0.005) and an improvement of femoral reactivity (response to acetylcholine). Thus induction of HO-1 accompanied with increased plasma adiponectin levels in diabetic hypertensive rats alters the phenotype through a reduction in oxidative stress, thereby permitting endothelial cells to maintain an anti-apoptotic environment and the restoration of endothelial responses thus preventing hypertension.

Genetic suppression of HO-1 exacerbates renal damage: reversed by an increase in the antiapoptotic signaling pathway.

Apoptosis has been shown to contribute to the development of acute and chronic renal failure. The antiapoptotic action of the heme oxygenase (HO) system may represent an important protective mechanism in kidney pathology. We examined whether the lack of HO-1 would influence apoptosis in clipped kidneys of two-kidney, one-clip (2K1C) rats. Five-day-old Sprague-Dawley rats were injected in the left ventricle with approximately 5 x 10(9) colony-forming units/ml of retrovirus containing rat HO-1 antisense (LSN-RHO-1-AS) or control retrovirus (LXSN). After 3 mo, a 0.25-mm U-shaped silver clip was placed around the left renal artery. Animals were killed 3 wk later. Clipping the renal artery in LSN-RHO-1-AS rats did not result in increased HO-1 expression. In contrast to LXSN animals, 2K1C LSN-RHO-1-AS rats showed increased expression of cyclooxygenase 2 (COX-2) and higher 3-nitrotyrosine (3-NT) content as well as increased expression of the proapoptotic protein Apaf-1 and caspase-3 activity. Clipping the renal artery in LXSN rats resulted in increased expression of the antiapoptotic proteins Bcl-2 and Bcl-xl, while clipping the renal artery in LSN-RHO-1-AS rats did not change Bcl-2 levels and decreased the levels of Bcl-xl. Treatment of LSN-RHO-1-AS rats with cobalt protoporphyrin resulted in induction of renal HO-1, which was accompanied by decreases in blood pressure, COX-2, 3-NT, and caspase-3 activity, and increased expression of anti-apoptotic molecules (Bcl-2, Bcl-xl, Akt and p-Akt) in the clipped kidneys. These findings underscore the prominent role of HO-1 in counteracting apoptosis in this 2K1C renovascular hypertension model.

Genetic ablation of the transcription repressor Bach1 leads to myocardial protection against ischemia/reperfusion in mice.

Bach1 is a transcriptional repressor of heme oxygenase-1 gene (Hmox-1) and beta-globin gene. Heme oxygenase (HO)-1 is an inducible cytoprotective enzyme that degrades pro-oxidant heme to carbon monoxide (CO) and biliverdin/bilirubin, which are thought to mediate anti-inflammatory and anti-oxidant actions of HO-1. In the present study, we investigated the role of Bach1 in tissue protection against myocardial ischemia/reperfusion (I/R) injury in vivo using mice lacking the Bach1 gene (Bach1(-/-)) and wild-type (Bach1(+/+)) mice. In Bach1(-/-) mice, myocardial expression of HO-1 protein was constitutively up-regulated by 3.4-fold compared to that in Bach1(+/+) mice. While myocardial I/R induced HO-1 protein in ischemic myocytes in both strains of mice, the extent of induction was significantly greater in Bach1(-/-) mice than in Bach1(+/+) mice. Myocardial infarction was markedly reduced in size by 48.4% in Bach1(-/-) mice. Pretreatment of Bach1(-/-) mice with zinc-protoporphyrin, an inhibitor of HO activity, abolished the infarction-reducing effect of Bach1 disruption, indicating that reduction in the infarct size was mediated, at least in part, by HO-1 activity. Thus, Bach1 plays a pivotal role in setting the levels of both constitutive and inducible expression of HO-1 in the myocardium. Bach1 inactivation during I/R appears to be a key mechanism controlling the activation level of cytoprotective program involving HO-1.

Induction of heme oxygenase-1 inhibits monocyte chemoattractant protein-1 mRNA expression in U937 cells.

Heme oxygenase-1 (HO-1) is a stress-inducible isoform of HO with potential cytoprotective effects. Monocyte activation/migration mediated by monocyte chemoattractant protein-1 (MCP-1) is one of the earliest and important events in the pathogenesis of atherosclerosis. We examined the effect of HO-1 on the production of lysophosphatidylcholine (Lyso-PC)-induced MCP-1 in the human promonocytic cell line U937. Increased HO-1 induction by hemin resulted in a significant decrease in the Lyso-PC-mediated induction of MCP-1 mRNA expression. SnPP (IX), the specific inhibitor of HO-1 enzymatic activity, prevented the hemin-mediated attenuation of MCP-1 mRNA expression. These results suggest that HO-1 may work as an anti-atherogenic agent through the attenuation of MCP-1 production.

Effects of genetic ablation of bach1 upon smooth muscle cell proliferation and atherosclerosis after cuff injury.

Bach1 is a transcriptional repressor of the cytoprotective enzyme heme oxygenase-1 (HO-1). Although HO-1 protects against atherosclerosis, the function of Bach1 in this process is poorly understood. We isolated peritoneal macrophages and aortic smooth muscle cells (SMC) from wild-type and bach1-deficient mice. bach1-Deficient macrophages expressed increased levels of HO-1 and showed elevated phagocytic activity when incubated with 0.75 microm microspheres. In SMC, bach1-ablation resulted in increased expression of HO-1 and decreased proliferation in bromodeoxyuridine incorporation assay as compared with wild-type cells. The up-regulated phagocytic activity and reduced SMC proliferation of bach1-deficient cells were not restored by Zinc (II) protoporphyrin IX, an inhibitor of HO, suggesting that HO-independent mechanisms are also involved in the regulation of phagocytosis of macrophages and proliferation of SMC by Bach1. In wild-type mice, cuff placement around femoral artery caused pronounced intimal proliferation without affecting the media, thus resulting in intimal to medial (I/M) volume ratio of 65.6%. bach1-deficient mice had less degree of intimal growth (I/M ratio of 45.6%). These results indicate that Bach1 plays a critical role in the regulation of HO-1 expression, macrophage function, SMC proliferation and neointimal formation. Bach1 may regulate gene expression in these cells during inflammation and atherogenesis.