Non-angiotensin II [125I] CGP42112 binding is a sensitive marker of neuronal injury in brainstem following unilateral nodose ganglionectomy: Comparison with markers for activated microglia

Angiotensin II AT2 Receptors Contribute to Regulate the Sympathoadrenal and Hormonal Reaction to Stress Stimuli

Angiotensin II, through AT1 receptor stimulation, mediates multiple cardiovascular, metabolic, and behavioral functions including the response to stressors. Conversely, the function of Angiotensin II AT2 receptors has not been totally clarified. In adult rodents, AT2 receptor distribution is very limited but it is particularly high in the adrenal medulla. Recent results strongly indicate that AT2 receptors contribute to the regulation of the response to stress stimuli. This occurs in association with AT1 receptors, both receptor types reciprocally influencing their expression and therefore their function. AT2 receptors appear to influence the response to many types of stressors and in all components of the hypothalamic-pituitary-adrenal axis. The molecular mechanisms involved in AT2 receptor activation, the complex interactions with AT1 receptors, and additional factors participating in the control of AT2 receptor regulation and activity in response to stressors are only partially understood. Further research is necessary to close this knowledge gap and to clarify whether AT2 receptor activation may carry the potential of a major translational advance.

Angiotensin II Type 2 Receptor Decreases Transforming Growth Factor-β Type II Receptor Expression and Function in Human Renal Proximal Tubule Cells

Transforming growth factor-β (TGF-β), via its receptors, induces epithelial-mesenchymal transition (EMT) and plays an important role in the development of renal tubulointersitial fibrosis. Angiotensin II type 2 receptor (AT₂R), which mediates beneficial renal physiological functions, has received attention as a prospective therapeutic target for renoprotection. In this study, we investigated the effect and underlying mechanism of AT₂R on the TGF-β receptor II (TGF-βRII) expression and function in human proximal tubular cells (HK-2). Here, we show that the AT₂R agonist CGP42112A decreased TGF-βRII protein expression in a concentration- and time-dependent manner in HK-2 cells. The inhibitory effect of the AT₂R on TGF-βRII expression was blocked by the AT₂R antagonists PD123319 or PD123177. Stimulation with TGF-β1 enhanced EMT in HK-2 cells, which was prevented by pre-treatment with CGP42112A. One of mechanisms in this regulation is associated with the increased TGF-βRII degradation after activation of AT₂R. Furthermore, laser confocal immunofluorescence microscopy showed that AT₂R and TGF-βRII colocalized in HK-2 cells. AT₂R and TGF-βRII coimmunoprecipitated and this interaction was increased after AT₂R agonist stimulation for 30 min. The inhibitory effect of the AT₂R on TGF-βRII expression was also blocked by the nitric oxide synthase inhibitor L-NAME, indicating that nitric oxide is involved in the signaling pathway. Taken together, our study indicates that the renal AT₂R regulates TGF-βRII expression and function via the nitric oxide pathway, which may be important in the control of renal tubulointerstitial fibrosis.

Sleeve gastrectomy and Roux-en-Y gastric bypass alter the gut-brain communication

This study investigated the anatomical integrity of vagal innervation of the gastrointestinal tract following vertical sleeve gastrectomy (VSG) and Roux-en-Y gastric bypass (RYGB) operations. The retrograde tracer fast blue (FB) was injected into the stomach to label vagal neurons originating from nodose ganglion (NG) and dorsal motor nucleus of the vagus (DMV). Microglia activation was determined by quantifying changes in the fluorescent staining of hindbrain sections against an ionizing calcium adapter binding molecule 1 (Iba1). Reorganization of vagal afferents in the hindbrain was studied by fluorescent staining against isolectin 4 (IB4). The density of Iba1- and IB4-immunoreactivity was analyzed using Nikon Elements software. There was no difference in the number of FB-labeled neurons located in NG and DMV between VSG and VSG-sham rats. RYGB, but not RYGB-sham rats, showed a dramatic reduction in number of FB-labeled neurons located in the NG and DMV. VSG increased, while the RYGB operation decreased, the density of vagal afferents in the nucleus tractus solitarius (NTS). The RYGB operation, but not the VSG procedure, significantly activated microglia in the NTS and DMV. Results of this study show that the RYGB, but not the VSG procedure, triggers microglia activation in vagal structures and remodels gut-brain communication.

Angiotensin II Type 2 Receptor Stimulation Initiated After Stroke Causes Neuroprotection in Conscious Rats

We have demonstrated previously that pretreatment with an angiotensin II type 2 receptor (AT 2 R) agonist is neuroprotective against a subsequent stroke independent of any changes in blood pressure. Therefore, in the current study, we have examined the potential neuroprotective effect of AT 2 R stimulation initiated after stroke induction to mimic the clinical setting. Intracerebroventricular administration of the AT 2 R agonist CGP42112 was commenced 6 hours after an ischemic stroke had been induced in conscious spontaneously hypertensive rats. CGP42112 given over 4 doses in the same rats (3 µg/kg per dose centrally) at 6, 24, 48, and 72 hours after stroke induction reduced total infarct volume (32±13 mm 3 versus vehicle, 170±49 mm 3 ; P <0.05) and improved motor function. Furthermore, we have demonstrated that AT 2 R stimulation after stroke increased neuronal survival, decreased apoptosis, and caused an increase in the number of activated microglia in the core region of damage. The effects of CGP42112 were partially reversed with the coadministration of an AT 2 R antagonist, PD123319. Thus, the current study has shown for the first time that delayed central AT 2 R stimulation after a cerebral incident is neuroprotective in a conscious rat model of stroke.

Angiotensin II Type 2 Receptor Stimulation Initiated After Stroke Causes Neuroprotection in Conscious Rats

We have demonstrated previously that pretreatment with an angiotensin II type 2 receptor (AT 2 R) agonist is neuroprotective against a subsequent stroke independent of any changes in blood pressure. Therefore, in the current study, we have examined the potential neuroprotective effect of AT 2 R stimulation initiated after stroke induction to mimic the clinical setting. Intracerebroventricular administration of the AT 2 R agonist CGP42112 was commenced 6 hours after an ischemic stroke had been induced in conscious spontaneously hypertensive rats. CGP42112 given over 4 doses in the same rats (3 µg/kg per dose centrally) at 6, 24, 48, and 72 hours after stroke induction reduced total infarct volume (32±13 mm 3 versus vehicle, 170±49 mm 3 ; P <0.05) and improved motor function. Furthermore, we have demonstrated that AT 2 R stimulation after stroke increased neuronal survival, decreased apoptosis, and caused an increase in the number of activated microglia in the core region of damage. The effects of CGP42112 were partially reversed with the coadministration of an AT 2 R antagonist, PD123319. Thus, the current study has shown for the first time that delayed central AT 2 R stimulation after a cerebral incident is neuroprotective in a conscious rat model of stroke.

Angiotensin II Type 2 Receptor Stimulation Initiated After Stroke Causes Neuroprotection in Conscious Rats

We have demonstrated previously that pretreatment with an angiotensin II type 2 receptor (AT 2 R) agonist is neuroprotective against a subsequent stroke independent of any changes in blood pressure. Therefore, in the current study, we have examined the potential neuroprotective effect of AT 2 R stimulation initiated after stroke induction to mimic the clinical setting. Intracerebroventricular administration of the AT 2 R agonist CGP42112 was commenced 6 hours after an ischemic stroke had been induced in conscious spontaneously hypertensive rats. CGP42112 given over 4 doses in the same rats (3 µg/kg per dose centrally) at 6, 24, 48, and 72 hours after stroke induction reduced total infarct volume (32±13 mm 3 versus vehicle, 170±49 mm 3 ; P <0.05) and improved motor function. Furthermore, we have demonstrated that AT 2 R stimulation after stroke increased neuronal survival, decreased apoptosis, and caused an increase in the number of activated microglia in the core region of damage. The effects of CGP42112 were partially reversed with the coadministration of an AT 2 R antagonist, PD123319. Thus, the current study has shown for the first time that delayed central AT 2 R stimulation after a cerebral incident is neuroprotective in a conscious rat model of stroke.

Angiotensin II Type 2 Receptor Stimulation Initiated After Stroke Causes Neuroprotection in Conscious Rats

We have demonstrated previously that pretreatment with an angiotensin II type 2 receptor (AT 2 R) agonist is neuroprotective against a subsequent stroke independent of any changes in blood pressure. Therefore, in the current study, we have examined the potential neuroprotective effect of AT 2 R stimulation initiated after stroke induction to mimic the clinical setting. Intracerebroventricular administration of the AT 2 R agonist CGP42112 was commenced 6 hours after an ischemic stroke had been induced in conscious spontaneously hypertensive rats. CGP42112 given over 4 doses in the same rats (3 µg/kg per dose centrally) at 6, 24, 48, and 72 hours after stroke induction reduced total infarct volume (32±13 mm 3 versus vehicle, 170±49 mm 3 ; P <0.05) and improved motor function. Furthermore, we have demonstrated that AT 2 R stimulation after stroke increased neuronal survival, decreased apoptosis, and caused an increase in the number of activated microglia in the core region of damage. The effects of CGP42112 were partially reversed with the coadministration of an AT 2 R antagonist, PD123319. Thus, the current study has shown for the first time that delayed central AT 2 R stimulation after a cerebral incident is neuroprotective in a conscious rat model of stroke.

Angiotensin II Type 2 Receptor Stimulation Initiated After Stroke Causes Neuroprotection in Conscious Rats

We have demonstrated previously that pretreatment with an angiotensin II type 2 receptor (AT 2 R) agonist is neuroprotective against a subsequent stroke independent of any changes in blood pressure. Therefore, in the current study, we have examined the potential neuroprotective effect of AT 2 R stimulation initiated after stroke induction to mimic the clinical setting. Intracerebroventricular administration of the AT 2 R agonist CGP42112 was commenced 6 hours after an ischemic stroke had been induced in conscious spontaneously hypertensive rats. CGP42112 given over 4 doses in the same rats (3 µg/kg per dose centrally) at 6, 24, 48, and 72 hours after stroke induction reduced total infarct volume (32±13 mm 3 versus vehicle, 170±49 mm 3 ; P <0.05) and improved motor function. Furthermore, we have demonstrated that AT 2 R stimulation after stroke increased neuronal survival, decreased apoptosis, and caused an increase in the number of activated microglia in the core region of damage. The effects of CGP42112 were partially reversed with the coadministration of an AT 2 R antagonist, PD123319. Thus, the current study has shown for the first time that delayed central AT 2 R stimulation after a cerebral incident is neuroprotective in a conscious rat model of stroke.

Angiotensin II Type 2 Receptor Stimulation Initiated After Stroke Causes Neuroprotection in Conscious Rats

We have demonstrated previously that pretreatment with an angiotensin II type 2 receptor (AT 2 R) agonist is neuroprotective against a subsequent stroke independent of any changes in blood pressure. Therefore, in the current study, we have examined the potential neuroprotective effect of AT 2 R stimulation initiated after stroke induction to mimic the clinical setting. Intracerebroventricular administration of the AT 2 R agonist CGP42112 was commenced 6 hours after an ischemic stroke had been induced in conscious spontaneously hypertensive rats. CGP42112 given over 4 doses in the same rats (3 µg/kg per dose centrally) at 6, 24, 48, and 72 hours after stroke induction reduced total infarct volume (32±13 mm 3 versus vehicle, 170±49 mm 3 ; P <0.05) and improved motor function. Furthermore, we have demonstrated that AT 2 R stimulation after stroke increased neuronal survival, decreased apoptosis, and caused an increase in the number of activated microglia in the core region of damage. The effects of CGP42112 were partially reversed with the coadministration of an AT 2 R antagonist, PD123319. Thus, the current study has shown for the first time that delayed central AT 2 R stimulation after a cerebral incident is neuroprotective in a conscious rat model of stroke.

Angiotensin II Type 2 Receptor Stimulation Initiated After Stroke Causes Neuroprotection in Conscious Rats

We have demonstrated previously that pretreatment with an angiotensin II type 2 receptor (AT 2 R) agonist is neuroprotective against a subsequent stroke independent of any changes in blood pressure. Therefore, in the current study, we have examined the potential neuroprotective effect of AT 2 R stimulation initiated after stroke induction to mimic the clinical setting. Intracerebroventricular administration of the AT 2 R agonist CGP42112 was commenced 6 hours after an ischemic stroke had been induced in conscious spontaneously hypertensive rats. CGP42112 given over 4 doses in the same rats (3 µg/kg per dose centrally) at 6, 24, 48, and 72 hours after stroke induction reduced total infarct volume (32±13 mm 3 versus vehicle, 170±49 mm 3 ; P <0.05) and improved motor function. Furthermore, we have demonstrated that AT 2 R stimulation after stroke increased neuronal survival, decreased apoptosis, and caused an increase in the number of activated microglia in the core region of damage. The effects of CGP42112 were partially reversed with the coadministration of an AT 2 R antagonist, PD123319. Thus, the current study has shown for the first time that delayed central AT 2 R stimulation after a cerebral incident is neuroprotective in a conscious rat model of stroke.

Angiotensin II type 2 receptor stimulation initiated after stroke causes neuroprotection in conscious rats

We have demonstrated previously that pretreatment with an angiotensin II type 2 receptor (AT(2)R) agonist is neuroprotective against a subsequent stroke independent of any changes in blood pressure. Therefore, in the current study, we have examined the potential neuroprotective effect of AT(2)R stimulation initiated after stroke induction to mimic the clinical setting. Intracerebroventricular administration of the AT(2)R agonist CGP42112 was commenced 6 hours after an ischemic stroke had been induced in conscious spontaneously hypertensive rats. CGP42112 given over 4 doses in the same rats (3 µg/kg per dose centrally) at 6, 24, 48, and 72 hours after stroke induction reduced total infarct volume (32 ± 13 mm(3) versus vehicle, 170 ± 49 mm(3); P<0.05) and improved motor function. Furthermore, we have demonstrated that AT(2)R stimulation after stroke increased neuronal survival, decreased apoptosis, and caused an increase in the number of activated microglia in the core region of damage. The effects of CGP42112 were partially reversed with the coadministration of an AT(2)R antagonist, PD123319. Thus, the current study has shown for the first time that delayed central AT(2)R stimulation after a cerebral incident is neuroprotective in a conscious rat model of stroke.

Changes in microglial activation within the hindbrain, nodose ganglia, and the spinal cord following subdiaphragmatic vagotomy

Damage to peripheral nerve branches triggers activation of microglia in CNS areas containing motor neuron soma and primary afferent terminals of the damaged fibers. Furthermore, microglial activation occurs in areas containing the soma and terminals of spared nerve branches of a damaged nerve. Because the abdominal viscera are innervated by spinal afferents as well as vagal afferents and efferents, we speculated that spinal nerves might respond like spared nerve branches following damage to vagal fibers. Therefore, we tested the hypothesis that damage to the abdominal vagus would result in microglial activation in vagal structures-the nucleus of the solitary tract (NTS), dorsal motor nucleus of the vagus nerve (DMV), and nodose ganglia (NG)-as well as spinal cord (SC) segments that innervate the abdominal viscera. To test this hypothesis, rats underwent subdiaphragmatic vagotomy or sham surgery and were treated with saline or the microglial inhibitor, minocycline. Microglial activation was determined by quantifying changes in the intensity of fluorescent staining with a primary antibody against ionizing calcium adapter binding molecule 1 (Iba1). We found that subdiaphragmatic vagotomy significantly activated microglia in the NTS, DMV, and NG two weeks post-vagotomy. Microglial activation remained significantly increased in the NG and DMV for at least 42 days. Surprisingly, vagotomy significantly decreased microglial activation in the SC. Minocycline treatment attenuated microglial activation in all studied areas. Our results indicate that microglial activation in vagal structures following abdominal vagal damage is accompanied by suppression of microglial activation in associated areas of the spinal cord.

The discovery of a novel macrophage binding site

1. During the course of studies directed to determine the transport of Angiotensin II AT(2) receptors in the rat brain, we found that stab wounds to the brain revealed a binding site recognized by the AT(2) receptor ligand CGP42112 but not by Angiotensin II. 2. We localized this novel site to macrophages/microglia associated with physical or chemical injuries of the brain. 3. The non-Angiotensin II site was also highly localized to inflammatory lesions of peripheral arteries. 4. In rodent tissues, high binding expression was limited to the spleen and to circulating monocytes. A high-affinity binding site was also characterized in human monocytes. 5. Lack of affinity for many ligands binding to known macrophage receptors indicated the possibility that the non-Angiotensin II CGP42112 binding corresponds to a novel site.6. CGP42112 enhanced cell attachment to fibronectin and collagen and metalloproteinase-9 secretion from human monocytes incubated in serum-free medium but did not promote cytokine secretion. 7. When added in the presence of lipopolysaccharide, CGP42112 reduced the lipopolysaccharide-stimulated secretion of the pro-inflammatory cytokines TNF-alpha, IL-1, IL-1 beta, and IL-6, and increased protein kinase A. 8. Molecular modeling revealed that a CGP42112 derivative was selective for the novel macrophage site and did not recognize the Angiotensin II AT(2) receptor. 9. These results demonstrate that CGP42112, previously considered as a selective Angiotensin II AT(2) ligand, recognizes an additional non-Angiotensin II site different from AT(2) receptors. 10. Our observations indicate that CGP42112 or related molecules could be considered of interest as potential anti-inflammatory compounds.

Minocycline treatment attenuates microglia activation and non-angiotensin II [125I] CGP42112 binding in brainstem following nodose ganglionectomy

We have previously shown that following unilateral nodose ganglionectomy, [125I] CGP42112 binds to a non-angiotensin II (Ang II) related binding site in rat dorsal motor nucleus of the vagus nerve, ambiguus nucleus and nucleus of the solitary tract. Furthermore, this up-regulated binding site localizes with activated microglia. Given that some tetracyclines may inhibit microglia activation in brain, we examined the effect of minocycline treatment on the binding of [125I] CGP42112 and [3H] PK11195 (an established radioligand for microglia), as well as OX-42 immunoreactivity (an immunomarker for activated microglia), following nodose ganglionectomy. Male Wistar Kyoto rats underwent unilateral nodose ganglionectomy or sham operation and were treated with saline or minocycline (50 mg/kg i.p.) 12 h before surgery and twice daily after surgery (each 50mg/kg i.p.) for 3 days. Subsequent to nodose ganglionectomy, [125I] CGP42112 binding (insensitive to PD123319 or Ang II) was increased approximately two-fold in the ipsilateral nucleus of the solitary tract and was also induced in the ipsilateral dorsal motor nucleus of the vagus nerve and ambiguus nucleus of saline-treated rats. Treatment with minocycline reduced this non-angiotensin II [125I] CGP42112 binding (40-50% reduction) in the nucleus of the solitary tract, dorsal motor nucleus of the vagus nerve and ambiguus nucleus. Analogous experiments using [3H] PK11195 also revealed up-regulated binding in the ipsilateral nucleus of the solitary tract ( approximately 205%), dorsal motor nucleus of the vagus nerve (approximately 80%) and ambiguus nucleus (approximately 210%) of saline-treated rats following nodose ganglionectomy, which was reduced by 40-100% with minocycline treatment. Immunoreactivity to OX-42 confirmed an increase in microglia activation and accumulation of macrophages in these brain stem nuclei following nodose ganglionectomy, which was also attenuated following treatment with minocycline. These data demonstrate that non-Ang II [125I] CGP42112 binding following nodose ganglionectomy is attenuated by minocycline treatment. This minocycline-induced effect was associated with reduced activation of microglia and an apparent reduction in the number of macrophages in the abovementioned nuclei. This evidence suggests that a non-Ang II [125I] CGP42112 binding site is located on, or associated with, activated microglia and macrophages, providing a useful tool with which to quantitate the neuroprotective effects of centrally acting anti-inflammatory compounds.