Narumi Hashikawa-Hobara

Candesartan Cilexetil Improves Angiotensin II Type 2 Receptor–Mediated Neurite Outgrowth via the PI3K-Akt Pathway in Fructose-Induced Insulin-Resistant Rats

We have shown previously that stimulation of the angiotensin II type 2 receptor (AT2R) results in nerve facilitation. In this study, we determined the capacity of candesartan to correct expression patterns characteristic of neuropathy and AT2R-mediated neurite outgrowth in the fructose-induced insulin-resistant rat, which is one of the human hyperinsulinemia models. Wistar rats received a 15% (w/v) fructose solution in their drinking water for 4 weeks (fructose-drinking rats [FDRs]), with or without candesartan (5 mg/kg/day). We evaluated physiological and behavioral parameters and performed immunohistochemical studies. We found that the FDR developed insulin resistance and downregulated both AT2R neuronal function and phosphorylated Akt expression in dorsal root ganglia (DRG) neurons. Candesartan improved neurite outgrowth in the FDR, which was associated with the restoration of AT2R and phosphorylated Akt expression. Furthermore, downregulation of phosphoinositide 3-kinase (PI3K) inhibited AT2R-mediated neurite outgrowth in control DRG cells. PI3K activation increased AT2R-mediated neurite outgrowth and phosphorylated Akt expression in FDR DRG cells. These results suggest that the decrease of AT2R-mediated neurite outgrowth in FDRs is likely to be the result of decreased PI3K-dependent Akt activation. Candesartan improved AT2R neuronal function and Akt phosphorylation, which were associated with sensory nerve defects and insulin sensitivity in the FDR.

Calcitonin gene-related peptide pre-administration acts as a novel antidepressant in stressed mice.

Calcitonin gene-related peptide (CGRP) is a neuropeptide that has potent vasodilator properties and is involved in various behavioral disorders. The relationship between CGRP and depression-like behavior is unclear. In this study, we used chronically stressed mice to investigate whether CGRP is involved in depression-like behavior. Each mouse was exposed to restraint and water immersion stress for 15 days. After stress exposure, mice were assessed using behavioral tests: open field test, forced swim test and sucrose preference test. Serum corticosterone levels, hippocampal proliferation and mRNA expression of neurotrophins were measured. After stress exposure, mice exhibited depression-like behavior and decreased CGRP mRNA levels in the hippocampus. Although intracerebroventricular CGRP administration (0.5 nmol) did not alter depression-like behavior after 15-day stress exposure, a single CGRP administration into the brain, before the beginning of the 15-day stress exposure, normalized the behavioral dysfunctions and increased nerve growth factor (Ngf) mRNA levels in stressed mice. Furthermore, in the mouse E14 hippocampal cell line, CGRP treatment induced increased expression of Ngf mRNA. The NGF receptor inhibitor K252a inhibited CGRP’s antidepressant-like effects in stressed mice. These results suggest that CGRP expression in the mouse hippocampus is associated with depression-like behavior and changes in Ngf mRNA levels.

Histamine 3 receptor activation reduces the expression of neuronal angiotensin II type 1 receptors in the heart.

In severe myocardial ischemia, histamine 3 (H3) receptor activation affords cardioprotection by preventing excessive norepinephrine release and arrhythmias; pivotal to this action is the inhibition of neuronal Na+/H+ exchanger (NHE). Conversely, angiotensin II, formed locally by mast cell-derived renin, stimulates NHE via angiotensin II type 1 (AT1) receptors, facilitating norepinephrine release and arrhythmias. Thus, ischemic dysfunction may depend on a balance between the NHE-modulating effects of H3 receptors and AT1 receptors. The purpose of this investigation was therefore to elucidate the H3/AT1 receptor interaction in myocardial ischemia/reperfusion. We found that H3 receptor blockade with clobenpropit increased norepinephrine overflow and arrhythmias in Langendorff-perfused guinea pig hearts subjected to ischemia/reperfusion. This coincided with increased neuronal AT1 receptor expression. NHE inhibition with cariporide prevented both increases in norepinephrine release and AT1 receptor expression. Moreover, norepinephrine release and AT1 receptor expression were increased by the nitric oxide (NO) synthase inhibitor NG-methyl-l-arginine and the protein kinase C activator phorbol myristate acetate. H3 receptor activation in differentiated sympathetic neuron-like PC12 cells permanently transfected with H3 receptor cDNA caused a decrease in protein kinase C activity and AT1 receptor protein abundance. Collectively, our findings suggest that neuronal H3 receptor activation inhibits NHE by diminishing protein kinase C activity. Reduced NHE activity sequentially causes intracellular acidification, increased NO synthesis, and diminished AT1 receptor expression. Thus, H3 receptor-mediated NHE inhibition in ischemia/reperfusion not only opposes the angiotensin II-induced stimulation of NHE in cardiac sympathetic neurons, but also down-regulates AT1 receptor expression. Cardioprotection ultimately results from the combined attenuation of angiotensin II and norepinephrine effects and alleviation of arrhythmias.

Decreased perivascular CGRP-containing nerves in Otsuka Long–Evans Tokushima Fatty rats with insulin resistance and hypertension

We previously reported that chronic hyperinsulinemia induced by drinking fructose elicited an abnormal neuronal regulation of vascular tone, which contributed to the development of hypertension. This study was designed to elucidate the possible mechanisms underlying the dysfunctional neuronal regulation of vascular tone induced by chronic hyperinsulinemia by comparing isolated mesenteric vascular beds from Otsuka Long–Evans Tokushima Fatty (OLETF) rats with those of control Long–Evans Tokushima Otsuka rat (LETO) rats. Insulin, triglyceride and total cholesterol levels in plasma, blood glucose concentrations, a glucose-insulin index, systolic blood pressure and perivascular innervations were assessed using biochemical and immunohistochemical methods. Mesenteric vascular beds isolated from OLETF and LETO rats were perfused with a Krebs solution containing methoxamine, and changes in perfusion pressure in response to periarterial nerve stimulation (PNS) and the perfusion of vasoactive agents were measured. OLETF rats (8–25 weeks old) showed age-related increases in insulin, triglycerides, total cholesterol, blood glucose, the glucose-insulin index (homeostasis model assessment ratio (HOMA-IR)) and systolic blood pressure compared with LETO rats. In perfused mesenteric vascular beds, the PNS-induced adrenergic nerve-mediated vasoconstrictor responses in OLETF rats were significantly greater than those in LETO rats, whereas the PNS-induced calcitonin gene-related peptide (CGRP) nerve-mediated vasodilator responses in OLETF rats were significantly smaller than those in LETO rats. In immunohistochemical experiments, the density of CGRP-immunopositive nerves in the mesenteric arteries of OLETF rats decreased significantly with age. The present findings suggest that the abnormal innervation of perivascular nerves in mesenteric resistance arteries induced by chronic hyperinsulinemia disturbs the neuronal regulation of vascular tone and may cause hypertension in OLETF rats.

Insulin Resistance-Induced Hypertension and a Role of Perivascular CGRPergic Nerves

Insulin resistance is defined as a preliminary step of type 2 diabetes mellitus with decreased insulin action evoked by continuous postprandial hyperglycemia, which is provoked by high fat and calories dieting, a lack of physical activity and obesity. In the early phase of type 2 diabetes mellitus, patients have a hyperinsulinemia to compensate deficient insulin action by increased secretion from the pancreas to maintain euglycemia. Then, pancreatic β cells progressively decrease secretion function, resulting in the development of diabetes mellitus with decreased serum insulin levels. Accumulating evidences show that insulin resistance is associated with hypertension. However, the mechanisms underlying hypertension associated with type 2 diabetes mellitus have still unknown. Therefore, to elucidate the mechanisms of insulin resistance-induced hypertension, we investigated that the effects of hyperinsulinemia or hyperglycemia on vascular responses mediated by perivascular nerves including sympathetic adrenergic nerves and calcitonin gene-related peptide (CGRP)-containing nerves (CGRPergic nerves). In this article, we show evidence that insulin resistance-induced hypertension could be resulted from increased density and function of sympathetic nerve, and decreased density and function of CGRPergic nerves. Furthermore, our findings provide a new insight into the research of therapeutic drugs for insulin resistance-induced hypertension.

Adrenergic stimulation-released 5-HT stored in adrenergic nerves inhibits CGRPergic nerve-mediated vasodilatation in rat mesenteric resistance arteries.

5‐HT is taken up by and stored in adrenergic nerves and periarterial nerve stimulation (PNS) releases 5‐HT to cause vasoconstriction in rat mesenteric arteries. The present study investigated whether PNS‐released 5‐HT stored in adrenergic nerves affects the function of perivascular calcitonin gene‐related peptide‐containing (CGRPergic) nerves.

The Akt-nitric oxide-cGMP pathway contributes to nerve growth factor-mediated neurite outgrowth in apolipoprotein E knockout mice

Apolipoprotein E (apo)-deficient [apoE(−/−)] mice have peripheral sensory nerve defects and a reduced and delayed response to noxious thermal stimuli. However, to date, no report has focused on the influence of apoE deficiency on calcitonin gene-related peptide (CGRP)-containing nerve fiber extensions. We have shown that the density of CGRP-containing nerve fibers decreases in mesenteric arteries of apoE(−/−) mice compared with wild-type mice. Here, we investigated whether apoE deficiency is involved in nerve growth factor (NGF)-induced CGRP-containing nerve regeneration using apoE(−/−) mice. NGF-mediated CGRP-like immunoreactivity (LI)-neurite outgrowth in apoE(−/−) cultured dorsal root ganglia (DRG) cells was significantly lower than that in wild-type cultures. However, the level of NGF receptor mRNA in apoE(−/−) DRG cells was similar to that in wild-type mice. To clarify the mechanism of the impaired ability of NGF-mediated neurite outgrowth, we focused on the Akt-nitric oxide (NO)-cGMP pathway. Expression of phosphorylated Akt was significantly reduced in apoE(−/−) DRG. The NO donor, sodium nitroprusside or S-nitroso-N-acetylpenicillamine, did not affect NGF-mediated neurite outgrowth in apoE(−/−) cultured DRG cells. However, 8-bromoguanosine 3′,5′-cyclic monophosphate sodium salt n-hydrate, a cGMP analog, induced NGF-mediated nerve facilitation similar to wild-type NGF-mediated neurite outgrowth levels. Furthermore, in apoE(−/−) DRG, soluble guanylate cyclase expression was significantly lower than that in wild-type DRG. These results suggest that in apoE(−/−) mice the Akt-NO-cGMP pathway is impaired, which may be caused by NGF-mediated CGRP-LI-neurite outgrowth defects.

Characterization of Perivascular Nerve Distribution in Rat Mesenteric Small Arteries

The distribution pattern of perivascular nerves in some branches of rat mesenteric arteries was studied. Mesenteric arteries isolated from 8-week-old Wistar rats were divided into the 1st-, 2nd-, and 3rd-order branches. The distribution of perivascular nerves in each branch was immunohistochemically evaluated using antibodies against neuropeptide Y (NPY), tyrosine hydroxylase (TH), calcitonin gene-related peptide (CGRP), substance P (SP), and neuronal nitric oxide synthase (nNOS). The density of NPY-, TH-, CGRP-, and SP-like immunoreactive (LI) nerves in the 2nd and 3rd branches was significantly greater than that in the 1st branch, and a negative relationship was found between nerve density and arterial diameter, except for TH-LI nerves. The density of NPY- and TH-LI nerves in all branches, which was similar, was greater than that of CGRP- (except for NPY-LI nerves in the 1st branch), SP-, or nNOS-LI nerves. Double immunostaining revealed that TH-LI nerves made contact with nNOS-LI, CGRP-LI, and SP-LI nerves and that CGRP-LI nerves made contact with TH-, NPY-, or nNOS-LI nerves, while TH-LI and CGRP-LI nerves nearly merged with NPY-LI and SP-LI nerves, respectively. These results suggest that the each branch of mesenteric arteries is densely innervated by vasoconstrictor nerves containing NPY, TH, and vasodilator CGRP nerves. They also suggest that the intense density of perivascular nerves in the 2nd and 3rd branches may contribute to maintaining vascular tone.

HSP105 prevents depression-like behavior by increasing hippocampal brain-derived neurotrophic factor levels in mice

The gastric ulcer drug teprenone has central nervous system effects, specifically reducing depression-like behavior in mice. Heat shock proteins (HSPs) are stress-induced chaperones that are involved in neurological disease. Although increasingly implicated in behavioral disorders, the mechanisms of HSP action, and the relevant functional pathways, are still unclear. We examined whether oral administration of geranylgeranylacetone (GGA), a known HSP inducer, produced an antidepressant effect in a social defeat stress model of depression in mice. We also investigated the possible molecular mechanisms involved, particularly focusing on hippocampal neurogenesis and neurotrophic factor expression. In stressed mice, hippocampal HSP105 expression decreased. However, administration of GGA increased HSP105 expression and improved depression-like behavior, induced hippocampal cell proliferation, and elevated brain-derived neurotrophic factor (BDNF) levels in mouse hippocampus. Co-treatment with GGA and the BDNF receptor inhibitor K252a suppressed the antidepressant effects of GGA. HSP105 knockdown decreased BDNF mRNA levels in HT22 hippocampal cell lines and hippocampal tissue and inhibited the GGA-mediated antidepressant effect. These observations suggest that GGA administration is a therapeutic candidate for depressive diseases by increasing hippocampal BDNF levels via HSP105 expression.

Protons modulate perivascular axo‐axonal neurotransmission in the rat mesenteric artery

Previous studies have demonstrated that nicotine releases protons from adrenergic nerves via stimulation of nicotinic ACh receptors and activates transient receptor potential vanilloid‐1 (TRPV1) receptors located on calcitonin gene‐related peptide (CGRP)‐containing (CGRPergic) vasodilator nerves, resulting in vasodilatation. The present study investigated whether perivascular nerves release protons, which modulate axon‐axonal neurotransmission.