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Biomedical subjects

Toshihiko Yanagita

Publications and source records attributed to Toshihiko Yanagita.

At least 19 recordsLinked to original sources
PubMed2006

Induction of aquaporin 1 by dexamethasone in lipid rafts in immortalized brain microvascular endothelial cells.

Water homeostasis in the brain is essential for brain function. We have studied how aquaporin (AQP) 1 expression in GP8 immortalized rat brain microvascular endothelial cells is regulated by glucocorticoid. AQP1 protein level was raised by dexamethasone treatment in a time- and concentration-dependent manner. The up-regulation of AQP1 protein by dexamethasone was associated with an increase of AQP1 mRNA level, with no change in the degradation rate of AQP1 mRNA. AQP1 was concentrated in detergent-insoluble fractions in the cells treated with or without dexamethasone, suggesting that function/trafficking of AQP1 may be regulated via the interaction with lipid rafts. Since glucocorticoid therapy has well known beneficial effects in the treatment of brain edema, the induction of AQP1 by dexamethasone raises a possibility that AQP1 plays a role in ameliorating brain edema.

Animals↗
PubMed2006

Constitutive activity of glycogen synthase kinase-3beta: positive regulation of steady-state levels of insulin receptor substrates-1 and -2 in adrenal chromaffin cells.

In cultured bovine adrenal chromaffin cells, 12-h treatment with 1-20 mM LiCl, an inhibitor of glycogen synthase kinase-3 (GSK-3), increased Ser(9) phosphorylation of GSK-3beta by approximately 44%, while decreasing insulin receptor substrate-1 (IRS-1) and IRS-2 protein levels by approximately 38 and approximately 62% in a concentration-dependent manner. Treatment with SB216763 (0.1-30 microM for 12 h), a selective inhibitor of GSK-3, lowered IRS-1 and IRS-2 levels by approximately 38 and approximately 48%, while increasing beta-catenin protein level by approximately 47%, due to the prevention of GSK-3-induced degradation of beta-catenin by SB216763. Insulin (100 nM for 24 h) increased Ser(9) phosphorylation of GSK-3beta by approximately 104%, while decreasing IRS-1 and IRS-2 levels by approximately 41 and approximately 72%; the insulin-induced Ser(9) phosphorylation of GSK-3beta, as well as down-regulations of IRS-1 and IRS-2 levels were restored to the control levels of nontreated cells at 24 h after the washout of the insulin (100 nM for 12 h)-treated cells. Either clasto-lactacystin beta-lactone or lactacystin (an inhibitor of proteasome) prevented LiCl- or SB216763-induced decreases of IRS-1 and IRS-2 levels by approximately 100 and approximately 69%, respectively. In contrast, calpastatin (an inhibitor of calpain) and leupeptin (an inhibitor of lysosome) failed to prevent the decreases of IRS-1 and IRS-2 levels caused by LiCl or SB216763. LiCl or SB216763 lowered IRS-2 mRNA level, with no effect on IRS-1 mRNA level. These results suggest that constitutive activity of GSK-3beta in quiescent cells positively maintains steady-state levels of IRS-1 and IRS-2 via regulating proteasomal degradation and/or synthesis of IRS-1 and IRS-2 proteins.

Acetylcysteine↗
PubMed2006

Enhancement of insulin-induced PI3K/Akt/GSK-3beta and ERK signaling by neuronal nicotinic receptor/PKC-alpha/ERK pathway: up-regulation of IRS-1/-2 mRNA and protein in adrenal chromaffin cells.

In cultured bovine adrenal chromaffin cells treated with nicotine (10 microm for 24 h), phosphorylation of Akt, glycogen synthase kinase-3beta (GSK-3beta) and extracellular signal-regulated kinase (ERK)1/2 induced by insulin (100 nm for 10 min) was enhanced by approximately 62%, without altering levels of these protein kinases. Nicotine produced time (> 12 h)- and concentration (EC(50) 3.6 and 13 microm)-dependent increases in insulin receptor substrate (IRS)-1 and IRS-2 levels by approximately 125 and 105%, without altering cell surface density of insulin receptors. In these cells, insulin-induced tyrosine phosphorylation of IRS-1/IRS-2 and recruitment of phosphoinositide 3-kinase (PI3K) to IRS-1/IRS-2 were augmented by approximately 63%. The increase in IRS-1/IRS-2 levels induced by nicotine was prevented by nicotinic acetylcholine receptor (nAChR) antagonists, the Ca(2+) chelator 1,2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetra-acetic acid tetrakis-acetoxymethyl ester, cycloheximide or actinomycin D. Nicotine increased IRS-1 and IRS-2 mRNA levels by approximately 57 and approximately 50%, and this was prevented by conventional protein kinase C (cPKC) inhibitor Gö6976, or ERK kinase inhibitors PD98059 and U0126. Nicotine phosphorylated cPKC-alpha, thereby increasing phosphorylation of ERK1/ERK2, as demonstrated by using Gö6976, PD98059 or U0126. Selective activation of cPKC-alpha by thymeleatoxin mimicked these effects of nicotine. Thus, stimulation of nAChRs up-regulated expression of IRS-1/IRS-2 via Ca(2+)-dependent sequential activation of cPKC-alpha and ERK, and enhanced insulin-induced PI3K/Akt/GSK-3beta and ERK signaling pathways.

Adrenal Medulla↗
PubMed2005

Lithium: potential therapeutics against acute brain injuries and chronic neurodegenerative diseases.

In addition to the well-documented mood-stabilizing effects of lithium in manic-depressive illness patients, recent in vitro and in vivo studies in rodents and humans have increasingly implicated that lithium can be used in the treatment of acute brain injuries (e.g., ischemia) and chronic neurodegenerative diseases (Alzheimer's disease, Parkinson's disease, tauopathies, and Huntington's disease). Consistent with this novel view, substantial evidences suggest that depressive illness is not a mere neurochemical disease, but is linked to gray matter atrophy due to the reduced number/size of neurons and glia in brain. Importantly, neurogenesis, that is, birth/maturation of functional new neurons, continues to occur throughout the lifetime in human adult brains (e.g., hippocampus); the neurogenesis is impaired by multiple not-fully defined factors (e.g., aging, chronic stress-induced increase of glucocorticoids, and excitotoxicity), accounting for brain atrophy in patients with depressive illness and neurodegenerative diseases. Chronic treatment of lithium, in agreement with the delayed-onset of mood-stabilizing effects of lithium, up-regulates cell survival molecules (e.g., Bcl-2, cyclic AMP-responsive element binding protein, brain-derived neurotrophic factor, Grp78, Hsp70, and beta-catenin), while down-regulating pro-apoptotic activities (e.g., excitotoxicity, p53, Bax, caspase, cytochrome c release, beta-amyloid peptide production, and tau hyperphosphorylation), thus preventing or even reversing neuronal cell death and neurogenesis retardation.

Acute Disease↗
PubMed2005

New twist on neuronal insulin receptor signaling in health, disease, and therapeutics.

Long after the pioneering studies documenting the existence of insulin (year 1967) and insulin receptor (year 1978) in brain, the last decade has witnessed extraordinary progress in the understanding of brain region-specific multiple roles of insulin receptor signalings in health and disease. In the hypothalamus, insulin regulates food intake, body weight, peripheral fat deposition, hepatic gluconeogenesis, reproductive endocrine axis, and compensatory secretion of counter-regulatory hormones to hypoglycemia. In the hippocampus, insulin promotes learning and memory, independent of the glucoregulatory effect of insulin. Defective insulin receptor signalings are associated with the dementia in normal aging and patients with age-related neurodegenerative diseases (e.g., Alzheimer's disease); the cognitive impairment can be reversed with systemic administration of insulin in the euglycemic condition. Intranasal administration of insulin enhances memory and mood and decreases body weight in healthy humans, without causing hypoglycemia. In the hypothalamus, insulin-induced activation of the phosphoinositide 3-kinase pathway followed by opening of ATP-sensitive K+ channel has been shown to be related to multiple effects of insulin. However, the precise molecular mechanisms of insulin's pleiotropic effects still remain obscure. More importantly, much remains unknown about the quality control mechanisms ensuring correct conformational maturation of the insulin receptor, and the cellular mechanisms regulating density of cell surface functional insulin receptors.

Animals↗
PubMed2005

Beyond vasodilation: the antioxidant effect of adrenomedullin in Dahl salt-sensitive rat aorta.

We have investigated the antioxidant effect of adrenomedullin (AM) on endothelial function in the Dahl salt-sensitive (DS) rat hypertension model. Dahl salt-resistant (DR) and DS rats were fed an 8% NaCl diet. In addition, the DS rats were subcutaneously infused with either saline or recombinant human AM for 4 weeks. Although systolic blood pressures measured weekly in AM- and saline-infused rats did not significantly differ, aortic O2*- levels were significantly (P<0.01) higher in the latter. Likewise, both endothelial nitric oxide synthase (eNOS) mRNA and protein were significantly higher in saline-infused DS rats. Infusion of AM reduced both O2*- and eNOS expression to levels comparable to those seen in DR rats. AM infusion also upregulated the gene expression of guanosine-5'-triphosphate cyclohydrolase I and downregulated the expression of p22(phox), suggesting that AM increased the NOS coupling and bioavailability of NO. AM possesses significant antioxidant properties that improve endothelial function.

Adrenomedullin↗
PubMed2004

Regulation of cell surface expression of voltage-dependent Nav1.7 sodium channels: mRNA stability and posttranscriptional control in adrenal chromaffin cells.

Regulated expression of Na+ channels is indispensable to physiological events, whereas dysregulated expression of otherwise silent or even normal Na+ channel isoforms causes Na+ channelopathies; however, the regulatory mechanisms remain unknown. In quiescent cultured bovine adrenal chromaffin cells, constitutive phosphorylation/activation of extracellular signal-regulated kinase-1 (ERK1) and ERK2 destabilized Nav l.7 Na+ channel alpha-subunit mRNA and decreased its level without altering alpha-subunit gene transcription, thus negatively regulating steady-state level of Na+ channels. Activation of protein kinase C (PKC) down-regulated Na+ channels via PKC isoform-specific mechanisms; conventional PKC-alpha promoted endocytic internalization of Na+ channels, whereas novel PKC-epsilon destabilized alpha-subunit mRNA without altering its gene transcription. Long-lasting (but not short-term) increase of cytoplasmic Ca2+ down-regulated Na+ channels; a slowly-developing moderate increase of Ca2+ activated PKC-alpha and calpain, promoting internalization of Na+ channels, whereas an immediate monophasic and salient plateau increase of Ca2+ lowered alpha- and beta1-subunit mRNA levels. Calcineurin, or FK506 binding protein- and rapamycin-associated protein (FRAP), a serine/threonine protein kinase, down-regulated, whereas insulin receptor tyrosine kinase or protein kinase A (PKA) up-regulated, Na+ channels via modulating Na+ channel internalization, and/or Na+ channel externalization from the trans-Golgi network. Neuroprotective, antiepiletic, antipsychotic, and local anesthetic drugs up-regulated Na+ channels via transcriptional/translational events.

Adrenal Medulla↗
PubMed2004

Molecular mechanisms and drug development in aquaporin water channel diseases: aquaporins in the brain.

Water homeostasis of the brain is essential for its neuronal activity. Changes in water content in the intra- and extra-cellular space affect ionic concentrations and therefore modify neuronal activity. Aquaporin (AQP) water channels may have a central role in keeping water homeostasis in the brain. Among AQP subtypes cloned in mammalian, only AQP1, AQP4, and AQP9 were identified in the brain. Changes in AQP expression may be correlated with edema formation of the brain. In this review, we describe the physiological function of AQPs and the regulatory mechanism of their expression in the brain.

Animals↗
PubMed2003

Expression of adrenomedullin and its receptor by chondrocyte phenotype cells.

For clarifying a process of de-differentiation in culturing chondrocytes, the present study was undertaken to investigate the secretion of adrenomedullin (AM) by chondrocyte phenotype cells and whether or not AM effects this proliferation in a cAMP-dependent fashion. Chondrocyte phenotype cells expressed AM and the AM receptor, and secreted high concentration of AM into the culture medium. When added to cultures, AM increased the intracellular cAMP level and decreased the number of these cells in a similar concentration-dependent fashion. Addition of forskolin and dibutyryl-cAMP caused a significant decrease in the number of these cells. Furthermore, the effect of AM was inhibited by a cAMP-dependent protein kinase A inhibitor (H89). The present findings indicate that AM has an autocrine/paracrine type of anti-proliferative effect on these cells mediated via a cAMP-dependent pathway and raise the possibility that AM plays a role in the local modulation of a process of de-differentiation by culturing chondrocyte phenotype cells.

Adrenomedullin↗
PubMed2003

Differential effects of bupivacaine enantiomers, ropivacaine and lidocaine on up-regulation of cell surface voltage-dependent sodium channels in adrenal chromaffin cells.

In cultured bovine adrenal chromaffin cells, (+/-)-bupivacaine inhibited veratridine-induced 22Na(+) influx (IC(50) 6.8 microM). The IC(50) of (+)-bupivacaine (2.8 microM) was 6.2-, 7.4-, and 17.1-fold lower than those of (-)-bupivacaine (17.3 microM), (-)-ropivacaine (20.6 microM), and lidocaine (47.8 microM). Chronic (i.e. 3-h) treatment of cells with (+/-)-bupivacaine increased cell surface [3H]saxitoxin ([3H]STX) binding capacity by 48% (EC(50) of 233 microM; t(1/2)=7.4 h), without changing the K(d) value. Treatment for 24 h with either (+)- or (-)-bupivacaine, or (-)-ropivacaine elevated [3H]STX binding, whereas 24-h treatment with lidocaine had no effect. The rise of [3H]STX binding by (+/-)-bupivacaine was prevented by cycloheximide, an inhibitor of protein synthesis, or brefeldin A, an inhibitor of cell surface vesicular exit from the trans-Golgi network; however, (+/-)-bupivacaine did not increase Na(+) channel alpha- and beta(1)-subunit mRNA levels. In cells subjected to (+/-)-bupivacaine treatment (1 mM for 24 h) followed by 3-h washout, veratridine-induced 22Na(+) influx was enhanced, even when measured in the presence of ouabain, an inhibitor of Na(+),K(+)-ATPase. Ptychodiscus brevis toxin-3 potentiated veratridine-induced 22Na(+) influx by 2.3-fold in the (+/-)-bupivacaine-treated cells, as in non-treated cells. These results suggest that lipophilic bupivacaine enantiomers or (-)-ropivacaine acutely inhibit Na(+) channel gating, whereas its chronic treatment up-regulates cell surface expression of Na(+) channels via translational and externalization events.

Amides↗
PubMed2003

Distinct effects of ketone bodies on down-regulation of cell surface insulin receptor and insulin receptor substrate-1 phosphorylation in adrenal chromaffin cells.

Treatment (>/=24 h) of cultured bovine adrenal chromaffin cells with ketoacidosis-related concentrations (>/=3 mM) of acetoacetate (but not beta-hydroxybutyrate, acetone, and acidic medium) caused a time- and concentration-dependent reduction of cell surface (125)I-insulin binding by ~38%, with no change in the K(d) value. The reduction of (125)I-insulin binding returned to control nontreated level at 24 h after the washout of acetoacetate-treated cells. Acetoacetate did not increase the internalization rate of cell surface insulin receptor (IR), as measured in the presence of brefeldin A, an inhibitor of cell surface vesicular exit from the trans-Golgi network. Acetoacetate (10 mM for 24 h) lowered cellular levels of the immunoreactive IR precursor molecule (approximately 190 kDa) and IR by 22 and 28%, respectively. Acetoacetate decreased IR mRNA levels by approximately 23% as early as 6 h, producing their maximum plateau reduction at 12 and 24 h. The half-life of IR mRNA was shortened by acetoacetate from 13.6 to 9.5 h. Immunoprecipitation followed by immunoblot analysis revealed that insulin-induced (100 nM for 10 min) tyrosine-phosphorylation of insulin receptor substrate-1 (IRS-1) was attenuated by 56% in acetoacetate-treated cells, with no change in IRS-1 level. These results suggest that chronic treatment with acetoacetate selectively down-regulated the density of cell surface functional IR via lowering IR mRNA levels and IR synthesis, thereby retarding insulin-induced activation of IRS-1.

3-Hydroxybutyric Acid↗
PubMed2003

Destabilization of Na(v)1.7 sodium channel alpha-subunit mRNA by constitutive phosphorylation of extracellular signal-regulated kinase: negative regulation of steady-state level of cell surface functional sodium channels in adrenal chromaffin cells.

In cultured bovine adrenal chromaffin cells expressing Na(v)1.7 isoform of voltage-dependent Na(+) channels, treatment (> or = 6 h) with serum deprivation, PD98059, or U0126 increased cell surface [(3)H]saxitoxin ([(3)H]STX) binding by approximately 58% (t(1/2) = 12.5 h), with no change in the K(d) value. Immunoblot analysis showed that either treatment attenuated constitutive phosphorylation of extracellular signal-regulated kinase (ERK) 1 and ERK2 but not of p38 mitogen-activated protein kinase and c-Jun N-terminal kinase (JNK) 1 and JNK2. The increase of [(3)H]STX binding and the attenuated phosphorylation of ERK1 and ERK2 returned to the control nontreated levels after the addition of serum or the washout of PD98059- or U0126-treated cells. Simultaneous treatment of serum deprivation with PD98059 or U0126 did not produce an additional increasing effect on [(3)H]STX binding, compared with either treatment alone. In cells subjected to either treatment, veratridine-induced maximum (22)Na(+) influx was augmented by approximately 47%, with no change in the EC(50) value; Ptychodiscus brevis toxin-3 enhanced veratridine-induced (22)Na(+) influx by 2-fold, as in nontreated cells. Serum deprivation, PD98059, or U0126 increased Na(+) channel alpha- but not beta(1)- subunit mRNA level by approximately 50% between 3 and 24 h; cycloheximide, an inhibitor of protein synthesis, increased alpha-subunit mRNA level and nullified additional increasing effect of either treatment on alpha-subunit mRNA level. Either treatment prolonged half-life of alpha-subunit mRNA from 17.5 to approximately 26.3 h without altering alpha-subunit gene transcription. Thus, constitutively phosphorylated/activated ERK destabilizes Na(+) channel alpha-subunit mRNA via translational event, which negatively regulates steady-state level of alpha-subunit mRNA and cell surface expression of functional Na(+) channels.

Adrenal Glands↗
PubMed2003

Pathophysiological function of adrenomedullin and proadrenomedullin N-terminal peptides in adrenal chromaffin cells.

Adrenomedullin (AM) and peptides of the proadrenomedullin N-terminal 20 peptide (PAMP20) family are multifunctional peptides abundantly expressed in the adrenal medulla. These peptides are released by regulated exocytosis along with catecholamines upon stimulation of adrenal chromaffin cells. They are also released gradually during culture, and this release is stimulated by a 3',5'-cyclic adenosine monophosphate (cAMP)-dependent pathway. The expression and release of AM increase under hypoxia in chromaffin cells. The expression of AM in pheochromocytoma PC12 cells is reduced during neuronal differentiation with nerve growth factor. On the other hand, PAMP20 and PAMP12 suppress catecholamine release and synthesis by interfering with nicotinic cholinergic receptors. AM increases blood flow in the adrenal gland, and causes a gradual release of catecholamine, but does not modify regulated exocytosis upon the stimulation of cells. Current data indicate that the expression of these peptides is regulated by intracellular signaling pathways, and changes under various physiological and pathological conditions. AM and PAMP20 family peptides have distinct physiological functions. PAMP20 and PAMP12 are endogenous peptides that modulate chromaffin cell function in an autocrine manner, whereas AM may mainly regulate vascular cell function in a paracrine manner.

Adrenal Medulla↗
PubMed2002

Regulation of voltage-dependent sodium channel expression in adrenal chromaffin cells: involvement of multiple calcium signaling pathways.

The density and electrical activity of cell surface voltage-dependent Na(+) channels are key determinants regulating the neuronal plasticity including development, differentiation, and regeneration. Abnormalities of Na(+) channels are associated with various neurological diseases. In this paper, we review the regulatory mechanisms of cell surface Na(+) channel expression mediated by Ca(2+) signaling pathways in cultured bovine adrenal chromaffin cells. Sustained, but not transient, elevation of intracellular Ca(2+) concentration reduced the number of cell surface Na(+) channels. The reduction of Na(+) channels was suppressed by an inhibitor of calpain, a Ca(2+)-dependent protease, and by an inhibitor of protein kinase C (PKC). The activation of conventional PKC-alpha and novel PKC-epsilon reduced cell surface Na(+) channels by the acceleration of internalization of the channels and by the increased degradation of Na(+) channel alpha-subunit mRNA, respectively. On the contrary, the activation of PKC-epsilon increased Na(+) channel beta(1)-subunit mRNA level. The inhibition of calcineurin, a Ca(2+)/calmodulin-dependent protein phosphatase 2B, by immunosuppressants upregulated cell surface Na(+) channels by both stimulating externalization and inhibiting internalization of the channels without changing Na(+) channel alpha- and beta(1)-subunit mRNA levels. Thus, the signal transduction pathways mediated by intracellular Ca(2+) modulate cell surface Na(+) channel expression via multiple Ca(2+)-dependent events, and the changes in the intracellular vesicular trafficking are the important mechanisms in the regulation of Na(+) channel expression.

Adrenal Glands↗
PubMed2002

Serum deprivation-induced upregulation of voltage-dependent sodium channels in adrenal chromaffin cells: selective involvement of extracellular signal-regulated kinase pathway.

In the present study, we investigated whether activation of the MAPK family could regulate the cell surface expression of Na channels in cultured bovine adrenal chromaffin cells. The results suggest that constitutively activated ERK (but not p38 or JNK), by various extracellular stimuli, down-modulates the density of cell surface Na channels, which was mediated via the destabilization of Na channel alpha-subunit mRNA.

Animals↗
PubMed2002

Differential effects of short and prolonged exposure to carvedilol on voltage-dependent Na(+) channels in cultured bovine adrenal medullary cells.

We examined the effects of short and prolonged exposure to carvedilol, an antihypertensive and beta-adrenoceptor blocking drug, on voltage-dependent Na(+) channels in cultured bovine adrenal medullary cells. Carvedilol (1-100 microM) reduced (22)Na(+) influx induced by veratridine, an activator of voltage-dependent Na(+) channels. Carvedilol also suppressed veratridine-induced (45)Ca(2+) influx and catecholamine secretion in a concentration-dependent manner similar to that of (22)Na(+) influx. Prolonged exposure of the cells to 10 microM carvedilol increased [(3)H]saxitoxin ([(3)H]STX) binding, which reached a plateau at 12 h and was still observed at 48 to 72 h. Scatchard analysis of [(3)H]STX binding revealed that carvedilol increased the B(max) value (control, 14.9 +/- 0.9 fmol/10(6) cells; carvedilol, 23.8 +/- 1.2 fmol/10(6) cells) (n = 3, P < 0.05) without altering the K(d) value, suggesting a rise in the number of cell surface Na(+) channels. The increase in [(3)H]STX binding by carvedilol was prevented by cycloheximide, an inhibitor of protein synthesis, whereas carvedilol changed neither alpha- nor beta(1)-subunit mRNA levels of Na(+) channels. The carvedilol-induced increase of [(3)H]STX binding was abolished by brefeldin A and H-89, inhibitors of intracellular vesicular trafficking of proteins from the trans-Golgi network and of cyclic AMP-dependent protein kinase (protein kinase A), respectively. The present findings suggest that short-term treatment with carvedilol reduces the activity of Na(+) channels, whereas prolonged exposure to carvedilol up-regulates cell surface Na(+) channels. This may add new pharmacological effects of carvedilol to our understanding in the treatment of heart failure and hypertension.

Adrenal Medulla↗