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Biomedical subjects

Kenneth Walsh

Publications and source records attributed to Kenneth Walsh.

At least 55 records · Page 3Linked to original sources
PubMed2004

Foxo transcription factors induce the atrophy-related ubiquitin ligase atrogin-1 and cause skeletal muscle atrophy.

Skeletal muscle atrophy is a debilitating response to fasting, disuse, cancer, and other systemic diseases. In atrophying muscles, the ubiquitin ligase, atrogin-1 (MAFbx), is dramatically induced, and this response is necessary for rapid atrophy. Here, we show that in cultured myotubes undergoing atrophy, the activity of the PI3K/AKT pathway decreases, leading to activation of Foxo transcription factors and atrogin-1 induction. IGF-1 treatment or AKT overexpression inhibits Foxo and atrogin-1 expression. Moreover, constitutively active Foxo3 acts on the atrogin-1 promoter to cause atrogin-1 transcription and dramatic atrophy of myotubes and muscle fibers. When Foxo activation is blocked by a dominant-negative construct in myotubes or by RNAi in mouse muscles in vivo, atrogin-1 induction during starvation and atrophy of myotubes induced by glucocorticoids are prevented. Thus, forkhead factor(s) play a critical role in the development of muscle atrophy, and inhibition of Foxo factors is an attractive approach to combat muscle wasting.

Adenoviridae↗
PubMed2004

Adiponectin stimulates angiogenesis in response to tissue ischemia through stimulation of amp-activated protein kinase signaling.

Obesity is a risk factor for the development of cardiovascular diseases that are associated with impaired angiogenesis. Adiponectin is an adipocyte-specific adipocytokine with anti-atherogenic and anti-diabetic properties, and its plasma levels are reduced in association with obesity-linked diseases. Here, we investigated whether adiponectin regulates angiogenesis in response to tissue ischemia using adiponectin knock-out (KO) mice. Angiogenic repair of ischemic hind limbs was impaired in adiponectin-KO mice compared with wild-type (WT) mice as evaluated by laser Doppler flow method and capillary density analyses. Adenovirus-mediated supplement of adiponectin accelerated angiogenic repair in both adiponectin-KO and WT mice. Intramuscular injection of an adenovirus encoding dominant-negative AMP-activated kinase diminished the improvement in limb perfusion seen in WT mice and abolished the adiponectin-induced enhancement of perfusion. These data indicate that adiponectin can function to stimulate angiogenesis in response to ischemic stress by promoting AMP-activated kinase signaling. Therefore, adiponectin may be useful in the treatment for obesity-related vascular deficiency diseases.

AMP-Activated Protein Kinases↗
PubMed2004

Impaired clearance of apoptotic cells promotes synergy between atherogenesis and autoimmune disease.

To clarify the link between autoimmune disease and hypercholesterolemia, we created the gld.apoE(-/-) mouse as a model of accelerated atherosclerosis. Atherosclerotic lesion area was significantly increased in gld.apoE(-/-) mice compared with apoE(-/-) mice. gld.apoE(-/-) mice also displayed increases in lymphadenopathy, splenomegaly, and autoantibodies compared with gld mice, and these effects were exacerbated by high cholesterol diet. gld.apoE(-/-) mice exhibited higher levels of apoptotic cells, yet a reduced frequency of engulfed apoptotic nuclei within macrophages. Infusion of lysophosphatidylcholine, a component of oxidized low density lipoprotein, markedly decreased apoptotic cell clearance in gld mice, indicating that hypercholesterolemia promotes autoimmune disease in this background. These data suggest that defects in apoptotic cell clearance promote synergy between atherosclerotic and autoimmune diseases.

Animals↗
PubMed2004

Nuclear targeting of Akt enhances kinase activity and survival of cardiomyocytes.

Heart failure is associated with death of cardiomyocytes leading to loss of contractility. Previous studies using membrane-targeted Akt (myristolated-Akt), an enzyme involved in antiapoptotic signaling, showed inhibition of cell death and prevention of pathogenesis induced by cardiomyopathic stimuli. However, recent studies by our group have found accumulation of activated Akt in the nucleus, suggesting that biologically relevant target(s) of Akt activity may be located there. To test this hypothesis, a targeted Akt construct was created to determine the antiapoptotic action of nuclear Akt accumulation. Nuclear localization of the adenovirally encoded Akt construct was confirmed by confocal microscopy. Cardiomyocytes expressing nuclear-targeted Akt showed no evidence of morphological remodeling such as altered myofibril density or hypertrophy. Nuclear-targeted Akt significantly elevated levels of phospho-Akt and kinase activity and inhibited apoptosis as effectively as myristolated-Akt in hypoxia-induced cell death. Transgenic overexpression of nuclear-targeted Akt did not result in hypertrophic remodeling, altered cardiomyocyte DNA content or nucleation, or enhanced phosphorylation of typical cytoplasmic Akt substrates, yet transgenic hearts were protected from ischemia-reperfusion injury. Gene array analyses demonstrated changes in the transcriptional profile of Akt/nuc hearts compared with nontransgenic controls distinct from prior characterizations of Akt expression in transgenic hearts. Collectively, these experiments show that targeting of Akt to the nucleus mediates inhibition of apoptosis without hypertrophic remodeling, opening new possibilities for therapeutic applications of nuclear-targeted Akt to inhibit cell death associated with heart disease.

Active Transport, Cell Nucleus↗
PubMed2004

Heat shock protein 70 participates in the neuroprotective response to intracellularly expressed beta-amyloid in neurons.

Intracellular beta-amyloid 42 (Abeta42) accumulation is increasingly recognized as an early event in the pathogenesis of Alzheimer's disease (AD). We have developed a doxycycline-inducible adenoviral-based system that directs intracellular Abeta42 expression and accumulation into the endoplasmic reticulum of primary neuronal cultures in a regulated manner. Abeta42 exhibited a perinuclear distribution in cell bodies and an association with vesicular compartments. Virally expressed intracellular Abeta42 was toxic to neuronal cultures 24 hr after induction in a dose-dependent manner. Abeta42 expression prompted the rapid induction of stress-inducible Hsp70 protein in neurons, and virally mediated Hsp70 overexpression rescued neurons from the toxic effects of intracellular Abeta accumulation. Together, these results implicate the cellular stress response as a possible modulator of Abeta-induced toxicity in neuronal cultures.

Adenoviridae↗
PubMed2004

Selective suppression of endothelial cell apoptosis by the high molecular weight form of adiponectin.

Adiponectin is an adipocyte-derived, antiatherogenic protein that is present in serum as three isoforms. Total adiponectin levels are decreased in obese or diabetic humans or animal models. This study was designed to elucidate the relative isoform distribution of adiponectin in human disease states and identify the active form of adiponectin toward vascular endothelial cells. The percentage of high molecular weight form (HMW) per total adiponectin was significantly lower in patients with coronary artery disease than control subjects, whereas the hexamer form was similar and the trimer form was significantly higher. During weight reduction in obese subjects, the HMW form increased and the trimer and hexamer forms decreased. Recombinant adiponectin dose-dependently suppressed apoptosis and caspase-3 activity in human umbilical vein endothelial cells (HUVECs). Transduction with dominant-negative AMP-activated protein kinase (AMPK) abolished the suppressive effect of adiponectin on HUVECs. Gel filtration chromatography was used to separate the adiponectin isoforms, and the antiapoptotic effect toward HUVECs was only observed with the HMW form. These data suggest that HMW adiponectin specifically confers the vascular-protective activities of this adipocytokine. The full text of this article is available online at http://circres.ahajournals.org.

AMP-Activated Protein Kinases↗
PubMed2004

Cardiac stem cell and myocyte aging, heart failure, and insulin-like growth factor-1 overexpression.

To determine whether cellular aging leads to a cardiomyopathy and heart failure, markers of cellular senescence, cell death, telomerase activity, telomere integrity, and cell regeneration were measured in myocytes of aging wild-type mice (WT). These parameters were similarly studied in insulin-like growth factor-1 (IGF-1) transgenic mice (TG) because IGF-1 promotes cell growth and survival and may delay cellular aging. Importantly, the consequences of aging on cardiac stem cell (CSC) growth and senescence were evaluated. Gene products implicated in growth arrest and senescence, such as p27Kip1, p53, p16INK4a, and p19ARF, were detected in myocytes of young WT mice, and their expression increased with age. IGF-1 attenuated the levels of these proteins at all ages. Telomerase activity decreased in aging WT myocytes but increased in TG, paralleling the changes in Akt phosphorylation. Reduction in nuclear phospho-Akt and telomerase resulted in telomere shortening and uncapping in WT myocytes. Senescence and death of CSCs increased with age in WT impairing the growth and turnover of cells in the heart. DNA damage and myocyte death exceeded cell formation in old WT, leading to a decreased number of myocytes and heart failure. This did not occur in TG in which CSC-mediated myocyte regeneration compensated for the extent of cell death preventing ventricular dysfunction. IGF-1 enhanced nuclear phospho-Akt and telomerase delaying cellular aging and death. The differential response of TG mice to chronological age may result from preservation of functional CSCs undergoing myocyte commitment. In conclusion, senescence of CSCs and myocytes conditions the development of an aging myopathy.

Aging↗
PubMed2004

The pro- and antiangiogenic effects of statins.

Clinical studies indicate that 3-hydroxyl-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor (statin) therapy has a cardiovascular protective activity that may result from an improvement in endothelial function. Experimental studies have shown that statins protect against ischaemia-reperfusion injury of the heart and stimulate the growth of new blood vessels in ischemic limbs of normocholesterolemic animals. The mechanisms underlying these serum lipid-independent effects of statins are not completely understood, but there is increasing evidence that they improve endothelial function through molecular mechanisms that mediate an increase in endothelium-derived nitric oxide. Recent research has revealed a link between statins and the serine/threonine protein kinase Akt that regulates multiple angiogenic processes in endothelial cells, including the generation of nitrous oxide. In contrast to these data, it has also been reported that higher doses of statins inhibit endothelial cell migration and angiogenesis. Thus, further studies on the actions of statins may lead to the identification of new pharmacological targets for the control of blood vessel growth.

Animals↗
PubMed2004

Different voices: reviewing and revising the politics of working with consumers in mental health.

Working with consumers is now a common expectation in contemporary mental health services. Yet health professionals may not entirely understand the difference between patient and consumer roles. Alternatively, they may feel they do not have the skills or resources to deal with people in roles other than patient or carer. Nor may they be able to separate out their personal experiences with particular consumers from the ideals and goals for effective consumer partnerships. This paper reviews a concept known as the politics of difference as well as the rise of the consumer movement in order to explore areas of difference between consumers and providers, to reexamine how power and marginalization practices occur. It reminds professionals that generalizing from one failed experience relating with a consumer is just as invalid as idealizing the current policy of consumer inclusion. Inviting, allowing, amplifying and improving the effectiveness of the consumer voice in mental health services today requires active commitment, educative processes and novel strategies to move beyond superficial relationships so that consumers and professionals work together to make enduring change.

Australia↗
PubMed2003

Vascular endothelial growth factor activates PI3K/Akt/forkhead signaling in endothelial cells.

OBJECTIVE: Vascular endothelial growth factor (VEGF) is a potent angiogenic growth factor that promotes endothelial cell (EC) survival, migration, and permeability. The forkhead transcription factors FKHR, FKHRL1, and AFX are mammalian orthologues of DAF-16, a forkhead protein that controls longevity in Caenorhabditis elegans. In this study, we examined whether VEGF is coupled to phosphatidyl inositol 3-kinase (PI3K)/Akt/forkhead in ECs. METHODS AND RESULTS: We demonstrate that human ECs express members of the forkhead family (FKHR, FKHRL1, and AFX) and that VEGF modulates the phosphorylation, subcellular localization, and transcriptional activity of one or more of these isoforms by a PI3K/Akt signaling pathway. VEGF inhibited EC apoptosis, promoted DNA synthesis and the G(1)-to-S transition, and reduced expression of the cyclin-dependent kinase inhibitor p27(kip1). Each of these effects was blocked by the PI3K inhibitor LY294002 or by a phosphorylation-resistant mutant of FKHRL1, but not by wild-type FKHRL1. CONCLUSIONS: These results suggest that VEGF signaling in ECs is coupled to forkhead transcription factors through a PI3K/Akt-dependent pathway.

Active Transport, Cell Nucleus↗
PubMed2003

Mobilized endothelial progenitor cells by granulocyte-macrophage colony-stimulating factor accelerate reendothelialization and reduce vascular inflammation after intravascular radiation.

BACKGROUND: Endothelial progenitor cells (EPCs) play a pivotal role in repair and regeneration of damaged vessels. We investigated the role of mobilized EPCs in the healing process after intravascular radiation therapy. METHODS AND RESULTS: One iliac artery of hypercholesterolemic rabbits was subjected to balloon injury and intravascular radiation with a Re-188 balloon and the contralateral iliac artery to balloon injury only. Rabbits received granulocyte-macrophage colony-stimulating factor (recombinant human GM-CSF) (60 microg/d subcutaneously) daily for 1 week, either 7 days before the angioplasty or at the time of angioplasty. Control rabbits received human albumin. GM-CSF significantly increased the double-positive (CD31+ and KDR+) fraction in peripheral blood monocytes and showed a higher number of EPCs than albumin after culture and, furthermore, enhanced migration and incorporation of EPCs. In the albumin group, intravascular radiation therapy reduced neointimal hyperplasia but delayed reendothelialization and aggravated monocyte infiltration. GM-CSF treatment significantly accelerated the reendothelialization and inhibited monocyte infiltration (reendothelialization index, 81+/-13% in the GM-CSF radiation [n=7] versus 30+/-11% in the control radiation [n=9] at 2 weeks, P<0.01). GM-CSF treatment produced an additional significant reduction in neointimal formation at 14 and 28 days after injury in the intravascular radiation groups (intima to media ratio, 0.14+/-0.11 in the GM-CSF radiation [n=5] versus 0.36+/-0.07 in the control radiation [n=5] at 4 weeks, P<0.01). CONCLUSIONS: GM-CSF treatment mobilizes EPCs, accelerates reendothelialization, and reduces monocytes infiltration after intravascular radiation therapy, suggesting that stem cell mobilization is a promising strategy for enhancing the vascular healing process after cytotoxic angioplasty.

Animals↗
PubMed2003

Adiponectin stimulates angiogenesis by promoting cross-talk between AMP-activated protein kinase and Akt signaling in endothelial cells.

Adiponectin is an adipocyte-specific adipocytokine with anti-atherogenic and anti-diabetic properties. Here, we investigated whether adiponectin regulates angiogenic processes in vitro and in vivo. Adiponectin stimulated the differentiation of human umbilical vein endothelium cells (HUVECs) into capillary-like structures in vitro and functioned as a chemoattractant in migration assays. Adiponectin promoted the phosphorylation of AMP-activated protein kinase (AMPK), protein kinase Akt/protein kinase B, and endothelial nitric oxide synthesis (eNOS) in HUVECs. Transduction with either dominant-negative AMPK or dominant-negative Akt abolished adiponectin-induced eNOS phosphorylation as well as adiponectin-stimulated HUVEC migration and differentiation. Dominant-negative AMPK also inhibited adiponectin-induced Akt phosphorylation, suggesting that AMPK is upstream of Akt. Dominant-negative Akt or the phosphatidylinositol 3-kinase inhibitor LY294002 blocked adiponectin-stimulated Akt and eNOS phosphorylation, migration, and differentiation without altering AMPK phosphorylation. Finally, adiponectin stimulated blood vessel growth in vivo in mouse Matrigel plug implantation and rabbit corneal models of angiogenesis. These data indicate that adiponectin can function to stimulate the new blood vessel growth by promoting cross-talk between AMP-activated protein kinase and Akt signaling within endothelial cells.

AMP-Activated Protein Kinases↗
PubMed2003

The Akt-regulated forkhead transcription factor FOXO3a controls endothelial cell viability through modulation of the caspase-8 inhibitor FLIP.

FLICE-inhibitory protein (FLIP) is a homolog of caspase-8 that lacks catalytic activity and has been shown to be important in protecting endothelial cells from apoptosis. The serine/threonine kinase Akt/PKB was recently reported to promote FLIP expression in endothelial and tumor cells. Here we examined the role of the forkhead transcription factor FOXO3a, a downstream target of Akt, in controlling FLIP regulation in endothelial cells. FOXO3a nuclear translocation was regulated by Akt in human umbilical vein endothelial cells. Transduction of a nonphosphorylatable, constitutively active mutant of FOXO3a (TM-FOXO3a) led to the down-regulation of FLIP levels. Transduction with TM-FOXO3a also increased caspase-8 activity and promoted apoptosis in endothelial cells. Conversely, transduction of a dominant-negative mutant of FOXO3a up-regulated FLIP levels and protected endothelial cells from apoptosis under serum deprivation conditions. Restoration of intracellular FLIP blocked caspase-8 activation and inhibited apoptosis in TM-FOXO3a-transduced cells. These data suggest that FOXO3a is a downstream target of Akt in endothelial cells that can promote apoptosis via FLIP down-regulation and activation of the extrinsic apoptotic pathway.

Active Transport, Cell Nucleus↗
PubMed2003

Akt activity negatively regulates phosphorylation of AMP-activated protein kinase in the heart.

In the heart, insulin stimulates a variety of kinase cascades and controls glucose utilization. Because insulin is able to activate Akt and inactivate AMP-activated protein kinase (AMPK) in the heart, we hypothesized that Akt can regulate the activity of AMPK. To address the potential existence of this novel signaling pathway, we used a number of experimental protocols to activate Akt in cardiac myocytes and monitored the activation status of AMPK. Mouse hearts perfused in the presence of insulin demonstrated accelerated glycolysis and glucose oxidation rates as compared with non-insulin-perfused hearts. In addition, insulin caused an increase in Akt phosphorylation and a decrease in AMPK phosphorylation at its major regulatory site (threonine 172 of the alpha catalytic subunit). Transgenic mice overexpressing a constitutively active mutant form of Akt1 displayed decreased phosphorylation of cardiac alpha-AMPK. Isolated neonatal cardiac myocytes infected with an adenovirus expressing constitutively active mutant forms of either Akt1 or Akt2 also suppressed AMPK phosphorylation. However, Akt-dependent depression of alpha-AMPK phosphorylation could be overcome in the presence of the AMPK activator, metformin, suggesting that an override mechanism exists that can restore AMPK activity. Taken together, this study suggests that there is cross-talk between the AMPK and Akt pathways and that Akt activation can lead to decreased AMPK activity. In addition, our data suggest that the ability of insulin to inhibit AMPK may be controlled via an Akt-mediated mechanism.

AMP-Activated Protein Kinases↗
PubMed2003

Akt signaling regulates side population cell phenotype via Bcrp1 translocation.

Akt is an important regulator of cell survival, growth, and glucose metabolism in many cell types, but the role of this signaling molecule in hematopoietic stem cells is poorly defined. Side population (SP) cells are enriched for hematopoietic stem cell activity and are defined by their ability to efficiently efflux Hoechst 33342. Bone marrow from Akt1-null mice exhibited a reduced SP fraction. However, bone marrow cellularity, growth factor-responsive progenitor cultures, and engraftable stem cells were normal in these mice. Treatment of bone marrow with LY294002, an inhibitor of the Akt effector protein phosphatidylinositol 3-kinase, led to a reversible loss of the SP fraction. Bcrp1, which encodes the Hoechst dye transporter, was translocated from the membrane to the intracellular compartment under conditions that promote the SP-depleted state. Lentivirus-mediated overexpression of Akt1 in bone marrow markedly increased the SP fraction, whereas there was no effect on bone marrow from Bcrp(-/-) mice. These data suggest that Akt signaling modulates the SP cell phenotype by regulating the expression of Bcrp1.

ATP Binding Cassette Transporter, Subfamily G, Mem↗
PubMed2003

Constitutively active glycogen synthase kinase-3beta gene transfer sustains apoptosis, inhibits proliferation of vascular smooth muscle cells, and reduces neointima formation after balloon injury in rats.

OBJECTIVE: Glycogen synthase kinase (GSK)-3beta is a crucial factor in many cellular signaling pathways and may play an important role in smooth muscle proliferation and apoptosis after angioplasty. METHODS AND RESULTS: To investigate the effect of GSK-3beta modulation on neointima formation, smooth muscle proliferation, and apoptosis after balloon injury in vivo, we delivered adenoviral vectors expressing the constitutively active form of GSK-3beta (GSK-S9A: 9th serine switched to alanine) or a control gene into rat carotid arterial segments after balloon injury with a 2F Fogarty catheter. Viral infusion mixtures (5x108 pfu) were incubated in the arterial lumen for 20 minutes, and the effects of gene delivery were evaluated 3 days and 2 weeks after gene delivery with morphometry and immunohistochemical staining for proliferating and apoptotic cells. There were no significant differences in intimal, medial, and lumen areas at 3 days after the procedure. However, 2 weeks after gene delivery, the active GSK-3beta gene transfer resulted in a significantly lower intima to media ratio (0.29+/-0.06 versus 0.86+/-0.09, P<0.01) and a greater lumen area (0.41+/-0.02 versus 0.31+/-0.01 mm2, P<0.01) compared with the control gene transfected group. This was attributable to a significant reduction in intimal area (0.05+/-0.01 versus 0.15+/-0.02 mm2, P<0.01), whereas the medial area was similar (0.17+/-0.01 versus 0.18+/-0.01 mm2, P=0.21). Proliferation index was significantly reduced both at 3 days and 2 weeks in the active GSK-3beta gene transferred group (2.97+/-0.29% versus 5.71+/-0.50%, P<0.01). In addition, apoptotic index, which was not significantly different between the 2 groups at 3 days, was significantly higher in the active GSK-3beta gene transferred group at 2 weeks (3.14+/-0.68% versus 22.7+/-1.63%, n=10, P<0.01, for control versus active GSK-3beta gene transfer). CONCLUSIONS: In vivo delivery of the active GSK-3beta gene inhibits smooth muscle proliferation, sustains apoptosis, and reduces neointima formation after balloon injury in rats and may be a future therapeutic target to limit neointima hyperplasia after angioplasty.

Animals↗
PubMed2003

AMP-activated protein kinase (AMPK) signaling in endothelial cells is essential for angiogenesis in response to hypoxic stress.

AMP-activated protein kinase (AMPK) is a stress-activated protein kinase that is regulated by hypoxia and other cellular stresses that result in diminished cellular ATP levels. Here, we investigated whether AMPK signaling in endothelial cells has a role in regulating angiogenesis. Hypoxia induced the activating phosphorylation of AMPK in human umbilical vein endothelial cells (HUVECs), and AMPK activation was required for the maintenance of pro-angiogenic Akt signaling under these conditions. Suppression of AMPK signaling inhibited both HUVEC migration to VEGF and in vitro differentiation into tube-like structures in hypoxic, but not normoxic cultures. Dominant-negative AMPK also inhibited in vivo angiogenesis in Matrigel plugs that were implanted subcutaneously in mice. These data identify AMPK signaling as a new regulator of angiogenesis that is specifically required for endothelial cell migration and differentiation under conditions of hypoxia. As such, endothelial AMPK signaling may be a critical determinant of blood vessel recruitment to tissues that are subjected to ischemic stress.

AMP-Activated Protein Kinases↗