IntroductionA common characteristic and main contributor to most cardiac diseases is cardiomyocyte death. Apoptosis, a major contributor to cardiomyocyte death, acts through the intrinsic pathway, ...which has been extensively studied, and the extrinsic pathway, some of which have been well characterized. However, numerous death receptors (DR) have been virtually unstudied in the context of cardiovascular disease. Our laboratory identified TNF-related apoptosis inducing ligand (TRAIL) and its receptor, DR5, as being altered in a chronic catecholamine administration model of heart failure. Furthermore, multiple clinical studies have identified TRAIL or DR5 as biomarkers in the prediction of severity and mortality following myocardial infarction and in heart failure development risk. While TRAIL/DR5 have been extensively studied as a potential cancer therapeutic due to their ability to selectively activate apoptosis in cancer cells, TRAIL and DR5 are highly expressed in the heart where their function is unknown.HypothesisOur goal was to determine the role of DR5 in the heart and we hypothesized that DR5 initiates non-canonical signaling resulting activation of pro-growth and survival pathways, which helps protect the heart during injury.Methods/ResultsHistological analysis of hearts from mice treated with a DR5 agonists showed no difference in cardiomyocyte death, fibrosis or function as measured by echocardigraphy, but increased hypertrophy. Studies using isolated cardiomyocytes identified ERK1/2 activation with DR5 agonist treatment. Furthermore, epidermal growth factor receptor (EGFR) was activated following DR5 agonist treatment through activation of MMP9. Specific inhibitors of MMP9 and EGFR prevented DR5-mediated ERK1/2 signaling and cardiomyocyte hypertrophy. Using an in vitro hypoxia/reoxygenation model, DR5 activation was found to protect cardiomyocytes from death and DR5 agonist administration in mice decreased infarct size and improved cardiac function following ischemia/reperfusion injury. Furthermore, administration of DR5 neutralizing antibodies potentiated cardiomyocyte death following ischemia/reperfusion and worsened outcome.ConclusionsTaken together, these studies identify a previously unidentified role for DR5 in the heart, which acting through non-canonical MMP9-EGFR-ERK1/2 signaling mechanisms contributes to cardiomyocyte hypertrophy and protection from oxidative stress.
Abstract only Circular RNA (circRNA) is a new addition to the list of growing body of non-coding RNAs.Recent studies highlighted that circRNA are dysregulated in cardiovascular disease. ...However,knowledge of the role of circRNAs in ischemic cardiac injury is limited. Using global circRNAexpression profiling, we identified several circRNA transcripts that were differentially regulatedpost-MI in mice, including circFNDC3b (derived from 2 and 3 exons of cognate FNDC3b gene)which is significantly down regulated. Cell fractionation experiments revealed that circFNDC3bis highly enriched in endothelial cells of post-MI mice. Notably, we found a circFNDC3b orthologin humans, which was also significantly down regulated in ischemic cardiomyopathy patients.Further, gene profile analysis of circFNDC3b overexpression in cardiac endothelial cellsdemonstrated an increase in angiogenic genes. Among them, vascular endothelial growthfactor-A (VEGF-A) was significantly elevated concomitant with reduced in vitro apoptosis ofcardiomyoblasts and endothelial cells, which also exhibited enhanced tube formation. Forcardiac overexpression of circFNDC3b, we generated AAV9 viral particles and found that in vivoover expression attenuated LV dysfunction post-MI and enhanced neovascularization.Mechanistically, circFNDC3b interacts with its potential target RNA binding protein FUS-1 (fusedin sarcoma) and regulate VEGF signaling, thereby reducing cardiomyocyte apoptosis andenhancing neovascularization and cardiac function post-MI. These results indicatethat circFNDC3b is a novel potential target to prevent cardiac remodeling and highlight theimportance of circRNAs in cardiovascular diseases.
Introductionβ-adrenergic receptors (βAR) are expressed in the heart and differentially impact cardiac function normally and during pathological states. βAR also regulate immune responses, a critical ...mediator of heart failure pathogenesis. β2AR is the most ubiquitously expressed subtype in the immune system where it regulates multiple facets of immune cell function. Prior studies have explored the impact of immune cell β2AR following acute myocardial infarction (MI). Using bone marrow transplant (BMT) experiments to generate immune cell specific β2AR knockout (KO) mice, we found that β2ARKO BMT have reduced leukocyte infiltration into the heart at acute time points due to impairments in egress of cells and altered responsiveness to chemokines. This demonstrates the importance of β2AR on acute responses after MI, however, inflammation also contributes to reparative processes that occur at later time points where the impact of β2AR is unknown.HypothesisWe hypothesized that β2AR regulates reparative immune cells to impact long-term remodeling follow MI.Methods and ResultsTo determine the impact of immune cell β2AR on long-term remodeling, WT or β2ARKO BMT mice received sham or MI surgery. Echocardiographic monitoring demonstrated improvements in cardiac morphology and contractility during the remodeling phase after MI with immune cell β2ARKO. Histological analysis 4wk post-MI showed decreased hypertrophy, dilation and infarct size in β2ARKO BMT mice. Isolectin B4 staining revealed increased capillary density in β2ARKO BMT hearts suggesting lack of β2AR on immune cells is beneficial for promoting angiogenesis. Macrophages isolated from WT and β2ARKO mice demonstrated increased endothelial marker expression on β2ARKO macrophages suggesting a pro-angiogenic phenotype. An antibody array identified alterations in a number of secreted pro- and anti-angiogenic factors from β2ARKO macrophages suggesting that β2ARKO on macrophage promotes angiogenesis through paracrine-dependent mechanisms, which was confirmed using conditioned media to look at critical aspects of endothelial cell function.ConclusionsThese findings show a novel role of macrophage β2AR in regulating remodeling after MI through their impact on angiogenesis.
Abstract only Recent studies highlighted that circular RNAs (circRNA) can play an important role in cardiac hypertrophy. However, the circRNAs in cardiac diseases is still limited. Using global ...circRNA expression profiling, we identified several circRNA transcripts that were differentially regulated post-MI in mice, including mmu_circ_008396 that is significantly down regulated. Cell fractionation experiments indicated that mmu_circ_008396 is highly enriched in endothelial cells in post-MI mice. Interestingly, we found a mmu_circ_008396 circRNA ortholog in humans, which was also significantly down regulated in ischemic cardiomyopathy patients. Further, overexpression of mmu_circ_008396 significantly enhanced tube formation and reduced apoptosis of human umbilical vein endothelial cells. For cardiac overexpression of mmu_circ_008396 circRNA, we created AAV9 viral particles and found that in vivo over expression attenuated LV dysfunction post-MI and enhanced neovascularization. Mechanistically, mmu_circ_008396 binds to its potential target miRNAs (mmu-miR-93-3p, mmu-miR-412-3p and mmu-miR-298-5p) and regulate hemeoxygenase-1/ VEGF signaling, thereby enhancing neovascularization and cardiac repair post-MI. These results indicate that mmu_circ_008396 circRNA might be a novel potential target to prevent cardiac remodeling and also highlight the significance of circRNAs in cardiovascular diseases.
The entorhinal cortex is closely associated with the consolidation and recall of memories, Alzheimer disease, schizophrenia, and temporal lobe epilepsy. Norepinephrine is a neurotransmitter that ...plays a significant role in these physiological functions and neurological diseases. Whereas the entorhinal cortex receives profuse noradrenergic innervations from the locus coeruleus of the pons and expresses high densities of adrenergic receptors, the function of norepinephrine in the entorhinal cortex is still elusive. Accordingly, we examined the effects of norepinephrine on neuronal excitability in the entorhinal cortex and explored the underlying cellular and molecular mechanisms. Application of norepinephrine-generated hyperpolarization and decreased the excitability of the neurons in the superficial layers with no effects on neuronal excitability in the deep layers of the entorhinal cortex. Norepinephrine-induced hyperpolarization was mediated by α2A adrenergic receptors and required the functions of Gαi proteins, adenylyl cyclase, and protein kinase A. Norepinephrine-mediated depression on neuronal excitability was mediated by activation of TREK-2, a type of two-pore domain K+ channel, and mutation of the protein kinase A phosphorylation site on TREK-2 channels annulled the effects of norepinephrine. Our results indicate a novel action mode in which norepinephrine depresses neuronal excitability in the entorhinal cortex by disinhibiting protein kinase A-mediated tonic inhibition of TREK-2 channels.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The entorhinal cortex (EC) is regarded as the gateway to the hippocampus and thus is essential for learning and memory. Whereas the EC expresses a high density of GABA sub(B) receptors, the functions ...of these receptors in this region remain unexplored. Here, we examined the effects of GABA sub(B) receptor activation on neuronal excitability in the EC and spatial learning. Application of baclofen, a specific GABA sub(B) receptor agonist, inhibited significantly neuronal excitability in the EC. GABA sub(B) receptor-mediated inhibition in the EC was mediated via activating TREK-2, a type of two-pore domain K super(+) channels, and required the functions of inhibitory G proteins and protein kinase A pathway. Depression of neuronal excitability in the EC underlies GABA sub(B) receptor-mediated inhibition of spatial learning as assessed by Morris water maze. Our study indicates that GABA sub(B) receptors exert a tight control over spatial learning by modulating neuronal excitability in the EC.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The entorhinal cortex is closely associated with the consolidation and
recall of memories, Alzheimer disease, schizophrenia, and temporal lobe
epilepsy. Norepinephrine is a neurotransmitter that ...plays a significant role
in these physiological functions and neurological diseases. Whereas the
entorhinal cortex receives profuse noradrenergic innervations from the locus
coeruleus of the pons and expresses high densities of adrenergic receptors,
the function of norepinephrine in the entorhinal cortex is still elusive.
Accordingly, we examined the effects of norepinephrine on neuronal
excitability in the entorhinal cortex and explored the underlying cellular and
molecular mechanisms. Application of norepinephrine-generated
hyperpolarization and decreased the excitability of the neurons in the
superficial layers with no effects on neuronal excitability in the deep layers
of the entorhinal cortex. Norepinephrine-induced hyperpolarization was
mediated by α
2A
adrenergic receptors and required the
functions of Gα
i
proteins, adenylyl cyclase, and protein
kinase A. Norepinephrine-mediated depression on neuronal excitability was
mediated by activation of TREK-2, a type of two-pore domain K
+
channel, and mutation of the protein kinase A phosphorylation site on TREK-2
channels annulled the effects of norepinephrine. Our results indicate a novel
action mode in which norepinephrine depresses neuronal excitability in the
entorhinal cortex by disinhibiting protein kinase A-mediated tonic inhibition
of TREK-2 channels.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The entorhinal cortex (EC) is regarded as the gateway to the hippocampus and thus is essential for learning and memory. Whereas the EC expresses a high density of GABA
B receptors, the functions of ...these receptors in this region remain unexplored. Here, we examined the effects of GABA
B receptor activation on neuronal excitability in the EC and spatial learning. Application of baclofen, a specific GABA
B receptor agonist, inhibited significantly neuronal excitability in the EC. GABA
B receptor-mediated inhibition in the EC was mediated via activating TREK-2, a type of two-pore domain K
+ channels, and required the functions of inhibitory G proteins and protein kinase A pathway. Depression of neuronal excitability in the EC underlies GABA
B receptor-mediated inhibition of spatial learning as assessed by Morris water maze. Our study indicates that GABA
B receptors exert a tight control over spatial learning by modulating neuronal excitability in the EC.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
IntroductionAging is one of the largest risk factors in developing cardiovascular disease (CVD). Many studies on molecular mechanisms and novel therapies of CVD are done in healthy, young mice and ...may not consider how aging will impact study results and translational power. G-protein coupled receptor kinase 2 (GRK2) has been shown to be crucial in negatively regulating β-adrenergic receptors (β-AR) of the heart, which are responsible for controlling cardiac rate and contractility. GRK2 activity and expression is pathologically increased up to 3-4 fold in CVD. With normal aging there is a reduction in β-AR density and reduced signal transduction. However, the role of GRK2 in aging is not well understood, much less how it impacts aging with CVD.HypothesisWe hypothesize that life-long over-activation of GRK2 will have negative effects on cardiovascular structure and function.MethodsWe generated a mouse line that globally expressed GRK2 at endogenous protein levels, but has increased activity by mutating a residue in the active site that is responsible for inactivation of GRK2’s kinase activity (GRK2-KI). We allowed GRK2-KI mice to age 1-1.5 years before study implementation to examine if there was any CV phenotype.ResultsLong term over-activation of GRK2 activity alone caused GRK2-KI mice to develop cardiac hypertrophy, as measured by increased HW/BW and cell areas. ANP and BNP expression was also increased compared to wild-type (WT) counterparts. GRK2-KI mice had impaired cardiac systolic function and mild diastolic dysfunction. When examining if increased GRK2 activity had any impact on fibrosis with aging, there was an increase in perivascular fibrosis compared to aged WT mice. No change was seen with interstitial fibrosis. Further examination of the vasculature revealed that aortic media layers contained fewer vascular smooth muscle cells. When testing the contractile function of aortic rings, GRK2-KI aortas produced less changes in force when exposed to KCl, phenylephrine or L-NAME. Relaxation responses induced with acetylcholine were unchanged.ConclusionsGRK2 alone is able to promote a phenotype of advanced cardiac aging. The molecular mechanisms of this unique phenotype will be investigated in further studies.
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