Previous studies have demonstrated improvement of cardiac function occurs with acute consumption high fat diet (HFD) after myocardial infarction (MI). However, no data exists addressing the effects of acute HFD upon the extent of injury after MI. This study investigates the hypothesis that short term HFD, prior to infarction, protects the heart against I/R injury through NF-?B-dependent regulation of cell death pathways in the heart. Data shows that acute HFD initiates cardioprotection against MI (>50% reduction in infarct size normalized to risk region) after 24h to 2 weeks of HFD, but protection is completely absent after 6 weeks of HFD, when mice are reported to develop pathophysiology related to the diet. Furthermore, cardioprotection after 24h of HFD persists after an additional 24h of normal chow feeding, and was found to be dependent upon NF-?B activation in cardiomyocytes. This study also indicates that short term HFD activates autophagic processes (Beclin-1, LC-3) pre-ischemia, as seen in other protective stimuli. Increases in Beclin-1 and LC-3 were found to be NF-?B-dependent, and administration of chloroquine, an inhibitor of autophagy, abrogated cardioprotection. Our results support that acute high fat feeding mediates cardioprotection against I/R injury associated with a NF-?B-dependent increase in autophagy and reduced apoptosis, as has been found for ischemic preconditioning.
The cardiac regenerative capacity of MRL/MpJ mouse remains a controversy. Although the MRL mouse has been reported to exhibit minimal scarring and subsequent cardiac regeneration after cryoinjury of the right ventricle, multiple studies have been unable to replicate this cardiac regenerative capacity after both cryogenic and coronary ligation cardiac injury. Therefore, we evaluated the cardiac regenerative wound-healing response and functional recovery of MRL mice compared to C57 mice, in response to a clinically relevant left ventricular (LV) coronary ligation. Male MRL/MpJ+/+ and C57BL/6 mice underwent left coronary artery ligation followed by reperfusion. Cardiac function was evaluated by echocardiography [LV ejection fraction (LVEF), LV end-diastolic volume (LVEDV), LV mass, wall thickness] at 24 hours post-ischemia and weekly for 13 weeks thereafter. Hearts were also analyzed histologically for individual cardiomyocyte hypertrophy and cardiac fibrosis. Our results show that contrary to prior reports of cardiac regenerations, MRL mice progress to heart failure more rapidly following I/R injury as marked by a significant decrease in LVEF, increase in LVEDV, LV mass, individual myocyte size, and fibrosis in the post-ischemic myocardium. Therefore, we conclude that MRL mice do not exhibit regeneration of the LV or enhanced functional improvement in response to coronary ligation. However, unlike prior studies, we matched initial infarct size in MRL and C57 mice, used high frequency echocardiography, and histological analysis to reach this conclusion. The prospect of cardiac regeneration after ischemia in MRL mice seems to have attenuated interest, given the multiple negative studies and the promise of stem cell cardiac regeneration. However, our novel observation that MRL may possess an impaired compensated hypertrophy response makes the MRL mouse strain an interesting model in the study of cardiac hypertrophy.
Transient receptor potential cation channels have been implicated in the regulation of cardiovascular function, but only recently has our laboratory described the vanilloid 2 subtype (TRPV2) in the cardiomyocyte, though its exact mechanism of action has not yet been established. This study tests the hypothesis that TRPV2 plays an important role in regulating myocyte contractility under physiological conditions. Therefore, we measured cardiac and vascular function in WT and TRPV2(-/-) mice in vitro and in vivo and found that TRPV2 deletion resulted in a decrease in basal systolic and diastolic function without affecting loading conditions or vascular tone. TRPV2 stimulation with probenecid, a relatively selective TRPV2 agonist, caused an increase in both inotropy and lusitropy in WT mice which was blunted in TRPV2(-/-) mice. We examined the mechanism of TRPV2 inotropy/lusitropy in isolated myocytes and found that it modulates Ca2+ transients and sarcoplasmic reticulum Ca2+ loading. Based on these data, we concluded that the activity of this channel is necessary for normal cardiac function, and that there is increased contractility in response to agonism of TRPV2 with probenecid.
Detailed studies in animal models to assess the importance of aging animals in cardiovascular research are rather scarce. The increase in mouse models used to study cardiovascular disease makes the establishment of physiologic aging parameters in myocardial function in both male and female mice critical. Forty-four FVB/N mice were studied at multiple time points between the ages of 3 and 16 mo using high-frequency echocardiography. Our study found that there is an age-dependent decrease in several systolic and diastolic function parameters in male mice, but not in female mice. This study establishes the physiologic age- and gender-related changes in myocardial function that occur in mice and can be measured with echocardiography. We report baseline values for traditional echocardiography and advanced echocardiographic techniques to measure discrete changes in cardiac function in the commonly employed FVB/N strain.
Cardiovascular disease is a leading cause of morbidity and mortality worldwide, encompassing a variety of cardiac and vascular conditions. Transient receptor potential vanilloid (TRPV) channels, specifically TRPV type 1 (TRPV1) and TRPV type 2 (TRPV2), are relatively recently described channels found throughout the body including within and around the cardiovascular system. They are activated by a variety of stimuli including high temperatures, stretch, and pharmacologic and endogenous ligands. The TRPV1 channel has been found to be an important player in the pathway of the detection of chest pain after myocardial injury. Activation of peripheral TRPV1 via painful stimuli or capsaicin has been shown to have cardioprotective effects, whereas genetic abrogation of TRPV1 results in increased myocardial damage after ischemia and reperfusion injury in comparison to wild-type mice. Furthermore, blood pressure changes have been noted upon TRPV1 stimulation. Similarly, the TRPV2 channel has also been associated with changes in blood pressure and cardiac function depending on how and where the channel is activated. Interestingly, overexpression of TRPV2 channels in the heart induces dystrophic cardiomyopathy; however, stimulation under physiologic conditions leads to improved cardiac function. Probenecid, a TRPV2 agonist, has been studied as a model therapy for its inotropic effects and potential use in the treatment of cardiomyopathy. In this review, we present an up to date account of the growing evidence that supports the study of TRPV1 and TRPV2 channels as targets for therapeutic agents of cardiovascular diseases.
Valvular disease is common in patients with Marfan syndrome and can lead to cardiomyopathy. However, some patients develop cardiomyopathy in the absence of hemodynamically significant valve dysfunction, suggesting alternative mechanisms of disease progression. Disruption of LDL receptor-related protein-1 (Lrp1) in smooth muscle cells has been shown to cause vascular pathologies similar to Marfan syndrome, with activation of smooth muscle cells, vascular dysfunction and aortic aneurysms. This study used echocardiography and blood pressure monitoring in mouse models to determine whether inactivation of Lrp1 in vascular smooth muscle leads to cardiomyopathy, and if so, whether the mechanism is a consequence of valvular disease. Hemodynamic changes during treatment with captopril were also assessed. Dilation of aortic roots was observed in young Lrp1-knockout mice and progressed as they aged, whereas no significant aortic dilation was detected in wild type littermates. Diastolic blood pressure was lower and pulse pressure higher in Lrp1-knockout mice, which was normalized by treatment with captopril. Aortic dilation was followed by development of aortic insufficiency and subsequent dilated cardiomyopathy due to valvular disease. Thus, smooth muscle cell Lrp1 deficiency results in aortic dilation and insufficiency that causes secondary cardiomyopathy that can be improved by captopril. These findings provide novel insights into mechanisms of cardiomyopathy associated with vascular activation and offer a new model of valvular cardiomyopathy.
N-type (Ca(v)2.2) voltage-dependent calcium channels (VDCC) play an important role in presynaptic neurotransmitter release in the autonomic nervous system and may be clinically relevant in the treatment of cardiovascular diseases. The physiological impact of N-type VDCC ablation on cardiac function, stimulus-release coupling and cardiac autonomic regulation was studied using mice deficient in the ?(1B) subunit of the N-type channel (N-type-/-).The positive inotropic effect (increase in +dP/dt) secondary to high frequency field stimulation (HFFS), mediated by the sympathetic nervous system, was decreased by 33 ± 12.6% in N-type-/- versus 89 ± 11.4% in Wild-Type (WT)(P<0.01), whereas the negative inotropic response (decrease in +dP/dt) following HFFS in the presence of propranolol, mediated by the parasympathetic nervous system, was similar to that in Wild-type (WT) animals 34 ± 5.0% and 35 ± 5.4%, respectively. There were no changes in the postsynaptic ?-adrenergic responsiveness, ?-adrenoreceptor density or adenylyl cyclase activity. N-type-/- hearts demonstrated an increased contractile response to ?(1)-adrenoreceptor (?(1)-ADR) stimulation with 10(-5)M phenylephrine in the presence of the ?-blocker propranolol, which might be attributed to an increased expression of PLC?1. Protein abundance of other signal transducers for ?(1) ADR transduction protein was not changed in the N-type-/- hearts. These results suggest that selective impairment of sympathetic inflow does not modulate postsynaptic ?-adrenergic responsiveness, but causes increased functional response to ?(1)-adrenergic stimulation.
The role of other STAT subtypes in conferring ischemic tolerance is unclear. We hypothesized that in STAT-3 deletion alternative STAT subtypes would protect myocardial function against ischemia-reperfusion injury. Wild-type (WT) male C57BL/6 mice or mice with cardiomyocyte STAT-3 knockout (KO) underwent baseline echocardiography. Langendorff-perfused hearts underwent ischemic preconditioning (IPC) or no IPC before ischemia-reperfusion. Following ex vivo perfusion, hearts were analyzed for STAT-5 and -6 phosphorylation by Western blot analysis of nuclear fractions. Echocardiography and postequilibration cardiac performance revealed no differences in cardiac function between WT and KO hearts. Phosphorylated STAT-5 and -6 expression was similar in WT and KO hearts before perfusion. Contractile function in WT and KO hearts was significantly impaired following ischemia-reperfusion in the absence of IPC. In WT hearts, IPC significantly improved the recovery of the maximum first derivative of developed pressure (+dP/dtmax) compared with that in hearts without IPC. IPC more effectively improved end-reperfusion dP/dtmax in WT hearts compared with KO hearts. Preconditioned and nonpreconditioned KO hearts exhibited increased phosphorylated STAT-5 and -6 expression compared with WT hearts. The increased subtype activation did not improve the efficacy of IPC in KO hearts. In conclusion, baseline cardiac performance is preserved in hearts with cardiac-restricted STAT-3 deletion. STAT-3 deletion attenuates preconditioning and is not associated with a compensatory upregulation of STAT-5 and -6 subtypes. The activation of STAT-5 and -6 in KO hearts following ischemic challenge does not provide functional compensation for the loss of STAT-3. JAK-STAT signaling via STAT-3 is essential for effective IPC.
Cardiac L-type voltage-dependent Ca(2+) channels are heteromultimeric polypeptide complexes of alpha(1)-, alpha(2)/delta-, and beta-subunits. The alpha(2)/delta-1-subunit possesses a stereoselective, high-affinity binding site for gabapentin, widely used to treat epilepsy and postherpetic neuralgic pain as well as sleep disorders. Mutations in alpha(2)/delta-subunits of voltage-dependent Ca(2+) channels have been associated with different diseases, including epilepsy. Multiple heterologous coexpression systems have been used to study the effects of the deletion of the alpha(2)/delta-1-subunit, but attempts at a conventional knockout animal model have been ineffective. We report the development of a viable conventional knockout mouse using a construct targeting exon 2 of alpha(2)/delta-1. While the deletion of the subunit is not lethal, these animals lack high-affinity gabapentin binding sites and demonstrate a significantly decreased basal myocardial contractility and relaxation and a decreased L-type Ca(2+) current peak current amplitude. This is a novel model for studying the function of the alpha(2)/delta-1-subunit and will be of importance in the development of new pharmacological therapies.
The current therapeutic options for acute decompensated heart failure are limited to afterload reducers and positive inotropes. The latter increases myocardial contractility through changes in myocyte calcium (Ca²?) handling (mostly through stimulation of the ?-adrenergic pathways [?-ADR]) and is associated with paradoxical effects of arrhythmias, cell death, and subsequently increased mortality. We have previously demonstrated that probenecid can increase cytosolic Ca²? levels in the cardiomyocyte resulting in an improved inotropic response in vitro and in vivo without activating the ?-ADR system. We hypothesize that, in contrast to other commonly used inotropes, probenecid functions through a system separate from that of ?-ADR and hence will increase contractility and improve function without damaging the heart. Furthermore, our goal was to evaluate the effect of probenecid on cell death in vitro and its use in vivo as a positive inotrope in a mouse model of ischemic cardiomyopathy. Herein, we demonstrate that probenecid induced an influx of Ca²? similar to isoproterenol, but does not induce cell death in vitro. Through a series of in vivo experiments we also demonstrate that probenecid can be used at various time points and with various methods of administration in vivo in mice with myocardial ischemia, resulting in improved contractility and no significant difference in infarct size. In conclusion, we provide novel data that probenecid, through its activity on cellular Ca²? levels, induces an inotropic effect without causing or exacerbating injury. This discovery may be translatable if this mechanism is preserved in man.
Probenecid is a highly lipid soluble benzoic acid derivative originally used to increase serum antibiotic concentrations. It was later discovered to have uricosuric effects and was FDA approved for gout therapy. It has recently been found to be a potent agonist of transient receptor potential vanilloid 2 (TRPV2). We have shown that this receptor is in the cardiomyocyte and report a positive inotropic effect of the drug. Using echocardiography, Langendorff and isolated myocytes, we measured the change in contractility and, using TRPV2(-/-) mice, proved that the effect was mediated by TRPV2 channels in the cardiomyocytes. Analysis of the expression of Ca(2+) handling and ?-adrenergic signaling pathway proteins showed that the contractility was not increased through activation of the ?-ADR. We propose that the response to probenecid is due to activation of TRPV2 channels secondary to SR release of Ca(2+).
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