semi-minimal-invasive-method-to-induce-myocardial-infarction-rats

Semi-Minimal Invasive Method to Induce Myocardial Infarction in Rats and the Assessment of Cardiac Function by an Isolated Working Heart System

Myocardial infarction (MI) remains the main contributor to morbidity and mortality worldwide. Therefore, research on this topic is mandatory. An easily ...

Medical University of Vienna

Hutchinson-Gilford progeria syndrome (HGPS) is a premature aging disorder characterized by accelerated cardiovascular disease with extensive fibrosis. It is caused by a mutation in LMNA leading to expression of truncated prelamin A (progerin) in the nucleus. To investigate the contribution of the endothelium to cardiovascular HGPS pathology, we generated an endothelium-specific HGPS mouse model with selective endothelial progerin expression. Transgenic mice develop interstitial myocardial and perivascular fibrosis and left ventricular hypertrophy associated with diastolic dysfunction and premature death. Endothelial cells show impaired shear stress response and reduced levels of endothelial nitric oxide synthase (eNOS) and NO. On the molecular level, progerin impairs nucleocytoskeletal coupling in endothelial cells through changes in mechanoresponsive components at the nuclear envelope, increased F-actin/G-actin ratios, and deregulation of mechanoresponsive myocardin-related transcription factor-A (MRTFA). MRTFA binds to the Nos3 promoter and reduces eNOS expression, thereby mediating a profibrotic paracrine response in fibroblasts. MRTFA inhibition rescues eNOS levels and ameliorates the profibrotic effect of endothelial cells in vitro. Although this murine model lacks the key anatomical feature of vascular smooth muscle cell loss seen in HGPS patients, our data show that progerin-induced impairment of mechanosignaling in endothelial cells contributes to excessive fibrosis and cardiovascular disease in HGPS patients.

Endothelial progerin expression causes cardiovascular pathology through an impaired mechanoresponse.

Tenascin C (TN-C) is considered to play a pathophysiological role in maladaptive left ventricular remodeling. Yet, the mechanism underlying TN-C-dependent cardiac dysfunction remains elusive.

Epigenetic modulation of tenascin C in the heart: implications on myocardial ischemia, hypertrophy and metabolism.

Neuronal nitric oxide synthase (nNOS) is considered a regulator of Ca1.2 L-type Ca channels and downstream Ca cycling in the heart. The commonest view is that nitric oxide (NO), generated by nNOS activity in cardiomyocytes, reduces the currents through Ca1.2 channels. This gives rise to a diminished Ca release from the sarcoplasmic reticulum, and finally reduced contractility. Here, we report that nNOS inhibitor substances significantly increase intracellular Ca transients in ventricular cardiomyocytes derived from adult mouse and rat hearts. This is consistent with an inhibitory effect of nNOS/NO activity on Ca cycling and contractility. Whole cell currents through L-type Ca channels in rodent myocytes, on the other hand, were not substantially affected by the application of various NOS inhibitors, or application of a NO donor substance. Moreover, the presence of NO donors had no effect on the single-channel open probability of purified human Ca1.2 channel protein reconstituted in artificial liposomes. These results indicate that nNOS/NO activity does not directly modify Ca1.2 channel function. We conclude that-against the currently prevailing view-basal Ca1.2 channel activity in ventricular cardiomyocytes is not substantially regulated by nNOS activity and NO. Hence, nNOS/NO inhibition of Ca cycling and contractility occurs independently of direct regulation of Ca1.2 channels by NO.

Neuronal nitric oxide synthase regulation of calcium cycling in ventricular cardiomyocytes is independent of Ca1.2 channel modulation under basal conditions.

Cardiac arrhythmias significantly contribute to mortality in Duchenne muscular dystrophy (DMD), a degenerative muscle disease triggered by mutations in the gene encoding for the intracellular protein dystrophin. A major source for the arrhythmias in patients with DMD is impaired ventricular impulse conduction, which predisposes for ventricular asynchrony, decreased cardiac output, and the development of reentrant mechanisms. The reason for ventricular conduction impairments and the associated arrhythmias in the dystrophic heart has remained unidentified. In the present study, we explored the hypothesis that dystrophin-deficient cardiac Purkinje fibers have reduced Na currents (), which would represent a potential mechanism underlying slowed ventricular conduction in the dystrophic heart. Therefore, by using a Langendorff perfusion system, we isolated Purkinje fibers from the hearts of adult wild-type control and dystrophin-deficient  mice. Enhanced green fluorescent protein (eGFP) expression under control of the connexin 40 gene allowed us to discriminate Purkinje fibers from eGFP-negative ventricular working cardiomyocytes after cell isolation. Finally, we recorded  from wild-type and dystrophic  Purkinje fibers for comparison by means of the whole cell patch clamp technique. We found substantially reduced  densities in  compared with wild-type Purkinje fibers, suggesting that dystrophin deficiency diminishes . Because Na channels in the Purkinje fiber membrane represent key determinants of ventricular conduction velocity, we propose that reduced  in Purkinje fibers at least partly explains impaired ventricular conduction and the associated arrhythmias in the dystrophic heart. Dystrophic cardiac Purkinje fibers have abnormally reduced Na current densities. This explains impaired ventricular conduction in the dystrophic heart.

Petra L. Szabo

Ludwig-Boltzmann-Institute for Cardiovascular Research at the Center for Biomedical Research

Medical University of Vienna

Semi-Minimal Invasive Method to Induce Myocardial Infarction in Rats and the Assessment of Cardiac Function by an Isolated Working Heart System