Increased Expression of Connexin43 on the Aortic Valve in the Hypercholesterolemic Rabbit Model

LRP5/canonical Wnt signalling and healing of ischemic myocardium

LRP5 (low-density lipoprotein receptor-related protein 5) activates canonical Wnt signalling. LRP5 plays multiple roles including regulation of lipoprotein and cholesterol homeostasis as well as innate immunity cell function. However, it is not known whether LRP5 has a role in the myocardium. The aim of this study was to investigate LRP5 and Wnt signalling in myocardial remodelling after acute myocardial infarction (MI). Wnt protein levels were determined in a hypercholesterolemic porcine model of MI, in Lrp5 ^-/- C57Bl6 mice, in cultured cardiomyocytes and in human explanted hearts with previous MI episodes. 21 days post-MI, there was upregulation of LRP5 in the ischemic myocardium of hypercholesterolemic pigs as well as an upregulated expression of proteins of the Wnt pathway. We demonstrate via overexpression and silencing experiments that LRP5 induces Wnt pathway activation in isolated cardiomyocytes. Hypoxia and lipid-loading induced the expression of Wnt proteins, whereas this effect is blocked in LRP5-silenced cardiomyocytes. To characterize the function of the LRP5-Wnt axis upregulation in the heart, we induced MI in wild-type and Lrp5 ^-/- mice. Lrp5 ^-/- mice had significantly larger infarcts than Wt mice, indicating a protective role of LRP5 in injured myocardium. The LRP5 upregulation in post-MI hearts seen in pigs and mice was also evident in human hearts as dyslipidemic patients with previous episodes of ischemia have higher expression of LRP5 and Wnt-signalling genes than non-ischemic dilated hearts. We demonstrate an upregulation of LRP5 and the Wnt signalling pathway that it is a prosurvival healing response of cardiomyocytes upon injury.

Animal models of organic heart valve disease

Heart valve disease is a frequently encountered pathology, related to high morbidity and mortality rates in industrialized and developing countries. Animal models are interesting to investigate the causality, but also underlying mechanisms and potential treatments of human valvular diseases. Recently, animal models of heart valve disease have been developed, which allow to investigate the pathophysiology, and to follow the progression and the potential regression of disease with therapeutics over time. The present review provides an overview of animal models of primary, organic heart valve disease: myxoid age-related, infectious, drug-induced, degenerative calcified, and mechanically induced valvular heart disease.

Characteristics of atrial substrates for atrial tachyarrhythmias induced in aged and hypercholesterolemic rabbits

BACKGROUND

Old age and dyslipidemia increase the occurrence of atrial tachyarrhythmias (ATR). This study investigated the effect of age and hypercholesterolemia on the atrial substrates for ATR.

METHODS

Five 3-year-old rabbits fed standard chow were categorized into an old-age group, five 3-month-old rabbits fed high cholesterol chow were used as a hypercholesterolemia group, and five 3-month-old rabbits fed standard chow were controls. Effective refractory period, atrial vulnerability to ATR, expressions of connexin40 (Cx40) and connexin43 (Cx43), phosphorylated c-Jun N-terminal Kinase (P-JNK), and degree of fibrosis in the right (RA) and left (LA) atria were compared.

RESULTS

Old-age and hypercholesterolemia rabbits were more vulnerable to ATR than the controls (18,628 ± 13,981 ms and 30,157 ± 39,548 ms vs 639 ± 325 ms, P < 0.05). Old-age rabbits had significantly decreased Cx40 expression in both atria (3.9-fold decrease in RA, P < 0.01 and 4.8-fold in LA, P < 0.01) and significantly decreased Cx43 in RA (14-fold, P < 0.01). Hypercholesterolemia rabbits had significantly decreased Cx40 expression in both atrial (18-fold decrease in RA, P < 0.01 and 17-fold in LA, P < 0.01) and significantly increased Cx43 expression in LA (five-fold increase, P < 0.01). Hypercholesterolemia, but not old-age rabbits, had greater expression of P-JNK in both atria (1.8-fold in RA and 2.3-fold in LA, P < 0.01). There were no significant group differences in ERP or degree of atrial fibrosis in both atria.

CONCLUSIONS

ATR is more easily induced in the atria of old-age and hypercholesterolemia rabbits than younger rabbits with normal cholesterol levels. The age and hypercholesterolemia induced changes in gap junctions expression may have partially contributed to the higher atrial vulnerability to ATR.