echocardiographic-histological-examination-cardiac-morphology

Echocardiographic and Histological Examination of Cardiac Morphology in the Mouse

An increasing number of genetically modified mouse models has become available in recent years. Moreover, the number of pharmacological studies performed ...

ETH Zurich

Alterations in the circadian blood pressure pattern are frequently observed in hypertension and lead to increased cardiovascular morbidity. However, there are no studies that have investigated a possible implication of the Period2 gene, a key component of the molecular circadian clock, on the circadian rhythms of blood pressure and heart rate. To address this question, we monitored blood pressure, heart rate, and locomotor activity 24 h a day by telemetry in mice carrying a mutation in the Period2 gene and in wild-type control mice. Under a standard 12:12-h light-dark cycle, mutant mice showed a mild cardiovascular phenotype with an elevated 24-h heart rate, a decreased 24-h diastolic blood pressure, and an attenuation of the dark-light difference in blood pressure and heart rate. Locomotor activity was similar in both groups and did not appear to explain the observed hemodynamic differences. When mice were placed under constant darkness during eight consecutive days, wild-type mice maintained 24-h rhythms, whereas there was an apparent progressive loss of 24-h rhythm of blood pressure, heart rate, and locomotor activity in mutant mice. However, a chi square periodogram revealed that circadian rhythms were preserved under complete absence of any light cue, but with shorter periods by approximately 40 min, leading to a cumulative phase shift toward earlier times of approximately 5 h and 20 min by the end of the 8th day. When heart rate, mean arterial pressure, and activity were recalculated according to the endogenous circadian periods of each individual mouse, the amplitudes of the circadian rhythms ("subjective night"-"subjective day" differences) were maintained for all variables studied. Our data show that mutation of the Period2 gene results in an attenuated dipping of blood pressure and heart rate during both light-dark cycles and constant darkness, and in shorter circadian periods during constant darkness.

Role of mutation of the circadian clock gene Per2 in cardiovascular circadian rhythms.

Period2 (Per2) is an important component of the circadian clock. Mutation of this gene is associated with vascular endothelial dysfunction and altered glucose metabolism. The aim of this study is to further characterize whole body glucose homeostasis and endothelial nitric oxide (NO) production in response to insulin in the mPer2(Brdm1) mice. We show that mPer2(Brdm1) mice exhibit compromised insulin receptor activation and Akt signaling in various tissues including liver, fat, heart, and aortas with a tissue-specific heterogeneous diurnal pattern, and decreased insulin-stimulated NO release in the aortas in both active and inactive phases of the animals. As compared to wild type (WT) mice, the mPer2(Brdm1) mice reveal hyperinsulinemia, hypoglycemia with lower fasting hepatic glycogen content and glycogen synthase level, no difference in glucose tolerance and insulin tolerance. The mPer2(Brdm1) mice do not show increased predisposition to obesity either on normal chow or high fat diet compared to WT controls. Thus, mice with Per2 gene mutation show altered glucose homeostasis and compromised insulin-stimulated NO release, independently of obesity.

Period2 gene mutant mice show compromised insulin-mediated endothelial nitric oxide release and altered glucose homeostasis.

The interplay between hepatic glycogen metabolism and blood glucose levels is a paradigm of the rhythmic nature of metabolic homeostasis. Here we show that mice lacking a functional PER2 protein (Per2 (Brdm1) ) display reduced fasting glycemia, altered rhythms of hepatic glycogen accumulation, and altered rhythms of food intake. Per2 (Brdm1) mice show reduced hepatic glycogen content and altered circadian expression during controlled fasting and refeeding. Livers from Per2 (Brdm1) mice display reduced glycogen synthase protein levels during refeeding, and increased glycogen phosphorylase activity during fasting. The latter is explained by PER2 action on the expression of the adapter proteins PTG and GL, which target the protein phosphatase-1 to glycogen to decrease glycogen phosphorylase activity. Finally, PER2 interacts with genomic regions of Gys2, PTG, and G L . These results indicate an important role for PER2 in the hepatic transcriptional response to feeding and acute fasting that promotes glucose storage to liver glycogen.

PER2 promotes glucose storage to liver glycogen during feeding and acute fasting by inducing Gys2 PTG and G L expression.

Fructose is a major component of dietary sugar and its overconsumption exacerbates key pathological features of metabolic syndrome. The central fructose-metabolising enzyme is ketohexokinase (KHK), which exists in two isoforms: KHK-A and KHK-C, generated through mutually exclusive alternative splicing of KHK pre-mRNAs. KHK-C displays superior affinity for fructose compared with KHK-A and is produced primarily in the liver, thus restricting fructose metabolism almost exclusively to this organ. Here we show that myocardial hypoxia actuates fructose metabolism in human and mouse models of pathological cardiac hypertrophy through hypoxia-inducible factor 1α (HIF1α) activation of SF3B1 and SF3B1-mediated splice switching of KHK-A to KHK-C. Heart-specific depletion of SF3B1 or genetic ablation of Khk, but not Khk-A alone, in mice, suppresses pathological stress-induced fructose metabolism, growth and contractile dysfunction, thus defining signalling components and molecular underpinnings of a fructose metabolism regulatory system crucial for pathological growth.

HIF-driven SF3B1 induces KHK-C to enforce fructolysis and heart disease.

Peroxisome proliferator-activated receptors are nuclear receptors which function as ligand-activated transcription factors. Among them, peroxisome proliferator-activated receptor beta/delta (PPARβ/δ) is highly expressed in the heart and thought to have cardioprotective functions due to its beneficial effects in metabolic syndrome. As we already showed that PPARβ/δ activation resulted in an enhanced cardiac angiogenesis and growth without impairment of heart function, we were interested to determine the effects of a specific activation of PPARβ/δ in the vasculature on cardiac performance under normal and in chronic ischemic heart disease conditions. We analyzed the effects of a specific PPARβ/δ overexpression in endothelial cells on the heart using an inducible conditional vascular-specific mouse model. We demonstrate that vessel-specific overexpression of PPARβ/δ induces rapid cardiac angiogenesis and growth with an increase in cardiomyocyte size. Upon myocardial infarction, vascular overexpression of PPARβ/δ, despite the enhanced cardiac vessel formation, does not protect against chronic ischemic injury. Our results suggest that the proper balance of PPARβ/δ activation in the different cardiac cell types is required to obtain beneficial effects on the outcome in chronic ischemic heart disease.

Inducible Conditional Vascular-Specific Overexpression of Peroxisome Proliferator-Activated Receptor Beta/Delta Leads to Rapid Cardiac Hypertrophy.

Andersen's syndrome (AS) is a rare autosomal disorder that has been defined by the triad of periodic paralysis, cardiac arrhythmia, and developmental anomalies. AS has been directly linked to over 40 different autosomal dominant negative loss-of-function mutations in the KCNJ2 gene, encoding for the tetrameric strong inward rectifying K(+) channel KIR2.1. While KIR2.1 channels have been suggested to contribute to setting the resting membrane potential (RMP) and to control the duration of the action potential (AP) in skeletal and cardiac muscle, the mechanism by which AS mutations produce such complex pathophysiological symptoms is poorly understood. Thus, we use an adenoviral transduction strategy to study in vivo subcellular distribution of wild-type (WT) and AS-associated mutant KIR2.1 channels in mouse skeletal muscle. We determined that WT and D71V AS mutant KIR2.1 channels are localized to the sarcolemma and the transverse tubules (T-tubules) of skeletal muscle fibers, while the ∆314-315 AS KIR2.1 mutation prevents proper trafficking of the homo- or hetero-meric channel complexes. Whole-cell voltage-clamp recordings in individual skeletal muscle fibers confirmed the reduction of inwardly rectifying K(+) current (IK1) after transduction with ∆314-315 KIR2.1 as compared to WT channels. Analysis of skeletal muscle function revealed reduced force generation during isometric contraction as well as reduced resistance to muscle fatigue in extensor digitorum longus muscles transduced with AS mutant KIR2.1. Together, these results suggest that KIR2.1 channels may be involved in the excitation-contraction coupling process required for proper skeletal muscle function. Our findings provide clues to mechanisms associated with periodic paralysis in AS.

Ana Vukolic

Institute for Molecular Health Sciences

ETH Zurich

Echocardiographic and Histological Examination of Cardiac Morphology in the Mouse