No abstract

Activating transcription factor 3 (ATF3), which is encoded by an adaptive-response gene induced by various stimuli, plays an important role in the cardiovascular system. However, the effect of ATF3 on cardiac hypertrophy induced by a pathological stimulus has not been determined. Here, we investigated the effects of ATF3 deficiency on cardiac hypertrophy using in vitro and in vivo models. Aortic banding (AB) was performed to induce cardiac hypertrophy in mice. Cardiac hypertrophy was estimated by echocardiographic and hemodynamic measurements and by pathological and molecular analysis. ATF3 deficiency promoted cardiac hypertrophy, dysfunction and fibrosis after 4 weeks of AB compared to the wild type (WT) mice. Furthermore, enhanced activation of the MEK-ERK1/2 and JNK pathways was found in ATF3-knockout (KO) mice compared to WT mice. In vitro studies performed in cultured neonatal mouse cardiomyocytes confirmed that ATF3 deficiency promotes cardiomyocyte hypertrophy induced by angiotensin II, which was associated with the amplification of MEK-ERK1/2 and JNK signaling. Our results suggested that ATF3 plays a crucial role in the development of cardiac hypertrophy via negative regulation of the MEK-ERK1/2 and JNK pathways.

The lysosomal cysteine peptidase cathepsin L (CTSL) is an important lysosomal proteinase involved in a variety of cellular functions including intracellular protein turnover, epidermal homeostasis, and hair development. Deficiency of CTSL in mice results in a progressive dilated cardiomyopathy. In the present study, we tested the hypothesis that cardiac overexpression of human CTSL in the murine heart would protect against cardiac hypertrophy in vivo. The effects of constitutive human CTSL expression on cardiac hypertrophy were investigated using in vitro and in vivo models. Cardiac hypertrophy was produced by aortic banding (AB) in CTSL transgenic mice and control animals. The extent of cardiac hypertrophy was quantitated by two-dimensional and M-mode echocardiography as well as by molecular and pathological analyses of heart samples. Constitutive overexpression of human CTSL in the murine heart attenuated the hypertrophic response, markedly reduced apoptosis, and fibrosis. Cardiac function was also preserved in hearts with increased CTSL levels in response to hypertrophic stimuli. These beneficial effects were associated with attenuation of the Akt/GSK3beta signaling cascade. Our in vitro studies further confirmed that CTSL expression in cardiomyocytes blunts cardiac hypertrophy through blocking of Akt/GSK3beta signaling. The study indicates that CTSL improves cardiac function and inhibits cardiac hypertrophy, inflammation, and fibrosis through blocking Akt/GSK3beta signaling.

Abstract-LIM domain proteins are important regulators in cell growth, cell fate determination, cell differentiation, and remodeling of the cell cytoskeleton. LIM and cysteine-rich domains 1 (Lmcd1) is a novel protein that contain 2 LIM domains with regular spacing in the carboxy-terminal region. However, its roles in cardiac growth remain unknown. Here, we investigated whether Lmcd1 regulates cardiac hypertrophy in vitro and in vivo and elucidated the underlying molecular mechanisms. We used primary cultured cardiac myocytes and cardiac-specific Lmcd1 transgenic mice. In wild-type mice subjected to the aortic banding, cardiac hypertrophy was evident at 8 weeks. In transgenic mice, however, cardiac hypertrophy was significantly greater than that in wild-type mice, as estimated by heart weight:body weight ratio, cardiomyocyte area, and echocardiographic measurements, as well as cardiac atrial natriuretic peptide and B-type natriuretic peptide mRNA and protein levels. Our results further showed that cardiac fibrosis observed in wild-type aortic banding mice was augmented in transgenic aortic banding mice. Importantly, calcineurin activity and nuclear factor of activated T cells activation level were increased more in transgenic mice than those in wild-type mice after 8-week aortic banding. In vitro experiments in cardiac myocytes further revealed that angiotensin II-induced calcineurin activity and nuclear factor of activated T cells activation were enhanced by overexpression but blunted by downregulation of Lmcd1. In conclusion, our results suggest that Lmcd1 plays a critical role in the development of cardiac hypertrophy via activation of calcineurin/nuclear factor of activated T cells signaling pathway. Key Words: cardiac hypertrophy Ⅲ fibrosis Ⅲ Lmcd1 Ⅲ calcineurin Ⅲ NFAT C ardiac hypertrophy is a response of the myocardium to increased workload, characterized by an increase of myocardial mass and accumulation of extracellular matrix, leading to left ventricular (LV) dilatation, fibrosis, and impaired systolic function, and it potentates the development of ventricular arrhythmias, heart failure, and subsequent cardiovascular mortality. 1,2 Although initially a beneficial adaptive response, prolonged hypertrophy may result in ventricular dilatation and heart failure, which is increasing in prevalence and is a debilitating disease with high rates of mortality and morbidity. [3][4][5][6] However, antihypertensive therapies and aortic valve replacement are the only 2 treatments proven to effectively reverse both structural and functional cardiac abnormalities associated with pathological cardiac hypertrophy. Understanding the underlying processes regulating cardiac remodeling will allow us to identify specific new therapies to improve the long-term outcomes of pathological cardiac hypertrophy in patients.LIM domain proteins are well recognized as key components of the regulatory machinery of the cell and are important regulators in cell growth, cell fate determination, cell differentiation, and remodeling of the ce...