Study Of Effect Of Tisp40on Cardiac Hypertrophy And The Mechanisms Involved In

BackgroundCardiac hypertrophy in response to a variety of extrinsic and intrinsic stimuli may be initially a compensatory event, which helps terminally differentiated cardiac myocytes to sustain workload. Prolonged hypertrophy is maladaptive and associated with a significant thickening of ventricular walls> contractile dysfunction, ventricular dilation, and resulting in progression to heart failure, even sudden death. It is a common pathological feature in the natural course of some cardiovascular diseases such as hypertension, myocardial infarction and aortic stenosis. The underlying pathology of cardiac hypertrophy involves neurohormonal over-activation, re-expressionof fetal genes, and the triggering of a complex signaling cascade in the heart. Up to now, the underlying molecular mechanisms contributing to the initiation of cardiac hypertrophy remain largely elusive. Thus, it is important to elucidate the molecular mechanism of cardiac hypertrophy for the purpose that novel molecular targets in cardiac hypertrophy and heart failure will be discoveried.Transcript induced in spermiogenesis40(Tisp40), also referred to as Creb314(cyclic AMP responsive element binding protein3-like4)?AlbZIP (androgen-induced bZIP), is a type II transmembrane protein. Tisp40is primarily detected in the prostate.As an important member of the cAMP response element binding protein (CREB)/active transcription factor (ATF) transcription factor family, Tisp40contains a bZIP (basic region-leucine zipper) domain, which mediates protein-protein as well as protein-DNA interactions, and allows it to associate with the endoplasmic reticulum (ER). Upon activation of Tisp40, via Golgi protease SIP cleavage, Tisp40translocates to the nucleus to regulate DNA targets.Tisp40is ubiquitously expressed in all tissues,and displays diverse physiological function. Accumulating evidence indicates that Tisp40may involve in endoplasmic reticulum stress?signal transduction, and energy metabolism. Tisp40also plays a critical role in the regulation of reproduction and development of tumour. However, the involvement of Tisp40in cardiac hypertrophy remains largely unexplored. In the present study, we employed both Tisp40-overexpressing and-absent mice to examine the role of Tisp40in protecting the heart during pressure overload induced by aortic banding (AB) and explored molecular mechanisms of its regulation. MethodsPart one:The experiments were initiated on8-10week old male wild-type C57BL/6(WT)mice weighing between23.5-27.5g. A mice model of cardiac hypertrophy was established by aortic banding. C57BL/6mice were randomly and equally divided into the following7groups (n=15in each group):groupl:the sham operation (sham); group2:AB-1day; group3:AB-3days; group4:AB-1week; group5:AB-2weeks; group6:AB-4weeks and group7:AB-8weeks.Part two:The experiments were initiated on8-10week old male Tisp40knockout (KO)mice; cardiac-specific overexpression of Tisp40(TG) mice, and their respective WT littermates, weighing between23.5-27.5g.They were randomized into AB group and sham group respectively(sham, n=15; AB, n=20), Tisp40-KO AB group, Tisp40-KO sham group, Tisp40-TG AB group, Tisp40-TG sham group,WT AB group, WT sham group. At the endpoint of the experiment, Cardiac function was evaluated by echocardiography and hemodynamics, and hypertrophic responses indexed by the HW/BW, LW/BW, and HW/TL. The morphology change was observed by H&E, WGA, and PSR staining. Real-time quantitative RT-PCR was used to detect changes in molecular markers of cardiac hypertrophy and fibrosis.Part three:The experiments were initiated on8-10week old male Tisp40knockout mice; cardiac specific-overexpression of Tisp40mice, and their respective WT littermates, weighing between23.5-27.5g.They were randomized into sham group and AB group(sham, n=15; AB, n=20), Tisp40-KO AB group, Tisp40-KO sham group, Tisp40-TG AB group, Tisp40-TG sham group,WT AB group, WT sham group.At the endpoint of the experiment, Western blot were performed to detect the levels of phosphorylated and total protein of MAPKs, and endoplasmic reticulum stress markers in hearts from each group.ResultsThe expression of cardiac Tisp40protein strongly increased at3day,lw,2w,4w and8w after AB compared with sham group (P<0.05vs. sham),as indicated by the results of Western blot. Tisp40protein translocates to the nucleus after AB surgery, as indicated by the results of immunofluorescence. At the endpoint of the experiment, the percentage increases in heart weight/body weight(HW/BW),lung weight/body weight (LW/BW),heart weight/tibia length(HW/TL), cross-sectional area(CSA) of cardiomyocytes, and left ventricular collagen volume fraction were significantly greater in Tisp40-KO AB group than WT AB group (P<0.05). Both left ventricular wall thickness and ventricular diameter in Tisp40-KO AB group and WT AB group were higher than sham group,and specifically,it apparently increased more in Tisp40-KO AB group,as compared with WT AB group. Meanwhile, left ventricular systolic and diastolic function were significantly decreased more in Tisp40-KO AB group, as compared with WT AB group (P<0.05). The mRNA levels of several cardiac hypertrophic and fibrotic markers,such as ANP, BNP, ?-MHC, TGF-?, CTGF, collagen l? and collagen ??, were significantly increased in Tisp40-KO AB group, as compared with WT AB group, a-MHC and SERCA2a were lower (P<0.05). Conversely, these pathological conditions were significantly improved in Tisp40-TG AB group.At the endpoint of the experiment, Western blot analysis indicated that Tisp40deficiency promoting the activation of MAPKs, and endoplasmic reticulum stress after AB(P<0.05), whereas overexpression of Tisp40was able to attenuate pressure overload-induced upregulation of MAPKs, and endoplasmic reticulum stress(P<0.05).Conclusions1.The expression of Tisp40is activated and upregulated in the left ventricles of WT mice subjected to AB,and expressed on nucleus.2. Tisp40absence may aggravate AB-induced cardiac hypertrophy and fibrosis, while overexpression Tisp40attenuates cardiac hypertrophy and fibrosis.3.The protective effect of Tisp40on cardiac hypertrophy is mediated by inhibition of MAPKs, and endoplasmic reticulum stress pathways.