Cardiac Remodeling In The Regulatory Mechanism Of Nuclear Calcium Signals

Myocardial Nuclear Calcium Signaling in Pressureoverload induced heart hypertrophy in Wistar RatsAbstractBackground:Ca2~ signaling is an area of intense research, and the basic mechanisms of cytosolic Ca2~ signals are beginning to be understood. It is now accepted that calcium signals do exist in the cell nucleus. But this has not always been so evident. Regulation of Ca> in the nucleus is a debated issue, essentially due to the presence in the envelope of the pores, which are large enough to permit the passive traffic of small molecules like Ca>. Work with a number of cell systems has shown that Ca> diffuses freely in and out of the nucleus, whereas other studies have suggested instead that the nuclear envelope could become an efficient Ca2~ filter, and the persistent nucleus cytoplasmic Ca> gradients have been also documented in various cell types. The question of the control of nuclear Ca> thus is still open debated and the mechanism of nuclear 2+ transport is still unknown.2+ nals regulate numerous cell functions, including proliferation, Ca sigsecretion, motility, cell survival, some forms of programmed cell death, andgene expression. Gene expression is particular important because it reflects2+decoding of the Ca signal within the nucleus. A number of studies showed that hypertensive myocardial hypertrophy is a potential risk factor in thedevelopment of sudden death and heart failure. However, the underlying mechanisms responsible for hypertensive myocardial hypertrophy induced by pressure over load are under the investigation. Some studies found that there existed disorder of cytosolic Ca> homeostasis and nuclear processes (reprogramming of genes expression). But how cytosolic Ca> signalsoriginatingcause2+at the plasma membraneCa changes in the nucleus andnuc1ear function shift are still unknown. In addition, some evidencesindicated that Ca2+ signal is the common event of most signaling pathways,that is Ca2+ signal also play a critical role in regulation of nuclear functions.So we hypothesized that disorder of cytosolic Ca2+ homeostasis induced byextracellular stimuli might cause nucleoplasm Ca2+ dishomeostasis through....impairing the nuclear envelope Ca2+ transporting systems that lead to nuc1eardysfunction and abnormal myocardia1 structure (remodeling).The intracellu1ar Ca2+ receptor calmodulin (CaM) coordinates responsesto extracellular stimuli by modulating the activities of its various bindingproteins. Recent reports suggest that, in addition to its familiar functions inthe cytoplasm, CaM may be directly involved in rapid signaling betweencytop1asm and nucleus. Here the relationship between [Ca'+] and nuclearaccumulation of CaM and transcription of myocardial nuclei in vitro werealso studied.Purposes: The purposes of present study are l) to determine whethernuclear Ca2+ is independently regulated from the cytosolic Ca2+ and itsmechanism, 2) to investigate if nuclear Ca'+ transport system plays animportant role in pressure-1oaded induced hypertension and myocardialhypertrophy in rats; 3) to study how does Ca2+ regulate some of Ca2+-sensitive nuclear functions.Methods: The changes of nuclear [Ca'+] ([Ca'+]n) and cytosolic [Ca'+]([Ca2+]c) and localization and distribution of Ca2+ signaling as well as themechanism of nuclear calcium transport system were studied in cultured ratneonatal cardiac myocytes and rat myocardial nuclei in vitro using fluo-4/AM as calcium probe and confOcal laser microscopy. Velocity andisopyknic gradient centrifugation was employed to fractionate rat myocardialnuclei. The fiuorescent staining of cardiac nuclei were investigated withcalcium probe F1uo-4 and other fluorescent probes for Ca'+-ATPase,IVryanodine receptor and inositol 1,4,5 triphosphates (IP3) receptor. Thecardiac hypertrophy model was prepared by pressure over1oad secondary toabdominal aortic coarctation in rats. Hundreds of adult Wistar rats weightedl50-180g were randomly divi...