The role of functional calcium handling during the early stages of mouse heart development

During development the heart is the first organ to form and function in the embryo proper. Along with being fundamental for contraction, Ca2+ is also a key signalling molecule known to regulate cardiac genes, however, it is unclear how Ca2+-handling feeds-back onto the initiation of beating and whether this directly impacts on early embryonic heart development per se. The aim of this study was to investigate how initial contractions of the early mouse heart are established and what the downstream consequences of function are on cardiac differentiation and heart development. Using ex vivo Ca2+ imaging we found evidence of randomly distributed Ca2+ transients in the forming cardiac crescent, prior to contraction, suggesting early Ca2+ handling is essential for cardiomyocyte differentiation and subsequent heart development. To study the downstream effects of early Ca2+ we used a murine embryonic stem cell (mESC) model of cardiomyocyte differentiation which recapitulated heart development in vivo. Assessment of Ca2+ handling proteins indicated that the Na+-Ca2+ exchanger (NCX) was one of the earliest sarcolemmal transporters to be expressed, prior to the L-type Ca2+ channel (LTCC). Pharmacological inhibition of NCX revealed an essential early role in establishing and maintaining the first Ca2+ transients through to initiation of contraction; a role superseded by the LTCC as differentiation progressed. Upon NCX blockade cardiomyocyte differentiation was inhibited, coincident with the down-regulation of signature cardiac genes and calmodulin kinase signalling, which culminated in the failure of beating cardiomyocytes to form. This study points to a novel mechanism by which form and function are intricately linked such that, from the outset, Ca2+ acts to initiate contraction as well as regulate cardiac differentiation and the formation of the heart, adding an important layer onto our current understanding of mammalian cardiovascular development

Calcium handling precedes cardiac differentiation to initiate the first heartbeat

The mammalian heartbeat is thought to begin just prior to the linear heart tube stage of development. How the initial contractions are established and the downstream consequences of the earliest contractile function on cardiac differentiation and morphogenesis have not been described. Using high-resolution live imaging of mouse embryos, we observed randomly distributed spontaneous asynchronous Ca2+-oscillations (SACOs) in the forming cardiac crescent (stage E7.75) prior to overt beating. Nascent contraction initiated at around E8.0 and was associated with sarcomeric assembly and rapid Ca2+ transients, underpinned by sequential expression of the Na+-Ca2+ exchanger (NCX1) and L-type Ca2+ channel (LTCC). Pharmacological inhibition of NCX1 and LTCC revealed rapid development of Ca2+ handling in the early heart and an essential early role for NCX1 in establishing SACOs through to the initiation of beating. NCX1 blockade impacted on CaMKII signalling to down-regulate cardiac gene expression, leading to impaired differentiation and failed crescent maturation

Inhibition of NAADP signalling on reperfusion protects the heart by preventing lethal calcium oscillations via two-pore channel 1 and opening of the mitochondrial permeability transition pore

Aims In the heart, a period of ischaemia followed by reperfusion evokes powerful cytosolic Ca2+ oscillations that can cause lethal cell injury. These signals represent attractive cardioprotective targets, but the underlying mechanisms of genesis are ill-defined. Here, we investigated the role of the second messenger nicotinic acid adenine dinucleotide phosphate (NAADP), which is known in several cell types to induce Ca2+ oscillations that initiate from acidic stores such as lysosomes, likely via two-pore channels (TPCs, TPC1 and 2). Methods and results An NAADP antagonist called Ned-K was developed by rational design based on a previously existing scaffold. Ned-K suppressed Ca2+ oscillations and dramatically protected cardiomyocytes from cell death in vitro after ischaemia and reoxygenation, preventing opening of the mitochondrial permeability transition pore. Ned-K profoundly decreased infarct size in mice in vivo. Transgenic mice lacking the endo-lysosomal TPC1 were also protected from injury. Conclusion NAADP signalling plays a major role in reperfusion-induced cell death and represents a potent pathway for protection against reperfusion injury

2009-2010 Master Class - Roy Poper (Trumpet)

https://spiral.lynn.edu/conservatory_masterclasses/1086/thumbnail.jp