Collins HE, Zhu-Mauldin X, Marchase RB, Chatham JC. STIM1/Orai1-mediated SOCE: current perspectives and potential roles in cardiac function and pathology. Am J Physiol Heart Circ Physiol 305: H446 -H458, 2013. First published June 21, 2013 doi:10.1152/ajpheart.00104.2013.-Store-operated Ca 2ϩ entry (SOCE) is critical for Ca 2ϩ signaling in nonexcitable cells; however, its role in the regulation of cardiomyocyte Ca 2ϩ homeostasis has only recently been investigated. The increased understanding of the role of stromal interaction molecule 1 (STIM1) in regulating SOCE combined with recent studies demonstrating the presence of STIM1 in cardiomyocytes provides support that this pathway co-exists in the heart with the more widely recognized Ca 2ϩ handling pathways associated with excitation-contraction coupling. There is now substantial evidence that STIM1-mediated SOCE plays a key role in mediating cardiomyocyte hypertrophy, both in vitro and in vivo, and there is growing support for the contribution of SOCE to Ca 2ϩ overload associated with ischemia/reperfusion injury. Here, we provide an overview of our current understanding of the molecular regulation of SOCE and discuss the evidence supporting the role of STIM1/Orai1-mediated SOCE in regulating cardiomyocyte function.store-operated Ca 2ϩ entry; stromal interaction molecule 1; orai1; cardiomyocytes STORE-OPERATED CA 2ϩ ENTRY (SOCE), also known as capacitative calcium entry (CCE), is the major mechanism of Ca 2ϩ entry in nearly all nonexcitable cells (97, 99). In addition, it is increasingly recognized to co-exist with voltage-gated Ca 2ϩ channels in excitable cells, including neurons, skeletal muscle cells, and cardiomyocytes (1,38,45,83,121). In response to inositol 1,4,5-triphosphate (IP 3 )-(43) or ryanodine receptor (RyR)-mediated (3) Ca 2ϩ release from ER/SR stores, SOCE facilitates the influx of Ca 2ϩ from the extracellular space, resulting in a sustained increase in cytosolic Ca 2ϩ levels. Thus, although one of the roles of SOCE is to rapidly refill the depleted ER/SR stores, the subsequent sustained increase in cytosolic Ca 2ϩ also regulates numerous gene transcription pathways (33,50,151). Indeed, aberrant SOCE has been observed in a growing number of diseases including severe combined immunodeficiency, acute pancreatitis, and Alzheimer's disease (86).The integration of SOCE into well-established models of Ca 2ϩ homeostasis was hampered for many years by the lack of specific molecular mediators; even as recently as 2004 there was considerable controversy as to the specific mechanisms regulating SOCE (90, 113). However, in 2005, stromal interaction molecule 1 (STIM1) was found to localize to the ER/SR membrane and shown to function as a primary mediator of SOCE (54, 102). The putative physiological and pathophysiological roles of SOCE and STIM1 that have been identified to date are summarized in Table 1. A number of studies have recently reported the presence of STIM1 in adult cardiomyocytes (37,59,153), and consistent with earlier evidence supporting a rol...

Young ME, Marchase RB, Chatham JC. Stromal interaction molecule 1 is essential for normal cardiac homeostasis through modulation of ER and mitochondrial function. Am J Physiol Heart Circ Physiol 306: H1231-H1239, 2014. First published February 28, 2014 doi:10.1152/ajpheart.00075.2014.-The endoplasmic reticulum (ER) Ca 2ϩ sensor stromal interaction molecule 1 (STIM1) has been implicated as a key mediator of store-dependent and store-independent Ca 2ϩ entry pathways and maintenance of ER structure. STIM1 is present in embryonic, neonatal, and adult cardiomyocytes and has been strongly implicated in hypertrophic signaling; however, the physiological role of STIM1 in the adult heart remains unknown. We, therefore, developed a novel cardiomyocyte-restricted STIM1 knockout ( cr STIM1-KO) mouse. In cardiomyocytes isolated from cr STIM1-KO mice, STIM1 expression was reduced by ϳ92% with no change in the expression of related store-operated Ca 2ϩ entry proteins, STIM2, and Orai1. Immunoblot analyses revealed that cr STIM1-KO hearts exhibited increased ER stress from 12 wk, as indicated by increased levels of the transcription factor C/EBP homologous protein (CHOP), one of the terminal markers of ER stress. Transmission electron microscopy revealed ER dilatation, mitochondrial disorganization, and increased numbers of smaller mitochondria in cr S-TIM1-KO hearts, which was associated with increased mitochondrial fission. Using serial echocardiography and histological analyses, we observed a progressive decline in cardiac function in cr STIM1-KO mice, starting at 20 wk of age, which was associated with marked left ventricular dilatation by 36 wk. In addition, we observed the presence of an inflammatory infiltrate and evidence of cardiac fibrosis from 20 wk in cr STIM1-KO mice, which progressively worsened by 36 wk. These data demonstrate for the first time that STIM1 plays an essential role in normal cardiac function in the adult heart, which may be important for the regulation of ER and mitochondrial function. store-operated Ca 2ϩ entry; STIM1; cardiomyocytes; ER stress; mitochondria

Our understanding of the role of protein O-GlcNAcylation in the regulation of the cardiovascular system has increased rapidly in recent years. Studies have linked increased O-GlcNAc levels to glucose toxicity and diabetic complications; conversely, acute activation of O-GlcNAcylation has been shown to be cardioprotective. However, it is also increasingly evident that O-GlcNAc turnover plays a central role in the delicate regulation of the cardiovascular system. Therefore, the goals of this minireview are to summarize our current understanding of how changes in O-GlcNAcylation influence cardiovascular pathophysiology and to highlight the evidence that O-GlcNAc cycling is critical for normal function of the cardiovascular system.The O-linked attachment of ␤-N-acetylglucosamine (O-GlcNAc) to serine/threonine residues of proteins is a dynamic, transient, and reversible process that is an essential, metabolically regulated, signal transduction mediator in all cells (1). O-GlcNAc transferase (OGT) 3 catalyzes O-GlcNAc formation, utilizing UDP-GlcNAc as the substrate. UDPGlcNAc is the end product of the hexosamine biosynthesis pathway (HBP), which is regulated primarily by L-glutamine:Dfructose-6-phosphate amidotransferase (GFAT). GFAT catalyzes the formation of glucosamine 6-phosphate from fructose 6-phosphate. It has been estimated that 2-5% of glucose entering glycolysis is diverted through GFAT, thereby contributing to UDP-GlcNAc and O-GlcNAc synthesis (2); however, quantitative analysis of glucose flux via the HBP in the heart has yet to be performed. Although glucose availability is an important factor in O-GlcNAc synthesis, glutamine is critical as the amine donor for glucosamine 6-phosphate, whereas fatty acid metabolism is likely the primary source for the acetyl moiety. Thus, multiple nutrients contribute to both UDP-GlcNAc and protein O-GlcNAc synthesis. In addition to its synthesis, the levels of protein O-GlcNAc are also regulated by the activity of ␤-Nacetylhexosaminidase (O-GlcNAcase (OGA)), which catalyzes removal of this post-translational modification.A little over a decade following the identification of O-GlcNAc protein modification by Torres and Hart (3), the small heat shock protein ␣B-crystallin was shown to be an O-GlcNAc target in rat heart (4). Using vascular smooth muscle cells, Han and Kudlow (5) demonstrated in 1997 that O-GlcNAcylation of the transcription factor Sp1 modulated its susceptibility to proteasomal degradation, concluding that this may provide a link between nutritional status and transcriptional regulation. In the same year, reported that OGT activity was significantly higher in rat heart compared with liver, fat, and other types of striated muscle; they also hypothesized that O-GlcNAcylation could be involved in mediating glucose toxicity in insulin-responsive tissues. To our knowledge, these were the first reports of O-GlcNAcylated proteins in cardiac or vascular tissues, as well as the first to suggest that protein O-GlcNAcylation may contribute to the adverse effects of i...

Store‐operated Ca2+ entry (SOCE) occurs following ER/SR Ca2+ depletion and is mediated by the ER/SR Ca2+ sensor, Stromal Interaction molecule 1 (STIM1) and plasma membrane Orai1 channels. The role of SOCE in the heart has not been widely explored; however, we recently reported that cardiomyocyte restricted deletion of STIM1 (crSTIM1‐KO) lead to increased ER stress, mitochondrial dysfunction, reduced cardiac function and the development of a dilated cardiomyopathy. Since Ca2+ plays a key role in the regulation of cardiac metabolism, we examined whether a lack of STIM1 altered cardiac metabolism.Using an isolated perfused working heart model we found that although contractile function was normal, hearts from 20 week crSTIM1‐KO mice exhibited significantly reduced glucose oxidation and glycolysis, with no significant changes in oleate oxidation. Pyruvate dehydrogenase kinase 4 protein expression was increased in crSTIM1‐KO hearts, consistent with the lower glucose oxidation. Although oleate oxidation was not changed, crSTIM1‐KO hearts contained an increased number of lipid droplets compared to control hearts, which may indicate an imbalance between fatty acid uptake and subsequent oxidation. While it is widely accepted that Ca2+ plays a key role in the regulation of cardiac metabolism, the specific Ca2+ handling pathways have not been elucidated. The results from this study suggest for the first time that STIM1 mediated Ca2+ signaling may play a key role in regulating cardiac metabolism. This work was supported by NIH grant R21‐HL‐110366 (JCC) and the UAB Comprehensive Cardiovascular Center William W. Featheringill Postdoctoral Fellowship (HEC).

Transmission electron microscopy (TEM) has long been an important technique, capable of high degree resolution and visualization of subcellular structures and organization. Over the last 20 years, TEM has gained popularity in the cardiovascular field to visualize changes at the nanometer scale in cardiac ultrastructure during cardiovascular development, aging, and a broad range of pathologies. Recently, the cardiovascular TEM enabled the studying of several signaling processes impacting mitochondrial function, such as mitochondrial fission/fusion, autophagy, mitophagy, lysosomal degradation, and lipophagy. The goals of this review are to provide an overview of the current usage of TEM to study cardiac ultrastructural changes; to understand how TEM aided the visualization of mitochondria, autophagy, and mitophagy under normal and cardiovascular disease conditions; and to discuss the overall advantages and disadvantages of TEM and potential future capabilities and advancements in the field.