RESUMEN
Since it was discovered, the citric acid cycle has been known to be central to cell metabolism and energy homeostasis. Mainly found in the mitochondrial matrix, some of the intermediates of the Krebs cycle are also present in the blood stream. Currently, there are several reports that indicate functional roles for Krebs intermediates out of its cycle. Succinate, for instance, acts as an extracellular ligand by binding to a G-protein coupled receptor, known as GPR91, expressed in kidney, liver, heart, retinal cells and possibly many other tissues, leading to a wide array of physiological and pathological effects. Through GPR91, succinate is involved in functions such as regulation of blood pressure, inhibition of lipolysis in white adipose tissue, development of retinal vascularization, cardiac hypertrophy and activation of stellate hepatic cells by ischemic hepatocytes. Along the current review, these new effects of succinate through GPR91 will be explored and discussed.
Asunto(s)
Ciclo del Ácido Cítrico , Receptores Acoplados a Proteínas G/metabolismo , Animales , Presión Sanguínea , Expresión Génica , Humanos , Hígado/metabolismo , Modelos Moleculares , Miocardio/metabolismo , Receptores Acoplados a Proteínas G/análisis , Receptores Acoplados a Proteínas G/genética , Retina/metabolismo , Transducción de Señal , Ácido Succínico/metabolismoRESUMEN
BACKGROUND: Succinate is an intermediate of the citric acid cycle as well as an extracellular circulating molecule, whose receptor, G protein-coupled receptor-91 (GPR91), was recently identified and characterized in several tissues, including heart. Because some pathological conditions such as ischemia increase succinate blood levels, we investigated the role of this metabolite during a heart ischemic event, using human and rodent models. RESULTS: We found that succinate causes cardiac hypertrophy in a GPR91 dependent manner. GPR91 activation triggers the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), the expression of calcium/calmodulin dependent protein kinase IIδ (CaMKIIδ) and the translocation of histone deacetylase 5 (HDAC5) into the cytoplasm, which are hypertrophic-signaling events. Furthermore, we found that serum levels of succinate are increased in patients with cardiac hypertrophy associated with acute and chronic ischemic diseases. CONCLUSIONS: These results show for the first time that succinate plays an important role in cardiomyocyte hypertrophy through GPR91 activation, and extend our understanding of how ischemia can induce hypertrophic cardiomyopathy.
Asunto(s)
Cardiopatías/metabolismo , Receptores Acoplados a Proteínas G/metabolismo , Ácido Succínico/metabolismo , Adulto , Animales , Animales Recién Nacidos , Presión Sanguínea/efectos de los fármacos , Calcio/metabolismo , Proteína Quinasa Tipo 2 Dependiente de Calcio Calmodulina/metabolismo , Cardiopatías/patología , Histona Desacetilasas/metabolismo , Humanos , Cirrosis Hepática/metabolismo , Ratones Noqueados , Persona de Mediana Edad , Quinasas de Proteína Quinasa Activadas por Mitógenos/metabolismo , Miocitos Cardíacos/metabolismo , Miocitos Cardíacos/patología , Ratas Wistar , Ácido Succínico/sangreRESUMEN
It is well established that inositol 1,4,5-trisphosphate (IP3) dependent Ca(2+) signaling plays a crucial role in cardiomyocyte hypertrophy. However, it is not yet known whether nuclear IP3 represents a Ca(2+) mobilizing pathway involved in this process. The goal of the current work was to investigate the specific role of nuclear IP3 in cardiomyocyte hypertrophic response. In this work, we used an adenovirus construct that selectively buffers IP3 in the nuclear region of neonatal cardiomyocytes. We showed for the first time that nuclear IP3 mediates endothelin-1 (ET-1) induced hypertrophy. We also found that both calcineurin (Cn)/nuclear factor of activated T Cells (NFAT) and histone deacetylase-5 (HDAC5) pathways require nuclear IP3 to mediate pathological cardiomyocyte growth. Additionally, we found that nuclear IP3 buffering inhibited insulin-like growth factor-1 (IGF-1) induced hypertrophy and prevented reexpression of fetal gene program. Together, these results demonstrated that nuclear IP3 is an essential and a conserved signal for both pathological and physiological forms of cardiomyocyte hypertrophy.
Asunto(s)
Cardiomegalia/patología , Núcleo Celular/metabolismo , Endotelina-1/metabolismo , Inositol 1,4,5-Trifosfato/metabolismo , Miocitos Cardíacos/metabolismo , Miocitos Cardíacos/patología , Animales , Calcineurina/metabolismo , Calcio/metabolismo , Cardiomegalia/metabolismo , Proliferación Celular , Histona Desacetilasas/metabolismo , Receptores de Inositol 1,4,5-Trifosfato/metabolismo , Factor I del Crecimiento Similar a la Insulina/metabolismo , Factores de Transcripción NFATC/metabolismo , Ratas , Ratas Wistar , Transducción de SeñalRESUMEN
UNLABELLED: Subcellular Ca(2+) signals control a variety of responses in the liver. For example, mitochondrial Ca(2+) (Ca(mit)(2+)) regulates apoptosis, whereas Ca(2+) in the nucleus regulates cell proliferation. Because apoptosis and cell growth can be related, we investigated whether Ca(mit)(2+) also affects liver regeneration. The Ca(2+)-buffering protein parvalbumin, which was targeted to the mitochondrial matrix and fused to green fluorescent protein, was expressed in the SKHep1 liver cell line; the vector was called parvalbumin-mitochondrial targeting sequence-green fluorescent protein (PV-MITO-GFP). This construct properly localized to and effectively buffered Ca(2+) signals in the mitochondrial matrix. Additionally, the expression of PV-MITO-GFP reduced apoptosis induced by both intrinsic and extrinsic pathways. The reduction in cell death correlated with the increased expression of antiapoptotic genes [B cell lymphoma 2 (bcl-2), myeloid cell leukemia 1, and B cell lymphoma extra large] and with the decreased expression of proapoptotic genes [p53, B cell lymphoma 2-associated X protein (bax), apoptotic peptidase activating factor 1, and caspase-6]. PV-MITO-GFP was also expressed in hepatocytes in vivo with an adenoviral delivery system. Ca(mit)(2+) buffering in hepatocytes accelerated liver regeneration after partial hepatectomy, and this effect was associated with the increased expression of bcl-2 and the decreased expression of bax. CONCLUSION: Together, these results reveal an essential role for Ca(mit)(2+) in hepatocyte proliferation and liver regeneration, which may be mediated by the regulation of apoptosis.
Asunto(s)
Apoptosis/fisiología , Calcio/metabolismo , Regeneración Hepática/fisiología , Mitocondrias Hepáticas/metabolismo , Animales , Señalización del Calcio/fisiología , Proliferación Celular , Masculino , Modelos Animales , Proteínas Proto-Oncogénicas c-bcl-2/metabolismo , Ratas , Ratas Sprague-Dawley , Proteína X Asociada a bcl-2/metabolismoRESUMEN
In the heart, cytosolic Ca(2+) signals are well-characterized events that participate in the activation of cell contraction. In contrast, nuclear Ca(2+) contribution to cardiomyocyte function remains elusive. Here, we examined functional consequences of buffering nuclear Ca(2+) in neonatal cardiomyocytes. We report that cardiomyocytes contain a nucleoplasmic reticulum, which expresses both ryanodine receptor (RyR) and inositol 1,4,5-trisphosphate receptor (InsP(3)R), providing a possible way for active regulation of nuclear Ca(2+). Adenovirus constructs encoding the Ca(2+) buffer protein parvalbumin were targeted to the nucleus with a nuclear localization signal (Ad-PV-NLS) or to the cytoplasm with a nuclear exclusion signal (Ad-PV-NES). A decrease in the amplitude of global Ca(2+) transients and RyR-II expression, as well as an increase in cell beating rate were observed in Ad-PV-NES and Ad-PV-NLS cells. When nuclear Ca(2+) buffering was imposed nuclear enlargement, increased calcineurin expression, NFAT translocation to the nucleus and subcellular redistribution of atrial natriuretic peptide were observed. Furthermore, prolongation of action potential duration occurred in adult ventricular myocytes. These results suggest that nuclear Ca(2+) levels underlie the regulation of specific protein targets and thereby modulate cardiomyocyte function. The local nuclear Ca(2+) signaling and the structures that control it constitute a novel regulatory motif in the heart.
Asunto(s)
Señalización del Calcio/fisiología , Calcio/metabolismo , Núcleo Celular/metabolismo , Receptores de Inositol 1,4,5-Trifosfato/metabolismo , Miocitos Cardíacos/metabolismo , Membrana Nuclear/metabolismo , Canal Liberador de Calcio Receptor de Rianodina/metabolismo , Adenoviridae/genética , Animales , Animales Recién Nacidos , Western Blotting , Citoplasma/metabolismo , Fluorescencia , Técnica del Anticuerpo Fluorescente , Inositol 1,4,5-Trifosfato/metabolismo , Miocitos Cardíacos/citología , Señales de Localización Nuclear , Parvalbúminas/genética , Parvalbúminas/metabolismo , Ratas , Ratas WistarRESUMEN
GPR91 is an orphan G-protein-coupled receptor (GPCR) that has been characterized as a receptor for succinate, a citric acid cycle intermediate, in several tissues. In the heart, the role of succinate is unknown. We now report that rat ventricular cardiomyocytes express GPR91. We found that succinate, through GPR91, increases the amplitude and the rate of decline of global Ca(2+) transient, by increasing the phosphorylation levels of ryanodine receptor and phospholamban, two well known Ca(2+) handling proteins. The effects of succinate on Ca(2+) transient were abolished by pre-treatment with adenylyl cyclase and cAMP-dependent protein kinase (PKA) inhibitors. Direct PKA activation by succinate was further confirmed using a FRET-based A-kinase activity reporter. Additionally, succinate decreases cardiomyocyte viability through a caspase-3 activation pathway, effect also prevented by PKA inhibition. Taken together, these observations show that succinate acts as a signaling molecule in cardiomyocytes, modulating global Ca(2+) transient and cell viability through a PKA-dependent pathway.