Detection of 28S RNA with the FGF-2 cDNA at high stringency through related G/C-rich sequences

Identification of a novel human subfamily of mitochondrial carriers with calcium-binding domains

Aralar1 and citrin were identified as calcium binding aspartate/glutamate carriers (AGC) in mitochondria. The presence of calcium binding motifs facing the extramitochondrial space allows the regulation of the transport activity of these carriers by cytosolic calcium and provides a new mechanism to transduce calcium signals in mitochondria without the requirement of calcium entry in the organelle. We now report the complete characterization of a second subfamily of human calcium binding mitochondrial carriers named SCaMC (short calcium-binding mitochondrial carriers). We have identified three SCaMC genes in the human genome. All code for highly conserved proteins (about 70-80% identity), of about 500 amino acids with a characteristic mitochondrial carrier domain at the C terminus, and an N-terminal extension harboring four EF-hand binding motifs with high similarity to calmodulin. All SCaMC proteins were found to be located exclusively in mitochondria, and their N-terminal extensions were dispensable for the correct mitochondrial targeting of the polypeptides. SCaMC-1 is the human orthologue of the rabbit Efinal protein, which was reported to be located in peroxisomes, and SCaMC-2 is the human orthologue of the rat MCSC protein, described as up-regulated by dexamethasone in AR42J cells. One of the SCaMC genes, SCaMC-2, has four variants generated by alternative splicing, resulting in proteins with a common C terminus but with variations in their N-terminal halves, including the loss of one to three EF-hand motifs. These results make SCaMC one of most complex subfamilies of mitochondrial carriers and suggest that the large number of isoforms and splice variants may confer different calcium sensitivity to the transport activity of these carriers.

Exacerbation of myocardial injury in transgenic mice overexpressing FGF-2 is T cell dependent

Fibroblast growth factor-2 (FGF-2) is cardioprotective when added exogenously, stimulates cardiac myocyte proliferation, and is a mediator of tissue repair after injury. Furthermore, transgenic (TG) mice overexpressing FGF-2 in cardiac muscle demonstrate increased resistance to injury in an isolated heart model of ischemia-reperfusion. We investigated how increasing the endogenous FGF-2 levels in the heart affects the extent of myocardial damage induced by isoproterenol in vivo. Histopathological evaluation of hearts after intraperitoneal injection of isoproterenol yielded significantly higher scores for myocardial damage in FGF-2 TG lines compared with non-TG mice. After 1 day, FGF-2 TG mouse hearts displayed more cellular infiltration correlating with increased tissue damage. Immunostaining of non-TG and FGF-2 TG mouse hearts showed the presence of leukocytes in the infiltrate, including T cells expressing FGF receptor-1. Treatment of mice with T cell suppressors cyclosporin A and anti-CD3epsilon significantly decreased the level of myocardial injury observed after isoproterenol and equalized the histopathology scores in FGF-2 TG and non-TG hearts. These data demonstrate a direct T cell involvement in the response to isoproterenol-induced injury in vivo. Moreover, the findings indicate that the exacerbation of myocardial damage in FGF-2 TG mice was dependent on T cell infiltration, implicating FGF-2 in the inflammatory response seen in cardiac tissue after injury in vivo.

Overexpression of FGF-2 increases cardiac myocyte viability after injury in isolated mouse hearts

We generated transgenic (TG) mice overexpressing fibroblast growth factor (FGF)-2 protein (22- to 34-fold) in the heart. Chronic FGF-2 overexpression revealed no significant effect on heart weight-to-body weight ratio or expression of cardiac differentiation markers. There was, however, a significant 20% increase in capillary density. Although there was no change in FGF receptor-1 expression, relative levels of phosphorylated c-Jun NH(2)-terminal kinase and p38 kinase as well as of membrane-associated protein kinase C (PKC)-alpha and total PKC-epsilon were increased in FGF-2-TG mouse hearts. An isolated mouse heart model of ischemia-reperfusion injury was used to assess the potential of increased endogenous FGF-2 for cardioprotection. A significant 34-45% increase in myocyte viability, reflected in a decrease in lactate dehydrogenase released into the perfusate, was observed in FGF-2 overexpressing mice and non-TG mice treated exogenously with FGF-2. In conclusion, FGF-2 overexpression causes augmentation of signal transduction pathways and increased resistance to ischemic injury. Thus, stimulation of endogenous FGF-2 expression offers a potential mechanism to enhance cardioprotection.

alpha1-Adrenergic stimulation of FGF-2 promoter in cardiac myocytes and in adult transgenic mouse hearts

Fibroblast growth factor (FGF-2), a mitogenic, angiogenic, and cardioprotective agent, is reported to be released from the postnatal heart by a mechanism of transient remodeling of the sarcolemma during contraction. This release can be increased with adrenergic stimulation. RNA blotting was used to assess whether FGF-2 synthesis in neonatal rat cardiomyocytes might also be regulated by adrenergic stimulation. FGF-2 RNA levels were increased after treatment with norepinephrine for 6 h or with the alpha-adrenergic agonist phenylephrine for 48 h. To assess an effect on transcription, neonatal rat cardiomyocytes were transfected with a hybrid rat FGF-2 promoter/luciferase gene (-1058FGFp.luc) and treated with norepinephrine or phenylephrine for 6 or 48 h, respectively. FGF-2 promoter activity was increased two- to sevenfold in an alpha1-specific manner. Putative phenylephrine-responsive elements (PEREs) were identified at positions -780 and -761 relative to a major transcription initiation site. However, deletion analysis of -1058FGFp.luc showed that the phenylephrine response was independent of the putative PEREs, cell contraction, and Ca2+ influx. In transgenic mice expressing -1058FGFp.luc, a significant three- to sevenfold stimulation of FGF-2 promoter activity was detected in the hearts of two independent lines 6 h after intraperitoneal administration of phenylephrine (50 mg/kg). This increase was still apparent at 24 h but was not detected at 48 h posttreatment. Analysis of FGF-2 mRNA in normal mouse hearts revealed accumulation of the 6.1-kb transcript at 24 h. Control of local FGF-2 synthesis at the transcriptional level through adrenergic stimulation may be important in the response to injury as well as in the maintenance of a healthy myocardium.