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

Cardioprotection by selective SGLT-2 inhibitors in a non-diabetic mouse model of myocardial ischemia/reperfusion injury: a class or a drug effect?

Major clinical trials with sodium glucose co-transporter-2 inhibitors (SGLT-2i) exhibit protective effects against heart failure events, whereas inconsistencies regarding the cardiovascular death outcomes are observed. Therefore, we aimed to compare the selective SGLT-2i empagliflozin (EMPA), dapagliflozin (DAPA) and ertugliflozin (ERTU) in terms of infarct size (IS) reduction and to reveal the cardioprotective mechanism in healthy non-diabetic mice. C57BL/6 mice randomly received vehicle, EMPA (10 mg/kg/day) and DAPA or ERTU orally at the stoichiometrically equivalent dose (SED) for 7 days. 24 h-glucose urinary excretion was determined to verify SGLT-2 inhibition. IS of the region at risk was measured after 30 min ischemia (I), and 120 min reperfusion (R). In a second series, the ischemic myocardium was collected (10th min of R) for shotgun proteomics and evaluation of the cardioprotective signaling. In a third series, we evaluated the oxidative phosphorylation capacity (OXPHOS) and the mitochondrial fatty acid oxidation capacity by measuring the respiratory rates. Finally, Stattic, the STAT-3 inhibitor and wortmannin were administered in both EMPA and DAPA groups to establish causal relationships in the mechanism of protection. EMPA, DAPA and ERTU at the SED led to similar SGLT-2 inhibition as inferred by the significant increase in glucose excretion. EMPA and DAPA but not ERTU reduced IS. EMPA preserved mitochondrial functionality in complex I&II linked oxidative phosphorylation. EMPA and DAPA treatment led to NF-kB, RISK, STAT-3 activation and the downstream apoptosis reduction coinciding with IS reduction. Stattic and wortmannin attenuated the cardioprotection afforded by EMPA and DAPA. Among several upstream mediators, fibroblast growth factor-2 (FGF-2) and caveolin-3 were increased by EMPA and DAPA treatment. ERTU reduced IS only when given at the double dose of the SED (20 mg/kg/day). Short-term EMPA and DAPA, but not ERTU administration at the SED reduce IS in healthy non-diabetic mice. Cardioprotection is not correlated to SGLT-2 inhibition, is STAT-3 and PI3K dependent and associated with increased FGF-2 and Cav-3 expression.

CorMatrix Cor™ PATCH for epicardial infarct repair

Contemporary management of ischemic heart disease lacks strategies to directly access the heart and promote reparative cellular mechanisms to improve postinfarct cardiac remodeling. Epicardial infarct repair (EIR) is an emerging technique whereby bioactive materials are sewn over ischemic areas of the heart at the time of surgical revascularization to promote adaptive cardiac repair. The CorMatrix Cor™ PATCH (CorMatrix Cardiovascular Inc., GA, USA) is an acellular bioactive material compatible with EIR. Herein, we review current preclinical and clinical data for the CorMatrix Cor PATCH and its use in EIR.

What Can We Learn from FGF-2 Isoform-Specific Mouse Mutants? Differential Insights into FGF-2 Physiology In Vivo

Fibroblast growth factor 2 (FGF-2), ubiquitously expressed in humans and mice, is functionally involved in cell growth, migration and maturation in vitro and in vivo. Based on the same mRNA, an 18-kilo Dalton (kDa) FGF-2 isoform named FGF-2 low molecular weight (FGF-2LMW) isoform is translated in humans and rodents. Additionally, two larger isoforms weighing 21 and 22 kDa also exist, summarized as the FGF-2 high molecular weight (FGF-2HMW) isoform. Meanwhile, the human FGF-2HMW comprises a 22, 23, 24 and 34 kDa protein. Independent studies verified a specific intracellular localization, mode of action and tissue-specific spatiotemporal expression of the FGF-2 isoforms, increasing the complexity of their physiological and pathophysiological roles. In order to analyze their spectrum of effects, FGF-2LMW knock out (ko) and FGF-2HMWko mice have been generated, as well as mice specifically overexpressing either FGF-2LMW or FGF-2HMW. So far, the development and functionality of the cardiovascular system, bone formation and regeneration as well as their impact on the central nervous system including disease models of neurodegeneration, have been examined. This review provides a summary of the studies characterizing the in vivo effects modulated by the FGF-2 isoforms and, thus, offers a comprehensive overview of its actions in the aforementioned organ systems.

Modulatory Effect of Myokines on Reactive Oxygen Species in Ischemia/Reperfusion

There is a growing body of evidence showing the importance of physical activity against acute ischemic events in various organs. Ischemia/reperfusion injury (I/R) is characterized by tissue damage as a result of restriction and subsequent restoration of blood supply to an organ. Oxidative stress due to increased reactive oxygen species formation and/or insufficient antioxidant defense is considered to play an important role in I/R. Physical activity not only decreases the general risk factors for ischemia but also confers direct anti-ischemic protection via myokine production. Myokines are skeletal muscle-derived cytokines, representing multifunctional communication channels between the contracting skeletal muscle and other organs through an endocrine manner. In this review, we discuss the most prominent members of the myokines (i.e., brain-derived neurotrophic factor (BDNF), cathepsin B, decorin, fibroblast growth factors-2 and -21, follistatin, follistatin-like, insulin-like growth factor-1; interleukin-6, interleukin-7, interleukin-15, irisin, leukemia inhibitory factor, meteorin-like, myonectin, musclin, myostatin, and osteoglycin) with a particular interest in their potential influence on reactive oxygen and nitrogen species formation or antioxidant capacity. A better understanding of the mechanism of action of myokines and particularly their participation in the regulation of oxidative stress may widen their possible therapeutic use and, thereby, may support the fight against I/R.

Phosphoproteomic analysis identifies phospho-Threonine-17 site of phospholamban important in low molecular weight isoform of fibroblast growth factor 2-induced protection against post-ischemic cardiac dysfunction

RATIONALE

Among its many biological roles, fibroblast growth factor 2 (FGF2) protects the heart from dysfunction and damage associated with an ischemic attack. Our laboratory demonstrated that its protection against myocardial dysfunction occurs by the low molecular weight (LMW) isoform of FGF2, while the high molecular weight (HMW) isoforms are associated with a worsening in post-ischemic recovery of cardiac function. LMW FGF2-mediated cardioprotection is facilitated by activation of multiple kinases, including PKCalpha, PKCepsilon, and ERK, and inhibition of p38 and JNK.

OBJECTIVE

Yet, the substrates of those kinases associated with LMW FGF2-induced cardioprotection against myocardial dysfunction remain to be elucidated.

METHODS AND RESULTS

To identify substrates in LMW FGF2 improvement of post-ischemic cardiac function, mouse hearts expressing only LMW FGF2 were subjected to ischemia-reperfusion (I/R) injury and analyzed by a mass spectrometry (MS)-based quantitative phosphoproteomic strategy. MS analysis identified 50 phosphorylation sites from 7 sarcoendoplasmic reticulum (SR) proteins that were significantly altered in I/R-treated hearts only expressing LMW FGF2 compared to those hearts lacking FGF2. One of those phosphorylated SR proteins identified was phospholamban (PLB), which exhibited rapid, increased phosphorylation at Threonine-17 (Thr17) after I/R in hearts expressing only LMW FGF2; this was further validated using Selected Reaction Monitoring-based MS workflow. To demonstrate a mechanistic role of phospho-Thr17 PLB in LMW FGF2-mediated cardioprotection, hearts only expressing LMW FGF2 and those expressing only LMW FGF2 with a mutant PLB lacking phosphorylatable Thr17 (Thr17Ala PLB) were subjected to I/R. Hearts only expressing LMW FGF2 showed significantly improved recovery of cardiac function following I/R (p < 0.05), and this functional improvement was significantly abrogated in hearts expressing LMW FGF2 and Thr17Ala PLB (p < 0.05).

CONCLUSION

The findings indicate that LMW FGF2 modulates intracellular calcium handling/cycling via regulatory changes in SR proteins essential for recovery from I/R injury, and thereby protects the heart from post-ischemic cardiac dysfunction.

Basic Fibroblast Growth Factor Attenuates Injury in Myocardial Infarction by Enhancing Hypoxia-Inducible Factor-1 Alpha Accumulation

Background

The combination of antiapoptotic and angiogenic actions may represent a pharmacotherapeutic strategy for the treatment of myocardial infarction. Fibroblast growth factor (FGF) is expressed in various cell types including endothelial and muscle cells and promotes their survival, migration, and proliferation.

Methods and Results

Myocardial microvascular endothelial cells were divided into four treatment groups, the sham, hypoxia, basic FGF (bFGF), and bFGF plus 2-methoxyestradiol groups, and subjected to in vitro apoptotic analysis and Matrigel assays. An in vivo model of myocardial infarction was established by ligaturing the left coronary artery of mice in the four treatment groups. Cardiac performance, myocardial injury, endothelial cell angiogenesis, and myocardial apoptosis were assessed. bFGF administration after myocardial infarction improved cardiac function and cell viability, attenuated myocardial injury and apoptosis, and enhanced angiogenesis. Western blotting of HIF-1α, p-AKT, VEGF, p53, BAX, and Bcl-2 showed that bFGF increased HIF-1α, p-AKT, VEGF, and Bcl-2 and decreased BAX protein levels.

Conclusion

The results of the present study indicated that bFGF attenuates myocardial injury by inhibiting apoptosis and promoting angiogenesis via a novel HIF-1α-mediated mechanism and a potential utility of bFGF in protecting against myocardial infarction.

Growth factors in pulmonary arterial hypertension: Focus on preserving right ventricular function

Pulmonary arterial hypertension (PAH) is a rare and progressive disease, characterized by increased vascular resistance leading to right ventricle (RV) failure. The extent of right ventricular dysfunction crucially influences disease prognosis; however, currently no therapies have specific cardioprotective effects. Besides discussing the pathophysiology of right ventricular adaptation in PAH, this review focuses on the roles of growth factors (GFs) in disease pathomechanism. We also summarize the involvement of GFs in the preservation of cardiomyocyte function, to evaluate their potential as cardioprotective biomarkers and novel therapeutic targets in PAH.

Cardiac actions of fibroblast growth factor 23

Fibroblast growth factors (FGF) are mitogenic signal mediators that induce cell proliferation and survival. Although cardiac myocytes are post-mitotic, they have been shown to be able to respond to local and circulating FGFs. While precise molecular mechanisms are not well characterized, some FGF family members have been shown to induce cardiac remodeling under physiologic conditions by mediating hypertrophic growth in cardiac myocytes and by promoting angiogenesis, both events leading to increased cardiac function and output. This FGF-mediated physiologic scenario might transition into a pathologic situation involving cardiac cell death, fibrosis and inflammation, and eventually cardiac dysfunction and heart failure. As discussed here, cardiac actions of FGFs - with the majority of studies focusing on FGF2, FGF21 and FGF23 - and their specific FGF receptors (FGFR) and precise target cell types within the heart, are currently under experimental investigation. Especially cardiac effects of endocrine FGFs entered center stage over the past five years, as they might provide communication routes that couple metabolic mechanisms, such as bone-regulated phosphate homeostasis, or metabolic stress, such as hyperphosphatemia associated with kidney injury, with changes in cardiac structure and function. In this context, it has been shown that elevated serum FGF23 can directly tackle cardiac myocytes via FGFR4 thereby contributing to cardiac hypertrophy in models of chronic kidney disease, also called uremic cardiomyopathy. Precise characterization of FGFs and their origin and regulation of expression, and even more importantly, the identification of the FGFR isoforms that mediate their cardiac actions should help to develop novel pharmacological interventions for heart failure, such as FGFR4 inhibition to tackle uremic cardiomyopathy.

Ascorbic acid-mediated enhanced cardiomyocyte differentiation of mouse ES-cells involves interplay of DNA methylation and multiple-signals

Embryonic stem cells (ES-cells) provide a good model system to study lineage-specific differentiation. Though, the differentiation of ES-cells to cardiomyocytes is documented, a clear understanding of the molecular mechanism of differentiation and improved functional-differentiation efficiency are yet to be achieved. In this regard, ascorbic acid (Aa) is shown to be one of the effective cardiac inducers in ES-cells. But, its mechanism is poorly understood. We therefore, investigated the mechanism of Aa-mediated cardiomyocyte differentiation of ES-cells. Here, we describe the potential involvement of epigenetic (DNA methylation) as well as integrin- and Erk- signaling systems during cardiomyocyte differentiation. Transgenic GS-2 ES-cells and wild-type D3 ES-cells were differentiated to cardiomyocytes, in the presence or absence of Aa and with or without inhibitors of Erk-, collagen- and integrin- pathways. At specific time points, differentiated states of ES-cells were scored by gene expression analyses and the proportion of functional cTnI⁺ cardiomyocytes. DNA methylation changes of Isl-1, BMP-2, GATA-4 and α-MHC in cardiogenic cells, following stimulation with Aa, were analyzed by using methylation specific PCR (MSP). We observed that Aa, when applied in initial phase of ES-cell differentiation, consistently enhanced cardiac differentiation (99%) over that observed during spontaneous differentiation (70%). This was associated with enhanced expressions of cardiogenesis-associated genes. A two-fold increase in cTnI⁺ cells was observed, with appropriate myofibril arrangement. The observed effect of Aa was due to enhanced collagen and integrin signaling, coupled with a high p-ERK1/2 expression, downstream. Besides, the involvement of DNA methylation in regulating the expression of cardiac genes i.e., Isl-1 and α-MHC was also observed. Overall, this study, for the first time, demonstrates that Aa-mediated cardiac enhancement is brought about, mechanistically, through the interplay of epigenetic changes in DNA methylation of cardiac genes (Isl-1 and α-MHC) and integrin signaling system.

Endothelial fibroblast growth factor receptor signaling is required for vascular remodeling following cardiac ischemia-reperfusion injury

Fibroblast growth factor (FGF) signaling is cardioprotective in various models of myocardial infarction. FGF receptors (FGFRs) are expressed in multiple cell types in the adult heart, but the cell type-specific FGFR signaling that mediates different cardioprotective endpoints is not known. To determine the requirement for FGFR signaling in endothelium in cardiac ischemia-reperfusion injury, we conditionally inactivated the Fgfr1 and Fgfr2 genes in endothelial cells with Tie2-Cre (Tie2-Cre, Fgfr1(f/f), Fgfr2(f/f) DCKO mice). Tie2-Cre, Fgfr1(f/f), Fgfr2(f/f) DCKO mice had normal baseline cardiac morphometry, function, and vessel density. When subjected to closed-chest, regional cardiac ischemia-reperfusion injury, Tie2-Cre, Fgfr1(f/f), Fgfr2(f/f) DCKO mice showed a significantly increased hypokinetic area at 7 days, but not 1 day, after reperfusion. Tie2-Cre, Fgfr1(f/f), Fgfr2(f/f) DCKO mice also showed significantly worsened cardiac function compared with controls at 7 days but not 1 day after reperfusion. Pathophysiological analysis showed significantly decreased vessel density, increased endothelial cell apoptosis, and worsened tissue hypoxia in the peri-infarct area at 7 days following reperfusion. Notably, Tie2-Cre, Fgfr1(f/f), Fgfr2(f/f) DCKO mice showed no impairment in the cardiac hypertrophic response. These data demonstrate an essential role for FGFR1 and FGFR2 in endothelial cells for cardiac functional recovery and vascular remodeling following in vivo cardiac ischemia-reperfusion injury, without affecting the cardiac hypertrophic response. This study suggests the potential for therapeutic benefit from activation of endothelial FGFR pathways following ischemic injury to the heart.

bFGF attenuates endoplasmic reticulum stress and mitochondrial injury on myocardial ischaemia/reperfusion via activation of PI3K/Akt/ERK1/2 pathway

Extensive research focused on finding effective strategies to prevent or improve recovery from myocardial ischaemia/reperfusion (I/R) injury. Basic fibroblast growth factor (bFGF) has been shown to have therapeutic potential in some heart disorders, including ischaemic injury. In this study, we demonstrate that bFGF administration can inhibit the endoplasmic reticulum (ER) stress and mitochondrial dysfunction induced in the heart in a mouse model of I/R injury. In vitro, bFGF exerts a protective effect by inhibiting the ER stress response and mitochondrial dysfunction proteins that are induced by tert-Butyl hydroperoxide (TBHP) treatment. Both of these in vivo and in vitro effects are related to the activation of two downstream signalling pathways, PI3K/Akt and ERK1/2. Inhibition of these PI3K/Akt and ERK1/2 pathways by specific inhibitors, LY294002 and PD98059, partially reduces the protective effect of bFGF. Taken together, our results indicate that the cardioprotective role of bFGF involves the suppression of ER stress and mitochondrial dysfunction in ischaemic oxidative damage models and oxidative stress-induced H9C2 cell injury; furthermore, these effects underlie the activation of the PI3K/Akt and ERK1/2 signalling pathways.

Heart-specific expression of FGF-16 and a potential role in postnatal cardioprotection

Fibroblast growth factor 16 (FGF-16) was originally cloned from rat heart. Subsequent investigation of mouse FGF-16, including generation of null mice, revealed a specific pattern of expression in the endocardium and epicardium, and role for FGF-16 during embryonic heart development. FGF-16 is expressed mainly in brown adipose tissue during rat embryonic development, but is expressed mainly in the murine heart after birth. There is also an apparent switch from limited endocardial and epicardial expression in the embryo to the myocardium in the perinatal period. The FGF-16 gene and its location on the X chromosome are conserved between human and murine species, and no other member of the FGF family shows this pattern of spatial and temporal expression. The human and murine FGF-16 gene promoter regions also share an equivalent location for TATA sequences, as well as adjacent putative binding sites for transcription factors linked to cardiac expression and response to stress. Recent evidence has implicated nonsense mutation of FGF-16 with increased cardiovascular risk, and FGF-16 supplementation with cardioprotection. Here we review the important role of FGF-16 in embryonic heart development, its gene regulation, and evidence for FGF-16 as an endogenous and exogenous cardiac-specific and protective factor in the postnatal heart. Moreover, given the conservation of the FGF-16 gene and its chromosomal location between species, the question of support for a cardiac role in the human population is also considered.

Cardiomyocyte FGF signaling is required for Cx43 phosphorylation and cardiac gap junction maintenance

Cardiac remodeling resulting from impairment of myocardial integrity leads to heart failure, through still incompletely understood mechanisms. The fibroblast growth factor (FGF) system has been implicated in tissue maintenance, but its role in the adult heart is not well defined. We hypothesized that the FGF system plays a role in the maintenance of cardiac homeostasis, and the impairment of cardiomyocyte FGF signaling leads to pathological cardiac remodeling. We showed that FGF signaling is required for connexin 43 (Cx43) localization at cell-cell contacts in isolated cardiomyocytes and COS7 cells. Lack of FGF signaling led to decreased Cx43 phosphorylation at serines 325/328/330 (S325/328/330), sites known to be important for assembly of gap junctions. Cx43 instability induced by FGF inhibition was restored by the Cx43 S325/328/330 phospho-mimetic mutant, suggesting FGF-dependent phosphorylation of these sites. Consistent with these in vitro findings, cardiomyocyte-specific inhibition of FGF signaling in adult mice demonstrated mislocalization of Cx43 at intercalated discs, whereas localization of N-cadherin and desmoplakin was not affected. This led to premature death resulting from impaired cardiac remodeling. We conclude that cardiomyocyte FGF signaling is essential for cardiomyocyte homeostasis through phosphorylation of Cx43 at S325/328/330 residues which are important for the maintenance of gap junction.

Low molecular weight fibroblast growth factor-2 signals via protein kinase C and myofibrillar proteins to protect against postischemic cardiac dysfunction

Among its many biological roles, fibroblast growth factor-2 (FGF2) acutely protects the heart from dysfunction associated with ischemia/reperfusion (I/R) injury. Our laboratory has demonstrated that this is due to the activity of the low molecular weight (LMW) isoform of FGF2 and that FGF2-mediated cardioprotection relies on the activity of protein kinase C (PKC); however, which PKC isoforms are responsible for LMW FGF2-mediated cardioprotection, and their downstream targets, remain to be elucidated. To identify the PKC pathway(s) that contributes to postischemic cardiac recovery by LMW FGF2, mouse hearts expressing only LMW FGF2 (HMWKO) were bred to mouse hearts not expressing PKCα (PKCαKO) or subjected to a selective PKCε inhibitor (εV(1-2)) before and during I/R. Hearts only expressing LMW FGF2 showed significantly improved postischemic recovery of cardiac function following I/R (P < 0.05), which was significantly abrogated in the absence of PKCα (P < 0.05) or presence of PKCε inhibition (P < 0.05). Hearts only expressing LMW FGF2 demonstrated differences in actomyosin ATPase activity as well as increases in the phosphorylation of troponin I and T during I/R compared with wild-type hearts; several of these effects were dependent on PKCα activity. This evidence indicates that both PKCα and PKCε play a role in LMW FGF2-mediated protection from cardiac dysfunction and that PKCα signaling to the contractile apparatus is a key step in the mechanism of LMW FGF2-mediated protection against myocardial dysfunction.

FGF10 Signaling Enhances Epicardial Cell Expansion during Neonatal Mouse Heart Repair

Unlike zebrafish and newt hearts, mammalian hearts have limited capacity to regenerate. Upon injury or disease, the adult mammalian hearts form a fibrotic scar. Recently, it was shown that neonatal mouse hearts can regenerate similarly to adult zebrafish hearts. However, this capacity quickly decreases after postnatal day 7 (P7). Understanding the molecular mechanisms underlying neonatal heart regeneration might lead to therapeutic approaches for regenerating adult mammalian hearts. In this study, we utilized an inducible transgenic mouse model to determine the effects of FGF10 growth factor over expression on neonatal mouse heart regeneration/repair. Over expression of FGF10 in myocardium enhanced the expansion of Wt1 positive epicardial cells at 21 days after heart injury through increased proliferation. However, this expansion of epicardial cells did not lead to increased epithelial-to-mesenchymal transition or affect fibroblast formation or fibrosis, as seen by vimentin expression, after heart injury. Furthermore, neither continuous nor transient expression of FGF10 did not affect scar thickness or length after heart injury in neonatal hearts. Our results suggest that FGF10 can regulate epicardial cell expansion of neonatal mouse hearts after injury; however, FGF10 alone is not sufficient to cause beneficial effects on heart repair.

The F-BAR protein NOSTRIN participates in FGF signal transduction and vascular development

F-BAR proteins are multivalent adaptors that link plasma membrane and cytoskeleton and coordinate cellular processes such as membrane protrusion and migration. Yet, little is known about the function of F-BAR proteins in vivo. Here we report, that the F-BAR protein NOSTRIN is necessary for proper vascular development in zebrafish and postnatal retinal angiogenesis in mice. The loss of NOSTRIN impacts on the migration of endothelial tip cells and leads to a reduction of tip cell filopodia number and length. NOSTRIN forms a complex with the GTPase Rac1 and its exchange factor Sos1 and overexpression of NOSTRIN in cells induces Rac1 activation. Furthermore, NOSTRIN is required for fibroblast growth factor 2 dependent activation of Rac1 in primary endothelial cells and the angiogenic response to fibroblast growth factor 2 in the in vivo matrigel plug assay. We propose a novel regulatory circuit, in which NOSTRIN assembles a signalling complex containing FGFR1, Rac1 and Sos1 thereby facilitating the activation of Rac1 in endothelial cells during developmental angiogenesis.

Fibroblast growth factor-2-induced cardioprotection against myocardial infarction occurs via the interplay between nitric oxide, protein kinase signaling, and ATP-sensitive potassium channels

Fibroblast growth factor-2 (FGF2) protects the heart from ischemia-reperfusion (I-R) injury via a vast network of protein kinases. In the heart, downstream effectors of these FGF2-triggered signals have not yet been identified. It is hypothesized that nitric oxide (NO) signaling and ATP-sensitive potassium (K(ATP)) channel activity are key effectors of protein kinases activated by FGF2-mediated cardioprotection. Hearts with a cardiac-specific overexpression of FGF2 (FGF2 Tg) were subjected to I-R injury in the absence or the presence of selective inhibitors of NO synthase (NOS) isoforms or sarcolemmal (sarcK(ATP)) and mitochondrial (mitoK(ATP)) K(ATP) channels. Multiple NOS isoforms are necessary for FGF2-mediated cardioprotection, and nitrite levels are significantly reduced in FGF2 Tg hearts upon inhibition of protein kinase C or mitogen-activated protein kinases. Likewise, sarcK(ATP) and mitoK(ATP) channels are important for cardioprotection elicited by endogenous FGF2. These findings suggest that FGF2-induced cardioprotection occurs via protein kinase-NOS pathways as well as K(ATP) channel activity.

Protection by endogenous FGF-2 against isoproterenol-induced cardiac dysfunction is attenuated by cyclosporine A

Fibroblast growth factor-2 (FGF-2) is implicated in cardioprotection. However, previously we found that chronic elevation in cardiac FGF-2 levels in transgenic mice was associated with exaggerated, cyclosporine A-preventable, cellular infiltration after isoproterenol-induced injury, suggestive of an adverse outcome, although this was not examined with functional studies. We have now used highly sensitive tissue Doppler imaging (TDI) to evaluate cardiac functional parameters after isoproterenol administration in transgenic mice overexpressing the 18 kDa FGF-2 in the heart in vivo. Cardiac function was assessed in conscious FGF-2 transgenic and non-transgenic mice at 24 h as well as 2 and 4 weeks after isoproterenol administration, and in the absence or presence of either cyclosporine A or anti-CD3ε treatments. Isoproterenol decreased left ventricular endocardial velocity and strain rate by 47-51% at 24 h in non-transgenic mice, but to a significantly lesser extent (by 24%) in transgenic mice. While additional decreases were seen in non-transgenic mice at 2 weeks, there was no further reduction in ventricular endocardial velocity or strain rate up to 4 weeks post-treatment in FGF-2 transgenic mice. Functional improvement at 2 and 4 weeks post-isoproterenol was reduced significantly by treatment with cyclosporine A but not anti-CD3ε; the latter targets T lymphocyte activation more specifically. TDI values in the presence of chronic FGF-2 overexpression are prognostic of an improved cardiac outcome and protection from isoproterenol induced cardiac dysfunction in vivo. Our data also suggest that cyclosporine A-sensitive infiltrating cell population(s) may contribute to the sustained beneficial effect of FGF-2 in vivo.

Building Cell Selectivity into CPP-Mediated Strategies

There is a pressing need for more effective and selective therapies for cancer and other diseases. Consequently, much effort is being devoted to the development of alternative experimental approaches based on selective systems, which are designed to be specifically directed against target cells. In addition, a large number of highly potent therapeutic molecules are being discovered. However, they do not reach clinical trials because of their low delivery, poor specificity or their incapacity to bypass the plasma membrane. Cell-penetrating peptides (CPPs) are an open door for cell-impermeable compounds to reach intracellular targets. Putting all these together, research is sailing in the direction of the design of systems with the capacity to transport new drugs into a target cell. Some CPPs show cell type specificity while others require modifications or form part of more sophisticated drug delivery systems. In this review article we summarize several strategies for directed drug delivery involving CPPs that have been reported in the literature.

The influence of FGF2 high molecular weight (HMW) isoforms in the development of cardiac ischemia-reperfusion injury

Fibroblast growth factor 2 (FGF2) consists of multiple protein isoforms (low [LMW] and high molecular weight [HMW]), which are localized to different cellular compartments, indicating unique biological activity. We previously showed that the LMW isoform is important in protecting the heart from myocardial dysfunction associated with ischemia-reperfusion (I/R) injury, but the roles of the HMW isoforms remain unknown. To elucidate the role of HMW isoforms in I/R and cardioprotection, hearts from novel mouse models, in which the murine FGF2 HMWs are knocked out (HMWKO) or the human FGF2 24 kDa HMW isoform is overexpressed (HMW Tg) and their wildtype (Wt) or non-transgenic (NTg) cohorts were subjected to an ex vivo work-performing heart model of I/R. There was a significant improvement in post-ischemic recovery of cardiac function in HMWKO hearts (76+/-5%, p<0.05) compared to Wt hearts (55+/-5%), with a corresponding decrease in HMW Tg function (line 20: 38+/-6% and line 28: 33+/-4%, p<0.05) compared to non-transgenic hearts (68+/-9%). FGF2 LMW isoform was secreted from Wt and HMWKO hearts during I/R, and a FGF receptor (FGFR) inhibitor, PD173074 caused a decrease in cardiac function when administered in I/R in Wt and FGF2 HMWKO hearts (p<0.05), indicating that FGFR is involved in FGF2 LMW isoform's biological effect in ischemia-reperfusion injury. Moreover, overexpression of HMW isoform reduced FGFR1 phosphorylation/activation with no further decrease in the phosphorylation state in the presence of the FGFR inhibitor. Overall, our data indicate that HMW isoforms have a detrimental role in the development of post-ischemic myocardial dysfunction.

Combined delivery of heme oxygenase-1 gene and fibroblast growth factor-2 protein for therapeutic angiogenesis

Ectopic expression of heme oxygenase-1 (HO-1) in ischemic tissue protects the tissue from apoptosis and necrosis and promotes angiogenesis. However, apoptosis and necrosis will decrease HO-1 gene transfection efficacy. We hypothesized that fibroblast growth factor-2 (FGF2) would attenuate ischemic damage during the incipient period, improve HO-1 gene transfection and, in turn, enhance neovascularization. To test this hypothesis, we employed a mouse model of hindlimb ischemia and treated the mice with HO-1 gene therapy alone, FGF2 alone, or HO-1 gene therapy plus FGF2. As controls, a group of mice was left untreated. At 12h, prior to the expression of exogenously delivered HO-1, apoptosis was significantly reduced in mice treated with FGF2, either alone or in combination with HO-1 gene therapy. At 3 days, HO-1 expression was greater in mice that also received FGF2 than in mice treated with HO-1 gene therapy alone. The expression of angiogenic growth factors and angiogenesis was greater in mice treated with HO-1 gene therapy plus FGF2 than in mice treated with HO-1 gene therapy alone. These data indicate that FGF2 rescued muscle necrosis prior to the exogenous expression of HO-1 and enhanced HO-1 gene transfection in ischemic murine limbs.

Gene targeted ablation of high molecular weight fibroblast growth factor-2

Fibroblast growth factor-2 (FGF2) is produced as high molecular weight isoforms (HMW) and a low molecular weight isoform (LMW) by means of alternative usage of translation start sites in a single Fgf2 mRNA. Although the physiological function of FGF2 and FGF2 LMW has been investigated in myocardial capillarogenesis during normal cardiac growth, the role of FGF2 HMW has not been determined. Here, we report the generation of FGF2 HMW-deficient mice in which FGF2 HMW isoforms are ablated by the Tag-and-Exchange gene targeting technique. These mice are normal and fertile with normal fecundity, and have a normal life span. Histological, immunohistochemical, and morphometric analyses indicate normal myocardial architecture, blood vessel, and cardiac capillary density in young adult FGF2 HMW-deficient mice. These mice along with the FGF2- and FGF2 LMW-deficient mice that we have generated previously will be very useful for elucidating the differential functions of FGF2 isoforms in pathophysiology of cardiovascular diseases.

Biological functions of the low and high molecular weight protein isoforms of fibroblast growth factor-2 in cardiovascular development and disease

Fibroblast growth factor 2 (FGF2) consists of multiple protein isoforms (low molecular weight, LMW, and high molecular weight, HMW) produced by alternative translation from the Fgf2 gene. These protein isoforms are localized to different cellular compartments, indicating unique biological activity. FGF2 isoforms in the heart have distinct roles in many pathological circumstances in the heart including cardiac hypertrophy, ischemia-reperfusion injury, and atherosclerosis. These studies suggest distinct biological activities of FGF2 LMW and HMW isoforms both in vitro and in vivo. Yet, due to the limitations that only the recombinant FGF2 LMW isoform is readily available and that the FGF2 antibody is nonspecific with regards to its isoforms, much remains to be determined regarding the role(s) of the FGF2 LMW and HMW isoforms in cellular behavior and in cardiovascular development and pathophysiology. This review summarizes the activities of LMW and HMW isoforms of FGF2 in cardiovascular development and disease.

Endothelium-targeted overexpression of constitutively active FGF receptor induces cardioprotection in mice myocardial infarction

Fibroblast growth factor receptor (FGFR) is expressed in a variety of cells and is involved in their proliferation/migration/survival. To elucidate FGFR-mediated specific action of vascular endothelial cells (ECs) on myocardial ischemia, we generated endothelium-targeted transgenic mice overexpressing constitutively active FGFR2 using Tie2 promoter (FGFR2-Tg). Infarct size, vessel formation and blood perfusion were significantly improved 28 days after myocardial infarction (MI) in FGFR2-Tg, compared with wild-type mice. Aortic ECs isolated from FGFR-Tg showed a marked increase in migratory capacity and tube formation. These in vitro angiogenic activities were blocked by PI3-kinase inhibitor. Whereas, parameters obtained from echocardiography were already improved at three days after MI. Cardiomyocyte apoptosis at the ischemic border zone was decreased in FGFR2-Tg (32.1%, p < 0.05) and cardiac mRNA expression of FGF2 (basic FGF) was also up-regulated (142%, p < 0.05) at 3 days after MI. 1% oxygen-mediated apoptosis was significantly inhibited in FGFR2-Tg-ECs and this inhibition was abolished by PI3-kinase inhibitor. FGFR2-Tg-ECs exposed to 1% oxygen exhibited enhanced phosphorylation of 416-Tyr-Src, 473-Ser-Akt, and HIF1alpha accumulation. The production of FGF2 was enhanced 2.1-fold in FGFR-Tg-ECs under 1% oxygen via the Src/Akt/HIF1alpha pathway, which induced the peri-vessel migration of vascular smooth muscle cells (VSMCs) and anti-apoptotic effects on VSMCs and cardiomyocytes. FGF receptor signaling in ECs promoted migration, survival and autocrine production of FGF2, leading to reduced infarct size, which is associated with anti-apoptotic action in the early stage and with enhanced angiogenesis in the late stage after MI.

Gene delivery into ischemic myocardium by double-targeted lipoplexes with anti-myosin antibody and TAT peptide

The treatment of myocardial ischemia using gene therapy is a rather novel but promising approach. Gene delivery to target cells may be enhanced by using double-targeted delivery systems simultaneously capable of extracellular accumulation and intracellular penetration. With this in mind, we have used low cationic liposomes-plasmid DNA complexes (lipoplexes) modified with cell-penetrating transactivating transcriptional activator (TAT) peptide (TATp) and/or with monoclonal anti-myosin monoclonal antibody 2G4 (mAb 2G4) specific toward cardiac myosin, for targeted gene delivery to ischemic myocardium. In vitro transfection of both normoxic and hypoxic cardiomyocytes was enhanced by the presence of TATp as determined by fluorescence microscopy and ELISA. The in vitro transfection was further enhanced by the additional modification with mAb 2G4 antibody in the case of hypoxic, but not normoxic cardiomyocytes. However, we did not observe a synergism between TATp and mAb 2G4 ligands under our experimental condition. In in vivo experiments, we have clearly demonstrated an increased accumulation of mAb 2G4-modified TATp lipoplexes in the ischemic rat myocardium and significantly enhanced transfection of cardiomyocytes in the ischemic zone. Thus, the genetic transformation of normoxic and hypoxic cardiomyocytes can be enhanced by using lipoplexes modified with TATp and/or mAb 2G4. Such complexes also demonstrate an increased accumulation in the ischemic myocardium and effective transfection of hypoxic cardiomyocytes in vivo.

FGF-16 is released from neonatal cardiac myocytes and alters growth-related signaling: a possible role in postnatal development

FGF-16 has been reported to be preferentially expressed in the adult rat heart. We have investigated the expression of FGF-16 in the perinatal and postnatal heart and its functional significance in neonatal rat cardiac myocytes. FGF-16 mRNA accumulation was observed by quantitative RT-PCR between neonatal days 1 and 7, with this increased expression persisting into adulthood. FGF-2 has been shown to increase neonatal rat cardiac myocyte proliferative potential via PKC activation. Gene array analysis revealed that FGF-16 inhibited the upregulation by FGF-2 of cell cycle promoting genes including cyclin F and Ki67. Furthermore, the CDK4/6 inhibitor gene Arf/INK4A was upregulated with the combination of FGF-16 and FGF-2 but not with either factor on its own. The effect on Ki67 was validated by protein immunodetection, which also showed that FGF-16 significantly decreased FGF-2-induced Ki67 labeling of cardiac myocytes, although it alone had no effect on Ki67 labeling. Inhibition of p38 MAPK potentiated cardiac myocyte proliferation induced by FGF-2 but did not alter the inhibitory action of FGF-16. Receptor binding assay showed that FGF-16 can compete with FGF-2 for binding sites including FGF receptor 1. FGF-16 had no effect on activated p38, ERK1/2, or JNK/SAPK after FGF-2 treatment. However, FGF-16 inhibited PKC-alpha and PKC-epsilon activation induced by FGF-2 and, importantly, IGF-1. Collectively, these data suggest that expression and release of FGF-16 in the neonatal myocardium interfere with cardiac myocyte proliferative potential by altering the local signaling environment via modulation of PKC activation and cell cycle-related gene expression.

Fibroblast growth factor-2 regulates myocardial infarct repair: effects on cell proliferation, scar contraction, and ventricular function

Fibroblast growth factor-2 (FGF2, bFGF) has been proposed to regulate wound healing and angiogenesis, but skin wound healing in FGF2-knockout (FGF2-KO) animals is only slightly delayed. To determine the role of FGF2 in myocardial infarct repair, we studied the evolution of left ventricular geometry, cell proliferation, matrix content, and cardiac function in mice lacking or overexpressing (FGF2-Tg) FGF2. Despite having no effect on initial infarct size, deletion of FGF2 resulted in reduced fibroblast proliferation and interstitial collagen deposition, decreased endothelial proliferation and vascular density, and decreased cardiomyocyte hypertrophy. Furthermore, FGF2-KO mice demonstrated a complete absence of scar contraction, resulting in increased final infarct size and marked increases in chamber size and infarct expansion. These deficits ultimately impaired left ventricular dP/dt compared with wild-type infarcted mice. Conversely, overexpression of FGF2 increased fibroblast proliferation and collagen deposition, accelerated endothelial proliferation, and enhanced cardiomyocyte hypertrophy after infarction. These changes curbed infarct expansion and preserved left ventricular function. Thus, FGF2 is an important regulator of cell proliferation, angiogenesis, collagen synthesis, myocyte hypertrophy, scar contraction, and, ultimately, left ventricular contractile function during infarct repair. FGF2 may be more important in healing of infarcts compared with skin wounds because of the mechanical stress under which infarcts heal.

Fibroblast growth factor-2 and cardioprotection

Boosting myocardial resistance to acute as well as chronic ischemic damage would ameliorate the detrimental effects of numerous cardiac pathologies and reduce the probability of transition to heart failure. Experimental cardiology has pointed to ischemic and pharmacological pre- as well as post-conditioning as potent acute cardioprotective manipulations. Additional exciting experimental strategies include the induction of true regenerative and/or angiogenic responses to the damaged heart, resulting in sustained structural and functional beneficial effects. Fibroblast growth factor-2 (FGF-2), an endogenous multifunctional protein with strong affinity for the extracellular matrix and basal lamina and well-documented paracrine, autocrine and intracellular modes of action, has been shown over the years to exert acute and direct pro-survival effects, irrespectively of whether it is administered before, during or after an ischemic insult to the heart. FGF-2 is also a potent angiogenic protein and a crucial agent for the proliferation, expansion, and survival of several cell types including those with stem cell properties. Human clinical trials have pointed to a good safety record for this protein. In this review, we will present a case for the low molecular weight isoform of fibroblast growth factor-2 (lo-FGF-2) as a very promising therapeutic agent to achieve powerful acute as well as sustained benefits for the heart, due to its cytoprotective and regenerative properties.

The protein kinase C pathway mediates cardioprotection induced by cardiac-specific overexpression of fibroblast growth factor-2

Elucidation of protective mechanisms against ischemia-reperfusion injury is vital to the advancement of therapeutics for ischemic heart disease. Our laboratory has previously shown that cardiac-specific overexpression of fibroblast growth factor-2 (FGF2) results in increased recovery of contractile function and decreased infarct size following ischemia-reperfusion injury and has established a role for the mitogen-activated protein kinase (MAPK) signaling cascade in the cardioprotective effect of FGF2. We now show an additional role for the protein kinase C (PKC) signaling cascade in the mediation of FGF2-induced cardioprotection. Overexpression of FGF2 (FGF2 Tg) in the heart resulted in decreased translocation of PKC-delta but had no effect on PKC-alpha, -epsilon, or -zeta. In addition, multiple alterations in PKC isoform translocation occur during ischemia-reperfusion injury in FGF2 Tg hearts as assessed by Western blot analysis and confocal immunofluorescent microscopy. Treatment of FGF2 Tg and nontransgenic (NTg) hearts with the PKC inhibitor bisindolylmaleimide (1 micromol/l) revealed the necessity of PKC signaling for FGF2-induced reduction of contractile dysfunction and myocardial infarct size following ischemia-reperfusion injury. Western blot analysis of FGF2 Tg and NTg hearts subjected to ischemia-reperfusion injury in the presence of a PKC pathway inhibitor (bisindolylmaleimide, 1 micromol/l), an mitogen/extracellular signal-regulated kinase/extracellular signal-regulated kinase (MEK/ERK) pathway inhibitor (U-0126, 2.5 micromol/l), or a p38 pathway inhibitor (SB-203580, 2 micromol/l) revealed a complicated signaling network between the PKC and MAPK signaling cascades that may participate in FGF2-induced cardioprotection. Together, these data suggest that FGF2-induced cardioprotection is mediated via a PKC-dependent pathway and that the PKC and MAPK signaling cascades are integrally connected downstream of FGF2.

The cardioprotective effect of the low molecular weight isoform of fibroblast growth factor-2: the role of JNK signaling

Our laboratory showed that overexpression of fibroblast growth factor-2 (FGF2) protected the heart against ischemia-reperfusion injury. FGF2 has different protein isoforms (low [LMW] and high [HMW] molecular weight isoforms) produced from alternative translation start sites. However, which FGF2 isoform(s) mediates this cardioprotection, and which signaling pathway (i.e., mitogen-activated protein kinase (MAPK)) elicits FGF2 isoform-induced cardioprotection remains to be elucidated.

METHODS AND RESULTS

Wildtype, Fgf2 KO (absence of all FGF2 isoforms) and FGF2 LMWKO (absence of LMW isoform) hearts were subjected to an ex vivo work-performing heart ischemic model of 60 min ischemia and 120 min reperfusion. There was a significant decrease in the recovery of post-ischemic contractile function (p<0.05) in Fgf2 KO and FGF2 LMWKO mouse hearts compared to wildtype hearts. Following ischemia-reperfusion injury, MKK4/7, JNK, and c-Jun were significantly phosphorylated (i.e., activated), and the levels of TUNEL-positive nuclei and caspase 3 cleavage were significantly increased in vehicle-treated Fgf2 KO and FGF2 LMWKO compared to wildtype hearts (p<0.05). A novel JNK pathway inhibitor, CEP11004 (50 nM), significantly restored the post-ischemic contractile function and reduced myocardial cell death, as measured by CK release and apoptotic markers, compared to DMSO-treated cohorts (p<0.05). Overall, our data indicate that the LMW isoform has an important role in restoring cardiac function after ischemia-reperfusion (I/R) injury. These results provide unequivocal evidence that inhibition of JNK signaling is involved in FGF2 LMW isoform-mediated cardioprotection and that the potential mechanism may be through inhibition of the apoptotic process.

A free radical scavenger but not FGF-2-mediated angiogenic therapy rescues myonephropathic metabolic syndrome in severe hindlimb ischemia

The therapeutic use of angiogenic factors shows promise in the treatment of critical limb ischemia; however, its potential for myonephropathic metabolic syndrome (MNMS), a fatal complication caused by arterial reconstruction, has not been elucidated. The objective of this study was to evaluate the effectiveness of recombinant Sendai virus-mediated gene transfer of fibroblast growth factor-2 (FGF-2) directly compared with that of a radical scavenger, MCI-186, in a rat model of MNMS. MNMS was surgically induced by aortic occlusion below renal arteries for 4 h, followed by 6 h of reperfusion. Administration of MCI-186 (twice; iv 5 min before induced ischemia and ip 5 min before reperfusion; 10 mg/kg, respectively), but not FGF-2 gene transfer (once, 48 h before induced ischemia), dramatically prevented the increase of serum biochemical markers as well as the edema of the gastrocnemius muscle. The effect of MCI-186 was accompanied by the marked suppression of the neutrophilic infiltration into the local (muscle) and remote (lung) organs. Although serum and muscular levels of a neutrophil-chemoattractant (growth-related oncogene/cytokine-induced neutrophil chemoattractant-1) were not affected by any treatment, the serum level of soluble intercellular adhesion molecule-1 was decreased by treatment with MCI-186 but not by treatment with FGF-2. These results suggest the distinct mechanism of MNMS from critical limb ischemia without reperfusion. Therefore, radical scavenging should be paid more attention than therapeutic angiogenesis when arterial circulation is reconstructed.

Platelet-Derived Growth Factor D Induces Cardiac Fibrosis and Proliferation of Vascular Smooth Muscle Cells in Heart-Specific Transgenic Mice

Platelet-derived growth factor (PDGF)-D is a member of the PDGF/vascular endothelial growth factor family that activates PDGF receptor β (PDGFR-β). We show that PDGF-D is highly expressed in the myocardium throughout development and adulthood, as well as by arterial vascular smooth muscle cells (vSMCs). To obtain further knowledge regarding the in vivo response to PDGF-D, we generated transgenic mice overexpressing the active core domain of PDGF-D in the heart. Transgenic PDGF-D stimulates proliferation of cardiac interstitial fibroblasts and arterial vSMCs. This results in cardiac fibrosis followed by dilated cardiomyopathy and subsequent cardiac failure. Transgenic mice also display vascular remodeling, including dilation of vessels, increased density of SMC-coated vessels, and proliferation of vSMCs, leading to a thickening of tunica media. The thickening of arterial walls is a unique feature of PDGF-D, because this is not seen when PDGF-C is overexpressed in the heart. These results show that PDGF-D, via PDGFR-β signaling, is a potent modulator of both vascular and connective tissue growth and may provide both paracrine and autocrine stimulation of PDGFR-β. Our data raise the possibility that this growth factor may be involved in cardiac fibrosis and atherosclerosis.

Beyond angiogenesis: the cardioprotective potential of fibroblast growth factor-2

In the field of cardiovascular research, a number of independent approaches have been explored to protect the heart from acute and chronic ischemic damage. Fibroblast growth factor-2 (FGF-2) recently has received considerable attention with respect to its angiogenic potential. While therapeutic angiogenesis may serve to salvage chronically ischemic myocardium, more acute treatments are in demand to increase cardiac resistance to injury (preconditioning) and to guard against secondary injury after an acute ischemic insult. Here, we look beyond the angiogenic potential of FGF-2 and examine its acute cardioprotective activity as demonstrated under experimental conditions, both as an agent of a preconditioning-like response and for secondary injury prevention at the time of reperfusion. Factors to consider in moving to the clinical setting will be discussed, including issues of dosage, treatment duration, and routes of administration. Finally, issues of safety and clinical trial design will be considered. The prospect of such a multipotent growth factor having clinical usefulness opens the door to effective treatment of both acute and chronic ischemic heart disease, something well worth the attention of the cardiovascular community.

FGF-2 controls the differentiation of resident cardiac precursors into functional cardiomyocytes

Recent evidence suggests that the heart possesses a greater regeneration capacity than previously thought. In the present study, we isolated undifferentiated precursors from the cardiac nonmyocyte cell population of neonatal hearts, expanded them in culture, and induced them to differentiate into functional cardiomyocytes. These cardiac precursors appear to express stem cell antigen-1 and demonstrate characteristics of multipotent precursors of mesodermal origin. Following infusion into normal recipients, these cells home to the heart and participate in physiological and pathophysiological cardiac remodeling. Cardiogenic differentiation in vitro and in vivo depends on FGF-2. Interestingly, this factor does not control the number of precursors but regulates the differentiation process. These findings suggest that, besides its angiogenic actions, FGF-2 could be used in vivo to facilitate the mobilization and differentiation of resident cardiac precursors in the treatment of cardiac diseases.

Therapeutic myocardial angiogenesis: past, present and future

One of the main goals in the treatment of myocardial ischemia is the development of effective therapy for angiogenesis and neovascularization. The first evidence demonstrating alleviation of myocardial ischemia and increased number of collateral blood vessels was reported in the early 90s following intra-coronary administration of basic fibroblast growth factor protein in canine. This study established the ground for extensive investigations to demonstrate the use of other angiogenic growth factor proteins, genes administered directly or incorporated in viruses, and more recently, endothelial progenitor stem cells (embryonic and adults). The positive results observed in animals failed, in most cases, to repeat themselves in clinical-trials in human patients. Therefore, additional experiments are warranted to allow full understanding of the mechanism underlying new blood vessel formation before further clinical studies are undertaken. This review will explore the milestones of angiogenic investigations and their clinical application.

Intracoronary administration of FGF-2: a computational model of myocardial deposition and retention

This study uses a computational model to characterize the myocardial deposition and retention of basic fibroblast growth factor (FGF-2) at the cellular level after intracoronary (IC) administration of exogenous FGF-2. The model is applied to the in situ conditions present within the myocardium of a dog for which the plasma pharmacokinetics resulting from IC injection of FGF-2 were recorded. Our estimates show that the processes involved in FGF-2 signaling are not diffusion limited; rather, the response time is determined by the reaction time of FGF-2 binding to cell surface receptors. Additionally, the processes of receptor secretion and internalization are found to play crucial roles in the FGF-2 dynamics; future experiments are required to quantify these processes. The model predictions obtained in this study suggest that IC administration of FGF-2 via either a single bolus or repetitive injections causes a transient increase (time scale of hours) in myocardial FGF-2 concentration if the endogenous level of free interstitial FGF-2 is low enough to allow permeation of FGF-2 molecules from the microvascular to the interstitial spaces. The model shows that the majority (64%) of the extracellular FGF-2 ligands are located within the interstitium, and similar fractions are found in the basement membrane and extracellular matrix. Among the FGF-2 molecules found within the interstitium, 2% are free and 98% are bound to interstitial heparan sulfate proteoglycans. These results support the theory of extracellular control of the bioavailability of FGF-2 via dynamic storage of FGF-2 within the basement membrane and extracellular matrix.

Sequence analysis of the fibroblast growth factor 2 gene from the spontaneously hypertensive and hypertrophic heart rats

We have previously reported a quantitative trait locus associated with pressure-independent cardiac hypertrophy in the spontaneously hypertensive rat (SHR) of the Okamoto strain. This locus (Lvm1; left ventricular mass locus 1) contains the gene Fgf2 that codes for the potent cardiac growth factor, Fibroblast Growth Factor 2 (FGF2). Given that FGF2 appears essential for the induction of certain forms of cardiac hypertrophy in the rat, we proposed this gene as a candidate for the cardiac enlargement seen in the SHR. Previous reports of elevated FGF2 mRNA levels in the SHR, led us to hypothesise that nucleotide sequence variations occurring in the coding regions or in putative transcriptional factor binding sites within the Fgf2 promoter might play a role in cardiac hypertrophy in this strain. Given that we have also recently derived from the SHR a rat strain that develops spontaneous cardiac hypertrophy in the absence of hypertension (the Hypertrophic Heart Rat; HHR), we also took the opportunity to examine the sequence of its Fgf2 promoter and coding region. However, extensive sequence analysis of the promoter and coding regions of the SHR and HHR Fgf2 genes failed to reveal any nucleotide variations between strains. Thus, we conclude that variations in the nucleotide sequence of the promoter and coding region of the SHR Fgf2 gene do not play a role in the cardiac hypertrophy of the SHR and HHR strains.

Cardiac-specific overexpression of fibroblast growth factor-2 protects against myocardial dysfunction and infarction in a murine model of low-flow ischemia

BACKGROUND

Preconditioning the heart before an ischemic insult has been shown to protect against contractile dysfunction, arrhythmias, and infarction. Pharmacological studies have suggested that fibroblast growth factor-2 (FGF2) is involved in cardioprotection. However, because of the number of FGFs expressed in the heart and the promiscuity of FGF ligand-receptor interactions, the specific role of FGF2 during ischemia-reperfusion injury remains unclear.

METHODS AND RESULTS

FGF2-deficient (Fgf2 knockout) mice and mice with a cardiac-specific overexpression of all 4 isoforms of human FGF2 (FGF2 transgenic [Tg]) were compared with wild-type mice to test whether endogenous FGF2 elicits cardioprotection. An ex vivo work-performing heart model of ischemia was developed in which murine hearts were subjected to 60 minutes of low-flow ischemia and 120 minutes of reperfusion. Preischemic contractile function was similar among the 3 groups. After ischemia-reperfusion, contractile function of Fgf2 knockout hearts recovered to 27% of its baseline value compared with a 63% recovery in wild-type hearts (P<0.05). In FGF2 Tg hearts, an 88% recovery of postischemic function occurred (P<0.05). Myocardial infarct size was also reduced in FGF2 Tg hearts compared with wild-type hearts (13% versus 30%, P<0.05). There was a 2-fold increase in FGF2 release from Tg hearts compared with wild-type hearts (P<0.05). No significant alterations in coronary flow or capillary density were detected in any of the groups, implying that the protective effect of FGF2 is not mediated by coronary perfusion changes.

CONCLUSIONS

These results provide evidence that endogenous FGF2 plays a significant role in the cardioprotective effect against ischemia-reperfusion injury.

Definition of a novel growth factor-dependent signal cascade for the suppression of bile acid biosynthesis

The nuclear bile acid receptor FXR has been proposed to play a central role in the feedback repression of the gene encoding cholesterol 7 alpha-hydroxylase (CYP7A1), the first and rate-limiting step in the biosynthesis of bile acids. We demonstrate that FXR directly regulates expression of fibroblast growth factor-19 (FGF-19), a secreted growth factor that signals through the FGFR4 cell-surface receptor tyrosine kinase. In turn, FGF-19 strongly suppresses expression of CYP7A1 in primary cultures of human hepatocytes and mouse liver through a c-Jun N-terminal kinase (JNK)-dependent pathway. This signaling cascade defines a novel mechanism for feedback repression of bile acid biosynthesis and underscores the vital role of FXR in the regulation of multiple pathways of cholesterol catabolism in the liver.

The role of fibroblast growth factors in vascular development

Fibroblast growth factors (FGFs) are considered angiogenic factors, yet the exact relationship between FGF and vascular development in normal and pathological tissue has long remained elusive. However, recent results from gene inactivation and transgenic studies in mice and in culture systems have demonstrated the role of FGFs in vessel assembly and sprouting. FGFs also promote blood-vessel branching and induce lymphangiogenesis. Novel players in FGF-mediated angiogenesis have been identified, such as p38 mitogen-activated protein kinase. Tumour angiogenesis is regulated by FGFs directly or indirectly via secondary angiogenesis factors, such as vascular endothelial growth factor. The newly established angiogenic role of FGFs makes FGF or molecules targeting FGF and its receptor promising candidates for the development of novel therapeutics.

Protection of myocytes from hypoxia-reoxygenation injury by nitric oxide is mediated by modulation of transforming growth factor-beta1

BACKGROUND

Reoxygenation injury is a result of several complex events, including release of reactive oxygen species, protein kinase C (PKC) activation, and altered expression of transforming growth factor-beta1 (TGF-beta(1)). Nitric oxide (NO) generally protects tissues from reperfusion injury.

METHODS AND RESULTS

We examined the modulation of TGF-beta1 expression and activity and PKC activation in cultured rat heart myocytes exposed to a brief period of hypoxia-reoxygenation (H-R) by NO donor 3-morpholino-sydnonimine (SIN-1). H-R resulted in an increased expression of total TGF-beta1 (mRNA and protein) but a decrease in the release of active TGF-beta1. Myocyte PKC-alpha protein level was not altered by H-R, but its phosphorylation was augmented. Pretreatment of myocytes with SIN-1 diminished myocyte injury quantified as lactate dehydrogenase release. Simultaneously, release of active TGF-beta1 increased and total TGF-beta1 expression decreased (all P<0.05 versus H-R alone). PKC-alpha phosphorylation increased further in cells treated with SIN-1. The effects of SIN-1 were blocked by the NO scavenger phenyl-tetramethyl-imidazoline-oxyl-oxide as well as by the PKC inhibitor staurosporine. To examine if another NO donor would have a similar effect, cardiomyocytes were treated with nitroglycerin before H-R. With nitroglycerin treatment, similar to SIN-1 treatment, myocyte injury was diminished, TGF-beta1 release increased, and total TGF-beta1 expression decreased.

CONCLUSIONS

These observations suggest modulation of TGF-beta1 expression as a novel mechanism of salutary effect of NO donors. PKC-alpha activation may play an important role in the protective effect of NO against H-R injury.

Acute protection of ischemic heart by FGF-2: involvement of FGF-2 receptors and protein kinase C

We examined the effect of fibroblast growth factor (FGF)-2 on myocardial resistance to injury when administered after the onset of ischemia, in vivo and ex vivo, and the role of FGF-2 receptors and protein kinase C (PKC). FGF-2 was injected into the left ventricle of rats undergoing permanent surgical coronary occlusion leading to myocardial infarction (MI). After 24 h, FGF-2-treated hearts displayed significantly reduced injury, determined by histological staining and troponin T release, and improved developed pressure compared with untreated controls. An FGF-2 mutant with diminished affinity for the tyrosine kinase FGF-2 receptor 1 (FGFR1) was not cardioprotective. FGF-2-treated hearts retained improved function and decreased damage at 6 wk after MI. In the ex vivo heart, FGF-2 administration during reperfusion after 30-min ischemia improved functional recovery and increased relative levels of PKC subtypes alpha, epsilon, and zeta in the particulate fraction, in a chelerythrine-preventable mode; it also decreased loss of energy metabolites. We conclude that intramyocardial FGF-2 administration shortly after the onset of ischemia confers protection from acute and chronic cardiac dysfunction and damage; FGF-2 delivered during reperfusion protects from ischemia-reperfusion injury; and protection by FGF-2 requires intact binding to FGFR1 and is likely mediated by PKC.

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.