Basic fibroblast growth factor in atria and ventricles of the vertebrate heart

The Microenvironment of the Pathogenesis of Cardiac Hypertrophy

Pathological cardiac hypertrophy is a key risk factor for the development of heart failure and predisposes individuals to cardiac arrhythmia and sudden death. While physiological cardiac hypertrophy is adaptive, hypertrophy resulting from conditions comprising hypertension, aortic stenosis, or genetic mutations, such as hypertrophic cardiomyopathy, is maladaptive. Here, we highlight the essential role and reciprocal interactions involving both cardiomyocytes and non-myocardial cells in response to pathological conditions. Prolonged cardiovascular stress causes cardiomyocytes and non-myocardial cells to enter an activated state releasing numerous pro-hypertrophic, pro-fibrotic, and pro-inflammatory mediators such as vasoactive hormones, growth factors, and cytokines, i.e., commencing signaling events that collectively cause cardiac hypertrophy. Fibrotic remodeling is mediated by cardiac fibroblasts as the central players, but also endothelial cells and resident and infiltrating immune cells enhance these processes. Many of these hypertrophic mediators are now being integrated into computational models that provide system-level insights and will help to translate our knowledge into new pharmacological targets. This perspective article summarizes the last decades' advances in cardiac hypertrophy research and discusses the herein-involved complex myocardial microenvironment and signaling components.

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.

Adequate Selection of a Therapeutic Site Enables Efficient Development of Collateral Vessels in Angiogenic Treatment With Bone Marrow Mononuclear Cells

Background

Induction of angiogenic mechanisms to promote development of collateral vessels is considered promising for the treatment of peripheral arterial diseases. Collateral vessels generally develop from preexisting arteriolar connections, bypassing the diseased artery. We speculated that induction of angiogenic mechanisms should be directed to such arteriolar connections to achieve efficient collateral development. The aim of this study was to verify this hypothesis using autologous transplantation of bone marrow mononuclear cells in the rabbit model of chronic limb ischemia.

Methods and Results

The left femoral artery was excised to induce limb ischemia in male rabbits. In this model, arteriolar connections in the left coccygeofemoral muscle tend to develop into collateral vessels, although this transformation is insufficient to alleviate the limb ischemia. In contrast, arteriolar connections in the closely located adductor muscle do not readily develop into collateral vessels. At 21 days after ischemia initiation, a sufficient number of automononuclear cells were selectively injected in the left coccygeofemoral muscle (coccygeo group) or left adductor muscle (adductor group). Evaluation of calf blood pressure ratios, blood flow in the left internal iliac artery, and angiographic scores at day 28 after injection revealed that collateral development and improvement of limb ischemia were significantly more efficient in the coccygeo group than in the adductor group. Morphometric analysis of the coccygeofemoral muscle at day 14 showed similar results.

Conclusions

Specific delivery of mononuclear cells to the coccygeofemoral but not the adductor muscle effectively improves collateral circulation in the rabbit model of limb ischemia and suggests that adequate site selection can facilitate therapeutic angiogenesis.

Disease and region-related cardiac fibroblast potassium current variations and potential functional significance

AIMS

Fibroblasts, which play an important role in cardiac function/dysfunction, including arrhythmogenesis, have voltage-dependent (Kv) currents of unknown importance. Here, we assessed the differential expression of Kv currents between atrial and ventricular fibroblasts from control dogs and dogs with an atrial arrhythmogenic substrate caused by congestive heart failure (CHF).

METHODS AND RESULTS

Left atrial (LA) and ventricular (LV) fibroblasts were freshly isolated from control and CHF dogs (2-week ventricular tachypacing, 240 bpm). Kv currents were measured with whole-cell voltage-clamp, mRNA by quantitative polymerase chain reaction (qPCR) and fibroblast proliferation by (3)H-thymidine incorporation. Robust voltage-dependent tetraethylammonium (TEA)-sensitive K(+) currents (IC50 ∼1 mM) were recorded. The morphologies and TEA responses of LA and LV fibroblast Kv currents were similar. LV fibroblast Kv-current densities were significantly greater than LA, and Kv-current densities were significantly less in CHF than control. The mRNA expression of Kv-channel subunits Kv1.5 and Kv4.3 was less in LA vs. LV fibroblasts and was down-regulated in CHF, consistent with K(+)-current recordings. Ca(2+)-dependent K(+)-channel subunit (KCa1.1) mRNA and currents were less expressed in LV vs. LA fibroblasts. Inhibiting LA fibroblast K(+) current with 1 mmol/L of TEA or KCa1.1 current with paxilline increased proliferation.

CONCLUSIONS

Fibroblast Kv-current expression is smaller in CHF vs. control, as well as LA vs. LV. KCa1.1 current is greater in LA vs. LV. Suppressing Kv current with TEA enhances fibroblast proliferation, suggesting that Kv current might act to check fibroblast proliferation and that reduced Kv current in CHF may contribute to fibrosis. Fibroblast Kv-current remodelling may play a role in the atrial fibrillation (AF) substrate; modulating fibroblast K(+) channels may present a novel strategy to prevent fibrosis and AF.

In vitro cellular models for cardiac development and pharmacotoxicology

Permanent cultures of cardiac cells described so far have limited value for studying cell biology and pharmacology of the developing heart because of the loss of proliferative capacity and cardiac-specific properties of cardiomyocytes during long-term cultivation. Pluripotent embryonic carcinoma (EC) and embryonic stem (ES) cells cultivated as permanent lines offer a new approach for studying cardiogenic differentiation in vitro. We describe cardiogenesis in vitro by differentiating EC and ES cells by way of embryo-like aggregates (embryoid bodies) into spontaneously beating cardiomyocytes. During cardiomyocyte differentiation three distinct developmental stages were defined by expression of specific action potentials and ionic currents measured by the whole-cell patch-clamp technique. Whereas early differentiated cardiomyocytes are characterized by action potentials and ionic currents typical for early pacemaker cells, terminally differentiated cardiomyocytes show action potentials and ionic currents inherent to ventricular-, atrial- or sinus nodal-like cells. These functional characteristics are in accordance with the expression of alpha- and beta-cardiac myosin heavy chain at early differentiation stages and the additional expression of ventricular-specific MLC-2V and atrial-specific ANF genes at terminal stages demonstrated by reverse transcription polymerase chain reaction (RT-PCR) analysis. Pharmacological studies performed by measuring chronotropic responses and by analysing the Ca(2+) channel activity correspond to data obtained with cardiac cells from living organisms. For testing the influence of exogenous compounds on cardiac differentiation the teratogenic compound retinoic acid (RA) was applied during distinct stages of embryoid body development. A temporally controlled influence of RA on cardiac differentiation and expression of cardiac-specific genes was found. We conclude that ES cell-derived cardiomyocytes provide an excellent cellular model to study early cardiac development and to perform pharmacological and embryotoxicological investigations.

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.

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.

Impaired myocardial capillarogenesis and increased adaptive capillary growth in FGF2-deficient mice

Basic fibroblast growth factor (FGF2) plays a major role in angiogenesis and capillary growth. In contrast to vascular endothelial growth factor, which is required for proliferation and survival of endothelial cells, FGF2 does not seem to be essential since the Fgf2 knockout is not lethal. Therefore, the precise genetic and physiological roles of FGF2 for capillary development and adaptation remain to be determined. Here we show that myocardial capillary supply is normal at birth, but significantly reduced by approximately 25% in adult Fgf2+/- and Fgf2-/- mice as compared with wild-type littermates. In contrast, after induction of myocardial hypertrophy by continuous infusion of angiotensin II (ANG II) for 6 days marked capillary growth was seen in both Fgf2+/- and Fgf2-/- mice, but not in wild-type littermates. These data demonstrate that two intact Fgf2 genes are necessary for normal capillary development after birth, whereas FGF2 seems to be dispensable for adaptive myocardial capillary growth in the adult mouse.

Extracellular matrix and growth factors during heart growth

The effects of growth factors on tissue remodeling and cell differentiation depend on the nature of the extracellular matrix, the type and organization of integrins, the activation of metalloproteinases and the presence of secreted proteins associated to the matrix. These interactions are actually poorly known in the cardiovascular system. We describe here: 1) the main components of extracellular matrix within the cardiovascular system; 2) the role of integrins in the transmission of growth signals; 3) the shift in the expression of the components of the extracellular matrix (fibronectin and collagens) and the stimulation of the synthesis of metalloproteinases during normal and hypertrophic growth of the myocardium; 4) the effects of growth factors, such as Angiotensin II, Fibroblast Growth Factors (FGF), Transforming Growth Factor-beta (TGF-beta), on the synthesis of proteins of the extracellular matrix in the heart.

Normal patterning of the coronary capillary plexus is dependent on the correct transmural gradient of FGF expression in the myocardium

The formation of the coronary vessel system is vital for heart development, an essential step of which is the establishment of a capillary plexus that displays a density gradient across the myocardial wall, being higher on the epicardial than the endocardial side. This gradient in capillary plexus formation develops concurrently with transmural gradients of myocardium-derived growth factors, including FGFs. To test the role of the FGF expression gradient in patterning the nascent capillary plexus, an ectopic FGF-over-expressing site was created in the ventricular myocardial wall in the quail embryo via retroviral infection from E2-2.5, thus abolishing the transmural gradient of FGFs. In FGF virus-infected regions of the ventricular myocardium, the capillary density across the transmural axis shifted away from that in control hearts at E7. This FGF-induced change in vessel patterning was more profound at E12, with the middle zone becoming the most vascularized. An up-regulation of FGFR-1 and VEGFR-2 in epicardial and subepicardial cells adjacent to FGF virus-infected myocardium was also detected, indicating a paracrine effect on induction of vascular signaling components in coronary precursors. These results suggest that correct transmural patterning of coronary vessels requires the correct transmural expression of FGF and, therefore, FGF may act as a template for coronary vessel patterning.

In vivo electroporation enhances plasmid-based gene transfer of basic fibroblast growth factor for the treatment of ischemic limb

BACKGROUND

Angiogenic therapy for ischemic tissues using angiogenic growth factors has been reported on an experimental and a clinical level. Electroporation enhances the efficiency of plasmid-based gene transfer in a variety of tissues. The purpose of this study was to evaluate the angiogenic effects of plasmid-based gene transfer using basic fibroblast growth factor (bFGF) in combination with electroporation.

MATERIALS AND METHODS

The transfection efficiency of in vivo electroporation in rabbit skeletal muscles was evaluated using pCAccluc+ encoding luciferase. To evaluate the angiogenic effects of bFGF gene in ischemic limb, we constructed a plasmid, pCAcchbFGFcs23, containing human bFGF cDNA fused with the secretory signal sequence of interleukin (IL)-2. Then, 500 microg of pCAcchbFGFcs23 or pCAZ3 (control plasmid) was injected into the ischemic thigh muscles in a rabbit model of hind limb ischemia with in vivo electroporation (bFGF-E(+) group and LacZ-E(+) group). Other sets of animals were injected with pCAcchbFGFcs23 (bFGF-E(-) group) or pCAZ3 (LacZ-E(-) group) without electroporation. Then 28 days later, calf blood pressure ratio, angiographic score, in vivo blood flow, and capillary density in the ischemic limb were measured.

RESULTS

Gene transfer efficiency increased markedly with the increase in voltage up to 100 V. Regarding angiogenic responses, calf blood pressure ratio, in vivo blood flow, and capillary density only in the bFGF-E(+) group were significantly higher than those in LacZ-E(-) group. Angiographic scores in the bFGF-E(+) and bFGF-E(-) groups were significantly higher than that in the LacZ-E(-) group.

CONCLUSION

These data suggest that in vivo electroporation enhances bFGF gene transfer for the treatment of ischemic limb muscles.

Epicardium is required for the full rate of myocyte proliferation and levels of expression of myocyte mitogenic factors FGF2 and its receptor, FGFR-1, but not for transmural myocardial patterning in the embryonic chick heart

Proper heart development requires patterning across the myocardial wall. Early myocardial patterning is characterized by a transmural subdivision of the myocardium into an outer, highly mitotic, compact zone and an inner, trabecular zone with lower mitotic activity. We have shown previously that fibroblast growth factor receptor (FGFR) -mediated signaling is central to myocyte proliferation in the developing heart. Consistent with this, FGFR-1 and FGF2 are more highly expressed in myocytes of the compact zone. However, the mechanism that regulates the transmural pattern of myocyte proliferation and expression of these mitogenic factors is unknown. The present study examined whether this transmural patterning occurs in a myocardium-autonomous manner or by signals from the epicardium. Microsurgical inhibition of epicardium formation in the embryonic chick gives rise to a decrease in myocyte proliferation, accounting for a thinner compact myocardium. We show that the transmural pattern of myocyte mitotic activity is maintained in these hearts. Consistent with this, the expression patterns of FGF1, FGF2, and FGFR-1 across the myocardium persist in the absence of the epicardium. However, FGF2 and FGFR-1 mRNA levels are reduced in proportion to the depletion of epicardium. The results suggest that epicardium-derived signals are essential for maintenance of the correct amount of myocyte proliferation in the compact myocardium, by means of levels of mitogen expression in the myocardium. However, initiation and maintenance of transmural patterning of the myocardium occurs largely independently of the epicardium.

Appropriate control of ex vivo gene therapy delivering basic fibroblast growth factor promotes successful and safe development of collateral vessels in rabbit model of hind limb ischemia

PURPOSE

In our previous study, adenovirus-mediated ex vivo gene transfer of basic fibroblast growth factor promoted significant collateral vessel development in a rabbit model of hind limb ischemia. The present study examined how to control the efficacy and safety of this gene therapy, and also evaluated the feasibility of repeat application of this procedure.

METHODS

Modified hFGF gene with the secretory signal sequence was adenovirally transferred to cultured autologous fibroblasts, and various numbers of the cells (2 x 10(5), 1 x 10(6), 5 x 10(6), or 2.5 x 10(7)) or vehicle was injected through the left internal iliac artery in rabbits in whom the left femoral artery had been excised 21 days previously. Twenty-eight days after cell administration, calf blood pressure ratio, angiographic score, blood flow in the internal iliac artery, and capillary density of muscle tissue were measured to analyze collateral vessel development and tissue perfusion in the ischemic limb. To assess delivery efficiency and viral contamination, the distribution of injected cells and the time course of blood anti-adenovirus antibody titer were examined in rabbits treated with various numbers of gene-transduced cells. In addition, animals received two injections, 21 days apart, of fibroblasts infected with adenovirus vector containing the luciferase gene, and luciferase expression was measured to evaluate whether the present therapy is repeatable.

RESULTS

At 28 days after cell administration, significant collateral vessel development without detectable side effects was observed in rabbits who received 5 x 10(6) or 2.5 x 10(7) cells, compared with those who received vehicle, and no significant development was detected in animals with fewer than 5 x 10(6) cells (P <.01 for calf blood pressure ratio and capillary density, P <.05 for angiographic score and maximum blood flow). There was no difference in collateral augmentation between rabbits with 5 x 10(6) and 2.5 x 10(7) cells. However, in animals with 2.5 x 10(7) cells a large number of injected cells accumulated in the lungs, anti-adenovirus antibody titer increased significantly, and calf blood pressure in the left hind limb of two rabbits decreased immediately after injection. Luciferase analysis showed very low gene expression after repeated administration.

CONCLUSION

These findings suggest that 5 x 10(6) is a suitable number of cells to induce appropriate collateral vessel development and minimize potential side effects of this procedure. Despite use of ex vivo gene transfer, repeat administration of the cells was not feasible. Clinical relevance Since the present study determined the appropriate conditions for effective and safe stimulation of collateral vessels, the clinical relevance of the ex vivo therapy might be carried forward. However, the findings raised another issue that should be resolved before clinical application; that is, the number of gene-transduced cells able to be injected was strictly limited. To estimate the therapeutic range of cell number in humans, additional experiments using large animals are desirable.

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.

Protective effect of basic fibroblast growth factor against myocyte death and arrhythmias in acute myocardial infarction in rats

The present study in rats investigated whether basic fibroblast growth factor (bFGF) plays an important role in cardioprotection against myocardial cell death and arrhythmias in acute myocardial infarction (AMI). After ligating the left coronary artery in 62 Wistar rats, 20 Eg of human recombinant bFGF was injected into the infarcted myocardium in 33 rats (group F), while saline was used for 29 control rats (group C). The development of ventricular tachyarrhythmias was assessed during the first 30 min of ischemia. After 24 h occlusion, the hearts of the surviving rats (group F: n=13, group C: n=10) were excised to assess minimum infarct wall thickness and infarct size, determine the number of TUNEL-positive cardiomyocytes and to analyze Bcl-2 and Bax expression by immunohistochemical staining and Western blotting. The incidence of ventricular tachycardia was higher in group C than in group F (p<0.05). The thinning ratio was higher in group F than in group C (p<0.05). There were fewer TUNEL-positive cardiomyocytes in the infarct border area in group F than in group C (p<.0001). Western blot analysis showed greater expression of Bcl-2 in group F than in group C (p<0.05), but similar expression of Bax in the 2 groups. In conclusion, intramyocardial administration of bFGF prevented ischemia-induced myocardial cell death and arrhythmias.

Cardiac endothelial-myocardial signaling: its role in cardiac growth, contractile performance, and rhythmicity

Experimental work during the past 15 years has demonstrated that endothelial cells in the heart play an obligatory role in regulating and maintaining cardiac function, in particular, at the endocardium and in the myocardial capillaries where endothelial cells directly interact with adjacent cardiomyocytes. The emerging field of targeted gene manipulation has led to the contention that cardiac endothelial-cardiomyocytal interaction is a prerequisite for normal cardiac development and growth. Some of the molecular mechanisms and cellular signals governing this interaction, such as neuregulin, vascular endothelial growth factor, and angiopoietin, continue to maintain phenotype and survival of cardiomyocytes in the adult heart. Cardiac endothelial cells, like vascular endothelial cells, also express and release a variety of auto- and paracrine agents, such as nitric oxide, endothelin, prostaglandin I(2), and angiotensin II, which directly influence cardiac metabolism, growth, contractile performance, and rhythmicity of the adult heart. The synthesis, secretion, and, most importantly, the activities of these endothelium-derived substances in the heart are closely linked, interrelated, and interactive. It may therefore be simplistic to try and define their properties independently from one another. Moreover, in relation specifically to the endocardial endothelium, an active transendothelial physicochemical gradient for various ions, or blood-heart barrier, has been demonstrated. Linkage of this blood-heart barrier to the various other endothelium-mediated signaling pathways or to the putative vascular endothelium-derived hyperpolarizing factors remains to be determined. At the early stages of cardiac failure, all major cardiovascular risk factors may cause cardiac endothelial activation as an adaptive response often followed by cardiac endothelial dysfunction. Because of the interdependency of all endothelial signaling pathways, activation or disturbance of any will necessarily affect the others leading to a disturbance of their normal balance, leading to further progression of cardiac failure.

Basic fibroblast growth factor is upregulated in hibernating myocardium

BACKGROUND

Ischemia is known to be a potent stimulus for the upregulation of angiogenic growth factors, such as basic fibroblast growth factor (bFGF). While previous investigations have shown that many angiogenic growth factors are upregulated in animal models of myocardial ischemia, the models used are limited in their ability to produce stable ischemia beyond a few weeks. Our laboratory uses a stable model of hibernating myocardium where later time points may be examined. Therefore, the goal of this study was to examine bFGF protein levels in the myocardium at baseline and 3 or 6 months following the onset of myocardial ischemia.

METHODS

A total of 18 miniswine were studied. Basal endogenous levels of bFGF were measured in control animals (n = 6) immediately following sacrifice, while 12 other pigs underwent a 90% left circumflex artery occlusion with documented hibernating myocardium by positron emission tomography ((13)N-ammonia) and dobutamine stress echocardiography. These animals were studied at 3 (n = 7) and 6 months (n = 5) postoperatively. At sacrifice, six 3 x 3 mm samples were harvested from the left circumflex (hibernating) myocardium. Basic FGF levels (picograms per microgram of protein) were determined using ELISA kits.

RESULTS

Basic FGF protein levels 3 months after the creation of hibernating myocardium were three times greater than in nonischemic control animals (P < 0.05), while levels at 6 months were increased sixfold compared to control animals (P < 0.05 versus both control and 3-month groups).

CONCLUSIONS

Endogenous bFGF production is upregulated at 3 and 6 months in hibernating porcine myocardium. The angiogenic effects of exogenous bFGF delivered into ischemic myocardium with varying levels of endogenous growth factors must be determined.

Formation of the biopulsatile vascular pump by cardiomyocyte transplants circumvallating the abdominal aorta

In spite of the fact that patients with heart diseases requiring heart transplantation are increasing in the world, there are a lack of donors, which makes it hard to offer them these life-saving transplants. As a way to overcome this dilemma, we have researched the addition of the new biopump, which consists of the cultured embryonic cardiomyocytes grafted around the abdominal aorta and contracts spontaneously, which subsequently supports the function of the host heart. Ventricular tissues from ICR 14-day-old embryos were cultured and were injected to BALB/c nude mice (male, 8-week-old) subperitoneally around the abdominal aorta. At 3 and 7 days after implantation, action potential of the grafts was measured. Grafts were prepared for histological study. The grafts survived, showed vigorous angiogenesis, and contracted spontaneously. The cardiomyocytes in the grafts showed irregular arrangement, containing myofibrils with sarcomeres and intercalated disks. It was confirmed by immunohistochemistry that the cardiomyocytes in the grafts matured in accordance with normal development. The grafts were very quickly invaded by small vessels from the surrounding tissues showing the formation of new circulation. Embryonic cardiomyocytes have the ability to remodel the abdominal aorta into a spontaneous pulsating apparatus and to function as a vascular pump.

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.

Dilated cardiomyopathy and impaired cardiac hypertrophic response to angiotensin II in mice lacking FGF-2

FGF-2 has been implicated in the cardiac response to hypertrophic stimuli. Angiotensin II (Ang II) contributes to maintain elevated blood pressure in hypertensive individuals and exerts direct trophic effects on cardiac cells. However, the role of FGF-2 in Ang II-induced cardiac hypertrophy has not been established. Therefore, mice deficient in FGF-2 expression were studied using a model of Ang II-dependent hypertension and cardiac hypertrophy. Echocardiographic measurements show the presence of dilated cardiomyopathy in normotensive mice lacking FGF-2. Moreover, hypertensive mice without FGF-2 developed no compensatory cardiac hypertrophy. In wild-type mice, hypertrophy was associated with a stimulation of the c-Jun N-terminal kinase, the extracellular signal regulated kinase, and the p38 kinase pathways. In contrast, mitogen-activated protein kinase (MAPK) activation was markedly attenuated in FGF-2-deficient mice. In vitro, FGF-2 of fibroblast origin was demonstrated to be essential in the paracrine stimulation of MAPK activation in cardiomyocytes. Indeed, fibroblasts lacking FGF-2 expression have a defective capacity for releasing growth factors to induce hypertrophic responses in cardiomyocytes. Therefore, these results identify the cardiac fibroblast population as a primary integrator of hypertrophic stimuli in the heart, and suggest that FGF-2 is a crucial mediator of cardiac hypertrophy via autocrine/paracrine actions on cardiac cells.

Adenovirus-mediated ex vivo gene transfer of basic fibroblast growth factor promotes collateral development in a rabbit model of hind limb ischemia

Adenovirus-mediated ex vivo gene transfer of basic fibroblast growth factor (bFGF), a new strategy for the treatment of chronic vascular occlusive disease, was examined in a rabbit model of hind limb ischemia. The left femoral artery was completely excised to induce an ischemic state in the hind limb of male rabbits. Simultaneously, a skin section was resected from the wound, and host fibroblasts were cultured. The cultured fibroblasts were infected with adenovirus vector containing modified human bFGF cDNA with the secretory signal sequence (AxCAMAssbFGF) or LacZ cDNA (AxCALacZ). At 21 days after femoral artery excision, the gene-transduced fibroblasts were administered through the left internal iliac artery. The fibroblasts significantly accumulated in the ischemic hind limb, and the AxCAMAssbFGF-treated cells secreted bFGF for less than 14 days without elevation of systemic bFGF level. At 28 days after cell administration, calf blood pressure ratio, angiographic score, capillary density of muscle tissue and blood flow of the left internal iliac artery were determined, and animals with AxCAMAssbFGF-treated cells showed significantly greater development of collateral vessels, as compared with those with AxCALacZ-treated cells. These findings suggest that adenovirus-mediated ex vivo gene transfer of bFGF was effective for improvement of chronic limb ischemia.

CUG-initiated FGF-2 induces chromatin compaction in cultured cardiac myocytes and in vitro

Fibroblast growth factor-2 (FGF-2) is a mitogen found in CUG-initiated 21-25 kDa ("hi") or AUG-initiated 16-18 kDa ("lo") forms. Previously we demonstrated that "hi"-but not "lo"-FGF-2 caused a distinct nuclear phenotype characterized by apparently condensed chromatin present as separate clumps in the nucleus of cardiac myocytes. In this manuscript we investigated whether these effects were related to apoptosis or mitosis and whether they reflected a direct effect of "hi" FGF-2 on chromatin. Myocytes overexpressing "hi" FGF-2 and presenting the clumped chromatin phenotype: (i) were not labeled above background with antibodies to phosphorylated histones H1 and H3 used as indicators of mitotic chromatin condensation; (ii) did not stain positive for TUNEL; (iii) their nuclear lamina, visualized by anti-laminB immunofluorescence, appeared intact; (iv) neither caspase inhibitors, nor Bcl-2 or "lo" FGF-2 overexpression prevented the manifestation of the compacted nuclear phenotype. Purified recombinant "hi" FGF-2 was more potent than "lo" FGF-2 in promoting the condensation/aggregation of chick erythrocyte chromatin partially reconstituted with histone H1 in vitro. We conclude that the DNA phenotype induced by "hi" FGF-2 in cardiac myocytes likely reflects a direct effect on chromatin structure that does not require the engagement of mitosis or apoptosis. By affecting chromatin compaction "hi" FGF-2 may contribute to the regulation of gene expression.

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.

FGF-2-induced imbalance in early embryonic heart cell proliferation: a potential cause of late cardiovascular anomalies

BACKGROUND

This laboratory previously demonstrated that placement of fibroblast growth factor-2 (FGF-2)-soaked beads adjacent to the developing ventricle at stage 24 caused cardiovascular anomalies by embryonic day 15. We sought to characterize early cellular changes that may suggest mechanisms for the abnormalities observed at day 15. Because levels of both myocyte proliferation and immunohistochemically detectable endogenous FGF-2 begin to decline before stage 24 in untreated embryos, it was of interest to determine whether exogenous FGF-2 might maintain cardiac myocyte proliferation at or near peak levels.

METHODS

Chick embryos were incubated to stage 18 (2.8 days), at which time beads soaked in phosphate-buffered saline (PBS) or 100 microg/ml FGF-2 were placed adjacent to the developing ventricle and development was allowed to continue. After 3 days (stage 29), bromodeoxyuridine (BrdU) was applied to mark dividing cells, followed by double fluorescent assessments to detect relative numbers of dividing and nondividing cells.

RESULTS

Quantitative image analysis, using Metamorph software, showed that exogenous FGF-2 caused a 62% increase in the overall number of dividing cells (P < 0.01), concomitant with a 25% increase in total cell number (cell density: P < 0.05). Expressed in relative terms, these changes corresponded to a 25% increase in the proliferation labeling index: 30% of all cells were proliferating in FGF-treated hearts, in contrast with only 24% in control hearts.

CONCLUSIONS

Taken together, these data suggest that an FGF-induced imbalance in myocardial cell proliferation at early developmental stages of heart development causes cardiovascular anomalies during late embryogenesis.

Therapeutic angiogenesis with intramyocardial administration of basic fibroblast growth factor

BACKGROUND

Basic fibroblast growth factor (bFGF) induces endothelial cell and smooth muscle cell proliferation and stimulates angiogenesis. This study was designed to evaluate the effects of intramyocardial administration of bFGF on myocardial blood flow, angiogenesis, and ventricular function in a canine acute infarction model.

METHODS

Myocardial infarction was induced in 12 dogs by ligation of the left anterior descending coronary artery. Within 5 minutes after coronary occlusion, 100 microg of human recombinant bFGF in 1 mL of saline was injected into the infarct and border zone in 6 dogs, whereas saline alone was used in 6 control dogs. Myocardial blood flow was determined with colored microspheres before and immediately after coronary ligation and again 3, 7, 14, and 28 days after treatment and it was expressed as percent of normal. Angiogenesis was evaluated by immunohistochemical studies 28 days later. Cardiac function was evaluated by repeated echocardiographic measurement.

RESULTS

Treatment with bFGF significantly increased the endocardial blood flow in the border zone (7 days after infarction, 75%+/-7% and 41% +/-7% in the bFGF and control groups, respectively, p<0.01) as well as epicardial blood flow in the infarcted zone. Treatment with bFGF significantly increased the capillary density (39.7+/-2.3 and 22.7+/-1.1 vessels per visual field in the bFGF and control groups, respectively, p<0.01) as well as arteriolar density in the border zone. Treatment with bFGF significantly reduced the change in ratio of thickness of the infarcted wall to the normal wall (44%+/-6% and 26% +/-5% in the bFGF and control groups, respectively, p<0.05). It improved the left ventricular ejection fraction (7 days after infarction, 0.54+/-0.02 and 0.37+/-0.03 in the bFGF and control groups, respectively, p<0.01).

CONCLUSIONS

Intramyocardial administration of bFGF increased the regional myocardial blood flow, reduced thinning of the infarcted region, and improved ventricular function in acute myocardial infarction. Intramyocardial administration of bFGF may be a new therapeutic approach for patients with acute myocardial infarction.

Fibroblast growth factor-2 mediates pressure-induced hypertrophic response

In vitro, fibroblast growth factor-2 (FGF2) has been implicated in cardiomyocyte growth and reexpression of fetal contractile genes, both markers of hypertrophy. However, its in vivo role in cardiac hypertrophy during pressure overload is not well characterized. Mice with or without FGF2 (Fgf2(+/+) and Fgf2(-/-), respectively) were subjected to transverse aortic coarctation (AC). Left ventricular (LV) mass and wall thickness were assessed by echocardiography preoperatively and once a week postoperatively for 10 weeks. In vivo LV function during dobutamine stimulation, cardiomyocyte cross-sectional area, and recapitulation of fetal cardiac genes were also measured. AC Fgf2(-/-) mice develop significantly less hypertrophy (4-24% increase) compared with AC Fgf2(+/+) mice (41-52% increase). Cardiomyocyte cross-sectional area is significantly reduced in AC Fgf2(-/-) mice. Noncoarcted (NC) and AC Fgf2(-/-) mice have similar beta-adrenergic responses, but those of AC Fgf2(+/+) mice are blunted. A lack of mitotic growth in both AC Fgf2(+/+) and Fgf2(-/-) hearts indicates a hypertrophic response of cardiomyocytes. Consequently, FGF2 plays a major role in cardiac hypertrophy. Comparison of alpha- and beta-cardiac myosin heavy chain mRNA and protein levels in NC and AC Fgf2(+/+) and Fgf2(-/-) mice indicates that myosin heavy chain composition depends on hemodynamic stress rather than on FGF2 or hypertrophy, and that isoform switching is transcriptionally, not posttranscriptionally, regulated.

Immunolocalization of the sarcolemmal Ca2+/Mg2+ ecto-ATPase (myoglein) in rat myocardium

Cardiac plasma membrane Ca2+/Mg2+ ecto-ATPase (myoglein) requires millimolar concentrations of either Ca2+ or Mg2+ for maximal activity. In this paper, we report its localization by employing an antiserum raised against the purified rat cardiac Ca2+/Mg2+ ATPase. As assessed by Western blot analysis, the antiserum and the purified immunoglobulin were specific for Ca2+/Mg2+ ecto-ATPase; no cross reaction was observed towards other membrane bound enzymes such as cardiac sarcoplasmic reticulum Ca(2+)-pump ATPase or sarcolemmal Ca(2+)-pump ATPase. On the other hand, the cardiac Ca2+/Mg2+ ecto-ATPase was not recognized by antibodies specific for either cardiac sarcoplasmic reticulum Ca(2+)-pump ATPase or plasma membrane Ca(2+)-pump ATPase. Furthermore, the immune serum inhibited the Ca2+/Mg2+ ecto-ATPase activity of the purified enzyme preparation. Immunofluorescence of cardiac tissue sections and neonatal cultured cardiomyocytes with the Ca2+/Mg2+ ecto-ATPase antibodies indicated the localization of Ca2+/Mg2+ ecto-ATPase in association with the plasma membrane of myocytes, in areas of cell-matrix or cell-cell contact. Staining for the Ca2+/Mg2+ ecto-ATPase was not cardiac specific since the antibodies detected the presence of membrane proteins in sections from skeletal muscle, brain, liver and kidney. The results indicate that Ca2+/Mg2+ ecto-ATPase is localized to the plasma membranes of cardiomyocytes as well as other tissues such as brain, liver, kidney and skeletal muscle.

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.

Physical, contractile and calcium handling properties of neonatal cardiac myocytes cultured on different matrices

Extracellular matrix components play a vital role in the determination of heart cell growth, development of spontaneous contractile activity and morphologic differentiation. In this work we studied the physical and contractile changes in neonatal rat cardiac myocytes over the first four days of growth on three different extracellular matrices. We compared commercial laminin and fibronectin, plus a fibroblast-derived extracellular matrix, which we have termed cardiogel. Myocytes cultured on cardiogel were characterized by greater cellular area and volume when compared to cells cultured on the other single-component matrices. Spontaneous contractile activity appeared first in the cells grown on cardiogel, sometimes as early as the first day post-plating, in contrast to day three in the cells cultured on laminin. Measurements of cardiac myocyte contractility i.e. percent shortening and time to peak contraction, were made on each of the first four days in each culture. Myocytes cultured on cardiogel developed maximum shortening more rapidly than the other cultures, and an earlier response to electrical pacing. Histochemical staining for myocyte mitochondrial content, revealed that the cardiogel-supported cells exhibited the earliest development of this organelle and, after four days, the greatest abundance. This reflects both a greater cell size, as well as response to increasing energy demands. Due to the increase in volume and contractile activity exhibited by the cardiogel grown myocytes, we employed calcium binding and uptake experiments to determine the comparative cellular capacities for calcium and as an indicator of sarcoplasmic reticulum development. Also whole cell phosphorylation in the presence of low detergent was assayed, to correlate calcium uptake with phosphorylation, in an attempt to examine possible increases in calcium pump number and other phosphorylatable proteins. In agreement with our physical and contractile data, we found that the cells grown on cardiogel showed a greater calcium uptake over the first four days of culture, and increased phosphorylation. However, calcium binding was not dramatically different comparing the three culture matrices. Based on our data, the fibroblast-derived cardiogel is the matrix of choice supporting earliest maturation of neonatal cardiomyocytes, in terms of spontaneous contractions, calcium handling efficiency, cell size and development of a subcellular organelle, the mitochondrion.

Impaired cerebral cortex development and blood pressure regulation in FGF-2-deficient mice

Fibroblast growth factor-2 (FGF-2) has been implicated in various signaling processes which control embryonic growth and differentiation, adult physiology and pathology. To analyze the in vivo functions of this signaling molecule, the FGF-2 gene was inactivated by homologous recombination in mouse embryonic stem cells. FGF-2-deficient mice are viable, but display cerebral cortex defects at birth. Bromodeoxyuridine pulse labeling of embryos showed that proliferation of neuronal progenitors is normal, whereas a fraction of them fail to colonize their target layers in the cerebral cortex. A corresponding reduction in parvalbumin-positive neurons is observed in adult cortical layers. Neuronal defects are not limited to the cerebral cortex, as ectopic parvalbumin-positive neurons are present in the hippocampal commissure and neuronal deficiencies are observed in the cervical spinal cord. Physiological studies showed that FGF-2-deficient adult mice are hypotensive. They respond normally to angiotensin II-induced hypertension, whereas neural regulation of blood pressure by the baroreceptor reflex is impaired. The present genetic study establishes that FGF-2 participates in controlling fates, migration and differentiation of neuronal cells, whereas it is not essential for their proliferation. The observed autonomic dysfunction in FGF-2-deficient adult mice uncovers more general roles in neural development and function.

Selective increase in cardiac IGF-1 in a rat model of ventricular hypertrophy

There is evidence that insulin-like growth factor-1 (IGF-1) plays a role in the development of left ventricular hypertrophy, but it is uncertain whether cardiac IGF-1 changes before or after hypertension is established, and whether circulating IGF-1 are involved in cardiac hypertrophy. We have investigated changes in circulating and left ventricular IGF-1 and in the expression of the IGF-1 gene in the left ventricles of rats during the development of hypertensive left ventricular hypertrophy (Goldblatt model; 2 kidney-1 clamped). Our results show that the left ventricular contents of IGF-1 and its mRNA were increased at one and four weeks of hypertension and hypertrophy, and that both returned to control values after nine weeks. These changes were unrelated to the seric concentration of IGF-1 in the blood. These results show that local rather than circulating IGF-1 levels contributed to the development of renovascular hypertensive left ventricular hypertrophy.

Leukemia inhibitory factor, a potent cardiac hypertrophic cytokine, activates the JAK/STAT pathway in rat cardiomyocytes

Leukemia inhibitory factor (LIF) is a member of the interleukin-6 family of cytokines, which induces a wide range of responses in a variety of cells. The aim of this study was to investigate whether LIF induces cardiomyocyte hypertrophy and transmits signals through the JAK/STAT (indicating just another kinase/signal transducer and activator of transcription) pathway in primary cultured neonatal rat cardiomyocytes. LIF increased protein content and [3H]phenylalanine uptake in cardiomyocytes in a dose-dependent manner. LIF (10(3) U/mL) induced rapid tyrosine phosphorylation of gp130, JAK1, JAK2, STAT1, and STAT3 but not Tyk2 or STAT2. LIF also induced autokinase activity of JAK1 in a time-dependent manner. Gel shift assays for interferon gamma activation site/interferon-stimulated responsive element and sis-inducible element (SIE) revealed that LIF induced dimerization of STAT1 and STAT3 and formation of sis-inducing factor complexes, which subsequently interacted with SIE in the promoter. Preincubation with anti-STAT1 and anti-STAT3 antibodies inhibited the binding of SIF complexes. In conclusion, LIF induces cardiac hypertrophy and directly stimulates the JAK/STAT pathway in cardiomyocytes.

Trophic effect of human pericardial fluid on adult cardiac myocytes. Differential role of fibroblast growth factor-2 and factors related to ventricular hypertrophy

Pericardial fluid (PF) may contain myocardial growth factors that exert paracrine actions on cardiac myocytes. The aims of this study were (1) to investigate the effects of human PF and serum, collected from patients undergoing cardiac surgery, on the growth of cultured adult rat cardiac myocytes and (2) to relate the growth activity of both fluids to the adaptive changes in overloaded human hearts. Both PF and serum increased the rate of protein synthesis, measured by [14C]phenylalanine incorporation in adult rat cardiomyocytes (PF, +71.9 +/- 8.2% [n = 17]; serum, +14.9 +/- 6.5% [n = 13]; both P < .01 versus control medium). The effects of both PF and serum on cardiomyocyte growth correlated positively with the respective left ventricular (LV) mass. However, the magnitude of change with PF was 3-fold greater than with serum (P < .01). These trophic effects of PF were mimicked by exogenous basic fibroblast growth factor (FGF2) and inhibited by anti-FGF2 antibodies and transforming growth factor-beta (TGF-beta), suggesting a relationship to FGF2. In addition, FGF2 concentration in PF was 20 times greater than in serum. On the other hand, the LV mass-dependent trophic effect, present in both fluids, was independent of FGF2 concentration or other factors, such as angiotensin II, atrial natriuretic factor, and TGF-beta. These data suggest that FGF2 in human PF is a major determining factor in normal myocyte growth, whereas unidentified LV mass-dependent factor(s), present in both PF and serum, participates in the development of ventricular hypertrophy.

Cell-cycle dependent anti-FGF-2 staining of chicken cardiac myocytes: movement from chromosomal to cleavage furrow- and midbody-associated sites

Fibroblast growth factor-2 (FGF-2) promotes cardiac myocyte proliferation and has been detected in extracellular as well as cytoplasmic and nuclear compartments. As a first step in examining the participation of intracellular FGF-2 in cardiac myocyte cell cycle we have investigated its localization in proliferative chicken cells during interphase and the various stages of mitosis in culture. We have used a previously characterized and affinity-purified anti-FGF-2 antibody preparation which recognizes the 19-22 kDa variants of chick FGF-2. By immunofluorescence, bright, punctate anti-FGF-2 labelling was observed in 26% of interphase nuclei from myocytes derived from 5 day embryonic heart ventricles; these nuclei were positive for anti-bromodeoxyuridine staining indicating that they are at the S- or G2 phase of the cell cycle. In prophase and metaphase, bright anti-FGF-2 staining was detected in apparent association with chromosomes. During anaphase, however, anti-FGF-2 staining dissociated from chromosomal locations distinctly remaining in strand-like structures in the area of ensuing cleavage furrow formation. In late telophase and cytokinesis, strong staining persisted in the area of the midbody and reappeared in a small fraction of newly formed daughter nuclei. Absorption of the antibody preparation with immobilized FGF-2 eliminated all staining. This dynamic pattern of anti-FGF-2 staining suggests that chick FGF-2 or immunologically related protein(s) not only increase in DNA-synthesizing nuclei but they may play a role in subsequent stages of mitosis and cytokinesis.

Adenovirus-mediated expression of the secreted form of basic fibroblast growth factor (FGF-2) induces cellular proliferation and angiogenesis in vivo

Blood supply through collateral arteries is of critical importance in occlusive arterial diseases such as coronary atherosclerosis. Induction of angiogenic growth factor within either the narrowing arteries or jeopardized myocardium may promote angiogenesis in vivo, leading to salvage of ischemic myocardium. We constructed a replication-defective adenovirus (AdCAsFGF-2) coding for human basic fibroblast growth factor (FGF)-2 that is modified, so that its secretion will be facilitated, by tagging a signal sequence derived from FGF-4. A large quantity of FGF-2 was detected in both the cell lysate and culture medium of COS cells infected with AdCAsFGF-2, indicating that FGF-2 was secreted at least partly from the infected cells. The conditioned medium from the infected COS cells stimulated DNA synthesis in and induced cellular proliferation of arterial smooth muscle cells. These effects were eliminated by adenovirus-mediated overexpression of a dominant-negative truncated FGF-receptor type 1. Implantation of a gel of basement membrane proteins containing fibroblasts infected with AdCAsFGF-2 into the ventral subcutaneous space of mice induced extensive cellular proliferation and the formation of functional arterioles. Cells surrounding the vessels were positively immunostained with antibodies recognizing either smooth muscle-specific alpha-actin or factor VIII antigen as a marker for endothelium. These results suggest that AdCAsFGF-2 may be useful for delivering functional FGF-2 into tissues and may lead to therapeutic angiogenesis in vivo.

Cardiac myocyte membrane wounding in the abruptly pressure-overloaded rat heart under high wall stress

The potential role of transient sarcolemmal membrane wounding as a signal transduction event for cardiomyocyte hypertrophy was evaluated in rats with short-term pressure overload caused by banding of the proximal aorta. This procedure resulted in significant increases in left ventricular systolic (1.5-fold) and end-diastolic (2.6-fold) pressures and wall stresses that were associated with significant wall thinning and cavitary enlargement. Quantitative image analysis of frozen sections of the stressed ventricles obtained 60 minutes after banding demonstrated a 6- to 10-fold increase in cytosolic staining with a horseradish peroxidase-labeled anti-albumin antibody compared with sham-operated controls, indicating that an increase in transient sarcolemmal membrane permeability (wounding) is an early response to an abrupt increase in hemodynamic load in vivo. We conclude that an intense hemodynamic stress in vivo can result in histologically detectable cardiomyocyte wounding.

Effect of fibroblast growth factors on outgrowth of facial mesenchyme

The ectoderm is required for outgrowth of facial prominences and facial ectoderm from all facial prominences is interchangeable. Signals provided by the ectoderm may include members of the fibroblast growth factor family (FGF). In order to test whether FGFs could replace facial ectoderm and promote outgrowth, stage 24 frontonasal mass or mandibular mesenchyme was grafted to a host chick limb and a bead soaked in FGF-2 or FGF-4 was placed on top of the mesenchyme. Following 7 days of incubation, the amount of outgrowth was quantified by measuring the rods of cartilage that formed from the grafts. FGF-2 and FGF-4 stimulated an increase in length of cartilage rods in mandibular grafts compared to mandibular mesenchyme grafted without ectoderm (P < 0.05). FGF-4 stimulated a small increase in length of frontonasal mass mesenchyme (P < 0.05) and both FGFs increased the frequency of egg tooth formation in frontonasal mass mesenchyme compared to frontonasal mass mesenchyme grafted without ectoderm. FGFs can partially but not completely replace facial ectoderm since homotypic recombinations of frontonasal mass and mandibular tissues were significantly longer than mesenchyme grafts treated with FGF-soaked beads (P < 0.05). The addition of a second FGF-soaked bead did not significantly increase the length of the frontonasal mass or the mandibular mesenchyme. We have determined that FGF-2 protein is expressed in facial ectoderm and could be an endogenous signal for outgrowth. In contrast, FGF-8 transcripts are not expressed in the ectoderm covering the areas of the face that were grafted; thus, it is less likely that FGF-8 is required for outgrowth. Our results indicate that FGFs are part of an endogenous signaling pathway involved in distal outgrowth and chondrogenesis of the facial prominences.

Protection of rat myocardium by mitogenic and non-mitogenic fibroblast growth factor during post-ischemic reperfusion

The effects of acidic fibroblast growth factor (FGF-1) and basic fibroblast growth factor (FGF-2) and a non mitogenic form of FGF1 on myocardial ischemia and reperfusion were assessed. Rats underwent 10 minutes of coronary artery occlusion followed by 24 hours of reperfusion. Creatinine kinase content of the affected myocardium showed that both fibroblast growth factors 1 and 2 effectively protected against ischemia reperfusion injury (p < 0.01), and that the vasoactive but nonmitogenic form of the FGF1 was equally protective (p < 0.01 versus control + vehicle). The results were confirmed by light and electron-microscopy histological studies. Histological evaluations after treatment with the non-mitogenic fibroblast growth factor 1 showed that it did not generate the severe hyperplasia and connective tissue disorganization observed with the native mitogenic proteins. The possibility of using a non-mitogenic form of fibroblast growth factor for cardio-protection circumvents many of the potentially undesirable effects that may derive from systemically introducing broad spectrum acting fibroblast growth factors in vivo. This myocardial protection observed 24 hours after the treatment with fibroblast growth factors, and the efficacy of the non-mitogenic form of the protein, also suggest that the protective effect of fibroblast growth factors may be due to the increased blood flow rather than to angiogenesis.

Fibroblast growth factor-2 decreases metabolic coupling and stimulates phosphorylation as well as masking of connexin43 epitopes in cardiac myocytes

Cardiac gap junction (GJ) channels, composed of connexins, allow electrical and metabolic couplings between cardiomyocytes, properties important for coordinated action of the heart as well as tissue homeostasis and control of growth and differentiation. Fibroblast growth factor-2 (FGF-2) is an endogenous growth-promoting protein, believed to participate in the short- and long-term responses of the heart to injury. We have examined short-term effects of FGF-2 on cardiac myocyte GJ-mediated metabolic coupling, using cultures of neonatal rat cardiomyocytes. FGF-2 decreased coupling between cardiomyocytes assessed by scrape dye loading as well as microinjection and dye transfer within 30 minutes of administration. Genistein blocked the effects of FGF-2. To determine the mechanism, we next assessed the effect of FGF-2 on expression, distribution, and phosphorylation of connexin43 (Cx43), which is a major cardiomyocyte connexin. FGF-2 did not affect Cx43 mRNA or protein accumulation and synthesis, and it did not change Cx43 localization at sites of intercellular contact as assessed by immunostaining with a polyclonal anti-Cx43 antibody raised against a synthetic peptide containing residues 346 to 363 of Cx43. FGF-2, however, decreased staining intensity at sites of intermyocyte contact when a monoclonal anti-Cx43 antibody was used, suggesting a localized masking of epitope(s) recognized by the monoclonal but not the polyclonal antibody. These epitopes appear to reside within residues 261 to 270 of Cx43, as indicated by full quenching of monoclonal antibody staining with synthetic peptides. In addition, FGF-2 induced a more than twofold increase in Cx43 phosphorylation. Phosphoamino acid analysis indicated increased phosphorylation of Cx43 on serine residues. Although tyrosine phosphorylation of Cx43 was not detected in either treated or control cells, a fraction of Cx43 was immunoprecipitated with anti-phosphotyrosine-specific antibodies in FGF-2-treated myocytes, suggesting interaction (and hence coprecipitation) with phosphotyrosine-containing protein(s). In conclusion, we have identified Cx43 and intercellular communication as targets of FGF-2-triggered and tyrosine phosphorylation-dependent signal transduction in cardiac myocytes. It is suggested that phosphorylation of Cx43 on serine induced by FGF-2 contributes to decreased metabolic coupling between cardiomyocytes.

Fibroblast growth factor receptor 1 in skeletal and heart muscle cells: expression during early avian development and regulation after notochord transplantation

Basic fibroblast growth factor (bFGF, FGF-2) mediates several biological functions during embryonic development. With regard to skeletal muscle formation, it has been suggested that FGF-2 is involved in the growth and differentiation of myogenic precursor cells. To identify the FGF-responsive cells we studied the expression of FGF receptor type I (FGFR-1) during early embryonic development of the chick. FGFR-1 immunoreactivity is present at all stages examined (embryonic day [E] 2-E5). Expression of FGFR-1 is found in the somite myotome, limb bud muscle cells, eye and tongue muscle cells, and myocardium. Transplantation of an additional notochord into the paraxial mesoderm, which prevents the formation of a myotome, reveals the absence of FGFR-1 immunoreactivity on the operated side. The distinct expression pattern of FGFR-1 in migrating and differentiating muscle cells indicates that in addition to the stimulation of proliferation of myoblasts, FGF-2 exerts other (nonmitogenic) effects on postmitotic myocytes.

Immunohistochemical analysis of platelet-derived growth factor and basic fibroblast growth factor in cardiac biopsy and autopsy specimens of heart transplant patients

The purposes of this study were to examine 250 heart biopsy specimens and 20 autopsy specimens from heart transplant patients for the presence and localization of platelet-derived growth factor (PDGF)and basic fibroblast growth factor (bFGF) and to correlate these findings with the histologic features of rejection and the autopsy findings of graft coronary vasculopathy and global ischemia. Positive specimen staining was significantly more prevalent for PDGF (78% of specimens) than for bFGF (54% of specimens) (p< 0.001). PDGF was distributed more in an interstitial (53%) than a vascular (28%) pattern and was associated with macrophages, whereas bFGF was distributed more in a vascular (50%) than an interstitial (12%) pattern. The prevalence of PDGF (but not bFGF) staining was significantly greater in biopsy specimens with at least grade 2 vascular rejection changes (81%) than in those without vascular rejection changes (58%) (p<0.001). In autopsy specimens, PDGF staining was present in the hearts of all 5 patients (100%) who died of graft failure from coronary vasculopathy and was present in all 11 hearts (100%) with global ischemic changes, but in only 4 of 9 (44%) of the hearts without global ischemia (p<0.01). PDGF staining was absent in nontransplanted heart specimens, whereas bFGF staining in nontransplanted heart specimen was similar to that in transplanted hearts. We conclude that PDGF is increased in transplanted hearts, is distributed more in an interstitial pattern, and is associated with macrophages. Furthermore, PDGF staining is increased in transplanted hearts with evidence of vascular rejection, coronary vasculopathy, or global ischemia.

Establishment of the mesodermal cell line QCE-6. A model system for cardiac cell differentiation

The QCE-6 cell line was derived from precardiac mesoderm of the Japanese quail. As previously reported, these cells are able to differentiate into two distinct cardiac cell types with myocardial or endocardial endothelial cell properties. This present communication describes in detail the derivation of this cell line and further characterizes the nontreated and induced myocardial and endothelial phenotypes of these cells. The QCE-6 cells exhibit an epithelial morphology, as well as the pattern of protein expression, that is characteristic of precardiac mesoderm. Treatment with retinoic acid, basic fibroblast growth factor (bFGF), transforming growth factor (TGF)-beta 2, and TGF-beta 3 induces these cells to differentiate and produce mixed cultures of epithelial and mesenchymal cells. The epithelial cells express myosin, desmin, and cardiac troponin I in a punctate pattern throughout the cytoplasm. These sarcomeric proteins become organized in a premyofibrillar pattern when TGF-beta 1, platelet-derived growth factor (PDGF)-BB, and insulin-like growth factor (IGF) II are added in combination along with retinoic acid, bFGF, TGF-beta 2, and TGF-beta 3. Also, these treatments induce Na+,K(+)-ATPase expression. When the QCE-6 cells are cultured on collagen type I, the mesenchymal cells that are promoted by retinoic acid, bFGF, TGF-beta 2, and TGF-beta 3 will invade the gel. These mesenchymal cells are positive for QH1 and JB3, which are both markers for presumptive endocardial cells within the early cardiogenic mesoderm. The addition of both PDGF-BB and IGF II to QCE-6 cell cultures will inhibit the ability of retinoic acid, bFGF, TGF-beta 2, and TGF-beta 3 to induce both the mesenchymal morphology and QH1 and JB3 expression. Collectively, these results suggest that the proces of cardiac cell differentiation is regulated by multiple signals and that early cardiogenic mesoderm contains a bipotential stem cell that can give rise to both the myocardial and endocardial lineages. More important, since the QCE-6 cells are representative of early cardiogenic cells, this cell line offers a unique model system to study cardiac cell differentiation.

Role of transiently altered sarcolemmal membrane permeability and basic fibroblast growth factor release in the hypertrophic response of adult rat ventricular myocytes to increased mechanical activity in vitro

One of the trophic factors that has been implicated in initiating or facilitating growth in response to increased mechanical stress in several tissues and cell types is basic fibroblast growth factor (bFGF; FGF-2). Although mammalian cardiac muscle cells express bFGF, it is not known whether it plays a role in mediating cardiac adaptation to increased load, nor how release of the cytosolic 18-kD isoform of bFGF would be regulated in response to increased mechanical stress. To test the hypothesis that increased mechanical activity induces transient alterations in sarcolemmal permeability that allow cytosolic bFGF to be released and subsequently to act as an autocrine and paracrine growth stimulus, we examined primary isolates of adult rat ventricular myocytes maintained in serum-free, defined medium that were continually paced at 3 Hz for up to 5 d. Paced myocytes, but not nonpaced control cells, exhibited a "hypertrophic" response, which was characterized by increases in the rate of phenylalanine incorporation, total cellular protein content, and cell size. These changes could be mimicked in control cells by exogenous recombinant bFGF and could be blocked in continually paced cells by a specific neutralizing anti-bFGF antibody. In addition, medium conditioned by continually paced myocytes contained significantly more bFGF measured by ELISA and more mitogenic activity for 3T3 cells, activity that could be reduced by a neutralizing anti-bFGF antibody. The hypothesis that transient membrane disruptions sufficient to allow release of cytosolic bFGF occur in paced myocytes was examined by monitoring the rate of uptake into myocytes from the medium of 10-kD dextran linked to fluorescein. Paced myocytes exhibited a significantly higher rate of fluoresceinlabeled dextran uptake. These data are consistent with the hypothesis that nonlethal, transient alterations in sarcolemmal membrane permeability with release of cytosolic bFGF is one mechanism by which increased mechanical activity could lead to a hypertrophic response in cardiac myocytes.

High and low molecular weight fibroblast growth factor-2 increase proliferation of neonatal rat cardiac myocytes but have differential effects on binucleation and nuclear morphology. Evidence for both paracrine and intracrine actions of fibroblast growth factor-2

Basic fibroblast growth factor (FGF-2) plays a vital role in the growth and differentiation of cardiac myocytes. It exists in high and low molecular weight forms because of the use of alternative initiation codons in the same mRNA. Higher levels of high molecular weight forms (molecular mass of 22 and 21.5 kD) are present in the rat heart during the neonatal stage, whereas the low molecular weight form (molecular mass of 18 kD) is predominant in the adult heart, suggesting different roles in development. Rat FGF-2 cDNAs that can preferentially express high or low molecular weight forms were introduced into neonatal rat ventricular myocyte cultures. Significant and comparable increases in overall cardiac myocyte DNA synthesis and proliferation were seen with 22/21.5- and 18-kD FGF-2 expression. A significantly higher mitotic index was seen in the vicinity of cardiac myocytes overexpressing high or low molecular weight forms of FGF-2 compared with nonoverexpressing cells. This increase was inhibited in the presence of neutralizing antibodies to FGF-2, pointing to a proximity-dependent paracrine effect of 22/21.5- and 18-kD FGF-2 on mitosis. By contrast, overexpression of high but not low molecular weight FGF-2 was associated with a significant increase in binucleation (approximately 36% of cardiac myocytes overexpressing 22/21.5-kD FGF-2 were binucleated compared with 9% of cardiac myocytes overexpressing 18-kD FGF-2), which was not affected by neutralizing antibodies to FGF-2. These results suggest that 22/21.5-kD FGF-2 and 18-kD FGF-2 have similar paracrine effects on proliferation but that 22-21.5-kD FGF-2 exerts a distinct intracrine effect on binucleation.

Abnormal bone growth and selective translational regulation in basic fibroblast growth factor (FGF-2) transgenic mice

Basic fibroblast growth factor (FGF-2) is a pleiotropic growth factor detected in many different cells and tissues. Normally synthesized at low levels, FGF-2 is elevated in various pathologies, most notably in cancer and injury repair. To investigate the effects of elevated FGF-2, the human full-length cDNA was expressed in transgenic mice under control of a phosphoglycerate kinase promoter. Overexpression of FGF-2 caused a variety of skeletal malformations including shortening and flattening of long bones and moderate macrocephaly. Comparison by Western blot of FGF-2 transgenic mice to nontransgenic littermates showed expression of human FGF-2 protein in all major organs and tissues examined including brain, heart, lung, liver, kidney, spleen, and skeletal muscle; however, different molar ratios of FGF-2 protein isoforms were observed between different organs and tissues. Some tissues preferentially synthesize larger isoforms of FGF-2 while other tissues produce predominantly smaller 18-kDa FGF-2. Translation of the high molecular weight isoforms initiates from unconventional CUG codons and translation of the 18-kDa isoform initiates from an AUG codon in the FGF-2 mRNA. Thus the Western blot data from the FGF-2 transgenic mice suggest that tissue-specific expression of FGF-2 isoforms is regulated translationally.

Angiogenic therapy of acute myocardial infarction by intrapericardial injection of basic fibroblast growth factor and heparin sulfate: an experimental study

To examine whether angiogenesis and myocardial salvage occur, 30 micrograms basic fibroblast growth factor (bFGF) and 3 mg heparin sulfate (HS) were injected through the right atrium into the pericardial cavity by a thin needle-tipped catheter in a canine model of acute myocardial infarction. One month later infarcted weight/left ventricle weight was 24% +/- 5.2%, 25% +/- 4.0%, 18% +/- 2.4%, and 10% +/- 1.8% (mean + SE) in saline solution, HS, bFGF alone, and bFGF plus HS groups, respectively. Vascular number in the infarcted area of the outer layer was 13 +/- 3.3, 20 +/- 2.2, 47 +/- 8.3, and 136 +/- 26.3/200 x 200 microns2 in saline solution, HS, bFGF alone, and bFGF plus HS groups, respectively. Thus the vascular number was the largest in the bFGF plus HS group. The vascular number was larger in the subepicardial than in the subendocardial infarcted areas. Vessels directed from the epicardium toward the subepicardial infarcted area were also observed. The transcatheter intrapericardial injection of bFGF plus HS caused angiogenesis and myocardial salvage. This method might bring about a selective therapeutic and preventive modality of myocardial infarction irrespective of coronary anatomy and contraindications for coronary interventions and surgery.

A comprehensive analysis of the distribution of FGF-2 and FGFR1 in the rat brain

We have examined the cellular distribution of both FGF-2 and FGFR1 immunoreactivity and their mRNAs throughout the normal adult rat brain in order to reconcile numerous disparate findings in the published literature. The results confirm a widespread distribution of FGF-2 and FGFR1 in the rat brain, and different regions express distinct patterns of FGF-2 and FGFR1 mRNA and protein: neuronal and non-neuronal cells show different subcellular distributions that vary according to the area where they are located. The intensity of the staining and hybridization also varies according to the loci examined and the cell type involved. Astrocytes contain the highest levels of FGF-2 and FGFR1 mRNAs, and characteristically, possess high levels of immunoreactive FGF-2 within the nucleus. Amongst non-neuronal cells, oligodendrocytes do not synthesize or contain significant levels of FGF-2 immunoreactivity however, they do express FGFR1 mRNA. In these cells, immunoreactive FGFR1 is mainly associated with the myelin sheaths of neuronal fibers. In ventricular systems, ependymal cells synthesize and contain immunoreactive FGFR1. In contrast, only cells lining the lateral wall of the IIIrd ventricle express FGF-2 mRNA. Subependymal cells contain high levels of both FGF-2 and FGFR1 immunoreactivity. Neurons express low levels of FGF-2 mRNA and immunoreactive FGF-2 is localized predominantly to the perikaryon. However, selected populations of neurons, such as CA2 field of the hippocampus, show high levels of FGF-2 mRNA, in which the nucleus is strongly immunopositive. Similarly, high levels of FGFR1 mRNA are localized to select populations of neurons (e.g. amygdala). FGFR1 immunoreactivity is mainly associated with myelinated fiber tracts (e.g. striatum), and some neurons show immunoreactivity in the perikaryon (e.g. hippocampus), the nucleus (e.g. mesencephalic trigeminal nucleus), or in axonal projections (e.g. hypothalamus). Remarkably, in many of the areas studied, FGF-2 and FGFR1 mRNA and/or their translated protein do not co-localize in neurons (e.g. neo-cortices) or even in the same regions of the brain (e.g. substantia nigra). In other instances, mRNAs for both FGF-2 and FGFR1 colocalize (e.g. supraoptic nucleus). The brain, in contrast to peripheral tissues, contains high levels of FGF-2 and actively expresses its gene under normal physiological conditions. The highly specific anatomical distribution of immunoreactive FGF-2 in neuronal and non-neuronal brain cells, supports the notion that it plays a multifunctional role in the CNS under normal physiology. By correlating the localization and the synthesis of FGF-2 and one of its high affinity receptors, FGFR1, in the CNS, it should be possible to obtain a better understanding of the roles of FGF-2 in normal and pathological conditions.

Some growth factors stimulate cultured adult rabbit ventricular myocyte hypertrophy in the absence of mechanical loading

Cultured adult rabbit cardiac myocytes treated with recombinant growth factors display enhanced rates of protein accumulation (ie, growth) in response to insulin and insulin-like growth factors (IGFs), but epidermal growth factor, acidic or basic fibroblast growth factor, and platelet-derived growth factor failed to increase contractile protein synthesis or growth of the heart cells. Insulin and IGF-1 increased growth rates by stimulating anabolic while simultaneously inhibiting catabolic pathways, whereas IGF-2 elevated growth modestly by apparently inhibiting lysosomal proteolysis. Neutralizing antibodies directed against either IGF-1 or IGF-2 or IGF binding protein 3 blocked protein accumulation. A monoclonal antibody directed against the IGF-1 receptor also inhibited changes in protein turnover provoked by recombinant human IGF-1 but not IGF-2. Of the other growth factors tested, only transforming growth factor-beta 1 increased the fractional rate of myosin heavy chain (MHC) synthesis, with beta-MHC synthesis being elevated and alpha-MHC synthesis being suppressed. However, the other growth factors were able to modestly stimulate the rate of DNA synthesis in this preparation. Bromodeoxyuridine labeling revealed that these growth factors increased DNA synthesis in myocytes and nonmyocytes alike, but the heart cells displayed neither karyokinesis or cytokinesis. In contrast, cocultures of cardiac myocytes and nonmyocytes and nonmyocyte-conditioned culture medium failed to enhance the rate of cardiac MHC synthesis or its accumulation, implying that quiescent heart cells do not respond to "conditioning" by cardiac nonmyocytes. These findings demonstrated that insulin and the IGFs promote passively loaded cultured adult rabbit heart cells to hypertrophy but suggest that other growth factors tested may be limited in this regard.