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

Fibroblast growth factor receptor signaling in cardiomyocytes is protective in the acute phase following ischemia-reperfusion injury

Fibroblast growth factor receptors (FGFRs) are expressed in multiple cell types in the adult heart. Previous studies have shown a cardioprotective effect of some FGF ligands in cardiac ischemia-reperfusion (I/R) injury and a protective role for endothelial FGFRs in post-ischemic vascular remodeling. To determine the direct role FGFR signaling in cardiomyocytes in acute cardiac I/R injury, we inactivated Fgfr1 and Fgfr2 (CM-DCKO) or activated FGFR1 (CM-caFGFR1) in cardiomyocytes in adult mice prior to I/R injury. In the absence of injury, inactivation of Fgfr1 and Fgfr2 in adult cardiomyocytes had no effect on cardiac morphometry or function. When subjected to I/R injury, compared to controls, CM-DCKO mice had significantly increased myocyte death 1 day after reperfusion, and increased infarct size, cardiac dysfunction, and myocyte hypertrophy 7 days after reperfusion. No genotype-dependent effect was observed on post-ischemic cardiomyocyte cross-sectional area and vessel density in areas remote to the infarct. By contrast, transient activation of FGFR1 signaling in cardiomyocytes just prior to the onset of ischemia did not affect outcomes after cardiac I/R injury at 1 day and 7 days after reperfusion. These data demonstrate that endogenous cell-autonomous cardiomyocyte FGFR signaling supports the survival of cardiomyocytes in the acute phase following cardiac I/R injury and that this cardioprotection results in continued improved outcomes during cardiac remodeling. Combined with the established protective role of some FGF ligands and endothelial FGFR signaling in I/R injury, this study supports the development of therapeutic strategies that promote cardiomyocyte FGF signaling after I/R injury.

In Vitro Assays for Endothelial Cell Functions Required for Angiogenesis: Proliferation, Motility, Tubular Differentiation, and Matrix Proteolysis

This chapter deconstructs the process of angiogenesis into its component parts in order to provide simple assays to measure discrete endothelial cell functions. The techniques described will be suitable for studying stimulators and/or inhibitors of angiogenesis and determining which aspect of the process is modulated. The assays are designed to be robust and straightforward, using human umbilical vein endothelial cells, but with an option to use other sources such as microvascular endothelial cells from various tissues or lymphatic endothelial cells. It must be appreciated that such reductionist approaches cannot cover the complexity of the angiogenic process as a whole, incorporating as it does a myriad of positive and negative signals, three-dimensional interactions with host tissues and many accessory cells including fibroblasts, macrophages, pericytes and platelets. The extent to which in vitro assays predict physiological or pathological processes in vivo (e.g., wound healing, tumor angiogenesis) or surrogate techniques such as the use of Matrigel™ plugs, sponge implants, corneal assays etc remains to be determined.

Fibroblast growth factor 2 is an essential cardioprotective factor in a closed-chest model of cardiac ischemia-reperfusion injury

Fibroblast growth factor 2 (FGF2) is cardioprotective in in vivo models of myocardial infarction; however, whether FGF2 has a protective role in in vivo ischemia‐reperfusion (IR) injury, a model that more closely mimics acute myocardial infarction in humans, is not known. To assess the cardioprotective efficacy of endogenous FGF2, mice lacking a functional Fgf2 gene (Fgf2^−/−) and wild‐type controls were subjected to closed‐chest regional cardiac IR injury (90 min ischemia, 7 days reperfusion). Fgf2^−/− mice had significantly increased myocardial infarct size and significantly worsened cardiac function compared to wild‐type controls at both 1 and 7 days post‐IR injury. Pathophysiological analysis showed that at 1 day after IR injury Fgf2^−/− mice have worsened cardiac strain patterns and increased myocardial cell death. Furthermore, at 7 days post‐IR injury, Fgf2^−/− mice showed a significantly reduced cardiac hypertrophic response, decreased cardiac vessel density, and increased vessel diameter in the peri‐infarct area compared to wild‐type controls. These data reveal both acute cardioprotective and a longer term proangiogenic potential of endogenous FGF2 in a clinically relevant, in vivo, closed‐chest regional cardiac IR injury model that mimics acute myocardial infarction.

The cardioprotective efficacy of endogenous FGF2 was tested using a closed‐chest regional cardiac IR injury model. Mice lacking FGF2 (Fgf2^−/−) mice had significantly increased myocardial infarct size and significantly worsened cardiac function compared to wild‐type controls at both 1 and 7 days post‐IR injury. These data reveal both acute cardioprotective and a longer term proangiogenic potential of endogenous FGF2 in a clinically relevant, in vivo, closed‐chest regional cardiac IR injury model that mimics acute myocardial infarction.

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.

FGF-2 protects cardiomyocytes from doxorubicin damage via protein kinase C-dependent effects on efflux transporters

AIMS

The anti-cancer anthracycline doxorubicin (DOX) increases the risk of cardiac damage, indicating a need to protect the heart and still allow the benefits of drug treatment. Fibroblast growth factor-2 (FGF-2) is cardioprotective against ischaemia-reperfusion injury. Our aim is to investigate: (i) the ability of FGF-2 to protect against DOX-induced cardiomyocyte damage and (ii) the contribution of efflux drug transport to any increase in injury-resistance.

METHODS AND RESULTS

Neonatal rat cardiomyocyte damage was assessed by measuring cell death markers and lactate dehydrogenase (LDH) activity in the culture medium. LDH activity was increased significantly after incubation with 0.5 μM DOX for 24 h in the absence but not presence of 10 nM FGF-2; this beneficial effect of FGF-2 was blocked by tyrosine kinase (FGF) receptor inhibition. An increase in efflux drug transporter RNA levels was also detected after FGF-2 treatment in the presence of DOX. The beneficial effect of FGF-2 against cell damage and increased transporter RNA levels were blunted with protein kinase C (PKC) inhibition. Finally, FGF-2 stimulated efflux transport of calcein and DOX, and treatment with efflux transporter inhibitors significantly attenuated the protective effect of FGF-2 from DOX-induced injury.

CONCLUSION

Administered FGF-2 increases resistance to DOX-induced cardiomyocyte damage, by a mechanism dependent on PKC as well as regulation of efflux transporter production and/or function.

Effects of mechanical stimulation induced by compression and medium perfusion on cardiac tissue engineering

Cardiac tissue engineering presents a challenge due to the complexity of the muscle tissue and the need for multiple signals to induce tissue regeneration in vitro. We investigated the effects of compression (1 Hz, 15% strain) combined with fluid shear stress (10(-2) -10(-1) dynes/cm(2) ) provided by medium perfusion on the outcome of cardiac tissue engineering. Neonatal rat cardiac cells were seeded in Arginine-Glycine-Aspartate (RGD)-attached alginate scaffolds, and the constructs were cultivated in a compression bioreactor. A daily, short-term (30 min) compression (i.e., "intermittent compression") for 4 days induced the formation of cardiac tissue with typical striation, while in the continuously compressed constructs (i.e., "continuous compression"), the cells remained spherical. By Western blot, on day 4 the expression of the gap junction protein connexin 43 was significantly greater in the "intermittent compression" constructs and the cardiomyocyte markers (α-actinin and N-cadherin) showed a trend of better preservation compared to the noncompressed constructs. This regime of compression had no effect on the proliferation of nonmyocyte cells, which maintained low expression level of proliferating cell nuclear antigen. Elevated secretion levels of basic fibroblast growth factor and transforming growth factor-β in the daily, intermittently compressed constructs likely attributed to tissue formation. Our study thus establishes the formation of an improved cardiac tissue in vitro, when induced by combined mechanical signals of compression and fluid shear stress provided by perfusion.

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.

Cardiac protection by basic fibroblast growth factor from ischemia/reperfusion-induced injury in diabetic rats

Diabetes impairs the expression and function of endogenous growth factors, leading to increased cardiovascular events in diabetic patients. Supplementation of fibroblast growth factors (FGFs) protected the heart from ischemia/reperfusion (I/R)-induced injury in animal models. However, it has not yet been tested in diabetic heart. The present study was thus to clarify whether basic fibroblast growth factor (bFGF) could protect the heart from I/R-induced damage under diabetic conditions using a rat model. Male Sprague Dawley rats were used to induce diabetes by intraperitoneal injection of streptozotocin. Eight weeks later, I/R injury was generated in diabetic rats and age-matched non-diabetic rats. All I/R rats were administrated bFGF or saline through intramyocardial injection. Seven days after I/R, cardiac infarction, structural changes, cell death and blood vessel density, serum malondialdehyde (MDA) and cardiac enzyme lactate dehydrogenase (LDH) were examined. We found that I/R induced significant increases in the cardiac infarction, blood MDA contents and LDH activities, and the expression of caspase-3. Treatment of I/R rats with bFGF simultaneously with reperfusion significantly attenuated I/R-induced pathological changes, along with a significant increase in the cardiac blood vessel density in both diabetic and non-diabetic rates. The protective effects of bFGF on I/R-induced cardiac injury in diabetic group are less than those in non-diabetic group. The results indicated that bFGF provide a protection of the heart against I/R-induced oxidative damage, cell death and infarction under diabetic conditions.

In vitro assays for endothelial cell functions related to angiogenesis: proliferation, motility, tubular differentiation, and proteolysis

This chapter covers the breakdown of the process of angiogenesis into simple assays to measure discrete endothelial cell functions. The techniques described are suitable for studying stimulators or inhibitors of angiogenesis and determining which aspect of the process is modulated. The procedures outlined are robust and straightforward but cannot cover the complexity of the angiogenic process as a whole, incorporating as it does myriad positive and negative signals, three-dimensional interactions with host tissues and many accessory cells, including fibroblasts, macrophages, pericytes, and platelets. The extent to which in vitro assays predict responses in vivo (e.g., wound healing, tumor angiogenesis, or surrogate techniques such as Matrigel plugs, sponge implants, corneal assays, etc.) remains to be determined.

The effect of the controlled release of basic fibroblast growth factor from ionic gelatin-based hydrogels on angiogenesis in a murine critical limb ischemic model

The localized delivery of exogenous, angiogenic growth factors has become a promising alternative treatment of peripheral artery disease (PAD) and critical limb ischemia. In the present study, we describe the development of a novel controlled release vehicle to promote angiogenesis in a murine critical limb ischemic model. Ionic, gelatin-based hydrogels were prepared by the carbodiimide-mediated amidation reaction between the carboxyl groups of gelatin or poly-L-glutamic acid molecules and the amine groups of poly-L-lysine or gelatin molecules, respectively. The degree of swelling of the synthesized hydrogels was assessed as a function of EDC/NHS ratios and the pH of the equilibrating medium, while the release kinetic profile of basic fibroblast growth factor (FGF-2) was evaluated in human fibroblast cultures. The degree of swelling (DS) decreased from 26.5+/-1.7 to 18.5+/-2.4 as the EDC concentration varied from 0.75 to 2.5 mg/ml. Eighty percent of the FGF-2 was released at controlled rates from gelatin-polylysine (gelatin-PLL) and gelatin-polyglutamic acid (gelatin-PLG) hydrogel scaffolds over a period of 28 days. Cell adhesion studies revealed that the negatively charged surface of the gelatin-PLG hydrogels exhibited superior adhesion capabilities in comparison to gelatin-PLL and control gelatin surfaces. Laser Doppler perfusion imaging as well as CD31(+) capillary immunostaining demonstrated that the controlled release of FGF-2 from ionic gelatin-based hydrogels is superior in promoting angiogenesis in comparison to the bolus administration of the growth factor. Over 4 weeks, FGF-2 releasing gelatin-PLG hydrogels exhibited marked reperfusion with a Doppler ratio of 0.889 (+/-0.04) which was 69.3% higher than in the control groups.

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.

Protective effects of non-mitogenic human acidic fibroblast growth factor on hydrogen peroxide-induced damage to cardiomyocytes in vitro

AIM: To study the protective effect of non-mitogenic human acidic fibroblast growth factor (FGF) on cardiac oxidative injury in vivo.

METHODS: Ventricular cardiomyocytes were isolated from 1- to 3-d-old neonatal SD mice and cultured in Dulbecco’s minimum essential medium supplemented with 15% fetal bovine serum under an atmosphere of 50 mL/L CO₂-95% air at 37 °C, as well as assessed by immunocyto-chemical assay. We constructed the cardiomyocyte injury model by exposure to a certain concentration of H₂O₂. Cellular viability, superoxide dismutase (SOD) activity, leakage of maleic dialdehyde and anti-apoptosis effect were included to evaluate the cardiac protective effect of non-mitogenic human acidic FGF.

RESULTS: Over 50% of the cardiomyocytes beat spontaneously on the 2^nd d of culture and synchronously beat after being cultured for 3 d. Forty-eight hours after plating was completed, the purity of such cultures was 95% myocytes, assessed by an immunocytochemical assay. Cellular viability dramatically decreased with the increasing of the concentration of H₂O₂. Non-mitogenic human acidic FGF showed significant resistance to the toxic effect of H₂O₂, significantly increased the cellular viability as well as the activity of SOD, and dramatically decreased the leakage of maleic dialdehyde as well as the cellular apoptosis rate.

CONCLUSION: Hydrogen peroxide shows strong cytotoxicity to the cultured cardiac myocytes, and non-mitogenic human acidic FGF shows strong cardio-protective effect when exposed to a certain concentration of H₂O₂.