Cardioprotective actions of transforming growth factor-β

Angiotensin II and Cardiac Fibrosis

The renin-angiotensin system has been linked to the pathogenesis of cardiac fibrosis through the use of experimental animal models and by clinical studies. This review emphasizes recent findings implicating the direct action of angiotensin II on cardiac cell types, particularly the cardiac fibroblast, as a causative factor in the development of cardiac fibrosis. The possible influence of other factors acting in concert with angiotensin II either to increase or to attenuate the fibrotic process is also discussed. Nitric oxide is considered as an example of a paracrine agent that can antagonize either the hemodynamic or cellular effects of angiotensin II during both physiological and pathological processes. (Trends Cardiovasc Med 1996;6:193-198).

TGF-beta1 release by volatile anesthetics mediates protection against renal proximal tubule cell necrosis

BACKGROUND/AIMS

We have previously demonstrated that clinically utilized volatile anesthetics protect against renal ischemia reperfusion injury in rats in vivo and reduce necrosis in vitro via activation of ERK and Akt and by upregulating HSP70. In this study, we further deciphered the upstream cellular signaling mechanism(s) of volatile anesthetic-mediated antinecrotic effects in vitro. We hypothesized that volatile anesthetics perturb the structure of the plasma membrane lipid bilayer, causing externalization of phosphatidylserine (PS) to the outer surface on renal tubule cells leading to the increased generation of transforming growth factor-beta1 (TGF-beta1), a cytokine with antinecrotic properties.

METHODS AND RESULTS

In human proximal tubule (HK-2) cell culture, 16-hour exposure to volatile anesthetics (isoflurane, halothane, sevoflurane) caused membrane externalization of PS detected by positive annexin-V staining and increased the release of TGF-beta1 into the cell culture media. Exogenous TGF-beta1 induced protection and neutralizing TGF-beta1 antibody prevented the cytoprotection by volatile anesthetics against hydrogen peroxide-induced HK-2 cell necrosis.

CONCLUSIONS

Volatile anesthetics induce a cytoprotective signaling cascade in proximal tubule cells via membrane externalization of PS initiating TGF-beta1-mediated cytoprotection.

Transforming growth factor-β1 downregulates beating frequency and remodeling of cultured rat adult cardiomyocytes

We have observed increased levels of transforming growth factor-beta1 (TGF-beta1) in human hibernating myocardium (HM). Impaired ventricular function in HM is known to be restored to normal following revascularization implying that myocardial structure in HM is to a certain degree preserved. We have therefore tested whether TGF-beta1 can imitate features of HM by reducing the number and frequency of beating cells (chronotropism) and structural remodeling of cultured adult rat cardiomyocytes (ARC), thus saving substrate, energy, and oxygen. Parameters measured were cell size, protein synthesis, protein degradation, protein content, myofibrillogenesis, and chronotropism. ARC were stimulated for 6 days with sera from patients with coronary heart disease, as this period led to a maximum response of cells. An increase of 90% in cell surface area following such treatment was reduced to a 20% increase of the original size by TGF-beta1. Concomitantly, the rate of protein synthesis dropped from 3.6-fold to 2.4-fold, and myofibrillogenesis was reduced. TGF-beta1 downregulated both the number of contracting cells from 81% to 10% and the frequency from 52 to nine beats per minute. However, TGF-beta1 treatment did not reduce the augmentation of protein content (1.28-fold versus 1.25-fold) indicating that protein degradation was also inhibited. Similar results were obtained with serum from healthy volunteers. The effects of TGF-beta1 were reversible. We conclude that TGF-beta1 constrains protein turnover and beating activity in underperfused myocardium, thus mediating protection by adapting myocytes to shortages in blood supply.

Renal fibrosis in mice treated with human recombinant transforming growth factor-beta2

BACKGROUND

The biologic responses to transforming growth factor-beta (TGF-beta) suggest many potential therapeutic applications; however, in the only clinical trial to examine the effect of the systemic administration of a TGF-beta isoform, patients experienced significant but reversible declines in renal function. We studied the effects of administering human recombinant TGF-beta2 to adult mice.

METHODS

The effect of daily administration of TGF-beta2 on tissue vasoconstriction, tissue levels of endothelin and angiotensin II, tissue hypoxia, and renal fibrosis were examined.

RESULTS

Daily administration of TGF-beta2 at 10 or 100 microg/kg caused apparent tissue vasoconstriction that was visualized by vascular casting, with the largest impact seen in the kidney. Tissue levels of endothelin 1 and angiotensin II were significantly elevated in kidneys of treated mice, as was urinary thromboxane beta2. Renal fibrosis was observed in the cortical tubular interstitium and vasculature, particularly at the cortical-medullary junction and medullary vasa recta; however, glomerular sclerosis was not observed. Fibrosis was correlated to focal tissue hypoxia as determined by immunohistochemical detection of tissue bound pimondazole.

CONCLUSION

We conclude that there are significant histopathologic consequences, focused in the kidney, resulting from the daily administration of high doses of human recombinant TGF-beta2, and we propose that selective vascular constriction with consequent tissue hypoxia is a contributing factor.

Acute and chronic renal effects of recombinant human TGF-beta2 in the rat

The expression of transforming growth factor-beta (TGF-beta) correlates with the incidence of renal glomerular and interstitial injury, however, nothing is known of the effect of these proteins on renal hemodynamics. This study examines the renal hemodynamic and morphologic effects of recombinant human TGF-beta2 in normal male Sprague Dawley rats. Acute infusion of TGF-beta (1.2 microg/kg per min) induced no hemodynamic changes, except for a modest though significant fall in mean arterial pressure. Administering TGF-beta2 at varying doses (20, 100, and 400 microg/kg) for 9 wk caused modest increases in systolic BP and proteinuria and minimal tubular interstitial fibrosis, however, renal hemodynamic end points were not significantly altered. TGF-beta2 (800 microg/kg) was also administered to volume-depleted rats for 7 consecutive days. In contrast to the findings in volume-replete animals, administration of TGF-beta2 to volume-depleted rats caused a marked reduction in GFR and medullary blood flow. Histologic fibrosis of the medullary vasa recta and cortical interstitium was seen, but glomeruli were unaffected. Thus, acute and short-term chronic TGF-beta2 administration did not induce major renal changes in the volume-replete state, however, TGF-beta2 combined with volume depletion caused medullary hypoperfusion and reduced GFR.

A model of bridging angiogenesis in the rat

A model of angiogenesis has been developed in the rat. The epigastric vascular pedicle was exposed in the groin, a 7 mm segment of epigastric artery was excised leaving the vein intact and, after a variable period of time for angiogenesis to occur between the ends of the artery, a skin flap was elevated on the epigastric vascular pedicle so that it depended completely for its blood supply on bridging angiogenesis across the created gap. Skin flap survival and vessel counts were measured as indices of the angiogenic response. In this model we observed a spontaneous increase in vessel counts between the ends of the artery, and a corresponding increase in skin flap tissue survival until day 10 after which time vessel counts plateaued whilst tissue survival continued to increase until day 14. In the angiogenic pedicle, a time-dependent development of granulation tissue containing numerous macrophages and mast cells, and capillary sprouting were documented. When flap elevation was performed 7 days after arterial excision skin flap survival was 42%. Thus, in this model, 7 days is a suitable interval for the future evaluation of the effects of either pro- or anti-angiogenic agents.

TGF-beta in the central nervous system: potential roles in ischemic injury and neurodegenerative diseases

The Transforming Growth Factor-betas (TGF-beta) are a group of multifunctional proteins whose cellular sites of production and action are widely distributed throughout the body, including the central nervous system (CNS). Within the CNS, various isoforms of TGF-beta are produced by both glial and neural cells. When evaluated in either cell culture or in vivo models, the various isoforms of TGF-beta have been shown to have potent effects on the proliferation, function, or survival of both neurons and all three glial cell types, astrocytes, microglia and oligodendrocytes. TGF-beta has also been shown to play a role in several forms of acute CNS pathology including ischemia, excitotoxicity and several forms of neurodegenerative diseases including multiple sclerosis, Parkinson's disease, AIDS dementia and Alzheimer's disease.

TGF-beta modulates the synthesis of proteoglycans by myocardial fibroblasts in culture

In this study we examined the production of proteoglycans by fibroblasts cultured from the left ventricular myocardium of normal adult rats. Various molecular species of proteoglycan were detected, either by labeling glycosaminoglycan chains with 35SO4 or by labeling the proteoglycan core protein with [35S]methionine. The medium of the cell cultures, which contained quantitatively most of the proteoglycans, appeared to consist mainly of biglycan, lesser amounts of decorin and proteoglycans of higher molecular weight. Biglycan and decorin were identified not only by the characteristic mobility of the intact protein and the core protein but also by immunolocation on Western blots. TGF-beta upregulated the synthesis of all these proteoglycans, coincident with elongation of glycosaminoglycan side chains observed for biglycan and decorin. The apparent molecular weight of the core protein of the two proteoglycans remained unaffected by TGF-beta. The results of these experiments suggest that with regard to proteoglycan synthesis and its regulation by TGF-beta, cultured fibroblasts originating from the myocardium share to a large extent the properties of cultured fibroblasts of other organs.

Cloning of a canine cDNA homologous to the human transforming growth factor-beta 1-encoding gene

A 1369-bp cDNA that encodes a homolog of the human transforming growth factor-beta 1 (TGF-beta 1) has been isolated from canine endothelial cells using a combination of PCR and traditional plaque-screening methods. The deduced 390-amino-acid sequence of the canine TGF-beta 1 precursor has 91-94% identity to those deduced from the previously described human and mouse TGF-beta 1 clones.

Controlling the vasculature: angiogenesis, anti-angiogenesis and vascular targeting of gene therapy

Angiogenesis is the development of new blood vessels from an existing vascular bed. Normal vascular proliferation occurs only during embryonic development, the female reproductive cycle and wound repair. By contrast, many pathological conditions (for example, cancer, atherosclerosis and diabetic retinopathy), are characterized by persistent, unregulated angiogenesis. Conversely, inadequate angiogenesis can lead to failure of ulcers to heal and myocardial infarction. Control of vascular development could permit new therapeutic approaches to these disorders. For example, several anti-angiogenic drugs are currently undergoing clinical trials for the treatment of cancer, whereas enhancement of angiogenesis by exogenous growth factors can prevent or limit the damage in chronic wounds and duodenal ulcers. Here Tai-Ping Fan, Rhys Jaggar and Roy Bicknell highlight recent achievements and discuss the prospects of receptor antagonists, enzyme inhibitors, tumour suppressor genes and vascular targeted approaches, especially that of gene therapy, in the future development of angiotherapy.

Transforming growth factor beta 1 preserves endothelial function after multiple brief coronary artery occlusions and reperfusion

The objective of this investigation was to determine the effect of transforming growth factor beta 1 (TGF-beta 1) on endothelium-dependent relaxation in isolated epicardial coronary artery rings obtained from anesthetized dogs after multiple brief episodes of coronary artery occlusion and reperfusion in vivo. Dogs were subjected to four 5-minute periods of left anterior descending coronary artery occlusion interspersed with 5 minutes of reperfusion and followed by a final 1-hour period of reperfusion. Normal left circumflex coronary arteries were used as control samples. Repetitive ischemia and reperfusion significantly (p < 0.01) inhibited the relaxation response to acetylcholine in rings preconstricted with potassium. In an additional group of dogs subjected to the same protocol, 10 micrograms of human recombinant TGF-beta 1 was infused into the left anterior descending coronary artery distal to the site of occlusion via a diagonal branch at 0.3 ml/min immediately before and during the repetitive occlusions and reperfusions. TGF-beta 1 prevented impaired endothelium-dependent relaxation after multiple brief occlusions and reperfusions. These results demonstrate a protective role for TGF-beta 1 in the endothelial injury that occurs during repeated episodes of coronary artery occlusion and reperfusion.