Barbara Kapeller

Hypoxia-inducible factor-1β (HIF-1β) is upregulated in a HIF-1α-dependent manner in 518A2 human melanoma cells under hypoxic conditions

Solid tumors include hypoxic areas due to excessive cell proliferation. Adaptation to low oxygen levels is mediated by the hypoxia-inducible factor (HIF) pathway promoting invasion, metastasis, metabolic alterations, chemo-resistance and angiogenesis. The transcription factor HIF-1, the major player within this pathway consists of HIF-1α and HIF-1β. The alpha subunit is continuously degraded under normoxia and becomes stabilized under reduced oxygen supply. In contrast, HIF-1β is generally regarded as constitutively expressed and being present in excess within the cell. However, there is evidence that the expression of this subunit is more complex. The aim of this study was to investigate the role of HIF-1β in human melanoma cells. Among a panel of five different cell lines, in 518A2 cells exposed to the hypoxia-mimetic cobalt chloride HIF-1β was rapidly elevated on protein level. Knockdown experiments performed under cobalt chloride-exposure and hypoxia revealed that this effect was mediated by HIF-1α. The non-canonical relationship between these subunits was further confirmed by pharmacologic inhibition of HIF-1α and by expression of a dominant-negative HIF mutant. Overexpression of HIF-1α showed a time delay in HIF-1β induction, thus arguing for HIF-1β de novo synthesis rather than protein stabilization by heterodimerization. A Hens egg test-chorioallantoic membrane model of angiogenesis and invasion indicated a local expression of HIF-1β and implies a biological relevance of these findings. In summary, this study demonstrates the HIF-1α-dependent regulation of HIF-1β under hypoxic conditions for the first time. The results indicate a novel cell specific mechanism which might prevent HIF-1β to become a limiting factor.

Microcurrent stimulation promotes reverse remodelling in cardiomyocytes

It has been shown that electrical stimulation can improve tissue repair in patients. Imbalances in the extracellular matrix composition induce manifestation of heart failure. Here we investigated the application of microcurrent (MC) to modulate the expression of matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinases (TIMPs) in cardiomyocytes in vitro and in vivo to reverse remodelling in the heart in spontaneous hypertensive rats (SHR).

Bioelectrical signals improve cardiac function and modify gene expression of extracellular matrix components

Beyond the influence of stimulating devices on cardiac excitation, their use in treating patients with heart failure has positive effects on the myocardium at the molecular level. Electrical signals can induce a wide spectrum of effects in living tissue. Therefore, we sought to determine whether applying electrical microcurrent directly to failing hearts leads to functional improvement.

CHANGES OF THE COLLAGEN COMPOSITION IN THE HEART CAUSED BY MICROCURRENT APPLICATION. AN EXPLANATION FOR THE IMPROVEMENT OF CARDIAC FUNCTION BY BI-VENTRICULAR PACING?

Objective Improvement of cardiac function by the unloading effect of a cardiac assist device mainly depends on the duration of heart failure (HF). Patients with a short history of HF ( 5 years) do not show significant cardiac function improvement is that the collagen composition of the extracellular matrix is irreversible. It is successful clinical practice to apply microcurrent in patients with bone fractures and wound healing disturbances in order to improve the healing process by modulation of the collagen synthesis. In order to examine whether microcurrent can also influence the collagen synthesis in the myocardium, the effect of microcurrent application on collagen synthesis of adult cardiomyocytes was investigated. Methods Adult cardiomyocytes were isolated and cultivated in 24 well cell culture plates. Current of different magnitudes (0, 20, 40, 60, 80, 100 :A) was applied via platinum electrodes by a special custom-made device. The whole equipment was incubated under cell culture conditions (+37°C, 5% CO2) over a period of 7 days. Changes of the collagen type I and type III synthesis were analyzed using immunohistochemical staining methods. Collagen type I and type III content was quantified using a special fluorescence confocal laser scanning microscopy system including special analysis software. Results Compared to cardiomyocytes exposed to 0 :A (control cells), collagen type I synthesis of cardiomyocytes showed no significant change after exposure to a moderate current magnitude(40, 60 :A) but a highly significant mean decrease (20.6 %) if exposed to high current (80, 100 :A). Collagen type III revealed a mean increase at moderate current of 29.7 % and a decrease of 25.2 % at high current exposure. As a side effect, we detected an increase in the cell proliferation rate at moderate and high current. Conclusion The results obtained in cell culture suggest that the application of micro-current is able to modulate the synthesis of collagen. In particular, in dependency of the current magnitude collagen type I can be up- or down-regulated. Collagen type I is responsible for the stiffness and the degree of dilatation of the heart. Therefore it can be envisaged that this method -if applied clinically - may help to improve cardiac function, as it helps to heal bone fractures.