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Rietdorf, Katja; MacQueen, Hilary and Bootman, Martin
(2015).
Abstract
The heart is surrounded by a layer of fat known as epicardial adipose tissue (EAT). The adipocytes within EAT are critical to the function of the heart; they are an essential source of free fatty acids, which cardiomyocytes utilise for energy. EAT also provides thermal insulation and physical protection for the heart. However, the beneficial functions of EAT can be negated by the release of signals that evoke pathological changes in cardiomyocytes. EAT releases molecules, such as adipokines and cytokines, and due to the close proximity of EAT to cardiomyocytes these adipose-derived factors can affect the heart in a paracrine manner. The thickness of EAT as a predictor for several types of cardiac diseases. It is not possible to co-culture adipocytes and cardiomyocytes in a 2 dimensional co-culture, because mature adipocytes do not attach to cell culture surfaces. As a result, most studies on the effects of adipocyte released factors on cardiomyocytes use the addition of adipocyte-conditioned medium to cardiomyocytes. However, this does not allow paracrine effects between both cell types to become established after their isolation, and does not allow the study of long-term interactions. Adipocytes can be trapped and maintained in a 3-dimensional collagen matrix. We are currently optimising such a 3-dimensional culture system to study the effects that adipocytes have on adjacent cardiomyocytes, and vice versa. The translucent nature of the collagen matrix allows studying cellular phenotypes, Ca2+ signalling and contractions within the cultures. We investigated whether signalling pathways are activated or inhibited by the addition of adipokines and cytokines, and whether co-culture with adipocytes affects the contractility of cardiomyocytes.
TNF-α (3 ng/ml), activin A (1 ng/ml) and adiponectin (10 µg/ml) were added to cardiomyocytes for a period of 6 hours, and the activity of signalling pathways was subsequently examined using a PathScan Signalling Array (Cell Signalling Technology). We found a significant up-regulation of cardiomyocyte pro-apoptic signalling pathways by TNF- α and Activin A. Whereas, adiponectin reduced ERK and mTOR activity, in line with its proposed cardioprotective effects.
Co-culture of cardiomyocytes with adipocytes for 3 days caused negative chronotropic and negative inotropic responses. The presence of adipocytes reduced the frequency of cardiomyocyte beating from 0.51 ± 0.0 to 0.32 ± 0.04 Hz, and reduced the amplitude of contraction from 6.9 ± 0.3 to 3.8 ± 0.5 µm (n= 10 regions, 3 wells each with or without adipocytes, mean ± SEM, unpaired t-test, P<0.05).
These data illustrate that adipose-derived cytokines and adipokines cause an up-regulation of inflammatory and pro-apoptotic pathways in rat ventricular cardiomyocytes. In addition, the proximity of adipocytes to cardiomyocytes leads to changes in contractility.
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