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The adipose tissue serves not only as an energy storage for the body, but also synthesizes and secretes many proteins, so-called adipokines. They are involved in a multitude of physiological and pathological processes via autocrine, paracrine and endocrine pathways.
Among these adipokines are also components of the renin-angiotensin system (RAS). Possibly they are key factors for the development and progression of obesity-associated diseases. Similarly to the rising number of overweight and obese humans, our cats and dogs are increasingly affected by overweight and its related diseases, so that the local adipose tissue RAS could be also relevant for these species. Thus, the aim of this thesis was to obtain basic findings of the adipose tissue RAS in cats and dogs. Another intention was to establish a primary culture of adipose tissue for prospective further in vitro research. For this purpose preadipocytes were obtained from adipose tissue and cultivated and differentiated by addition of several agents successfully. Furthermore, the effect of mature adipocytes on the differentiation capacity of preadipocytes was examined in a co-culture experiment and the cell culture methods ceiling culture as well as explants culture were utilized to test alternative methods for gaining adipocyte progenitor cells. To investigate the gene expression during adipogenesis, purchased feline preadipocytes were differentiated to adipocytes in vitro and, besides the expression of the adipogenesis markers PPAR-γ, pref-1, adiponectin and leptin, the expression of the RAS components angiotensinogen, renin, ACE, ACE2, AT1, AT2, MAS and (pro)reninreceptor were measured at five time points using real time PCR. Whereby it was shown that there are differences in the expression of these components between preadipocytes and the various differentiation stages.
Interestingly, the two enzymes ACE and ACE2 showed an opposite expression course.
Because ACE2 abolishes the effects of ACE through metabolizing Angiotensin I and Angiotensin II, this could be a compensatory mechanism that has also been found in other tissues. In addition to the analysis of cultivated cells, the gene expression of mature adipocytes that were isolated from the adipose tissue of cats and dogs were investigated. So it was proved for the first time that the local RAS is also expressed in vivo in feline and canine adipocytes. For the species cat the expression between subcutaneous and visceral adipocytes and between adipocytes of animals with different nutritional status were compared. This demonstrated that ACE and AT1 are expressed significantly more in subcutaneous adipocytes.
Concerning the nutritional status a significant lower expression of ACE2 was observed in moderately overweight animals in the subcutaneous adipocytes. Testing the mRNA expression results on correlation revealed a positive relationship between ACE and leptin, an adipokine which expression augments with increasing body weight.
On the contrary, ACE2 correlated negative with leptin. This leads to the assumption that with increasing body weight the ACE / ACE2 balance shifts towards the ACE / Ang II / AT1 axis. Consequently, these results could provide a new approach for the explanation of the pathophysiological effects of the local adipose tissue RAS in the development of obesity-associated diseases.