Transforming growth factor alpha and atrial natriuretic peptide in white adipose tissue depots in rats

Abstract

To detect the presence in adipose tissue of peptides known to affect tissue growth and to investigate potential regional differences, epididymal and perirenal adipose tissue depots from male Sprague-Dawley rats were separated into adipocyte and stroma-vascular fractions by collagenase digestion, sequential centrifugation and filtration. Identity and integrity of the fractions were demonstrated by light and electron microscopy, while dose-response curves for angiotensin-converting enzyme (ACE) were performed, revealing maintained functional capacity of the stroma-vascular fraction. ACE, atrial natriuretic peptide (ANP), and transforming growth factor-alpha (TGF-alpha) concentrations were significantly greater in epididymal than perirenal stroma-vascular tissue. Adipocyte fractions from both depots contained significant concentrations of ANP and TGF-alpha. There was no detectable ACE in the adipocyte fractions, indicating that no contaminating stromal-vascular cells were present in these fractions. These data show significant concentrations of peptides with effects on growth in subfractions of adipose tissue and demonstrate regional differences in concentrations between fat depots.

Angiotensin-converting enzyme signalling in human preadipocytes and adipocytes

“…Expression is not regulated during the 14 days post-confluence neither with nor without induction of adipose conversion. These results are in agreement with previously published mRNA data from human [23,24], but not rat adipose tissue [29]. As preadipocytes change the expression of classic "housekeepers" like actin during adipose conversion [30], γ-tubulin was therefore chosen as loading control.…”

“…This picture seems to hold true for rat adipose tissue [29], but previously published data on ACE mRNA expression in human adipose tissue [23,24,37] and the results presented herein have shown ACE to be expressed not only in preadipocytes but also in differentiated adipocytes. As each adipocyte is in direct contact with at least one capillary and ACE peptidase activity towards blood borne substrates should not be limiting for adipocytes.…”

“…ACE has long been described as a specific surface marker for endothelial cells and tissue expression accepted to be limited to the vasculature [29,36]. This picture seems to hold true for rat adipose tissue [29], but previously published data on ACE mRNA expression in human adipose tissue [23,24,37] and the results presented herein have shown ACE to be expressed not only in preadipocytes but also in differentiated adipocytes.…”

Comparative expression analysis of the renin–angiotensin system components between white and brown perivascular adipose tissue

“…ACE has been detected in WATs ( Jonsson et al 1994, Engeli et al 1999, Schling et al 1999, Giacchetti et al 2002, whereas there are no data in the literature regarding ACE expression in BAT. ACE mRNA was found in subcutaneous and visceral adipose tissue in rodents (Crandall et al 1992, Pinterova et al 2000 and humans ( Jonsson et al 1994, Engeli et al 1999, Giacchetti et al 2002. Moreover, ACE activity was detected in human preadipocytes (Schling et al 1999).…”

Obesity and cardiovascular hemodynamic function

“…On one hand, blood volume is known to be increased in obesity perhaps in order to meet the perfusion requirements of expanding adipose tissue, which can comprise as much as 50% of total weight [11]. Interestingly, adipose tissue has recently also been recognized as a direct source of peptide hormones that regulate fluid homeostasis such as atrial natriuretic peptide [12] or the renin-substrate angiotensinogen [13,14]. On the other hand, a recent study by Daniels et al [15] suggests that in children and adolescents, lean body mass rather than fat mass is a major determinant of stroke volume and cardiac output.…”