Endocrine Abstracts

Acylation stimulating protein (ASP) synthesis occurs through the interaction between complement C3, factor B and adipsin in adipose tissue. ASP demonstrates potent lipogenic effects that are modulated by sex hormones in vivo and in vitro. In this study, an ex vivo investigation was carried out to analyse expression of genes related to ASP production and function. Adipose tissue was harvested from ovariectomized rats (n=6), and treated with sex steroids at physiological concentrations (progesterone, estrogen, P&E and testosterone) and chylomicrons. The addition of chylomicrons to the media of cultured adipocytes has been shown to stimulate ASP production. Tissue explants were cultured for 24 hours at 37 °C and 5% CO2. The results showed that ASP production was only influenced by co-treatment with P&E in both visceral and subcutaneous tissue (P=0.011 and P=0.007, respectively) compared to the control group. Interestingly, in P&E treated subcutaneous tissue along with a reduction in ASP concentration, factor B gene expression decreased significantly (P=0.032) and C5L2 receptor expression increased significantly (P=0.05) compared to the control. DGAT1 expression increased significantly (P=0.032) and correlated positively with C5L2 receptor (P=0.045, r=0.51). In addition, factor B and factor D were positively correlated with ASP concentration (P=0.012, r=0.61 and P=0.013, r=0.61 respectively).

In summary, the findings showed that ASP concentration and expression of precursors and related lipogenic factors may regulated only under the combined (P&E) treatment compared to individual hormone effects. The unexpected decrease in ASP production in subcutaneous tissue may be explained by the increased expression of C5L2 receptor and this suggest increased uptake of ASP by adipocytes. The positive correlation between C5L2 and DGAT suggests a regulatory effect of P&E hormones on the ASP-C5L2 signaling pathway and triglyceride uptake. Further analysis of the mechanism involved may clarify the influence of female hormones on fat storage and distribution.