Prostaglandin E2 Secretion and Effect on Adipocyte Lipogenesis

Author

Patrick Allen Wortman, University of Tennessee, Knoxville

Date of Award

12-2004

Degree Type

Thesis

Degree Name

Master of Science

Major

Nutrition

Major Professor

Naima Moustaid-Moussa

Committee Members

Jay Whelan, Betsy Haughton

Abstract

With the current focus on the role of n-3 PUFAs as beneficial dietary interventions in the fields of cardiovascular disease and cancer, there has been a vastly increased awareness and focus on the mechanism of action for these essential fatty acids.

Many of the effects of PUFAs are mediated via changes in prostaglandin (PG) levels. One primary substrate for PGs is arachidonic acid (AA) (20:4 n-6), which results in the production of 2-series PGs. Increased concentrations of AA have been shown to increase levels of PGE₂ in vitro and in vivo. The omega-3 fatty acid EPA (20:5 n-3) is of particular interest due to its incorporation into cell membrane phospholipids in competition with AA. EPA can also serve as a substrate for prostaglandin production when present in tissue and results in the production of 3-series PGs, which do not appear to produce the same effects as 2-series PGs, although data is extremely limited. The secretion of prostaglandins (PGs), and specifically PGE₂ has been demonstrated in human and rodent adipocytes, and the presence of PGE₂ receptors in these tissues has also been demonstrated. PGE₂ can act in an autocrine/paracrine fashion in adipocytes to decrease lipolysis via G-protein coupled receptors. Preliminary data from our lab on Apc^Min/+ mice showed that cyclooxygenase (COX) inhibition significantly reduced the activity of fatty acid synthase (FAS) in adipose tissue, and PGE₂ receptor agonists partially but significantly reversed this effect.

Our overall objective was to determine whether treatment with EPA or selective COX-2 inhibitors would lead to a reduction in measured PGE₂ that would in turn regulate markers of lipogenesis. We hypothesized that increased levels of EPA would competitively reduce tissue AA levels, and consequently PGE₂ production, leading to decreased activity of markers specific to adipogenesis, specifically the FAS enzyme. Selective COX-2 inhibition was expected to produce similar effects via inhibition of COX metabolism of AA to PGs. Studies were conducted on 3T3-L1 adipocytes. Dose-response studies demonstrated a clear relationship between increasing doses of EPA or AA and measured PGE₂/PGE₃ levels. Manipulation of PGE₂ levels via addition of EPA to culture media led to significant changes in measured PGE₂ levels versus AA, but did not result in a significant decrease in FAS enzyme activity. Addition of celecoxib, a selective COX-2 inhibitor (CI), to culture media resulted in a significant decrease in PGE₂levels and FAS activity. Addition of exogenous PGE₂ to CI treatment did not reverse the decreased FAS enzyme activity. These results indicate that addition of EPA can displace AA in cell membrane phospholipids and reduce PGE₂ production, but does not impact FAS activity. Suppression of PGE₂ by selective COX-2 inhibition does lead to decreased FAS activity, which is not reversed by exogenous PGE₂ addition.

Recommended Citation

Wortman, Patrick Allen, "Prostaglandin E2 Secretion and Effect on Adipocyte Lipogenesis. " Master's Thesis, University of Tennessee, 2004.
https://trace.tennessee.edu/utk_gradthes/4825