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Updated: Jun 23, 2026
Determination of Fatty Acid Oxidation and Lipogenesis in Mouse Primary Hepatocytes
Published on: August 27, 2015
Preliminary report: inhibition of cellular proteasome activity by free fatty acids
1Omaha VA Medical Center, Omaha, NE 68105, USA. fghamel@unmc.edu
Abstract:
There is evidence in animal studies that free fatty acids (FFA) can decrease protein degradation, but the exact mechanism is not known. We have shown that FFA can inhibit proteasome activity in vitro by interacting with insulin-degrading enzyme. Here we show that FFA can also inhibit the proteasome in whole cells. HepG2 cells were treated with various FFA, and proteasome activity was measured using a cell-permeable substrate for the chymotrypsin-like activity. Octanoic acid, a medium-chain fatty acid, did not affect proteasome activity. However, oleic and linoleic acids inhibited the chymotrypsin-like activity up to 80%, with approximate IC50s of 80 and 40 micromol/L, respectively. Insulin also inhibited but was not additive with the FFA, suggesting that they work through the same mechanism. These results show that the proteasome can be inhibited by FFA in whole cells and suggest that insulin-degrading enzyme may mediate this effect. This mechanism may be applicable to whole animals and represents a means to integrate hormonal and nutrient signals on the control of protein degradation.
Insights
Free fatty acids (FFA) inhibit proteasome activity in whole cells, potentially through insulin-degrading enzyme. This finding offers insights into how nutrient signals regulate protein degradation in animals.
Area of Science:
- Biochemistry
- Cell Biology
- Molecular Biology
Background:
- Animal studies suggest free fatty acids (FFA) reduce protein degradation.
- The precise mechanism underlying FFA's effect on protein degradation remains unclear.
- Previous in vitro research indicated FFA may inhibit proteasome activity via insulin-degrading enzyme.
Purpose of the Study:
- To investigate whether free fatty acids (FFA) can inhibit proteasome activity in whole cells.
- To explore the potential role of insulin-degrading enzyme in mediating this effect.
- To understand how nutrient and hormonal signals integrate to control protein degradation.
Main Methods:
- HepG2 cells were treated with various free fatty acids (FFA).
- Proteasome activity was assessed using a cell-permeable substrate for chymotrypsin-like activity.
- Dose-response experiments were conducted to determine IC50 values and assess additivity with insulin.
Main Results:
- Oleic and linoleic acids significantly inhibited chymotrypsin-like proteasome activity in HepG2 cells (up to 80%).
- The IC50 values for oleic and linoleic acids were approximately 80 and 40 micromol/L, respectively.
- Insulin also inhibited proteasome activity, and its effect was not additive with FFA, suggesting a shared mechanism.
Conclusions:
- Free fatty acids (FFA) can inhibit proteasome activity within whole cells.
- Insulin-degrading enzyme is a likely mediator of FFA-induced proteasome inhibition.
- This mechanism provides a link between nutrient availability and hormonal regulation of protein breakdown, potentially applicable in vivo.
