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Mouse macrophage paraoxonase 2 activity is increased whereas cellular paraoxonase 3 activity is decreased under
Mira Rosenblat1, Dragomir Draganov, Catherine E Watson
1The Lipid Research Laboratory, Technion Faculty of Medicine, The Rappaport Family Institute for Research in the Medical Sciences and Rambam Medical Center, Haifa, Israel.
Objective:
To determine whether paraoxonases (PONs) are expressed in macrophages and to analyze the oxidative stress effect on their expression and activities.
Methods And Results:
We demonstrated the presence (mRNA, protein, activity) of PON2 and PON3 but not PON1 in murine macrophages, whereas in human macrophages, only PON2 was expressed. Under oxidative stress as present in mouse peritoneal macrophages (MPMs) from apoE-deficient (E0) mice as well as in C57BL6 mice, MPMs that were incubated with buthionine sulfoximine, with angiotensin II, with 7-ketocholesterol, or with oxidized phosphatidylcholine, PON2 mRNA levels and lactonase activity toward dihydrocoumarin significantly increased (by 50% to 130%). In contrast, PON3 lactonase activity toward lovastatin was markedly reduced (by 29% to 57%) compared with control cells. The supplementation of E0 mice with dietary antioxidants (vitamin E, pomegranate juice) significantly increased macrophage PON3 activity (by 23% to 40%), suggesting that oxidative stress was the cause for the reduced macrophage PON3 activity. Incubation of purified PON2 or PON3 with E0 mice MPMs resulted in reduced cellular lipid peroxides content by 14% to 19% and inhibition of cell-mediated LDL oxidation by 32% to 39%.
Conclusions:
Increased macrophage PON2 expression under oxidative stress could represent a selective cellular response to reduce oxidative burden, which may lead to attenuation of macrophage foam cell formation.
Insights
Paraoxonases (PONs) like PON2 are found in macrophages. Oxidative stress increases PON2 but decreases PON3 activity, suggesting a cellular defense against oxidative damage and foam cell formation.
Area of Science:
- Biochemistry
- Immunology
- Oxidative Stress Research
Background:
- Paraoxonases (PONs) are enzymes involved in protecting against oxidative stress.
- Macrophages play a critical role in immune responses and are susceptible to oxidative damage.
- Understanding PON expression in macrophages is crucial for investigating cellular defense mechanisms.
Purpose of the Study:
- To investigate the expression of paraoxonases (PONs) in macrophages.
- To determine the impact of oxidative stress on PON expression and activity within macrophages.
Main Methods:
- Demonstration of PON2 and PON3 mRNA, protein, and activity in murine macrophages.
- Analysis of PON expression and activity in human macrophages.
- Exposure of macrophages to various oxidative stressors (e.g., buthionine sulfoximine, angiotensin II, 7-ketocholesterol, oxidized phosphatidylcholine).
- Assessment of antioxidant supplementation effects in vivo.
Main Results:
- PON2 and PON3 were expressed in murine macrophages; only PON2 in human macrophages.
- Oxidative stress significantly increased PON2 mRNA and activity, while reducing PON3 activity.
- Dietary antioxidants reversed the reduction in macrophage PON3 activity.
- PON2 and PON3 reduced cellular lipid peroxides and inhibited LDL oxidation by macrophages.
Conclusions:
- Macrophage PON2 expression increases under oxidative stress, potentially as a protective mechanism.
- This PON2 upregulation may help reduce oxidative burden and attenuate macrophage foam cell formation.
- PON3 activity is sensitive to oxidative stress, but can be restored by antioxidants.