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AMPK-Activated Protein Kinase Suppresses Ccr2 Expression by Inhibiting the NF-κB Pathway in RAW264.7 Macrophages
Fumiaki Kumase1, Kimio Takeuchi1, Yuki Morizane1,2
1Retina Service, Angiogenesis Laboratory, Massachusetts Eye and Ear Infirmary, Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts, United States of America.
Abstract:
C-C chemokine receptor 2 (Ccr2) is a key pro-inflammatory marker of classic (M1) macrophage activation. Although Ccr2 is known to be expressed both constitutively and inductively, the full regulatory mechanism of its expression remains unclear. AMP-activated protein kinase (AMPK) is not only a master regulator of energy homeostasis but also a central regulator of inflammation. In this study, we sought to assess AMPK's role in regulating RAW264.7 macrophage Ccr2 protein levels in resting (M0) or LPS-induced M1 states. In both M0 and M1 RAW264.7 macrophages, knockdown of the AMPKα1 subunit by siRNA led to increased Ccr2 levels whereas pharmacologic (A769662) activation of AMPK, attenuated LPS-induced increases in Ccr2 expression in an AMPK dependent fashion. The increases in Ccr2 levels by AMPK downregulation were partially reversed by NF-κB inhibition whereas TNF-a inhibition had minimal effects. Our results indicate that AMPK is a negative regulator of Ccr2 expression in RAW264.7 macrophages, and that the mechanism of action of AMPK inhibition of Ccr2 is mediated, in part, through the NF-κB pathway.
Insights
AMP-activated protein kinase (AMPK) negatively regulates C-C chemokine receptor 2 (Ccr2) expression in macrophages. AMPK activation reduces Ccr2 levels, partly via the NF-κB pathway, impacting inflammation.
Area of Science:
- Cellular and Molecular Immunology
- Macrophage Biology
- Inflammation Research
Background:
- C-C chemokine receptor 2 (Ccr2) is a critical marker for pro-inflammatory M1 macrophage activation.
- The precise regulatory mechanisms governing Ccr2 expression are not fully understood.
- AMP-activated protein kinase (AMPK) plays a significant role in both energy homeostasis and inflammation.
Purpose of the Study:
- To investigate the role of AMPK in regulating Ccr2 protein levels in RAW264.7 macrophages.
- To determine AMPK's influence on Ccr2 expression in both resting (M0) and LPS-induced M1 states.
Main Methods:
- Utilized siRNA to knockdown the AMPKα1 subunit in RAW264.7 macrophages.
- Employed pharmacologic AMPK activation using A769662.
- Assessed Ccr2 protein levels in M0 and M1 macrophages under various conditions.
- Investigated the involvement of NF-κB and TNF-α pathways.
Main Results:
- Knockdown of AMPKα1 increased Ccr2 levels in both M0 and M1 macrophages.
- Pharmacologic activation of AMPK attenuated LPS-induced increases in Ccr2 expression.
- AMPK downregulation's effect on Ccr2 was partially reversed by NF-κB inhibition.
- TNF-α inhibition showed minimal impact on Ccr2 levels.
Conclusions:
- AMPK acts as a negative regulator of Ccr2 expression in RAW264.7 macrophages.
- AMPK's inhibitory effect on Ccr2 is, in part, mediated through the NF-κB pathway.
- These findings elucidate a novel regulatory mechanism for Ccr2 in macrophage activation.
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