Inhibition of macrophage fatty acid β-oxidation exacerbates palmitate-induced inflammatory and endoplasmic reticulum stress responses.
OBJECTIVE
Saturated fatty acids (SFAs) such as palmitate activate inflammatory pathways and elicit an endoplasmic reticulum (ER) stress response in macrophages, thereby contributing to the development of insulin resistance linked to the metabolic syndrome. This study addressed the question of whether or not mitochondrial fatty acid β-oxidation (FAO) affects macrophage responses to SFA.


METHODS
We modulated the activity of carnitine palmitoyl transferase 1A (CPT1A) in macrophage-differentiated THP-1 monocytic cells using genetic or pharmacological approaches, treated the cells with palmitate and analysed the proinflammatory and ER stress signatures.


RESULTS
To inhibit FAO, we created THP-1 cells with a stable knockdown (KD) of CPT1A and differentiated them to macrophages. Consequently, in CPT1A-silenced cells FAO was reduced. CPT1A KD in THP-1 macrophages increased proinflammatory signalling, cytokine expression and ER stress responses after palmitate treatment. In addition, in human primary macrophages CPT1A KD elevated palmitate-induced inflammatory gene expression. Pharmacological inhibition of FAO with etomoxir recapitulated the CPT1A KD phenotype. Conversely, overexpression of a malonyl-CoA-insensitive CPT1A M593S mutant reduced inflammatory and ER stress responses to palmitate in THP-1 macrophages. Macrophages with a CPT1A KD accumulated diacylglycerols and triacylglycerols after palmitate treatment, while ceramide accumulation remained unaltered. Moreover, lipidomic analysis of ER phospholipids revealed increased palmitate incorporation into phosphatidylethanolamine and phosphatidylserine classes associated with the CPT1A KD.


CONCLUSIONS
Our data indicate that FAO attenuates inflammatory and ER stress responses in SFA-exposed macrophages, suggesting an anti-inflammatory impact of drugs that activate FAO.
Faculty of Medicine, Institute of Biochemistry I/ZAFES, Goethe University Frankfurt, Theodor-Stern-Kai 7, 60590, Frankfurt, Germany.
Dmitry
D
Namgaladze
Sebastian
S
Lips
Thomas J
TJ
Leiker
Robert C
RC
Murphy
Kim
K
Ekroos
Nerea
N
Ferreiros
Gerd
G
Geisslinger
Bernhard
B
Brüne
D002334:Carnitine O-Palmitoyltransferase / Q000378:metabolism; D045744:Cell Line, Tumor; D004075:Diglycerides / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D059865:Endoplasmic Reticulum Stress; D005227:Fatty Acids / Q000378:metabolism*; D006801:Humans; D007249:Inflammation; D007333:Insulin Resistance; D008264:Macrophages / Q000378:metabolism*; D021962:Membrane Microdomains; D024821:Metabolic Syndrome / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*; D010168:Palmitates / Q000378:metabolism*; D014280:Triglycerides / Q000378:metabolism
D004075:Diglycerides; D005227:Fatty Acids; D010168:Palmitates; D014280:Triglycerides; C577474:CPT1A protein, human; D002334:Carnitine O-Palmitoyltransferase; D010100:Oxygen