ALOX15B controls macrophage cholesterol homeostasis via lipid peroxidation, ERK1/2 and SREBP2

Authors: BENATZY, YVONNE - Goethe University; PALMER, MEGAN - Goethe University; KANDLER, JOSHUA - Goethe University; LUTJOHANN, DIETER - University Of Bonn; ANGIONI, CARLO - University Of Bonn; BOJKOVA, DENISA - Goethe University; FUHRMANN, DOMINIK - Goethe University; THOMAS, DOMINIQUE - Goethe University; Snodgrass, Ryan; BRUNE, BERNHARD - Goethe University

Submitted to: Nature Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/2024
Publication Date: 4/3/2024
Citation: Benatzy, Y., Palmer, M.A., Kandler, J.D., Lutjohann, D., Angioni, C., Bojkova, D., Fuhrmann, D.C., Thomas, D., Snodgrass, R.G., Brune, B. 2024. ALOX15B controls macrophage cholesterol homeostasis via lipid peroxidation, ERK1/2 and SREBP2. Nature Communications. 72/103149. https://doi.org/10.1016/j.redox.2024.103149.
DOI: https://doi.org/10.1016/j.redox.2024.103149

Interpretive Summary: Lipoxygenases are a family of six iron-containing enzymes that help add an oxygen molecule to poly-unsaturated fatty acids to produce fatty acid hydroperoxides. While the role of most lipoxygenases are well understood, the biological function of arachidonate 15-lipoxygenase type B (ALOX15B) has not yet been characterized. Here, we show that suppressing ALOX15B expression in primary human macrophages reduces sterol regulatory element-binding protein 2 (SREBP2) protein. SREBP2 is the major transcription factor involved in endogenous cholesterol biosynthesis which is an essential component of mammalian cell membranes and serves as a precursor for oxysterols, bile acids, and steroid hormones. In line with its role as a transcriptional regulator, global transcriptome analysis revealed extensive reductions in SREBP2-dependent gene expression without alterations in the expression of liver X receptor target genes which also regulate cellular cholesterol homeostasis. Although sterol intermediates, including Desmosterol and Lathosterol, and oxysterols 25- and 27-hydroxycholesterol were reduced in ALOX15B-silenced macrophages, total cellular cholesterol levels remained unchanged. Subcellular analysis indicated altered cholesterol distribution in ALOX15B-attenuated macrophages with increased endoplasmic reticulum cholesterol and decreased plasma membrane cholesterol. Additionally, ALOX15B-silenced macrophages were refractory to SREBP2 activation following cellular cholesterol depletion. Given the significance of cellular cholesterol in the viral lifecycle, we also performed infections with Middle East respiratory syndrome coronavirus and human coronavirus 229E and found ALOX15B-silenced macrophages contained reduced viral loads compared to control macrophages. Collectively, our results indicate a role for ALOX15B in cholesterol homeostasis and antiviral immunity.

Technical Abstract: Cellular cholesterol biosynthesis is regulated by sterol regulatory element-binding protein 2 (SREBP2). Here, we show that knockdown (KD) of the lipid-peroxidizing enzyme ALOX15B in primary human macrophages reduces nuclear and cytosolic SREBP2 protein. In line with its function as a master transcriptional regulator, global transcriptome analysis revealed extensive reductions in SREBP2-dependent gene expression without coordinate increases in liver X receptor target gene expression. Although sterol intermediates and oxysterols were reduced in ALOX15B KD macrophages, total cellular cholesterol levels remained unchanged. Subcellular analysis indicated altered cholesterol distribution in ALOX15B KD macrophages with increased ER cholesterol and decreased plasma membrane cholesterol. Additionally, ALOX15B KD macrophages were refractory to cholesterol depletion-induced SREBP2 activation. Given the significance of cellular cholesterol in the viral lifecycle, we performed infections with Middle East respiratory syndrome coronavirus and human coronavirus 229E and found ALOX15B KD macrophages contained reduced viral loads compared to control macrophages. Collectively, our results indicate a role for ALOX15B in cholesterol homeostasis and antiviral immunity.