Mobilization efficiency is critically regulated by fat via marrow PPARδ

The efficiency of mobilization of hematopoietic stem/progenitor cells from bone marrow into the circulation by granulocyte colony-stimulating factor (G-CSF) is extremely varied in humans and mice and a mechanistic explanation for poor mobilizers is lacking. A mechanism of regulating mobilization efficiency by dietary fat was assessed in mice. Compared to a normal diet, a fat-free diet for 2 weeks greatly increased mobilization. The bone marrow mRNA level of peroxisome proliferatoractivated receptorδ (PPARδ), a receptor for lipid mediators, was markedly upregulated by G-CSF in mice fed a normal diet and displayed a strong positive correlation with widely varied mobilization efficiency. It was hypothesized that the bone marrow fat ligand for PPARδ might inhibit mobilization. A PPARδ agonist inhibited mobilization in mice fed a normal diet and enhanced mobilization by a fat-free diet. Mice treated with a PPARδ antagonist and chimeric mice with PPARδ+/- bone marrow showed enhanced mobilization. Immunohistochemical staining and flow cytometry revealed that bone marrow PPARδ expression was enhanced by G-CSF mainly in mature/immature neutrophils. Analysis of bone marrow lipid mediators revealed that G-CSF treatment and a fat-free diet resulted in exhaustion of ω3-polyunsaturated fatty acids such as eicosapentaenoic acid. Eicosapentaenoic acid induced the upregulation of genes downstream of PPARδ, such as Cpt1α and Angptl4, in mature/immature neutrophils in vitro and inhibited enhanced mobilization in mice fed with a fatfree diet in vivo. Treatment of wild-type mice with anti-Angptl4 antibody enhanced mobilization as well as bone marrow vascular permeability. Collectively, PPARδ signaling in mature/immature bone marrow neutrophils induced by dietary fatty acids negatively regulates mobilization, at least partially, via Angptl4 production.