Received for publication August 20, 2004.
Revised January 10, 2005.
Accepted for publication February 28, 2005.

Retinoids potentiate PPAR action in differentiation, gene expression and lipid metabolic processes in developing myeloid cells

Abstract

Nuclear hormone receptors have been shown to be important transcription factors for regulating lipid metabolism in myeloid cells and were also implicated in differentiation processes of the myeloid lineage and macrophages. Peroxisome Proliferator-Activated Receptor gamma (PPAR) appears to be a key component of lipid uptake by inducing the scavenger receptor CD36 that mediates oxidized low-density lipoprotein (oxLDL) uptake in macrophages. Retinoic Acid Receptors (RAR) on the other hand were also shown to play important roles in myeloid cell differentiation. Here we present evidence for a crosstalk between these two nuclear receptor pathways in myeloid cells. We show that expression level of PPAR increases with the degree of monocyte/macrophage commitment during maturation. Activation of PPAR leads to the increased expression of maturation markers (e.g. CD14, CD36). Interestingly, retinoid treatment potentiates PPAR's ability to induce transcription of its target genes. Retinoid-increased PPAR response is sufficient for enhancing lipid uptake. Our data taken together indicate that the expression level of PPAR increases during monocyte/macrophage development. PPAR activity can be enhanced by retinoids at least in part via increasing PPAR expression level. These observations can be exploited to enhance therapeutically beneficial PPAR-responses in myeloid cells.

Key words: PPARs, Regulation of gene expression, Cholesterol metabolism/lipoproteins