Unraveling the Role of Peroxisome Proliferator-Activated Receptor β/Δ (PPAR β/Δ) in Angiogenesis Associated with Multiple Myeloma

Growing evidence suggests a role for peroxisome proliferator-activated receptor b/delta (PPAR b/delta) in the angiogenesis, growth, and metastasis of solid tumors, but little is known about its role in multiple myeloma (MM). Angiogenesis in the bone marrow (BM) is characteristic of disease transition from monoclonal gammopathy of undetermined significance (MGUS) to MM. We examined the expression and function of PPAR b/beta in endothelial cells (EC) from the BM of MGUS (MGEC) and MM (MMEC) patients and showed that PPAR b/beta was expressed at higher levels in MMEC than in MGEC and that the overexpression depended on myeloma plasma cells. The interaction between myeloma plasma cells and MMEC promoted the release of the PPAR b/d ligand prostaglandin I2 (PGI2) by MMEC, leading to the activation of PPAR b/delta. We also demonstrated that PPAR b/d was a strong stimulator of angiogenesis in vitro and that PPAR b/d inhibition by a specific antagonist greatly impaired the angiogenic functions of MMEC. These findings define PGI2-PPAR beta/delta signaling in EC as a potential target of anti-angiogenic therapy. They also sustain the use of PPAR b/d inhibitors in association with conventional drugs as a new therapeutic approach in MM.