Pioglitazone suppresses macrophage proliferation in apolipoprotein-E deficient mice by activating PPARγ

Local macrophage proliferation is linked to enhanced atherosclerosis progression. Our previous study found that troglitazone, a thiazolidinedione (TZD), suppressed oxidized low-density lipoprotein (Ox-LDL)-induced macrophage proliferation. However, its effects and mechanisms are unclear. Therefore, we investigated the effects of pioglitazone, another TZD, on macrophage proliferation.

Normal chow (NC)- or high-fat diet (HFD)-fed apolipoprotein E-deficient (Apoe^-/-) mice were treated orally with pioglitazone (10 mg/kg/day) or vehicle (water) as a control. Mouse peritoneal macrophages were used in in vitro assays.

Atherosclerosis progression was suppressed in aortic sinuses of pioglitazone-treated Apoe^-/- mice, which showed fewer proliferating macrophages in plaques. Pioglitazone suppressed Ox-LDL-induced macrophage proliferation in a dose-dependent manner. However, treatment with peroxisome proliferator-activated receptor-γ (PPARγ) siRNA ameliorated pioglitazone-induced suppression of macrophage proliferation. Low concentrations (less than 100 μmol/L) of pioglitazone, which can suppress macrophage proliferation, activated PPARγ in macrophages, but did not induce macrophage apoptosis. Pioglitazone treatment did not induce TUNEL-positive cells in atherosclerotic plaques of aortic sinuses in Apoe^-/- mice.

Pioglitazone suppressed macrophage proliferation through PPARγ without inducing macrophage apoptosis. These findings imply that pioglitazone could prevent macrovascular complications in diabetic individuals.