Abstract
Metabolic syndrome and type 2 diabetes mellitus are associated with an increased number of macrophage cells that infiltrate white adipose tissue (WAT). Previously, we demonstrated that the treatment of subjects with impaired glucose tolerance (IGT) with the peroxisome proliferator-activated receptor gamma (PPARgamma) agonist pioglitazone resulted in a decrease in macrophage number in adipose tissue. Here, adipose tissue samples from IGT subjects treated with pioglitazone were examined for apoptosis with terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) staining. TUNEL-positive cells were identified, and there was a significant 42% increase in TUNEL-positive cells following pioglitazone treatment. Overlay experiments with anti-CD68 antibody demonstrated that most of the TUNEL-positive cells were macrophages. To determine whether macrophage apoptosis was a direct or indirect effect of pioglitazone treatment, human THP1 cells were treated with pioglitazone in vitro, demonstrating increased TUNEL staining in a dose- and time-dependent manner. Furthermore, the appearance of the active proteolytic subunits of caspase-3 and caspase-9 were detected in cell lysate from THP1 cells and also increased in a dose- and time-dependent manner following pioglitazone treatment. Pretreatment with a PPARgamma inhibitor, GW9662, prevented pioglitazone induction of the apoptotic pathway in THP1 cells. Differentiated human adipocytes did not show any significant increase in apoptosis after treatment in vitro with piolgitazone. These findings indicate that PPARgamma has distinct functions in different cell types in WAT, such that pioglitazone reduces macrophage infiltration by inducing apoptotic cell death specifically in macrophages through PPARgamma activation.
Highlights
Metabolic syndrome and type 2 diabetes mellitus are associated with an increased number of macrophage cells that infiltrate white adipose tissue (WAT)
To further understand the mechanisms leading to this decrease in macrophage number, double staining of human subcutaneous adipose tissue was performed to examine cells staining for CD68 in conjunction with transferase-mediated dUTP-biotin nick end labeling (TUNEL)-positive cells
Recent studies have indicated that much of the TNFa and IL-6 secreted by adipose tissue is derived from the macrophage fraction [2], and monocyte chemoattractant protein-1 (MCP-1) is expressed by both macrophages and adipocytes [4]
Summary
Metabolic syndrome and type 2 diabetes mellitus are associated with an increased number of macrophage cells that infiltrate white adipose tissue (WAT). TUNEL-positive cells were identified, and there was a significant 42% increase in TUNELpositive cells following pioglitazone treatment. To determine whether macrophage apoptosis was a direct or indirect effect of pioglitazone treatment, human THP1 cells were treated with pioglitazone in vitro, demonstrating increased TUNEL staining in a dose- and time-dependent manner. Differentiated human adipocytes did not show any significant increase in apoptosis after treatment in vitro with piolgitazone. These findings indicate that PPARg has distinct functions in different cell types in WAT, such that pioglitazone reduces macrophage infiltration by inducing apoptotic cell death in macrophages through PPARg activation.— Bodles, A.
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