Although peroxisome proliferator-activated receptor gamma (PPAR␥) agonists such as thiazolidinediones (TZDs) are widely used to treat type 2 diabetes, how its activation in individual tissues contributes to TZD's therapeutic action remains controversial. As TZDs are known to have receptor-independent effects, we sought to establish gain-offunction animal models to delineate the receptor's insulin-sensitizing actions. Unexpectedly, we find that selective activation of PPAR␥ in adipocytes, but not in macrophages, is sufficient for whole-body insulin sensitization equivalent to systemic TZD treatment. In addition to improved adipokine, inflammatory, and lipid profiles, PPAR␥ activation in mature adipocytes normalizes serum insulin without increased adipogenesis. Co-culture studies indicated that PPAR␥-activated adipocytes broadly suppress induction of inflammatory cytokines and C-X-C family chemokines in macrophages. Collectively, these data describe an ''adipocentric'' model in which adipose activation of PPAR␥ is sufficient for complete insulin sensitization and suggest a specific application for fat selective PPAR␥ modulators in diabetic therapy.inflammation ͉ insulin signaling ͉ metabolic syndrome ͉ nuclear hormone receptors

Cellular and tissue defects associated with insulin resistance are coincident with transcriptional abnormalities and are improved after insulin sensitization with thiazolidinedione (TZD) PPAR␥ ligands. We characterized 72 human subjects by relating their clinical phenotypes with functional pathway alterations. We transcriptionally profiled 364 biopsies harvested before and after hyperinsulinemic-euglycemic clamp studies, at baseline and after 3-month TZD treatment. We have identified molecular and functional characteristics of insulin resistant subjects and distinctions between TZD treatment responder and nonresponder subjects. Insulin resistant subjects exhibited alterations in skeletal muscle (e.g., glycolytic flux and intramuscular adipocytes) and adipose tissue (e.g., mitochondrial metabolism and inflammation) that improved relative to TZD-induced insulin sensitization. Pre-TZD treatment expression of MLXIP in muscle and HLA-DRB1 in adipose tissue from insulin resistant subjects was linearly predictive of post-TZD insulin sensitization. We have uniquely characterized coordinated cellular and tissue functional pathways that are characteristic of insulin resistance, TZD-induced insulin sensitization, and potential TZD responsiveness. muscle and adipose tissue ͉ transcriptional mechanisms ͉ diabetes ͉ branched chain amino acid (BCAA) ͉ inflammation I nsulin resistance is a pathological state in which insulin action is impaired in target tissues including liver, skeletal muscle, and adipose tissue. Insulin resistance is a defining feature of the metabolic syndrome and the primary defect leading to type 2 diabetes (1, 2). Impaired insulin-stimulated glucose uptake in skeletal muscle and lipid metabolism in adipocytes are central characteristics of insulin-resistance. Other manifestations of the condition include elevated intramuscular fat content (3), dysregulation of adipokine secretion, and chronic lowgrade inflammation in adipose tissue (4). Macrophage infiltration in adipose tissue activates inflammatory pathways that induce insulin resistance and modulate the effects of adipose tissue on whole-body metabolism (5). Several studies have shown that decreased mitochondrial protein and oxidative phosphorylation (OXPHOS) in skeletal muscle and adipocytes are also underlying factors of insulin resistance (6, 7).Thiazolidinediones (TZDs) are insulin-sensitizing drugs used to treat type 2 diabetes. TZDs enhance insulin sensitivity by improving glucose and lipid metabolism, altering adipokine secretion, and reducing adipose tissue inflammation (4, 8). Although TZDs improve insulin sensitivity and the glycemic, lipid, and inflammatory profiles of most patients, approximately 30% of diabetic subjects do not respond to TZD treatment, as gauged by fasting plasma glucose or HbA1c levels (9, 10). TZDs are ligands of peroxisome proliferator-activated receptor gamma (PPAR␥) through which they alter the expression of hundreds of genes in skeletal muscle, adipocytes, and macrophages. PPAR␥-mediated gene regulation is the predom...

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer death worldwide, with approximately 70% of cases resulting from hepatitis B and C viral infections, aflatoxin exposure, chronic alcohol use or genetic liver diseases. The remaining approximately 30% of cases are associated with obesity, type 2 diabetes and related metabolic diseases, although a direct link between these pathologies and HCCs has not been established. We tested the long-term effects of high-fat and low-fat diets on males of two inbred strains of mice and discovered that C57BL/6J but not A/J males were susceptible to non-alcoholic steatohepatitis (NASH) and HCC on a high-fat but not low-fat diet. This strain-diet interaction represents an important model for genetically controlled, diet-induced HCC. Susceptible mice showed morphological characteristics of NASH (steatosis, hepatitis, fibrosis and cirrhosis), dysplasia and HCC. mRNA profiles of HCCs versus tumor-free liver showed involvement of two signaling networks, one centered on Myc and the other on NFkappaB, similar to signaling described for the two major classes of HCC in humans. miRNA profiles revealed dramatically increased expression of a cluster of miRNAs on the X chromosome without amplification of the chromosomal segment. A switch from high-fat to low-fat diet reversed these outcomes, with switched C57BL/6J males being lean rather than obese and without evidence for NASH or HCCs at the end of the study. A similar diet modification may have important implications for prevention of HCCs in humans.

Tumor-associated macrophages are known to influence cancer progression by modulation of immune function, angiogenesis, and cell metastasis, however, little is known about the chemokine signaling networks that regulate this process. Utilizing CT26 colon cancer cells and RAW 264.7 macrophages as a model cellular system, we demonstrate that treatment of CT26 cells with RAW 264.7 conditioned medium induces cell migration, invasion and metastasis. Inflammatory gene microarray analysis indicated CT26-stimulated RAW 264.7 macrophages upregulate SDF-1α and VEGF, and that these cytokines contribute to CT26 migration in vitro. RAW 264.7 macrophages also showed a robust chemotactic response towards CT26-derived chemokines. In particular, microarray analysis and functional testing revealed CSF-1 as the major chemoattractant for RAW 264.7 macrophages. Interestingly, in the chick CAM model of cancer progression, RAW 264.7 macrophages localized specifically to the tumor periphery where they were found to increase CT26 tumor growth, microvascular density, vascular disruption, and lung metastasis, suggesting these cells home to actively invading areas of the tumor, but not the hypoxic core of the tumor mass. In support of these findings, hypoxic conditions down regulated CSF-1 production in several tumor cell lines and decreased RAW 264.7 macrophage migration in vitro. Together our findings suggest a model where normoxic tumor cells release CSF-1 to recruit macrophages to the tumor periphery where they secrete motility and angiogenic factors that facilitate tumor cell invasion and metastasis.

Subramaniam S, Sears DD. Multi-tissue, selective PPAR␥ modulation of insulin sensitivity and metabolic pathways in obese rats. Am