Thrombospondin1 Deficiency Reduces Obesity-Associated Inflammation and Improves Insulin Sensitivity in a Diet-Induced Obese Mouse Model

BACKGROUND: Obesity is prevalent worldwide and is associated with insulin resistance. Advanced studies suggest that obesity-associated low-grade chronic inflammation contributes to the development of insulin resistance and other metabolic complications. Thrombospondin 1 (TSP1) is a multifunctional extracellular matrix protein that is up-regulated in inflamed adipose tissue. A recent study suggests a positive correlation of TSP1 with obesity, adipose inflammation, and insulin resistance. However, the direct effect of TSP1 on obesity and insulin resistance is not known. Therefore, we investigated the role of TSP1 in mediating obesity-associated inflammation and insulin resistance by using TSP1 knockout mice. METHODOLOGY/PRINCIPAL FINDINGS: Male TSP1-/- mice and wild type littermate controls were fed a low-fat (LF) or a high-fat (HF) diet for 16 weeks. Throughout the study, body weight and fat mass increased similarly between the TSP1-/- mice and WT mice under HF feeding conditions, suggesting that TSP1 deficiency does not affect the development of obesity. However, obese TSP1-/- mice had improved glucose tolerance and increased insulin sensitivity compared to the obese wild type mice. Macrophage accumulation and inflammatory cytokine expression in adipose tissue were reduced in obese TSP1-/- mice. Consistent with the local decrease in pro-inflammatory cytokine levels, systemic inflammation was also decreased in the obese TSP1-/- mice. Furthermore, in vitro data demonstrated that TSP1 deficient macrophages had decreased mobility and a reduced inflammatory phenotype. CONCLUSION: TSP1 deficiency did not affect the development of high-fat diet induced obesity. However, TSP1 deficiency reduced macrophage accumulation in adipose tissue and protected against obesity related inflammation and insulin resistance. Our data demonstrate that TSP1 may play an important role in regulating macrophage function and mediating obesity-induced inflammation and insulin resistance. These data suggest that TSP1 may serve as a potential therapeutic target to improve the inflammatory and metabolic complications of obesity

Thrombospondin1 Deficiency Reduces Obesity-Associated Inflammation and Improves Insulin Sensitivity in a Diet-Induced Obese Mouse Model

Obesity is prevalent worldwide and is associated with insulin resistance. Advanced studies suggest that obesity-associated low-grade chronic inflammation contributes to the development of insulin resistance and other metabolic complications. Thrombospondin 1 (TSP1) is a multifunctional extracellular matrix protein that is up-regulated in inflamed adipose tissue. A recent study suggests a positive correlation of TSP1 with obesity, adipose inflammation, and insulin resistance. However, the direct effect of TSP1 on obesity and insulin resistance is not known. Therefore, we investigated the role of TSP1 in mediating obesity-associated inflammation and insulin resistance by using TSP1 knockout mice.Male TSP1-/- mice and wild type littermate controls were fed a low-fat (LF) or a high-fat (HF) diet for 16 weeks. Throughout the study, body weight and fat mass increased similarly between the TSP1-/- mice and WT mice under HF feeding conditions, suggesting that TSP1 deficiency does not affect the development of obesity. However, obese TSP1-/- mice had improved glucose tolerance and increased insulin sensitivity compared to the obese wild type mice. Macrophage accumulation and inflammatory cytokine expression in adipose tissue were reduced in obese TSP1-/- mice. Consistent with the local decrease in pro-inflammatory cytokine levels, systemic inflammation was also decreased in the obese TSP1-/- mice. Furthermore, in vitro data demonstrated that TSP1 deficient macrophages had decreased mobility and a reduced inflammatory phenotype.TSP1 deficiency did not affect the development of high-fat diet induced obesity. However, TSP1 deficiency reduced macrophage accumulation in adipose tissue and protected against obesity related inflammation and insulin resistance. Our data demonstrate that TSP1 may play an important role in regulating macrophage function and mediating obesity-induced inflammation and insulin resistance. These data suggest that TSP1 may serve as a potential therapeutic target to improve the inflammatory and metabolic complications of obesity

Metabolic regulation of insulin secretion: the link between excess glucose, mechanistic target of rapamycin complex 1 & hyperinsulinemia

Obesity, a major risk factor in the development of Type 2 Diabetes (T2D), is commonly associated with insulin resistance and hyperinsulinemia. The long accepted view has been that insulin resistance drives hyperinsulinemia; however, there are multiple lines of evidence that hyperinsulinemia can precede and drive insulin resistance. The signals and mechanisms by which chronic excess nutrients promote pancreatic β-cell dysfunction remain poorly understood. This prompted us to define the signaling events that contribute to basal insulin hypersecretion induced by excess glucose. Of particular interest is signaling through mechanistic target of rapamycin complex 1 (mTORC1), a nutrient sensitive kinase complex whose hyperactivation has been shown to promote hyperinsulinemia. Clonal ß-cells (INS-1 cells) with and without mTORC1 inhibition were pre-exposed to physiological (5mM) or excess (11mM) glucose for 4 to 24 hrs. Basal insulin secretion, respiration and metabolites were measured. Pre-exposure to excess glucose resulted in sustained mTORC1 hyperactivation, basal insulin secretion, higher basal respiration and increased maximal respiratory capacity, due to accelerated mitochondrial pyruvate metabolism. Inhibition of mTORC1 reduced basal insulin secretion, basal respiration and maximal respiratory capacity. Moreover, cells challenged with excess glucose had increased levels of glycolysis and TCA cycle intermediates. Our results suggest that hyperactivation of mTORC1 induced by excess glucose results in increased energy demand and in the generation of metabolic factors that can lead to basal insulin hypersecretion. Therefore, targeting mitochondrial pyruvate metabolism and /or mTORC1 signaling could potentially lead to specific therapies to control hyperinsulinemia and diabetes progression

MCP-1 levels in plasma and in adipose tissue from four groups of mice.

<p>(A). Plasma MCP-1 levels were measured using a mouse adipokine assay kit (from Millipore); (B). MCP-1 mRNA levels in adipose tissue from four groups of mice were determined by real-time PCR. Data ate represented as mean±SE (n = 3 mice/group).</p

Effect of TSP1 on macrophage migration and adhesion from WT and CD36 -/- mice.

<p>Peritoneal macrophages were isolated from WT or CD36 -/- mice. (A). Ability of macrophages to migrate toward purified TSP1 (5 µg/ml) was determined using modified Boyden Chamber. (B). Ability of macrophages to spread on LAB-TEK slides precoated with purified TSP1 (5 µg/ml) was determined. Data ate represented as mean±SE of three experiments.</p

Obesity-induced inflammation was reduced in adipose tissue from TSP1-/- mice.

<p>Relative mRNA expression of macrophage and inflammatory markers in epididymal fat tissue from WT or TSP1-/- mice fed a LF or HF diet was determined by real-time PCR. Data are represented as mean±SE (n = 3 mice/group). *P<0.05 vs. WT HF group. **p<0.01 vs. WT HF group.</p

Obesity induced systemic inflammation was reduced in TSP1-/- mice.

<p>Plasma IL-6, TNF-α, and PAI-1 levels were measured as described in Material and Methods section. Data are represented as mean±SE (n = 6 mice/group). *P<0.05 vs. WT HF group.</p

Sequences of primers used in the study.

<p>Sequences of primers used in the study.</p

TSP1 deficiency had no effect on obesity development in a high fat diet induced obese mouse model.

<p>Male TSP1-/- mice and wild type littermate controls were fed LF or HF diet for 16 weeks. <b>A):</b> Graphs showing the increase of body weight over time on diets. <b>B):</b> Fat and lean mass of different groups of animals. Data are represented as mean±SE (n = 10 mice/group).</p