Expression Regulation And Function Of The Erythropoietin Receptor

National Institute Of Diabetes And Digestive And Kidney Diseases

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Abstract

Mice with erythropoietin receptor restricted to erythroid tissue show a disproportionate increase in fat mass, glucose intolerance and insulin resistance, with a greater degree of obesity in female mice with age. Accompanying the increased erythropoiesis with erythropoietin treatment in mice is an improvement in glucose tolerance and a decrease in blood glucose level. Erythropoietin treatment also decreases fat mass, especially evident in obese male mice and obese ovariectomized female mice. In ovariectomized female mice, estrogen protection against diet induced obesity is greater than erythropoietin treatment and erythropoietin has no added effect when administered in combination with estrogen, suggesting that estrogen blunts the protective effect of erythropoietin against diet-induced obesity in mice. In mice, high-fat diet increases fat mass, body weight and inflammation of white adipose tissue. Insulin resistance is associated with white adipose tissue inflammation and infiltration of pro-inflammatory macrophages that give rise to crown-like structures in white adipose tissue of macrophages arranged around dead adipocytes. Erythropoietin treatment in diet-induced obese mice reduces white adipose tissue inflammation, macrophage infiltration and crown-like structures, and shifts the macrophage population toward anti-inflammatory macrophages. Glycogen synthase kinase 3, a serine/threonine kinase that phosphorylates and inhibits glycogen synthase, is negatively regulated by phosphorylation at serine 9. In diet-induced obese mice, glycogen synthase kinase 3 phosphorylation is decreased in white adipose tissue, including the macrophage containing stromal-vascular fraction. Inhibition of glycogen synthase kinase 3 in obese mice suppresses white adipose tissue inflammation and macrophage infiltration with a shift toward the anti-inflammatory macrophage subtype. Reduction in inflammation and promotion of an anti-inflammatory phenotype in white adipose tissue likely contribute to the associated improvement in insulin resistance associated with erythropoietin treatment and with glycogen synthase kinase 3 inhibition in diet-induced obese mice.