BMP4 gene therapy enhances insulin sensitivity but not adipose tissue browning in obese mice

Jenny M. Hoffmann, John R. Grünberg, Ann Hammarstedt, Tobias Kroon, Thomas U. Greiner, Stefanie Maurer, Ivet Elias, Vilborg Palsdottir, Fatima Bosch, Jeremie Boucher, Shahram Hedjazifar, Ulf Smith

One of the early and central events in white adipocyte commitment is the action of bone morphogenetic protein 4 (BMP4). Overexpression or gene therapy with BMP4 can protect from obesity. Hoffmann and colleagues tested whether BMP4 gene therapy can also be used to treat already established obesity. Their results show that obesity is not reduced but that BMP4 improves whole-body insulin sensitivity, enhances insulin signaling in all key metabolic tissues, and reduces key gluconeogenic enzymes in the liver despite no weight loss.

Objective: Bone morphogenetic protein 4 (BMP4) adeno-associated viral vectors of serotype 8 (AAV8) gene therapy targeting the liver prevents the development of obesity in initially lean mice by browning the large subcutaneous white adipose tissue (WAT) and enhancing energy expenditure. Here, we examine whether this approach could also reduce established obesity.

Methods: Dietary-induced obese C57BL6/N mice received AAV8 BMP4 gene therapy at 17–18 weeks of age. They were kept on a high-fat diet and phenotypically characterized for an additional 10–12 weeks. Following termination, the mice underwent additional characterization in vitro.

Results: Surprisingly, we observed no effect on body weight, browning of WAT, or energy expenditure in these obese mice, but whole-body insulin sensitivity and glucose tolerance were robustly improved. Insulin signaling and insulin-stimulated glucose uptake were increased in both adipose cells and skeletal muscle. BMP4 also decreased hepatic glucose production and reduced gluconeogenic enzymes in the liver, but not in the kidney, in addition to enhancing insulin action in the liver.

Conclusions: Our findings show that BMP4 prevents, but does not reverse, established obesity in adult mice, while it improves insulin sensitivity independent of weight reduction. The BMP antagonist Noggin was increased in WAT in obesity, which may account for the lack of browning.