NG ,NG -Dimethylarginine Dimethylaminohydrolase 1 Expression Is Dispensable for Cold- or Diet-Induced Thermogenesis.

The strategy to activate thermogenic adipocytes has therapeutic potential to overcome obesity as they dissipate surplus energy as heat through various mechanisms. NG,NG-dimethylarginine dimethylaminohydrolases (DDAHs) are enzymes involved in the nitric oxide-protein kinase G signaling axis which increases thermogenic gene expression. However, the role of DDAHs in thermogenic adipocytes has not been elucidated. The adipocyte-specific Ddah1 knockout mice are generated by crossing Ddah1fl/fl mice with adiponectin Cre recombinase mice. Adipocyte-specific DDAH1 overexpressing mice are generated using adeno-associated virus-double-floxed inverse open reading frame (AAV-DIO) system. These mice are analyzed under basal, cold exposure, or high-fat diet (HFD) conditions. Primary inguinal white adipose tissue cells from adipocyte-specific Ddah1 knockout mice expressed comparable amounts of Ucp1 mRNA. Adipocyte-specific DDAH1 overexpressing mice do not exhibit enhanced activation of thermogenic adipocytes. In addition, when these mice are exposed to cold environment or fed an HFD, their body temperature/weight and thermogenesis-related gene and protein expressions are unchanged. These findings indicate that DDAH1 does not play a role in either cold- or diet-induced thermogenesis. Therefore, adipocyte targeting DDAH1 gene therapy for the treatment of obesity is unlikely to be effective.

AAV-mediated skeletal muscle specific irisin expression does not contribute to weight loss in mice.

Obesity, a chronic disease, significantly increases the risk of various diseases, including diabetes, cardiovascular diseases, and cancers. Exercise is crucial for weight management not only through energy expenditure by muscle activity but also through stimulating the secretion of myokines, which affect various tissues. Irisin, derived from the proteolytic processing of fibronectin type III domain-containing protein 5 (Fndc5), is a well-studied myokine with beneficial effects on metabolism. This study explored the feasibility of adeno-associated virus (AAV)-mediated Fndc5 gene therapy to treat obesity in a mouse model using the AAV-DIO system to express Fndc5 specifically in skeletal muscle, and investigated its anti-obesity effect. Although Fndc5 was specifically expressed in the muscle, no significant impact on body weight under normal chow or high-fat diets was observed, and no change in thermogenic gene expression in inguinal white adipose tissue was detected. Notably, Fndc5 transduction did affect bone metabolism, consistent with previous reports. These findings suggest that AAV-mediated Fndc5 gene therapy may not be an efficient strategy for obesity, contrary to our expectations. Further research is needed to elucidate the complex mechanisms involved in irisin's role in obesity and related disorders.