Haddish Kiros, Yun Jong Won
Department of Biotechnology, Daegu University, Gyeongsan, Gyeongbuk, 38453, Republic of Korea.
Pflugers Arch. 2023 Jun;475(6):757-773. doi: 10.1007/s00424-023-02816-w. Epub 2023 Apr 27.
The activation of beige fat and muscle tissues is an interesting and encouraging target for therapeutic intervention in obesity owing to their remarkable lipolytic activity and energy-consuming futile cycles. This study examined the effect of dopamine receptor D4 (DRD4) on lipid metabolisms as well as UCP1- and ATP-dependent thermogenesis in Drd4-silenced 3T3-L1 adipocytes and C2C12 muscle cells. Silencing of Drd4, followed by quantitative real-time PCR, immunoblot analysis, immunofluorescence, and staining methods, were applied to evaluate the effects of DRD4 on diverse target genes and proteins of both cells. The findings showed that DRD4 was expressed in the adipose and muscle tissues of normal and obese mice. Furthermore, the knockdown of Drd4 upregulated the expression of brown adipocyte-specific genes and proteins while downregulating lipogenesis and the adipogenesis marker proteins. Drd4 silencing also upregulated the expression of key signaling molecules involved in ATP-dependent thermogenesis in both cells. This was further elucidated by mechanistic studies showing that a Drd4 knockdown mediates UCP1-dependent thermogenesis via the cAMP/PKA/p38MAPK pathway in 3T3-L1 adipocytes and UCP1-independent thermogenesis via the cAMP/SLN/SERCA2a pathway in C2C12 muscle cells. In addition, siDrd4 also mediates myogenesis via the cAMP/PKA/ERK1/2/Cyclin D3 pathway in C2C12 muscle cells. Silencing of Drd4 promotes β3-AR-dependent browning in 3T3-L1 adipocytes and α1-AR/SERCA-based thermogenesis through an ATP-consuming futile process in C2C12 muscle cells. Understanding the novel functions of DRD4 on adipose and muscle tissues in terms of its ability to enhance energy expenditure and regulate whole-body energy metabolism will aid in developing novel obesity intervention techniques.
由于米色脂肪和肌肉组织具有显著的脂肪分解活性和耗能的无效循环，激活它们是肥胖治疗干预中一个有趣且令人鼓舞的靶点。本研究检测了多巴胺受体D4（DRD4）对Drd4基因沉默的3T3-L1脂肪细胞和C2C12肌肉细胞脂质代谢以及UCP1依赖和ATP依赖的产热的影响。采用Drd4基因沉默，随后通过定量实时PCR、免疫印迹分析、免疫荧光和染色方法，评估DRD4对两种细胞不同靶基因和蛋白质的影响。研究结果表明，DRD4在正常和肥胖小鼠的脂肪组织和肌肉组织中均有表达。此外，Drd4基因敲低上调了棕色脂肪细胞特异性基因和蛋白质的表达，同时下调了脂肪生成和脂肪生成标记蛋白。Drd4基因沉默还上调了两种细胞中参与ATP依赖产热的关键信号分子的表达。机制研究进一步阐明，Drd4基因敲低在3T3-L1脂肪细胞中通过cAMP/PKA/p38MAPK途径介导UCP1依赖的产热，在C2C12肌肉细胞中通过cAMP/SLN/SERCA2a途径介导非UCP1依赖的产热。此外，siDrd4在C2C12肌肉细胞中还通过cAMP/PKA/ERK1/2/细胞周期蛋白D3途径介导肌生成。Drd4基因沉默通过一个耗能的无效过程促进3T3-L1脂肪细胞中β3-AR依赖的褐变以及C2C12肌肉细胞中α1-AR/ SERCA依赖的产热。了解DRD4在脂肪组织和肌肉组织中的新功能，即其增强能量消耗和调节全身能量代谢的能力，将有助于开发新的肥胖干预技术。
