Increased CGMP Promotes Healthy Expansion and Browning of White Adipose Tissue

With more than half a billion individuals affected worldwide, obesity has reached pandemic proportions. Development of "brown-like" or "brite" adipocytes within white adipose tissue (WAT) has potential antiobesity and insulin-sensitizing effects. We investigated the role of cyclic GMP (cGMP) signaling, focusing on cGMP-dependent protein kinase I (PKGI) in WAT. PKGI is expressed in murine WAT, primary adipocytes, and 3T3-L1. Treatment of adipocytes with cGMP resulted in increased adipogenesis, with a 54% increase in expression of peroxisome proliferator-activated receptor-γ. Lentiviral overexpression of PKGI further increased adipogenesis, whereas loss of PKGI significantly reduced adipogenic differentiation. In addition to adipogenic effects, PKGI had an antihypertrophic and anti-inflammatory effect via RhoA phosphorylation and reduction of proinflammatory adipokine expression. Moreover, PKGI induced a 4.3-fold increase in abundance of UCP-1 and the development of a brown-like thermogenic program in primary adipocytes. Notably, treatment of C57BL/6 mice with phosphodiesterase inhibitor sildenafil (12 mg/kg/d) for 7 d caused 4.6-fold increase in uncoupling protein-1 expression and promoted establishment of a brown fat cell-like phenotype ("browning") of WAT in vivo. Taken together, PKGI is a key regulator of cell size, adipokine secretion and browning of white fat depots and thus could be a valuable target in developing novel treatments for obesity.