White Adipocyte Adiponectin Exocytosis is Stimulated Via β3 Adrenergic Signaling and Activation of Epac1: Catecholamine Resistance in Obesity and Type 2 Diabetes
We investigated the physiological regulation of adiponectin exocytosis in health and metabolic disease by a combination of membrane capacitance patch-clamp recordings and biochemical measurements of short-term (30 min incubations) adiponectin secretion. Adrenaline or the β3 adrenergic receptor agonist CL 316,243 (CL) stimulated adiponectin exocytosis/secretion in cultured 3T3-L1 and in primary subcutaneous mouse adipocytes and the stimulation was inhibited by the Epac (Exchange Protein directly Activated by cAMP) antagonist ESI-09. The adrenergic receptor (AR) β3 was highly expressed in cultured and primary adipocytes while other ARs were detected at lower levels. 3T3-L1 and primary adipocytes expressed Epac1 whereas Epac2 was undetectable. Adiponectin secretion could not be stimulated by adrenaline or CL in adipocytes isolated from obese/type 2 diabetic mice while basal (unstimulated) adiponectin release was 2-fold elevated. Gene expression of β3AR and Epac1 was reduced in adipocytes from obese animals and corresponded to a respective ∼35% and ∼30% reduction at the protein level. siRNA-mediated knockdown of β3AR (∼60%) and Epac1 (∼50%) was associated with abrogated catecholamine-stimulated adiponectin secretion. We propose that adiponectin exocytosis is stimulated via adrenergic signaling pathways mainly involving β3ARs. We further suggest that adrenergically stimulated adiponectin secretion is disturbed in obesity/type 2 diabetes due to reduced expression of β3ARs and Epac1 in a state we define as catecholamine resistance.
* Those authors contributed equally to this work and their names appear in alphabetical order.
- Received November 20, 2015.
- Accepted August 8, 2016.
- © 2016 by the American Diabetes Association.