ATP Release and Purinergic Signaling Potentiate β-Adrenergic Effects on Brown Adipocytes

Brown adipose tissue (BAT) specializes in energy consumption and thermogenesis in response to cold stress. Brown adipocytes (BA) express purinergic receptors, yet little is known about the source of extracellular ATP and the role of purinergic signaling, and the potential interaction with β-adrenergic signaling. We aimed at elucidating whether: BA could release extracellular ATP; ATP/purinergic signaling impacts β-adrenergic responses; and the expression of purinergic receptors in BAT of mice and cultured BA.

Real-time ATP release was monitored in a mature BA cell model exposed to adrenergic agonists, insulin, glucose, and pharmacological inhibitors. Cellular assays included oxygen consumption, glycolysis, and lipolysis assays, and Ca²⁺ imaging. The protein level of ATP-release protein, pannexin-1, was determined. RNA-sequencing was performed on mouse BAT and cultured BA.

We show that β-adrenergic stimulation of BA causes ATP release through pannexin-1 in a cAMP-protein kinase A-dependent manner. ATP release is increased with glucose but decreased with insulin, the latter due to phosphodiesterase 3 activation. β-Adrenergic stimulation increases oxygen consumption, glycolysis, and lipolysis, while apyrase and pannexin-1 inhibitors decrease these effects. Both extracellular ATP and β-adrenergic stimulation induce Ca²⁺ signals, albeit with different kinetics. BAT from mice exposed to cold and BA treated with norepinephrine show regulation of several purinergic receptors.

The present study demonstrates that ATP is released from BA via pannexin-1 channels in response to β-adrenergic stimulation, that extracellular ATP, acting through P2 receptor signaling, potentiates β-adrenergic effects on BA function, and that expression of several purinergic receptors changes in response to β-adrenergic stimulation.