Abstract

Norepinephrine (NE) controls many vital body functions by activating adrenergic receptors (AR). Average core body temperature (CBT) in mice is 37 {degree sign}C. Of note, CBT fluctuates between 36 and 38 {degree sign}C within 24 h, but little is known about the effects of CBT changes on the pharmacodynamics of NE. Here we used Peltier-element-controlled incubators and challenged murine hypothalamic mHypoA-2/10 cells with temperature changes of {plus minus} 1.0 {degree sign}C. We observed enhanced NE-induced activation of a cAMP-dependent luciferase reporter at 36 compared to 38 {degree sign}C. mRNA analysis and subtype specific antagonists, revealed that NE activates β₂- and β₃-AR in mHypoA-2/10 cells. Agonist binding to the β₂-AR was temperature-insensitive, but measurements of cytosolic cAMP accumulation revealed an increase in efficacy of 45 {plus minus} 27 % for NE and of 62 {plus minus} 33 % for the β₂-AR-selective agonist salmeterol (Sal) at 36 {degree sign}C. When monitoring NE-promoted cAMP efflux, we observed an increase in the absolute efflux at 36 {degree sign}C. However, the ratio of exported to cytosolic accumulated cAMP is higher at 38 {degree sign}C. We also stimulated cells with NE at 37 {degree sign}C and measured cAMP degradation at 36 and 38 {degree sign}C afterwards. We observed increased cAMP degradation at 38 {degree sign}C, indicating enhanced PDE activity at higher temperatures. In line with these data, NE-induced activation of the thyreoliberin promoter was found to be enhanced at 36 {degree sign}C. Overall, we show that physiological temperature changes fine-tune NE-induced cAMP signaling in hypothalamic cells via β₂-AR by modulating cAMP degradation and the ratio of intra- and extracellular cAMP.

Significance Statement Increasing cytosolic cAMP levels by activation of G protein-coupled receptors (GPCR) such as the β₂-adrenergic receptor (β₂-AR) is essential for many body functions. Changes in core body temperature are fundamental and universal factors of mammalian life. Here, we provide first data linking physiologically relevant temperature fluctuations to β₂-AR-induced cAMP signaling, highlighting a so far unappreciated role of body temperature as a modulator of the prototypic class A GPCR.