β-Arrestin1 mediates nicotinic acid–induced flushing, but not its antilipolytic effect, in mice
Robert W. Walters, Arun K. Shukla, Jeffrey J. Kovacs, Jonathan D. Violin, Scott M. DeWire, Christopher M. Lam, J. Ruthie Chen, Michael J. Muehlbauer, Erin J. Whalen, Robert J. Lefkowitz
Robert W. Walters, Arun K. Shukla, Jeffrey J. Kovacs, Jonathan D. Violin, Scott M. DeWire, Christopher M. Lam, J. Ruthie Chen, Michael J. Muehlbauer, Erin J. Whalen, Robert J. Lefkowitz
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Research Article Cardiology

β-Arrestin1 mediates nicotinic acid–induced flushing, but not its antilipolytic effect, in mice

Abstract

Nicotinic acid is one of the most effective agents for both lowering triglycerides and raising HDL. However, the side effect of cutaneous flushing severely limits patient compliance. As nicotinic acid stimulates the GPCR GPR109A and Gi/Go proteins, here we dissected the roles of G proteins and the adaptor proteins, β-arrestins, in nicotinic acid–induced signaling and physiological responses. In a human cell line–based signaling assay, nicotinic acid stimulation led to pertussis toxin–sensitive lowering of cAMP, recruitment of β-arrestins to the cell membrane, an activating conformational change in β-arrestin, and β-arrestin–dependent signaling to ERK MAPK. In addition, we found that nicotinic acid promoted the binding of β-arrestin1 to activated cytosolic phospholipase A2 as well as β-arrestin1–dependent activation of cytosolic phospholipase A2 and release of arachidonate, the precursor of prostaglandin D2 and the vasodilator responsible for the flushing response. Moreover, β-arrestin1–null mice displayed reduced cutaneous flushing in response to nicotinic acid, although the improvement in serum free fatty acid levels was similar to that observed in wild-type mice. These data suggest that the adverse side effect of cutaneous flushing is mediated by β-arrestin1, but lowering of serum free fatty acid levels is not. Furthermore, G protein–biased ligands that activate GPR109A in a β-arrestin–independent fashion may represent an improved therapeutic option for the treatment of dyslipidemia.

Authors

Robert W. Walters, Arun K. Shukla, Jeffrey J. Kovacs, Jonathan D. Violin, Scott M. DeWire, Christopher M. Lam, J. Ruthie Chen, Michael J. Muehlbauer, Erin J. Whalen, Robert J. Lefkowitz

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Figure 1

Nicotinic acid–induced decrease in cAMP, and increase in β-arrestin membrane recruitment, in GPR109A-expressing HEK-293 cells.

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Nicotinic acid–induced decrease in cAMP, and increase in β-arrestin memb...
Cells also expressing the ICUE2 biosensor (see Methods) were treated with forskolin and increasing concentrations of nicotinic acid (NA). (A) Nicotinic acid (open circles) decreased cAMP in a dose-dependent fashion, and this response was inhibited by pertussis toxin (PTX; filled circles). Data are mean ± SEM of 3 independent experiments. CFP, cyan fluorescent protein; FRET, fluorescence resonance energy transfer. (B) Cells were transfected with either β-arrestin1–mYFP or β-arrestin2–mYFP. Both β-arrestin isoforms resided in the cytosol prior to nicotinic acid stimulation (control; Con), and translocated to bind GPR109A in the membrane in response to treatment with 10 μM nicotinic acid. No translocation was noted in cells lacking GPR109A (not shown). Images are representative of 4 independent experiments. Original magnification, ×100.