Abstract Body: Objective:
We have shown that in cardiomyocytes exposed to ischemia-reperfusion injury, G protein-coupled receptor kinase 2 (GRK2) translocates to the mitochondria and inhibits mitochondrial pyruvate utilization. Inflammation is a major outcome of myocardial infarction (MI), and arises from the infiltrating of circulating monocytes that adopt a pro-inflammatory macrophage state. Modes of glucose utilization have been shown to influence macrophage polarization into a pro- or anti-inflammatory state. In this study, we hypothesized that mitochondrial GRK2 translocation in response to beta-adrenergic receptor activation alters GRK2 mitochondrial localization and mitochondrial function in monocytes.

Methods:
THP-1 cells were cultured in RPMI-1640 medium with 10% heat-inactivated FBS and 1% Pen-Strep. Cells were counted and prepared for mitochondrial functional assays in RPMI medium supplemented with 2 mM glutamine and 11.1 mM glucose. Cells were stimulated with norepinephrine, isoproterenol, or vehicle followed by a mitochondrial stress test. A subset of cells was exposed to PD-184352 for 10 minutes prior to the respiratory recordings to determine the involvement of ERK activation. Results were normalized using the total protein content of each well and analyzed offline.

Results:
Acute b-adrenergic receptor activation mediates a transitory mitochondrial translocation of GRK2. Acute b-adrenergic receptor activation increases maximal respiration and spare respiratory capacity. Inhibition of ERK increases proton leak, prevents bAR-mediated increases in ATP-linked respiration, and prevents augmentation in spare respiratory capacity.

Conclusions and Broader Impacts:
Mitochondrial translocation of GRK2 occurs in monocytes and impacts mitochondrial function. Acutely, bAR-mediated GRK2 mitochondrial translocation is rapid and transitory. bAR activation increases maximal respiration and increases spare respiratory capacity. The increase in spare capacity is dependent on ERK activation. Future studies in chronic bAR stimulation are needed to determine whether mitochondrial GRK2 participates in pro-inflammatory polarization of macrophages.