Novel role of GRK2 in isoprenaline-induced activation of Na+/H+ exchanger 3 independent of β2-adrenergic receptor signaling.

Abstract

Background: The activation of Na⁺/H⁺ exchanger 3 (NHE3) by β2-adrenergic receptor (β2-AR) signaling is well-established. Our research indicates that isoprenaline (ISO) induces activation of NHE3 independent of β2AR signaling but through a different way that has not been elucidated before.

Methods: The activation of NHE3 in HK-2 cell lines was quantified using the fluorescence probe BCECF/AM. The expression levels of G protein-coupled receptor kinase 2 (GRK2) and its downstream effector, β-arrestin 1 (ARRB1), were assessed through Western blot analysis and immunohistochemical staining. ISO-induced β2-AR signaling was blocked by ICI 118,551, a β2-AR antagonist, in HK-2 cells.

Results: ISO treatment significantly enhanced NHE3 activity, which was reduced by 64.5% with a GRK2 inhibitor (GRK2-IN) and completely inhibited by propranolol (PRO), a non-selective β-adrenergic receptor blocker. Neither GRK2-IN nor PRO impacted NHE3 activity in the absence of ISO. Additionally, while GRK2 expression remained unchanged, ISO markedly decreased ARRB1 expression. This decrease was mitigated by 64.08% with GRK2-IN and entirely blocked by PRO. GRK2-IN and PRO alone did not significantly alter ARRB1 expression.

Conclusion: Our study suggests that ISO triggers downstream GRK2/ARRB1 signaling to increase NHE3 activity independent of traditional β2AR signaling. Given the fundamental role of NHE3 in renal water-sodium reabsorption, these insights may contribute to new strategies for the prevention and treatment of hypertension.