Membrane cholesterol oxidation downregulates atrial β-adrenergic responses in ROS-dependent manner

Oxidation of membrane cholesterol is a hallmark of many pathological conditions, including cardiovascular diseases. Cholesterol could be oxidized in a result of free radical and enzymatic reactions. Here, we studied the effect of cholesterol oxidation by cholesterol oxidase (ChO) on responses to β-AR stimulation in isolated mouse atria. Acute exposure to ChO led to partial cholesterol oxidation without a significant change in atrial membrane cholesterol content. Pretreatment with ChO itself did not affect contractions and Ca²⁺ transient amplitude. However, cholesterol oxidation markedly suppressed β-AR-mediated increase in contractility and Ca²⁺ transient as well as NO levels. At the same time, ChO markedly facilitated β-AR-induced reactive oxygen species (ROS) production. Antioxidant and protein kinase C inhibitor prevented the depressant action of ChO on ISO-dependent contractility, Ca²⁺ transient and NO production. Similar effects had a selective β₂-AR antagonist, which also suppressed the increase in ROS levels after ChO pretreatment. These results suggest that membrane cholesterol oxidation enhances β₂-AR-dependent elevation of ROS production, leading to suppression of β-AR-mediated increase in contractility, Ca²⁺ transient and NO synthesis in mice atria. The oxidative cholesterol modification could contribute to disturbance in β-AR signaling in pathological conditions.