Background
Beta-2 adrenergic receptor (β2AR) agonists are critical treatments for asthma. However, receptor desensitization can lead to loss of therapeutic effects. While desensitization to repeated use of β2 agonists is well studied, Type-2 inflammation could also impact β2AR function.
Objective
To evaluate the impact of the Type-2 cytokine, IL-13, on β2AR desensitization in human airway epithelial cells (HAECs) and determine whether 15-Lipoxygenase-1 (15LO1) binding with phosphatidylethanolamine binding protein-1 (PEBP1) contributes to desensitization through release of G-protein Receptor Kinase-2 (GRK2).
Methods
HAECs in air-liquid-interface (ALI) culture with/without IL-13 (48 hrs) or isoproterenol (ISO) (30 min) pretreatment were stimulated with ISO (10min). cAMP was measured by ELISA and β2AR and GRK2 phosphorylation by Western Blot. siRNA was utilized for 15LO1 knockdown. Interactions of GRK2, PEBP1 and 15LO1 were detected by Immunoprecipitation/Western Blot and immunofluorescence. HAECs and airway tissue from controls and asthmatics were evaluated for I5LO1, PEBP1 and GRK2.
Results
Pretreatment with ISO or IL-13 decreased ISO-induced cAMP generation compared to ISO for 10 min alone, paralleled by increases in β2AR and GRK2 phosphorylation. GRK2 associated with PEBP1 after 10 min of ISO in association with low pGRK2 levels. In contrast, in the presence of IL-13+ISO (10 min), binding of GRK2 to PEBP1 decreased, while 15LO1 binding and pGRK2 increased. 15LO1 knockdown restored ISO-induced cAMP generation. These findings were recapitulated in freshly brushed HAEC from asthmatic cells and tissue.
Conclusion
IL-13 treatment of HAECs leads to β2AR desensitization which involves 15LO1/PEBP1 interactions to free GRK2 and allow it to phosphorylate (and desensitize) β2ARs, suggesting beneficial effects of β2 agonists could be blunted in Type-2 associated asthma.