Influence of beta 2-adrenergic receptor genotypes on signal transduction in human airway smooth muscle cells.

TLDR

The phenotypic impact of β2‑adrenergic receptor (β2AR) allelic variation in lung cells, particularly on airway smooth muscle responsiveness, remains unknown. The study aimed to investigate how β2AR genotypes at codons 16 and 27 influence signal transduction in human airway smooth muscle cells. Primary cultures of airway smooth muscle cells from autopsy tissue were established, and allele‑specific PCR was used to genotype the β2AR polymorphisms. Radioligand binding showed ~70 fmol/mg β2AR, with normal agonist binding and adenylyl cyclase activation, but long‑term isoproterenol exposure produced genotype‑dependent downregulation: Arg16 77.8 %, Gly16 95.6 % (significantly higher), and Glu27 only 29.5 %, leading to markedly reduced functional desensitization in Glu27 cells. The abstract is truncated at 250 words.

Abstract

The phenotypic relevance of allelic variation in the structure of the beta 2-adrenergic receptor (beta 2AR) expressed in lung cells is unknown. In particular, altered responsiveness of the beta 2AR expressed on airway smooth muscle, which are responsible for bronchodilation in the treatment of asthma, may be an important factor in the ultimate physiologic response to agonist. To approach this, we established primary cultures of human airway smooth muscle cells obtained at autopsy and developed a method to determine the beta 2AR genotype at the polymorphic loci of codons 16 and 27, using allele-specific polymerase chain reactions. Radioligand binding studies revealed that these cells expressed approximately 70 fmol/mg of receptor which was exclusively of the beta 2AR subtype. All cell lines obtained (n = 10) exhibited normal agonist binding and receptor-mediated activation of the adenylyl cyclase second messenger pathway. However, distinct differences were found in the response to long-term agonist exposure between the different beta 2AR genotypes. Cells expressing Arg at codon 16 (Arg16) traditionally referred to as wild-type, underwent 77.8 +/- 8.1% downregulations of beta 2AR following prolonged (24-h) exposure to the beta 2AR agonist isoproterenol (10 microM). In contrast, cells expressing Gly16 beta 2AR underwent enhanced agonist-promoted downregulation (95.6 +/- 1.7%, P < 0.05 versus Arg16), whereas cells expressing Glu27 beta 2AR were relatively resistant to such downregulation (29.5 +/- 12.7%, P < 0.01 versus Arg16). For cells expressing Glu27 beta 2AR, this difference resulted in a significant attenuation of agonist-promoted functional desensitization (33 +/- 7 versus 90 +/- 5% desensitization for Arg16, P < 0.001) following preincubation with 1 microM isoproterenol. (ABSTRACT TRUNCATED AT 250 WORDS)