Abstract
Purpose: :
To quantitatively evaluate the relative gene expression of various adrenergic receptor subtypes in human Müller’s muscle tissue obtained from patients with clinical ptosis responsive to topical phenylephrine.
Methods: :
Conjunctiva-Müller’s muscle resections were obtained from consenting patients undergoing ptosis repair. Pre-operative phenylephrine testing was performed in all patients in order to document response. Müller’s muscle cells were then harvested from resected tissue under direct histological visualization using laser capture microdissection. Quantitative polymerase chain reaction was then performed to evaluate the relative gene expression levels of the α1A, α1B, α1D, α2A, α2B, α2C, β1, β2, and β3 adrenergic receptor subtypes.
Results: :
In total, Müller’s muscle samples from 9 eyes in 6 patients were analyzed. Overall, β2 represented the predominant receptor subtype expressed, accounting for a mean 58.8% (range, 14.5% to 74.9%) of total receptor expression, followed by the α1A (mean, 18.4%; range, 5.3% to 57.4%), and α1D (mean, 10.0%; range 3.6% to 25.9%) subtypes. Relatively less abundant, were the α1B (mean, 6.9%), α2C (mean, 3.7%), β1 (mean, 1.5%), α2B (mean, 0.63%), and α2A adrenoceptor subtypes (mean, 0.02%). Only β2, α1A, α1D, and α2C were conserved across all studied tissue samples. β3 was notably undetectable in all samples. The profile of receptor subtype expression varied considerably between samples, even in the 3 cases where bilateral samples were taken from the same patient. In all such cases, asymmetric ptosis and phenylephrine response was noted pre-operatively.
Conclusions: :
The adrenergic receptor gene expression profile in any given sample of human Müller’s muscle is complex and highly variable. The predominance of the β2 receptor subtype in our study suggests that β2 adrenergic activity may play a critical role in Müller’s muscle function, presumably through mediation of muscle relaxation. Likewise, significant expression of the α1A subtype as the predominant α1 type adrenergic receptor also suggests that α1A subtype-specific expression plays an important role in mediating Müller’s muscle function. Further studies with larger sample sizes may be required to identify potential correlations between receptor subtype expression and clinical phenylephrine testing.
Keywords: eyelid • receptors • gene/expression