Changes in muscarinic acetylcholine receptor expression in form deprivation myopia in guinea pigs.

PURPOSE Muscarinic receptor signaling is involved in ocular development and implicated in myopia. The aims of this study were to identify the presence of muscarinic acetylcholine receptors (mAChRs) in normal ocular tissues of guinea pigs and to determine if ocular expression of mRNA and protein changes in guinea pigs with or without form-deprived myopia (FDM). METHODS One- to two-week-old guinea pigs were monocularly treated with a translucent lens. Twenty-one days after the induction of FDM, we collected the retina, choroid, sclera, and iris-ciliary body. We used a semiquantitative reverse-transcription polymerase chain reaction (RT-PCR) to detect changes in mRNA expression for mAChRs. Western blotting analysis was used to investigate changes in protein expression for mAChRs. Levels of mAChRs as well as mRNA and protein expression were statistically compared among FDM, internal, and normal eyes. RESULTS We observed expression of mRNA for muscarinic subtypes M1 to M5 in the retina, choroid, sclera, and iris-ciliary body. Proteins for the M1 to M5 subtypes were present in normal ocular tissues. Their molecular weights ranged from 80 kDa for M5 to 52 kDa for M1 as noted on Western blotting. Twenty-one days after the induction of myopia, we observed statistically significant increases in mRNA expression for subtypes M1 (+18.67%) and M4 (+26.48%) as well as in protein expression for M1 (+24.65%) and M4 (+49.11%) in the posterior sclera of FDM-affected eyes (p<0.05 vs. internal control and normal eyes). CONCLUSIONS The ocular tissues of guinea pigs express muscarinic subtypes M1 to M5. In the posterior sclera, expression of the M1 and M4 subtypes significantly increased in FDM eyes. This finding indicates that muscarinic antagonists may have the potential to act directly on the sclera as a strategy to prevent myopia.