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[Matrix metalloproteinase-2 mRNA expression in the posterior sclera of chick form-deprivation myopia].

OBJECTIVE
To investigate the dynamic changes of matrix metalloproteinase-2 (MMP-2) mRNA expression in the posterior sclera of chick form-deprivation myopia (FDM) and its possible molecular mechanism.


METHODS
Fifty white 1-day-old leghorn chicks were divided randomly and equally into 5 groups. The right eye of each chick was covered with a plastic goggle at 4, 7, 14, 21, and 30 postborn days respectively to induce FDM, and the left eye served as a self-control. Meanwhile, normal age-matched chicks were provided as negative control speciments for each group. Removing the goggle at every experiment point, refractive status and axial length were determined with streak retinoscopy (without cycloplegia) and A-scan ultra-sonography under topical anaesthesia, respectively. Both eyes were collected after the chicks were killed. The total RNA in the posterior sclera was extracted traditionally using TRIZOL reagent, and then the expression levels of MMP-2 messenger RNA were analyzed by one step reverse transcriptiontase-polymerase chain reaction.


RESULTS
Compared with the normal and self-control groups, the expression levels of MMP-2 mRNA in the deprived eyes significantly increased (P < 0.001). With the delay of form-deprivation duration, MMP-2 mRNA expression levels increased significantly and especially reached a highest point at the 14th day of monocular deprivation. After that the level decreased slightly, but maintained at a high level. Although there was no significant difference between the normal control group and the self-control one (P > 0.05), MMP-2 mRNA expressed slightly higher in the self-controlled eyes.


CONCLUSION
As a primary element to trigger early active sclera extracellular matrix remodeling process, MMP-2 gene is probably involved in the development of FDM by excessive degradation of extraceller matrix which can make sclera thinner and the eye axis longer.