TIMP-3 in Bruch's membrane: changes during aging and in age-related macular degeneration

Abstract

Purpose: To assess the distribution, content, and function of tissue inhibitor of metalloproteinases (TIMP)-3 during aging in normal eyes for comparison with the levels observed in eyes with age-related macular degeneration (AMD).

Methods: Donor tissues analyzed included 36 normal eyes (14-96 years old) and 15 AMD eyes (74 -98 years old). A tissue strip including the fovea was used for immunohistochemistry. Western blot analysis was performed on extracts of the retinal pigment epithelium (RPE)- choroid complex from the posterior part of each eye. Immunoreactivity of TIMP-3 bands in each western blot was densitometrically quantitated. The inhibitory function of TIMP-3 was evaluated with reverse zymography.

Results: TIMP-3 was present uniformly across Bruch's membrane in the normal samples. In samples from donors more than 50 years of age, immunostaining was intense. TIMP-3 content ranged from 92 to 1061 ng/cm2 and increased with age (r = 0.66). In AMD eyes, TIMP-3 distribution in Bruch's membrane was abundant in areas of continuous soft drusen but absent in areas below RPE atrophy. TIMP-3 levels in AMD eyes were significantly higher than in age-matched normal eyes (577 versus 877 ng/cm2; P = 0.009). Inhibitory activity correlated well with TIMP-3 content (r = 0.82) and was also significantly higher in AMD eyes than in age-matched normal eyes (P < 0.001).

Conclusions: During normal aging, TIMP-3 content in Bruch's membrane of the macula shows a significant increase. TIMP-3 content in AMD eyes was elevated relative to that of age-matched normal eyes. Higher levels of TIMP-3 may contribute to the thickening of Bruch's membrane observed in AMD.