Developmental and age-related changes to the elastic lamina of Bruch's membrane in mice

Abstract

Background: Fibrillin-1, tropoelastin, fibulin-5, and latent transforming growth factor beta-binding protein-2 and protein-4 (LTBP-2 and LTBP-4) are essential proteins for the elastic lamina (EL). In this study, we analyzed each of these molecules in the EL of Bruch's membrane (BM) through development and aging.

Methods: C57BL/6 mice (embryonic (E) days E12.5, E15.5, and E18.5; postnatal (P) days P1, P4, and P7 and P3, P6, and P75 weeks of age) were used. To investigate localization, immunohistochemical staining (IH) was performed. Transmission electron microscopy (TEM) was used to evaluate the formation of microfibrils and tropoelastin. mRNA expression was determined by quantitative real-time PCR (qRT-PCR).

Results: All five proteins were expressed in the EL of BM by IH except in embryonic mice. TEM results showed that tropoelastin co-stained with microfibrils. Between 3 and 6 weeks of age, microfibrils became longer and thicker. It was difficult to evaluate the EL of BM in senile mice at 75 weeks of age because of abundant deposits which correspond to drusen. mRNA levels of each protein increased dramatically from E15.5 to P1 days and plateaued by P3 weeks as shown by qRT-PCR.

Conclusions: In conclusion, these five proteins are possibly involved in elastic fiber assembly in BM. We define the date of full assembly of the EL of BM as 3 weeks of age in mice.

Keywords: Elastic lamina of Bruch’s membrane; Fibulin-5; LTBP-2; LTBP-4; Tropoelastin; fibrillin1.