Abstract
Purpose: :
To investigate the structural remodeling in the gap junction plaques associated with cholesterol redistribution during fiber cell differentiation and maturation in the adult chicken lens. The preservation of the C-terminus of Cx50 (Cx45.6) in the mature gap junction plaques is also evaluated.
Methods: :
Filipin cytochemistry and freeze-fracture TEM were applied to visualize structural remodeling of gap junction connexons associated with cholesterol redistribution during fiber cell maturation in adult leghorn chickens (51-62 weeks old). Freeze-fracture immunogold labeling (FRIL) was used to label the specific connexin antibodies in various structural configurations of gap junction plaques.
Results: :
Cortical fiber cells of the adult lenses contained three subtypes of cholesterol-containing gap junctions, i.e., cholesterol-rich, cholesterol-intermediate and cholesterol-poor or -free, in both outer and inner cortical zones within a range of 900 µm deep from the capsule surface. Quantitative study showed that approximately 81% of gap junction plaques in the outer cortical region were cholesterol-rich gap junctions whereas approximately 78% of gap junctions in the inner cortical region were cholesterol-free gap junctions. Interestingly, all cholesterol-rich gap junction connexons in the outer cortex displayed loosely-packed configuration whereas cholesterol-free gap junction connexons in the deep zone exhibited tightly-packed, hexagonal crystalline arrangement. Furthermore, FRIL demonstrated that while the labeling of Cx50 antibody generated from the loop was seen in all form of gap junction plaques, the C-terminus antibody was only labeled in a few tightly-packed gap junctions in the deep cortex.
Conclusions: :
Gap junctions undergo significant structural remodeling during fiber cell maturation and aging in the adult lens. The loosely-packed gap junction plaques are enriched with cholesterol whereas the tightly-packed, hexagonal crystalline plaques are devoid of cholesterol. This suggests that membrane cholesterol plays an important role in regulating connexons packing. Moreover, the C-terminus of Cx50 appears to be lost in most crystalline gap junctions in the mature fiber cells. The functional significance of the connexons remodeling during fiber cell maturation and aging awaits further investigation.
Keywords: gap junctions/coupling • lipids • aging