Experimental formation of 100 nm periodic fibrils in the mouse corneal stroma and trabecular meshwork

The so-called long-spacing collagen that exhibits approximately 100 nm periodicity has been observed in the interstitial connective tissue of various organs under normal and pathological conditions. Although we, as well as many other investigators, have reported an increasing amount of these structures with age in the human trabecular meshwork, the pathological significance and the mechanism of its formation are still unknown. We incubated mouse ocular tissues in culture medium containing 20 mM ATP and prepared them for electron microscopic observation according to the method of Bruns et al (J Cell Biol 103:393, 1986). After the incubation, abundant 100 nm periodic fibrils were observed in the corneal stroma and the region of the trabecular meshwork, both of which show no structure of 100 nm periodicity under normal conditions. For the experimental formation of 100 nm periodic fibrils, ATP, acidic condition and temperature around 37°C are necessary. The 100 nm periodic fibrils observed in our experiment were very similar to long-spacing collagen, in that the dark transverse bands have 100 nm intervals and very fine filaments of 6-7 nm diameter axially connect the bands. Long-spacing collagen is not usually observed in the human cornea, even in aged persons. The results of our study suggest that the occurrence of long-spacing collagen is related to special conditions developing in the trabecular meshwork with age but not in the corneal stroma. Experimental studies of 100 nm periodic fibril formation in mice offer a useful model for the age-related increase of long-spacing collagen in the trabecular meshwork of the human eye.