Collagen types in various layers of the human aorta and their changes with the atherosclerotic process

The types of collagen components extracted from human aortas by repeated pepsin digestion were investigated by SDS-polyacrylamide gel electrophoresis (SDS-PAGE), after differential salt precipitation, cyanogen bromide (CNBr) cleavage and beta-mercaptoethanol reduction. For further extraction of collagen components, repeated pepsin digestion was carried out, and two extracts, the former and latter, were obtained. The greatest increase was seen in type V collagen followed by type III in the former extract. Type I collagen was continually extracted, so the proportion of type I to other types became greater with the number of extractions. SDS-PAGE of the residue treated with CNBr revealed that it contained the greatest amount of type I, followed by the latter extract. Type I collagen comprised approximately two-thirds of the total collagen. It was the most predominant in the intima and adventitia but was also obviously abundant in the media. The proportion of type III collagen to total collagen fell slightly with advancing atherosclerosis, since the amounts of types I and V showed some increase. A band of the alpha 3(V) chain of type V collagen in the intima was occasionally detected between the bands of the alpha 1(V) and alpha 2(V) chains. Basement membrane collagen, type IV, which was extracted predominantly from the intima and subintima, showed a heterogenous distribution as to molecular size, ranging from 50 Kd to 140 Kd. The alpha 1(IV) and alpha 2(IV) collagens were found at positions corresponding to 100 Kd and 80 Kd, respectively. The content of collagen type IV also increased with the proliferative fibrotic process. Type VI collagen was found in the intima and subintima of the human aorta at a position corresponding to an approximate molecular weight of 150 Kd, and it was reduced to fragments of 40 Kd, 45 Kd and 52 Kd.