Age-related changes of wall composition and collagen cross-linking in the rat carotid artery - In relation with arterial mechanics.

In association with age-related changes in arterial wall mechanics, the composition of connective tissues, the fraction and size of vascular smooth muscle cells (SMCs), and the degree of collagen cross-linking were studied with common carotid arteries harvested from 8, 16, 32, and 64 week-old Wistar rats. For histomorphometric studies, each arterial segment was fixed under in vivo operating force condition, and then sequentially sliced into thin specimens, followed by selective staining for the observation of collagen, elastin, and SMCs. Then, the fraction of each component, and the number and size of SMCs were determined with an image analyzer. The content of collagen and elastin, their ratio, and the number and the area fraction of SMCs showed no significant correlations with age, while the density and the size of SMCs were significantly smaller and larger, respectively, in 64 week-old animals than in the others. The results of collagen and elastin cannot explain the biomechanical data obtained in our previous study using the same animal model, which showed that the elastic modulus and wall stiffness were significantly larger in 64 week-old animals compared to younger ones. To investigate the reason for the discrepancy between the histological and the biomechanical results, a hydrothermal isometric tension method was applied to the analysis of the cross-linking of collagen, and we found that the amount of cross-links was significantly greater in 64 week-old arteries than in the others. This result corresponded well with the biomechanical results, and therefore the higher wall stiffness and elastic modulus in older arteries might be ascribed to their larger amount of collagen cross-links.

Human FAN1 promotes strand incision in 5'-flapped DNA complexed with RPA.

Fanconi anaemia (FA) is a human infantile recessive disorder. Seventeen FA causal proteins cooperatively function in the DNA interstrand crosslink (ICL) repair pathway. Dual DNA strand incisions around the crosslink are critical steps in ICL repair. FA-associated nuclease 1 (FAN1) is a DNA structure-specific endonuclease that is considered to be involved in DNA incision at the stalled replication fork. Replication protein A (RPA) rapidly assembles on the single-stranded DNA region of the stalled fork. However, the effect of RPA on the FAN1-mediated DNA incision has not been determined. In this study, we purified human FAN1, as a bacterially expressed recombinant protein. FAN1 exhibited robust endonuclease activity with 5'-flapped DNA, which is formed at the stalled replication fork. We found that FAN1 efficiently promoted DNA incision at the proper site of RPA-coated 5'-flapped DNA. Therefore, FAN1 possesses the ability to promote the ICL repair of 5'-flapped DNA covered by RPA.