Age-related changes in proliferating cell nuclear antigen levels

Abstract

To clarify the effect of aging on rat liver regeneration, we compared proliferating cell nuclear antigen (PCNA) levels in control and regenerating livers from young and aged rats 48 h after partial hepatectomy. The nucleoplasm and cytoplasm from regenerating livers of 2-month and 24 month-old rats were fractionated by phosphocellulose column chromatography, aliquots of fractions were transferred to nitrocellulose filters and the amounts of PCNA in each fraction were measured by an immunostaining method. Two forms of PCNA, L type (eluted at low concentrations of KCl) and H type (eluted at high KCl concentrations) were observed in the nucleoplasm from both control and regenerating young rat liver. On the other hand, the cytoplasm contained P type (eluted in the pass-through fraction), L type and H type PCNA. In control liver from aged rats, three types of PCNA in the cytoplasm and two types in the nucleoplasm were present at decreased levels. In regenerating liver from young rats, the increases in L type in the cytoplasm and H type in the nucleoplasm were remarkable. However, none of the three PCNA types increased significantly during liver regeneration in aged rats. Treatment with DNase resulted in the disappearance of the H type with a concomitant increase in the P and L types. These results suggest that the H type is a complex form consisting of the P and L types of PCNA and DNA. These results suggest that the increase in the L type in the cytoplasm reflects newly synthesized PCNA production for cellular proliferation and that the increase in the H type in the nucleoplasm is a reflection of binding to DNA and the fundamental role of PCNA itself in liver regeneration in young rats. On the other hand, there was little increase in any of the three types in regenerating liver from 24-month-old rats. Thus, PCNA content may be closely related to the decrease in the rate of cellular proliferation in aged animals.