Study of in vitro Cellular Aging among the Macaques

Abstract

Human fibroblasts have a limited replicative lifespan and never undergo infinite cell division in vitro. In contrast, rodent fibroblasts spontaneously and highly frequently immortalize in vitro. Therefore, rodent is inappropriate as a model animal to study human aging in vitro. To test effects of macaque monkey as the model system, macaque adherent cells were cultured and passaged in vitro and analyzed cytologically.Long-tailed macaque (Macaca fascicularis), Japanese macaque (Macaca fuscata), and bonnet monkey (Macaca radiata) were subjected to the study. Adherent cells were isolated from their skin, kidney, and lung. A total of 19 cell cultures were examined until terminating cell division.Most of the cultures (17/19) exhibited senescence by 7-25 Population Doubling Levels (PDLs), showing enlargement of cell size, decrease of saturation density and extension of doubling interval, and then terminated cell division [Mortality stage 1 (M1)]. The remaining two cell cultures showed distinct pattern. They first exhibited senescent morphology at around 20PDLs, but continued cell division through M1 up to 106 PDLs and then went into crisis stage [Mortality stage 2 (M2)]. In all cell cultures tested, telomerase activity was not detected. Consistently, telomeres appeared to be shortened by every PDLs.Macaque cells showed an intermediate pattern of in vitro aging between human and rodent cells, whereas, they showed no telomerase activity similarly to human cells. Therefore, the macaques must serve as an excellent animal model to study human cellular aging and provide us with a key to study the mechanism of the transition to critical stages in cellular aging.