Aged and post-mitotic cells share a very stable higher-order structure in the cell nucleus in vivo

Abstract

In the mammalian liver the quiescent primary hepatocytes preserve a proliferating potential in vivo, yet natural aging correlates with loss of proliferating potential and progression towards terminal differentiation of the hepatocytes. Thus aged, terminally-differentiated hepatocytes may survive in a de facto post-mitotic state, similarly to early post-mitotic cells, like neurons, suggesting that there might be a common factor linking both cellular states. In the interphase of metazoan cells the nuclear DNA is organized in supercoiled loops anchored to a proteinaceous substructure known as the nuclear matrix (NM). The DNA-NM interactions define a higher-order structure in the cell nucleus (NHOS). Natural aging of the rat liver correlates with a progressive strengthening of the NM framework and the stabilization of the DNA-NM interactions in the hepatocytes indicating that the NHOS becomes highly stable with age. We compared the NHOS of post-mitotic rat neurons with that of aged rat hepatocytes. Our results indicate that a very stable NHOS is a common feature of both aged and post-mitotic cells in vivo.

Differential Proteomic Analysis of Mammalian Tissues Using SILAM

“…Our data suggests that the nuclear matrix is more abundant in the brain compared to the liver. Consistent with our data, it has been reported neurons possess a more stable and larger nuclear matrix than liver hepatocytes [68]. The most significant pathway represented in our brain phosphoproteome was the PKA (protein kinase A) signaling pathway with a p-value <1.05×10 −9 (Table S8), which measures how likely the observed association between a specific pathway and our dataset would be if it was only due to random chance.…”

Continued Stabilization of the Nuclear Higher-Order Structure of Post-Mitotic Neurons In Vivo

“…See Table 2 for statistical analysis of data, n = 50 for each set.. The data sets for P7 and P540 were taken from our previous work [21]. The corresponding average DNA loop size can be deduced from the measurement of the DNA halos as it has been previously described [20]: P0 = 42 kbp±4.02; P7 = 36 kbp±3.05; P80 = 44 kbp±4.6; P540 = 40.6 kbp±5.9.…”

“…Each time-point value corresponds to the average of independent experiments using separate animals as the source of nucleoids (P0 n = 4; P7 n = 5; P80 n = 5; P540 n = 4). The data sets for P7 and P540 were taken from our previous work [21]. The topological zones relative to the NM for the corresponding kinetics were established considering the local slopes between pairs of time points (Table 3) and the corresponding S.D.…”

“…A self-stabilizing model for DNA-NM interactions as a function of age, in which a stochastic but time-dependent (age-dependent) process leads to a significant increase of DNA-NM interactions, resulting in an integral and highly-stable structural system, has been proposed for explaining a common physical basis for both stochastic RS senescence and the post-mitotic state [50]. We have recently shown that aged hepatocytes and early post-mitotic neurons have similar highly-stable NHOS [21]. The present work expands such result by showing that continued stabilization of the NHOS occurs in post-mitotic neurons even after the fourth post-natal week when according to microanatomical criteria they formally become TD [22]–[24].…”

“…This fact correlates on the one hand with a dramatic strengthening of the NM framework and the stabilization of such DNA-NM interactions and on the other hand, with reduction of the cell proliferating potential and progression towards terminal differentiation of the hepatocytes with age [20]. We have also compared the NHOS of aged rat hepatocytes with that of early post-mitotic rat neurons, the results indicated that a very stable NHOS is a common feature of both aged and post-mitotic cells in vivo [21]. In the present work we compared the NHOS in rat neurons from different post-natal ages and our results show that the trend towards further stabilization of the NHOS continues in neurons beyond the fourth post-natal week, when the synapses in the cerebral cortex become indistinguishable for those in the adult rat brain and so the neurons are formally regarded as terminally differentiated [22]–[24].…”