Reduction of the Cell Cycle Length by Decreasing G₁ Phase and Cell Cycle Reentry Expand Neuronal Progenitor Cells in the Subventricular Zone of Adult Rat after Stroke

Abstract

A critical determinant of proliferation of progenitor cells is the duration of the cell division cycle. Stroke increases proliferation of progenitor cells in the subventricular zone (SVZ). Using cumulative and single S-phase labeling with 5-bromo-2 0 -deoxyuridine, we examined cell cycle kinetics of neural progenitor cells in the SVZ after stroke. In nonstroke rats, 20% of the SVZ cell population was proliferating. However, stroke significantly increased dividing cells up to 31% and these cells had a cell cycle length (T C ) of 15.3 h, significantly (P < 0.05) shorter than the 19 h Tc in nonstroke SVZ cells. Few terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling-positive cells were detected in the SVZ cells of nonstroke and stroke groups, suggesting that the majority of dividing cells in the SVZ do not undergo apoptosis. Cell cycle phase analysis revealed that stroke substantially shortened the length of the G 1 phase (9.6 h) compared with the G 1 phase of 12.6 h in nonstroke SVZ cells (P < 0.03). This reduction in G 1 contributes to stroke-induced reduction of T C because no significant changes were detected on the length of S, G 2 and M phases between two groups. Furthermore, compared with progenitor cells in nonstroke SVZ (10%), a greater proportion (14%) of progenitor cells in stroke SVZ reentered the cell cycle after mitosis (P < 0.05). These results show that an increase in proliferating progenitor cells in the SVZ contributes to stroke-induced neurogenesis and this increase is regulated by shortening the length of the cell cycle, decreasing the G 1 phase and increasing cell cycle reentry.

The linkage of neural progenitor cell cycle profiles between embryonic and adult stroke models: Analytical approach II

“…The mathematical model estimated that there were 11 and 8 cell cycles for the first and second 6 days, respectively, during 2 to 14 days after stroke, which is consistent with our previous findings that stroke augments neurogenesis by acutely expanding the neural progenitor pool during 2 to 7 days after stroke (Zhang et al, 2001;Zhang et al, 2006). Although the number of cell cycles is different between stroke-induced neurogenesis and embryonic cortical neurogenesis, rapid expansion of a progenitor pool is observed in the embryonic model, suggesting that the adult progenitor cells after stroke recaptures the cell cycle kinetics of the embryonic progenitors.…”

“…The G 1 phase has been identified as the key regulation phase during neurogenesis in the developing brain (Takahashi et al,1995b;Caviness, Jr. et al, 1999;Siegenthaler and Miller, 2005). The reduction of total cycle length led to the reduction in G 1 length (Takahashi et al, 1995b;Zhang et al, 2006), however, the report of the T C and T G1 relationship was rather descriptive. In this study, the correlation coefficient was calculated for both the stroke model and the embryonic model (Takahashi et al, 1995b).…”

“…The middle cerebral artery (MCA) was occluded by placement of an embolus at the origin of the MCA (Zhang et al, 1997). Experiments were initiated in rats at 2, 4, 7, and 14 days after stroke, corresponding to the maximum period of stroke induced neurogenesis (Zhang et al, 2001;Zhang et al, 2004a;Zhang et al, 2004b;Zhang et al, 2006).…”

“…Using cumulative and single pulse bromodeoxyuridine (BrdU) labeling methods, Nowakowski and his colleagues (1989) have determined the length of the cell cycle and established the cell cycle interval of mice during neocortical formation, the embryonic model. By adapting this approach, we found that stroke significantly increases the proliferating population of SVZ neural progenitor cells in rats subjected to 7 days of embolic middle cerebral artery occlusion (S7), which is associated with the reduction of the cell cycle length (Tc), especially the length in G 1 phase (T G1 ) (Zhang et al, 2006). Using the enhanced analytic approach which permits the precision for cell cycle kinetic parameters, we further demonstrate that migration of neural progenitor cells out of the SVZ can be ignored in the estimation of the cell cycle parameters (Lu et al, 2007).…”

Lengthening the G1 Phase of Neural Progenitor Cells is Concurrent with An Increase of Symmetric Neuron Generating Division after Stroke

“…Rats without stroke were subjected to the same injection protocol of BrdU and were used as a control group . To estimate the G 2 and M phases (T G2 + M ) of the cell cycle, a single-pulse BrdU protocol was used (Nowakowski et al, 1989;Takahashi et al, 1993;Zhang et al, 2006). Rats subjected to 2, 4, and 14 days of stroke received a single injection of BrdU (intraperitoneally, 50 mg/kg) at 0800 hours and were killed 30,40,50,60,90,120,160, and 180 mins after the injection, with 3 to 4 rats per time point .…”