Segregated hepatocyte proliferation and metabolic states within the regenerating mouse liver

Abstract

Mammalian partial hepatectomy (PH) induces an orchestrated compensatory hyperplasia, or regeneration, in remaining tissue to restore liver mass; during this process, liver functions are maintained. We probed this process in mice with feeding‐ and light/dark‐entrained animals subjected to sham or PH surgery. Early on (i.e., 10 hours), irrespective of sham or PH surgery, hepatocytes equidistant from the portal and central veins (i.e., midlobular) accumulated the G1‐phase cell‐division‐cycle marker cyclin D1. By 24 hours, however, cyclin D1 disappeared absent PH but was reinforced in midlobular hepatocytes after PH. At 48 hours after PH and 2 hours fasting, synchronously mitotic hepatocytes possessed less glycogen than surrounding nonproliferating hepatocytes. The differential glycogen content generated a conspicuous entangled pattern of proliferating midlobular and nonproliferating periportal and pericentral hepatocytes. The nonproliferating hepatocytes maintained aspects of normal liver properties. Conclusion: In the post‐PH regenerating mouse liver, a binary switch segregates midlobular cells to proliferate side‐by‐side with nonproliferating periportal and pericentral cells, which maintain metabolic functions. Our results also indicate that mechanisms of liver regeneration display evolutionary flexibility. (Hepatology Communications 2017;1:871–885)

Cycles of gene expression and genome response during mammalian tissue regeneration

“…Globally, the clustering dendrogram revealed three groups of samples (labeled I, II, and III): Group I represents samples similar to the resting 0 h C0 time point, Group II includes 4, 10, 20, and 28 h post-PH samples along with 4- and 10-h sham samples, and Group III represents 36–72 h post-PH samples. Importantly, replicate samples never fell into different groups I–III, indicating that the PH protocol [ 10 ] was highly reproducible. Thus, in the ChIP-Seq analyses described below, where we pooled samples to have sufficient material for analysis, the signals were probably not significantly blurred.…”

“…In mice, the first round of hepatocyte division is accomplished within 60 h post-PH; subsequent cell-division cycles together with cell growth lead to regeneration of the complete mass of the liver—compensatory hyperplasia—within 2–3 weeks [ 7 – 9 ]. We have used a characterized PH-induced mouse liver regeneration protocol [ 10 ] to study how a program of cell-division-cycle gene expression—dormant in the quiescent liver—is re-activated in the context of a differentiated tissue.…”

Cycles of gene expression and genome response during mammalian tissue regeneration

“…Prior to 70% PH, mice were entrained for two weeks on 12 h dark/12 h light cycles with food provided only during the dark (waking) period (see Additional File 1: Figure S1a; and Additional File 10: Supplemental Material). PH was performed at Zeitgeber Time (ZT) 2, where ZT0 represents the beginning of the light/fasting period, and samples were collected at 1,4,10,20,28,36,44,48,60, and 72 h, as well as 1 and 4 weeks post PH (labeled X). To identify non-PH-related effects of the PH surgery, we performed parallel sham surgeries in which all procedures but the liver resection were included and collected samples at 1, 4, 10, 20 and 48 h post sham surgery (labeled S).…”

“…Mouse entrainment and surgical procedures were as described [10]. Briefly, 12-14 week-old C57/BL6 male mice were used for PH or sham surgery after four weeks entrainment: two weeks with a ZT0-ZT12 light and ZT12-ZT24 dark circadian cycle followed by two weeks of ZT0-ZT12 light with fasting and ZT12-ZT24 dark with feeding.…”

“…In mice, the first-round of hepatocyte division is accomplished within 60 h post PH; subsequent cell-division cycles together with cell growth lead to regeneration of the complete mass of the liver -compensatory hyperplasia -within two to three weeks [7,8,9]. We have used a characterized PH-induced mouse liver regeneration protocol [10] to study how a program of cell-division-cycle gene expression -dormant in the quiescent liver -is re-activated in the context of a differentiated tissue.…”