PPARβ Regulates Liver Regeneration by Modulating Akt and E2f Signaling

The current study tests the hypothesis that peroxisome proliferator-activated receptor β (PPARβ) has a role in liver regeneration due to its effect in regulating energy homeostasis and cell proliferation. The role of PPARβ in liver regeneration was studied using two-third partial hepatectomy (PH) in Wild-type (WT) and PPARβ-null (KO) mice. In KO mice, liver regeneration was delayed and the number of Ki-67 positive cells reached the peak at 60 hr rather than at 36-48 hr after PH shown in WT mice. RNA-sequencing uncovered 1344 transcriptomes that were differentially expressed in regenerating WT and KO livers. About 70% of those differentially expressed genes involved in glycolysis and fatty acid synthesis pathways failed to induce during liver regeneration due to PPARβ deficiency. The delayed liver regeneration in KO mice was accompanied by lack of activation of phosphoinositide-dependent kinase 1 (PDK1)/Akt. In addition, cell proliferation-associated increase of genes encoding E2f transcription factor (E2f) 1-2 and E2f7-8 as well as their downstream target genes were not noted in KO livers 36-48 hr after PH. E2fs have dual roles in regulating metabolism and proliferation. Moreover, transient steatosis was only found in WT, but not in KO mice 36 hr after PH. These data suggested that PPARβ-regulated PDK1/Akt and E2f signaling that controls metabolism and proliferation is involved in the normal progression of liver regeneration.