Project description:Two major functions of the epigenome are to regulate gene expression and to suppress transposons. It is unclear how these functions are balanced during physiological challenges requiring tissue regeneration, where exquisite coordination of gene expression is essential. Transcriptomic analysis of seven time points following partial hepatectomy identified the epigenetic regulator UHRF1, which is essential for DNA methylation, as dynamically expressed during liver regeneration in mice. UHRF1 deletion in hepatocytes (Uhrf1HepKO) caused genome-wide DNA hypomethylation but, surprisingly, had no measurable effect on gene or transposon expression or liver homeostasis. Partial hepatectomy of Uhrf1HepKO livers resulted in early and sustained activation of proregenerative genes and enhanced liver regeneration. This was attributed to redistribution of H3K27me3 from promoters to transposons, effectively silencing them and, consequently, alleviating repression of liver regeneration genes, priming them for expression in Uhrf1HepKO livers. Thus, epigenetic compensation safeguards the genome against transposon activation, indirectly affecting gene regulation.
Project description:Mammalian tissues have a limited regenerative capacity. Previous studies showed that dedifferentiation contributes to tissue regeneration in non-mammalian vertebrate species such as zebrafish and newt. However, dedifferentiation is rarely observed in mammalian tissues even in the neonatal stage and therefore artificial induction of dedifferentiation might enhance regeneration in mammalian tissues. Here we demonstrate that short-term expression of Yamanaka 4 factors (4F) induces dedifferentiation and proliferation in the liver by using lineage-traceable, hepatocyte-specific 4F inducible mouse model. Global transcriptome analysis shows that 4F expression transiently reduces the expression of hepatic-lineage markers and induces the expression of a large set of proliferative markers and epigenetic modifiers along with global epigenetic changes as assessed by DNA-accessibility analysis. More importantly, lineage-tracing experiments showed that 4F-expressing hepatocytes acquire liver stem/progenitor cell markers, suggesting that 4F induces partial reprogramming. Moreover, 4F enhances MyoD-mediated transdifferentiation in the liver, suggesting that 4F endows hepatocytes with plasticity. Lastly, 4F expression attenuated liver injury associated with more proliferative capacity and better survival rate, indicating that 4F enhances liver regeneration. Taken together, these results demonstrate that liver-specific 4F expression induces dedifferentiation and promotes liver regeneration.
Project description:The liver is the only organ in mammals, which fully regenerates after injury. To identify novel regulators of liver regeneration, we performed quantitative large-scale proteomics analysis of subcellular fractions from normal versus regenerating mouse liver. Proteins of the ubiquitin-proteasome pathway were rapidly regulated by partial hepatectomy, with the ubiquitin ligase Nedd4-1 being among the top hits. Knock-down of Nedd4-1 in hepatocytes in vivo through nanoparticle-mediated delivery of siRNA caused severe liver damage after partial hepatectomy and impaired regeneration, resulting in liver failure. Mechanistically, we demonstrate that Nedd4-1 is required for efficient activation of Erk1/2 signaling by receptor tyrosine kinases involved in liver regeneration through inhibition of receptor internalization, thus controlling a major pro-mitogenic and cytoprotective signaling pathway in the regenerating liver. These results highlight the power of large-scale proteomics to identify key players in liver regeneration and the importance of posttranslational regulation of growth factor signaling in this process.
Project description:SOCS2 Ensures Metabolic Function and Mass Restoration During Liver Regeneration - SOCS2 plays distinct and contrasting roles during liver regeneration. Early after injury, SOCS2 expression increases and limits the rate of regeneration, preserving metabolic activity. Surprisingly, at later times, the role of SOCS2 reverses to promote liver regeneration by stimulating GH release from the pituitary via effects on serum levels of insulin-like growth factor 1. Loss of SOCS2 promotes GH signaling by increasing growth hormone receptor levels and driving phosphorylation of proteins in the GH pathway, establishing a state of hyper-responsiveness to GH. These findings suggest a single protein can play contrasting roles at different times after liver injury and modulation of GH signaling achieves an optimal rate of liver regeneration to balance metabolic and restorative needs. To further understand the mechanism by which SOCS2 increases early liver regeneration, we performed microarray analysis of Socs2-null mice wildtype mice at 24 and 36 hours after hepatectomy. C57BL/6 mice where used as wildtype controls. Socs2-null animals were maintained on a C57BL/6 background. Both wildtype and Socs2-null adult mice were subjected to 2/3 hepatectomy and liver tissue isolated at 24 hours and 36 hours post hepatectomy. Time zero was without hepatectomy in age-matched mice for each genotype. Total RNA isolated from collected liver tissues was pooled for three animals at each time point and two biological replicates (3 pooled liver RNAs each) were labeled for array analysis. This results in a total of 12 microarrays.
Project description:Receptor tyrosine kinases MET and EGFR are critically involved in initiation of liver regeneration. Other cytokines and signaling molecules also help in the early part of the process. Regeneration employs effective redundancy schemes to compensate for missing signals. Elimination of any single signaling pathway only delays but does not abolish the process. Our present study, however, shows that combined systemic elimination of MET and EGFR signaling abolishes liver regeneration, prevents restoration of liver mass and leads to liver decompensation. Our results demonstrate that liver function is dependent on synchronous availability of signaling from these two pathways. The study shows that MET and EGFR separately control many non-overlapping signaling endpoints, allowing for compensation when only one of the signals is blocked. The combined elimination of the signals however was not tolerated. The results provide critical new information on interactive MET and EGFR signaling and the contribution of their combined absence to regeneration arrest and liver decompensation. We used microarrays to detail the global programme of gene expression in METKO-canertinib mouse liver following a partial hepatectomy
Project description:To elucidate the role of PPARα activation in liver progenitor cell-mediated liver regeneration, we used Tg(fabp10a:pt-β-catenin) zebrafish transgenic line where liver progenitor cell-mediated liver regeneration is induced by oncogene overexpression
Project description:We identify a new phase of functional compensation following acute liver injury that occurs prior to cellular proliferation. By coupling single-cell RNA-seq with in situ transcriptional analyses in two independent murine liver injury models, we discover adaptive reprogramming to ensure expression of both injury response and core liver function genes dependent on macrophage-derived WNT/b-catenin signaling. Interestingly, transcriptional compensation is most prominent in non-proliferating cells, clearly delineating two separate phases of liver recovery. Overall, our work describes a new mechanism by which the liver maintains essential physiological functions prior to cellular reconstitution and characterizes macrophage-derived WNT signals required for this compensation.
Project description:A unique feature of the liver is its high regenerative capacity, which is essential to maintain liver homeostasis. However, key regulators of liver regeneration (LR) remain ill-defined. Here, we identify hepatic miR-182-5p as a key regulator of LR. Suppressing miR-182-5p, whose expression is significantly induced in the liver of mice post two-thirds partial hepatectomy (PH), abrogates PH-induced LR in mice. In contrast, liver-specific overexpression of miR-182-5p promotes LR in mice with PH. Overexpression of miR-182-5p failed to promote proliferation in hepatocytes, but stimulates proliferation when hepatocytes are cocultured with stellate cells. Mechanistically, miR-182-5p stimulates Cyp7a1-mediated cholic acid production in hepatocytes, which promotes hedgehog (Hh) ligand production in stellate cells, leading to the activation of Hh signaling in hepatocytes and consequent cell proliferation. Collectively, our study identified miR-182-5p as a critical regulator of LR and uncovers a Cyp7a1/cholic acid-dependent mechanism by which hepatocytes crosstalk to stellate cells to facilitate LR.