The role of Arid1a and Tet1 in ductal cell-driven liver regeneration

Title: The role of Arid1a and Tet1 in ductal cell-driven regeneration Author: Mikel Alexander Mckie The liver has several robust and potent mechanisms of repair after damage despite slow homeostatic turnover. In cases of extreme toxic damage, where the hepatocyte compartment is severely compromised and unable to proliferate, a bi-potent ductal population arises that is able to expand and differentiate into both hepatocytes and ductal cells. The regulation of the activation of this ductal progenitor population is poorly understood. We have taken advantage of 3D organoid cultures that model the activation of bi-potent ductal progenitors to identify potential candidates involved in organoid establishment and maintenance. Using knock down experiments, we identified the epigenetic modifiers Arid1a and Tet1 as important candidates for ductal progenitor maintenance and establishment, respectively, in vitro. Further in vitro analysis of several genetic models of Arid1a showed that reduction but not ablation of Arid1a results in enhanced proliferation and survival of organoid culture. In addition, Arid1a defective organoids lacked the ability to differentiate into functional hepatocytes in vitro. Therefore, Arid1a is important for regulating the differentiation and proliferative nature of ductal progenitors in vitro. On the other hand, we found that reduction or loss of Tet1 resulted in abolished establishment and maintenance of organoid culture, suggesting an important role of Tet1 in the activation of the progenitor state from a mature ductal cell. In line with this, we found that a hypomorphic mouse model of Tet1 showed a significantly reduced ductal regenerative response when challenged with acute liver damage. Furthermore, chronically damaged hypomorphic mice maintained significant fibrosis over WT mice. Finally, ductal specific genetic ablation of Tet1 coupled with lineage tracing showed that Tet1 mutant ductal cells formed significantly smaller regenerative hepatocyte clusters. As a result, Tet1 is crucial for the activation and function of ductal bi-potent progenitors both in vivo and in vitro. Taken together, the role of Arid1a and Tet1 in organoid culture and liver regeneration suggests that regulation of the epigenetic landscape is crucial to determine cell fate decisions during the damage-regeneration response.MRC doctoral training grant (grant no. MR/K50127X/1

Cellular plasticity in the adult liver and stomach.

Adult tissues maintain function and architecture through robust homeostatic mechanisms mediated by self-renewing cells capable of generating all resident cell types. However, severe injury can challenge the regeneration potential of such a stem/progenitor compartment. Indeed, upon injury adult tissues can exhibit massive cellular plasticity in order to achieve proper tissue regeneration, circumventing an impaired stem/progenitor compartment. Several examples of such plasticity have been reported in both rapidly and slowly self-renewing organs and follow conserved mechanisms. Upon loss of the cellular compartment responsible for maintaining homeostasis, quiescent or slowly proliferating stem/progenitor cells can acquire high proliferation potential and turn into active stem cells, or, alternatively, mature cells can de-differentiate into stem-like cells or re-enter the cell cycle to compensate for the tissue loss. This extensive cellular plasticity acts as a key mechanism to respond to multiple stimuli in a context-dependent manner, enabling tissue regeneration in a robust fashion. In this review cellular plasticity in the adult liver and stomach will be examined, highlighting the diverse cell populations capable of repairing the damaged tissue.MH is a Wellcome Trust Sir Henry Dale Fellow and is jointly funded by the Wellcome Trust and the Royal Society (104151/Z/14/Z). MM is an MRC PhD fellow (PMAG/440).This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1113/JP27176

Epigenetic remodelling licences adult cholangiocytes for organoid formation and liver regeneration.

Following severe or chronic liver injury, adult ductal cells (cholangiocytes) contribute to regeneration by restoring both hepatocytes and cholangiocytes. We recently showed that ductal cells clonally expand as self-renewing liver organoids that retain their differentiation capacity into both hepatocytes and ductal cells. However, the molecular mechanisms by which adult ductal-committed cells acquire cellular plasticity, initiate organoids and regenerate the damaged tissue remain largely unknown. Here, we describe that ductal cells undergo a transient, genome-wide, remodelling of their transcriptome and epigenome during organoid initiation and in vivo following tissue damage. TET1-mediated hydroxymethylation licences differentiated ductal cells to initiate organoids and activate the regenerative programme through the transcriptional regulation of stem-cell genes and regenerative pathways including the YAP-Hippo signalling. Our results argue in favour of the remodelling of genomic methylome/hydroxymethylome landscapes as a general mechanism by which differentiated cells exit a committed state in response to tissue damage.RCUK Cancer Research UK ERC H2020 Wellcome Trus

Multicentre evaluation of renal impairment in thoracic surgery (MERITS): a retrospective cohort study.

OBJECTIVES: To measure the unit-level variation in Acute Kidney Injury (AKI) incidence post-thoracic surgery over a contemporary 1-year period. Secondary aims include examining the associations with sex, age group, operation type, length of stay and mortality. DESIGN: A multicentre, observational, retrospective study in thoracic surgery. SETTING: 17 of 35 Society for Cardiothoracic Surgery of Great Britain and Ireland (SCTS) units participated. The student wing, known as SCTS STUDENTS, supported data collection. PARTICIPANTS: Overall, 15 229 patients were collected of which 15 154 were included for analysis after exclusions. All patients (age≥18 years) undergoing any thoracic surgery from 1 April 2016 to 31 March 2017 were included. For analysis, we excluded patients with preoperative end-stage renal failure and those with incomplete data. MAIN OUTCOME MEASURES: The primary outcome is the incidence of AKI within 7 days of the procedure or discharge date if earlier. Secondary outcomes include assessing associations with patient demographics (age, sex), type of procedure (open and minimally invasive), length of stay and mortality. RESULTS: Out of 15 154 patients AKI was diagnosed in 1090 patients (7.2%) within 7 days of surgery with AKI stage 1 (4.8%), stage 2 (1.7%) and stage 3 (0.7%). There was a statistically significant variation in AKI incidence between units from 3.1 to 16.1% (p<0.05). Significant differences between AKI and non-AKI were found in post-operative length of stay (7 vs 3 days, p<0.001), 30-day mortality (9 vs 1.6%, p<0.001), 90-day mortality (14.7 vs 4.4%, p<0.001) and 1-year mortality (23.1 vs 12.2 %, p<0.001). CONCLUSIONS: Following thoracic surgery, AKI incidence ranged from 3.1% to 16.1% between units (p<0.05) with associations between AKI and both length of stay and mortality. We propose AKI as a suitable comparative and absolute quality measure in thoracic surgery. Reducing rates of AKI may improve patient outcomes, length of stay and reduce costs

Positioning imatinib for pulmonary arterial hypertension: A phase I/II design comprising dose finding and single-arm efficacy.

Pulmonary arterial hypertension is an unmet clinical need. Imatinib, a tyrosine kinase inhibitor, 200 to 400 mg daily reduces pulmonary artery pressure and increases functional capacity in this patient group, but is generally poorly tolerated at the higher dose. We have designed an open-label, single-arm clinical study to investigate whether there is a tolerated dose of imatinib that can be better targeted to patients who will benefit. The study consists of two parts. Part 1 seeks to identify the best tolerated dose of Imatinib in the range from 100 and up to 400 mg using a Bayesian Continuous Reassessment Method. Part 2 will measure efficacy after 24 weeks treatment with the best tolerated dose using a Simon's two-stage design. The primary efficacy endpoint is a binary variable. For patients with a baseline pulmonary vascular resistance (PVR) >1000 dynes · s · cm-5, success is defined by an absolute reduction in PVR of ≥300 dynes · s · cm-5 at 24 weeks. For patients with a baseline PVR ≤1000 dynes · s · cm-5, success is a 30% reduction in PVR at 24 weeks. PVR will also be evaluated as a continuous variable by genotype as an exploratory analysis. Evaluating the response to that dose by genotype may inform a prospective biomarker-driven study