Absent expansion of AXIN2+ hepatocytes and altered physiology in Axin2CreERT2 mice challenges the role of pericentral hepatocytes in homeostatic liver regeneration

BACKGROUND & AIMS

Mouse models of lineage tracing have helped to describe the important subpopulations of hepatocytes responsible for liver regeneration. However, conflicting results have been obtained from different models. Herein, we aimed to reconcile these conflicting reports by repeating a key lineage-tracing study from pericentral hepatocytes and characterising this Axin2CreERT2 model in detail.

METHODS

We performed detailed characterisation of the labelled population in the Axin2CreERT2 model. We lineage traced this cell population, quantifying the labelled population over 1 year and performed in-depth phenotypic comparisons, including transcriptomics, metabolomics and analysis of proteins through immunohistochemistry, of Axin2CreERT2 mice to WT counterparts.

RESULTS

We found that after careful definition of a baseline population, there are marked differences in labelling between male and female mice. Upon induced lineage tracing there was no expansion of the labelled hepatocyte population in Axin2CreERT2 mice. We found substantial evidence of disrupted homeostasis in Axin2CreERT2 mice. Offspring are born with sub-Mendelian ratios and adult mice have perturbations of hepatic Wnt/β-catenin signalling and related metabolomic disturbance.

CONCLUSIONS

We find no evidence of predominant expansion of the pericentral hepatocyte population during liver homeostatic regeneration. Our data highlight the importance of detailed preclinical model characterisation and the pitfalls which may occur when comparing across sexes and backgrounds of mice and the effects of genetic insertion into native loci.

IMPACT AND IMPLICATIONS

Understanding the source of cells which regenerate the liver is crucial to harness their potential to regrow injured livers. Herein, we show that cells which were previously thought to repopulate the liver play only a limited role in physiological regeneration. Our data helps to reconcile differing conclusions drawn from results from a number of prior studies and highlights methodological challenges which are relevant to preclinical models more generally.

Public views on an extended role for community pharmacy

The acceptability to the general public of an extended role for community pharmacy was investigated using a social survey methodology. Within one locality, a sample of 133 respondents was drawn from four population groups who were likely to be extensive users of community pharmacy services: active elderly people, mothers of young children, carers of people with disabilities and people in full-time employment. The evidence from the interview survey was supplemented by discussions with community groups representative of the same sections of the population. The results indicate that there is considerable public support for the development of a range of new services in community pharmacies, with a majority of respondents supporting the provision of more information on prescribed medicines, opportunity to discuss minor symptoms with the pharmacist, medicine delivery services, and the holding of patient medication records. There is less support for discussing health promotion with the pharmacist, while cost was found to be a major obstacle to the acceptability of diagnostic testing. Elderly people found all aspects of the extended role less acceptable than did other respondent groups. It is concluded that there is a need to market unfamiliar services, and, if an extended role is to be developed effectively, the nature of the relationship between the roles of the community pharmacist and the GP needs to be demonstrated more clearly to service users.

Model systems for the evaluation of mucolytic drugs: acetylcysteine and S-carboxymethylcysteine

The therapeutic place of mucolytic drugs remains uncertain; clinical studies have seldom demonstrated significant benefit and the activity of such agents is poorly understood. In this study the effects of the mucolytic agents acetylcysteine (AC) and S-carboxymethylcysteine (SCMC) have been assessed in-vitro, using purified mucus gels and tracheal explant systems and in-vivo, in the mini-pig tracheal pouch model, in order to elucidate their mechanisms of action. A reduction in the elastic modulus (up to 70% over the frequency range 0.2-20 Hz) was apparent after treatment of mucus gels in-vitro with AC (P less than 0.05), but not with SCMC. Gel chromatography indicated that AC reduced the mucus glycoprotein to smaller subunits and a breakdown of gel structure was apparent when visualized using a cryofracture technique. SCMC treated gels were comparable with control samples. Mucus production was assessed in isolated rat trachea by monitoring the uptake and release of [3H] glucosamine. AC (5-15 mM) did not affect secretion whereas SCMC (5 and 10 mM) reduced the production of radiolabelled material (24 and 37%, respectively) over 24 h (P less than 0.05). Single oral doses of SCMC and AC (20 mg kg-1) were administered to mini-pigs and mucus collected from tracheal pouches; no significant changes in the rheological or biochemical properties of the secretion could be determined. The in-vitro mucolytic activity of AC depends upon a direct action on the secretion, SCMC appears able to reduce production of the mucus glycoprotein. Wide inter- and intra-individual variation in the properties of the secretion would suggest that such effects are not readily demonstrated in-vivo.