Defining cell proliferation tracing for regeneration research

Written by:

Qing-Dong Wang

Senior Principal Scientist, Bioscience, Research and Early Development, Cardiovascular, Renal and Metabolism, BioPharmaceuticals R&D

Regeneration could be considered the “holy grail” in research of new therapeutic modalities and by understanding the fundamental mechanisms we hope to identify the right targets that promote cell proliferation, which is the main mechanism in heart and liver regeneration. Such regenerative approaches could offer therapeutic approaches for cardiovascular, liver and renal diseases allowing us to move from targeting risk factors to targeting the underlying cause of the disease.

Previously we conducted research which helped to change the perception of regenerative cell types in this field. c-Kit-positive cells and stem cell antigen-1 (Sca-1)-positive cells in the heart were thought to play an intrinsic role in regeneration, however our research demonstrated that endogenous progenitor cells of this type neither contributed to new cardiomyocyte formation under physiological conditions nor after myocardial infarction. These data suggested that during cardiac repair and regeneration, new cardiomyocytes are more likely to be derived from pre-existing cardiomyocytes via proliferation, rather than through the differentiation of endogenous cardiac progenitor cells. These data have been published in three high profile journals, namely CirculationCell Research and Nature Medicine.

Our new publication in Science explores cell proliferation specifically in the liver. We collaborated with Professor Bin Zhou, University of Chinese Academy of Sciences, Shanghai, China, who is a world leader in this field and has contributed much scientific evidence on the role of cardiac stem cells and cardiomyocyte proliferation. He has developed a novel genetic system called ProTracer, which uses dual recombinases to develop an inducible genetic tracing system for continuous genetic recording of cell proliferation in mouse tissues.

ProTracer enabled tissue-specific recording of in vivo cell proliferation and non-invasive long-term monitoring of cell proliferation over time in live animals. This is important as cell proliferation is temporally and spatially dependent and we are interested in recording the proliferation of entire cell populations in organs.

The results showed that in the liver, more hepatocyte proliferation occurs in distinct zones during liver homeostasis, injury repair, and regeneration. Clonal analysis showed that the majority of hepatocytes labelled by ProTracer have undergone cell division.

The ProTracer uses Cre-loxP and Dre-rox recombination. Until recently, this approach has been limited by the small number of Dre recombinase driver constructs available. Earlier this month, again in collaboration with Professor Bin Zhou’s team, we published an article in Cell Stem Cell which outlined more than 70 new intersectional drivers that developed to better target diverse cell lineages. In addition to lineage tracing, this new suite of recombinase drivers could be used to knock out genes in complex tissues, such as white adipocytes and lymphatic vessels, expanding the intersectional genetic approach while enhancing its precision.

With the publication of these results, the validation of the ProTracer system will enable future studies to explore the regenerative potential of diverse cell compartments in various organs. Similar research has been conducted by the Research and Early Development, Cardiovascular, Renal and Metabolism team in collaboration with Professor Bin Zhou on cardiac cell proliferation and is currently being reviewed for publication.