Vrije Universiteit Brussel

 

Generation and regeneration of beta cell mass

The existence of stem cells in the adult pancreas is one of the most controversial issues in diabetes research. Our research group has been able to find these "sleeping beauties" and awake them (Xu et al, 2008). Therefore we used a robust injury model called partial duct ligation whereby the channel that drains the digestive enzymes of the tail of pancreas was clamped. This manipulation results in doubling of the beta cell mass. To answer the question whether the doubling of the beta cell mass was caused by recruitment of progenitor cells or by division of pre-existing beta cells we traced a cell type known to give rise to the different endocrine cell types during embryonic development of the pancreas and thus accepted as a bona fide progenitor.

Adult progenitors of islet cells (blue bGal+) can be detected near the exocrine ducts in injured pancreas from Ngn3-LacZ mice. Cytokeratin is green. DNA is red.

Development of the embryonic endocrine pancreas depends on cells that express Neurogenin 3 (Ngn3), a transcription factor that is hardly expressed in the adult pancreas under normal physiological conditions and that was used as reporter for the process of progenitor cell activation. Following clamping of the duct Ngn3 appeared in adult pancreas. When a fluorescent protein was expressed under the control of the Ngn3 promoter, the activated progenitor cells were detected by the appearance of fluorescence and could be isolated by flow cytometry. The isolated adult Ngn3-positive cells were almost indistinguishable from the embryonic Ngn3 cells at the level of ultrastructure and global gene expression and were capable to differentiate to all 4 endocrine pancreas cell types among which were glucose responsive beta cells. Our findings reveal the significance to invetigate the feasibility of (i) isolating facultative beta cell progenitors and newly formed beta cells from human pancreas in order to expand and differentiate them in vitro and transplant them in diabetic patients and (ii) composing a mix of factors able to activate beta cell progenitors to expand and differentiate in situ in patients with an absolute or relative deficiency in insulin.

Explanted pancreas from embryonic mice (left) injected with adult islet progenitor cells (green, right).


The technology developed during the course of this project created a platform for beta cell differentiation experiments under normal and regenerative conditions: Injection of recombinant viruses (for over-expression or knockdown) in the pancreatic duct results in highly efficient transduction of exocrine cells; injection of stem/progenitor cells in explanted embryonic pancreas provides them with a microenvironment that contains all growth and differentiation factors needed to generate all pancreatic cell types and transduction with recombinant viral constructs modifies gene expression at will.

A parallel research project investigates the feasibility to normalize alloxan-induced hyperglycemia in mice by transplantation of bone marrow-derived cells and the mechanisms involved.

 

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© 2008 • BENE • Vrije Universiteit Brussel • Faculteit Geneeskunde & Farmacie • Laarbeeklaan 103 • 1090 Jette •
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