Isolation and characterization of mesenchymal stem cells from cultured human pancreatic islets of langerhans

Abstract

Replacement of insulin producing β-cells that reside within pancreatic islets represents an almost ideal treatment for patients with diabetes mellitus type 1. But, transplantation of pancreatic islets or the entire pancreas is limited by the lack of donor organs. Stem cell derived insulin producing β-cells represent an attractive alternative. The major goal of our research project is the ex vivo generation of insulin producing cells using adult human stem cells that express nestin. Nestin is an intermediate filament protein that was originally described as a marker for embryonic and adult stem / progenitor cells of the central nervous system. Recently it has been also proposed to be a potential stem cell marker in rodent and human islets of Langerhans. Role and function of nestin positive pancreatic cells during development or adult life however are not well defined and matter of controversial debates. The first aim of our research project was to isolate a pure population of nestin expressing cells from human pancreatic islets of Langerhans for further characterization. For this purpose single cell derived colonies were isolated from cultured human islets. These colonies were immortalized and in a second step selected for cells with highest nestin promoter activity using promoter targeted selection of nestin expressing cells. The second aim was to characterize these cell lines especially their stem cell properties and differentiation potential. We characterized them finally as potential mesenchymal stem cells (MSC) of pancreatic origin based on their expression of different stem cell markers including nestin together with the transcription factor Islet-1 (Isl-1) and their ability to differentiate in vitro into mesoderm lineages (adipocytes and osteoblast-like cells). We could also demonstrate that they are multipotential and capable of differentiation into albumin producing liver-like cells in vivo and cells with a pancreatic endocrine phenotype in vitro. Based on these observations, we wanted to test the hypothesis that human nestin expressing MSC from bone marrow and adipose tissue could equally harbour the potential to differentiate into insulin producing cells ex vivo. We found that bone marrow and adipose tissue derived MSC are also able to differentiate into cells expressing various pancreatic endocrine genes in vitro including several crucial transcription factors as well as the islet hormones insulin and glucagon. As a limitation of the presented work, we were not yet able to generate functional cells that secrete insulin in response to glucose. But, we can show for the first time that nestin positive MSC isolated from human adult pancreas, bone marrow and adipose tissue represent stem / progenitor cells with the potential to induce pancreatic developmental genes. These cells may have the capacity to become insulin secreting cells if further manipulated and exposed to appropriate microenvironment.