Investigation of the properties of peripheral blood insulin producing cells, and their therapeutic potential for regenerating the diabetic pancreas

Abstract

Type 1 diabetes (T1D) is a complex disease which normally develops in early adolescence and is marked by the destruction of insulin producing β-cells in the pancreas, and the sudden onset of hyperglycaemia . The destruction of β-cells is the result of an autoimmune attack which is hypothesised to be caused by a combination of genetic and environmental factors. There is no cure for T1D and treatments involve daily insulin injections with frequent monitoring of blood sugar levels. Regenerative medicine heralds a promising new era in medicine where organs ravaged by trauma and disease might be repaired using stem cells acquired from the patient’s own body. Adult stem cells transdifferentiated to produce insulin represent a potential source of transplantable cells to treat T1D. One particular recent publication by Zhao et al. (2007) reported that there were stem-like cells within human peripheral blood that have the ability to express insulin. These cells uniquely attach to positively charged hydrophobic plates, and amazingly start producing insulin on culture without forced differentiation. Similar studies have reported that blood monocytes and mesenchymal stem cells can be differentiated into insulin producing cells by culture with pancreatic factors and other differentiating agents The aim of this project was to determine whether human blood cells that attach to positively charged hydrophobic plates actually do produce insulin on culture, and whether they could be differentiated into cells that closely resemble β-cells. This study was not able to replicate the results obtained by Zhao et al, but nevertheless protocols were developed by which the cells could be differentiated to produce insulin. Culture of the adherent population of peripheral blood mononuclear cells in Stemline Hematopoietic stem cell expansion media produced large multinucleated cells that expressed insulin and other pancreatic proteins including Pdx-1 and Glut-2. The cells also show varying expression of the macrophage/monocytic markers HLA-DR, CD-14 and CD68, suggesting they had not fully lost their monocytic character. Expression of insulin appeared to be intracellular as documented by confocal microscopy. The cells possessed dense granules, as observed by transmission electron microscopy, which may represent insulin-containing secretory granules. Similar insulinproducing cells could be derived from the blood of T1D patients. This study provides important foundations for further research to be undertaken to determine whether the insulin-expressing cells reported here represent a potential source of cells for restoring the insulin-producing capacity of the pancreas in the treatment of T1D.