Human mesenchymal stem cells protect human islets from pro-inflammatory cytokines

Abstract

Transplantation of human islets is an attractive alternative to daily insulin injections for patients with type 1 diabetes. However, the majority of islet recipients lose graft function within five years. Inflammation is a primary contributor to graft loss, and inhibiting pro-inflammatory cytokine activity can reverse inflammation mediated dysfunction of islet grafts. As mesenchymal stem cells (MSCs) possess numerous immunoregulatory properties, we hypothesized that MSCs could protect human islets from pro-inflammatory cytokines. Five hundred human islets were co-cultured with 0.5 or 1.0 × 10(6) human MSCs derived from bone marrow or pancreas for 24 hours followed by 48 hour exposure to interferon-γ, tumor necrosis factor-α and interleukin 1β. Controls include islets cultured alone (± cytokines) and with human dermal fibroblasts (± cytokines). For all conditions, glucose stimulated insulin secretion (GSIS), total islet cellular insulin content, islet β cell apoptosis, and potential cytoprotective factors secreted in the culture media were determined. Cytokine exposure disrupted human islet GSIS based on stimulation index and percentage insulin secretion. Conversely, culture with 1.0 × 10(6) bMSCs preserved GSIS from cytokine treated islets. Protective effects were not observed with fibroblasts, indicating that preservation of human islet GSIS after exposure to pro-inflammatory cytokines is MSC dependent. Islet β cell apoptosis was observed in the presence of cytokines; however, culture of bMSCs with islets prevented β cell apoptosis after cytokine treatment. Hepatocyte growth factor (HGF) as well as matrix metalloproteinases 2 and 9 were also identified as putative secreted cytoprotective factors; however, other secreted factors likely play a role in protection. This study, therefore, demonstrates that MSCs may be beneficial for islet engraftment by promoting cell survival and reduced inflammation.

Figure 1. Protection of human islets from cytokine induced apoptosis by bone marrow derived MSCs.

A-C) 500 Islets, D-F) 500 Islets + cytokines, G-I) 500 Islets +1.0×10⁶ bMSCs, + cytokines. Tissues were stained for insulin (A,D,G) in red and TUNEL (B,E,H) in green. The merge of the red and green images are presented in panels C, F, and I. Islets cultured without cytokines demonstrated minimal TUNEL positive cells. After cytokine exposure, the number of TUNEL positive cells increased; TUNEL and insulin co-expression was also increased with cytokine treatment. Alteration of native islet organization was observed. After cytokine exposure, co-expression of insulin and TUNEL did not increase in the islets + bMSCs group; cytokines – cocktail of IFNγ, TNFα and IL-1β described in materials and methods. Scale bar represents 100 µm.