2013 - CTS 2013 Congress


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Oral Communications 6

13.5 - Endothelial progenitor cell (EPC) co-transplantation enhances the engraftment of pancreatic islets and may involve connexin 36 (Cx36) interactions

Presenter: Claire, Jessup, Bedford Park, Australia
Authors: Daniella Penko1,2,3,4,5,6, Heshan Peiris1,2,3,4,5,6, Darling Rojas-Canales1,2,3,4,5,6, Daisy Mohanasundaram1,2,3,4,5,6, Christopher Drogemuller1,2,3,4,5,6, Toby Coates1,2,3,4,5,6, Claudine Bonder1,2,3,4,5,6, Claire Jessup1,2,3,4,5,6

Endothelial progenitor cell (EPC) co-transplantation enhances the engraftment of pancreatic islets and may involve connexin 36 (Cx36) interactions

Daniella Penko1,2,3,4,5,6, Heshan Peiris1,2,3,4,5,6, Darling Rojas-Canales1,2,3,4,5,6, Daisy Mohanasundaram1,2,3,4,5,6, Christopher Drogemuller1,2,3,4,5,6, Toby Coates1,2,3,4,5,6, Claudine Bonder1,2,3,4,5,6, Claire Jessup1,2,3,4,5,6

1Central Northern Adelaide Renal and Transplantation Service, Royal Adelaide Hospital, Adelaide, Australia; 2Discipline of Medicine, University of Adelaide, Adelaide, Australia; 3Human Physiology, Flinders University of SA, Adelaide, Australia; 4Centre for Neuroscience, Flinders University of SA, Adelaide, Australia; 5Centre for Stem Cell Research, University of Adelaide, Adelaide, Australia; 6Centre for Cancer Biology, SA Pathology, Adelaide, Australia

Islet transplantation is limited by apoptosis of insulin-secreting β-cells and suboptimal revascularization post-transplant. EPCs have the potential to promote islet engraftment, but their mechanism of interaction with β-cells is unknown. Cx36 is expressed on β-cellsand may be involved in intercellular communication within islets. The interaction between islets and EPCs was investigated in vitro, and theability of EPCs to improve islet transplantation was tested in vivo in a syngeneic marginal mass mouse model. C57B6 islets were isolated by Liberase® digestion and density purification. Bone marrow-derived EPCs were enriched by culture in defined mediumand confirmed to express endothelial markers (CD31 and E-selectin), bind lectin and uptake acetylated low-density lipoprotein by flow cytometry. To investigate soluble mechanisms, islets were cultured with EPC-conditioned medium and tested for glucose-stimulated insulin release. Secreted insulin was detected by ELISA and corrected for total protein. Stimulation indices were calculated as secretion at 20mM glucose divided by basal secretion (at 3mM).  EPC-conditioned islets had an increased basal insulin release (0.7±0.22 ng/min/mg total protein; n=7) compared to controls (0.2±0.04 ng/min/mg; n=6; p<0.05). However, they had reduced ability to upregulate insulin release in high glucose (stimulation index = 1.3±0.5 compared to 4.2±0.9 for controls; p<0.05). Effects on gene expression were analysed by PCR using Taqman® primers (normalizing to the house-keeping gene B2m) following non-contact co-cultures where islets were cultured above EPC monolayers. Co-cultured islets down-regulated the expression of Cx36(0.4±0.05 fold relative to control islets; n=18; p<0.05). There was no difference in expression of the Insulin gene between groups. These data suggest that Cx36 expression is modulated during intercellular communication between β-cells and EPCs, resulting in dysregulated insulin release. Diabetes was induced in C57B6 mice by streptozotocin (200mg/kg) and a marginal mass of islets (200) was transplanted under the kidney capsule with or without d7 EPCs (1x106 cells). Blood glucose levels (BGL) were monitored for 28d with cure defined by two consecutive BGL<11.1mM. Graft function was assessed in cured mice by intraperitoneal glucose tolerance test (IPGTT) with 2g/kg glucose. Mice co-transplanted with EPCs had an improved cure rate (83% at d14; n=12) compared to mice receiving islets alone (20%; n=10; p=0.002). There was no significant difference in IPGTT. Conclusions: The interaction of islets with EPCs causes the modulation of Cx36 in vitroand the improvement of islet engraftment during pancreatic islet transplantation.This may represent the adoption of a ‘survival’ islet phenotype where baseline insulin secretion is maintained during vascular remodeling – albeit in a dysregulated fashion.


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