Diabetes 2013 Aug-2

 

Insulin-Like growth factor-II (IGF-II) prevents proinflammatory cytokine-induced apoptosis and significantly improves islet survival after transplantation.

Transplantation. 2013 Mar 15;95(5):671-8.

Hughes A, Mohanasundaram D, Kireta S, Jessup CF, Drogemuller CJ, Coates PT.

Renal Transplantation and Immunobiology Laboratory, The Royal Adelaide Hospital, Adelaide, South Australia, Australia.

 

Abstract

BACKGROUND: The early loss of functional islet mass (50-70%) due to apoptosis after clinical transplantation contributes to islet allograft failure. Insulin-like growth factor (IGF)-II is an antiapoptotic protein that is highly expressed in β-cells during development but rapidly decreases in postnatal life.

METHODS: We used an adenoviral (Ad) vector to overexpress IGF-II in isolated rat islets and investigated its antiapoptotic action against exogenous cytokines interleukin-1β- and interferon-γ-induced islet cell death in vitro. Using an immunocompromised marginal mass islet transplant model, the ability of Ad-IGF-II-transduced rat islets to restore euglycemia in nonobese diabetic/severe combined immunodeficient diabetic recipients was assessed.

RESULTS: Ad-IGF-II transduction did not affect islet viability or function. Ad-IGF-II cytokine-treated islets exhibited decreased cell death (40% ± 2.8%) versus Ad-GFP and untransduced control islets (63.2% ± 2.5% and 53.6% ± 2.3%, respectively). Ad-IGF-II overexpression during cytokine treatment resulted in a marked reduction in terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling-positive apoptotic cells (8.3% ± 1.4%) versus Ad-GFP control (41% ± 4.2%) and untransduced control islets (46.5% ± 6.2%). Western blot analysis confirmed that IGF-II inhibits apoptosis via activation of the phosphatidylinositol 3-kinase/Akt signaling pathway. Transplantation of IGF-II overexpressing islets under the kidney capsule of diabetic mice restored euglycemia in 77.8% of recipients compared with 18.2% and 47.5% of Ad-GFP and untransduced control islet recipients, respectively (P<0.05, log-rank [Mantel-Cox] test).

CONCLUSIONS: Antiapoptotic IGF-II decreases apoptosis in vitro and significantly improved islet transplant outcomes in vivo. Antiapoptotic gene transfer is a potentially powerful tool to improve islet survival after transplantation.

PMID: 23364485

 

Scientific rationale:

A major limitation to the success of clinical islet transplantation is the early loss of up to 70% of the islet mass 24 – 48 hours post-transplantation. Early transplant stresses such as apoptosis may be overcome through the use of ex vivo gene therapy strategies to deliver anti-apoptotic genes to the islets to improve post-transplant islet viability. The phosphoinositide-3-kinase (PI3K)/Akt pathway plays a central role in preventing apoptotic cell death. Upon activation, Akt induces phosphorylation of BAD, a pro-apoptotic member of the Bcl-2 family of proteins. Under normal conditions, BAD will inhibit Bcl-2 and various members of the Bcl-2 family by direct binding (253). Phosphorylation of BAD changes its affinity for Bcl-2 molecules, and localizes BAD to the cytosol where its pro-apoptotic activity is neutralized. Insulin-like Growth Factor-II is a potent -cell growth factor, which exerts the majority of its effects, including inhibition of apoptosis via the PI3K/Akt pathway (Figure 1). Based on this, our study aimed to investigate the utility of a novel IGF-II gene therapy strategy to promote islet graft survival following transplantation.

Conclusions/Interpretation:

1. Adenoviral (Ad)-IGF-II mediates local and specific over expression of IGF-II in transduced islet cells without affecting islet viability or function

2. IGF-II promotes islet survival against pro-inflammatory cytokine induced apoptosis in vitro and improves transplant outcomes in vivo, a process shown in our paper to be mediated via the interaction of anti-apoptotic IGF-II with the IGF-1R on the islet cell surface

3. The major novel aspect of this work is the finding that up to a 34-fold lower concentration of human IGF-II is required to prevent in vitro and in vivo islet cell apoptosis, compared to that of previously published studies. Furthermore, the use of a transient Ad-based vector to over express IGF-II negates the need for every islet cell to be transduced, as IGF-II works to inhibit apoptosis via autocrine and paracrine mechanisms. Thus, clinically Ad-IGF-II represents a promising candidate vector to improve islet survival in the peri- and post-transplant period.

 

Amy Hughes-2

Figure Legend

Insulin-Like Growth Factor-II Signalling Pathway. IGF-II mediates its anti apoptotic effects through binding the IGF-IR. Following receptor activation, the phosphoinositide-3-kinase (PI3K)/Akt pathway plays a central role in controlling both cell growth and cell survival. Akt induces phosphorylation of BAD, a pro-apoptotic member of the bcl-2 family of proteins. Under normal conditions, BAD inhibits Bcl-2 and various members of the Bcl-2 family by direct binding. However, phosphorylation of BAD changes its affinity for Bcl-2 molecules, and localizes BAD to the cytosol where its pro-apoptotic activity is neutralized.

 

 

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