Nerve growth factor is associated with islet graft failure following intraportal transplantation

Retinal Pigment Epithelium Specific Metabolic Phenotypes Are Regulated by High-Mobility Group Protein N1

Purpose

The retinal pigment epithelium (RPE) performs life-long phagocytosis of lipid-rich photoreceptor outer segments and exchanges energy metabolites with photoreceptors to support retinal function. The metabolites of glucose and lipid metabolism are interconnected, but it is unclear how the specialized lipid metabolism of RPE and glucose metabolism are regulated. We have investigated this unique mechanism.

Methods

To identify factors involved in regulation of metabolism in RPE we compared and screened the human retinal pigment epithelial cell line, ARPE-19 under different conditions. Using the results of these experiments we selected the high-mobility group nucleosome-associated protein 1 (HMGN1) as a candidate and analyzed HMGN1 deleted ARPE-19 (HGMN1-/--ARPE-19) and Hmgn1 knock-out mice (Hmgn1-/- mice).

Results

HMGN1 was identified as being involved in energy metabolism via altered expression. HMGN1-/--ARPE-19 cells prefer fatty acid oxidation over glucose metabolism as an energy source. Hmgn1-/- mice had a lower lipid weight of epididymal fat mass and serum lipids than those of control on a standard diet and showed impaired glucose tolerance. The mice also showed retinal dysfunction, similar to that observed in aged control retina as measured by electroretinogram. However, a palmitate-rich diet, as well as RPE-specific HMGN1 re-expression mitigated retinal dysfunction. HMGN1 is specifically downregulated in the RPE/choroid with aging, which is reminiscent of age-related metabolic changes in RPE/choroid.

Conclusions

HMGN1 is involved in energy metabolism and its altered expression modulates RPE-specific metabolic phenotypes.

A gelatin hydrogel nonwoven fabric improves outcomes of subcutaneous islet transplantation

Subcutaneous islet transplantation is a promising treatment for severe diabetes; however, poor engraftment hinders its prevalence. We previously reported that a recombinant peptide (RCP) enhances subcutaneous islet engraftment. However, it is impractical for clinical use because RCP must be removed when transplanting islets. We herein investigated whether a novel bioabsorbable gelatin hydrogel nonwoven fabric (GHNF) could improve subcutaneous islet engraftment. A silicon spacer with or without GHNF was implanted into the subcutaneous space of diabetic mice. Syngeneic islets were transplanted into the pretreated space or intraportally (Ipo group). Blood glucose, intraperitoneal glucose tolerance, immunohistochemistry, CT angiography and gene expression were evaluated. The cure rate and glucose tolerance of the GHNF group were significantly better than in the control and Ipo groups (p < 0.01, p < 0.05, respectively). In the GHNF group, a limited increase of vWF-positive vessels was detected in the islet capsule, whereas laminin (p < 0.05), collagen III and IV were considerably enhanced. TaqMan arrays revealed a significant upregulation of 19 target genes (including insulin-like growth factor-2) in the pretreated space. GHNF markedly improved the subcutaneous islet transplantation outcomes, likely due to ECM compensation and protection of islet function by various growth factors, rather than enhanced neovascularization.

Human Adipose-Derived Mesenchymal Stem Cells Respond to Short-Term Hypoxia by Secreting Factors Beneficial for Human Islets In Vitro and Potentiate Antidiabetic Effect In Vivo

Adipose-derived mesenchymal stem cells (ASCs) release factors beneficial for islets in vitro and protect against hyperglycemia in rodent models of diabetes. Oxygen tension has been shown to induce metabolic changes and alter ASCs' release of soluble factors. The effects of hypoxia on the antidiabetic properties of ASCs have not been explored. To investigate this, we incubated human ASCs for 48 h in 21% (normoxia) or 1% O₂ (hypoxia) and compared viability, cell growth, surface markers, differentiation capability, and soluble factors in the conditioned media (CM). Human islets were exposed to CM from ASCs incubated in either normoxia or hypoxia, and islet function and apoptosis after culture with or without proinflammatory cytokines were measured. To test hypoxic preconditioned ASCs' islet protective effects in vivo, ASCs were incubated for 48 h in normoxia or hypoxia before being injected into Balb/c Rag 1^-/- immunodeficient mice with streptozotocin-induced insulitis. Progression of diabetes and insulin content of pancreas were measured. We found that incubation in hypoxia was well tolerated by ASCs and that levels of VEGF-A, FGF-2, and bNGF were elevated in CM from ASCs incubated in hypoxia compared to normoxia, while levels of HGF, IL-8, and CXCL1 were reduced. CM from ASCs incubated in hypoxia significantly improved human islet function and reduced apoptosis after culture, and reduced cytokine-induced apoptosis. In our mouse model, pancreas insulin content was higher in both groups receiving ASCs compared to control, but the mice receiving preconditioned ASCs had lower random and fasting blood glucose, as well as improved oral glucose tolerance compared to untreated mice. In conclusion, our in vitro results indicate that the islet protective potential of ASCs improves in hypoxia, and we give insight into factors involved in this. Finally we show that hypoxic preconditioning potentiates ASCs' antidiabetic effect in vivo.

Nerve Growth Factor Improves Survival and Function of Transplanted Islets Via TrkA-mediated β Cell Proliferation and Revascularization

BACKGROUND

Nerve growth factor (NGF), which plays important roles in promoting growth and differentiation of nerve cells, has recently been reported as a regulator in pancreatic β cells in terms of insulin releasing function. In this study, we examined whether NGF stimulation would promote islet graft survival and function in islet transplantation.

METHODS

We found that supplementation of cultured islets with NGF improved the viability of islet cells and induced the production of insulin, vascular endothelial growth factor, and cellular proliferative markers. Because a specific inhibitor of TrkA, K252a, blocked all these effects, we propose that the TrkA receptor is the mediator of NGF stimulation.

RESULTS

After transplantation to the kidney subcapsule and liver of syngenic diabetic mice, a higher rate of normoglycemic achievement, increased serum insulin, and improved glucose tolerance were observed in the mice transplanted with NGF-pretreated islet grafts. Histological analysis revealed higher expression of insulin and vascular endothelial growth factor, an increase in proliferative β cells, and revascularization in NGF-pretreated islet grafts without activation of any inflammatory cells.

CONCLUSIONS

The NGF treatment can therefore serve as a new and promising therapeutic tool for improving islet graft viability and function in islet transplantation.