Intraislet Endothelial Cells Research Articles

116.4: Crosstalk signaling mechanisms that regulate intra-islet endothelial cells survival and peri-islet vessel formation: Role of novel intra-pancreatic microvessel fragments

116.4: Crosstalk signaling mechanisms that regulate intra-islet endothelial cells survival and peri-islet vessel formation: Role of novel intra-pancreatic microvessel fragments

302.2: Beneficial effects of microvascular fragments and stromal vascular fraction cells collected from human peripancreatic fat for stimulating intra-islet endothelial cells to form peri-islet vessels in human islets during co-culture and co-transplantation

302.2: Beneficial effects of microvascular fragments and stromal vascular fraction cells collected from human peripancreatic fat for stimulating intra-islet endothelial cells to form peri-islet vessels in human islets during co-culture and co-transplantation

UPREGULATION OF ISLET-1 IN ISLETS CO-CULTURED WITH BONE MARROW MESENCHYMAL STEM CELLS PROMOTES ANGIOGENESIS THROUGH NF-ΚB PATHWAYS

Purpose: Deficient angiogenesis in the early stage of islets transplantation is one of the main obstacles to its clinical application. Several studies have confirmed that co-transplantation of bone marrow mesenchymal stem cells (BMSCs) and islets can improve the angiogenesis in early transplanted islets, but the mechanism remaining further characterized. Islet-1 (Isl1) is a (LIM)-homeodomain transcription factor important for pancreatic islet cells development, maturation, and function.Importantly Isl1 can enhance the release of vascular endothelial growth factor-a (VEGF-A) in human umbilical vein endothelial cells and plays a vital role in angiogenesis. The aim of this study was to investigate whether upregulation of Isl1expression in islets co-cultured with BMSCs improved the poor angiogenesis in the early stage of islets transplantation. Methods: Primary islet cells isolated from Lewis rats and rat β cell line (INS-1) were cultured with or without BMSCs for 48 hours respectively, and then the islets function was detected by glucose-stimulated insulin secretion (GSIS). Viability of islets was measured using fluorescein diacetate and PI staining. The apoptosis assay of islets was performed by cytometry. Quantitative RT-PCR, immunoblot and immunofluorescence were enrolled to examine the mRNA and protein expression of Isl1 and VEGF-A of primary islet cells or INS-1 in co-culture and culture groups.Besides, we used lentiviral vector, GV358-Isl1, to increase Isl1 in INS-1 and corroborated the increase of Isl1,activator of the nuclear factor-kappa B (NF-κB) and VEGF protein levels by immunoblot analysis. Results: Co-culture of rat islet cells with BMSCs can improve rat survival rate and maintain glucose-induced insulin secretion. Though BMSCs cannot improve the loss of intraislet endothelial cells in early islet cells, it can reduce the early apoptosis rate of islet cells.Importantly, co-culture with BMSCs provoked both the mRNA and protein expressions of Isl1 and induced the expression of VEGF-A in islet cells.Our further study found that Isl1 overexpression of INS-1 greatly enhanced expression of NF-κB p65 and VEGF-A. Conclusion: Co-culture with BMSCs could induce the expression of ISL1 in islets, which promote angiogenesis by NF-κB pathways and ultimately ameliorate ischemia and hypoxia to improve the graft’s activity and survival rate. National Nature Science Foundation of China (grant no. 81970670).. National Nature Science Foundation of China (grant no. 81970688).. Correspondence to: Dr Xiaoming Ding, Department of Kidney Transplantation, Nephropathy Hospital, the First Affiliated Hospital of Xi’an Jiaotong University, Xi’an, People’s Republic of China.

Extracellular Matrix-Associated Factors Play Critical Roles in Regulating Pancreatic β-Cell Proliferation and Survival.

This review describes formation of the islet basement membrane and the function of extracellular matrix (ECM) components in β-cell proliferation and survival. Implications for islet transplantation are discussed. The insulin-producing β-cell is key for maintaining glucose homeostasis. The islet microenvironment greatly influences β-cell survival and proliferation. Within the islet, β-cells contact the ECM, which is deposited primarily by intraislet endothelial cells, and this interaction has been shown to modulate proliferation and survival. ECM-localized growth factors, such as vascular endothelial growth factor and cellular communication network 2, signal through specific receptors and integrins on the β-cell surface. Further understanding of how the ECM functions to influence β-cell proliferation and survival will provide targets for enhancing functional β-cell mass for the treatment of diabetes.

299-LB: Endothelial Regulation of Pancreatic ß-Cell Homeostasis in Diabetes

Diabetes is the result of having an inadequate supply of functional insulin-producing β-cells. Efforts in research and development that focused on using systemic pathway to induce β-cell regeneration have had limited clinical success. Emerging studies implicate local islet molecular and cellular factors in pancreatic β-cell homeostasis. Intraislet endothelial cells (IECs), a key ally of pancreatic β-cells, secrete factors that could affect β-cell survival and insulin production. Fibroblast growth factor (FGF) 21 is an endocrine hormone that regulates energy homeostasis and insulin sensitivity. The function of endogenous FGF-21 derived from ECs is undefined in diabetes. With a loss-of-function approach, this study sought to determine the role of EC-FGF-21 in pancreatic β-cell homeostasis in STZ-induced diabetic mice and high-fat diet (HFD)-induced obese mice. Mice with EC-specific deletion of FGF-21 gene (EC-FKO) were generated by crossing Tie2-Cre mice with FGF-21loxP mice. In 8-to-10-week-old male mice (n=15/group) treated with STZ (50 mg/kg, i.p. for consecutive 5d and killed 4 weeks later), EC-FKO vs. wild type C57BL/6J (WT) mice displayed more severe hyperglycemia, degeneration of insulin-producing β-cells, and expansion of glucagon-producing α-cells. Both groups showed similar changes in pancreatic Glut2 and PARP1 protein levels and vascular density. In 8-to-10-week-old WT male mice (n=15/group) fed an HFD (TestDiet: 60% energy from fat) for 16 weeks, obesity and insulin resistance developed, along with lipid accumulation in the islet and compensatory expansion of β-cell mass, all of which were worsened, except for less β-cell mass expansion, in EC-FKO mice. Our latest immunofluorescent data showed a significant reduction of IEC-FGF-21 protein staining in WT mice treated with STZ or HFD vs. non-treated mice. Our findings suggest that EC-FGF-21 is required to maintain β-cell homeostasis under stress conditions. Loss of IEC-FGF-21 may contribute, at least in part, to β-cell degeneration in diabetes. Disclosure M. Li: None. M. Qian: None. J. Xu: None. Funding National Institutes of Health

Pancreatic Islets in Short Duration Type 2 Diabetes (T2D) Show Macrophage Infiltration and Increased Inflammatory Signaling

T2D is characterized by progressive pancreatic islet dysfunction; however, dissecting causes of this dysfunction in humans is challenging due to disease heterogeneity and the difficulty of obtaining relevant pancreatic samples. To address these challenges, we used an integrated approach to functionally and molecularly study the native pancreas and isolated islets from the same human T2D cadaveric donor. Using associated donor clinical information, we focused on donors with short disease duration (n=10, age 47-66 years, 2-7-year duration, oral medications). Compared to age-matched control islets, T2D islets had dysfunctional insulin (decreased) and glucagon (increased) secretion despite similar insulin and glucagon content. Tissue-section analysis of T2D pancreata showed no difference in relative endocrine (α, β and δ) cell composition. To assess for changes in the islet microenvironment, we analyzed macrophages by staining with Iba1 and endothelial cells with Caveolin-1 and found a 2-fold increase in intraislet macrophages (T2D vs. control: 3.01% vs. 1.45% by area) but no change in intraislet endothelial cell area (T2D vs. control: 8.97% vs. 8.21% by area). Interestingly, costaining with Iba1 and thioflavin S demonstrated that T2D islets with amyloid did not have increased macrophage infiltration compared to T2D islets without amyloid although a close spatial association of macrophages and amyloid deposits was noted. RNA-sequencing analysis of FACS-purified α and β cells from T2D islets showed increased inflammatory signaling pathways in both cell types. Specifically, transcripts for cytokine receptors such as IL6R, IL1R1, and IFNGR1 as well as downstream regulators including NFKB1 and NFKB2 were elevated in T2D α and/or β cells. Together, these data suggest that early in the course of T2D, increased macrophages in the islet microenvironment may lead to elevated α and β cell inflammatory signaling and contribute to human α and β cell dysfunction. Disclosure J.T. Walker: None. S. Shrestha: None. N. Prasad: None. T. Richardson: None. R. Aramandla: None. G. Poffenberger: None. R. Bottino: None. M. Brissova: None. A.C. Powers: None.

Local Sphingosine Kinase 1 Activity Improves Islet Transplantation.

Pancreatic islet transplantation is a promising clinical treatment for type 1 diabetes, but success is limited by extensive β-cell death in the immediate posttransplant period and impaired islet function in the longer term. Following transplantation, appropriate vascular remodeling is crucial to ensure the survival and function of engrafted islets. The sphingosine kinase (SK) pathway is an important regulator of vascular beds, but its role in the survival and function of transplanted islets is unknown. We observed that donor islets from mice deficient in SK1 (Sphk1 knockout) contain a reduced number of resident intraislet vascular endothelial cells. Furthermore, we demonstrate that the main product of SK1, sphingosine-1-phosphate, controls the migration of intraislet endothelial cells in vitro. We reveal in vivo that Sphk1 knockout islets have an impaired ability to cure diabetes compared with wild-type controls. Thus, SK1-deficient islets not only contain fewer resident vascular cells that participate in revascularization, but likely also a reduced ability to recruit new vessels into the transplanted islet. Together, our data suggest that SK1 is important for islet revascularization following transplantation and represents a novel clinical target for improving transplant outcomes.

Intra-islet endothelial cell and β-cell crosstalk: Implication for islet cell transplantation.

The intra-islet microvasculature is a critical interface between the blood and islet endocrine cells governing a number of cellular and pathophysiological processes associated with the pancreatic tissue. A growing body of evidence indicates a strong functional and physical interdependency of β-cells with endothelial cells (ECs), the building blocks of islet microvasculature. Intra-islet ECs, actively regulate vascular permeability and appear to play a role in fine-tuning blood glucose sensing and regulation. These cells also tend to behave as “guardians”, controlling the expression and movement of a number of important immune mediators, thereby strongly contributing to the physiology of islets. This review will focus on the molecular signalling and crosstalk between the intra-islet ECs and β-cells and how their relationship can be a potential target for intervention strategies in islet pathology and islet transplantation.

Mechanisms of Angiogenesis Process after Pancreatic Islet Cell Transplantation: Role of Intra-islet Endothelial Cells

Angiogenic sprouting is a complex, multi-step process involving highly integrated cell behaviours, initial interaction with the environment and signalling pathways. Endothelial cells (ECs) are central to the angiogenic process, with recent insights establishing how these cells communicate with each other and with their microenvironment to form branched vascular networks. Using pancreatic islets as a model for vascularized tissue, this review will present a general overview of EC behaviour dynamics in sprouting angiogenesis, particularly focusing on the interplay between VEGF and Notch pathways. A better understanding of molecular mechanisms associated with intra-islet EC cross-talk and its micro-environment may present exciting new perspectives on islet graft to host revascularization and in supporting islet graft survival.

ALK5 inhibition maintains islet endothelial cell survival but does not enhance islet graft revascularisation or function.

Islet transplantation is a potential treatment for Type 1 diabetes but long term graft function is suboptimal. The rich supply of intraislet endothelial cells diminishes rapidly after islet isolation and culture, which affects the revascularisation rate of islets after transplantation. The ALK5 pathway inhibits endothelial cell proliferation and thus inhibiting ALK5 is a potential target for improving endothelial cell survival. The aim of the study was to establish whether ALK5 inhibition prevents the loss of intraislet endothelial cells during islet culture and thus improves the functional survival of transplanted islets by enhancing their subsequent revascularisation after implantation. Islets were cultured for 48 h in the absence or presence of 2 different ALK inhibitors: SB-431542 or A-83-01. Their vascular density after culture was analysed using immunohistochemistry. Islets pre-cultured with the ALK5 inhibitors were implanted into streptozotocin-diabetic mice for either 3 or 7 days and blood glucose concentrations were monitored and vascular densities of the grafts were analysed. Islets cultured with ALK5 inhibitors had higher vascular densities than control-cultured islets. Three days after implantation, endothelial cell numbers in islet grafts were minimal, irrespective of treatment during culture. Seven days after implantation, endothelial cells were evident within the islet grafts but there was no difference between control-cultured islets and islets pre-treated with an ALK5 inhibitor. Blood glucose concentrations were no different between the treatment groups. In conclusion, inhibition of ALK5 improved intraislet endothelial cell numbers after islet culture, but this effect was lost in the early post-transplantation period.

Vascular endothelial growth factor coordinates islet innervation via vascular scaffolding

Neurovascular alignment is a common anatomical feature of organs, but the mechanisms leading to this arrangement are incompletely understood. Here, we show that vascular endothelial growth factor (VEGF) signaling profoundly affects both vascularization and innervation of the pancreatic islet. In mature islets, nerves are closely associated with capillaries, but the islet vascularization process during embryonic organogenesis significantly precedes islet innervation. Although a simple neuronal meshwork interconnects the developing islet clusters as they begin to form at E14.5, the substantial ingrowth of nerve fibers into islets occurs postnatally, when islet vascularization is already complete. Using genetic mouse models, we demonstrate that VEGF regulates islet innervation indirectly through its effects on intra-islet endothelial cells. Our data indicate that formation of a VEGF-directed, intra-islet vascular plexus is required for development of islet innervation, and that VEGF-induced islet hypervascularization leads to increased nerve fiber ingrowth. Transcriptome analysis of hypervascularized islets revealed an increased expression of extracellular matrix components and axon guidance molecules, with these transcripts being enriched in the islet-derived endothelial cell population. We propose a mechanism for coordinated neurovascular development within pancreatic islets, in which endocrine cell-derived VEGF directs the patterning of intra-islet capillaries during embryogenesis, forming a scaffold for the postnatal ingrowth of essential autonomic nerve fibers.

The endocrine role between β cells and intra-islet endothelial cells [Review

The islets of Langerhans is the endocrine function region of pancreas, which exist in five cell types. The majority of endocrine cells are insulin-secreting β cells, mixed up with glucagon-secreting α-cells. The islets of Langerhans are highly vascularized, and the capillary network around the islet is about five times denser than that in the exocrine tissues. It guarantees endocrine cells adequately contact with the capillary networks. Above mentioned is the basis of deep study the interaction between β cells and capillary. Increasing number of studies contribute to the consensus that endothelial cells have positive effects in the islet microenvironment. Endothelial cells can act as endocrine cells which release many active substances, such as hepatocyte growth factors (HGF), thrombospondin-1(TSP-1), laminins, and collagens by means of different molecule pathways, inducing β cells differentiation, proliferation, survivor, and insulin release next to the vessels. Apart from the effect of endothelial cells on β cells by paracrine fashion, the islets can utilize VEGF-A, angiopoietin-1 and insulin signaling to increase the interaction with endothelial cells. As the endocrine role of endothelial cells to β cells, it may be a novel target to stimulate β cells regeneration, promote vascularization post islet transplantation strategy in the treatment of diabetes mellitus.

The β-Cell/EC Axis: How Do Islet Cells Talk to Each Other?

Within the pancreatic islet, the β-cell represents the ultimate biosensor. Its central function is to accurately sense glucose levels in the blood and consequently release appropriate amounts of insulin. As the only cell type capable of insulin production, the β-cell must balance this crucial workload with self-preservation and, when required, regeneration. Evidence suggests that the β-cell has an important ally in intraislet endothelial cells (ECs). As well as providing a conduit for delivery of the primary input stimulus (glucose) and dissemination of its most important effector (insulin), intraislet blood vessels deliver oxygen to these dense clusters of metabolically active cells. Furthermore, it appears that ECs directly impact insulin gene expression and secretion and β-cell survival. This review discusses the molecules and pathways involved in the crosstalk between β-cells and intraislet ECs. The evidence supporting the intraislet EC as an important partner for β-cell function is examined to highlight the relevance of this axis in the context of type 1 and type 2 diabetes. Recent work that has established the potential of ECs or their progenitors to enhance the re-establishment of glycemic control following pancreatic islet transplantation in animal models is discussed.

Pancreatic Islet Vasculature Adapts to Insulin Resistance Through Dilation and Not Angiogenesis

Pancreatic islets adapt to insulin resistance through a complex set of changes, including β-cell hyperplasia and hypertrophy. To determine if islet vascularization changes in response to insulin resistance, we investigated three independent models of insulin resistance: ob/ob, GLUT4+/−, and mice with high-fat diet–induced obesity. Intravital blood vessel labeling and immunocytochemistry revealed a vascular plasticity in which islet vessel area was significantly increased, but intraislet vessel density was decreased as the result of insulin resistance. These vascular changes were independent of islet size and were only observed within the β-cell core but not in the islet periphery. Intraislet endothelial cell fenestration, proliferation, and islet angiogenic factor/receptor expression were unchanged in insulin-resistant compared with control mice, indicating that islet capillary expansion is mediated by dilation of preexisting vessels and not by angiogenesis. We propose that the islet capillary dilation is modulated by endothelial nitric oxide synthase via complementary signals derived from β-cells, parasympathetic nerves, and increased islet blood flow. These compensatory changes in islet vascularization may influence whether β-cells can adequately respond to insulin resistance and prevent the development of diabetes.

Donor Islet Endothelial Cells in Pancreatic Islet Revascularization

OBJECTIVEFreshly isolated pancreatic islets contain, in contrast to cultured islets, intraislet endothelial cells (ECs), which can contribute to the formation of functional blood vessels after transplantation. We have characterized how donor islet endothelial cells (DIECs) may contribute to the revascularization rate, vascular density, and endocrine graft function after transplantation of freshly isolated and cultured islets.RESEARCH DESIGN AND METHODSFreshly isolated and cultured islets were transplanted under the kidney capsule and into the anterior chamber of the eye. Intravital laser scanning microscopy was used to monitor the revascularization process and DIECs in intact grafts. The grafts’ metabolic function was examined by reversal of diabetes, and the ultrastructural morphology by transmission electron microscopy.RESULTSDIECs significantly contributed to the vasculature of fresh islet grafts, assessed up to 5 months after transplantation, but were hardly detected in cultured islet grafts. Early participation of DIECs in the revascularization process correlated with a higher revascularization rate of freshly isolated islets compared with cultured islets. However, after complete revascularization, the vascular density was similar in the two groups, and host ECs gained morphological features resembling the endogenous islet vasculature. Surprisingly, grafts originating from cultured islets reversed diabetes more rapidly than those originating from fresh islets.CONCLUSIONSIn summary, DIECs contributed to the revascularization of fresh, but not cultured, islets by participating in early processes of vessel formation and persisting in the vasculature over long periods of time. However, the DIECs did not increase the vascular density or improve the endocrine function of the grafts.

Effects of atorvastatin on the regeneration of pancreatic β-cells after streptozotocin treatment in the neonatal rodent

To investigate the role of statins in beta-cell regeneration a model of streptozotocin (STZ)-induced beta-cell injury was used in the neonatal rat. We hypothesized that beta-cell growth and regeneration would increase following treatment with atorvastatin and that this would be associated with intraislet vasculogenesis. Pregnant Wistar rats were gavaged with 20 or 40 mg/kg atorvastatin for 21 days commencing on gestation day 15. Atorvastatin was detected in the circulation of the offspring. On postnatal day 4, the pups were given either a control or STZ (70 mg/kg ip) injection. beta-Cell mass had partially recovered by postnatal day 44 following STZ treatment, and atorvastatin (20 mg/kg) significantly increased beta-cell mass in both STZ-treated and control animals. An increase in the numbers of small islets at postnatal day 44 was seen in STZ-treated animals following atorvastatin, suggestive of neogenesis, and glucose tolerance was improved. Treatment with atorvastatin caused an increase in the numbers of intraislet endothelial cells at postnatal day 14 and the percentage of endothelial cells undergoing DNA synthesis, suggesting that angiogenesis had preceded the increase in beta-cell mass. The results indicate that functional beta-cell mass was expanded with atorvastatin in both control and STZ-treated neonatal rats and suggests a novel effect of a statin in promoting islet plasticity.

Changes in islet microvasculature following streptozotocin-induced β-cell loss and subsequent replacement in the neonatal rat

Neonatal rats undergo considerable beta-cell regeneration after depletion with streptozotocin (STZ). Since the intraislet vasculature is necessary for both beta-cell growth and function, we examined changes in vascular morphology following STZ. Neonatal Wistar rats (4 days) were injected with 70 mg/kg STZ, or buffer, and were examined between days 4 and 40 postinjection. Animals receiving STZ were relatively hyperglycemic for eight days, but became normoglycemic subsequent to a partial recovery of beta-cell mass. However, glucose tolerance remained impaired. The intraislet area occupied by capillaries was significantly reduced by approximately 20% following STZ, mainly within the beta-cell-rich islet core, but had recovered by day 40. Vascular endothelial growth factor (VEGF) was localized to beta-cells, and pancreatic VEGF mRNA levels in control animals showed a progressive increase between days 4 and 20. This rise was delayed following STZ, but by day 20 VEGF mRNA abundance exceeded that in control pancreas. Hepatocyte growth factor (HGF) was localized to intraislet endothelial cells. Levels of HGF mRNA increased until day 16 in control rats, but subsequently declined to low levels. Following STZ, HGF mRNA had declined prematurely after day 12. Type IV collagen was localized to the extracellular matrix around the intraislet vasculature. The islet area immunopositive for collagen was significantly reduced at all times following STZ. Results indicate that there is a relative loss of intraislet vasculature following STZ, which may limit subsequent beta-cell regeneration through both local growth factor and extracellular matrix interactions.

Effects of Anti-Vascular Endothelial Growth Factor (VEGF) on Pancreatic Islets in Mouse Model of Type 2 Diabetes Mellitus

Background: Vascular endothelial growth fact or (VEGF) is associated with the development of diabetic complications. However, it is unknown whether systemic VEGF tre atment has any effects on the pancreatic islets in an animal model of type 2 diabetes mellitus. Methods: Anti-VEGF peptide (synthetic ATWLPPR, VEGF receptor type 2 ant agonist) was injected into db/db mice for 12 weeks. We analyzed pancreatic islet morphology and quantified beta-cell mass. Endothelial cell proliferation and the severity of islet fibrosis were also measured. VEGF expression in isolated islets was determined using Western blot analysis. Results: When anti-VEGF was administered, db/db mice exhibited more severe hyperglycemia and associated delayed weight gain than non-treated db/db mice. Pancreas weight and pancreatic beta-cell mass were also significantly decreased in the anti-VEGF-treated group. VEGF and VEGF receptor proteins (types 1 and 2) were expressed in the pancreatic islets, and their expression was significantly increased in the db/db group compared with the db/dm group. However, the elevated VEGF expression was significantly reduced by anti-VEGF treatment compared with the db/db group. T he anti-VEGF-treated group had more prominent islet fibrosis and islet destruction than db/db mice. Intra-islet endothelial cell proliferation was also remarkably reduced by the anti-VEGF peptide. Conclusion: Inhibition of VEGF action by the VEGF receptor 2 antagonist not only suppressed the proliferation of intra-islet endothelial cells but also accelerated pancreatic islet destruction and aggravated hyperglycemia in a type 2 diabetes mouse model. Therefore, the potential effects of anti-VEGF treatment on pancreatic beta cell damage should be considered. (Korean Diabetes J 33:185-197, 2009)

An Islet-Stabilizing Implant Constructed Using a Preformed Vasculature

Islet transplantation for the purpose of treating insulin-sensitive diabetes is currently limited by several factors, including islet survival posttransplantation. In the current study, a tissue-engineered prevascularized pancreatic encapsulating device (PPED) was developed. Isolated islets were placed in collagen gels, and they exhibited fourfold more insulin release than islets not in collagen. The insulin released by beta-cells in islets encapsulated in collagen exhibited unobstructed diffusion within the collagen gels. Subsequent studies evaluated the ability to create a sandwich comprised of two layers of prevascularized collagen gels around a central collagen gel containing islets. In vitro characterization of the islets showed that islets are functional and responded to glucose stimulation. The PPEDs were implanted subcutaneously into severe combined immunodeficient mice. Islet survival was assessed after 7, 14, and 28 days. Immunohistochemical analysis was performed on the implants to detect insulin and the presence of intraislet endothelial cells. At all time points, insulin was localized in association with intact and partially dissociated islets. Moreover, cells that exhibited insulin staining were colocalized with intraislet endothelial cells. These data indicate that the PPED enhances islet survival by supporting islet viability and maintaining intraislet endothelial cell structures.

Role of Intra-Islet Endothelial Cells in Islet Allo-Immunity

Intra-islet endothelial cells (IECs) express high levels of major histocompatibility complex (MHC) and are pivotal for posttransplant islet revascularization. We postulated that donor-specific sensitization would result in hyperacute rejection of IECs and prevent islet engraftment. Furthermore, ligation of endothelial cells with subsaturating concentrations of anti-MHC class I antibody (Ab) results in "accommodation" conferring protection against Ab/complement-mediated lysis. Therefore, we investigated whether accommodation of IECs would prevent hyperacute rejection of islets in sensitized recipients. Islets were transplanted beneath the kidney capsule and allograft survival monitored using daily blood glucose (diabetes >300 mg/dL, normoglycemia <150 mg/dL). Recipients were presensitized with donor islets, splenocytes, or skin. Accommodation was induced by incubating human or murine islets with varying concentrations of anti-MHC class I Ab ex vivo. Isografts remained functional for >100 days, whereas allografts were rejected by day 14. Islet allo-transplantation induced donor-specific but not third-party anti-MHC Abs. Donor-specific, but not third-party, sensitization induced hyperacute rejection of subsequent islet allografts (median survival 1 day) associated with complement deposition. Preincubation of islets with subsaturating concentrations of anti-MHC-I Abs (1-100 ng/mL) up-regulated Bcl-2, Bcl-xl, and HO-1 within CD31+ IEC. These accommodated islets were resistant against hyperacute rejection when transplanted into donor-(splenocyte) sensitized recipients without any immunosuppression (median survival 6 days). Pretransplant sensitization against donor antigens results in hyperacute rejection of murine islets. IECs may play a crucial role in development of donor-specific immunity after islet transplantation. Significantly, accommodation of IEC may confer resistance to hyperacute rejection in sensitized recipients.