Linalool inhibits the angiogenic activity of endothelial cells by downregulating intracellular ATP levels and activating TRPM8.

Angiogenesis crucially contributes to various diseases, such as cancer and diabetic retinopathy. Hence, anti-angiogenic therapy is considered as a powerful strategy against these diseases. Previous studies reported that the acyclic monoterpene linalool exhibits anticancer, anti-inflammatory and anti-oxidative activity. However, the effects of linalool on angiogenesis still remain elusive. Therefore, we investigated the action of (3R)-(-)-linalool, a main enantiomer of linalool, on the angiogenic activity of human dermal microvascular endothelial cells (HDMECs) by a panel of angiogenesis assays. Non-cytotoxic doses of linalool significantly inhibited HDMEC proliferation, migration, tube formation and spheroid sprouting. Linalool also suppressed the vascular sprouting from rat aortic rings. In addition, Matrigel plugs containing linalool exhibited a significantly reduced microvessel density 7 days after implantation into BALB/c mice. Mechanistic analyses revealed that linalool promotes the phosphorylation of extracellular signal-regulated kinase (ERK), downregulates the intracellular level of adenosine triphosphate (ATP) and activates the transient receptor potential cation channel subfamily M (melastatin) member (TRPM)8 in HDMECs. Inhibition of ERK signaling, supplementation of ATP and blockade of TRPM8 significantly counteracted linalool-suppressed HDMEC spheroid sprouting. Moreover, ATP supplementation completely reversed linalool-induced ERK phosphorylation. In addition, linalool-induced ERK phosphorylation inhibited the expression of bone morphogenetic protein (BMP)-2 and linalool-induced TRPM8 activation caused the inhibition of ß1 integrin/focal adhesion kinase (FAK) signaling. These findings indicate an anti-angiogenic effect of linalool, which is mediated by downregulating intracellular ATP levels and activating TRPM8.

The Marine-Derived Triterpenoid Frondoside A Inhibits Thrombus Formation.

BACKGROUND: The marine-derived triterpenoid frondoside A inhibits the phosphatidylinositol-3-kinase (PI3K) pathway in cancer cells. Because this pathway is also crucially involved in platelet activation, we studied the effect of frondoside A on thrombus formation. METHODS: Frondoside A effects on platelet viability, surface adhesion molecule expression, and intracellular signaling were analyzed by flow cytometry and Western blot. The effect of frondoside A was analyzed by photochemically induced thrombus formation in the mouse dorsal skinfold chamber model and by tail vein bleeding. RESULTS: Concentrations of up to 15 µM frondoside A did not affect the viability of platelets, but reduced their surface expression of P-selectin (CD62P) and the activation of glycoprotein (GP)IIb/IIIa after agonist stimulation. Additional mechanistic analyses revealed that this was mediated by downregulation of PI3K-dependent Akt and extracellular-stimuli-responsive kinase (ERK) phosphorylation. Frondoside A significantly prolonged the complete vessel occlusion time in the mouse dorsal skinfold chamber model of photochemically induced thrombus formation and also the tail vein bleeding time when compared to vehicle-treated controls. CONCLUSION: Our findings demonstrated that frondoside A inhibits agonist-induced CD62P expression and activation of GPIIb/IIIa. Moreover, frondoside A suppresses thrombus formation. Therefore, this marine-derived triterpenoid may serve as a lead compound for the development of novel antithrombotic drugs.

Regulatory Mechanisms of Somatostatin Expression.

Somatostatin is a peptide hormone, which most commonly is produced by endocrine cells and the central nervous system. In mammals, somatostatin originates from pre-prosomatostatin and is processed to a shorter form, i.e., somatostatin-14, and a longer form, i.e., somatostatin-28. The two peptides repress growth hormone secretion and are involved in the regulation of glucagon and insulin synthesis in the pancreas. In recent years, the processing and secretion of somatostatin have been studied intensively. However, little attention has been paid to the regulatory mechanisms that control its expression. This review provides an up-to-date overview of these mechanisms. In particular, it focuses on the role of enhancers and silencers within the promoter region as well as on the binding of modulatory transcription factors to these elements. Moreover, it addresses extracellular factors, which trigger key signaling pathways, leading to an enhanced somatostatin expression in health and disease.

Protein Kinase CK2 Controls CaV2.1-Dependent Calcium Currents and Insulin Release in Pancreatic ß-Cells.

The regulation of insulin biosynthesis and secretion in pancreatic ß-cells is essential for glucose homeostasis in humans. Previous findings point to the highly conserved, ubiquitously expressed serine/threonine kinase CK2 as having a negative regulatory impact on this regulation. In the cell culture model of rat pancreatic ß-cells INS-1, insulin secretion is enhanced after CK2 inhibition. This enhancement is preceded by a rise in the cytosolic Ca2+ concentration. Here, we identified the serine residues S2362 and S2364 of the voltage-dependent calcium channel CaV2.1 as targets of CK2 phosphorylation. Furthermore, co-immunoprecipitation experiments revealed that CaV2.1 binds to CK2 in vitro and in vivo. CaV2.1 knockdown experiments showed that the increase in the intracellular Ca2+ concentration, followed by an enhanced insulin secretion upon CK2 inhibition, is due to a Ca2+ influx through CaV2.1 channels. In summary, our results point to a modulating role of CK2 in the CaV2.1-mediated exocytosis of insulin.

Nerve/glial antigen 2 is crucially involved in the revascularization of freely transplanted pancreatic islets.

Pancreatic islets are highly vascularized endocrine units. Accordingly, their adequate revascularization is of major importance for successful islet transplantation. The proteoglycan, nerve/glial antigen 2 (NG2) expressed in pericytes is a crucial regulator of angiogenesis. Therefore, we herein analyze whether this surface protein contributes to the revascularization of grafted islets. Islets were isolated from NG2+/+ (wild-type) and NG2-/- mice and their cellular composition was analyzed by immunohistochemical detection of insulin, glucagon, somatostatin and CD31. Moreover, insulin secretion was assessed by enzyme-linked immunosorbent assay (ELISA). In addition, isolated islets were transplanted into dorsal skinfold chambers of wild-type mice and their revascularization was determined by intravital fluorescence microscopy and immunohistochemistry. NG2+/+ and NG2-/- islets did not differ in their cellular composition and insulin secretion. However, transplanted NG2-/- islets exhibited a significantly lower functional capillary density and a reduced number of CD31-positive microvessels. These findings demonstrate that the loss of NG2 impairs the revascularization of transplanted islets, underlining the importance of this pericytic proteoglycan for islet engraftment.

Protein Kinase CK2-A Putative Target for the Therapy of Diabetes Mellitus?

Since diabetes is a global epidemic, the development of novel therapeutic strategies for the treatment of this disease is of major clinical interest. Diabetes is differentiated in two types: type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM). T1DM arises from an autoimmune destruction of insulin-producing ß-cells whereas T2DM is characterized by an insulin resistance, an impaired insulin reaction of the target cells, and/or dysregulated insulin secretion. In the past, a growing number of studies have reported on the important role of the protein kinase CK2 in the regulation of the survival and endocrine function of pancreatic ß-cells. In fact, inhibition of CK2 is capable of reducing cytokine-induced loss of ß-cells and increases insulin expression as well as secretion by various pathways that are regulated by reversible phosphorylation of proteins. Moreover, CK2 inhibition modulates pathways that are involved in the development of diabetes and prevents signal transduction, leading to late complications such as diabetic retinopathy. Hence, targeting CK2 may represent a novel therapeutic strategy for the treatment of diabetes.

Quinalizarin inhibits adipogenesis through down-regulation of transcription factors and microRNA modulation.

BACKGROUND: Protein kinase CK2 is induced early in adipogenesis whereas later on, this kinase seems to be dispensable. Here, we have analysed how CK2 might be involved in early steps of differentiation of 3T3-L1 cells. METHODS: 3T3-L1 cells were differentiated to adipocytes in the absence or presence of quinalizarin. The expression and localization of important transcription factors was analysed by Western blot and immunofluorescence. DNA binding capacity and transactivation was analysed with pull-down assays and with luciferase reporter experiments, respectively. mRNA was detected with qRT-PCR, miRNAs with Northern hybridization and qRT-PCR. RESULTS: We show that clonal expansion was considerably repressed upon inhibition of CK2 with quinalizarin. Moreover, to prevent adipogenesis CK2 inhibition had to take place before day 4 of differentiation. Neither the expression at the protein or at the RNA level nor the subcellular localization of the transcription factors C/EBPß and C/EBPδ was affected by CK2 inhibition. There was, however, a drastic reduction in the mRNA and protein levels of C/EBPα and PPARγ2. Upon inhibition of CK2, we found a significant up-regulation of the level of the microRNAs miR-27a and miR-27b, which are known to target PPARγ mRNA. CONCLUSIONS: Time course experiments revealed that CK2 seems to be required at early time points after the induction of differentiation. One important target of CK2 was identified as PPARγ, which is down-regulated after inhibition of CK2. GENERAL SIGNIFICANCE: This is the first report about i) cellular targets of CK2 during adipogenesis and ii) a role of CK2 in microRNA regulation.

HACE1 deficiency causes an autosomal recessive neurodevelopmental syndrome.

BACKGROUND: The genetic aetiology of neurodevelopmental defects is extremely diverse, and the lack of distinctive phenotypic features means that genetic criteria are often required for accurate diagnostic classification. We aimed to identify the causative genetic lesions in two families in which eight affected individuals displayed variable learning disability, spasticity and abnormal gait. METHODS: Autosomal recessive inheritance was suggested by consanguinity in one family and by sibling recurrences with normal parents in the second. Autozygosity mapping and exome sequencing, respectively, were used to identify the causative gene. RESULTS: In both families, biallelic loss-of-function mutations in HACE1 were identified. HACE1 is an E3 ubiquitin ligase that regulates the activity of cellular GTPases, including Rac1 and members of the Rab family. In the consanguineous family, a homozygous mutation p.R219* predicted a truncated protein entirely lacking its catalytic domain. In the other family, compound heterozygosity for nonsense mutation p.R748* and a 20-nt insertion interrupting the catalytic homologous to the E6-AP carboxyl terminus (HECT) domain was present; western blot analysis of patient cells revealed an absence of detectable HACE1 protein. CONCLUSION: HACE1 mutations underlie a new autosomal recessive neurodevelopmental disorder. Previous studies have implicated HACE1 as a tumour suppressor gene; however, since cancer predisposition was not observed either in homozygous or heterozygous mutation carriers, this concept may require re-evaluation.

A role and mechanism for redox sensing by SENP1 in ß-cell responses to high fat feeding.

Pancreatic ß-cells respond to metabolic stress by upregulating insulin secretion, however the underlying mechanisms remain unclear. Here we show, in ß-cells from overweight humans without diabetes and mice fed a high-fat diet for 2 days, insulin exocytosis and secretion are enhanced without increased Ca2+ influx. RNA-seq of sorted ß-cells suggests altered metabolic pathways early following high fat diet, where we find increased basal oxygen consumption and proton leak, but a more reduced cytosolic redox state. Increased ß-cell exocytosis after 2-day high fat diet is dependent on this reduced intracellular redox state and requires the sentrin-specific SUMO-protease-1. Mice with either pancreas- or ß-cell-specific deletion of this fail to up-regulate exocytosis and become rapidly glucose intolerant after 2-day high fat diet. Mechanistically, redox-sensing by the SUMO-protease requires a thiol group at C535 which together with Zn+-binding suppresses basal protease activity and unrestrained ß-cell exocytosis, and increases enzyme sensitivity to regulation by redox signals.

Targeting Pancreatic Islet NLRP3 Improves Islet Graft Revascularization.

Hypoxia-induced islet cell death, caused by an insufficient revascularization of the grafts, is a major obstacle for successful pancreatic islet transplantation. Recently, it has been reported that the nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome is expressed in pancreatic islets and that its loss protects against hypoxia-induced cell death. Therefore, we hypothesized that the inhibition of NLRP3 in islets improves the survival and endocrine function of the grafts. The transplantation of Nlrp3-/- islets or wild-type (WT) islets exposed to the NLRP3 inhibitor CY-09 into mouse dorsal skinfold chambers resulted in an improved revascularization compared with controls. An increased insulin release after NLRP3 inhibition caused the enhanced angiogenic response. Moreover, the inhibition of NLRP3 in hypoxic ß-cells triggered insulin gene expression by inducing the shuttling of MafA and pancreatic and duodenal homeobox-1 into the nucleus. This was mediated by a reduced interaction of NLRP3 with the thioredoxin-interacting protein (TXNIP). Transplantation of Nlrp3-/- islets or WT islets exposed to CY-09 under the kidney capsule of diabetic mice markedly improved the restoration of normoglycemia. These findings indicate that the inhibition of NLRP3 in isolated islets represents a promising therapeutic strategy to improve engraftment and function of the islets.

The loss of pancreatic islet NADPH oxidase (NOX)2 improves islet transplantation.

Islet transplantation is a promising treatment strategy for type 1 diabetes mellitus (T1DM) patients. However, oxidative stress-induced graft failure due to an insufficient revascularization is a major problem of this therapeutic approach. NADPH oxidase (NOX)2 is an important producer of reactive oxygen species (ROS) and several studies have already reported that this enzyme plays a crucial role in the endocrine function and viability of ß-cells. Therefore, we hypothesized that targeting islet NOX2 improves the outcome of islet transplantation. To test this, we analyzed the cellular composition and viability of isolated wild-type (WT) and Nox2-/- islets by immunohistochemistry as well as different viability assays. Ex vivo, the effect of Nox2 deficiency on superoxide production, endocrine function and anti-oxidant protein expression was studied under hypoxic conditions. In vivo, we transplanted WT and Nox2-/- islets into mouse dorsal skinfold chambers and under the kidney capsule of diabetic mice to assess their revascularization and endocrine function, respectively. We found that the loss of NOX2 does not affect the cellular composition and viability of isolated islets. However, decreased superoxide production, higher glucose-stimulated insulin secretion as well as expression of nuclear factor erythroid 2-related factor (Nrf)2, heme oxygenase (HO)-1 and superoxide dismutase 1 (SOD1) was detected in hypoxic Nox2-/- islets when compared to WT islets. Moreover, we detected an early revascularization, a higher take rate and restoration of normoglycemia in diabetic mice transplanted with Nox2-/- islets. These findings indicate that the suppression of NOX2 activity represents a promising therapeutic strategy to improve engraftment and function of isolated islets.

Early Cytokine-Induced Transient NOX2 Activity Is ER Stress-Dependent and Impacts ß-Cell Function and Survival.

In type 1 diabetes (T1D) development, proinflammatory cytokines (PIC) released by immune cells lead to increased reactive oxygen species (ROS) production in ß-cells. Nonetheless, the temporality of the events triggered and the role of different ROS sources remain unclear. Isolated islets from C57BL/6J wild-type (WT), NOX1 KO and NOX2 KO mice were exposed to a PIC combination. We show that cytokines increase O2•- production after 2 h in WT and NOX1 KO but not in NOX2 KO islets. Using transgenic mice constitutively expressing a genetically encoded compartment specific H2O2 sensor, we show, for the first time, a transient increase of cytosolic/nuclear H2O2 in islet cells between 4 and 5 h during cytokine exposure. The H2O2 increase coincides with the intracellular NAD(P)H decrease and is absent in NOX2 KO islets. NOX2 KO confers better glucose tolerance and protects against cytokine-induced islet secretory dysfunction and death. However, NOX2 absence does not counteract the cytokine effects in ER Ca2+ depletion, Store-Operated Calcium Entry (SOCE) increase and ER stress. Instead, the activation of ER stress precedes H2O2 production. As early NOX2-driven ROS production impacts ß-cells' function and survival during insulitis, NOX2 might be a potential target for designing therapies against early ß-cell dysfunction in the context of T1D onset.

Erythropoietin exposure of isolated pancreatic islets accelerates their revascularization after transplantation.

AIMS: The exposure of isolated pancreatic islets to pro-angiogenic factors prior to their transplantation represents a promising strategy to accelerate the revascularization of the grafts. It has been shown that erythropoietin (EPO), a glycoprotein regulating erythropoiesis, also induces angiogenesis. Therefore, we hypothesized that EPO exposure of isolated islets improves their posttransplant revascularization. METHODS: Flow cytometric, immunohistochemical and quantitative real-time (qRT)-PCR analyses were performed to study the effect of EPO on the viability, cellular composition and gene expression of isolated islets. Moreover, islets expressing a mitochondrial or cytosolic H2O2 sensor were used to determine reactive oxygen species (ROS) levels. The dorsal skinfold chamber model in combination with intravital fluorescence microscopy was used to analyze the revascularization of transplanted islets. RESULTS: We found that the exposure of isolated islets to EPO (3 units/mL) for 24 h does not affect the viability and the production of ROS when compared to vehicle-treated and freshly isolated islets. However, the exposure of islets to EPO increased the number of CD31-positive cells and enhanced the gene expression of insulin and vascular endothelial growth factor (VEGF)-A. The revascularization of the EPO-cultivated islets was accelerated within the initial phase after transplantation when compared to both controls. CONCLUSION: These findings indicate that the exposure of isolated islets to EPO may be a promising approach to improve clinical islet transplantation.

Microvascular fragment spheroids: Three-dimensional vascularization units for tissue engineering and regeneration.

Adipose tissue-derived microvascular fragments (MVF) serve as vascularization units in tissue engineering and regenerative medicine. Because a three-dimensional cellular arrangement has been shown to improve cell function, we herein generated for the first time MVF spheroids to investigate whether this further increases their vascularization potential. These spheroids exhibited a morphology, size, and viability comparable to that of previously introduced stromal vascular fraction (SVF) spheroids. However, MVF spheroids contained a significantly higher number of CD31-positive endothelial cells and α-smooth muscle actin (SMA)-positive perivascular cells, resulting in an enhanced angiogenic sprouting activity. Accordingly, they also exhibited an improved in vivo vascularization and engraftment after transplantation into mouse dorsal skinfold chambers. These findings indicate that MVF spheroids are superior to SVF spheroids and, thus, may be highly suitable to improve the vascularization of tissue defects and implanted tissue constructs.

Transient NADPH oxidase 2-dependent H2O2 production drives early palmitate-induced lipotoxicity in pancreatic islets.

Modern lifestyles, including lack of physical activity and poor nutritional habits, are driving the rapidly increasing prevalence of obesity and type 2 diabetes. Increased levels of free fatty acids (FFAs), particularly saturated FFAs, in obese individuals have been linked to pancreatic ß-cell failure. This process, termed lipotoxicity, involves activation of several stress responses, including ER stress and oxidative stress. However, the molecular underpinnings and causal relationships between the disparate stress responses remain unclear. Here we employed transgenic mice, expressing a genetically-encoded cytosolic H2O2 sensor, roGFP2-Orp1, to monitor dynamic changes in H2O2 levels in pancreatic islets in response to chronic palmitate exposure. We identified a transient increase in H2O2 levels from 4 to 8 h after palmitate addition, which was mirrored by a concomitant decrease in cellular NAD(P)H levels. Intriguingly, islets isolated from NOX2 knock-out mice displayed no H2O2 transient upon chronic palmitate treatment. Furthermore, NOX2 knockout rescued palmitate-dependent impairment of insulin secretion, calcium homeostasis and viability. Chemical inhibition of NOX activity protected islets from palmitate-induced impairment in insulin secretion, however had no detectable impact upon the induction of ER stress. In summary, our results reveal that transient NOX2-dependent H2O2 production is a likely cause of early palmitate-dependent lipotoxic effects.

Improvement of islet transplantation by the fusion of islet cells with functional blood vessels.

Pancreatic islet transplantation still represents a promising therapeutic strategy for curative treatment of type 1 diabetes mellitus. However, a limited number of organ donors and insufficient vascularization with islet engraftment failure restrict the successful transfer of this approach into clinical practice. To overcome these problems, we herein introduce a novel strategy for the generation of prevascularized islet organoids by the fusion of pancreatic islet cells with functional native microvessels. These insulin-secreting organoids exhibit a significantly higher angiogenic activity compared to freshly isolated islets, cultured islets, and non-prevascularized islet organoids. This is caused by paracrine signaling between the ß-cells and the microvessels, mediated by insulin binding to its corresponding receptor on endothelial cells. In vivo, the prevascularized islet organoids are rapidly blood-perfused after transplantation by the interconnection of their autochthonous microvasculature with surrounding blood vessels. As a consequence, a lower number of islet grafts are required to restore normoglycemia in diabetic mice. Thus, prevascularized islet organoids may be used to improve the success rates of clinical islet transplantation.

Darbepoetin-α increases the blood volume flow in transplanted pancreatic islets in mice.

AIMS: The minimal-invasive transplantation of pancreatic islets is a promising approach to treat diabetes mellitus type 1. However, islet transplantation is still hampered by the insufficient process of graft revascularization, leading to a poor clinical outcome. Accordingly, the identification of novel compounds, which accelerate and improve the revascularization of transplanted islets, is of great clinical interest. Previous studies have shown that darbepoetin (DPO)-α, a long lasting analogue of erythropoietin, is capable of promoting angiogenesis. Hence, we investigated in this study whether DPO improves the revascularization of transplanted islets. METHODS: Islets were isolated from green fluorescent protein-positive FVB/N donor mice and transplanted into dorsal skinfold chambers of FVB/N wild-type animals, which were treated with DPO low dose (2.5 µg/kg), DPO high dose (10 µg/kg) or vehicle (control). The revascularization was assessed by repetitive intravital fluorescence microscopy over an observation period of 14 days. Subsequently, the cellular composition of the grafts was analyzed by immunohistochemistry. RESULTS: The present study shows that neither low- nor high-dose DPO treatment accelerates the revascularization of free pancreatic islet grafts. However, high-dose DPO treatment increased the blood volume flow of the transplanted islet. CONCLUSIONS: These findings demonstrated that DPO treatment does not affect the revascularization of transplanted islets. However, the glycoprotein increases the blood volume flow of the grafts, which results in an improved microvascular function and may facilitate successful transplantation.

Chronic activation of GPR40 does not negatively impact upon BRIN-BD11 pancreatic ß-cell physiology and function.

BACKGROUND: Free fatty acids (FFAs) are known for their dual effects on insulin secretion and pancreatic ß-cell survival. Short-term exposure to FFAs, such as palmitate, increases insulin secretion. On the contrary, long-term exposure to saturated FFAs results in decreased insulin secretion, as well as triggering oxidative stress and endoplasmic reticulum (ER) stress, culminating in cell death. The effects of FFAs can be mediated either via their intracellular oxidation and consequent effects on cellular metabolism or via activation of the membrane receptor GPR40. Both pathways are likely to be activated upon both short- and long-term exposure to FFAs. However, the precise role of GPR40 in ß-cell physiology, especially upon chronic exposure to FFAs, remains unclear. METHODS: We used the GPR40 agonist (GW9508) and antagonist (GW1100) to investigate the impact of chronically modulating GPR40 activity on BRIN-BD11 pancreatic ß-cells physiology and function. RESULTS: We observed that chronic activation of GPR40 did not lead to increased apoptosis, and both proliferation and glucose-induced calcium entry were unchanged compared to control conditions. We also observed no increase in H2O2 or superoxide levels and no increase in the ER stress markers p-eIF2α, CHOP and BIP. As expected, palmitate led to increased H2O2 levels, decreased cell viability and proliferation, as well as decreased metabolism and calcium entry. These changes were not counteracted by the co-treatment of palmitate-exposed cells with the GPR40 antagonist GW1100. CONCLUSIONS: Chronic activation of GPR40 using GW9508 does not negatively impact upon BRIN-BD11 pancreatic ß-cells physiology and function. The GPR40 antagonist GW1100 does not protect against the deleterious effects of chronic palmitate exposure. We conclude that GPR40 is probably not involved in mediating the toxicity associated with chronic palmitate exposure.

Protein Kinase CK2 Regulates Nerve/Glial Antigen (NG)2-Mediated Angiogenic Activity of Human Pericytes.

Protein kinase CK2 is a crucial regulator of endothelial cell proliferation, migration and sprouting during angiogenesis. However, it is still unknown whether this kinase additionally affects the angiogenic activity of other vessel-associated cells. In this study, we investigated the effect of CK2 inhibition on primary human pericytes. We found that CK2 inhibition reduces the expression of nerve/glial antigen (NG)2, a crucial factor which is involved in angiogenic processes. Reporter gene assays revealed a 114 bp transcriptional active region of the human NG2 promoter, whose activity was decreased after CK2 inhibition. Functional analyses demonstrated that the pharmacological inhibition of CK2 by CX-4945 suppresses pericyte proliferation, migration, spheroid sprouting and the stabilization of endothelial tubes. Moreover, aortic rings of NG2-/- mice showed a significantly reduced vascular sprouting when compared to rings of NG2+/+ mice, indicating that NG2 is an important regulator of the angiogenic activity of pericytes. In vivo, implanted Matrigel plugs containing CX-4945-treated pericytes exhibited a lower microvessel density when compared to controls. These findings demonstrate that CK2 regulates the angiogenic activity of pericytes through NG2 gene expression. Hence, the inhibition of CK2 represents a promising anti-angiogenic strategy, because it does not only target endothelial cells, but also vessel-associated pericytes.

Erythropoietin accelerates the revascularization of transplanted pancreatic islets.

BACKGROUND AND PURPOSE: Pancreatic islet transplantation is a promising therapeutic approach for Type 1 diabetes. A major prerequisite for the survival of grafted islets is a rapid revascularization after transplantation. Erythropoietin (EPO), the primary regulator of erythropoiesis, has been shown to promote angiogenesis. Therefore, we investigated in this study whether EPO improves the revascularization of transplanted islets. EXPERIMENTAL APPROACH: Islets from FVB/N mice were transplanted into dorsal skinfold chambers of recipient animals, which were daily treated with an intraperitoneal injection of EPO (500 IU·kg-1 ) or vehicle (control) throughout an observation period of 14 days. In a second set of experiments, animals were only pretreated with EPO over a 6-day period prior to islet transplantation. The revascularization of the grafts was assessed by repetitive intravital fluorescence microscopy and immunohistochemistry. In addition, a streptozotocin-induced diabetic mouse model was used to study the effect of EPO-pretreatment on the endocrine function of the grafts. KEY RESULTS: EPO treatment slightly accelerated the revascularization of the islet grafts. This effect was markedly more pronounced in EPO-pretreated animals, resulting in significantly higher numbers of engrafted islets and an improved perfusion of endocrine tissue without affecting systemic haematocrit levels when compared with controls. Moreover, EPO-pretreatment significantly accelerated the recovery of normoglycaemia in diabetic mice after islet transplantation. CONCLUSION AND IMPLICATIONS: These findings demonstrate that, particularly, short-term EPO-pretreatment represents a promising therapeutic approach to improve the outcome of islet transplantation, without an increased risk of thromboembolic events.