No abstract

Adverse metabolic factors, including oxidized small and dense low density lipoprotein (ox-dmLDL) can contribute to the reduced number and the impaired functions of circulating endothelial progenitors (EPC) in diabetic patients. To elucidate the molecular mechanisms involved, EPC from normal donors were cultured in the presence of ox-dmLDL. Under these experimental conditions EPC undergo to senescent-like growth arrest. This effect is associated with Akt activation, p21 expression, p53 accumulation, and retinoblastoma protein dephosphorylation and with a reduced protective effect against oxidative damage. Moreover, depletion of endogenous p53 expression by small interfering RNA demonstrates that the integrity of this pathway is essential for senescence to occur. Activation of the Akt/p53/p21 signaling pathway and accelerated onset of senescence are also detectable in EPC from diabetic patients. Finally, diabetic EPC depleted of endogenous p53 do not undergo to senescence-growth arrest and acquire the ability to form tube-like structures in vitro. These observations identify the activation of the p53 signaling pathway as a crucial event that can contribute to the impaired neovascularization in diabetes.

Granulocyte-macrophage colony-stimulating factor (GM-CSF), supports proliferation, differentiation, and functional activation of hemopoietic cells by its interaction with a heterodimeric receptor. Although GM-CSF receptor is devoid of tyrosine kinase enzymatic activity, GM-CSF-induced peripheral blood polymorphonuclear leukocytes (PMN) functional activation is mediated by the phosphorylation of a large number of intracellular signaling molecules. We have previously shown that JAK2 becomes tyrosine-phosphorylated in response to GM-CSF in PMN. In the present study we demonstrate that also the signal transducers and activators of transcription (STAT) family members STAT1 p91 and STAT3 p92 and the product of the c-fps/fes protooncogene become tyrosine-phosphorylated upon GM-CSF stimulation and physically associated with both GM-CSF receptor ␤ common subunit and JAK2. Moreover GM-CSF was able to induce JAK2 and p93 fes catalytic activity. We also demonstrate that the association of the GM-CSF receptor ␤ common subunit with JAK2 is ligand-dependent.Finally we demonstrate that GM-CSF induces a DNAbinding complex that contains both p91 and p92. These results identify a new signal transduction pathway activated by GM-CSF and provide a mechanism for rapid activation of gene expression in GM-CSF-stimulated PMN.

OBJECTIVEAcylated ghrelin (AG) is a diabetogenic and orexigenic gastric polypeptide. These properties are not shared by the most abundant circulating form, which is unacylated (UAG). An altered UAG/AG profile together with an impairment of circulating endothelial progenitor cell (EPC) bioavailability were found in diabetes. Based on previous evidence for the beneficial cardiovascular effects of AG and UAG, we investigated their potential to revert diabetes-associated defects.RESEARCH DESIGN AND METHODSHealthy human subjects, individuals with type 2 diabetes, and ob/ob mice were AG or UAG infused. EPC mobilization in patients and mice was evaluated, and the underlying molecular mechanisms were investigated in bone marrow stromal cells. Recovered EPCs were also evaluated for the activity of senescence regulatory pathways and for NADPH oxidase activation by knocking down p47phox and Rac1. Finally, UAG modulation of human EPC vasculogenic potential was investigated in an in vivo mouse model.RESULTSNeither AG nor UAG had any effect in healthy subjects. However, systemic administration of UAG, but not AG, prevented diabetes-induced EPC damage by modulating the NADPH oxidase regulatory protein Rac1 and improved the vasculogenic potential both in individuals with type 2 diabetes and in ob/ob mice. In addition, unlike AG, UAG facilitated the recovery of bone marrow EPC mobilization. Crucial to EPC mobilization by UAG was the rescue of endothelial NO synthase (eNOS) phosphorylation by Akt, as UAG treatment was ineffective in eNOS knockout mice. Consistently, EPCs expressed specific UAG-binding sites, not recognized by AG.CONCLUSIONSThese data provide the rationale for clinical applications of UAG in pathologic settings where AG fails.

BackgroundSurgical treatment of peripheral artery disease, even if successful, does not prevent reoccurrence. Under these conditions, increased oxidative stress is a crucial determinant of tissue damage. Given its reported antioxidant effects, we investigated the potential of unacylated‐ghrelin (UnAG) to reduce ischemia‐induced tissue damage in a mouse model of peripheral artery disease.Methods and ResultsWe show that UnAG but not acylated ghrelin (AG) induces skeletal muscle regeneration in response to ischemia via canonical p38/mitogen‐actived protein kinase signaling UnAG protected against reactive oxygen species–induced cell injuries by inducing the expression of superoxide dismutase‐2 (SOD‐2) in satellite cells. This led to a reduced number of infiltrating CD68+ cells and was followed by induction of the myogenic process and a reduction in functional impairment. Moreover, we found that miR‐221/222, previously linked to muscle regeneration processes, was up‐regulated and negatively correlated with p57Kip2 expression in UnAG‐treated mice. UnAG, unlike AG, promoted cell‐cycle entry in satellite cells of mice lacking the genes for ghrelin and its receptor (GHSR1a). UnAG‐induced p38/mitogen‐actived protein kinase phosphorylation, leading to activation of the myogenic process, was prevented in SOD‐2–depleted SCs. By siRNA technology, we also demonstrated that SOD‐2 is the antioxidant enzyme involved in the control of miR‐221/222–driven posttranscriptional p57Kip2 regulation. Loss‐of‐function experiments targeting miR‐221/222 and local pre–miR‐221/222 injection in vivo confirmed a role for miR‐221/222 in driving skeletal muscle regeneration after ischemia.ConclusionsThese results indicate that UnAG‐induced skeletal muscle regeneration after ischemia depends on SOD‐2–induced miR‐221/222 expression and highlight its clinical potential for the treatment of reactive oxygen species–mediated skeletal muscle damage.

Soluble factors and cell-derived extracellular vesicles (EVs) control vascular cell fate during inflammation. The present study investigates the impact of Interleukin 3 (IL-3) on EV release by endothelial cells (ECs), the mechanisms involved in EV release and paracrine actions. We found that IL-3 increases EV release, which is prevented by IL-3Ralpha blockade. EVs released upon IL-3 stimulation were able to induce pro-angiogenic signals as shown by chromatin immunoprecipitation (ChIP) assay performed on the promoter region of cyclin D1 and tridimensional tube-like structure formation. We herein demonstrate that these effects rely on the transfer of miR-126-3p, pre-miR-126 and, more importantly, of activated signal transduction and activator of transcription 5 (pSTAT5) from IL-3-EV cargo into recipient ECs. We show, using the dominant negative form (ΔN)STAT5 and an activated STAT5 (1*6STAT5) constructs, that STAT5 drives IL-3-mediated EV release, miR-126-3p and pSTAT5 content. Finally, using EVs recovered from ΔNSTAT5 expressing ECs, we provide evidence that miR-126-3p and pSTAT5 trafficking is relevant for IL-3-mediated paracrine pro-angiogenic signals. These results indicate that IL-3 regulates EC-EV release, cargo and IL-3 angiogenic paracrine action via STAT5. Moreover, these results provide evidence that EC-derived IL-3-EVs can serve as pro-angiogenic clinical delivery wound healing devices.

Reactive oxygen species (ROS) are crucial in longterm diabetes complications, including peripheral artery disease (PAD). In this study, we have investigated the potential clinical impact of unacylated ghrelin (UnAG) in a glucose intolerance and PAD mouse model. We demonstrate that UnAG is able to protect skeletal muscle and endothelial cells (ECs) from ROS imbalance in hind limb ischemiasubjected ob/ob mice. This effect translates into reductions in hind limb functional impairment. We show that UnAG rescues sirtuin 1 (SIRT1) activity and superoxide dismutase-2 (SOD-2) expression in ECs. This leads to SIRT1-mediated p53 and histone 3 lysate 56 deacetylation and results in reduced EC senescence in vivo. We demonstrate, using small interfering RNA technology, that SIRT1 is also crucial for SOD-2 expression. UnAG also renews micro-RNA (miR)-126 expression, resulting in the posttranscriptional regulation of vascular cell adhesion molecule 1 expression and a reduced number of infiltrating inflammatory cells in vivo. Loss-of-function experiments that target miR-126 demonstrate that miR-126 also controls SIRT1 and SOD-2 expression, thus confirming its role in driving UnAG-mediated EC protection against ROS imbalance. These results indicate that UnAG protects vessels from ROS imbalance in ob/ob mice by rescuing miR-126 expression, thus emphasizing its potential clinical impact in avoiding limb loss in PAD.

We investigated the role of c-Kit and the membrane-bound ligand (mbKitL) in endothelial progenitor cell (EPC) recruitment by microvascular endothelial cells (ECs). We demonstrated that inflammatory activation induced the expression of the mbKitL on ECs both in vitro and in vivo, and that recruitment of EPCs depended on c-Kit/mbKitL interaction. Depletion of endogenous c-Kit or inhibition of c-Kit enzymatic activity by imatinib mesylate prevented adhesion of EPCs to activated ECs both in vitro and in vivo, indicating that a functional c-Kit on EPCs is essential. We also demonstrate that Akt was the downstream molecule regulating cell adhesion. A potential role of the c-Kit/mbKitL interaction in pathological settings is sustained by the expression of the mbKitL on ECs lining intraplaque neovessels. Thus, our results provide new insights into the mechanisms underlying EPC recruitment and the bases for novel strategies to hinder pathological angiogenesis.