Recovery from hind limb ischemia is less effective in type 2 than in type 1 diabetic mice: roles of endothelial nitric oxide synthase and endothelial progenitor cells

Power-Doppler Ultrasonic Imaging of Peripheral Perfusion in Diabetic Mice

OBJECTIVE

We explored the capabilities of power-Doppler ultrasonic (PD-US) imaging without contrast enhancement for monitoring changes in muscle perfusion over time.

METHODS

Ischemic recovery was observed in healthy and type II diabetic male and female mice with and without exercise. In separate studies, perfusion was measured during and after 5-min ischemic periods and during four-week recovery periods following irreversible femoral ligation. A goal was to assess how well PD-US estimates tracked the diabetic-related changes in endothelial function that influenced perfusion.

RESULTS

The average perfusion recovery time following femoral ligation increased 47% in diabetic males and 74% in diabetic females compared with non-diabetic mice. Flow-mediated dilation in conduit arteries and the reactive hyperemia index in resistive vessels each declined by one half in sedentary diabetic mice compared with sedentary non-diabetic mice. We found that exercise reduced the loss of endothelial function from diabetes in both sexes. The reproducibility of perfusion measurements was limited primarily by our ability to select the same region in muscle and to effectively filter tissue clutter.

CONCLUSIONS/SIGNIFICANCE

PD-US measurements can precisely follow site-specific changes in skeletal muscle perfusion related to diabetes over time, which fills the need for techniques capable of regularly monitoring atherosclerotic changes leading to ischemic vascular pathologies.

A KLF2-BMPER-Smad1/5 checkpoint regulates high fluid shear stress-mediated artery remodeling

Vascular remodeling to match arterial diameter to tissue requirements commonly fails in ischemic disease. Endothelial cells sense fluid shear stress (FSS) from blood flow to maintain FSS within a narrow range in healthy vessels. Thus, high FSS induces vessel outward remodeling, but mechanisms are poorly understood. We previously reported that Smad1/5 is maximally activated at physiological FSS. Smad1/5 limits Akt activation, suggesting that inhibiting Smad1/5 may facilitate outward remodeling. Here we report that high FSS suppresses Smad1/5 by elevating KLF2, which induces the bone morphogenetic protein (BMP) pathway inhibitor, BMP-binding endothelial regulator (BMPER), thereby de-inhibiting Akt. In mice, surgically induced high FSS elevated BMPER expression, inactivated Smad1/5 and induced vessel outward remodeling. Endothelial BMPER deletion impaired blood flow recovery and vascular remodeling. Blocking endothelial cell Smad1/5 activation with BMP9/10 blocking antibodies improved vascular remodeling in mouse models of type 1 and type 2 diabetes. Suppression of Smad1/5 is thus a potential therapeutic approach for ischemic disease.

Uncovering the link between diabetes and cardiovascular diseases: insights from adipose-derived stem cells

Cardiovascular diseases (CVDs) are the leading causes of morbidity and mortality worldwide. The escalating global occurrence of obesity and diabetes mellitus (DM) has led to a significant upsurge in individuals afflicted with CVDs. As the prevalence of CVDs continues to rise, it is becoming increasingly important to identify the underlying cellular and molecular mechanisms that contribute to their development and progression, which will help discover novel therapeutic avenues. Adipose tissue (AT) is a connective tissue that plays a crucial role in maintaining lipid and glucose homeostasis. However, when AT is exposed to diseased conditions, such as DM, this tissue will alter its phenotype to become dysfunctional. AT is now recognized as a critical contributor to CVDs, especially in patients with DM. AT is comprised of a heterogeneous cellular population, which includes adipose-derived stem cells (ADSCs). ADSCs resident in AT are believed to regulate physiological cardiac function and have potential cardioprotective roles. However, recent studies have also shown that ADSCs from various adipose tissue depots become pro-apoptotic, pro-inflammatory, less angiogenic, and lose their ability to differentiate into various cell lineages upon exposure to diabetic conditions. This review aims to summarize the current understanding of the physiological roles of ADSCs, the impact of DM on ADSC phenotypic changes, and how these alterations may contribute to the pathogenesis of CVDs.

Dapagliflozin restores diabetes-associated decline in vasculogenic capacity of endothelial progenitor cells via activating AMPK-mediated inhibition of inflammation and oxidative stress

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) provide added vascular protection beyond glucose lowering to patients with type 2 diabetes mellitus (T2DM). Endothelial progenitor cells (EPCs) are an important endogenous repair mechanism for diabetic vascular complications. Yet, whether SGLT2i protect vessels in diabetic patients by improving the function of EPCs remains to be elucidated. Here we enrolled Sixty-three T2DM patients and 60 healthy participants and 15 of T2DM group took dapagliflozin for 3 months. Retinal capillary density (RCD) was examined before and after meditation. Moreover, vasculogenic capacity of EPCs cocultured with or without dapagliflozin in vitro and in vivo (hind limb ischemia model) were assessed. Mechanically, genes related to inflammation/oxidative stress, and the AMPK signaling of EPCs were determined. Our results found T2DM demonstrated a declined RCD and a decreased number of circulating EPCs compared with healthy controls. Compared with the EPCs from healthy individuals, vasculogenic capacity of T2DM EPCs was significantly impaired, which could be restored by dapagliflozin meditation or dapagliflozin coculture. Increased expression of inflammation correlative genes and decreased anti-oxidative stress related genes expression were found in EPCs form T2DM, which were accompanied with reduced phosphorylation level of AMPK. Dapagliflozin treatment activated AMPK signaling, decreased the level of inflammation and oxidative stress, and rescued vasculogenic capacity of EPCs from T2DM. Furthermore, AMPK inhibitor pretreatment diminished the enhancement vasculogenic capacity of diabetic EPCs from dapagliflozin treatment. This study demonstrates for the first time that dapagliflozin restores vasculogenic capacity of EPCs via activating AMPK-mediated inhibition of inflammation and oxidative stress in T2DM.

Diabetes mellitus in peripheral artery disease: Beyond a risk factor

Peripheral artery disease (PAD) is one of the major cardiovascular diseases that afflicts a large population worldwide. PAD results from occlusion of the peripheral arteries of the lower extremities. Although diabetes is a major risk factor for developing PAD, coexistence of PAD and diabetes poses significantly greater risk of developing critical limb threatening ischemia (CLTI) with poor prognosis for limb amputation and high mortality. Despite the prevalence of PAD, there are no effective therapeutic interventions as the molecular mechanism of how diabetes worsens PAD is not understood. With increasing cases of diabetes worldwide, the risk of complications in PAD have greatly increased. PAD and diabetes affect a complex web of multiple cellular, biochemical and molecular pathways. Therefore, it is important to understand the molecular components that can be targeted for therapeutic purposes. In this review, we describe some major developments in enhancing the understanding of the interactions of PAD and diabetes. We also provide results from our laboratory in this context.

Vascular repair and regeneration in cardiometabolic diseases

Chronic cardiometabolic assaults during type 2 diabetes (T2D) and obesity induce a progenitor cell imbalance in the circulation characterized by overproduction and release of pro-inflammatory monocytes and granulocytes from the bone marrow alongside aberrant differentiation and mobilization of pro-vascular progenitor cells that generate downstream progeny for the coordination of blood vessel repair. This imbalance can be detected in the peripheral blood of individuals with established T2D and severe obesity using multiparametric flow cytometry analyses to discern pro-inflammatory vs. pro-angiogenic progenitor cell subsets identified by high aldehyde dehydrogenase activity, a conserved progenitor cell protective function, combined with lineage-restricted cell surface marker analyses. Recent evidence suggests that progenitor cell imbalance can be reversed by treatment with pharmacological agents or surgical interventions that reduce hyperglycaemia or excess adiposity. In this state-of-the-art review, we present current strategies to assess the progression of pro-vascular regenerative cell depletion in peripheral blood samples of individuals with T2D and obesity and we summarize novel clinical data that intervention using sodium-glucose co-transporter 2 inhibition or gastric bypass surgery can efficiently restore cell-mediated vascular repair mechanisms associated with profound cardiovascular benefits in recent outcome trials. Collectively, this thesis generates a compelling argument for early intervention using current pharmacological agents to prevent or restore imbalanced circulating progenitor content and maintain vascular regenerative cell trafficking to sites of ischaemic damage. This conceptual advancement may lead to the design of novel therapeutic approaches to prevent or reverse the devastating cardiovascular comorbidities currently associated with T2D and obesity.

Plicosepalus acacia Extract and Its Major Constituents, Methyl Gallate and Quercetin, Potentiate Therapeutic Angiogenesis in Diabetic Hind Limb Ischemia: HPTLC Quantification and LC-MS/MS Metabolic Profiling

Plicosepalus acacia (Fam. Loranthaceae) has been reported to possess hypoglycemic, antioxidant, antimicrobial, and anti-inflammatory effects. Liquid chromatography combined with tandem mass spectrometry (LC-MS/MS) analysis revealed the presence of a high content of polyphenolic compounds that are attributed to the therapeutic effects of the crude extract. In addition, methyl gallate and quercetin were detected as major phytomedicinal agents at concentrations of 1.7% and 0.062 g%, respectively, using high-performance thin layer chromatography (HPTLC). The present study investigated the effect of the P. acacia extract and its isolated compounds, methyl gallate and quercetin, on hind limb ischemia induced in type 1 diabetic rats. Histopathological examination revealed that treatment with P. acacia extract, methyl gallate, and quercetin decreased degenerative changes and inflammation in the ischemic muscle. Further biochemical assessment of the hind limb tissue showed decreased oxidative stress, increased levels of nitric oxide and endothelial nitric oxide synthase (eNOS), and enhancement of the levels of heme oxygenase-1 (HO-1) and vascular endothelial growth factor (VEGF) in the groups treated with methyl gallate and quercetin. Expression levels of hypoxia inducible factor-1 alpha (HIF-1α), VEGF, fibroblast growth factor-2 (FGF-2), and miR-146a were upregulated in the muscle tissue of methyl gallate- and quercetin-treated groups along with downregulation of nuclear factor kappa B (NF-κB). In conclusion, P. acacia extract and its isolated compounds, methyl gallate and quercetin, mediated therapeutic angiogenesis in diabetic hind limb ischemia.

Effects of Sodium-Glucose Co-Transporter 2 Inhibitors on Vascular Cell Function and Arterial Remodeling

Cardiovascular disease is the leading cause of morbidity and mortality in diabetes. Recent clinical studies indicate that sodium-glucose co-transporter 2 (SGLT2) inhibitors improve cardiovascular outcomes in patients with diabetes. The mechanism underlying the beneficial effect of SGLT2 inhibitors is not completely clear but may involve direct actions on vascular cells. SGLT2 inhibitors increase the bioavailability of endothelium-derived nitric oxide and thereby restore endothelium-dependent vasodilation in diabetes. In addition, SGLT2 inhibitors favorably regulate the proliferation, migration, differentiation, survival, and senescence of endothelial cells (ECs). Moreover, they exert potent antioxidant and anti-inflammatory effects in ECs. SGLT2 inhibitors also inhibit the contraction of vascular smooth muscle cells and block the proliferation and migration of these cells. Furthermore, studies demonstrate that SGLT2 inhibitors prevent postangioplasty restenosis, maladaptive remodeling of the vasculature in pulmonary arterial hypertension, the formation of abdominal aortic aneurysms, and the acceleration of arterial stiffness in diabetes. However, the role of SGLT2 in mediating the vascular actions of these drugs remains to be established as important off-target effects of SGLT2 inhibitors have been identified. Future studies distinguishing drug- versus class-specific effects may optimize the selection of specific SGLT2 inhibitors in patients with distinct cardiovascular pathologies.

Endothelial progenitor cells as critical mediators of environmental air pollution-induced cardiovascular toxicity

Environmental air pollution exposure is a leading cause of death worldwide, and with increasing industrialization and urbanization, its disease burden is expected to rise even further. The majority of air pollution exposure-associated deaths are linked to cardiovascular disease (CVD). Although ample research demonstrates a strong correlation between air pollution exposure and CVD risk, the mechanisms by which inhalation of polluted air affects cardiovascular health are not completely understood. Inhalation of environmental air pollution has been associated with endothelial dysfunction, which suggests that air pollution exposure impacts CVD health by inducing endothelial injury. Interestingly, recent studies demonstrate that air pollution exposure affects the number and function of endothelial progenitor cells (EPCs), subpopulations of bone marrow-derived proangiogenic cells that have been shown to play an essential role in maintaining cardiovascular health. In line with their beneficial function, chronically low levels of circulating EPCs and EPC dysfunction (e.g., in diabetic patients) have been associated with vascular dysfunction, poor cardiovascular health, and increases in the severity of cardiovascular outcomes. In contrast, treatments that improve EPC number and function (e.g., exercise) have been found to attenuate cardiovascular dysfunction. Considering the critical, nonredundant role of EPCs in maintaining vascular health, air pollution exposure-induced impairments in EPC number and function could lead to endothelial dysfunction, consequently increasing the risk for CVD. This review article covers novel aspects and new mechanistic insights of the adverse effects of air pollution exposure on cardiovascular health associated with changes in EPC number and function.

Current Status of Angiogenic Cell Therapy and Related Strategies Applied in Critical Limb Ischemia

Critical limb ischemia (CLI) constitutes the most severe form of peripheral arterial disease (PAD), it is characterized by progressive blockade of arterial vessels, commonly correlated to atherosclerosis. Currently, revascularization strategies (bypass grafting, angioplasty) remain the first option for CLI patients, although less than 45% of them are eligible for surgical intervention mainly due to associated comorbidities. Moreover, patients usually require amputation in the short-term. Angiogenic cell therapy has arisen as a promising alternative for these "no-option" patients, with many studies demonstrating the potential of stem cells to enhance revascularization by promoting vessel formation and blood flow recovery in ischemic tissues. Herein, we provide an overview of studies focused on the use of angiogenic cell therapies in CLI in the last years, from approaches testing different cell types in animal/pre-clinical models of CLI, to the clinical trials currently under evaluation. Furthermore, recent alternatives related to stem cell therapies such as the use of secretomes, exosomes, or even microRNA, will be also described.

Growth Factor Deregulation and Emerging Role of Phosphatases in Diabetic Peripheral Artery Disease

Peripheral artery disease is caused by atherosclerosis of lower extremity arteries leading to the loss of blood perfusion and subsequent critical ischemia. The presence of diabetes mellitus is an important risk factor that greatly increases the incidence, the progression and the severity of the disease. In addition to accelerated disease progression, diabetic patients are also more susceptible to develop serious impairment of their walking abilities through an increased risk of lower limb amputation. Hyperglycemia is known to alter the physiological development of collateral arteries in response to ischemia. Deregulation in the production of several critical pro-angiogenic factors has been reported in diabetes along with vascular cell unresponsiveness in initiating angiogenic processes. Among the multiple molecular mechanisms involved in the angiogenic response, protein tyrosine phosphatases are potent regulators by dephosphorylating pro-angiogenic tyrosine kinase receptors. However, evidence has indicated that diabetes-induced deregulation of phosphatases contributes to the progression of several micro and macrovascular complications. This review provides an overview of growth factor alterations in the context of diabetes and peripheral artery disease, as well as a description of the role of phosphatases in the regulation of angiogenic pathways followed by an analysis of the effects of hyperglycemia on the modulation of protein tyrosine phosphatase expression and activity. Knowledge of the role of phosphatases in diabetic peripheral artery disease will help the development of future therapeutics to locally regulate phosphatases and improve angiogenesis.

Heat therapy improves body composition and muscle function but does not affect capillary or collateral growth in a model of obesity and hindlimb ischemia

Heat therapy (HT) has emerged as a potential adjunctive therapy to alleviate the symptoms of peripheral artery disease (PAD), but the mechanisms underlying the positive effects of this treatment modality remain undefined. Using a model of diet-induced obesity (DIO) and ischemia-induced muscle damage, we tested the hypothesis that HT would alter body composition, promote vascular growth and mitochondrial biogenesis, and improve skeletal muscle function. Male DIO C57Bl/6J mice underwent bilateral ligation of the femoral artery and were randomly allocated to receive HT or a control intervention for 30 min daily over 3 wk. When compared with a group of lean, sham-operated animals, ligated DIO mice exhibited increases in body and fat masses, exercise intolerance, and contractile dysfunction of the isolated soleus (SOL) and extensor digitorum longus (EDL) muscles. Repeated HT averted an increase in body mass induced by high-fat feeding due to reduced fat accrual. Fat mass was ∼25% and 29% lower in the HT group relative to controls after 2 and 3 wk of treatment, respectively. Muscle mass relative to body mass and maximal absolute force of the EDL, but not SOL, were higher in animals exposed to HT. There were no group differences in skeletal muscle capillarization, the expression of angiogenic factors, mitochondrial content, and the diameter of the gracilis arteries. These findings indicate that HT reduces diet-induced fat accumulation and rescues skeletal muscle contractile dysfunction. This practical treatment may prove useful for diabetic and obese PAD patients who are unable to undergo conventional exercise regimens.NEW & NOTEWORTHY The epidemic of obesity-related dyslipidemia and diabetes is a central cause of the increasing burden of peripheral artery disease (PAD), but few accessible therapies exist to mitigate the metabolic and functional abnormalities in these patients. We report that daily exposure to heat therapy (HT) in the form of lower-body immersion in water heated to 39 °C for 3 weeks attenuates fat accumulation and weight gain, and improves muscle strength in obese mice with femoral artery occlusion.

TUG1 enhances high glucose-impaired endothelial progenitor cell function via miR-29c-3p/PDGF-BB/Wnt signaling

BACKGROUND

Diabetes is associated with the dysfunction of endothelial progenitor cells (EPCs), characterized as impaired angiogenesis, a phenomenon thought to be involved in the development of diabetic foot. lncRNA plays an essential role in microvascular dysfunction and signaling pathways in patients with diabetes. lncRNA taurine upregulated gene 1 (TUG1) participates in angiogenesis in various cells. However, the mechanisms of TUG1 activity in EPCs have not been elucidated.

METHODS

We isolated and then characterized EPCs from the peripheral blood of mice using immunofluorescence and flow cytometry. Western blot detected the wnt/β-catenin pathway in high glucose-treated EPCs. Bioinformatics analysis predicted a putative binding site for TUG1 on miR-29c-3p. The interactions among TUG1, platelet-derived growth factor-BB (PDGF-BB), and miR-29c-3p were analyzed by luciferase assays. In vivo, diabetic mouse ischemic limb was treated with normal saline or TUG1 overexpression lentiviruses.

RESULTS

We found that EPC migration, invasion, and tube formation declined after treatment with high glucose, but improved with TUG1 overexpression. Mechanically, wnt/β-catenin pathway and autophagy were involved in the function of TUG1 overexpression in high glucose-treated EPCs. Moreover, TUG1 regulates the PDGF-BB/wnt pathway and function of high glucose-treated EPCs via miR-29c-3p. In vivo, injection of TUG1 lentivirus in a diabetic mouse ischemic limb model stimulated angiogenesis.

CONCLUSIONS

Our findings suggest that TUG1 restores high glucose-treated EPC function by regulating miR-29c-3p/PDGF-BB/Wnt signaling.

ADMA (asymmetric dimethylarginine) and angiogenic potential in patients with type 2 diabetes and prediabetes

Asymmetric dimethylarginine is an endogenous competitive inhibitor of nitric oxide synthase and marker of endothelial dysfunction, but the question remains as to whether asymmetric dimethylarginine is a marker of cardiovascular episodes or their independent risk factor. ADMA/DDAH (dimethylaminohydrolase) pathway regulates vascular endothelial growth factor (VEGF)-mediated angiogenesis due to its impact on the NO formation. The aim of the study was to assess the concentrations of asymmetric dimethylarginine and the angiogenic potential in the blood of subjects with type 2 diabetes (T2DM, n = 33) and patients with prediabetes (n = 32)-impaired fasting glycemia and/or impaired glucose tolerance (WHO criteria). The study found that both the prediabetes group and subjects with T2DM had significantly elevated concentrations of asymmetric dimethylarginine, significantly high levels of VEGF-A, low ratio of sVEGF-R1/VEGF-A, and sVEGF-R2/VEGF-A. This may suggest endothelial damage at early stages of carbohydrate metabolism dysfunction-before T2DM is diagnosed. Higher proangiogenic potential in prediabetes and T2DM patients than in healthy subjects, is not only the effect of an increase in VEGF-A levels, but also reduced inhibition of circulating receptors.

Targeting QKI-7 in vivo restores endothelial cell function in diabetes

Vascular endothelial cell (EC) dysfunction plays a key role in diabetic complications. This study discovers significant upregulation of Quaking-7 (QKI-7) in iPS cell-derived ECs when exposed to hyperglycemia, and in human iPS-ECs from diabetic patients. QKI-7 is also highly expressed in human coronary arterial ECs from diabetic donors, and on blood vessels from diabetic critical limb ischemia patients undergoing a lower-limb amputation. QKI-7 expression is tightly controlled by RNA splicing factors CUG-BP and hnRNPM through direct binding. QKI-7 upregulation is correlated with disrupted cell barrier, compromised angiogenesis and enhanced monocyte adhesion. RNA immunoprecipitation (RIP) and mRNA-decay assays reveal that QKI-7 binds and promotes mRNA degradation of downstream targets CD144, Neuroligin 1 (NLGN1), and TNF-α-stimulated gene/protein 6 (TSG-6). When hindlimb ischemia is induced in diabetic mice and QKI-7 is knocked-down in vivo in ECs, reperfusion and blood flow recovery are markedly promoted. Manipulation of QKI-7 represents a promising strategy for the treatment of diabetic vascular complications.

Coronary and peripheral artery plaques: do differences in plaque characteristics translate to differences in lipid management?

Optimal medical management of patients with peripheral arterial disease (PAD) includes statin therapy, which has been shown to decrease the risk of major cardiovascular events. However, the relationship between low-density lipoprotein (LDL) lowering, PAD progression and limb outcomes remains controversial. Although prevention of coronary and cerebrovascular events is a priority, limb outcomes are still important determinants of quality of life and healthcare spending. This review will highlight differences between coronary artery disease (CAD) and PAD, and in particular, the more prevalent role of lipids and LDL cholesterol in CAD versus calcification in PAD. This difference may contribute to the differential impact of LDL cholesterol levels on coronary events and outcomes versus limb outcomes. Beyond LDL lowering, immune modulators have emerged as another agent to treat atherosclerosis in CAD, however similar data in PAD are lacking. Small studies have suggested that other lipids besides LDL cholesterol, such as triglycerides or small dense LDL, may have a greater impact on limb outcomes in patients with PAD. Although statin therapy is central in the management of patients with PAD, current understanding of the distinctions between PAD and CAD suggest that there may be other non-LDL targets for risk reduction that require further study.

Surface Tethering of Inflammation-Modulatory Nanostimulators to Stem Cells for Ischemic Muscle Repair

Stem cell transplantation has been a promising treatment for peripheral arterial diseases in the past decade. Stem cells act as living bioreactors of paracrine factors that orchestrate tissue regeneration. Prestimulated adipose-derived stem cells (ADSCs) have been proposed as potential candidates but have been met with challenges in activating their secretory activities for clinical use. Here, we propose that tethering the ADSC surface with nanoparticles releasing tumor necrosis factor α (TNFα), named nanostimulator, would stimulate cellular secretory activity in situ. We examined this hypothesis by complexing octadecylamine-grafted hyaluronic acid onto a liposomal carrier of TNFα. Hyaluronic acid increased the liposomal stability and association to CD44 on ADSC surface. ADSCs tethered with these TNFα carriers exhibited up-regulated secretion of proangiogenic vascular endothelial growth factor and immunomodulatory prosteoglandin E2 (PGE₂) while decreasing secretion of antiangiogenic pigment epithelium-derived factors. Accordingly, ADSCs tethered with nanostimulators promoted vascularization in a 3D microvascular chip and enhanced recovery of perfusion, walking, and muscle mass in a murine ischemic hindlimb compared to untreated ADSCs. We propose that this surface tethering strategy for in situ stimulation of stem cells would replace the costly and cumbersome preconditioning process and expedite clinical use of stem cells for improved treatments of various injuries and diseases.

Hydrogen Sulfide Protects Against High Glucose-Induced Human Umbilical Vein Endothelial Cell Injury Through Activating PI3K/Akt/eNOS Pathway

Purpose

Dysfunction of endothelial cells plays a key role in the pathogenesis of diabetic atherosclerosis. High glucose (HG) has been found as a key factor in the progression of diabetic complications, including atherosclerosis. PI3K/Akt/eNOS signaling pathway has been shown to involve in HG-induced vascular injuries. Hydrogen sulfide (H₂S) has been found to exhibit protective effects on HG-induced vascular injuries. Moreover, H₂S activates PI3K/Akt/eNOS pathway in endothelial cells. Thus, the present study aimed to determine if H₂S exerts protective effects against HG-induced injuries of human umbilical vein endothelial cells (HUVECs) via activating PI3K/Akt/eNOS signaling.

Materials and Methods

The endothelial protective effects of H₂S were evaluated and compared to the controlled groups. Cell viability, cell migration and tube formation were determined by in vitro functional assays; protein levels were evaluated by Western blot assay and ELISA; cell apoptosis was determined by Hoechst 33258 nuclear staining; Reactive oxygen species (ROS) production was evaluated by the ROS detection kit.

Results

HG treatment significantly inhibited PI3K/Akt/eNOS signaling in HUVECs, which was partially reversed by the H2S treatment. HG treatment inhibited cell viability of HUVECs, which were markedly prevented by H₂S or PI3K agonist Y-P 740. HG treatment also induced HUVEC cell apoptosis by increasing the protein levels of cleaved caspase 3, Bax and Bcl-2, which were significantly attenuated by H₂S or 740 Y-P. ROS production and gp91^phox protein level were increased by HG treatment in HUVECs and this effect can be blocked by the treatment with H₂S or Y-P 740. Moreover, HG treatment increased the protein levels of pro-inflammatory cytokines, caspase-1 and phosphorylated JNK, which was significantly attenuated by H₂S or Y-P 740. Importantly, the cytoprotective effect of H₂S against HG-induced injury was inhibited by LY294002 (an inhibitor of PI3K/Akt/eNOS signaling pathway).

Conclusion

The present study demonstrated that exogenous H₂S protects endothelial cells against HG-induced injuries by activating PI3K/Akt/eNOS pathway. Based on the above findings, we proposed that reduced endogenous H₂S levels and the subsequent PI3K/Akt/eNOS signaling impairment may be the important pathophysiological mechanism underlying hyperglycemia-induced vascular injuries.

Effects of dietary glutamine supplementation on immune cell polarization and muscle regeneration in diabetic mice with limb ischemia

PURPOSE

Diabetes is a chronic inflammatory disorder resulting in endothelial dysfunction which contributes to peripheral arterial disease and limb ischemia. Leukocytes play critical roles in vascular and tissue remodelling after ischemia. This study investigated the effects of dietary glutamine (GLN) supplementation on immune cell polarization in diabetic mice subjected to limb ischemia.

METHODS

Diabetes was induced by an intraperitoneal injection of streptozotocin for 5 consecutive days in C57BL/6J mice. Diabetic mice were fed the AIN-93 diet or an AIN-93 diet in which a part of the casein was replaced by GLN. After 3 weeks of the dietary intervention, mice were subjected to unilateral femoral artery ligation to induce limb ischemia.

RESULTS

GLN supplementation enhanced the proportion of anti-inflammatory monocytes and regulatory T cells in the blood. Expression of C-C motif chemokine receptor 5 by activated CD4⁺ T cells was promoted and prolonged in the GLN-supplemented group. GLN downregulated the percentage of M1 macrophages in muscle tissues which was correlated with lower levels of C-C motif chemokine ligand 2 in plasma. The muscle M1/M2 ratio was also reduced in the GLN group. Gene expression of interleukin-6 was suppressed by GLN supplementation, while expression levels of the peroxisome proliferator-activated receptor γ and myogenic differentiation 1 genes were elevated in post-ischemic muscles. Histological findings also indicated that muscle regeneration was accelerated in the GLN group.

CONCLUSIONS

GLN supplementation in diabetic mice may exert more-balanced polarization of CD4⁺ T cells, monocytes, and macrophages, thus attenuating inflammatory responses and contributing to muscle regeneration after limb ischemia.

The Role of the Stem Cells Therapy in the Peripheral Artery Disease

Vascular complications of diabetes mellitus are an important issue for all clinicians involved in the management of this complex pathology. Although many therapeutic advances have been reached, peripheral arterial disease is still an unsolved problem that each year compromises the quality of life and life span of affected patients. Oftentimes, patients, after ineffective attempts of revascularization, undergo greater amputations. At the moment, there is no effective and definitive treatment available. In this scenario, the therapeutic use of stem cells could be an interesting option. The aim of the present review is to gather all the best available evidence in this regard and to define a new role of the stem cells therapy in this field, from biomarker to possible therapeutic target.

Canagliflozin Inhibits Human Endothelial Cell Proliferation and Tube Formation

Recent clinical trials revealed that sodium-glucose co-transporter 2 (SGLT2) inhibitors significantly reduce cardiovascular events in type 2 diabetic patients, however, canagliflozin increased limb amputations, an effect not seen with other SGLT2 inhibitors. Since endothelial cell (EC) dysfunction promotes diabetes-associated vascular disease and limb ischemia, we hypothesized that canagliflozin, but not other SGLT2 inhibitors, impairs EC proliferation, migration, and angiogenesis. Treatment of human umbilical vein ECs (HUVECs) with clinically relevant concentrations of canagliflozin, but not empagliflozin or dapagliflozin, inhibited cell proliferation. In particular, 10 μM canagliflozin reduced EC proliferation by approximately 45%. The inhibition of EC growth by canagliflozin occurred in the absence of cell death and was associated with diminished DNA synthesis, cell cycle arrest, and a striking decrease in cyclin A expression. Restoration of cyclin A expression via adenoviral-mediated gene transfer partially rescued the proliferative response of HUVECs treated with canagliflozin. A high concentration of canagliflozin (50 μM) modestly inhibited HUVEC migration by 20%, but markedly attenuated their tube formation by 65% and EC sprouting from mouse aortas by 80%. A moderate 20% reduction in HUVEC migration was also observed with a high concentration of empagliflozin (50 μM), while neither empagliflozin nor dapagliflozin affected tube formation by HUVECs. The present study identified canagliflozin as a robust inhibitor of human EC proliferation and tube formation. The anti-proliferative action of canagliflozin occurs in the absence of cell death and is due, in part, to the blockade of cyclin A expression. Notably, these actions are not seen with empagliflozin or dapagliflozin. The ability of canagliflozin to exert these pleiotropic effects on ECs may contribute to the clinical actions of this drug.

Allogeneic Mesenchymal Stromal Cells (MSCs) are of Comparable Efficacy to Syngeneic MSCs for Therapeutic Revascularization in C57BKSdb/db Mice Despite the Induction of Alloantibody

Intramuscular administration of mesenchymal stromal cells (MSCs) represents a therapeutic option for diabetic critical limb ischemia. Autologous or allogeneic approaches may be used but disease-induced cell dysfunction may limit therapeutic efficacy in the former. Our aim was to compare the efficacy of allogeneic and autologous MSC transplantation in a model of hindlimb ischemia in diabetes mellitus and to determine whether allogeneic transplantation would result in the activation of an immune response. MSCs were isolated from C57BL/6 (B6) and diabetic obese C57BKS^db/db mice. Phosphate-buffered saline (control group), and MSCs (1 × 10⁶) from B6 (allogeneic group) or C57BKS^db/db (syngeneic group) were administered intramuscularly into the ischemic thigh of C57BKS^db/db mice following the induction of hindlimb ischemia. MSCs derived from both mouse strains secrete several angiogenic factors, suggesting that the potential therapeutic effect is due to paracrine signaling. Administration of allogeneic MSCs significantly improved blood perfusion as compared with the control group on week 2 and 3, post-operatively. In comparison with the control group, syngeneic MSCs significantly improved blood perfusion at week 2 only. There was no statistical difference in blood perfusion between allogeneic and syngeneic MSC groups at any stages. There was no statistical difference in ambulatory and necrosis score among the three groups. Amputation of toes was only observed in the control group (one out of seven animals). Alloantibody was detected in three out of the eight mice that received allogeneic MSCs but was not observed in the other groups. In summary, we demonstrated comparable efficacy after transplantation of autologous and allogeneic MSCs in a diabetic animal model despite generation of an immune response.

Restoring vasculogenic potential of endothelial cells from diabetic patients through spheroid formation

Introduction

Diabetes is an emerging epidemic in the developing world and represents a major risk factor for cardiovascular disease. Among other issues, patients with diabetes suffer from diminished endothelial cell (EC) function, which contributes to impaired vasculogenesis and recovery from ischemic insult. The formation of cells into three-dimensional spheroids promotes cell survival and activates key signaling pathways through the upregulation of cell-cell contacts, providing an opportunity to overcome shortcomings associated with individual autologous cells.

Methods

We hypothesized that forming human microvascular endothelial cells (HMVECs) from diabetic patients into spheroids would restore their vasculogenic potential following upregulation of these cell-cell interactions. HMVEC spheroids were formed and suspended in fibrin gels to quantify vasculogenic potential.

Results

Individual HMVECs from diabetic patients exhibited similar proliferative and chemotactic potential to cells from healthy donors but reduced tubulogenesis. HMVEC spheroids formed from diabetic donors formed more sprouts than spheroids from healthy donors, and more sprouts than individual cells from either population.

Conclusions

Compared to cells from healthy donors, sprout formation was more efficiently abrogated in HMVECs from diabetic patients by blocking matrix metalloproteinase activity. This study demonstrates a promising approach for restoring the diminished vasculogenic potential of endothelial cells in diabetic patients.

Changes in lipid metabolism and capillary density of the skeletal muscle following low-intensity exercise training in a rat model of obesity with hyperinsulinemia

Although exercise is effective in improving obesity and hyperinsulinemia, the exact influence of exercise on the capillary density of skeletal muscles remains unknown. The aim of this study was to investigate the effects of low-intensity exercise training on metabolism in obesity with hyperinsulinemia, focusing specifically on the capillary density within the skeletal muscle. Otsuka Long-Evans Tokushima fatty (OLETF) rats were used as animal models of obesity with hyperinsulinemia, whereas Long-Evans Tokushima Otsuka (LETO) rats served as controls (no obesity, no hyperinsulinemia). The animals were randomly assigned to either non-exercise or exercise groups (treadmill running for 60 min/day, for 4 weeks). The exercise groups were further divided into subgroups according to training mode: single bout (60 min, daily) vs. multiple bout (three bouts of 20 min, daily). Fasting insulin levels were significantly higher in OLETF than in LETO rats. Among OLETF rats, there were no significant differences in fasting glucose levels between the exercise and the non-exercise groups, but the fasting insulin levels were significantly lower in the exercise group. Body weight and triacylglycerol levels in the liver were significantly higher in OLETF than in LETO rats; however, among OLETF rats, these levels were significantly lower in the exercise than in the non-exercise group. The capillary-to-fiber ratio of the soleus muscle was significantly higher in OLETF than in LETO rats; however, among OLETF rats, the ratio was lower in the exercise group than in the non-exercise group. No significant differences in any of the studied parameters were noted between the single-bout and multiple-bout exercise training modes among either OLETF or LETO rats. These results suggest that low-intensity exercise training improves insulin sensitivity and fatty liver. Additionally, the fact that attenuation of excessive capillarization in the skeletal muscle of OLETF rats was accompanied by improvement in increased body weight.

Reduction of Endoplasmic Reticulum Stress Improves Angiogenic Progenitor Cell function in a Mouse Model of Type 1 Diabetes

Persistent vascular injury and degeneration in diabetes are attributed in part to defective reparatory function of angiogenic cells. Our recent work implicates endoplasmic reticulum (ER) stress in high-glucose-induced bone marrow (BM) progenitor dysfunction. Herein, we investigated the in vivo role of ER stress in angiogenic abnormalities of streptozotocin-induced diabetic mice. Our data demonstrate that ER stress markers and inflammatory gene expression in BM mononuclear cells and hematopoietic progenitor cells increase dynamically with disease progression. Increased CHOP and cleaved caspase­ 3 levels were observed in BM­-derived early outgrowth cells (EOCs) after 3 months of diabetes. Inhibition of ER stress by ex vivo or in vivo chemical chaperone treatment significantly improved the generation and migration of diabetic EOCs while reducing apoptosis of these cells. Chemical chaperone treatment also increased the number of circulating angiogenic cells in peripheral blood, alleviated BM pathology, and enhanced retinal vascular repair following ischemia/reperfusion in diabetic mice. Mechanistically, knockdown of CHOP alleviated high-glucose-induced EOC dysfunction and mitigated apoptosis, suggesting a pivotal role of CHOP in mediating ER stress-associated angiogenic cell injury in diabetes. Together, our study suggests that targeting ER signaling may provide a promising and novel approach to enhancing angiogenic function in diabetes.

Type 2 diabetes impairs the ability of skeletal muscle pericytes to augment postischemic neovascularization in db/db mice

Peripheral artery disease is an atherosclerotic occlusive disease that causes limb ischemia and has few effective noninterventional treatments. Stem cell therapy is promising, but concomitant diabetes may limit its effectiveness. We evaluated the therapeutic potential of skeletal muscle pericytes to augment postischemic neovascularization in wild-type and type 2 diabetic (T2DM) mice. Wild-type C57BL/6J and leptin receptor spontaneous mutation db/db T2DM mice underwent unilateral femoral artery excision to induce limb ischemia. Twenty-four hours after ischemia induction, CD45^-CD34^-CD146⁺ skeletal muscle pericytes or vehicle controls were transplanted into ischemic hindlimb muscles. At postoperative day 28, pericyte transplantation augmented blood flow recovery in wild-type mice (79.3 ± 5% vs. 61.9 ± 5%; P = 0.04), but not in T2DM mice (48.6% vs. 46.3 ± 5%; P = 0.51). Pericyte transplantation augmented collateral artery enlargement in wild-type (26.7 ± 2 μm vs. 22.3 ± 1 μm, P = 0.03), but not T2DM mice (20.4 ± 1.4 μm vs. 18.5 ± 1.2 μm, P = 0.14). Pericyte incorporation into collateral arteries was higher in wild-type than in T2DM mice ( P = 0.002). Unexpectedly, pericytes differentiated into Schwann cells in vivo. In vitro, Insulin increased Nox2 expression and decreased tubular formation capacity in human pericytes. These insulin-induced effects were reversed by N-acetylcysteine antioxidant treatment. In conclusion, T2DM impairs the ability of pericytes to augment neovascularization via decreased collateral artery enlargement and impaired engraftment into collateral arteries, potentially via hyperinsulinemia-induced oxidant stress. While pericytes show promise as a unique form of stem cell therapy to increase postischemic neovascularization, characterizing the molecular mechanisms by which T2DM impairs their function is essential to achieve their therapeutic potential.

Diabetic Microvascular Disease: An Endocrine Society Scientific Statement

Both type 1 and type 2 diabetes adversely affect the microvasculature in multiple organs. Our understanding of the genesis of this injury and of potential interventions to prevent, limit, or reverse injury/dysfunction is continuously evolving. This statement reviews biochemical/cellular pathways involved in facilitating and abrogating microvascular injury. The statement summarizes the types of injury/dysfunction that occur in the three classical diabetes microvascular target tissues, the eye, the kidney, and the peripheral nervous system; the statement also reviews information on the effects of diabetes and insulin resistance on the microvasculature of skin, brain, adipose tissue, and cardiac and skeletal muscle. Despite extensive and intensive research, it is disappointing that microvascular complications of diabetes continue to compromise the quantity and quality of life for patients with diabetes. Hopefully, by understanding and building on current research findings, we will discover new approaches for prevention and treatment that will be effective for future generations.

DJ‑1 alleviates high glucose‑induced endothelial cells injury via PI3K/Akt‑eNOS signaling pathway

Hyperglycemia mediated endothelial cells (ECs) injury is closely associated with diabetic vascular complications. It was revealed that DJ‑1 possesses cellular protective effects by suppressing oxidative stress. The present study aimed to investigate the beneficial effects of DJ‑1 on high glucose (HG)‑induced human umbilical vein endothelial cell (HUVEC) injury and to elucidate its underlying mechanisms. HUVECs were incubated under 5.5 mM (control group) or 25 mM D‑glucose (HG group) and then transfected with recombinant adenoviral vectors to overexpression of DJ‑1. Cell proliferation and apoptosis were measured using the EdU incorporation assay and flow cytometry with Annexin V-FITC/propidium iodide double staining, respectively. Apoptotic‑related proteins were determined using western blot analysis. Reactive oxygen species (ROS) production, lactate dehydrogenase (LDH) and nitric oxide (NO) levels, the content of malondialdehyde (MDA), and the activities of superoxide dismutase (SOD) were measured. Results demonstrated that overexpression of DJ‑1 promoted cell proliferation and inhibited HUVECs apoptosis stimulated by HG. DJ‑1 also suppressed the HG‑induced reduction in the Bcl‑2/Bax ratio and HG activated ROS generation in HUVECs. Furthermore, HG significantly increased the levels of LDH and MDA, and reduced the level of SOD; however, these effects were reversed by Ad‑DJ‑1 transfection. Furthermore, the cellular protective effect of overexpression of DJ‑1 enhanced p‑Akt/Akt ratio, eNOS activation and NO production, and these trends were partially reversed by a phosphatidylinositol‑4,5‑bisphosphate 3‑kinase (PI3K) inhibitor (LY294002). Taken together, the present study highlighted the involvement of DJ‑1 in HG‑related EC injury and identified that DJ‑1 exerts a cellular protective effect in HUVECs exposed to HG induced oxidative stress via activation of the PI3K/Akt‑eNOS signaling pathway.

Considerations on the harvesting site and donor derivation for mesenchymal stem cells-based strategies for diabetes

Mesenchymal Stem Cells (MSCs) possess important characteristics that could be exploited in therapeutic strategies for Type 1 Diabetes (T1D) and for certain complications of Type 2 Diabetes (T2D). MSCs can inhibit autoimmune, alloimmune and inflammatory processes. Moreover, they can promote the function of endogenous and transplanted pancreatic islets. Furthermore, they can stimulate angiogenesis. MSC functions are largely mediated by their secretome, which includes growth factors, exosomes, and other extracellular vesicles. MSCs have shown a good safety profile in clinical trials. MSC-derived exosomes are emerging as an alternative to the transplantation of live MSCs. MSCs harvested from different anatomical locations (e.g. bone marrow, umbilical cord, placenta, adipose tissue, and pancreas) have shown differences in gene expression profiles and function. Data from clinical trials suggest that umbilical cord-derived MSCs could be superior to bone marrow-derived MSCs for the treatment of T1D. Autologous MSCs from diabetic patients may present abnormal functions. BM-MSCs from T1D patients exhibit gene expression differences that may impact in vivo function. BM-MSCs from T2D patients seem to be significantly impaired due to the T2D diabetic milieu. In this review, we highlight how the harvesting site and donor derivation can affect the efficacy of MSC-based treatments for T1D and T2D.

Endothelial Cell Redox Regulation of Ischemic Angiogenesis

The endothelium produces and responds to reactive oxygen and nitrogen species (RONS), providing important redox regulation to the cardiovascular system in physiology and disease. In no other situation are RONS more critical than in the response to tissue ischemia. Here, tissue healing requires growth factor-mediated angiogenesis that is in part dependent on low levels of RONS, which paradoxically must overcome the damaging effects of high levels of RONS generated as a result of ischemia. Although the generation of endothelial cell RONS in hypoxia/reoxygenation is acknowledged, the mechanism for their role in angiogenesis is still poorly understood. During ischemia, the major low molecular weight thiol glutathione (GSH) reacts with RONS and protein cysteines, producing GSH-protein adducts. Recent data indicate that GSH adducts on certain proteins are essential to growth factor responses in endothelial cells. Genetic deletion of the enzyme glutaredoxin-1, which selectively removes GSH protein adducts, improves, whereas its overexpression impairs revascularization of the ischemic hindlimb of mice. Ischemia-induced GSH adducts on specific cysteine residues of several proteins, including p65 NF-kB and the sarcoplasmic reticulum calcium ATPase 2, evidently promote ischemic angiogenesis. Identifying the specific proteins in the redox response to ischemia has provided therapeutic opportunities to improve clinical outcomes of ischemia.

Peripheral artery disease, redox signaling, oxidative stress - Basic and clinical aspects

Reactive oxygen and nitrogen species (ROS and RNS, e.g. H2O2, nitric oxide) confer redox regulation of essential cellular signaling pathways such as cell differentiation, proliferation, migration and apoptosis. At higher concentrations, ROS and RNS lead to oxidative stress and oxidative damage of biomolecules (e.g. via formation of peroxynitrite, fenton chemistry). Peripheral artery disease (PAD) is characterized by severe ischemic conditions in the periphery leading to intermittent claudication and critical limb ischemia (end stage). It is well known that redox biology and oxidative stress play an important role in this setting. We here discuss the major pathways of oxidative stress and redox signaling underlying the disease progression with special emphasis on the contribution of inflammatory processes. We also highlight therapeutic strategies comprising pharmacological (e.g. statins, angiotensin-converting enzyme inhibitors, phosphodiesterase inhibition) and non-pharmacological (e.g. exercise) interventions. Both of these strategies induce potent indirect antioxidant and anti-inflammatory mechanisms that may contribute to an improvement of PAD associated complications and disease progression by removing excess formation of ROS and RNS (e.g. by ameliorating primary complications such as hyperlipidemia and hypertension) as well as the normalization of the inflammatory phenotype suppressing the progression of atherosclerosis.

Deletion of TXNIP Mitigates High-Fat Diet-Impaired Angiogenesis and Prevents Inflammation in a Mouse Model of Critical Limb Ischemia

Background: Previous work demonstrated that high-fat diet (HFD) triggered thioredoxin-interacting protein (TXNIP) and that silencing TXNIP prevents diabetes-impaired vascular recovery. Here, we examine the impact of genetic deletion of TXNIP on HFD-impaired vascular recovery using hind limb ischemia model. Methods: Wild type mice (WT, C57Bl/6) and TXNIP knockout mice (TKO) were fed either normal chow diet (WT-ND and TKO-ND) or 60% high-fat diet (WT-HFD and TKO-HFD). After four weeks of HFD, unilateral hind limb ischemia was performed and blood flow was measured using Laser doppler scanner at baseline and then weekly for an additional three weeks. Vascular density, nitrative stress, infiltration of CD68+ macrophages, and expression of inflammasome, vascular endothelial growth factor (VEGF), VEGF receptor-2 were examined by slot blot, Western blot and immunohistochemistry. Results: By week 8, HFD caused similar increases in weight, cholesterol and triglycerides in both WT and TKO. At week 4 and week 8, HFD significantly impaired glucose tolerance in WT and to a lesser extent in TKO. HFD significantly impaired blood flow and vascular density (CD31 labeled) in skeletal muscle of WT mice compared to ND but not in TKO. HFD and ischemia significantly induced tyrosine nitration, and systemic IL-1β and infiltration of CD68+ cells in skeletal muscle from WT but not from TKO. HFD significantly increased cleaved-caspase-1 and IL-1 β compared to ND. Under both ND, ischemia tended to increase VEGF expression and increased VEGFR2 activation in WT only but not TKO. Conclusion: Similar to prior observation in diabetes, HFD-induced obesity can compromise vascular recovery in response to ischemic insult. The mechanism involves increased TXNIP-NLRP3 (nucleotide-binding oligomerization domain-like receptor protein 3) inflammasome activation, nitrative stress and impaired VEGFR2 activation. Deletion of TXNIP restored blood flow, reduced nitrative stress and blunted inflammasome-mediated inflammation; however, it did not impact VEGF/VEGFR2 in HFD. Targeting TXNIP-NLRP3 inflammasome can provide potential therapeutic target in obesity-induced vascular complication.

Netrin-1 restores cell injury and impaired angiogenesis in vascular endothelial cells upon high glucose by PI3K/AKT-eNOS

Diabetic foot ulceration (DFU) represents a common vascular complication of diabetes mellitus (DM) with high morbidity and disability resulting from amputation. Netrin-1 level was decreased in type 2 DM patients and has been identified as a protective regulator against diabetes-triggered myocardial infarction and nephropathy. Unfortunately, its role and molecular mechanism in DFU remain poorly elucidated. Here, netrin-1 levels were reduced in DM and DFU patients relative to healthy controls, with netrin-1 levels being the lowest in DFU patients. Moreover, exposure to high glucose (HG) also suppressed netrin-1 expression in human umbilical vein endothelial cells (HUVECs). Elevated netrin-1 expression by infection with Ad-netrin-1 adenovirus vector protected against HUVEC injury in response to HG by ameliorating the inhibitory effects on cell viability, lactate dehydrogenase (LDH) and malondialdehyde (MDA) levels, cell apoptotic rate and caspase-3 activity. Importantly, HG-impaired angiogenesis was improved after netrin-1 overexpression by elevating cell migration, capillary-like tube formation and VEGF production. Mechanism assay substantiated that netrin-1 elevation increased the phosphorylation levels of AKT and eNOS, and NO production, which was notably suppressed by HG, indicating that netrin-1 overexpression restored HG-triggered impairment of the PI3K/AKT-eNOS pathway. More intriguingly, preconditioning with LY294002 (PI3K/AKT antagonist) or N^G-monomethyl-l-arginine (eNOS inhibitor) antagonized netrin-1-induced activation of the PI3K/AKT-eNOS pathway. Concomitantly, treatment with these antagonists also attenuated the protective role of netrin-1 in endothelial dysfunction upon HG stimulation. These results suggest that elevation of netrin-1 may restore HG-triggered impairment of HUVEC and angiogenesis by activating the PI3K/AKT-eNOS pathway, indicating a potential agent for wound healing in DFU patients.

Pro-angiogenic Role of Insulin: From Physiology to Pathology

The underlying molecular mechanisms involve in the regulation of the angiogenic process by insulin are not well understood. In this review article, we aim to describe the role of insulin and insulin receptor activation on the control of angiogenesis and how these mechanisms can be deregulated in human diseases. Functional expression of insulin receptors and their signaling pathways has been described on endothelial cells and pericytes, both of the main cells involved in vessel formation and maturation. Consequently, insulin has been shown to regulate endothelial cell migration, proliferation, and in vitro tubular structure formation through binding to its receptors and activation of intracellular phosphorylation cascades. Furthermore, insulin-mediated pro-angiogenic state is potentiated by generation of vascular growth factors, such as the vascular endothelial growth factor, produced by endothelial cells. Additionally, diseases such as insulin resistance, obesity, diabetes, and cancer may be associated with the deregulation of insulin-mediated angiogenesis. Despite this knowledge, the underlying molecular mechanisms need to be elucidated in order to provide new insights into the role of insulin on angiogenesis.

Human Placenta-Derived Mesenchymal Stromal-Like Cells Enhance Angiogenesis via T Cell-Dependent Reprogramming of Macrophage Differentiation

Peripheral arterial disease (PAD) is a leading cause of limb loss and mortality worldwide with limited treatment options. Mesenchymal stromal cell (MSC) therapy has demonstrated positive effects on angiogenesis in preclinical models and promising therapeutic efficacy signals in early stage clinical studies; however, the mechanisms underlying MSC-mediated angiogenesis remain largely undefined. Here, we investigated the mechanism of action of human placenta-derived MSC-like cells (PDA-002) in inducing angiogenesis using mice hind limb ischemia model. We showed that PDA-002 improved blood flow and promoted collateral vessel formation in the injured limb. Histological analysis demonstrated that PDA-002 increased M2-like macrophages in ischemic tissue. Analysis of the changes in functional T cell phenotype in the draining lymph nodes revealed that PDA-002 treatment was associated with the induction of cytokine and gene expression signatures of Th2 response. Angiogenic effect of PDA-002 was markedly reduced in Balb/c nude mice compared with wild type. This reduction in efficacy was reversed by T cell reconstitution, suggesting T cells are essential for PDA-002-mediated angiogenesis. Furthermore, effect of PDA-002 on macrophage differentiation was also T cell-dependent as a PDA-002-mediated M2-like macrophage skewing was only observed in wild type and T cell reconstituted nude mice, but not in nude mice. Finally, we showed that PDA-002-treated animals had enhanced angiogenic recovery in response to the second injury when PDA-002 no longer persisted in vivo. These results suggest that PDA-002 enhances angiogenesis through an immunomodulatory mechanism involving T cell-dependent reprogramming of macrophage differentiation toward M2-like phenotype. Stem Cells 2017;35:1603-1613.

The potential effect of biological sealants on colorectal anastomosis healing in experimental research involving severe diabetes

Colorectal anastomoses continuous to pose a significant challenge in current surgical practice. Anastomotic leakage remains one of the most frequent and dramatic complications of colorectal surgery, even in centres of high specialisation. Diabetes is a well-established independent factor which results in higher anastomotic leakage rates. Fibrin sealants have been applied in experimental and clinical studies for the prevention of anastomotic dehiscence. However, little is known regarding their impact on diabetic patients. Several fibrin sealants have been proposed as adjunct to standard surgical techniques to prevent leakage from colonic anastomoses following the reversal of temporary colostomies, approved for general haemostasis. This review summarises current advances in colorectal anastomoses and provides evidence that may strengthen the need for tissue sealants in colorectal anastomoses of diabetic patients. We searched Medline (1966-2016) and Scopus (2004-2016) for current evidence in the field. To date, there is no evidence to support the use of fibrin sealants as an adjunct in diabetic patients who undergo colorectal surgery. Experimental animal models with extreme diabetes could be of significant use in the present field and further research is needed prior to application of fibrin sealants in a clinical setting.

Muscle Derived Stem Cells Stimulate Muscle Myofiber Repair and Counteract Fat Infiltration in a Diabetic Mouse Model of Critical Limb Ischemia

Background

Critical Limb Ischemia (CLI) affects patients with Type 2 Diabetes (T2D) and obesity, with high risk of amputation and post-surgical mortality, and no effective medical treatment. Stem cell therapy, mainly with bone marrow mesenchymal, adipose derived, endothelial, hematopoietic, and umbilical cord stem cells, is promising in CLI mouse and rat models and is in clinical trials. Their general focus is on angiogenic repair, with no reports on the alleviation of necrosis, lipofibrosis, and myofiber regeneration in the ischemic muscle, or the use of Muscle Derived Stem Cells (MDSC) alone or in combination with pharmacological adjuvants, in the context of CLI in T2D.

Methods

Using a T2D mouse model of CLI induced by severe unilateral femoral artery ligation, we tested: a) the repair efficacy of MDSC implanted into the ischemic muscle and the effects of concurrent intraperitoneal administration of a nitric oxide generator, molsidomine; and b) whether MDSC may partially counteract their own repair effects by stimulating the expression of myostatin, the main lipofibrotic agent in the muscle and inhibitor of muscle mass.

Results

MDSC: a) reduced mortality, and b) in the ischemic muscle, increased stem cell number and myofiber central nuclei, reduced fat infiltration, myofibroblast number, and myofiber apoptosis, and increased smooth muscle and endothelial cells, as well as neurotrophic factors. The content of myosin heavy chain 2 (MHC-2) myofibers was not restored and collagen was increased, in association with myostatin overexpression. Supplementation of MDSC with molsidomine failed to stimulate the beneficial effects of MDSC, except for some reduction in myostatin overexpression. Molsidomine given alone was rather ineffective, except for inhibiting apoptosis and myostatin overexpression.

Conclusions

MDSC improved CLI muscle repair, but molsidomine did not stimulate this process. The combination of MDSC with anti-myostatin approaches should be explored to restore myofiber MHC composition.

AMP-Activated Protein Kinase α2 in Neutrophils Regulates Vascular Repair via Hypoxia-Inducible Factor-1α and a Network of Proteins Affecting Metabolism and Apoptosis

RATIONALE

The AMP-activated protein kinase (AMPK) is stimulated by hypoxia, and although the AMPKα1 catalytic subunit has been implicated in angiogenesis, little is known about the role played by the AMPKα2 subunit in vascular repair.

OBJECTIVE

To determine the role of the AMPKα2 subunit in vascular repair.

METHODS AND RESULTS

Recovery of blood flow after femoral artery ligation was impaired (>80%) in AMPKα2^-/- versus wild-type mice, a phenotype reproduced in mice lacking AMPKα2 in myeloid cells (AMPKα2^ΔMC). Three days after ligation, neutrophil infiltration into ischemic limbs of AMPKα2^ΔMC mice was lower than that in wild-type mice despite being higher after 24 hours. Neutrophil survival in ischemic tissue is required to attract monocytes that contribute to the angiogenic response. Indeed, apoptosis was increased in hypoxic neutrophils from AMPKα2^ΔMC mice, fewer monocytes were recruited, and gene array analysis revealed attenuated expression of proangiogenic proteins in ischemic AMPKα2^ΔMC hindlimbs. Many angiogenic growth factors are regulated by hypoxia-inducible factor, and hypoxia-inducible factor-1α induction was attenuated in AMPKα2-deficient cells and accompanied by its enhanced hydroxylation. Also, fewer proteins were regulated by hypoxia in neutrophils from AMPKα2^ΔMC mice. Mechanistically, isocitrate dehydrogenase expression and the production of α-ketoglutarate, which negatively regulate hypoxia-inducible factor-1α stability, were attenuated in neutrophils from wild-type mice but remained elevated in cells from AMPKα2^ΔMC mice.

CONCLUSIONS

AMPKα2 regulates α-ketoglutarate generation, hypoxia-inducible factor-1α stability, and neutrophil survival, which in turn determine further myeloid cell recruitment and repair potential. The activation of AMPKα2 in neutrophils is a decisive event in the initiation of vascular repair after ischemia.

Modulating putative endothelial progenitor cells for the treatment of endothelial dysfunction and cardiovascular complications in diabetes

Diabetes induces a decrease in the number and function of different pro-angiogenic cell types generically designated as putative endothelial progenitor cells (EPC), which encompasses cells from myeloid origin that act in a paracrine fashion to promote angiogenesis and putative "true" EPC that contribute to endothelial replacement. This not only compromises neovasculogenesis in ischemic tissues but also impairs, at an early stage, the reendotheliziation process at sites of injury, contributing to the development of endothelial dysfunction and cardiovascular complications. Hyperglycemia, insulin resistance and dyslipidemia promote putative EPC dysregulation by affecting the SDF-1/CXCR-4 and NO pathways and the p53/SIRT1/p66Shc axis that contribute to their mobilization, migration, homing and vasculogenic properties. To optimize the clinical management of patients with hypoglycemic agents, statins and renin-angiotensin system inhibitors, which display pleiotropic effects on putative EPC, is a first step to improve their number and angiogenic potential but specific strategies are needed. Among them, mobilizing therapies based on G-CSF, erythropoietin or CXCR-4 antagonism have been developed to increase putative EPC number to treat ischemic diseases with or without prior cell isolation and transplantation. Growth factors, genetic and pharmacological strategies are also evaluated to improve ex vivo cultured EPC function before transplantation. Moreover, pharmacological agents increasing in vivo the bioavailability of NO and other endothelial factors demonstrated beneficial effects on neovascularization in diabetic ischemic models but their effects on endothelial dysfunction remain poorly evaluated. More experiments are warranted to develop orally available drugs and specific agents targeting p66Shc to reverse putative EPC dysfunction in the expected goal of preventing endothelial dysfunction and diabetic cardiovascular complications.

Targeted Expression of Catalase to Mitochondria Protects Against Ischemic Myopathy in High-Fat Diet-Fed Mice

Patients with type 2 diabetes respond poorly to treatments for peripheral arterial disease (PAD) and are more likely to present with the most severe manifestation of the disease, critical limb ischemia. The underlying mechanisms linking type 2 diabetes and the severity of PAD manifestation are not well understood. We sought to test whether diet-induced mitochondrial dysfunction and oxidative stress would increase the susceptibility of the peripheral limb to hindlimb ischemia (HLI). Six weeks of high-fat diet (HFD) in C57BL/6 mice was insufficient to alter skeletal muscle mitochondrial content and respiratory function or the size of ischemic lesion after HLI, despite reducing blood flow. However, 16 weeks of HFD similarly decreased ischemic limb blood flow, but also exacerbated limb tissue necrosis, increased the myopathic lesion size, reduced muscle regeneration, attenuated muscle function, and exacerbated ischemic mitochondrial dysfunction. Mechanistically, mitochondrial-targeted overexpression of catalase prevented the HFD-induced ischemic limb necrosis, myopathy, and mitochondrial dysfunction, despite no improvement in limb blood flow. These findings demonstrate that skeletal muscle mitochondria are a critical pathological link between type 2 diabetes and PAD. Furthermore, therapeutically targeting mitochondria and oxidant burden is an effective strategy to alleviate tissue loss and ischemic myopathy during PAD.

Impaired Mobilization of Vascular Reparative Bone Marrow Cells in Streptozotocin-Induced Diabetes but not in Leptin Receptor-Deficient db/db Mice

Diabetes is associated with impaired mobilization of bone marrow stem/progenitor cells that accelerate vascularization of ischemic areas. This study characterized mobilization of vascular reparative bone marrow progenitor cells in mouse models of diabetes. Age-matched control or streptozotocin (STZ)-induced diabetic, and db/db mice with lean-controls were studied. Mobilization induced by G-CSF, AMD3100 or ischemia was evaluated by flow cytometric enumeration of circulating Lin(-)Sca-1(+)cKit(+) (LSK) cells, and by colony forming unit (CFU) assay. The circulating WBCs and LSKs, and CFUs were reduced in both models with a shorter duration (10-12 weeks) of diabetes compared to their respective controls. Longer duration of STZ-diabetes (≥20 weeks) induced impairment of G-CSF- or AMD3100-mobilization (P < 0.01, n = 8). In db/db mice, mobilization by G-CSF or AMD3100 was either increased or unaffected (P < 0.05, n = 6 to 8). Proliferation, migration, and ischemia-induced mobilization, of LSK cells were impaired in both models. Leptin receptor antagonist, PESLAN-1, increased G-CSF- or AMD3100-mobilization of WBCs and LSKs, compared to the untreated. Leptin increased basal WBCs, decreased basal and AMD3100-mobilized LSK cells, and had no effect on G-CSF. These results suggest that mobilopathy is apparent in STZ-diabetes but not in db/db mice. Leptin receptor antagonism would be a promising approach for reversing diabetic bone marrow mobilopathy.

Physical exercise and epigenetic adaptations of the cardiovascular system

During the last decade, epigenetics became one of the fastest growing research fields in numerous clinical and basic science disciplines. Evidence suggests that chromatin modifications (e.g., histone modifications and DNA methylation) as well as the expression of micro-RNA molecules play a crucial role in the pathogenesis of several cardiovascular diseases. On the one hand, they are involved in the development of general risk factors like chronic inflammation, but on the other hand, epigenetic modifications are conducive to smooth muscle cell, cardiomyocyte, and endothelial progenitor cell proliferation/differentiation as well as to extracellular matrix processing and endothelial function (e.g., endothelial nitric oxide synthase regulation). Therefore, epigenetic medical drugs have gained increased attention and provided the first promising results in the context of cardiovascular malignancies. Beside other lifestyle factors, physical activity and sports essentially contribute to cardiovascular health and regeneration. In this review we focus on recent research proposing physical activity as a potent epigenetic regulator that has the potential to counteract pathophysiological alterations in almost all the aforementioned cardiovascular cells and tissues. As with epigenetic medical drugs, more knowledge about the molecular mechanisms and dose-response relationships of exercise is needed to optimize the outcome of preventive and rehabilitative exercise programs and recommendations.

A systematic approach to assess locoregional differences in angiogenesis

Skeletal muscle tissue differs with regard to the abundance of glycolytic and oxidative fiber types. In this context, capillary density has been described to be higher in muscle tissue with more oxidative metabolism as compared to that one with more glycolytic metabolism, and the highest abundance of capillaries has been found in boneward-oriented moieties of skeletal muscle tissue. Importantly, capillary formation is often analyzed as a measure for angiogenesis, a process that describes neo-vessel formation emanating from preexisting vessels, occurring, i.e., after arterial occlusion. However, a standardized way for investigation of calf muscle capillarization after surgically induced unilateral hind limb ischemia in mice, especially considering these locoregional differences, has not been provided so far. In this manuscript, a novel, methodical approach for reliable analysis of capillary density was established using anatomic-morphological reference points, and a software-assisted way of capillary density analysis is described. Thus, the systematic approach provided conscientiously considers intra-layer differences in capillary formation and therefore guarantees for a robust, standardized analysis of capillary density as a measure for angiogenesis. The significance of the methodology is further supported by the observation that capillary density in the calf muscle layers analyzed negatively correlates with distal lower limb perfusion measured in vivo.

Enhanced endoplasmic reticulum stress in bone marrow angiogenic progenitor cells in a mouse model of long-term experimental type 2 diabetes

AIMS/HYPOTHESIS

Bone marrow-derived circulating angiogenic cells (CACs) play an important role in vascular repair. In diabetes, compromised functioning of the CACs contributes to the development of diabetic retinopathy; however, the underlying mechanisms are poorly understood. We examined whether endoplasmic reticulum (ER) stress, which has recently been linked to endothelial injury, is involved in diabetic angiogenic dysfunction.

METHODS

Flow cytometric analysis was used to quantify bone marrow-derived progenitors (Lin(-)/c-Kit(+)/Sca-1(+)/CD34(+)) and blood-derived CACs (Sca-1(+)/CD34(+)) in 15-month-old Lepr (db) (db/db) mice and in their littermate control (db/+) mice used as a model of type 2 diabetes. Markers of ER stress in diabetic (db/db) and non-diabetic (db/+) bone marrow-derived early outgrowth cells (EOCs) and retinal vascular density were measured.

RESULTS

The numbers of bone-marrow progenitors and CACs were significantly reduced in db/db mice. Vascular density was markedly decreased in the retinas of db/db mice, and this was accompanied by vascular beading. Microglial activation was enhanced, as was the production of hypoxia inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF). The production of ER stress markers (glucose-regulated protein-78 [GRP-78], phosphorylated inositol-requiring enzyme-1α [p-IRE-1α], phosphorylated eukaryotic translation initiation factor-2α [p-eIF2α], activating transcription factor-4 [ATF4], C/EBP homologous protein [CHOP] and spliced X-box binding protein-1 [XBP1s]) was significantly increased in bone marrow-derived EOCs from db/db mice. In addition, mouse EOCs cultured in high-glucose conditions demonstrated higher levels of ER stress, reduced colony formation, impaired migration and increased apoptosis, all of which were largely prevented by the chemical chaperone 4-phenylbutyrate.

CONCLUSIONS/INTERPRETATION

Taken together, our results indicate that diabetes increases ER stress in bone marrow angiogenic progenitor cells. Thus, targeting ER stress may offer a new approach to improving angiogenic progenitor cell function and promoting vascular repair in diabetes.

Decelerated vascularization in tissue-engineered constructs in association with diabetes mellitus in vivo

AIMS

Rapid blood vessel ingrowth in transplanted tissue engineering constructs is the key factor for successful incorporation, but many potential patients who may use engineered tissues suffer from widespread diseases that limit the capacity of neovascularization (e.g. diabetes). Thus, in vivo vascularization analyses of tissue-engineered constructs in angiogenically affected organisms are required.

METHODS

We therefore investigated the in vivo incorporation of collagen-coated and cell-seeded poly-L-lactide-co-glycolide scaffolds in diabetic B6.BKS(D)-Lepr(db)/J mice using repetitive intravital fluorescence microscopy over a time period of two weeks. For this purpose, scaffolds were seeded with osteoblast-like or bone marrow mesenchymal stem cells and implanted into the dorsal skinfold chambers of diabetic and non-diabetic (C57BL/6) mice.

RESULTS

Apart from slightly increased inflammatory parameters, diabetic mice showed significantly reduced capillary densities compared with non-diabetic animals from day 6 onward. In line with previous studies, more densely meshed microvascular networks were demonstrated in cell-seeded than in collagen-coated scaffolds from day 6 onward within the single groups (diabetic and control).

CONCLUSIONS

A large number of patients who suffer from systemic diseases that affect angiogenesis would profit from tissue engineering. Therefore, the challenge for the clinical introduction of tissue-engineered constructs will be to overcome the decreased angiogenesis in diabetic organisms.