Amelioration of glucose control mobilizes circulating pericyte progenitor cells in type 2 diabetic patients with microangiopathy

Stem Cell-Based Therapy: A Promising Treatment for Diabetic Foot Ulcer

Diabetic foot ulcer (DFU) is a severe complication of diabetes and a challenging medical condition. Conventional treatments for DFU have not been effective enough to reduce the amputation rates, which urges the need for additional treatment. Stem cell-based therapy for DFU has been investigated over the past years. Its therapeutic effect is through promoting angiogenesis, secreting paracrine factors, stimulating vascular differentiation, suppressing inflammation, improving collagen deposition, and immunomodulation. It is controversial which type and origin of stem cells, and which administration route would be the most optimal for therapy. We reviewed the different types and origins of stem cells and routes of administration used for the treatment of DFU in clinical and preclinical studies. Diabetes leads to the impairment of the stem cells in the diseased patients, which makes it less ideal to use autologous stem cells, and requires looking for a matching donor. Moreover, angioplasty could be complementary to stem cell therapy, and scaffolds have a positive impact on the healing process of DFU by stem cell-based therapy. In short, stem cell-based therapy is promising in the field of regenerative medicine, but more studies are still needed to determine the ideal type of stem cells required in therapy, their safety, proper dosing, and optimal administration route.

A historical perspective on the interactions of insulin at the blood-brain barrier

Subsequent to the discovery of insulin in 1921, the role of insulin in the brain has been investigated throughly. The ability of insulin to act within the brain to regulate peripheral glucose levels helped evolve the research surrounding the ability of insulin to be transported into the brain. Investigations aiming to determine the transport of insulin into the brain from the circulation soon followed. Once it was established that insulin could enter the brain, the ability of insulin to bind brain microvessels and regulators of this process were determined. As technology advanced, quantitative measurements to specify the transport rate of insulin across the blood-brain barrier (BBB) and the impact of physiological conditions and diseases were the logical next steps. Lastly, with the advent of genetic mouse models and high-specificity antagonists, the specific role of the insulin receptor in mediating insulin transport could begin to be explored. In this review, we summarise the main findings throughout the decades regarding the interactions of insulin at the BBB.

Diabetic macroangiopathy: Pathogenetic insights and novel therapeutic approaches with focus on high glucose-mediated vascular damage

Diabetic macroangiopathy - a specific form of accelerated atherosclerosis - is characterized by intra-plaque new vessel formation due to excessive/abnormal neovasculogenesis and angiogenesis, increased vascular permeability of the capillary vessels, and tissue edema, resulting in frequent atherosclerotic plaque hemorrhage and plaque rupture. Mechanisms that may explain the premature and rapidly progressive nature of atherosclerosis in diabetes are multiple, and to a large extent still unclear. However, mechanisms related to hyperglycemia certainly play an important role. These include a dysregulated vascular regeneration. In addition, oxidative and hyperosmolar stresses, as well as the activation of inflammatory pathways triggered by a dysregulated activation of membrane channel proteins aquaporins, have been recognized as key events. Here, we review recent knowledge of cellular and molecular pathways of macrovascular disease related to hyperglycemia in diabetes. We also here highlight how new insights into pathogenic mechanisms of vascular damage in diabetes may indicate new targets for prevention and treatment.

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.

Occurring of In Vitro Functional Vasculogenic Pericytes from Human Circulating Early Endothelial Precursor Cell Culture

Pericytes are periendothelial cells of the microcirculation which contribute to tissue homeostasis and hemostasis by regulating microvascular morphogenesis and stability. Because of their multipotential ex vivo differentiation capabilities, pericytes are becoming very interesting in regenerative medicine field. Several studies address this issue by attempting to isolate pericyte/mesenchymal-like cells from peripheral blood; however the origin of these cells and their culture conditions are still debated. Here we showed that early Endothelial Progenitor Cells (EPCs) expressing CD45+/CD146+/CD31+ can be a source of cells with pericyte/mesenchymal phenotype and function, identified as human Progenitor Perivascular Cells (hPPCs). We provided evidence that hPPCs have an immunophenotype consistent with Mesenchymal Stem Cells (MSCs) from human adipose tissue (hASCs) and fetal membranes of term placenta (FM-hMSCs). In addition, hPPCs can be subcultured and exhibit expression of pluripotent genes (OCT-4, KLF-4, and NANOG) as well as a remarkable vasculogenic potential. Our findings could be helpful to develop innovative cell-based therapies for future clinical applications with distinct therapeutic purposes.

Endothelial progenitor cells in diabetic retinopathy

Diabetic retinopathy (DR) is a leading cause of visual impairment worldwide. Patients with DR may irreversibly lose sight as a result of the development of diabetic macular edema (DME) and/or proliferative diabetic retinopathy (PDR); retinal blood vessel dysfunction and degeneration plays an essential role in their pathogenesis. Although new treatments have been recently introduced for DME, including intravitreal vascular endothelial growth factor inhibitors (anti-VEGFs) and steroids, a high proportion of patients (~40-50%) do not respond to these therapies. Furthermore, for people with PDR, laser photocoagulation remains a mainstay therapy despite this being an inherently destructive procedure. Endothelial progenitor cells (EPCs) are a low-frequency population of circulating cells known to be recruited to sites of vessel damage and tissue ischemia where they promote vascular healing and re-perfusion. A growing body of evidence suggests that the number and function of EPCs are altered in patients with varying degrees of diabetes duration, metabolic control, and in the presence or absence of DR. Although there are no clear-cut outcomes from these clinical studies, there is mounting evidence that some EPC sub-types may be involved in the pathogenesis of DR and may also serve as biomarkers for disease progression and stratification. Moreover, some EPC sub-types have considerable potential as therapeutic modalities for DME and PDR in the context of cell therapy. This study presents basic clinical concepts of DR and combines this with a general insight on EPCs and their relation to future directions in understanding and treating this important diabetic complication.

Diversified expression of NG2/CSPG4 isoforms in glioblastoma and human foetal brain identifies pericyte subsets

NG2/CSPG4 is a complex surface-associated proteoglycan (PG) recognized to be a widely expressed membrane component of glioblastoma (WHO grade IV) cells and angiogenic pericytes. To determine the precise expression pattern of NG2/CSPG4 on glioblastoma cells and pericytes, we generated a panel of >60 mouse monoclonal antibodies (mAbs) directed against the ectodomain of human NG2/CSPG4, partially characterized the mAbs, and performed a high-resolution distributional mapping of the PG in human foetal, adult and glioblastoma-affected brains. The reactivity pattern initially observed on reference tumour cell lines indicated that the mAbs recognized 48 immunologically distinct NG2/CSPG4 isoforms, and a total of 14 mAbs was found to identify NG2/CSPG4 isoforms in foetal and neoplastic cerebral sections. These were consistently absent in the adult brain, but exhibited a complementary expression pattern in angiogenic vessels of both tumour and foetal tissues. Considering the extreme pleomorphism of tumour areas, and with the aim of subsequently analysing the distributional pattern of the NG2/CSPG4 isoforms on similar histological vessel typologies, a preliminary study was carried out with endothelial cell and pericyte markers, and with selected vascular basement membrane (VBM) components. On both tumour areas characterized by 'glomeruloid' and 'garland vessels', which showed a remarkably similar cellular and molecular organization, and on developing brain vessels, spatially separated, phenotypically diversified pericyte subsets with a polarized expression of key surface components, including NG2/CSPG4, were disclosed. Interestingly, the majority of the immunolocalized NG2/CSPG4 isoforms present in glioblastoma tissue were present in foetal brain, except for one isoform that seemed to be exclusive of tumour cells, being absent in foetal brain. The results highlight an unprecedented, complex pattern of NG2/CSPG4 isoform expression in foetal and neoplastic CNS, discriminating between phenotype-specific and neoplastic versus non-neoplastic variants of the PG, thus opening up vistas for more selective immunotherapeutic targeting of brain tumours.

Restoring stem cell mobilization to promote vascular repair in diabetes

Diabetes triggers endothelial dysfunction, which is linked to increased risk of cardiovascular diseases. Stem and progenitor cells from the bone marrow are involved in the maintenance of vascular integrity. Diabetic patients show a dysfunction of these cells, which might represent a novel pathophysiological mechanism of vascular disease. Specifically, stem and progenitor cells fail to egress from the bone marrow (BM) due to BM pathological alterations and unresponsiveness to mobilizing stimuli. In this review, we describe impaired stem cell mobilization in diabetes as a mechanism of failed vascular repair and we provide evidence that pharmacological strategies can restore mobilization. We discuss recent advances in the knowledge of aberrant organization of the diabetic BM and its implications for impaired mobilization. Finally, we describe in detail the pharmacological exploitation of the G-CSF/DPP-4(CD26)/SDF-1α axis as a novel strategy to improve mobilization and attain vascular repair in diabetes.

Adverse effect of high glucose concentration on stem cell therapy

Stem cell therapy could have great potential for the treatment of a wide variety of diseases. Stem cells might have the ability to differentiate into a widespread cell types, and to repopulate and revitalize the damaged cells with healthy tissue, and improve its performance. We provide here the evidence supporting the critical use of stem cell as a treatment in disease conditions existing with high glucose complaint such as diabetes. The reduction of glucose stimulated cell proliferation and high glucose enhanced apoptosis in rat model, which may be a problem in therapeutic strategies based on ex vivo expansion of stem cell, and may also propagate the development of osteoporosis in high glucose complaint such as diabetes. This leads to the hypothesis that, high glucose could be more deleterious to stem cell therapy that may be due to the aggravation of oxidative stress triggered by high glucose. These findings may help to understand the possible reasons associated with high glucose induced detrimental effects on stem cells as well as provide novel therapeutic strategies for preventing the adverse effects of glucose on the development and progression of stem cells in patients with diabetes.

Myocardial dysfunction in patients with type 2 diabetes mellitus: role of endothelial progenitor cells and oxidative stress

BACKGROUND

Endothelial progenitor cells (EPCs) are responsible for angiogenesis and maintenance of microvascular integrity, the number of EPCs is correlated with oxidative stress. Their relation to myocardial dysfunction in patients with type 2 diabetes mellitus (T2DM) is nonetheless unknown.

METHODS

Eighty-seven patients with T2DM and no history of coronary artery disease were recruited. Transthoracic echocardiography and detailed evaluation of left ventricular (LV) systolic function by 2-dimensional (2D) speckle tracking derived strain analysis in 3 orthogonal directions was performed. Four subpopulations of EPCs, including CD34+, CD133+, CD34+/kinase insert domain-containing receptor (KDR) + and CD133+/KDR + EPCs, were measured by flow cytometry. Oxidative stress was assessed by superoxide dismutase (SOD).

RESULTS

The mean age of the patients was 62 ± 9 years and 39.6% were male. Those with an impaired longitudinal strain had a lower number of CD34+ EPCs (2.82 ± 1.87% vs. 3.74 ± 2.12%, P < 0.05) than those with preserved longitudinal strain. When compared with those with preserved circumferential strain, patients with an impaired circumferential strain had a lower number of CD34+ EPCs (2.63 ± 1.80% vs. 3.87 ± 2.10%, P < 0.01) and SOD level (0.13 ± 0.06U/ml vs. 0.20 ± 0.08U/ml, P < 0.01). Patients with an impaired radial strain nonetheless had a lower number of CD34+ EPCs (2.62 ± 2.08% vs. 3.69 ± 1.99%, P < 0.05). Multivariate analysis demonstrated that only impaired global circumferential strain remained significantly associated with CD34 + EPCs and SOD.

CONCLUSIONS

LV global circumferential strain was independently associated with number of CD34+ EPCs and SOD. These findings suggest that myocardial dysfunction in patients with T2DM is related to depletion of EPCs and increased oxidative stress.

Patients with an HbA1c in the prediabetic and diabetic range have higher numbers of circulating cells with osteogenic and endothelial progenitor cell markers

CONTEXT

Vascular calcification, an important feature of diabetic vasculopathy, is an active process potentially mediated by endothelial progenitor cells (EPCs) coexpressing the osteoblastic marker osteocalcin (OCN).

OBJECTIVE

In this study we tested the hypothesis that cells expressing these markers are associated with the presence of elevated glycated hemoglobin (HbA1c).

DESIGN, SETTING, AND PATIENTS

This was a cross-sectional comparison. Patients (n = 133, aged 57.4 ± 15.7 yr) were divided into two groups according to the presence of an HbA1c in a (pre-)diabetic (>5.6) or normal range at the time of blood sampling.

METHODS

Using flow cytometry of peripheral blood mononuclear cells (MNCs), cells positive for OCN, the EPC markers (CD34/KDR and CD133(+)/CD34(-)/KDR(+)) and OCN(+) EPCs were counted.

RESULTS

Patients with elevated HbA1c compared with those with normal HbA1c had a significantly higher percentage of circulating OCN(+) MNCs [4.6 (interquartile range 2.68-7.81%) vs. 3.12 (0.99-7.81%), P = 0.035], higher numbers of OCN(+)/CD133(+)/CD34(-)/KDR(+) cells [20 (9-74) vs. 8 (0-19) counts per 100,000 gated events, P < 0.001] and a higher fraction of CD133(+)/CD34(-)/KDR(+) and CD34/KDR cells coexpressing OCN (23.7 ± 24.3 vs. 40.5 ± 34.6%, P = 0.002 and 37.1 ± 39.5 vs. 59.7 ± 37.7%, P = 0.002, respectively). The association between circulating OCN(+)/CD133(+)/CD34(-)/KDR(+) cells and an HbA1c in the (pre-) diabetic range remained strong, even after adjusting for differences in obesity and cardiovascular risk factors, disease, and medications in a multivariate model [odds ratio 1.72 (1.21-2.61), P =0.002].

CONCLUSION

This study demonstrated that patients with HbA1c in the (pre-)diabetic range have a significant increase in OCN(+) MNCs, and OCN(+)/CD133(+)/CD34(-)/KDR(+) cells, in particular. Whether these cells increase vascular calcification in (pre-)diabetes warrants further studies.

A diseased bone marrow fuels atherosclerosis in diabetes

Diabetes accelerates atherosclerosis through shortage of vascular regenerative cells derived from the bone marrow (BM). In addition, diabetes shifts the differentiation of BM progenitor cells to pro-calcific and smooth muscle phenotypes. In a paper published in Atherosclerosis, Fledderus et al. demonstrate that the accelerated atherosclerosis in diabetic ApoE(-/-) mice is associated with an increased amount of BM-derived smooth muscle cells in the plaques. The role of ApoE in the regulation of vascular BM progenitors may explain inconsistencies in the literature on the contribution of extraparietal cells to atherosclerotic lesions. Herein, the pathophysiological meaning of a deranged kinetic of smooth muscle progenitor cells in diabetes is discussed.

It is all in the blood: the multifaceted contribution of circulating progenitor cells in diabetic complications

Diabetes mellitus (DM) is a worldwide growing disease and represents a huge social and healthcare problem owing to the burden of its complications. Micro- and macrovascular diabetic complications arise from excess damage through well-known biochemical pathways. Interestingly, microangiopathy hits the bone marrow (BM) microenvironment with features similar to retinopathy, nephropathy and neuropathy. The BM represents a reservoir of progenitor cells for multiple lineages, not limited to the hematopoietic system and including endothelial cells, smooth muscle cells, cardiomyocytes, and osteogenic cells. All these multiple progenitor cell lineages are profoundly altered in the setting of diabetes in humans and animal models. Reduction of endothelial progenitor cells (EPCs) along with excess smooth muscle progenitor (SMP) and osteoprogenitor cells creates an imbalance that promote the development of micro- and macroangiopathy. Finally, an excess generation of BM-derived fusogenic cells has been found to contribute to diabetic complications in animal models. Taken together, a growing amount of literature attributes to circulating progenitor cells a multi-faceted role in the pathophysiology of DM, setting a novel scenario that puts BM and the blood at the centre of the stage.