The Vasoreparative Function of Myeloid Angiogenic Cells Is Impaired in Diabetes Through the Induction of IL1β

The Use of Autologous Cell Therapy in Diabetic Patients with Chronic Limb-Threatening Ischemia

Autologous cell therapy (ACT) is primarily used in diabetic patients with chronic limb-threatening ischemia (CLTI) who are not candidates for standard revascularization. According to current research, this therapy has been shown in some studies to be effective in improving ischemia parameters, decreasing the major amputation rate, and in foot ulcer healing. This review critically evaluates the efficacy of ACT in patients with no-option CLTI, discusses the use of mononuclear and mesenchymal stem cells, and compares the route of delivery of ACT. In addition to ACT, we also describe the use of new revascularization strategies, e.g., nanodiscs, microbeads, and epigenetics, that could enhance the therapeutic effect. The main aim is to summarize new findings on subcellular and molecular levels with the clinical aspects of ACT.

A Review Into the Insights of the Role of Endothelial Progenitor Cells on Bone Biology

In addition to its important transport functions, the skeletal system is involved in complex biological activities for the regulation of blood vessels. Endothelial progenitor cells (EPCs), as stem cells of endothelial cells (ECs), possess an effective proliferative capacity and a powerful angiogenic capacity prior to their differentiation. They demonstrate synergistic effects to promote bone regeneration and vascularization more effectively by co-culturing with multiple cells. EPCs demonstrate a significant therapeutic potential for the treatment of various bone diseases by secreting a combination of growth factors, regulating cellular functions, and promoting bone regeneration. In this review, we retrospect the definition and properties of EPCs, their interaction with mesenchymal stem cells, ECs, smooth muscle cells, and immune cells in bone regeneration, vascularization, and immunity, summarizing their mechanism of action and contribution to bone biology. Additionally, we generalized their role and potential mechanisms in the treatment of various bone diseases, possibly indicating their clinical application.

Exploring Endothelial Colony-Forming Cells to Better Understand the Pathophysiology of Disease: An Updated Review

Endothelial cell (EC) dysfunction has been implicated in a variety of pathological conditions. The collection of ECs from patients is typically conducted postmortem or through invasive procedures, such as surgery and interventional procedures, hampering efforts to clarify the role of ECs in disease onset and progression. In contrast, endothelial colony-forming cells (ECFCs), also termed late endothelial progenitor cells, late outgrowth endothelial cells, blood outgrowth endothelial cells, or endothelial outgrowth cells, are obtained in a minimally invasive manner, namely, by the culture of human peripheral blood mononuclear cells in endothelial growth medium. ECFCs resemble mature ECs phenotypically, genetically, and functionally, making them excellent surrogates for ECs. Numerous studies have been performed that examined ECFC function in conditions such as coronary artery disease, diabetes mellitus, hereditary hemorrhagic telangiectasia, congenital bicuspid aortic valve disease, pulmonary arterial hypertension, venous thromboembolic disease, and von Willebrand disease. Here, we provide an updated review of studies using ECFCs that were performed to better understand the pathophysiology of disease. We also discuss the potential of ECFCs as disease biomarkers and the standardized methods to culture, quantify, and evaluate ECFCs and suggest the future direction of research in this field.

Lipids, hyperreflective crystalline deposits and diabetic retinopathy: potential systemic and retinal-specific effect of lipid-lowering therapies

The metabolically active retina obtains essential lipids by endogenous biosynthesis and from the systemic circulation. Clinical studies provide limited and sometimes conflicting evidence as to the relationships between circulating lipid levels and the development and progression of diabetic retinopathy in people with diabetes. Cardiovascular-system-focused clinical trials that also evaluated some retinal outcomes demonstrate the potential protective power of lipid-lowering therapies in diabetic retinopathy and some trials with ocular primary endpoints are in progress. Although triacylglycerol-lowering therapies with fibrates afforded some protection against diabetic retinopathy, the effect was independent of changes in traditional blood lipid classes. While systemic LDL-cholesterol lowering with statins did not afford protection against diabetic retinopathy in most clinical trials, and none of the trials focused on retinopathy as the main outcome, data from very large database studies suggest the possible effectiveness of statins. Potential challenges in these studies are discussed, including lipid-independent effects of fibrates and statins, modified lipoproteins and retinal-specific effects of lipid-lowering drugs. Dysregulation of retinal-specific cholesterol metabolism leading to retinal cholesterol accumulation and potential formation of cholesterol crystals are also addressed.

Multiple roles of cardiac macrophages in heart homeostasis and failure

Macrophages are essential components of the immune system and play a role in the normal functioning of the cardiovascular system. Depending on their origin and phenotype, cardiac macrophages perform various functions. In a steady-state, these cells play a beneficial role in maintaining cardiac homeostasis by defending the body from pathogens and eliminating apoptotic cells, participating in electrical conduction, vessel patrolling, and arterial tone regulation. However, macrophages also take part in adverse cardiac remodeling that could lead to the development and progression of heart failure (HF) in such HF comorbidities as hypertension, obesity, diabetes, and myocardial infarction. Nevertheless, studies on detailed mechanisms of cardiac macrophage function are still in progress, and could enable potential therapeutic applications of these cells. This review aims to present the latest reports on the origin, heterogeneity, and functions of cardiac macrophages in the healthy heart and in cardiovascular diseases leading to HF. The potential therapeutic use of macrophages is also briefly discussed.

Heme Oxygenase-1 in Macrophages Impairs the Perfusion Recovery After Hindlimb Ischemia by Suppressing Autolysosome-Dependent Degradation of NLRP3

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Current understanding of the molecular and cellular pathology of diabetic retinopathy

Diabetes mellitus has profound effects on multiple organ systems; however, the loss of vision caused by diabetic retinopathy might be one of the most impactful in a patient's life. The retina is a highly metabolically active tissue that requires a complex interaction of cells, spanning light sensing photoreceptors to neurons that transfer the electrochemical signal to the brain with support by glia and vascular tissue. Neuronal function depends on a complex inter-dependency of retinal cells that includes the formation of a blood-retinal barrier. This dynamic system is negatively affected by diabetes mellitus, which alters normal cell-cell interactions and leads to profound vascular abnormalities, loss of the blood-retinal barrier and impaired neuronal function. Understanding the normal cell signalling interactions and how they are altered by diabetes mellitus has already led to novel therapies that have improved visual outcomes in many patients. Research highlighted in this Review has led to a new understanding of retinal pathophysiology during diabetes mellitus and has uncovered potential new therapeutic avenues to treat this debilitating disease.

Akkermansia muciniphila promotes type H vessel formation and bone fracture healing by reducing gut permeability and inflammation

Improving revascularization is one of the major measures in fracture treatment. Moderate local inflammation triggers angiogenesis, whereas systemic inflammation hampers angiogenesis. Previous studies showed that Akkermansia muciniphila, a gut probiotic, ameliorates systemic inflammation by tightening the intestinal barrier. In this study, fractured mice intragastrically administrated with A. muciniphila were found to display better fracture healing than mice treated with vehicle. Notably, more preosteclasts positive for platelet-derived growth factor-BB (PDGF-BB) were induced by A. muciniphila at 2 weeks post fracture, coinciding with increased formation of type H vessels, a specific vessel subtype that couples angiogenesis and osteogenesis, and can be stimulated by PDGF-BB. Moreover, A. muciniphila treatment significantly reduced gut permeability and inflammation at the early stage. Dextran sulfate sodium (DSS) was used to disrupt the gut barrier to determine its role in fracture healing and whether A. muciniphila still can stimulate bone fracture healing. As expected, A. muciniphila evidently improved gut barrier, reduced inflammation and restored the impaired bone healing and angiogenesis in DSS-treated mice. Our results suggest that A. muciniphila reduces intestinal permeability and alleviates inflammation, which probably induces more PDGF-BB+ preosteoclasts and type H vessel formation in callus, thereby promoting fracture healing. This study provides the evidence for the involvement of type H vessels in fracture healing and suggests the potential of A. muciniphila as a promising strategy for bone healing.This article has an associated First Person interview with the first author of the paper.

Skin well-being in diabetes: Role of macrophages

Macrophages are key players in wound healing- along with mediating the acute inflammatory response, macrophages activate cutaneous epithelial cells and promote tissue repair. Diabetes complications, including diabetic chronic wounds, are accompanied by persistent inflammation and macrophage malfunction. Several studies indicate that hyperglycemia induces various alterations that affect macrophage function in wound healing including epigenetic changes, imbalance between pro- and anti-inflammatory modulators, and insensitivity to proliferative stimuli. In this review, we briefly summarize recent studies regarding those alterations and their implications on skin well-being in diabetes.

Vascular Regeneration for Ischemic Retinopathies: Hope from Cell Therapies

Retinal vascular diseases, such as diabetic retinopathy, retinopathy of prematurity, retinal vein occlusion, ocular ischemic syndrome and ischemic optic neuropathy, are leading causes of vision impairment and blindness. Whilst drug, laser or surgery-based treatments for the late stage complications of many of these diseases are available, interventions that target the early vasodegenerative stages are lacking. Progressive vasculopathy and ensuing ischemia is an underpinning pathology in many of these diseases, leading to hypoperfusion, hypoxia, and ultimately pathological neovascularization and/or edema in the retina and other ocular tissues, such as the optic nerve and iris. Therefore, repairing the retinal vasculature may prevent progression of ischemic retinopathies into late stage vascular complications. Various cell types have been explored for their vascular repair potential. Endothelial progenitor cells, mesenchymal stem cells and induced pluripotent stem cells are studied for their potential to integrate with the damaged retinal vasculature and limit ischemic injury. Clinical trials for some of these cell types have confirmed safety and feasibility in the treatment of ischemic diseases, including some retinopathies. Another promising avenue is mobilization of endogenous endothelial progenitors, whereby reparative cells are moved from their niche to circulating blood to target and home into ischemic tissues. Several aspects and properties of these cell types have yet to be elucidated. Nevertheless, we foresee that cell therapy, whether through delivery of exogenous or enhancement of endogenous reparative cells, will become a valuable and beneficial treatment for ischemic retinopathies.

Endothelial cells and organ function: applications and implications of understanding unique and reciprocal remodelling

The microvasculature is a heterogeneous, dynamic and versatile component of the systemic circulation, with a unique ability to locally self-regulate and to respond to organ demand and environmental stimuli. Endothelial cells from different organs display considerable variation, but it is currently unclear to what extent functional properties of organ-specific endothelial cells are intrinsic, acquired and/or reprogrammable. Vascular function is a fundamental pillar of homeostasis, and dysfunction results in systemic consequences for the organism. Additionally, vascular failure can occur downstream of organ disease or environmental stress, often driving an exacerbation of symptoms and pathologies originally independent of the local circulation. The understanding of the molecular mechanisms underlying endothelial physiology and metabolism holds the promise to inform and improve diagnosis, prognosis and treatment options for a myriad of conditions as unrelated as cancer, neurodegeneration or pulmonary hypertension, and likely everything in between, if we consider that also treatments for such conditions are primarily distributed via the bloodstream. However, studying endothelial function has its challenges: the origin, isolation, culture conditions and preconditioning stimuli make this an extremely variable cell type to study and difficult to source. Animal models exist but are neither trivial to generate, nor necessarily adequately translatable to human disease. In this article, we aim to illustrate the breadth of microvascular functions in different environments, highlighting current and pioneering studies that have advanced our insight into the importance of the integrity of this tissue, as well as the limitations posed by its heterogeneity and plasticity.

Bone Marrow-Derived Cells Restore Functional Integrity of the Gut Epithelial and Vascular Barriers in a Model of Diabetes and ACE2 Deficiency

RATIONALE

There is incomplete knowledge of the impact of bone marrow cells on the gut microbiome and gut barrier function.

OBJECTIVE

We postulated that diabetes mellitus and systemic ACE2 (angiotensin-converting enzyme 2) deficiency would synergize to adversely impact both the microbiome and gut barrier function.

METHODS AND RESULTS

Bacterial 16S rRNA sequencing and metatranscriptomic analysis were performed on fecal samples from wild-type, ACE2^-/y, Akita (type 1 diabetes mellitus), and ACE2^-/y-Akita mice. Gut barrier integrity was assessed by immunofluorescence, and bone marrow cell extravasation into the small intestine was evaluated by flow cytometry. In the ACE2^-/y-Akita or Akita mice, the disrupted barrier was associated with reduced levels of myeloid angiogenic cells, but no increase in inflammatory monocytes was observed within the gut parenchyma. Genomic and metatranscriptomic analysis of the microbiome of ACE2^-/y-Akita mice demonstrated a marked increase in peptidoglycan-producing bacteria. When compared with control cohorts treated with saline, intraperitoneal administration of myeloid angiogenic cells significantly decreased the microbiome gene expression associated with peptidoglycan biosynthesis and restored epithelial and endothelial gut barrier integrity. Also indicative of diabetic gut barrier dysfunction, increased levels of peptidoglycan and FABP-2 (intestinal fatty acid-binding protein 2) were observed in plasma of human subjects with type 1 diabetes mellitus (n=21) and type 2 diabetes mellitus (n=23) compared with nondiabetic controls (n=23). Using human retinal endothelial cells, we determined that peptidoglycan activates a noncanonical TLR-2 (Toll-like receptor 2) associated MyD88 (myeloid differentiation primary response protein 88)-ARNO (ADP-ribosylation factor nucleotide-binding site opener)-ARF6 (ADP-ribosylation factor 6) signaling cascade, resulting in destabilization of p120-catenin and internalization of VE-cadherin as a mechanism of deleterious impact of peptidoglycan on the endothelium.

CONCLUSIONS

We demonstrate for the first time that the defect in gut barrier function and dysbiosis in ACE2^-/y-Akita mice can be favorably impacted by exogenous administration of myeloid angiogenic cells.

Dysfunction and Therapeutic Potential of Endothelial Progenitor Cells in Diabetes Mellitus

Diabetes mellitus (DM) is a chronic, multifactorial metabolic disease whereby insulin deficiency or resistance results in hyperglycemia. Endothelial cells (ECs) form the innermost layer of the blood vessel and produce and release a variety of vasoactive substances and growth factors to regulate vascular homeostasis and angiogenesis. Hyperglycemia and insulin resistance can cause endothelial dysfunction, leading to vascular complications such as coronary artery disease, peripheral arterial disease, diabetic nephropathy, neuropathy and retinopathy. The detrimental effect exerted on ECs by hyperglycemia and insulin resistance underlines the importance of reparatory mechanisms in DM. Endothelial progenitor cells (EPCs), derived from bone marrow, have been recognized as endogenous cells involved in endothelial repair and new blood vessel formation. Initially isolated from a subset of circulating CD34+ mononuclear cells, EPCs were found to possess the ability to differentiate into ECs when cultured in vitro and incorporate into newly formed vessels upon transplantation in animal models of ischemia. Due to the low frequency of CD34+ cells in circulation, the vast majority of studies investigating EPC actions have used cells that are generated through the culture of peripheral blood mononuclear cells (PBMNCs) for 4 - 7 days in endothelial selective medium. These cells, mainly of myeloid hematopoietic cell origin, were termed “Early EPCs,” of which, few expressed stem/progenitor-cell markers. Therefore, early EPCs were also termed “myeloid angiogenic cells” (MACs). When PBMNCs are cultured for over 2 weeks, early EPCs gradually diminish while so-called late EPCs appear. Late EPCs share phenotypic features with mature ECs and are therefore also termed blood-derived ECs; they will not be addressed in this review. MAC dysfunction has been observed in a variety of disease conditions including DM. In this article we review the activities and therapeutic potential of MACs in DM. We will interchangeably use “EPCs” and “MACs” to refer to the cells procured by culture of PBMNCs in EC selective medium for approximately 7 days.