Homing to hypoxia: HIF-1 as a mediator of progenitor cell recruitment to injured tissue

Circulating Progenitor Cells and Coronary Collaterals in Chronic Total Occlusion

BACKGROUND

The role of circulating progenitor cells (CPC) in collateral formation that occurs in the presence of chronic total occlusions (CTO) of a coronary artery is not well established. In stable patients with a CTO, we investigated whether CPC levels are associated with (a) collateral development and (b) ischemic burden, as measured by circulating high sensitivity troponin-I (hsTn-I) levels.

METHODS

CPCs were enumerated by flow cytometry as CD45med+ blood mononuclear cells expressing CD34 and both CD34 and CD133 epitopes. The association between CPC counts and both Rentrop collateral grade (0, 1, 2, or 3) and hsTn-I levels were evaluated using multivariate regression analysis, after adjusting for demographic and clinical characteristics.

RESULTS

In 89 patients (age 65.5, 72% male, 27% Black), a higher CPC count was positively associated with a higher Rentrop collateral grade; [CD34+ adjusted odds ratio (OR) 1.49 95% confidence interval (CI) (0.95, 2.34) P = 0.082] and [CD34+/CD133+ OR 1.57 95% CI (1.05, 2.36) P = 0.028]. Every doubling of CPC counts was also associated with lower hsTn-I levels [CD34+ β -0.35 95% CI (-0.49, -0.15) P = 0.002] and [CD34+/CD133+ β -0.27 95% CI (-0.43, -0.08) P = 0.009] after adjustment.

CONCLUSION

Individuals with higher CPC counts have greater collateral development and lower ischemic burden in the presence of a CTO.

Advanced Immunomodulatory Biomaterials for Therapeutic Applications

The multifaceted biological defense system modulating complex immune responses against pathogens and foreign materials plays a critical role in tissue homeostasis and disease progression. Recently developed biomaterials that can specifically regulate immune responses, nanoparticles, graphene, and functional hydrogels have contributed to the advancement of tissue engineering as well as disease treatment. The interaction between innate and adaptive immunity, collectively determining immune responses, can be regulated by mechanobiological recognition and adaptation of immune cells to the extracellular microenvironment. Therefore, applying immunomodulation to tissue regeneration and cancer therapy involves manipulating the properties of biomaterials by tailoring their composition in the context of the immune system. This review provides a comprehensive overview of how the physicochemical attributes of biomaterials determine immune responses, focusing on the physical properties that influence innate and adaptive immunity. This review also underscores the critical aspect of biomaterial-based immune engineering for the development of novel therapeutics and emphasizes the importance of understanding the biomaterials-mediated immunological mechanisms and their role in modulating the immune system.

Gene therapy for heart failure: A novel treatment for the age old disease

Across the globe, cardiovascular disease (CVD) is the leading cause of mortality. According to reports, around 6.2 million people in the United states have heart failure. Current standards of care for heart failure can delay but not prevent progression of disease. Gene therapy is one of the novel treatment modalities that promises to fill this limitation in the current standard of care for Heart Failure. In this paper we performed an extensive search of the literature on various advances made in gene therapy for heart failure till date. We review the delivery methods, targets, current applications, trials, limitations and feasibility of gene therapy for heart failure. Various methods have been employed till date for administering gene therapies including but not limited to arterial and venous infusion, direct myocardial injection and pericardial injection. Various strategies such as AC6 expression, S100A1 protein upregulation, VEGF-B and SDF-1 gene therapy have shown promise in recent preclinical trials. Furthermore, few studies even show that stimulation of cardiomyocyte proliferation such as through cyclin A2 overexpression is a realistic avenue. However, a considerable number of obstacles need to be overcome for gene therapy to be part of standard treatment of care such as definitive choice of gene, gene delivery systems and a suitable method for preclinical trials and clinical trials on patients. Considering the challenges and taking into account the recent advances in gene therapy research, there are encouraging signs to indicate gene therapy for heart failure to be a promising treatment modality for the future. However, the time and feasibility of this option remains in a situation of balance.

Advances in Chronic Wound Management: From Conventional Treatment to Novel Therapies and Biological Dressings

Chronic wounds can be classified as diabetic foot ulcers, pressure ulcers, or venous leg ulcers. Chronic wound management has become a threat to clinicians and constitutes a major healthcare burden. The healing process of chronic wounds requires many factors to work in concert to achieve optimal healing. Various treatment options, ranging from hypoxia to infection, have evolved considerably to address the challenges associated with chronic wound healing. The conventional and accelerating treatments for chronic wounds still represent an unmet medical need due to the complex pathophysiology of the chronic wound microenvironment. In clinical settings, traditional chronic wound care practices rely on nonspecific topical treatment, which can reduce pain and alleviate disease progression with varying levels of success but fail to completely cure the wounds. Conventional wound dressings, such as hydrocolloids, gauze, foams, and films, have also shown limited success for the treatment of chronic wounds and only act as a physical barrier and absorb wound exudates. Emerging advances in treatment approaches, including novel therapies (stem cells, microRNAs, and nanocarrier-based delivery systems) and multifunctional biological dressings, have been reported for chronic wound repair. This review summarizes the challenges offered by chronic wounds and discusses recent advancements in chronic wound treatment.

Prognostic Value of Endothelial Progenitor Cells in Acute Myocardial Infarction Patients

Objective

To determine prognostic role of endothelial progenitor cells (EPCs) in intensive care patients with acute myocardial infarction (AMI).

Materials and Methods

From December 2018 to July 2021, a total of 91 eligible patients with AMI were consecutively examined in a single intensive care unit (ICU) in China. Patients with a history of acute coronary artery disease were excluded from the study. Samples were collected within 24 hr of onset of symptoms. EPCs, defined as coexpression of CD34+/CD133+ cells or CD133+/CD34+/KDR+, were studied using flow cytometry and categorized by quartiles. Based on the 28-days mortality outcome, the patients were further divided into two groups: death and survival. The study incorporated various variables, including cardiovascular risk factors such as body mass index, hypertension, diabetes, hypercholesterolemia, atherosclerotic burden, and medication history, as well as clinical characteristics such as APACHEⅡscore, central venous-arterial carbon dioxide difference (GAP), homocysteine, creatinine, C-reactive protein, HbAlc, and cardiac index. Cox regression analysis was employed to conduct a multivariate analysis.

Results

A total of 91 patients with AMI who were admitted to the ICU were deemed eligible for inclusion in the study. Among these patients, 23 (25.3%) died from various causes during the follow-up period. The counts of EPCs were found to be significantly higher in the survival group compared to the death group (P < 0.05). In the univariate analysis, it was observed that the 28-days mortality rate was associated with the several factors, including the APACHEⅡscore (P=0.00), vasoactive inotropic score (P=0.03), GAP (P=0.00), HCY (P=0.00), creatinine (P=0.00), C-reactive protein (P=0.00), HbAlc (P=0.00), CI (P=0.01), quartiles of CD34+/CD133+ cells (P=0.00), and quartiles of CD34+/CD133+/KDR+ cells (P=0.00). CD34+/CD133+/KDR+ cells retained statistical significance in Cox regression models even after controlling for clinical variables (HR: 6.258 × 10-10 and P=0.001). Nevertheless, no significant correlation was observed between CD34+/CD133+ cells and all-cause mortality.

Conclusions

The decreased EPCs levels, especially for CD34+/CD133+/KDR+ cells subsets, were an independent risk factor for 28-days mortality in AMI patients.

Local and systemic inflammation triggers different outcomes of tumor growth related to infiltration of anti-tumor or pro-tumor macrophages

BACKGROUND

Previous evidence suggests inflammation may be a double-edged sword with cancer-promoting and cancer suppressing function. In this study, we explore the impact of local and systemic inflammation on cancer growth.

METHODS

Female BALB/C mice were subcutaneously implanted with foreign body (plastic plates) to build up a local inflammation and intraperitoneally injected with PolyIC or lipopolysaccharides (LPS) to build up a systemic inflammation, followed by subcutaneous injection of 5  × 10 5 colon cancer cells. Immunohistochemistry and enzyme linked immunosorbent assay were utilized to detect the Ki67 and interleukin (IL) 6, IL-1β, and monocyte chemoattractant protein-1 expression in the tumor tissues and serum, respectively. The distributions of immune cells and expression of toll-like receptors (TLRs) were evaluated by flow cytometry (FCM) and quantitative real time-polymerase chain reaction.

RESULTS

The results showed that local inflammation induced by foreign body implantation suppressed tumor growth with decreased tumor weight ( P   =  0.001), volume ( P   =  0.004) and Ki67 index ( P   <  0.001). Compared with the control group, myeloid-derived suppressive cells sharply decreased ( P   =  0.040), while CD4 + T cells slightly increased in the tumor tissues of the group of foreign body-induced local inflammation ( P   =  0.035). Moreover, the number of M1 macrophages ( P   =  0.040) and expression of TLRs, especially TLR3 ( P  < 0.001) and TLR4 ( P  < 0.001), were significantly up-regulated in the foreign body group. Contrarily, tumor growth was significantly promoted in LPS or PolyIC-induced systemic inflammation ( P   =  0.009 and 0.006). FCM results showed M1 type macrophages ( P   =  0.017 and 0.006) and CD8 + T cells ( P   =  0.031 and 0.023) were decreased, while M2 type macrophages ( P  = 0.002 and 0.007) were significantly increased in tumor microenvironment of LPS or PolyIC-induced systemic inflammation group. In addition, the decreased expression of TLRs was detected in LPS or PolyIC group.

CONCLUSIONS

The foreign body-induced local inflammation inhibited tumor growth, while LPS or PolyIC- induced systemic inflammation promoted tumor growth. The results suggested that the different outcomes of tumor growth might be attributed to the infiltration of anti-tumor or pro-tumor immune cells, especially M1 or M2 type macrophages into tumor microenvironment.

Copper-Lithium-Doped Nanohydroxyapatite Modulates Mesenchymal Stem Cells Homing to Treat Glucocorticoids-Related Osteonecrosis of the Femoral Head

In situ tissue regeneration has been demonstrated to promote bone repair. To identify a better approach for treating osteonecrosis of the femoral head (ONFH), we prepared scaffolds using copper-lithium-doped nanohydroxyapatite (Cu-Li-nHA), which has the potential to modulate mesenchymal stem cells (MSCs) homing. The scaffold was fabricated using the gas foaming method and the migration, angiogenesis, and osteogenesis activities of MSCs were detected using Transwell assays, tube formation assays, alkaline phosphatase and alizarin red S staining, respectively. We then implanted the Cu-Li-nHA scaffold into the femoral heads of ONFH rabbits, and CFSE labeled exogenous MSCs were injected intravenously to verify cell homing. The repair effect was subsequently examined using micro-CT and histological analysis in vivo. The results showed that Cu-Li-nHA significantly promoted MSCs migration and homing by upregulating the HIF-1α/SDF-1 pathway. The Cu-Li-nHA group showed optimal osteogenesis and angiogenesis and greater improvements in new bone formation in ONFH rabbits. To summarize, Cu-Li-nHA promoted homing and induced the osteogenic differentiation of MSCs, thereby enhancing bone regeneration during ONFH repair. Thus, Cu-Li-nHA implantation may serve as a potential therapeutic strategy for ONFH in the future.

Conductive nanocomposite hydrogel and mesenchymal stem cells for the treatment of myocardial infarction and non-invasive monitoring via PET/CT

Background

Injectable hydrogels have great promise in the treatment of myocardial infarction (MI); however, the lack of electromechanical coupling of the hydrogel to the host myocardial tissue and the inability to monitor the implantation may compromise a successful treatment. The introduction of conductive biomaterials and mesenchymal stem cells (MSCs) may solve the problem of electromechanical coupling and they have been used to treat MI. In this study, we developed an injectable conductive nanocomposite hydrogel (GNR@SN/Gel) fabricated by gold nanorods (GNRs), synthetic silicate nanoplatelets (SNs), and poly(lactide-co-glycolide)-b-poly (ethylene glycol)-b-poly(lactide-co-glycolide) (PLGA-PEG-PLGA). The hydrogel was used to encapsulate MSCs and ⁶⁸Ga³⁺ cations, and was then injected into the myocardium of MI rats to monitor the initial hydrogel placement and to study the therapeutic effect via ¹⁸F-FDG myocardial PET imaging.

Results

Our data showed that SNs can act as a sterically stabilized protective shield for GNRs, and that mixing SNs with GNRs yields uniformly dispersed and stabilized GNR dispersions (GNR@SN) that meet the requirements of conductive nanofillers. We successfully constructed a thermosensitive conductive nanocomposite hydrogel by crosslinking GNR@SN with PLGA₂₀₀₀-PEG₃₄₀₀-PLGA₂₀₀₀, where SNs support the proliferation of MSCs. The cation-exchange capability of SNs was used to adsorb ⁶⁸Ga³⁺ to locate the implanted hydrogel in myocardium via PET/CT. The combination of MSCs and the conductive hydrogel had a protective effect on both myocardial viability and cardiac function in MI rats compared with controls, as revealed by ¹⁸F-FDG myocardial PET imaging in early and late stages and ultrasound; this was further validated by histopathological investigations.

Conclusions

The combination of MSCs and the GNR@SN/Gel conductive nanocomposite hydrogel offers a promising strategy for MI treatment.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01432-7.

Influence of Irradiation on Capsules of Silicone Implants Covered with Acellular Dermal Matrix in Mice

BACKGROUND

In advanced breast cancer, radiotherapy is recommended as adjuvant therapy following breast reconstructive surgery. This inevitably led to growing concerns over possible complications of radiotherapy on implants. In this experimental animal study, we investigated the utility of acellular dermal matrix (ADM) wraps around implants as preventive management for radiotherapy complications.

METHODS

Black mice (C57NL6; n = 32) were assigned to groups that either received radiation or did not: groups A and B underwent surgery using implants without radiotherapy; while groups C and D underwent surgery using implants with radiotherapy for one and three months, respectively. The hemispheric silicone implants with an 0.8-cm-diameter were inserted on the left back of each mouse, and implants wrapped by ADM were inserted on the right back. The Clinic 23EX LINAC model was used for irradiation at 10 Gy. The samples were evaluated by gross assessment, histological analysis, immunohistochemical analysis, and the Western blotting test.

RESULTS

The H&E staining analysis showed that membrane thickness is smallest in group A, followed by groups C, D, and B. In a Masson trichrome histological analysis, collagen fibers became less dense and more widespread over time in the groups that received an ADM. Immunohistochemistry findings were similarly constant. However, the expression of TGF-β1 was increased in the irradiated groups, whereas it was decreased in the non-irradiated groups as observed over time.

CONCLUSIONS

Radiotherapy was shown to increase risk factors for capsular contracture, including inflammatory response, pseudoepithelium, thinning of membrane, and TGF-β1 expression over time; however, the accompanying framework using an ADM as a barrier between implant and tissue was shown to be effective in alleviating these risks.

NO LEVEL ASSIGNED

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The significance of the SDF-1/CXCR4 signaling pathway in the normal development

Chemokines are chemoattractants that can regulate cell movement and adhesion. SDF-1 [stromal cell-derived factor-1 (SDF-1)] is a homeostatic CXC chemokine. SDF-1 and its receptors [CXC chemokine receptor 4 (CXCR4)] form a signaling pathway that plays critical roles in different pathological and physiological mechanisms, including embryogenesis, wound healing, angiogenesis, tumor growth, and proliferation. Therefore, the current review aimed to summarize the related studies that addressed the molecular signature of the SDF-1/CXCR4 pathway and to explain how this axis is involved in normal events.

Single Intraosseous Simvastatin Application Induces Endothelial Progenitor Cell Mobilization and Therapeutic Angiogenesis in a Diabetic Hindlimb Ischemia Rat Model

BACKGROUND

Endothelial progenitor cells have shown the ability to enhance neovascularization. In this study, the authors tested whether intraosseous delivery of simvastatin could mobilize endothelial progenitor cells and enhance recovery in a hindlimb ischemia model.

METHODS

There are eight groups of rats in this study: normal control; type 1 diabetes mellitus control group control without drug intervention; and type 1 diabetes mellitus rats that randomly received intraosseous simvastatin (0, 0.5, or 1 mg) or oral simvastatin administration (0, 20, or 400 mg). All type 1 diabetes mellitus rats had induced hindlimb ischemia. The number of endothelial progenitor cells in peripheral blood, and serum markers, were detected. The recovery of blood flow at 21 days after treatment was used as the main outcome.

RESULTS

The authors demonstrated that endothelial progenitor cell mobilization was increased in the simvastatin 0.5- and 1-mg groups compared with the type 1 diabetes mellitus control and simvastatin 0-mg groups at 1, 2, and 3 weeks. Serum vascular endothelial growth factor levels were significantly increased at 2 weeks in the simvastatin 0.5- and 1-mg groups, in addition to the increase of the blood flow and the gastrocnemius weight at 3 weeks. Similar increase can also been seen in simvastatin 400 mg orally but not in simvastatin 20 mg orally.

CONCLUSION

These findings demonstrate that a single intraosseous administration of simvastatin mobilized endothelial progenitor cells at a dose one-hundredth of the required daily oral dose in rats, and this potent mobilization of endothelial progenitor cells markedly improved diabetic limb ischemia by means of neovascularization.

Potential Mechanisms and Perspectives in Ischemic Stroke Treatment Using Stem Cell Therapies

Ischemic stroke (IS) remains one of the major causes of death and disability due to the limited ability of central nervous system cells to regenerate and differentiate. Although several advances have been made in stroke therapies in the last decades, there are only a few approaches available to improve IS outcome. In the acute phase of IS, mechanical thrombectomy and the administration of tissue plasminogen activator have been widely used, while aspirin or clopidogrel represents the main therapy used in the subacute or chronic phase. However, in most cases, stroke patients fail to achieve satisfactory functional recovery under the treatments mentioned above. Recently, cell therapy, especially stem cell therapy, has been considered as a novel and potential therapeutic strategy to improve stroke outcome through mechanisms, including cell differentiation, cell replacement, immunomodulation, neural circuit reconstruction, and protective factor release. Different stem cell types, such as mesenchymal stem cells, marrow mononuclear cells, and neural stem cells, have also been considered for stroke therapy. In recent years, many clinical and preclinical studies on cell therapy have been carried out, and numerous results have shown that cell therapy has bright prospects in the treatment of stroke. However, some cell therapy issues are not yet fully understood, such as its optimal parameters including cell type choice, cell doses, and injection routes; therefore, a closer relationship between basic and clinical research is needed. In this review, the role of cell therapy in stroke treatment and its mechanisms was summarized, as well as the function of different stem cell types in stroke treatment and the clinical trials using stem cell therapy to cure stroke, to reveal future insights on stroke-related cell therapy, and to guide further studies.

Association Between Change in Circulating Progenitor Cells During Exercise Stress and Risk of Adverse Cardiovascular Events in Patients With Coronary Artery Disease

Importance

Stem and progenitor cells mobilize from the bone marrow in response to myocardial ischemia. However, the association between the change in circulating progenitor cell (CPC) counts and disease prognosis among patients with ischemia is unknown.

Objective

To investigate the association between the change in CPC counts during stress testing and the risk of adverse cardiovascular events in patients with stable coronary artery disease (CAD).

Design, Setting, and Participants

This prospective cohort study included a population-based sample of 454 patients with stable CAD who were recruited between June 1, 2011, and August 15, 2014, at Emory University-affiliated hospitals and followed up for 3 years. Data were analyzed from September 15, 2018, to October 15, 2018.

Exposures

Myocardial perfusion imaging with technetium Tc 99m sestamibi at rest and 30 to 60 minutes after conventional stress testing.

Main Outcomes and Measures

Circulating progenitor cells were enumerated with flow cytometry as CD34-expressing mononuclear cells (CD45med/CD34+), with additional quantification of subsets coexpressing the chemokine (C-X-C motif) receptor 4 (CD34+/CXCR4+). Changes in CPC counts were calculated as poststress minus resting CPC counts. Cox proportional hazards regression models were used to identify factors associated with the combined end point of cardiovascular death and myocardial infarction after adjusting for clinical covariates, including age, sex, race, smoking history, body mass index, and history of heart failure, hypertension, dyslipidemia, and diabetes.

Results

Of the 454 patients (mean [SD] age, 63 [9] years; 76% men) with stable CAD enrolled in the study, 142 (31.3%) had stress-induced ischemia and 312 (68.7%) did not, as measured by single-photon emission computed tomography. During stress testing, patients with stress-induced ischemia had a mean decrease of 20.2% (interquartile range [IQR], -45.3 to 5.5; P < .001) in their CD34+/CXCR4+ counts, and patients without stress-induced ischemia had a mean increase of 3.2% (IQR, -20.6 to 35.1; P < .001) in their CD34+/CXCR4+ counts. Twenty-four patients (5.2%) experienced adverse events. After adjustment, baseline CPC counts were associated with worse adverse outcomes, but this association was not present after stress-induced ischemia was included in the model. However, the change in CPC counts during exercise remained significantly associated with adverse events (hazard ratio, 2.59; 95% CI, 1.15-5.32, per 50% CD34+/CXCR4+ count decrease), even after adjustment for clinical variables and the presence of ischemia. The discrimination of risk factors associated with incident adverse events improved (increase in C statistic from 0.72 to 0.77; P = .003) with the addition of the change in CD34+/CXCR4+ counts to a model that included clinical characteristics, baseline CPC count, and ischemia.

Conclusions and Relevance

In this study of patients with CAD, a decrease in CPC counts during exercise is associated with a worse disease prognosis compared with the presence of stress-induced myocardial ischemia. Further studies are needed to evaluate whether strategies to improve CPC responses during exercise stress will be associated with improvements in the prognosis of patients with CAD.

Circulating stem cells and cardiovascular outcomes: from basic science to the clinic

The cardiovascular and haematopoietic systems have fundamental inter-relationships during development, as well as in health and disease of the adult organism. Although haematopoietic stem cells (HSCs) emerge from a specialized haemogenic endothelium in the embryo, persistence of haemangioblasts in adulthood is debated. Rather, the vast majority of circulating stem cells (CSCs) is composed of bone marrow-derived HSCs and the downstream haematopoietic stem/progenitors (HSPCs). A fraction of these cells, known as endothelial progenitor cells (EPCs), has endothelial specification and vascular tropism. In general, the levels of HSCs, HSPCs, and EPCs are considered indicative of the endogenous regenerative capacity of the organism as a whole and, particularly, of the cardiovascular system. In the last two decades, the research on CSCs has focused on their physiologic role in tissue/organ homoeostasis, their potential application in cell therapies, and their use as clinical biomarkers. In this review, we provide background information on the biology of CSCs and discuss in detail the clinical implications of changing CSC levels in patients with cardiovascular risk factors or established cardiovascular disease. Of particular interest is the mounting evidence available in the literature on the close relationships between reduced levels of CSCs and adverse cardiovascular outcomes in different cohorts of patients. We also discuss potential mechanisms that explain this association. Beyond CSCs' ability to participate in cardiovascular repair, levels of CSCs need to be interpreted in the context of the broader connections between haematopoiesis and cardiovascular function, including the role of clonal haematopoiesis and inflammatory myelopoiesis.

HIF/Ca2+/NO/ROS is critical in roxadustat treating bone fracture by stimulating the proliferation and migration of BMSCs

AIMS

Fracture site is regionally hypoxic resulting from vasculature disruption. HIF-1αplays an essential role in fracture repair. This study aims to investigate the influence of FG4592 on the femur fracture of SD rats and the proliferation, migration of BMSCs.

MATERIALS AND METHODS

After the femoral fracture model was established, computed tomography imaging and histological analyses were used to quantify bone healing and the expression of CD90, HIF-1α, VEGF were observed by means of immunohistochemistry method on Day 10 and Day 20. In addition, CCK-8 assay, transwell, flow cytometric analysis, laser confocal microscopy assay, western blot and rT-PCR were performed to text the proliferation and migration of BMSCs using FG4592.

KEY FINDINGS

In vivo, FG4592 facilitated the repair of bone fracture by increasing the number of BMSCs and cartilage formation. In vitro, FG4592 markedly improved the proliferation, migration of BMSCs via upregulation of intracellular Ca²⁺, NO and concomitant decrease of ROS. Gene silencing of HIF-1α resulted in the opposite phenomenon in BMSCs with the treatment of FG4592.

SIGNIFICANCE

The transplantation of BMSCs is the most promising candidate for the treatment of fracture non-union. We illustrated that FG4592 promoted the proliferation, migration of BMSCs via the HIF/Ca²⁺/NO/ROS pathway and further accelerated fracture healing. These results provide a deeper understanding for the mechanism of HIF in promoting fracture healing.

Predicting in vivo therapeutic efficacy of bioorthogonally labeled endothelial progenitor cells in hind limb ischemia models via non-invasive fluorescence molecular tomography

Human embryonic stem cells-derived endothelial progenitor cells (hEPCs) were utilized as cell therapeutics for the treatment of ischemic diseases. However, in vivo tracking of hEPCs for predicting their therapeutic efficacy is very difficult. Herein, we developed bioorthogonal labeling strategy of hEPCs that could non-invasively track them after transplantation in hind limb ischemia models. First, hEPCs were treated with tetraacylated N-azidomannosamine (Ac₄ManNAz) for generating unnatural azide groups on the hEPCs surface. Second, near-infrared fluorescence (NIRF) dye, Cy5, conjugated dibenzocylooctyne (DBCO-Cy5) was chemically conjugated to the azide groups on the hEPC surface via copper-free click chemistry, resulting Cy5-hEPCs. The bioorthogonally labeled Cy5-hEPCs showed strong NIRF signal without cytotoxicity and functional perturbation in tubular formation, oxygen consumption and paracrine effect of hEPCs in vitro. In hind limb ischemia models, the distribution and migration of transplanted Cy5-hEPCs were successfully monitored via fluorescence molecular tomography (FMT) for 28 days. Notably, blood reperfusion and therapeutic neovascularization effects were significantly correlated with the initial transplantation forms of Cy5-hEPCs such as 'condensed round shape' and 'spread shape' in the ischemic lesion. The condensed transplanted Cy5-hEPCs substantially increased the therapeutic efficacy of hind limb ischemia, compared to that of spread Cy5-hEPCs. Therefore, our new stem cell labeling strategy can be used to predict therapeutic efficacy in hind limb ischemia and it can be applied a potential application in developing cell therapeutics for regenerative medicine.

IMMUNOMEDIATOR GENE TRANSCRIPTION PROFILING IN BELUGA WHALE (DELPHINAPTERUS LEUCAS) CLINICAL CASES

There is an unmet need for specific diagnostics of immune perturbations and inflammation in beluga whale (Delphinapterus leucas) clinical care. Quantitative real-time polymerase chain reaction (qPCR) has been used to measure immunomediator gene transcription in beluga whales. The study hypothesis was that a qPCR-based immunomediator assay would supplement routine clinical data with specific and sensitive information on immune status. Two beluga whale clinical cases provided an opportunity to test this hypothesis: a whale with a skin laceration and a whale with gastrointestinal inflammation. Mitogen-stimulated immunomediator gene transcription (MSIGT) was compared between the cases and healthy contact whales. In both case studies, mitogens increased transcription of IL1B, PTGS2 (Cox-2), TNF, HIF1A, and IL2 but decreased IL10 transcription in peripheral blood mononuclear cells (PBMC) from the abnormal whale over the control. Correlations were identified between most immunomediators tested and one or more standard blood clinical values. Considering all 15 immunomediators tested, the whale with gastrointestinal inflammation had a more unique MSIGT signature than the whale with a laceration. These results support further elucidation of beluga whale PBMC cytokine profiles for use as immune biomarkers.

Electrospun PCL Fiber Mats Incorporating Multi-Targeted B and Co Co-Doped Bioactive Glass Nanoparticles for Angiogenesis

Vascularization is necessary in tissue engineering to keep adequate blood supply in order to maintain the survival and growth of new tissue. The synergy of biologically active ions with multi-target activity may lead to superior angiogenesis promotion in comparison to single-target approaches but it has been rarely investigated. In this study, polycaprolactone (PCL) fiber mats embedded with B and Co co-doped bioactive glass nanoparticles (BCo.BGNs) were fabricated as a tissue regeneration scaffold designed for promoting angiogenesis. BCo.NBGs were successfully prepared with well-defined spherical shape using a sol-gel method. The PCL fiber mats embedding co-doped bioactive glass nanoparticles were fabricated by electrospinning using benign solvents. The Young’s moduli of the nanoparticle containing PCL fiber mats were similar to those of the neat fiber mats and suitable for scaffolds utilized in soft tissue repair approaches. The mats also showed non-cytotoxicity to ST-2 cells. PCL fiber mats containing BCo.BGNs with a relatively high content of B and Co promoted the secretion of vascular endothelial growth factor to a greater extent than PCL fiber mats with a relatively low B and Co contents, which demonstrates the potential of dual ion release (B and Co) from bioactive glasses to enhance angiogenesis in soft tissue engineering.

Characterization of Diabetic and Non-Diabetic Foot Ulcers Using Single-Cell RNA-Sequencing

Background: Recent advances in high-throughput single-cell sequencing technologies have led to their increasingly widespread adoption for clinical applications. However, challenges associated with tissue viability, cell yield, and delayed time-to-capture have created unique obstacles for data processing. Chronic wounds, in particular, represent some of the most difficult target specimens, due to the significant amount of fibrinous debris, extracellular matrix components, and non-viable cells inherent in tissue routinely obtained from debridement. Methods: Here, we examined the feasibility of single cell RNA sequencing (scRNA-seq) analysis to evaluate human chronic wound samples acquired in the clinic, subjected to prolonged cold ischemia time, and processed without FACS sorting. Wound tissue from human diabetic and non-diabetic plantar foot ulcers were evaluated using an optimized 10X Genomics scRNA-seq platform and analyzed using a modified data pipeline designed for low-yield specimens. Cell subtypes were identified informatically and their distributions and transcriptional programs were compared between diabetic and non-diabetic tissue. Results: 139,000 diabetic and non-diabetic wound cells were delivered for 10X capture after either 90 or 180 min of cold ischemia time. cDNA library concentrations were 858.7 and 364.7 pg/µL, respectively, prior to sequencing. Among all barcoded fragments, we found that 83.5% successfully aligned to the human transcriptome and 68% met the minimum cell viability threshold. The average mitochondrial mRNA fraction was 8.5% for diabetic cells and 6.6% for non-diabetic cells, correlating with differences in cold ischemia time. A total of 384 individual cells were of sufficient quality for subsequent analyses; from this cell pool, we identified transcriptionally-distinct cell clusters whose gene expression profiles corresponded to fibroblasts, keratinocytes, neutrophils, monocytes, and endothelial cells. Fibroblast subpopulations with differing fibrotic potentials were identified, and their distributions were found to be altered in diabetic vs. non-diabetic cells. Conclusions: scRNA-seq of clinical wound samples can be achieved using minor modifications to standard processing protocols and data analysis methods. This simple approach can capture widespread transcriptional differences between diabetic and non-diabetic tissue obtained from matched wound locations.

The Pathogenesis of Adenomyosis vis-à-vis Endometriosis

Adenomyosis is used to be called endometriosis interna, and deep endometriosis is now called adenomyosis externa. Thus, there is a question as to whether adenomyosis is simply endometriosis of the uterus, either from the perspective of pathogenesis or pathophysiology. In this manuscript, a comprehensive review was performed with a literature search using PubMed for all publications in English, related to adenomyosis and endometriosis, from inception to June 20, 2019. In addition, two prevailing theories, i.e., invagination—based on tissue injury and repair (TIAR) hypothesis—and metaplasia, on adenomyosis pathogenesis, are briefly overviewed and then critically scrutinized. Both theories have apparent limitations, i.e., difficulty in falsification, explaining existing data, and making useful predictions. Based on the current understanding of wound healing, a new hypothesis, called endometrial-myometrial interface disruption (EMID), is proposed to account for adenomyosis resulting from iatrogenic trauma to EMI. The EMID hypothesis not only highlights the more salient feature, i.e., hypoxia, at the wounding site, but also incorporates epithelial mesenchymal transition, recruitment of bone-marrow-derived stem cells, and enhanced survival and dissemination of endometrial cells dispersed and displaced due to iatrogenic procedures. More importantly, the EMID hypothesis predicts that the risk of adenomyosis can be reduced if certain perioperative interventions are performed. Consequently, from a pathogenic standpoint, adenomyosis is not simply endometriosis of the uterus, and, as such, may call for interventional procedures that are somewhat different from those for endometriosis to achieve the best results.

Acidosis induces antimicrobial peptide expression and resistance to uropathogenic E. coli infection in kidney collecting duct cells via HIF-1α

Acute pyelonephritis is frequently associated with metabolic acidosis. We previously reported that metabolic acidosis stimulates expression of hypoxia-inducible factor (HIF)-1α-induced target genes such as stromal derived factor-1 and cathelicidin, an antimicrobial peptide. Since the collecting duct (CD) plays a pivotal role in regulating acid-base homeostasis and is the first nephron segment encountered by an ascending microbial infection, we examined the contribution of HIF-1α to innate immune responses elicited by acid loading of an M-1 immortalized mouse CD cell line. Acid loading of confluent M-1 cells was achieved by culture in pH 6.8 medium supplemented with 5-(N-ethyl-N-isopropyl)-amiloride to block Na+/H+ exchange activity for 24 h. Acid loading induced antimicrobial peptide [cathelicidin and β-defensin (Defb2 and Defb26)] mRNA expression and M-1 cell resistance to uropathogenic Escherichia coli infection to an extent similar to that obtained by inhibition of HIF prolyl hydroxylases, which promote HIF-1α protein degradation. The effect of acid loading on M-1 cell resistance to uropathogenic E. coli infection was reduced by inhibition of HIF-1α (PX-478), and, in combination with prolyl hydroxylase inhibitors, acidosis did not confer additional resistance. Thus, metabolic stress of acidosis triggers HIF-1α-dependent innate immune responses in CD (M-1) cells. Whether pharmacological stabilization of HIF prevents or ameliorates pyelonephritis in vivo warrants further investigation.

Recent advances in the application of mesoporous silica-based nanomaterials for bone tissue engineering

Silica nanomaterials (SNMs) and their composites have recently been investigated as scaffolds for bone tissue engineering. SNM scaffolds possess the ability to encourage bone cell growth and also allow the simultaneous delivery of biologically active biomolecules that are encapsulated in the mesopores. Their high mechanical strength, low cytotoxicity, ability to stimulate both the proliferation and osteogenic differentiation of progenitor cells make the SNMs appropriate scaffolds. Their physiochemical properties facilitate the cell spreading process, allow easy access to nutrients and help the cell-cell communication process during bone tissue engineering. The ability to deliver small biomolecules, such as dexamethasone, different growth factors, vitamins and mineral ions depends on the morphology, porosity, and crystallinity of SNMs and their composites with other polymeric materials. In this review, the abilities of SNMs to perform as suitable scaffolds for bone tissue engineering are comprehensively discussed.

Stromal cell-derived factor-1/CXC chemokine receptor 4 axis in injury repair and renal transplantation

Stem cell therapy has shown promise in treating a variety of pathologies, such as myocardial infarction, ischaemic stroke and organ transplantation. The stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor-4 (CXCR4) axis plays a key role in stem cell mobilization. This review describes the important role of SDF-1 in tissue injury and how it works in tissue revascularization and regeneration via CXCR4. Furthermore, factors influencing the SDF-1/CXCR4 axis and its clinical potential in ischaemia reperfusion injury, such as renal transplantation, are discussed. Exploring signalling pathways of the SDF-1/CXCR4 axis will contribute to the development of stem cell therapy so that more clinical problems can be solved. Controlling directional homing of stem cells through the SDF-1/CXCR4 axis is key to improving the efficacy of stem cell therapy for tissue injury. CXCR4 antagonists may also be effective in increasing circulating levels of adult stem cells, thereby exerting beneficial effects on damaged or inflamed tissues in diseases that are currently not treated by standard approaches.

Age-Dependent Systemic Effects of a Systemic Intermittent Hypoxic Therapy In Vivo

Introduction: The adaptive response to systemic intermittent hypoxic therapy (SIHT) may be used for therapeutic advances due to the activation of multiple pathways involved in angiogenesis, immunomodulation, and tissue homeostasis. The aim of this study was to investigate the early age-dependent systemic response of different exposures of SIHT in mice. Materials and Methods: Sixty-four C57BL/6NRj female mice in three different age groups, young (4-5 weeks), adolescent (8-10 weeks), and adults (23-32 weeks), were exposed to SIHT. Different algorithms for equal hypoxic challenges (oxygen-decrease*time) were investigated to allow examination of the role of absolute hypoxia (oxygen-decrease) compared with relative hypoxia (total oxygen depletion over time). The systemic effects of angiogenetic regulation were investigated using blood samples analyzed by ELISA, proteome profiles, and proximity extension immunoassay. One-way analysis of variance with post hoc Bonferroni analyses was performed. Results: The early systemic response to SIHT was dependent on the absolute hypoxia rather than relative hypoxia over time. Serum erythropoietin (EPO) levels were increased significantly in young mice receiving low-oxygen SIHT treatments (10% and 15% oxygen). The expression of angiogenic proteins differed between the different age groups indicating an age-dependent response to SIHT. Focusing on hypoxia-inducible factor-1 (HIF-1) signaling, there was a trend toward upregulated angiogenetic response with younger age. Furthermore, clustering of protein expression in low-oxygen SIHT algorithms were found between young and adolescent mice. In adult mice, the majority of the proteins were downregulated as a response to SIHT. The systemic response of metabolites expressions was most pronounced in young mice. Systemic levels of cardiac troponin I (Tnni3) was unaffected by SIHT independent of age groups. Conclusions: The systemic response to SIHT is dependent on the absolute hypoxic exposure rather than the relative hypoxic depletion over time. Age-dependent effects of a short-term SIHT were associated with an increase in EPO, upregulation of angiogenetic pathways, and select metabolic and cell-surface proteins.

Dysregulation of proangiogeneic factors in pressure-overload left-ventricular hypertrophy results in inadequate capillary growth

Background:

Pressure-overload left-ventricular hypertrophy (LVH) is an increasingly prevalent pathological condition of the myocardial muscle and an independent risk factor for a variety of cardiac diseases. We investigated changes in expression levels of proangiogeneic genes in a small animal model of LVH.

Methods:

Myocardial hypertrophy was induced by transaortic constriction (TAC) in C57BL/6 mice and compared with sham-operated controls. The myocardial expression levels of vascular endothelial growth factor (VEGF), its receptors (KDR and FLT-1), stromal-cell-derived factor 1 (SDF1) and the transcription factors hypoxia-inducible factor-1 and 2 (HIF1 and HIF2) were analyzed by quantitative polymerase chain reaction over the course of 25 weeks. Histological sections were stained for caveolin-1 to visualize endothelial cells and determine the capillary density. The left-ventricular morphology and function were assessed weekly by electrocardiogram-gated magnetic resonance imaging.

Results:

The heart weight of TAC animals increased significantly from week 4 to 25 (p = 0.005) compared with sham-treated animals. At 1 day after TAC, the expression of VEGF and SDF1 also increased, but was downregulated again after 1 week. The expression of HIF2 was significantly downregulated after 1 week and remained at a lower level in the subsequent weeks. The expression level of FLT-1 was also significantly decreased 1 week after TAC. HIF-1 and KDR showed similar changes compared with sham-operated animals. However, the expression levels of HIF1 after 4 and 8 weeks were significantly decreased compared with day 1. KDR changes were significantly decreased after 1, 2, 4, 8 and 25 weeks compared with week 3. After 4 weeks post-TAC, the size of the capillary vessels increased (p = 0.005) while the capillary density itself decreased (TAC: 2143 ± 293 /mm²versus sham: 2531 ± 321 /mm²; p = 0.021). Starting from week 4, the left-ventricular ejection fraction decreased compared with controls (p = 0.049).

Conclusions:

The decrease in capillary density in the hypertrophic myocardium appears to be linked to the dysregulation in the expression of proangiogeneic factors. The results suggest that overcoming this dysregulation may lead to reconstitution of capillary density in the hypertrophic heart, and thus be beneficial for cardiac function and survival.

CYP4A/20-HETE regulates ischemia-induced neovascularization via its actions on endothelial progenitor and preexisting endothelial cells

20-Hydroxyeicosatetraenoic acid (20-HETE) was recently identified as a novel contributor of ischemia-induced neovascularization based on the key observation that pharmacological interferences of CYP4A/20-HETE decrease ischemic neovascularization. The objective of the present study is to examine whether the underlying cellular mechanisms involve endothelial progenitor cells (EPCs) and preexisting endothelial cells (ECs). We found that ischemia leads to a time-dependent increase of cyp4a12 expression and 20-HETE production, which are endothelial in origin, using immunofluorescent microscopy, Western blot analysis, and LC-MS/MS. This is accompanied by increases in the tissue stromal cell-derived factor-1α (SDF-1α) expressions as well as SDF-1α plasma levels, EPC mobilization from bone marrow, and subsequent homing to ischemic tissues. Pharmacological interferences of CYP4A/20-HETE with a 20-HETE synthesis inhibitor, dibromo-dodecenyl-methylsulfimide (DDMS), or a 20-HETE antagonist, N-(20-hydroxyeicosa-6(Z), 15(Z)-dienoyl) glycine (6, 15-20-HEDGE), significantly attenuated these increases. Importantly, we also determined that 20-HETE plays a novel role in maintaining EPC functions and increasing the expression of Oct4, Sox2, and Nanog, which are indicative of increased progenitor cell stemness. Flow cytometric analysis revealed that pharmacological interferences of CYP4A/20-HETE decrease the EPC population in culture, whereas 20-HETE increases the cultured EPC population. Furthermore, ischemia also markedly increased the proliferation, oxidative stress, and ICAM-1 expression in the preexisting EC in the hindlimb gracilis muscles. We found that these increases were markedly negated by DDMS and 6, 15-20-HEDGE. Taken together, CYP4A/20-HETE regulates ischemia-induced compensatory neovascularization via its combined actions on promoting EPC and local preexisting EC responses that are associated with increased neovascularization. NEW & NOTEWORTHY CYP4A/20-hydroxyeicosatetraenoic acid (20-HETE) was recently discovered as a novel contributor of ischemia-induced neovascularization. However, the underlying molecular and cellular mechanisms are completely unknown. Here, we show that CYP4A/20-HETE regulates the ischemic neovascularization process via its combined actions on both endothelial progenitor cells (EPCs) and preexisting endothelial cells. Moreover, this is the first study, to the best of our knowledge, that associates CYP4A/20-HETE with EPC differentiation and stemness.

Matrix-assisted cell transplantation for tissue vascularization

Cell therapy offers much promise for the treatment of ischemic diseases by augmenting tissue vasculogenesis. Matrix-assisted cell transplantation (MACT) has been proposed as a solution to enhance cell survival and integration with host tissue following transplantation. By designing semi synthetic matrices (sECM) with the correct physical and biochemical signals, encapsulated cells are directed towards a more angiogenic phenotype. In this review, we describe the choice of cells suitable for pro-angiogenic therapies, the properties that should be considered when designing sECM for transplantation and their relative importance. Pre-clinical models where MACT has been successfully applied to promote angiogenesis are reviewed to show the great potential of this strategy to treat ischemic conditions.

Biopolymer-delivered vascular endothelial growth factor improves renal outcomes following revascularization

Renal angioplasty and stenting (PTRAs) resolves renal artery stenosis, but inconsistently improves renal function, possibly due to persistent parenchymal damage. We developed a bioengineered fusion of a drug delivery vector (elastin-like polypeptide, ELP) with vascular endothelial growth factor (VEGF), and showed its therapeutic efficacy. We tested the hypothesis that combined ELP-VEGF therapy with PTRAs improves renal recovery more efficiently than PTRAs alone, by protecting the stenotic renal parenchyma. Unilateral renovascular disease (RVD) was induced by renal artery stenosis in 14 pigs. Six weeks later, stenotic kidney blood flow (RBF) and glomerular filtration rate (GFR) were quantified in vivo using multidetector CT. Blood and urine were collected during in vivo studies. All pigs underwent PTRAs and then were randomized into single intrarenal ELP-VEGF administration or placebo (n = 7 each) groups. Pigs were observed for four additional weeks, in vivo CT studies were repeated, and then pigs were euthanized for ex vivo studies to quantify renal microvascular (MV) density, angiogenic factor expression, and morphometric analysis. Renal hemodynamics were similarly blunted in all RVD pigs. PTRAs resolved stenosis but modestly improved RBF and GFR. However, combined PTRAs+ ELP-VEGF improved RBF, GFR, regional perfusion, plasma creatinine, asymmetric dimethlyarginine (ADMA), and albuminuria compared with PTRAs alone, accompanied by improved angiogenic signaling, MV density, and renal fibrosis. Greater improvement of renal function via coadjuvant ELP-VEGF therapy may be driven by enhanced MV proliferation and repair, which ameliorates MV rarefaction and fibrogenic activity that PTRAs alone cannot offset. Thus, our study supports a novel strategy to boost renal recovery in RVD after PTRAs.

Hypoxia and matrix viscoelasticity sequentially regulate endothelial progenitor cluster-based vasculogenesis

Vascular morphogenesis is the formation of endothelial lumenized networks. Cluster-based vasculogenesis of endothelial progenitor cells (EPCs) has been observed in animal models, but the underlying mechanism is unknown. Here, using O₂-controllabe hydrogels, we unveil the mechanism by which hypoxia, co-jointly with matrix viscoelasticity, induces EPC vasculogenesis. When EPCs are subjected to a 3D hypoxic gradient ranging from <2 to 5%, they rapidly produce reactive oxygen species that up-regulate proteases, most notably MMP-1, which degrade the surrounding extracellular matrix. EPC clusters form and expand as the matrix degrades. Cell-cell interactions, including those mediated by VE-cadherin, integrin-β2, and ICAM-1, stabilize the clusters. Subsequently, EPC sprouting into the stiffer, intact matrix leads to vascular network formation. In vivo examination further corroborated hypoxia-driven clustering of EPCs. Overall, this is the first description of how hypoxia mediates cluster-based vasculogenesis, advancing our understanding toward regulating vascular development as well as postnatal vasculogenesis in regeneration and tumorigenesis.

Small molecule inhibition of dipeptidyl peptidase-4 enhances bone marrow progenitor cell function and angiogenesis in diabetic wounds

In diabetes, stromal cell-derived factor-1 (SDF-1) expression and progenitor cell recruitment are reduced. Dipeptidyl peptidase-4 (DPP-4) inhibits SDF-1 expression and progenitor cell recruitment. Here we examined the impact of the DPP-4 inhibitor, MK0626, on progenitor cell kinetics in the context of wound healing. Wildtype (WT) murine fibroblasts cultured under high-glucose to reproduce a diabetic microenvironment were exposed to MK0626, glipizide, or no treatment, and SDF-1 expression was measured with ELISA. Diabetic mice received MK0626, glipizide, or no treatment for 6 weeks and then were wounded. Immunohistochemistry was used to quantify neovascularization and SDF-1 expression. Gene expression was measured at the RNA and protein level using quantitative polymerase chain reaction and ELISA, respectively. Flow cytometry was used to characterize bone marrow-derived mesenchymal progenitor cell (BM-MPC) population recruitment to wounds. BM-MPC gene expression was assayed using microfluidic single cell analysis. WT murine fibroblasts exposed to MK0626 demonstrated increased SDF-1 expression. MK0626 treatment significantly accelerated wound healing and increased wound vascularity, SDF-1 expression, and dermal thickness in diabetic wounds. MK0626 treatment increased the number of BM-MPCs present in bone marrow and in diabetic wounds. MK0626 had no effect on BM-MPC population dynamics. BM-MPCs harvested from MK0626-treated mice exhibited increased chemotaxis in response to SDF-1 when compared to diabetic controls. Treatment with a DPP-4 inhibitor significantly improved wound healing, angiogenesis, and endogenous progenitor cell recruitment in the setting of diabetes.

Fat Chance: The Rejuvenation of Irradiated Skin

Radiotherapy (RT) helps cure and palliate thousands of patients with a range of malignant diseases. A major drawback, however, is the collateral damage done to tissues surrounding the tumor in the radiation field. The skin and subcutaneous tissue are among the most severely affected regions. Immediately following RT, the skin may be inflamed, hyperemic, and can form ulcers. With time, the dermis becomes progressively indurated. These acute and chronic changes cause substantial patient morbidity, yet there are few effective treatment modalities able to reduce radiodermatitis. Fat grafting is increasingly recognized as a tool able to reverse the fibrotic skin changes and rejuvenate the irradiated skin. This review outlines the current progress toward describing and understanding the cellular and molecular effects of fat grafting in irradiated skin. Identification of the key factors involved in the pathophysiology of fibrosis following RT will inform therapeutic interventions to enhance its beneficial effects.

Hypoxia changes chemotaxis behaviour of mesenchymal stem cells via HIF-1α signalling

Mesenchymal stem cells (MSCs) have drawn great attention because of their therapeutic potential. It has been suggested that intra‐venous infused MSCs could migrate the site of injury to help repair the damaged tissue. However, the mechanism for MSC migration is still not clear so far. In this study, we reported that hypoxia increased chemotaxis migration of MSCs. At 4 and 6 hours after culturing in hypoxic (1% oxygen) conditions, the number of migrated MSCs was significantly increased. Meanwhile, hypoxia also increased the expression of HIF‐1α and SDF‐1. Using small interference RNA, we knocked down the expression of HIF‐1α in MSCs to study the role of HIF‐1α in hypoxia induced migration. Our data indicated that knocking down the expression of HIF‐1α not only abolished the migration of MSCs, but also reduced the expression of SDF‐1. Combining the results of migration assay and expression at RNA and protein level, we demonstrated a novel mechanism that controls the increase of MSCs migration. This mechanism involved HIF‐1α mediated SDF‐1 expression. These findings provide new insight into the role of HIF‐1α in the hypoxia induced MSC migration and can be a benefit for the development of MSC‐based therapeutics for wound healing.

Hypoxia and Renal Tubulointerstitial Fibrosis

Hypoxia, one of the most common causes of kidney injury, is a key pathological condition in various kidney diseases. Renal fibrosis is the terminal pathway involved in the continuous progression of chronic kidney disease (CKD), characterized by glomerulosclerosis and tubulointerstitial fibrosis (TIF). Recent studies have shown that hypoxia is a key factor promoting the progression of TIF. Loss of microvasculature, reduced oxygen dispersion, and metabolic abnormality of cells in the kidney are the main causes of the hypoxic state. Hypoxia can, in turn, profoundly affect the tubular epithelial cells, endothelial cells, pericytes, fibroblasts, inflammatory cells, and progenitor cells. In this chapter, we reviewed the critical roles of hypoxia in the pathophysiology of TIF and discussed the potential of anti-hypoxia as its promising therapeutic target.

Emerging Strategies for Stem Cell Lineage Commitment in Tissue Engineering and Regenerative Medicine

Stem cells have transformed the fields of tissue engineering and regenerative medicine, and their potential to further advance these fields cannot be overstated. The stem cell niche is a dynamic microenvironment that determines cell fate during development and tissue repair following an injury. Classically, stem cells were studied in isolation of their microenvironment; however, contemporary research has produced a myriad of evidence that shows the importance of multiple aspects of the stem cell niche in regulating their processes. In the context of tissue engineering and regenerative medicine studies, the niche is an artificial environment provided by culture conditions. In vitro culture conditions may involve coculturing with other cell types, developing specific biomaterials, and applying relevant forces to promote the desired lineage commitment. Considerable advance has been made over the past few years toward directed stem cell differentiation; however, the unspecific differentiation of stem cells yielding a mixed population of cells has been a challenge. In this review, we provide a systematic review of the emerging strategies used for lineage commitment within the context of tissue engineering and regenerative medicine. These strategies include scaffold pore-size and pore-shape gradients, stress relaxation, sonic and electromagnetic effects, and magnetic forces. Finally, we provide insights and perspectives into future directions focusing on signaling pathways activated during lineage commitment using external stimuli.

The Immunopathophysiology of Endometriosis

Endometriosis is a chronic, inflammatory, estrogen-dependent disease characterized by the growth of endometrial tissue outside of the uterine cavity. Although the etiology of endometriosis remains elusive, immunological dysfunction has been proposed as a critical facilitator of ectopic lesion growth following retrograde menstruation of endometrial debris. However, it is not clear whether this immune dysfunction is a cause or consequence of endometriosis. Thus, here we provide in-depth insights into our current understanding of the immunopathophysiology of endometriosis and highlight challenges and opportunities for future research. With the explosion of successful immune-based therapies targeting various chronic inflammatory conditions, it is crucial to determine whether immune dysfunction can be therapeutically targeted in endometriosis.

Acceleration of Diabetic Wound Healing with PHD2- and miR-210-Targeting Oligonucleotides

In diabetes-associated chronic wounds, the normal response to hypoxia is impaired and many cellular processes involved in wound healing are hindered. Central to the hypoxia response is hypoxia-inducible factor-1α (HIF-1α), which activates multiple factors that enhance wound healing by promoting cellular motility and proliferation, new vessel formation, and re-epithelialization. Prolyl hydroxylase domain-containing protein 2 (PHD2) regulates HIF-1α activity by targeting it for degradation under normoxia. HIF-1α also upregulates microRNA miR-210, which in turn regulates proteins involved in cell cycle control, DNA repair, and mitochondrial respiration in ways that are antagonistic to wound repair. We have identified a highly potent short synthetic hairpin RNA (sshRNA) that inhibits expression of PHD2 and an antisense oligonucleotide (antimiR) that inhibits miR-210. Both oligonucleotides were chemically modified for improved biostability and to mitigate potential immunostimulatory effects. Using the sshRNA to silence PHD2 transcripts stabilizes HIF-1α and, in combination with the antimiR targeting miR-210, increases proliferation and migration of keratinocytes in vitro. To assess activity and delivery in an impaired wound healing model in diabetic mice, PHD2-targeting sshRNAs and miR-210 antimiRs both alone and in combination were formulated for local delivery to wounds using layer-by-layer (LbL) technology. LbL nanofabrication was applied to incorporate sshRNA into a thin polymer coating on a Tegaderm mesh. This coating gradually degrades under physiological conditions, releasing sshRNA and antimiR for sustained cellular uptake. Formulated treatments were applied directly to splinted full-thickness excisional wounds in db/db mice. Cellular uptake was confirmed using fluorescent sshRNA. Wounds treated with a single application of PHD2 sshRNA or antimiR-210 closed 4 days faster than untreated wounds, and wounds treated with both oligonucleotides closed on average 4.75 days faster. Markers for neovascularization and cell proliferation (CD31 and Ki67, respectively) were increased in the wound area following treatment, and vascular endothelial growth factor (VEGF) was increased in sshRNA-treated wounds. Our results suggest that silencing of PHD2 and miR-210 either together or separately by localized delivery of sshRNAs and antimiRs is a promising approach for the treatment of chronic wounds, with the potential for rapid clinical translation.

The pleiotropic cardiovascular effects of dipeptidyl peptidase-4 inhibitors

Patients with Type 2 diabetes have an excess risk for cardiovascular disease. One of the several approaches, included in the guidelines for the management of Type 2 diabetes, is based on dipeptidyl peptidase 4 (DPP-4; also termed CD26) inhibitors, also called gliptins. Gliptins inhibit the degradation of glucagon-like peptide-1 (GLP-1): this effect is associated with increased circulating insulin-to-glucagon ratio, and a consequent reduction of HbA1c. In addition to incretin hormones, there are several proteins that may be affected by DPP-4 and its inhibition: among these some are relevant for the cardiovascular system homeostasis such as SDF-1α and its receptor CXCR4, brain natriuretic peptides, neuropeptide Y and peptide YY. In this review, we will discuss the pathophysiological relevance of gliptin pleiotropism and its translational potential.

Progenitor Cells and Clinical Outcomes in Patients With Acute Coronary Syndromes

RATIONALE

Circulating progenitor cells (CPCs) mobilize in response to ischemic injury, but their predictive value remains unknown in acute coronary syndrome (ACS).

OBJECTIVE

We aimed to investigate the number of CPCs in ACS compared with those with stable coronary artery disease (CAD), relationship between bone marrow PCs and CPCs, and whether CPC counts predict mortality in patients with ACS.

METHODS AND RESULTS

In 2028 patients, 346 had unstable angina, 183 had an acute myocardial infarction (AMI), and the remaining 1499 patients had stable CAD. Patients with ACS were followed for the primary end point of all-cause death. CPCs were enumerated by flow cytometry as mononuclear cells expressing a combination of CD34+, CD133+, vascular endothelial growth factor receptor 2+, or chemokine (C-X-C motif) receptor 4+. CPC counts were higher in subjects with AMI compared those with stable CAD even after adjustment for age, sex, race, body mass index, renal function, hypertension, diabetes mellitus, hyperlipidemia, and smoking; CD34+, CD34+/CD133+, CD34+/CXCR4+, and CD34+/VEGFR2+ CPC counts were 19%, 25%, 28%, and 142% higher in those with AMI, respectively, compared with stable CAD. There were strong correlations between the concentrations of CPCs and the PC counts in bone marrow aspirates in 20 patients with AMI. During a 2 (interquartile range, 1.31-2.86)-year follow-up period of 529 patients with ACS, 12.4% died. In Cox regression models adjusted for age, sex, body mass index, heart failure history, estimated glomerular filtration rate, and AMI, subjects with low CD34+ cell counts had a 2.46-fold (95% confidence interval, 1.18-5.13) increase in all-cause mortality, P=0.01. CD34+/CD133+ and CD34+/CXCR4+, but not CD34+/VEGFR2+ PC counts, had similar associations with mortality. Results were validated in a separate cohort of 238 patients with ACS.

CONCLUSIONS

CPC levels are significantly higher in patients after an AMI compared with those with stable CAD and reflect bone marrow PC content. Among patients with ACS, a lower number of hematopoietic-enriched CPCs are associated with a higher mortality.

Prostaglandin F-2α Stimulates The Secretion of Vascular Endothelial Growth Factor and Induces Cell Proliferation and Migration of Adipose Tissue Derived Mesenchymal Stem Cells

Objective

Tissue engineering today uses factors that can induce differentiation of mesenchymal stem cells (MSCs) into other cell types. However, the problem of angiogenesis in this differentiated tissue remains an unresolved area of research interest. The aim of this study was to investigate the effects of prostaglandin F-2α (PGF-2α) on the expression of vascular endothelial growth factor (VEGF) in human adipose tissue derived MSCs.

Materials and Methods

In this experimental research, human adipose tissue was digested using collagenase. The isolated MSCs cells were treated with PGF-2α (up to 5 μg/ml) and incubated for 96 hours. Cell proliferation, secretion of VEGF and cell migration were spontaneously assayed by MTT, BrdU, ELISA, RT-PCR and scratching methods.

Results

Cell growth at 1.0, 2.5, 5 µg/ml of PGF-2α was not significantly reduced compared to control cells, suggesting that these concentrations of PGF-2α are not toxic to cell growth. The results of the BrdU incorporation assay indicated that, in comparison to untreated cells, BrdU incorporation was respectively 1.08, 1.96, 2.0 and 1.8 fold among cells treated with 0.1, 1.0, 2.5 and 5.0 µg/ml of PGF-2α. The scratching test also demonstrated a positive influence on cell proliferation and migration. Cells treated with 1.0 µg/ml of PGF-2α for 12 hours showed the highest relative migration and coverage in comparison to untreated cells. Quantitative VEGF ELISA and RT- PCR results indicated an increase in VEGF expression and secretion in the presence of PGF-2α. The amount of VEGF produced in response to 0.1, 1.0, 2.5 and 5.0 µg/ml of PGF-2α was 62.4 ± 3.2 , 66.3 ± 3.7, 53.1 ± 2.6 and 49.0 ± 2.3 pg/ml, respectively, compared to the 35.2 ± 2.1 pg/ml produced by untreated cells.

Conclusion

Stimulation of VEGF secretion by PGF-2α treated MSCs could be useful for the induction of angiogenesis in tissue engineering in vitro.

Mesoporous silicate nanoparticles/3D nanofibrous scaffold-mediated dual-drug delivery for bone tissue engineering

Controlled delivery systems play a critical role in the success of bone morphogenetic proteins (i.e., BMP2 and BMP7) for challenged bone repair. Instead of single-drug release that is currently and commonly prevalent, dual-drug delivery strategies are highly desired to achieve effective bone regeneration because natural bone repair process is driven by multiple factors. Particularly, angiogenesis is essential for osteogenesis and requires more than just one factor (e.g., Vascular Endothelial Growth Factor, VEGF). Therefore, we developed a novel mesoporous silicate nanoparticles (MSNs) incorporated-3D nanofibrous gelatin (GF) scaffold for dual-delivery of BMP2 and deferoxamine (DFO). DFO is a hypoxia-mimetic drug that can activate hypoxia-inducible factor-1 alpha (HIF-1α), and trigger subsequent angiogenesis. Sustained BMP2 release system was achieved through encapsulation into large-pored MSNs, while the relative short-term release of DFO was engineered through covalent conjugation with chitosan to reduce its cytotoxicity and elongate its half-life. Both MSNs and DFO were incorporated onto a porous 3D GF scaffold to serve as a biomimetic osteogenic microenvironment. Our data indicated that DFO and BMP2 were released from a scaffold at different release rates (10 vs 28 days) yet maintained their angiogenic and osteogenic ability, respectively. Importantly, our data indicated that the released DFO significantly improved BMP2-induced osteogenic differentiation where the dose/duration was important for its effects in both mouse and human stem cell models. Thus, we developed a novel and tunable MSNs/GF 3D scaffold-mediated dual-drug delivery system and studied the potential application of the both FDA-approved DFO and BMP2 for bone tissue engineering.

The Challenge in Using Mesenchymal Stromal Cells for Recellularization of Decellularized Cartilage

Some decellularized musculoskeletal extracellular matrices (ECM)s derived from tissues such as bone, tendon and fibrocartilaginous meniscus have already been clinical use for tissue reconstruction. Repair of articular cartilage with its unique zonal ECM architecture and composition is still an unsolved problem, and the question is whether allogenic or xenogeneic decellularized cartilage ECM could serve as a biomimetic scaffold for this purpose.Hence, this survey outlines the present state of preparing decellularized cartilage ECM-derived scaffolds or composites for reconstruction of different cartilage types and of reseeding it particularly with mesenchymal stromal cells (MSCs).The preparation of natural decellularized cartilage ECM scaffolds hampers from the high density of the cartilage ECM and lacking interconnectivity of the rather small natural pores within it: the chondrocytes lacunae. Nevertheless, the reseeding of decellularized ECM scaffolds before implantation provided superior results compared with simply implanting cell-free constructs in several other tissues, but cartilage recellularization remains still challenging. Induced by cartilage ECM-derived scaffolds MSCs underwent chondrogenesis.Major problems to be addressed for the application of cell-free cartilage were discussed such as to maintain ECM structure, natural chemistry, biomechanics and to achieve a homogenous and stable cell recolonization, promote chondrogenic and prevent terminal differentiation (hypertrophy) and induce the deposition of a novel functional ECM. Some promising approaches were proposed including further processing of the decellularized ECM before recellularization of the ECM with MSCs, co-culturing of MSCs with chondrocytes and establishing bioreactor culture e.g. with mechanostimulation, flow perfusion pressure and lowered oxygen tension. Graphical Abstract Synopsis of tissue engineering approaches based on cartilage-derived ECM.

Cardiac Progenitor Cells and the Interplay with Their Microenvironment

The microenvironment plays a crucial role in the behavior of stem and progenitor cells. In the heart, cardiac progenitor cells (CPCs) reside in specific niches, characterized by key components that are altered in response to a myocardial infarction. To date, there is a lack of knowledge on these niches and on the CPC interplay with the niche components. Insight into these complex interactions and into the influence of microenvironmental factors on CPCs can be used to promote the regenerative potential of these cells. In this review, we discuss cardiac resident progenitor cells and their regenerative potential and provide an overview of the interactions of CPCs with the key elements of their niche. We focus on the interaction between CPCs and supporting cells, extracellular matrix, mechanical stimuli, and soluble factors. Finally, we describe novel approaches to modulate the CPC niche that can represent the next step in recreating an optimal CPC microenvironment and thereby improve their regeneration capacity.

Porcine Bone Scaffolds Adsorb Growth Factors Secreted by MSCs and Improve Bone Tissue Repair

An ideal tissue-engineered bone graft should have both excellent pro-osteogenesis and pro-angiogenesis properties to rapidly realize the bone regeneration in vivo. To meet this goal, in this work a porcine bone scaffold was successfully used as a Trojan horse to store growth factors produced by mesenchymal stem cells (MSCs). This new scaffold showed a time-dependent release of bioactive growth factors, such as vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF), in vitro. The biological effect of the growth factors-adsorbed scaffold on the in vitro commitment of MSCs into osteogenic and endothelial cell phenotypes has been evaluated. In addition, we have investigated the activity of growth factor-impregnated granules in the repair of critical-size defects in rat calvaria by means of histological, immunohistochemical, and molecular biology analyses. Based on the results of our work bone tissue formation and markers for bone and vascularization were significantly increased by the growth factor-enriched bone granules after implantation. This suggests that the controlled release of active growth factors from porcine bone granules can enhance and promote bone regeneration.

A hypoxia response element in the Vegfa promoter is required for basal Vegfa expression in skin and for optimal granulation tissue formation during wound healing in mice

Hypoxia in skin wounds is thought to contribute to healing through the induction of hypoxia inducible factor-1 (HIF-1). Although HIF-1 can regulate the expression of vascular endothelial growth factor A (Vegfa), whether hypoxia and HIF-1 are required to induce Vegfa expression in the context of wound healing is unknown. To test this hypothesis, we evaluated Vegfa expression and wound healing in mutant mice that lack a functional HIF-1 binding site in the Vegfa promoter. Full-thickness excisional wounds were made using a biopsy punch, left to heal by second intention, and granulation tissue isolated on a time course during healing. mRNA levels of Vegfa and its target genes platelet-derived growth factors B (Pdgfb) and stromal cell-derived factor-1 (Sdf1) were measured by RT-qPCR, and HIF-1alpha and VEGFA protein levels measured by immunoblotting. Lower levels of Vegfa, Pdgf1 and Sdf1 mRNA were found in intact skin of mutant mice relative to wild-type controls (n = 6 mice/genotype), whereas levels in granulation tissue during wound healing were unaltered. VEGFA protein levels were also lower in intact skin of the mutant versus the wild-type mice. Decreased Vegfa mRNA levels in skin of mutant mice could not be attributed to decreased HIF-1alpha protein expression, and were therefore a consequence of the loss of HIF-1 responsiveness of the Vegfa promoter. Comparative histologic analyses of healing wounds in mutant and wild-type mice (n = 8 mice/genotype) revealed significant defects in granulation tissue in the mutant mice, both in terms of quantity and capillary density, although epithelialization and healing rates were unaltered. We conclude that HIF-1 is not a major regulator of Vegfa expression during wound healing; rather, it serves to maintain basal levels of expression of Vegfa and its target genes in intact skin, which are required for optimal granulation tissue formation in response to wounding.

The effect of endothelial cell activation and hypoxia on placental chorionic mesenchymal stem/stromal cell migration

INTRODUCTION

Chorionic mesenchymal stem/stromal cells (CMSC) can be isolated from the placenta in large numbers. Although their functions are yet to be fully elucidated, they have a role in tissue development and repair. To fulfil such a role, CMSC must be able to migrate to the microenvironment of the injury site. This process is not fully understood and the aim of this study therefore, was to examine in vitro CMSC migration in response to tissue inflammation and hypoxic conditioning.

METHODS

CMSC were derived from the chorionic villi. A trans-endothelium migration (TEM) assay was used to study CMSC migration through an activated endothelial cell monolayer using the HMEC-1 cell line. A cytokine array was used to identify and compare the cytokine production profile of activated versus non-activated HMEC-1.

RESULTS

There were significant changes in cytokine production by HMEC-1 cells following lipopolysaccharide (LPS) treatment and hypoxic conditioning. Despite this, results from the TEM assay showed no significant change in the average number of CMSC that migrated through the LPS activated HMEC-1 layer compared to the untreated control. Furthermore, there was no significant change in the average number of CMSC that migrated through the HMEC-1 monolayer when exposed to hypoxic (1% O₂), normoxic (8% O₂) or hyperoxic (21% O₂) conditions.

CONCLUSION

These data suggest that cell functions such as transendothelial migration can vary between MSC derived from different tissues in response to the same biological cues.

Transplantation of Bone Marrow-Derived Stem Cells: A Promising Therapy for Stroke

Stroke remains a major cause of death in the US and around the world. Over the last decade, stem cell therapy has been introduced as an experimental treatment for stroke. Transplantation of stem cells or progenitors into the injured site to replace the nonfunctional cells, and enhancement of proliferation or differentiation of endogenous stem or progenitor cells stand as the two major cell-based strategies. Potential sources of stem/progenitor cells for stroke include fetal neural stem cells, embryonic stem cells, neuroteratocarcinoma cells, umbilical cord blood-derived nonhematopoietic stem cells, and bone marrow-derived stem cells. The goal of this article is to provide an update on the preclinical use of bone marrow-derived stem cells with major emphasis on mesenchymal stem cells (MSCs) and multipotent adult progenitor cells (MAPCs) because they are currently most widely applied in experimental stroke studies and are now being phased into early clinical trials. The phenotypic features of MSCs and MAPCs, as well as their application in stroke, are described.

Regenerative Therapy for Stroke

Stroke remains a leading cause of death and disability worldwide. An increasing number of animal studies and preclinical trials have, however, provided evidence that regenerative cell-based therapies can lead to functional recovery in stroke patients. Stem cells can differentiate into neural lineages to replace lost neurons. Moreover, they provide trophic support to tissue at risk in the penumbra surrounding the infarct area, enhance vasculogenesis, and help promote survival, migration, and differentiation of the endogenous precursor cells after stroke. Stem cells are highly migratory and seem to be attracted to areas of brain pathology such as ischemic regions. The pathotropism may follow the paradigm of stem cell homing to bone marrow and leukocytes migrating to inflammatory tissue. The molecular signaling therefore may involve various chemokines, cytokines, and integrins. Among these, stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor-4 (CXCR4) signaling is required for the interaction of stem cells and ischemia-damaged host tissues. SDF-1 is secreted primarily by bone marrow fibroblasts and is required for BMSC homing to bone marrow. Overexpression of SDF-1 in ischemic tissues has been found to enhance stem cell recruitment from peripheral blood and to induce neoangiogenesis. Furthermore, SDF-1 expression in the lesioned area peaked within 7 days postischemia, in concordance with the time window of G-CSF therapy for stroke. Recent data have shown that SDF-1 expression is directly proportional to reduced tissue oxygen tension. SDF-1 gene expression is regulated by hypoxic-inducible factor-1 (HIF-1), a hypoxia-dependent stabilization transcription factor. Thus, ischemic tissue may recruit circulating progenitors regulated by hypoxia through differential expression of HIF-1α and SDF-1. In addition to SDF-1, β2-integrins also play a role in the homing of hematopoietic progenitor cells to sites of ischemia and are critical for their neovascularization capacity. In our recent report, increased expression of β1-integrins apparently contributed to the local neovasculization of the ischemic brain as well as its functional recovery. Identification of the molecular pathways involved in stem cell homing into the ischemic areas could pave the way for the development of new treatment regimens, perhaps using small molecules, designed to enhance endogeneous mobilization of stem cells in various disease states, including chronic stroke and other neurodegenerative diseases. For maximal functional recovery, however, regenerative therapy may need to follow combinatorial approaches, which may include cell replacement, trophic support, protection from oxidative stress, and the neutralization of the growth-inhibitory components for endogenous neuronal stem cells.