Local delivery of protease-resistant stromal cell derived factor-1 for stem cell recruitment after myocardial infarction

Benchmarking AlphaFold-Generated Structures of Chemokine-Chemokine Receptor Complexes

AlphaFold and AlphaFold-Multimer have become two essential tools for the modeling of unknown structures of proteins and protein complexes. In this work, we extensively benchmarked the quality of chemokine-chemokine receptor structures generated by AlphaFold-Multimer against experimentally determined structures. Our analysis considered both the global quality of the model, as well as key structural features for chemokine recognition. To study the effects of template and multiple sequence alignment parameters on the results, a new prediction pipeline called LIT-AlphaFold (https://github.com/LIT-CCM-lab/LIT-AlphaFold) was developed, allowing extensive input customization. AlphaFold-Multimer correctly predicted differences in chemokine binding orientation and accurately reproduced the unique binding orientation of the CXCL12-ACKR3 complex. Further, the predictions of the full receptor N-terminus provided insights into a putative chemokine recognition site 0.5. The accuracy of chemokine N-terminus binding mode prediction varied between complexes, but the confidence score permitted the distinguishing of residues that were very likely well positioned. Finally, we generated a high-confidence model of the unsolved CXCL12-CXCR4 complex, which agreed with experimental mutagenesis and cross-linking data.

Enhancement of tracheal cartilage regeneration by local controlled release of stromal cell-derived factor 1α with gelatin hydrogels and systemic administration of high-mobility group box 1 peptide

Introduction

This present study evaluated the effect of combination therapy with stromal cell-derived factor 1α (SDF-1α) and high-mobility group box 1 (HMGB1) peptide on the regeneration of tracheal injury in a rat model.

Methods

To improve this effect, SDF-1α was incorporated into a gelatin hydrogel, which was then applied to the damaged tracheal cartilage of rats for local release. Furthermore, HMGB1 peptide was repeatedly administered intravenously. Regeneration of damaged tracheal cartilage was evaluated in terms of cell recruitment.

Results

Mesenchymal stem cells (MSC) with C-X-C motif chemokine receptor 4 (CXCR4) were mobilized more into the injured area, and consequently the fastest tracheal cartilage regeneration was observed in the combination therapy group eight weeks after injury.

Conclusions

The present study demonstrated that combination therapy with gelatin hydrogel incorporating SDF-1α and HMGB1 peptide injected intravenously can enhance the recruitment of CXCR4-positive MSC, promoting the regeneration of damaged tracheal cartilage.

Elevated levels of plasma inactive stromal cell derived factor-1α predict poor long-term outcomes in diabetic patients following percutaneous coronary intervention

BACKGROUND

Since the complication of diabetes mellitus (DM) is a risk for adverse cardiovascular outcomes in patients with coronary artery disease (CAD), appropriate risk estimation is needed in diabetic patients following percutaneous coronary intervention (PCI). However, there is no useful biomarker to predict outcomes in this population. Although stromal cell derived factor-1α (SDF-1α), a circulating chemokine, was shown to have cardioprotective roles, the prognostic impact of SDF-1α in diabetic patients with CAD is yet to be fully elucidated. Moreover, roles of SDF-1α isoforms in outcome prediction remain unclear. Therefore, this study aimed to assess the prognostic implication of three forms of SDF-1α including total, active, and inactive forms of SDF-1α in patients with DM and after PCI.

METHODS

This single-center retrospective analysis involved consecutive patients with diabetes who underwent PCI for the first time between 2008 and 2018 (n = 849). Primary and secondary outcome measures were all-cause death and the composite of cardiovascular death, non-fatal myocardial infarction, and ischemic stroke (3P-MACE), respectively. For determining plasma levels of SDF-1α, we measured not only total, but also the active type of SDF-1α by ELISA. Inactive isoform of the SDF-1α was calculated by subtracting the active isoform from total SDF-1α.

RESULTS

Unadjusted Kaplan-Meier analyses revealed increased risk of both all-cause death and 3P-MACE in patients with elevated levels of inactive SDF-1α. However, plasma levels of total and active SDF-1α were not associated with cumulative incidences of outcome measures. Multivariate Cox hazard analyses repeatedly indicated the 1 higher log-transformed inactive SDF-1α was significantly associated with increased risk of all-cause death (hazard ratio (HR): 2.64, 95% confidence interval (CI): 1.28-5.34, p = 0.008) and 3P-MACE (HR: 2.51, 95% CI: 1.12-5.46, p = 0.02). Moreover, the predictive performance of inactive SDF-1α was higher than that of total SDF-1α (C-statistics of inactive and total SDF-1α for all-cause death: 0.631 vs 0.554, for 3P-MACE: 0.623 vs 0.524, respectively).

CONCLUSION

The study results indicate that elevated levels of plasma inactive SDF-1α might be a useful indicator of poor long-term outcomes in diabetic patients following PCI.

TRIAL REGISTRATION

This study describes a retrospective analysis of a prospective registry database of patients who underwent PCI at Juntendo University Hospital, Tokyo, Japan (Juntendo Physicians' Alliance for Clinical Trials, J-PACT), which is publicly registered (University Medical Information Network Japan-Clinical Trials Registry, UMIN-CTR 000035587).

Recent advances in mesenchymal stem cell therapy for myocardial infarction

Myocardial infarction refers to the ischemic necrosis of myocardium, characterized by a sharp reduction or interruption of blood flow in the coronary arteries due to the coronary artery occlusion, resulting in severe and prolonged ischemia in the corresponding myocardium and ultimately leading to ischemic necrosis of the myocardium. Given its high risk, it is considered as one of the most serious health threats today. In current clinical practice, multiple approaches have been explored to diminish myocardial oxygen consumption and alleviate symptoms, but notable success remains elusive. Accumulated clinical evidence has showed that the implantation of mesenchymal stem cell for treating myocardial infarction is both effective and safe. Nevertheless, there persists controversy and variability regarding the standardizing MSC transplantation protocols, optimizing dosage, and determining the most effective routes of administration. Addressing these remaining issues will pave the way of integration of MSCs as a feasible mainstream cardiac treatment.

Nanoghosts: Harnessing Mesenchymal Stem Cell Membrane for Construction of Drug Delivery Platforms Via Optimized Biomimetics

Mesenchymal stem cells (MSCs) are becoming hotspots for application in disease therapies recently, combining with biomaterials and drug delivery system. A major advantage of MSCs applied in drug delivery system is that these cells enable specific targeting and releasing of cargos to the disease sites. However, the potential tumor tropic effects of MSCs raised concerns on biosafety. To solve this problem, there are emerging methods of isolating cell membranes and developing nanoformulations to perform drug delivery, which avoids concerns on biosafety without disturbing the membrane functions of specific polarizing and locating. These cargoes are so called "nanoghosts." This review article summarizes the current applications of nanoghosts, the promising potential of MSCs to be applied in membrane isolation and nanoghost construction, and possible approaches to develop better drug delivery system harnessing from MSC ghost cell membranes.

In-situ wound healing by SDF-1-mimic peptide-loaded click crosslinked hyaluronic acid scaffold

Endogenous stem cell-based in-situ tissue regeneration has recently gained considerable attention. In this study, we investigated the potential of a chemokine, SDF-1-mimic peptide (SMP), to promote endogenous stem cell-based in-situ wound healing. Our approach involved the development of a click crosslinked hyaluronic acid scaffold loaded with SMP (Cx-HA + SMP) to release SMP in a wound site. The Cx-HA scaffold maintained its structural integrity throughout the wound healing process and also captured endogenous stem cells. Gradual SMP release from the Cx-HA + SMP scaffold established a concentration gradient at the wound site. In animal wound experiments, Cx-HA + SMP exhibited faster wound contraction compared to Cx-HA + SDF-1. Additionally, Cx-HA + SMP resulted in approximately 1.2-1.6 times higher collagen formation compared to Cx-HA + SDF-1. SMP released from the Cx-HA + SMP scaffold promoted endogenous stem cell migration to the wound site 1.5 times more effectively than Cx-HA + SDF-1. Moreover, compared to Cx-HA + SDF-1, Cx-HA + SMP exhibited higher expression of CXCR4 and CD31, as well as the positive markers CD29 and CD44 for endogenous stem cells. The endogenous stem cells that migrated through Cx-HA + SMP regenerated into wound skin with minimal scar granule formation, similar to the normal tissue. In conclusion, SMP peptide offers greater convenience, while efficiently attracting migrating endogenous stem cells compared to the SDF protein. Our findings suggest that Cx-HA + SMP scaffolds hold promise as a strategy to enhance endogenous stem cell-based in-situ wound healing.

CD13 facilitates immune cell migration and aggravates acute injury but promotes chronic post-stroke recovery

INTRODUCTION

Acute stroke leads to the activation of myeloid cells. These cells express adhesion molecules and transmigrate to the brain, thereby aggravating injury. Chronically after stroke, repair processes, including angiogenesis, are activated and enhance post-stroke recovery. Activated myeloid cells express CD13, which facilitates their migration into the site of injury. However, angiogenic blood vessels which play a role in recovery also express CD13. Overall, the specific contribution of CD13 to acute and chronic stroke outcomes is unknown.

METHODS

CD13 expression was estimated in both mice and humans after the ischemic stroke. Young (8-12 weeks) male wild-type and global CD13 knockout (KO) mice were used for this study. Mice underwent 60 min of middle cerebral artery occlusion (MCAO) followed by reperfusion. For acute studies, the mice were euthanized at either 24- or 72 h post-stroke. For chronic studies, the Y-maze, Barnes maze, and the open field were performed on day 7 and day 28 post-stroke. Mice were euthanized at day 30 post-stroke and the brains were collected for assessment of inflammation, white matter injury, tissue loss, and angiogenesis. Flow cytometry was performed on days 3 and 7 post-stroke to quantify infiltrated monocytes and neutrophils and CXCL12/CXCR4 signaling.

RESULTS

Brain CD13 expression and infiltrated CD13+ monocytes and neutrophils increased acutely after the stroke. The brain CD13+lectin+ blood vessels increased on day 15 after the stroke. Similarly, an increase in the percentage area CD13 was observed in human stroke patients at the subacute time after stroke. Deletion of CD13 resulted in reduced infarct volume and improved neurological recovery after acute stroke. However, CD13KO mice had significantly worse memory deficits, amplified gliosis, and white matter damage compared to wild-type animals at chronic time points. CD13-deficient mice had an increased percentage of CXCL12+cells but a reduced percentage of CXCR4+cells and decreased angiogenesis at day 30 post-stroke.

CONCLUSIONS

CD13 is involved in the trans-migration of monocytes and neutrophils after stroke, and acutely, led to decreased infarct size and improved behavioral outcomes. However, loss of CD13 led to reductions in post-stroke angiogenesis by reducing CXCL12/CXCR4 signaling.

Angiogenesis induction as a key step in cardiac tissue Regeneration: From angiogenic agents to biomaterials

Cardiovascular diseases are the leading cause of death worldwide. After myocardial infarction, the vascular supply of the heart is damaged or blocked, leading to the formation of scar tissue, followed by several cardiac dysfunctions or even death. In this regard, induction of angiogenesis is considered as a vital process for supplying nutrients and oxygen to the cells in cardiac tissue engineering. The current review aims to summarize different approaches of angiogenesis induction for effective cardiac tissue repair. Accordingly, a comprehensive classification of induction of pro-angiogenic signaling pathways through using engineered biomaterials, drugs, angiogenic factors, as well as combinatorial approaches is introduced as a potential platform for cardiac regeneration application. The angiogenic induction for cardiac repair can enhance patient treatment outcomes and generate economic prospects for the biomedical industry. The development and commercialization of angiogenesis methods often involves collaboration between academic institutions, research organizations, and biomedical companies.

Stimuli-responsive hydrogels: smart state of-the-art platforms for cardiac tissue engineering

Biomedicine and tissue regeneration have made significant advancements recently, positively affecting the whole healthcare spectrum. This opened the way for them to develop their applications for revitalizing damaged tissues. Thus, their functionality will be restored. Cardiac tissue engineering (CTE) using curative procedures that combine biomolecules, biomimetic scaffolds, and cells plays a critical part in this path. Stimuli-responsive hydrogels (SRHs) are excellent three-dimensional (3D) biomaterials for tissue engineering (TE) and various biomedical applications. They can mimic the intrinsic tissues' physicochemical, mechanical, and biological characteristics in a variety of ways. They also provide for 3D setup, adequate aqueous conditions, and the mechanical consistency required for cell development. Furthermore, they function as competent delivery platforms for various biomolecules. Many natural and synthetic polymers were used to fabricate these intelligent platforms with innovative enhanced features and specialized capabilities that are appropriate for CTE applications. In the present review, different strategies employed for CTE were outlined. The light was shed on the limitations of the use of conventional hydrogels in CTE. Moreover, diverse types of SRHs, their characteristics, assembly and exploitation for CTE were discussed. To summarize, recent development in the construction of SRHs increases their potential to operate as intelligent, sophisticated systems in the reconstruction of degenerated cardiac tissues.

Therapeutic angiogenesis based on injectable hydrogel for protein delivery in ischemic heart disease

Ischemic heart disease (IHD) remains the leading cause of death and disability worldwide and leads to myocardial necrosis and negative myocardial remodeling, ultimately leading to heart failure. Current treatments include drug therapy, interventional therapy, and surgery. However, some patients with severe diffuse coronary artery disease, complex coronary artery anatomy, and other reasons are unsuitable for these treatments. Therapeutic angiogenesis stimulates the growth of the original blood vessels by using exogenous growth factors to generate more new blood vessels, which provides a new treatment for IHD. However, direct injection of these growth factors can cause a short half-life and serious side effects owing to systemic spread. Therefore, to overcome this problem, hydrogels have been developed for temporally and spatially controlled delivery of single or multiple growth factors to mimic the process of angiogenesis in vivo. This paper reviews the mechanism of angiogenesis, some important bioactive molecules, and natural and synthetic hydrogels currently being applied for bioactive molecule delivery to treat IHD. Furthermore, the current challenges of therapeutic angiogenesis in IHD and its potential solutions are discussed to facilitate real translation into clinical applications in the future.

Combined effect of SDF-1 peptide and angiogenic cues in co-axial PLGA/gelatin fibers for cutaneous wound healing in diabetic rats

Skin regeneration is hindered by poor vascularization, prolonged inflammation, and excessive scar tissue formation, which necessitate newer strategies to simultaneously induce blood vessel regeneration, resolve inflammation, and induce host cell recruitment. Concurrent deployment of multiple biological cues to realize synergistic reparative effects may be an enticing avenue for wound healing. Herein, we simultaneously deployed SDF (stromal cell-derived factor)- 1α, VEGF (vascular endothelial growth factor)-binding peptide (BP), and GLP (glucagon like peptide)- 1 analog, liraglutide (LG) in core/shell poly(L-lactide-co-glycolide)/gelatin fibers to harness their synergistic effects for skin repair in healthy as well as diabetic wound models in rats. Microscopic techniques, such as SEM and TEM revealed fibrous and core/shell type morphology of membranes. Boyden chamber assay and scratch-wound assay displayed significant migration of HUVECs (human umbilical vein endothelial cells) in SDF-1α containing fibers. Subcutaneous implantation of membranes revealed higher cellular infiltration in SDF-1α loaded fibers, especially, those which were co-loaded with LG or BP. Implantation of membranes in an excisional wound model in healthy rats further showed significant and rapid wound closure in dual cues loaded groups as compared to control or single cue loaded groups. Similarly, the implantation of dressings in type 2 diabetes rat model revealed fast healing, skin appendages regeneration, and blood vessel regeneration in dual cues loaded fibers (SDF-1α/LG, SDF-1α/BP). Taken together, core/shell type fibers containing bioactive peptides significantly promoted wound repair in healthy as well as diabetic wound models in rats.

SDF-1α-Releasing Microspheres Effectively Extend Stem Cell Homing after Myocardial Infarction

Ischemic heart disease (IHD) is one of the main focuses in today's healthcare due to its implications and complications, and it is predicted to be increasing in prevalence due to the ageing population. Although the conventional pharmacological and interventional methods for the treatment of IHD presents with success in the clinical setting, the long-term complications of cardiac insufficiency are on a continual incline as a result of post-infarction remodeling of the cardiac tissue. The migration and involvement of stem cells to the cardiac muscle, followed by differentiation into cardiac myocytes, has been proven to be the natural process, though at a slow rate. SDF-1α is a novel candidate to mobilize stem cells homing to the ischemic heart. Endogenous SDF-1α levels are elevated after myocardial infarction, but their presence gradually decreases after approximately seven days. Additional administration of SDF-1α-releasing microspheres could be a tool for the extension of the time the stem cells are in the cardiac tissue after myocardial infarction. This, in turn, could constitute a novel therapy for more efficient regeneration of the heart muscle after injury. Through this practical study, it has been shown that the controlled release of SDF-1α from biodegradable microspheres into the pericardial sac fourteen days after myocardial infarction increases the concentration of exogenous SDF-1α, which persists in the tissue much longer than the level of endogenous SDF-1α. In addition, administration of SDF-1α-releasing microspheres increased the expression of the factors potentially involved in the involvement and retention of myocardial stem cells, which constitutes vascular endothelial growth factor A (VEGFA), stem cell factor (SCF), and vascular cell adhesion molecules (VCAMs) at the site of damaged tissue. This exhibits the possibility of combating the basic limitations of cell therapy, including ineffective stem cell implantation and the ability to induce the migration of endogenous stem cells to the ischemic cardiac tissue and promote heart repair.

Pericardial Grafting of Cardiac Progenitor Cells in Self-Assembling Peptide Scaffold Improves Cardiac Function After Myocardial Infarction

Many studies have explored cardiac progenitor cell (CPC) therapy for heart disease. However, optimal scaffolds are needed to ensure the engraftment of transplanted cells. We produced a three-dimensional hydrogel scaffold (CPC-PRGmx) in which high-viability CPCs were cultured for up to 8 weeks. CPC-PRGmx contained an RGD peptide-conjugated self-assembling peptide with insulin-like growth factor-1 (IGF-1). Immediately after creating myocardial infarction (MI), we transplanted CPC-PRGmx into the pericardial space on to the surface of the MI area. Four weeks after transplantation, red fluorescent protein-expressing CPCs and in situ hybridization analysis in sex-mismatched transplantations revealed the engraftment of CPCs in the transplanted scaffold (which was cellularized with host cells). The average scar area of the CPC-PRGmx-treated group was significantly smaller than that of the non-treated group (CPC-PRGmx-treated group = 46 ± 5.1%, non-treated MI group = 59 ± 4.5%; p < 0.05). Echocardiography showed that the transplantation of CPC-PRGmx improved cardiac function and attenuated cardiac remodeling after MI. The transplantation of CPCs-PRGmx promoted angiogenesis and inhibited apoptosis, compared to the untreated MI group. CPCs-PRGmx secreted more vascular endothelial growth factor than CPCs cultured on two-dimensional dishes. Genetic fate mapping revealed that CPC-PRGmx-treated mice had more regenerated cardiomyocytes than non-treated mice in the MI area (CPC-PRGmx-treated group = 0.98 ± 0.25%, non-treated MI group = 0.25 ± 0.04%; p < 0.05). Our findings reveal the therapeutic potential of epicardial-transplanted CPC-PRGmx. Its beneficial effects may be mediated by sustainable cell viability, paracrine function, and the enhancement of de novo cardiomyogenesis.

Ablation of CXCR4 expression in cardiomyocytes exacerbates isoproterenol‑induced cell death and heart failure

CXCR4 is a seven‑transmembrane‑spanning Gi‑coupled receptor for the SDF‑1 chemokine and plays a critical role in cardiovascular development and post‑injury repair. However, the specific role of CXCR4 in cardiomyocytes is incompletely understood. It was hypothesized that CXCR4 activation in cardiomyocytes antagonizes β‑adrenoceptor/Gs signaling‑induced cardiac dysfunction. Cardiomyocyte‑specific CXCR4 knockout (CXCR4‑^CMKO) mice were generated by crossing CXCR4^fl/fl and MHC‑Cre^+/‑ mice. Their cardiac structure and function in the basal state are equivalent to that of the control MHC‑Cre^+/‑ littermates until at least 4 months old. However, following continuous subcutaneous administration of isoproterenol (Iso) via an osmotic mini‑pump, the ventricular myocardial contractility, dilation, cardiomyocyte apoptosis, and interstitial fibrosis are worse in CXCR4‑^CMKO mice than in MHC‑Cre^+/‑ littermates. In the cultured H9C2 cardiomyocytes, SDF‑1 treatment markedly attenuated Iso‑induced apoptosis and reduction in phospho‑Akt, and this protective effect was lost by knockdown of CXCR4 or by co‑treatment with Gi inhibitors. In conclusion, CXCR4 promotes cardiomyocyte survival and heart function during β‑adrenergic stress.

Controlled Release of Encapsuled Stromal-Derived Factor 1α Improves Bone Marrow Mesenchymal Stromal Cells Migration

Stem cell treatment is a promising method of therapy for the group of patients whose conventional options for treatment have been limited or rejected. Stem cells have the potential to repair, replace, restore and regenerate cells. Moreover, their proliferation level is high. Owing to these features, they can be used in the treatment of numerous diseases, such as cancer, lung diseases or ischemic heart diseases. In recent years, stem cell therapy has greatly developed, shedding light on stromal-derived factor 1α (SDF-1α). SDF-1α is a mobilizing chemokine for application of endogenous stem cells to injury sites. Unfortunately, SDF-1α presented short-term results in stem cell treatment trials. Considering the tremendous benefits of this therapy, we developed biodegradable polymeric microspheres for the release of SDF-1α in a controlled and long-lasting manner. The microspheres were designed from poly(L-lactide/glycolide/trimethylene carbonate) (PLA/GA/TMC). The effect of controlled release of SDF-1α from microspheres was investigated on the migration level of bone marrow Mesenchymal Stromal Cells (bmMSCs) derived from a pig. The study showed that SDF-1α, released from the microspheres, is more efficient at attracting bmMSCs than SDF-1α alone. This may enable the controlled delivery of selected and labeled MSCs to the destination in the future.

Controlling Doxorubicin Release from a Peptide Hydrogel through Fine-Tuning of Drug-Peptide Fiber Interactions

Hydrogels are versatile materials that have emerged in the last few decades as promising candidates for a range of applications in the biomedical field, from tissue engineering and regenerative medicine to controlled drug delivery. In the drug delivery field, in particular, they have been the subject of significant interest for the spatially and temporally controlled delivery of anticancer drugs and therapeutics. Self-assembling peptide-based hydrogels, in particular, have recently come to the fore as potential candidate vehicles for the delivery of a range of drugs. In order to explore how drug–peptide interactions influence doxorubicin (Dox) release, five β-sheet-forming self-assembling peptides with different physicochemical properties were used for the purpose of this study, namely: FEFKFEFK (F8), FKFEFKFK (FK), FEFEFKFE (FE), FEFKFEFKK (F8K), and KFEFKFEFKK (KF8K) (F: phenylalanine; E: glutamic acid; K: lysine). First, Dox-loaded hydrogels were characterized to ensure that the incorporation of the drug did not significantly affect the hydrogel properties. Subsequently, Dox diffusion out of the hydrogels was investigated using UV absorbance. The amount of drug retained in F8/FE composite hydrogels was found to be directly proportional to the amount of charge carried by the peptide fibers. When cation−π interactions were used, the position and number of end-lysine were found to play a key role in the retention of Dox. In this case, the amount of Dox retained in F8/KF8K composite hydrogels was linked to the amount of end-lysine introduced, and an end-lysine/Dox interaction stoichiometry of 3/1 was obtained. For pure FE and KF8K hydrogels, the maximum amount of Dox retained was also found to be related to the overall concentration of the hydrogels and, therefore, to the overall fiber surface area available for interaction with the drug. For 14 mM hydrogel, ∼170–200 μM Dox could be retained after 24 h. This set of peptides also showed a broad range of susceptibilities to enzymatic degradation opening the prospect of being able to control also the rate of degradation of these hydrogels. Finally, the Dox released from the hydrogel was shown to be active and affect 3T3 mouse fibroblasts viability in vitro. Our study clearly shows the potential of this peptide design as a platform for the formulation of injectable or sprayable hydrogels for controlled drug delivery.

Stem Cell Homing in Intrathecal Applications and Inspirations for Improvement Paths

A transplanted stem cell homing is a directed migration from the application site to the targeted tissue. Intrathecal application of stem cells is their direct delivery to cerebrospinal fluid, which defines the homing path from the point of injection to the brain. In the case of neurodegenerative diseases, this application method has the advantage of no blood–brain barrier restriction. However, the homing efficiency still needs improvement and homing mechanisms elucidation. Analysis of current research results on homing mechanisms in the light of intrathecal administration revealed a discrepancy between in vivo and in vitro results and a gap between preclinical and clinical research. Combining the existing research with novel insights from cutting-edge biochips, nano, and other technologies and computational models may bridge this gap faster.

A Hydrogel as a Bespoke Delivery Platform for Stromal Cell-Derived Factor-1

The defined self-assembly of peptides (SAPs) into nanostructured bioactive hydrogels has great potential for repairing traumatic brain injuries, as they maintain a stable, homeostatic environment at an injury site, preventing further degeneration. They also present a bespoke platform to restore function via the naturalistic presentation of therapeutic proteins, such as stromal-cell-derived factor 1 (SDF-1), expressed by meningeal cells. A key challenge to the use of the SDF protein, however, is its rapid diffusion and degradation. Here, we engineered a homeostatic hydrogel produced by incorporating recombinant SDF-1 protein within a self-assembled peptide hydrogel to create a supportive milieu for transplanted cells. Our hydrogel can concomitantly deliver viable primary neural progenitor cells and sustained active SDF-1 to support the nascent graft, resulting in increased neuronal differentiation. Moreover, this homeostatic hydrogel can ensure a healthy and larger graft core without impeding neuronal fiber growth and innervation. These findings demonstrate the regenerative potential of these hydrogels to improve the integration of grafted cells to treat neural injuries and diseases.

The secretion profile of mesenchymal stem cells and potential applications in treating human diseases

Mesenchymal stromal/stem cells (MSCs) possess multi-lineage differentiation and self-renewal potentials. MSCs-based therapies have been widely utilized for the treatment of diverse inflammatory diseases, due to the potent immunoregulatory functions of MSCs. An increasing body of evidence indicates that MSCs exert their therapeutic effects largely through their paracrine actions. Growth factors, cytokines, chemokines, extracellular matrix components, and metabolic products were all found to be functional molecules of MSCs in various therapeutic paradigms. These secretory factors contribute to immune modulation, tissue remodeling, and cellular homeostasis during regeneration. In this review, we summarize and discuss recent advances in our understanding of the secretory behavior of MSCs and the intracellular communication that accounts for their potential in treating human diseases.

Efficacy of Stem Cell Therapy in Large Animal Models of Ischemic Cardiomyopathies: A Systematic Review and Meta-Analysis

Stem-cell therapy provides a promising strategy for patients with ischemic heart disease. In recent years, numerous studies related to this therapeutic approach were performed; however, the results were often heterogeneous and contradictory. For this reason, we conducted a systematic review and meta-analysis of trials, reporting the use of stem-cell treatment against acute or chronic ischemic cardiomyopathies in large animal models with regard to Left Ventricular Ejection Fraction (LVEF). The defined research strategy was applied to the PubMed database to identify relevant studies published from January 2011 to July 2021. A random-effect meta-analysis was performed on LVEF mean data at follow-up between control and stem-cell-treated animals. In order to improve the definition of the effect measure and to analyze the factors that could influence the outcomes, a subgroup comparison was conducted. Sixty-six studies (n = 1183 animals) satisfied our inclusion criteria. Ischemia/reperfusion infarction was performed in 37 studies, and chronic occlusion in 29 studies; moreover, 58 studies were on a pig animal model. The meta-analysis showed that cell therapy increased LVEF by 7.41% (95% Confidence Interval 6.23−8.59%; p < 0.001) at follow-up, with significative heterogeneity and high inconsistency (I2 = 82%, p < 0.001). By subgroup comparison, the follow-up after 31−60 days (p = 0.025), the late cell injection (>7 days, p = 0.005) and the route of cellular delivery by surgical treatment (p < 0.001) were significant predictors of LVEF improvement. This meta-analysis showed that stem-cell therapy may improve heart function in large animal models and that the swine specie is confirmed as a relevant animal model in the cardiovascular field. Due to the significative heterogeneity and high inconsistency, future translational studies should be designed to take into account the evidenced predictors to allow for the reduction of the number of animals used.

Important role of the SDF-1/CXCR4 axis in the homing of systemically transplanted human amnion-derived mesenchymal stem cells (hAD-MSCs) to ovaries in rats with chemotherapy-induced premature ovarian insufficiency (POI)

Background

Chemotherapy can induce premature ovarian insufficiency (POI). POI causes multiple sequelae and is currently incurable. As shown in our previous studies, systemically transplanted human amnion-derived mesenchymal stem cells (hAD-MSCs) home to ovaries with chemotherapy-induced POI and subsequently reduce ovarian injury and improve ovarian function in rats with POI. However, the cellular mechanisms that direct the migration and homing of hAD-MSCs to ovaries with chemotherapy-induced POI are incompletely understood. This study investigated the role of the SDF-1/CXCR4 axis in the migration and homing of systemically transplanted hAD-MSCs to ovaries with chemotherapy-induced POI and its relevant downstream signalling pathways.

Methods

CXCR4 expression in hAD-MSCs was assessed using Western blotting and immunofluorescence staining. hAD-MSC migration was tested using Transwell migration assays. SDF-1 levels were detected using ELISA. Seventy-two female SD rats were randomly divided into the control, POI, hAD-MSCs and hAD-MSCs + AMD3100 groups. Cyclophosphamide was used to establish rat POI models. For inhibitor treatment, hAD-MSCs were pretreated with AMD3100 before transplantation. PKH26-labeled hAD-MSCs were injected into the tail vein of POI rats 24 h after chemotherapy. After hAD-MSC transplantation, the homing of hAD-MSCs to ovaries and ovarian function and pathological changes were examined. We further investigated the molecular mechanisms by detecting the PI3K/Akt and ERK1/2 signalling pathways.

Results

hAD-MSCs expressed CXCR4. SDF-1 induced hAD-MSC migration in vitro. SDF-1 levels in ovaries and serum were significantly increased in rats with chemotherapy-induced POI, and ovaries with POI induced the homing of hAD-MSCs expressing CXCR4. Blocking the SDF-1/CXCR4 axis with AMD3100 significantly reduced the number of hAD-MSCs homing to ovaries with POI and further reduced their efficacy in POI treatment. The binding of SDF-1 to CXCR4 activated the PI3K/Akt signalling pathway, and LY294002 significantly inhibited hAD-MSC migration induced by SDF-1 in vitro. Moreover, inhibition of the PI3K/Akt signalling pathway significantly reduced the number of systemically transplanted hAD-MSCs homing to chemotherapy-induced ovaries in rats with POI.

Conclusions

SDF-1/CXCR4 axis partially mediates the migration and homing of systemically transplanted hAD-MSCs to the ovaries of rats with chemotherapy-induced POI, and the PI3K/Akt signalling pathway might be involved in the migration and homing of hAD-MSCs mediated by the SDF-1/CXCR4 axis.

HMGB1-Mediated Activation of the Inflammatory-Reparative Response Following Myocardial Infarction

Different cell types belonging to the innate and adaptive immune system play mutually non-exclusive roles during the different phases of the inflammatory-reparative response that occurs following myocardial infarction. A timely and finely regulation of their action is fundamental for the process to properly proceed. The high-mobility group box 1 (HMGB1), a highly conserved nuclear protein that in the extracellular space can act as a damage-associated molecular pattern (DAMP) involved in a large variety of different processes, such as inflammation, migration, invasion, proliferation, differentiation, and tissue regeneration, has recently emerged as a possible regulator of the activity of different immune cell types in the distinct phases of the inflammatory reparative process. Moreover, by activating endogenous stem cells, inducing endothelial cells, and by modulating cardiac fibroblast activity, HMGB1 could represent a master regulator of the inflammatory and reparative responses following MI. In this review, we will provide an overview of cellular effectors involved in these processes and how HMGB1 intervenes in regulating each of them. Moreover, we will summarize HMGB1 roles in regulating other cell types that are involved in the different phases of the inflammatory-reparative response, discussing how its redox status could affect its activity.

Liposomal SDF-1 Alpha Delivery in Nanocomposite Hydrogels Promotes Macrophage Phenotype Changes and Skin Tissue Regeneration

Skin regeneration in chronic wounds is often delayed due to persistent inflammation induced by underlying conditions such as diabetes. This effect is mediated, in part, by macrophages present in the wound, which can be stimulated to adopt either pro- or anti-inflammatory phenotypes depending on the status of the local microenvironment. In this work, the prohealing chemokine stromal cell-derived factor-1 alpha (SDF-1α) is controllably released from a hydrogel-based biomaterial to promote skin tissue regeneration and wound closure. This innovative nanocomposite hydrogel system releases liposomal stromal cell-derived factor-1 alpha (lipoSDF) as a new treatment approach for dorsal full-thickness skin wounds in wild-type and diabetic mice. Using this strategy, the recruitment and polarization of macrophages primarily of the anti-inflammatory phenotype were observed, along with a decreased amount of open wound surface area in diabetic mice after 28 days. This was accompanied by histological observations of increased epidermal stratification and dermal angiogenesis. These findings represent an important step of investigation distinctive in its field for developing immunomodulatory biomaterials that are able to influence macrophage phenotype and promote healing as hydrogel-based wound dressings.

Protease-Triggered Release of Stabilized CXCL12 from Coated Scaffolds in an Ex Vivo Wound Model

Biomaterials are designed to improve impaired healing of injured tissue. To accomplish better cell integration, we suggest to coat biomaterial surfaces with bio-functional proteins. Here, a mussel-derived surface-binding peptide is used and coupled to CXCL12 (stromal cell-derived factor 1α), a chemokine that activates CXCR4 and consequently recruits tissue-specific stem and progenitor cells. CXCL12 variants with either non-releasable or protease-mediated-release properties were designed and compared. Whereas CXCL12 was stabilized at the N-terminus for protease resistance, a C-terminal linker was designed that allowed for specific cleavage-mediated release by matrix metalloproteinase 9 and 2, since both enzymes are frequently found in wound fluid. These surface adhesive CXCL12 derivatives were produced by expressed protein ligation. Functionality of the modified chemokines was assessed by inositol phosphate accumulation and cell migration assays. Increased migration of keratinocytes and primary mesenchymal stem cells was demonstrated. Immobilization and release were studied for bioresorbable PCL-co-LC scaffolds, and accelerated wound closure was demonstrated in an ex vivo wound healing assay on porcine skin grafts. After 24 h, a significantly improved CXCL12-specific growth stimulation of the epithelial tips was already observed. The presented data display a successful application of protein-coated biomaterials for skin regeneration.

Role of Stromal Cell-Derived Factor-1 in Endothelial Progenitor Cell-Mediated Vascular Repair and Regeneration

Endothelial progenitor cells (EPCs) are immature endothelial cells that participate in vascular repair and postnatal neovascularization and provide a novel and promising therapy for the treatment of vascular disease. Studies in different animal models have shown that EPC mobilization through pharmacological agents and autologous EPC transplantation contribute to restoring blood supply and tissue regeneration after ischemic injury. However, these effects of the progenitor cells in clinical studies exhibit mixed results. The therapeutic efficacy of EPCs is closely associated with the number of the progenitor cells recruited into ischemic regions and their functional abilities and survival in injury tissues. In this review, we discussed the regulating role of stromal cell-derived factor-1 (also known CXCL12, SDF-1) in EPC mobilization, recruitment, homing, vascular repair and neovascularization, and analyzed the underlying machemisms of these functions. Application of SDF-1 to improve the regenerative function of EPCs following vascular injury was also discussed. SDF-1 plays a crucial role in mobilizing EPC from bone marrow into peripheral circulation, recruiting the progenitor cells to target tissue and protecting against cell death under pathological conditions; thus improve EPC regenerative capacity. SDF-1 are crucial for regulating EPC regenerative function, and provide a potential target for improve therapeutic efficacy of the progenitor cells in treatment of vascular disease.

Improvement of wound healing by the development of ECM-inspired biomaterial coatings and controlled protein release

Implant design has evolved from biochemically inert substrates, minimizing cell and protein interaction, towards sophisticated bioactive substrates, modulating the host response and supporting the regeneration of the injured tissue. Important aspects to consider are the control of cell adhesion, the discrimination of bacteria and non-local cells from the desired tissue cell type, and the stimulation of implant integration and wound healing. Here, the extracellular matrix acts as a role model providing us with inspiration for sophisticated designs. Within this scope, small bioactive peptides have proven to be miscellaneously deployable for the mediation of surface, cell and matrix interactions. Combinations of adhesion ligands, proteoglycans, and modulatory proteins should guide multiple aspects of the regeneration process and cooperativity between the different extracellular matrix components, which bears the chance to maximize the therapeutic efficiency and simultaneously lower the doses. Hence, efforts to include multiple of these factors in biomaterial design are well worth. In the following, multifunctional implant coatings based on bioactive peptides are reviewed and concepts to implement strong surface anchoring for stable cell adhesion and a dynamic delivery of modulator proteins are discussed.

SDF-1 Molecularly Imprinted Biomimetic Scaffold as a Potential Strategy to Repair the Infarcted Myocardium

Background:

In situ cardiac tissue engineering aims to heal the infarcted myocardium by guiding tissue regeneration within the patient body. A key step in this approach is the design of a bioactive scaffold, able to stimulate tissue repair at the site of damage.

In the development of bioactive scaffolds, molecular imprinting nanotechnology has been recently proposed as a new functionalization strategy.

Objectives:

In this work, Molecularly Imprinted Particles (MIP) with recognition properties towards the stromal-derived factor-1 (SDF-1) were synthesized, characterized and used for the functionalization of a biomimetic scaffold. MIP are expected to favor the enrichment of the SDF-1 bioactive molecule within the scaffold, thereby promoting myocardial regeneration.

Methods:

MIP were obtained by precipitation polymerization, using the SDF-1 molecule as a template. Alginate/gelatin/elastin sponges were fabricated by freeze-drying and functionalized by MIP deposition. Morphological, physicochemical and functional analyses were performed both on MIP and on MIP-modified scaffolds. A preliminary biological in vitro investigation was also carried out using rat cardiac progenitor cells (rCPCs).

Results:

Imprinted nanoparticles with an average diameter between 0.6 and 0.9 µm were obtained. Infrared analysis of MIP confirmed the expected chemical structure. Recognition and selectivity tests showed that MIP were able to selectively recognize and rebind the template, even after their deposition on the scaffold. In vitro biological tests showed that cell adhesion to the scaffold was promoted by MIP functionalization.

Conclusion:

Results obtained in the present study suggest that biomimetic alginate/gelatin/elastin sponges, functionalized by MIP with recognition properties towards SDF-1, could be successfully used for tissue engineering approaches to repair the infarcted heart.

KLF15 negatively regulates cardiac fibrosis by which SDF-1β attenuates cardiac fibrosis in type 2 diabetic mice

Diabetic cardiomyopathy (DCM) is a serious diabetic complication that lacks effective preventive or therapeutic approaches. Wild-type and Klf15 knockout (Klf15-KO) mice were fed with either high fat diet (HFD, 60% kcal from fat) or normal diet (ND, 10% kcal from fat) for 3 months and then injected with streptozotocin or vehicle, to induce type 2 diabetes (T2D). All T2D and age-matched control mice were treated with or without SDF-1β at 5 mg/kg body-weight twice a week and also continually received HFD or ND for 3 months. At the end of 6-month study, after cardiac functions were measured, mice were euthanized to collect heart tissue. For in vitro mechanistic study, H9c2 cells were exposed to palmitate to mimic in vivo condition of T2D. SDF-1β prevented T2D-induced cardiac dysfunction and fibrosis and T2D-down-regulated KLF15 expression in wild-type diabetic heart tissue. However, the preventive effects of SDF-1β on both KLF15 expression and fibrosis was abolished, with partial cardiac protection in Klf15-KO/T2D mice. These results demonstrate partial KLF15-dependence for SDF-1β's cardiac fibrotic protection from T2D, but not on SDF-1β's protective effects on T2D-induced cardiac dysfunction. Further study showed that SDF-1β inhibited palmitate-induced cardiomyocyte fibrosis through its receptor CXCR7-mediated activation of p38β MAPK signaling pathway.

Fabrication of Stromal Cell-Derived Factor-1 Contained in Gelatin/Hyaluronate Copo006Cymer Mixed with Hydroxyapatite for Use in Traumatic Bone Defects

Bone defects of orthopedic trauma remain a challenge in clinical practice. Regarding bone void fillers, besides the well-known osteoconductivity of most bone substitutes, osteoinductivity has also been gaining attention in recent years. It is known that stromal cell-derived factor-1 (SDF-1) can recruit mesenchymal stem cells (MSCs) in certain circumstances, which may also play an important role in bone regeneration. In this study, we fabricated a gelatin/hyaluronate (Gel/HA) copolymer mixed with hydroxyapatite (HAP) and SDF-1 to try and enhance bone regeneration in a bone defect model. After material characterization, these Gel/HA–HAP and Gel/HA–HAP–SDF-1 composites were tested for their biocompatibility and ability to recruit MSCs in vitro. A femoral condyle bone defect model of rats was used for in vivo studies. For the assessment of bone healing, micro-CT analysis, second harmonic generation (SHG) imaging, and histology studies were performed. As a result, the Gel/HA–HAP composites showed no systemic toxicity to rats. Gel/HA–HAP composite groups both showed better bone generation compared with the control group in an animal study, and the composite with the SDF-1 group even showed a trend of faster bone growth compared with the composite without SDF-1 group. In conclusion, in the management of traumatic bone defects, Gel/HA–HAP–SDF-1 composites can be a feasible material for use as bone void fillers.

Peptide-based supramolecular hydrogels for local drug delivery

Peptide-based supramolecular hydrogels have shown great promise as drug delivery systems (DDSs) because of their excellent biocompatibility, biodegradability, biological function, synthetic feasibility, and responsiveness to external stimuli. Self-assembling peptide molecules are able rationally designed into specific nanoarchitectures in response to the different environmental factors under different circumstances. Among all stimuli that have been investigated, utilizing inherent biological microenvironment, such as metal ions, enzymes and endogenous redox species, to trigger self-assembly endows such systems spatiotemporal controllability to transport therapeutics more accurately. Materials formed by weak non-covalent interactions result in the shear-thinning and immediate recovery behavior. Thus, they are injectable via a syringe or catheter, making them the ideal vehicles to deliver drugs. Based on the above merits, self-assembling peptide-based DDSs have been applied to treat various diseases via direct administration at the lesion site. Herein, in this review, we outline the triggers for inducing peptide-based hydrogels formation and serving as DDSs. We also described the advancements of peptide-based supramolecular hydrogels for local drug delivery, including intratumoral, subcutaneous, ischemia-related tissue (intramyocardial, intrarenal, and ischemic hind limb), and ocular administration. Finally, we give a brief perspective about the prospects and challenges in this field.

Self-assembling peptides as vectors for local drug delivery and tissue engineering applications

Molecular self-assembly has forged a new era in the development of advanced biomaterials for local drug delivery and tissue engineering applications. Given their innate biocompatibility and biodegradability, self-assembling peptides (SAPs) have come in the spotlight of such applications. Short and water-soluble SAP biomaterials associated with enhanced pharmacokinetic (PK) and pharmacodynamic (PD) responses after the topical administration of the therapeutic systems, or improved regenerative potential in tissue engineering applications will be the focus of the current review. SAPs are capable of generating supramolecular structures using a boundless array of building blocks, while peptide engineering is an approach commonly pursued to encompass the desired traits to the end composite biomaterials. These two elements combined, expand the spectrum of SAPs multi-functionality, constituting them potent biomaterials for use in various biomedical applications.

Exosomes secreted by hiPSC-derived cardiac cells improve recovery from myocardial infarction in swine

Cell therapy treatment of myocardial infarction (MI) is mediated, in part, by exosomes secreted from transplanted cells. Thus, we compared the efficacy of treatment with a mixture of cardiomyocytes (CMs; 10 million), endothelial cells (ECs; 5 million), and smooth muscle cells (SMCs; 5 million) derived from human induced pluripotent stem cells (hiPSCs), or with exosomes extracted from the three cell types, in pigs after MI. Female pigs received sham surgery; infarction without treatment (MI group); or infarction and treatment with hiPSC-CMs, hiPSC-ECs, and hiPSC-SMCs (MI + Cell group); with homogenized fragments from the same dose of cells administered to the MI + Cell group (MI + Fra group); or with exosomes (7.5 mg) extracted from a 2:1:1 mixture of hiPSC-CMs:hiPSC-ECs:hiPSC-SMCs (MI + Exo group). Cells and exosomes were injected into the injured myocardium. In vitro, exosomes promoted EC tube formation and microvessel sprouting from mouse aortic rings and protected hiPSC-CMs by reducing apoptosis, maintaining intracellular calcium homeostasis, and increasing adenosine 5'-triphosphate. In vivo, measurements of left ventricular ejection fraction, wall stress, myocardial bioenergetics, cardiac hypertrophy, scar size, cell apoptosis, and angiogenesis in the infarcted region were better in the MI + Cell, MI + Fra, and MI + Exo groups than in the MI group 4 weeks after infarction. The frequencies of arrhythmic events in animals from the MI, MI + Cell, and MI + Exo groups were similar. Thus, exosomes secreted by hiPSC-derived cardiac cells improved myocardial recovery without increasing the frequency of arrhythmogenic complications and may provide an acellular therapeutic option for myocardial injury.

Preseeding of Mesenchymal Stem Cells Increases Integration of an iPSC-Derived CM Sheet into a Cardiac Matrix

Cell sheet technology has demonstrated great promise in delivering a large amount of therapeutic cells for tissue repair, including in the myocardium. However, the lack of host integration remains one of the key challenges in using cell sheets for cardiac repair. Paracrine factors secreted by mesenchymal stem cells (MSCs) have been reported to facilitate tissue repair and regeneration in a variety of ways. It has been demonstrated that paracrine factors from MSCs could enhance scaffold recellularization and vascularization. In this study, we used an in vitro cardiac matrix mimic platform to examine the effects of hMSCs preseeding on the interactions between cell sheets and cardiac matrix. The fabricated human induced pluripotent stem cells-derived cardiomyocyte sheets were attached to a decellularized porcine myocardium slice with or without preseeding of hMSCs. The hMSCs preseeding significantly enhanced the interactions between cardiomyocyte sheets and cardiac matrix in terms of cell migration distance, cell distribution, and mature vascular and cardiomyocyte marker expressions in the matrix. Growth factor and matrix metalloproteinases array analysis suggested that hMSCs- induced vascularization and MMPs regulation are the two possible mechanisms that lead to the improved CMs and cardiac matrix interactions. Further examination of these two mechanisms will enable the development of new approaches to facilitate transplanted cells for tissue repair.

Hydrogels and Dentin-Pulp Complex Regeneration: From the Benchtop to Clinical Translation

Dentin-pulp complex is a term which refers to the dental pulp (DP) surrounded by dentin along its peripheries. Dentin and dental pulp are highly specialized tissues, which can be affected by various insults, primarily by dental caries. Regeneration of the dentin-pulp complex is of paramount importance to regain tooth vitality. The regenerative endodontic procedure (REP) is a relatively current approach, which aims to regenerate the dentin-pulp complex through stimulating the differentiation of resident or transplanted stem/progenitor cells. Hydrogel-based scaffolds are a unique category of three dimensional polymeric networks with high water content. They are hydrophilic, biocompatible, with tunable degradation patterns and mechanical properties, in addition to the ability to be loaded with various bioactive molecules. Furthermore, hydrogels have a considerable degree of flexibility and elasticity, mimicking the cell extracellular matrix (ECM), particularly that of the DP. The current review presents how for dentin-pulp complex regeneration, the application of injectable hydrogels combined with stem/progenitor cells could represent a promising approach. According to the source of the polymeric chain forming the hydrogel, they can be classified into natural, synthetic or hybrid hydrogels, combining natural and synthetic ones. Natural polymers are bioactive, highly biocompatible, and biodegradable by naturally occurring enzymes or via hydrolysis. On the other hand, synthetic polymers offer tunable mechanical properties, thermostability and durability as compared to natural hydrogels. Hybrid hydrogels combine the benefits of synthetic and natural polymers. Hydrogels can be biofunctionalized with cell-binding sequences as arginine-glycine-aspartic acid (RGD), can be used for local delivery of bioactive molecules and cellularized with stem cells for dentin-pulp regeneration. Formulating a hydrogel scaffold material fulfilling the required criteria in regenerative endodontics is still an area of active research, which shows promising potential for replacing conventional endodontic treatments in the near future.

Angiogenesis after acute myocardial infarction

Acute myocardial infarction (MI) inflicts massive injury to the coronary microcirculation leading to vascular disintegration and capillary rarefication in the infarct region. Tissue repair after MI involves a robust angiogenic response that commences in the infarct border zone and extends into the necrotic infarct core. Technological advances in several areas have provided novel mechanistic understanding of postinfarction angiogenesis and how it may be targeted to improve heart function after MI. Cell lineage tracing studies indicate that new capillary structures arise by sprouting angiogenesis from pre-existing endothelial cells (ECs) in the infarct border zone with no meaningful contribution from non-EC sources. Single-cell RNA sequencing shows that ECs in infarcted hearts may be grouped into clusters with distinct gene expression signatures, likely reflecting functionally distinct cell populations. EC-specific multicolour lineage tracing reveals that EC subsets clonally expand after MI. Expanding EC clones may arise from tissue-resident ECs with stem cell characteristics that have been identified in multiple organs including the heart. Tissue repair after MI involves interactions among multiple cell types which occur, to a large extent, through secreted proteins and their cognate receptors. While we are only beginning to understand the full complexity of this intercellular communication, macrophage and fibroblast populations have emerged as major drivers of the angiogenic response after MI. Animal data support the view that the endogenous angiogenic response after MI can be boosted to reduce scarring and adverse left ventricular remodelling. The improved mechanistic understanding of infarct angiogenesis therefore creates multiple therapeutic opportunities. During preclinical development, all proangiogenic strategies should be tested in animal models that replicate both cardiovascular risk factor(s) and the pharmacotherapy typically prescribed to patients with acute MI. Considering that the majority of patients nowadays do well after MI, clinical translation will require careful selection of patients in need of proangiogenic therapies.

Repairing the heart: State-of the art delivery strategies for biological therapeutics

Myocardial infarction (MI) is one of the leading causes of mortality worldwide. It is caused by an acute imbalance between oxygen supply and demand in the myocardium, usually caused by an obstruction in the coronary arteries. The conventional therapy is based on the application of (a combination of) anti-thrombotics, reperfusion strategies to open the occluded artery, stents and bypass surgery. However, numerous patients cannot fully recover after these interventions. In this context, new therapeutic methods are explored. Three decades ago, the first biologicals were tested to improve cardiac regeneration. Angiogenic proteins gained popularity as potential therapeutics. This is not straightforward as proteins are delicate molecules that in order to have a reasonably long time of activity need to be stabilized and released in a controlled fashion requiring advanced delivery systems. To ensure long-term expression, DNA vectors-encoding for therapeutic proteins have been developed. Here, the nuclear membrane proved to be a formidable barrier for efficient expression. Moreover, the development of delivery systems that can ensure entry in the target cell, and also correct intracellular trafficking towards the nucleus are essential. The recent introduction of mRNA as a therapeutic entity has provided an attractive intermediate: prolonged but transient expression from a cytoplasmic site of action. However, protection of the sensitive mRNA and correct delivery within the cell remains a challenge. This review focuses on the application of synthetic delivery systems that target the myocardium to stimulate cardiac repair using proteins, DNA or RNA.

Doevendans P, Schiffelers RM, Lei Z, Sluijter JP. Cellular and Molecular Mechanism of Cardiac Regeneration: A Comparison of Newts, Zebrafish, and Mammals

Cardiovascular disease is the leading cause of death worldwide. Current palliative treatments can slow the progression of heart failure, but ultimately, the only curative treatment for end-stage heart failure is heart transplantation, which is only available for a minority of patients due to lack of donors' hearts. Explorative research has shown the replacement of the damaged and lost myocardium by inducing cardiac regeneration from preexisting myocardial cells. Lower vertebrates, such as the newt and zebrafish, can regenerate lost myocardium through cardiomyocyte proliferation. The preexisting adult cardiomyocytes replace the lost cells through subsequent dedifferentiation, proliferation, migration, and re-differentiation. Similarly, neonatal mice show complete cardiac regeneration post-injury; however, this regenerative capacity is remarkably diminished one week after birth. In contrast, the adult mammalian heart presents a fibrotic rather than a regenerative response and only shows signs of partial pathological cardiomyocyte dedifferentiation after injury. In this review, we explore the cellular and molecular responses to myocardial insults in different adult species to give insights for future interventional directions by which one can promote or activate cardiac regeneration in mammals.

A novel chemotactic factor derived from the extracellular matrix protein decorin recruits mesenchymal stromal cells in vitro and in vivo

Soft tissue is composed of cells surrounded by an extracellular matrix that is made up of a diverse array of intricately organized proteins. These distinct components work in concert to maintain homeostasis and respond to tissue damage. During tissue repair, extracellular matrix proteins and their degradation products are known to influence physiological processes such as angiogenesis and inflammation. In this study we developed a discovery platform using a decellularized extracellular matrix biomaterial to identify new chemotrophic factors derived from the extracellular matrix. An in vitro culture of RAW.264 macrophage cells with the biomaterial ovine forestomach matrix led to the identification of a novel ~12 kDa chemotactic factor, termed ‘MayDay’, derived from the N-terminal 31–188 sequence of decorin. The recombinant MayDay protein was shown to be a chemotactic agent for mesenchymal stromal cells in vitro and in vivo. We hypothesize that the macrophage-induced cleavage of decorin, via MMP-12, leads to the release of the chemotactic molecule MayDay, that in turn recruits cells to the site of damaged tissue.

Local SDF-1α application enhances the therapeutic efficacy of BMSCs transplantation in osteoporotic bone healing

Bone defect healing is markedly impaired in osteoporotic patient due to poor bone regeneration ability. Stromal cell derived factor-1α (SDF-1α) plays a pivotal role in the repair of various injured tissues including bone. Here, we definite that SDF-1α hydrogels potentiates in vivo osteogenesis of bone marrow-derived stromal stem cells (BMSCs) in osteoporosis. The characteristics of rat primary BMSCs including superficial markers by flow cytometry and multi-lineage differentiation by induction were determined. At different time intervals, the release media from the SDF-1α-releasing hydrogels were collected to identificate SDF-1α exhibited a sustained release profile and maintained its bioactivity after release from the hydrogels to stimulate chemotaxis of BMSCs in a time dependent manner. Bilateral alveolar defects were operated in ovariectomized (OVX) rats and repaired with systemic BMSCs transplantation with or without the hydrogels. Local administration of SDF-1α significantly enhanced BMSCs recruitment and promoted more bone regeneration as well as the expression of OCN and Runx2 compared with the effect of BMSCs transplantation alone. Moreover, after BMSCs transplantation with SDF-1α delivery, macrophage polarization was promoted toward the M2 phenotype, that is identified as an important symbol in tissue regeneration process. Taken together, local SDF-1α application enhances the efficacy of BMSCs transplantation therapy in osteoporotic bone healing, suggesting clinical potential of SDF-1α to serve as a therapeutic drug target for osteoporosis treatment.

A liposome/gelatin methacrylate nanocomposite hydrogel system for delivery of stromal cell-derived factor-1α and stimulation of cell migration

Chronic, non-healing skin and soft tissue wounds are susceptible to infection, difficult to treat clinically, and can severely reduce a patient's quality of life. A key aspect of this issue is the impaired recruitment of mesenchymal stem cells (MSCs), which secrete regenerative cytokines and modulate the phenotypes of other effector cells that promote healing. We have engineered a therapeutic delivery system that can controllably release the pro-healing chemokine stromal cell derived factor-1α (SDF-1α) to induce the migration of MSCs. In order to protect the protein cargo from hydrolytic degradation and control its release, we have loaded SDF-1α in anionic liposomes (lipoSDF) and embedded them in gelatin methacrylate (GelMA) to form a nanocomposite hydrogel. In this study, we quantify the release of SDF-1α from our hydrogel system and measure the induced migration of MSCs in vitro via a transwell assay. Lastly, we evaluate the ability of this system to activate intracellular signaling in MSCs by using Western blots to probe for the phosphorylation of key proteins in the mTOR pathway. To our knowledge, this is the first study to report the delivery of liposomal SDF-1α using a nanocomposite approach. The results of this study expand on our current understanding of factors that can be modified to affect MSC behavior and phenotype. Furthermore, our findings contribute to the development of new hydrogel-based therapeutic delivery strategies for clinical wound healing applications. STATEMENT OF SIGNIFICANCE: Chronic, non-healing wounds promote an inflammatory environment that inhibits the migration of mesenchymal stem cells (MSCs), which secrete pro-healing and regenerative cytokines. The goal of this project is to apply principles of tissue engineering to achieve controllable release of the pro-healing chemokine SDF-1α to modulate the intracellular signaling and migratory behavior of MSCs. In this work, we introduce a nanocomposite strategy to tailor the release of SDF-1α using a liposome/gelatin methacrylate hydrogel approach. We are the first group to report the delivery of liposomal SDF-1α using this strategy. Our findings aim to further elucidate the role of MSCs in directing wound healing and guide the development of immunomodulatory and therapeutic delivery strategies for clinical wound healing applications.

Non-invasively enhanced intracranial transplantation of mesenchymal stem cells using focused ultrasound mediated by overexpression of cell-adhesion molecules

Although there have been reports of promising results regarding the transplantation of mesenchymal stem cells (MSCs) for neurodegenerative diseases through the use of neuronal differentiation or control of the microenvironment, traditional surgical transplantation methods like parenchymal or intravenous injection have limitations such as secondary injuries in the brain, infection, and low survival rate of stem cells in the target site. Focused ultrasound (FUS) treatment is an emerging modality for the treatment of brain diseases, including neurodegenerative disorders. The various biological effects of FUS treatment have been investigated; therefore, the goal is now to improve the delivery efficiency and function of MSCs by capitalizing on the advantages of FUS. In this study, we demonstrated that FUS increases MSC transplantation into brain tissue by >2-fold, and that this finding might be related to the activation of intercellular adhesion molecule-1 in endothelial and subendothelial cells and vascular adhesion molecule-1 in endothelial cells.

The role of endothelial miRNAs in myocardial biology and disease

The myocardium is a highly structured pluricellular tissue which is governed by an intricate network of intercellular communication. Endothelial cells are the most abundant cell type in the myocardium and exert crucial roles in both healthy myocardium and during myocardial disease. In the last decade, microRNAs have emerged as new actors in the regulation of cellular function in almost every cell type. Here, we review recent evidence on the regulatory function of different microRNAs expressed in endothelial cells, also called endothelial microRNAs, in healthy and diseased myocardium. Endothelial microRNA emerged as modulators of angiogenesis in the myocardium, they are implicated in the paracrine role of endothelial cells in regulating cardiac contractility and homeostasis, and interfere in the crosstalk between endothelial cells and cardiomyocytes.

Stromal cell derived factor-1 and long-term prognosis in acute coronary syndrome

Aim: To explore long-term prognostic value of SDF-1 in acute coronary syndrome (ACS). Materials & methods: We included 254 patients with ACS. Plasma SDF-1 was measured and patients were classified into tertiles of SDF-1. Results: Multivariate analysis showed third tertile of SDF-1 as an independent predictor of all-cause death (HR: 2.5; 95% CI: 1.2-5.2; p = 0.011) and the composite of major adverse cardiovascular and cerebrovascular events (HR: 1.8; 95% CI: 1.1-3.1; p = 0.031). SDF-1 added to a clinical model can improve all-cause death prediction (net reclassification improvement 0.362; 95% CI: 0.423-0.681; p = 0.027). Conclusion: SDF-1 is an independent predictor of all-cause mortality and major adverse cardiovascular and cerebrovascular events in long-term follow-up of patients with ACS and adds prognostic information beyond traditional cardiovascular risks factors.

The Development of Gelatin/Hyaluronate Copolymer Mixed with Calcium Sulfate, Hydroxyapatite, and Stromal-Cell-Derived Factor-1 for Bone Regeneration Enhancement

In clinical practice, bone defects still remain a challenge. In recent years, apart from the osteoconductivity that most bone void fillers already provide, osteoinductivity has also been emphasized to promote bone healing. Stromal-cell-derived factor-1 (SDF-1) has been shown to have the ability to recruit mesenchymal stem cells (MSCs), which play an important role in the bone regeneration process. In this study, we developed a gelatin–hyaluronate (Gel-HA) copolymer mixed with calcium sulfate (CS), hydroxyapatite (HAP), and SDF-1 in order to enhance bone regeneration in a bone defect model. The composites were tested in vitro for biocompatibility and their ability to recruit MSCs after material characterization. For the in vivo test, a rat femoral condyle bone defect model was used. Micro computed tomography (Micro-CT), two-photon excitation microscopy, and histology analysis were performed to assess bone regeneration. As expected, enhanced bone regeneration was well observed in the group filled with Gel-HA/CS/HAP/SDF-1 composites compared with the control group in our animal model. Furthermore, detailed blood analysis of rats showed no obvious systemic toxicity or side effects after material implantation. In conclusion, the Gel-HA/CS/HAP/SDF-1 composite may be a safe and applicable material to enhance bone regeneration in bone defects.

The bifunctional SDF-1-AnxA5 fusion protein protects cardiac function after myocardial infarction

Stromal cell‐derived factor‐1 (SDF‐1) is a well‐characterized cytokine that protects heart from ischaemic injury. However, the beneficial effects of native SDF‐1, in terms of promoting myocardial repair, are limited by its low concentration in the ischaemic myocardium. Annexin V (AnxA5) can precisely detect dead cells in vivo. As massive cardiomyocytes die after MI, we hypothesize that AnxA5 can be used as an anchor to carry SDF‐1 to the ischaemic myocardium. In this study, we constructed a fusion protein consisting of SDF‐1 and AnxA5 domains. The receptor competition assay revealed that SDF‐1‐AnxA5 had high binding affinity to SDF‐1 receptor CXCR4. The treatment of SDF‐1‐AnxA5 could significantly promote phosphorylation of AKT and ERK and induce chemotactic response, angiogenesis and cell survival in vitro. The binding membrane assay and immunofluorescence revealed that AnxA5 domain had the ability to specifically recognize and bind to cells injured by hypoxia. Furthermore, SDF‐1‐AnxA5 administered via peripheral vein could accumulate at the infarcted myocardium in vivo. The treatment with SDF‐1‐AnxA5 attenuated cell apoptosis, enhanced angiogenesis, reduced infarcted size and improved cardiac function after mouse myocardial infarction. Our results suggest that the bifunctional SDF‐1‐AnxA5 can specifically bind to dead cells. The systemic administration of bifunctional SDF‐1‐AnxA5 effectively provides cardioprotection after myocardial infarction.