Extracellular high mobility group box 1 plays a role in the effect of bone marrow mononuclear cell transplantation for heart failure

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.

HMGB1 and repair: focus on the heart

High-mobility group box 1 (HMGB1) is one of the most abundant proteins in eukaryotes and the best characterized damage-associated molecular pattern (DAMP). The biological activities of HMGB1 depend on its subcellular location, context and post-translational modifications. Inside the nucleus, HMGB1 is engaged in many DNA events such as DNA repair, transcription regulation and genome stability; in the cytoplasm, its main function is to regulate the autophagic flux while in the extracellular environment, it possesses more complicated functions and it is involved in a large variety of different processes such as inflammation, migration, invasion, proliferation, differentiation and tissue regeneration. Due to this pleiotropy, the role of HMGB1 has been vastly investigated in various pathological diseases and a large number of studies have explored its function in cardiovascular pathologies. However, in this contest, the precise mechanism of action of HMGB1 and its therapeutic potential are still very controversial since is debated whether HMGB1 is involved in tissue damage or plays a role in tissue repair and regeneration. The main focus of this review is to provide an overview of the effects of HMGB1 in different ischemic heart diseases and to discuss its functions in these pathological conditions.

Fibrin Glue-aided, Instant Epicardial Placement Enhances the Efficacy of Mesenchymal Stromal Cell-Based Therapy for Heart Failure

Transplantation of mesenchymal stromal cells (MSCs) is a promising new therapy for heart failure. However, the current cell delivery routes result in poor donor cell engraftment. We therefore explored the role of fibrin glue (FG)-aided, instant epicardial placement to enhance the efficacy of MSC-based therapy in a rat ischemic cardiomyopathy model. We identified a feasible and reproducible method to instantly produce a FG-MSC complex directly on the heart surface. This complex exhibited prompt, firm adhesion to the heart, markedly improving initial retention of donor MSCs compared to intramyocardial injection. In addition, maintenance of retained MSCs was enhanced using this method, together contributing the increased donor cell presence. Such increased donor cell quantity using the FG-aided technique led to further improved cardiac function in association with augmented histological myocardial repair, which correlated with upregulation of tissue repair-related genes. We identified that the epicardial layer was eliminated shortly after FG-aided epicardial placement of MSCs, facilitating permeation of the donor MSC's secretome into the myocardium enabling myocardial repair. These data indicate that FG-aided, on-site, instant epicardial placement enhances MSC engraftment, promoting the efficacy of MSC-based therapy for heart failure. Further development of this accessible, advanced MSC-therapy is justified.

The origin and distribution of CD68, CD163, and αSMA+ cells in the early phase after meniscal resection in a parabiotic rat model

We previously reported that circulating peripheral blood-borne cells (PBCs) contribute to early-phase meniscal reparative change. Because macrophages and myofibroblasts are important contributors of tissue regeneration, we examined their origin and distribution in the reparative meniscus. Reparative menisci were evaluated at 1, 2, and 4 weeks post-meniscectomy by immunohistochemistry to locate monocytes and macrophages (stained positive for CD68 and CD163), and myofibroblasts (stained positive for αSMA). Of the total number of cells, 13% were CD68⁺ at 1 week post-meniscectomy, which decreased to 1% by 4 weeks post-meniscectomy; of these, almost half of CD68⁺ cells (49.4%: 98.8% as PBCs) were green fluorescent protein (GFP)-positive post-meniscectomy (1, 2, and 4 weeks), indicating that the majority of CD68⁺ cells were derived from PBCs. Of the total cells, 6% were CD163⁺ at 1 week post-meniscectomy, which decreased to 1% by week 4. Of the CD163⁺ cells, the majority were GFP-positive (42.5%: 85.0% as PBCs) after 1 week; however, this decreased significantly over time, which indicates that the majority of CD163⁺ cells are derived from PBCs during the early phase of meniscal reparative change, but are derived from resident cells at later time points. Of the total cells, 38% were αSMA⁺ at 1 week post-meniscectomy, which decreased to 3% by 4 weeks. The proportion of GFP-positive αSMA⁺ cells was 2.8% after 1 week, with no significant change over time, which indicates that the majority of αSMA⁺ cells originated from resident cells. Here, we describe the origin and distribution of macrophages and myofibroblasts during meniscal reparative change.

Cell Size Critically Determines Initial Retention of Bone Marrow Mononuclear Cells in the Heart after Intracoronary Injection: Evidence from a Rat Model

Intracoronary injection of bone marrow mononuclear cells (BMMNC) is an emerging treatment for heart failure. Initial donor cell retention in the heart is the key to the success of this approach, but this process remains insufficiently characterized. Although it is assumed that cell size of injected cells may influence their initial retention, no scientific evidence has been reported. We developed a unique model utilizing an ex-vivo rat heart perfusion system, enabling quantitative assessment of retention of donor cells after intracoronary injection. The initial (5 minutes after intracoronary injection) retention rate of BMMNC was as low as approximately 20% irrespective of donor cell doses injected (1×10⁶, 8×10⁶, 4×10⁷). Quantitative cell-size assessment revealed a positive relationship between the size of BMMNC and retention ratio; larger subpopulations of BMMNC were more preferentially retained compared to smaller ones. Furthermore, a larger cell type—bone marrow-derived mesenchymal stromal cells (median size = 11.5μm versus 7.0μm for BMMNC)—had a markedly increased retention rate (77.5±1.8%). A positive relationship between the cell size and retention ratio was also seen in mesenchymal stromal cells. Flow-cytometric studies showed expression of cell-surface proteins, including integrins and selectin-ligands, was unchanged between pre-injection BMMNC and those exited from the heart, suggesting that biochemical interaction between donor cells and host coronary endothelium is not critical for BMMNC retention. Histological analyses showed that retained BMMNC and mesenchymal stromal cells were entrapped in the coronary vasculature and did not extravasate by 60 minutes after transplantation. Whilst BMMNC did not change coronary flow after intracoronary injection, mesenchymal stromal cells reduced it, suggesting coronary embolism, which was supported by the histological finding of intravascular cell-clump formation. These data indicate that cell-size dependent, passive (mechanical), intravascular entrapment is responsible for the initial donor cell retention after intracoronary injection of BMMNC in the heart having normal vasculatures (at least).

Allogeneic Mesenchymal Stromal Cells Transplanted Onto the Heart Surface Achieve Therapeutic Myocardial Repair Despite Immunologic Responses in Rats

Background

Transplantation of allogeneic mesenchymal stromal cells (MSCs) is a promising treatment for heart failure. We have shown that epicardial placement of cell sheets markedly increases donor cell survival and augments therapeutic effects compared with the current methods. Although immune rejection of intramyocardially injected allogeneic MSCs have been suggested, allogeneic MSCs transplanted on the heart surface (virtual space) may undergo different courses. This study aimed to elucidate immunologic response against epicardially placed allogeneic MSCs, rejection or acceptance of these cells, and their therapeutic effects for heart failure.

Methods and Results

At 4 weeks after coronary artery ligation, Lewis rats underwent epicardial placement of MSC sheets from syngeneic Lewis or allogeneic Fischer 344 rats or sham treatment. At days 3 and 10 after treatment, similar ratios (≈50% and 30%, respectively) of grafted MSCs survived on the heart surface in both MSC sheet groups. By day 28, survival of syngeneic MSCs was substantially reduced (8.9%); survival of allogeneic MSCs was more extensively reduced (0.2%), suggesting allorejection. Correspondingly, allogeneic MSCs were found to have evoked an immunologic response, albeit low level, as characterized by accumulation of CD4⁺ T cells and upregulation of interleukin 6. Despite this alloimmune response, the allogeneic MSC sheet achieved myocardial upregulation of reparative factors, enhanced repair of the failing myocardium, and improved cardiac function to the equivalent degree observed for the syngeneic MSC sheet.

Conclusions

Allogeneic MSCs placed on the heart surface evoked an immunologic response; however, this allowed sufficient early phase donor cell survival to induce equivalent therapeutic benefits to syngeneic MSCs. Further development of this approach toward clinical application is warranted.

Novel cardioprotective strategy combining three different preconditioning methods to prevent ischemia/reperfusion injury in aged hearts in an improved rabbit model

The use of ischemic preconditioning (IPC) to protect the myocardium is usually not effective in elderly patients. The aim of the present study was to design new methods to achieve enhanced myocardial protection, based on the differential role of endogenous adenosine (ADO) and ADO receptors (ARs) in the effects of IPC on young and old animals. An improved New Zealand white rabbit model of ischemia/reperfusion was established based on the Langendorff model. Adult or elderly rabbit hearts, with or without exposure to IPC, were used in order to assess the roles of ADO and ARs in the different effects of IPC. Different protective methods were designed based on a combination of endogenous and exogenous interventions. Cardiac function, as well as biochemical, histopathological and apoptotic indices, were measured in the different intervention groups. The improved Langendorff model was stable, reliable and suitable for the undertaking of the experiments. The ADO levels in the aged rabbit hearts pre- and post-IPC were lower than those in the adult hearts, indicating that ADO levels may be an endogenous factor influencing IPC. A new protection strategy combining ADO-enhanced IPC, A₁AR agonist 2-chloro-N(6)-cyclopentyladenosine preconditioning and cold crystalloid cardioplegia had a significant protective effect in aged hearts. The results of the present study suggested that endogenous ADO enhancement, A₁AR agonist preconditioning and exogenous treatment yield an additive effect in aged rabbit hearts. The simultaneous application of these three types of intervention provided the most effective myocardial protection in the improved aged rabbit heart model.

Epicardial placement of mesenchymal stromal cell-sheets for the treatment of ischemic cardiomyopathy; in vivo proof-of-concept study

Transplantation of bone marrow mesenchymal stromal cells (MSCs) is an emerging treatment for heart failure. We have reported that epicardial placement of MSC-sheets generated using temperature-responsive dishes markedly increases donor MSC survival and augments therapeutic effects in an acute myocardial infarction (MI) model, compared to intramyocardial (IM) injection. This study aims to expand this knowledge for the treatment of ischemic cardiomyopathy, which is likely to be more difficult to treat due to mature fibrosis and chronically stressed myocardium. Four weeks after MI, rats underwent either epicardial MSC-sheet placement, IM MSC injection, or sham treatment. At day 28 after treatment, the cell-sheet group showed augmented cardiac function improvement, which was associated with over 11-fold increased donor cell survival at both days 3 and 28 compared to IM injection. Moreover, the cell-sheet group showed improved myocardial repair, in conjunction with amplified upregulation of a group of reparative factors. Furthermore, by comparing with our own previous data, this study highlighted similar dynamics and behavior of epicardially placed MSCs in acute and chronic stages after MI, while the acute-phase myocardium may be more responsive to the stimuli from donor MSCs. These proof-of-concept data encourage further development of the MSC-sheet therapy for ischemic cardiomyopathy toward clinical application.