Impaired mobilization of hematopoietic stem/progenitor cells in C5-deficient mice supports the pivotal involvement of innate immunity in this process and reveals novel promobilization effects of granulocytes.

We reported that complement cascade (CC) becomes activated in bone marrow (BM) during granulocyte colony-stimulating factor (G-CSF) mobilization of hematopoietic stem/progenitor cells (HSPCs) and showed that, although third CC component (C3)-deficient mice are easy mobilizers, fifth CC component (C5)-deficient mice mobilize very poorly. To explain this, we postulated that activation/cleavage of CC releases C3a and C5a anaphylatoxins that differently regulate mobilization. Accordingly, C3a, by enhancing responsiveness of HSPCs to decreasing concentrations of stromal-derived growth factor-1 (SDF-1) in BM, prevents mobilization and promotes their BM retention. Therefore, in this study, we focused on the mobilization-enhancing role of C5a. We found that C5a receptor (C5aR) is not expressed on the surface of HSPCs, and that C5a-mediated promobilization effects are mediated by stimulation of granulocytes. Overall, our data support the following model. First C5aR(+) granulocytes are chemoattracted by plasma C5 cleavage fragments, being the first wave of cells leaving BM. This facilitates a subsequent egress of HSPCs. In the next step, after leaving BM, granulocytes undergo degranulation in response to plasma C5a and secrete some cationic peptides (cathelicidin, beta-defensin) that, as shown here for the first time, highly enhance the responsiveness of HSPCs to plasma SDF-1 gradient. In conclusion, our data reveal the underappreciated central role of innate immunity in mobilization, in which C5 cleavage fragments through granulocytes orchestrate this process.

Novel epigenetic mechanisms that control pluripotency and quiescence of adult bone marrow-derived Oct4(+) very small embryonic-like stem cells.

Recently, we identified in adult tissues a population of Oct4(+)SSEA-1(+)Sca-1(+)lin(-)CD45(-) very small embryonic-like stem cells (VSELs). First, to address recent controversies on Oct4 expression in cells isolated from adult organs, we show here evidence that Oct4 promoter in bone marrow (BM)-derived VSELs has an open chromatin structure and is actively transcribed. Next, to explain VSELs quiescence and lack of teratoma formation, we demonstrate a unique DNA methylation pattern at some developmentally crucial imprinted genes, showing hypomethylation/erasure of imprints in paternally methylated and hypermethylation of imprints in maternally methylated ones. These epigenetic characteristics leading to upregulation in VSELs of H19 and p57(KIP2) (also known as Cdkn1c) and repression of Igf2 and Rasgrf1 explain VSEL's quiescent status. Interestingly, this unique pattern in imprinted gene methylation is reverted in cocultures with a C2C12 supportive cell-line when VSELs are induced to form VSEL-derived spheres (VSEL-DSs) enriched for stem cells able to differentiate into all three germ layers. Therefore, we suggest that the proliferative/developmental potential of Oct4(+) VSELs is epigenetically regulated by expression of Oct4 and some imprinted genes, and postulate that restoring the proper methylation pattern of imprinted genes will be a crucial step for using these cells in regenerative medicine.

Bone marrow-derived mesenchymal stems cells and cardiac repair.

UNLABELLED: Cardiovascular disease continues to be the most prevalent cause of morbidity and mortality worldwide. While pharmaceutical agents and interventional strategies have contributed greatly to therapy, new and superior treatment modalities are urgently needed given the overall disease burden. In this regard, therapy with adult stem cells has shown great promise toward inducing infarct repair and restoring cardiac function. Because of their inherent multipotent nature and the ability to secrete a multitude of growth factors and cytokines, adult bone marrow-derived mesenchymal stem cells (BMMSCs) have been utilized for cardiac repair with encouraging RESULTS: Numerous animal studies have established the feasibility and efficacy of this approach with further definition of molecular pathways underlying the reparative benefits. Early clinical trials have also confirmed the safety and efficacy of BMMSC therapy in patients with acute MI as well as ischemic heart failure. Following a brief historical perspective and description of the biological features of BMMSCs, this review will focus on the evidence from preclinical and clinical studies of cardiac repair with BMMSCs, the underlying mechanisms, and various cellular modification strategies aimed at enhancing the outcomes.

Very small embryonic-like stem cells in adult tissues-potential implications for aging.

Recently our group identified in murine bone marrow (BM) and human cord blood (CB), a rare population of very small embryonic-like (VSEL) stem cells. We hypothesize that these cells are deposited during embryonic development in BM as a mobile pool of circulating pluripotent stem cells (PSC) that play a pivotal role in postnatal tissue turnover both of non-hematopoietic and hematopoietic tissues. During in vitro co-cultures with murine myoblastic C2C12 cells, VSELs form spheres that contain primitive stem cells. Cells isolated from these spheres may give rise to cells from all three germ layers when plated in tissue specific media. The number of murine VSELs and their ability to form spheres decreases with the age and is reduced in short-living murine strains. Thus, developmental deposition of VSELs in adult tissues may potentially play an underappreciated role in regulating the rejuvenation of senescent organs. We envision that the regenerative potential of these cells could be harnessed to decelerate aging processes.

Cardiac stem cell therapy for myocardial regeneration. A clinical perspective.

Myocardial infarction and other pathologic conditions of the heart result in loss of cardiomyocytes, scar formation, ventricular remodeling, and eventually heart failure. Since pharmacologic and interventional strategies fail to regenerate dead myocardium, heart failure continues to be a major health problem worldwide. Recent studies in animal models of myocardial infarction and heart failure have demonstrated that various subsets of adult primitive cells can regenerate functional cardiomyocytes and cardiac vasculature with improvement in cardiac structure and function. Small clinical trials of cell therapy in patients with myocardial infarction and ischemic cardiomyopathy have recapitulated these beneficial effects in humans with infarct size reduction and improvement in ejection fraction, myocardial perfusion, and wall motion. Several phenotypically distinct cell populations have been utilized for cardiac regeneration, and the relative merits of one cell over another remain to be determined. The recent discovery of adult cardiac stem cells has sparked intense hope for myocardial regeneration with cells that are from the heart itself and are thereby inherently programmed to reconstitute cardiac tissue. The purpose of this review is to summarize the evidence regarding the feasibility of cardiac repair in humans via adult stem/progenitor cells, and to discuss the potential utility of cardiac stem cells for therapeutic myocardial regeneration.