Tissue distribution of endothelial cells in vivo following intravenous injection

Stem Cells in Regenerative Cardiology

The common prevalence of heart failure and limitations in its treatment are leading cause of attention and interest towards the induction of cardiac regeneration with novel approaches. Recent studies provide growing evidence regarding bona fide cardiac regeneration post genetic manipulations, administration of stimulatory factors and myocardial injuries in animal models and human studies. To this end, stem cells of different sources have been tested to treat heart failure for the development of cellular therapies. Endogenous and exogenous stem cells sources used in regenerative cardiology have provided a proof of concept and applicability of cellular therapies in myocardial improvement. Recent clinical studies, especially, based on the endogenous cardiac progenitor and stem cells highlighted the possibility to regenerate lost cardiomyocytes in the myocardium. This review discusses emerging concepts in cardiac stem cell therapy, their sources and route of administration, and plausibility of de novo cardiomyocyte formation.

Placental growth factor expression is required for bone marrow endothelial cell support of primitive murine hematopoietic cells

Two distinct microenvironmental niches that regulate hematopoietic stem/progenitor cell physiology in the adult bone marrow have been proposed; the endosteal and the vascular niche. While extensive studies have been performed relating to molecular interactions in the endosteal niche, the mechanisms that regulate hematopoietic stem/progenitor cell interaction with bone marrow endothelial cells are less well defined. Here we demonstrate that endothelial cells derived from the bone marrow supported hematopoietic stem/progenitor cells to a higher degree than other endothelial or stromal cell populations. This support was dependant upon placental growth factor expression, as genetic knockdown of mRNA levels reduced the ability of endothelial cells to support hematopoietic stem/progenitor cells in vitro. Furthermore, using an in vivo model of recovery from radiation induced myelosuppression, we demonstrate that bone marrow endothelial cells were able to augment the recovery of the hematopoietic stem/progenitor cells. However, this effect was diminished when the same cells with reduced placental growth factor expression were administered, possibly owing to a reduced homing of the cells to the bone marrow vasculature. Our data suggest that placental growth factor elaborated from bone marrow endothelial cells mediates the regulatory effects of the vascular niche on hematopoietic stem/progenitor cell physiology.

Real-time PCR to determine transgene copy number and to quantitate the biolocalization of adoptively transferred cells from EGFP-transgenic mice

Quantitative real-time PCR (qPCR) is a sensitive technique for the detection and quantitation of specific DNA sequences. Here we describe a Taqman qPCR assay for quantification of tissue-localized, adoptively transferred enhanced green fluorescent protein (EGFP)-transgenic cells. A standard curve constructed from serial dilutions of a plasmid containing the EGFP transgene was (i) highly reproducible, (ii) detected as few as two copies, and (iii) was included in each qPCR assay. qPCR analysis of genomic DNA was used to determine transgene copy number in several mouse strains. Fluorescent microscopy of tissue sections showed that adoptively transferred vascular endothelial cells (VEC) from EGFP-transgenic mice specifically localized to tissue with metastatic tumors in syngeneic recipients. VEC microscopic enumeration of liver metastases strongly correlated with qPCR analysis of identical sections (Pearson correlation 0.81). EGFP was undetectable in tissue from control mice by qPCR. In another study using intra-tumor EGFP-VEC delivery to subcutaneous tumors, manual cell count and qPCR analysis of alternating sections also strongly correlated (Pearson correlation 0.82). Confocal microscopy of the subcutaneous tumor sections determined that visual fluorescent signals were frequently tissue artifacts. This qPCR methodology offers specific, objective, and rapid quantitation, uncomplicated by tissue autofluorescence, and should be readily transferable to other in vivo models to quantitate the biolocalization of transplanted cells.

Preliminary Survival Studies on Autologous Cultured Skin Fibroblasts Transplantation by Injection

In the correction of aesthetic impairments on the face, dermal, and superficial subcutaneous defects, adequately safe implant material is required. Cultured autologous skin fibroblasts, as a protein repair system, create a living injectable system that has been utilized effectively to treat rhytids, depressed scars, subcutaneous atrophy, acne irregularities, and laser wounds. To evaluate the new method, we have investigated the survival and collagen secretion of autologous transplanted fibroblasts. In this study, rabbit fibroblasts were cultured and expanded. Cells (8 × 107/ml) were injected into the superficial and deep dermal junction of the dorsal ears. Two rabbits were injected independently with labeled [3H]TdR fibroblasts; similarly, eight rabbits were given unlabeled transplanted cells in the right ear and vehicle in the left. Each site was injected three times with the same amount of cells every 2 weeks. The grafts were evaluated for 5 months. After explantation, the samples were collected from the injected sites and stained with autoradiography, H&E, and sirius red, respectively. According to the histological observations, the [3H]TdR-labeled cells survived and large amounts of embryo fibroblasts were found in the experimental subgroup of the labeled cell group. The depth of dermis was significantly different between the experimental subgroup (701.3 ± 31.5 μm) and the control subgroup (638.3 ± 23.9 μm) of the unlabeled group (p < 0.01). There was also a significant difference of collagen III between the experimental subgroup (2.63 ± 1.41 cm2) and the control subgroup (1.05 ± 0.90 cm2) (p < 0.05). There was no significant difference of collagen I between the experimental subgroup (56.25 ± 14.41 cm2) and the control subgroup (55.41 ± 16.59 cm2) (p > 0.05). The results obtained demonstrate that the distinction of the depth of dermis should be interpreted by the increase of collagen III, instead of collagen I, which is produced by the transplanted fibroblasts. The investigation indicated that transplanted autologous skin fibroblasts could provide a potential and effective approach to treat minor facial tissue deficiencies.

Involvement of marrow-derived endothelial cells in vascularization

Until recently, the adult neovasculature was thought to arise only through angiogenesis, the mechanism by which new blood vessels form from preexisting vessels through endothelial cell migration and proliferation. However, recent studies have provided evidence that postnatal neovasculature can also arise though vasculogenesis, a process by which endothelial progenitor cells are recruited and differentiate into mature endothelial cells to form new blood vessels. Evidence for the existence of endothelial progenitors has come from studies demonstrating the ability of bone marrow-derived cells to incorporate into adult vasculature. However, the exact nature of endothelial progenitor cells remains controversial. Because of the lack of definitive markers of endothelial progenitors, the in vivo contribution of progenitor cells to physiological and pathological neovascularization remains unclear. Early studies reported that endothelial progenitor cells actively integrate into the adult vasculature and are critical in the development of many types of vascular-dependent disorders such as neoplastic progression. Moreover, it has been suggested that endothelial progenitor cells can be used as a therapeutic strategy aimed at promoting vascular growth in a variety of ischemic diseases. However, increasing numbers of studies have reported no clear contribution of endothelial progenitors in physiological or pathological angiogenesis. In this chapter, we discuss the origin of the endothelial progenitor cell in the embryo and adult, and we discuss the cell's link to the primitive hematopoietic stem cell. We also review the potential significance of endothelial progenitor cells in the formation of a postnatal vascular network and discuss the factors that may account for the current lack of consensus of the scientific community on this important issue.