Where new approaches can stem from: Focus on stem cell identification

Of Cytometry, Stem Cells and Fountain of Youth

Outlined are advances of cytometry applications to identify and sort stem cells, of laser scanning cytometry and ImageStream imaging instrumentation to further analyze morphometry of these cells, and of mass cytometry to classify a multitude of cellular markers in large cell populations. Reviewed are different types of stem cells, including potential candidates for cancer stem cells, with respect to their "stemness", and other characteristics. Appraised is further progress in identification and isolation of the "very small embryonic-like stem cells" (VSELs) and their autogenous transplantation for tissue repair and geroprotection. Also assessed is a function of hyaluronic acid, the major stem cells niche component, as a guardian and controller of stem cells. Briefly appraised are recent advances and challenges in the application of stem cells in regenerative medicine and oncology and their future role in different disciplines of medicine, including geriatrics.

The hematopoietic stem cell niche--home for friend and foe?

The hematopoietic stem cell (HSC) niche is involved in the maintainance and regulation of quiescence, self-renewal and differentiation of hematopoietic stem cells and the fate of their progeny in mammals dealing with the daily stresses to the hematopoietic system. From the discovery that perturbations of the HSC niche can lead to hematopoietic disorders, we have now arrived at the prospect that the HSC niche may play a role in hematological malignancies and that this HSC niche may be a target for therapy. This review attempts to capture the discoveries of the last few years regarding the normal and malignant hematopoietic stem cell niche and possible ways to target this niche.

Neural differentiation of rat aorta pericyte cells

Pericyte perivascular cells, believed to originate mesenchymal stem cells (MSC), are characterized by their capability to differentiate into various phenotypes and participate in tissue reconstruction of different organs, including the brain. We show that these cells can be induced to differentiation into neural-like phenotypes. For these studies, pericytes were obtained from aorta ex-plants of Sprague-Dawley rats and differentiated into neural cells following induction with trans retinoic acid (RA) in serum-free defined media or differentiation media containing nerve growth and brain-derived neuronal factor, B27, N2, and IBMX. When induced to differentiation with RA, cells express the pluripotency marker protein stage-specific embryonic antigen-1, neural-specific proteins β3-tubulin, neurofilament-200, and glial fibrillary acidic protein, suggesting that pericytes undergo differentiation, similar to that of neuroectodermal cells. Differentiated cells respond with intracellular calcium transients to membrane depolarization by KCl indicating the presence of voltage-gated ion channels and express functional N-methyl-D-aspartate receptors, characteristic for functional neurons. The study of neural differentiation of pericytes contributes to the understanding of induction of neuroectodermal differentiation as well as providing a new possible stem-cell source for cell regeneration therapy in the brain.

Endothelial progenitor cells and exercise-induced redox regulation

Endothelial progenitor cells (EPCs) are thought to participate in endothelial cell regeneration and neovascularization in either a direct or an indirect way. The number of circulating EPCs is influenced by many factors like disease status, medication, age, and fitness level and is an independent predictor of disease progression and cardiovascular events. Experimental as well as clinical studies during the last 10 years clearly demonstrated that physical exercise training has a beneficial effect on endothelial function, which is a clear predictive value for cardiovascular mortality. Over the last years mainly clinical studies provided solid evidence for an exercise training induced mobilization of EPCs from the bone marrow, thereby possibly influencing the regeneration of the endothelial cell layer. This review will discuss the mechanisms how exercise induces mobilization of EPCs from the bone marrow with a focus on the influence on the redox balance.

Introduction A: recent advances in cytometry instrumentation, probes, and methods--review

Cytometric techniques are continually being improved, refined, and adapted to new applications. This chapter briefly outlines recent advances in the field of cytometry with the main focus on new instrumentations in flow and image cytometry as well as new probes suitable for multiparametric analyses. There is a remarkable trend for miniaturizing cytometers, developing label-free and fluorescence-free analytical approaches, and designing "intelligent" probes. Furthermore, new methods for analyzing complex data for extracting relevant information are reviewed.

Simultaneous characterization of progenitor cell compartments in adult human liver

The human liver is a complex tissue consisting of epithelial, endothelial, hematopoietic, and mesenchymal elements that probably derive from multiple lineage-committed progenitors, but no comprehensive study aimed at identifying and characterizing intrahepatic precursors has yet been published. Cell suspensions for this study were obtained by enzymatic digestion of liver specimens taken from 20 patients with chronic liver disease and 13 multiorgan donors. Stem and progenitor cells were first isolated, amplified, and characterized ex vivo according to previously validated methods, and then optimized flow cytometry was used to assess their relative frequencies and characterize their immunophenotypes in the clinical specimens. Stem and progenitor cells committed to hematopoietic, endothelial, epithelial, and mesenchymal lineages were clearly identifiable in livers from both healthy and diseased subjects. Within the mononuclear liver cell compartment, epithelial progenitors [epithelial cell adhesion molecule (EpCAM)(+)/CD49f(+)/CD29(+)/CD45(-)] accounted for 2.7-3.5% whereas hematopoietic (CD34(+)/CD45(+)), endothelial [vascular endothelial growth factor-2 (KDR)(+)/CD146(+)/CD45(-)], and mesenchymal [CD73(+)/CD105(+)/CD90 (Thy-1)(+)/CD45 (-)] stem cells and progenitors accounted for smaller fractions (0.02-0.6%). The patients' livers had higher percentages of hematopoietic and endothelial precursors than those of the donors. In conclusion, we identified and characterized precursors committed to four different lineages in adult human liver. We also optimized a flow cytometry approach that will be useful in exploring the contribution of these cells to the pathogenesis of liver disease.

Phenotypes of stem cells from diverse origin

Stem cells have turned into promising tools for studying the mechanisms of development, regeneration, and for cell therapy of various disorders. Stem cells are found in the embryo and in most adult tissues participating in endogenous tissue regeneration. They are capable of autorenovation, often maintain their multipotency of differentiation into various tissues of their germ line and are, therefore, ideal candidates for cellular therapy taken that they can be unequivocally identified and isolated. In this review, we report stem cell marker expression used for identification of various stem cell lineages, including very small embryonic stem cells, neural, hematopoietic, mesenchymal, epithelial and limbal epithelial stem cells, endothelial progenitor cells, supra-adventitial adipose stromal cells, adipose pericytes, and cancer stem cells. These cells usually cannot be distinguished by a single stem cell marker, because their expression partially overlaps between lineages. Recent advances in flow cytometry allowing the simultaneous detection of various markers have facilitated stem cell identification for clinical diagnosis and research. So far experimental evidence suggests the existence of cells with different properties, i.e., the capability to different in various cell types. Several studies indicate that expression of classical markers for stem cell classification, such as CD34, CD45, and CD133, may differ between the virtually same stem and progenitor cells, i.e., endothelial progenitor or mesenchymal stem cells, when they were obtained from different tissues. This finding raises questions whether phenotypic differences are due to the source or if it is only caused by different isolation and experimental conditions.

Recognition of biomarkers and cell-specific molecular signatures: aptamers as capture agents

RNA and DNA aptamers developed by systematic evolution of ligands by exponential enrichment (SELEX) have turned into important tools in diagnostics, research, and therapeutics. Unlike antibodies, high-affinity and specific aptamers identified through an in vitro selection process can be chemically modified to gain nuclease resistances in biological fluids and to extend their bioavailability in animals. Aptamers can be raised against virtually any target including those which are toxic or do not elicit any immune response in animals. They can be developed in automated processes against various protein targets and then easily modified by attaching fluorescence reporters, nanoparticles or biotin moieties, rival antibodies in high-throughput proteomics and cell separations. In this review, we will discuss the high competence of aptamers in recognizing biomarkers and molecular signatures of cell surfaces, and how these unique features can be exploited for the identification and isolation of cancer, stem cells and even detection of parasite-infected cells.