Endothelial cells and hematopoiesis: a light microscopic study of fetal, normal, and pathologic human bone marrow in plastic-embedded sections

Bone marrow evaluation for pediatric patients

Due to the immaturity of the hematopoietic system at birth and different oxygenation and immune response needs of the growing organism, the bone marrow composition at birth and early infancy differs as compared to older children and adults. These age-related differences, while generally recognized, are not well known to the world of hematopathology. The purpose of this article is to address the current limitation of the literature by reviewing the bone marrow ontology, its composition at birth, and the changes occurring during early infancy, and to compare these findings to adults. The review also provides a useful framework for bone marrow examination in children.

Radionuclide therapy with bone-seeking compounds: Monte Carlo calculations of dose-volume histograms for bone marrow in trabecular bone

The purpose of the present work was to investigate how haematopoietic stem cell survival is affected by the differences in the dose distribution that arise from different radionuclides contained in bone-seeking radiopharmaceuticals. This was carried out in three steps: (a) calculations of representative dose distributions in individual bone marrow cavities that are irradiated by sources of 89Sr, 186Re, 117mSn or 153Sm, uniformly distributed on the bone surfaces; (b) assessment of the corresponding haematopoietic stem cell survival and (c) a comparison of these results with results obtained using the assumption of a uniform dose distribution. Two different idealized models of the geometry of trabecular bone were formulated, each consisting of an infinite array of identical elements. Monte Carlo simulations were used to generate dose-volume histograms that were used to assess haematopoietic stem cell survival with two different assumptions about spatial cell distributions. Compared with a homogeneous dose distribution, the estimated cell survival was markedly higher for 117mSn and 153Sm, and only slightly different for 89Sr and 186Re. The quantitative results differed between the two geometric models and the assumptions about spatial cell distribution, but the trends were the same. The results imply that it is necessary to include dose distributions for individual bone marrow cavities in considerations concerning bone marrow toxicity.

Tubedown-1, a novel acetyltransferase associated with blood vessel development

We have used an embryonic endothelial cell line (IEM cells) as an experimental system for identifying and characterizing new molecules which are regulated during blood vessel development. A novel gene isolated from IEM cells, tubedown-1 (tbdn-1), is expressed at high levels in unstimulated IEM cells and is downregulated during formation of capillary tube structures by the IEM cells induced by basic fibroblast growth factor (bFGF) and leukemia inhibitory factor (LIF) in vitro. Tbdn-1 is also downregulated in M1 myeloid leukemia cells after differentiation in response to LIF in vitro. Tbdn-1 is homologous to the yeast NAT-1 N-terminal acetyltransferases and encodes a novel protein of approximately 69 kDa associated with an acetyltransferase activity. Levels and distribution of tbdn-1 expression are regulated in both endothelial and hematopoietic cells during development in tissues such as the yolk sac blood islands, heart, and liver blood vessels. In the adult, tbdn-1 expression is low or undetected in most organs examined with the exception of the atrial endocardium, the endothelial and myeloid compartments of bone marrow, and the remodeling vascular bed of atretic ovarian follicles. The distribution and regulation of expression of tbdn-1 suggest that this novel acetyltransferase may be involved in regulating vascular and hematopoietic development and physiologic angiogenesis.

Monoclonal antibody against adult marrow-derived mesenchymal stem cells recognizes developing vasculature in embryonic human skin

We have described previously a monoclonal antibody (SH2) that specifically recognizes undifferentiated mesenchymal progenitor cells isolated from adult human bone marrow. These cells, which we operationally refer to as mesenchymal stem cells, have the capacity to differentiate and form distinct mesenchymal tissues such as bone and cartilage when the isolated cells are placed in the appropriate in vivo or in vitro environment. We report here the partial biochemical characterization of the antigen recognized by the SH2 antibody. Metabolically radiolabelled adult marrow-derived mesenchymal stem cells in culture were extracted and immunoprecipitated with the SH2 antibody. The purified antigen migrated as a single band of 90 kDa after sodium dodecyl sulfate polyacrylamide gel electrophoresis was performed under reducing conditions. The SH2-immunoprecipitated protein exhibited a molecular weight band shift after removal of N-linked oligosaccharides. We investigated the expression of the SH2 antigen, along with the endothelial markers factor VIII-related antigen and Ulex europaeus I (UEA-I) lectin during specific developmental periods in human dermal embryogenesis and in the postnatal period through aged adults. Frozen sections of human embryonic, fetal, or postnatal skin ranging from 8 weeks estimated gestational age (EGA) through 84 years of age were immunostained or double immunolabelled with antibodies SH2, UEA-I, or factor VIII-related antigen followed by second antibodies with fluorescent markers. Positive cell surface reactivity with the SH2 antibody was seen in cells in the vascular plane in the earliest specimens (day 55 EGA) corresponding to the late cellular dermis period. During the period of the cellular to fibrous transition, in which the initiation of appendage development occurs, most SH2-reactive cells colocalized with vasculature markers UEA-I and factor VIII-related antigen, although there was a subset of cells recognized by SH2 antibody that did not colocalize with the endothelial markers. In contrast to the endothelial markers UEA-I and factor VIII-related antigen, in which the number of immunopositive cells became more prominent with age and maturation of the dermis, the frequency of cells that contained the SH2-reactive antigen diminished with age. The SH2 reactivity evident in embryonic, fetal, and early postnatal periods was not observed in human skin specimens taken from adults greater than 30 years old. These observations support the hypothesis that the SH2 antigen is a cell surface marker of developing microvasculature and may play a role in dermal embryogenesis and angiogenesis.

Reticulo-endothelial stroma of the head-kidney from the seawater teleost gilthead seabream (Sparus aurata L.): an ultrastructural and cytochemical study

BACKGROUND

Head-kidney, considered the major fish lympho-haemopoietic tissue, consists of cells of the different haemopoietic series supported by a network of stromal cells whose morphofunctional properties have not been established. We report the ultrastructure and cytochemical features of the reticulo-endothelial stroma of the head-kidney from the seawater teleost gilthead seabream (Sparus aurata L.).

METHODS

Samples of head-kidney were processed for electron microscopic study. Some of the samples were incubated for acid and alkaline phosphatase, peroxidase, glucose-6-phosphatase, or ATPase.

RESULTS

The reticulo-endothelial stroma of gilthead seabream head-kidney consists of sinusoidal cells (endothelial and adventitial cells) and reticular cells (macrophage-type reticulum and fibroblast-like reticular cells). Transcytosis vesicles and rounded medium electron-dense granules were observed in the cytoplasm of the endothelial cells. The adventitial cells partially covered the outside surface of the endothelial cells and were joined by desmosomes. The macrophage-type reticulum cells were characterized by their cytoplasmic processes and acid phosphatase positive lysosomes. The fibroblast-like reticular cells were joined by desmosomes and formed an extensive network between the haemopoietic parenchyma. They were peroxidase negative and acid and alkaline phosphatase, glucose-6-phosphatase, beta-glucuronidase, and ATPase positive.

CONCLUSIONS

The ultrastructural and cytochemical features of the reticulo-endothelial stroma of the gilthead seabream head-kidney are similar to those of mammalian bone marrow, suggesting phylogenetic analogies between both tissues.

Role of vascular endothelial cells in bone biology

Bone development and remodeling depend on complex interactions between bone-forming osteoblasts, bone-degrading osteoclasts, and other cells present within the bone microenvironment. Balanced control of bone formative and degradative processes is normally carefully maintained in the adult skeleton but becomes uncoupled in the course of aging or in various pathological disease states. Systemic regulators of bone metabolism and local mediators, including matrix molecules, cytokines, prostaglandins, leukotrienes, and other autocrine or paracrine factors, regulate the recruitment, differentiation, and function of cells participating in bone formation and turnover. Although some of these interactions are now understood, many yet remain to be elucidated. Recent studies have begun exploring in detail how vascular endothelial cells and their products function in bone physiology. The findings are revealing that bone vascular endothelial cells may be members of a complex communication network in bone which operates between endothelial cells, osteoblasts, osteoclasts, macrophages, stromal cells, and perhaps other cell types found in bone as well. Therefore, multiple systemic and locally produced signals may be received, transduced, and integrated by individual cells and then propagated by the release from these cells of further signals targeted to other members of the bone cell network. In this manner, bone cell activities may be continuously coordinated to afford concerted actions and rapid responses to physiological changes. The bone microvasculature may play a pivotal role in these processes, both in linking circulatory and local signals with cells of the bone microenvironment and in actively contributing itself to the regulation of bone cell physiology.(ABSTRACT TRUNCATED AT 250 WORDS)