Analysis of the mitogenic effect of fetuin preparations on arterial smooth muscle cells: the role of contaminant platelet-derived growth factor

Fetuin, a major protein of fetal calf serum, partially purified by the method of Pedersen, stimulated growth of aortic smooth muscle cells. More highly purified fetuin preparations stimulated growth less than Pedersen fetuin, as previously described for other cell types, suggesting that this activity is due to a contaminant. Recently bovine alpha 2-macroglobulin or "Embryonin" has been proposed as the mitogenic component of crude fetuin preparations. We found that active fetuin preparations did contain alpha 2-macroglobulin that stimulated smooth muscle cell growth. However, alpha 2-macroglobulin purified directly from platelet-poor bovine plasma or fetuin purified from Pedersen fetuin by gel filtration lacked appreciable mitogenic effect on smooth muscle cells. Since alpha 2-macroglobulin can bind platelet-derived growth factor (PDGF), and since highly acidic fetuin might bind the very basic PDGF molecule non-specifically, we measured the PDGF content of various fetuin preparations and found a good correlation between the PDGF content and mitogenic activity. Gel filtration experiments demonstrated that in Pedersen fetuin PDGF occurred both free, and in association with alpha 2-macroglobulin. We conclude that the principal mitogenic component for smooth muscle cells in crude fetuin preparations is PDGF, since purified bovine alpha 2-macroglobulin or fetuin do not appreciably affect growth of these cells. These results help to resolve a long-standing controversy regarding the nutrition of cultured cells. In addition, we suggest that before alpha 2-macroglobulin or "Embryonin" is accepted as a bona fide growth factor for a given cell type, the role of contamination with PDGF should be assessed.     

Shifts in macrophyte species composition as a result of eutrophication and pollution in Dutch transboundary streams over the past decades

The catchment areas of transboundary streams in the Netherlands have been subject to increasing agricultural and industrial activities over the past decades. To evaluate the effects of these activities on the aquatic vegetation, a study has been carried out in 28 Dutch transboundary lowland streams. Recent data on distribution of 58 aquatic plant species and their growth forms were compared with historical data and were correlated with abiotic variables. Most of these streams lost species that are characteristic for streams and are sensitive to turbidity, eutrophication and pollution (e.g. Potamogeton alpinus, P. polygonifolius, P. densus, Ranunculus peltatus ssp. heterophyllus, Callitriche stagnalis and Myriophyllum alterniflorum.) Species, not common in streams but tolerant to turbidity, eutrophication or pollution (e.g. Potamogeton trichoides, Elodea nuttallii) appeared in many streams or increased in abundance. There was also a shift in growth forms: submerged species decreased or were replaced by emergent/floating-leaved species. Correspondence analysis was carried out to study the relation between the observed changes and the abiotic characteristic of the streams. The magnitude of the shift in species composition was positively correlated with the PO₄ ^3- concentration and pH (which was highly correlated with Cd²⁺) of the water. This leads to the hypothesis that increased input of sewage, agricultural and industrial water causes a change in species composition and main growth forms of aquatic plant species in lowland streams.     

Applications of proteomic methodologies to human pregnancy research: a growing gestation approaching delivery?

Maternal and perinatal morbidity and mortality rates are significantly higher in pregnancies complicated by preterm labor, pre-eclampsia and fetal growth restriction. Decades of research have not translated into a clear understanding of the underlying pathophysiologies or effective identification of women who are at high risk of developing these complications. Often the severity of these diseases does not correlate with the clinical symptoms, and current diagnostic methods are unable to accurately predict the conditions prior to clinical presentation. Though several potential markers have been proposed for each of these disorders, to date none have proven clinical utility. Emerging proteomic technology is only beginning to be employed in pregnancy research. A comprehensive analysis of gestational tissues can be expected to contribute to the elucidation of the complex molecular mechanisms of pregnancy and related complications. Comparison of the expression profiles of normal and pathogenic tissues and biofluids may also highlight novel candidate marker proteins that have so far remained undetected. More interestingly, rapidly evolving technologies using sophisticated bioinformatic tools are demonstrating their potential in disease diagnostics by using overall protein profiles to detect diseases. The clinical significance of these methodological advances is enormous. Early diagnosis together with improved understanding of underlying molecular mechanisms can enhance outcomes and increase effective management and therapeutic options.     

The role of osteocytes in bone regulation: mineral homeostasis versus mechanoreception

Early work on the role of osteocytes in bone regulation suggested that the primary function of these cells was osteolysis. This lytic function was not precisely defined but included mineral homeostasis and at least the initiation of matrix remodeling, if not a primary role in remodeling. This paper is an attempt to promote the concept of osteocytic osteolysis as a method of systemic mineral homeostasis and to separate it from bone remodeling. Although recent investigations have pointed to mechanotransduction as a primary function of osteocytes, resulting in a general abandonment of the osteocytic osteolysis concept, the corpus of evidence suggests that osteocytes likely have a multipurpose role in the biology of bone. The osteocyte network represents an enormous surface area over which the cells interface with the surrounding matrix, useful for both strain detection and matrix mineral access. Osteocytes have been found to possess receptors for PTH, a known regulator of mineral ion homeostasis. Cultured osteocytes placed on dentin slices demonstrated no capacity to pit the dentin, but they were not treated with a regulating factor such as PTH, nor does mineral homeostasis require substantial bone volume removal. Scaling relationships suggest that osteocyte density is inversely proportional to body mass, R(2) = 0.86, and thus directly proportional to metabolic rate. Thus, species with higher metabolic rates (and therefore a greater demand for immediate access to minerals) have more osteocytes per bone volume. Finally, osteocytes express molecules typically associated with nerve cells and which are involved with glutamate neurotransmission. By this system, almost instantaneous messages may be transmitted throughout the network, an important feature in cells whose homeostatic function would be utilized on a scale of seconds, rather than hours or days. Experimental procedures for determining the role of the osteocyte in mineral homeostasis would require calcium mobilization from the bone matrix on a relatively immediate time scale. The experimental procedure would then be coupled with a high resolution histomorphometric analysis of lacunar radiographic area and mineral density. Added to this would be an in vitro study of mineral activation capacity via cultured osteocytes treated with PTH. Osteocytic osteolysis would be confirmed by an increase in the demineralized volume of osteocytic lacunae and the identification of a chemical mechanism by which osteocytes can readily access the mineral portion of their immediate bone matrix. It should also be true that a reverse capacity exists by which osteocytes can remineralize their immediate matrix utilizing alkaline phosphatase for example, a chemical which they, like osteoblasts, are known to generate. It is thus proposed that osteocytes are both mechanoreceptors and systemic mineral homeostasis regulators.     

Fracture healing as a post-natal developmental process: molecular,spatial, and temporal aspects of its regulation

Fracture healing is a specialized post-natal repair process that recapitulates aspects of embryological skeletal development. While many of the molecular mechanisms that control cellular differentiation and growth during embryogenesis recur during fracture healing, these processes take place in a post-natal environment that is unique and distinct from those which exist during embryogenesis. This Prospect Article will highlight a number of central biological processes that are believed to be crucial in the embryonic differentiation and growth of skeletal tissues and review the functional role of these processes during fracture healing. Specific aspects of fracture healing that will be considered in relation to embryological development are: (1) the anatomic structure of the fracture callus as it evolves during healing; (2) the origins of stem cells and morphogenetic signals that facilitate the repair process; (3) the role of the biomechanical environment in controlling cellular differentiation during repair; (4) the role of three key groups of soluble factors, pro-inflammatory cytokines, the TGF-beta superfamily, and angiogenic factors, during repair; and (5) the relationship of the genetic components that control bone mass and remodeling to the mechanisms that control skeletal tissue repair in response to fracture.