https://www.seas.upenn.edu/%7Edischer/pdfs/Cell_on_Gel-CELLpaper.pdf

Matrix elasticity directs stem cell lineage specification.

Fibroblasts can condense a hydrated collagen lattice to a tissue-like structure 1/28th the area of the starting gel in 24 hr. The rate of the process can be regulated by varying the protein content of the lattice, the cell number, or the con- centration of an inhibitor such as Colcemid. Fibroblasts of high population doubling level propagated in vitro, which have left the cell cycle, can carry out the contraction at least as efficiently as cycling cells. The potential uses of the system as an immu- nologically tolerated "tissue" for wound hea ing and as a model for studying fibroblast function are discussed.

Production of a tissue-like structure by contraction of collagen lattices by human fibroblasts of different proliferative

Effect of bone extracellular matrix synthesized in vitro on the osteoblastic differentiation of marrow stromal cells

Influence of platelet-rich plasma (PRP) on osteogenic differentiation of rat bone marrow stromal cells. An in vitro study.

In this review the roles of specific proteins during the first step of mineralization and nucleation are discussed. Mineralization is initiated inside the extracellular organelles-matrix vesicles (MVs). MVs, containing relatively high concentrations of Ca2+ and inorganic phosphate (Pi), create an optimal environment to induce the formation of hydroxyapatite (HA). Special attention is given to two families of proteins present in MVs, annexins (AnxAs) and tissue-nonspecific alkaline phosphatases (TNAPs). Both families participate in the formation of HA crystals. AnxAs are Ca2+ - and lipid-binding proteins, which are involved in Ca2+ homeostasis in bone cells and in extracellular MVs. AnxAs form calcium ion channels within the membrane of MVs. Although the mechanisms of ion channel formation by AnxAs are not well understood, evidence is provided that acidic pH or GTP contribute to this process. Furthermore, low molecular mass ligands, as vitamin A derivatives, can modulate the activity of MVs by interacting with AnxAs and affecting their expression. AnxAs and other anionic proteins are also involved in the crystal nucleation. The second family of proteins, TNAPs, is associated with Pi homeostasis, and can hydrolyse a variety of phosphate compounds. ATP is released in the extracellular matrix, where it can be hydrolyzed by TNAPs, ATP hydrolases and nucleoside triphosphate (NTP) pyrophosphohydrolases. However, TNAP is probably not responsible for ATP-dependent Ca2+/phosphate complex formation. It can hydrolyse pyrophosphate (PPi), a known inhibitor of HA formation and a byproduct of NTP pyrophosphohydrolases. In this respect, antagonistic activities of TNAPs and NTP pyrophosphohydrolases can regulate the mineralization process.

/pdf/the-roles-of-annexins-and-alkaline-phosphatase-in-45gxdtruoz.pdf

The roles of annexins and alkaline phosphatase in mineralization process

Adult human osteoblastic cells were grown in a native type I collagen gel. Proliferation and viability analyses showed that cells rapidly stopped dividing and became blocked in the G0G1 phase (91% on day 13). Carboxyfluorescein diacetate cell staining and flow cytometry showed that osteoblasts were viable for the first 16 days and then viability decreased (58% viable cells on day 22). Osteoblasts were able to retract the matrix. Betaglycerophosphate (βGP) stimulated the deposition of mineral particles in the collagen network, and electron probe microanalysis showed that they were principally calcium and phosphorus, with a Ca/P ratio of about 1.7. Various times of βGP supply were tested. We compared 10 mM βGP added only once at day 0, or continuously from day 0, day 8, or day 21. Mineralization was observed in conditions where βGP was added at day 0. Furthermore, 10 mM βGP added once during gel preparation was sufficient to induce mineralization with mineral accumulation up to day 15 whereas the speed of the gel contraction decreased. In every condition, cultures expressed high alkaline phosphatase (ALP) levels as early as day 3, which decreased afterwards. These kinetics might explain why the other conditions did not prove favorable to the mineralization process. The model was used to study the influence of blocking gel retraction. Blocking retraction delayed the ALP activity decrease, but had no effect on mineralization. In conclusion, human adult osteoblasts cultured in native collagen gel stopped proliferation and underwent mineralization very early. This model should be used to investigate the influence of effectors on the early stages of culture.

Mineralization and alkaline phosphatase activity in collagen lattices populated by human osteoblasts.

Resume La cholecystokinine fait l'objet depuis plusieurs annees de nombreuses publications scientifiques car il s'agit d'un ensemble de peptides regulateurs dont l'action se situe a plusieurs niveaux de l'organisme, avec une fonction importante dans le domaine nutritionnel et un role dans la regulation de la prise alimentaire par le declenchement de la sensation de satiete Cet article passe en revue de facon detaillee la biosynthese et la structure de cette famille de peptides, les recepteurs de la cholecystokinine ainsi que les aspects digestifs, nutritionnels, metaboliques et de controle de la satiete de ce peptide regulateur Les aspects psychocomportementaux de la CCK ne seront pas ou peu abordes ici

A. Chamson

Papers

Mineralization and alkaline phosphatase activity in collagen lattices populated by human osteoblasts.

La cholécystokinine : mise au point