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Biomedical subjects

K Medina

Publications and source records attributed to K Medina.

13 recordsLinked to original sources
PubMed2000

Multiple cellular phenotypes in an insertional mutation in mouse affecting bone development.

The 6093 line of transgenic mice exhibits altered bone development as a result of an insertional mutation by the transgene. Female transgenic mice show a marked kyphosis as early as 2 weeks of age. Vertebrae from female mice have lower total bone area and mineral content than age-matched, gender-matched controls, although the bone mineral density is not changed. The femur and tibia exhibit the opposite effect-increased bone area and mineral content. Fluorescent bone label experiments indicated an increased rate of bone mineral deposition in the femur during the early postnatal growth period, and bone marrow from femurs of 6093 females had increased numbers of fibroblast colony-forming units. Transgenic females also are obese and have altered thymocyte development, suggesting that the insertional mutation affects multiple cell populations. We hypothesize that these phenotypes arise as a result of an alteration in the function or developmental potential of a stromal cell or mesenchymal stem cell.

Animals↗
PubMed1999

Adenosine regulates renal nitric oxide production in hypothyroid rats.

In the hypothyroid kidney, exogenous adenosine (ADO) produces vasodilation and restores renal function to near-normal values. This study evaluates whether this response is mediated by nitric oxide synthesis stimulated by adenosine. GFR and urinary excretion of NO2-/NO3- (UNO2-/NO3-) were measured in normal (NL) and hypothyroid (HTX) rats under basal conditions and during infusion of: intra-aortic ADO, intravenously, 1,3-dipropyl-8p-sulfophenylxanthine (DPSPX), 8-cyclopentyl-1,3-dipropyl xanthine (DPCPX), N(omega)-nitro-L-arginine methylester (L-NAME) + ADO, L-NAME + PSPX, L-NAME + DPCPX, and intrarenal (IR) ADO or DPCPX + IR ADO. Intra-aortic ADO induced a fall in GFR and increased UNO2-/NO3- slightly in NL rats; in HTX rats, both GFR and UNO2-/NO3- increased significantly. DPSPX and DPCPX increased UNO2-/NO3- excretion in NL animals with minor changes in GFR; the blockers increased both GFR and UNO2-/ NO3- in HTX rats. L-NAME completely blocked the increase in NO2-/NO3- induced by ADO, DPSPX, and DPCPX. The intrarenal infusion of ADO at 1, 10, and 35 nmol/kg per min progressively decreased GFR with a slight increase in UNO2-/ NO3- in NL rats; in the HTX, GFR increased with the highest dose and UNO2-/NO3- progressively increased. DPCPX prevented the fall in GFR induced by intrarenal ADO in NL rats, with no further changes in UNO2-/NO3-; in HTX rats, intrarenal ADO under A1 blockade further increased GFR and UNO2-/NO3-. Arterial and venous ADO concentrations were lower in the HTX rats. In the HTX kidney, NO production was stimulated by ADO, most likely through activation of A2 or A3 receptors, whereas A1 receptors had an inhibitory effect. Thus, ADO receptors are involved in the regulation of kidney function in pathophysiologic conditions.

Adenosine↗
PubMed1998

Blood cell precursors in context. Composition of the bone marrow microenvironment that supports B lymphopoiesis.

New molecular approaches are rapidly yielding information about the composition of bone marrow and culture studies suggest possible functions for many molecules in that organ. However, the marrow is extraordinarily complex with respect to interactions between cells and their behaviour may not be adequately modeled in culture. It is becoming apparent that post-translational modifications and function of proteins can be highly influenced by the cellular and extracellular environment. Therefore, in vivo studies will continue to be important for understanding this remarkable organ.

Apoptosis↗
PubMed1997

Nitrogen availability of grape juice limits killer yeast growth and fermentation activity during mixed-culture fermentation with sensitive commercial yeast strains.

The competition between selected or commercial killer strains of type K2 and sensitive commercial strains of Saccharomyces cerevisiae was studied under various conditions in sterile grape juice fermentations. The focus of this study was the effect of yeast inoculation levels and the role of assimilable nitrogen nutrition on killer activity. A study of the consumption of free amino nitrogen (FAN) by pure and mixed cultures of killer and sensitive cells showed no differences between the profiles of nitrogen assimilation in all cases, and FAN was practically depleted in the first 2 days of fermentation. The effect of the addition of assimilable nitrogen and the size of inoculum was examined in mixed killer and sensitive strain competitions. Stuck and sluggish wine fermentations were observed to depend on nitrogen availability when the ratio of killer to sensitive cells was low (1:10 to 1:100). A relationship between the initial assimilable nitrogen content of must and the proportion of killer cells during fermentation was shown. An indirect relationship was found between inoculum size and the percentage of killer cells: a smaller inoculum resulted in a higher proportion of killer cells in grape juice fermentations. In all cases, wines obtained with pure-culture fermentations were preferred to mixed-culture fermentations by sensory analysis. The reasons why killer cells do not finish fermentation under competitive conditions with sensitive cells are discussed.

Antibiosis↗
PubMed1996

Antibody ligation of CD9 modifies production of myeloid cells in long-term cultures.

The KMC8.8 monoclonal antibody was made by immunizing rats with the BMS2 stromal cell clone, and was selected for further study because its ability to inhibit production of myeloid cells in Dexter cultures but not that of lymphoid cells in Whitlock-Witte cultures. The influence on myeloid progenitors might have been indirect, since the antibody did not prevent responsiveness to colony-stimulating factors in semisolid agar cultures. Furthermore, there was no inhibition, and some augmentation, of cell production when the antibody was added to established Dexter cultures. A cDNA clone that encoded the KMC8.8-recognized molecule was isolated by expression cloning and found to be identical in sequence to a previously published murine CD9 homologue. The antibody and cDNA clone were used to establish that CD9 is expressed by stromal cells, megakaryocytes, platelets, myeloid cells, and subpopulations of mature lymphocytes in mice. Treatment with the KMC8.8/CD9 antibody slightly augmented adhesion between myeloid cells and stromal cells, consistent with previous reports that this member of the tetraspan family of proteins can transmit proadhesive signals to human platelets and lymphoid cells. CD9 might participate in cell-cell interactions critical for correct orientation and movement of maturing myeloid cells in bone marrow.

Animals↗
PubMed1995

Estrogen suppresses stromal cell-dependent lymphopoiesis in culture.

Numbers of pre-B cells change dramatically and reciprocally in response to estrogen levels in mice, suggesting that normal lymphopoiesis may be under hormonal control. However, little is known of the mechanisms involved in this process. We found that estrogen receptor mRNA was detectable by RT-PCR in lymphocyte supporting stromal cells as well as B lymphocyte precursors. Unlike glucocorticoids, estrogen did not induce apoptosis in isolated B lineage lymphocytes or interfere with their responsiveness to IL-7 in semisolid agar. Estrogen did inhibit clonal expansion of B cell precursors in a limiting dilution-type assay when the lymphocytes were cultured on a stromal cell clone. In other experiments, B cell precursors at particular stages of differentiation were isolated by cell sorting and cocultured with stromal cells for 4 days. This revealed that some subsets were more sensitive to an estrogen-containing environment than others. Although numbers of recovered cells were greatly reduced, the remaining lymphocytes had undergone relatively normal differentiation. The surviving population was enriched in cells that had acquired cytoplasmic mu chains, BP-1 Ag, and clonability with IL-7. Hormone-mediated inhibition occurred in serum and phenol-red free medium, and in cultures replete with IL-7. Direct contact between stromal cells and lymphocytes was not required. Furthermore, suppression resulted when stromal cells alone were treated with the hormone. These findings indicate that estrogen may regulate B lymphopoiesis via its influence on the microenvironment and that estrogen-induced stromal cell genes merit further study.

Animals↗
PubMed1993

Modulation of lymphohematopoiesis in long-term cultures by gamma interferon: direct and indirect action on lymphoid and stromal cells.

Gamma interferon (IFN-gamma) is the product of multiple cell types within the bone marrow microenvironment and has been demonstrated to act as a potent inhibitor of myelopoiesis in vitro and in vivo. The action of this cytokine on lymphohematopoiesis has now been examined on both long-term bone marrow cultures and representative cloned cellular components of the bone marrow microenvironment. In myelopoietic (Dexter) cultures, the half maximal inhibitory concentration of IFN-gamma was between 1 and 10 U/mL. In comparable lymphopoietic (Whitlock/Witte) cultures, IFN-gamma inhibited the production of B-lineage lymphoid cells with a half maximal effective concentration of less than 1 U/mL. In a clonal assay for pre-B cells, IFN-gamma inhibited colony formation with a half maximal concentration of 1 to 5 U/mL. Not all B-lineage lymphoid cells displayed the same sensitivity, however. Growth of the IL-7-dependent B cell line (2E8) in methylcellulose assays was unaffected by IFN-gamma while the replication of other lymphoid lines was partially or completely inhibited. IFN-gamma induced the expression of cell surface proteins (MHC Class I and II) on both B-lineage cells and stromal cells. In cloned stromal cell lines, IFN-gamma increased the steady state mRNA levels for the cytokines interleukin-6 (IL-6) and JE, a member of the IL-8 family. These data indicate that IFN-gamma acts within the lymphohematopoietic microenvironment through both direct and indirect actions on the hemopoietic and stromal cell populations.

Animals↗
PubMed1992

Adipogenesis in a myeloid supporting bone marrow stromal cell line.

The bone marrow stroma contains pre-adipocyte cells which are part of the hemopoietic microenvironment. Cloned stromal cell lines differ both in their ability to support myeloid and lymphoid development and in their ability to undergo adipocyte differentiation in vitro. These processes have been examined in the +/+2.4 murine stromal cell line and compared to other stromal and pre-adipocyte cell lines. In long-term cultures, the +/+2.4 stromal cells support myeloid cell growth, consistent with their expression of macrophage-colony stimulating factor mRNA. However, despite the presence of mRNA for the lymphoid supportive cytokines interleukins 6 and 7, +/+2.4 cells failed to support stromal cell dependent B lineage lymphoid cells in vitro, suggesting that these stromal cells exhibit only a myelopoietic support function. The +/+2.4 cells differentiate into adipocytes spontaneously when cultured in 10% fetal bovine serum. The process of adipogenesis can be accelerated by a number of agonists based on morphologic and gene marker criteria. Following induction with hydrocortisone, methylisobutylxanthine, indomethacin, and insulin in combination, a time dependent increase in the steady state mRNA and enzyme activity levels of the following adipocyte specific genes was observed: adipocyte P2, adipsin, CAAT/enhancer binding protein, and lipoprotein lipase. In contrast, adipogenesis was accompanied by a slight decrease in the signal intensity of the macrophage-colony stimulating factor mRNA level, similar to that which has been reported in other bone marrow stromal cell lines. These data demonstrate that although the lympho-hematopoietic support function of pre-adipocyte bone marrow stromal cell lines is heterogeneous, they share a common mechanism of adipogenesis.

Adipose Tissue↗
PubMed1991

A VCAM-like adhesion molecule on murine bone marrow stromal cells mediates binding of lymphocyte precursors in culture.

Two new mAbs (M/K-1 and M/K-2) define an adhesion molecule expressed on stromal cell clones derived from murine bone marrow. The protein is similar in size to a human endothelial cell adhesion molecule known as VCAM-1 or INCAM110. VCAM-1 is expressed on endothelial cells in inflammatory sites and recognized by the integrin VLA-4 expressed on lymphocytes and monocytes. The new stromal cell molecule is a candidate ligand for the VLA-4 expressed on immature B lineage lymphocytes and a possible homologue of human VCAM-1. We now report additional similarities in the distribution, structure, and function of these proteins. The M/K antibodies detected large cells in normal bone marrow, as well as rare cells in other tissues. The antigen was constitutively expressed and functioned as a cell adhesion molecule on cultured murine endothelial cells. It correlated with the presence of mRNA which hybridized to a human VCAM-1 cDNA probe. Partial NH2 terminal amino acid sequencing of the murine protein revealed similarities to VCAM-1 and attachment of human lymphoma cells to murine endothelial cell lines was inhibited by the M/K antibodies. All of these observations suggest that the murine and human cell adhesion proteins may be related. The antibodies selectively interfered with B lymphocyte formation when included in long term bone marrow cultures. Moreover, they caused rapid detachment of lymphocytes from the adherent layer when added to preestablished cultures. The VCAM-like cell adhesion molecule on stromal cells and VLA-4 on lymphocyte precursors may both be important for B lymphocyte formation.

Amino Acid Sequence↗
PubMed1991

Stromal-cell and cytokine-dependent lymphocyte clones which span the pre-B- to B-cell transition.

Five stromal-cell-dependent lymphocyte clones are described that correspond to late pre-B or early B-cell stages of differentiation. They are useful for determining the molecular requirements for pre-B replication, for studying the stromal cells that supply those factors, and for delineating the final sequence of differentiation events as newly formed lymphocytes prepare to exit the bone marrow. The efficiency of lymphocyte growth at limiting dilution varied substantially on different stromal-cell clones and may reflect functional heterogeneity of stromal cells. Most lymphocyte clones were similar to uncloned lymphocytes from Whitlock-Witte cultures in that they responded only transiently to interleukin-7 (IL-7) and then died, unless maintained on a stromal-cell clone. One unusual lymphocyte clone (2E8) was propagated for more than 1 year in IL-7 alone and was selectively responsive to that cytokine. Most of the lymphocyte clones were not tumorigenic in immunodeficient mice. However, one pre-B clone (1A9) grew autonomously in culture when held at high density, responded to conditioned medium from a number of cell lines, and was tumorigenic. Tumors derived from this clone were infiltrated by stromal cells and lymphocytes taken from the tumors' retained characteristics of the original clone. Ly-6 antigens were inducible on 2E8 and 1A9 cells, but the lymphocytes were otherwise arrested in differentiation. The 2E8 cells had rearranged and expressed kappa light-chain genes but displayed them on the surface along with surrogate light chains and mu heavy chains. Thus, expression of authentic light chain need not coincide with termination of surrogate light-chain utilization in newly formed B cells. Several glycoproteins have recently been demonstrated to be associated with surface immunoglobulin (Ig) on mature B-lineage cells and plasma-cell tumors. We now show that one member of this family (approximately 33 kD) was associated with the mu+surrogate light-chain complex on the 1A9 pre-B-cell clone. When compared to mature B lymphomas, fewer bands coprecipitated with the surface-labeled Ig isolated from pre-B- and early B-cell lines, suggesting that components of the antigen receptor are sequentially acquired during development. The normal replication and differentiation of pre-B cells is probably regulated by complex interactions with multiple cytokines and matrix components of the marrow microenvironment. Cloned lymphocyte lines that are dependent on stromal cells should continue to be important tools for molecular definition of those interactions.

Animals↗
PubMed1990

Adipogenesis in a murine bone marrow stromal cell line capable of supporting B lineage lymphocyte growth and proliferation: biochemical and molecular characterization.

Recent advances in long-term bone marrow (BM) culture techniques have allowed investigators to dissect cellular components responsible for lympho hematopoiesis. Consequently, a number of "stromal" cell clones have been developed which are capable of supporting B lineage lymphocyte growth and proliferation in vitro by direct cell-cell interactions and the release of cytokines. While much work has focused on the support function of these cells, questions remain regarding their own differentiation potential. We have examined adipogenesis in the cloned BM stromal cell, BMS2. The presence of hydrocortisone, methylisobutylxanthine, or 30% fetal calf serum each accelerated adipocyte differentiation. This process was accompanied by the accumulation of triglycerides and cholesterol esters along with the induction of adipocyte-specific enzymes. Likewise, the steady-state level of mRNA transcripts increased for genes related to lipid metabolism. However, the pattern of mRNA expression in BMS2 adipocytes differed from that of a well-established, pre-adipocyte cell line, 3T3-L1, with respect to the following genes: glycerol phosphate dehydrogenase, CAAT/enhancer binding protein and angiotensinogen. Adipocyte BMS2 cells retailed the ability to support stromal cell-dependent B lineage lymphocytes in methylcellulose assays. The adipocytes continued to express macrophage-colony-stimulating factor mRNA constitutively and interleukin 6 mRNA in an inducible manner, similar to the BMS2 pre-adipocytes. Together, these data document a close developmental relationship between a specialized fibroblasts and adipocytes in the BM and suggest that adipocyte stromal cells may play an active role in lympho-hematopoiesis.

Adipose Tissue↗