Biomedical subjects

D Naot

Publications and source records attributed to D Naot.

10 recordsLinked to original sources

PubMed2006

Preptin, another peptide product of the pancreatic beta-cell, is osteogenic in vitro and in vivo.

Several hormones that regulate nutritional status also impact on bone metabolism. Preptin is a recently isolated 34-amino acid peptide hormone that is cosecreted with insulin and amylin from the pancreatic beta-cells. Preptin corresponds to Asp(69)-Leu(102) of pro-IGF-II. Increased circulating levels of a pro-IGF-II peptide complexed with IGF-binding protein-2 have been implicated in the high bone mass phenotype observed in patients with chronic hepatitis C infection. We have assessed preptin's activities on bone. Preptin dose-dependently stimulated the proliferation (cell number and DNA synthesis) of primary fetal rat osteoblasts and osteoblast-like cell lines at periphysiological concentrations (>10(-11) M). In addition, thymidine incorporation was stimulated in murine neonatal calvarial organ culture, likely reflecting the proliferation of cells from the osteoblast lineage. Preptin did not affect bone resorption in this model. Preptin induced phosphorylation of p42/p44 MAP kinases in osteoblastic cells in a dose-dependent manner (10(-8)-10(-10) M), and its proliferative effects on primary osteoblasts were blocked by MAP kinase kinase inhibitors. Preptin also reduced osteoblast apoptosis induced by serum deprivation, reducing the number of apoptotic cells by >20%. In vivo administration of preptin increased bone area and mineralizing surface in adult mice. These data demonstrate that preptin, which is cosecreted from the pancreatic beta-cell with amylin and insulin, is anabolic to bone and may contribute to the preservation of bone mass observed in hyperinsulinemic states such as obesity.

Animals↗

PubMed2006

Lactoferrin and bone; structure-activity relationships.

The maintenance of the mechanical integrity of the skeleton depends on bone remodeling, the well-coordinated balance between bone formation by osteoblasts and bone resorption by osteoclasts. The coupled action of osteoblasts and osteoclasts is regulated by the action of many local and circulating hormones and factors as well as central regulation by a neurological mechanism. We have previously shown that lactoferrin can promote bone growth. At physiological concentrations, lactoferrin potently stimulates the proliferation and differentiation of primary osteoblasts and acts as a survival factor. Lactoferrin also affects osteoclasts, potently inhibiting their formation. In vivo, local injection of lactoferrin results in substantial increases in bone formation and bone area. In a critical bone-defect model in vivo, lactoferrin was also seen to promote bone growth. The mitogenic effect of lactoferrin in osteoblast-like cells is mediated mainly through low-density lipoprotein-receptor protein-1 (LRP1), a member of the low-density lipoprotein-receptor-related proteins that are primarily known as endocytic receptors; however, LRP1 is not necessary for the anti-apoptotic actions of lactoferrin. Lactoferrin also induces the activation of p42/44 mitogen-activated protein kinase (MAPK) signalling and the PI3-kinase-dependent phosphorylation of Akt in osteoblasts. In this study, we examined other properties of lactoferrin and the way they affect osteogenic activity. The degree of glycosylation, iron-binding, and the structure-activity relationships indicate that lactoferrin maintains osteogenic activity in deglycosylated, holo, and apo forms, and in with various small fragments of the molecule. These data suggest that lactoferrin signals through more than 1 membrane-bound receptor to produce its anabolic skeletal effects, and that it signals through diverse pathways. We conclude that lactoferrin might have a physiological role in bone growth and healing and a potential therapeutic role as an anabolic factor in osteoporosis.

Amino Acid Sequence↗

PubMed2003

Adrenomedullin--a regulator of bone formation.

Bone growth and maintenance are highly regulated processes. Throughout life, bone constantly undergoes remodelling, maintaining a balance between bone formation by osteoblasts and bone resorption by osteoclasts. This balance depends on the coordinated activities of many systemic hormones and locally acting factors in the bone microenvironment. Understanding the mechanisms of action of these factors provides a better appreciation of the cellular and molecular basis of bone remodelling. Adrenomedullin has recently been found to stimulate the proliferation of osteoblasts in vitro, and to increase indices of bone formation when administered either locally or systemically in vivo. Adrenomedullin receptors, as well as adrenomedullin itself, are expressed in primary osteoblasts and in osteoblast-like cell lines. In this paper we discuss the anabolic effect of adrenomedullin in bone, and present new evidence for a possible role of adrenomedullin in the regulation of cartilage cells. We show that adrenomedullin stimulates proliferation of primary chondrocytes in culture and that mRNA for adrenomedullin and for adrenomedullin receptors are expressed in these cells. Studies of structure-activity relationships have demonstrated that osteotropic effects of adrenomedullin can be retained in peptide fragments of the molecule which lack the parent molecule's vasodilatory properties. Thus, these small peptides, or their analogues, are attractive candidates as anabolic therapies for osteoporosis.

Adrenomedullin↗

PubMed2002

Leptin directly regulates bone cell function in vitro and reduces bone fragility in vivo.

Fat mass is an important determinant of bone density, but the mechanism of this relationship is uncertain. Leptin, as a circulating peptide of adipocyte origin, is a potential contributor to this relationship. Recently it was shown that intracerebroventricular administration of leptin is associated with bone loss, suggesting that obesity should be associated with low bone mass, the opposite of what is actually found. Since leptin originates in the periphery, an examination of its direct effects on bone is necessary to address this major discrepancy. Leptin (>10(-11) m) increased proliferation of isolated fetal rat osteoblasts comparably with IGF-I, and these cells expressed the signalling form of the leptin receptor. In mouse bone marrow cultures, leptin (>or=10(-11) m) inhibited osteoclastogenesis, but it had no effect on bone resorption in two assays of mature osteoclasts. Systemic administration of leptin to adult male mice (20 injections of 43 micro g/day over 4 weeks) reduced bone fragility (increased work to fracture by 27% and displacement to fracture by 21%, P<0.001). Changes in tibial histomorphometry were not statistically significant apart from an increase in growth plate thickness in animals receiving leptin. Leptin stimulated proliferation of isolated chondrocytes, and these cells also expressed the signalling form of the leptin receptor. It is concluded that the direct bone effects of leptin tend to reduce bone fragility and could contribute to the high bone mass and low fracture rates of obesity. When administered systemically, the direct actions of leptin outweigh its centrally mediated effects on bone, the latter possibly being mediated by leptin's regulation of insulin sensitivity.

Animals↗

PubMed2002

Amylin and adrenomedullin: novel regulators of bone growth.

Bone growth is regulated by circulating hormones and locally generated factors. Understanding their mechanisms of action enables us to obtain a better appreciation of the cellular and molecular basis of bone remodelling, and could therefore be valuable in approaches to new therapies. In this review, we consider the actions on bone tissue of the peptide hormones amylin and adrenomedullin, known to circulate at picomolar concentrations. Adrenomedullin is also produced locally in bone. Amylin and adrenomedullin are related peptides with some homology to both calcitonin and calcitonin gene-related peptide. These peptides have recently been found to stimulate the proliferation of osteoblasts in vitro, and to increase indices of bone formation when administered either locally or systemically in vivo. In addition, amylin inhibits bone resorption. Both amylin and adrenomedullin have also been found to act on chondrocytes, stimulating their proliferation in culture and increasing tibial growth plate thickness when administered systemically to adult mice. Like the peptides themselves, the receptors for the calcitonin family are also related to each other. Each peptide seems to act through its own distinct high affinity receptor, as well as through other receptors for the family, usually with lower affinity. Characterisation of the putative receptors expressed in osteoblasts, has provided some understanding of the physiological effects of amylin and adrenomedullin in these cells. Studies of structure-activity relationships have demonstrated that osteotropic effects of amylin and adrenomedullin can be retained in peptide fragments of the molecule whilst losing the parent molecule's effects on carbohydrate metabolism or vasodilatory properties respectively. Thus, these small peptides, or their analogues, are attractive candidates as anabolic therapies for osteoporosis.

Adrenomedullin↗

PubMed2001

Lysophosphatidic acid is an osteoblast mitogen whose proliferative actions involve G(i) proteins and protein kinase C, but not P42/44 mitogen-activated protein kinases.

The simple glycerophospholipid lysophosphatidic acid (LPA) acts both as an intermediary in phospholipid metabolism and as an intercellular signaling molecule in its own right. In various cell types, LPA signals through its membrane-bound, G protein-coupled receptors to influence cellular processes such as proliferation, survival, and cytoskeletal function. Its actions in bone cells have not been studied. Here we show that the LPA receptor, LP(A1)/edg-2/vzg-1, is expressed in primary rat osteoblasts and the UMR 106-01 osteoblastic cell line. LPA potently induces DNA synthesis and an increase in cell number in cultures of osteoblastic cells. LPA rapidly (within 10 min) stimulates phosphorylation of p42/44 mitogen-activated protein (MAP) kinases in osteoblastic cells, an effect that is sensitive to inhibition of G(i) proteins, inhibition of influx of extracellular calcium, and inhibition of protein kinase C. LPA-induced DNA synthesis is partially inhibited by either pertussis toxin or calphostin C, but is insensitive to specific inhibitors of MEK, the kinase upstream of p42/44 MAP kinases, or of phosphatidylinositol-3 kinases. These data demonstrate that LPA is an osteoblast mitogen whose signaling effects in osteoblastic cells include activation of p42/44 MAP kinases. However, the LPA mitogenic signal in osteoblastic cells, while requiring G(i) proteins and protein kinase C, is independent of the activity of p42/44 MAP kinases.

Animals↗

PubMed2001

A potential role for adrenomedullin as a local regulator of bone growth.

Bone remodeling is a complex process of coordinated resorption and formation of bone, which is regulated by systemic hormones and by local factors. We have previously shown that the peptide hormone adrenomedullin is mitogenic to osteoblastic cells in vitro and that it promotes bone growth in vivo. The aim of the present study was to characterize the expression of molecules that may mediate adrenomedullin signaling in osteoblasts and to investigate the expression of adrenomedullin itself in these cells. The first adrenomedullin receptor that was cloned is the seven-transmembrane G protein-coupled receptor, L1. Two additional receptors for adrenomedullin, which arise from interactions between calcitonin receptor-like receptor and receptor activity modifying proteins 2 or 3, have now been described. In the current study, we used RT-PCR and Northern blot analysis to demonstrate that messenger RNA for the three adrenomedullin receptors, as well as for adrenomedullin itself, is expressed in primary rat osteoblasts. Treating primary osteoblasts with transforming growth factor-beta and insulin-like growth factor-I moderately reduced adrenomedullin RNA levels, whereas PTH had no effect. We have shown by immunocytochemistry that adrenomedullin peptide is present in osteoblasts, and by competitive binding assays that (125)I-adrenomedullin binds with high affinity to intact osteoblasts and to osteoblast cell membranes. Coexpression of adrenomedullin and adrenomedullin receptors in osteoblasts, taken together with our previous finding that adrenomedullin is mitogenic to these cells, raises the possibility that this peptide is a local regulator of bone growth.

Adrenomedullin↗

PubMed1995

Induction of a gene encoding an oleosin homologue in cultured citrus cells exposed to salt stress.

A cDNA clone (C3) with high homology to plant oleosins was isolated from citrus cultured cells. The 827-bp cDNA insert has an open reading frame of 144 amino-acid residues. The central hydrophobic domain of the protein is nearly identical to oleosins from Brassica napus and maize, and the C-terminal hydrophilic region following the hydrophobic domain is also highly conserved. The steady-state level of mRNA hybridizing to C3 was significantly increased upon exposure of citrus cells to 0.2 M NaCl. A lower level of transcript was found in seeds, but none could be detected in any other vegetative tissue (leaves, roots or fruit) even in the presence of salt under the conditions used. The induction of the oleosin homologue in citrus cells by salt does not depend on the developmental stage of the cells.

Amino Acid Sequence↗

PubMed1995

Drought, heat and salt stress induce the expression of a citrus homologue of an atypical late-embryogenesis Lea5 gene.

In a search for genes that are induced in citrus cell suspension in response to salt stress, a cDNA clone with high homology to cotton Lea5 gene was isolated. Data base analysis of the protein deduced from the nucleotide sequence indicates that, like in cotton, the protein from citrus contains regions with significant hydropathic character. The gene, designated C-Lea5, is expressed in citrus leaves as well as cell suspension. The steady-state level of C-Lea5 is increased in cell suspension that is grown in the presence of 0.2 M NaCl. This phenomenon is also observed in leaves of citrus plants irrigated with NaCl and in citrus seedlings which are exposed to drought and heat stress. We suggest that the osmotic stress resulted from elevated level of salt is responsible for the increase in the level of C-Lea5.

Amino Acid Sequence↗

PubMed1993

Numerous candidate plasticity-related genes revealed by differential cDNA cloning.

Plasticity is a property of the nervous system that allows it to modify its response to an altered input. This capacity for change suggests that there are molecular mechanisms in neurons that can couple stimuli to long-term alterations in phenotype. Neuronal excitation elicits rapid transcriptional activation of several immediate-early genes, for example c-fos, c-jun and zif268. Many immediate-early genes encode transcription factors that control expression of downstream genes whose products are believed to bring about long-term plastic changes. Here we use a highly sensitive differential complementary DNA cloning procedure to identify genes that may participate in long-term plasticity. We cloned 52 cDNAs of genes induced by the glutamate analogue kainate in the hippocampus dentate gyrus. The number of these candidate plasticity-related genes (CPGs) is estimated to be 500-1,000. One of the cloned CPGs (16C8), encoding a protease inhibitor, is induced by a stimulus producing long-term potentiation and during dentate gyrus development; a second, cpg1, is dependent on activation of the NMDA (N-methyl-D-aspartate) receptor for induction and encodes a new small, dentate-gyrus-specific protein. Seventeen of the cloned CPGs encode known proteins, including six suggesting that strong neuronal activation leads to de novo synthesis of vesicular and other synaptic components.

Amino Acid Sequence↗