Biomedical subjects

David L Lacey

Publications and source records attributed to David L Lacey.

10 recordsLinked to original sources

PubMed2006

Dkk1-mediated inhibition of Wnt signaling in bone results in osteopenia.

Mutations affecting the activity of the Wnt co-receptors LRP5 and LRP6 that cause alterations in skeletal biology confirmed the involvement of Wnt signaling in bone formation. We evaluated the potential role of Dkk1, an inhibitor of LRP5/6 activity, in bone formation by examining the normal expression pattern of Dkk1 in normal young mice and by assessing the consequences of osteoblast overexpression of Dkk1 in transgenic mice. Endogenous Dkk1 expression was detected primarily in osteoblasts and osteocytes. Transgenic over-expression of Dkk1 using two different rat collagen 1A1 promoters resulted in distinct bone phenotypes. More widespread Dkk1 expression (driven by the Col1A1 3.6 kb promoter) yielded osteopenia with forelimb deformities and hairlessness, while expression restricted to osteoblasts (driven by the Col1A1 2.3 kb promoter) induced severe osteopenia without limb defects or alopecia. The decrease in bone mass in vivo resulted from a significant 49% reduction in osteoblast numbers and was reflected in a 45% reduction in serum osteocalcin concentration; an in vitro study revealed that Dkk1 caused a dose-dependent suppression of osteoblast matrix mineralization. These data indicate that Dkk1 may directly influence bone formation and suggest that osteopenia develops in mice over-expressing Dkk1 at least in part due to diminished bone formation resulting from reduced osteoblast numbers.

3T3 Cells↗

PubMed2004

Regulation of protein catabolism by muscle-specific and cytokine-inducible ubiquitin ligase E3alpha-II during cancer cachexia.

The progressive depletion of skeletal muscle is a hallmark of many types of advanced cancer and frequently is associated with debility, morbidity, and mortality. Muscle wasting is primarily mediated by the activation of the ubiquitin-proteasome system, which is responsible for degrading the bulk of intracellular proteins. E3 ubiquitin ligases control polyubiquitination, a rate-limiting step in the ubiquitin-proteasome system, but their direct involvement in muscle protein catabolism in cancer remains obscure. Here, we report the full-length cloning of E3alpha-II, a novel "N-end rule" ubiquitin ligase, and its functional involvement in cancer cachexia. E3alpha-II is highly enriched in skeletal muscle, and its expression is regulated by proinflammatory cytokines. In two different animal models of cancer cachexia, E3alpha-II was significantly induced at the onset and during the progression of muscle wasting. The E3alpha-II activation in skeletal muscle was accompanied by a sharp increase in protein ubiquitination, which could be blocked by arginine methylester, an E3alpha-selective inhibitor. Treatment of myotubes with tumor necrosis factor alpha or interleukin 6 elicited marked increases in E3alpha-II but not E3alpha-I expression and ubiquitin conjugation activity in parallel. E3alpha-II transfection markedly accelerated ubiquitin conjugation to endogenous cellular proteins in muscle cultures. These findings show that E3alpha-II plays an important role in muscle protein catabolism during cancer cachexia and suggest that E3alpha-II is a potential therapeutic target for muscle wasting.

Amino Acid Sequence↗

PubMed2003

Osteoclast differentiation and activation.

Osteoclasts are specialized cells derived from the monocyte/macrophage haematopoietic lineage that develop and adhere to bone matrix, then secrete acid and lytic enzymes that degrade it in a specialized, extracellular compartment. Discovery of the RANK signalling pathway in the osteoclast has provided insight into the mechanisms of osteoclastogenesis and activation of bone resorption, and how hormonal signals impact bone structure and mass. Further study of this pathway is providing the molecular basis for developing therapeutics to treat osteoporosis and other diseases of bone loss.

Animals↗

PubMed2003

Surfactant protein A is a required mediator of keratinocyte growth factor after experimental marrow transplantation.

We reported an association between the ability of recombinant human keratinocyte growth factor (rHuKGF) to upregulate the expression of surfactant protein A (SP-A) and to downregulate pulmonary inflammation that occurs after allogeneic bone marrow transplantation (BMT). To establish a causal relationship, rHuKGF (5 mg/kg) was administered subcutaneously for three consecutive days before irradiation to SP-A-sufficient and -deficient [SP-A(+/+) and SP-A(-/-), respectively] mice given inflammation-inducing allogeneic spleen T cells at the time of BMT. In contrast with SP-A(+/+) mice, rHuKGF failed to suppress the high levels of TNF-alpha, IFN-gamma, and nitric oxide contained in bronchoalveolar lavage fluids collected on day 7 after BMT from SP-A(-/-) mice. Early post-BMT weight loss was attenuated by rHuKGF in both SP-A(+/+) and SP-A(-/-) recipients. In the absence of supportive respiratory care, however, SP-A deficiency eventually abolished the ability of rHuKGF to prevent weight loss and to improve survival monitored for 1 mo after allogeneic BMT. In further experiments, the addition of cyclophosphamide (which is known to cause severe injury to the alveolar epithelium in donor T cell-recipient mice) to the conditioning regimen prevented rHuKGF-induced upregulation of SP-A and suppression of lung inflammation in both SP-A(+/+) and SP-A(-/-) mice. We conclude that endogenous baseline SP-A levels and optimal upregulation of SP-A are required for the anti-inflammatory protective effects of KGF after allogeneic transplantation.

Animals↗

PubMed2003

Genetic models in applied physiology: selected contribution: effects of spaceflight on immunity in the C57BL/6 mouse. I. Immune population distributions.

There are several aspects of the spaceflight environment that may lead to changes in immunity: mission-related psychological stress, radiation, and changes in gravity. On December 5, 2001, the space shuttle Endeavor launched for a 12-day mission to examine these effects on C57BL/6 mice for the first time. On their return, assays were performed on the spleen, blood, and bone marrow. In response to flight, there were no significant differences in the general circulating leukocyte proportions. In contrast, there was an increase in splenic lymphocyte percentages, with a corresponding decrease in granulocytes. There was an overall shift in splenic lymphocytes away from T cells toward B cells, and a decrease in the CD4-to-CD8 ratios due to a decrease in T helpers. In contrast, there were proportional increases in bone marrow T cells, with decreases in B cells. Although the blast percentage and count were decreased in flight mice, the CD34(+) population was increased. The data were more consistent with a shift in bone marrow populations rather than a response to changes in the periphery. Many of the results are similar to those using other models. Clearly, spaceflight can influence immune parameters ranging from hematopoiesis to mature leukocyte mechanisms.

Animals↗

PubMed2003

Role of RANK ligand in mediating increased bone resorption in early postmenopausal women.

Studies in rodents have implicated various cytokines as paracrine mediators of increased osteoclastogenesis during estrogen deficiency, but increases in RANKL, the final effector of osteoclastogenesis, have not been demonstrated. Thus, we isolated bone marrow mononuclear cells expressing RANKL on their surfaces by two-color flow cytometry using FITC-conjugated osteoprotegerin-Fc (OPG-Fc-FITC) as a probe. The cells were characterized as preosteoblastic marrow stromal cells (MSCs), T lymphocytes, or B lymphocytes by using Ab's against bone alkaline phosphatase (BAP), CD3, and CD20, respectively, in 12 premenopausal women (Group A), 12 early postmenopausal women (Group B), and 12 age-matched, estrogen-treated postmenopausal women (Group C). Fluorescence intensity of OPG-Fc-FITC, an index of the surface concentration of RANKL per cell, was increased in Group B over Groups A and C by two- to threefold for MSCs, T cells, B cells, and total RANKL-expressing cells. Moreover, in the merged groups, RANKL expression per cell correlated directly with the bone resorption markers, serum C-terminal telopeptide of type I collagen and urine N-telopeptide of type I collagen, in all three cell types and inversely with serum 17beta-estradiol for total RANKL-expressing cells. The data suggest that upregulation of RANKL on bone marrow cells is an important determinant of increased bone resorption induced by estrogen deficiency.

Adult↗

PubMed2002

Genetic models in applied physiology: selected contribution: effects of spaceflight on immunity in the C57BL/6 mouse. II. Activation, cytokines, erythrocytes, and platelets.

This portion of the study quantified the effects of a 12-day space shuttle mission (Space Transport System-108/UF-1) on body and lymphoid organ masses, activation marker expression, cytokine secretion, and erythrocyte and thrombocyte characteristics in C57BL/6 mice. Animals in flight (Flt group) had 10-12% lower body mass compared with ground controls housed either in animal enclosure modules or under standard vivarium conditions (P < 0.001) and the smallest thymus and spleen masses. Percentages of CD25(+) lymphocytes, CD3(+)/CD25(+) T cells, and NK1.1(+)/CD25(+) natural killer cells from Flt mice were higher compared with both controls (P < 0.05). In contrast, CD71 expression was depressed in the Flt and animal enclosure module control mice compared with vivarium control animals (P < 0.001). Secretion of interferon-gamma, IL-2, and IL-4, but not tumor necrosis factor-alpha and IL-5, by splenocytes from Flt mice was decreased relative to either one or both ground controls (P < 0.05). Flt mice also had high red blood cell and thrombocyte counts compared with both sets of controls; low red blood cell volume and distribution width, percentage of reticulocytes, and platelet volume were also noted (P < 0.05) and were consistent with dehydration. These data indicate that relatively short exposure to the spaceflight environment can induce profound changes that may become significant during long-term space missions.

Animals↗

PubMed2002

Keratinocyte growth factor preserves normal thymopoiesis and thymic microenvironment during experimental graft-versus-host disease.

Thymus-dependent reconstitution of the peripheral T-cell compartment is critical for the successful outcome of bone marrow transplantation. However, graft-versus-host disease (GVHD) affects thymic stromal function and thus prevents normal T-cell maturation and selection. To determine whether cytoprotection of thymic epithelial cells (TECs) by keratinocyte growth factor (KGF) averts GVHD-related injury to the thymus, a nonirradiated murine parent-->F(1) transplantation model was investigated. Administration of KGF between days -3 and +3 of GVHD induction preserved normal thymic size, cellularity, and thymocyte phenotype when measured 2 weeks after transplantation and compared with saline-treated parent-->F(1) mice that received allogeneic transplants. Moreover, the characteristic GVHD-induced impairment in cell cycle progression of pro- and pre-T cells was prevented by KGF. However, the normal phenotypic and functional status of the thymus did not correlate with the higher number of GVHD-inducing mature donor T cells in thymi of KGF-treated mice. Importantly, extensive analysis of the different TEC populations within the thymic cortex and medulla revealed an almost normal stromal architecture and composition in GVHD mice treated with KGF. These observations are likely to reflect an indirect effect of KGF on thymopoiesis as KGF-receptor expression was demonstrated to be restricted to TECs. Thus, pharmacologic doses of KGF appear to exert a potent effect on TEC function, which in turn allows for normal T lymphopoiesis to occur during acute GVHD.

Animals↗

PubMed2002

Protection from thymic epithelial cell injury by keratinocyte growth factor: a new approach to improve thymic and peripheral T-cell reconstitution after bone marrow transplantation.

Decreased thymopoietic capacity contributes to the severe and clinically significant immune deficiency seen after bone marrow transplantation (BMT). One mechanism for thymopoietic failure is damage to the interleukin 7 (IL-7)-producing thymic epithelial cells (TECs) by irradiation and chemotherapy, which can be partially treated by IL-7 administration. Pretreatment of BMT recipients with keratinocyte growth factor (KGF, or Fgf7), an epithelial cell-specific growth factor, protects mucosal, cutaneous, and pulmonary epithelial cells from cytotoxic therapy-induced damage in experimental murine models. Like other epithelial cells, TECs specifically express KGF receptors. Because KGF specifically protects KGF receptor-bearing epithelial cells and post-BMT immune deficiency is caused by loss of TECs, we hypothesized that KGF pretreatment would improve post-BMT thymic function. To test the hypothesis, BMT recipient mice were given KGF or placebo prior to congenic or allogeneic BMT. Administration of KGF before murine BMT significantly increased the capacity of the thymus to generate donor-derived thymocytes. KGF pretreatment also normalized the proportion of thymic subpopulations, increased the number of naive T cells in the periphery, and improved the response to neoantigen immunization. KGF treatment caused increased production of intrathymic IL-7, and the thymopoietic effects of KGF required an intact IL-7 signaling pathway. These results demonstrate that KGF may have immunomodulatory effects by a unique mechanism of protection of TECs. Furthermore, thymic injury and prolonged posttransplantation immune deficiency in BMT recipients can be prevented by KGF administration.

Animals↗

PubMed2002

rHuKGF ameliorates symptoms in DSS and CD4(+)CD45RB(Hi) T cell transfer mouse models of inflammatory bowel disease.

There is an acute need for effective therapy for inflammatory bowel disease (IBD), particularly at the level of repair of the damaged epithelium. We evaluated the efficacy of recombinant human keratinocyte growth factor (rHuKGF) in both the dextran sodium sulfate (DSS) and the CD4(+)CD45RB(Hi) T cell transfer models of IBD. Disease was induced either by the ad libitum administration to normal mice of 4% DSS in the drinking water or by the injection of 4 x 10(5) CD4(+)CD45RB(Hi) T cells into immunodeficient scid/scid mice. rHuKGF was administered by subcutaneous injection at doses of 1.0 or 3.0 mg/kg in both preventative and therapeutic regimens during both studies. rHuKGF significantly improved survival and body weight loss in the DSS model in both preventative and therapeutic dosing regimens. It also improved diarrhea, hematochezia, and hematological parameters, as well as large intestine histopathology. In the T cell transfer model, rHuKGF improved body weight loss, diarrhea, and levels of serum amyloid A, as well as large intestine histopathology. In both models of IBD, the colonic levels of intestinal trefoil factor (ITF) were elevated by the disease state and further elevated by treatment with rHuKGF. These data suggest that rHuKGF may prove useful in the clinical management of IBD and its effects are likely mediated by its ability to locally increase the levels of ITF.

Animals↗