SEARCH · PubMed Health

Results for “knockout”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,423 records · Page 79Linked to original sources

PubMed2005

Role of heme oxygenase-1 in hydrogen peroxide-induced VEGF synthesis: effect of HO-1 knockout.

Hydrogen peroxide is an important mediator of intracellular signaling, which potently enhances the expression of heme oxygenase-1 (HO-1) and upregulates synthesis of vascular endothelial growth factor (VEGF). The purpose of the present study was to explore the involvement of HO-1 in regulation of H(2)O(2)-mediated induction of VEGF synthesis. We provide genetic evidence that basal and H(2)O(2)-induced VEGF synthesis is partially dependent on HO-1. Inhibition of HO-1 activity by tin protoporphyrin (SnPPIX) resulted in downregulation of VEGF synthesis in murine fibroblasts and human keratinocytes. The relationship between HO-1 and VEGF was corroborated by using cells derived from HO-1 knockout mice, which demonstrated lower basal and H(2)O(2)-induced production of VEGF. Additionally, knock out of HO-1 gene impaired induction of VEGF by hemin, lysophosphatidylcholine, and prostaglandin-J(2). Our results provide confirmation for the involvement of HO-1 in regulation of angiogenesis.

Animals↗

PubMed2005

Voluntary exercise delays monogenetic obesity and overcomes reproductive dysfunction of the melanocortin-4 receptor knockout mouse.

The melanocortin system is involved in hypothalamic regulation of energy homeostasis. The melanocortin-4 receptor (MC4R) has been linked to both obesity and reproductive dysfunction. Deletion of the MC4R from the mouse genome has resulted in phenotypes including adult onset obesity, hyperphagia, and difficulty in reproducing when homozygote parents are bred. Additionally, polymorphisms of the human MC4R have been identified in morbidly obese children and adults. Herein, we have identified that voluntary exercise, provided via the presence of a running wheel, impedes the monogenetic obesity (at 20 weeks of age running wheel housed body weight=31+/-1.8 g versus conventionally housed body weight=41+/-2.3 g, a 25% decrease in body weight p<0.01), hyperphagia (average cumulative food intake is not statistically different than wild type mice housed in running wheel cages), and reproductive dysfunction phenotypes associated with the MC4R knockout mice housed by conventional means. These data demonstrate the novel finding that voluntary exercise at a young age may hinder genetically induced obesity.

Age Factors↗

PubMed2005

The effect of insulin deficiency on tau and neurofilament in the insulin knockout mouse.

Complications of diabetes mellitus within the nervous system are peripheral and central neuropathy. In peripheral neuropathy, defects in neurofilament and microtubules have been demonstrated. In this study, we examined the effects of insulin deficiency within the brain in insulin knockout mice (I-/-). The I-/- exhibited hyperphosphorylation of tau, at threonine 231, and neurofilament. In addition, we showed hyperphosphorylation of c-Jun N-terminal kinase (JNK) and glycogen synthase kinase 3 beta (GSK-3 beta) at serine 9. Extracellular signal-regulated kinase 1 (ERK 1) showed decrease in phosphorylation, whereas ERK 2 showed no changes. Ultrastructural examination demonstrated swollen mitochondria, endoplasmic reticulum, and Golgi apparatus, and dispersion of the nuclear chromatin. Microtubules showed decrease in the number of intermicrotubule bridges and neurofilament presented as bunches. Thus, lack of insulin brain stimulation induces JNK hyperphosphorylation followed by hyperphosphorylation of tau and neurofilament, and ultrastructural cellular damage, that over time may induce decrease in cognition and learning disabilities.

Animals↗

PubMed2005

Generation and characterization of Sca2 (ataxin-2) knockout mice.

Ataxin-2, the gene product of the Spinocerebellar Ataxia Type 2 (SCA2) gene, is a protein of unknown function with abundant expression in embryonic and adult tissues. Its interaction with A2BP1/Fox-1, a protein with an RNA recognition motif, suggests involvement of ataxin-2 in mRNA translation or transport. To study the effects of in vivo ataxin-2 function, we generated an ataxin-2 deficient mouse strain. Ataxin-2 deficient mice were viable. Genotypic analysis of litters from mating of heterozygous mice showed segregation distortion with a significant reduction in the birth of Sca-/- females. Detailed macroscopic and microscopic analysis of surviving nullizygous Sca2 knockout mice showed no major histological abnormalities. On a fat-enriched diet, ataxin-2 deficient animals had increased weight gain. Our results demonstrate that ataxin-2, although widely expressed, is not essential in development or during adult survival in the mouse, but leads to adult-onset obesity.

Animals↗

PubMed2006

Testatin transgenic and knockout mice exhibit normal sex-differentiation.

Testatin is identified as a member of the Cystatin family and expressed in germ cells and somatic cells in reproductive tissues. Testatin transcription detectable in males and females at 9.5 days post coitum, before sex-differentiation, is up-regulated just after the onset of sry expression in the male gonads, while is down-regulated to undetectable levels in the female gonads. These expression patterns suggest that Testatin might have some roles in sex-differentiation. To address Testatin function in sex-differentiation, we analyzed the effects of ectopic-expression in females and null-expression in males with testatin transgenic and knockout mice. In the transgenic females, testatin expression was constitutively elevated from embryonic gonad to adult ovary, and its expression was as high as the wild-type male gonads. However, both types of mice were fertile and did not exhibit detectable abnormalities. This suggests that the decrease of endogenous testatin in female gonad is not critical, and the increase of testatin in male gonad is dispensable for sex-differentiation.

Animals↗

PubMed2006

Suppression of atherogenesis by delivery of TGFbeta1ACT using adeno-associated virus type 2 in LDLR knockout mice.

TGFbeta(1) deficiency has been attributed to the development of atherosclerosis. There is, however, little direct evidence for this concept. To examine this hypothesis, low-density lipoprotein receptor knockout (LDLR(-/-)) mice were injected via tail vein with recombinant adeno-associated virus type 2 (rAAV) carrying a bioactive TGFbeta(1) mutant (AAV/TGFbeta1ACT, n=10) or granulocyte-macrophage-colony stimulating factor (AAV/GM-CSF, n=10, a negative control) or saline (n=9, control), and then put on a high cholesterol diet. At 18 weeks, blood lipids were found to be similarly elevated in all LDLR(-/-) mice. TGFbeta1ACT and GM-CSF (DNA, mRNA, and protein) were highly expressed in the tissues of mice given TGFbeta1ACT or AAV/GM-CSF, respectively, showing sustained transfection following gene delivery by the systemic route. Saline-treated and AAV/GM-CSF-treated LDLR(-/-) mice showed extensive areas of atherosclerotic lesion formation. There was evidence of intense oxidative stress (nitrotyrosine staining), inflammation (CD68 staining), and expression of adhesion molecules and the ox-LDL receptor LOX-1 (gene array analysis) in the atherosclerotic tissues. Importantly, atherosclerotic lesion formation was markedly inhibited in the LDLR(-/-) mice given AAV/TGFbeta1ACT. Expression of adhesion molecules and LOX-1, oxidative stress, and inflammatory response all were inhibited in the mice given AAV/TGFbeta1ACT (P<0.05 vs. saline-treated or GM-CSF-treated LDLR(-/-) mice). These data for the first time demonstrate that systemic delivery of TGFbeta1ACT gene via AAV can inhibit formation of atherosclerotic lesions, possibly via anti-inflammatory and anti-oxidant mechanisms. These findings suggest a novel view of TGFbeta(1) in atherogenesis and a potential new gene therapy for treatment of atherosclerosis.

Adenoviridae↗

PubMed2006

IGF-1R tyrosine kinase expression and dependency in clones of IGF-1R knockout cells (R-).

Insulin-like growth factor 1 receptor (IGF-1R) plays many crucial roles in cancer, like anti-apoptotic activity and necessity for transformation. IGF-1R knockout cells (R-) represent a useful tool for molecular mapping of biological properties of the receptor. R- cells have been shown to be refractory to transformation by viral and cellular oncogenes, highlighting the necessity of this receptor for transformation. Surprisingly, more recent studies have shown that these cells can undergo spontaneous transformation. This observation raises the question as whether R- cells over the years have acquired some properties mimicking those of IGF-1R. Using an IGF-1R inhibitor (cyclolignan PPP) we have identified clones of R- (R-s) that are sensitive to this compound. Since, PPP is closely related to podophyllotoxin, which is an efficient microtubule inhibitor, we first investigated if such a mechanism could explain the sensitivity to PPP. However, highly purified PPP showed no or very slight tubulin binding. Further analysis of R-s revealed expression of a 90 kDa protein being reactive to IGF-1R beta-subunit antibodies. This protein was weakly but constitutively tyrosine phosphorylated and was downregulated by siRNA targeting IGF-1R. This downregulation was paralleled by decreased R-s survival. Taken together, our study suggests that clones of R- express IGF-1R activity and dependency, which in turn may explain that R- can undergo spontaneous transformation.

Animals↗

PubMed2006

Role of MAPKs in development and differentiation: lessons from knockout mice.

The ERK, p38MAPK, JNK mitogen-activated protein kinases (MAPKs) are intracellular signaling pathways that play a pivotal role in many essential cellular processes such as proliferation and differentiation. These cascades are activated by a large variety of stimuli and display a high degree of homology. So far, seven MAPK isoforms have been invalidated in mice leading to the discovery of their important functions in development and differentiation. As we could expect because of their multiple and specific properties in vitro, knockout (KO) of MAPK pathways leads to distinct phenotypes in mice. Surprisingly, into a given cascade, KOs of the various isoforms assign specific non-redundant biological functions to each isoform, without compensation by the others. These results emphasize the notion that, although initiated by the same external stimuli, these intracellular cascades activate kinase isoforms each with its own specific role.

Animals↗

PubMed2003

Abnormal behavioral phenotypes of serotonin transporter knockout mice: parallels with human anxiety and depression.

Evidence of a link between genetic variation of the serotonin transporter and depression and anxiety prompted the generation of serotonin transporter knockout mice. Loss of serotonin reuptake function in knock-outs causes reduced clearance of extracellular serotonin and associated alterations in serotonin neuronal firing and receptor function. Behavioral phenotyping function in knock-outs revealed genetic background-related abnormalities, including increased anxiety-like behaviors, reduced aggression, and exaggerated stress responses. Ongoing studies focus on identifying environmental, genetic, and developmental factors interacting with the htt mutation to produce these abnormalities. Serotonin transporter null mutant mice provide a model system to study how genetic variation in serotonin transporter function affects risk for neuropsychiatric disease.

Animals↗

PubMed2006

Nur77 gene knockout alters dopamine neuron biochemical activity and dopamine turnover.

BACKGROUND: Transcription factors of the Nur family (Nurr1, Nur77, and Nor-1) are orphan nuclear receptors closely associated with dopamine neurotransmission in the central nervous system. Nur77 expression is strongly modulated by antipsychotic and ant-parkinsonian drugs in dopaminoceptive brain areas. However, the role of Nur77 in dopamine neuron activity and turnover remains elusive. METHODS: We compared various behavioral and biochemical parameters between Nur77 knockout -/- and wild-type +/+ mice in basal and haloperidol-challenged conditions. RESULTS: We report here that Nur77-deficient mice display enhanced spontaneous locomotor activity, greater sensitivity to a small dose of the dopamine D2 receptor agonist quinpirole acting mainly at autoreceptor sites, and higher levels of the dopamine metabolite DOPAC relative to wild-type mice. Dopamine turnover disturbances are also found after acute challenge with haloperidol, a dopamine D2 receptor antagonist. These alterations are associated with increased tyrosine hydroxylase expression and activity, and reduced catechol-O-methyltransferase expression. CONCLUSION: Taken together, these results are consistent with the involvement of Nur77 in dopamine neuron biochemical activity and dopamine turnover.

Analysis of Variance↗

PubMed2005

Osteopenia and impaired fracture healing in aged EP4 receptor knockout mice.

The EP4 receptor, one of the subtypes of the prostaglandin E2 (PGE2) receptor, plays a critical role in the anabolic effects of PGE2 on bone. However, its role in the maintenance of bone mass in aged animals and its role in fracture healing is not well known. Our studies addressed these issues by characterizing the skeletal phenotype of aged, EP4 receptor knockout (KO) mice, and by comparing fracture healing in aged KO mice versus wild type (WT) mice. There was no significant difference in body weight and femoral length between KO and WT mice at 15 to 16 months of age. Lower bone mass was seen radiographically in both axial and long bones of KO mice relative to WT mice. Micro-CT images of the distal femurs showed thinner cortices, fewer trabeculae, and a deteriorated trabecular network in KO mice. Total bone content, trabecular content, and cortical content, as assessed by pQCT in the distal femur, were lower in KO mice than WT controls. Histomorphometric measurements showed that trabecular bone volume and bone formation rate were significantly decreased whereas osteoclast number on trabecular surface and eroded surface on endocortical surface were significantly increased in KO mice. These data indicated that deleting the EP4 receptor resulted in an imbalance in bone resorption over formation, leading to a negative bone balance. The lower bone formation rate in EP4 KO mice was primarily due to decreased mineralizing surface, suggesting that the defect in overall bone formation was mainly due to the defect in osteoblastogenesis. Fracture healing was examined in KO and WT mice subjected to a transverse femoral fracture. Callus formation was significantly delayed as evidenced both radiographically and histologically in the fractured femurs of KO mice compared with those of WT mice. KO mice had significant decreases in total callus area, cartilaginous callus area, and bony callus area 2 weeks after fracture. By 4 weeks, complete bony bridging was seen in WT mice but not in KO mice. These data demonstrate that the absence of the EP4 receptor decreases bone mass and impairs fracture healing in aged male mice. Our findings indicate that the EP4 receptor is a positive regulator in the maintenance of bone mass and fracture healing.

Aging↗

PubMed2005

Ataxia telangiectasia mutated (Atm) knockout mice as a model of osteopenia due to impaired bone formation.

ATM is a member of the PI-3 kinase protein family, encoded by the gene, ATM, responsible for ataxia telangiectasia (AT). AT is recognized as a genomic instability syndrome, sharing accelerated senescence symptoms in human and mouse. Here, we present evidence that the bone phenotype of Atm knockout (AtmKO) mice is similar to that observed in disuse and/or aging syndromes. A significant decrease in 3-dimensional bone volume fraction (BV/TV) of the fifth lumbar vertebra was observed in AtmKO mice by microCT, compared with heterozygous control mice at 10 weeks of age. Bone histomorphometry revealed that both BFR/BS and Oc.S/BS were significantly decreased in KO mice. To determine the cellular basis of this bone phenotype, we employed in vitro osteoclastogenesis and colony formation assays using bone marrow cells derived from KO and control mice. There was no difference in osteoclast formation in ex vivo cultures. CFU-F was markedly reduced in AtmKO-derived cultures compared with control mice, whereas differentiation of calvaria-derived osteoblasts did not differ between the genotypes. Furthermore, expression levels of IGF1R were significantly decreased, and p38 was aberrantly phosphorylated in marrow stromal cells from AtmKO mice. These results indicate that the pathogenesis of the osteopenic phenotype in AtmKO mice is similar to that of disuse and/or aging syndromes and is caused, at least in part, by a stem cell defect due to lack of IGF signaling.

Animals↗

PubMed2005

Glucose-dependent insulinotropic polypeptide receptor knockout mice have altered bone turnover.

Glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone, which is secreted from endocrine cells in the small intestine after meal ingestion. GIP has been shown to affect osteoblastic function in vitro; however, the in vivo effects of GIP on bone remodeling remain unclear. In the present study, we investigated the role of GIP in modulating bone turnover, by evaluating serum markers of bone turnover, bone density, bone morphology, and changes in biomechanical bone strength over time (one to five months) in GIP receptor knockout mice (GIPR-/- mice). The GIPR-/- mice showed a decreased bone size, lower bone mass, altered bone microarchitecture and biomechanical properties, and altered parameters for bone turnover, especially in bone formation. Moreover, the effects of GIP on bone mass were site-specific and compensatory mechanism developed over time and ameliorated the impact of the loss of GIP signaling on bone mass. Further, GIPR-/- mice had earlier age-related changes than wild-type mice in body composition, including bone mass, lean body mass, and fat percentage. In summary, our results indicate that GIP has an anabolic effect on bone mass and bone quality and suggests that GIP may be a hormonal link between nutrient ingestion and utilization.

Absorptiometry, Photon↗

PubMed2006

TGFbeta inducible early gene-1 knockout mice display defects in bone strength and microarchitecture.

TGFbeta inducible early gene-1 (TIEG) is a member of the Sp/Krüppel-like transcription factor family originally cloned from human osteoblasts. We have previously demonstrated that TIEG plays a role in the expression of important osteoblast marker genes and in the maturation/differentiation of osteoblasts. To elucidate the function of TIEG in skeletal development and maintenance, we have generated a TIEG knockout (KO) mouse. Three-point bending tests demonstrated that the femurs of TIEG KO mice are significantly weaker than those of wild-type animals. pQCT analysis of tibias revealed significant decreases in bone content, density and size in KO animals compared to wild-type mice. Micro-CT analysis of the femoral head and vertebrae revealed increases in femoral head trabecular separation and decreases in cortical bone thickness and vertebral bone volume in KO mice relative to wild-type controls. In addition, electron microscopy indicated a significant decrease in osteocyte number in the femurs of KO mice. Taken together, these data demonstrate that the bones of TIEG KO mice display an osteopenic phenotype with significantly weaker bones and reduced amounts of cortical and trabecular bone. In summary, an important role for TIEG in skeletal development and/or homeostasis is indicated.

Animals↗

PubMed2004

Cerebral ischemia in 5-lipoxygenase knockout mice.

Cerebral ischemia induces 5-lipoxygenase translocation and leukotriene production in the brain. We tried to clarify the pathological significance of 5-lipoxygenase on cerebral ischemia using 5-lipoxygenase knockout mice. No significant difference was observed in the infarct size following permanent and transient ischemia for 60 min between both types of mice. The present study did not support the idea that leukotriene production is involved in infarct expansion in focal cerebral ischemia.

Animals↗

PubMed2004

Region-specific alterations in insulin-like growth factor-I receptor in the central nervous system of nNOS knockout mice.

In the present study, we investigated layer-specific changes in insulin-like growth factor-I (IGF-I) receptor localization in the cerebral cortex, hippocampus and cerebellum of neuronal nitric oxide synthase knockout (nNOS-/-) mice using immunohistochemistry. In the cerebral cortex of control mice, moderately stained cells were seen through the layers II-VI in several cortical regions. In nNOS-/- mice, there was a significant decrease in IGF-I receptor immunoreactivity in the same cortical regions. In the hippocampus of control mice, a distinct immunoreactivity pattern was observed in the CA1-3 areas and dentate gyrus. The immunoreactivity for IGF-I receptor was differentially decreased in each layer in nNOS-/- mice. In nNOS-/- cerebellum, IGF-I receptor immunoreactivity was also significantly decreased in each layer of cerebellar cortex and cerebellar nuclei. To clarify whether decreased expression of IGF-I receptor in nNOS-/- mice was specific, the expression of other receptors for IGF-I was also evaluated. Receptor tyrosine kinase type A (TrkA receptor) and TrkB receptor were differentially decreased in each layer of the hippocampus or cerebellum of nNOS-/- mice. Although further studies of functional features of IGF-I systems in the nNOS-/- mice are required, our first morphological data may provide insights into NO-induced changes in trophic support as well as basic knowledge required for the study of NO-associated neurological diseases.

Animals↗

PubMed2005

Chronic gliosis induced by loss of S-100B: knockout mice have enhanced GFAP-immunoreactivity but blunted response to a serotonin challenge.

Serotonin (5-HT) can induce a release of intraglial S-100B and produce a change in glial morphology. Because S-100B can inhibit polymerization of glial fibrillary acidic protein (GFAP), we hypothesize that glial reactivity may reflect the loss of intraglial S-100B. Adult male transgenic S-100B homozygous knockout (-/-) mice (KO) and wild-type CD-1 (WT) mice were studied. S-100B-immunoreactivity (IR) was seen in the brain tissue of WT (CD-1) but not S-100B KO (-/-) mice. GFAP-IR was seen in both WT (CD-1) and S-100B KO (-/-) glia cells, but S-100B KO (-/-) GFAP-IR cells appeared larger, darker, and more branched than in WT (CD-1). To compare the response of GFAP-IR cells to 5-HT in S-100B KO (-/-) and WT (CD-1) mice, we injected animals with para-chloroamphetamine (PCA) over 2 days (5 and 10 mg/ml). PCA is a potent 5-HT releaser which can induce gliosis in the rodent brain. In WT (CD-1) mice, the size, branching, and density of GFAP-IR cells were significantly increased after PCA injections. No increase in GFAP-IR activation was seen in the S-100B KO (-/-) after PCA injections. Cell-specific densitometry (set at a threshold of 0-150 based on a scale of 255) in these animals statistically showed an increase in GFAP-IR after PCA injections in WT (CD-1) but not S-100B KO (-/-) mice. These results are consistent with the hypothesis that 5-HT may modulate glial morphology by inducing a release of intracellular S-100B, and this pathway is inoperable in the S-100B KO (-/-).

Animals↗

PubMed2005

Anesthetic effects of progesterone are undiminished in progesterone receptor knockout mice.

Progesterone has sedative and anesthetic effects but the underlying molecular mechanisms remain unclear. The two possible mechanisms by which progesterone affects the function of the brain include binding to intracellular progesterone receptors (PR) and metabolism to GABA(A) receptor-modulating neurosteroids. In this study, PR knockout (PRKO) mice were used as model to study the role of PRs in the anesthetic activity of progesterone. The progesterone-induced anesthetic activity was undiminished in female PRKO mice (ED50, 172 mg/kg) as compared to their wild-type littermates (ED50, 167 mg/kg). The progesterone-induced anesthetic activity was highly correlated with increased plasma allopregnanolone levels. Pretreatment of PRKO mice with the 5alpha-reductase inhibitor finasteride significantly reduced the progesterone-induced anesthetic activity. Allopregnanolone also evoked dose-dependent anesthetic activity in PRKO mice, which was similar to those of wild-type mice. Thus, the anesthetic activity of progesterone is not mediated by its interaction with PRs. The neurosteroid allopregnanolone partially mediates the anesthetic activity of progesterone by potentiation of GABA(A) receptor function.

Analysis of Variance↗