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 1,315 records · Page 73Linked to original sources

PubMed2000

Apoptotic photoreceptor death in the rhodopsin knockout mouse in the presence and absence of c-fos.

A combined total of approximately 100 mutations have been encountered within the rhodopsin gene in retinitis pigmentosa (RP) and congenital night blindness. Mice carrying a targeted disruption of the rhodopsin gene phenotypically mimic RP, losing their photoreceptors over a period of 3 months and having no recordable rod electroretinogram. These animals will serve as a model for both recessive and dominant disease (in the latter case, the presence of normal and mutant human rod opsin transgenes on the murine Rho(-/-)background). Precise knowledge of apoptotic photoreceptor cell death, together with factors which may influence apoptosis will be required for optimum utility of Rho(-/-)mice as a model for therapeutic genetic intervention. A peak phase of apoptosis of the photoreceptors of Rho(-/-)mice was shown to occur at 24 days post-birth. The extent of apoptosis appeared to be similar, irrespective of whether or not the rod opsin knockout was present on a c-fos(+/+)or c-fos(-/-)genetic background, the latter known to favor survival of photoreceptors following exposure of mouse retinas to excessive light. These data clearly support the existence in animals of distinct apoptotic pathways in light-induced, as opposed to mutation-induced apoptosis, and together with similar observations recently reported in studies of the naturally occurring rd mouse, may assist in focusing future research on precisely defining the distinct molecular pathways giving rise to such dichotomy.

Animals↗

PubMed2001

The effect of aging on glutathione peroxidase-i knockout mice-resistance of the lens to oxidative stress.

Populations of control, C, and glutathione peroxidase-1 (GPx-1) knockout mice, K, were studied over a period of 2 years. No significant difference was observed between the C and K populations with respect to longevity, vitality, weight, lens biochemistry or morphology based on light and electron microscopy. It was concluded that under normal animal room barrier facilities, GPx-1 is not required. Furthermore, C and K lenses placed in organ culture and observed over a 24 hr period were indistinguishable. Organ cultured C lenses degraded medium H(2)O(2)levels at only a slightly greater rate than K lenses and this did not appear to change with age. However, tertiary butyl hydroperoxide (TBHP) was degraded less effectively by K lenses and this deficiency increased with age. No indication of change in redox non-protein SH (equivalent to GSH) status was observed between C and K whole lenses or epithelial cell fractions. With H(2)O(2)stress, the drop in C and K non-protein SH was comparable and there was little change with age. Examination of the impact of photochemical stress with 1.5 microM riboflavin and 4% O(2)upon choline transport indicated considerable damage with both C and K lenses, but little difference between the two populations until 1 or 2 years of age when the K lenses appear more vulnerable. With TBHP, the detrimental effect on the K lenses is greater and is observed earlier than with photochemical stress suggesting that the K lens membrane function is more susceptible to phospholipid hydroperoxide stress than are C lenses. Light and electron microscopy of the oxidative stressed lenses indicates significant damage which was generally somewhat greater in the K lenses. TBHP was a more potent oxidant than photochemically generated oxidants particularly at the anterior pole. The overall results suggest that under normal conditions, at any age, the lens does not require the presence of GPx-1 but depending on the type of oxidative stress, the enzyme may significantly contribute to its defense and this dependency may increase with age.

Aging↗

PubMed2000

Chronic brain oxidation in a glutathione peroxidase knockout mouse model results in increased resistance to induced epileptic seizures.

Systemic administration of kainic acid (KA) to rodents results in limbic seizures and subsequent neurodegeneration similar to that observed in certain types of human epilepsy, and it is a commonly used animal model for this disease. Oxidative stress has been suggested to play a role in the neuronal injury associated with KA administration. Based on this observation, chronic treatment with antioxidants has been proposed as a possible protective therapy against neuronal damage associated with epileptic seizures. Here we demonstrate by histochemical, electrophysiological, and biochemical means that knockout mice with decreased activity of the protective antioxidant enzyme glutathione peroxidase, which display elevated basal brain oxidative stress levels, are resistant to KA-induced seizure activity and neurodegeneration. This appears to be a result of decreased NMDA receptor function due to oxidation of its NR1 subunit. This suggests that the chronic use of antioxidants as antiepileptic agents to modulate NMDA-dependent seizure-induced neurodegeneration may be detrimental rather than protective and calls into question their use as a therapeutic agent in the treatment of epilepsy.

Animals↗

PubMed2001

Impairment of the blood-nerve and blood-brain barriers in apolipoprotein e knockout mice.

Apolipoprotein E (apoE) is well characterized as a plasma lipoprotein involved in lipid and cholesterol metabolism. Recent studies implicating apoE in Alzheimer's disease and successful recovery from neurological injury have stimulated much interest in the functions of apoE within the brain. To explore the functions of apoE within the nervous system, we examined apoE knockout (KO) mice. Previously, we showed that apoE KO mice have a delayed response to noxious thermal stimuli associated with a loss and abnormal morphology of unmyelinated fibers in the sciatic nerve. From these data, we hypothesized that apoE KO mice could have an impaired blood-nerve barrier (BNB). In this report, we demonstrate functionally impaired blood-nerve and blood-brain barriers (BBB) in apoE KO mice using immunofluorescent detection of serum protein leakage into nervous tissue as a diagnostic for decreased BNB and BBB integrity. Extensive extravasation of serum immunoglobulin G (IgG) is detected in the sciatic nerve, spinal cord, and cerebellum of apoE KO but not WT mice. In a subpopulation of apoE KO mice, IgG also extravasates into discrete cortical and subcortical locations, including hippocampus. Loss of BBB integrity was additionally confirmed by the ability of exogenously supplied Evans blue dye to penetrate the BBB and to colocalize with IgG immunoreactivity in CNS tissue. These observations support a role for apoE in maintaining the integrity of the BNB/BBB and suggest a novel relationship between apoE and neural injury.

Animals↗

PubMed2001

Treatment with anti-interferon-gamma monoclonal antibodies modifies experimental autoimmune encephalomyelitis in interferon-gamma receptor knockout mice.

The role of interferon-gamma (IFN-gamma) in the pathogenesis of multiple sclerosis and experimental autoimmune encephalomyelitis (EAE) is still controversial. We have studied the function of IFN-gamma and its receptor in the EAE model using two different IFN-gamma receptor knockout (IFN-gamma R(-/-)) mouse types: C57Bl/6x129Sv, with a disruption of the IFN-gamma receptor cytoplasmic domain, and 129Sv, homozygous for a disrupted IFN-gamma receptor gene. Mice were immunized with peptide 40-55 from rat myelin oligodendrocyte glycoprotein. A subgroup of mice was treated with anti-IFN-gamma monoclonal antibodies (mAb) on day 8 postimmunization. Clinical scoring and both histological and immunohistochemical studies were undertaken for all groups. We hereby show that treatment with anti-IFN-gamma mAb worsened the disease course of 129Sv wild-type mice. However, it decreased the mean daily score in IFN-gamma R(-/-) 129Sv and the incidence of the disease down to 50% in C57Bl/6x129Sv IFN-gamma R(-/-) mice. Moreover, after anti-IFN-gamma mAb treatment, oxidative stress levels, metallothionein I and II antioxidant protein expression, and apoptoticneuronal death were increased in wild-type mice while decreased in IFN-gamma R(-/-) mice. These results suggest a putative alternative mechanism of action of this cytokine that works independent of its receptor.

Animals↗

PubMed1998

Encephalitozoon intestinalis: humoral responses in interferon-gamma receptor knockout mice infected with a microsporidium pathogenic in AIDS patients.

IFN-gamma receptor knockout mice and wild-type mice were infected per os with Encephalitozoon intestinalis. Both groups developed an infection that was chronic in the mutant mice whereas it was only transient in wild-type mice. The infection of mutant mice was characterized by the continual shedding of spores in feces, splenomegaly, the enlargement of the biliary tract, and the occurrence of numerous nodules in the liver and in the small intestine wall. The humoral response was studied by ELISA, IFA, and Western blotting. ELISA titers of anti-E. intestinalis antibodies of IgG, IgM, and IgA isotypes were higher in IFN-gamma R0/0 mice than in wild-type mice and they increased in time after infection. Levels of IgG2a were inferior to those of IgG1 in mutant mice in contrast to wild-type mice. High levels of parasite specific antibodies were accompanied by an increase in type 2 cytokines (IL-4 and IL-10) secretion in the duodenum of IFN-gamma R0/0 mice. The E. intestinalis spore wall was recognized by IgM, IgG, and IgA from all infected mice whereas the extruded polar tube only reacted with IgG and IgA from IFN-gamma R0/0 mice after 45 days of the infection. IFN-gamma R0/0 mice IgG and IgA reacting with polar tube identified also a series of proteins which could be components of this structure. On the proteins recognized by all infected mice sera, two were first recognized by IgM at day 15 and then by IgG at day 30 in wild-type (WT) mice. The persistent reactivity of all proteins in mutant mice is consistent with the chronicity of the infection in these animals; in contrast, their resorption at day 30 in WT animals corroborates the transient character of the infection in these mice. The correlation between the evolution of the proteic pattern and the development of the infection provides evidence of the validity of this murine model to study human microsporidiosis. Indeed the reported results confirm the potential value of serological methods for diagnosing E. intestinalis infection in immunocompetent and in immunocompromised human subjects, for elucidating the age pattern of the microsporidiosis and also for identifying risk groups.

AIDS-Related Opportunistic Infections↗

PubMed2001

Implications of multiple phenotypes observed in prolactin receptor knockout mice.

The development of a mouse line deficient in the PRL receptor (PRLR) would be an ideal means to better understand the multiple functions of prolactin. We were worried initially that removal of the PRLR from the mouse genome might be lethal and were surprised to find this not to be the case. We identified numerous deficiencies in PRLR knockout (KO) animals. Female homozygous mice are completely infertile and lack normal mammary development, while hemizygotes are unable to lactate following their first pregnancy. PRLR KO males and females have markedly elevated (30- to 100-fold) serum prolactin levels and in some instances pituitary hyperplasia is present. Maternal behavior is severely affected in both hemizygous and heterozygous animals. Bone formation is reduced in young animals and adults (males and females). Recently, we noticed that older KO animals show a slight reduction in body weight which appears to be due to reduced abdominal fat deposition.

Animals↗

PubMed1997

What nature's knockout teaches us about GnRH activity: hypogonadal mice and neuronal grafts.

The hypogonadal mouse is one of "nature's knockouts," bearing a specific deletion in the gene for gonadotropin-releasing hormone (GnRH), with the result that no GnRH peptide is detectable in the brain. The lack of reproductive development after birth provides an animal model that has proved fruitful in clarifying the role of GnRH in reproductive behavior and physiology. Behavioral studies with hypogonadal mice convincingly demonstrate that although GnRH may facilitate the appearance of sexual behavior, this peptide is not essential for either male or female sexual behavior in the mouse. Administration of GnRH to hypogonadal mice with regimens mimicking GnRH pulsatility initiates reproductive development. Surprisingly, continuous exposure to GnRH stimulates remarkable ovarian and uterine growth and increased FSH release, although pituitary content of LH and FSH remains unchanged. In contrast, when brain grafts of normal fetal preoptic area (POA), containing GnRH cells, are implanted in the third ventricle of adult hypogonadal mice, both pituitary and plasma gonadotropin levels increase. Grafted GnRH neurons innervate the median eminence of the host and support pulsatile LH secretion in the majority of animals with graft-associated gonadal development. Studies of hypogonadal mice with POA grafts demonstrate that distinct components of reproductive function are dissociable: hosts may demonstrate reflex but not spontaneous ovulation; others may show positive but not negative feedback. Activation of grafted GnRH cells in response to sensory input to the host, as revealed in Fos expression studies, is an example of the integration of the graft with the host brain that underlies such capabilities. A goal of these studies is to elucidate the specific connectivity underlying discrete aspects of reproductive function.

Animals↗

PubMed2002

Genotype/age interactions on aggressive behavior in gonadally intact estrogen receptor beta knockout (betaERKO) male mice.

Estrogen, as an aromatized metabolite of testosterone, has a facilitatory effect on male aggressive behavior in mice. Two subtypes of estrogen receptors, alpha (ER-alpha) and beta (ER-beta), in the brain are known to bind estrogen. Previous studies revealed that the lack of ER-alpha gene severely reduced the induction of male aggressive behavior. In contrast, mice that lacked the ER-beta gene tended to be more aggressive than wild type (WT) control mice, although the behavioral effects of ER-beta gene disruption were dependent on their social experience. These findings lead us to hypothesize that estrogen may facilitate aggression via ER-alpha whereas it may inhibit aggression via ER-beta. In the present study, we further investigated the role of ER-beta in the regulation of aggressive behavior by examining developmental changes starting at the time of first onset, around the age of puberty. Aggressive behaviors of ER-beta gene knockout (betaERKO) mice were examined in three different age groups, puberty, young-adult, and adult. Each mouse was tested every other day for three times in a resident-intruder paradigm against olfactory bulbectomized intruder mice and their trunk blood was collected for measurements of serum testosterone after the completion of the study. Overall, betaERKO mice were significantly more aggressive than WT. These genotype differences were more pronounced in puberty and young adult age groups, but not apparent in the adult age group, in which betaERKO mice were less aggressive than those in two younger age groups. Serum testosterone levels of betaERKO mice were significantly higher than those of WT mice only in the pubertal age group, but not in young adult (when betaERKO mice were still significantly more aggressive than WT mice) and adult (when no genotype differences in aggression were found) age groups. These results suggest that ER-beta mediated actions of gonadal steroids may more profoundly be involved in the inhibitory regulation of aggressive behavior in pubertal and young adult mice.

Age Factors↗

PubMed1997

Rat pancreatic islet and skin xenograft survival in CD4 and CD8 knockout mice.

The relative contributions of the CD4+ and CD8+ T cell subpopulations in xenotransplant rejection were studied using CD4 and CD8 knockout (KO) mice. Wistar Furth (WF, RT1a) rat pancreatic islet or skin xenografts were transplanted into either CD4 or CD8 KO recipients and compared to wild-type controls. Long-term survival of WF islet xenografts was observed in the CD4 KO mice (MST, >66+/-8 days) whereas CD8 KO mice rejected their islet xenografts within 8 days, similar to controls (MST, 7+/-0.2 days). In contrast, WF skin xenografts were rejected in both CD4 and CD8 KO recipients within 8 days. CD4 KO recipients which maintained xenoislets >90 days posttransplant rejected WF skin grafts within 9 days, without rejecting their original islet xenografts. These results suggest that CD4+ cells are essential for mediating islet xenograft rejection. These data also suggest that the absence of either CD4+ or CD8+ T cells is not sufficient to prevent rejection of skin xenografts.

Animals↗

PubMed1999

Contribution of NO to ischemia-reperfusion injury in the saline-perfused heart: a study in endothelial NO synthase knockout mice.

The contribution of endogenous NO to ischemia-reperfusion injury was studied in isolated perfused hearts of wild-type (WT) and endothelial NO synthase knockout (eNOS-) mice. The hearts were subjected to a 16-min period of global no-flow ischemia and were subsequently reperfused for 1 h. Cardiac contractile function was evaluated and 31P-NMR spectroscopy was used to monitor myocardial energy status and the intracellular pH. During both baseline and ischemia, there were neither significant differences in mechanical function nor in energetic parameters between the two groups, for example at baseline left ventricular developed pressure (LVDP) was 56.5+/-5.4 mmHg in WT and 58.7+/-5.2 mmHg in eNOS-and phosphocreatine (PCr) level was 12.9+/-1.3 m m in WT and 12.7+/-1.7 m m in eNOS-. In reperfusion, however, a significant improvement of the post-ischemic functional and metabolic recovery became apparent in the eNOS-hearts. While in the WT group, LVDP recovered only to 38. 4+/-5.3 mmHg, LVDP in the eNOS-group attained 49.4+/-5.5 mmHg at the end of 60 min reperfusion (P<0.05, n=8). Similarly, the recovery of PCr was significantly enhanced in the transgenic hearts as compared to WT (10.4+/-1.6 vs 8.1+/-1.3 m m, P<0.05). eNOS-hearts also showed a better restoration of dP/d t and a significant lower left ventricular enddiastolic pressure. In an additional series of wild-type hearts, the NO synthase inhibitor NG-monomethyl-L-arginine methyl ester (100 microm) also tended to improve the recovery of both LVDP (43.8+/-6.8 mmHg) and PCr (9.5+/-1.6 m m) in reperfusion (1 h), but the restoration of functional and metabolic parameters was less pronounced when compared with eNOS-. The results provide clear evidence that endogenously formed NO significantly contributes to ischemia-reperfusion injury in the saline-perfused mouse heart, most likely by peroxynitrite formation from NO.

Animals↗

PubMed2000

Canine coronary microvessel NO production regulates oxygen consumption in ecNOS knockout mouse heart.

We have previously shown that NO production by tissues following stimulation with bradykinin or other agonists can regulate oxygen consumption in skeletal muscle, heart and kidney. From those studies and from those using agonists, which classically release NO from blood vessels and which are unable to regulate tissue oxygen consumption in heart from ecNOS knockout mice, we concluded that vascular NO production is capable of regulating tissue oxygen consumption. The goal of these studies was to directly address the concept that NO production by blood vessels can regulate tissue oxygen consumption using a classical transfer paradigm. Microvessels, capable of producing NO, were prepared from canine hearts using a sieving technique, cardiac tissue was taken from mice lacking the ability to produce NO from ecNOS (ecNOS -/- mice) and tissue oxygen consumption measured in vitro using a Clark type electrode in a sealed chamber. Bradykinin (10(-7)to 10(-4)M) had no effect on tissue oxygen consumption when administered to heart from ecNOS -/mice as expected and no effect on oxygen consumption by isolated canine coronary microvessels (0+/-5% at 10(-5)M). However when coronary microvessels were co-incubated with heart from ecNOS -/- mice, bradykinin caused a dose dependent reduction in tissue oxygen consumption reaching a maximum of 44+/-10% at 10(-4)M. The effects of bradykinin were entirely abolished by L -NAME. The calculated concentration range for NO in these studies was 2.9 to 293 n M, within estimated physiologic range for the activity of NO on cytochrome oxidase. These data indicate that coronary microvessels can regulate cardiac oxygen consumption through a NO dependent mechanism.

Animals↗

PubMed2002

Alpha(1)-adrenoceptor subtypes mediate negative inotropy in myocardium from alpha(1A/C)-knockout and wild type mice.

Cardiac alpha(1)-adrenoceptors (AR) have two predominant subtypes (alpha(1A)-AR and alpha(1B)-AR) however, their roles in regulating contraction are unclear. We determined the effects of stimulating alpha(1A)-AR (using the subtype-selective agonist A61603) and alpha(1B)-AR (using a gene knockout mouse lacking alpha(1A)-AR) separately, and together (using phenylephrine) on Ca(2+) transients, intracellular pH, and contraction of mouse cardiac trabeculae. Stimulation of alpha(1)-AR subtypes separately or together caused a triphasic contractile response. After a transient ( approximately 3%) force rise (phase 1), force declined markedly (phase 2), then partially recovered (phase 3). In phase 2, the force decline (% of initial) with combined alpha(1A)-AR plus alpha(1B)-AR stimulation (50+/-3%) was more than with separate subtype stimulation (P<0.01), suggesting alpha(1A)-AR and alpha(1B)-AR mediate additive effects during phase 2. Force decline in phase 2 paralleled decreases of Ca(2+) transients that were reduced more with combined vs. separate subtype stimulation. During phase 3 the final force reduction was similar with stimulation of alpha(1A)-AR (20+/-5%), or alpha(1B)-AR (20+/-3%), or both (26+/-4%) suggesting alpha(1A)-AR and alpha(1B)-AR mediate non-additive effects during phase 3. In contrast, Ca(2+) transients recovered fully in phase 3 suggesting reduced force in phase 3 involved decreased myofilament Ca(2+)-sensitivity. Decreased Ca(2+)-sensitivity was not mediated by changes of intracellular pH since this was not affected by alpha(1)-AR stimulation. In contrast to mouse trabeculae, rat trabeculae demonstrated a positive inotropic response to alpha(1)-AR stimulation. In conclusion, for mouse myocardium in vitro both alpha(1)-adrenoceptor subtypes mediate negative inotropy involving decreased Ca(2+) transients and a decreased Ca(2+) sensitivity that does not involve altered intracellular pH.

Animals↗

PubMed1998

Mechanism of increased lung injury after acute pancreatitis in IL-10 knockout mice.

BACKGROUND: IL-10 is a potent anti-inflammatory cytokine which inhibits inflammatory cytokine release from all tissue sites. Hepatic cytokine release from Kupffer cells (KC) is one important source of inflammatory cytokines and may be the main one causing lung damage in acute pancreatitis (AP). Here we studied the KC contribution to lung injury in IL-10 knockout (KO) mice, in which tissue inflammatory cytokine release from all sites is unrestrained, and AP is more severe. METHODS: Three- to 4-week-old C57BL/6J mice and KO mice on a C57BL/6J background were used. Control mice received regular chow and gadolinium chloride (GD; 1 mg/100 g iv), to inhibit KC activity, or saline. Pancreatitis mice received a choline-deficient, ethionine-supplemented diet for 66 h to induce AP and saline or GD injections iv. After 66 h, lung tissue was assessed for edema, myeloperoxidase (MPO), and superoxide dismutase (SOD). Histology was scored in a blinded fashion. RESULTS: In pancreatitis KO mice, KC blockade had no effect on the degree of lung edema, lung neutrophil infiltration, and lung histology score. As expected, each of these parameters was more severe in the KO mice than in the normal mice: lung wet/dry ratio 5.3 +/- 0.2 versus 4.3 +/- 0.13; lung MPO (U/g) 1.9 +/- 0.2 versus 1.1 +/- 0.08; histology score 7.1 +/- 0.8 versus 5.3 +/- 0.5. CONCLUSION: Endogenous IL-10 is important in reducing the lung injury in this model of AP. KC-derived cytokines were of minor importance, compared to those derived from all other tissue sites.

Acute Disease↗

PubMed1998

Defective whisker follicles and altered brainstem patterns in activin and follistatin knockout mice.

Whisker pad innervation and whisker-specific pattern formation were examined in mice lacking the gene for activin betaA or for follistatin. Both strains of mice die within 24 h after birth. A normal array of whisker follicles is present in the snout of either phenotype. However, activin betaA-deficient mice lack whiskers, and in follistatin-deficient mice the whiskers are thin and curled. We examined the effects of aberrant, albeit innervated, follicles on the formation of whisker-specific patterns (barrelettes) in the trigeminal brainstem. Activin betaA knockout mice lack barrelettes, although the trigeminal afferent topography is not compromised. Physiological recordings suggest that trigeminal ganglion cells in these mice are less responsive to stimulation of whisker follicles. Barrelettes in follistatin-deficient mice are not as well developed as in controls, but can be discerned in some cases. These results are consistent with the notion that formation of barrelettes depends on neural activity initiated by the whiskers.

Activins↗

PubMed2002

Role of heparin-binding growth-associated molecule (HB-GAM) in hippocampal LTP and spatial learning revealed by studies on overexpressing and knockout mice.

Heparin-binding growth-associated molecule (HB-GAM) is an extracellular matrix-associated protein with neurite outgrowth-promoting activity and which is suggested to be implicated in hippocampal synaptic plasticity. To study the functions of HB-GAM in adult brain we have produced HB-GAM overexpressing mice and compared phenotypic changes in the transgenic mice to those in the HB-GAM null mice. Both mutants were viable and displayed no gross morphological abnormalities. The basal synaptic transmission was normal in the area CA1 of hippocampal slices from the genetically modified mice. However, long-term potentiation (LTP) was attenuated in the mice overexpressing HB-GAM, whereas enhanced LTP was detected in the HB-GAM-deficient mice. Changes in LTP seen in vitro were paralleled by behavioral alterations in vivo. The animals overexpressing HB-GAM displayed faster learning in water maze and decreased anxiety in elevated plus-maze, while the HB-GAM knockouts demonstrated an opposite behavioral phenotype. These results show that HB-GAM suppresses LTP in hippocampus and plays a role in regulation of learning-related behavior.

Animals↗

PubMed2002

High-level expression of receptor tyrosine kinase Ret and responsiveness to Ret-activating ligands in pheochromocytoma cell lines from neurofibromatosis knockout mice.

Pheochromocytoma cell lines derived from neurofibromatosis knockout mice express high levels of the receptor tyrosine kinase Ret, which is involved in the pathogenesis of human pheochromocytomas in hereditary multiple endocrine neoplasia syndrome type 2 (MEN2). Mouse pheochromocytoma (MPC) cells respond to the Ret-activating ligand GDNF by exhibiting Ret phosphorylation, neurite outgrowth, decreased proliferation, and altered expression of catecholamine biosynthetic enzymes. GDNF exerts similar effects on human pheochromocytoma cells in primary cultures. Ret is minimally expressed by normal mouse chromaffin cells, from which pheochromocytomas are derived. Its expression at high levels by MPC cells suggests possible relationships between two previously unrelated tumor syndromes, neurofibromatosis, and MEN2. The responsiveness of these cells to GDNF suggests that they may be a valuable new model for neurobiology.

Animals↗

PubMed2002

Straight-chain acyl-CoA oxidase knockout mouse accumulates extremely long chain fatty acids from alpha-linolenic acid: evidence for runaway carousel-type enzyme kinetics in peroxisomal beta-oxidation diseases.

Extremely long chain polyunsaturated fatty acids (ELCPs) with >24 carbons and four or more double bonds are normally found in excitatory tissues but have no known function, and are greatly increased in brain and other tissues of humans with peroxisomal disorders. Straight-chain acyl-CoA oxidase (AOX) catalyzes the first, rate-limiting step of peroxisomal beta-oxidation of very-long-chain saturated and unsaturated fatty acids. We have studied the polyunsaturated fatty acid metabolism of AOX knockout mice (AOX-/- as a model of human AOX deficiency (pseudo-neonatal adrenoleukodystrophy), and as a genetic tool to test the putative peroxisomal beta-oxidation involvement in polyunsaturated fatty acid synthesis. Liver lipids of 26-day-old weanling AOX-/- mice livers accumulate n-3 and n-6 ELCPs from C24 to C30 with 5 and 6 double bonds, have 356 +/- 66 microg/g docosahexaenoic acid (22:6n-3), similar to congenic (AOX -/* = AOX+/+ and AOX+/-) controls (401 +/- 96 microg/g), but increased 22:5n-6 (22.4 +/- 3.7 vs 6.4 +/- 1.5 microg/g). AOX+/* mice injected intraperitoneally at 23 days with [U-(13)C]-18:3n-3 show strong labeling of 22:6n-3 after 72 h, whereas AOX -/- mice display less labeling of 22:6n-3 but strong tracer incorporation into 24:6n-3, 26:6n-3, and 28:6n-3, after the same period. These data suggest that ELCPs are natural runaway elongation by-products of 22:6n-3 and 22:5n-6 synthesis, which are normally disposed of by peroxisomal beta-oxidation. Under conditions with impaired peroxisomal beta-oxidation, such as Zellweger syndrome and adrenoleukodystrophies, ELCPs accumulate due to increased synthesis and impaired disposal. Two mechanisms for the formation of these runaway elongation by-products and the involvement of secondary carnitine deficiency in this process are proposed: n-3 ELCPs are synthesized by a carnitine-dependent multifunctional mitochondrial docosahexaenoic acid synthase (mtDHAS) which normally synthesizes primarily 22:6n-3, while n-6 ELCPs are synthesized by independent elongation enzymes in the endoplasmic reticulum.

Acyl-CoA Oxidase↗