Biomedical subjects

R L Hamilton

Publications and source records attributed to R L Hamilton.

At least 19 recordsLinked to original sources

PubMed2000

Predictors of progression in patients with AD and Lewy bodies.

OBJECTIVE: To examine the differences in the pattern of progression between AD and AD with Lewy bodies (AD+LB). METHODS: The authors examined predictors of functional and cognitive disability, institutionalization, and death, as well as time to the development of psychosis (e.g., delusions, hallucinations), extrapyramidal signs (EPS), diurnal hypersomnia, and depression in 185 patients with definite AD and 60 with autopsy-confirmed AD+LB. In addition, they analyzed a selected group of patients who did not have comorbid systemic or CNS disease that may have affected progression of the disease (AD = 98 versus AD+LB = 44). The mean follow-up was 58.91 +/- 35.2 months. RESULTS: All cases: Patients with AD+LB had faster time to the development of EPS and diurnal hypersomnia, but not to the development of psychosis or depression. The rate of cognitive and functional decline, time to institutionalization, and physical survival was not different between AD+LB and AD. Selected cases: Patients with AD+LB developed earlier EPS and diurnal hypersomnia than AD patients, and there was a trend to develop earlier major depression, but no differences were noted in time to psychosis. Patients with AD+LB had a faster time to institutionalization than those with AD. The rate of cognitive and functional decline and physical survival was not different between AD+LB and AD in these selected cases. CONCLUSION: Patients with AD+LB can develop EPS and diurnal hypersomnia earlier and have faster time to institutionalization than those with AD alone, but cognitive and functional decline and physical survival are similar between these two entities.

Aged↗

PubMed2000

Severity of cognitive impairment and the clinical diagnosis of AD with Lewy bodies.

OBJECTIVE: 1) To examine the clinical differences between AD and AD with Lewy bodies (AD+LB); and 2) to determine the accuracy of Consensus guidelines for the clinical diagnosis of dementia with Lewy bodies (DLB) at different levels of dementia severity. METHODS: The authors examined the clinical characteristics of 185 patients with pathologically diagnosed AD alone and 60 with AD+LB. The relationship between clinical symptoms and AD+LB was determined by multivariate analyses, controlled by age, duration of symptoms, presence of cerebrovascular disease, and dementia severity. RESULTS: Mild dementia syndrome: No specific clinical symptom was associated with the presence of AD+LB. The sensitivity of the diagnosis of DLB was 62% and specificity was 54%. Moderate dementia syndrome: Extrapyramidal signs (EPS), especially cogwheel rigidity, and major depression were associated with AD+LB. The sensitivity for DLB was 82% and specificity was 31%. Severe dementia syndrome: Cogwheel rigidity and diurnal hypersomnia were associated with AD+LB. The sensitivity for DLB was 93% and specificity was 16%. CONCLUSIONS: The presence of EPS is not useful in differentiating AD+LB from AD in patients with mild dementia. However, as the disease progressed, they emerge as defining features, especially cogwheel rigidity. The accuracy of AD+LB diagnosis varies according the severity of the dementia syndrome. The low sensitivity and specificity in AD+LB patients with mild dementia suggest that in early stages AD+LB patients do not present the clinical characteristics of DLB. By contrast, the high sensitivity and low specificity for the diagnosis of DLB in moderate/severe dementia stages suggests that AD patients can also have characteristic symptoms of DLB. These results indicate that the antemortem diagnosis of AD+LB is difficult in all dementia stages, and better clinical and biologic differentiations of these entities are needed.

Aged↗

PubMed2000

Differential expression of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 in chronic murine retroviral encephalitis.

The cell adhesion molecules, intercellular adhesion molecule (ICAM)-1 and vascular cell adhesion molecule (VCAM)-1, are important mediators of immune interactions within the central nervous system (CNS). A wide variety of pro-inflammatory insults to the brain, including viral infection, result in upregulation of these molecules on brain endothelial cells, astrocytes, and microglia. This study investigated the expression of ICAM-1 and VCAM-1 in chronic encephalitis induced by infection with a temperature sensitive (ts-1) strain of Moloney murine leukaemia virus (MoMuLV), an ecotropic murine retrovirus. During the late stages of disease, viral antigen was present in both endothelial cells and microglia, but not astrocytes, in regions of spongiform change and gliosis. In these areas, ICAM-1 staining was detected on activated microglia, but not on endothelial cells or astrocytes. In contrast, no cells showed increased VCAM-1 expression in the CNS. These findings demonstrate that there is cell-specific, differential expression of these adhesion molecules in ts-1 retroviral encephalitis. The lack of endothelial cell expression correlates with the characteristic lack of lymphocytic infiltrate in this chronic retroviral encephalitis and suggests that increased microglial ICAM-1 expression may play a role in the pathogenesis of MoMuLV (ts-1)-mediated neurodegeneration.

Animals↗

PubMed2000

An intrasylvian "fibroma" in a child with cystic fibrosis: case report.

OBJECTIVE AND IMPORTANCE: Intracranial fibrous tumors are uncommon during childhood. An unusual case of benign intrasylvian "fibroma" that has remained clinically and radiographically stable more than 3 years after a subtotal resection is described. CLINICAL PRESENTATION: A 9-year-old girl with cystic fibrosis presented with new-onset focal seizures referable to a large calcified left sylvian fissure mass. INTERVENTION: An open biopsy with subtotal resection of the lesion revealed a benign process characterized by exuberant fibrocollagenous tissue intermeshed with chronic inflammatory cells and foreign body giant cells, encompassing islands of gliotic brain tissue. Immunohistochemical analysis showed staining for epithelial membrane antigen and reticulin within some of the spindle cells, although the majority were nonreactive. The majority of tumor cells exhibited staining for laminin; CD34 staining was absent. Ultrastructural studies were also suggestive of a fibroblastic rather than a meningothelial origin of the lesion, with elongated cells separated by abundant extracellular collagen. Although dense adherence of the mass to the pial surface and the middle cerebral artery vessels precluded a complete resection, the patient remains seizure-free without anticonvulsant therapy more than 3 years postoperatively with no evidence of growth of the lesion. CONCLUSION: The lesion in this patient bears morphological similarity to a rare group of tumors referred to as "intracerebral fibromas," although a variety of other rare mesenchymal neoplasms were also considered within the differential diagnosis. However, the absence of any definite neoplastic features, the finding of chronic inflammatory changes, and the lack of growth of the residual tumor during an extended follow-up interval indicate that the mass may represent either an extremely indolent neoplasm or a nonneoplastic process. The differential diagnosis of intracranial fibrous tumors is contrasted with that of the reported case.

Brain Neoplasms↗

PubMed2000

Lewy bodies in Alzheimer's disease: a neuropathological review of 145 cases using alpha-synuclein immunohistochemistry.

Antibodies to alpha-synuclein (AS) now provide a sensitive and specific method for the detection of Lewy bodies (LBs) and their use will allow a more accurate determination of the prevalence of LBs in Alzheimer's Disease (AD). Studies using AS immunohistochemistry (IHC) have found LBs in the amygdala of over 60% early onset familial AD and in 50% of Down's syndrome patients with AD, however, no studies have reported the use of AS IHC to detect LBs in a large cohort of sporadic AD. This study examined 145 sporadic AD cases diagnosed using CERAD criteria from 1995-1999 for the presence of LBs using AS IHC. AS IHC detected LBs in 88/145 (60.7%) of sporadic AD cases. Similarly, LBs were found in 56.8% of the 95 cases fulfilling the more stringent NIA-RI criteria for the diagnosis of AD (Braak stage 5-6). In all cases with LBs, the amygdala was involved and LBs were always most numerous in this area, however, in some cases LBs in the substantia nigra were rare or not present. In conclusion, this study found that AS IHC detects LBs in the majority of sporadic AD cases and that the amygdala is the most commonly affected region.

Alzheimer Disease↗

PubMed2000

X-34, a fluorescent derivative of Congo red: a novel histochemical stain for Alzheimer's disease pathology.

X-34, a lipophilic, highly fluorescent derivative of Congo red, was examined as a histochemical stain for pathological changes in Alzheimer's disease (AD). X-34 intensely stained neuritic and diffuse plaques, neurofibrillary tangles (NFTs), neuropil threads, and cerebrovascular amyloid. Comparison to standard methods of demonstrating AD pathology showed that X-34 correlated well with Bielschowsky and thioflavin-S staining. X-34 staining of NFTs correlated closely with anti-TAU antibody staining. A 1:1 correspondence of X-34 and anti-A beta antibody staining of plaques and cerebrovascular amyloid was observed. Both X-34 and thioflavin-S staining were eliminated by formic acid pretreatment, suggesting that beta-sheet secondary protein structure is a necessary determinant of staining. X-34 may be a general amyloid stain, like Congo red, because it also stains systemic amyloid deposits due to lambda-light chain monoclonal gammopathy. In conclusion, X-34 is a highly fluorescent marker for beta-sheet structures and intensely labels amyloid plaques, NFTs, neuropil threads, and vascular amyloid in AD brains. It can be used with both paraffin-embedded and frozen tissues as well as in combination with immunohistochemistry for double labeling. The intensity of staining and the simplicity and reproducibility of the technique suggest that it may be a useful addition to the standard techniques for evaluation of AD neuropathology. (J Histochem Cytochem 48:1223-1232, 2000)

Aged↗

PubMed1999

Tyramide signal amplification method in multiple-label immunofluorescence confocal microscopy.

The tyramide signal amplification (TSA) method has recently been introduced to improve the detection sensitivity of immunohistochemistry. We present three examples of applying this method to immunofluorescence confocal laser microscopy: (1) single labeling for CD54 in frozen mouse brain tissue; (2) double labeling with two unconjugated primary antibodies raised in the same host species (human immunodeficiency virus type 1 p24 and CD68) in paraffin-biopsied human lymphoid tissue; and (3) triple labeling for brain-derived neurotrophic factor, glial fibrillary acidic protein, and HLA-DR in paraffin-autopsied human brain tissue. The TSA method, when properly optimized to individual tissues and primary antibodies, is an important tool for immunofluorescence microscopy. Furthermore, the TSA method and enzyme pretreatment can be complementary to achieve a high detection sensitivity, particularly in formalin-fixed paraffin-embedded archival tissues. Using multiple-label immunofluorescence confocal microscopy to characterize the cellular localization of antigens, the TSA method can be critical for double labeling with unconjugated primary antibodies raised in the same host species.

Acquired Immunodeficiency Syndrome↗

PubMed1999

Absence of brain-derived neurotrophic factor and trkB receptor immunoreactivity in glia of Alzheimer's disease.

Alterations in the neuronal expression of some neurotrophins have been shown in various neurodegenerative processes, particularly Alzheimer's disease (AD). Glia may up-regulate neurotrophins and their high-affinity tyrosine kinase (trk) receptors in response to neural injury. In human immunodeficiency virus type 1 (HIV-1) encephalitis, activated microglia were shown to express brain-derived neurotrophic factor (BDNF), while reactive astrocytes expressed trkB receptor. This observation has suggested the existence of local neurotrophic regulation between different glial populations. To characterize the glial cellular distribution of BDNF and trkB receptor proteins in AD, we studied selected regions of postmortem brains from four AD and three age-matched control patients by double-immunofluorescence confocal microscopy. In both groups, BDNF immunoreactivity was distributed in neuronal perikarya and neuritic processes in the neocortex and hippocampus. No BDNF immunoreactivity was observed in microglia or astrocytes within and between senile plaques of AD. Catalytic trkB receptor immunoreactivity was present in neuronal perikarya in the neocortex and hippocampus. Reactive astrocytes and microglia were not immunoreactive for catalytic trkB. The absence of BDNF and trkB proteins in glia in AD patients is in contrast to the finding in patients with HIV-1 encephalitis. This difference suggests that glial expression of BDNF and trkB proteins may be characteristic of particular disease processes, rather than merely representing a stereotyped response to any type of neural injury.

Aged↗

PubMed1999

Estrogen induction of VLDLy assembly in egg-laying hens.

The yolk of a 60-g chicken egg contains 6 g of triacylglycerols transported to the oocyte from the liver of the laying hen in apolipoprotein (apo) B-containing particles. With the onset of egg production, estrogen shifts hepatocytic lipoprotein production from generic VLDL to VLDLy (yolk targeted). These VLDLy are triacylglycerol-rich particles; they are reduced in size by one half, are resistant to lipoprotein lipase and are taken up intact by oocyte receptors. The VLDLy pathway for apoB provides sufficient energy for the caloric requirements of chick development. VLDLy size reduction occurs in spite of surplus liver triacylglycerols and is necessary for VLDL particles to pass through the granulosa basal lamina and reach the receptors located on the oocyte surface. New ultrastructural data show that some proximal tubule cells of bird kidney secrete generic VLDL, perhaps providing energy and other VLDL-associated nutrients to tissues bypassed by VLDLy. Birds are an apoB100-only species, providing a natural in vivo model with which to investigate mechanisms of apoB100 VLDL assembly. Preliminary studies of liver lipoprotein assembly intermediates isolated from the biosynthetic membranes (endoplasmic reticulum) of the laying hen are consistent with the presence of both putative first- and second-step precursor particles of VLDLy. These findings suggest that the two-step mechanism of apoB core lipidation is an ancient development in apoB biology, handed down to mammals from oviparous ancestors.

Animals↗

PubMed1999

Increases in Bcl-2 and cleavage of caspase-1 and caspase-3 in human brain after head injury.

The bcl-2 and caspase families are important regulators of programmed cell death in experimental models of ischemic, excitotoxic, and traumatic brain injury. The Bcl-2 family members Bcl-2 and Bcl-xL suppress programmed cell death, whereas Bax promotes programmed cell death. Activated caspase-1 (interleukin-1beta converting enzyme) and caspase-3 (Yama/Apopain/Cpp32) cleave proteins that are important in maintaining cytoskeletal integrity and DNA repair, and activate deoxyribonucleases, producing cell death with morphological features of apoptosis. To address the question of whether these Bcl-2 and caspase family members participate in the process of delayed neuronal death in humans, we examined brain tissue samples removed from adult patients during surgical decompression for intracranial hypertension in the acute phase after traumatic brain injury (n=8) and compared these samples to brain tissue obtained at autopsy from non-trauma patients (n=6). An increase in Bcl-2 but not Bcl-xL or Bax, cleavage of caspase-1, up-regulation and cleavage of caspase-3, and evidence for DNA fragmentation with both apoptotic and necrotic morphologies were found in tissue from traumatic brain injury patients compared with controls. These findings are the first to demonstrate that programmed cell death occurs in human brain after acute injury, and identify potential pharmacological and molecular targets for the treatment of human head injury.

Adolescent↗

PubMed1999

Coexistence of a ganglioglioma and Rasmussen's encephalitis.

A small number of recent reports have documented coexisting cerebral pathologic entities in patients with Rasmussen's encephalitis. We report the case of a 4-year-old boy who presented with refractory seizures and was found to have both a ganglioglioma and Rasmussen's encephalitis of the same hemisphere. The patient ultimately underwent a functional hemispherectomy with excellent seizure control. We also review the clinical and pathologic hallmarks of both gangliogliomas and Rasmussen's encephalitis. We hope that the addition of this patient to the small but growing literature on dual pathology in Rasmussen's encephalitis may help shed some light on the etiology of this mysterious disease.

Brain↗

PubMed1999

Disruption of LDL receptor gene in transgenic SREBP-1a mice unmasks hyperlipidemia resulting from production of lipid-rich VLDL.

Transgenic mice that overexpress the nuclear form of sterol regulatory element binding protein-1a (SREBP-1a) in liver (TgBP-1a mice) were shown previously to overproduce cholesterol and fatty acids and to accumulate massive amounts of cholesterol and triglycerides in hepatocytes. Despite the hepatic overproduction of lipids, the plasma levels of cholesterol ( approximately 45 mg/dl) and triglycerides ( approximately 55 mg/dl) were not elevated, perhaps owing to degradation of lipid-enriched particles by low-density lipoprotein (LDL) receptors. To test this hypothesis, in the current studies we bred TgBP-1a mice with LDL receptor knockout mice. As reported previously, LDLR-/- mice manifested a moderate elevation in plasma cholesterol ( approximately 215 mg/dl) and triglycerides ( approximately 155 mg/dl). In contrast, the doubly mutant TgBP-1a;LDLR-/- mice exhibited marked increases in plasma cholesterol ( approximately 1,050 mg/dl) and triglycerides ( approximately 900 mg/dl). These lipids were contained predominantly within large very-low-density lipoprotein (VLDL) particles that were relatively enriched in cholesterol and apolipoprotein E. Freshly isolated hepatocytes from TgBP-1a and TgBP-1a;LDLR-/- mice overproduced cholesterol and fatty acids and secreted increased amounts of these lipids into the medium. Electron micrographs of livers from TgBP-1a mice showed large amounts of enlarged lipoproteins within the secretory pathway. We conclude that the TgBP-1a mice produce large lipid-rich lipoproteins, but these particles do not accumulate in plasma because they are degraded through the action of LDL receptors.

Animals↗

PubMed1999

Analysis of the role of microsomal triglyceride transfer protein in the liver of tissue-specific knockout mice.

A deficiency in microsomal triglyceride transfer protein (MTP) causes the human lipoprotein deficiency syndrome abetalipoproteinemia. However, the role of MTP in the assembly and secretion of VLDL in the liver is not precisely understood. It is not clear, for instance, whether MTP is required to move the bulk of triglycerides into the lumen of the endoplasmic reticulum (ER) during the assembly of VLDL particles. To define MTP's role in hepatic lipoprotein assembly, we recently knocked out the mouse MTP gene (Mttp). Unfortunately, achieving our objective was thwarted by a lethal embryonic phenotype. In this study, we produced mice harboring a "floxed" Mttp allele and then used Cre-mediated recombination to generate liver-specific Mttp knockout mice. Inactivating the Mttp gene in the liver caused a striking reduction in VLDL triglycerides and large reductions in both VLDL/LDL and HDL cholesterol levels. The Mttp inactivation lowered apo B-100 levels in the plasma by >95% but reduced plasma apo B-48 levels by only approximately 20%. Histologic studies in liver-specific knockout mice revealed moderate hepatic steatosis. Ultrastructural studies of wild-type mouse livers revealed numerous VLDL-sized lipid-staining particles within membrane-bound compartments of the secretory pathway (ER and Golgi apparatus) and few cytosolic lipid droplets. In contrast, VLDL-sized lipid-staining particles were not observed in MTP-deficient hepatocytes, either in the ER or in the Golgi apparatus, and there were numerous cytosolic fat droplets. We conclude that MTP is essential for transferring the bulk of triglycerides into the lumen of the ER for VLDL assembly and is required for the secretion of apo B-100 from the liver.

Alleles↗

PubMed1999

A rapid calcium precipitation method of recovering large amounts of highly pure hepatocyte rough endoplasmic reticulum.

We sought a rapid and non-ultracentrifugal method of recovering large amounts of highly pure rough endoplasmic reticulum (RER) membranes from livers. By substantially modifying a 20-year-old calcium precipitation technique, we obtained a RER fraction from rat liver and established its high degree of purity by quantitating classic membrane markers for different subcellular organelles. This RER fraction is highly enriched in four known proteins (or enzyme activities) required for lipoprotein assembly: apolipoprotein B, microsomal triglyceride transfer protein, acyl CoA:diacylglycerol acyltransferase, and acyl CoA:cholesterol acyltransferase, when compared to two classical RER markers, RNA and glucose-6-phosphatase. From one 10-12 g rat liver, we recover ten to twelve RER pellets of 1.5-1.6 cm in diameter containing approximately 110-125 mg of total protein, about half of which is sodium carbonate-releasable. By electron microscopy, these large RER pellets from rat livers are homogeneously comprised largely of non-vesiculated short strips of ribosome-rich membranes. This novel technique for isolating RER membranes from liver may provide a useful tool for future studies on the assembly of apolipoprotein B-containing lipoproteins as well as for research focused on mechanisms of secretory and membrane protein translation, translocation, and folding.

Acyltransferases↗

PubMed1999

Epidermal growth factor receptor expression and gene amplification in high-grade non-brainstem gliomas of childhood.

Epidermal growth factor receptor (EGFR) is commonly overexpressed in adult high-grade gliomas. Forty to 50% of such tumors demonstrate amplification of the EGFR gene, often with rearrangement and constitutive activation of the gene product, suggesting that EGFR might play a role in the malignant progression of a subset of these neoplasms. In this regard, several groups have shown that overexpression of EGFR is associated with an adverse outcome in adult gliomas. In contrast to the extensive studies of EGFR status that have been performed in adult high-grade gliomas, little information has been reported about EGFR expression and amplification, as well as their prognostic relevance in high-grade gliomas of childhood, which carry a somewhat more favorable prognosis than their adult counterparts. To address this issue, we examined the expression of EGFR using immunohistochemistry and screened for amplification of the EGFR gene using a competitive PCR in a series of 27 archival pediatric high-grade nonbrainstem gliomas treated consecutively at our institution between 1975 and 1992. Tumors were categorized based on protein expression patterns, and the association between expression status and outcome was examined. Although elevated immunoreactivity for EGFR was observed in 80% of tumors, only two of the cases had gene amplification. No difference in outcome was observed between tumors that exhibited extensive EGFR immunoreactivity and those that did not (P > 0.3). Although EGFR expression did not seem to be of prognostic relevance for the outcome of pediatric patients harboring high-grade nonbrainstem gliomas, the consistently high levels of expression of EGFR in these neoplasms suggest that this receptor plays a role in the malignant phenotype of these tumors. Accordingly, treatment approaches targeting EGFR might be of potential therapeutic benefit for high-grade gliomas of childhood.

Adolescent↗

PubMed1999

Apolipoprotein B-related gene expression and ultrastructural characteristics of lipoprotein secretion in mouse yolk sac during embryonic development.

In mice, the yolk sac appears to play a crucial role in nourishing the developing embryo, especially during embryonic days (E) 7;-10. Lipoprotein synthesis and secretion may be essential for this function: embryos lacking apolipoprotein (apo) B or microsomal triglyceride transfer protein (MTP), both of which participate in the assembly of triglyceride-rich lipoproteins, are apparently defective in their ability to export lipoproteins from yolk sac endoderm cells and die during mid-gestation. We therefore analyzed the embryonic expression of apoB, MTP, and alpha-tocopherol transfer protein (alpha-TTP), which have been associated with the assembly and secretion of apoB-containing lipoproteins in the adult liver, at different developmental time points. MTP expression or activity was found in the yolk sac and fetal liver, and low levels of activity were detected in E18.5 placentas. alpha-TTP mRNA and protein were detectable in the fetal liver, but not in the yolk sac or placenta. Ultrastructural analysis of yolk sac visceral endoderm cells demonstrated nascent VLDL within the luminal spaces of the rough endoplasmic reticulum and Golgi apparatus at E7.5 and E8.5. The particles were reduced in diameter at E13.5 and reduced in number at E18.5;-19. The data support the hypothesis that the yolk sac plays a vital role in providing lipids and lipid-soluble nutrients to embryos during the early phases (E7;-10) of mouse development. secretion in mouse yolk sac during embryonic development.

Animals↗

PubMed1998

Lamellar lipoproteins uniquely contribute to hyperlipidemia in mice doubly deficient in apolipoprotein E and hepatic lipase.

Remnants of triglyceride-rich lipoproteins containing apolipoprotein (apo) B-48 accumulate in apo E-deficient mice, causing pronounced hypercholesterolemia. Mice doubly deficient in apo E and hepatic lipase have more pronounced hypercholesterolemia, even though remnants do not accumulate appreciably in mice deficient in hepatic lipase alone. Here we show that the doubly deficient mice manifest a unique lamellar hyperlipoproteinemia, characterized by vesicular particles 600 A-1,300 A in diameter. As seen by negative-staining electron microscopy, these lipoproteins also contain an electron-lucent region adjacent to the vesicle wall, similar to the core of typical lipoproteins. Correlative chemical analysis indicates that the vesicle wall is composed of a 1:1 molar mixture of cholesterol and phospholipids, whereas the electron-lucent region appears to be composed of cholesteryl esters (about 12% of the particle mass). Like the spherical lipoproteins of doubly deficient mice, the vesicular particles contain apo B-48, but they are particularly rich in apo A-IV. We propose that cholesteryl esters are removed from spherical lipoproteins of these mice by scavenger receptor B1, leaving behind polar lipid-rich particles that fuse to form vesicular lipoproteins. Hepatic lipase may prevent such vesicular lipoproteins from accumulating in apo E-deficient mice by hydrolyzing phosphatidyl choline as scavenger receptor B1 removes the cholesteryl esters and by gradual endocytosis of lipoproteins bound to hepatic lipase on the surface of hepatocytes.

Animals↗

PubMed1998

A gene-targeted mouse model for familial hypobetalipoproteinemia. Low levels of apolipoprotein B mRNA in association with a nonsense mutation in exon 26 of the apolipoprotein B gene.

Familial hypobetalipoproteinemia, a syndrome characterized by abnormally low plasma levels of low density lipoprotein cholesterol, is caused by mutations in the apolipoprotein (apo) B gene that interfere with the synthesis of a full-length apoB100. In many cases of familial hypobetalipoproteinemia, nonsense or frameshift mutations result in the synthesis of a truncated apoB protein. To understand why these mutations result in low plasma cholesterol levels, we used gene targeting in mouse embryonic stem cells to introduce a nonsense mutation (N1785Stop) into exon 26 of the mouse Apob gene. The sole product of this mutant Apob allele was a truncated apoB, apoB39. Mice homozygous for this "apoB39-only" (Apob39) allele had low plasma levels of apoB39 and markedly reduced plasma levels of very low density lipoprotein and low density lipoprotein cholesterol when fed a high fat diet. Analysis of liver and intestinal RNA from heterozygous apoB39-only mice revealed that the Apob39 mRNA levels were 60-70% lower than those from the wild-type allele. Interestingly, apoB39 was not cleared as rapidly from the plasma as apoB48. The apoB39-only mice provide new insights into the mechanisms of familial hypobetalipoproteinemia and the structural features of apoB that are important for lipoprotein metabolism.

Animals↗