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Biomedical subjects

M R Hayden

Publications and source records attributed to M R Hayden.

At least 91 records · Page 5Linked to original sources
PubMed1999

Two common mutations (D9N, N291S) in lipoprotein lipase: a cumulative analysis of their influence on plasma lipids and lipoproteins in men and women.

We assessed the effect of two common mutations in the lipoprotein lipase gene (LPL), D9N and N291S, which have been shown to modulate plasma lipids in a wide spectrum of patients. A total of 1114 men and 1 144 women from the Framingham Offspring Study (FOS) were analyzed for these two LPL variants. Subsequently, the association with fasting plasma lipids and risk of coronary artery disease (CHD) was determined. We extended our study by calculating weighed means of lipids and lipoproteins in carriers and non-carriers for these LPL mutations in patients with genetic dyslipidemias, CHD patients and healthy controls. In the FOS sample, the D9N and N291S alleles were associated with lower high-density lipoprotein-cholesterol (HDL-C) (delta = - 0.07 mmol/ 1, p = 0.03) and a trend towards increased triglycerides (delta = 0.25 mmol/ 1, p = 0.07). In women, a trend towards the high triglyceride, low HDL-C phenotype was evident (delta = - 0.02 mmol/1 for HDL-C and delta = 0.14 mmol/l for triglycerides, respectively). Cumulative analysis of other studies of male carriers of the D9N and N291S revealed higher levels of triglycerides (D291N; 2.60(1.85) mmol/l vs. 1.62(1.18) mmol/l: p < 0.0001) (D9N; 1.94 (1.19) mmol/l vs. 1.74(1.17) mmol/l: p < 0.001) and lower HDL-C (N291S; 1.04(0.32) mmol/l vs. 1.15(0.28) mmol/l: p < 0.0001) (D9N; 1.08(0.24) mmol/l vs. 1.16(0.28) mmol/l: p < 0.0001). In females, results differed with higher TG levels (N291S; 1.70(0.99) mmol/l vs. 1.10(0.63) mmol/l: p < 0.001) (D9N; 1.08(0.76) mmol/l vs. 0.96(0.51) mmol/l: p < 0.01) and lower HDL-C levels (N291S; 1.27(0.33) mmol/l vs. 1.51(0.32) mmol/l: p < 0.0001); however, the HDL-C levels for D9N carriers were similar to non-carriers (D9N; 1.52(0.29) mmol/l vs. 1.53(0.35) mmol/l: p = 0.83). Our data provide evidence that common variants of the LPL gene are significant modulators of lipid and lipoprotein levels in both men and women.

Cholesterol, HDL↗
PubMed1999

Mutations in ABC1 in Tangier disease and familial high-density lipoprotein deficiency.

Genes have a major role in the control of high-density lipoprotein (HDL) cholesterol (HDL-C) levels. Here we have identified two Tangier disease (TD) families, confirmed 9q31 linkage and refined the disease locus to a limited genomic region containing the gene encoding the ATP-binding cassette transporter (ABC1). Familial HDL deficiency (FHA) is a more frequent cause of low HDL levels. On the basis of independent linkage and meiotic recombinants, we localized the FHA locus to the same genomic region as the TD locus. Mutations in ABC1 were detected in both TD and FHA, indicating that TD and FHA are allelic. This indicates that the protein encoded by ABC1 is a key gatekeeper influencing intracellular cholesterol transport, hence we have named it cholesterol efflux regulatory protein (CERP).

ATP Binding Cassette Transporter 1↗
PubMed1999

Lipid and lipoprotein analysis of cats with lipoprotein lipase deficiency.

BACKGROUND: We have previously described a colony of domestic cats with a naturally occurring mutation in the lipoprotein lipase (LPL) gene. We have now further characterized cats homozygous for LPL deficiency (LPL -/-, homozygotes), and have contrasted these with heterozygotes (LPL +/-) and normal cats (LPL +/+). MATERIALS AND METHODS: Density gradient ultracentrifugation with subsequent lipid analysis, agarose and polyacrylamide gel electrophoresis was used to examine detailed liproprotein differences between the genotypes. Oral fat loading studies and breast milk fatty acid analysis were also performed to further characterize the phenotypic expression of LPL deficiency in this model system. RESULTS: Several lipid abnormalities associated with homozygosity for LPL deficiency were evident. Triglyceride-rich lipoprotein-triglycerides (TRL-TG) and cholesterol (TRL-C) were higher (TRL-TG 2.09 +/- 1.14 vs. 0.15 +/- 0.04 mmol L-1, P < 0.001; TRL-C 0.42 +/- 0.30 vs. 0.11 +/- 0.16 mmol L-1, P < 0.05) in male -/- than in male +/+ cats, as was HDL-cholesterol (HDL-C, 1.75 +/- 0.24 vs. 1.41 +/- 0.14 mmol L-1, P < 0.05). LDL-C levels were lower in homozygous cats than in control cats, similar to what is seen in human LPL deficiency. Oral fat loading studies revealed that homozygous cats have a marked reduced ability to clear plasma TGs in terms of peak time (7 h vs. 3 h), peak height (9.36 vs. 1.1 mmol L-1), area under the TG clearance curve (AUC, 280.3 vs. 2.2 h mmol L-1) and time to return to baseline. Fasting lipid and lipoprotein levels were not significantly different between heterozygous and normal cats. However, oral fat loading in heterozygotes revealed an intermediate phenotype (peak of 2.35 mmol L-1 at 5 h, AUC 13.1 h mmol L-1), highlighting the impaired TG clearance in these animals. CONCLUSION: Thus, LPL deficiency in the cat results in a lipid and lipoprotein phenotype that predominantly parallels human LPL deficiency, further validating the use of these animals in studies on the pathobiology of LPL.

Animals↗
PubMed1999

Kennedy's disease: caspase cleavage of the androgen receptor is a crucial event in cytotoxicity.

X-linked spinal and bulbar muscular atrophy (SBMA), Kennedy's disease, is a degenerative disease of the motor neurons that is associated with an increase in the number of CAG repeats encoding a polyglutamine stretch within the androgen receptor (AR). Recent work has demonstrated that the gene products associated with open reading frame triplet repeat expansions may be substrates for the cysteine protease cell death executioners, the caspases. However, the role that caspase cleavage plays in the cytotoxicity associated with expression of the disease-associated alleles is unknown. Here, we report the first conclusive evidence that caspase cleavage is a critical step in cytotoxicity; the expression of the AR with an expanded polyglutamine stretch enhances its ability to induce apoptosis when compared with the normal AR. The AR is cleaved by a caspase-3 subfamily protease at Asp146, and this cleavage is increased during apoptosis. Cleavage of the AR at Asp146 is critical for the induction of apoptosis by AR, as mutation of the cleavage site blocks the ability of the AR to induce cell death. Further, mutation of the caspase cleavage site at Asp146 blocks the ability of the SBMA AR to form perinuclear aggregates. These studies define a fundamental role for caspase cleavage in the induction of neural cell death by proteins displaying expanded polyglutamine tracts, and therefore suggest a strategy that may be useful to treat neurodegenerative diseases associated with polyglutamine repeat expansions.

Carcinogens↗
PubMed1999

Life without huntingtin: normal differentiation into functional neurons.

Huntington disease (HD) is a neurodegenerative disorder associated with polyglutamine expansion in a recently identified protein, huntingtin. Huntingtin is widely expressed and plays a crucial role in development, because gene-targeted HD-/- mouse embryos die early in embryogenesis. To analyze the function of normal huntingtin, we have generated HD-/- embryonic stem (ES) cells and used an in vitro model of ES cell differentiation to analyze their ability to develop into neuronal cells. Expression analysis of wild-type ES cells revealed that huntingtin is expressed at all stages during ES cell differentiation with high expression in neurons. Expression levels increased with the maturation of differentiating neurons, demonstrating that expression of huntingtin is developmentally regulated in cell culture and resembles the pattern of expression observed in differentiating neurons in the mouse brain. It is interesting that HD-/- ES cells could differentiate into mature postmitotic neurons that expressed functional voltage- and neurotransmitter-gated ion channels. Moreover, both excitatory and inhibitory spontaneous postsynaptic currents were observed, indicating the establishment of functional synapses in the absence of huntingtin. These results demonstrate that huntingtin is not required for the generation of functional neurons with features characteristic of postmitotic neurons in the developing mouse brain.

Animals↗
PubMed1999

Subtype-specific enhancement of NMDA receptor currents by mutant huntingtin.

Evidence suggests that NMDA receptor-mediated neurotoxicity plays a role in the selective neurodegeneration underlying Huntington's disease (HD). The gene mutation that causes HD encodes an expanded polyglutamine tract of >35 in huntingtin, a protein of unknown function. Both huntingtin and NMDA receptors interact with cytoskeletal proteins, and, for NMDA receptors, such interactions regulate surface expression and channel activity. To determine whether mutant huntingtin alters NMDA receptor expression or function, we coexpressed mutant or normal huntingtin, containing 138 or 15 glutamine repeats, respectively, with NMDA receptors in a cell line and then assessed receptor channel function by patch-clamp recording and surface expression by western blot analysis. It is interesting that receptors composed of NR1 and NR2B subunits exhibited significantly larger currents when coexpressed with mutant compared with normal huntingtin. Moreover, this effect was selective for NR1/NR2B, as NR1/NR2A showed similar currents when coexpressed with mutant versus normal huntingtin. However, ion channel properties and total surface expression of the NR1 subunit were unchanged in cells cotransfected with NR1/NR2B and mutant huntingtin. Our results suggest that mutant huntingtin may increase numbers of functional NR1/NR2B-type receptors at the cell surface. Because NR1/NR2B is the predominant NMDA receptor subtype expressed in medium spiny neostriatal neurons, our findings may help explain the selective vulnerability of these neurons in HD.

Cell Line↗
PubMed1999

Recent insights into the molecular pathogenesis of Huntington disease.

Huntington disease (HD) is a neurodegenerative disorder caused by a CAG repeat expansion in the HD gene resulting in expression of an uninterrupted polyglutamine stretch within the N-terminus of its protein product huntingtin (htt). In this article we review the clinical, genetic, and neuropathological features of HD and discuss recent insights into the pathogenesis of HD. Examining the role of CAG repeat size on age of onset and penetrance in HD using a refined database of human HD patients has provided further support for the importance of the CAG repeat in the pathogenesis of HD and information leading to a predictive model for the likelihood of being affected by a specific age for a particular CAG expansion. In a YAC transgenic mouse model that replicates key elements of the HD phenotype, the development of selective striatal neurodegeneration is coincident with cleavage of htt and translocation of the N-terminal htt fragment into the nucleus. We also review in vitro evidence that htt is a substrate for cleavage by a group of cysteine proteases involved in apoptotic death-the caspases, and that caspase cleavage of htt results in the generation of a toxic N-terminal fragment. Inhibiting caspase cleavage of huntingtin eliminates the toxicity of the mutant htt protein. These results suggest that cleavage of huntingtin resulting in production of a truncated N-terminal fragment may be a crucial step in the pathogenesis of Huntington disease and that inhibition of this process may be a potential therapeutic strategy for this currently untreatable disorder.

Animals↗
PubMed1999

A worldwide assessment of the frequency of suicide, suicide attempts, or psychiatric hospitalization after predictive testing for Huntington disease.

Prior to the implementation of predictive-testing programs for Huntington disease (HD), significant concern was raised concerning the likelihood of catastrophic events (CEs), particularly in those persons receiving an increased-risk result. We have investigated the frequency of CEs-that is, suicide, suicide attempt, and psychiatric hospitalization-after an HD predictive-testing result, through questionnaires sent to predictive-testing centers worldwide. A total of 44 persons (0.97%) in a cohort of 4,527 test participants had a CE: 5 successful suicides, 21 suicide attempts, and 18 hospitalizations for psychiatric reasons. All persons committing suicide had signs of HD, whereas 11 (52.4%) of 21 persons attempting suicide and 8 (44.4%) of 18 who had a psychiatric hospitalization were symptomatic. A total of 11 (84.6%) of 13 asymptomatic persons who experienced a CE during the first year after HD predictive testing received an increased-risk result. Factors associated with an increased risk of a CE included (a) a psychiatric history </=5 years prior to testing and (b) unemployed status. The frequency of CEs did not differ between those persons receiving results of predictive testing through linkage analysis in whom there was only changes in direction of risk and those persons receiving definitive results after analysis for the mutation underlying HD. These findings provide insights into the frequency, associated factors, and timing of CEs in a worldwide cohort of persons receiving predictive-testing results and, as such, highlight persons for whom ongoing support may be beneficial.

Cohort Studies↗
PubMed1999

In vitro evidence for both the nucleus and cytoplasm as subcellular sites of pathogenesis in Huntington's disease.

A unifying feature of the CAG expansion diseases is the formation of intracellular aggregates composed of the mutant polyglutamine-expanded protein. Despite the presence of aggregates in affected patients, the precise relationship between aggregates and disease pathogenesis is unresolved. Results from in vivo and in vitro studies of mutant huntingtin have lead to the hypothesis that nuclear localization of aggregates is critical for the pathology of Huntington's disease (HD). We tested this hypothesis using a 293T cell culture model system that compared the frequency and toxicity of cytoplasmic and nuclear huntingtin aggregates. We first assessed the mode of nuclear transport of N-terminal fragments of huntingtin, and show that the predicted endogenous NLS is not functional, providing data in support of passive nuclear transport. This result suggests that proteolysis is a necessary step for nuclear entry of huntingtin. Additionally, insertion of nuclear import or export sequences into huntingtin fragments containing 548 or 151 amino acids was used to reverse the normal localization of these proteins. Changing the subcellular localization of the fragments did not influence their total aggregate frequency. There were also no significant differences in toxicity associated with the presence of nuclear compared with cytoplasmic aggregates. The findings of nuclear and cytoplasmic aggregates in affected brains, together with these in vitro data, support the nucleus and cytosol as subcellular sites for pathogenesis in HD.

Amino Acid Sequence↗
PubMed1999

A frequent mutation in the lipoprotein lipase gene (D9N) deteriorates the biochemical and clinical phenotype of familial hypercholesterolemia.

The D9N substitution is a common mutation in the lipoprotein lipase (LPL) gene. This mutation has been associated with reduced levels of HDL cholesterol and elevated triglycerides (TG) in a wide variety of patients. We investigated the influence of this D9N mutation on lipid and lipoprotein levels and risk for cardiovascular disease (CVD) in patients with familial hypercholesterolemia (FH). A total of 2091 FH heterozygotes, all of Dutch extraction, were screened for the D9N mutation using standard polymerase chain reaction techniques, followed by specific enzyme digestion. A total of 94 FH subjects carried the D9N mutation at a carrier frequency of 4.5%. Carriers of other common LPL mutations, such as the N291S and the S447X were excluded. Clinical data on 80 FH individuals carrying the D9N were available and were compared with a FH control group matched for age, sex, and body mass index (n=203). Analysis revealed significantly higher TG (P=0.01) and lower HDL-cholesterol levels (P=0.002). Dyslipidemia was more pronounced in D9N carriers with higher body mass index. Moreover, FH patients carrying this common LPL mutation were at higher risk for CVD, (odds ratio=2.8; 95% CI, 1.43 to 5.32; P=0.002). The common D9N LPL mutation leads to increased TG and decreased HDL plasma levels in patients with FH. These effects are most apparent in those FH heterozygotes with an increased body mass index. Furthermore, this mutation, present in 4.5% of Dutch FH heterozygotes, leads to increased risk for CVD.

Adolescent↗
PubMed1999

Lipoprotein lipase activity is decreased in a large cohort of patients with coronary artery disease and is associated with changes in lipids and lipoproteins.

Lipoprotein lipase (LPL) is crucial in the hydrolysis of triglycerides (TG) in TG-rich lipoproteins in the formation of HDL particles. As both these lipoproteins play an important role in the pathogenesis of atherosclerotic vascular disease, we sought to assess the relationship between post-heparin LPL (PH-LPL) activity and lipids and lipoproteins in a large, well-defined cohort of Dutch males with coronary artery disease (CAD). These subjects were drawn from the REGRESS study, totaled 730 in number and were evaluated against 75 healthy, normolipidemic male controls. Fasting mean PH-LPL activity in the CAD subjects was 108 46 mU/ml, compared to 138 44 mU/ml in controls (P < 0.0001). When these patients were divided into activity quartiles, those in the lowest versus the highest quartile had higher levels of TG (P < 0.001), VLDLc and VLDL-TG (P = 0.001). Conversely, levels of TC, LDL, and HDLc were lower in these patients (P = 0.001, P = 0.02, and P = 0.001, respectively). Also, in this cohort PH-LPL relationships with lipids and lipoproteins were not altered by apoE genotypes. The frequency of common mutations in the LPL gene associated with partial LPL deficiency (N291S and D9N carriers) in the lowest quartile for LPL activity was more than double the frequency in the highest quartile (12.0% vs. 5.0%; P = 0.006). By contrast, the frequency of the S447X LPL variant rose from 11.5% in the lowest to 18.3% (P = 0.006) in the highest quartile. This study, in a large cohort of CAD patients, has shown that PH-LPL activity is decreased (22%; P = 0.001) when compared to controls; that the D9N and N291S, and S447X LPL variants are genetic determinants, respectively, in CAD patients of low and high LPL PH-LPL activities; and that PH-LPL activity is strongly associated with changes in lipids and lipoproteins.

Adult↗
PubMed1998

Ile225Thr loop mutation in the lipoprotein lipase (LPL) gene is a de novo event.

Mutations in the lipoprotein lipase (LPL) gene are the most important cause of familial chylomicronemia with over 70 mutations being recorded to date. Thus far de novo mutations have not been described. Here we report on the molecular analysis of the family of a patient previously reported to be LPL deficient on the basis of compound heterozygosity for the Arg243His and Ile225Thr mutations, the latter being the first and only mutation identified in the loop region of LPL. Both parents of the propositus were screened for the presence of these two mutations to confirm their status as obligate heterozygotes and to determine the mutation allocation. Although paternal inheritance of the Arg243His allele could be established, maternal DNA did not show carrier status for the Ile225Thr substitution. An examination of maternity, using LPL restriction fragment length polymorphisms four polymorphic CA repeats and ApoE genotypes, was consistent with correct biological parentage for the propositus. Therefore, we conclude that the Ile225Thr mutation constitutes a de novo event, the first to be reported in the LPL gene.

Adult↗
PubMed1998

The influence of huntingtin protein size on nuclear localization and cellular toxicity.

Huntington disease is an autosomal dominant neurodegenerative disorder caused by the pathological expansion of a polyglutamine tract. In this study we directly assess the influence of protein size on the formation and subcellular localization of huntingtin aggregates. We have created numerous deletion constructs expressing successively smaller fragments of huntingtin and show that these smaller proteins containing 128 glutamines form both intranuclear and perinuclear aggregates. In contrast, larger NH2-terminal fragments of huntingtin proteins with 128 glutamines form exclusively perinuclear aggregates. These aggregates can form in the absence of endogenous huntingtin. Furthermore, expression of mutant huntingtin results in increased susceptibility to apoptotic stress that is greater with decreasing protein length and increasing polyglutamine size. As both intranuclear and perinuclear aggregates are clearly associated with increased cellular toxicity, this supports an important role for toxic polyglutamine-containing fragments forming aggregates and playing a key role in the pathogenesis of Huntington disease.

Animals↗
PubMed1998

Caspase cleavage of gene products associated with triplet expansion disorders generates truncated fragments containing the polyglutamine tract.

The neurodegenerative diseases Huntington disease, dentatorubropallidoluysian atrophy, spinocerebellar atrophy type 3, and spinal bulbar muscular atrophy are caused by expansion of a polyglutamine tract within their respective gene products. There is increasing evidence that generation of truncated proteins containing an expanded polyglutamine tract may be a key step in the pathogenesis of these disorders. We now report that, similar to huntingtin, atrophin-1, ataxin-3, and the androgen receptor are cleaved in apoptotic extracts. Furthermore, each of these proteins is cleaved by one or more purified caspases, cysteine proteases involved in apoptotic death. The CAG length does not modulate susceptibility to cleavage of any of the full-length proteins. Our results suggest that by generation of truncated polyglutamine-containing proteins, caspase cleavage may represent a common step in the pathogenesis of each of these neurodegenerative diseases.

Amino Acid Sequence↗
PubMed1998

A common mutation in the lipoprotein lipase gene (N291S) alters the lipoprotein phenotype and risk for cardiovascular disease in patients with familial hypercholesterolemia.

BACKGROUND: Recently, a mutation in the lipoprotein lipase (LPL) gene (N291S) has been reported in 2% to 5% of individuals in western populations and is associated with increased triglyceride (TG) and reduced HDL cholesterol (HDLC) concentrations. METHODS AND RESULTS: Here we report a significant alteration in biochemical and clinical phenotype in subjects with familial hypercholesterolemia (FH) who are heterozygous for this N291S LPL mutation. Sixty-four FH heterozygotes carrying the N291S mutation had significantly a higher TG level (P=.004), a higher ratio of total cholesterol to HDLC (P<.001), and lower HDLC concentrations (P=.002) compared with 175 FH heterozygotes without this LPL mutation. Moreover, the N291S mutation conferred a significantly greater risk for developing cardiovascular disease in FH heterozygotes compared with FH heterozygotes without this LPL mutation (odds ratio, 3.875; P=.006). CONCLUSIONS: These data provide evidence that a common LPL variant (N291S) significantly influences the biochemical phenotype and risk for cardiovascular disease in patients with FH.

Adult↗
PubMed1998

Gene structure and map location of the murine homolog of the Huntington-associated protein, Hap1.

Huntington's Disease (HD) is an inherited progressive neurodegenerative disorder associated with a mutation in a gene expressed in both affected and non-affected tissues. The selective neuropathology in HD is thought to be mediated in part through interactions with other proteins including the Huntington Associated Protein, HAP-1, which is predominantly expressed in the brain. We have mapped its murine homolog, Hap1, to mouse Chr 11 (band D), which shares extensive synteny with human Chr 17 including the region 17q21-q22, where the gene for 'frontotemporal dementia and parkinsonism linked to chromosome 17' has bee mapped. In addition, we have sequenced a 21,984 base pair (bp) genomic clone encompassing the entire Hap1 gene. It is organized as 11 exons and flanked by exons from potentially one or more novel genes. At least three Hap1 transcripts (Hap1-A; Hap1-B; Hap1-C) can be formed by alternative splicing at the 3' end of the gene leading to protein isoforms with novel C-termini.

Algorithms↗