Frequency of known mutations in early-onset Parkinson disease: implication for genetic counseling: the consortium on risk for early onset Parkinson disease study

OBJECTIVE

To assess the frequency and clinical characteristics of carriers of previously identified mutations in 6 genes associated with early-onset Parkinson disease (PD) and provide empirical data that can be used to inform genetic counseling.

DESIGN

Cross-sectional observational study.

SETTING

Thirteen movement disorders centers.

PATIENTS

Nine hundred fifty-three individuals with early-onset PD defined as age at onset (AAO) younger than 51 years. Participants included 77 and 139 individuals of Hispanic and Jewish ancestry, respectively. Intervention Mutations in SNCA, PRKN, PINK1, DJ1, LRRK2, and GBA were assessed. A validated family history interview and the Unified Parkinson Disease Rating Scale were administered. Demographic and phenotypic characteristics were compared among groups defined by mutation status. Main Outcome Measure Mutation carrier frequency stratified by AAO and ethnic background.

RESULTS

One hundred fifty-eight (16.6%) participants had mutations, including 64 (6.7%) PRKN, 35 (3.6%) LRRK2 G2019S, 64 (6.7%) GBA, and 1 (0.2%) DJ1. Mutation carriers were more frequent in those with an AAO of 30 years or younger compared with those with AAO between 31 and 50 years (40.6% vs 14.6%, P < .001), in individuals who reported Jewish ancestry (32.4% vs 13.7%, P < .001), and in those reporting a first-degree family history of PD (23.9% vs 15.1%, P = .01). Hispanic individuals were more likely to be PRKN carriers than non-Hispanic individuals (15.6% vs 5.9%, P = .003). The GBA L444P mutation was associated with a higher mean Unified Parkinson Disease Rating Scale III score after adjustment for covariates.

CONCLUSION

Individuals of Jewish or Hispanic ancestry with early-onset PD, those with AAO of 30 years or younger, and those with a history of PD in a first-degree relative may benefit from genetic counseling.

Predictors of parkin mutations in early-onset Parkinson disease: the consortium on risk for early-onset Parkinson disease study

BACKGROUND

Mutations in the parkin gene are the most common genetic cause of early-onset Parkinson disease (PD). Results from a multicenter study of patients with PD systematically sampled by age at onset have not been reported to date.

OBJECTIVE

To determine risk factors associated with carrying parkin mutations.

DESIGN

Cross-sectional observational study.

SETTING

Thirteen movement disorders centers.

PARTICIPANTS

A total of 956 patients with early-onset PD, defined as age at onset younger than 51 years.

MAIN OUTCOME MEASURES

Presence of heterozygous, homozygous, or compound heterozygous parkin mutations.

RESULTS

Using a previously validated interview, 14.7% of patients reported a family history of PD in a first-degree relative. Sixty-four patients (6.7%) had parkin mutations (3.9% heterozygous, 0.6% homozygous, and 2.2% compound heterozygous). Copy number variation was present in 52.3% of mutation carriers (31.6% of heterozygous, 83.3% of homozygous, and 81.0% of compound heterozygous). Deletions in exons 3 and 4 and 255delA were common among Hispanics (specifically Puerto Ricans). Younger age at onset (<40 years) (odds ratio [OR], 5.0; 95% confidence interval [CI], 2.8-8.8; P = .001), Hispanic race/ethnicity (OR compared with white non-Hispanic race/ethnicity, 2.7; 95% CI, 1.3-5.7; P = .009), and family history of PD in a first-degree relative (OR compared with noncarriers, 2.8; 95% CI, 1.5-5.3; P = .002) were associated with carrying any parkin mutation (heterozygous, homozygous, or compound heterozygous). Hispanic race/ethnicity was associated with carrying a heterozygous mutation (OR compared with white non-Hispanic race/ethnicity, 2.8; 95% CI, 1.1-7.2; P = .03) after adjustment for covariates.

CONCLUSIONS

Age at onset, Hispanic race/ethnicity, and family history of PD are associated with carrying any parkin mutation (heterozygous, homozygous, or compound heterozygous) and heterozygous mutations alone. The increased odds of carrying a parkin mutation among Hispanics warrants further study.

Motor phenotype of LRRK2 G2019S carriers in early-onset Parkinson disease

OBJECTIVE

To determine the motor phenotype of LRRK2 G2019S mutation carriers. LRRK2 mutation carriers were previously reported to manifest the tremor dominant motor phenotype, which has been associated with slower motor progression and less cognitive impairment compared with the postural instability and gait difficulty (PIGD) phenotype.

DESIGN

Cross-sectional observational study.

SETTING

Thirteen movement disorders centers.

PARTICIPANTS

Nine hundred twenty-five early-onset Parkinson disease cases defined as age at onset younger than 51 years.

MAIN OUTCOME MEASURES

LRRK2 mutation status and Parkinson disease motor phenotype: tremor dominant or PIGD. Demographic information, family history of Parkinson disease, and the Unified Parkinson's Disease Rating Scale score were collected on all participants. DNA samples were genotyped for LRRK2 mutations (G2019S, I2020T, R1441C, and Y1699C). Logistic regression was used to examine associations of G2019S mutation status with motor phenotype adjusting for disease duration, Ashkenazi Jewish ancestry, levodopa dose, and family history of Parkinson disease.

RESULTS

Thirty-four cases (3.7%) (14 previously reported) were G2019S carriers. No other mutations were found. Carriers were more likely to be Ashkenazi Jewish (55.9% vs 11.9%; P < .001) but did not significantly differ in any other demographic or disease characteristics. Carriers had a lower tremor score (P = .03) and were more likely to have a PIGD phenotype (92.3% vs 58.9%; P = .003). The association of the G2019S mutation with PIGD phenotype remained after controlling for disease duration and Ashkenazi Jewish ancestry (odds ratio, 17.7; P < .001).

CONCLUSION

Early-onset Parkinson disease G2019S LRRK2 carriers are more likely to manifest the PIGD phenotype, which may have implications for disease course.

Association of glucocerebrosidase mutations with dementia with lewy bodies

BACKGROUND

Mutations in the glucocerebrosidase (GBA) gene are associated with Lewy body (LB) disorders.

OBJECTIVE

To determine the relationship of GBA mutations and APOE4 genotype to LB and Alzheimer disease (AD) pathological findings.

DESIGN

Case-control study.

SETTING

Academic research.

PARTICIPANTS

The 187 subjects included patients with primary neuropathological diagnoses of LB disorders with or without AD changes (95 cases), randomly selected patients with AD (without significant LB pathological findings; 60 cases), and controls with neither LB nor AD pathological findings (32 cases).

MAIN OUTCOME MEASURES

GBA mutation status, APOE4 genotype, LB pathological findings (assessed according to the third report of the Dementia With Lewy Body Consortium), and Alzheimer plaque and tangle pathological findings (rated by criteria of Braak and Braak, the Consortium to Establish a Registry for Alzheimer Disease, and the National Institute on Aging-Reagan Institute).

RESULTS

GBA mutations were found in 18% (34 of 187) of all subjects, including 28% (27 of 95) of those with primary LB pathological findings compared with 10% (6 of 60) of those with AD pathological findings and 3% (1 of 32) of those without AD or LB pathological findings (P=.001). GBA mutation status was significantly associated with the presence of cortical LBs (odds ratio, 6.48; 95% confidence interval, 2.45-17.16; P<.001), after adjusting for sex, age at death, and presence of APOE4. GBA mutation carriers were significantly less likely to meet AD pathological diagnostic (National Institute on Aging-Reagan Institute intermediate or high likelihood) criteria (odds ratio, 0.35; 95% confidence interval, 0.15-0.79; P=.01) after adjustment for sex, age at death, and APOE4.

CONCLUSION

GBA mutations may be associated with pathologically "purer" LB disorders, characterized by more extensive (cortical) LB, and less severe AD pathological findings and may be a useful marker for LB disorders.

Mutations in the glucocerebrosidase gene are associated with early-onset Parkinson disease

OBJECTIVE

To evaluate the frequency of glucocerebrosidase (GBA) mutations in cases and controls enrolled in the Genetic Epidemiology of Parkinson's Disease (GEPD) study.

METHODS

We sequenced all exons of the GBA gene in 278 Parkinson disease (PD) cases and 179 controls enrolled in GEPD, with a wide range of age at onset (AAO), and that included a subset of 178 Jewish cases and 85 Jewish controls. Cases and controls were recruited without knowledge of family history of PD, and cases were oversampled in the AAO < 50 years category.

RESULTS

13.7% of PD cases (38/278) carried GBA mutations, compared with 4.5% of controls (8/179) (odds ratio [OR] 3.4, 95% CI 1.5 to 7.4). The frequency of GBA mutations was 22.2% in 90 cases with AAO < or = 50 years, compared with 9.7% in 185 cases with AAO > 50 years (OR 2.7, 95% CI 1.3 to 5.3). Adjusting for age at the time of evaluation, sex, family history of PD, and Jewish ancestry, GBA carriers had a 1.7-year-earlier AAO of PD (95% CI 0.5 to 3.3, p < 0.04) than noncarriers. The average AAO of PD was 2.5 years earlier in carriers with an AAO < or = 50 years compared with noncarriers (95% CI 0.6 to 4.5, p < 0.01) and this was not seen in the AAO > 50 years group. The frequency of GBA mutations was higher in a subset of 178 cases that reported four Jewish grandparents (16.9%) than in cases who did not report Jewish ancestry (8.0%) (p < 0.01). Nine different GBA mutations were identified in PD cases, including 84insGG, E326K, T369M, N370S, D409H, R496H, L444P, RecNciI, and a novel mutation, P175P.

CONCLUSIONS

This study suggests that the Glucocerebrosidase gene may be a susceptibility gene for Parkinson disease and that Glucocerebrosidase mutations may modify age at onset.

Biomarkers of oxidative stress in schizophrenic and control subjects

Increasing evidence indicates that oxidative injury exists in schizophrenia. Although it may not be the main cause, oxidative damage has been suggested to contribute to the pathophysiology and may account for deteriorating course and poor outcome in schizophrenia. A human study was undertaken, therefore, to investigate possible differences in biomarkers of DNA, lipid and protein oxidation in schizophrenic (n=16) and control subjects (n=17). Plasma vitamin C levels were also compared in both groups. Cellular DNA damage and plasma protein carbonyl levels were increased in the schizophrenic group compared to control subjects but not significantly. However, DNA damage in lymphocytes from the male schizophrenic group was significantly higher than the female group. Biomarkers of lipid peroxidation and plasma vitamin C levels also revealed no significant difference between the two groups under investigation, although a significant elevation in plasma vitamin C was observed in the female control group when compared to the male groups.

Relative contributions of genes, environment, and interactions to blood lipid concentrations in a general adult population

The authors evaluated the contributions of nine genetic (G) variants (selected from 275 single nucleotide polymorphisms in 11 reverse cholesterol transport pathway genes), five environmental (E) factors (selected from 10), and G x G, E x E, and G x E interactions in explaining population variance of blood lipid concentrations. Total cholesterol, triglycerides, and high density lipoprotein (HDL) cholesterol were measured, and low density lipoprotein (LDL) cholesterol and HDL cholesterol/LDL cholesterol ratio were calculated in a population-based random sample of 1,543 men and women in Geneva, Switzerland, aged 35-74 years in 1999-2001. Explained variances (R2) for HDL cholesterol/LDL cholesterol ratio, HDL cholesterol, and LDL cholesterol, respectively, were 34%, 33%, and 19%, decomposed into main effects of G (6%, 4%, and 5%) and E (25%, 28%, and 11%), with just 3%, 2%, and 3% due to G x G, E x E, and G x E interactions, respectively. Risk factor clustering was only moderate: 70% of study subjects had < or =3 variants, 75% had < or =2 environmental exposures, and 69% had < or =5 of both types of factors. Multiple genes with weak associations, together with more dominating environmental factors, are involved in determining blood lipid concentrations. Interactions added little explained variance. Increasing trends in hypercholesterolemia are attributable to environmental changes affecting populations as a whole. Reducing obesity and smoking and moderating alcohol intake in entire populations should remain the primary strategies for lipid control.

Population-based study of SR-BI genetic variation and lipid profile

The variability of the Class B Type I Scavenger Receptor (SR-BI) gene in human populations and the relation of its variants to blood lipids was investigated in a random sample of 1756 untreated adult residents of Geneva, Switzerland, during 1999-2000. A three-step study approach yielded the following results: (1) resequencing the gene's exons and flanking regions in 95 subjects identified four common single nucleotide polymorphisms (SNPs with rare allele frequency >3%); (2) association study of the four common SNPs in subjects with extreme HDL-cholesterol (HDL-C) and LDL-C phenotypes (186 "atherogenic cases" and 185 "non-atherogenic controls") showed that the synonymous exon 8 C-T (allelic frequency 48%) polymorphism, A350A, was associated with atheroprotection in men (odds ratios (OR) = 0.36, 95% confidence intervals (CI) = 0.15-0.90, P < 0.03), but not in women (2.09, 0.79-5.49, P = 0.14); and (3) population clinical effects of A350A genotypes assessed in all 1756 subjects, showed that the case-control study findings reflected a protective HDL-C effect in men (CC: 1.17 mmol/L, CT: 1.22 mmol/L, and TT: 1.24 mmol/L, trend P = 0.0062) and a deleterious LDL-C effect in women (CC: 3.58 mmol/L, CT: 3.72 mmol/L, and TT: 3.79 mmol/L, trend P = 0.014). The allelic frequencies of the common SR-BI variants appear to be very similar in European and North American populations. The HDL-C effect increased with age. SR-BI A350A appears to have gender-specific and age-related effects on cholesterol transport lipoproteins.

Association of extreme blood lipid profile phenotypic variation with 11 reverse cholesterol transport genes and 10 non-genetic cardiovascular disease risk factors

This study explored the genetic basis of the combination of extreme blood levels of HDL-C and LDL-C, a well-studied endophenotype for CVD, which has several attractive features as a target for genetic analysis: (1) the trait is moderately heritable; (2) non-genetic risk factors account for a significant but still limited portion of the phenotypic variance; (3) it is known to be moderated by a number of gene products. We exhaustively surveyed 11 candidate genes for allelic variation in a random population-based sample characterized for known CVD risk factors and blood lipid profiles. With the goal of generating specific etiological hypotheses, we compared two groups of subjects with extreme lipid phenotypes, from the same source population, using a case-control design. Cases (n=186) were subjects, within the total sample of 1708 people, who scored in the upper tertile of LDL-C and the lowest tertile of HDL-C, while controls (n=185) scored in the lowest tertile of LDL-C and the upper tertile of HDL-C. We used logistic regression and a four-tiered, systematic model building strategy with internal cross-validation and bootstrapping to investigate the relationships between the trait and 275 genetic variants in the presence of 10 non-genetic risk factors. Our results implicate a subset of nine genetic variants, spanning seven candidate genes, together with five environmental risk factors, in the etiology of extreme lipoprotein phenotypes. We propose a model involving these 14 genetic and non-genetic risk factors for evaluation in future independent studies.

Association between lipoprotein lipase (LPL) gene and blood lipids: a common variant for a common trait?

S447X, a serine substitution by a stop codon on base 99 of exon 9 of the lipoprotein lipase (LPL) gene, has beneficial effects on blood lipids. Other LPL alleles are associated with lipid levels, but whether one of these variants predominates remains elusive. We performed a systematic survey to identify single-nucleotide polymorphisms (SNPs) in all 10 LPL exons and flanking regions by resequencing the gene in 95 subjects. Of 24 variants, 14 were common (> or = 3%). We assayed the common SNPs in 186 cases with atherogenic lipid profiles (low HDL, high LDL) and 185 nonatherogenic controls (high HDL, low LDL). Only S447X and exons 6 (base +73) and 10 (base -11) were individually associated with case-control status (P<0.05, adjusted for major nongenetic covariates with known lipid effects). There were no significant SNP x gender interactions. In adjusted multi-SNP and haplotypic analyses, S447X was interpretable as the sole predictor, with a 2-3-fold reduction in the odds of being atherogenic vs. nonatherogenic (adjusted OR, 0.39; 95% CI, 0.21-0.73). S447X and base -11 of exon 10 were statistically interchangeable because they are strongly associated (r=0.92, P<0.0001), but we posit that the LPL association with lipid profile is more likely attributable to the functional S447X rather than the nonfunctional exon 10 SNP. It appears that the S447X variant of LPL may be another rare example (like APOE4, factor V-Leiden, and PPAR gamma Pro12Ala) of a common variant predisposing to a common disorder.

Chronic cocaine administration reduces phospholipase A(2) activity in rat brain striatum

BACKGROUND

Phospholipase A(2) (PLA(2)) catalyses the release of free fatty acids used for eicosanoid biosynthesis. We previously reported that calcium-stimulated PLA(2) activity is reduced in the brain of cocaine users and patients with schizophrenia, and have speculated that this is due to dopaminergic hyperactivity in both conditions.

METHODS

To investigate these observations under controlled conditions, PLA(2) activity was measured in brain of rats exposed to cocaine and the dopamine receptor antagonist haloperidol.

RESULTS

As compared with saline-treated controls, calcium-stimulated PLA(2) activity was reduced (-30%; P<0.01) in the dopamine-rich striatum of animals sacrificed 1 h after chronic (20 mg/kg/day) injection of cocaine, but was normal in haloperidol- (2 mg/kg/day) treated animals, and in the dopamine-poor cortex and cerebellum of animals treated with either drug.

CONCLUSION

This confirms and extends our observations in human brain, and further suggests a link between the brain dopaminergic and phospholipid catabolic systems.

Dopamine D1-stimulated adenylyl cyclase activity in cerebral cortex of autopsied human brain

Although the cerebral cortical dopamine D(1) receptor is considered to play a role in normal and abnormal brain function, little information is available on its characteristics in human brain. We compared dopamine-stimulated adenylyl cyclase (AC) activity in homogenates of cerebral cortex (frontal, temporal, parietal, occipital and cingulate cortex) of autopsied brain of neurologically normal subjects to that in striatum. Cerebral cortical AC activity was modestly and dose-dependently stimulated by dopamine (maximal 20-30%) with low microM EC50s and such stimulation was inhibited by the selective dopamine D1 receptor antagonist SCH23390. The magnitude of the maximal stimulation by dopamine was similar in autopsied and biopsied cerebral cortex. The extent of maximal stimulation was similar to that in dopamine-rich striatum (caudate, putamen and nucleus accumbens), despite much lower density of dopamine D1 receptors in cerebral cortex vs. striatum. The EC50 for dopamine stimulation in cerebral cortex (approximately 1 microM) was lower than that for caudate and putamen (approximately 3 microM). No detectable dopamine stimulation was observed in cerebellar cortex, thalamus or hippocampus. Dopamine stimulation in both cerebral cortex and striatum was independent of calcium activation. We conclude that dopamine stimulated AC can be measured in cerebral cortex of human brain allowing for the possibility that this process can be examined in human brain disorders in which dopaminergic abnormalities are suspected.

An animal model of nicotinic-acid-induced vasodilation: effect of haloperidol, caffeine and nicotine upon nicotinic acid response

BACKGROUND

The normal vasodilatory response to ingestion of nicotinic acid (NA) is impaired in some patients with schizophrenia. It is unclear whether the impairment is a feature of the disorder itself or to a confounding factor such as neuroleptics, caffeine or nicotine use.

METHODS

To address this question in a controlled manner, we have developed an animal (rat) model of NA-induced vasodilation, in which response is monitored by measuring change in skin temperature.

RESULTS

We observed that (i) acute administration of acetylsalicylic acid (100mg/kg), caffeine (2.5mg/kg) and haloperidol (0.1 or 0.5mg/kg) and (ii) chronic administration of haloperidol (0.2mg/kg/day) significantly inhibited NA (30 mg/kg) response, whereas neither acute (0.25mg/kg) or chronic (0.5mg/kg/day for 14 days) administration of nicotine, or chronic administration of caffeine (5mg/kg/day for 14 days) had any significant effect upon NA response.

CONCLUSIONS

Our data suggest that at least one drug commonly used to treat schizophrenia (haloperidol) can interfere with the vasodilatory response to NA. Studies using non-medicated patients with schizophrenia are required to determine whether reduced vasodilatory response to NA in schizophrenia is a feature of the disorder or a consequence of treatment.

Elevated activity of phospholipid biosynthetic enzymes in substantia nigra of patients with Parkinson's disease

We reported that the activities of phospholipase A2, phosphocholine cytidylyltransferase and phosphoethanolamine cytidylyltransferase, key phospholipid metabolic enzymes, are low in substantia nigra of normal human brain and that this might reduce the ability of nigral neurons to repair damage to cell membranes. To determine whether adaptive changes in nigral phospholipid metabolism can occur in idiopathic Parkinson's disease we compared activities of 11 catabolic and anabolic enzymes in autopsied brain of 10 patients with Parkinson's disease to those in control subjects. Nigral activity of the catabolic enzyme phospholipase A2 was normal in the Parkinson's disease group, whereas that of the biosynthetic enzymes phosphoethanolamine cytidylyltransferase, phosphocholine cytidylyltransferase, and phosphatidylserine synthase were elevated 193, 48 and 38%, respectively, possibly representing a compensatory response to repair membrane phospholipids. Enzyme activities were normal in all other brain areas with the exception of increased (+26%) activity of calcium-stimulated phospholipase A2 in putamen, a change which could be consequent to either decreased dopaminergic striatal input or to a dopamine nerve terminal degenerative process. Our data indicate that the normally low rate of membrane phospholipid synthesis in the substantia nigra, the primary area of neurodegeneration in Parkinson's disease, is increased during the course of the disorder. We suggest that pharmacotherapies which augment this compensatory response might have utility as a treatment for Parkinson's disease.

The human nucleus accumbens is highly susceptible to G protein down-regulation by methamphetamine and heroin

Although the nucleus accumbens is assumed to be a critical brain "pleasure center," its function in humans is unknown. As animal data suggest that a unique feature of this small brain area is its high sensitivity to down-regulation of an inhibitory G protein by drugs of abuse, we compared G protein levels in postmortem nucleus accumbens with those in seven other brain regions of chronic users of cocaine, methamphetamine, and heroin, and of matched controls. Biochemical changes were restricted to the nucleus accumbens in which concentrations of G(alpha)1 and/or G(alpha)2 were reduced by 32-49% in the methamphetamine and heroin users. This selective responsiveness to these abused drugs implies a special role for the human nucleus accumbens in mechanisms of drug reinforcement and suggests that some features of the drug-dependent state (e.g., tolerance) might be related to inhibition of G(alpha)1-linked receptor activity.

Abnormal activity of membrane phospholipid synthetic enzymes in the brain of patients with Friedreich's ataxia and spinocerebellar atrophy type-1

Much evidence, derived from biochemical studies of both blood and autopsied brain, has suggested that phospholipid metabolism is abnormal in patients with Friedreich's ataxia (FA), a disorder characterized by severe neuronal loss in the spinal cord and lower brain stem with no, or only modest, damage in other brain regions. To establish the cause of our recent finding of reduced brain levels of phospholipids in FA, we assayed activities of 10 phospholipid-metabolizing enzymes in the autopsied cerebellar cortex of patients with the disorder and, for comparison, in a group of patients with spinocerebellar ataxia type 1 (SCA-1), a disease characterized, unlike FA, by marked neuronal loss in the cerebellar cortex. Enzyme activities were also measured in four brain areas which are relatively unaffected morphologically in both FA and SCA-1. We found that ethanolamine kinase activity was increased in multiple brain regions of patients with FA (increased 31%-137%) and, more modestly, in SCA-1 (increased 39%-60%), suggesting a nonspecific enhancement of phosphoethanolamine production in both disorders. In contrast, the activity of phosphoethanolamine cytidylyltransferase (PECT), the rate-limiting enzyme of phosphatidylethanolamine synthesis, was significantly and markedly decreased by 35%-78% in the cerebellar, frontal, and occipital cortices of patients with FA but was normal in SCA-1. Reduced PECT activity in FA may explain the lower brain levels of phosphatidylethanolamine in the disorder. Moreover, because decreased PECT activity in FA occurs in brain regions having no, or only modest, morphologic damage, this may represent a systemic change consequent to the frataxin gene defect. Our data also suggest that therapeutic intervention in FA designed to increase synthesis of membrane phospholipids may warrant further investigation.

Null mutation of the murine ATP7B (Wilson disease) gene results in intracellular copper accumulation and late-onset hepatic nodular transformation

The Atp7b protein is a copper-transporting ATPase expressed predominantly in the liver and to a lesser extent in most other tissues. Mutations in the ATP7B gene lead to Wilson disease, a copper toxicity disorder characterized by dramatic build-up of intracellular hepatic copper with subsequent hepatic and neuro-logical abnormalities. Using homologous recombination to disrupt the normal translation of ATP7B, we have generated a strain of mice that are homozygous mutants (null) for the Wilson disease gene. The ATP7B null mice display a gradual accumulation of hepatic copper that increases to a level 60-fold greater than normal by 5 months of age. An increase in copper concentration was also observed in the kidney, brain, placenta and lactating mammary glands of homo-zygous mutants, although milk from the mutant glands was copper deficient. Morphological abnormalities resembling cirrhosis developed in the majority of the livers from homozygous mutants older than 7 months of age. Progeny of the homozygous mutant females demonstrated neurological abnormalities and growth retardation characteristic of copper deficiency. Copper concentration in the livers of the newborn homozygous null mutants was decreased dramatically. In summary, inactivation of the murine ATP7B gene produces a form of cirrhotic liver disease that resembles Wilson disease in humans and the 'toxic milk' phenotype in the mouse.

Clinical subtyping reveals significant differences in calcium-dependent phospholipase A2 activity in schizophrenia

BACKGROUND

Inconsistent results in the study of phospholipid metabolism in schizophrenia may reflect the heterogeneous nature of the illness(es). Differences in patients' responses to niacin, a compound causing vasodilation via stimulation of phospholipid dependent signaling cascades, defines more homogeneous patient subgroups in which the rate limiting enzyme of this signaling pathway, phospholipase A2 (PLA2), can be studied.

METHODS

Subjects were categorized as niacin-insensitive (10 schizophrenic patients and 1 control) or niacin-sensitive (13 schizophrenic patients and 29 controls). Comparisons of serum calcium-dependent PLA2 were undertaken with and without consideration of niacin sensitivity.

RESULTS

Significantly more schizophrenic patients were niacin-insensitive than controls (chi 2 (1) = 12.8, p < .001). Comparison of mean serum calcium-dependent PLA2 level of all schizophrenic subjects with all healthy controls revealed no statistical difference (t(51) = .79, NS). Subtyping the schizophrenia group by niacin sensitivity/insensitivity, however, allowed significant differences to emerge (F(2,49) = 4.40, p = .018). Post-hoc tests showed the mean PLA2 activity level of niacin-sensitive subjects was lower than that of healthy subjects.

CONCLUSIONS

Treatment strategies which increase calcium-dependent PLA2 activity may aid in reducing states of excess dopaminergic activity by activating second messenger systems rather than receptor blockade.

Phosphatidylcholine and phosphatidylethanolamine metabolites may regulate brain phospholipid catabolism via inhibition of lysophospholipase activity

Brain levels of glycerophosphocholine (GPC) and glycerophosphoethanolamine (GPE), abundant metabolites of phosphatidylcholine and phosphatidylethanolamine, are increased in several disorders of the human brain. To determine whether accumulation of these compounds may alter phospholipid metabolism, we assessed the ability of GPE and GPC to modulate the activities of phospholipase A(2), lysophospholipase, and other enzymes involved in phospholipid metabolism, in preparations of human brain parietal cortex. GPC and GPE acted as competitive inhibitors of lysophospholipase activity, but failed to alter the activity of the other enzymes tested. Our results suggest that GPC and GPE may normally act to inhibit lysophospholipid hydrolysis, thereby reducing the rate of membrane phospholipid degradation.

Modest cholinergic deafferentation fails to alter hippocampal G-proteins

The integrity of hippocampal G-protein mediated signalling following ibotenate induced lesion of the medial septum was examined. The lesion was confined histologically to the septum and induced a 23% reduction in hippocampal choline acetyltransferase (ChAT) activity and G-proteins levels and related enzyme activities were measured in the hippocampus following a 21 day survival period. The relative levels of five G-protein subunits (Gbeta, G(alpha)o, G(alpha)i1, G(alpha)i2, and G(alpha)s-L), basal GTPase, the degree of carbachol- or baclofen-stimulated GTPase activities, and the basal and fluoroaluminate-stimulated adenylate cyclase activities were apparently unaffected. To determine if our assay methodology was sensitive to changes in pre-synaptic signalling, we compared G-protein density in synaptosomes with total hippocampal homogenates. The concentration of G(alpha)q/11, G(alpha)i1, and G(alpha)i2. were significantly lower in synaptosomes, while G(alpha)o, was only marginally reduced. Thus, modest lesions of the medial-septal nucleus fail to alter G-protein signalling. However, our findings that G-protein density is lower in synaptosomal membranes than in total homogenates, indicates that the analysis of signalling events in synaptosomes following deafferentation could clarify adaptive changes which may occur at the presynaptic level.

Probing the interaction of T7 RNA polymerase with promoter

Transcription is the fundamental process by which RNA is synthesized by RNA polymerases on double-stranded DNA templates. One structurally simple RNA polymerase is encoded by bacteriophage T7. T7 RNA polymerase is an excellent candidate for studying structural aspects of transcription, because unlike the eucaryotic and bacterial RNA polymerases, it is a single subunit enzyme and does not require additional factors to carry out the entire process of transcription from start to finish. An important advantage of studying transcription using this enzyme is that the high-resolution crystal structure of T7 RNA polymerase has been solved. However, a cocrystal structure of the polymerase complexed with promoter has not yet been published. Here, we have used cross-linking techniques to understand the interaction of promoter with T7 RNA polymerase. We constructed promoters that were substituted with the photo-cross-linkable nucleotide 5-iodo uracil at every dT in the promoter from -17 to -1. This substitution replaces the 5-methyl in dT with an iodine atom. The substituted promoters were photo-cross-linked to T7 RNAP, and the efficiency of cross-linking was quantitated at every position. In the melting domain, the strongest contacts occurred at -3 and at -1 on the template strand while very weak cross-linking was seen at -2 and at -4 on the nontemplate strand. In the binding domain, the strongest contacts were seen at -16, -15, and -13 and at -10 on the template strand while at -17 and -14 on the nontemplate strand very weak cross-linking was observed. Cross-linking was poor in the intervening region between the binding and the melting domains. These results suggested that, in the T7 RNA polymerase-promoter complex, the polymerase molecule mainly contacts the template bases in the TATA box while the upstream contacts are used as an anchor for DNA binding. For a systematic study designed to probe the nature of base-specific interactions in the polymerase-promoter complex, we used neutral salts from the Hofmeister series. In general, the order of perturbation was sulfate > citrate > acetate for anions and ammonium > magnesium > potassium for cations. Using acrylamide, a neutral hydrophobic agent to probe for nonionic contacts, we observed that at -2, -4, and -17 the contacts had a hydrophobic component, while at many other positions there was no significant effect, suggesting that the contacts in the promoter-polymerase complexes were predominantly ionic but at certain positions nonionic interactions also existed. To localize a specific interaction in the melting domain, we proteolyzed the cross-linked T7 RNAP and analyzed the fragments using gel electrophoresis, mass spectrometry, and amino acid composition. High-resolution mapping indicated that amino acid residues 614-627 may be in the vicinity of the melting domain. Specifically, Y623 may contact -3 on the template strand.

Differential alteration of phospholipase A2 activities in brain of patients with schizophrenia

We recently reported that the activity of a calcium-independent subtype of phospholipase A2 is increased in blood of patients with schizophrenia. The present investigation examined whether similar changes take place in brain of patients with this disorder, and for comparison, in patients with bipolar disorder. The activity of two classes of PLA2, calcium-stimulated and independent, were assayed in autopsied temporal, prefrontal and occipital cortices, putamen, hippocampus and thalamus of 10 patients with schizophrenia, 8 patients with bipolar disorder and 12 matched control subjects. Calcium-independent PLA2 activity was increased by 45% in the temporal cortex of patients with schizophrenia as compared with the controls but was not significantly altered in other brain areas. In contrast, calcium-stimulated PLA2 activity was decreased by 27-42% in the temporal and prefrontal cortices and putamen, with no significant alterations in other brain regions. Brain PLA2 activity was normal in patients with bipolar disorder. Calcium-stimulated PLA2 activity was normal in cortex, cerebellum and striatum of rats treated acutely or chronically with haloperidol, whereas calcium-independent PLA2 activity was decreased in striatum of chronically treated animals, indicating that altered PLA2 activity in patients with schizophrenia is unlikely to be a direct effect of medication. Studies of the cellular role played by PLA2 suggest that decreased calcium-stimulated PLA2 activity, as also occurs in striatum of chronic human cocaine users, may be due, in part, to increased dopaminergic activity in the disorder, whereas increased calcium-independent PLA2 activity may be related to abnormal fatty acid metabolism and oxidative stress in schizophrenia.

Brain glyceraldehyde-3-phosphate dehydrogenase activity in human trinucleotide repeat disorders

BACKGROUND

Although the abnormal gene products responsible for several hereditary neurodegenerative disorders caused by repeat CAG trinucleotides have been identified, the mechanism by which the proteins containing the expanded polyglutamine domains cause cell death is unknown. The observation that several of the mutant proteins interact in vitro with the key glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) suggests that interaction between the different gene products and GAPDH might damage brain neurons.

OBJECTIVE

To measure the activity of GAPDH in postmortem brain of patients with CAG repeat disorders.

PATIENTS AND METHODS

Activity of GAPDH was measured in morphologically affected and unaffected brain areas of patients with 4 different CAG repeat disorders (Huntington disease, spinocerebellar ataxia 1 [SCA1], SCA2, and SCA3-Machado-Joseph disease), in brains of patients with Friedreich ataxia (a GAA repeat disorder) and Alzheimer disease, and in brains of matched control subjects.

RESULTS

Brain GAPDH activity was normal in all groups with the exception of a slight but statistically significant region-specific reduction in the patients with Huntington disease (caudate nucleus, -12%) and Alzheimer disease (temporal cortex, -19%).

CONCLUSION

The presence of the polyglutamine-containing proteins in CAG repeat disorders does not result in substantial irreversible inactivation or in increased activity of GAPDH in human brain.

Brain phospholipids and fatty acids in Friedreich's ataxia and spinocerebellar atrophy type-1

Previous studies of patients with spinocerebellar atrophy type 1 (SCA-1) and Friedreich's ataxia (FA) have suggested the occurrence of membrane disturbances in both disorders. We measured concentrations of phosphatidylcholine (PC), diacyl and plasmalogen phosphatidylethanolamine (PE), and phosphatidylserine (PS), along with their fatty acid profiles, in the brains of eight patients with Friedreich's ataxia (FA) and nine patients with dominantly inherited spinocerebellar atrophy type 1 (SCA-1). Compared with the controls, levels of all phospholipid types (PE, PS, and PC) were reduced in the cerebellar but not occipital cortex of SCA-1 patients. In contrast, in the FA group, levels of PS and PE, but not PC, were reduced in both cerebellar and occipital cortices. The fatty acid composition of individual brain phospholipids was altered in both FA and SCA-1 patients, most markedly in the plasmalogen PE and PS classes of cerebellar phospholipids. Given the neuropathologic characteristics of each disorder, it is likely that altered fatty acid composition and phospholipid levels in SCA-1 cerebellar cortex occur as a consequence of pronounced cerebellar degeneration. In contrast, reduced phospholipid levels in FA cerebellar and occipital cortex, areas characterized by, at most, minimal neuronal loss in FA, may represent a widespread alteration in cellular phospholipid metabolism occurring in response to the specific gene defect in the disorder.

RNA-binding site in T7 RNA polymerase

Recent models of RNA polymerase transcription complexes have invoked the idea that enzyme-nascent RNA contacts contribute to the stability of the complexes. Although much progress on this topic has been made with the multisubunit Escherichia coli RNA polymerase, there is a paucity of information regarding the structure of single-subunit phage RNA polymerase transcription complexes. Here, we photo-cross-linked the RNA in a T7 RNA polymerase transcription complex and mapped a major contact site between amino acid residues 144 and 168 and probably a minor contact between residues 1 and 93. These regions of the polymerase are proposed to interact with the emerging RNA during transcription because the 5' end of the RNA was cross-linked. The contacts are both ionic and nonionic (hydrophobic). The specific inhibitor of T7 transcription, T7 lysozyme, does not compete with T7 RNA polymerase for RNA cross-linking, implying that the RNA does not bind the lysozyme. However, lysozyme may act indirectly via a conformational change in the polymerase. In the current model, the DNA template lies in the polymerase cleft and the fingers subdomain may contact or maintain a template bubble, and a region in the N terminus forms a partly solvent-accessible binding channel for the emerging RNA.

Mechanisms for the processing of a frozen topoisomerase-DNA conjugate by human cell-free extracts

The metabolic fate of covalently linked DNA-protein complexes (cross-links) is not clearly understood. Our aim was to investigate the processing of protein-DNA cross-links by cellular enzymes. As an example of a DNA-protein cross-link, we have constructed frozen topoisomerase-DNA conjugates and investigated their processing by human cell-free extracts. A suicide DNA substrate was constructed that upon reaction with vaccinia type I topoisomerase yielded a highly stable covalent DNA-protein cross-link. When this conjugate was treated with human nuclear or whole cell extracts, two sites of DNA breakpoints were detected: one set of double-stranded breaks occurred close to the 3' side of the topoisomerase (topo) conjugation site, and there was another set of nicks about 30 nucleotides 3' to the topo site. The double-stranded breaks were not made by extracts from xeroderma pigmentosum group A mutant cells, suggesting that the xeroderma pigmentosum group A damage recognition protein may be required for the occurrence of DNA breakage. In addition to these DNA breakage reactions, there was an activity that resulted in the delinking of the frozen topoisomerase (or proteolytic fragments thereof) from the DNA substrate, which was followed by a ligation step that restored the continuity of the broken DNA strand at the erstwhile topo attachment site. We suggest that frozen topoisomerase-DNA conjugates (and perhaps other types of covalent DNA-protein complexes) are processed by multiple pathways that may involve the cleavage of the DNA in the covalent protein-DNA complex and/or enzymatic delinking followed by ligation of the broken DNA ends. These processes may represent the "repair" of DNA-protein cross-links.

Low activity of key phospholipid catabolic and anabolic enzymes in human substantia nigra: possible implications for Parkinson's disease

To determine whether increased oxidative stress in substantia nigra of patients with idiopathic Parkinson's disease might be related to decreased ability of nigral cells to detoxify oxidized membrane phospholipids, we compared levels of the major phospholipid metabolizing enzymes in autopsied substantia nigra with those in non-nigral (n = 11) brain areas of the normal human brain. Whereas most enzymes possessed a relatively homogeneous distribution, the activity of the major phospholipid catabolizing enzyme phospholipase A2, assayed in the presence of calcium ions, varied amongst different regions, with substantia nigra possessing the lowest activity. Similarly, calcium-independent phospholipase A2 activity, although possessing a relatively homogeneous regional distribution, was also low in the substantia nigra. This, coupled with low activity of phosphoethanolamine- and phosphocholine-cytidylyltransferases, major regulatory enzymes of phospholipid synthesis, in this brain region, suggest that the rate of phospholipid turnover is low in the substantia nigra. Low activity of key phospholipid catabolic and anabolic enzymes in human substantia nigra might result in reduced ability to repair oxidative membrane damage, as may occur in Parkinson's disease.

Homozygosity and physical mapping of the autosomal recessive retinitis pigmentosa locus (RP14) on chromosome 6p21.3

Retinitis pigmentosa (RP) is a heterogeneous genetic disorder with autosomal dominant, autosomal recessive, and X-linked forms. We previously mapped an additional arRP locus to chromosome 6p21 (RP14) in a single extended kinship from the Dominican Republic. Aided by a second linked RP pedigree from the same region of the Dominican Republic, we have refined the disease locus to a 2-cM region that is homozygous-by-descent in both pedigrees. A complete YAC, and a partial BAC, contig of the RP14 locus was constructed between the markers D6S1560 and D6S291, encompassing approximately 2.1 Mb. The contig contains 12 YACs and 31 BACs and is characterized by 45 markers including 8 microsatellite markers, 6 gene-derived sequences/ESTs obtained from the databases, and 28 new STSs and 4 new ESTs obtained by BLAST search using DNA sequence from the ends of the BAC and YAC inserts. With a STS density of approximately 1 every 20 kilobases, this contig significantly enhances available maps of the region.

Phospholipid-metabolizing enzymes in Alzheimer's disease: increased lysophospholipid acyltransferase activity and decreased phospholipase A2 activity

Damage to brain membrane phospholipids may play an important role in the pathogenesis of Alzheimer's disease (AD); however, the critical metabolic processes responsible for the generation and repair of membrane phospholipids affected by the disease are unknown. We measured the activity of key phospholipid catabolic and anabolic enzymes in morphologically affected and spared areas of autopsied brain of patients with AD and in matched control subjects. The activity of the major catabolic enzyme phospholipase A2 (PLA2), measured in both the presence and absence of Ca2+, was significantly decreased (-35 to -53%) in parietal and temporal cortices of patients with AD. In contrast, the activities of lysophospholipid acyltransferase, which recycles lysophospholipids into intact phospholipids, and glycerophosphocholine phosphodiesterase, which returns phospholipid catabolites to be used in phospholipid resynthesis, were increased by approximately 50-70% in the same brain areas. Brain activities of enzymes involved in de novo phospholipid synthesis (ethanolamine kinase, choline kinase, choline phosphotransferase, phosphoethanolamine cytidylyltransferase, and phosphocholine cytidylyltransferase) were either normal or only slightly altered. The activities of PLA2 and acyltransferase were normal in the degenerating cerebellum of patients with spinocerebellar atrophy type 1, whereas the activity of glycerophosphocholine phosphodiesterase was reduced, suggesting that the alterations in AD brain were not nonspecific consequences of neurodegeneration. Our data suggest that compensatory phospholipid metabolic changes are present in AD brain that reduce the rate of phospholipid loss via both decreased catabolism (PLA2) and increased phospholipid resynthesis (acyltransferase and glycerophosphocholine phosphodiesterase).

TULP1 mutation in two extended Dominican kindreds with autosomal recessive retinitis pigmentosa

The RP14 autosomal recessive Retinitis pigmentosa (arRP) locus has been mapped to a 2cM region of chromosome 6p21.3. TULP1 (the gene encoding tubby-like protein 1) is a candidate target for the disease mutation because it maps to the RP14 minimum genetic region and because a mutation in the highly homologous mouse tub gene leads to obesity, deafness and early progressive retinal degeneration. Here we report a splice-site mutation (IVS14+1, G-->A) that is homozygous in all affected individuals (N=33) and heterozygous in all obligate carriers (N=50) from two RP14-linked kindreds. The mutation was not observed in 210 unrelated controls. The data indicate that impairment of TULP1 protein function is a rare cause of arRP and that the normal protein plays an essential role in the physiology of the retina.

Identification and analysis of mutations in the Wilson disease gene (ATP7B): population frequencies, genotype-phenotype correlation, and functional analyses

Wilson disease (WD) is an autosomal recessive disorder characterized by toxic accumulation of copper in the liver and subsequently in the brain and other organs. On the basis of sequence homology to known genes, the WD gene (ATP7B) appears to be a copper-transporting P-type ATPase. A search for ATP7B mutations in WD patients from five population samples, including 109 North American patients, revealed 27 distinct mutations, 18 of which are novel. A composite of published findings shows missense mutations in all exons-except in exons 1-5, which encode the six copper-binding motifs, and in exon 21, which spans the carboxy-terminus and the poly(A) tail. Over one-half of all WD mutations occur only rarely in any population sample. A splice-site mutation in exon 12 accounts for 3% of the WD mutations in our sample and produces an in-frame, 39-bp insertion in mRNA of patients homozygous, but not heterozygous, for the mutation. The most common WD mutation (His1069Glu) was represented in approximately 38% of all the WD chromosomes from the North American, Russian, and Swedish samples. In several population cohorts, this mutation deviated from Hardy-Weinberg equilibrium, with an overrepresentation of homozygotes. We did not find a significant correlation between His1069Glu homozygosity and several clinical indices, including age of onset, clinical manifestation, ceruloplasmin activity, hepatic copper levels, and the presence of Kayser-Fleischer rings. Finally, lymphoblast cell lines from individuals homozygous for His1069Glu and 4 other mutations all demonstrated significantly decreased copper-stimulated ATPase activity.

Extensive DNA deletion associated with severe disease alleles on spinal muscular atrophy homologues

Spinal muscular atrophy (SMA) is a motor neuron disease presenting with a wide spectrum of phenotypic variations. The primary cause of most, if not all, forms of childhood-onset spinal muscular atrophy appears to be the homozygous loss of the telomeric copy of the survival motor neuron (SMNT) gene. It is interesting that approximately half of all affected patients are likewise homozygous nulls for the neuronal apoptosis inhibitory protein (NAIP) gene and a somewhat lesser fraction for the basal transcription factor, p44 subunit (BTF2p44) gene. It has been proposed that homozygous loss of SMNT is the primary cause of spinal muscular atrophy while the loss of NAIP and perhaps other genes primarily affects the severity of disease manifestation. We explored this hypothesis by evaluating the extent of gene deletions in three multigenerational families with spinal muscular atrophy exhibiting dramatic intrafamilial phenotypic variation. Using somatic cell hybrid lines to sequester individual spinal muscular atrophy homologues, we show that homologues missing several contiguous genes correlate with "severe" disease alleles and homologues missing only SMNT correlate with "mild" disease alleles. These observations support the hypothesis that phenotypic severity among the childhood-onset spinal muscular atrophies is directly correlated with the extent of disease-specific deletions.

Increased phospholipid breakdown in schizophrenia. Evidence for the involvement of a calcium-independent phospholipase A2

BACKGROUND

Magnetic resonance spectroscopy studies have suggested above-normal turnover of membrane phospholipids in brains of patients with schizophrenia. One possible explanation for these findings is increased activity of the phospholipid-catabolizing enzyme phospholipase A2 (PLA2). However, attempts to demonstrate higher PLA2 activity in the serum of subjects with schizophrenia have led to conflicting results. We hypothesized that this was due to serum PLA2 activity consisting of a family of different enzymes, with each group of investigators measuring activity of different PLA2 forms.

DESIGN

Activity of PLA2 in serum samples obtained from 24 individuals with schizophrenia was compared with serum obtained from 33 age- and sex-matched control subjects, using both fluorometric and radiometric assays with different substrates. Each method had previously yielded conflicting results concerning the status of the enzyme in schizophrenia.

RESULTS

With the fluorometric assay, serum PLA2 activity in individuals with schizophrenia was markedly increased by 49% compared with control subjects (P < .001). In contrast, radiometric assay of the same serum samples resulted in PLA2 activity not significantly different between patients and control subjects. Further investigations demonstrated that, whereas the radiometric assay measured activity of a calcium-dependent enzyme, the fluorometric assay detected a calcium-insensitive enzyme possessing an acid-neutral pH optimum.

CONCLUSIONS

Increased calcium-independent PLA2 activity was seen in the serum of patients with schizophrenia. This change, if present also in the brain, may well explain the increased levels of phosphodiesters observed using magnetic resonance spectroscopy and therefore may contribute to the pathophysiological features of the disorder.

Phospholipid biosynthetic enzymes in human brain

Growing evidence suggests an involvement of brain membrane phospholipid metabolism in a variety of neurodegenerative and psychiatric conditions. This has prompted the use of drugs (e.g., CDPcholine) aimed at elevating the rate of neural membrane synthesis. However, no information is available regarding the human brain enzymes of phospholipid synthesis which these drugs affect. Thus, the objective of our study was to characterize the enzymes involved, in particular, whether differences existed in the relative affinity of substrates for the enzymes of phosphatidylethanolamine (PE) compared to those of phosphatidylcholine (PC) synthesis. The concentration of choline in rapidly frozen human brain biopsies ranged from 32-186 nmol/g tissue, a concentration similar to that determined previously for ethanolamine. Since human brain ethanolamine kinase possessed a much lower affinity for ethanolamine (Km = 460 microM) than choline kinase did for choline (Km = 17 microM), the activity of ethanolamine kinase in vivo may be more dependent on substrate availability than that of choline kinase. In addition, whereas ethanolamine kinase was inhibited by choline, and to a lesser extent by phosphocholine, choline kinase activity was unaffected by the presence of ethanolamine, or phosphoethanolamine, and only weakly inhibited by phosphocholine. Phosphoethanolamine cytidylyltransferase (PECT) and phosphocholine cytidylyltransferase (PCCT) also displayed dissimilar characteristics, with PECT and PCCT being located predominantly in the cytosolic and particulate fractions, respectively. Both PECT and PCCT exhibited a low affinity for CTP (Km approximately 1.2 mM), suggesting that the activities of these enzymes, and by implication, the rate of phospholipid synthesis, are highly dependent upon the cellular concentration of CTP. In conclusion our data indicate different regulatory properties of PE and PC synthesis in human brain, and suggest that the rate of PE synthesis may be more dependent upon substrate (ethanolamine) availability than that of PC synthesis.

Nuclease activity of T7 RNA polymerase and the heterogeneity of transcription elongation complexes

We have discovered that T7 RNA polymerase, purified to apparent homogeneity from overexpressing Escherichia coli cells, possesses a DNase and an RNase activity. Mutations in the active center of T7 RNA polymerase abolished or greatly decreased the nuclease activity. This nuclease activity is specific for single-stranded DNA and RNA oligonucleotides and does not manifest on double-stranded DNAs. Under the conditions of promoter-driven transcription on double-stranded DNA, no nuclease activity was observed. The nuclease attacks DNA oligonucleotides in mono- or dinucleotide steps. The nuclease is a 3' to 5' exonuclease leaving a 3'-OH end, and it degrades DNA oligonucleotides to a minimum size of 3 to 5 nucleotides. It is completely dependent on Mg2+. The T7 RNA polymerase-nuclease is inhibited by T7 lysozyme and heparin, although not completely. In the presence of rNTPs, the nuclease activity is suppressed but an unusual 3'-end-initiated polymerase activity is unmasked. RNA from isolated pre-elongation and elongation complexes arrested by a psoralen roadblock or naturally paused at the 3'-end of an oligonucleotide template exhibited evidence of nuclease activity. The nuclease activity of T7 RNA polymerase is unrelated to pyrophosphorolysis. We propose that the nuclease of T7 RNA polymerase acts only in arrested or paused elongation complexes, and that in combination with the unusual 3'-end polymerizing activity, causes heterogeneity in elongation complexes. Additionally, during normal transcription elongation, the kinetic balance between nuclease and polymerase is shifted in favor of polymerase.

Probing the mechanisms of T7 RNA polymerase transcription initiation using photochemical conjugation of psoralen to a promoter

We have dissected the steps in T7 RNA polymerase transcription initiation using psoralen cross-linking. DNA templates containing cross-links at either -14/-13, -2/-1, or -4/-3 were constructed. These cross-links are within the DNA-contacting region in the initiation complex. A cross-link at -2/-1 did not affect T7 RNA polymerase binding affinity, whereas a cross-link at -14/-13 reduced binding affinity by less than 2-fold. Transcription initiation was completely blocked by cross-links at -14/-13 or at -2/-1. A cross-link at -4/-3 inhibited neither binding nor the first RNA phosphodiester bond but greatly inhibited further RNA chain extension. Circular dichroism spectroscopy revealed that DNA melting in the -4/-3 cross-link was greatly inhibited, indicating that inhibition of RNA chain extension was a melting defect. Transcription shutoff on the -14/-13 cross-link may be due to inhibition of conformational changes in the polymerase-DNA complex. Because the -2/-1 cross-link is immediately upstream of the start site (+1), open complex formation may have been completely inhibited by this cross-link, accounting for the shutoff of transcription. Thus, depending on their location, psoralen cross-links affected different steps in the initiation process. We propose that promoter melting is progressive and that melting of one or two bp upstream of the +1 site is sufficient for formation of the first phosphodiester bond while further RNA chain extension within the promoter depends on greater upstream melting of the promoter, which may be required for stabilization of the initiation complex.

Cross-linking of DNA-binding proteins to DNA with psoralen and psoralen furan-side monoadducts. Comparison of action spectra with DNA-DNA cross-linking

We have developed a novel photocross-linking technique using free 8-methoxypsoralen and DNA furan-side monoadducts plus long wave ultraviolet light (UVA). Both sequence-specific (Max) and nonspecific (RecA and T7 RNA polymerase) DNA-binding proteins were cross-linked. The macroscopic equilibrium binding constant ( approximately 10(9) M-1) and DNase I footprinting indicated that binding of Max to its cognate sequence (E-box) was unimpaired by 8-methoxypsoralen and that cross-linking occurred in normal complexes. RecA protein and T7 RNA polymerase were cross-linked to a 12-mer DNA furan-side monoadduct with UVA. Cross-link yields were directly proportional to the UVA dose. Cross-links were stable to 8 M urea, 1-10% SDS, commonly used alcohols, and mild acids (5% trichloroacetic acid). The DNA in cross-links was reversed with 254 nm UV (photoreversal) or with hot base (base-catalyzed reversal), consistent with (2 + 2) cycloaddition via the 4',5'-furan of the psoralen. Comparative action spectra for DNA-DNA cross-linking and DNA-protein cross-linking revealed that the latter occurred maximally at 300 nm, while the former occurred maximally at 320 nm. This 20-nm blue shift suggested a higher potential energy surface for an excited psoralen participating in protein-DNA cross-linking as compared with DNA-DNA cross-linking. As with DNA-DNA cross-linking, DNA-protein cross-linking is a two-photon process. Absorption of the first photon formed a 4',5'-adduct with DNA, which then absorbed a second photon, leading to cross-linking to protein. Based on the action spectra and the known excited states of psoralen, it is suggested that the triplet n,pi* transition localized in the C-2=O of psoralen may be involved in protein-psoralen photoreactions.

A multicopy transcription-repair gene, BTF2p44, maps to the SMA region and demonstrates SMA associated deletions

The childhood-onset spinal muscular atrophies are a clinically heterogeneous group of autosomal recessive disorders characterized by selective degeneration of the anterior horn cells with subsequent weakness and atrophy of limb muscles. The disease locus has been mapped to a region of chromosome 5q13 characterized by genetic instability and DNA duplication. Among the duplicated genes in this region, SMNT (telomeric copy; survival motor neuron) is thought to be the major disease determining gene since it is missing in the majority of SMA patients and since small, intragenic mutations in the gene have been associated with the disorder. Approximately half of the severely affected SMA I patients are also missing both homologues of a neighboring gene, the neuronal apoptosis inhibitory protein (NAIP). These data indicate that loss of NAIP may affect disease severity and further, that the molecular events underlying the childhood-onset SMAs are complex, possibly involving multiple genes. We report a third multicopy gene in the SMA region, encoding the p44 subunit of basal transcription factor II (BTF2p44). One copy of this transcription-repair gene is deleted in at least 15% of all SMA cases.

A direct real-time spectroscopic investigation of the mechanism of open complex formation by T7 RNA polymerase

Initiation of transcription occurs through a series of steps starting with the binding of RNA polymerase to a promoter DNA and formation of a closed complex. The closed complexes, then isomerize to open complexes. In the open complexes a portion of the promoter DNA is unwound. Using fluorescence spectroscopy, we have investigated in real-time the mechanism of unwinding of promoter DNA during the transition from closed to open complexes of T7 RNA polymerase. We synthesized DNA templates containing the fluorescent base analog 2-aminopurine in place of adenine at specific positions in a T7 RNA polymerase promoter. We located the 2-aminopurine residues in the presumed melting domain of the promoter at -1, -4, and at -6. The fluorescence of 2-aminopurine increases when the DNA goes from a double-stranded form to a single-stranded form. By spectroscopically monitoring the increase in fluorescence of 2-aminopurine in DNA-T7 RNA polymerase complexes, we obtained kinetic and thermodynamic information for DNA unwinding. In the presence of the initiating nucleotide GTP, conformational transitions in the polymerase-promoter complex leading to strand opening were slower than in its absence. The rate of base pair disruption at -1, -6, and at -4 was also slower in the presence of GTP than in its absence. At 37 degrees C, base pair disruption occurred first at -1 followed by -6 and finally at -4. Open complex formation was temperature-sensitive. Temperature effects at -1, -6, and at -4 were consistent with this order of base pair disruption. The apparent activation energies (Ea) for base pair disruption around -1 and -6 were 14 kcal mol-1 and 50 kcal mol-1, respectively, also suggesting this order of base pair disruption. Transcription initiation assays using G-ladder synthesis revealed that initiation rates were almost the same on all three templates containing the modified base. Unlike strand opening, we did not observe lag times for G-ladder synthesis. We suggest that facile base pair disruption at -1 is sufficient for transcription initiation. Based on these data, it is proposed that the polymerase makes contacts at or near -1 and -6 resulting in untwisting of these base pairs thus creating at least two base pair disruption events at -1 and at -6, which are followed by bidirectional propagation to -4.

Phospholipase A2 activity is selectively decreased in the striatum of chronic cocaine users

Dopamine-mediated stimulation of arachidonic acid metabolism, via activation of the phospholipid metabolizing enzyme phospholipase A2 (PLA2), has recently been implicated in dopamine neurotransmitter function. We examined the status of PLA2 in autopsied brain of 10 chronic users of cocaine, a dopamine reuptake inhibitor. PLA2 activity, assayed at pH 8.5 in the presence of Ca2+, was significantly (p < 0.01) decreased by 31% in the putamen of cocaine users (n = 10) compared with that in controls (n = 10), whereas activity was normal in the frontal and occipital cortices, subcortical white matter, and cerebellum. In contrast, calcium-independent PLA2 activity, assayed at pH 7.0, was normal in all brain regions examined. Our finding of altered PLA2 activity restricted to a region of high dopamine receptor density suggests that modulation of PLA2 may be involved in mediating some of the dopamine-related behavioral effects of cocaine and could conceivably contribute to dopamine-related processes in the normal brain.

Characterization of survival motor neuron (SMNT) gene deletions in asymptomatic carriers of spinal muscular atrophy

Previous reports have established that the telomeric copy of the survival motor neuron (SMNT) gene and the intact copy of the neuronal apoptosis inhibitory protein (NAIP) gene are preferentially deleted in patients with spinal muscular atrophy (SMA). Although deletions or mutations in the SMNT gene are most highly correlated with SMA, it is not clear to what extent NAIP or other genes influence the SMA phenotype, or whether a small fraction of SMA patients actually have functional copies of both SMNT and NAIP. To evaluate further the part of SMNT in the development of SMA, we analyzed 280 asymptomatic SMA family members for the presence or absence of SMNT exons 7 and 8. We report the following observations: (i) 4% of the sample harbored a polymorphic variant of SMNT exon 7 that looks like a homozygous deletion; (ii) approximately 1% of the parents are homozygously deleted for both exons 7 and 8; (iii) one asymptomatic parent lacking both copies of SMNT exons 7 and 8 displays a 'subclinical phenotype' characterized by mild neurogenic pathology; (iv) another asymptomatic parent lacking both SMNT exons showed no signs of motor neuron disorder by clinical and neurodiagnostic analyses. The demonstration of polymorphic variants of exon 7 that masquerade as homozygous nulls, and the identification of SMA parents who harbor two disease alleles, serve as a caution to those conducting prenatal tests with these markers.

Multiple forms of the enzyme glycerophosphodiesterase are present in human brain

Brain levels of glycerophosphodiesters, including glycerophosphocholine (GPC) and glycerophosphoethanolamine (GPE), are altered in many human central nervous system disorders. Although much information is available on the enzymes responsible for the formation of these phospholipid metabolites, little information is known regarding their catabolism, by glycerophosphodiesterases, in human brain. In both autopsied and biopsied temporal cortex, a phosphocholine-producing glycerophosphodiesterase activity was observed. In the presence of 1 mM EDTA, the enzyme possessed a pH optimum of 9.0, while the addition of 5 mM zinc acetate shifted the pH optimum to 10.5. When assayed at pH 9.0 in the absence of zinc acetate, the Km and Vmax were 104 +/- 2 microM and 77 +/- 18 nmol/h/mg protein, respectively, while assaying at pH 10.5 in the presence of 5mM zinc acetate yielded a Km of 964 +/- 56 microM, and a Vmax of 534 +/- 114 nmol/h/mg protein. Furthermore, whereas submillimolar concentrations of zinc acetate stimulated the activity of the enzyme in a dose-dependent manner when assayed at pH 10.5 (EC50 =20.3 +/- 3.0 microM), this did not result in a reciprocal inhibition of glycerophosphocholine phosphodiesterase (GPC PD) activity when assayed at a more acidic pH. This may suggest that human brain contains two phosphocholine-producing GPC PD activities, differentiable by their sensitivity to zinc ions. An activity capable of hydrolyzing GPE to form phosphoethanolamine could not be detected in either biopsied or autopsied brain. However, a choline/ethanolamine-producing glycerophosphodiesterase activity could be readily detected in biopsied, but not autopsied brain. this novel enzyme possessed a neutral pH optimum and was dependent upon divalent cations for activity. In conclusion, human brain contains at least two different glycerophosphodiesterases, a phosphocholine, and a choline/ethanolamine-producing activity, only one of which can be detected in autopsied tissue. The results of previous studies measuring brain glycerophosphodiesterase activity in degenerative brain conditions may need to be reevaluated in the light of these observations.

Characterization of a novel phospholipase A2 activity in human brain

Phospholipases A2 (PLA2) are a family of enzymes that catalyze the removal of fatty acid residues from phosphoglycerides. The enzyme is postulated to be involved in several human brain disorders, although little is known regarding the status of PLA2 activity in human CNS. We therefore have characterized some aspects of the PLA2 activity present in the temporal cortex of human brain. More PLA2 activity was found in the membrane (particulate) fraction than in the cytosolic fraction. The enzyme could be solubilized from particulate material using 1 M potassium chloride, and was capable of hydrolyzing choline phosphoglyceride (CPG) and ethanolamine phosphoglyceride (EPG), with a preference (approximately eightfold) for EPG over CPG. When the solubilized particulate enzyme was subjected to gel filtration chromatography, PLA2 activity eluted in a high molecular mass fraction (approximately 180 kDa). PLA2 activity was weakly stimulated by dithiothreitol, strongly stimulated by millimolar concentrations of calcium ions, and inhibited by brief heat treatment at 57 degrees C, bromophenacyl bromide, the arachidonic acid derivative AACOCF3, gamma-linolenoyl amide, and N-methyl gamma-linolenoyl amide. Thus, whereas the human brain enzyme(s) characterized in our study displays some of the characteristics of previously characterized PLA2s, it differs in several key features.

Transgenic mice expressing the human heat shock protein 70 have improved post-ischemic myocardial recovery

Heat shock treatment induces expression of several heat shock proteins and subsequent post-ischemic myocardial protection. Correlations exist between the degree of stress used to induce the heat shock proteins, the amount of the inducible heat shock protein 70 (HSP70) and the level of myocardial protection. The inducible HSP70 has also been shown to be protective in transfected myogenic cells. Here we examined the role of human inducible HSP70 in transgenic mouse hearts. Overexpression of the human HSP70 does not appear to affect normal protein synthesis or the stress response in transgenic mice compared with nontransgenic mice. After 30 min of ischemia, upon reperfusion, transgenic hearts versus nontransgenic hearts showed significantly improved recovery of contractile force (0.35 +/- 0.08 versus 0.16 +/- 0.05 g, respectively, P < 0.05), rate of contraction, and rate of relaxation. Creatine kinase, an indicator of cellular injury, was released at a high level (67.7 +/- 23.0 U/ml) upon reperfusion from nontransgenic hearts, but not transgenic hearts (1.6 +/- 0.8 U/ml). We conclude that high level constitutive expression of the human inducible HSP70 plays a direct role in the protection of the myocardium from ischemia and reperfusion injury.

Refinement of the spinal muscular atrophy locus by genetic and physical mapping

We report the mapping and characterization of 12 microsatellite markers including 11 novel markers. All markers were generated from overlapping YAC clones that span the spinal muscular atrophy (SMA) locus. PCR amplification of 32 overlapping YAC clones shows that 9 of the new markers (those set in italics) map to the interval between the two previous closest flanking markers (D5S629 and D5S557): cen-D5S6-D5S125-D5S435-D5S1407- D5S629-D5S1410-D5S1411/D5S1412-D5S1413- D5S1414-D5Z8-D5Z9-CATT1-D5Z10/D5Z6- D5S557-D5S1408-D5S1409-D5S637-D5S351-MA P1B-tel. Four of these new markers detect multiple loci in and out of the SMA gene region. Genetic analysis of recombinant SMA families indicates that D5S1413 is a new proximal flanking locus for the SMA gene. Interestingly, among the 40 physically mapped loci, the 14 multilocus markers map contiguously to a genomic region that overlaps, and perhaps helps define, the minimum genetic region encompassing the SMA gene(s).

Characterization of lysophospholipid metabolizing enzymes in human brain

Lysophospholipids are generated during the turnover and breakdown of membrane phospholipids. We have identified and partially characterized three enzymes involved in the metabolism of lysophospholipids in human brain, namely, lysophospholipase, lysophospholipid:acyl-CoA acyltransferase (acyltransferase), and lysophospholipid:lysophospholipid transacylase (transacylase). Each enzyme displayed comparable levels of activity in biopsied and autopsied human brain, although in all cases the activity was somewhat lower in human than that in rat brain. All three enzymes were localized predominantly in the particulate fraction, with lysophospholipase possessing the greatest activity followed by acyltransferase and transacylase. Lysophosphatidylcholine possessed a Km in the micromolar range for lysophospholipase and transacylase, and in the millimolar range for acyltransferase, whereas arachidonyl-CoA displayed a Km in the micromolar range for acyltransferase. The three enzymes differed in their pH optima, with lysophospholipase being most active at pH 8.0, transacylase at pH 7.5, and acyltransferase at pH 6.0. Both bromophenacyl bromide and N-ethylmaleimide inhibited lysophospholipase activity and, to a lesser extent, that of acyltransferase and transacylase. None of the enzyme activities were affected by the presence of dithiothreitol or EDTA, although particulate lysophospholipase was activated approximately two-fold by the addition of 5 mM MgCl2 or CaCl2 but not KCl. Transacylating activity was stimulated by CoA, the EC50 of activation being 6.8 microM. Acyltransferase displayed an approximately threefold preference for arachidonyl-CoA over palmitoyl-CoA, whereas the acylation rate of different lysophospholipids was in the order lysophosphatidylinositol > 1-palmitoyl lysophosphatidylcholine > 1-oleoyl lysophosphatidylcholine >> lysophosphatidylserine > lysophosphatidylethanolamine. This, and the preference of human brain phospholipase A2 for phosphatidylinositol, suggests that this phospholipid may possess a higher turnover rate than the other phospholipid classes examined. Human brain homogenates also possessed the ability to transfer fatty acid from lysophosphatidylcholine to lysophosphatidylethanolamine. In addition, we also present evidence that diacylglycerophospholipids can act as acyl donors for the transacylation of lysophospholipids. We have therefore demonstrated the presence of, and partially characterized, three enzymes that are involved in the metabolism of lysophospholipids in human brain. Our results suggest that lysophospholipase may be the major route by which lysophospholipids are removed from the cell membrane in human brain. However, all three enzymes likely play an important role in the remodeling of membrane composition and thereby contribute to the overall functioning of membrane-associated processes.

Characterization of the Wilson disease gene encoding a P-type copper transporting ATPase: genomic organization, alternative splicing, and structure/function predictions

Wilson disease is an autosomal recessive disorder of copper transport. Disease symptoms develop from the toxic build-up of copper primarily in the liver, and subsequently in the brain, kidney, cornea and other tissues. A candidate gene for WD (ATP7B) has recently been identified based upon apparent disease-specific mutations and a striking amino acid homology to the gene (ATP7A) responsible for another human copper transport disorder, X-linked Menkes disease (MNK). The cloning of WD and MNK genes provides the first opportunity to study copper homeostasis in humans. A preliminary analysis of the WD gene is presented which includes: isolation and characterization of the 5'-end of the gene; construction of a genomic restriction map; identification of all 21 exon/intron boundaries; characterization of extensive alternative splicing in brain; prediction of structure/function features of the WD and MNK proteins which are unique to the subset of heavy metal-transporting P-type ATPases; and comparative analysis of the six metal-binding domains. The analysis indicates that WD and MNK proteins belong to a subset of transporting ATPases with several unique features presumably reflecting their specific regulation and function. It appears that the mechanism of alternative splicing serves to regulate the amount of functional WD protein produced in brain, kidney, placenta, and possibly in liver.

Alterations in the activity of adenylate cyclase and high affinity GTPase in Alzheimer's disease

The aim of this study was to assess the effect of Alzheimer's disease has on the functional integrity of several signal transduction proteins. The relative levels of the G-protein alpha subunits Gs alpha-L, Gs alpha-S, Gi alpha-2 and G(o) alpha were measured by western blotting and found to be unchanged in membranes prepared from Alzheimer-diseased frontal cortex or hippocampus compared to control brains. However the activity of the G-protein associated enzyme, high affinity GTPase, was found to be reduced in the frontal cortex (reduced by 25%) and by a similar magnitude in the hippocampus (reduced by 27%) of Alzheimer subjects. The same membrane preparations were also assayed for the activity of adenylate cyclase. Basal enzyme activity was not significantly altered in Alzheimer diseased hippocampus, but was markedly reduced (by 45%) in the frontal cortex. The ability of fluoride and aluminium ions to stimulate adenylate cyclase was not significantly changed in either brain region. This suggests that G-proteins, especially Gs, are still able to interact with this enzyme. These results indicate that although the presence of Alzheimer's disease does not significantly alter G-protein levels, changes have taken place in the overall activity of these proteins. However this alteration does not affect their ability to stimulate adenylate cyclase activity.