Pro-inflammatory activation of microglia in the brain of patients with sepsis

Aims

Experimental data suggest that systemic immune activation may create a pro‐inflammatory environment with microglia activation in the central nervous system in the absence of overt inflammation, which in turn may be deleterious in conditions of neurodegenerative disease. The extent to which this is relevant for the human brain is unknown. The central aim of this study is to provide an in‐depth characterization of the microglia and macrophage response to systemic inflammation.

Methods

We used recently described markers to characterize the origin and functional states of microglia/macrophages in white and grey matter in patients who died under septic conditions and compared it to those patients without systemic inflammation.

Results

We found pro‐inflammatory microglia activation in septic patients in the white matter, with very little activation in the grey matter. Using a specific marker for resident microglia (TMEM119), we found that parenchyma microglia were activated and that there was additional recruitment of perivascular macrophages. Pro‐inflammatory microglia activation occurred in the presence of homeostatic microglia cells. In contrast to inflammatory or ischaemic diseases of the brain, the anti‐inflammatory microglia markers CD163 or CD206 were not expressed in acute sepsis. Furthermore, we found pronounced upregulation of inducible nitric oxide synthase not only in microglia, but also in astrocytes and endothelial cells.

Conclusion

Our results demonstrate the pronounced effects of systemic inflammation on the human brain and have important implications for the selection of control populations for studies on microglia activation in human brain disease.

Low testosterone is associated with disability in men with multiple sclerosis

BACKGROUND

Gonadal steroids may modulate disease course in multiple sclerosis (MS).

OBJECTIVE

To assess the prevalence and clinical associations of hypogonadism in men with MS.

METHODS

Male patients, aged 18-65 years, with relapsing-remitting MS (RRMS) or clinically-isolated syndrome (CIS) and their first symptom < 10 years prior were selected from a longitudinal clinical study. We measured their hormones in stored morning blood samples, and collected their Expanded Disability Status Scale (EDSS) scores every 6 months and their Symbol Digit Modalities Test (SDMT) results annually.

RESULTS

Our analysis included 96 men with a mean age of 40 years, EDSS of 1.1 and disease duration of 4.6 years. Of these men, 39% were hypogonadal (total testosterone < 288 ng/dL); none showed compensatory elevations in luteinizing hormone. Their low testosterone levels and testosterone:estradiol ratios were negatively correlated with body mass index (BMI) and leptin, and showed no correlation with 25-hydroxy-vitamin D levels. In our primary cross-sectional analyses, there was a negative age-adjusted correlation between total testosterone and EDSS (p = 0.044). In the age-adjusted longitudinal analyses, higher baseline testosterone levels were associated with less decline in SDMT (p = 0.012).

CONCLUSIONS

Men with MS may experience hypogonadotropic hypogonadism. Low testosterone levels may be associated with worse clinical outcomes. A potential neuroprotective role for testosterone warrants further investigation.

MRI characterization and longitudinal study of focal cerebellar lesions in a young tuberous sclerosis cohort

BACKGROUND AND PURPOSE

There are few articles characterizing cerebellar lesions in patients with TSC and no published series documenting longitudinal evaluation of these lesions, to our knowledge. Recent suggestion of a correlation between autism and cerebellar lesions in patients with TSC heightens the importance of understanding these lesions. Our purpose was to characterize cerebellar lesions in a cohort of young patients with TSC with specific interest in assessing longitudinal changes.

MATERIALS AND METHODS

We retrospectively reviewed MR images from 145 pediatric and young adult patients with tuberous sclerosis (mean age, 7.6 years). A number of imaging characteristics of cerebellar tubers were recorded, and patients were evaluated for SGAs. Patients with follow-up scans >3 months from the original scan were further analyzed for longitudinal tuber characterization.

RESULTS

There were 24.1% of patients with focal cerebellar lesions; 52.4% of patients with cerebellar lesions demonstrated change in imaging characteristics during longitudinal analysis. Fifty-one percent of the lesions were enhanced after gadolinium administration. Twenty percent of the patients with cerebellar lesions had pathologically confirmed SGAs compared with the incidence of 11% in the 145 patients with TSC reviewed.

CONCLUSIONS

In our large cohort of young patients with TSC, cerebellar tubers were common and 52% of patients had tubers that changed with time. A higher percentage of patients with cerebellar lesions developed SGAs than patients with TSC without cerebellar lesions. Because this is the first reported longitudinal study of cerebellar lesions in TSC, further investigation may provide additional insight into TSC pathology and associated clinical manifestations, such as autism, developmental delay, and seizures.

Conditioning history and the control of human avoidance and escape responding

Inter-subject differences in response rates under free-operant avoidance and escape schedules are commonly obtained from humans. Data are presented which demonstrate that such differences can be controlled experimentally by giving subjects different conditioning histories. Subjects given a fixed-ratio history avoided and/or escaped from "point-loss periods" at higher rates than subjects given a differential-reinforcement-of-low-rates history. History related differences in response rates were maintained during 40 hr of escape responding. For low-rates history subjects, response rates under escape contingencies decreased as the rate of point-loss periods decreased.

Instructional control of human operant responding during extinction following fixed-ratio conditioning

When given pre-conditioning instructions correctly indicating the maximum number of reinforcements obtainable, subjects made few responses during extinction following FR 10 conditioning. More extinction responses occurred when the maximum-reinforcement instructions suggested that reinforcements were obtainable during extinction. The highest rates of responding during extinction were produced by subjects who had no maximum-reinforcement instructions.

Controlling human fixed-interval performance

Both high and relatively constant rates of responding without post-reinforcement pauses and lower rates with pauses after reinforcement are produced by human subjects under fixed-interval (FI) schedules. Such FI rates and patterns may be controlled when subjects are provided with different histories of conditioning and different conditions of response cost (reinforcement penalties per response). Subjects with a conditioning history under ratio schedules typically produce high and relatively constant rates of responding under FI schedules; this responding does not change systematically with changes in FI value. In contrast, subjects with a history under schedules which produce little or no responding between reforcements [such as differential-reinforcement-of-low-rate (DRL) schedules] tend to pause after reinforcement and respond at low rates under FI schedules, whether or not they also have ratio conditioning histories; cost increases the likelihood of this type of performance. For DRL-history subjects, post-reinforcement pauses increase and response rates decrease as FI values increase.

An operant analysis of human altruistic responding

Human altruistic responding (called give responding), which delivered a reinforcer to someone other than the responder, was compared to responding where the responder was the recipient of the reinforcer (called earn responding). The same type of response (button pressing), the same reinforcer (a point representing a penny), and the same reinforcer contingency (a 40-response fixed-ratio schedule) were used for both give and earn responding. Since points representing pennies were used to reinforce give and earn responding, responding for points not worth money was also assessed. Give, earn, and point responding were arranged as concurrent incompatible operants. Lowest rates were obtained for point responding. Compared to earn responding, give responding occurred at lower rates, was more susceptible to cessation when point responding was possible, extinguished more rapidly in the absence of money, and produced less responding during reconditioning compared to conditioning when reconditioning followed a period of nonreinforcement. Give responding was less when it reduced the giver's opportunity to earn. Finally, histories of getting reinforcement from others were shown to determine give responding.

Number of nitrate groups determines reactivity and potency of organic nitrates: a proof of concept study in ALDH-2-/- mice

BACKGROUND AND PURPOSE

Mitochondrial aldehyde dehydrogenase (ALDH-2) has been shown to provide a pathway for bioactivation of organic nitrates and to be prone to desensitization in response to highly potent, but not to less potent, nitrates. We therefore sought to support the hypothesis that bioactivation by ALDH-2 critically depends on the number of nitrate groups within the nitrovasodilator.

EXPERIMENTAL APPROACH

Nitrates with one (PEMN), two (PEDN; GDN), three (PETriN; glyceryl trinitrate, GTN) and four (pentaerithrityl tetranitrate, PETN) nitrate groups were investigated. Vasodilatory potency was measured in isometric tension studies using isolated aortic segments of wild type (WT) and ALDH-2-/- mice. Activity of the cGMP-dependent kinase-I (reflected by levels of phosphorylated VAsodilator Stimulated Phosphoprotein, P-VASP) was quantified by Western blot analysis, mitochondrial dehydrogenase activity by HPLC. Following incubation of isolated mitochondria with PETN, PETriN-chromophore and PEDN, metabolites were quantified using chemiluminescence nitrogen detection and mass spectrometry.

KEY RESULTS

Compared to WT, vasorelaxation in response to PETN, PETriN and GTN was attenuated about 10fold in ALDH-2-/- mice, identical to WT vessels preincubated with inhibitors of ALDH-2. Reduced vasodilator potency correlated with reduced P-VASP formation and diminished biotransformation of the tetranitrate- and trinitrate-compounds. None of these findings were observed for PEDN, GDN and PEMN.

CONCLUSIONS AND IMPLICATIONS

Our results support the crucial role of ALDH-2 in bioactivating highly reactive nitrates like GTN, PETN and PETriN. ALDH-2-mediated relaxation by organic nitrates therefore depends mainly on the number of nitrate groups. Less potent nitrates like PEDN, GDN and PEMN are apparently biotransformed by other pathways.

A randomized blinded trial of combination therapy with cyclophosphamide in patients-with active multiple sclerosis on interferon beta

OBJECTIVE

To evaluate the efficacy and safety of combination therapy with pulse cyclophosphamide given with methylprednisolone (MP) and interferon beta (IFNbeta)-Ia in multiple sclerosis (MS) patients with active disease during IFNbeta monotherapy.

METHODS

This was a randomized, single-blind, parallel-group, multicenter trial in MS patients with a history of active disease during IFNbeta treatment. Patients were randomized to either cyclophosphamide 800 mg/m2 plus methylprednisolone 1 g IV (CY/MP) or methylprednisolone once a month for six months and then followed for an additional 18 months. All patients received three days of methylprednisolone 1 g IV at screening and 30 mcg IFNbeta-Ia IM weekly for the entire 24 months. The primary endpoint was change from baseline in the mean number of gadolinium-enhancing (Gd+) lesions. Secondary clinical endpoints included time to treatment failure.

RESULTS

Fifty-nine patients were randomized to treatment: 30 to CY/MP and 29 to MP Change from baseline in the number of Gd+ lesions was significantly different between treatment groups at three (P =0.01), six (P =0.04) and 12 months (P =0.02), with fewer lesions in the CY/MP group. The cumulative rate of treatment failure was significantly lower in the CY/MP group compared with the MP group (rate ratio =0.30; 95% confidence interval, 0.12-0.75; P =0.011). CY/MP treatment was well tolerated.

CONCLUSION

Combination therapy with CY/MP and IFNbeta-Ia decreased the number of Gd+ lesions and slowed clinical activity in patients with previously active disease on IFNbeta alone.

Bacterial signal peptide recognizes HeLa cell mitochondrial import receptors and functions as a mitochondrial leader sequence

Phage display was used to identify new components of the mammalian mitochondrial receptor complex using Tom20 as a binding partner. Two peptides were identified. One had partial identity (SMLTVMA) with a bacterial signal peptide from Toho-1, a periplasmic protein. The other had partial identity with a mitochondrial inner membrane glutamate carrier. The bacterial signal peptide could carry a protein into mitochondria both in vivo and in vitro. The first six residues of the sequence, SMLTVM, were necessary for import but the two adjacent arginine residues in the 30-amino-acid leader were not critical for import. The signal peptides of Escherichia coli beta-lactamase and Bacillsus subtilis lipase could not carry proteins into mitochondria. Presumably, the Toho-1 leader can adopt a structure compatible for recognition by the import apparatus.

Stable Transformation of CHO Cells and Human NARP Cybrids Confers Oligomycin Resistance (olir) Following Transfer of a Mitochondrial DNA–Encoded olirATPase6 Gene to the Nuclear Genome: A Model System for mtDNA Gene Therapy

Point and deletion mutations and a general depletion of mammalian mitochondrial DNA (mtDNA) give rise to a wide variety of medical syndromes that are refractory to treatment, possibly including aging itself. While gene therapy directed at correcting such deficits in the mitochondrial genome may offer some therapeutic benefits, there are inherent problems associated with a direct approach. These problems are primarily due to the high mitochondrial genome copy number in each cell and the mitochondrial genome being "protected" inside the double-membrane mitochondrial organelle. In an alternative approach there is evidence that genes normally present in the mitochondrial genome can be incorporated into the nuclear genome. To extend such studies, we modified the Chinese Hamster Ovary (CHO) mtDNA-located ATPase6 gene (possessing a mutation which confers oligomycin resistance- oli(r)) by altering the mtDNA code to the universal code (U-code) to permit the correct translation of its mRNA in the cytoplasm. The U-code construct was inserted into the nuclear genome (nucDNA) of a wild type CHO cell. The expressed transgene products enabled the transformed CHO cell lines to grow in up to 1000 ng mL(-1) oligomycin, while untransformed sensitive CHO cells were eliminated in 1 ng mL(-1) oligomycin. This approach, termed allotopic expression, provides a model that may make possible the transfer of all 13 mtDNA mammalian protein-encoding genes to the nucDNA, for treatments of mtDNA disorders. The CHO mtATPase6 protein is 85% identical to both the mouse and human mtATPase6 protein; these proteins are highly conserved in the region of the oligomycin resistance mutation. They are also well conserved in the regions of the oligomycin resistance mutation of the mouse, and in the region of a mutation found in Leigh's syndrome (T8993G), also called NARP (neurogenic weakness, ataxia, retinitis pigmentosum). It is likely that the CHO oli(r) mtATPase6 Ucode construct could impart oligomycin-resistance in human and mouse cells, as well as function in place of the mutant ATPase subunit in a NARP cell line. Preliminary experiments on human cybrids homoplasmic for the NARP mutation (kindly supplied by D.C. Wallace), transformed with our construct, display an increased oligomycin resistance that supports these suppositions.

The Sonic Hedgehog-Gli pathway regulates dorsal brain growth and tumorigenesis

The mechanisms that regulate the growth of the brain remain unclear. We show that Sonic hedgehog (Shh) is expressed in a layer-specific manner in the perinatal mouse neocortex and tectum, whereas the Gli genes, which are targets and mediators of SHH signaling, are expressed in proliferative zones. In vitro and in vivo assays show that SHH is a mitogen for neocortical and tectal precursors and that it modulates cell proliferation in the dorsal brain. Together with its role in the cerebellum, our findings indicate that SHH signaling unexpectedly controls the development of the three major dorsal brain structures. We also show that a variety of primary human brain tumors and tumor lines consistently express the GLI genes and that cyclopamine, a SHH signaling inhibitor, inhibits the proliferation of tumor cells. Using the in vivo tadpole assay system, we further show that misexpression of GLI1 induces CNS hyperproliferation that depends on the activation of endogenous Gli1 function. SHH-GLI signaling thus modulates normal dorsal brain growth by controlling precursor proliferation, an evolutionarily important and plastic process that is deregulated in brain tumors.

Repeat endoscopic third ventriculostomy: is it worth trying?

OBJECT

The goal of this study was to evaluate the safety, efficacy, and indications for repeat endoscopic third ventriculostomies (ETV).

METHODS AND RESULTS

We reviewed the records of 20 patients who had undergone repeat ETV from 1987 to 1999. Their ages ranged from 8 months to 53 years (mean 17 years). The primary etiologies of hydrocephalus were: primary aqueductal stenosis (9 cases), tumor (5), Chiari malformation (2), prior infection (2), prior intraventricular hemorrhage (1), and blocked foramen of Monro (1 patient). The interval between the first and second ETVs ranged from 8 days to almost 6 years (mean 12.8 months). The intraoperative findings at repeat surgery were: occlusion of the primary orifice by scar (10 cases), virginal floor of the third ventricle (5 cases), pinhole ventriculostomy (3 cases), incompletely penetrated membrane (1 case), and blood clot occluding the orifice (1 case). The follow-up period ranged from 3 to 47 months (median 20 months). Repeat ETV was successful in 13 patients (65%). These patients did not require further shunting or other procedures during follow-up. Seven patients (35%) required placement of a shunt after repeat ETV. Several complications were observed in 1 patient (5%), including seizures, elevated ICP, bilateral pulmonary edema, and cardiac arrhythmia. This patient ultimately recovered fully; the ETV was successful, and the patient did not require a shunt.

CONCLUSIONS

Based on the experience of this group of patients, repeat ETV is as effective and as safe as a primary ETV procedure, and should be attempted in selected patients.

The N-terminal portion of mature aldehyde dehydrogenase affects protein folding and assembly

Human liver cytosolic (ALDH1) and mitochondrial (ALDH2) aldehyde dehydrogenases are both encoded in the nucleus and synthesized in the cytosol. ALDH1 must fold in the cytosol, but ALDH2 is first synthesized as a precursor and must remain unfolded during import into mitochondria. The two mature forms share high identity (68%) at the protein sequence level except for the first 21 residues (14%); their tertiary structures were found to be essentially identical. ALDH1 folded faster in vitro than ALDH2 and could assemble to tetramers while ALDH2 remained as monomers. Import assay was used as a tool to study the folding status of ALDH1 and ALDH2. pALDH1 was made by fusing the presequence of precursor ALDH2 to the N-terminal end of ALDH1. Its import was reduced about 10-fold compared to the precursor ALDH2. The exchange of the N-terminal 21 residues from the mature portion altered import, folding, and assembly of precursor ALDH1 and precursor ALDH2. More of chimeric ALDH1 precursor was imported into mitochondria compared to its parent precursor ALDH1. The import of chimeric ALDH2 precursor, the counterpart of chimeric ALDH1 precursor, was reduced compared to its parent precursor ALDH2. Mature ALDH1 proved to be more stable against urea denaturation than ALDH2. Urea unfolding improved the import of precursor ALDH1 and the chimeric precursors but not precursor ALDH2, consistent with ALDH1 and the chimeric ALDHs being more stable than ALDH2. The N-terminal segment of the mature protein, and not the presequence, makes a major contribution to the folding, assembly, and stability of the precursor and may play a role in folding and hence the translocation of the precursor into mitochondria.

Antibodies to assess phosphorylation of spinach leaf nitrate reductase on serine 543 and its binding to 14-3-3 proteins

To monitor site-specific phosphorylation of spinach leaf nitrate reductase (NR) and binding of the enzyme to 14-3-3 proteins, serum antibodies were raised that select for either serine 543 phospho- or dephospho-NR. The dephospho-specific antibodies blocked NR phosphorylation on serine 543. The phospho-specific antibodies prevented NR binding to 14-3-3s, NR inhibition by 14-3-3s, NR dephosphorylation on serine 543, and did not precipitate 14-3-3s together with NR. Together, this confirms that 14-3-3s bind to NR at hinge 1 after it has been phosphorylated on serine 543. The amounts of individual NR forms were determined in leaf extracts by immunoblotting and immunoprecipitation. The phosphorylation state of NR on serine 543 increased 2-3-fold in leaves upon a light/ dark transition. Before the transition, one-third of NR was already phosphorylated on serine 543 but was not bound to 14-3-3s. Phosphorylation of serine 543 seems not to be enough to bind to 14-3-3s in leaves.

Protective autoimmunity is a physiological response to CNS trauma

Primary damage caused by injury to the CNS is often followed by delayed degeneration of initially spared neurons. Studies in our laboratory have shown that active or passive immunization with CNS myelin-associated self-antigens can reduce this secondary loss. Here we show, using four experimental paradigms in rodents, that CNS trauma spontaneously evokes a beneficial T cell-dependent immune response, which reduces neuronal loss. (1) Survival of retinal ganglion cells in rats was significantly higher when optic nerve injury was preceded by an unrelated CNS (spinal cord) injury. (2) Locomotor activity of rat hindlimbs (measured in an open field using a locomotor rating scale) after contusive injury of the spinal cord (T8) was significantly better (by three to four score grades) after passive transfer of myelin basic protein (MBP)-activated splenocytes derived from spinally injured rats than in untreated injured control rats or rats similarly treated with splenocytes from naive animals or with splenocytes from spinally injured rats activated ex vivo with ovalbumin or without any ex vivo activation. (3) Neuronal survival after optic nerve injury was 40% lower in adult rats devoid of mature T cells (caused by thymectomy at birth) than in normal rats. (4) Retinal ganglion cell survival after optic nerve injury was higher (119 +/- 3.7%) in transgenic mice overexpressing a T cell receptor (TcR) for MBP and lower (85 +/- 1.3%) in mice overexpressing a T cell receptor for the non-self antigen ovalbumin than in matched wild types. Taken together, the results imply that CNS injury evokes a T cell-dependent neuroprotective response.

Mitochondrial aldehyde dehydrogenase activity is required for male fertility in maize

Some plant cytoplasms express novel mitochondrial genes that cause male sterility. Nuclear genes that disrupt the accumulation of the corresponding mitochondrial gene products can restore fertility to such plants. The Texas (T) cytoplasm mitochondrial genome of maize expresses a novel protein, URF13, which is necessary for T cytoplasm-induced male sterility. Working in concert, functional alleles of two nuclear genes, rf1 and rf2, can restore fertility to T cytoplasm plants. Rf1 alleles, but not Rf2 alleles, reduce the accumulation of URF13. Hence, Rf2 differs from typical nuclear restorers in that it does not alter the accumulation of the mitochondrial protein necessary for T cytoplasm-induced male sterility. This study established that the rf2 gene encodes a soluble protein that accumulates in the mitochondrial matrix. Three independent lines of evidence establish that the RF2 protein is an aldehyde dehydrogenase (ALDH). The finding that T cytoplasm plants that are homozygous for the rf2-R213 allele are male sterile but accumulate normal amounts of RF2 protein that lacks normal mitochondrial (mt) ALDH activity provides strong evidence that rf2-encoded mtALDH activity is required to restore male fertility to T cytoplasm maize. Detailed genetic analyses have established that the rf2 gene also is required for anther development in normal cytoplasm maize. Hence, it appears that the rf2 gene was recruited recently to function as a nuclear restorer. ALDHs typically have very broad substrate specificities. Indeed, the RF2 protein is capable of oxidizing at least three aldehydes. Hence, the specific metabolic pathway(s) within which the rf2-encoded mtALDH acts remains to be discovered.

Making an Oriental equivalent of the yeast cytosolic aldehyde dehydrogenase as well as making one with positive cooperativity in coenzyme binding by mutations of glutamate 492 and arginine 480

Yeast has at least three partially characterized aldehyde dehydrogenases. Previous studies by gene disrupted in our laboratory revealed that the Saccharomyces cerevisiae cytosol ALDH1 played an important role in ethanol metabolism as did the class 2 mitochondrial enzyme. To date, few mutagenesis studies have been performed with the yeast enzymes. An important human variant of ALDH is one found in Asian People. In it, the glutamate at position 487 is replaced by a lysine. This glutamate interacts with an arginine (475) that is located in the subunit that makes up the dimer pair in the tetrameric enzyme. Sequence alignment shows that these two residues are located at positions 492 and 480, respectively, in the yeast class 1 enzyme which shares just 45% sequence identity with the human enzymes. Mutating glutamate 492 to lysine produced an enzyme with altered kinetic properties when compared to the wild-type glutamate-enzyme. The K(m) for NADP of E492K increased to nearly 3600 microM compare to 40 microM for wild-type enzyme. The specific activity decreased more than 10-fold with respect to the recombinant wild-type yeast enzyme. Moreover, substituting a glutamine for a glutamate was not detrimental in that the E492Q had wild-type-like K(m) for NADP and V(max). These properties were similar to the changes found with the human class 2 E487K mutant form. Further, mutating arginine 480 to glutamine produced an enzyme that exhibited positive cooperativity in NADP binding. The K(m) for NADP increased 11-fold with a Hill coefficient of 1.6. The NADP-dependent activity of R480Q mutant was 60% of wild-type enzyme. Again, these results are very similar to what we recently showed to occur with the human enzyme [Biochemistry 39 (2000) 5295-5302]. These findings show that the even though the glutamate and arginine residues are not conserved, similar changes occur in both the human and the yeast enzyme when either is mutated.

Role of the C-terminal tail on the quaternary structure of aldehyde dehydrogenases

To assess the importance of the C-terminal tail in the structure of aldehyde dehydrogenases (ALDH), mutants of tetrameric ALDH1 were generated by adding a tail of 5 amino acids (ALDH1-5aa) or the tail from the class 3 enzyme. A mutant of dimeric ALDH3 was made, where 17 amino acids from the C-terminus were deleted to generate ALDH3DeltaTail. The expression and solubility of the ALDH1 mutants was slightly lower than the wild type. Expression of ALDH3DeltaTail mutant was similar to wild type, but the solubility was only about 30%. The activity of ALDH1-5aa mutant was 30%, while ALDH1-H3Tail mutant was 60% active, compared to the wild type. The activity of the class 3 mutant was similar to the activity of the parent ALDH3 enzyme. Analysis of stability against temperature demonstrated that ALDH1-5aa was more stable than ALDH1 wild type, while the ALDH1-H3Tail mutant was considerably less stable than ALDH1, showing a stability similar to ALDH3. However, native gel and size exclusion analysis, showed no changes in the oligomerization state of these mutants. ALDH3DeltaTail mutant was more stable than wild type; the stability against temperature was similar to ALDH1. The ALDH3DeltaTail mutant showed an elution similar to that of ALDH1 from the size exclusion column, indicating that it was possibly a tetramer. These results show that the tail in ALDH3, is involved in the determination of the quaternary structure of ALDH3, but has no effect on the ALDH1 enzyme; the absence of the C-terminal tail is not the only factor participating in holding the dimers together. Thus, the interaction between single residues, or interactions with the N-terminal region might be more important for maintaining stable tetramers.

Subunit communication in tetrameric class 2 human liver aldehyde dehydrogenase as the basis for half-of-the-site reactivity and the dominance of the oriental subunit in a heterotetramer

Data has been published showing that in heterotetrameric liver mitochondrial aldehyde dehydrogenase composed of the active (E487) and the inactive Oriental-variant (K487) subunit, the Oriental variant was dominant and caused the inactivation of the E487 subunit. The published structures of the enzyme showed that the glutamate at position 487 is salt bonded to an arginine (475) in a different subunit. Arg475 was mutated to a glutamine to test for its importance in causing the Oriental variant to be an enzyme with a high Km for NAD and a low specific activity. Unexpectedly, the R475Q mutant exhibited positive cooperativity in NAD binding with a Hill coefficient of 2. Individual heterotetramers composed of subunits of E487 and K487 were produced by making changes to two residues on the surface of the enzyme and then co-expressing both cDNAs in E. coli. The E(3)K form had essentially 50% the activity of the E(4) homotetrameric form while EK(3) had essentially the same properties as did the homotetrameric K(4) Oriental variant. This showed that in a dimer pair composed of one K- and one E- subunit the K-subunit became dominant and caused the inactivation of its E-partner. Further, pre-steady state burst data and steady state kinetic data make it appear that there was one functioning active subunit in each of the dimer pairs that made up the tetrameric enzyme. Thus, the half-of-the-site reactivity is a result of having one functioning and one non-functioning subunit in each dimer pair. The actual structural basis for this is still not understood, but could be related to the E487-R475 inter-dimer salt bond.

Interaction of human aldehyde dehydrogenase with aromatic substrates and ligands

The substrate benzaldehyde (but not propionaldehyde) could elute aldehyde dehydrogenase from a p-hydroxyacetophenone-affinity column, and inhibit the esterase activity (K(i)=47 microM), indicating that this simple aromatic aldehyde binds to the free enzyme and possibly in the substrate-binding site. Thus, the kinetic mechanism for aldehyde dehydrogenase might be dependent upon which aldehyde is used in the reaction. Chloramphenicol which also elutes the enzyme from the affinity column, shows a discriminatory effect by inhibiting the ALDH1 oxidation of benzaldehyde and activating that of propionaldehyde while showing no effect when assayed with hexanal or cyclohexane-carboxaldehyde. Chloramphenicol is an uncompetitive inhibitor against NAD when benzaldehyde is the substrate. We propose that this drug might interact with both the benzaldehyde and NAD binding sites.

Basis for half-of-the-site reactivity and the dominance of the K487 oriental subunit over the E487 subunit in heterotetrameric human liver mitochondrial aldehyde dehydrogenase

Human liver mitochondrial aldehyde dehydrogenase is a tetrameric enzyme composed of 4 identical 500 amino acid containing subunits arranged such that the protein is a dimer of dimers. No kinetic evidence for subunit interactions has been reported. However, the enzyme exhibits half-of-the-site reactivity in that there is a pre-steady-state burst of 2 mol of NADH per mole of enzyme. A variant of the enzyme, found in Asian people, contains a lysine rather than a glutamate at position 487. This enzyme has a high K(M) for NAD(+) and a low specific activity. In heterotetramers composed of both subunit types, it appeared that the lysine-containing subunit was dominant over the glutamate-containing subunits. To allow for the separation of various heterotetrameric forms of the enzyme, surface residues were changed. Each of the five possible tetrameric forms of the modified enzyme was isolated and characterized with respect to steady-state kinetics and pre-steady-state burst magnitudes. The data best fit a model where in each dimer pair there is one functioning and one nonfunctioning subunit. Further, the lysine subunit affects the properties only of its dimer partner. Residue 487 is located at the dimer interface, and the glutamate forms salt bonds with two arginine residues. One is to Arg(264) in the same subunit; the other is to Arg(475) located in the other subunit. Most likely the presence of a lysine affects these salt bonds so the lysine subunit can cause the other subunit to become essentially nonfunctional.

Binding to 14-3-3 proteins is not sufficient to inhibit nitrate reductase in spinach leaves

To assess the role of 14-3-3 proteins in the magnesium-dependent inhibition of nitrate reductase (NR) we tested the effect of magnesium on NR binding to 14-3-3s by coimmunoprecipitation and gel filtration. The stability of the 14-3-3 complex of NR was, unlike its activity, unaffected by magnesium. We therefore conclude that binding to 14-3-3s per se does not inhibit NR. Magnesium inhibited 14-3-3-bound NR much more strongly than 14-3-3-free NR. 14-3-3s possibly reinforce NR inhibition by magnesium.

Nitrate reductases from leaves of Ricinus (Ricinus communis L.) and spinach (Spinacia oleracea L.) have different regulatory properties

The activity of nitrate reductase (+Mg(2+), NR(act)) in illuminated leaves from spinach, barley and pea was 50-80% of the maximum activity (+EDTA, NR(max)). However, NR from leaves of Ricinus communis L. had a 10-fold lower NR(act), while NR(max) was similar to that in spinach leaves. The low NR(act) of Ricinus was independent of day-time and nitrate nutrition, and varied only slightly with leaf age. Possible factors in Ricinus extracts inhibiting NR were not found. NR(act) from Ricinus, unlike the spinach enzyme, was very low at pH 7.6, but much higher at more acidic pH with a distinct maximum at pH 6.5. NR(max) had a broad pH response profile that was similar for the spinach and the Ricinus enzyme. Accordingly, the Mg(2+)-sensitivity of NR from Ricinus was strongly pH-dependent (increasing sensitivity with increasing pH), and as a result, the apparent activation state of NR from a Ricinus extract varied dramatically with pH and Mg(2+)concentration. Following a light-dark transition, NR(act) from Ricinus decreased within 1 h by 40%, but this decrease was paralleled by NR(max). In contrast to the spinach enzyme, Ricinus-NR was hardly inactivated by incubating leaf extracts with ATP plus okadaic acid. A competition analysis with antibodies against the potential 14-3-3 binding site around ser 543 of the spinach enzyme revealed that Ricinus-NR contains the same site. Removal of 14-3-3 proteins from Ricinus-NR by anion exchange chromatography, activated spinach-NR but caused little if any activation of Ricinus-NR. It is suggested that Mg(2+)-inhibition of Ricinus-NR does not require 14-3-3 proteins. The rather slow changes in Ricinus-NR activity upon a light/dark transient may be mainly due to NR synthesis or degradation.

Alzheimer's disease comorbidity in normal pressure hydrocephalus: prevalence and shunt response

The clinical impact of Alzheimer's disease pathology at biopsy was investigated in 56 cognitively impaired patients undergoing shunt surgery for idiopathic normal pressure hydrocephalus (NPH). Cognition was measured by means of the global deterioration scale (GDS), the mini mental status examination (MMSE) and a battery of six psychometric tests. Gait was assessed using objective measurements of velocity and the ambulatory index (AI). The prevalence of cases exhibiting neuritic plaques (positive biopsies) increased in parallel with dementia severity from 18% for patients with GDS 3 to 75% for patients with GDS scores > or =6. Patients with positive biopsies were more cognitively impaired (higher GDS and lower MMSE scores) as well as more gait impaired (higher AI scores and slower velocities) than patients with negative biopsies. After surgery, gait velocity and AI scores improved significantly and to a comparable degree for patients with and without positive biopsies. Similar proportions of positive and negative biopsy patients also had improved gait as assessed by means of subjective video tape comparisons. There were no significant differences between the biopsy groups in the magnitude of postoperative psychometric change or in the proportion of cases exhibiting improved urinary control. Alzheimer's disease pathology is a common source of comorbidity in older patients with idiopathic NPH where it contributes to the clinical impairment associated with this disorder. For patients accurately diagnosed with NPH, concomitant Alzheimer's disease pathology does not strongly influence the clinical response to shunt surgery.

Cooperativity in nicotinamide adenine dinucleotide binding induced by mutations of arginine 475 located at the subunit interface in the human liver mitochondrial class 2 aldehyde dehydrogenase

The low-activity Oriental variant of human mitochondrial aldehyde dehydrogenase possesses a lysine rather than a glutamate at residue 487 in the 500 amino acid homotetrameric enzyme. The glutamate at position 487 formed two salt bonds, one to an arginine at position 264 in the same subunit and the other to arginine 475 in a different subunit [Steinmetz, C. G., Xie, P.-G.,Weiner, H., and Hurley, T. D. (1997) Structure 5, 2487-2505]. Mutating arginine 264 to glutamine produced a recombinantly expressed enzyme with nativelike properties; in contrast, mutating arginine 475 to glutamine produced an enzyme that exhibited positive cooperativity in NAD binding. The K(M) for NAD increased 23-fold with a Hill coefficient of 1.8. The binding of both NAD and NADH was affected by the mutation at position 475. Restoring the salt bonds between residues 487 and either or both 264 and 475 did not restore nativelike properties to the Oriental variant. Further, the R475Q mutant was thermally less stable than the native enzyme, Oriental variant, or other mutants. The presence of NAD restored nativelike stability to the mutant. It is concluded that movement of arginine 475 disrupted salt bonds between it and residues other than the one at 487, which caused the apo-R475Q mutant to have properties typical of an enzyme that exhibits positive cooperativity in substrate binding. Breaking the salt bond between glutamate 487 in the Oriental variant and the two arginine residues cannot be the only reason that this enzyme has altered catalytic properties.