Serum Levels of α-Klotho Are Correlated with Cerebrospinal Fluid Levels and Predict Measures of Cognitive Function

BACKGROUND

α-klotho might play a role in neurodegenerative diseases.

OBJECTIVE

To determine levels of α-klotho and apoE in serum and cerebrospinal fluid (CSF) samples and their relationship with the Mini-Mental State Examination (MMSE) and Clinical Dementia Rating (CDR).

METHODS

All subjects were between age 39 to 83+ (n = 94). CDR and MMSE were administered to all participants. CSF was collected in the early afternoon by lumbar puncture.

RESULTS

Serum and CSF levels of α-klotho are positively correlated and both predict scores on the MMSE and CDR, regardless of sex or apoE4 status.

CONCLUSION

Our results demonstrate that α-klotho may be an important biomarker of cognitive health and neurodegeneration, and that relatively non-invasive sampling of α-klotho from serum is likely highly reflective of CSF levels.

Cyanide and the human brain: perspectives from a model of food (cassava) poisoning

Threats by fundamentalist leaders to use chemical weapons have resulted in renewed interest in cyanide toxicity. Relevant insights may be gained from studies on cyanide mass intoxication in populations relying on cyanogenic cassava as the main source of food. In these populations, sublethal concentrations (up to 80 μmol/l) of cyanide in the blood are commonplace and lead to signs of acute toxicity. Long-term toxicity signs include a distinct and irreversible spastic paralysis, known as konzo, and cognition deficits, mainly in sequential processing (visual-spatial analysis) domains. Toxic culprits include cyanide (mitochondrial toxicant), thiocyanate (AMPA-receptor chaotropic cyanide metabolite), cyanate (protein-carbamoylating cyanide metabolite), and 2-iminothiazolidine-4-carboxylic acid (seizure inducer). Factors of susceptibility include younger age, female gender, protein-deficient diet, and, possibly, the gut functional metagenome. The existence of uniquely exposed and neurologically affected populations offers invaluable research opportunities to develop a comprehensive understanding of cyanide toxicity and test or validate point-of-care diagnostic tools and treatment options to be included in preparedness kits in response to cyanide-related threats.

Common variants in CASQ2, GPD1L, and NOS1AP are significantly associated with risk of sudden death in patients with coronary artery disease

BACKGROUND

Recent evidence suggests a genetic component for sudden cardiac death (SCD) in subjects with coronary artery disease (CAD). We conducted a systematic candidate-gene approach using haplotype-tagging single nucleotide polymorphisms (htSNPs) to identify genes associated with SCD risk in the context of CAD.

METHODS AND RESULTS

We investigated 1424 htSNPs representing 18 genes with mutations described in patients with ventricular arrhythmias in 291 subjects from the Oregon Sudden Unexpected Death Study (Ore-SUDS). The Ore-SUDS is an ongoing prospective investigation of SCD in the Portland, OR, metropolitan area (population, 1 000 000). SCD cases were ascertained from multiple sources and medical records were reviewed to determine the presence of CAD. A total of 36 SNPs were associated with risk of SCD (uncorrected probability values <0.01) in the initial study sample. These SNPs were subsequently tested for replication in an independent case-control study sample from the Ore-SUDS (n=688). The association analysis in the replication stage revealed 6 SNPs associated with SCD: CASQ2 region (rs17500488, P=0.04; rs3010396, P=0.007; rs7366407; P=0.04), NOS1AP (rs12084280, P=0.04; rs10918859, P=0.02), and 1 SNP located ≈26 kb upstream of GPD1L (rs9862154, P=0.04).

CONCLUSIONS

Common variations in or near CASQ2, GPD1L, and NOS1AP are associated with increased risk of SCD in patients with CAD. These findings provide further evidence for overlap between the genetic architecture of rare and common forms of SCD, and replication in additional populations is warranted.

Discordant expression of miR-103/7 and pantothenate kinase host genes in mouse

miR-103 and miR-107, microRNAs hosted by pantothenate kinase genes, are proposed to regulate cellular lipid metabolism. microRNA-mediated regulation is complex, potentially affecting expression of the host gene, related enzymes within the same pathway, or apparently distinct targets. Using qRT-PCR, we demonstrate that miR-103 and miR-107 expression does not correlate with expression of host pantothenate kinase genes in mouse tissues. The miR-103/7 family thus provides an intriguing model for dissecting microRNA transcription, processing and coordinated function within host genes.

Neurodegeneration associated with genetic defects in phospholipase A(2)

OBJECTIVE

Mutations in the gene encoding phospholipase A(2) group VI (PLA2G6) are associated with two childhood neurologic disorders: infantile neuroaxonal dystrophy (INAD) and idiopathic neurodegeneration with brain iron accumulation (NBIA). INAD is a severe progressive psychomotor disorder in which axonal spheroids are found in brain, spinal cord, and peripheral nerves. High globus pallidus iron is an inconsistent feature of INAD; however, it is a diagnostic criterion of NBIA, which describes a clinically and genetically heterogeneous group of disorders that share this hallmark feature. We sought to delineate the clinical, radiographic, pathologic, and genetic features of disease resulting from defective phospholipase A(2).

METHODS

We identified 56 patients clinically diagnosed with INAD and 23 with idiopathic NBIA and screened their DNA for PLA2G6 mutations.

RESULTS

Eighty percent of patients with INAD had mutations in PLA2G6, whereas mutations were found in only 20% of those with idiopathic NBIA. All patients with two null mutations had a more severe phenotype. On MRI, nearly all mutation-positive patients had cerebellar atrophy, and half showed brain iron accumulation. We observed Lewy bodies and neurofibrillary tangles in association with PLA2G6 mutations.

CONCLUSION

Defects in phospholipase A(2) lead to a range of phenotypes. PLA2G6 mutations are associated with nearly all cases of classic infantile neuroaxonal dystrophy but a minority of cases of idiopathic neurodegeneration with brain iron accumulation, and genotype correlates with phenotype. Cerebellar atrophy predicts which patients are likely to be mutation-positive. The neuropathologic changes that are caused by defective phospholipase A(2) suggest a shared pathogenesis with both Parkinson and Alzheimer diseases.

PLA2G6, encoding a phospholipase A2, is mutated in neurodegenerative disorders with high brain iron

Neurodegenerative disorders with high brain iron include Parkinson disease, Alzheimer disease and several childhood genetic disorders categorized as neuroaxonal dystrophies. We mapped a locus for infantile neuroaxonal dystrophy (INAD) and neurodegeneration with brain iron accumulation (NBIA) to chromosome 22q12-q13 and identified mutations in PLA2G6, encoding a calcium-independent group VI phospholipase A2, in NBIA, INAD and the related Karak syndrome. This discovery implicates phospholipases in the pathogenesis of neurodegenerative disorders with iron dyshomeostasis.

Novel compound heterozygous mutations in the PANK2 gene in a Chinese patient with atypical pantothenate kinase-associated neurodegeneration

We investigated the presence of mutations in the pantothenate kinase (PANK2) gene in a 27-year-old male Chinese patient with atypical pantothenate kinase-associated neurodegeneration (PKAN), formerly Hallervorden-Spatz syndrome. Automated DNA sequence analyses revealed compound heterozygous mutations in the exon 3 and 5. This patient had a 10-year history of PKAN characterized by a slight tremor of the right hand when writing at onset and a slow progressive rigidity of the neck and the right arm and resting tremor in upper extremities. Dysarthria, dysphagia, and dystonic-athetoid movements of the face and right fingers were marked. Magnetic resonance showed the typical "eye-of-the-tiger" sign.

A novel 3-bp deletion in the PANK2 gene of Dutch patients with pantothenate kinase-associated neurodegeneration: evidence for a founder effect

Mutation analysis was performed in four apparently unrelated Dutch families with pantothenate kinase-associated neurodegeneration, formerly known as Hallervorden-Spatz syndrome. A novel 3-bp deletion encompassing the nucleotides GAG at positions 1,142 to 1,144 of exon 5 of the PANK2 gene was found in all patients. One patient was compound heterozygous; she also carried a novel nonsense mutation (Ser68Stop). The other patients were homozygous for the 1142_1144delGAG mutation. The 1142_1144delGAG mutation was also found in a German patient of unknown descent. We used polymorphic microsatellite markers flanking the PANK2 gene (spanning a region of approximately 8 cM) for haplotype analyses in all these families. A conserved haplotype of 1.5 cM was found for the 1142_1144delGAG mutation carriers. All the Dutch families originated from the same geographical region within the Netherlands. The results indicate a founder effect and suggest that the 1142_1144delGAG mutation probably originated from one common ancestor. It was estimated that this mutation arose at the beginning of the ninth century, approximately 38 generations ago.

Neuro-ophthalmologic and electroretinographic findings in pantothenate kinase-associated neurodegeneration (formerly Hallervorden-Spatz syndrome)

PURPOSE

The onset of pantothenate kinase-associated neurodegeneration (PKAN) occurs in the first and second decade of life and a pigmentary retinal degeneration is a feature of the disorder. Since the neuro-ophthalmologic and electroretinographic (ERG) features have never been well delineated, we describe them in 16 patients with PKAN.

DESIGN

Observational case series.

METHODS

Sixteen patients with genetic and neuroimaging-confirmed PKAN were examined. Ten underwent neuro-ophthalmologic examination and all had ERGs.

RESULTS

Of the 10 who underwent neuro-ophthalmologic examination, all showed saccadic pursuits and eight showed hypometric or slowed vertical saccades. Seven of eight had inability to suppress the vestibulo-ocular reflex; two patients could not cooperate. Two had square wave jerks and four had poor convergence. Vertical optokinetic responses were abnormal in five, and two patients had blepharospasm. Eight patients had sectoral iris paralysis and partial loss of the pupillary ruff consistent with Adie's pupils in both eyes. Only four of 10 examined patients showed a pigmentary retinopathy, but 11 of 16 had abnormal ERGs ranging from mild cone abnormalities to severe rod-cone dysfunction. No patient had optic atrophy. The PANK2 mutations of all of the patients were heterogeneous.

CONCLUSIONS

Adie's-like pupils, abnormal vertical saccades, and saccadic pursuits were very common. These findings suggest that mid-brain degeneration occurs in PKAN more frequently than previously thought. ERG abnormalities were present in approximately 70% and no patient had optic atrophy. Although genotype-ocular phenotype correlations could not be established, allelic differences probably contributed to the variable clinical expression of retinopathy and other clinical characteristics in these patients.

Deficiency of pantothenate kinase 2 (Pank2) in mice leads to retinal degeneration and azoospermia

Pantothenate kinase-associated neurodegeneration (PKAN, formerly known as Hallervorden-Spatz syndrome) is a rare but devastating neurodegenerative disorder, resulting from an inherited defect in coenzyme A biosynthesis. As pathology in the human condition is limited to the central nervous system, specifically the retina and globus pallidus, we have generated a mouse knock-out of the orthologous murine gene (Pank2) to enhance our understanding of the mechanisms of disease and to serve as a testing ground for therapies. Over time, the homozygous null mice manifest retinal degeneration, as evidenced by electroretinography, light microscopy and pupillometry response. Specifically, Pank2 mice show progressive photoreceptor decline, with significantly lower scotopic a- and b-wave amplitudes, decreased cell number and disruption of the outer segment and reduced pupillary constriction response when compared with those of wild-type littermates. Additionally, the homozygous male mutants are infertile due to azoospermia, a condition that was not appreciated in the human. Arrest occurs in spermiogenesis, with complete absence of elongated and mature spermatids. In contrast to the human, however, no changes were observed in the basal ganglia by MRI or by histological exam, nor were there signs of dystonia, even after following the mice for one year. Pank2 mice are 20% decreased in weight when compared with their wild-type littermates; however, dysphagia was not apparent. Immunohistochemistry shows staining consistent with localization of Pank2 to the mitochondria in both the retina and the spermatozoa.

Mitochondrial Localization of Human PANK2 and Hypotheses of Secondary Iron Accumulation in Pantothenate Kinase-Associated Neurodegeneration

Mutations in the pantothenate kinase 2 gene (PANK2) lead to pantothenate kinase-associated neurodegeneration (PKAN, formerly Hallervorden-Spatz syndrome). This neurodegenerative disorder is characterized by iron accumulation in the basal ganglia. Pantothenate kinase is the first enzyme in the biosynthesis of coenzyme A from pantothenate (vitamin B(5)). PANK2, one of four human pantothenate kinase genes, is uniquely predicted to be targeted to mitochondria. We demonstrate mitochondrial localization of PANK2 and speculate on mechanisms of secondary iron accumulation in PKAN. Furthermore, PANK2 uses an unconventional translational start codon, CUG, which is polymorphic in the general population. The variant sequence, CAG (allele frequency: 0.05), leads to skipping of the mitochondrial targeting signal and cytosolic localization of PANK2. This common variant may cause mitochondrial dysfunction and impart susceptibility to late-onset neurodegenerative disorders with brain iron accumulation, including Parkinson's disease.

Genetic, clinical, and radiographic delineation of Hallervorden-Spatz syndrome

BACKGROUND

Hallervorden-Spatz syndrome is an autosomal recessive disorder characterized by dystonia, parkinsonism, and iron accumulation in the brain. Many patients with this disease have mutations in the gene encoding pantothenate kinase 2 (PANK2); these patients are said to have pantothenate kinase-associated neurodegeneration. In this study, we compared the clinical and radiographic features of patients with Hallervorden-Spatz syndrome with and without mutations in PANK2.

METHODS

One hundred twenty-three patients from 98 families with a diagnosis of Hallervorden-Spatz syndrome were classified on the basis of clinical assessment as having classic disease (characterized by early onset with rapid progression) or atypical disease (later onset with slow progression). Their genomic DNA was sequenced for PANK2 mutations.

RESULTS

All patients with classic Hallervorden-Spatz syndrome and one third of those with atypical disease had PANK2 mutations. Whereas almost all mutations in patients with atypical disease led to amino acid changes, those in patients with classic disease more often resulted in predicted protein truncation. Patients with atypical disease who had PANK2 mutations were more likely to have prominent speech-related and psychiatric symptoms than patients with classic disease or mutation-negative patients with atypical disease. In all patients with pantothenate kinase-associated neurodegeneration, whether classic or atypical, T2-weighted magnetic resonance imaging (MRI) of the brain showed a specific pattern of hyperintensity within the hypointense medial globus pallidus. This pattern was not seen in any patients without mutations.

CONCLUSIONS

PANK2 mutations are associated with all cases of classic Hallervorden-Spatz syndrome and one third of cases of atypical disease. A specific MRI pattern distinguishes patients with PANK2 mutations. Predicted levels of pantothenate kinase 2 protein correlate with the severity of disease.

HARP syndrome is allelic with pantothenate kinase-associated neurodegeneration

HARP (hypoprebetalipoproteinemia, acanthocytosis, retinitis pigmentosa, and pallidal degeneration) is a rare syndrome with many clinical similarities to pantothenate kinase-associated neurodegeneration (PKAN, formerly Hallervorden-Spatz syndrome). Despite these common features, lipoprotein abnormalities have not been reported in PKAN. After the recent discovery of the genetic defect in PKAN, we report a homozygous nonsense mutation in exon 5 of the PANK2 gene that creates a stop codon at amino acid 371 (R371X) in the original HARP patient. This finding establishes that HARP is part of the PKAN disease spectrum.

A novel pantothenate kinase gene (PANK2) is defective in Hallervorden-Spatz syndrome

Hallervorden-Spatz syndrome (HSS) is an autosomal recessive neurodegenerative disorder associated with iron accumulation in the brain. Clinical features include extrapyramidal dysfunction, onset in childhood, and a relentlessly progressive course. Histologic study reveals iron deposits in the basal ganglia. In this respect, HSS may serve as a model for complex neurodegenerative diseases, such as Parkinson disease, Alzheimer disease, Huntington disease and human immunodeficiency virus (HIV) encephalopathy, in which pathologic accumulation of iron in the brain is also observed. Thus, understanding the biochemical defect in HSS may provide key insights into the regulation of iron metabolism and its perturbation in this and other neurodegenerative diseases. Here we show that HSS is caused by a defect in a novel pantothenate kinase gene and propose a mechanism for oxidative stress in the pathophysiology of the disease.

Virion encapsidation of tRNA(3Lys)-ribozyme chimeric RNAs inhibits HIV infection

Retroviruses require a specific host cellular tRNA primer for initiation of first-strand DNA synthesis. This primer is bound by viral proteins and copackaged into virions. We have exploited this property in the design and testing of an antiviral ribozyme fused to tRNA(3Lys), the primer used for lentiviral replication, including human immunodeficiency virus (HIV-1 and HIV-2). The chimera consists of tRNA(3Lys) covalently attached to a hammerhead ribozyme, which is targeted to the region immediately upstream of the primer binding site of the HIV-1 genome. The tRNA-ribozyme chimeric transcript is catalytically active in vitro and is efficiently bound by HIV reverse transcriptase with an affinity similar to that of tRNA(3Lys). We have expressed the chimeric RNAs from either the tRNA(3Lys) intragenic RNA polymerase III promoter or from a human U6 snRNA promoter. The U6 promoter results in up to 10-fold enhanced expression of the tRNA-ribozyme. Most importantly, the tRNA(3Lys)-ribozymes are encapsidated in HIV-1 virions such that they are effective in substantially reducing the level of infectious virus produced from cells cotransfected with HIV-1 proviral DNA. These results demonstrate the feasibility of using this novel strategy to reduce HIV infectivity and more generally indicate the potential power of using the retroviral primer tRNAs as tools for expressing and delivering ribozymes and other antiretroviral RNAs to the virion capsid.

A chimeric tRNA(Lys3)-ribozyme inhibits HIV replication following virion assembly

Co-localization of ribozymes with their appropriate target is one method utilized to increase their effectiveness in vivo. Effective antiviral ribozymes will likely rely on mechanisms which direct the ribozyme to the genomic or subgenomic RNAs. Exploiting the fact that a specific host cellular tRNA primer is bound by viral proteins and co-packaged with viral genomes in newly synthesized virions, ribozymes were fused to the 3'-terminus of tRNA(Lys3) in an attempt to direct their activity to cleave the HIV-1 genome. This chimeric ribozyme is catalytically active in vitro, and is efficiently recognized and bound by HIV-1 reverse transcriptase with affinities similar to tRNA(Lys3). The intragenic RNA polymerase III promoter entity of the tRNA allows for high levels of expression of the tRNA-RBZ and the preferential localization of transcript within the cytoplasm in transfected cells. This ribozyme was effective in reducing the infectivity of a viral stock which was produced from transiently transfected cells bearing the chimeric gene. These results demonstrate the feasibility of using tRNAs as a means of co-localizing ribozymes with their viral genomic RNA targets. The possibility exists to fuse stable RNAs to ribozymes as a means of increasing their stability and localizing them to their appropriate target sites.

Novel activity of a yeast ligase deletion polypeptide. Evidence for GTP-dependent tRNA splicing

Yeast tRNA ligase possesses multiple activities which are required for the joining of tRNA halves during the tRNA splicing process: cyclic phosphodiesterase, kinase, adenylylate synthetase, and ligase. A deletion polypeptide of a dihydrofolate reductase-ligase fusion protein, designated DAC, was previously shown to join tRNA halves although ATP-dependent kinase activity was not measurable in the assay used. We describe here a characterization of the mechanism of joining used by DAC and the structure of the tRNA product. DAC produces a joined tRNA and a splice junction with a structure identical to that produced by DAKC, the full-length dihydrofolate reductase-ligase fusion. Furthermore, DAC can use GTP as the sole cofactor in the joining reaction, in contrast to DAKC, which can only complete splicing in the presence of ATP. Both enzymes exhibit GTP-dependent kinase activity at 100-fold greater efficiency than with ATP. These results suggest that a potential function for the center domain of tRNA ligase (missing in DAC) is to provide structural integrity and aid in substrate interactions and specificity. They also support the hypothesis that ligase may prefer to use two different cofactors during tRNA splicing.

Multiple nucleotide cofactor use by yeast ligase in tRNA splicing. Evidence for independent ATP- and GTP-binding sites

We have examined multiple cofactor usage by yeast tRNA ligase in splicing in vitro. The ligase mechanism of action requires expenditure of two molar equivalents of nucleotide cofactor per mole of tRNA product. Recent evidence (Westaway, S.K., Belford, H.G., Apostol, B.L., Abelson, J., and Greer, C.L. (1993) J. Biol. Chem. 268, 2435-2443) demonstrated that the ligase-associated kinase activity is more efficient with GTP as cofactor than with ATP. Employing a ligase fusion construct with dihydrofolate reductase (Apostol, B.L., Westaway, S.K., Abelson, J., and Greer, C.L. (1991) J. Biol. Chem. 266, 7445-7455) for purposes of enzyme purification, we performed joining assays demonstrating that ATP and GTP are the most effective combination of cofactors. ATP was essential to the joining reaction, while UTP, CTP, or ATP replaced GTP inefficiently. Specific and functionally independent binding sites were confirmed for ATP and GTP by direct binding measurement. A third site was implicated in UTP- and CTP-ligase interactions. Comparison of binding constants with Kapp values determined for nucleotide-dependent joining suggested both that nucleotide triphosphate binding may be limiting in tRNA joining and that tRNA ligation occurs most efficiently using GTP for the kinase reaction and ATP as the adenylylate synthetase cofactor.

Deletion analysis of a multifunctional yeast tRNA ligase polypeptide. Identification of essential and dispensable functional domains

Splicing of tRNA precursors in extracts of Saccharomyces cerevisiae requires the action of two enzymes: a site specific endonuclease and a tRNA ligase. The tRNA ligase contains three distinct enzymatic activities: a polynucleotide kinase, a cyclic phosphodiesterase, and an RNA ligase. The polypeptide also has a high affinity pre-tRNA binding site based on its ability to form stable complexes with pre-tRNA substrates. To investigate the organization of functional enzymatic and binding elements within the polypeptide a series of defined tRNA ligase gene deletions were constructed and corresponding proteins were expressed in Escherichia coli as fusions with bacterial dihydrofolate reductase (DHFR). The DHFR/ligase derivative proteins were then efficiently purified by affinity chromatography. The complete ligase fusion protein retained enzymatic and binding activities which were unaffected by the presence of the DHFR segment. Examination of tRNA ligase deletion derivatives revealed that the amino-terminal region was required for adenylylation, while the carboxyl-terminal region was sufficient for cyclic phosphodiesterase activity. Deletions within the central region affected kinase activity. Pre-tRNA binding activity was not strictly correlated with a distinct enzymatic domain. A DHFR/ligase-derived protein lacking kinase activity efficiently joined tRNA halves. We postulate that this variant utilizes a novel RNA ligation mechanism.

Structure and function of the yeast tRNA ligase gene

We report here the DNA sequence of the entire coding region of the Saccharomyces cerevisiae tRNA ligase gene. tRNA ligase is one of two enzymes required for tRNA splicing in yeast, and the enzyme is likely a single polypeptide with multiple activities. We find that tRNA ligase is a basic protein of 827 amino acids corresponding to a molecular weight of approximately 95,400. The inferred amino acid sequence for tRNA ligase is not significantly homologous to that of other known proteins of similar activity. In addition to the tRNA ligase reading frame and several other unidentified open reading frames, we have found two open reading frames, ORF1 and ORF2, near the 5'-end of the ligase structural gene. One of these, ORF2, produces a divergent transcript which initiates only 125 nucleotides upstream of the tRNA ligase transcript, and is present in approximately the same relative abundance as the transcript for tRNA ligase.