Apparent loss and hypertrophy of interneurons in a mouse model of neuronal ceroid lipofuscinosis: evidence for partial response to insulin-like growth factor-1 treatment.
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The neuronal ceroid lipofuscinoses (NCL) are progressive neurodegenerative disorders with onset from infancy to adulthood that are manifested by blindness, seizures, and dementia. In NCL, lysosomes accumulate autofluorescent proteolipid in the brain and other tissues. The mnd/mnd mutant mouse was first characterized as exhibiting adult-onset upper and lower motor neuron degeneration, but closer examination revealed early, widespread pathology similar to that seen in NCL. We used the autofluorescent properties of accumulated storage material to map which CNS neuronal populations in the mnd/mnd mouse show NCL-like pathological changes. Pronounced, early accumulation of autofluorescent lipopigment was found in subpopulations of GABAergic neurons, including interneurons in the cortex and hippocampus. Staining for phenotypic markers normally present in these neurons revealed progressive loss of staining in the cortex and hippocampus of mnd/mnd mice, with pronounced hypertrophy of remaining detectable interneurons. In contrast, even in aged mutant mice, many hippocampal interneurons retained staining for glutamic acid decarboxylase. Treatment with insulin-like growth factor-1 partially restored interneuronal number and reduced hypertrophy in some subregions. These results provide the first evidence for the involvement of interneurons in a mouse model of NCL. Moreover, our findings suggest that at least some populations of these neurons persist in a growth factor-responsive state. (+info)
Mutational analysis of the defective protease in classic late-infantile neuronal ceroid lipofuscinosis, a neurodegenerative lysosomal storage disorder.
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The late-infantile form of neuronal ceroid lipofuscinosis (LINCL) is a progressive and ultimately fatal neurodegenerative disease of childhood. The defective gene in this hereditary disorder, CLN2, encodes a recently identified lysosomal pepstatin-insensitive acid protease. To better understand the molecular pathology of LINCL, we conducted a genetic survey of CLN2 in 74 LINCL families. In 14 patients, CLN2 protease activities were normal and no mutations were identified, suggesting other forms of NCL. Both pathogenic alleles were identified in 57 of the other 60 LINCL families studied. In total, 24 mutations were associated with LINCL, comprising six splice-junction mutations, 11 missense mutations, 3 nonsense mutations, 3 small deletions, and 1 single-nucleotide insertion. Two mutations were particularly common: an intronic G-->C transversion in the invariant AG of a 3' splice junction, found in 38 of 115 alleles, and a C-->T transition in 32 of 115 alleles, which prematurely terminates translation at amino acid 208 of 563. An Arg-->His substitution was identified, which was associated with a late age at onset and protracted clinical phenotype, in a number of other patients originally diagnosed with juvenile NCL. (+info)
Defective intracellular transport of CLN3 is the molecular basis of Batten disease (JNCL)
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Batten disease [juvenile-onset neuronal ceroid lipofuscinosis (JNCL)], the most common progressive encephalopathy of childhood, is caused by mutations in a novel lysosomal membrane protein (CLN3) with unknown function. In this study, we have confirmed the lysosomal localization of the CLN3 protein by immunoelectron microscopy by co-localizing it with soluble and membrane-associated lysosomal proteins. We have analysed the intracellular processing and localization of two mutants, 461-677del, which is present in 85% of CLN3 alleles and causes the classical JNCL, and E295K [corrected], which is a rare missense mutation associated with an atypical form of JNCL. Pulse-chase labelling and immunoprecipitation of the two mutant proteins in COS-1-cells indicated that 461-677del is synthesized as an approximately 24 kDa truncated polypeptide, whereas the maturation of E295K [corrected] resembles that of the wild-type CLN3 polypeptide. Transient expression of the two mutants in BHK cells showed that 461-677del is retained in the endoplasmic reticulum, whereas E295K [corrected] was capable of reaching the lysosomal compartment. The CLN3 polypeptides were expressed further in mouse primary neurons where the wild-type CLN3 protein was localized both in the cell soma and in neuronal extensions, whereas the 461-677del mutant was arrested in the cell soma. Interestingly, co-localization of the wild-type CLN3 and E295K [corrected] proteins with a synaptic vesicle marker indicates that the CLN3 protein might participate in synaptic vesicle transport/transmission. The data presented here provide clear evidence for a cellular distinction between classical and atypical forms of Batten disease both in neural and non-neural cells. (+info)
Phenotypic reversal of the btn1 defects in yeast by chloroquine: a yeast model for Batten disease.
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BTN1 of Saccharomyces cerevisiae encodes an ortholog of CLN3, the human Batten disease gene. We have reported previously that deletion of BTN1, btn1-Delta, resulted in a pH-dependent resistance to D-(-)-threo-2-amino-1-[p-nitrophenyl]-1,3-propanediol (ANP). This phenotype was caused by btn1-Delta strains having an elevated ability to acidify growth medium through an elevated activity of the plasma membrane H(+)-ATPase, resulting from a decreased vacuolar pH during early growth. We have determined that growing btn1-Delta strains in the presence of chloroquine reverses the resistance to ANP, decreases the rate of medium acidification, decreases the activity of plasma membrane H(+)-ATPase, and elevates vacuolar pH. However, an additional effect of this phenotypic reversal is that activity of plasma membrane H(+)-ATPase is decreased further and vacuolar pH is increased further as btn1-Delta strains continue to grow. This phenotypic reversal of btn1-Delta can be considered for developing a therapy for Batten disease. (+info)
Secondary carnitine deficiency and impaired docosahexaenoic (22:6n-3) acid synthesis: a common denominator in the pathophysiology of diseases of oxidative phosphorylation and beta-oxidation.
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A critical analysis of the literature of mitochondrial disorders reveals that genetic diseases of oxidative phosphorylation are often associated with impaired beta-oxidation, and vice versa, and preferentially affect brain, retina, heart and skeletal muscle, tissues which depend on docosahexaenoic (22:6n-3)-containing phospholipids for functionality. Evidence suggests that an increased NADH/NAD(+) ratio generated by reduced flux through the respiratory chain inhibits beta-oxidation, producing secondary carnitine deficiency while increasing reactive oxygen species and depleting alpha-tocopherol (alpha-TOC). These events result in impairment of the recently elucidated mitochondrial pathway for synthesis of 22:6n-3-containing phospholipids, since carnitine and alpha-TOC are involved in their biosynthesis. Therapeutic supplementation with 22:6n-3 and alpha-TOC is suggested. (+info)
Batten disease: evaluation of CLN3 mutations on protein localization and function.
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Juvenile neuronal ceroid lipofuscinosis (JNCL), Batten disease, is an autosomal recessive lysosomal storage disease associated with mutations in CLN3. CLN3 has no known homology to other proteins and a function has not yet been described. The predominant mutation in CLN3 is a 1.02 kb genomic deletion that accounts for nearly 85% of the disease alleles. In this mutation, truncation of the protein by a premature stop codon results in the classical phenotype. Additional missense and nonsense mutations have been described. Some missense substitutions result in a protracted phenotype, with delays in the onset of classical clinical features, whereas others lead to classical JNCL. In this study, we examined the effect of naturally occurring point mutations on the intracellular localization of CLN3 and their ability to complement the CLN3-deficient yeast, btn1-Delta. We also examined a putative farnesylation motif thought to be involved in CLN3 trafficking. All of the point mutations, like wild-type CLN3, were highly associated with lysosome-associated membrane protein II in non-neuronal cells and with synaptophysin in neuronal cell lines. In the yeast functional assay, point mutations correlating with a mild phenotype also demonstrated CLN3 activity, whereas the mutations associated with severe disease failed to restore CLN3 function completely. CLN3 with a mutation in the farnesylation motif trafficked normally but was functionally impaired. These data suggest that these clinically relevant point mutations, causative of Batten disease, do not affect protein trafficking but rather exert their effects by impairing protein function. (+info)
The crystal structure of palmitoyl protein thioesterase 1 and the molecular basis of infantile neuronal ceroid lipofuscinosis.
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Mutations in palmitoyl-protein thioesterase 1 (PPT1), a lysosomal enzyme that removes fatty acyl groups from cysteine residues in modified proteins, cause the fatal inherited neurodegenerative disorder infantile neuronal ceroid lipofuscinosis. The accumulation of undigested substrates leads to the formation of neuronal storage bodies that are associated with the clinical symptoms. Less severe forms of PPT1 deficiency have been found recently that are caused by a distinct set of PPT1 mutations, some of which retain a small amount of thioesterase activity. We have determined the crystal structure of PPT1 with and without bound palmitate by using multiwavelength anomalous diffraction phasing. The structure reveals an alpha/beta-hydrolase fold with a catalytic triad composed of Ser115-His289-Asp233 and provides insights into the structural basis for the phenotypes associated with PPT1 mutations. (+info)
Structural basis for the insensitivity of a serine enzyme (palmitoyl-protein thioesterase) to phenylmethylsulfonyl fluoride.
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Palmitoyl-protein thioesterase-1 (PPT1) is a newly described lysosomal enzyme that hydrolyzes long chain fatty acids from lipid-modified cysteine residues in proteins. Deficiency in this enzyme results in a severe neurodegenerative storage disorder, infantile neuronal ceroid lipofuscinosis. Although the primary structure of PPT1 contains a serine lipase consensus sequence, the enzyme is insensitive to commonly used serine-modifying reagents phenylmethylsulfonyl fluoride (PMSF) and diisopropylfluorophosphate. In the current paper, we show that the active site serine in PPT1 is modified by a substrate analog of PMSF, hexadecylsulfonylfluoride (HDSF) in a specific and site-directed manner. The apparent K(i) of the inhibition was 125 micrometer (in the presence of 1.5 mm Triton X-100), and the catalytic rate constant for sulfonylation (k(2)) was 3.3/min, a value similar to previously described sulfonylation reactions. PPT1 was crystallized after inactivation with HDSF, and the structure of the inactive form was determined to 2.4 A resolution. The hexadecylsulfonyl was found to modify serine 115 and to snake through a narrow hydrophobic channel that would not accommodate an aromatic sulfonyl fluoride. Therefore, the geometry of the active site accounts for the reactivity of PPT1 with HDSF but not PMSF. These observations suggest a structural explanation as to why certain serine lipases are resistant to modification by commonly used serine-modifying reagents. (+info)