Lee, Chris W.

Krabbe disease (KD) is a progressive and devasting neurological disorder that leads to the toxic accumulation of psychosine in the white matter of the central nervous system (CNS). The condition is inherited via biallelic, loss-of-function mutations in the galactosylceramidase (GALC) gene. To rescue GALC gene function in the CNS of the twitcher mouse model of KD, an adeno-associated virus serotype 1 vector expressing murine GALC under control of a chicken β-actin promoter (AAV1-GALC) was administered to newborn mice by unilateral intracerebroventricular injection. AAV1-GALC treatment significantly improved body weight gain and survival of the twitcher mice (n = 8) when compared with untreated controls (n = 5). The maximum weight gain after postnatal day 10 was significantly increased from 81% to 217%. The median lifespan was extended from 43 days to 78 days (range: 74–88 days) in the AAV1-GALC-treated group. Widespread expression of GALC protein and alleviation of KD neuropathology were detected in the CNS of the treated mice when examined at the moribund stage. Functionally, elevated levels of psychosine were completely normalized in the forebrain region of the treated mice. In the posterior region, which includes the mid- and the hindbrain, psychosine was reduced by an average of 77% (range: 53–93%) compared to the controls. Notably, psychosine levels in this region were inversely correlated with body weight and lifespan of AAV1-GALC-treated mice, suggesting that the degree of viral transduction of posterior brain regions following ventricular injection determined treatment efficacy on growth and survivability, respectively. Overall, our results suggest that viral vector delivery via the cerebroventricular system can partially correct psychosine accumulation in brain that leads to slower disease progression in KD.

Poly(GP) proteins are a promising pharmacodynamic marker for developing and testing therapeutics for treating C9ORF72 -associated amyotrophic lateral sclerosis.

A mouse model for ALS A G4C2 repeat expansion in C9ORF72 is known to be the major genetic cause of frontotemporal dementia and amyotrophic lateral sclerosis (c9FTD/ALS). However, a lack of animal models recapitulating key disease features has hindered efforts to understand and prevent c9FTD/ALS-related neurodegeneration. Until now. Chew et al. describe a mouse model that mimics both neuropathological and clinical phenotypes of c9FTD/ALS. Science , this issue p. 1151

Sortilin 1 regulates the levels of brain progranulin (PGRN), a neurotrophic growth factor that, when deficient, is linked to cases of frontotemporal lobar degeneration with TAR DNA-binding protein-43 (TDP-43)–positive inclusions (FTLD-TDP). We identified a specific splicing enhancer element that regulates the inclusion of a sortilin exon cassette (termed Ex17b) not normally present in the mature sortilin mRNA. This enhancer element is consistently present in sortilin RNA of mice and other species but absent in primates, which carry a premature stop codon within the Ex17b sequence. In the absence of TDP-43, which acts as a regulatory inhibitor, Ex17b is included in the sortilin mRNA. In humans, in contrast to mice, the inclusion of Ex17b in sortilin mRNA generates a truncated, nonfunctional, extracellularly released protein that binds to but does not internalize PGRN, essentially acting as a decoy receptor. Based on these results, we propose a potential mechanism linking misregulation of sortilin splicing with altered PGRN metabolism.

ABSTRACT Globoid cell leukodystrophy (GLD), also known as Krabbe disease, is a devastating, degenerative neurological disorder. It is inherited as an autosomal recessive trait caused by loss‐of‐function mutations in the galactocerebrosidase (GALC) gene. Previously, we have shown that peripheral injection of recombinant GALC, administered every other day, results in a substantial improvement in early clinical phenotype in the twitcher mouse model of GLD. While we did detect active enzyme in the brain following peripheral administration, most of the administered enzyme was localized to the periphery. Given the substantial central nervous system (CNS) involvement in this disease, we were interested in determining whether or not a single‐dose administration of the recombinant enzyme directly to the CNS, which could potentially be achieved clinically, would result in any substantial improvement. Following intracerebroventricu‐lar (icv) administration of GALC we noted a significant, 16.5%, reduction in the GALC substrate psychosine, the abnormal accumulation of which is believed to play a pivotal role in the CNS pathology observed in this disease. Moreover, recombinant GALC was found not only in periventricular regions but also at sites distant to the injection such as the cerebral cortex and cerebellum. Most importantly, animals receiving a single icv dose of the enzyme at postnatal day 20 survived up to 51 days, which compares favorably to the control twitcher animals, which normally only live to postnatal day 40/42. These results indicate that even a single icv administration of the recombinant enzyme can have significant clinical impact and suggests that other lysosomal storage disorders with significant CNS involvement may similarly benefit.—Lee, W.C., Tsoi, Y.K., Troendle, F.J., DeLucia, M.W., Ahmed, Z., Dicky, C.A., Dickson, D.W., Eckman, C.B. Single dose intracerebroventricular administration of galactocerebrosidase improves survival in a mouse model of globoid cell leukodystrophy. FASEB J. 21, 2520–2527 (2007)

ABSTRACT Neurofibrillary tangles (NFTs) are a characteristic neuropathological feature of Alzheimer's disease (AD), and molecular chaperones appear to be involved in the removal of disease‐associated hyperphosphorylated tau, a primary component of NFTs. Here, novel HSP90 inhibitors were used to examine the impact of chaperone elevation on clearance of different tau species in transfected cells using a unique quantitative assay. The HSP90 inhibitors reduced levels of tau phosphorylated at proline‐directed Ser/Thr sites (pS202/T205, pS396/S404) and conformationally altered (MC‐1) tau species, an epitope that is immeasurable by standard Western blot techniques. The selective clearance of these phospho‐tau species and MC‐1 tau was mediated via the proteasome, while lysosomal‐mediated tau degradation seems to lack specificity for certain tau species, suggesting a more general role in total tau removal. Interestingly, tau phosphorylated at S262/S356 within the tau microtubule binding domain was minimally affected by chaperone induction. Overall, our data show that chaperone induction results in the selective clearance of specific phospho‐tau and conformationally altered tau species mediated by the proteasome; however, the apparent stability of pS262/S356 tau may also explain why MARK is able to regulate normal tau function yet still be linked to the initiation of pathogenic tau hyperphosphorylation in AD.

ABSTRACT Globoid cell leukodystrophy (GLD) or Krabbe disease is a devastating, degenerative neurological disorder caused by mutations in the galactosylceramidase (GALC) gene that severely affect enzyme activity. Currently, treatment options for this disorder are very limited. Enzyme replacement therapy (ERT) has been shown to be effective in lysosomal storage disorders with predominantly peripheral manifestations such as type I Gaucher's and Fabry's disease. Little however is known about the possible benefit of ERT in GLD, which has a substantial central nervous system component. In this study, we examined the effect of peripheral GALC injections in the twitcher mouse model of the disease. Although we were unable to block the precipitous decline that normally occurs just before death, we did observe significant early improvements in motor performance, a substantial attenuation in the initial failure to thrive, and an increase in life span. Immunohistochemical and activity analyses demonstrated GALC uptake in multiple tissues, including the brain. This was associated with a decrease in the abnormal accumulation of the GALC substrate psychosine, which is thought to play a pivotal role in disease pathology. These results indicate that peripheral ERT is likely to be beneficial in GLD.