Mitochondrial deficits and abnormal mitochondrial retrograde axonal transport play a role in the pathogenesis of mutant Hsp27-induced Charcot Marie Tooth Disease.

Mutations in the small heat shock protein Hsp27, encoded by the HSPB1 gene, have been shown to cause Charcot Marie Tooth Disease type 2 (CMT-2) or distal hereditary motor neuropathy (dHMN). Protein aggregation and axonal transport deficits have been implicated in the disease. In this study, we conducted analysis of bidirectional movements of mitochondria in primary motor neuron axons expressing wild type and mutant Hsp27. We found significantly slower retrograde transport of mitochondria in Ser135Phe, Pro39Leu and Arg140Gly mutant Hsp27 expressing motor neurons than in wild type Hsp27 neurons, although anterograde movement velocities remained normal. Retrograde transport of other important cargoes, such as the p75 neurotrophic factor receptor was minimally altered in mutant Hsp27 neurons, implicating that axonal transport deficits primarily affect mitochondria and the axonal transport machinery itself is less affected. Investigation of mitochondrial function revealed a decrease in mitochondrial membrane potential in mutant Hsp27 expressing motor axons, as well as a reduction in mitochondrial complex 1 activity, increased vulnerability of mitochondria to mitochondrial stressors, leading to elevated superoxide release and reduced mitochondrial glutathione (GSH) levels, although cytosolic GSH remained normal. This mitochondrial redox imbalance in mutant Hsp27 motor neurons is likely to cause low level of oxidative stress, which in turn will contribute to, and indeed may be the underlying cause of the deficits in mitochondrial axonal transport. Together, these findings suggest that the mitochondrial abnormalities in mutant Hsp27-induced neuropathies may be a primary cause of pathology, leading to further deficits in the mitochondrial axonal transport and onset of disease.

A novel p.Gln175X [corrected] premature stop mutation in the C-terminal end of HSP27 is a cause of CMT2.

Mutations in the gene HSPB1, encoding the small heat shock protein 27 (HSP27), are a cause of distal hereditary motor neuropathy (dHMN) and axonal Charcot-Marie-Tooth disease (CMT2). dHMN and CMT2 are differentiated by the presence of a sensory neuropathy in the latter although in the case of HSPB1 this division is artificial as CMT2 secondary to HSPB1 mutations is predominantly a motor neuropathy with only minimal sensory involvement. A recent study in mice has suggested that mutations in the C-terminus result in a motor only phenotype resembling dHMN, whereas mutations at the N-terminus result in a CMT2-like phenotype. However, we present a family with a novel mutation in the C-terminus of HSP27 (p.Gln175X) [corrected] with a motor predominant distal neuropathy but with definite sensory involvement compatible with CMT2. This case highlights the artificial distinction between patients with motor predominant forms of CMT2 and dHMN and argues against the hypothesis that mutations in the C-terminus have no sensory involvement.

Accelerated lipofuscinosis and ubiquitination in granulin knockout mice suggest a role for progranulin in successful aging.

Progranulin (PGRN) is involved in wound repair, inflammation, and tumor formation, but its function in the central nervous system is unknown. Roles in development, sexual differentiation, and long-term neuronal survival have been suggested. Mutations in the GRN gene resulting in partial loss of the encoded PGRN protein cause frontotemporal lobar degeneration with ubiquitin immunoreactive inclusions. We sought to understand the neuropathological consequences of loss of PGRN function throughout the lifespan of GRN-deficient ((-/+) and (-/-)) mice. An aged series of GRN-deficient and wild-type mice were compared by histology, immunohistochemistry, and electron microscopy. Although GRN-deficient mice were viable, GRN(-/-) mice were produced at lower than predicted frequency. Neuropathologically, GRN(-/+) were indistinguishable from controls; however, GRN(-/-) mice developed age-associated, abnormal intraneuronal ubiquitin-positive autofluorescent lipofuscin. Lipofuscin was noted in aged GRN(+/+) mice at levels comparable with those of young GRN(-/-) mice. GRN(-/-) mice developed microgliosis, astrogliosis, and tissue vacuolation, with focal neuronal loss and severe gliosis apparent in the oldest GRN(-/-) mice. Although no overt frontotemporal lobar degeneration with ubiquitin immunoreactive inclusions type- or TAR DNA binding protein-43-positive lesions were observed, robust lipofuscinosis and ubiquitination in GRN(-/-) mice is strikingly similar to changes associated with aging and cellular decline in humans and animal models. Our data suggests that PGRN plays a key role in maintaining neuronal function during aging and supports the notion that PGRN is a trophic factor essential for long-term neuronal survival.

Overexpression of wild-type murine tau results in progressive tauopathy and neurodegeneration.

Here, we describe the generation and characterization of a novel tau transgenic mouse model (mTau) that overexpresses wild-type murine tau protein by twofold compared with endogenous levels. Transgenic tau expression was driven by a BAC transgene containing the entire wild-type mouse tau locus, including the endogenous promoter and the regulatory elements associated with the tau gene. The mTau model therefore differs from other tau models in that regulation of the genomic mouse transgene mimics that of the endogenous gene, including normal exon splicing regulation. Biochemical data from the mTau mice demonstrated that modest elevation of mouse tau leads to tau hyperphosphorylation at multiple pathologically relevant epitopes and accumulation of sarkosyl-insoluble tau. The mTau mice show a progressive increase in hyperphosphorylated tau pathology with age up to 15 to 18 months, which is accompanied by gliosis and vacuolization. In contrast, older mice show a decrease in tau pathology levels, which may represent hippocampal neuronal loss occurring in this wild-type model. Collectively, these results describe a novel model of tauopathy that develops pathological changes reminiscent of early stage Alzheimer's disease and other related neurodegenerative diseases, achieved without overexpression of a mutant human tau transgene. This model will provide an important tool for understanding the early events leading to the development of tau pathology and a model for analysis of potential therapeutic targets for sporadic tauopathies.

A metabolomic study of the CRND8 transgenic mouse model of Alzheimer's disease.

Alzheimer's disease is the most common neurodegenerative disease of the central nervous system characterized by a progressive loss in memory and deterioration of cognitive functions. In this study the transgenic mouse TgCRND8, which encodes a mutant form of the amyloid precursor protein 695 with both the Swedish and Indiana mutations and develops extracellular amyloid beta-peptide deposits as early as 2-3 months, was investigated. Extract from eight brain regions (cortex, frontal cortex, cerebellum, hippocampus, olfactory bulb, pons, midbrain and striatum) were studied using (1)H NMR spectroscopy. Analysis of the NMR spectra discriminated control from APP695 tissues in hippocampus, cortex, frontal cortex, midbrain and cerebellum, with hippocampal and cortical region being most affected. The analysis of the corresponding loading plots for these brain regions indicated a decrease in N-acetyl-L-aspartate, glutamate, glutamine, taurine (exception hippocampus), gamma-amino butyric acid, choline and phosphocholine (combined resonances), creatine, phosphocreatine and succinate in hippocampus, cortex, frontal cortex (exception gamma-amino butyric acid) and midbrain of affected animals. An increase in lactate, aspartate, glycine (except in midbrain) and other amino acids including alanine (exception frontal cortex), leucine, iso-leucine, valine and water soluble free fatty acids (0.8-0.9 and 1.2-1.3 ppm) were observed in the TgCRND8 mice. Our findings demonstrate that the perturbations in metabolism are more widespread and include the cerebellum and midbrain. Furthermore, metabolic perturbations are associated with a wide range of metabolites which could improve the diagnosis and monitoring of the progression of Alzheimer's disease.