Francesco Scaravilli

Inhibition of mTOR induces autophagy and reduces toxicity of polyglutamine expansions in fly and mouse models of Huntington disease

Huntington disease is one of nine inherited neurodegenerative disorders caused by a polyglutamine tract expansion. Expanded polyglutamine proteins accumulate abnormally in intracellular aggregates. Here we show that mammalian target of rapamycin (mTOR) is sequestered in polyglutamine aggregates in cell models, transgenic mice and human brains. Sequestration of mTOR impairs its kinase activity and induces autophagy, a key clearance pathway for mutant huntingtin fragments. This protects against polyglutamine toxicity, as the specific mTOR inhibitor rapamycin attenuates huntingtin accumulation and cell death in cell models of Huntington disease, and inhibition of autophagy has the converse effects. Furthermore, rapamycin protects against neurodegeneration in a fly model of Huntington disease, and the rapamycin analog CCI-779 improved performance on four different behavioral tasks and decreased aggregate formation in a mouse model of Huntington disease. Our data provide proof-of-principle for the potential of inducing autophagy to treat Huntington disease.

Magnetization transfer ratio and myelin in postmortem multiple sclerosis brain

Several quantitative magnetic resonance (MR) measures are used to investigate multiple sclerosis (MS) in vivo. Precise quantitative investigation of the histopathological correlates of such measures has, to date, been limited. This study investigates the relationship of quantitative measures of myelin content, axonal density, and gliosis with quantitative MR measures in postmortem (PM) MS tissue. MR imaging (MRI) was performed on a 1.5T scanner and T1‐relaxation time (T1‐RT) and magnetization transfer ratio (MTR) maps were acquired in fresh PM brain of 20 MS subjects. Myelin content, axonal counts, and the extent of gliosis all were quantified using morphometric and digital imaging techniques. MRI and pathological data were in most cases coregistered using stereotactic navigation. Using multiple regression analysis, we detected significant correlations between myelin content (Trmyelin) and MTR (r = −0.84, p < 0.001) and myelin content and axonal count (−0.80, p < 0.001); MTR correlated with T1‐RT (r = −0.79, p < 0.001). No association was detected between the extent of gliosis and either MR measure. MTR was significantly higher in remyelinated than demyelinated lesions (means: 30.0 [standard deviation, 2.9] vs 23.8 [standard deviation, 4.3], p = 0.008). In conclusion, MTR is affected by myelin content in MS white matter. Ann Neurol 2004

Neuropathology of early HIV-1 infection

Early HIV‐1 invasion of the central nervous system has been demonstrated by many cerebrospinal fluid studies; however, most HIV‐1 carriers remain neurologically unimpaired during the so called “asymptomatic” period lasting from seroconversion to symptomatic AIDS. Therefore, neuropathological studies in the early pre‐AIDS stages are very few, and the natural history of central nervous system changes in HIV‐1 infection remains poorly understood. Examination of brains of asymptomatic HIV‐1 positive individuals who died accidentally and of rare cases with acute fatal encephalopathy revealing HIV infection, and comparison with experimental simian immunodeficiency virus and feline immunodeficiency virus infections suggest that, invasion of the CNS by HIV‐1 occurs at the time of primary infection and induces an immunological process in the central nervous system. This includes an inflammatory T‐cell reaction with vasculitis and leptomeningitis, and immune activation of brain parenchyma with increased number of microglial cells, upregulation of major histocompatibility complex class II antigens and local production of cytokines. Myelin pallor and gliosis of the white matter are usually found and are likely to be the consequence of opening of the blood brain barrier due to vasculitis; direct damage to oligodendrocytes by cytokines may also interfere. These white matter changes may explain, at least partly, the early cerebral atrophy observed, by magnetic resonance imaging, in asymptomatic HIV‐1 carriers. In contrast, cortical damage seems to be a late event in the course of HIV‐1 infection. There is no significant neuronal loss at the early stages of the disease, no accompanying increase in glial fibrillary acid protein staining in the cortex, and only exceptional neuronal apoptosis. Although HIV‐1 proviral DNA may be demonstrated in a number of brains, viral replication remains very low during the asymptomatic stage of HIV‐1 infection. This makes it likely that, although opening of the blood brain barrier may facilitate viral entry into the brain, specific immune responses including both neutralising antibodies and cytotoxic T‐lymphocytes, continuously inhibits viral replication at that stage.

Lewy body Parkinson's disease in a large pedigree with 77 Parkin mutation carriers

We report the clinical, genetic, and neuropathological findings of a seven generation–spanning pedigree with 196 individuals, 25 of whom had levodopa‐responsive parkinsonism. Genetic analyses indicated Parkin mutations in 77 subjects. Among the 25 patients, 5 carried compound heterozygous mutations and met criteria for definite Parkinsons disease (PD) according to UK PD Society Brain Bank guidelines; 8 subjects carried only a heterozygous Parkin mutation. The mutational status of five deceased patients was unknown, and seven PD patients had no Parkin mutation. Survival analyses showed a significant difference in the age‐at‐onset distribution between patients with compound heterozygous mutations and the groups of heterozygous carriers and subjects without detectable Parkin mutations. Autopsy of a 73‐year‐old patient, who carried two mutant Parkin alleles (delExon7 + del1072T), showed PD‐type cell loss, reactive gliosis, and α‐synuclein–positive Lewy bodies in the substantia nigra and locus ceruleus. Surviving neurons were reactive with antibodies to the N terminus of Parkin but not the In‐Between‐RING (“IBR”) domain, which had been deleted by both mutations. This large Parkin pedigree represents a unique opportunity to prospectively study the role of heterozygous Parkin mutations as a PD risk factor, to identify additional contributors to the expression of late‐onset PD in heterozygous carriers, and to reexamine the role of Parkin in inclusion formation. Ann Neurol 2005;58:411–422

Neuronal apoptosis does not correlate with dementia in HIV infection but is related to microglial activation and axonal damage

To characterize the distribution of apoptotic neurons and their relationships with the stage of disease, a history of HIV‐dementia, and the degree of productive HIV infection, microglial activation and axonal damage, we examined the brains of 40 patients. Samples of frontal and temporal cortex, basal ganglia and brain stem were taken post‐mortem from 20 patients with AIDS (including three with HIV‐dementia, and eight with cognitive disorders that did not fulfil the criteria for HIV‐dementia), 10 HIV‐positive asymptomatic cases and 10 seronegative controls. Neuronal apoptosis was demonstrated by in situ end labelling in 18 AIDS cases and two pre‐AIDS cases; a single apoptotic neuron was present in the temporal cortex of a control. Semiquantitative evaluation showed that the severity of neuronal apoptosis in the cerebral cortex correlated with the presence of cerebral atrophy, but not with a history of HIV dementia. There was no global quantitative correlation between neuronal apoptosis and HIV encephalitis or microglial activation. However, there was some topographical correlation between these changes. In the basal ganglia, apoptotic neurons were much more abundant in the vicinity of multinucleated giant cells and/or p24 expressing cells. Microglial activation was constantly present in these areas. Axonal damage was identified using β‐amyloid‐precursor protein (βAPP) immunostaining in 17 AIDS and eight pre‐AIDS brains. Although no global quantitative correlation could be established between axonal damage and neuronal apoptosis there was an obvious topographic correlation supporting the view that axonal damage, either secondary to local microglial activation or due to the intervention of systemic factors, may also contribute to neuronal apoptosis.

High field MRI correlates of myelin content and axonal density in multiple sclerosis--a post-mortem study of the spinal cord.

Abstract.Different MRI techniques are used to investigate multiple sclerosis (MS) in vivo. The pathological specificity of these techniques is poorly understood, in particular their relationship to demyelination and axonal loss.The aim of this study was to evaluate the pathological substrate of high field MRI in post-mortem (PM) spinal cord (SC) of patients with MS. MRI was performed in PMSCs of four MS patients and a healthy subject on a 7 Tesla machine.Quantitative MRI maps (PD; T2; T1; magnetization transfer ratio, MTR; diffusion weighted imaging) were obtained. After scanning, the myelin content and the axonal density of the specimens were evaluated neuropathologically using quantitative techniques. Myelin content and axonal density correlated strongly with MTR, T1, PD, and diffusion anisotropy, but only moderately with T2 and weakly with the apparent diffusion coefficient.Quantitative MR measures provide a promising tool to evaluate components of MS pathology that are clinically meaningful. Further studies are warranted to investigate the potential of new quantitative MR measures to enable a distinction between axonal loss and demyelination and between demyelinated and remyelinated lesions.

Quantitative magnetic resonance of postmortem multiple sclerosis brain before and after fixation

Unfixed and fixed postmortem multiple sclerosis (MS) brain is being used to probe pathology underlying quantitative MR (qMR) changes. Effects of fixation on qMR indices in MS brain are unknown. In 15 postmortem MS brain slices T1, T2, MT ratio (MTR), macromolecular proton fraction (fB), fractional anisotropy (FA), and mean, axial, and radial diffusivity (MD, Dax, and Drad) were assessed in white matter (WM) lesions (WML) and normal appearing WM (NAWM) before and after fixation in formalin. Myelin content, axonal count, and gliosis were quantified histologically. Students t‐test and regression were used for analysis. T1, T2, MTR, and fB obtained in unfixed MS brain were similar to published values obtained in patients with MS in vivo. Following fixation T1, T2 (NAWM, WML) and MTR (NAWM) dropped, whereas fB (NAWM, WML) increased. Compared to published in vivo data all diffusivity measures were lower in unfixed MS brain, and dropped further following fixation (except for FA). MTR was the best predictor of Tmyelin (inversely related to myelin) in unfixed MS brain (r = −0.83; P < 0.01) whereas postfixation T2 (r = 0.92; P < 0.01), T1 (r = 0.89; P < 0.01), and fB (r = −0.86; P < 0.01) were superior. All diffusivity measures (except for Dax in unfixed tissue) were predictors of myelin content. Magn Reson Med 59:268–277, 2008.

Fewer thymic changes in MuSK antibody-positive than in MuSK antibody-negative MG

In generalized myasthenia gravis (MG) patients without detectable acetylcholine receptor (AChR) antibodies (SNMG), the thymus is often reported as “normally involuted.” We analyzed thymic compartments in 67 patients with generalized MG, with AChR antibodies (AChR+, n = 23), with muscle‐specific kinase (MuSK) antibodies (MuSK+, n = 14) or with neither (MuSK−, n = 30), and in 11 non‐MG controls. Four of 14 MuSK+ thymi had rare small germinal centers, but overall they were not different from age‐matched controls. However, approximately 75% MuSK− samples showed lymph node–type infiltrates similar to those in AChR+ patients, but with fewer germinal centers. These variations may explain some apparent differences in responses to thymectomy in SNMG. Ann Neurol 2005;57:444–448

Parallel changes in bladder suburothelial vanilloid receptor TRPV1 and pan‐neuronal marker PGP9.5 immunoreactivity in patients with neurogenic detrusor overactivity after intravesical resiniferatoxin treatment

To compare PGP9.5 and transient receptor potential vanilloid receptor (TRPV1) suburothelial immunoreactivity between controls and patients with spinal neurogenic detrusor overactivity (NDO) before and after treatment with intravesical resiniferatoxin, as suburothelial PGP9.5‐staining nerve fibres decrease in patients with spinal NDO who respond to intravesical capsaicin, and TRPV1 is present on these suburothelial nerve fibres in normal and overactive human urinary bladder.

Quantitative Magnetization Transfer Imaging in Postmortem Multiple Sclerosis Brain

To investigate the relationship of myelin content, axonal density, and gliosis with the fraction of macromolecular protons (fB) and T2 relaxation of the macromolecular pool (T2B) acquired using quantitative magnetization transfer (qMT) MRI in postmortem brains of subjects with multiple sclerosis (MS).