Elsevier

The Lancet

Volume 359, Issue 9325, 29 June 2002, Pages 2242-2247
The Lancet

Mechanisms of Disease
Association between conformational mutations in neuroserpin and onset and severity of dementia

https://doi.org/10.1016/S0140-6736(02)09293-0Get rights and content

Summary

Background

The aggregation of specific proteins is a common feature of the familial dementias, but whether the formation of neuronal inclusion bodies is a causative or incidental factor in the disease is not known. To clarify this issue, we investigated five families with typical neuroserpin inclusion bodies but with various neurological manifestations.

Methods

Five families with neurodegenerative disease and typical neuronal inclusions had biopsy or autopsy material available for further examination. Immunostaining confirmed that the inclusions were formed of neuroserpin aggregates, and the responsible mutations in neuroserpin were identified by sequencing of the neuroserpin gene (SERPINI1) in DNA from blood samples or from extraction of histology specimens. Molecular modelling techniques were used to predict the effect of the gene mutations on three-dimensional protein structure. Brain sections were stained and the topographic distribution of the neuroserpin inclusions plotted.

Findings

Each of the families was heterozygous for an aminoacid substitution that affected the conformational stability of neuroserpin. The least disruptive of these mutations (S49P), as predicted by molecular modelling, resulted in dementia after age 45 years, and presence of neuroserpin inclusions in only a few neurons. By contrast, the most severely disruptive mutation (G392E) resulted, at age 13 years, in progressive myoclonus epilepsy, with many inclusions present in almost all neurons.

Interpretation

The findings provide evidence that inclusion-body formation is in itself a sufficient cause of neurodegeneration, and that the onset and severity of the disease is associated with the rate and magnitude of neuronal protein aggregation.

Introduction

Neuronal or perineuronal protein aggregates are a characteristic feature of the common dementias,1, 2 as with the deposits of β-amyloid in Alzheimer's disease and prion protein in the spongiform encephalopathies. In sporadic and familial Parkinson's disease, α-synuclein accumulates within neurons to form discrete Lewy bodies;3 similarly, Pick bodies of aggregated tau protein are present in some forms of familial frontotemporal dementia.4 A further type of neuronal inclusion, the collins body, has also been found in association with familial neurodegenerative disease.5, 6, 7 The particular importance of this finding is that Collins bodies are formed of aggregated neuroserpin, a neuron-specific protease inhibitor8, 9 that is closely related in structure10 to the well studied plasma protease inhibitor α1-antitrypsin—another serpin.11 In particular, the mutations causing the aggregation of neuroserpin were found to be homologous to mutations known to cause the aggregation of α1-antitrypsin in hepatocytes.12, 13 This aggregation of α1-antitrypsin, and not its accompanying deficiency, is responsible for hepatocyte damage and the eventual development of cirrhosis. The identification of the same type of polymeric linkage in neuroserpin indicates a shared molecular pathophysiology in the associated neurodegenerative and cirrhotic processes.14 Each disease arises from the same destabilising mutations,15 and polymerisation of the conformationally unstable protein occurs intracellularly at the site of synthesis to give a cumulative loss over time of hepatocytes with aggregates of α1-antitrypsin, and of neurons with aggregates of neuroserpin.

These findings highlight a disputed question: is the formation of protein aggregates an incidental feature of the dementias or is it a causative factor? Are the neuronal Lewy bodies, Pick bodies, and amyloid plaques just histological markers or are they the cause of the neurodegeneration? To answer this question, we investigated five families with different clinical presentations of familial encephalopathies with neuroserpin inclusion bodies (FENIB).

Section snippets

Participating families

Families were selected after a literature search and from referred families, the criteria for selection being the presence of Collins bodies together with the availability of brain tissue for further investigation. Probands from five families with histories of neurodegenerative disease (panel 1) were assessed. Tissue was available from autopsy in three of these (cases 1, 2, and 3), and from brain biopsies in two others (cases 4 and 5).

Procedures

Brain-tissue specimens were fixed in formalin, embedded in

Results

Immunostaining revealed that Collins bodies in the probands from each family assessed contained neuroserpin. This finding was further confirmed in case 3 by isolation of inclusions from paraffin-embedded brain tissue sections by laser-capture microscopy. SDS-PAGE of the solubilised inclusions showed a single band on silver-stained gels, identified as neuroserpin by Western blot analysis. All cases were heterozygous for mutations resulting in aminoacid substitutions in neuroserpin. The mutations

Discussion

The concept of the conformational diseases28 was initially based on the aggregation of α1-antitrypsin, which results in progressive hepatocellular damage and the eventual development of cirrhosis.12, 13 An accompanying prediction28 was that a similar process would explain the slow development and late onset of inclusion-body neurodegenerative diseases. This prediction was confirmed with the finding5 of two families with dementia due to mutations in neuroserpin, a brain-specific protein8, 9

GLOSSARY

collins bodies
Characteristic eosinophilic inclusion bodies positive by periodic-acid-Schiff staining and resistant to diastase, formed by the aggregation of neuroserpin within the endoplasmic reticulum of neurons.
neuroserpin
A brain-specific serpin synthesised and secreted by neurons, particularly during their growth.
progressive myoclonus epilepsy (PME)
Progressive neurological deterioration characterised by myoclonus, tonic-clonic seizures, cerebellar ataxia, and dementia.
serpins
A family of

References (33)

  • SE Ryu et al.

    The native strains in the hydrophobic core and flexible reactive loop of a serine protease inhibitor: crystal structure of an uncleaved alpha1-antitrypsin at 2.7 Å

    Structure

    (1996)
  • K Jochmans et al.

    Antithrombin-Gly 424 Arg: a novel point mutation responsible for type 1 antithrombin deficiency and neonatal thrombosis

    Blood

    (1994)
  • RW Carrell et al.

    Conformational diseases

    Lancet

    (1997)
  • H Shimura et al.

    Ubiquitination of a new form of alpha-synuclein by parkin from human brain: implications for Parkinson's disease

    Science

    (2001)
  • JR Murrell et al.

    Tau gene mutation G389R causes a tauopathy with abundant pick body-like inclusions and axonal deposits

    J Neuropathol Exp Neurol

    (1999)
  • RL Davis et al.

    Familial dementia caused by polymerisation of mutant neuroserpin

    Nature

    (1999)
  • Cited by (142)

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