Intranuclear inclusions, neuronal loss and CAG mosaicism in two patients with Machado–Joseph disease

https://doi.org/10.1016/S0022-510X(02)00110-7Get rights and content

Abstract

The presence of neuronal intranuclear inclusions (NIIs) and neuronal mosaicism has been described in some autosomal dominant spinocerebellar ataxias (SCA), but their implication in neurodegenerative mechanisms still remains unclear. Objective: To investigate the correlation between neuronal loss and NIIs, and the size of CAG triplet expansion in selected areas of the CNS in two SCA3 patients. Material and methods: Postmortem neuropathological study was carried out, and the regional distribution of neuronal loss was compared with NIIs. CAG expansion was analysed by PCR amplification in the same regions. Results: Marked neuronal loss was seen in the anterior horn of the spinal cord, pontine nuclei and motor nuclei of the brain stem. Moderate neurone loss was found in the locus ceruleus, colliculus and substantia nigra. Loss of granule and Purkinje cells was found in the cerebellum, mainly in the vermis. NIIs were present in neurones of the involved nuclei of the anterior horn of the spinal cord, medulla oblongata and pons, but not in the locus ceruleus, substantia nigra and cerebellum. A few NIIs were found in the striatum. The number of CAG repeats was 27/70 in the first patient and 21/74 in the second patient. The variation of the expanded allele size among different cerebral areas was ±1–3 CAG repeats. Conclusion: The partial correlation between neuronal loss and NIIs suggests that other factors distinct from NII formation may be involved in the neuronal death. Moreover, the low degree of mosaicism between regions without neuronal loss and regions with marked neuronal loss points to the existence of selective cellular vulnerability to the genetic defect.

Introduction

Spinocerebellar ataxias (SCA) constitute a heterogeneous group of diseases clinically characterised by a progressive cerebellar syndrome, but also with symptoms and signs suggesting involvement of the brain stem, spinal cord, basal ganglia or peripheral nerves in many cases. The CAG repeat expansion in a specific locus in different chromosomes is the mutation responsible for autosomal dominant ataxias such as SCA1, SCA2, SCA3, SCA6, SCA7, dentato–rubro–pallido–luysian atrophy (DRPLA) and SCA12. The CAG expansion is translated except in SCA12 into a protein that is expanded in polyglutamine residues. The number of CAG repeats influences the age at onset and the disease severity in many cases. SCA3 or Machado–Joseph disease is associated with the CAG expansion on the chromosome 14q32.1 [1] that results in the abnormal expression of the polyglutamine-expanded mutant protein ataxin-3. Both the normal and mutant ataxin-3 are widely expressed in all regions of the brain [2], [3]. It has been proposed that this abnormal expanded protein is the cause of the neuronal death in vitro and in vivo [4]. However, the mechanism of mutant ataxin-3-induced cell death is poorly understood. It has been suggested that the formation of neuronal intranuclear inclusions (NIIs) is a common pathogenic mechanism involved in the neurodegeneration in most of the CAG triplet-repeat disorders [5], including SCA3 [6], [7]. The corresponding expanded and normal protein and ubiquitin are components of NIIs [6]. The formation of NIIs still remains unclear, but the presence of the mutated protein in the nucleus is required, and the interaction with the proteasome [8] and nuclear matrix [9] is probably needed.

The CAG expansion size varies in different cell lines from the same individual (somatic mosaicism). The presence of neuronal mosaicism in SCA3 has been reported in some studies [2], [10], [11], [12]. However, the correlation between NII formation and the degree of mosaicism in SCA3 has not been investigated in detail. The objective of the present study was to examine whether there is any association between neuronal loss and the presence of NIIs, and the size of the CAG expansion in several CNS regions in two patients who had suffered from SCA3.

Section snippets

Patient 1

This patient was a woman who consulted our service at the age of 78. The first symptoms appeared at the age of 50 years and the condition was characterised by slowly progressive gait ataxia and dysarthria. She was able to walk without help until she was 77 years old. The family history revealed the presence of a cerebellar syndrome in many family members with an autosomal dominant pattern of inheritance (Fig. 1). The clinical and neuropathological findings supporting Machado–Joseph disease in

Patient 1

The brain weight was 1200 g. There was mild cerebral atrophy, and marked atrophy of the cerebellum, particularly the vermis, and pons. Loss of pigment was noticed in the substantia nigra and locus ceruleus. Marked neuronal loss was seen in the anterior horn of the spinal cord, motor nuclei of the medulla oblongata, facial nucleus and oculomotor nuclei. Moderate loss of neurones was observed in the periaqueductal gray matter and colliculus. Moderate neuronal loss occurred in the locus ceruleus

Discussion

The main clinical symptoms and neuropathological findings were similar in both cases and consistent with previous observations in Machado–Joseph disease in the same family [13]. One of the patients was very old and had additional lesions of Alzheimer's disease and diffuse Lewy body disease. The major severity of lesions in the cerebellum in this case is probably related to the more prolonged duration of the disease.

We have only found a partial correlation between the neuronal loss and the

Acknowledgements

This work was supported in part by a grant FIS 99-1118. We wish to thank T. Yohannan for editorial assistance.

References (27)

  • M.K. Perez et al.

    Recruitment and the role of nuclear localization in polyglutamine-mediated aggregation

    J. Cell Biol.

    (1998)
  • Y. Chai et al.

    Evidence for proteasome involvement in polyglutamine disease: localization to nuclear inclusions in SCA3/MJD and suppression of polyglutamine aggregation in vitro

    Hum. Mol. Genet.

    (1999)
  • M.K. Perez et al.

    Ataxin-3 with an altered conformation that exposes the polyglutamine domain is associated with the nuclear matrix

    Hum. Mol. Genet.

    (1999)
  • Cited by (29)

    • Development of an AAV-Based MicroRNA Gene Therapy to Treat Machado-Joseph Disease

      2019, Molecular Therapy Methods and Clinical Development
      Citation Excerpt :

      In the cerebellum, neurodegeneration is observed in dentate nucleus. The cerebellar cortex seems less affected, but loss of granule and Purkinje cells has been reported in the cerebellar vermis.1,69–72 Main areas affected in the brain stem include the vestibular, pontine, and motor nuclei.1,70,73

    • The modulation of Amyotrophic Lateral Sclerosis risk by Ataxin-2 intermediate polyglutamine expansions is a specific effect

      2012, Neurobiology of Disease
      Citation Excerpt :

      Similar to the polyQ-expansions of sizes ≥ 34 in the polysome-associated protein ATXN2 causing Spinocerebellar Ataxia Type 2 (SCA2), polyQ expansions of sizes ≥ 52 in the deubiquitinating transcription repressor Ataxin-3 (ATXN3) cause Spinocerebellar Ataxia Type 3 (SCA3). Both in SCA2 and in SCA3 the pattern of affected neuron populations extends beyond the spinocerebellar circuits to involve the peripheral and central motoneurons as well as the dopaminergic substantia nigra neurons (Lastres-Becker et al., 2008; Munoz et al., 2002). In consequence, SCA2 and SCA3 usually manifest with ataxia and dysarthria in their clinical pictures, which cannot be distinguished with certainty on clinical grounds.

    • Machado-Joseph disease/spinocerebellar ataxia type 3

      2012, Handbook of Clinical Neurology
      Citation Excerpt :

      As in other polyglutamine disease proteins, the disease protein in MJD accumulates within inclusions in various brain regions. These inclusions are often found inside the cell nuclei of specific populations of neurons (Paulson et al., 1997a; Schmidt et al., 1998; Munoz et al., 2002; Uchihara et al., 2002). Neuronal intranuclear inclusions (NIs) are ubiquitin-positive spheres of one to several microns in diameter that also contain other proteins.

    • P53 activation mediates polyglutamine-expanded ataxin-3 upregulation of Bax expression in cerebellar and pontine nuclei neurons

      2011, Neurochemistry International
      Citation Excerpt :

      To confirm the involvement of p53-upregulated Bax expression in the pathogenesis of SCA3 neurodegeneration, SCA3 transgenic mice were used to test the possibility that polyglutamine-expanded ataxin-3 increases Bax mRNA and protein levels in the cerebellum and pontine nuclei. Previous neuropathological studies reported that polyglutamine-expanded ataxin-3-induced neuronal death in the pontine nuclei of SCA3 patients is more prominent than that in the SCA3 cerebellum (Durr et al., 1996; Munoz et al., 2002; Riess et al., 2008). Similar to SCA3 human brain, immunohistochemical staining of neuronal marker NeuN demonstrated a prominent and selective neuronal death (43 ± 4% loss, n = 6 animals; Fig. 2A) in the pontine nuclei of 4–5-month-old SCA3 transgenic mice (for wild-type mice, number of NeuN-positive cells per mm2 = 545 ± 50; for SCA3 mice, number of NeuN-positive cells per mm2 = 310 ± 30).

    View all citing articles on Scopus
    View full text