Intracytoplasmic inclusion bodies of the substantia nigra in myotonic dystrophy. Immunohistochemical observations

Human brain pathology in myotonic dystrophy type 1: A systematic review

Brain involvement in myotonic dystrophy type 1 (DM1) is characterized by heterogeneous cognitive, behavioral, and affective symptoms and imaging alterations indicative of widespread grey and white matter involvement. The aim of the present study was to systematically review the literature on brain pathology in DM1. We conducted a structured search in EMBASE (index period 1974–2017) and MEDLINE (index period 1887–2017) on December 11, 2017, using free text and index search terms related to myotonic dystrophy type 1 and brain structures or regions. Eligible studies were full‐text studies reporting on microscopic brain pathology of DM1 patients without potentially interfering comorbidity. We discussed the findings based on the anatomical region and the nature of the anomaly. Neuropathological findings in DM1 can be classified as follows: (1) protein and nucleotide deposits; (2) changes in neurons and glial cells; and (3) white matter alterations. Most findings are unspecific to DM1 and may occur with physiological aging, albeit to a lesser degree. There are similarities and contrasts with Alzheimer's disease; both show the appearance of neurofibrillary tangles in the limbic system without plaque occurrence. Likewise, there is myelin loss and gliosis, and there are dilated perivascular spaces in the white matter resemblant of cerebral small vessel disease. However, we did not find evidence of lacunar infarction or microbleeding. The various neuropathological findings in DM1 are reflective of the heterogeneous clinical and neuroimaging features of the disease. The strength of conclusions from this study's findings is bounded by limited numbers of participants in studies, methodological constraints, and lack of assessed associations between histopathology and clinical or neuroimaging findings.

Parallel enlargement of Marinesco bodies and nuclei and progressive deposition of p62 in pigmented neurons of the substantia nigra

Marinesco bodies (MBs) are spherical nuclear inclusions found in pigmented neurons of the substantia nigra. Although MBs are abundant in senescent brains, how they are related to aging processes remains unclear. Here, we performed a morphometric analysis of midbrain pigmented neurons to identify the possible influence of MBs on nuclear size. The transected area of the nucleus (nuclear area) was larger in the presence of MBs and was correlated with the area of MB (MB area) in all tested brains. The MB-associated nuclear enlargement was significant even after MB areas were subtracted from nuclear areas. Moreover, higher MB immunoreactivity of p62 was detected in the nucleoplasm of the enlarged MB-associated nuclei. This study on human brains is the first quantitative approach demonstrating MB-associated nuclear enlargement and progressive accumulation of small nucleoplasmic materials. Although cellular hypertrophy is usually considered to be an indication of the upregulation of cellular function, this might not always be the case. These findings suggest that an age-related decline of ubiquitin-proteasome and autophagy system activity and stagnation of undegradable materials are one of the candidate mechanisms to explain the age-related decline of neural activity in the substantia nigra.

A Patient with Myotonic Dystrophy Type 1 Presenting as Parkinsonism

The current body of literature contains 5 reports of myotonic dystrophy (DM) with parkinsonism: 4 reports of DM type 2 and 1 report of clinically suspected DM type 1. To date, there have been no genetically proven cases of DM type 1 with parkinsonism. Here, we report the first case of genetically proven DM type 1 and parkinsonism that developed ahead of muscle symptoms with bilateral putaminal, presynaptic dopaminergic deficits on imaging. A 54-year-old female patient presented with bradykinesia, axial and bilateral limb rigidity, stooped posture, and hypomimia, which did not respond to levodopa. At age 56, she developed neck flexion weakness. Examination showed bilateral facial weakness, percussion and grip myotonia, and electromyography confirmed myotonic discharges. A genetic study of DM type 1 showed a DMPK mutation. At age 58, gait freezing, postural instability, and frequent falling developed and did not respond to increasing doses of levodopa. At age 59, the patient died from asphyxia.

Novel eosinophilic neuronal cytoplasmic inclusions in the external cuneate nucleus of humans

We report the occurrence of neuronal cytoplasmic inclusions (NCIs) in the external cuneate nucleus of humans. The NCIs appeared as accumulations of eosinophilic rod-like structures in the neuronal somata in 20 (9.5%) of 211 consecutive autopsy cases. Histochemically, the NCIs were stained bright red with Gomori trichrome, Azan-Mallory and methyl green-pyronin, indicating that they contain protein and RNA. Immunohistochemically, the NCIs were positive for stress granule marker proteins, including Hu-antigen R, eukaryotic translation initiation factor 3 and poly(A)-binding protein 1, but negative for ubiquitin- and autophagy-related proteins. Ultrastructurally, the NCIs were composed of randomly oriented arrays of parallel fibrillar crystalline material with a well-defined substructure consisting of longitudinal striations, and were often associated with ribosome-like granules. These NCIs are morphologically, immunohistochemically and topographically distinct from any other inclusions previously described. Their incidence was found to increase with age. A high incidence was also observed in individuals with noninfectious inflammatory disease. These findings suggest that eosinophilic NCIs in the external cuneate nucleus are novel inclusions and might be formed under stress conditions.

Mechanisms underlying synaptic vulnerability and degeneration in neurodegenerative disease

Recent developments in our understanding of events underlying neurodegeneration across the central and peripheral nervous systems have highlighted the critical role that synapses play in the initiation and progression of neuronal loss. With the development of increasingly accurate and versatile animal models of neurodegenerative disease it has become apparent that disruption of synaptic form and function occurs comparatively early, preceding the onset of degenerative changes in the neuronal cell body. Yet, despite our increasing awareness of the importance of synapses in neurodegeneration, the mechanisms governing the particular susceptibility of distal neuronal processes are only now becoming clear. In this review we bring together recent developments in our understanding of cellular and molecular mechanisms regulating synaptic vulnerability. We have placed a particular focus on three major areas of research that have gained significant interest over the last few years: (i) the contribution of synaptic mitochondria to neurodegeneration; (ii) the contribution of pathways that modulate synaptic function; and (iii) regulation of synaptic degeneration by local posttranslational modifications such as ubiquitination. We suggest that targeting these organelles and pathways may be a productive way to develop synaptoprotective strategies applicable to a range of neurodegenerative conditions.

Neurofibrillary tangles and deposition of oxidative products in the brain in cases of myotonic dystrophy

Myotonic dystrophy (MyD) is a neuromuscular degenerative disorder that is neuropathologically characterized by minor changes, such as the presence of neurofibrillary tangles (NFT), thalamic inclusions and functional brainstem lesions. In the current study, we conducted an immunohistochemical analysis to examine the distribution of NFT and formation of oxidative products in the brain specimens of 12 patients with MyD. Neurofibrillary tangles were found in the limbic system and/or the brainstem of all the cases examined but there were no senile plaques. The density of distribution of the NFT was not significantly correlated with clinicopathological findings, although cases with fewer NFTin the brain frequently showed sleep disturbances and lack of spontaneity. Nuclear and cytoplasmic immunoreactivities for 8-hydroxy-2'-deoxyguanosine and advanced glycation end products were observed in the glial cells and/or neurons in the brainstem, but not in the cerebral cortex. On the other hand, 10 out of the 12 cases showed cytoplasmic immunoreactivity for 4-hydroxy-2-nonenal-modified protein (4-HNE) in neurons of the temporal cortex and raphe nucleus. Deposition of 4-HNE was also recognized in the hippocampus and mesencephalic central gray matter, but not in the subiculum. The distribution pattern of the immunoreactivity for 4-HNE showed no clear correlation with either the psychological disturbances or the distribution of the NFT. Altered expression of monoaminergic neurons in the brainstem of MyD patients has already been reported, and it is worth noting that most of our cases showed NFT in the brainstem. The selective deposition of 4-HNE in the limbic system and brainstem suggests that lipid peroxidation may be involved in the neurodegenerative process in MyD. Using immunohistochemical analysis to determine the distribution of neurotransmitters in the mesencephalic central gray matter and/or pontine raphe nucleus may help elucidate the relationship between the clinical abnormalities, distribuion of NFT, and 4-HNE deposition in the brain in patients with MyD.

Substantia nigra Marinesco bodies are associated with decreased striatal expression of dopaminergic markers

Marinesco bodies are nuclear inclusions found in pigmented neurons of the substantia nigra and locus ceruleus of humans and monkeys. It has long been known that the frequency of these inclusions increases with advancing age, but no pathologic associations have ever been established. We quantified Marinesco body frequency in human autopsy subjects, classified as young normal controls, elderly controls, dementia with Lewy bodies (DLB), Alzheimer disease (AD), and Parkinson disease (PD). Elderly controls, AD cases, and DLB cases had significantly increased Marinesco body frequencies relative to young controls and DLB cases had significantly increased frequencies relative to elderly controls, while PD cases did not differ from young controls; cases with AD did not differ from elderly controls. Lewy body-containing neurons had significantly higher Marinesco body frequencies than non-Lewy body-containing neurons. Marinesco body frequency in elderly control cases correlated significantly, in inverse fashion, with striatal concentrations of the dopaminergic neuron markers dopamine transporter and tyrosine hydroxylase. These statistical associations suggest that Marinesco bodies constitute or mark a pathologic process that may be related to, or contribute to, age-related motor dysfunction and/or Lewy body disorders. Further studies are needed to ascertain the molecular basis of Marinesco body formation; preliminary studies indicate that proteasome dysfunction can lead to similar abnormalities in cultured cells.

Magnetization transfer measurements of cerebral white matter in patients with myotonic dystrophy

To determine whether patients with myotonic dystrophy (MyD) have structural changes in the cerebral white matter, we performed magnetization transfer (MT) imaging of the cerebral white matter in 14 MyD patients and 11 age-matched normal controls. We calculated MT ratios in both the white matter lesions (WMLs) and the normal-appearing white matter (NAWM) of MyD patients using region of interest (ROI) analysis. MT ratios in WMLs were markedly decreased, and all ROIs in NAWM also showed significantly lower MT ratios in MyD patients than in normal controls. The average MT ratio of all ROIs in WMLs and NAWM in each patient showed a significant negative correlation with duration of illness, but not with the patient's age or age at onset. The results of the present study indicate not only the presence of pathological changes in WMLs but also the widespread involvement of NAWM in MyD patients. The results also suggest that structural changes in the white matter may be progressive during the clinical course of MyD.

Heavy-ion-induced mutations in the gpt delta transgenic mouse: effect of p53 gene knockout

The influence of the loss of p53 gene on heavy-ion-induced mutations was examined by constructing a new line of transgenic mice, p53 knockout (p53(-/-)) gpt delta. In this mouse model, deletions in lambda DNA integrated into the mouse genome are preferentially selected as Spi(-) phages, which can then be subjected to molecular analysis. Mice were exposed to 10 Gy of whole-body carbon-ion irradiation. The carbon ions were accelerated to 135 MeV/u by the RIKEN Ring Cyclotron. The p53 defect markedly enhanced the Spi(-) mutant frequency (MF) in the kidneys of mice exposed to C-ion irradiation: the Spi(-) MF increased 4.4- and 2.8-fold over the background level after irradiation in p53(-/-) and p53(+/+) mice, respectively. There was no significant difference in the background Spi(-) MF between p53(-/-) and p53(+/+) mice. Sequence analysis of the Spi(-) mutants indicated that the enhancement of kidney Spi(-) MF in p53(-/-) mice was primarily due to an increase in complex or rearranged-type deletions. In contrast to the kidney, the p53 defect had no effect on the Spi(-) MF in liver: Spi(-) MF increased 3.0- and 2.7-fold after the irradiation in p53(-/-) and p53(+/+) mice, respectively. Our results suggest that p53 suppresses deletion mutations induced by heavy-ion irradiation in an organ-specific manner.

Abnormal patterns of microtubule-associated protein-2 (MAP-2) immunolabeling in neuronal nuclei and Lewy bodies in Parkinson's disease substantia nigra brain tissues

Parkinson's disease (PD) is a neurodegenerative disorder associated with the appearance of cytoplasmic Lewy bodies (LBs) in dopaminergic neurons of the substantia nigra and the progressive loss of these neurons. Cytoskeleton alterations and associated impairments of neuronal transport may contribute to neuronal death. Microtubule-associated protein-2 (MAP-2), a cytoskeleton protein is localized primarily in neuronal dendrites and is known to stabilize microtubule assembly and mediate their interactions with other neuronal cell components. To determine if alterations in MAP-2 morphology are present in PD neurons, we used single and double immunohistochemical and immunofluorescent techniques to characterize MAP-2 in PD neuronal tissues. We report abnormal MAP-2 immunolabeling in some neurons of the substantia nigra of PD brain tissues, which were not observed in the normal, age-matched, control brain tissues. Furthermore, MAP-2 was co-localized with alpha-synuclein and ubiquitin in cytoplasmic LBs of neurons. Surprisingly, MAP-2 was also found to form fibrous aggregates and crystal-like structures within neuronal nuclei. These PD-associated alterations in MAP-2 morphology and distribution suggest that impaired neuronal transport may contribute to the progression of neuronal loss in the brains of PD patients.