Mohamed Bouzrou

The brainstem pathologies of Parkinson's disease and dementia with Lewy bodies.

Parkinsons disease (PD) and dementia with Lewy bodies (DLB) are among the human synucleinopathies, which show alpha‐synuclein immunoreactive neuronal and/or glial aggregations and progressive neuronal loss in selected brain regions (eg, substantia nigra, ventral tegmental area, pedunculopontine nucleus). Despite several studies about brainstem pathologies in PD and DLB, there is currently no detailed information available regarding the presence of alpha‐synuclein immunoreactive inclusions (i) in the cranial nerve, precerebellar, vestibular and oculomotor brainstem nuclei and (ii) in brainstem fiber tracts and oligodendroctyes. Therefore, we analyzed the inclusion pathologies in the brainstem nuclei (Lewy bodies, LB; Lewy neurites, LN; coiled bodies, CB) and fiber tracts (LN, CB) of PD and DLB patients. As reported in previous studies, LB and LN were most prevalent in the substantia nigra, ventral tegmental area, pedunculopontine and raphe nuclei, periaqueductal gray, locus coeruleus, parabrachial nuclei, reticular formation, prepositus hypoglossal, dorsal motor vagal and solitary nuclei. Additionally we were able to demonstrate LB and LN in all cranial nerve nuclei, premotor oculomotor, precerebellar and vestibular brainstem nuclei, as well as LN in all brainstem fiber tracts. CB were present in nearly all brainstem nuclei and brainstem fiber tracts containing LB and/or LN. These findings can contribute to a large variety of less well‐explained PD and DLB symptoms (eg, gait and postural instability, impaired balance and postural reflexes, falls, ingestive and oculomotor dysfunctions) and point to the occurrence of disturbances of intra‐axonal transport processes and transneuronal spread of the underlying pathological processes of PD and DLB along anatomical pathways.

Precortical Phase of Alzheimer's Disease (AD)‐Related Tau Cytoskeletal Pathology

Alzheimers disease (AD) represents the most frequent progressive neuropsychiatric disorder worldwide leading to dementia. We systematically investigated the presence and extent of the AD‐related cytoskeletal pathology in serial thick tissue sections through all subcortical brain nuclei that send efferent projections to the transentorhinal and entorhinal regions in three individuals with Braak and Braak AD stage 0 cortical cytoskeletal pathology and fourteen individuals with Braak and Braak AD stage I cortical cytoskeletal pathology by means of immunostainings with the anti‐tau antibody AT8. These investigations revealed consistent AT8 immunoreactive tau cytoskeletal pathology in a subset of these subcortical nuclei in the Braak and Braak AD stage 0 individuals and in all of these subcortical nuclei in the Braak and Braak AD stage I individuals. The widespread affection of the subcortical nuclei in Braak and Braak AD stage I shows that the extent of the early subcortical tau cytoskeletal pathology has been considerably underestimated previously. In addition, our novel findings support the concept that subcortical nuclei become already affected during an early ‘pre‐cortical’ evolutional phase before the first AD‐related cytoskeletal changes occur in the mediobasal temporal lobe (i.e. allocortical transentorhinal and entorhinal regions). The very early involved subcortical brain regions may represent the origin of the AD‐related tau cytoskeletal pathology, from where the neuronal cytoskeletal pathology takes an ascending course toward the secondarily affected allocortex and spreads transneuronally along anatomical pathways in predictable sequences.

Huntington's Disease (HD): Degeneration of Select Nuclei, Widespread Occurrence of Neuronal Nuclear and Axonal Inclusions in the Brainstem

Huntingtons disease (HD) is a progressive polyglutamine disease that leads to a severe striatal and layer‐specific neuronal loss in the cerebral neo‐and allocortex. As some of the clinical symptoms (eg, oculomotor dysfunctions) suggested a degeneration of select brainstem nuclei, we performed a systematic investigation of the brainstem of eight clinically diagnosed and genetically confirmed HD patients. This post‐mortem investigation revealed a consistent neuronal loss in the substantia nigra, pontine nuclei, reticulotegmental nucleus of the pons, superior and inferior olives, in the area of the excitatory burst neurons for horizontal saccades, raphe interpositus nucleus and vestibular nuclei. Immunoreactive intranuclear neuronal inclusions were present in all degenerated and apparently spared brainstem nuclei and immunoreactive axonal inclusions were observed in all brainstem fiber tracts of the HD patients. Degeneration of brainstem nuclei can account for a number of less well‐understood clinical HD symptoms (ie, cerebellar, oculomotor and vestibular symptoms), while the formation of axonal aggregates may represent a crucial event in the cascades of pathological events leading to neurodegeneration in HD.

Polyglutamine aggregation in Huntington's disease and spinocerebellar ataxia type 3: similar mechanisms in aggregate formation

Polyglutamine (polyQ) diseases are characterized by the expansion of a polymorphic glutamine sequence in disease‐specific proteins and exhibit aggregation of these proteins. This is combated by the cellular protein quality control (PQC) system, consisting of chaperone‐mediated refolding as well as proteasomal and lysosomal degradation pathways. Our recent study in the polyQ disease spinocerebellar ataxia type 3 (SCA3) suggested a distinct pattern of protein aggregation and PQC dysregulation.

Huntington's Disease (HD): Neurodegeneration of Brodmann's Primary Visual Area 17 (BA17)

Huntingtons disease (HD), an autosomal dominantly inherited polyglutamine or CAG repeat disease along with somatomotor, oculomotor, psychiatric and cognitive symptoms, presents clinically with impairments of elementary and complex visual functions as well as altered visual‐evoked potentials (VEPs). Previous volumetric and pathoanatomical post‐mortem investigations pointed to an involvement of Brodmanns primary visual area 17 (BA17) in HD. Because the involvement of BA17 could be interpreted as an early onset brain neurodegeneration, we further characterized this potential primary cortical site of HD‐related neurodegeneration neuropathologically and performed an unbiased estimation of the absolute nerve cell number in thick gallocyanin‐stained frontoparallel tissue sections through the striate area of seven control individuals and seven HD patients using Cavalieris principle for volume and the optical disector for nerve and glial cell density estimations. This investigation showed a reduction of the estimated absolute nerve cell number of BA17 in the HD patients (71 044 037 ± 12 740 515 nerve cells) of 32% in comparison with the control individuals (104 075 067 ± 9 424 491 nerve cells) (Mann–Whitney U‐test; P < 0.001). Additional pathoanatomical studies showed that nerve cell loss was most prominent in the outer pyramidal layer III, the inner granular layers IVa and IVc as well as in the multiform layer VI of BA17 of the HD patients. Our neuropathological results in BA17 confirm and extend previous post‐mortem, biochemical and in vivo neuroradiological HD findings and offer suitable explanations for the elementary and complex visual dysfunctions, as well as for the altered VEP observed in HD patients.

On the distribution of intranuclear and cytoplasmic aggregates in the brainstem of patients with spinocerebellar ataxia type 2 and 3

The polyglutamine (polyQ) diseases are a group of genetically and clinically heterogeneous neurodegenerative diseases, characterized by the expansion of polyQ sequences in unrelated disease proteins, which form different types of neuronal aggregates. The aim of this study was to characterize the aggregation pathology in the brainstem of spinocerebellar ataxia type 2 (SCA2) and 3 (SCA3) patients. For good recognition of neurodegeneration and rare aggregates, we employed 100 µm PEG embedded brainstem sections, which were immunostained with the 1C2 antibody, targeted at polyQ expansions, or with an antibody against p62, a reliable marker of protein aggregates. Brainstem areas were scored semiquantitatively for neurodegeneration, severity of granular cytoplasmic staining (GCS) and frequency of neuronal nuclear inclusions (NNI). SCA2 and SCA3 tissue exhibited the same aggregate types and similar staining patterns. Several brainstem areas showed statistically significant differences between disease groups, whereby SCA2 showed more severe GCS and SCA3 showed more numerous NNI. We observed a positive correlation between GCS severity and neurodegeneration in SCA2 and SCA3 and an inverse correlation between the frequency of NNI and neurodegeneration in SCA3. Although their respective disease proteins are unrelated, SCA2 and SCA3 showed the same aggregate types. Apparently, the polyQ sequence alone is sufficient as a driver of protein aggregation. This is then modified by protein context and intrinsic properties of neuronal populations. The severity of GCS was the best predictor of neurodegeneration in both disorders, while the inverse correlation of neurodegeneration and NNI in SCA3 tissue implies a protective role of these aggregates.

Involvement of the Cerebellum in Parkinson Disease and Dementia with Lewy Bodies

Brains from patients with Parkinson disease or dementia with Lewy bodies show aggregation of alpha‐synuclein in precerebellar brainstem structures. Furthermore, patients exhibit resting tremor, unstable gait, and impaired balance, which may be associated with cerebellar dysfunction. Therefore, we screened the cerebella of 12 patients with alpha‐synucleinopathies for neuropathological changes. Cerebellar nuclei and neighboring white matter displayed numerous aggregates, whereas lobules were mildly affected. Cerebellar aggregation pathology may suggest a prionlike spread originating from affected precerebellar structures, and the high homogeneity between patients with dementia with Lewy bodies and Parkinson disease shows that both diseases likely belong to the same neuropathological spectrum. Ann Neurol 2017;81:898–903

First patho-anatomical investigation of the brain of a SCA19 patient

Spinocerebellar ataxia type 19 (SCA19) is a very recently characterized, rare, autosomal dominantly inherited spinocerebellar ataxia (SCA) that was initially described in a Dutch pedigree [1]. Until recently, no neuropathological studies have been performed on SCA19 tissue. In this article we describe the neuropathology of the first SCA19 patient brain available for post mortem analysis. The SCAs are a clinically, neuropathologically and genetically heterogeneous group of comparatively rare, autosomal-dominantly inherited cerebellar ataxias (ADCA) [2]. Primary disease symptoms include cerebellar ataxia, dysarthria and oculomotor symptoms, while secondary symptoms (e.g. Parkinsonism, dysphagia, retinal degeneration, psychiatric symptoms, dysfunction of touch, sight, hearing and proprioception) vary depending on the genetic SCA subtype [2]. SCA19 was initially described in 2001 in a Dutch pedigree spanning four generations with 12 gene carriers as an ADCA with normal life expectancy [1]. Affected patients initially exhibited periodic attacks of ataxia and dizziness, sometimes coupled with dysarthria, which progressed slowly into a chronic cerebellar syndrome with late involvement of the upper limbs. Additionally, patients displayed oculomotor dysfunction (that is, nystagmus, saccadic smooth pursuits and dysmetric saccades). Rarely present were slow tremor of the head, neck and arms, peripheral neuropathy or abnormal motor and sensory nerve conduction [3]. Relatively early in the disease course, patients also exhibited psychiatric symptoms (that is, mood swings and impulsive behaviour), as well as impaired learning and poor performance at the Wisconsin card sorting test, which is indicative of frontal lobe dysfunction [4]. The patients’ IQ and their performance at the Mini-Mental State Examination (MMSE), a standard psychiatric test to assess the severity of cognitive impairment in dementing syndromes, were only slightly below average and still in the normal range [3,4]. SCA19 was first linked to the chromosomal locus 1p21-q2, and later shown to be caused by mutations in the KCND3 gene situated in this region [5,6]. This gene encodes the Kv4.3 voltage-gated potassium channel which is expressed at specific locations in the brain, including the hippocampus (CA1 interneurones, CA2 and 3 pyramidal cells, dentate gyrus: granule cells), cerebellum (molecular layer interneurones, Purkinje cells and granule cells), pars compacta of the substantia nigra and raphe nuclei. Mutations (that is, M373I, S390N, T352P) in this gene can affect the stability, activity and/or localization of the Kv4.3 protein [7–10]. The different mutations lead to minor differences in the SCA19 phenotype and may be correlated with the disease severity and age of onset [8]. Interestingly, another spinocerebellar ataxia, SCA22, which was originally described as a separate clinical entity with a slightly different phenotype, is caused by a different set of mutations in the KCND3 gene [9]. As of yet little is known about the brain pathology of SCA19. In vivo magnetic resonance imaging (MRI) scans showed pronounced volume loss of the cerebellar hemispheres coupled with moderate involvement of the vermis and, in two out of seven patients of the index pedigree, minor involvement of the cerebrum (frontal cortex, white matter lesions) [1,3]. The index patient of this study was a member of the Dutch pedigree in which the SCA19 phenotype was initially described (patient IV-4) [1]. She manifested initial symptoms of SCA19 at age 30, which progressed slowly until her death at age 94. Her father, three siblings and her son were also affected by the disease. She exhibited major symptoms of SCA19, including gait, stance and limb ataxia, dysarthria and oculomotor dysfunctions. Her upper limb, knee and ankle reflexes were decreased, as was her sense of vibration. Her MMSE test results were within the normal range (25/29 at age 87), but she exhibited learning deficits, moderate depression and impaired visuospatial memory. MRI scans disclosed mild atrophy in the cerebellar hemispheres and the frontal cortex [3,4]. A single study of selected cerebellar sections revealed loss of cerebellar Purkinje cells [8]. In the present investigation we studied the brain of the index patient, along with the brains from five individuals without medical histories of neuropsychiatric disease

Huntington's Disease (HD): Degeneration of Select Nuclei, Widespread Occurrence of Neuronal Nuclear and Axonal Inclusions in the Brainstem: The Brainstem in Huntington's Disease

Huntingtons disease (HD) is a progressive polyglutamine disease that leads to a severe striatal and layer‐specific neuronal loss in the cerebral neo‐and allocortex. As some of the clinical symptoms (eg, oculomotor dysfunctions) suggested a degeneration of select brainstem nuclei, we performed a systematic investigation of the brainstem of eight clinically diagnosed and genetically confirmed HD patients. This post‐mortem investigation revealed a consistent neuronal loss in the substantia nigra, pontine nuclei, reticulotegmental nucleus of the pons, superior and inferior olives, in the area of the excitatory burst neurons for horizontal saccades, raphe interpositus nucleus and vestibular nuclei. Immunoreactive intranuclear neuronal inclusions were present in all degenerated and apparently spared brainstem nuclei and immunoreactive axonal inclusions were observed in all brainstem fiber tracts of the HD patients. Degeneration of brainstem nuclei can account for a number of less well‐understood clinical HD symptoms (ie, cerebellar, oculomotor and vestibular symptoms), while the formation of axonal aggregates may represent a crucial event in the cascades of pathological events leading to neurodegeneration in HD.

Polyglutamine aggregation in Huntington's disease and spinocerebellar ataxia type 3: similar mechanisms in aggregate formation: Polyglutamine aggregation in SCA3 and Huntington's disease

Polyglutamine (polyQ) diseases are characterized by the expansion of a polymorphic glutamine sequence in disease‐specific proteins and exhibit aggregation of these proteins. This is combated by the cellular protein quality control (PQC) system, consisting of chaperone‐mediated refolding as well as proteasomal and lysosomal degradation pathways. Our recent study in the polyQ disease spinocerebellar ataxia type 3 (SCA3) suggested a distinct pattern of protein aggregation and PQC dysregulation.