Mitochondria and Alzheimer’s Disease: An Electron Microscopy Study

Alzheimer’s disease is a progressive, irreversible presenile or senile neurodegenerative disorder, implicating mainly the mental faculties, characterized by decline of memory and judgment, learning impairment, loss of professional skills and verbal capacities, alterations of social behavior, decline of motor skills and eventual disarrangement of the autonomic equilibrium. Among the pathogenetic factors, oxidative stress and mitochondrial dysfunction may play an essential role. Alterations of mitochondria may enhance amyloid toxicity, which in turn may aggravate mitochondrial dysfunction. We describe ultrastructural alterations of mitochondria in the soma of neurons, in axons, dendritic profiles and synaptic terminals, in astrocytes in early cases of Alzheimer’s disease on various areas of the cerebral and the cerebellar cortex, the hippocampus, the hypothalamus, the mammillary bodies and the medial geniculate body. The morphological and morphometric study of the mitochondria revealed an impressive polymorphism at any area of the brain. The mitochondria demonstrated variation of size and shape, fragmentation of the cristae and marked changes of their structure. The most dramatic mitochondrial alterations were observed in dendritic profiles, spines and synaptic terminals. A substantial number of astrocytes demonstrated mitochondrial alterations, which coexisted with fragmentation of Golgi apparatus and dilatation of the cisternae of the smooth endoplasmic reticulum. On the basis of our observations, we feel that therapeutic strategies aiming at protecting the mitochondria might be beneficial in the treatment of early cases of AD

Mitochondria in the Cerebral and Cerebellar Cortex in Alzheimer’s Disease, Target for a Therapeutic Approach

Alzheimer’s disease remains the main cause of dementia in advanced age worldwide. Among the etiopathological background of the disease mitochondrial alterations may play a crucial role, given that they are closely related to metabolic and energy deficiency in neurons, glia, and endothelial cells in Alzheimer’s disease and other neurodegenerative disorders. In a series of morphological and morphometric studies of mitochondria in the cerebrum and the cerebellar cortex in Alzheimer’s disease, by electron microscopy, we described marked morphological and morphometric alterations. The most frequent ultrastructural alterations of the mitochondria consist of disruption of the cristae, accumulation of osmiophilic material, and marked changes of shape and size in comparison with the normal controls. Mitochondrial alterations were particularly prominent in dendritic profiles and dendritic spines. The ultrastructural study of a substantial number of neurons in the cerebellum revealed that mitochondrial alterations do not coexist, as a rule, with the typical Alzheimer’s pathology, such as cytoskeletal alterations, amyloid deposits, and tau pathology, though they are frequently observed coexisting with alterations of the cisternae of the Golgi apparatus. Therapeutical regimes targeting mitochondria may be beneficial in early cases of Alzheimer’s disease

Pericytes of the Brain in Demyelinating Conditions

The pericytes play a very important role in the central nervous system (CNS), concerning the formation of the functional neurovascular unit, serving as a substantial component in the development and maintenance of the stability of the blood-brain barrier (BBB). Besides, as pluripotent cells of neuroectodermal origin, the pericytes participate in autoimmune reactions and modulations, controlling the penetration of immune cells via BBB and playing an active role in lymphocytic trafficking and functional regulation, via cytokine secretion and activation. In demyelinating conditions, they participate in the restoration of the myelin sheath by modulating oligodendrocytes and stimulating the differentiation of oligodendrocyte progenitors. In the experimental model of allergic encephalomyelitis (EAE), electron microscopy reveals the proliferation and the morphological alterations of the pericytes as well as their interactions with endothelial cells and astrocytes, thus underlining the crucial role that pericytes play in the integrity of the BBB and the immune reactions of the CNS

The Hypothalamus in Alzheimer’s Disease

Alzheimer’s disease is a progressive, irreversible neurodegenerative disorder, characterized by gradual decline of mental faculties, including learning capacity, emotional and behavioral alterations, serious decline of motor skills, and dysfunction of the autonomic nervous system with disruption of circadian rhythms. Among the potential modifiable risk factors, diabetes and obesity may play a considerable role in the pathogenetic background of the disease. We describe some of the morphological alterations of the hypothalamic nuclei in early cases of Alzheimer’s disease, using silver impregnation techniques and electron microscopy. The morphological and morphometric study revealed substantial decrease of the neuronal population, which was particularly marked in the suprachiasmatic, the supraoptic, and the paraventricular nuclei of the hypothalamus. The silver staining demonstrated an obvious shortage of the dendritic arborization of neurons, associated with marked spinal pathology and axonal dystrophy. It must be underlined that Alzheimer’s pathology, such as neuritic plaques and neurofibrillary degeneration, was minimal in the hypothalamus in comparison with other cortical and subcortical areas of the brain. Mitochondrial alterations and fragmentation of Golgi complex were observed by electron microscopy in a substantial number of neurons and astrocytes in the hypothalamic nuclei. The hypothalamic pathology may be related to instability of autonomic regulation which occurs gradually in Alzheimer’s disease

DENDRITIC AND SPINAL PATHOLOGY OF THE PURKINJE CELLS FROM THE HUMAN CEREBELLAR VERMIS IN ALZHEIMER’S DISEASE

Background: Alzheimer’s disease constitutes one of the main causes of dementia. It is clinically characterized by memory impairment, deterioration of intellectual faculties and loss of professional skills. Furthermore changes in equilibrium and limb coordination are clinically demonstrable in persons with Alzheimer’s disease. In the present study we tried to figure out possible changes of the Purkinje cells in Alzheimer’s disease brains. Subjects and methods: We studied the Purkinje cells from the vermis of the cerebellum in 5 Alzheimer’ disease brains Golgi technique. Results: In the Purkinje cells from the inferior surface of the cerebellar hemispheres severe dendritic and spinal pathology consisting of loss of distal dendritic segments and alterations of dendritic spine morphology can be noticed in Alzheimer’s disease brains. Conclusions: The morphological and morphometric estimation of the dendrites and the dendritic spines of the Purkinje cells from the inferior surface of the cerebellar hemispheres in Alzheimer’s disease brains revealed substantial alterations of the dendritic arborization and marked loss of the dendritic spines, which may be related to cognitive impairment and motor deficits in Alheimer’s disease

Unraveling the Possible Routes of SARS-COV-2 Invasion into the Central Nervous System

Purpose of Review: To describe the possible neuroinvasion pathways of Severe Acute Respiratory Syndrome-related Coronavirus-2 (SARS-CoV-2), the virus responsible for the Coronavirus disease-19 (Covid-19) pandemic. Recent Findings: We present data regarding the family of Coronaviruses (CoVs) and the central nervous system (CNS), and describe parallels between SARS-CoV-2 and other members of the family, which have been investigated in more depth and combine these findings with the recent advancements regarding SARS-CoV-2. Summary: SARS-CoV-2 like other CoVs is neuroinvasive, neurotropic and neurovirulent. Two main pathways of CNS penetration seem to be the strongest candidates, the hematogenous and the neuronal. Τhe olfactory route in particular appears to play a significant role in neuroinvasion of coronaviruses and SARS-CoV-2, as well. However, existing data suggest that other routes, involving the nasal epithelium in general, lymphatic tissue and the CSF may also play roles in SARS-CoV-2 invasion into the CNS

Mitochondria Are Related to Synaptic Pathology in Alzheimer's Disease

Morphological alterations of mitochondria may play an important role in the pathogenesis of Alzheimer's disease, been associated with oxidative stress and Aβ-peptide-induced toxicity. We proceeded to estimation of mitochondria on electron micrographs of autopsy specimens of Alzheimer's disease. We found substantial morphological and morphometric changes of the mitochondria in the neurons of the hippocampus, the neocortex, the cerebellar cortex, the thalamus, the globus pallidus, the red nucleus, the locus coeruleus, and the climbing fibers. The alterations consisted of considerable changes of the cristae, accumulation of osmiophilic material, and modification of the shape and size. Mitochondrial alterations were prominent in neurons, which showed a depletion of dendritic spines and loss of dendritic branches. Mitochondrial alterations are not related with the accumulation of amyloid deposits, but are prominent whenever fragmentation of the Golgi apparatus exists. Morphometric analysis showed also that mitochondria are significantly reduced in neurons, which demonstrated synaptic pathology