Oligodendrocyte degeneration in AD

Apolipoprotein E ε4 Mediates Myelin Breakdown by Targeting Oligodendrocytes in Sporadic Alzheimer Disease

White matter degradation in the frontal lobe is one of the earliest detectable changes in aging and Alzheimer disease. The ε4 allele of apolipoprotein E (APOE4) is strongly associated with such myelin pathology but the underlying cellular mechanisms remain obscure. We hypothesized that, as a lipid transporter, APOE4 directly triggers pathology in the cholesterol-rich myelin sheath independent of AD pathology. To test this, we performed immunohistochemistry on brain tissues from healthy controls, sporadic, and familial Alzheimer disease subjects. While myelin basic protein expression was largely unchanged, in frontal cortex the number of oligodendrocytes (OLs) was significantly reduced in APOE4 brains independent of their Braak stage or NIA-RI criteria. This high vulnerability of OLs was confirmed in humanized APOE3 or APOE4 transgenic mice. A gradual decline of OL numbers was found in the aging brain without associated neuronal loss. Importantly, the application of lipidated human APOE4, but not APOE3, proteins significantly reduced the formation of myelinating OL in primary cell culture derived from Apoe-knockout mice, especially in cholesterol-depleted conditions. Our findings suggest that the disruption of myelination in APOE4 carriers may represent a direct OL pathology, rather than an indirect consequence of amyloid plaque formation or neuronal loss.

Protein-Induced Pluripotent Stem Cells Ameliorate Cognitive Dysfunction and Reduce Aβ Deposition in a Mouse Model of Alzheimer's Disease

Transplantation of stem cells into the brain attenuates functional deficits in the central nervous system via cell replacement, the release of specific neurotransmitters, and the production of neurotrophic factors. To identify patient‐specific and safe stem cells for treating Alzheimer's disease (AD), we generated induced pluripotent stem cells (iPSCs) derived from mouse skin fibroblasts by treating protein extracts of embryonic stem cells. These reprogrammed cells were pluripotent but nontumorigenic. Here, we report that protein‐iPSCs differentiated into glial cells and decreased plaque depositions in the 5XFAD transgenic AD mouse model. We also found that transplanted protein‐iPSCs mitigated the cognitive dysfunction observed in these mice. Proteomic analysis revealed that oligodendrocyte‐related genes were upregulated in brains injected with protein‐iPSCs, providing new insights into the potential function of protein‐iPSCs. Taken together, our data indicate that protein‐iPSCs might be a promising therapeutic approach for AD. Stem Cells Translational Medicine2017;6:293–305

Decreased oligodendrocyte nuclear diameter in Alzheimer's disease and Lewy body dementia

To better understand the pathogenesis of dementia, it is important to understand histopathologic changes in neurodegenerative diseases because they might highlight key aspects of the degenerative process. In this study, the nuclear diameter of neurons and oligodendrocytes in selected temporal lobe areas were determined in autopsy tissue sections from patients with Alzheimer's disease (AD), Lewy body dementia (LBD) and controls. Our morphometric studies targeted neurons in the CA4 region of the pyramidal cell layer of the hippocampus, neurons in the granular layer of the dentate gyrus and oligodendrocytes in parahippocampal white matter. Mean neuronal nuclear diameters were not different among the studied groups. However, our studies revealed a statistically significant reduction of mean oligodendrocyte nuclear diameter in AD and LBD relative to controls. The reduction of the mean nucleus diameter of oligodendrocytes in LBD was independent of the presence of associated AD pathology in LBD. These findings for the first time identify decreased oligodendrocyte nucleus diameter as a morphologic feature of AD and LBD and may lead to a better understanding of the role of oligodendrocytes in AD and LBD pathogenesis.

Demyelination, astrogliosis, and accumulation of ubiquitinated proteins, hallmarks of CNS disease in hsf1-deficient mice

The heat shock transcription factors (Hsfs) are responsible for the heat shock response, an evolutionarily conserved process for clearance of damaged and aggregated proteins. In organisms such as Caenorhabditis elegans, which contain a single Hsf, reduction in the level of Hsf is associated with the appearance of age-related phenotypes and increased accumulation of protein aggregates. Mammalian cells express three hsfs (hsf1, hsf2, hsf4) and their role in CNS homeostasis remains unclear. In this study, we examined the effects of deletion of single or multiple hsf genes in the CNS using mutant mice. Our results show that hsf1-/- mice display progressive myelin loss that accompanies severe astrogliosis and this is exacerbated in the absence of either the hsf2 or hsf4 gene. Magnetic resonance imaging and behavioral studies indicate reduction in the white matter tracts of the corpus callosum, and deficiencies in motor activity, respectively, in aged hsf1-/- mice. Concomitantly, hsf1-/- aged CNS exhibit increased activated microglia and apoptotic cells that are mainly positive for GFAP, an astrocyte-specific marker. Studies based on the expression of short-lived ubiquitinated green fluorescent protein (GFPu) in living hsf1-/- cells indicate that they exhibit reduced ability to degrade ubiquitinated proteins, accumulate short-lived GFPu, and accumulate aggregates of the Huntington's model of GFP containing trinucleotide repeats (Q103-GFP). Likewise, hsf1-/- brain and astrocytes exhibit higher than wild-type levels of ubiquitinated proteins, increased levels of protein oxidation, and increased sensitivity to oxidative stress. These studies indicate a critical role for mammalian hsf genes, but specifically hsf1, in the quality control mechanisms and maintenance of CNS homeostasis during the organism's lifetime.

Neuroglia in the inferior olivary nucleus during normal aging and Alzheimer's disease

It is likely that neuronal loss occurs in certain brain regions in Alzheimer's Disease (AD) without any neurofibrillary pathology. In the human principle inferior olivary nucleus (PO), we have shown that neuronal loss is about 34% (Lasn et al. Journal of Alzheimer Disease, 2001; 3: 159–168), but the fate of the neuroglial cells is unknown. Since the unique network of neurons and neuroglial cells and their cohabitation are essential for normal functioning of CNS, we designed a study to estimate the total number of oligodendrocytes and astrocytes in normally aged and AD brains. The study is based on 10 control and 11 AD post-mortem human brains. An unbiased stereological fractionator method was used. We found significant oligodendroglial cell loss (46%) in AD as compared to control brains, while the total number of astrocytes showed a tendency to decrease. It is likely that the ratio of oligodendroglial cells to neurons remains unchanged even in degenerative states, indicating that oligodendroglial cells parallel neuronal loss. Astroglial cells did not increase in total number, but the ratio to neurons was significantly increased due to the neuronal loss. Using a novel unbiased quantitative method, we were able to describe significant oligodendroglial loss in the PO but the pathogenic mechanism behind remains unknown.

Nogo-A expression in the human hippocampus in normal aging and in Alzheimer disease

Myelin-associated proteins are involved in the formation and stabilization of myelin sheaths. In addition, they prevent axon regeneration and plasticity in the adult brain. Recent evidence suggests that the expression of certain myelin-associated proteins (e.g. Nogo-A) can be regulated by synaptic activity or by over-expression after neural lesions in brain syndromes such as temporal lobe epilepsy. However, no studies on Alzheimer disease (AD) have been reported in which cell loss and significant synaptic reorganization occurs. In the present study, we analyze in detail the expression of Nogo-A in the hippocampal formation in normal human aging and in AD. Our results indicate that Nogo-A is expressed by oligodendrocytes and neurons in the aged hippocampal formation. In addition, both granule cells and mossy fiber connections are also labeled in the old-aged hippocampi. Interestingly, Nogo-A is over-expressed by hippocampal neurons in AD and is associated with beta-amyloid deposits in senile plaques. Taken together, our results reinforce the hypothesis that Reticulon proteins such as Nogo-A participate in the neuronal responses stemming from hippocampal formation during senescence, and particularly in AD. These findings also indicate that Reticulon proteins could be considered as new putative drug targets in therapies of neurodegenerative disorders.

White matter mapping in Alzheimer's disease: A neuropathological study

White matter disease (WMD) with pervasive non-focal subtotal tissue loss is frequently seen in Alzheimer's disease (AD) upon neuropathological examination. Although WMD has varying effects on AD symptoms, accurate clinical detection is difficult due partly to scarcity of correlative structural imaging and histopathological studies. Neuropathological studies of WMD severity and distribution have been conducted earlier using semi-quantitative methods. A technique for quantifying WMD objectively in large white matter areas, based on optical density (OD) measurements on images of scanned whole-brain sections, was developed and was validated using conventional microscopic assessment. Altogether, 16 AD cases with concomitant WMD (AD-WMD) and 9 cases of AD without WMD (AD-only) were analysed. The OD values correlated significantly with the neuropathological severity of WMD and were significantly lower in AD-WMD than in AD-only in frontal, frontoparietal, temporal and parietal white matter but not in the occipital white matter, the frontal OD difference being greatest. Useful baseline information on WMD distribution in AD to relate to in vivo imaging results was obtained.

Dopamine D2 and D3 receptor agonists limit oligodendrocyte injury caused by glutamate oxidative stress and oxygen/glucose deprivation

Dopamine receptor activation is thought to contribute adversely to several neuropathological disorders, including Parkinson's disease and schizophrenia. In addition, dopamine may have a neuroprotective role: dopamine receptor agonists are reported to protect nerve cells by virtue of their antioxidant properties as well as by receptor-mediated mechanisms. White matter injury can also be a significant factor in neurological disorders. Using real-time RT-PCR, we show that differentiated rat cortical oligodendrocytes express dopamine D2 receptor and D3 receptor mRNA. Oligodendrocytes were vulnerable to oxidative glutamate toxicity and to oxygen/glucose deprivation injury. Agonists for dopamine D2 and D3 receptors provided significant protection of oligodendrocytes against these two forms of injury, and the protective effect was diminished by D2 and D3 antagonists. Levels of oligodendrocyte D2 receptor and D3 receptor protein, as measured by Western blotting, appeared to increase following combined oxygen and glucose deprivation. Our results suggest that dopamine D2 and D3 receptor activation may play an important role in oligodendrocyte protection against oxidative glutamate toxicity and oxygen-glucose deprivation injury.