Down syndrome (DS), the most common genetic cause of mental retardation, is characterized by reduced number of neurons and delayed myelination. Though non-neuronal cells in the brain are vital for the development, survival, and function of neurons, there is a paucity of comparative studies of normal development and DS, in particular in the temporal lobe, a region of interest for cognitive decline. We evaluated immunoreactivity for CD68 (macrophage), HLA-DR (microglia), Olig2 and TPPP/p25 (oligodendroglia), and GFAP (astroglia) in the germinal matrix (GM), temporal lobe white matter (TeWM) and hippocampus from 14 weeks of gestations to newborn in 28 DS patients and 30 age-matched controls. The rate of increase of CD68 positive cells in the GM, CA1 hippocampal subregion and subiculum was significantly higher in DS. The density of Olig2 positive cells in the GM was lower in DS brains at early stages, then showed a transient increase contrasting controls. Olig2 expression increased more in the TeWM in DS, suggesting an altered pattern of oligodendrocyte progenitor generation. GFAP-immunoreactivity in DS was significantly lower in the middle pregnancy period in the TeWM and did not increase between early and middle periods in the GM compared to controls, likely reflecting a defect in astrocyte production. The altered expression of non-neuronal cell markers during normal development and DS may play a role in, or reflect, defective neurogenesis, leading to reduced number of neurons and delayed myelination in the developing DS brain. This has implications for the understanding of the mental retardation in DS patients.
Down’s syndrome (DS) is characterized by intellectual disabilities and Alzheimer-type dementia. Cystathionine-β synthase (CBS) plays a role in the production of hydrogen sulfide (H2S) in the brain and is encoded by a gene which is localized in the DS critical region of chromosome 21. The expression of CBS was compared during development and aging. Therefore, cerebri (temporal lobe) and cerebelli from fetuses and adults were studied in 22 normal controls and 21 DS patients using immunohistochemical methods. During normal development, CBS-positive astrocytes appeared in the cortical layer at 14 weeks of gestation (GW), remained elevated until 34 GW and decreased slightly during the infantile period (1–11 months of age). A few CBS-positive neurons were transiently found in the deep cortical layer only at 35 GW. In the cerebellum, CBS-positive Bergmann glial cells were found from 26 GW to adulthood in both controls and DS patients. In DS, there were greater numbers of CBS-positive astrocytes, situated predominantly in granular cell layers II and IV, compared to the controls. In addition, CBS-positive astrocytes were also increased around senile plaques in adults with DS. The high level of CBS in the granular cell layers in DS may be related to an abnormal development of inhibitory neurons and may be responsible for the pathogenesis of intellectual disability, while the increased CBS observed in adult DS may be related to the pathogenesis of Alzheimer-type dementia.
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