Astrocytic changes with aging and Alzheimer's disease‐type pathology in chimpanzees

Abstract

Astrocytes are the main homeostatic cell of the central nervous system. In addition, astrocytes mediate an inflammatory response when reactive to injury or disease known as astrogliosis. Astrogliosis is marked by an increased expression of glial fibrillary acidic protein (GFAP) and cellular hypertrophy. Some degree of astrogliosis is associated with normal aging and degenerative conditions such as Alzheimer's disease (AD) and other dementing illnesses in humans. The recent observation of pathological markers of AD (amyloid plaques and neurofibrillary tangles) in aged chimpanzee brains provided an opportunity to examine the relationships among aging, AD‐type pathology, and astrocyte activation in our closest living relatives. Stereologic methods were used to quantify GFAP‐immunoreactive astrocyte density and soma volume in layers I, III, and V of the prefrontal and middle temporal cortex, as well as in hippocampal fields CA1 and CA3. We found that the patterns of astrocyte activation in the aged chimpanzee brain are distinct from humans. GFAP expression does not increase with age in chimpanzees, possibly indicative of lower oxidative stress loads. Similar to humans, chimpanzee layer I astrocytes in the prefrontal cortex are susceptible to AD‐like changes. Both prefrontal cortex layer I and hippocampal astrocytes exhibit a high degree of astrogliosis that is positively correlated with accumulation of amyloid beta and tau proteins. However, unlike humans, chimpanzees do not display astrogliosis in other cortical layers. These results demonstrate a unique pattern of cortical aging in chimpanzees and suggest that inflammatory processes may differ between humans and chimpanzees in response to pathology.

Questions and (some) answers on reactive astrocytes

“…The human aging brain displays higher GFAP immunoreactivity and mRNA levels [see references in (Munger et al, )], and it was assumed that aging causes progressive astrocyte reaction. But, this idea is not consensual (see Table ).…”

Plasma glial fibrillary acidic protein detects Alzheimer pathology and predicts future conversion to Alzheimer dementia in patients with mild cognitive impairment

“…Aβ plaques cause astrogliosis, i.e., functional and morphological changes in the surrounding astrocytes, which are glial cells involved in brain signaling, modulation of synapses, transport of nutrients, homeostasis, and structural support [3,4]. Animal and cell studies have shown the presence of astrogliosis around Aβ plaques and the involvement of reactive astrocytes in Aβ production and toxicity [5][6][7][8]. Studies conducted with PET tracers targeting astrocytes have shown that astrogliosis is an early feature in the pathological cascade of AD, which decreases over the course of disease as opposed to the increase of Aβ plaque load [9][10][11].…”

Plasma Glial Fibrillary Acidic Protein Detects Alzheimer Pathology and Predicts Future Conversion to Alzheimer Dementia in Patients With Mild Cognitive Impairment

“…functional and morphological changes in the surrounding astrocytes, glial cells involved in brain signaling, modulation of synapses, transport of nutrients, homeostasis and structural support (3,4). Animal and cell studies have shown the presence of astrogliosis around Aβ plaques and the involvement of reactive astrocytes in Aβ production and toxicity (5)(6)(7)(8). Studies conducted with PET tracers targeting astrocytes have shown that astrogliosis is an early feature in the pathological cascade of AD, which decreases over the course of disease as opposed to the increase of Aβ plaque load (9)(10)(11).…”