Investigating the role of glial cells in neurodegenerative disorders by depleting astrocytes and oligodendrocytes in a model of amyloid-beta induced cytotoxicity in organotypic hippocampal slice cultures
The etiology of Alzheimer’s disease, the most common cause of dementia, is still under debate. On the molecular level, AD is characterized by the accumulation of the beta-Amyloid protein as well as neurofibrillary tangles. Additionally, evidence pinpoints to a crucial role of inflammatory processes in the progression of the disease. The cellular mechanisms leading to neuroinflammation and neuronal death observed in Alzheimer’s disease are still unclear.
It has long been thought that the immune system of the brain is unique and separated from the blood and the remaining organism by the blood brain barrier. Actually, the central nervous system has a special set of defence mechanisms against pathogens and invaders that is distinct from the innate or adaptive immune system. Important players of this defence system are glial cells. Glial cells are non-neuronal cells that are subdivided into three cell types, including microglia, astrocytes and oligodendrocytes, with different modes of action and function. Astrocytes and microglia actively take part in the defence process, whereas oligodendrocytes seem to have a more supportive function. To understand and characterize the role of glial cells in neuroinflammatory processes, it is crucial to establish a model system that displays the pathology of Alzheimer’s disease and allows the individual study of cells. It was already shown that microglia could successfully be depleted using the bisphosphate clodronate from organotypic hippocampal slice cultures. However, there is still a lack of a system to study the individual role of astrocytes and oligodendrocytes ex vivo. Here, two different approaches were tested on their ability to be useful in ablation studies of astrocytes and oligodendrocytes in vitro and ex vivo. For in vitro studies primary derived cells from either embryonic or postnatal mice were used. Ex vivo studies were exerted on murine organotypic hippocampal slice cultures that in general serve as an excellent model system to study cell to cell interactions and communications. The depletion of astrocytes by antibody-toxin conjugates was promising in vitro but lacking efficacy ex vivo. The cell surface transporter GLAST-1 was found to be a promising candidate, since internalization signals were strongest and treatment of slices responded in a concentration-dependent manner. Treatment of slices with the L-alpha-aminoadipic acid led to depletion of astrocytes and provides evidence for their impor-tance in maintaining cytoarchitecture and thereby influenc-ing the viability of neuronal cells. Antibody-toxin conjugates were also used for the ablation of Oli-neu cells in vitro. Among them, a combination containing the antibody against the cell surface protein Claudin-11 showed greater effects on the viability than the combination of the receptor antibody GPR17. The underlying processes for the internalization are of great interest since this method could be further developed for drug-delivery studies to different specific cells. This method could lead to a broader spectrum of ways for drug-targeting as it is used in cancer treatment
