Molecular and cellular preconditiong - powerful strategies for neuroprotection
Neuronal preconditioning describes a phenomenon that affords robust brain tolerance against neurodegenerative insults. This adaptive cytoprotection is a fundamental capability of living cells, allowing them to survive exposure to potentially recurrent stressors. The research of the molecular and cel...
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|Summary:||Neuronal preconditioning describes a phenomenon that affords robust brain tolerance against neurodegenerative insults. This adaptive cytoprotection is a fundamental capability of living cells, allowing them to survive exposure to potentially recurrent stressors. The research of the molecular and cellular signaling during this self-protecting process is an important tool to develop novel strategies for the treatment of diseases that are characterized by neuronal cell death, which causes progressive loss of brain tissue and function after acute brain injury and in chronic neurodegenerative diseases.
The major aim of this study was to investigate preconditioning effects in a model of neuronal cell death on the molecular and cellular level. This issue was addressed in immortalized mouse hippocampal HT-22 neurons exposed to glutamate toxicity, which selectively induces oxidative stress through glutathione depletion.
The first part of the present study investigates, whether the neuroprotective effect mediated by the depletion of the pro-apoptotic protein AIF is attributed to mitochondrial preconditioning. AIF is a mitochondrial protein that mediates caspase-independent cell death after translocation into the nucleus by chromatin condensation and large-scale DNA fragmentation. The findings of this study demonstrate that AIF gene silencing protects mitochondrial function and integrity in a paradigm of lethal oxidative stress in the used neural cell line. Depletion of AIF preserved mitochondrial morphology, mitochondrial membrane potential, and ATP levels after induction of oxidative stress in HT-22 cells, and this mitoprotective effect also significantly attenuated the secondary increase in lipid peroxidation which was associated with mitochondrial damage and cell death in this model system. Furthermore, AIF depletion was associated with reduced complex I expression levels, and similar to protective effects achieved by low doses of the complex I inhibitor rotenone. These results suggest for the first time that AIF silencing provides protection against oxidative cell death at the level of mitochondria by preconditioning and not at the level of apoptotic DNA damage in the nucleus.
The second part of this thesis investigated conditioned medium (CM), which was generated by neural progenitor cells (NPCs) that undergo starvation-induced apoptosis after growth factor withdrawal. It is well established that transplantation of stem/progenitor cells to the brain improve abnormal motor behavior and memory function in a broad spectrum of neurodegenerative diseases and after acute brain injury. However, stem cell-based therapy still holds many risks and unresolved issues regarding the mode of action and the optimal application. The validation of a CM from dying NPCs reflects the conditions after stem/progenitor cell injection since only very few cells survive after the transplantation. The findings of the present study clearly demonstrate that CM provides very potent, long-lasting, and stable neuroprotective effects that can even be further increased by heat activation. The data also indicate that cell lysis is essential for the generation of protective properties. Thus, the release of neuroprotective substances during the cell death of stem/progenitor cells seems to be a kind of cellular communication that protects neighboring cells and other tissues. Interestingly, a variety of proteins were identified as potential candidates that mediated the neuroprotective effect of CM, such as prdx-1 and gal-1. Further, the contribution of a low molecular weight cofactor was found. Thus, the results of these investigations are the basis for the development of a highly potent, standardized composition for the therapy of neurodegenerative diseases and acute brain injury.
In summary, the data from this thesis highlight the neuroprotective potential of preconditioning effects for the regulation of cell survival after neurodegenerative insults. In addition, they indicate the importance of understanding the underlying mechanisms to develop new strategies for the therapy of neurodegenerative diseases.|