A Mitochondrial Role of SV2a Protein in Aging and Alzheimer's Disease: Studies with Levetiracetam.

Aberrant neuronal network activity associated with neuronal hyperexcitability seems to be an important cause of cognitive decline in aging and Alzheimer's disease (AD). Out of many antiepileptics, only levetiracetam improved cognitive dysfunction in AD patients and AD animal models by reducing hyperexcitability. As impaired inhibitory interneuronal function, rather than overactive neurons, seems to be the underlying cause, improving impaired neuronal function rather than quieting overactive neurons might be relevant in explaining the lack of activity of the other antiepileptics. Interestingly, improvement of cognitive deficits by levetiracetam caused by small levels of soluble Aß was accompanied by improvement of synaptic function and plasticity. As the negative effects of Aß on synaptic plasticity strongly correlate with mitochondrial dysfunction, wehypothesized that the effect of levetiracetam on synaptic activity might be raised by an improved mitochondrial function. Accordingly, we investigated possible effects of levetiracetam on neuronal deficits associated with mitochondrial dysfunction linked to aging and AD. Levetiracetam improved several aspects of mitochondrial dysfunction including alterations of fission and fusion balance in a cell model for aging and early late-onset AD. We demonstrate for the first time, using immunohistochemistry and proteomics, that the synaptic vesicle protein 2A (SV2a), the molecular target of levetiracetam, is expressed in mitochondria. In addition, levetiracetam shows significant effect on the opening of the mitochondrial permeability transition pore. Importantly, the effects of levetiracetam were significantly abolished when SV2a was knockdown using siRNA. In conclusion, interfering with the SV2a protein at the mitochondrial level and thereby improving mitochondrial function might represent an additional therapeutic effect of levetiracetam to improve symptoms of late-onset AD.

Characterization of common and distinctive adjustments of wild barley leaf proteome under drought acclimation, heat stress and their combination.

In nature, plants are often exposed to combinations of different stresses at the same time, while in many laboratory studies of molecular stress induction phenomena, single stress responses are analyzed. This study aims to identify the common (i.e. more general stress-responsive) and the stress-specific adjustments of the leaf proteome of wild barley to two often co-occurring stress phenomena, i.e. in response to (long-term) drought acclimation (DA) or to (transient) heat stress (HS). In addition, we analyzed those alterations which are specific for the combination of both stresses. Leaf proteome analysis was performed using 2D difference gel electrophoresis followed by protein identification via mass spectrometry with a 1.5 threshold value of changes in relative protein contents. DA resulted in specific upregulation of proteins with cell detoxification functions, water homeostasis maintenance, amino acids synthesis and lipid metabolism and distinct forms of heat shock proteins (HSPs) and proteins with chaperon functions while proteins related to nitrogen metabolism were downregulated. This response was distinguished from the response to transient HS, which included upregulation of a broad range of HSP products. The common response to both stressors revealed upregulation of additional forms of HSPs and the downregulation of enzymes of the photosynthetic apparatus and chlorophyll binding proteins. The simultaneous exposure to both stress conditions resulted mostly in a combination of both stress responses and to unique abundance changes of proteins with yet unclear functions.