Mitochondrial membrane permeabilisation by amyloid aggregates and protection by polyphenols

Alzheimer's disease and Parkinson's disease are neurodegenerative disorders characterised by the misfolding of proteins into soluble prefibrillar aggregates. These aggregate complexes disrupt mitochondrial function, initiating a pathophysiological cascade leading to synaptic and neuronal degeneration. In order to explore the interaction of amyloid aggregates with mitochondrial membranes, we made use of two in vitro model systems, namely: (i) lipid vesicles with defined membrane compositions that mimic those of mitochondrial membranes, and (ii) respiring mitochondria isolated from neuronal SH-SY5Y cells. External application of soluble prefibrillar forms, but not monomers, of amyloid-beta (Aβ42 peptide), wild-type α-synuclein (α-syn), mutant α-syn (A30P and A53T) and tau-441 proteins induced a robust permeabilisation of mitochondrial-like vesicles, and triggered cytochrome c release (CCR) from isolated mitochondrial organelles. Importantly, the effect on mitochondria was shown to be dependent upon cardiolipin, an anionic phospholipid unique to mitochondria and a well-known key player in mitochondrial apoptosis. Pharmacological modulators of mitochondrial ion channels failed to inhibit CCR. Thus, we propose a generic mechanism of thrilling mitochondria in which soluble amyloid aggregates have the intrinsic capacity to permeabilise mitochondrial membranes, without the need of any other protein. Finally, six small-molecule compounds and black tea extract were tested for their ability to inhibit permeation of mitochondrial membranes by Aβ42, α-syn and tau aggregate complexes. We found that black tea extract and rosmarinic acid were the most potent mito-protectants, and may thus represent important drug leads to alleviate mitochondrial dysfunction in neurodegenerative diseases.

Granulocyte colony stimulating factor (GCSF) improves memory and neurobehavior in an amyloid-β induced experimental model of Alzheimer's disease

GCSF is an endogenous neuronal hematopoietic factor that displays robust in vitro and in vivo neuroprotective activity. The present study aimed to evaluate the effect of GCSF on Aβ-induced memory loss in an Alzheimer's disease model of rats. A total of 42 male adult Wistar rats weighing 200-250 g were used in the study and were divided into 7 experimental groups. Animals were subjected to intracerebroventricular (ICV) injection stereotaxically at day 0 to instill amyloid-β(1-42) (Aβ(1-42)) or PBS (sham operated group) at 10 μl (5 μl bilaterally). GCSF treatment was given from day 7 to 12 of Aβ injection. On day 21, behavioral tests (short term memory, exploratory behavior and motor coordination) in all groups were evaluated. Biochemical parameters and RNA expression were measured to ensure the efficacy of GCSF. GCSF (35 and 70 μg/kg, s.c.) showed statistically significant improvement in memory as compared to control and sham operated groups (p<0.05). Mean time spent in the platform placed quadrant was found to be significantly increased in the GCSF (70 μg/kg, s.c.) as compared to GCSF (35 μg/kg, s.c.) and GCSF (10 μg/kg, s.c.) groups (p<0.001). GCSF (35 and 70 μg/kg, s.c.) also improved motor coordination and exploratory behavior significantly as compared to naïve sham operated and GCSF (10 μg/kg, s.c.) groups (p<0.05). Improvement in memory by GCSF (35 and 70 μg/kg, s.c.) was coupled with marked reduction of lipid peroxidation, acetylcholinesterase levels and a significant increase in antioxidant enzymes as well as total RNA expression in the brain. Additionally, GCSF (35 and 70 μg/kg, s.c.) significantly increased progenitor cells (iPSCs) and surface marker CD34+ in the brain and hence induced neurogenesis. The present findings demonstrate an improvement of memory and neurobehavioral function with GCSF in Aβ-induced Alzheimer's disease model in rats.