Unique Properties of Synaptosomes and Prospects for Their Use for the Treatment of Alzheimer's Disease.

Alzheimer's disease (AD) is a severe neurodegenerative condition affecting millions worldwide. Prevalence of AD correlates with increased life expectancy and aging population in the developed countries. Considering that AD is a multifactorial disease involving various pathological processes such as synaptic dysfunction, neuroinflammation, oxidative stress, and improper protein folding, a comprehensive approach targeting multiple pathways may prove effective in slowing the disease progression. Cellular therapy and its further development in the form of cell vesicle and particularly mitochondrial transplantation represent promising approaches for treating neurodegeneration. The use of synaptosomes, due to uniqueness of their contents, could mark a new stage in the development of comprehensive therapies for neurodegenerative diseases, particularly AD. Synaptosomes contain unique memory mitochondria, which differ not only in size but also in functionality compared to the mitochondria in the neuronal soma. These synaptosomal mitochondria actively participate in cellular communication and signal transmission within synapses. Synaptosomes also contain other elements such as their own protein synthesis machinery, synaptic vesicles with neurotransmitters, synaptic adhesion molecules, and microRNAs - all crucial for synaptic transmission and, consequently, cognitive processes. Complex molecular ensemble ensures maintenance of the synaptic autonomy of mitochondria. Additionally, synaptosomes, with their affinity for neurons, can serve as an optimal platform for targeted drug delivery to nerve cells. This review discusses unique composition of synaptosomes, their capabilities and advantages, as well as limitations of their suggested use as therapeutic agents for treating neurodegenerative pathologies, particularly AD.

Intranasal administration of mitochondria improves spatial memory in olfactory bulbectomized mice.

Here, we found that functionally active mitochondria isolated from the brain of NMRI donor mice and administrated intranasally to recipient mice penetrated the brain structures in a dose-dependent manner. The injected mitochondria labeled with the MitoTracker Red localized in different brain regions, including the neocortex and hippocampus, which are responsible for memory and affected by degeneration in patients with Alzheimer's disease. In behavioral experiments, intranasal microinjections of brain mitochondria of native NMRI mice improved spatial memory in the olfactory bulbectomized (OBX) mice with Alzheimer's type degeneration. Control OBX mice demonstrated loss of spatial memory tested in the Morris water maze. Immunocytochemical analysis revealed that allogeneic mitochondria colocalized with the markers of astrocytes and neurons in hippocampal cell culture. The results suggest that a non-invasive route intranasal administration of mitochondria may be a promising approach to the treatment of neurodegenerative diseases characterized, like Alzheimer's disease, by mitochondrial dysfunction.

Proteolytic degradation patterns of the receptor for advanced glycation end products peptide fragments correlate with their neuroprotective activity in Alzheimer's disease models.

The receptor for advanced glycation end products (RAGE) plays an essential role in Alzheimer's disease (AD). We previously demonstrated that a fragment (60-76) of RAGE improved the memory of olfactory bulbectomized (OBX) and Tg 5 × FAD mice - animal models of AD. The peptide analog (60-76) with protected N- and C-terminal groups was more active than the free peptide in Tg 5 × FAD mice. This study investigated proteolytic cleavage of the RAGE fragment (60-76) and its C- and N-terminally modified analog by blood serum using HPLC and mass spectrometry. The modified peptide was proteolyzed slower than the free peptide. Degrading the protected analog resulted in shortened fragments with memory-enhancing effects, whereas the free peptide yielded inactive fragments. After administering the different peptides to OBX mice, their performance in a spatial memory task revealed that the effective dose of the modified peptide was five times lower than that of the free peptide. HPLC and mass spectrometry analysis of the proteolytic products allowed us to clarify the differences in the neuroprotective activity conferred by administering these two peptides to AD animal models. The current study suggests that the modified RAGE fragment is more promising for the development of anti-AD therapy than its free analog.

Synthetic Fragments of Receptor for Advanced Glycation End Products Bind Beta-Amyloid 1-40 and Protect Primary Brain Cells From Beta-Amyloid Toxicity.

Receptor for advanced glycation end products (RAGE) is involved in the pathogenesis of Alzheimer's disease. We have previously revealed that RAGE fragment sequence (60-76) and its shortened analogs sequence (60-70) and (60-65) under intranasal insertion were able to restore memory and improve morphological and biochemical state of neurons in the brain of bulbectomized mice developing major AD features. In the current study, we have investigated the ability of RAGE peptide (60-76) and five shortened analogs to bind beta-amyloid (Aß) 1-40 in an fluorescent titration test and show that all the RAGE fragments apart from one [sequence (65-76)] were able to bind Aß in vitro. Moreover, we show that all RAGE fragments apart from the shortest one (60-62), were able to protect neuronal primary cultures from amyloid toxicity, by preventing the caspase 3 activation induced by Aß 1-42. We have compared the data obtained in the present research with the previously published data in the animal model of AD, and offer a probable mechanism of neuroprotection of the RAGE peptide.

Effect of weak combined static and extremely low-frequency alternating magnetic fields on spatial memory and brain amyloid-ß in two animal models of Alzheimer's disease.

Subchronic effect of a weak combined magnetic field (MF), produced by superimposing a constant component, 42 µT and an alternating MF of 0.08 µT, which was the sum of two frequencies of 4.38 and 4.88 Hz, was studied in olfactory bulbectomized (OBE) and transgenic Tg (APPswe, PSEN1) mice, which were used as animal models of sporadic and heritable Alzheimer's disease (AD) accordingly. Spatial memory was tested in a Morris water maze on the following day after completion of training trials with the hidden platform removed. The amyloid-ß (Aß) level was determined in extracts of the cortex and hippocampus of mice using a specific DOT analysis while the number and dimensions of amyloid plaques were detected after their staining with thioflavin S in transgenic animals. Exposure to the MFs (4 h/day for 10 days) induced the decrease of Aß level in brain of OBE mice and reduced the number of Aß plaques in the cortex and hippocampus of Tg animals. However, memory improvement was revealed in Tg mice only, but not in the OBE animals. Here, we suggest that in order to prevent the Aß accumulation, MFs could be used at early stage of neuronal degeneration in case of AD and other diseases with amyloid protein deposition in other tissues.

Synthetic Fragment of Receptor for Advanced Glycation End Products Prevents Memory Loss and Protects Brain Neurons in Olfactory Bulbectomized Mice.

Activation of receptor for advanced glycation end products (RAGE) plays an essential role in the development of Alzheimer's disease (AD). It is known that the soluble isoform of the receptor binds to ligands and prevents negative effects of the receptor activation. We proposed that peptide fragments from RAGE prevent negative effects of the receptor activation during AD neurodegeneration. We have synthesized peptide fragments from surface-exposed regions of RAGE. Peptides were intranasally administrated into olfactory bulbectomized (OBX) mice, which developed some characteristics similar to AD neurodegeneration. We have found that only insertion of fragment (60-76) prevents the memory of OBX mice. Immunization of OBX mice with peptides showed that again only (60-76) peptide protected the memory of animals. Both intranasal insertion and immunization decreased the amyloid-ß (Aß) level in the brain. Activity of shortened fragments of (60-76) peptide was tested and showed only the (60-70) peptide is responsible for manifestation of activity. Intranasal administration of (60-76) peptide shows most protective effect on morpho-functional characteristics of neurons in the cortex and hippocampal areas. Using Flu-(60-76) peptide, we revealed its penetration in the brain of OBX mice as well as colocalization of Flu-labeled peptide with Aß in the brain regions in transgenic mice. Flu-(60-76) peptide complex with trimer of Aß was detected by SDS-PAGE. These data indicate that Aß can be one of the molecular target of (60-70) peptide. These findings provide a new peptide molecule for design of anti-AD drug and for investigation of RAGE activation ways in progression of AD neurodegeneration.

Molecular Mechanisms Underlying Neuroprotective Effect of Intranasal Administration of Human Hsp70 in Mouse Model of Alzheimer's Disease.

Heat shock protein 70, encoded by the HSPA1A gene in humans, is a key component of the machinery that protects neuronal cells from various stress conditions and whose production significantly declines during the course of aging and as a result of several neurodegenerative diseases. Herein, we investigated whether sub-chronic intranasal administration of exogenous Hsp70 (eHsp70) exerts a neuroprotective effect on the temporal cortex and areas of the hippocampus in transgenic 5XFAD mice, a model of Alzheimer's disease. The quantitative analysis of neuronal pathologies in the compared groups, transgenic (Tg) versus non-transgenic (nTg), revealed high level of abnormalities in the brains of transgenic mice. Treatment with human recombinant Hsp70 had profound rejuvenation effect on both neuronal morphology and functional state in the temporal cortex and hippocampal regions in transgenic mice. Hsp70 administration had a smaller, but still significant, effect on the functional state of neurons in non-transgenic mice as well. Using deep sequencing, we identified multiple differentially expressed genes (DEGs) in the hippocampus of transgenic and non-transgenic mice. Furthermore, this analysis demonstrated that eHsp70 administration strongly modulates the spectrum of DEGs in transgenic animals, reverting to a pattern similar to that observed in non-transgenic age-matched mice, which included upregulation of genes responsible for amine transport, transmission of nerve impulses and other pathways that are impaired in 5XFAD mice. Overall, our data indicate that Hsp70 treatment may be an effective therapeutic against old age diseases of the Alzheimer's type.

Interplay between recombinant Hsp70 and proteasomes: proteasome activity modulation and ubiquitin-independent cleavage of Hsp70.

The heat shock protein 70 (Hsp70, human HSPA1A) plays indispensable roles in cellular stress responses and protein quality control (PQC). In the framework of PQC, it cooperates with the ubiquitin-proteasome system (UPS) to clear damaged and dysfunctional proteins in the cell. Moreover, Hsp70 itself is rapidly degraded following the recovery from stress. It was demonstrated that its fast turnover is mediated via ubiquitination and subsequent degradation by the 26S proteasome. At the same time, the effect of Hsp70 on the functional state of proteasomes has been insufficiently investigated. Here, we characterized the direct effect of recombinant Hsp70 on the activity of 20S and 26S proteasomes and studied Hsp70 degradation by the 20S proteasome in vitro. We have shown that the activity of purified 20S proteasomes is decreased following incubation with recombinant human Hsp70. On the other hand, high concentrations of Hsp70 activated 26S proteasomes. Finally, we obtained evidence that in addition to previously reported ubiquitin-dependent degradation, Hsp70 could be cleaved independent of ubiquitination by the 20S proteasome. The results obtained reveal novel aspects of the interplay between Hsp70 and proteasomes.

Exogenous Hsp70 delays senescence and improves cognitive function in aging mice.

Molecular chaperone Heat Shock Protein 70 (Hsp70) plays an important protective role in various neurodegenerative disorders often associated with aging, but its activity and availability in neuronal tissue decrease with age. Here we explored the effects of intranasal administration of exogenous recombinant human Hsp70 (eHsp70) on lifespan and neurological parameters in middle-aged and old mice. Long-term administration of eHsp70 significantly enhanced the lifespan of animals of different age groups. Behavioral assessment after 5 and 9 mo of chronic eHsp70 administration demonstrated improved learning and memory in old mice. Likewise, the investigation of locomotor and exploratory activities after eHsp70 treatment demonstrated a significant therapeutic effect of this chaperone. Measurements of synaptophysin show that eHsp70 treatment in old mice resulted in larger synaptophysin-immunopositive areas and higher neuron density compared with control animals. Furthermore, eHsp70 treatment decreased accumulation of lipofuscin, an aging-related marker, in the brain and enhanced proteasome activity. The potential of eHsp70 intranasal treatment to protect synaptic machinery in old animals offers a unique pharmacological approach for various neurodegenerative disorders associated with human aging.

The Fate of Exogenous Human HSP70 Introduced into Animal Cells by Different Means.

Over the last decade, it has become evident that in mammals, including humans, heat shock protein 70 (HSP70), apart from its intracellular localization, is found in extracellular space, where it may execute various protective functions. Furthermore, the upregulation of HSP70 family members can be beneficial in the prevention and treatment of various human neurodegenerative diseases and cancer. Here, we demonstrate that recombinant human HSP70 after intranasal administration can penetrate various brain regions of mice in its native form and subsequently undergo rapid degradation. It was also shown that labeled HSP70 added to culture medium of different human and mouse cell lines enters the cells with strikingly different kinetics, which positively correlates with the basic levels of membrane bound Toll-like receptors (TLR) that are characteristic of these cell lines. HSP70 administration does not significantly modulate the level of TLR expression at the protein or RNA level. The degradation of the introduced recombinant HSP70 after entering the cells is likely proteasome-dependent and varies significantly depending on the cells type and origin. These results should be considered when developing HSP70-based therapies.

Therapeutic effect of exogenous hsp70 in mouse models of Alzheimer's disease.

Brain deterioration resulting from "protein folding" diseases, such as the Alzheimer's disease (AD), is one of the leading causes of morbidity and mortality in the aging human population. Heat shock proteins (Hsps) constitute the major cellular quality control system for proteins that mitigates the pathological burden of neurotoxic protein fibrils and aggregates. However, the therapeutic effect of Hsps has not been tested in a relevant setting. Here we report the dramatic neuroprotective effect of recombinant human Hsp70 in the bilateral olfactory bulbectomy model (OBX mice) and 5XFAD mouse models of neurodegeneration. We show that intranasally-administered Hsp70 rapidly enters the afflicted brain regions and mitigates multiple AD-like morphological and cognitive abnormalities observed in model animals. In particular, in both cases it normalizes the density of neurons in the hippocampus and cortex which correlates with the diminished accumulation of amyloid-ß (Aß) peptide and, in the case of 5XFAD mice, reduces Aß plaque formation. Consistently, Hsp70 treatment also protects spatial memory in OBX and 5XFAD mice. These studies demonstrate that exogenous Hsp70 may be a practical therapeutic agent for treatment of neurodegenerative diseases associated with abnormal protein biogenesis and cognitive disturbances, such as AD, for which neuroprotective therapy is urgently needed.