Fast and efficient synaptosome isolation and post-synaptic density enrichment from hiPSC-motor neurons by biochemical sub-cellular fractionation

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.

Integrative proteomics highlight presynaptic alterations and c-Jun misactivation as convergent pathomechanisms in ALS

Amyotrophic Lateral Sclerosis (ALS) is a fatal neurodegenerative disease mainly affecting upper and lower motoneurons. Several functionally heterogeneous genes have been associated with the familial form of this disorder (fALS), depicting an extremely complex pathogenic landscape. This heterogeneity has limited the identification of an effective therapy, and this bleak prognosis will only improve with a greater understanding of convergent disease mechanisms. Recent evidence from human post-mortem material and diverse model systems has highlighted the synapse as a crucial structure actively involved in disease progression, suggesting that synaptic aberrations might represent a shared pathological feature across the ALS spectrum. To test this hypothesis, we performed the first comprehensive analysis of the synaptic proteome from post-mortem spinal cord and human iPSC-derived motoneurons carrying mutations in the major ALS genes. This integrated approach highlighted perturbations in the molecular machinery controlling vesicle release as a shared pathomechanism in ALS. Mechanistically, phosphoproteomic analysis linked the presynaptic vesicular phenotype to an accumulation of cytotoxic protein aggregates and to the pro-apoptotic activation of the transcription factor c-Jun, providing detailed insights into the shared pathobiochemistry in ALS. Notably, sub-chronic treatment of our iPSC-derived motoneurons with the fatty acid docosahexaenoic acid exerted a neuroprotective effect by efficiently rescuing the alterations revealed by our multidisciplinary approach. Together, this study provides strong evidence for the central and convergent role played by the synaptic microenvironment within the ALS spinal cord and highlights a potential therapeutic target that counteracts degeneration in a heterogeneous cohort of human motoneuron cultures.

Bringing synapses into focus: Recent advances in synaptic imaging and mass-spectrometry for studying synaptopathy

Synapses are integral for healthy brain function and are becoming increasingly recognized as key structures in the early stages of brain disease. Understanding the pathological processes driving synaptic dysfunction will unlock new therapeutic opportunities for some of the most devastating diseases of our time. To achieve this we need a solid repertoire of imaging and molecular tools to interrogate synaptic biology at greater resolution. Synapses have historically been examined in small numbers, using highly technical imaging modalities, or in bulk, using crude molecular approaches. However, recent advances in imaging techniques are allowing us to analyze large numbers of synapses, at single-synapse resolution. Furthermore, multiplexing is now achievable with some of these approaches, meaning we can examine multiple proteins at individual synapses in intact tissue. New molecular techniques now allow accurate quantification of proteins from isolated synapses. The development of increasingly sensitive mass-spectrometry equipment means we can now scan the synaptic molecular landscape almost in totality and see how this changes in disease. As we embrace these new technical developments, synapses will be viewed with clearer focus, and the field of synaptopathy will become richer with insightful and high-quality data. Here, we will discuss some of the ways in which synaptic interrogation is being facilitated by methodological advances, focusing on imaging, and mass spectrometry.