Background: Alpha-synuclein is a key protein involved in the pathogenesis of Parkinson disease (PD). Its intermediate aggregated forms disturb the normal function of dopaminergic (DA) neurons. Furthermore, the loss of intraneuronal connections may precede nerve cell death in PD. Disturbance of presynaptic functions of alpha-synuclein and its family members, beta- and gamma-synuclein, can apparently be the first step in nigrostriatal system dysfunction. Based on their structure homology and subcellular localization, the three synuclein proteins could have overlapping functions. This also indicates necessitates to study each protein in isolation. Methods: We have established a unique mouse line with conditional knockout (KO) of alpha-synuclein inactivation on the background of gamma-synuclein KO. Results: During the early phase of alpha-synuclein loss of function, mice demonstrate reduced explorer activity, decreased gene expression of Mao-B in the midbrain, and transiently increased levels of beta-synuclein protein in the striatum after alpha-synuclein inactivation, as results, metabolism of dopamine stays unscathed. These changes can be caused by specific regulation of Mao-B by alpha-synuclein or can be a physiological reaction aimed at restoring alpha-synuclein levels. No significant changes in gene expression patterns of dopamine-related enzymes in the midbrain or protein levels in the striatum and midbrain were observed. Conclusions: Our data suggest that sudden alpha-synuclein depletion leads to an increase in beta-synuclein levels, likely as functional replacement. This result supports that beta-synuclein can compensate the loss of alpha-synuclein. In general, this process may characterize synapse reconstruction in early alpha-synuclein dysfunction with gamma-synuclein absence and form the basis for replacement therapeutic strategies in PD.

Background: The three Synuclein family members (α-, β-, and γ-synuclein) are presynaptic proteins that regulate synaptic vesicle trafficking and thereby influence neurotransmitter release. Synucleins belong to a class of intrinsically disordered proteins and are prone to aggregation into pathological deposits, which may impair their physiological synaptic functions. Knockout (KO) mouse lines, commonly used to model synuclein depletion in the nervous system, reveal a range of phenotypes with different motor and behavioral deficits. However, given the high sequence homology and functional interplay among the three synucleins, the specific contribution of each family member to these phenotypes remains poorly understood. Objective: In this study, we conducted a comparative phenotypic analysis of γ-synuclein KO, α- and β-synuclein KO, and αβγ-synuclein KO mice. Methods: Mice were subjected to a battery of behavioral tests assessing motor activity and coordination, anxiety-like behavior, and spatial learning and memory. Synaptic vesicle proteins were analyzed in brain tissues using Western blotting. Results: We observed that knocking out γ-synuclein but not α- and β-synucleins reduces mouse lifespan and leads to sustained reduction in muscle strength implicating that γ-synuclein is essential for longevity and motor system function. Another consequence of γ-synuclein deficiency is altered anxiety-like behavior manifested as a diminished aversive response, while exploratory behavior and memory remain intact. The triple KO mice mirror γ-synuclein KO mice in some behavioral changes, including shortened lifespan, reduced muscle strength, and decreased anxiety-like behavior. However, the triple KO mice additionally exhibit hyperactivity, which is not present in the other groups. No changes in synaptic vesicle marker levels were detected, indicating that the observed motor and behavioral abnormalities are not attributable to impaired synaptic connectivity. Conclusions: Taken together, these findings demonstrate nonredundant functions of individual synuclein family members and highlight a distinct role of γ-synuclein in regulating motor performance and behavioral responses.

Актуальность. Нарушение дофаминовой нейротрансмиссии характерно для многих нейродегенеративных заболеваний с моторной дисфункцией. Участие белков-синуклеинов в регуляции гомеостаза дофамина делает актуальным их изучение в контексте патологии. Целью исследования является характеристика изменений моторной функции мышей с различными комбинациями нокаутов по генам белков семейства синуклеинов с возрастом. Материалы и методы. Восемь групп животных проходили тестирование в автоматизированной системе CatWalk XT, а их мышечная сила оценивалась с помощью теста «Сила хвата» (Grip Strength Test Meter) в возрасте 6, 12, 18 и 24 месяца. Статистическая обработка данных проводилась в программе «GraphPad Prism Software 7.0». Результаты. Было выявлено достоверное снижение параметра «длина следа» с возрастом в группах животных без функционального альфа-синуклеина. Также у этих животных отмечены и другие нарушения походки. По данным нашего исследования, отсутствие бета- и гамма-синуклеина приводит к достоверному снижению массы тела и ухудшению силы хвата. Заключение. Показана важная роль белков семейства синуклеинов в ухудшении двигательной функции животных с возрастом и выявлены некоторые скрытые параметры, вносящие изменения в походку животных с различным комбинациями нокаутов по генам белков семейства синуклеинов. Actuality. Dopamine neurotransmission impairment is a common phenomenon in neurodegenerative diseases associated with motor dysfunction. The involvement of synuclein proteins in the regulation of dopamine homeostasis renders their study pertinent in the context of pathology. The aim of this study is to identify the impact of different combinations on motor function developed with ageing, in knockouts of synuclein family genes. Materials and methods. Eight groups of animals were tested in the CatWalk XT automated system, and their muscle strength was evaluated using the Grip Strength Test Meter at 6, 12, 18 and 24 months of age. Statistical analysis was carried out using GraphPad Prism Software 7.0. Results. A significant reduction in the ‘print length’ parameter with age was observed in the groups of animals lacking functional alpha-synuclein. Furthermore, other gait abnormalities were observed in these animals. Our study indicates that the absence of beta- and gamma-synuclein is associated with a significant reduction in body weight and impaired grip strength. Conclusion. The present study has demonstrated the pivotal role of synuclein family proteins in the impairment of motor function in animals with age. Furthermore, it has identified several hidden parameters that introduce changes in the gait of animals with different combinations of synuclein genes knockouts.

Background: The three Synuclein family members (α-, β-, and γ-synuclein) are presynaptic proteins that regulate synaptic vesicle trafficking and thereby influence neurotransmitter release. Synucleins belong to a class of intrinsically disordered proteins and are prone to aggregation into pathological deposits, which may impair their physiological synaptic functions. Knockout (KO) mouse lines, commonly used to model synuclein depletion in the nervous system, reveal a range of phenotypes with different motor and behavioral deficits. However, given the high sequence homology and functional interplay among the three synucleins, the specific contribution of each family member to these phenotypes remains poorly understood. Objective: In this study, we conducted a comparative phenotypic analysis of γ-synuclein KO, α- and β-synuclein KO, and αβγ-synuclein KO mice. Methods: Mice were subjected to a battery of behavioral tests assessing motor activity and coordination, anxiety-like behavior, and spatial learning and memory. Synaptic vesicle proteins were analyzed in brain tissues using Western blotting. Results: We observed that knocking out γ-synuclein but not α- and β-synucleins reduces mouse lifespan and leads to sustained reduction in muscle strength implicating that γ-synuclein is essential for neuromuscular function. Another consequence of γ-synuclein deficiency is altered anxiety-like behavior manifested as a diminished aversive response, while exploratory behavior and memory remain intact. The triple KO mice mirror γ-synuclein KO mice in some behavioral changes, including shortened lifespan, reduced muscle strength, and decreased anxiety-like behavior. However, the triple KO mice additionally exhibit hyperactivity, which is not present in the other groups. No changes in synaptic vesicle marker levels were detected, indicating that the observed motor and behavioral abnormalities are not attributable to impaired synaptic connectivity. Conclusions: Taken together, these findings demonstrate nonredundant functions of individual synuclein family members and highlight a distinct role of γ-synuclein in regulating motor performance and behavioral responses.