P1.10. SH3BP2- A NEW REGULATOR OF NEUROMUSCULAR SYNAPSES
Bhola Shankar Pradhan1,2, Krzysztof Bernadzki2, Yauhen Bandaruk1, Anna Siudzińska1, Teresa De Cicco1, Małgorzata Sotomska1, Marta Gawor2, Joanna Krzemień2, Grzegorz Chodaczek1, Said Hashemolhosseini3,1, Tomasz J. Prószyński1,2
1 Łukasiewicz Research Network — PORT Polish Center for Technology Development, 147 Stabłowicka Street, 54-066 Wrocław, Poland.
2 Nencki Institute of Experimental Biology, Polish Academy of Sciences, 3 Pasteur Street, 02- 093 Warsaw, Poland
3 Institute of Biochemistry, Friedrich-Alexander University Erlangen-Nürnberg, 91054 Erlangen, Germany
INTRODUCTION: The neuromuscular junction (NMJ) plays a critical role in muscle function, yet the molecular mechanisms governing its development and maintenance remain incompletely understood. Dysfunction of these synapses is linked to severe genetic and autoimmune disorders, highlighting the need to identify key regulatory components. We identified SH3BP2 as a potential interactor of αDB1, but its localization and function in skeletal muscles remain unexplored.
AIM(S): The aim is to determine the function of SH3BP2 in skeletal muscles.
METHOD(S): We used protein interaction analysis (peptide pull-downs, co-immunoprecipitation, mass spectrometry) combined with functional analysis using siRNA knock-down in C2C12 myotubes and muscle-specific SH3BP2 knockout in mice. NMJ morphology was assessed using confocal and electron microscopy. Additionally muscle performance and electrophysiological recordings were analyzed in the study.
RESULTS: Our experiments identified that SH3BP2 is strongly concentrated at the NMJ where, in a polyvalent way, it interacts with the dystroglycan complex (DGC) and Acetylcholine receptor (AChR) pentamers. We demonstrated that SH3BP2 works as a scaffold clustering AChR. On the mechanistic level, SH3BP2 self-interacts organizing high molecular mass dynamic protein droplets that recruit AChR molecules. Consistently, muscle-specific SH3BP2 KO leads to NMJ fragmentation, abnormal ultrastructure, impaired synaptic transmission, decreased muscle strength and physical fitness of mutant mice.
CONCLUSIONS: We identify SH3BP2 as a novel postsynaptic regulator at the NMJ. This scaffold protein through polyvalent molecular interactions and phase separation-dependent process contributes to AChR clustering. Further studies should address if SH3BP2 plays similar functions in the brain.
FINANCIAL SUPPORT: This work has been supported by the Polish National Science Centre, grants: 2016/21/B/NZ3/03638 and 2020/39/D/NZ5/02004 and German Research Council grants HA3309/7-1.