Matrix Metalloproteinase 2 Controls Trans-Synaptic Homeostatic Plasticity in Drosophila

ABSTRACT Synapses in the nervous system are key in signal transmission, computation, and learning. They adaptively modify during information processing and storage, influencing behavioral responses while maintaining synaptic stability. Homeostatic signaling plays a crucial role at synaptic, neuronal and circuit levels, ensuring stable neuronal function and network activity within physiological limits, essential for consistent brain functionality. Disruptions in these homeostatic signaling pathways are linked to neurological disorders including epilepsy, schizophrenia, and neurodegeneration. The molecular architecture of homeostatic signaling in the nervous system remains to be elucidated. Our research focuses on the Drosophila neuromuscular junction (NMJ) as a model synapse for understanding synaptic homeostatic control mechanisms. At this glutamatergic synapse, inhibiting postsynaptic glutamate receptors triggers a compensatory increase in presynaptic neurotransmitter release, maintaining synaptic strength. This process, known as Presynaptic Homeostatic Potentiation (PHP), is a conserved phenomenon across species. PHP begins with reduced glutamate receptor activity on the postsynaptic side, but manifests as enhanced presynaptic neurotransmitter release. This indicates a need for retrograde signaling to counteract postsynaptic changes and restore baseline muscle excitation. Previous studies highlight the role of the extracellular matrix (ECM) protein Multiplexin, Drosophila homologue to mammalian collagen XV/XVIII, in PHP. Particularly, its C-terminal domain, Endostatin, released upon proteolytic cleavage, facilitates neurotransmitter release during PHP via presynaptic calcium channels. The protease responsible for releasing Endostatin from Multiplexin is still unknown. Drosophila has two matrix metalloproteinases, MMP1 and MMP2. Our preliminary data, derived from a CRISPR-generated mmp2null mutant, indicate MMP2's essential role in PHP induction and maintenance. This project aims to systematically investigate the role of MMP2 in PHP, employing multifaceted techniques including electrophysiology, immunohistochemistry, biochemistry, confocal calcium imaging, and super resolution imaging. AIM1 focuses on dissecting MMP2's cell- specific function in PHP and whether MMP2 directly cleaves Multiplexin to release Endostatin during PHP. AIM2 delves into the cellular mechanisms of MMP2 in modulating presynaptic calcium influx and calcium channel localization during PHP. This study will elucidate key signaling elements in the dynamic regulation of ECM during PHP and provide valuable insights into synaptic stabilization mechanisms.