PSD95beta regulates plasma membrane Ca2+ pump localization at the photoreceptor synapse

Area of Science:

• Neuroscience
• Cell Biology
• Molecular Biology

Background:

• The precise localization of plasma membrane Ca2+-ATPase (PMCA), a calcium extruder, at the photoreceptor presynaptic plasma membrane is vital for synaptic function.
• This localization is mediated by a specific protein complex involving membrane palmitoylated protein 4 (MPP4) and postsynaptic density protein 95 (PSD95).

Purpose of the Study:

• To investigate the specific roles of MPP4 and PSD95 in the assembly and function of the PMCA-containing protein complex at the photoreceptor synapse.
• To elucidate the molecular mechanisms by which MPP4 and PSD95 regulate PMCA localization and activity.

Main Methods:

• Utilized Mpp4 and Psd95 mutant mice to study the effects of protein deficiency on synaptic complex localization.
• Employed lentivirus-mediated molecular replacement to express specific PSD95 isoforms in retinal explants.
• Investigated the impact of truncating C-terminal domains of MPP4 and PSD95 on complex member localization.
• Assessed the effects of Psd95 gene silencing on MPP4 and PMCA1 localization.

Main Results:

• MPP4 deficiency led to the complete loss of both PMCA and PSD95 from the photoreceptor synapse.
• Truncation of MPP4's C-terminus caused PSD95 loss and PMCA mislocalization, while PSD95 C-terminal truncation had no effect on complex members.
• Silencing Psd95 resulted in the loss of presynaptic MPP4 and PMCA1.
• Expression of PSD95beta isoform restored plasma membrane localization of MPP4 and PMCA1 in Mpp4 mutant explants.

Conclusions:

• Both scaffold proteins, PSD95beta and MPP4, are essential for maintaining PMCA levels at the presynaptic plasma membrane.
• These scaffold proteins play a critical role in modulating photoreceptor synaptic calcium handling through their regulation of PMCA localization.