Nischarin protein increases during postnatal hippocampal maturation, regulating cofilin phosphorylation and nuclear translocation

The hippocampus is crucial for memory integration and synaptic plasticity, processes that rely on dynamic cytoskeletal reorganization. This reorganization is tightly controlled by cofilin phosphorylation, a key regulator of actin dynamics. While Nischarin is known as a tumor-suppressive scaffold protein, its specific role in neurodevelopment and hippocampal maturation, particularly concerning cofilin regulation, has remained largely unexplored. Understanding this interaction could reveal new therapeutic targets for neurodegenerative diseases characterized by cofilin dysregulation.

Researchers investigated Nischarin's expression and its impact on cofilin during postnatal hippocampal maturation in rats. They used western blot and quantitative reverse transcription-polymerase chain reaction (qPCR) to track Nischarin expression from postnatal day 7 to P28. To explore mechanistic roles, shRNA-mediated knockdown of Nischarin was performed in adult rat hippocampal neurons and Neuro-2a cells. Primary endpoints included Nischarin protein and mRNA levels, phosphorylated cofilin levels, activity of PAK1/LIMK1 kinases, and the subcellular distribution of phosphorylated cofilin via immunofluorescence.

Nischarin expression significantly increased from postnatal day 7 to P28 in the rat hippocampus, showing a clear developmental upregulation. This increase in Nischarin inversely correlated with a decline in phosphorylated cofilin levels during the same period. Mechanistically, Nischarin reduced phosphorylated cofilin levels by suppressing the activity of the PAK1/LIMK1 pathway. This suggests a direct regulatory role for Nischarin in cofilin dephosphorylation. Furthermore, immunofluorescence studies revealed that Nischarin knockdown profoundly disrupted the subcellular distribution of phosphorylated cofilin. > Nischarin knockdown specifically impeded the translocation of phosphorylated cofilin from the cytoplasm to the nucleus, indicating a critical role in its spatial regulation. These findings collectively demonstrate that Nischarin regulates cofilin activity through a dual mechanism: inhibiting phosphorylation via PAK1/LIMK1 and modulating its nuclear translocation.