Copper dependent ERK1/2 phosphorylation is essential for the viability of neurons and not glia.

Intracellular copper [Cu(I)] has been hypothesized to play role in the differentiation of the neurons. This necessitates understanding the role of Cu(I) not only in the neurons but also in the glia considering their anatomical proximity, contribution towards ion homeostasis, and neurodegeneration. In this study, we did a systematic investigation of the changes in the cellular copper homeostasis during neuronal and glial differentiation and the pathways triggered by them. Our study demonstrates increased mRNA for the plasma membrane copper transporter CTR1 leading to increased Cu(I) during the neuronal (PC-12) differentiation. ATP7A is retained in the trans-Golgi network (TGN) despite high Cu(I) demonstrating its utilization towards the neuronal differentiation. Intracellular copper triggers pathways essential for neurite generation and ERK1/2 activation during the neuronal differentiation. ERK1/2 activation also accompanies the differentiation of the foetal brain derived neuronal progenitor cells. The study demonstrates that ERK1/2 phosphorylation is essential for the viability of the neurons. In contrast, differentiated C-6 (glia) cells contain low intracellular copper and significant downregulation of the ERK1/2 phosphorylation demonstrating that ERK1/2 activation does not regulate the viability of the glia. But ATP7A shows vesicular localization despite low copper in the glia. In addition to the TGN, ATP7A localizes into RAB11 positive recycling endosomes in the glial neurites. Our study demonstrates the role of copper dependent ERK1/2 phosphorylation in the neuronal viability. Whereas glial differentiation largely involves sequestration of Cu(I) into the endosomes potentially (i) for ready release and (ii) rendering cytosolic copper unavailable for pathways like the ERK1/2 activation.