Depletion of intracellular zinc down-regulates expression of Uch-L1 mRNA and protein, and CREB mRNA in cultured hippocampal neurons.

Zinc deficiency has been associated with impaired learning and memory function in animals and human beings. However, the molecular mechanisms remain obscure. In light of evidence that ubiquitin C-terminal hydrolase L1 (Uch-L1) and cAMP-responsive element-binding protein (CREB) are required for synaptic and memory function and the possible regulation of CREB by Uch-L1, this present study was conducted to investigate the effect of zinc depletion on Uch-L1 protein expression and on Uch-L1 and CREB mRNA expression in cultured hippocampal neurons. Cultured hippocampal neurons were exposed to a cell membrane-permeant zinc chelator TPEN (2 microM), and to TPEN plus zinc sulphate (5 microM) for 24 h. Cultures were then processed to detect neuronal injury by lactate dehydrogenase (LDH) assay, Uch-L1 protein levels by Western blot, and Uch-L1 and CREB mRNAs levels by RT-PCR. The LDH release rate in TPEN-incubated neurons was notably increased compared to non-treated controls. Significant down-regulation of Uch-L1 protein level and mRNA levels for Uch-L1 and CREB were observed in TPEN-treated neurons. Co-addition of zinc almost completely reversed TPEN-induced neuronal injury and the alterations in Uch-L1 and CREB expression. The results demonstrated that zinc modulated the expression of Uch-L1 and CREB at the protein and/or transcription levels in hippocampal neurons, which implies that down-regulation of both Uch-L1 and CREB might participate in memory dysfunction induced by zinc deficiency.