Carboxypeptidase E Protects Hippocampal Neurons During Stress in Male Mice by Up-regulating Pro-survival BCL2 Protein Expression

Abstract

Prolonged chronic stress causing elevated plasma glucocorticoids leads to neurodegeneration. Adaptation to stress (allostasis) through neuroprotective mechanisms can delay this process. Studies on hippocampal neurons have identified carboxypeptidase E (CPE) as a novel neuroprotective protein that acts extracellularly, independent of its enzymatic activity, although the mechanism of action is unclear. Here, we aim to determine if CPE plays a neuroprotective role in allostasis in mouse hippocampus during chronic restraint stress (CRS), and the molecular mechanisms involved. Quantitative RT-PCR/in situ hybridization and Western blots were used to assay for mRNA and protein. After mild CRS (1 h/d for 7 d), CPE protein and mRNA were significantly elevated in the hippocampal CA3 region, compared to naïve littermates. In addition, luciferase reporter assays identified a functional glucocorticoid regulatory element within the cpe promoter that mediated the up-regulation of CPE expression in primary hippocampal neurons following dexamethasone treatment, suggesting that circulating plasma glucocorticoids could evoke a similar effect on CPE in the hippocampus in vivo. Overexpression of CPE in hippocampal neurons, or CRS in mice, resulted in elevated prosurvival BCL2 protein/mRNA and p-AKT levels in the hippocampus; however, CPE(-/-) mice showed a decrease. Thus, during mild CRS, CPE expression is up-regulated, possibly contributed by glucocorticoids, to mediate neuroprotection of the hippocampus by enhancing BCL2 expression through AKT signaling, and thereby maintaining allostasis.

Carboxypeptidase E promotes cancer cell survival, but inhibits migration and invasion

“…CPE is secreted from (neuro)endocrine tumor and glioblastoma (GBM) cell lines., It was found that CPE acts as a pro-growth, but anti-metastatic factor [6]. Another recent study has shown that CPE acts extracellularly as a negative regulator of the canonical Wnt signaling pathway [13] and as a neurotrophic factor to protect neurons against oxidative stress induced cell death [9] or during chronic stress [14]. However, the mechanism of action of CPE in these functions is not fully understood.…”

Rosiglitazone‐activated PPARγ induces neurotrophic factor‐α1 transcription contributing to neuroprotection

“…) and after chronic restraint stress in mice (Murthy et al . ). In addition, CPE has recently been identified as a neuroprotective protein, now also known as neurotrophic factor‐α1 (henceforth referred to as NF‐α1 in this work), which is secreted from neurons and acts extra‐cellularly in an autocrine or paracrine manner (Woronowicz et al .…”

Carboxypeptidase E (CPE) inhibits the secretion and activity of Wnt3a

“…17,8 CPE has also been implicated in cancer progression [18][19][20][21] and as a neuro-trophic factor regulating brain functions. [22][23][24][25][26] Lately, it was found that CPE is also involved in other biological processes such as bone homeostasis 27 and bowel disease. 28 We have previously shown that CPE negatively regulates the oncogenic canonical Wnt signaling pathway by interacting with Wnt3a leading to decreased β-catenin protein levels and reduced Wnt signaling levels.…”