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Front. Mol. Biosci. | doi: 10.3389/fmolb.2018.00099

Loss of Ca2+/Calmodulin Dependent Protein Kinase Kinase 2 leads to aberrant transferrin phosphorylation and trafficking: a potential biomarker for Alzheimer’s disease.

  • 1St. Boniface Research Centre, Canada

Ca2+/calmodulin-dependent protein kinase kinase 2 (CaMKK2) is a serine/threonine kinase that is activated following an increase in the intracellular Ca2+ concentration and activates multiple signaling cascades that control physiologically important neuronal processes. CaMKK2 has been implicated in schizophrenia, bipolar disease, neurodegeneration, and cancer. Using isolectric focusing (IEF) and mass spectrometry based proteomic analysis, it was found that knockdown (KD) of CaMKK2 in cultured adult primary dorsal root ganglion (DRG) neurons resulted in the reduction of transferrin (TF) phosphorylation at multiple functionally relevant residues which corresponded to loss of an acidic fraction (pH3-4) of TF. In vitro studies using CRISPR/Cas9 based CaMKK2 knockout (KO) HEK293 and HepG2 cells lines validated previous findings and revealed that loss of CaMKK2 interfered with TF trafficking and turnover. TF is an iron transporter glycoprotein. Abnormal accumulation of iron and/or deregulated Ca2+ homeostasis leads to neurodegeneration in Alzheimer’s disease (AD). Therefore, it was hypothesized that aberrant CaMKK2 in AD may lead to aberrant phosphorylated transferrin (P-TF: pH3-4 fraction) which may serve as a hallmark biomarker for AD. A significant reduction of P-TF in the brain and serum of CaMKK2 KO mice and a triple-transgenic mouse model of AD (3xTg-AD) supported this hypothesis. In addition, analysis of early (<65 years) and late-stage (>65 years) postmortem human AD cerebrospinal fluid (CSF) and serum samples revealed that aberrant P-TF (pH3-4 fraction) profile was associated with both early and late-stage AD compared to age-matched controls. This indicates P-TF (pH3-4 fraction) profile may be useful as a minimally invasive biomarker for AD. In addition, this study provides a link between aberrant CaMKK2 with TF trafficking and turnover which provides a novel insight into the neurodegeneration process.

Keywords: Transferrin (TF), CaMKK2, calcium/calmodulin-dependent kinase kinase 2, trafficking, biomarker, Isoelecrtic focusing, Mass spectometry, post translation modification, phsohporylation, Serum, Cerebrospical fluid (CSF), CRiSPR/Cas, Knockout (KO) mice

Received: 14 Aug 2018; Accepted: 25 Oct 2018.

Edited by:

Sanjeev K. Srivastava, Mitchell Cancer Institute, United States

Reviewed by:

Mahendra P. Kashyap, University of Alabama at Birmingham, United States
Ritesh K. Srivastava, University of Alabama at Birmingham, United States  

Copyright: © 2018 Sabbir. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Mohammad G. Sabbir, St. Boniface Research Centre, Winnipeg, Manitoba, Canada,