Differential contributions of microglial and neuronal IKKbeta in synaptic plasticity and associative learning in mice

The small heat shock protein alpha B-crystallin (cryab) is expressed by oligodendrocytes (OL) and astrocytes at several stages of multiple sclerosis (MS) lesions. Cryab has been shown to be protective and therapeutic in the EAE model of MS, possibly due to its anti-apoptotic functions and regulation of inflammatory pathways. In addition, using the cuprizonemodel of demyelinationwe observed differential roles for cryab in demyelination and remyelination. As a molecular chaperone, cryab is thought to exert its biological function through binding unfolded and misfolded proteins. One of the most important post-translational modifications of cryab is phosphorylation, which affects both the localization and function of the protein. Cryab can be phosphorylated at three serine residues, Ser19, Ser45 and Ser59, and several of these phosphorylations have been shown to be required for the cytoprotective function of cryab. In this study, we further assessed the differential phosphorylation of cryab in astrocytes and oligodendrocyte progenitor cells (OPCs). Using phosphospecific antibodies, we analyzed the presence of the different phosphorylated forms of cryab in demyelinated lesions. We observed that cryab is differentially phosphorylated in (reactive) astrocytes and oligodendrocyte lineage cells in vivo. In addition, we show that differential phosphorylation of cryab determines its localization in these cells in vitro. Furthermore, taking a proteomics approach using a pull-down assay with phosphospecific antibodies we identified proteins that are bound by the phosphorylated forms of cryab in both astrocytes and OPC. This analysis revealed that there is clear differential binding of protein targets due to specific phosphorylation of cryab. In addition, we found that this binding pattern is cell specific, showing different binding targets in astrocytes and OPC. Further analysis of the individual targets of phosphorylated cryab will reveal the impact of its binding to these targets in astrocyte and OPC biology. Together, our data suggest that the phosphorylation of cryab confers diversity in its biological function through cell-specific differential phosphorylation. This diversity might underlie the differential role that we observe for cryab in deand remyelination.