Sequential phosphorylation of NDEL1 by the DYRK2-GSK3β complex is critical for neuronal morphogenesis

Neuronal morphogenesis requires multiple regulatory pathways to appropriately determine axonal and dendritic structures, thereby to enable the functional neural connectivity. Yet, however, the precise mechanisms and components that regulate neuronal morphogenesis are still largely unknown. Here, we newly identified the sequential phosphorylation of NDEL1 critical for neuronal morphogenesis through the human kinome screening and phospho-proteomics analysis of NDEL1 from mouse brain lysate. DYRK2 phosphorylates NDEL1 S336 to prime the phosphorylation of NDEL1 S332 by GSK3β. TARA, an interaction partner of NDEL1, scaffolds DYRK2 and GSK3β to form a tripartite complex and enhances NDEL1 S336/S332 phosphorylation. This dual phosphorylation increases the filamentous actin dynamics. Ultimately, the phosphorylation enhances both axonal and dendritic outgrowth and promotes their arborization. Together, our findings suggest the NDEL1 phosphorylation at S336/S332 by the TARA-DYRK2-GSK3β complex as a novel regulatory mechanism underlying neuronal morphogenesis.

Characterization of pathology-inducing α-synuclein species from human diseased brain tissue

Synucleinopathies are a group of neurodegenerative diseases characterized by the presence of pathological accumulations of misfolded, phosphorylated α-synuclein (αSyn) protein. Multiple lines of evidence indicate that synucleinopathy disease progression is driven by a prion-like process of transmission of a pathologic form of αSyn. One potential therapeutic approach to prevent cell-to-cell propagation is to target this transmissible species with selective antibodies. In this study, a rodent primary neuronal culture reporter system was developed to monitor induction of detergent-insoluble, phosphorylated (pS129) aggregates of αSyn. Induction of pS129 αSyn pathology was observed with both synthetic αSyn fibrils (PFFs) and brain lysates from multiple system atrophy (MSA) patients but not αSyn monomers or human brain lysate controls. The induction-competent species in MSA lysates could be enriched by high-speed centrifugation suggesting that it is present as a high molecular weight aggregate. Furthermore, samples derived from brain lysates from Parkinson’s disease (PD) and Dementia with Lewy Bodies (DLB) patients also induced pS129 αSyn pathology, but required longer incubation times. Lastly, the potential of αSyn selective antibodies to immunodeplete induction-competent forms of αSyn from both PFF and synucleinopathy brain samples is described. The results demonstrate that antibodies targeting the C-terminal of αSyn are most effective for immunodepletion of pathology-inducing forms of αSyn from samples derived from human synucleinopathy brains. Furthermore, the data support the hypothesis that antibodies that recognize a C-terminal epitope and exhibit selectivity for oligomeric forms over monomeric forms of αSyn represent a desirable target for immunotherapy for synucleinopathy patients.

Characterization of Antibodies that Detect Human GFAP after Traumatic Brain Injury

After traumatic brain injury (TBI), glial fibrillary acidic protein (GFAP) and other brain-derived proteins and their breakdown products are released into biofluids such as CSF and blood. Recently, a sandwich ELISA was constructed that measured GFAP concentrations in CSF or serum from human mild-moderate TBI patients. The goals of the present study were to characterize the same two antibodies used in this ELISA, and to determine which GFAP bands are detected by this antibody combination. Here, both antibodies recognized GFAP specifically in human brain and post-TBI CSF in a cluster of bands ranging from 50–38 kDa, that resembled bands from calpain-cleaved GFAP. By immunoprecipitation, the anti-GFAP Capture antibody recovered full length GFAP and its breakdown products from human brain lysate and post-TBI CSF. These findings demonstrate that the anti-GFAP ELISA antibodies non-preferentially detect intact GFAP and GFAP breakdown products, underscoring their utility for detecting brain injury in human patients.

Interaction of two proline-rich sequences of cell adhesion kinase β with SH3 domains of p130Cas-related proteins and a GTPase-activating protein, Graf

Cell adhesion kinase β (CAKβ) is a protein tyrosine kinase closely related to focal adhesion kinase (FAK) in structure. CAKβ contains two proline-rich sequences within its C-terminal region. Since proline-rich sequences present in the corresponding region of FAK are known to mediate protein-protein interactions by binding to SH3 domains, we investigated binding of CAKβ to a panel of SH3 domains. Affinity precipitation from rat brain lysate revealed selective interactions of CAKβ with glutathione S-transferase (GST)-fused SH3 domains of p130Cas(Cas)-related proteins and Graf. Mutational analysis indicated that the proline-rich sequences of CAKβ mediate this interaction. Each of the two proline-rich sequences fused to GST bound directly to these SH3 domains in dot blot analysis. A competitive binding assay revealed that the first proline-rich sequence of CAKβ preferentially associated with the SH3 domain of Cas. The second proline-rich sequence of CAKβ bound to the SH3 domain of Graf with higher specificity than the corresponding proline-rich sequence of FAK. Finally, we showed co-immunoprecipitation of CAKβ with Graf from rat brain lysate. These results indicate that CAKβ associates in vivo with Graf through its SH3 domain.