In Silico Identification of a TDP-43–AKT2 Interaction: A Novel Candidate Driver of Schwann Cell Dysfunction, Peripheral Glial Neuroinflammation and Neurodegeneration in ALS

Authors

Anna Poghosyan · Hrant Shadyan

Anna Poghosyan – University of Montpellier, France · Hrant Shadyan – Wesleyan University, CT, USA

Abstract

TDP-43 aggregation is a major pathological hallmark of ALS. Although the consequences of its aggregation in neurons are being heavily studied, the consequences that it holds on glial cells require further investigation. Among glial cells, the role of Schwann Cells (SC), the primary myelinating glia of the peripheral nervous system, and the effects TDP-43 inclusions have on its myelinating function are obscure. One of the major cell-autonomous pathways involved in myelin synthesis for Schwann Cells is the AKT/PI3K pathway, with notably Protein Kinase B 2 (AKT2). Although phosphorylated TDP-43 aggregations have been found in SC, prior to phosphorylation, TDP-43 can also be found in the cytoplasm in the form of liquid droplets; the impairment of nucleocytoplasmic transport leads to passive cytoplasmic leakage of unphosphorylated TDP-43 in neurons. Given that this impairment pathway is common for primary glial cells, we suggest that unphosphorylated TDP-43 inclusions in the cytoplasm may also occur for SC. Given the context, we hypothesized that early-stage TDP-43 aggregation in SCs characterized by the cytoplasmic presence of unphosphorylated TDP-43 may drive the dysfunction of the AKT/PI3K pathway by interacting with AKT2, potentially leading to its inactivation and preventing it from properly fulfilling its physiological function. The dysfunction of the AKT/PI3K pathway leads to a dysfunctional lipid metabolism in SC, which causes an accumulation of acylcarnitines. Acylcarnitines being pro-inflammatory agents, TDP-43 contributes indirectly to peripheral neuroinflammation, which is a well-established promoter of neurodegeneration via the initiation of distal axonopathy. In order to test our hypothesis, in silico static molecular dockings, interface residues and MM/GBSA estimations were performed, coupled with GROMACS molecular dynamics involving RMSD, Radius of Gyration, Number of intermolecular contacts, Hydrogen Bonds and Trajectory-Based MM/GBSA calculations, averaging over a short timescale of 40 nanoseconds since our technical limitations did not allow us to push for 200 nanoseconds. The results support the hypothesis that AKT (AKT2 in particular) and TDP-43 can form a stable interaction in the short term of 40 ns, and as static analysis revealed, the interaction involves key Serine-474 AKT2 residue that are required to be phosphorylated for its full activation as well as residues from its kinase domain, which raises the possibility that longer-term interactions could be relevant to pathways of neuroinflammation and neurodegeneration.

Keywords: ALS, TDP-43, AKT2, Schwann cells, molecular docking, molecular dynamics

Contact the Authors

Anna Poghosyan — anna.pghs@gmail.com

Hrant Shadyan — hshadyan@wesleyan.edu