Microtubule plus-end tracking proteins: novel modulators of cardiac sodium channels and arrhythmogenesis

Figures

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  Figure 1. NaV1.5 structure, function, and cellular distribution. (A) Protein structure of the α-subunit of the cardiac sodium channel, NaV1.5, encoded by SCN5A, and (B) visualization of the 3D structure and binding of interacting proteins. (C) INa modulated by NaV1.5 (top panel) and its effect on the action potential in ventricular cardiomyocytes (upstroke phase, bottom panel). (D) Schematic visualization of NaV1.5 localization in adult cardiomyocytes, with localization at the lateral membrane and enrichment at the intercalated discs.

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  Figure 2. MT-dependent trafficking and proposed mechanism of targeted delivery of NaV1.5. (A) Schematic overview of MT-dependent anterograde trafficking and regulators of MTs. From left to right: The nucleus is surrounded by the ER, and the Golgi apparatus. The MT-organizing centre co-localizes with Golgi apparatus and contains the MT minus-EB proteins, which stabilize the minus-end (−) of MTs. Vesicles containing cargo originating from the Golgi apparatus can be loaded on MTs and transported to the MT plus-end (+) by motor proteins. MTs are regulated by +TIPs, which bind the MT plus-end, controlling MT dynamics and stability, as well as allowing for interactions to mediate cargo delivery. (B) Proposed mechanism regulating NaV1.5 targeted delivery by associations between +TIPs and NaV1.5 interacting proteins. NaV1.5 interacting proteins bait growing MTs through attracting +TIPs, and allow MT stabilization upon interacting with +TIPs, promoting NaV1.5 delivery. These NaV1.5 interacting proteins differ between cardiomyocyte subcellular domains (i.e. lateral membrane, intercalated discs), attracting specific +TIPs to these distinct locations. Associations between NaV1.5 interacting proteins…

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  Figure 3. Impact of the MT plus EB proteins EB1 and EB2 on NaV1.5, INa, and cardiac conduction. Top panel: Lentiviral transduction of EB1 in hiPSC-derived cardiomyocytes (hiPSC-CM) increased membrane NaV1.5 cluster density and INa (left), whereas knockdown of Mapre1/EB1 in zebrafish and hiPSC-CM induced cardiac conduction slowing and reduced INa, respectively (right). Reproduced from,11 with permission. Lower panel: MAPRE2/EB2 was identified in a GWAS for Brugada syndrome (BrS) (left), and knockdown of Mapre2/EB2 in zebrafish and hiPSC-CM-induced cardiac conduction slowing and reduced INa, respectively (right). Reproduced from,12 with permission.

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  Figure 4. Subdomain-specific modulation of INa and NaV1.5. In mouse cardiomyocytes, the compound SB216763 (SB2) increased NaV1.5 cluster density (A) and INa (B) at the intercalated discs but not at the lateral membrane. (C) SB2 prevents GSK3β-mediated CLASP2 phosphorylation, thereby enhancing EB1-CLASP2-MT interactions, resulting in increased NaV1.5 delivery at the intercalated discs. Redrawn from,11 with permission.

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  Figure 5. Interactions between +TIPs and NaV1.5 interacting proteins. Overview of described interactions between +TIPs (left, orange) and NaV1.5 interacting proteins (right) specifically located at the lateral membrane (cyan), at the intercalated discs (purple) or which are not specifically located at the lateral membrane or intercalated discs (blue). (A) Direct associations between +TIPs and NaV1.5 interacting proteins. (B) Indirect associations via adaptor proteins (centre, green). Interactions between +TIPs and NaV1.5 interacting proteins or adaptor proteins are marked by a solid, coloured line. Interactions between individual adaptor proteins are illustrated by a dashed grey line.

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  Figure 6. +TIPs may impact on cardiac conduction and arrhythmogenesis through various mechanisms.