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Neurodegenerative diseases are characterized by the abnormal filamentous assembly of specific proteins in the central nervous system1. Human genetic studies have established a causal role for protein assembly in neurodegeneration2. However, the underlying molecular mechanisms remain largely unknown, which is limiting progress in developing clinical tools for these diseases. Recent advances in cryo-electron microscopy have enabled the structures of the protein filaments to be determined from the brains of patients1. All neurodegenerative diseases studied to date have been characterized by the self-assembly of proteins in homomeric amyloid filaments, including that of TAR DNA-binding protein 43 (TDP-43) in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with TDP-43 inclusions (FTLD-TDP) types A and B3,4. Here we used cryo-electron microscopy to determine filament structures from the brains of individuals with FTLD-TDP type C, one of the most common forms of sporadic FTLD-TDP. Unexpectedly, the structures revealed that a second protein, annexin A11 (ANXA11), co-assembles with TDP-43 in heteromeric amyloid filaments. The ordered filament fold is formed by TDP-43 residues G282/G284–N345 and ANXA11 residues L39–Y74 from their respective low-complexity domains. Regions of TDP-43 and ANXA11 that were previously implicated in protein–protein interactions form an extensive hydrophobic interface at the centre of the filament fold. Immunoblots of the filaments revealed that the majority of ANXA11 exists as an approximately 22 kDa N-terminal fragment lacking the annexin core domain. Immunohistochemistry of brain sections showed the colocalization of ANXA11 and TDP-43 in inclusions, redefining the histopathology of FTLD-TDP type C. This work establishes a central role for ANXA11 in FTLD-TDP type C. The unprecedented formation of heteromeric amyloid filaments in the human brain revises our understanding of amyloid assembly and may be of significance for the pathogenesis of neurodegenerative diseases.
Neurodegenerative diseases are characterized by the abnormal filamentous assembly of specific proteins in the central nervous system1. Human genetic studies have established a causal role for protein assembly in neurodegeneration2. However, the underlying molecular mechanisms remain largely unknown, which is limiting progress in developing clinical tools for these diseases. Recent advances in cryo-electron microscopy have enabled the structures of the protein filaments to be determined from the brains of patients1. All neurodegenerative diseases studied to date have been characterized by the self-assembly of proteins in homomeric amyloid filaments, including that of TAR DNA-binding protein 43 (TDP-43) in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with TDP-43 inclusions (FTLD-TDP) types A and B3,4. Here we used cryo-electron microscopy to determine filament structures from the brains of individuals with FTLD-TDP type C, one of the most common forms of sporadic FTLD-TDP. Unexpectedly, the structures revealed that a second protein, annexin A11 (ANXA11), co-assembles with TDP-43 in heteromeric amyloid filaments. The ordered filament fold is formed by TDP-43 residues G282/G284–N345 and ANXA11 residues L39–Y74 from their respective low-complexity domains. Regions of TDP-43 and ANXA11 that were previously implicated in protein–protein interactions form an extensive hydrophobic interface at the centre of the filament fold. Immunoblots of the filaments revealed that the majority of ANXA11 exists as an approximately 22 kDa N-terminal fragment lacking the annexin core domain. Immunohistochemistry of brain sections showed the colocalization of ANXA11 and TDP-43 in inclusions, redefining the histopathology of FTLD-TDP type C. This work establishes a central role for ANXA11 in FTLD-TDP type C. The unprecedented formation of heteromeric amyloid filaments in the human brain revises our understanding of amyloid assembly and may be of significance for the pathogenesis of neurodegenerative diseases.
Annexin A11 mutations are a rare cause of amyotrophic lateral sclerosis (ALS), wherein replicated protein variants P36R, G38R, D40G and D40Y are located in a small-alpha helix within the long, disordered N-terminus. To elucidate disease mechanisms, we characterised the phenotypes induced by a genetic loss of function (LoF) and by misexpression of G38R and D40G in vivo. Loss of Annexin A11 results in a low-penetrant behavioural phenotype and aberrant axonal morphology in zebrafish homozygous knockout larvae, which is rescued by human WT Annexin A11. Both Annexin A11 knockout/down and ALS variants trigger nuclear dysfunction characterised by Lamin B2 mis-localisation. The Lamin B2 signature also presented in anterior horn, spinal cord neurons from post-mortem ALS+/-FTD patient tissue possessing G38R and D40G protein variants. These findings suggest mutant Annexin A11 acts as a dominant negative, revealing a potential early nucleopathy highlighting nuclear envelope abnormalities preceding behavioural abnormality in animal models.
SUMMARYNeurodegenerative diseases are characterised by the abnormal filamentous assembly of specific proteins in the central nervous system1. Human genetic studies established a causal role for protein assembly in neurodegeneration2. However, the underlying molecular mechanisms remain largely unknown, which is limiting progress in developing clinical tools for these diseases. Recent advances in electron cryo-microscopy (cryo-EM) have enabled the structures of the protein filaments to be determined from patient brains1. All diseases studied to date have been characterised by the self-assembly of a single intracellular protein in homomeric amyloid filaments, including that of TAR DNA-binding protein 43 (TDP-43) in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration with TDP-43 inclusions (FTLD-TDP) Types A and B3,4. Here, we used cryo-EM to determine filament structures from the brains of individuals with FTLD-TDP Type C, one of the most common forms of sporadic FTLD-TDP. Unexpectedly, the structures revealed that a second protein, annexin A11 (ANXA11), co-assembles with TDP-43 in heteromeric amyloid filaments. The ordered filament fold is formed by TDP-43 residues G282/284–N345 and ANXA11 residues L39–L74 from their respective low-complexity domains (LCDs). Regions of TDP-43 and ANXA11 previously implicated in protein-protein interactions form an extensive hydrophobic interface at the centre of the filament fold. Immunoblots of the filaments revealed that the majority of ANXA11 exists as a ∼22 kDa N-terminal fragment (NTF) lacking the annexin core domain. Immunohistochemistry of brain sections confirmed the co-localisation of ANXA11 and TDP-43 in inclusions, redefining the histopathology of FTLD-TDP Type C. This work establishes a central role for ANXA11 in FTLD-TDP Type C. The unprecedented formation of heteromeric amyloid filaments in human brain revises our understanding of amyloid assembly and may be of significance for the pathogenesis of neurodegenerative diseases.
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