Riordan, R. | bioRxiv Science

bioRxiv2026

TMEM106B C-Terminal fragment aggregation exacerbates α-synuclein and TDP-43 proteinopathy phenotypes.

Genetic variation in the human gene encoding the lysosomal transmembrane protein 106B (TMEM106B) drives risk of neurodegenerative dementia. A C-terminal fragment of TMEM106B (TMEM CT) accumulates in lesions across neurodegenerative disease, potentially contributing to neurotoxicity and hampering efficacy of therapeutic interventions. Previously, we developed the first transgenic organism model of TMEM CT neuronal aggregation in Caenorhabditis elegans (C. elegans). We demonstrated that TMEM CT neuronal aggregation drives severe neuronal dysfunction and neuronal loss. To investigate the potential synergistic interaction of TMEM CT aggregation with other types of aggregated neurotoxic proteinopathies occurring in dementia, we assessed neuronal degeneration and pathogenic protein accumulation in bigenic C. elegans expressing TMEM CT and other key proteinopathies of neurodegeneration including a-synuclein, tau, and TAR DNA binding protein 43 (TDP-43). Our results showed strong neurotoxic synergy of TMEM106B with TDP-43 or -synuclein. However, we detected only mild synergy between TMEM106B and tau. This work provides evidence in support of TMEM CT aggregation as a significant participant in the neurodegenerative process attributed to other toxic protein aggregates. The work also highlights the importance of considering secondary proteinopathy contributions including TMEM CT aggregation when developing interventions against primary TDP-43 or -synuclein proteinopathies.

neuroscience↗

bioRxiv2024

TMEM106B C-terminal fragments aggregate and drive neurodegenerative proteinopathy.

Genetic variation in the lysosomal and transmembrane protein 106B (TMEM106B) modifies risk for a diverse range of neurodegenerative disorders, especially frontotemporal lobar degeneration (FTLD) with progranulin (PGRN) haplo-insufficiency, although the molecular mechanisms involved are not yet understood. Through advances in cryo-electron microscopy (cryo-EM), homotypic aggregates of the C-Terminal domain of TMEM106B (TMEM CT) were discovered as a previously unidentified cytosolic proteinopathy in the brains of FTLD, Alzheimers disease, progressive supranuclear palsy (PSP), and dementia with Lewy bodies (DLB) patients. While it remains unknown what role TMEM CT aggregation plays in neuronal loss, its presence across a range of aging related dementia disorders indicates involvement in multi-proteinopathy driven neurodegeneration. To determine the TMEM CT aggregation propensity and neurodegenerative potential, we characterized a novel transgenic C. elegans model expressing the human TMEM CT fragment constituting the fibrillar core seen in FTLD cases. We found that pan-neuronal expression of human TMEM CT in C. elegans causes neuronal dysfunction as evidenced by behavioral analysis. Cytosolic aggregation of TMEM CT proteins accompanied the behavioral dysfunction driving neurodegeneration, as illustrated by loss of GABAergic neurons. To investigate the molecular mechanisms driving TMEM106B proteinopathy, we explored the impact of PGRN loss on the neurodegenerative effect of TMEM CT expression. To this end, we generated TMEM CT expressing C. elegans with loss of pgrn-1, the C. elegans ortholog of human PGRN. Neither full nor partial loss of pgrn-1 altered the motor phenotype of our TMEM CT model suggesting TMEM CT aggregation occurs downstream of PGRN loss of function. We also tested the ability of genetic suppressors of tauopathy to rescue TMEM CT pathology. We found that genetic knockout of spop-1, sut-2, and sut-6 resulted in weak to no rescue of proteinopathy phenotypes, indicating that the mechanistic drivers of TMEM106B proteinopathy may be distinct from tauopathy. Taken together, our data demonstrate that TMEM CT aggregation can kill neurons. Further, expression of TMEM CT in C. elegans neurons provides a useful model for the functional characterization of TMEM106B proteinopathy in neurodegenerative disease.

neuroscience↗