Monomerization of TDP-43 is a key determinant for inducing TDP-43 pathology in amyotrophic lateral sclerosis

Abstract

The cytoplasmic aggregation of TAR DNA binding protein-43 (TDP-43), also known as TDP-43 pathology, is the pathological hallmark of amyotrophic lateral sclerosis (ALS). However, the mechanism underlying TDP-43 cytoplasmic mislocalization and subsequent aggregation remains unclear. Here, we show that TDP-43 dimerization/multimerization is impaired in the postmortem brains and spinal cords of patients with sporadic ALS and that N-terminal dimerization–deficient TDP-43 consists of pathological inclusion bodies in ALS motor neurons. Expression of N-terminal dimerization–deficient mutant TDP-43 in Neuro2a cells and induced pluripotent stem cell–derived motor neurons recapitulates TDP-43 pathology, such as Nxf1-dependent cytoplasmic mislocalization and aggregate formation, which induces seeding effects. Furthermore, TDP-DiLuc, a bimolecular luminescence complementation reporter assay, could detect decreased N-terminal dimerization of TDP-43 before TDP-43 pathological changes caused by the transcription inhibition linked to aberrant RNA metabolism in ALS. These findings identified TDP-43 monomerization as a critical determinant inducing TDP-43 pathology in ALS.

Simulating growth of TDP-43 cytosolic inclusion bodies in neuron soma

“…i In cases of ALS, patients typically succumb to the disease within 2-5 years from the onset of symptoms [3,5,6,13]. It is probable that the growth of TDP-43 inclusion bodies commenced even before the manifestation of the disease symptoms.…”

“…According to [5], the initial stage of TDP-43 aggregation involves the monomerization of TDP-43 dimers: To simulate TDP-43 aggregation, a phenomenological two-step Finke-Watzky (F-W) model, as described in [21,22], was employed. The F-W model, which has been successfully applied to fit experimental data on neurological protein aggregation [21], simulates polymer aggregation through two pseudoelementary, parallel, and competing processes: continuous nucleation and autocatalytic surface growth [23].…”

“…The presence of TDP-43 inclusion bodies stands out as a pathological hallmark in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) diseases [1][2][3][4]. ALS is distinguished by the gradual decline of motor neurons, resulting in skeletal muscle weakness and, ultimately, fatality within a span of 3 to 5 years [5,6]. TDP-43, a nuclear, intrinsically disordered, soluble protein [7,8] with a molecular weight of 43 kDa [9], is synthesized in the cytoplasm, and in healthy neurons, it predominantly resides in the nucleus [10][11][12].…”

“…Under pathological conditions, TDP-43 undergoes a conversion from its native dimeric state [15] to a monomeric form. This transformation results in TDP-43 mislocalization from the nucleus to the cytoplasm, where it forms irreversible, amorphous aggregates [16,5]. Subsequently, these aggregates grow into inclusion bodies.…”

“…The presence of TDP-43 inclusion bodies stands out as a pathological hallmark in amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) diseases [1-4]. ALS is distinguished by the gradual decline of motor neurons, resulting in skeletal muscle weakness and, ultimately, fatality within a span of 3 to 5 years [5,6].…”