TDP‐43 is recruited to stress granules in conditions of oxidative insult

Abstract

Transactive response DNA‐binding protein 43 (TDP‐43) forms abnormal ubiquitinated and phosphorylated inclusions in brain tissues from patients with amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration. TDP‐43 is a DNA/RNA‐binding protein involved in RNA processing, such as transcription, pre‐mRNA splicing, mRNA stabilization and transport to dendrites. We found that in response to oxidative stress and to environmental insults of different types TDP‐43 is capable to assemble into stress granules (SGs), ribonucleoprotein complexes where protein synthesis is temporarily arrested. We demonstrated that a specific aminoacidic interval (216–315) in the C‐terminal region and the RNA‐recognition motif 1 domain are both implicated in TDP‐43 participation in SGs as their deletion prevented the recruitment of TDP‐43 into SGs. Our data show that TDP‐43 is a specific component of SGs and not of processing bodies, although we proved that TDP‐43 is not necessary for SG formation, and its gene silencing does not impair cell survival during stress. The analysis of spinal cord tissue from ALS patients showed that SG markers are not entrapped in TDP‐43 pathological inclusions. Although SGs were not evident in ALS brains, we speculate that an altered control of mRNA translation in stressful conditions may trigger motor neuron degeneration at early stages of the disease.

Addition of exogenous SOD1 aggregates causes TDP-43 mislocalisation and aggregation

“…TDP-43 mislocalisation is a common response to a variety of stressors including oxidative stress (Colombrita et al 2009), heat shock stress (Chang et al 2013), and proteosomal stress (Scotter et al 2014). Indeed, extranuclear accumulation of WT TDP-43 has been shown to be a common pathology in sALS, FTD and Alzheimer's disease, and therefore may be a general consequence of cellular stress (Wilson et al 2011).…”

Mitochondrial Dysfunction and Decrease in Body Weight of a Transgenic Knock-in Mouse Model for TDP-43

“…In the nucleus, TDP-43 is involved in microRNA biogenesis (16) and splicing regulation, where it causes exon inclusion or exclusion, depending on the number and localization of its UGenriched target sequences (17)(18)(19)(20)(21)(22). Upon stress exposure, TDP-43 is recruited to stress granules in cultured cells, which serve as cytoplasmic storage of RNAs that become instantly available for translation without further transcription processes (10,(23)(24)(25). Under pathological conditions, TDP-43 is ubiquitinated and phosphorylated and forms neuronal cytoplasmic inclusions in upper and lower motor neurons (26,27).…”

Linking RNA Dysfunction and Neurodegeneration in Amyotrophic Lateral Sclerosis

“…Within the nucleus, TDP43 has essential roles in RNA transcription, splicing, and stability [13,14,[47][48][49][50], and transports select mRNA to localized sites of translation within the cytoplasm [20,51,52]. In addition to its function in RNA trafficking, cytoplasmic TDP43 also helps regulate RNA translation and homeostasis by sequestering transcripts in RNA granules [53][54][55][56]. Thus, the loss of TDP43 function stemming from inadequate nuclear protein, a gain of function arising from the accumulation of cytoplasmic TDP43, or both, might result in RNA misprocessing and subsequent neurodegeneration.…”

“…Prion-like domains are also found in mammalian proteins whose function requires reversible selfaggregation, including proteins that are involved in the formation of stress granules [89], RNA-dense cytoplasmic particles that sequester nonessential mRNAs and prevent their translation when cells are under duress [90]. TDP43 and FUS are incorporated into cytoplasmic stress granules upon exposure to oxidative, heat, or endoplasmic reticulum stress, but return to their normal (predominantly nuclear) localization when the stress is removed [41,53,55,56,91,92]. The reversible aggregation of TDP43 and FUS, and the resulting sequestration of any bound RNAs, may be essential to their physiological functions [87]; however, disrupting the precarious balance between aggregate formation and dissolution may also contribute to the irreversible development of inclusions and the pathogenic deposition of RNA binding proteins in ALS [93] (Fig.…”