RNA dependent suppression of C9orf72 ALS/FTD associated neurodegeneration by Matrin-3

Abstract

The most common genetic cause of amyotrophic lateral sclerosis (ALS) is a GGGGCC (G4C2) hexanucleotide repeat expansions in first intron of the C9orf72 gene. The accumulation of repetitive RNA sequences can mediate toxicity potentially through the formation of intranuclear RNA foci that sequester key RNA-binding proteins (RBPs), and non-ATG mediated translation into toxic dipeptide protein repeats. However, the contribution of RBP sequestration to the mechanisms underlying RNA-mediated toxicity remain unknown. Here we show that the ALS-associated RNA-binding protein, Matrin-3 (MATR3), colocalizes with G4C2 RNA foci in patient tissues as well as iPSC-derived motor neurons harboring the C9orf72 mutation. Hyperexpansion of C9 repeats perturbed subcellular distribution and levels of endogenous MATR3 in C9-ALS patient-derived motor neurons. Interestingly, we observed that ectopic expression of human MATR3 strongly mitigates G4C2-mediated neurodegeneration in vivo. MATR3-mediated suppression of C9 toxicity was dependent on the RNA-binding domain of MATR3. Importantly, we found that expression of MATR3 reduced the levels of RAN-translation products in mammalian cells in an RNA-dependent manner. Finally, we have shown that knocking down endogenous MATR3 in C9-ALS patient-derived iPSC neurons decreased the presence of G4C2 RNA foci in the nucleus. Overall, these studies suggest that MATR3 genetically modifies the neuropathological and the pathobiology of C9orf72 ALS through modulating the RNA foci and RAN translation.

Interplay of RNA-Binding Proteins and microRNAs in Neurodegenerative Diseases

“…HuD binds to and regulates circular RNAs derived from genes regulating neuronal development and synaptic plasticity and may act as a sponge for the miRNAs such as miR-125a-5p, which has previously been reported to be associated with aging [147,148]. Matrin-3 was recently found to be strongly linked to the pathogenesis of ALS [149][150][151] and has been shown to regulate processing of the synaptic miR-138-5p [152] (Table 2). [129] is reduced in the frontal cortex of ALS patients [129] TAF15 miR-17-92 CDKN1A/p21 regulates miRNA biogenesis to decrease genes related to cell proliferation [132] is reduced in an SOD1 G93A mouse model [133] hnRNP A1 miR-590-3p n.d. is cooperatively regulated in neuronal maintenance ?…”

“…HuD binds to and regulates circular RNAs derived from genes regulating neuronal development and synaptic plasticity and may act as a sponge for the miRNAs such as miR-125a-5p, which has previously been reported to be associated with aging [ 147 , 148 ]. Matrin-3 was recently found to be strongly linked to the pathogenesis of ALS [ 149 , 150 , 151 ] and has been shown to regulate processing of the synaptic miR-138-5p [ 152 ] ( Table 2 ).…”

Altered Phase Separation and Cellular Impact in C9orf72-Linked ALS/FTD

“…G 4 C 2 repeat RNA also binds to the nuclear speckle protein SRSF1, sequestering it into RNA foci and this interaction leads to increased nuclear export of G 4 C 2 RNA, thereby increasing RAN translation and enhancing DPR toxicity (Hautbergue et al, 2017). The transcriptional regulators Pur-α, a binding partner of SRSF1, and Matrin-3 can also bind G 4 C 2 repeat RNA and modify toxicity; both are also mislocalized to the cytoplasm upon G 4 C 2 RNA expression (Xu et al, 2013;Ramesh et al, 2020), with Pur-α being recruited to stress granules (Rossi et al, 2015). Similarly, to SRSF1, Matrin-3 also reduced levels of RAN-translation products (Ramesh et al, 2020).…”

“…The transcriptional regulators Pur-α, a binding partner of SRSF1, and Matrin-3 can also bind G 4 C 2 repeat RNA and modify toxicity; both are also mislocalized to the cytoplasm upon G 4 C 2 RNA expression (Xu et al, 2013;Ramesh et al, 2020), with Pur-α being recruited to stress granules (Rossi et al, 2015). Similarly, to SRSF1, Matrin-3 also reduced levels of RAN-translation products (Ramesh et al, 2020). HnRNP H is also a strong interactor of G 4 C 2 repeat RNA and is sequestered into RNA foci in patients where its depletion results in the reduction in alternative splicing of its targets (Lee et al, 2013;Conlon et al, 2016).…”

Dysfunction of RNA/RNA-Binding Proteins in ALS Astrocytes and Microglia

“…Yet, this observation is a proof of concept that G4C2 expansion might induce toxicity in these cells. In neurons, RNA foci are suggested to cause defects in RNA processing through sequestration of RNA-binding proteins [ 115 , 116 , 117 , 118 , 119 , 120 , 121 ], but it is still little explored if this might also occur in glial cells. However, a first clue comes from a report that shows a significant colocalization of the splicing factor hnRNP H with G4C2 RNA foci in cultured astrocytes from C9orf72 post-mortem tissues compared to control cells [ 122 ].…”