TIA1-mediated stress granules promote neurodegeneration by sequestering <i>HSP70</i> mRNA in C9orf72 mice

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease with progressive loss of motor neurons in the central nervous system. Recent studies have reported that there are mutations at the T-cell antigen-1 (TIA1) domain site in some ALS patients. TIA1 is a key component of stress granules (SGs), but its role and mechanism in ALS pathogenesis remain unclear. In this study, we found that TIA1 was upregulated in the motor cortex of post-mortem ALS patients as well as in the motor cortex neurons of C9orf72-poly-Gly-Ala (GA) mice (ALS mice). TIA1 knockout in the CNS [TIA1Nestin-conditional knockout (CKO) mice] alleviated motor neuron loss, neuroinflammation and motor dysfunction in C9orf72-poly-GA mice. Mechanistically, RNA sequencing combined with the C9orf72-ALS/frontotemporal dementia patient single nucleus RNA-sequencing database revealed that mRNA of heat shock protein 70 (HSP70) family member genes such as HSPa1b were upregulated in the motor cortex of TIA1Nestin-CKO ALS mice. We further found that TIA1-mediated SG formation was increased during ALS pathogenesis, leading to HSP70 mRNA being sequestered into SGs. This reduced HSP70 expression, impairing the degradation of poly-GA aggregates by the UBQLN2-HSP70 pathway and exacerbating C9orf72-ALS progression. Taken together, these findings highlight a previously unrecognized role of TIA1-mediated SGs in promoting ALS pathogenesis by sequestering HSP70 mRNA, suggesting potential therapeutic targets for ALS treatment.