TDP-43 pathology is linked to motor neuron loss but is independent of stress granules in vivo
Nuclear depletion and cytoplasmic aggregation of TDP-43 define a pathological signature across amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), Alzheimers disease, and limbic-predominant age-related TDP-43 encephalopathy (LATE). Stress granule persistence and chronic activation of the integrated stress response (ISR) have been proposed to trigger this pathology, yet clinical trials targeting these pathways have failed despite robust target engagement suggesting that the prevailing model may be incomplete. Here, we use a physiologically relevant recurrent hyperthermia paradigm to directly test the relationship between stress granules and TDP-43 pathology in vivo. We find that RNA-binding proteins typically associated with stress granules persist as dynamic, phase-separated cytoplasmic assemblies in spinal motor neurons of both wild-type and mutant TDP-43 mice. These structures resolve spontaneously and are spatially distinct from TDP-43 puncta. Strikingly, in mutant TDP-43 mice with a compromised acute stress granule response, stress exposure provokes TDP-43 nuclear export and cytoplasmic deposition, culminating in selective loss of spinal -motor neurons after recurrent stress. Our results reveal that TDP-43 nuclear clearance and cytoplasmic aggregation can occur independently of stress granules in vivo, overturning a central assumption of TDP-43 pathogenesis. This paradigm shift reframes the mechanistic link between cellular stress and TDP-43 pathology, providing a new perspective for therapeutic strategies related to ISR modulation.