TDP-43 LLPS and mitochondrial dysfunction in neurodegeneration

PROJECT SUMMARY Autosomal dominant mutations in TDP-43 (transactive response DNA binding protein of 43 kDa) are associated with amyotrophic lateral sclerosis (ALS), the most common motor disease characterized by progressive motor neuron degeneration in the brain stem and spinal cord. And, TDP-43 has been increasingly recognized as the common hallmark disease protein for a wide range of neurodegenerative diseases including ALS, frontotemporal dementia (FTD), limbic-predominant age-related TDP-43 encephalopathy (LATE), cerebral age-related TDP-43 with sclerosis (CARTS), Alzheimer's Disease (AD), and other AD related dementias (ADRD). Mitochondria are closely linked to neurodegeneration, and have been implicated as a critical target of TDP-43. Previous studies have established that TDP-43 can undergo liquid-liquid phase separation (LLPS), a dynamic process by which cells sequester biomolecules into membraneless condensates. Despite a growing body of evidence indicating the significant involvement of mitochondria and LLPS in TDP-43 related neurodegeneration, whether and how mitochondria and LLPS-mediated TDP-43 condensates interact and relate to one another remain largely unknown, presenting a compelling area of research about the intricate mechanisms underlying neurodegenerative diseases. Based on recently generated cell and mouse models, our pilot studies have found significantly increased oxygen consumption in response to LLPS loss, revealing an unexpected role of TDP-43 LLPS in the regulation of mitochondrial bioenergetics. Cytosolic condensations of TDP-43 are dynamically associated with mitochondria, and notably, the inhibition of LLPS not only significantly suppresses TDP-43 mitochondrial localization, but also strikingly alleviates TDP-43-induced mitochondrial dysfunction and neuronal loss, underscoring the critical role of LLPS and mitochondria interaction. Using multiple cell and animal models with altered TDP-43 LLPS, this project will systematically investigate whether and how LLPS regulates TDP-43 mitochondrial localization, and contributes to TDP-43 induced mitochondrial and neuronal dysfunction in vitro and in vivo. The presence of TDP-43 proteinopathy is a prominent pathological hallmark found in a spectrum of major neurodegenerative diseases, which includes ALS and AD/ADRD. The proposed investigations into TDP- 43 LLPS, its interactions with mitochondria, and its role in driving neuronal loss and disease progression in mouse models are important for our understanding of neurodegenerative diseases at a broad and fundamental level.