Fructose-2,6-bisphosphate restores TDP-43 pathology-driven genome repair deficiency in motor neuron diseases

TAR DNA-binding protein 43 (TDP-43) proteinopathy plays a critical role in neurodegenerative diseases, including amyotrophic lateral sclerosis and frontotemporal dementia (FTD). In our recent discovery, we identified that TDP-43 plays an essential role in DNA double-strand break (DSB) repair via the non-homologous end joining (NHEJ) pathway. Here, we found persistent DNA damage in the brains of ALS/FTD patients, primarily in the transcribed regions of the genome. We further investigated the underlying mechanism and found that polynucleotide kinase 3'-phosphatase (PNKP) activity was severely impaired in the nuclear extracts of both patient brains and TDP-43-depleted cells. PNKP is a key player in DSB repair within the transcribed genome, where its 3'-P termini processing activity is crucial for preventing persistent DNA damage and neuronal death. The inactivation of PNKP in ALS/FTD was due to reduced levels of its interacting partner, phosphofructo-2-kinase fructose 2,6 bisphosphatase (PFKFB3), and its biosynthetic product, fructose-2,6-bisphosphate (F2,6BP), an allosteric modulator of glycolysis. Recent work from our group has shown that F2,6BP acts as a positive modulator of PNKP activity in vivo. Notably, exogenous supplementation with F2,6BP restored PNKP activity in nuclear extracts from ALS/FTD brain samples and patient-derived induced pluripotent stem (iPS) cells harboring pathological mutations. Furthermore, we demonstrate that supplementation of F2,6BP restores genome integrity and partially rescues motor phenotype in a Drosophila model of ALS. Our findings underscore the possibility of exploring the therapeutic potential of F2,6BP or its analogs in TDP-43 pathology-associated motor neuron diseases.