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

Abstract

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 a critical role in DNA double-strand break (DSB) repair via the non-homologous end joining (NHEJ) pathway. Here, we found persistent DNA damage in brains of ALS/FTD patients, primarily in the transcribed regions of the genome. We further investigated the underlying mechanism and found that the activity of polynucleotide kinase 3' phosphatase (PNKP) was severely impaired in the nuclear extracts of both the 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 both nuclear extracts from ALS/FTD brain samples and in patient-derived induced pluripotent stem (iPS) cells harboring pathological mutations. Our findings underscore the possibility of exploring the therapeutic potential of F2,6BP or its analogs in TDP-43 pathology-associated motor neuron diseases.