Relation between pH alterations in cellular models of amyotrophic lateral sclerosis and TDP-43 protein aggregation

Amyotrophic lateral sclerosis (ALS) is the most common degenerative disease of the motor neuron. TDP-43 aggregates constitute a hallmark of ALS and play a major role in the motoneuron degeneration. Several factors can influence the ability of TDP-43 to form aggregates. It was previously shown that, in vitro, mild pH modification can induce a conformational change in TDP-43 structure thus increasing its propensity to aggregate. Therefore, we first analyzed the intracellular pH alterations in a cellular model of ALS as well as fibroblasts derived from ALS patients. HEK293T cells overexpressing wildtype TDP-43 presented an increase in the fluorescence signal of the probe BCECF, which is sensitive to low pH. We also observed an increase in BCECF signal (i.e., low pH) in cultures of fibroblasts obtained from ALS patients as compared to controls. On the other hand, we tested the effect of pH alterations on the localization and aggregation of TDP-43. HEK293T cells overexpressing wildtype TDP-43 were incubated for 1h or 2h with solutions of different pH (6.4, 7.2 and 8.0). Incubation of cells for 1h in solutions of pH 6.4 and 8.0 increased TDP-43 aggregates, an effect lost after a 2h incubation. In these conditions, TDP-43 aggregation was accompanied by its mislocalization to the cytoplasm. Our results suggest that a decrease in cellular pH is observed in a cellular model of TDP-43 proteinopathy and in fibroblasts derived from ALS patients compared to controls. Alterations in cellular pH also seemed to have an effect on the aggregation and cellular localization of TDP-43. Further studies should focus on understanding how cellular pH alterations affect TDP-43, which might offer a new way to mitigate TDP-43 pathology in ALS.