4R-tau isoform induction via TDP-43 in neurons in response to insulin: converging signaling pathways with implications for neurodegenerative disease.

Tau protein isoforms, regulated during development, are influenced by the nuclear factor TDP-43, which plays a crucial role in tau mRNA stability and exon 10 inclusion. Both tau and TDP-43 are prone to pathological phosphorylation and aggregation, with specific phosphorylated forms of TDP-43 linked to cytoplasmic mislocalization and alterations in the 3R/4R tau ratio as detected in different pathologies. In this study, we show that insulin treatment of embryonic mouse primary cortical neurons-cells that normally express only 3R-tau-induces the expression of 4R-tau, suggesting that metabolic signaling can influence tau isoform expression in a developmentally immature neuronal context. In addition, experiments in HEK293 cells revealed isoform-specific stabilization effects and showed that insulin promotes TDP-43 redistribution to the cytoplasm along with a phosphorylation pattern. These results underscore the complex interplay between TDP-43 and tau isoforms and metabolic signaling pathways that play a crucial role in their expression and localization with potential implications for understanding mechanisms of neurodegenerative disease onset and progression.