Calcineurin depletion coincides with phosphorylated TDP-43 deposition in a mouse model of ALS/FTLD-TDP

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD-TDP) exhibit predominantly cytoplasmic phosphorylated inclusions of the protein TDP-43 as the major neuropathological lesion. Phosphorylated TDP-43 can modify protein aggregation and promote neuronal dysfunction and neurodegeneration in models of ALS and FTLD-TDP. The phosphatase calcineurin has previously been shown to directly dephosphorylate TDP-43 in vitro and prevent accumulation of phosphorylated TDP-43 in vivo in C. elegans. However, it is unknown whether dysregulation of calcineurin contributes to increased TDP-43 phosphorylation and neurodegeneration in the mammalian brain. Here we show in an inducible mouse model of ALS/FTLD-TDP driven by expression and cytoplasmic mislocalization of human TDP-43 (rNLS8 mice), calcineurin protein decreases dramatically in the brain. This depletion coincides with increased levels of the TDP-43 kinase CDC7 and accumulation of phosphorylated TDP-43, and precedes frank neurodegeneration. Using brain-wide single nucleus RNA sequencing (snRNAseq) in symptomatic rNLS8 mice, we find cell-type selective reduced expression of catalytic and regulatory subunits of calcineurin predominantly in GABAergic and glutamatergic neurons. In mouse primary neuron culture and C. elegans models of ALS/FTLD-TDP, we demonstrate activation or overexpression of calcineurin protects against accumulation of phosphorylated TDP-43, neurotoxicity, and neurodegeneration. Taken together, our data suggests calcineurin dysregulation may be a major contributor to loss of brain resilience mechanisms against phosphorylated TDP-43. Restoring calcineurin activity may present a new target for intervening in TDP-43 proteinopathies, including ALS and FTLD-TDP.