Hemizygous deletion of Tbk1 worsens neuromuscular junction pathology in TDP-43G298S transgenic mice.

Mutations in the genes TARDBP (encoding the TDP-43 protein) and TBK1 can cause familial ALS. Neuronal cytoplasmatic accumulations of the misfolded, hyperphosphorylated RNA-binding protein TDP-43 are the pathological hallmark of most ALS cases and have been suggested to be a key aspect of ALS pathogenesis. Pharmacological induction of autophagy has been shown to reduce mutant TDP-43 aggregates and alleviate motor deficits in mice. TBK1 is exemplary for several other ALS genes that regulate autophagy. Consequently, we employed double mutant mice with both a heterozygous Tbk1 deletion and transgenic expression of human TDP-43G298S to test the hypothesis that impaired autophagy reduces intracellular clearance of an aggregation-prone protein and enhances toxicity of mutant TDP-43. The heterozygous deletion of Tbk1 did not change expression or cellular distribution of TDP-43 protein, motor neuron loss or reactive gliosis in the spinal cord of double-mutant mice at the age of 19 months. However, it aggravated muscle denervation and, albeit to a small and variable degree, motor dysfunction in TDP-43G298S transgenic mice, as similarly observed in the SOD1G93A transgenic mouse model for ALS before. Conclusively, our findings suggest that TBK1 mutations can affect the neuromuscular synapse.

Heterozygous Tbk1 loss has opposing effects in early and late stages of ALS in mice.

Heterozygous loss-of-function mutations of TANK-binding kinase 1 (TBK1 ) cause familial ALS, yet downstream mechanisms of TBK1 mutations remained elusive. TBK1 is a pleiotropic kinase involved in the regulation of selective autophagy and inflammation. We show that heterozygous Tbk1 deletion alone does not lead to signs of motoneuron degeneration or disturbed autophagy in mice during a 200-d observation period. Surprisingly, however, hemizygous deletion of Tbk1 inversely modulates early and late disease phases in mice additionally overexpressing ALS-linked SOD1G93A , which represents a "second hit" that induces both neuroinflammation and proteostatic dysregulation. At the early stage, heterozygous Tbk1 deletion impairs autophagy in motoneurons and prepones both the clinical onset and muscular denervation in SOD1G93A/Tbk1+/- mice. At the late disease stage, however, it significantly alleviates microglial neuroinflammation, decelerates disease progression, and extends survival. Our results indicate a profound effect of TBK1 on brain inflammatory cells under pro-inflammatory conditions and point to a complex, two-edged role of TBK1 in SOD1-linked ALS.