Knockdown of transactive response DNA-binding protein TDP-43 downregulates histone deacetylase 6

TDP-43 is an RNA/DNA-binding protein implicated in transcriptional repression and mRNA processing. Inclusions of TDP-43 are hallmarks of frontotemporal dementias and amyotrophic lateral sclerosis. Besides aggregation of TDP-43, loss of nuclear localization is observed in disease. To identify relevant targets of TDP-43, we performed an expression profiling study. Thereby, histone deacetylase 6 (HDAC6) downregulation was discovered upon TDP-43 silencing on mRNA and protein level in human embryonic kidney HEK293E and neuronal SH-SY5Y cells. This was accompanied by accumulation of the major HDAC6 substrate, acetyl-tubulin. Expression of wild-type but neither RNA-binding- nor nuclear-localization-deficient TDP-43 restored HDAC6 expression. Moreover, TDP-43 bound specifically to HDAC6 mRNA arguing for a direct functional interaction. Importantly, in vivo validation in TDP-43 knockout Drosophila melanogaster also showed HDAC6 mRNA decrease. HDAC6 is necessary for protein aggregate formation and degradation. Indeed, downregulation of HDAC6 reduced aggregate formation and increased cytotoxicity of expanded poly-glutamine ataxin-3 in TDP-43 silenced cells. This was completely restored by co-transfection with HDAC6. In conclusion, loss of functional TDP-43 causes HDAC6 downregulation and might thereby contribute to pathogenesis. Comparison of TDP-43 knockdown in HEK293E cells against cells transfected with scrambled siRNA. 4 independend transfections per siRNA were used.