Kinase signalling in excitatory neurons regulates sleep quantity and depth.

Progress has been made in the elucidation of sleep and wakefulness regulation at the neurocircuit level1,2. However, the intracellular signalling pathways that regulate sleep and the neuron groups in which these intracellular mechanisms work remain largely unknown. Here, using a forward genetics approach in mice, we identify histone deacetylase 4 (HDAC4) as a sleep-regulating molecule. Haploinsufficiency of Hdac4, a substrate of salt-inducible kinase 3 (SIK3)3, increased sleep. By contrast, mice that lacked SIK3 or its upstream kinase LKB1 in neurons or with a Hdac4S245A mutation that confers resistance to phosphorylation by SIK3 showed decreased sleep. These findings indicate that LKB1-SIK3-HDAC4 constitute a signalling cascade that regulates sleep and wakefulness. We also performed targeted manipulation of SIK3 and HDAC4 in specific neurons and brain regions. This showed that SIK3 signalling in excitatory neurons located in the cerebral cortex and the hypothalamus positively regulates EEG delta power during non-rapid eye movement sleep (NREMS) and NREMS amount, respectively. A subset of transcripts biased towards synaptic functions was commonly regulated in cortical glutamatergic neurons through the expression of a gain-of-function allele of Sik3 and through sleep deprivation. These findings suggest that NREMS quantity and depth are regulated by distinct groups of excitatory neurons through common intracellular signals. This study provides a basis for linking intracellular events and circuit-level mechanisms that control NREMS.

Middle East respiratory syndrome coronavirus ORF4b protein inhibits TLR7- and TLR9-dependent alpha interferon induction.

The Toll-like receptor (TLR)7- and TLR9-dependent signalling cascade is responsible for production of a large amount of alpha interferon by plasmacytoid dendritic cells upon viral infection. Here, we show that Middle East respiratory syndrome coronavirus (MERS-CoV) accessory protein ORF4b has the most potential among the MERS-CoV accessory proteins to inhibit the TLR7/9-signaling-dependent alpha interferon production. ORF4b protein, which has a bipartite nuclear localization signal, was found to bind to IKKα, a kinase responsible for phosphorylation of interferon regulatory factor (IRF)7. This interaction caused relocation of a large proportion of IKKα from the cytoplasm to the nucleus. Studies using ORF4b and IKKα mutants demonstrated that ORF4b protein inhibited IKKα-mediated IRF7 phosphorylation by sequestering IKKα in the nucleus and by impeding the phosphorylation process of cytoplasmic IKKα.