A wake-like state in vitro induced by transmembrane TNF/soluble TNF receptor reverse signaling

Tumor necrosis factor alpha (TNF) has sleep regulatory and brain development roles. TNF promotes sleep in vivo and in vitro while TNF inhibition diminishes sleep. Transmembrane (tm) TNF and the tmTNF receptors (Rs), are cleaved by tumor necrosis factor alpha convertase to produce soluble (s) TNF and sTNFRs. Reverse signaling occurs in cells expressing tmTNF upon sTNFR binding. sTNFR administration in vivo inhibits sleep, thus we hypothesized that a wake-like state in vitro would be induced by sTNFR-tmTNF reverse signaling. Somatosensory cortical neuron/glia co-cultures derived from male and female mice lacking both TNFRs (TNFRKO), or lacking TNF (TNFKO) and wildtype (WT) mice were plated onto six-well multi-electrode arrays. Daily one-hour electrophysiological recordings were taken on culture days 4 through 14. sTNFR1 (0.0, 0.3, 3, 30, 60, and 120 ng/µL) was administered on day 14. A final one-hour recording was taken on day 15. Four measures were characterized that are also used to define sleep in vivo: action potentials (APs), burstiness index (BI), synchronization of electrical activity (SYN), and slow wave power (SWP; 0.25-3.75 Hz). Development rates of these emergent electrophysiological properties increased in cells from mice lacking TNF or both TNFRs compared to cells from WT mice. Decreased SWP, after the three lowest doses (0.3, 3 and 30 ng/µL) of the sTNFR1, indicate a wake-like state in cells from TNFRKO mice. A wake-like state was also induced after 3 ng/µl sTNFR1 treatment in cells from TNFKO mice, which express the TNFR1 ligand, lymphotoxin alpha. Cells from WT mice showed no treatment effects. Results are consistent with prior studies demonstrating involvement of TNF in brain development, TNF reverse signaling, and sleep regulation in vivo. Further, the current demonstration of sTNFR1 induction of a wake-like state in vitro is consistent with the idea that small neuronal/glial circuits manifest sleep- and wake-like states analogous to those occurring in vivo. Finally, that sTNF forward signaling enhances sleep while sTNFR1 reverse signaling enhances a wake-like state is consistent with other sTNF/tmTNF/sTNFR1 brain actions having opposing activities.

Sleep- and time of day-linked RNA transcript expression in wild-type and IL1 receptor accessory protein-null mice

Sleep regulation involves interleukin-1β (IL1) family members, TNF, and circadian clock genes. Previously, we characterized spontaneous sleep and sleep after 8 h of sleep deprivation (SD) ending at zeitgeber time (ZT)4 and ZT16 in wild-type (WT) and IL1 receptor accessory protein (AcP)- and brain-specific AcP (AcPb)-knockout (KO) mice. Here, we applied quantitative reverse transcriptase polymerase chain reaction and Spearman gene pair expression correlation methods to characterize IL1, IL1 receptor 1 (IL1R1), AcP, AcPb, Period 1 (Per1), Clock, adenosine deaminase (Ada), peptidoglycan recognition protein 1 (Pglyrp1), and TNF mRNA expressions under conditions with distinct sleep phenotypes. In WT mice, IL1, IL1R1, AcP, Ada, and Clock mRNAs were higher at ZT4 (mid-sleep period) than at ZT16. mRNA expressions differed substantially in AcP and AcPb KO mice at those times. After SD ending at ZT4, only WT mice had a non-rapid eye movement sleep (NREMS) rebound, and AcPb and IL1R1 mRNA increases were unique to WT mice. In AcPb KO mice, which have spontaneous high EEG slow wave power, AcP and Pglyrp1 mRNAs were elevated relative to WT mice at ZT4. At ZT4, the AcPb KO - WT Spearman correlation difference networks showed high positive correlations between IL1R1 and IL1, Per1, and Clock and high negative correlations between TNF and Pglyrp1 and Ada. At ZT16, the WT mice gene pair expression network was mostly negative, whereas in AcP KO mice, which have substantially more rapid eye movement sleep than WT mice, it was all positive. We conclude that gene pair expression correlations depend on the presence of AcP and AcPb.NEW & NOTEWORTHY Spearman gene pair expression correlations depend upon the presence or absence of interleukin-1 receptor accessory protein and upon sleep phenotype.

Interleukin-1 receptor accessory proteins are required for normal homeostatic responses to sleep deprivation

Interleukin-1β (IL1) is a sleep regulatory substance. The IL1/IL1 type 1 receptor complex requires a receptor accessory protein (AcP) to signal. There are three isoforms of AcP. In the current experiments, mice lacking a neuron-specific isoform, called AcPb knockout (AcPb KO), or mice lacking AcP + AcPb isoforms (AcP KO) or wild-type (WT) mice were used. Spontaneous sleep and sleep responses to sleep deprivation (SD) between zeitgeber time (ZT) 20-ZT4 and ZT8-ZT16 were characterized. Furthermore, somatosensory cortical protein extracts were examined for phosphorylated (p) proto-oncogene tyrosine-protein kinase sarcoma (Src) and p38MAPK levels at ZT4 and ZT16 and after SD. Spontaneous sleep was similar in the three strains, except rapid eye movement sleep (REMS) duration between ZT12-ZT16 was greater in AcP KO than WT mice. After SD at ZT4, only WT mice had non-REMS (NREMS) rebounds. All mouse strains lacked an NREMS rebound after SD at ZT16. All strains after both SD periods had REMS rebounds. AcPb KO mice, but not AcP KO mice, had greater EEG delta wave (0.5-4 Hz) power during NREMS than WT mice. p-Src was very low at ZT16 but high at ZT4, whereas p-p38MAPK was low at ZT4 and high at ZT16. p-p38MAPK levels were not sensitive to SD. In contrast, p-Src levels were less after SD at the P = 0.08 level of significance in the strains lacking AcPb. We conclude that AcPb is required for NREMS responses to sleep loss, but not for SD-induced EEG delta wave or REMS responses.NEW & NOTEWORTHY Interleukin-1β (IL1), a well-characterized sleep regulatory substance, requires an IL1 receptor accessory protein (AcP); one of its isoforms is neuron-specific (called AcPb). We showed that in mice, AcPb is required for nonrapid eye movement sleep responses following 8 h of sleep loss ending 4 h after daybreak but did not affect rapid eye movement sleep rebound. Sleep loss reduced phosphorylation of proto-oncogene tyrosine-protein kinase sarcoma but not of the less sensitive p38MAPK, downstream IL1 signaling molecules.