Lithium effects on circadian rhythms in fibroblasts and suprachiasmatic nucleus slices from Cry knockout mice

Abstract

Lithium is widely used as a treatment of bipolar disorder, a neuropsychiatric disorder associated with disrupted circadian rhythms. Lithium is known to lengthen period and increase amplitude of circadian rhythms. One possible pathway for these effects involves inhibition of glycogen synthase kinase-3β (GSK-3β), which regulates degradation of CRY2, a canonical clock protein determining circadian period. Although there is no evidence that GSK-3β directly phosphorylates CRY1, it is known to play important roles in regulating circadian period and phase. In this paper, we tested the hypothesis that lithium affects circadian rhythms through CRYs. We cultured fibroblasts and slices of the suprachiasmatic nucleus (SCN), the master circadian pacemaker of the brain, from Cry1-/-, Cry2-/-, or wild-type (WT) mice bearing the PER2∷LUC circadian reporter. Lithium was applied in the culture medium, and circadian rhythms of PER2 expression were measured. In WT and Cry2-/- fibroblasts, 10 mM lithium increased PER2 expression and rhythm amplitude, but 1 mM lithium did not affect either period or amplitude. In non-rhythmic Cry1-/- fibroblasts, 10 mM lithium increased PER2 expression. In SCN slices, 1 mM lithium lengthened period ∼1 h in all genotypes, but did not affect amplitude except in Cry2-/- SCN. Thus, the amplitude-enhancing effect of lithium in WT fibroblasts was unaffected by Cry2 knockout and occurred in the absence of period-lengthening, whereas the period-lengthening effect of lithium in WT SCN was unaffected by Cry1 or Cry2 knockout and occurred in the absence of rhythm amplification, suggesting that these two effects of lithium on circadian rhythms are independent of CRYs and of each other.

GSK3 activity regulates rhythms in hippocampal clock gene expression and synaptic plasticity

“…Second, we found that chronic GSK3 inhibition shortened the cycle of the hippocampal molecular clock, consistent with evidence in other mammalian cell types and brain areas (Besing et al, ; Hirota et al, ; Li, Lu, Beesley, Loudon, & Meng, ). Although it is well documented that the GSK3 inhibitor lithium lengthens the period of circadian rhythms (Abe, Herzog, & Block, ; Dokucu, Yu, & Taghert, ; Hirota et al, ; Iwahana, Hamada, Uchida, & Shibata, ; LeSauter & Silver, ; Li et al, ; Mason & Biello, ; Mohawk, Miranda‐Anaya, Tataroglu, & Menaker, ; Noguchi, Lo, Diemer, & Welsh, ; Osland et al, ), our results with a more selective GSK3 inhibitor suggest that lithium‐induced effects may be due to other nonspecific targets such as inositol phosphatase inhibition (Quiroz, Gould, & Manji, ).…”

Circadian rhythm bifurcation induces flexible phase resetting by reducing circadian amplitude

“…For measuring luminescence rhythms from explants, we placed the sealed 35‐mm culture dishes into a luminometer (LumiCycle, Actimetrics, Inc., Wilmette, IL), inside a standard tissue culture incubator set at 35°C, dry, 0% CO 2 . Luminescence from each dish was measured by a photomultiplier tube for 70 s at intervals of 10 min and recorded as counts/s over 6 days as described previously (Noguchi, Lo, Diemer, & Welsh, 2016). When the average bioluminescence intensity over 6 days did not exceed 40 counts/s above the background level (10–50 counts/s) or dropped to background level within 4 days, the explant was considered damaged, and was excluded from analysis (59/490 explants).…”

In vivo evaluation of the effect of lithium on peripheral circadian clocks by real-time monitoring of clock gene expression in near-freely moving mice

“…It is possible that similar biological processes may occur in the SCN of mice receiving lithium for a long period of time because lithium imposes a non-24 h circadian period on mice. Second, although brain and blood concentrations of lithium are similar 32 , a few reports, as described above, have indicated that the SCN clock is more sensitive to lithium than peripheral clocks 4,30 , suggesting that a longer period of time is needed to eliminate the effect of lithium on the SCN clock compared to peripheral clocks. The incomplete reversibility of the effect of lithium on circadian period length in locomotor activity observed in the previous report may be due to prolonged aftereffects on the SCN clock.…”

“…Given that the therapeutically effective concentration of lithium in serum (approximately 0.5–1.5 mM) is lower than the IC50 of lithium for the inhibition of GSK3β (approximately 2 mM) 29 , inhibition of GSK3β by lithium at therapeutic levels may also be insufficient to contribute significantly to mood stabilization. Although a few reports indicated that low doses of lithium (1–2 mM) lengthen circadian period elongation in the suprachiasmatic nucleus (SCN) under ex vivo culture conditions 4,30 , this conclusion remain controversial 5 . The effect of lithium on core-clock gene expression, particularly of peripheral clocks, has not yet been investigated in vivo because, as already explained, detection of changes in period length in vivo using traditional experimental approaches is technically difficult.…”