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© 2016 Bipolar disorder (BD) is characterized by depression, mania, and circadian rhythm abnormalities. Lithium, a treatment for BD stabilizes mood and increases circadian rhythm amplitude. However, in fibroblasts grown from BD patients, lithium has weak effects on rhythm amplitude compared to healthy controls. To understand the mechanism by which lithium differentially affects rhythm amplitude in BD cells, we investigated the extracellular-signal-regulated kinase (ERK) and related signaling molecules linked to BD and circadian rhythms. In fibroblasts from BD patients, controls and mice, we assessed the contribution of the ERK pathway to lithium-induced circadian rhythm amplification. Protein analyses revealed low phospho-ERK1/2 (p-ERK) content in fibroblasts from BD patients vs. controls. Pharmacological inhibition of ERK1/2 by PD98059 attenuated the rhythm amplification effect of lithium, while inhibition of two related kinases, c-Jun N-terminal kinase (JNK), and P38 did not. Knockdown of the transcription factors CREB and EGR-1, downstream effectors of ERK1/2, reduced baseline rhythm amplitude, but did not alter rhythm amplification by lithium. In contrast, ELK-1 knockdown amplified rhythms, an effect that was not increased further by the addition of lithium, suggesting this transcription factor may regulate the effect of lithium on amplitude. Augmentation of ERK1/2 signaling through DUSP6 knockdown sensitized NIH3T3 cells to rhythm amplification by lithium. In BD fibroblasts, DUSP6 knockdown reversed the BD rhythm phenotype, restoring the ability of lithium to increase amplitude in these cells. We conclude that the inability of lithium to regulate circadian rhythms in BD may reflect reduced ERK activity, and signaling through ELK-1.

UnlabelledBipolar disorder (BD) is associated with mood episodes and low amplitude circadian rhythms. Previously, we demonstrated that fibroblasts grown from BD patients show weaker amplification of circadian rhythms by lithium compared to control cells. Since calcium signals impact upon the circadian clock, and L-type calcium channels (LTCC) have emerged as genetic risk factors for BD, we examined whether loss of function in LTCCs accounts for the attenuated response to lithium in BD cells. We used fluorescent dyes to measure Ca(2+) changes in BD and control fibroblasts after lithium treatment, and bioluminescent reporters to measure Per2::luc rhythms in fibroblasts from BD patients, human controls, and mice while pharmacologically or genetically manipulating calcium channels. Longitudinal expression of LTCC genes (CACNA1C, CACNA1D and CACNB3) was then measured over 12-24 h in BD and control cells. Our results indicate that independently of LTCCs, lithium stimulated intracellular Ca(2+) less effectively in BD vs. control fibroblasts. In longitudinal studies, pharmacological inhibition of LTCCs or knockdown of CACNA1A, CACNA1C, CACNA1D and CACNB3 altered circadian rhythm amplitude. Diltiazem and knockdown of CACNA1C or CACNA1D eliminated lithium's ability to amplify rhythms. Knockdown of CACNA1A or CACNB3 altered baseline rhythms, but did not affect rhythm amplification by lithium. In human fibroblasts, CACNA1C genotype predicted the amplitude response to lithium, and the expression profiles of CACNA1C, CACNA1D and CACNB3 were altered in BD vs.ControlsWe conclude that in cells from BD patients, calcium signaling is abnormal, and that LTCCs underlie the failure of lithium to amplify circadian rhythms.