Assessment of circadian function in fibroblasts of patients with bipolar disorder

Abstract

Previous studies have implicated the circadian system in the pathophysiology of bipolar disorder, but conclusive evidence for altered circadian clocks is lacking. Cultured fibroblasts harbor circadian clocks representative of those in the master clock resident in the suprachiasmatic nuclei, providing a new avenue to investigate the core clock machinery in patients with bipolar illness. We examined the rhythmic expression patterns of core clock genes (BMAL1, PER1, PER2, REV-ERBa, DEC2, DBP) in fibroblasts from 12 bipolar patients and 12 healthy controls. Although we did not detect differences in the circadian period between bipolar patients and controls, the amplitude of rhythmic expression for BMAL1, REVERBa and DBP, as well as the overall mRNA expression level for DEC2 and DBP was reduced in fibroblasts from bipolar patients. Bonferroni's correction for multiple comparisons still resulted in significantly reduced DBP expression level, and trends toward reduced overall expression level of DEC2 and circadian amplitude of BMAL1, in fibroblasts from bipolar patients. We next examined an expanded cohort of 18 bipolar patients and 35 healthy controls for mRNA expression levels of four kinases (CKId, CKIe, GSK3a and GSK3b) and the protein and phosphorylation levels of two of them (GSK3a and GSK3b). We did not detect differences in steady-state mRNA levels or protein levels of these kinases between bipolar patients and controls, but the level of GSK3b phosphorylation was significantly reduced in bipolar patients within an Old Order Amish bipolar kindred. Our results suggest that the reduced amplitudes and overall expression levels of circadian genes, and the decreased phosphorylation level of GSK3b may lead to dysregulation of downstream genes, which could explain some pathological features of bipolar disorder.

Coming to grips with complex disorders: Genetic risk prediction in bipolar disorder using panels of genes identified through convergent functional genomics

“…These mice display a bipolar-like phenotype [Le-Niculescu et al, 2008c], which is modulated by stress. Decreases in DBP expression have also been recently reported in fibroblasts from bipolar subjects [Yang et al, 2008]. In parallel, work carried out by us using an expanded CFG approach in a mouse pharmacogenomic model for bipolar disorder identified ARNTL and a series of other clock genes (CRY2, CSNK1Ds, and CCR4/nocturnin), as potential bipolar candidate genes [Ogden et al, 2004].…”

Convergent functional genomics of genome‐wide association data for bipolar disorder: Comprehensive identification of candidate genes, pathways and mechanisms

“…These mice display a bipolar-like phenotype [Le-Niculescu et al, 2008b], which is modulated by stress. Decreases in Dbp expression have also been recently reported in fibroblasts from bipolar subjects [Yang et al, 2008]. In parallel, work carried out by us using an expanded CFG approach in a mouse pharmacogenomic model for bipolar disorder identified Arntl and a series of other clock genes (Cry2, Csnk1d, and Ccr4/nocturnin), as potential bipolar candidate genes [Ogden et al, 2004].…”

Genetic contributions to circadian activity rhythm and sleep pattern phenotypes in pedigrees segregating for severe bipolar disorder

“…From this analysis, we will obtain information on the period length of the cells as well as parameters such as amplitude, phase, and entrainment. Compared with behavioral phenotypes, circadian phenotypes resulting from this analysis will more directly reflect the underlying genetic properties of the clock (34,35).…”