Circadian mechanisms in murine and human bone marrow mesenchymal stem cells following dexamethasone exposure

A core group of regulatory factors control circadian rhythms in mammalian cells. While the suprachiasmatic nucleus in the brain serves as the central core circadian oscillator, circadian clocks also exist within peripheral tissues and cells. A growing body of evidence has demonstrated that > 20% of expressed mRNAs in bone and adipose tissues oscillate in a circadian manner. The current manuscript reports evidence of the core circadian transcriptional apparatus within primary cultures of murine and human bone marrow-derived mesenchymal stein cells (BMSCs). Exposure of confluent, quiescent BMSCs to dexamethasone synchronized the oscillating expression of the rnRNAs encoding the albumin D binding protein (dbp), brain-muscle arnt-like 1 (bmall), period 3 (per3), rev-erb alpha (Rev A), and rev-erb beta (Rev B). The genes displayed a mean oscillatory period of 22.2 to 24.3 h. The acrophase or peak expression of rnRNAs encoding "positive" (bmall) and "negative" (per3) components of the circadian regulatory apparatus were out of phase with each other by similar to 8-12 h, consistent with in vivo observations. In vivo, phosphyrylation by glycogen synthase kinase 3 beta (GSK3 beta) is known to regulate the turnover of per3 and components of the core circadian regulatory apparatus. In vitro addition of lithium chloride, a GSK3 beta inhibitor, significantly shifted the acrophase of all genes by 4.2-4.7 h oscillation in BMSCs; however, only the male murine BMSCs displayed a significant increase in the length of the period of oscillation. We conclude that human and murine BMSCs represent a valid in vitro model for the analysis of circadian mechanisms in bone metabolism and stem cell biology. (c) 2008 Elsevier Inc. All rights reserved.