The Physiological Period Length of the Human Circadian Clock In Vivo Is Directly Proportional to Period in Human Fibroblasts

Abstract

BackgroundDiurnal behavior in humans is governed by the period length of a circadian clock in the suprachiasmatic nuclei of the brain hypothalamus. Nevertheless, the cell-intrinsic mechanism of this clock is present in most cells of the body. We have shown previously that for individuals of extreme chronotype (“larks” and “owls”), clock properties measured in human fibroblasts correlated with extreme diurnal behavior.Methodology/Principal FindingsIn this study, we have measured circadian period in human primary fibroblasts taken from normal individuals and, for the first time, compared it directly with physiological period measured in vivo in the same subjects. Human physiological period length was estimated via the secretion pattern of the hormone melatonin in two different groups of sighted subjects and one group of totally blind subjects, each using different methods. Fibroblast period length was measured via cyclical expression of a lentivirally delivered circadian reporter. Within each group, a positive linear correlation was observed between circadian period length in physiology and in fibroblast gene expression. Interestingly, although blind individuals showed on average the same fibroblast clock properties as sighted ones, their physiological periods were significantly longer.Conclusions/SignificanceWe conclude that the period of human circadian behaviour is mostly driven by cellular clock properties in normal individuals and can be approximated by measurement in peripheral cells such as fibroblasts. Based upon differences among sighted and blind subjects, we also speculate that period can be modified by prolonged unusual conditions such as the total light deprivation of blindness.

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).…”

Serum factors in older individuals change cellular clock properties

“…Using such reporters, we have shown previously that many differences in human circadian behavior also can be seen at a molecular level in peripheral cells. For example, the cellular clocks of early chronotypes (i.e., "larks") have shorter circadian periods than those of later chronotypes ("owls") (23), and circadian period length in vitro is proportional to physiological period in vivo (24). Under entrained conditions in which cellular clocks are constrained to 24 h via an entrainment protocol that mimics diurnal variations in mammalian body temperature (25), fibroblasts show the early or late circadian phases of their owners (23).…”

Alzheimer’s amyloid-β peptide disturbs P2X7 receptor-mediated circadian oscillations of intracellular calcium

“…Our study extends previous results by showing the existence of daily fluctuations in cytosolic calcium in peripheral oscillators, the human skin fibroblasts. This cell line was previously shown to exhibit circadian rhythms of clock genes, and the clock properties of these peripheral cells closely mimic those measured physiologically and behaviorally in humans [10,57]. Therefore, skin fibroblasts are a good in vitro model for studying molecular mechanisms of circadian rhythms.…”

“…1). We used human primary fibroblasts since these cells are an excellent in vitro model of peripheral oscillators [10,56,57] and show a disturbed Ca 2+ homeostasis in AD patients [31,39].…”

“…Therefore the aim of this study was to deepen our understanding of the molecular mechanisms involved in AD-related circadian clock alterations, by investigating i) the clock-dependent regulation of intracellular calcium levels in a peripheral tissue, and; ii) the effect of Aβ peptides on the changes of cytosolic calcium levels around the clock. For this purpose, we used primary cultures of human fibroblasts because: i) fibroblasts coming from AD patients present a disturbed Ca 2+ homeostasis [31,39]; and ii) fibroblasts are a valuable in vitro model of peripheral oscillators [10,56,57].…”