Potassium has been identified as the key to circadian rhythms in red blood cells by the University of Surrey and Cambridge’s MRC Laboratory of Molecular Biology.
Red blood cells, similar to other cells in the body, have 24-hour biological clocks, known as circadian rhythms, that alter their activity between day and night. Unlike other cells, red blood cells do not have DNA and the ‘clock genes’ that control rhythms are not present.
Until now it has been unknown how such cells are regulated.
Many aspects of cellular biology show circadian regulation, from metabolism and signal transduction to mitosis and differentiation. Clock disruption is strongly associated with chronic diseases, as well as deregulation of acute responses such as inflammation.
Using a novel technique called dielectrophoresis, and new technology developed at the University of Surrey, researchers were able to study the electrochemical properties of human red blood cells, providing an in depth analysis on their workings.
[caption id=“attachment_93831” align=“aligncenter” width=“680”] Circadian rhythms in human RBC electrophysiology are detected by dielectrophoresis.
a) Dielectrophoresis induces RBC movement towards the periphery (negative DEP) or centre (positive DEP) of each well as a function of applied AC frequency; this is measured by the variation in transmitted light intensity across each well.
b) Several electrophysiological parameters can be derived from this readout.
c) Human RBCs are isolated, and aliquots synchronised in parallel using 12 h:12 h 37 °C:32 °C temperature cycles over 2 days. RBCs are then maintained at constant 37 °C with a separate aliquot from each donor being analysed by DEP every 3 or 4 h over 2 days.
d) Effective membrane conductance (Geff) exhibits significant variation, p < 0.0001 for time effect by two-way ANOVA (n = 4, df = 12, F = 6.4).
e) Whole-cell capacitance (C WC) shows no significant variation over time, p = 0.2092 for time effect by two-way ANOVA (n = 4, df = 12, F = 1.4).
f) Cytoplasmic conductivity (σ cyt) also showed significant variation, p = 0.0123 for time effect by two-way ANOVA (n = 4, df = 12, F = 2.6)
Credit: Erin A. Henslee et al. CC-BY[/caption]
Researchers observed a significant variation in potassium content in the cells which corresponded with the circadian rhythm – increased levels during the day followed by a decrease at night.
By changing the amount of potassium the cell receives, the researchers were able to increase and decrease its levels in the cell and observe the effects on their circadian rhythms. The researchers found that higher levels of potassium negatively impacted the circadian rhythm of the cell, whilst lower levels were observed as extending the duration of the cell’s perceived “day” by several hours.
Lead investigator Dr Fatima Labeed, Senior Lecturer at the University of Surrey, said:
“This exciting discovery gives us a unique insight into the workings of red blood cell membrane physiology and its clock mechanism — where ion transport seems to be of particular importance. The study of circadian rhythms in red blood cells can potentially help us understand when and why heart attacks mostly occur during the morning. We will be looking into this further in our forthcoming studies."
Dielectrophoresis can be performed in minutes, the authors note. So it could have potential as a circadian phase marker. Furthermore, red blood cells make up around 99% of circulating blood cells, so it is possible that accurate measurements could be made from acutely sampled whole blood, without requiring purification to remove white blood cells.
The work was supported by funding from the Engineering and Physical Research Council, Medical Research Council, Wellcome Trust, and The Francis Crick Institute.
Erin A. Henslee, Priya Crosby, Stephen J. Kitcatt, Jack S. W. Parry, Andrea Bernardini, Rula G. Abdallat, Gabriella Braun, Henry O. Fatoyinbo, Esther J. Harrison, Rachel S. Edgar, Kai F. Hoettges, Akhilesh B. Reddy, Rita I. Jabr, Malcolm von Schantz, John S. O’Neill & Fatima H. Labeed Rhythmic potassium transport regulates the circadian clock in human red blood cells Nature Communications 8, Article number: 1978 (2017) doi:10.1038/s41467-017-02161-4
Top Image: David Gregory & Debbie Marshall, Wellcome Images