Extracellular low pH affects circadian rhythm expression in human primary fibroblasts

Area of Science:

• Chronobiology
• Cell Biology
• Human Physiology

Background:

• Circadian rhythms are crucial for physiological regulation.
• The nature and function of circadian clocks in human primary cells remain largely unexplored.
• Extracellular pH is a significant factor influencing human physiology.

Purpose of the Study:

• To investigate the impact of extracellular pH on circadian clock properties in human primary cells.
• To monitor circadian rhythm expression in human skin fibroblasts under varying pH conditions.
• To determine if observed changes in circadian rhythms are linked to cell viability.

Main Methods:

• Utilized in vitro real-time circadian rhythm monitoring.
• Established primary human skin fibroblast cultures from healthy subjects.
• Transfected cells with a Bmal1-luciferase reporter gene for rhythm tracking.
• Recorded circadian rhythms at standard (pH 7.2) and reduced (pH 6.7) extracellular pH.

Main Results:

• Robust circadian rhythms with a period of ~24.5 hours were observed at pH 7.2.
• At pH 6.7, circadian rhythms persisted but showed a significantly shortened period (~22.6 hours), increased amplitude, and decreased damping rate.
• Cell morphology and MTT assays indicated no significant impact on cell viability at pH 6.7.
• The observed effects on circadian period length were reversible upon return to normal pH.

Conclusions:

• Extracellular pH significantly influences circadian rhythm expression in human primary fibroblasts.
• A reduced extracellular pH (6.7) alters key parameters of the circadian clock, including period length, amplitude, and damping.
• These alterations occur without compromising cell viability, suggesting a direct effect on the molecular clockwork.