Modulation of circadian rhythms in articular cartilage by heat pulse.

OBJECTIVE

Disruption of the circadian clock, such as during ageing, is linked to cartilage degeneration in mice and increased osteoarthritis (OA) risk in humans. This study investigated whether heat pulses can resynchronise dampened circadian rhythms in articular cartilage.

METHODS

Femoral head cartilage explants were isolated from PER2::LUC circadian reporter mice. Tissues were exposed to heat shock at various temperatures and durations. Circadian bioluminescence from explants was recorded in real-time over several days. Pharmacological compounds were used to investigate the pathways involved in clock resynchronisation.

RESULTS

We established that a 60-min pulse at 43 °C resynchronises PER2::LUC rhythms in cartilage explants from young and aged mice. The heat shock was able to counteract circadian disruption caused by IL-1α treatment. Mechanistically, inhibition of HSP90 activity or perturbation of F-actin polymerisation markedly attenuated the heat-induced resynchronisation of circadian rhythms.

CONCLUSION

An acute 43 °C heat pulse enhanced the circadian amplitude and reset the phase of damped PER2::LUC rhythms in ex vivo murine cartilage. Pharmacological sensitivity to 17-DMAG (HSP90 inhibitor) and agents affecting actin/Rho-ROCK signalling implicates these pathways in the response. These findings identify heat as an experimental synchronising cue for cartilage clocks and support further investigations of heating regimens in OA-relevant models.