The Effect of Sleep on Tendon Cellular Adaptation (TSS)

Recent clinical evidence has linked poor sleep with increased risk of musculoskeletal injury while evidence from basic biological models indicates that growth hormone and cortisol may regulate the turnover of collagen, a key structural protein in tendons. Growth hormone concentration in the blood surges during deep sleep (~1-2 hr after sleep onset), while cortisol concentration reaches a nadir at this same time. It remains unclear whether serum containing these hormones, collected during sleep itself, can modulate collagen turnover processes. Therefore, the purpose of this study is to evaluate the effect of hormones which surge or diminish during different stages of sleep on collagen turnover in tendon cells.

This study will use a within-subjects design to collect serum for ex vivo experiments. The total study duration will be ~8 days. Participants will first be screened to ensure compliance with our inclusion and exclusion criteria. Written informed consent will be obtained from participants that pass screening. Twelve participants will be recruited in total (6 male, 6 female). Participants will complete a 7 night sleep diary while wearing two wearable devices (an accelerometer to measure physical activity and basic sleep outcomes, worn on the waist; a Fitbit to estimate sleep stages and sleep onset). After the sleep diary, participants will arrive at the laboratory following an overnight fast for a resting venous blood collection. They will return to the laboratory to sleep overnight in the Nutrition and Metabolism Research Group's Bed Rest Facility. Approximately 95 minutes following sleep onset, participants will be briefly awoken for a venous blood draw (i.e., deep sleep sample), before returning to sleep. Four hours after the deep sleep sample, participants will be briefly woken up for a venous blood draw (i.e., REM sleep sample). Participants will then be allowed to finish their night of sleep in the facility.

Commercially available human tenocytes will be treated with serum from the different timepoints (morning, deep/early sleep, REM/late sleep) for 7 days. Following the 7 day treatment period, tenocytes will be collected and collagen I and III expression will be assessed by immunoblot while stable isotope tracers will be used to quantify collagen synthesis and breakdown.

The primary objective of the study is to evaluate the effect of the nocturnal biochemical milieu on human tenocyte-derived collagen expression in vitro. The secondary objectives of the study is to assess whether changes in collagen expression are due to altered collagen synthesis and/or breakdown.