Human tenocyte responses to combined mild hyperthermia and cyclic mechanical strain: A preliminary in vitro study.

Tendon injuries are common in occupations involving repetitive mechanical loading, and environmental heat exposure may further increase injury risk by altering tissue tolerance to strain. This study investigated cytoskeletal organization (F-actin), microRNA expression (miR-21-5p, miR-29a-3p, and miR-192-5p) and intracellular and extracellular heat shock protein 72 (HSP72) responses to combined heat under hyperthermic conditions (39 °C) and cyclic tensile strain in human achilles tendon-derived tenocytes from a single donor. Tenocytes were maintained at 37 °C without strain or exposed for 3 h to 39 °C without strain, 5% cyclic strain at 39 °C, or 10% cyclic strain at 39 °C. Moderate strain at 39 °C was associated with partially preserved F-actin organization, while higher strain at 39 °C produced greater qualitative disruption of the cytoskeleton. miR-21-5p and miR-29a-3p exhibited condition-dependent regulation, while miR-192-5p did not show a statistically significant change. In addition, intracellular and extracellular HSP72 levels varied across the experimental conditions, indicating activation of cellular stress responses under combined thermal and mechanical exposure. These preliminary findings demonstrate acute cytoskeletal remodeling, molecular and biochemical responses of human tenocytes to combined mild hyperthermia and cyclic mechanical strain providing a basis for further investigation of potential biological indicators of tendon stress in occupational settings.