Skeletal muscle angiogenic, regulatory and heat shock protein responses to prolonged passive hyperthermia of the human lower limb

Abstract

Passive hyperthermia induces a range of physiological responses including augmenting skeletal muscle mRNA expression. This experiment aimed to examine gene and protein responses to prolonged passive leg hyperthermia. Seven young participants underwent 3 h of resting unilateral leg heating (HEAT) followed by a further 3 h of rest, with the contralateral leg serving as an unheated control (CONT). Muscle biopsies were taken at baseline (0 h), and 1.5, 3, 4, and 6 h in HEAT and 0 and 6 h in CONT to assess changes in selected mRNA expression via qRT-PCR, and HSP72 and VEGFα concentration via ELISA. Muscle temperature (Tm) increased in HEAT plateauing from 1.5 to 3 h (+3.5±1.5°C from 34.2±1.2°C baseline value; p<0.001), returning to baseline at 6 h. No change occurred in CONT. eNOS, FOXO-1, Hsp72, and VEGFα mRNA increased in HEAT (p<0.05) however post-hoc analysis identified that only Hsp72 mRNA statistically increased (at 4 h vs. baseline). When peak change during HEAT was calculated ANGPT-2 decreased (-0.4±0.2-fold), and CCL2 (+2.9±1.6-fold), FOXO-1 (+6.2±4.4-fold), Hsp27 (+2.9±1.7-fold), Hsp72 (+8.5±3.5-fold), Hsp90α (+4.6±3.7-fold), and VEGFα (+5.9±3.1-fold) increased from baseline (all p<0.05). At 6 h Tm were not different between limbs (p=0.582; CONT=32.5±1.6°C, HEAT=34.3±1.2°C), and only ANGPT-2 (p=0.031;-1.3±1.4-fold) and VEGFα (p=0.030;1.1±1.2-fold) differed between HEAT and CONT. No change in VEGFα or HSP72 protein concentration were observed over time, however, peak change in VEGFα did increase (p<0.05) in HEAT (+140±184 pg.mL-1) vs CONT (+7±86 pg.mL-1). Passive hyperthermia transiently augmented ANGPT-2, CCL2, eNOS, FOXO-1, Hsp27, Hsp72, Hsp90α and VEGFα mRNA, and VEGFα protein.