PL - 039 Heat Shock Proteins in human single skeletal muscle fibres resist age associated alterations and differentially respond to high-intensity exercise training

Objective Heat shock proteins (HSPs) are ubiquitously expressed proteins that help preserve cellular homeostasis. Within mammalian skeletal muscle three of the better characterised HSPs are HSP72, HSP27 and αB-crystallin. Among other roles, these three HSPs are involved in regulation of muscle mass and function and may be of importance in ageing. HSP’s are fibre-type dependent in rat skeletal muscle and thus examining these proteins in humans should be completed on the single fibre level, particularly in ageing where maladaptations primarily occur in Type II fibres. High-Intensity Training (HIT) is a commonly used method to improve muscle health and function in the elderly, but HSP adaptability to training has not yet been investigated.   Methods This study examined isolated single muscle fibre segments collected from freeze-dried vastus lateralis muscle samples from young (25 /- 3 year old) and older (70 /- 4 year old) healthy individuals.  A further sample was collected from the older individuals following 12 weeks of HIT, where they performed 4 x 4 min @ ~90-95% of peak heart rate (HR), with 4 min active recovery at 50-60% peak HR Results Basal expression of HSP’s in skeletal muscle: HSP70 tended to be higher in Type I fibres compared to Type II in young adults (p=0.08) and was higher in Type I compared to Type II fibres of older adults (p=0.03). HSP27 abundance was higher in Type I fibres compared to Type II in young adults (p=0.01) and tended to be higher in Type I compared to Type II fibres in older adults (p=0.07). The abundance of αβ-crystallin was more abundant in Type I fibres compared to Type II in both young and older adults (p<0.05).  Preliminary data revealed that the abundance of pABCser59 and pHSP2782 displayed no fibre-type specific abundances in either young or older adults. Age effects on HSP’s: There was no difference in the abundance of HSP70, HSP27, ABC or pHSP2782 between young and older adults in either Type I or Type II fibres. There was an increase in the abundance of pABCser59 in Type I fibres in older adults compared to Type I fibres of young adults (p=0.03), with no difference in Type II fibres. Effects of HIT on HSP’s:  HIT in the older individuals increased the abundance of HSP70 in Type I fibres (p<0.01) but not Type II. HIT tended to decrease the abundance of HSP27 in Type I fibres (0.92±0.66, p=0.06) and tended to increase the abundance of αβ-crystallin in Type I fibres (1.03±1.51 p=0.07). Conclusions These results revealed that in healthy, older individuals, the basal levels of HSP27, ABC or pHSP2782 are not different to those in young adults in either Type I or Type II fibres. This could indicate that the muscle from the older individuals was not compromised.  Interestingly, in response to HIT there were varying changes between these HSP’s, and of note these occurred only in Type I fibres.  Given that during HIT Type II fibres would be activated to a greater extent, it appears that the recovery phases of the HIT were most responsive to HSPs

Quantification of plasma kynurenine metabolites following one bout of sprint interval exercise

The kynurenine pathway of tryptophan degradation produces several neuroactive metabolites suggested to be involved in a wide variety of diseases and disorders, however, technical challenges in reliably detecting these metabolites hampers cross-comparisons. The main objective of this study was to develop an accurate, robust and precise bioanalytical method for simultaneous quantification of ten plasma kynurenine metabolites. As a secondary aim, we applied this method on blood samples taken from healthy subjects conducting 1 session of sprint interval exercise (SIE). It is well accepted that physical exercise is associated with health benefits and reduces risks of psychiatric illness, diabetes, cancer and cardiovascular disease, but also influences the peripheral and central concentrations of kynurenines. In line with this, we found that in healthy old adults (n = 10; mean age 64 years), levels of kynurenine increased 1 hour (P = .03) after SIE, while kynurenic acid (KYNA) concentrations were elevated after 24 hours (P = .02). In contrast, no significant changes after exercise were seen in young adults (n = 10; mean age 24 years). In conclusion, the described method performs well in reliably detecting all the analyzed metabolites in plasma samples. Furthermore, we also detected an age-dependent effect on the degree by which a single intense training session affects kynurenine metabolite levels

Vitamin C and E treatment blocks changes in kynurenine metabolism triggered by three weeks of sprint interval training in recreationally active elderly humans

The kynurenine pathway (KP) is gaining attention in several clinical fields. Recent studies show that physical exercise offers a therapeutic way to improve ratios of neurotoxic to neuroprotective KP metabolites. Antioxidant supplementation can blunt beneficial responses to physical exercise. We here studied the effects of endurance training in the form of sprint interval training (SIT; three sessions of 4-6 × 30 s cycling sprints per week for three weeks) in elderly (~65 years) men exposed to either placebo (n = 9) or the antioxidants vitamin C (1 g/day) and E (235 mg/day) (n = 11). Blood samples and muscle biopsies were taken under resting conditions in association with the first (untrained state) and last (trained state) SIT sessions. In the placebo group, the blood plasma level of the neurotoxic quinolinic acid was lower (~30%) and the neuroprotective kynurenic acid to quinolinic acid ratio was higher (~50%) in the trained than in the untrained state. Moreover, muscle biopsies showed a training-induced increase in kynurenine aminotransferase (KAT) III in the placebo group. All these training effects were absent in the vitamin-treated group. In conclusion, KP metabolism was shifted towards neuroprotection after three weeks of SIT in elderly men and this shift was blocked by antioxidant treatment

Loss of α-actinin-3 during human evolution provides superior cold resilience and muscle heat generation

The protein α-actinin-3 expressed in fast-twitch skeletal muscle fiber is absent in 1.5 billion people worldwide due to homozygosity for a nonsense polymorphism in ACTN3 (R577X). The prevalence of the 577X allele increased as modern humans moved to colder climates, suggesting a link between α-actinin-3 deficiency and improved cold tolerance. Here, we show that humans lacking α-actinin-3 (XX) are superior in maintaining core body temperature during cold-water immersion due to changes in skeletal muscle thermogenesis. Muscles of XX individuals displayed a shift toward more slow-twitch isoforms of myosin heavy chain (MyHC) and sarcoplasmic reticulum (SR) proteins, accompanied by altered neuronal muscle activation resulting in increased tone rather than overt shivering. Experiments on Actn3 knockout mice showed no alterations in brown adipose tissue (BAT) properties that could explain the improved cold tolerance in XX individuals. Thus, this study provides a mechanism for the positive selection of the ACTN3 X-allele in cold climates and supports a key thermogenic role of skeletal muscle during cold exposure in humans