Human skeletal muscle type 1 fibre distribution and response of stress-sensing proteins along the titin molecule after submaximal exhaustive exercise

Abstract

Early responses of stress-sensing proteins, muscle LIM protein (MLP), ankyrin repeat proteins (Ankrd1/CARP and Ankrd2/Arpp) and muscle-specific RING finger proteins (MuRF1 and MuRF2), along the titin molecule were investigated in the present experiment after submaximal exhaustive exercise. Ten healthy men performed continuous drop jumping unilaterally on a sledge apparatus with a submaximal height until complete exhaustion. Five stress-sensing proteins were analysed by mRNA measurements from biopsies obtained immediately and 3 h after the exercise from exercised vastus lateralis muscle while control biopsies were obtained from non-exercised legs before the exercise. Decreased maximal jump height and increased serum creatine kinase activities as indirect markers for muscle damage and HSP27 immunostainings on muscle biopsies as a direct marker for muscle damage indicated that the current exercised protocol caused muscle damage. mRNA levels for four (MLP, Ankrd1/CARP, MuRF1 and MuRF2) out of the five studied stress sensors significantly (p < 0.05) increased 3 h after fatiguing exercise. The magnitude of MLP and Ankrd2 responses was related to the proportion of type 1 myofibres. Our data showed that the submaximal exhaustive exercise with subject's own physical fitness level activates titin-based stretch-sensing proteins. These results suggest that both degenerative and regenerative pathways are activated in very early phase after the exercise or probably already during the exercise. Activation of these proteins represents an initial step forward adaptive remodelling of the exercised muscle and may also be involved in the initiation of myofibre repair.

A novel voluntary weightlifting model in mice promotes muscle adaptation and insulin sensitivity with simultaneous enhancement of autophagy and mTOR pathway

“…Nr4a3 gene is highly responsive to endurance exercise and has been shown to promote oxidative phenotype, autophagy, and hypertrophy . Ankrd1 (also known as Carp ) mRNA showed a 11‐fold increase following overnight weightlifting, which has previously been shown to be induced by eccentric contractions in mice and by exhaustive jumping exercise in humans . Finally, a robust upregulation of Atf3 mRNA (8‐fold) was observed following weightlifting (Figure 2D).…”

Molecular and Cellular Markers in Skeletal Muscle Damage after Acute Voluntary Exercise Containing Eccentric Muscle Contractions

“…HSP27 immunostainings in longitudinal sections of unexercised skeletal muscle fibers appear as fine lines (Figure 2A) indicating that HSP27 is localized to the Z-disks and/or I-band [11]. Immediately and 3 h after the exercise, in this case continuous drop jumping unilaterally on a sledge apparatus with a submaximal height until complete exhaustion, HSP27 immunostainings showed intensively stained and variable-sized clusters in both cross-sectional and longitudinal sections of skeletal muscle fiber HSP27 ( Figure 2C-F) [12]. These stained clusters were probably formed due to translocation and accumulation of HSP27 on cytoskeletal/myofibrillar structures [11].…”

“…Dystrophin (green) immunostaining was used to visualize the borders of muscle fibers and DAPI (blue) stained nuclei. Published in Koskinen et al[12].…”

In focus in HCB

“…Through its interaction with various proteins, titin is linked to diverse signaling pathways including hypertrophic signaling (Knöll et al 2011). Koskinen et al (2017) have investigated the early responses of stress-sensing proteins along titin after fatiguing exercise (exhausting stretch-shortening cycle exercise on a sledge apparatus by continuous drop jumping) on the physical fitness level of individual subjects. mRNA levels for muscle LIM protein (MLP), ankyrin repeat protein Ankrd1/CARP, and muscle-specific RING finger proteins in biopsies from exercised vastus lateralis muscle were significantly increased 3 h after the exercise, and the magnitude of MLP and Ankrd2 responses was related to the proportion of type 1 myofibers.…”