Muscle inflammation susceptibility: a prognostic index of recovery potential after hip arthroplasty?

While elective total hip arthroplasty (THA) for end-stage osteoarthritis (OA) improves pain, mobility function, and quality of life in most cases, a large proportion of patients suffer persistent muscle atrophy, pain, and mobility impairment. Extensive skeletal muscle damage is unavoidable in these surgical procedures, and it stands to reason that poor recovery and long-term mobility impairment among some individuals after THA is linked to failed muscle regeneration and regrowth following surgery and that local muscle inflammation susceptibility (MuIS) is a major contributing factor. Here we present results of two integrated studies. In study 1, we compared muscle inflammation and protein metabolism signaling in elective THA (n=15) vs. hip fracture/trauma (HFX; n=11) vs. nonsurgical controls (CON; n=19). In study 2, we compared two subgroups of THA patients dichotomized into MuIS⁺ (n=7) or MuIS⁻ (n=7) based on muscle expression of TNF-like weak inducer of apoptosis (TWEAK) receptor (Fn14). As expected, HFX demonstrated overt systemic and local muscle inflammation and hypermetabolism. By contrast, no systemic inflammation was detected in elective THA patients; however, local muscle inflammation in the perioperative limb was profound in MuIS⁺ and was accompanied by suppressed muscle protein synthesis compared with MuIS⁻. Muscle from the contralateral limb of MuIS⁺ was unaffected, providing evidence of a true inflammation susceptibility localized to the muscle surrounding the hip with end-stage OA. We suggest MuIS status assessed at the time of surgery may be a useful prognostic index for muscle recovery potential and could therefore provide the basis for a personalized approach to postsurgery rehabilitation.

Serum from human burn victims impairs myogenesis and protein synthesis in primary myoblasts.

The pathophysiological response to a severe burn injury involves a robust increase in circulating inflammatory/endocrine factors and a hypermetabolic state, both of which contribute to prolonged skeletal muscle atrophy. In order to characterize the role of circulating factors in muscle atrophy following a burn injury, human skeletal muscle satellite cells were grown in culture and differentiated to myoblasts/myotubes in media containing serum from burn patients or healthy, age, and sex-matched controls. While incubation in burn serum did not affect NFκB signaling, cells incubated in burn serum displayed a transient increase in STAT3 phosphorlyation (Tyr705) after 48 h of treatment with burn serum (≈ + 70%; P < 0.01), with these levels returning to normal by 96 h. Muscle cells differentiated in burn serum displayed reduced myogenic fusion signaling (phospho-STAT6 (Tyr641), ≈-75%; ADAM12, ≈-20%; both P < 0.01), and reduced levels of myogenin (≈-75%; P < 0.05). Concomitantly, myotubes differentiated in burn serum demonstrated impaired myogenesis (assessed by number of nuclei/myotube). Incubation in burn serum for 96 h did not increase proteolytic signaling (assessed via caspase-3 and ubiquitin levels), but reduced anabolic signaling [p-p70S6k (Ser421/Thr424), -30%; p-rpS6 (Ser240/244), ≈-50%] and impaired protein synthesis (-24%) (P < 0.05). This resulted in a loss of total protein content (-18%) and reduced cell size (-33%) (P < 0.05). Overall, incubation of human muscle cells in serum from burn patients results in impaired myogenesis and reduced myotube size, indicating that circulating factors may play a significant role in muscle loss and impaired muscle recovery following burn injury.

Changes in vascular hemodynamics in older women following 16 weeks of combined aerobic and resistance training.

The purpose of this study was to determine whether combined (aerobic and anaerobic) training decreases blood pressure (BP) and improves vascular properties. Seventy-nine postmenopausal women were randomly assigned to 3 groups that trained at different frequencies. Maximum oxygen uptake, body composition, BP, and arterial elasticity were evaluated prior to training and after 16 weeks of training. There was a significant time effect (decrease) for resting systolic BP (SBP) and rate pressure product. Exercise SBP, diastolic BP (DBP), heart rate, and RPP also decreased. Changes in total vascular impedance were related to SBP and changes in systemic vascular resistance were related to changes in DBP independent of body composition changes. Our findings suggest that combined training reduces SBP and improves vascular properties and that combined training 1 d/wk decreases BP similar to more frequent combined training. Training-induced changes in arterial resistance and impedance may be involved in inducing changes in BP.