Samuel T. Windham

Heightened muscle inflammation susceptibility may impair regenerative capacity in aging humans

The regenerative response of skeletal muscle to mechanically induced damage is impaired with age. Previous work in our laboratory suggests this may result from higher proinflammatory signaling in aging muscle at rest and/or a greater inflammatory response to damage. We, therefore, assessed skeletal muscle proinflammatory signaling at rest and 24 h after unaccustomed, loaded knee extension contractions that induced modest muscle damage (72% increase in serum creatine kinase) in a cohort of 87 adults across three age groups (AGE40, AGE61, and AGE76). Vastus lateralis muscle gene expression and protein cell signaling of the IL-6 and TNF-α pathways were determined by quantitative PCR and immunoblot analysis. For in vitro studies, cell signaling and fusion capacities were compared among primary myoblasts from young (AGE28) and old (AGE64) donors treated with TNF-α. Muscle expression was higher (1.5- to 2.1-fold) in AGE76 and AGE61 relative to AGE40 for several genes involved in IL-6, TNF-α, and TNF-like weak inducer of apoptosis signaling. Indexes of activation for the proinflammatory transcription factors signal transducer and activator of transcription-3 and NF-κB were highest in AGE76. Resistance loading reduced gene expression of IL-6 receptor, muscle RING finger 1, and atrogin-1, and increased TNF-like weak inducer of apoptosis receptor expression. Donor myoblasts from AGE64 showed impaired differentiation and fusion in standard media and greater NF-κB activation in response to TNF-α treatment (compared with AGE28). We show for the first time that human aging is associated with muscle inflammation susceptibility (i.e., higher basal state of proinflammatory signaling) that is present in both tissue and isolated myogenic cells and likely contributes to the impaired regenerative capacity of skeletal muscle in the older population.

Injury rates among restrained drivers in motor vehicle collisions: The role of body habitus

BACKGROUND Previous studies have examined the independent effects of occupant height, obesity, and body mass index in motor vehicle collisions and identified related injury patterns. The hypothesis of this study was that as the drivers body habitus diverges from the 50% percentile male Hybrid III Crash Dummy (H3CD), the frequency of injury changes. METHODS The 1995 to 1999 National Automotive Sampling System Crashworthiness Data System was used. Study entry was limited to restrained drivers who were then subdivided into height and weight categories. Incidence rates were calculated for injuries to selected body regions as defined by the Abbreviated Injury Scale for overall, frontal, and drivers side collisions. RESULTS When grouped according to height and weight as descriptors of body habitus, injury rates for restrained drivers were increased as well as decreased in several subgroups. This association was seen in overall, frontal, and drivers side collisions. CONCLUSION The H3CD plays a major role in vehicular cabin interior design and crash testing. For drivers with a body habitus different from that of the H3CD, the vehicle cabin/body fit changes and the safety features may perform differently, which could account for these observations.

Identifying Injuries and Motor Vehicle Collision Characteristics that Together Are Suggestive of Diaphragmatic Rupture

BACKGROUND Diaphragmatic rupture (DR) remains a diagnostic challenge because of the lack of an accurate test demonstrating the injury. Our purpose was to identify motor vehicle collision (MVC) characteristics and patient injuries that collectively could identify the presence of a DR. METHODS The National Automotive Sampling System was used to identify occupants involved in MVCs from 1995 to 1999 who sustained abdominal (Abbreviated Injury Scale score >or= 2) and/or thoracic injuries (Abbreviated Injury Scale score >or= 2). Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated to quantify the association between patient injuries, vehicle collision characteristics, and DR. Sensitivity and specificity were also calculated to determine the ability of organ injury and MVC characteristics to correctly classify patients with and without DR. RESULTS Overall, occupants sustaining a DR had a significantly higher delta-V (DeltaV) (49.8 kilometers per hour [kph] vs. 33.8 kph, p< 0.0001) and a greater degree of occupant compartment intrusion (70.6 cm vs. 48.3 cm, p< 0.0001). Specific abdominal and thoracic organ injuries were associated with DR, including thoracic aortic tears (OR, 5.2; 95% CI, 2.2-12.5), splenic injury (OR, 8.4; 95% CI, 3.9-17.8), pelvic fractures (OR, 4.7; 95% CI, 2.7-8.0), and hepatic injuries (OR, 4.2; 95% CI, 1.7-10.6). Combining frontal or near-side lateral occupant compartment intrusion >or= 30 cm or DeltaV >or= 40 kph with specific organ injuries generated a sensitivity for indicating the likelihood of diaphragm injury ranging from 68% to 89%. Patients with any of the following characteristics had a sensitivity for detecting DR of 91%: splenic injury, pelvic fracture, DeltaV >or= 40 kph, or occupant compartment intrusion from any direction >or= 30 cm. CONCLUSION Specific MVC characteristics combined with patient injuries have been identified that are highly suggestive of DR. For this subpopulation, additional invasive procedures including exploratory laparotomy, laparoscopy, or thoracoscopy may be warranted to exclude DR.

Novel, high-intensity exercise prescription improves muscle mass, mitochondrial function, and physical capacity in individuals with Parkinson's disease

We conducted, in persons with Parkinsons disease (PD), a thorough assessment of neuromotor function and performance in conjunction with phenotypic analyses of skeletal muscle tissue, and further tested the adaptability of PD muscle to high-intensity exercise training. Fifteen participants with PD (Hoehn and Yahr stage 2-3) completed 16 wk of high-intensity exercise training designed to simultaneously challenge strength, power, endurance, balance, and mobility function. Skeletal muscle adaptations (P < 0.05) to exercise training in PD included myofiber hypertrophy (type I: +14%, type II: +36%), shift to less fatigable myofiber type profile, and increased mitochondrial complex activity in both subsarcolemmal and intermyofibrillar fractions (I: +45-56%, IV: +39-54%). These adaptations were accompanied by a host of functional and clinical improvements (P < 0.05): total body strength (+30-56%); leg power (+42%); single leg balance (+34%); sit-to-stand motor unit activation requirement (-30%); 6-min walk (+43 m), Parkinsons Disease Quality of Life Scale (PDQ-39, -7.8pts); Unified Parkinsons Disease Rating Scale (UPDRS) total (-5.7 pts) and motor (-2.7 pts); and fatigue severity (-17%). Additionally, PD subjects in the pretraining state were compared with a group of matched, non-PD controls (CON; did not exercise). A combined assessment of muscle tissue phenotype and neuromuscular function revealed a higher distribution and larger cross-sectional area of type I myofibers and greater type II myofiber size heterogeneity in PD vs. CON (P < 0.05). In conclusion, persons with moderately advanced PD adapt to high-intensity exercise training with favorable changes in skeletal muscle at the cellular and subcellular levels that are associated with improvements in motor function, physical capacity, and fatigue perception.

Ribosome biogenesis may augment resistance training-induced myofiber hypertrophy and is required for myotube growth in vitro

Resistance exercise training (RT) is the most effective method for increasing skeletal muscle mass in older adults; however, the amount of RT-induced muscle growth is highly variable between individuals. Recent evidence from our laboratory and others suggests ribosome biogenesis may be an important factor regulating RT-induced hypertrophy, and we hypothesized that the extent of hypertrophy is at least partly regulated by the amount of RT-induced ribosome biogenesis. To examine this, 42 older adults underwent 4 wk of RT aimed at inducing hypertrophy of the knee extensors (e.g., 2 sets of squat, leg press, and knee extension, 10-12 repetition maximums, 3 days/wk), and vastus lateralis muscle biopsies were performed pre- and post-RT. Post hoc K-means cluster analysis revealed distinct differences in type II myofiber hypertrophy among subjects. The percent change in type II myofiber size in nonresponders (Non; n = 17) was -7%, moderate responders (Mod; n = 19) +22%, and extreme responders (Xtr; n = 6) +83%. Total muscle RNA increased only in Mod (+9%, P < 0.08) and Xtr (+26%, P < 0.01), and only Xtr increased rRNA content (+40%, P < 0.05) and myonuclei/type II fiber (+32%, P < 0.01). Additionally, Mod and Xtr had a greater increase in c-Myc protein levels compared with Non (e.g., approximately +350 and +250% vs. +50%, respectively, P < 0.05). In vitro studies showed that growth factor-induced human myotube hypertrophy is abolished when rRNA synthesis is knocked down using the Pol I-specific inhibitor CX-5461. Overall, these data implicate ribosome biogenesis as a key process regulating the extent of RT-induced myofiber hypertrophy in older adults.

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.

Skeletal muscle signaling associated with impaired glucose tolerance in spinal cord-injured men and the effects of contractile activity

The mechanisms underlying poor glucose tolerance in persons with spinal cord injury (SCI), along with its improvement after several weeks of neuromuscular electrical stimulation-induced resistance exercise (NMES-RE) training, remain unclear, but presumably involve the affected skeletal musculature. We, therefore, investigated skeletal muscle signaling pathways associated with glucose transporter 4 (GLUT-4) translocation at rest and shortly after a single bout of NMES-RE in SCI (n = 12) vs. able-bodied (AB, n = 12) men. Subjects completed an oral glucose tolerance test during visit 1 and ≈90 NMES-RE isometric contractions of the quadriceps during visit 2. Muscle biopsies were collected before, and 10 and 60 min after, NMES-RE. We assessed transcript levels of GLUT-4 by quantitative PCR and protein levels of GLUT-4 and phosphorylated- and total AMP-activated protein kinase (AMPK)-α, CaMKII, Akt, and AS160 by immunoblotting. Impaired glucose tolerance in SCI was confirmed by higher (P < 0.05) plasma glucose concentrations than AB at all time points after glucose ingestion, despite equivalent insulin responses to the glucose load. GLUT-4 protein content was lower (P < 0.05) in SCI vs. AB at baseline. Main group effects revealed higher phosphorylation in SCI of AMPK-α, CaMKII, and Akt (P < 0.05), and Akt phosphorylation increased robustly (P < 0.05) following NMES-RE in SCI only. In SCI, low skeletal muscle GLUT-4 protein concentration may, in part, explain poor glucose tolerance, whereas heightened phosphorylation of relevant signaling proteins (AMPK-α, CaMKII) suggests a compensatory effort. Finally, it is encouraging to find (based on Akt) that SCI muscle remains both sensitive and responsive to mechanical loading (NMES-RE) even ≈22 yr after injury.

Randomized, four-arm, dose-response clinical trial to optimize resistance exercise training for older adults with age-related muscle atrophy

Purpose: The myriad consequences of age‐related muscle atrophy include reduced muscular strength, power, and mobility; increased risk of falls, disability, and metabolic disease; and compromised immune function. At its root, aging muscle atrophy results from a loss of myofibers and atrophy of the remaining type II myofibers. The purpose of this trial (NCT02442479) was to titrate the dose of resistance training (RT) in older adults in an effort to maximize muscle regrowth and gains in muscle function. Methods: A randomized, four‐arm efficacy trial in which four, distinct exercise prescriptions varying in intensity, frequency, and contraction mode/rate were evaluated: (1) high‐resistance concentric‐eccentric training (H) 3 d/week (HHH); (2) H training 2 d/week (HH); (3) 3 d/week mixed model consisting of H training 2 d/week separated by 1 bout of low‐resistance, high‐velocity, concentric only (L) training (HLH); and (4) 2 d/week mixed model consisting of H training 1 d/week and L training 1 d/week (HL). Sixty‐four randomized subjects (65.5 ± 3.6 y) completed the trial. All participants completed the same 4 weeks of pre‐training consisting of 3 d/week followed by 30 weeks of randomized RT. Results: The HLH prescription maximized gains in thigh muscle mass (TMM, primary outcome) and total body lean mass. HLH also showed the greatest gains in knee extension maximum isometric strength, and reduced cardiorespiratory demand during steady‐state walking. HHH was the only prescription that led to increased muscle expression of pro‐inflammatory cytokine receptors and this was associated with a lesser gain in TMM and total body lean mass compared to HLH. The HL prescription induced minimal muscle regrowth and generally lesser gains in muscle performance vs. the other prescriptions. Major conclusions: The HLH prescription offers distinct advantages over the other doses, while the HL program is subpar. Although limited by a relatively small sample size, we conclude from this randomized dose‐response trial that older adults benefit greatly from 2 d/week high‐intensity RT, and may further benefit from inserting an additional weekly bout of low‐load, explosive RT. Trial registration: ClinicalTrials.gov NCT02442479 HighlightsHLH maximized gains in thigh muscle mass and total body lean mass.HLH induced the greatest gains in knee extension maximum isometric strength.HLH reduced cardiorespiratory demand during steady‐state walking.HHH led to increased muscle expression of pro‐inflammatory cytokine receptors.The HL prescription induced minimal muscle regrowth and lesser gains in performance.

MECHANOSENSITIVITY MAY BE ENHANCED IN SKELETAL MUSCLES OF SPINAL CORD–INJURED VERSUS ABLE-BODIED MEN

We investigated the effects of an acute bout of neuromuscular electrical stimulation–induced resistance exercise (NMES‐RE) on intracellular signaling pathways involved in translation initiation and mechanical loading–induced muscle hypertrophy in spinal cord–injured (SCI) versus able‐bodied (AB) individuals. AB and SCI individuals completed 90 isometric knee extension contractions at 30% of maximum voluntary or evoked contraction, respectively. Muscle biopsies were collected before, and 10 and 60 min after NMES‐RE. Protein levels of α7‐ and β1‐integrin, phosphorylated and total GSK‐3α/β, S6K1, RPS6, 4EBP1, and FAK were assessed by immunoblotting. SCI muscle appears to be highly sensitive to muscle contraction even several years after the injury, and in fact it may be more sensitive to mechanical stress than AB muscle. Heightened signaling associated with muscle mechanosensitivity and translation initiation in SCI muscle may be an attempted compensatory response to offset elevated protein degradation in atrophied SCI muscle. Muscle Nerve 50: 599–601, 2014

Heightened TWEAK-NF-κB signaling and inflammation-associated fibrosis in paralyzed muscles of men with chronic spinal cord injury.

Individuals with long-standing spinal cord injury (SCI) often present with extreme muscle atrophy and impaired glucose metabolism at both the skeletal muscle and whole body level. Persistent inflammation and increased levels of proinflammatory cytokines in the skeletal muscle are potential contributors to dysregulation of glucose metabolism and atrophy; however, to date no study has assessed the effects of long-standing SCI on their expression or intracellular signaling in the paralyzed muscle. In the present study, we assessed the expression of genes (TNFαR, TNFα, IL-6R, IL-6, TWEAK, TWEAK R, atrogin-1, and MuRF1) and abundance of intracellular signaling proteins (TWEAK, TWEAK R, NF-κB, and p-p65/p-50/105) that are known to mediate inflammation and atrophy in skeletal muscle. In addition, based on the effects of muscle inflammation on promotion of skeletal muscle fibrosis, we assessed the degree of fibrosis between myofibers and fascicles in both groups. For further insight into the distribution and variability of muscle fiber size, we also analyzed the frequency distribution of SCI fiber size. Resting vastus lateralis (VL) muscle biopsy samples were taken from 11 men with long-standing SCI (≈22 yr) and compared with VL samples from 11 able-bodied men of similar age. Our results demonstrated that chronic SCI muscle has heightened TNFαR and TWEAK R gene expression and NF-κB signaling (higher TWEAK R and phospho-NF-κB p65) and fibrosis, along with substantial myofiber size heterogeneity, compared with able-bodied individuals. Our data suggest that the TWEAK/TWEAK R/NF-κB signaling pathway may be an important mediator of chronic inflammation and fibrotic adaptation in SCI muscle.