Search

Satellite cells are skeletal muscle stem cells that contribute to postnatal muscle growth, and they endow skeletal muscle with the ability to regenerate after a severe injury. Here we discover that this myogenic potential of satellite cells requires a protein called tripartite motif-containing 28 (TRIM28). Interestingly, different from the role reported in a previous study based on C2C12 myoblasts, multiple lines of both in vitro and in vivo evidence reveal that the myogenic function of TRIM28 is not dependent on changes in the phosphorylation of its serine 473 residue. Moreover, the functions of TRIM28 are not mediated through the regulation of satellite cell proliferation or differentiation. Instead, our findings indicate that TRIM28 regulates the ability of satellite cells to progress through the process of fusion. Specifically, we discover that TRIM28 controls the expression of a fusogenic protein called myomixer and concomitant fusion pore formation. Collectively, the outcomes of this study expose the framework of a novel regulatory pathway that is essential for myogenesis., (© 2024. The Author(s).)

An increase in mechanical loading, such as that which occurs during resistance exercise, induces radial growth of muscle fibers (i.e. an increase in cross-sectional area). Muscle fibers are largely composed of myofibrils, but whether radial growth is mediated by an increase in the size of the myofibrils (i.e. myofibril hypertrophy) and/or the number of myofibrils (i.e. myofibrillogenesis) is not known. Electron microscopy (EM) can provide images with the level of resolution that is needed to address this question, but the acquisition and subsequent analysis of EM images is a time- and cost-intensive process. To overcome this, we developed a novel method for visualizing myofibrils with a standard fluorescence microscope (fluorescence imaging of myofibrils with image deconvolution [FIM-ID]). Images from FIM-ID have a high degree of resolution and contrast, and these properties enabled us to develop pipelines for automated measurements of myofibril size and number. After extensively validating the automated measurements, we used both mouse and human models of increased mechanical loading to discover that the radial growth of muscle fibers is largely mediated by myofibrillogenesis. Collectively, the outcomes of this study offer insight into a fundamentally important topic in the field of muscle growth and provide future investigators with a time- and cost-effective means to study it., Competing Interests: KJ, JH, RS, AL, JG, PM, BR, MM, AK, MR, TH No competing interests declared, (© 2023, Jorgenson et al.)

The ability to measure the in vivo rate of protein degradation is a major limitation in numerous fields of biology. Here, we present a protocol for quantifying this rate in mice using a pulse-chase technique that utilizes an azide-bearing non-canonical amino acid called azidohomoalanine (AHA). We describe steps for using chow containing AHA to pulse-label the animal's proteome. We then detail the quantification of AHA-labeled proteins in whole-tissue lysates or histological sections using a copper-catalyzed azide-alkyne cycloaddition 'click' reaction. For complete details on the use and execution of this protocol, please refer to Steinert et al. (2023). 1 ., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

The maintenance of skeletal muscle mass plays a fundamental role in health and issues associated with quality of life. Mechanical signals are one of the most potent regulators of muscle mass, with a decrease in mechanical loading leading to a decrease in muscle mass. This concept has been supported by a plethora of human- and animal-based studies over the past 100 years and has resulted in the commonly used term of 'disuse atrophy'. These same studies have also provided a great deal of insight into the structural adaptations that mediate disuse-induced atrophy. For instance, disuse results in radial atrophy of fascicles, and this is driven, at least in part, by radial atrophy of the muscle fibers. However, the ultrastructural adaptations that mediate these changes remain far from defined. Indeed, even the most basic questions, such as whether the radial atrophy of muscle fibers is driven by the radial atrophy of myofibrils and/or myofibril hypoplasia, have yet to be answered. In this review, we thoroughly summarize what is known about the macroscopic, microscopic, and ultrastructural adaptations that mediated disuse-induced atrophy and highlight some of the major gaps in knowledge that need to be filled.

Stand-up paddle boarding (SUP) as both a competitive and recreational sport has grown in popularity over the last decade. Better understanding paddling kinematics is beneficial for both injury prevention and informing coaching practices in this growing sport. The purpose of this study was to analyze sagittal plane kinematics during both standing and kneeling paddling postures commonly adopted by injury-free, recreational SUP participants. Eighteen recreational SUP participants (seven males/eleven females) were asked to complete a series of paddling tasks on a SUP ergometer in two postures, during which kinematic data were acquired. Sagittal plane kinematic data were analyzed for joint excursion, or range of motion used, while paddling on both sides of the body in each posture. Analysis of variance was used to compare joint excursions across tasks. There were no significant differences in hip or trunk sagittal plant excursion between postures. However, there was significantly greater sagittal plane excursion at the shoulder in the kneeling as compared to the standing posture with the shoulder opposite the paddling side demonstrating the greatest total excursion. These results help establish the parameters of the paddling technique currently in use among injury-free SUP participants and may be used in the future to inform coaching practices.

Abstract: Hibbert, JE, Klawiter, DP, Schubert, MM, Nessler, JA, and Asakawa, DS. Strength, cardiovascular fitness, and blood lipid measures in law enforcement personnel after a 12-week health promotion program. J Strength Cond Res 36(11): 3105-3112, 2022-Law enforcement personnel often have high rates of cardiovascular disease and injury. Health promotion programs have been found to successfully encourage behavior change among law enforcement personnel, but these programs can often be intensive and expensive. Thus, the purpose of this study was to examine the efficacy of a health promotion program on body composition, metabolic health, muscle strength, and cardiovascular endurance in law enforcement personnel. Active duty officers from a local law enforcement agency were invited to participate in a 12-week health promotion program that included activity tracking and exercise and nutrition education. Eighteen subjects underwent measurements of body composition, V̇ o2 max through treadmill test, knee extensor strength, and blood lipids. An a priori alpha level for significance was set at 0.05, and comparisons were assessed using paired t -tests. Overall, subjects improved blood lipid levels evidenced by movement of mean values toward established healthy ranges. Although 8 subjects improved their V̇ o2 max (range: 1.3-30% change), there was large variability and no statistically significant differences in measures of V̇ o2 max (pre: 38.48 ± 5.86 ml·kg·min -1 ; post: 39.27 ± 5.26 ml·kg·min -1 ), body composition (pre: 26.52 ± 8.02% body fat; post: 26.44 ± 7.45% body fat), and strength normalized to body mass (isometric pre: 1.45 ± 0.45; post: 1.08 ± 0.36). Although no significant changes were noted, promising trends in these data suggest that health promotion programs with a modified focus may lead to positive changes in overall health., (Copyright © 2021 National Strength and Conditioning Association.)

This study describes a mouse model of progressive resistance exercise that utilizes a full-body/multi-joint exercise (weight pulling) along with a training protocol that mimics a traditional human paradigm (three training sessions per week, ~8-12 repetitions per set, 2 min of rest between sets, approximately two maximal-intensity sets per session, last set taken to failure, and a progressive increase in loading that is based on the individual's performance). We demonstrate that weight pulling can induce an increase in the mass of numerous muscles throughout the body. The relative increase in muscle mass is similar to what has been observed in human studies, and is associated with the same type of long-term adaptations that occur in humans (e.g., fiber hypertrophy, myonuclear accretion, and, in some instances, a fast-to-slow transition in Type II fiber composition). Moreover, we demonstrate that weight pulling can induce the same type of acute responses that are thought to drive these long-term adaptations (e.g., the activation of signaling through mTORC1 and the induction of protein synthesis at 1 h post-exercise). Collectively, the results of this study indicate that weight pulling can serve as a highly translatable mouse model of progressive resistance exercise.

A practice session is common prior to strength testing. However, the benefits of practice have not been previously reported. The purpose of this study was to determine the effect of a practice session on peak torque, mean torque and between trial variability across three test days. We hypothesized that peak and mean torque would be higher and less variable the second and third test days than the first. Twenty-five healthy, young participants completed 3 maximal voluntary isometric and isokinetic knee extensions on three separate days. No difference in isometric torque was found between days 1 and 2, but there was a significant decrease in isokinetic torque (8.45 Nm). There was a significant decrease in both mean isometric and isokinetic torque from day 1 to day 3 (12.67 and 13.59 Nm). Contrary to our hypothesis, no benefit from a practice session was found. Healthy, young adults are able to produce peak knee extensor torques on the first day of testing and do not demonstrate any benefit from additional testing. Thus, a practice day preceding isometric and isokinetic knee extensor strength testing may not be necessary when testing healthy, young participants, and may, in fact, negatively impact subsequent strength measurements.

Running is an activity with a consistently high injury rate. Running footwear design that mimics barefoot running has been proposed to reduce injury rate by increasing the strength of foot structures. However, there is little evidence to support this. The purpose of the current study is to use shear wave ultrasound elastography to examine material properties (shear modulus) of intrinsic foot structures in experienced minimally and traditionally shod runners. It is hypothesized that minimalist runners will exhibit increased stiffness compared to controls demonstrating the strengthening of these structures. Eighteen healthy runners (8 minimalist and 10 traditionalist), running a minimum of 10 mi · wk -1 , participated. Elastography scans were performed on the left foot of each participant. There is no apparent stiffening of foot structures associated with wearing minimalist shoes. Only the FHB tendon is different between shoe types and, contrary to the hypothesis, was stiffer in traditionalist compared to minimalist runners (257.26 ± 51.64 kPa vs 160.88 ± 27.79 kPa, respectively). A moderate positive (r = 0.7) relationship between training load and tendon stiffness suggests strengthening of tendon when running in traditional shoes. If running in minimalist shoes increases loading on these structures without resulting in stronger tissues, it is possible that minimalist footwear may increase injury risk.

Background: Preterm infants are at a high risk of developing late-onset sepsis (LOS). Lactoferrin is one of the most abundant endogenous antimicrobial proteins expressed in breast milk, stools, and blood, and a candidate for preventive intervention. Large clinical trials have recently investigated whether enteral supplementation with bovine lactoferrin reduces LOS., Aim: To characterize lactoferrin levels in preterm infants with and without LOS during the first month of life., Methods: Very preterm and term infants were recruited and serial biosamples collected during the first month of life. Lactoferrin levels were determined by immunoassay in cord blood and peripheral blood on days 1, 7, 14, 21, and 28; in the stools on days 1 and 28; and in the mother's breast milk on days 7 and 21. Furthermore, we assessed the capacity of the peripheral blood to release lactoferrin in response to an in vitro challenge with live Staphylococcus epidermidis, lipopolysaccharide, and fibroblast-stimulating lipopeptide 1., Results: Plasma lactoferrin levels were higher in cord blood and day 1 peripheral blood and declined during the first month of life. Plasma lactoferrin levels were similar in term infants and in preterm infants with (n = 32) and without LOS (n = 53). S. epidermidis-induced lactoferrin levels were lower following the sepsis episode., Conclusions: Endogenous lactoferrin expression in preterm infants does not appear to affect their risk of developing LOS. These findings are in line with the lack of benefit recently observed in large trials of enteral supplementation with bovine lactoferrin to prevent LOS., (© 2020 S. Karger AG, Basel.)

Neonates, especially those born preterm, are at increased risk of sepsis and adverse long-term effects associated with infection-related inflammation. Distinct neonatal immune responses and dysregulated inflammation are central to this unique susceptibility. The traditional separation of sepsis into an initial hyper-inflammatory response followed by hypo-inflammation is continually under review with new developments in this area of research. There is evidence to support the association of mortality in the early acute phase of sepsis with an overwhelming hyper-inflammatory immune response. Emerging evidence from adults suggests that hypo- and hyper-inflammation can occur during any phase of sepsis and that sepsis-immunosuppression is associated with increased mortality, morbidity, and risk to subsequent infection. In adults, sepsis-induced immunosuppression (SII) is characterised by alterations of innate and adaptive immune responses, including, but not limited to, a prominent bias toward anti-inflammatory cytokine secretion, diminished antigen presentation to T cells, and reduced activation and proliferation of T cells. It is unclear if sepsis-immunosuppression also plays a role in the adverse outcomes associated with neonatal sepsis. This review will focus on exploring if key characteristics associated with SII in adults are observed in neonates with sepsis.

Regulated exocytosis is one of the defining features of eukaryotic cells, underlying many conserved and essential functions. Definitively assigning specific roles to proteins and lipids in this fundamental mechanism is most effectively accomplished using a model system in which distinct stages of exocytosis can be effectively separated. Here we discuss the establishment of sea urchin cortical vesicle fusion as a model to study regulated exocytosis-a system in which the docked, release-ready, and late Ca(2+)-triggered steps of exocytosis are isolated and can be quantitatively assessed using the rigorous coupling of functional and molecular assays. We provide an overview of the insights this has provided into conserved molecular mechanisms and how these have led to and integrate with findings from other regulated exocytotic cells.

Background: The Alberta Hip and Knee Replacement Project developed a new evidence-based clinical pathway (NCP) for total hip (THR) and knee (TKR) replacement. The aim was to facilitate the delivery of services in a timely and cost-effective manner while achieving the highest quality of care for the patient across the full continuum of care from patient referral to an orthopedic surgeon through surgery, recovery, and rehabilitation. The purpose of this article is to provide an overview of the study design, rationale, and execution of this project as a model for health technology assessment based on comparative effectiveness of alternative clinical pathways., Methods: A pragmatic randomized controlled trial study design was used to evaluate the NCP compared with the standard of care (SOC) for these procedures. The pragmatic study design was selected as a rigorous approach to produce high quality evidence suitable for informing decisions between relevant interventions in real clinical practice. The NCP was evaluated in three of the nine regional health authorities (RHAs) in Alberta with dedicated central intake clinics offering multidisciplinary care teams, constituting 80 percent of THR and TKR surgeries performed annually in Alberta. Patients were identified in the offices of twenty orthopedic surgeons who routinely performed THR or TKR surgeries. Evaluation outcome measures were based on the six dimensions of the Alberta Quality Matrix for Health (AQMH): acceptability, accessibility, appropriateness, effectiveness, efficiency and safety. Data were collected prospectively through patient self-completed questionnaires at baseline and 3 and 12 months after surgery, ambulatory and inpatient chart reviews, and electronic administrative data., Results: The trial design was successful in establishing similar groups for rigorous evaluation. Of the 4,985 patients invited to participate, 69 percent of patients consented. A total of 3,434 patients were randomized: 1,712 to SOC and 1,722 to the NCP. The baseline characteristics of patients in the two study arms, including demographics, comorbidity as measured by CDS and exposure to pain medications, and health-related quality of life, as measured by Western Ontario and McMaster Universities Osteoarthritis Index and Short Form-36, were similar., Conclusions: The Alberta Hip and Knee Replacement Project demonstrates the feasibility and advantages of applying a pragmatic randomized controlled trial to ascertain comparative effectiveness. This is a model for health technology assessment that incorporates how clinical pathways can be effectively evaluated.

Actin has been suggested as an essential component in the membrane fusion stage of exocytosis. In some model systems disruption of the actin filament network associated with exocytotic membranes results in a decrease in secretion. Here we analyze the fast Ca2+-triggered membrane fusion steps of regulated exocytosis using a stage-specific preparation of native secretory vesicles (SV) to directly test whether actin plays an essential role in this mechanism. Although present on secretory vesicles, selective pharmacological inhibition of actin did not affect the Ca2+-sensitivity, extent, or kinetics of membrane fusion, nor did the addition of exogenous actin or an anti-actin antibody. There was also no discernable affect on inter-vesicle contact (docking). Overall, the results do not support a direct role for actin in the fast, Ca2+-triggered steps of regulated membrane fusion. It would appear that actin acts elsewhere within the exocytotic cycle.

Complexes of specific presynaptic proteins have been hypothesized to drive or catalyze the membrane fusion steps of exocytosis. Here we use a stage-specific preparation to test the roles of SNAREs, synaptotagmin, and SNARE-binding proteins in the mechanism of Ca2+-triggered membrane fusion. Excess exogenous proteins, sufficient to block SNARE interactions, did not inhibit either the Ca2+ sensitivity, extent, or kinetics of fusion. In contrast, despite a limited effect on SNARE and synaptotagmin densities, treatments with high doses of chymotrypsin markedly inhibited fusion. Conversely, low doses of chymotrypsin had no effect on the Ca2+ sensitivity or extent of fusion but did alter the kinetic profile, indicating a more direct involvement of other proteins in the triggered fusion pathway. SNAREs, synaptotagmin, and their immediate binding partners are critical to exocytosis at a stage other than membrane fusion, although they may still influence the triggered steps.