Fiber-specific and whole-muscle LRP130 expression in rested, exercised, and fasted human skeletal muscle

Comprehensive review on leucine-rich pentatricopeptide repeat-containing protein (LRPPRC, PPR protein): A burgeoning target for cancer therapy

Leucine-rich pentatricopeptide repeat-containing (LRPPRC), known as the gene mutations that cause Leigh Syndrome French Canadian, encodes a high molecular weight PPR protein (157,905 Da), LRPPRC. LRPPRC binds to DNA, RNA, and proteins to regulate transcription and translation, leading to changes in cell fate. Increasing evidence indicates that LRPPRC plays a pivotal role in various human diseases, particularly cancer in recent years. Here, we review the structure, function, molecular mechanism, as well as inhibitors of LRPPRC. LRPPRC expression elevates in most cancer types and high expression of LRPPRC predicts the poor prognosis of cancer patients. Targeting LRPPRC suppresses tumor progression by affecting several cancer hallmarks, including signal transduction, cancer metabolism, and immune regulation. LRPPRC is a promising target in cancer research, serving as both a biomarker and therapeutic target. Further studies are required to extend the understanding of LRPPRC function and molecular mechanism, as well as to refine novel therapeutic strategies targeting LRPPRC in cancer therapy.

Redox signaling and skeletal muscle adaptation during aerobic exercise

Redox regulation is a fundamental physiological phenomenon related to oxygen-dependent metabolism, and skeletal muscle is mainly regarded as a primary site for oxidative phosphorylation. Several studies have revealed the importance of reactive oxygen and nitrogen species (RONS) in the signaling process relating to muscle adaptation during exercise. To date, improving knowledge of redox signaling in modulating exercise adaptation has been the subject of comprehensive work and scientific inquiry. The primary aim of this review is to elucidate the molecular and biochemical pathways aligned to RONS as activators of skeletal muscle adaptation and to further identify the interconnecting mechanisms controlling redox balance. We also discuss the RONS-mediated pathways during the muscle adaptive process, including mitochondrial biogenesis, muscle remodeling, vascular angiogenesis, neuron regeneration, and the role of exogenous antioxidants.

N-acetylneuraminate pyruvate lyase controls sialylation of muscle glycoproteins essential for muscle regeneration and function

Deleterious variants in N-acetylneuraminate pyruvate lyase (NPL) cause skeletal myopathy and cardiac edema in humans and zebrafish, but its physiological role remains unknown. We report generation of mouse models of the disease: NplR63C, carrying the human p.Arg63Cys variant, and Npldel116 with a 116-bp exonic deletion. In both strains, NPL deficiency causes drastic increase in free sialic acid levels, reduction of skeletal muscle force and endurance, slower healing and smaller size of newly formed myofibers after cardiotoxin-induced muscle injury, increased glycolysis, partially impaired mitochondrial function, and aberrant sialylation of dystroglycan and mitochondrial LRP130 protein. NPL-catalyzed degradation of sialic acid in the muscle increases after fasting and injury and in human patient and mouse models with genetic muscle dystrophy, demonstrating that NPL is essential for muscle function and regeneration and serves as a general marker of muscle damage. Oral administration of N-acetylmannosamine rescues skeletal myopathy, as well as mitochondrial and structural abnormalities in NplR63C mice, suggesting a potential treatment for human patients.

Examining interindividual differences in select muscle and whole-body adaptations to continuous endurance training

NEW FINDINGS

What is the central question of the study? Do interindividual differences in trainability exist for morphological and molecular skeletal muscle responses to aerobic exercise training? What is the main finding and its importance? Interindividual differences in trainability were present for some, but not all, morphological and molecular outcomes included in our study. Our findings suggest that is inappropriate, and perhaps erroneous, to assume that variability in observed responses reflects interindividual differences in trainability in skeletal muscle responses to aerobic exercise training.

ABSTRACT

Studies have interpreted a wide range of morphological and molecular changes in human skeletal muscle as evidence of interindividual differences in trainability. However, these interpretations fail to account for the influence of random measurement error and within-subject variability. The purpose of the present study was to use the standard deviation of individual response (SD_IR ) statistic to test the hypothesis that interindividual differences in trainability are present for some but not all skeletal muscle outcomes. Twenty-nine recreationally-active males (age: 21±2 years; BMI: 24±3; VO₂ peak: 45±7 mL/kg/min) completed four weeks of continuous training (REL; n = 14) or control (CTRL; n = 15). Maximal enzyme activities (citrate synthase and β-HAD), capillary density, fibre type composition, fibre-specific SDH activity and substrate storage (IMTG and glycogen), and markers of mitophagy (BNIP3, NIX, PRKN, and PINK1) were measured in vastus lateralis samples collected before and after the intervention. We also calculated SD_IR values for VO₂ peak, peak work rate, and the onset of blood lactate accumulation for REL and a separate group that exercised at the negative talk test (TT) stage. Although positive SD_IR values - indicating interindividual differences in trainability - were obtained for aerobic capacity outcomes, maximal enzyme activities, capillary density, all fibre-specific outcomes, and BNIP3 protein content, the remaining outcomes produced negative SD_IR values indicating a large degree of random measurement error and/or within-subject variability. Our findings question the interpretation of heterogeneity in observed responses as evidence of interindividual differences in trainability and highlight the importance of including control groups when analyzing individual skeletal muscle response to exercise training. This article is protected by copyright. All rights reserved.

Moving human muscle physiology research forward: an evaluation of fiber type-specific protein research methodologies

Human skeletal muscle is a heterogeneous tissue composed of multiple fiber types that express unique contractile and metabolic properties. While analysis of mixed fiber samples predominates and holds value, increasing attention has been directed toward studying proteins segregated by fiber type, a methodological distinction termed “fiber type-specific.” Fiber type-specific protein studies have the advantage of uncovering key molecular effects that are often missed in mixed fiber homogenate studies but also require greater time and resource-intensive methods, particularly when applied to human muscle. This review summarizes and compares current methods used for fiber type-specific protein analysis, highlighting their advantages and disadvantages for human muscle studies, in addition to recent advances in these techniques. These methods can be grouped into three categories based on the initial processing of the tissue: 1) muscle-specific fiber homogenates, 2) cross sections of fiber bundles, and 3) isolated single fibers, with various subtechniques for performing fiber type identification and protein quantification. The relative implementation for each unique methodological approach is analyzed from 83 fiber type-specific studies of proteins in live human muscle found in the literature to date. These studies have investigated several proteins involved in a wide range of cellular functions that are important to muscle tissue. The second half of this review summarizes key findings from this ensemble of fiber type-specific human protein studies. We highlight examples of where this analytical approach has helped to improve understanding of important physiological topics such as insulin sensitivity, muscle hypertrophy, muscle fatigue, and adaptation to different exercise programs.

Repeatability of training-induced skeletal muscle adaptations in active young males

OBJECTIVES

Measurements of protein content, enzymatic activity, and/or capillarization are frequently utilized as markers of skeletal muscle adaptation following exercise training. Whether changes in these markers of muscle adaptation are repeatable when individuals are repeatedly exposed to the same training stimulus is unknown. The purpose of this study was to test the repeatability of skeletal muscle adaptations to two identical training periods.

METHODS

Ten active young males (age: 22 ± 2 years; VO₂max: 57 ± 7 ml/kg/min) were exposed to two identical four-week periods of supervised high-intensity interval running (4 × 4 min at 90-95% of HRmax interspersed with 3-min at 70-75% HRmax) separated by a 3-month wash-out period. Vastus lateralis biopsies were obtained before and after each training period for the measurement of protein content, enzyme activity, and capillary density.

RESULTS

Training-induced changes in citrate synthase (CS) maximal activity, protein content (PGC-1α, OXPHOS, and LDH-A), and capillary density were not repeatable within individuals (r = -0.52-0.15; ICCs: -0.42-0.04; CVs: 11-67%). Several OXPHOS complex subunits also demonstrated dissimilar group-level adaptations (period × time interaction effects, p < 0.05) with large differences (η_p² > 0.4) between training periods. A large (η_p² = 0.65) increase in capillary density was apparent irrespective of training period (main effect of time, p = 0.05).

CONCLUSIONS

An individual (or a group of individuals) may exhibit dissimilar skeletal muscle adaptations when re-exposed to the same training stimulus. Our findings challenge the utility of classifying of individuals as high/low responders using measurements of mitochondrial protein content, CS activity and/or capillary density following a single training period.