Changes In Muscle Research Articles

A joint local spatial and global temporal CNN-Transformer for dynamic facial expression recognition

Unlike conventional video action recognition, Dynamic Facial Expression Recognition (DFER) tasks exhibit minimal spatial movement of objects. Addressing this distinctive attribute, we propose an innovative CNN-Transformer model, named LSGTNet, specifically tailored for DFER tasks. Our LSGTNet comprises three stages, each composed of a spatial CNN (Spa-CNN) and a temporal transformer (T-Former) in sequential order. The Spa-CNN extracts spatial features from images, yielding smaller-sized feature maps to alleviate the computational complexity for subsequent T-Former. The T-Former integrates global temporal information from the same spatial positions across different time frames while retaining the feature map dimensions. The alternating interplay between Spa-CNN and T-Former ensures a continuous fusion of spatial and temporal information, leading our model to excel across various real-world datasets. To the best of our knowledge, this is the first method to address the DFER challenge by focusing on capturing the temporal changes in muscles within local spatial regions. Our method has achieved state-of-the-art results on multiple in-the-wild datasets and datasets under laboratory conditions.

Deciphering the Therapeutic Role of Lactate in Combating Disuse-Induced Muscle Atrophy: An NMR-Based Metabolomic Study in Mice.

Disuse muscle atrophy (DMA) is a significant healthcare challenge characterized by progressive loss of muscle mass and function resulting from prolonged inactivity. The development of effective strategies for muscle recovery is essential. In this study, we established a DMA mouse model through hindlimb suspension to evaluate the therapeutic potential of lactate in alleviating the detrimental effects on the gastrocnemius muscle. Using NMR-based metabolomic analysis, we investigated the metabolic changes in DMA-injured gastrocnemius muscles compared to controls and evaluated the beneficial effects of lactate treatment. Our results show that lactate significantly reduced muscle mass loss and improved muscle function by downregulating Murf1 expression, decreasing protein ubiquitination and hydrolysis, and increasing myosin heavy chain levels. Crucially, lactate corrected perturbations in four key metabolic pathways in the DMA gastrocnemius: the biosynthesis of phenylalanine, tyrosine, and tryptophan; phenylalanine metabolism; histidine metabolism; and arginine and proline metabolism. In addition to phenylalanine-related pathways, lactate also plays a role in regulating branched-chain amino acid metabolism and energy metabolism. Notably, lactate treatment normalized the levels of eight essential metabolites in DMA mice, underscoring its potential as a therapeutic agent against the consequences of prolonged inactivity and muscle wasting. This study not only advances our understanding of the therapeutic benefits of lactate but also provides a foundation for novel treatment approaches aimed at metabolic restoration and muscle recovery in conditions of muscle wasting.

Abdominal Aortic Calcification is Associated with Degeneration of The Paraspinal Muscles - A Retrospective cross-sectional Study.

Retrospective cohort study. To analyze the relationship of abdominal aortic calcification (AAC) and a reduction in the cross-sectional area (CSA) and the fatty infiltration (FI) of the paravertebral muscles in patients undergoing lumbar fusion surgery. Both AAC and paraspinal muscle degeneration have been shown to be associated with poorer outcomes after surgical treatment of degenerative diseases of the lumbar spine. However, there is a lack of data on the association between AAC and paraspinal muscle changes in patients undergoing spine surgery. We retrospectively analyzed patients undergoing lumbar fusion for degenerative spinal pathologies. Muscular and spinal degeneration were measured on magnetic resonance imaging (MRI). AAC was classified on lateral lumbar radiographs. The association of AAC and paraspinal muscle composition was assessed by a multivariate regression analysis adjusted for age, sex, body mass index (BMI), comorbidities, and lumbar degeneration. A total of 301 patients was included. Patients with AAC showed significantly higher degrees of intervertebral disc and facet joint degeneration as well as higher total endplate scores at the L3/4 level. The univariable regression analysis showed a significant positive correlation between the degree of AAC and the FI of the erector spinae (b=0.530, P<0.001) and multifidus (b=0.730, P<0.001). The multivariable regression analysis showed a significant positive correlation between the degree of AAC and the FI of the erector spinae (b=0.270, P=0.006) and a significant negative correlation between the degree of AAC and the CSA of the psoas muscle (b=-0.260, P=0.003). This study demonstrates a significant and independent association between AAC and degeneration of the erector spinae and the psoas muscles in patients undergoing lumbar fusion. As both AAC and degeneration of paraspinal muscles impact postoperative outcomes negatively, preoperative assessment of AAC may aid in identifying patients at higher risk after lumbar surgery.

Investigating the effects of synbiotic supplementation on functional movement, strength and muscle health in older Australians: a study protocol for a double-blind, randomized, placebo-controlled trial

BackgroundAging has been associated with a progressive loss of skeletal muscle quality, quantity and strength, which may result in a condition known as sarcopenia, leading to a decline in physical performance, loss of independence and reduced quality of life. While the cause of impaired physical functioning observed in elderly populations appears to be multifactorial, recent evidence suggests that age-associated alterations in gut microbiota could be a contributing factor. The primary objective will be to assess the effects of a dietary synbiotic formulation on sarcopenia-related functional outcomes such as handgrip strength, gait speed and physical performance within older individuals living independently. The secondary objective will be to examine associations between changes in gut microbiota composition, functional performance and lean muscle mass.MethodsSeventy-four elderly (60–85 years) participants will be randomized in a double-blind, placebo-controlled fashion to either an intervention or control group. The intervention group (n = 37) will receive oral synbiotic formulation daily for 16 weeks. The control group (n = 37) will receive placebo. Assessments of physical performance (including Short Physical Performance Battery, handgrip strength and timed up-and-go tests) and muscle ultrasonography will be performed at 4 time points (baseline and weeks 8, 16 and 20). Likewise, body composition via bioelectric impedance analysis and blood and stool samples will be collected at each time point. Dual-energy X-ray absorptiometry will be performed at baseline and week 16. The primary outcomes will be between-group changes in physical performance from baseline to 16 weeks. Secondary outcomes include changes in body composition, muscle mass and architecture, fecal microbiota composition and diversity, and fecal and plasma metabolomics.DiscussionGut-modulating supplements appear to be effective in modifying gut microbiota composition in healthy older adults. However, it is unclear whether these changes translate into functional and/or health improvements. In the present study, we will investigate the effects of a synbiotic formulation on measures of physical performance, strength and muscle health in healthy older populations.Trial registrationThis study was prospectively registered with the Australian New Zealand Clinical Trials Registry (ACTRN12622000652774) in May 2022.

Advancing body composition assessment in patients with cancer: First comparisons of traditional versus multicompartment models

Background and aimsMeasurement of body composition using computed tomography (CT) scans may be a viable clinical tool for low muscle mass assessment in oncology. However, longitudinal assessments are often infeasible with CT. Clinically accessible body composition technologies can be used to track changes in fat-free mass (FFM) or muscle, though their accuracy may be impacted by cancer-related physiological changes. The purpose of this study was to examine the agreement among accessible body composition method with criterion methods for measures of whole-body FFM measurements and, when possible, muscle mass for the classification of low muscle in patients with cancer. MethodsPatients with colorectal cancer were recruited to complete measures of whole-body DXA, air displacement plethysmography (ADP), and bioelectrical impedance analysis (BIA). These measures were used alone, or in combination to construct the criterion multicompartment (4C) mode for estimating FFM. Patients also underwent abdominal CT scans as part of routine clinical assessment. Agreement of each method with 4C model was analyzed using mean constant error (CE = criterion – alternative), linear regression including root mean square error (RMSE), Bland-Altman limits of agreement (LoA) and mean percentage difference (MPD). Additionally, appendicular lean soft tissue index (ALSTI) measured by DXA and predicted by CT were compared for the absolute agreement, while the ALSTI values and skeletal muscle index by CT were assessed for agreement on the classification of low muscle mass. ResultsForty-five patients received all measures for the 4C model and 25 had measures within proximity of clinical CT measures. Compared to 4C, DXA outperformed ADP and BIA by showing the strongest overall agreement (CE = 1.96 kg, RMSE = 2.45 kg, MPD = 98.15 ± 2.38%), supporting its use for body composition assessment in patients with cancer. However, CT cutoffs for skeletal muscle index or CT-estimated ALSTI were lower than DXA ALSTI (average 1.0 ± 1.2 kg/m2) with 24.0% to 32.0% of patients having a different low muscle classification by CT when compared to DXA. ConclusionsDespite discrepancies between clinical body composition assessment and the criterion multicompartment model, DXA demonstrates the strongest agreement with 4C. Disagreement between DXA and CT for low muscle mass classification prompts further evaluation of the measures and cutoffs used with each technique. Multicompartment models may enhance our understanding of body composition variations at the individual patient level and improve the applicability of clinically accessible technologies for classification and monitoring change over time.

Metabolome in Tibialis and Soleus Muscles in Wild-Type and Pin1 Knockout Mice through High-Resolution Magic Angle Spinning 1H Nuclear Magnetic Resonance Spectroscopy.

Skeletal muscles are heterogenous tissues composed of different myofiber types that can be classified as slow oxidative, fast oxidative, and fast glycolytic which are distinguished on the basis of their contractile and metabolic properties. Improving oxidative metabolism in skeletal muscles can prevent metabolic diseases and plays a protective role against muscle wasting in a number of neuromuscular diseases. Therefore, achieving a detailed understanding of the factors that regulate myofiber metabolic properties might provide new therapeutic opportunities for these diseases. Here, we investigated whether peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN1) is involved in the control of myofiber metabolic behaviors. Indeed, PIN1 controls glucose and lipid metabolism in a number of tissues, and it is also abundant in adult skeletal muscles; however, its role in the control of energy homeostasis in this tissue is still to be defined. To start clarifying this topic, we compared the metabolome of the tibialis anterior muscle (mainly glycolytic) and soleus muscle (oxidative) in wild-type and Pin1 knockout mice with High-Resolution Magic Angle Spinning (HR-MAS) NMR on intact tissues. Our analysis reveals a clear demarcation between the metabolomes in the two types of muscles and allows us to decode a signature able to discriminate the glycolytic versus oxidative muscle phenotype. We also detected some changes in Pin1-depleted muscles that suggest a role for PIN1 in regulating the metabolic phenotype of skeletal muscles.

Disuse-Induced Muscle Fatigue: Facts and Assumptions.

Skeletal muscle unloading occurs during a wide range of conditions, from space flight to bed rest. The unloaded muscle undergoes negative functional changes, which include increased fatigue. The mechanisms of unloading-induced fatigue are far from complete understanding and cannot be explained by muscle atrophy only. In this review, we summarize the data concerning unloading-induced fatigue in different muscles and different unloading models and provide several potential mechanisms of unloading-induced fatigue based on recent experimental data. The unloading-induced changes leading to increased fatigue include both neurobiological and intramuscular processes. The development of intramuscular fatigue seems to be mainly contributed by the transformation of soleus muscle fibers from a fatigue-resistant, "oxidative" "slow" phenotype to a "fast" "glycolytic" one. This process includes slow-to-fast fiber-type shift and mitochondrial density decline, as well as the disruption of activating signaling interconnections between slow-type myosin expression and mitochondrial biogenesis. A vast pool of relevant literature suggests that these events are triggered by the inactivation of muscle fibers in the early stages of muscle unloading, leading to the accumulation of high-energy phosphates and calcium ions in the myoplasm, as well as NO decrease. Disturbance of these secondary messengers leads to structural changes in muscles that, in turn, cause increased fatigue.

The Apparent Diffusion Coefficient of the Paraspinal and Psoas Muscles Are of Prognostic Relevance in Patients With Hepatocellular Carcinoma Undergoing Transarterial Radioembolization.

Transarterial radioembolization (TARE) is a treatment option for early or intermediate stage hepatocellular carcinoma (HCC). Sarcopenia is defined as loss of muscle strength and quality which can be estimated by imaging modalities and has been associated with prognosis and treatment response in HCC patients. Apparent diffusion coefficient (ADC) values derived from diffusion-weighted imaging (DWI) can reflect the tissue composition and might be better to determine muscle changes of sarcopenia than the standard method of computed tomography (CT). The present study sought to elucidate ADC values of the abdominal wall muscles as a prognostic factor in patients undergoing TARE. A retrospective analysis was performed between 2016 and 2020. Overall, 52 patients, 9 women (17.3%) and 43 men (82.7%), with a mean age of 69±8.5 years were included into the analysis. In every case, the first pre-interventional magnetic resonance imaging (MRI) including DWI was used to measure the ADC values of paraspinal and psoas muscle. The 12-month survival after TARE was used as the primary study outcome. Overall, 40 patients (76.9%) of the patient cohort died within the 12-month observation period. Mean overall survival was 10.9 months after TARE for all patients. Mean ADC values for all muscles were 1.31±0.13×10-3mm2/s. The ADC values of the paraspinal muscles were statistically significantly higher compared to the ADC values of the psoas muscles (p=0.0031). A positive correlation was identified between mean ADC and the thrombocyte count (r=0.37, p=0.005) and serum bilirubin (r=-0.30, p=0.03). In the multivariate Cox regression analysis, the mean ADC values of all muscles were associated with the survival after 12 months (HR=0.98, 95% CI=0.97-0.99, p=0.04). ADC values of the abdominal wall muscles could be used as a prognostic biomarker in patients with HCC undergoing TARE. These preliminary results should be confirmed by further studies using external validation cohorts and other treatment modalities.

Skeletal muscle myosin heavy chain expression and 3D capillary network changes in streptozotocin-induced diabetic female mice.

It is not well-understood how type 1 diabetes (T1DM) affects skeletal muscle histological phenotype, particularly capillarisation. This study aimed to analyze skeletal muscle myosin heavy chain (MyHC) fibre type changes and 3D capillary network characteristics in experimental T1DM mice. Female C57BL/6J-OlaHsd mice were categorized into streptozotocin (STZ)-induced diabetic (n = 12) and age-matched non-diabetic controls (n =12). The muscle fibre phenotype of the soleus, gluteus maximus, and gastrocnemius muscles were characterized based on the expression of MyHC isoforms, while capillaries of the gluteus maximus were assessed with immunofluorescence staining, confocal laser microscopy and 3D image analysis. STZ-induced diabetic mice exhibited elevated glucose levels, reduced body weight, and prolonged thermal latency, verifying the T1DM phenotype. In both T1DM and non-diabetic mice, the gluteus maximus and gastrocnemius muscles predominantly expressed fast-twitch type 2b fibers, with no significant differences noted. However, the soleus muscle in non-diabetic mice had a greater proportion of type 2a fibers and comparable type 1 fiber densities (26.2 ± 14.6% vs 21.9 ± 13.5%) relative to diabetic mice. T1DM mice showed reduced fiber diameters (P = 0.026), and the 3D capillary network analysis indicated a higher capillary length per muscle volume in the gluteus maximus of diabetic mice compared to controls (P < 0.05). Overall, T1DM induced significant changes in the skeletal muscle, including shifts in MyHC fibre types, decreased fibre diameters, and increased relative capillarisation, possibly due to muscle fibre atrophy. Our findings emphasize the superior detail provided by the 3D analytical method for characterizing skeletal muscle capillary architecture, highlighting caution in interpreting 2D data for capillary changes in T1DM.

Differences in thick filament activation in fast rodent skeletal muscle and slow porcine cardiac muscle.

There is a growing appreciation that regulation of muscle contraction requires both thin filament and thick filament activation in order to fully activate the sarcomere. The prevailing mechano-sensing model for thick filament activation was derived from experiments on fast-twitch muscle. We address the question whether, or to what extent, this mechanism can be extrapolated to the slow muscle in the hearts of large mammals, including humans. We investigated the similarities and differences in structural signatures of thick filament activation in porcine myocardium as compared to fast rat extensor digitorum longus (EDL) skeletal muscle under relaxed conditions and sub-maximal contraction using small angle X-ray diffraction. Thick and thin filaments were found to adopt different structural configurations under relaxing conditions, and myosin heads showed different changes in configuration upon sub-maximal activation, when comparing the two muscle types. Titin was found to have an X-ray diffraction signature distinct from those of the overall thick filament backbone, and its spacing change appeared to be positively correlated to the force exerted on the thick filament. Structural changes in fast EDL muscle were found to be consistent with the mechano-sensing model. In porcine myocardium, however, the structural basis of mechano-sensing is blunted suggesting the need for additional activation mechanism(s) in slow cardiac muscle. These differences in thick filament regulation can be related to their different physiological roles where fast muscle is optimized for rapid, burst-like, contractions, and the slow cardiac muscle in large mammalian hearts adopts a more finely tuned, graded response to allow for their substantial functional reserve. KEY POINTS: Both thin filament and thick filament activation are required to fully activate the sarcomere. Thick and thin filaments adopt different structural configurations under relaxing conditions, and myosin heads show different changes in configuration upon sub-maximal activation in fast extensor digitorum longus muscle and slow porcine cardiac muscle. Titin has an X-ray diffraction signature distinct from those of the overall thick filament backbone and this titin reflection spacing change appeared to be directly proportional to the force exerted on the thick filament. Mechano-sensing is blunted in porcine myocardium suggesting the need for additional activation mechanism(s) in slow cardiac muscle. Fast skeletal muscle is optimized for rapid, burst-like contractions, and the slow cardiac muscle in large mammalian hearts adopts a more finely tuned graded response to allow for their substantial functional reserve.

Comparing changes to the skeletal muscle transcriptome of young and aged mice to young and aged humans in response to acute eccentric contractions

Resistance exercise alters several molecular events in skeletal muscle that change muscle size and function, including changes to the transcriptome. The signals altering the muscle transcriptome in response to resistance exercise remain ill defined. Defining those regulatory signals in muscle requires non-human models where manipulations can assess cause and effect. The electrically induced, unilateral eccentric contraction model of resistance exercise in rodents is widely used to mimic resistance exercise. However, the transcriptional changes that occur in response to eccentric contractions in the rodent model and the continuity of the rodent model to resistance exercise in humans are not well known. The purpose of this study was to define the transcriptional changes in skeletal muscle that occur in response to acute eccentric contractions in young and aged mice and define their continuity to transcriptional changes in the muscle of young and aged humans. Four-month-old and 24-month-old male C57BL/6 mice were subjected to a bout of electrically induced, unilateral eccentric contractions of the tibialis anterior (TA) muscle. RNA was isolated from the TA and subjected to RNA Sequencing. Lists of differentially expressed genes (DEGs) from the TA of young and aged mice were compared to RNA Sequencing datasets generated from the vastus lateralis muscle of young and aged humans following acute eccentric contractions. L andscape I n S ilico deletion A nalysis (Lisa) was used to predict the magnitude of transcription factor regulation of the DEGs. DEGs for mice or humans were categorized into age specific DEGs (specific to young or aged) or DEGs shared by both ages. The number of DEGs for mice or humans were distributed equally to each category, showing an age specific distribution that was conserved in both mice and humans. However, the DEGs in young and aged mice had very little overlap to the DEGs in young and aged humans. Only 113 DEGs were common across all ages and species. Interestingly, the relationship of transcription factors predicted to regulate DEGs between young and aged mice or young and aged humans was very strong. However, the relationship of transcription factors predicted to regulate DEGs of young mice and young humans or aged mice and aged humans was rather weak. In all, these data highlight the consistencies and differences in the muscle transcriptomic response to eccentric contractions. This work was supported in part by NIH R03AG073445 (BSG). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Magnetic resonance imaging findings in patients with dropped head syndrome

BackgroundDropped head syndrome (DHS) is difficult to diagnose only by clinical examination. Although characteristic images on X-rays of DHS have been studied, changes in soft tissue of the disease have remained largely unknown. Magnetic resonance imaging (MRI) is useful for evaluating soft tissue, and we therefore performed this study with the purpose of investigating the characteristic signal changes of DHS on MRI by a comparison with those of cervical spondylosis. MethodsThe study involved 35 patients diagnosed with DHS within 6 months after the onset and 32 patients with cervical spondylosis as control. The signal changes in cervical extensor muscles, interspinous tissue, anterior longitudinal ligament (ALL) and Modic change on MRI were analyzed. ResultsSignal changes of cervical extensor muscles were 51.4% in DHS and 6.3% in the control group, those of interspinous tissue were 85.7% and 18.8%, and those of ALL were 80.0% and 21.9%, respectively, suggesting that the frequency of signal changes of cervical extensor muscles, interspinous tissue and ALL was significantly higher in the DHS group (p < 0.05). The presence of Modic change of acute phase (Modic type I) was also significantly higher in the DHS group than in the control group (p < 0.001). ConclusionMRI findings of DHS within 6 months after the onset presented the characteristic signal changes in cervical extensor muscles, interspinous tissue, ALL and Modic change. Evaluation of MRI signal changes is useful for an objective evaluation of DHS.

Defining Architectural Changes in Mouse Pelvic Floor Muscles During Pregnancy to Withstand Physiological Distension Associated with Parturition

Pelvic floor disorders (PFDs), which are present in ~25% of women, profoundly impact quality of life. During childbirth, pelvic floor muscles (PFMs) endure substantial mechanical strain, which can lead to PFM dysfunction. As such, vaginal childbirth is a major risk factor for PFDs. Previous studies in rats demonstrate important structural adaptations in the PFMs that help to withstand the mechanical strain of childbirth, including muscle fiber lengthening by sarcomerogenesis. However, it is diffcult to establish a comprehensive understanding of the molecular mechanisms underlying PFM dysfunction during childbirth in rat models. Here, our objective was to determine if mouse PFMs undergo similar adaptations to rats during pregnancy and vaginal distension. We hypothesized that, akin to rats, PFMs in mice would undergo muscle fiber elongation through sarcomerogenesis during pregnancy. The PFMs (coccygeus [C], iliocaudalis [ICa], pubocaudalis [PCa]) and a non-pelvic floor muscle (tibialis anterior [TA]) were collected from late-pregnant (E16.5) and non-pregnant C57BL/6NJ (3 months old) mice. These animals were subjected or not subjected to physiological vaginal distension to mimic vaginal parturition (N = 4/group); in anesthetized mice, a 6F transurethral catheter was inserted into the vagina, and it was inflated with 0.3 mL (which best approximated fetal head circumference), and a 13 g weight was attached to the catheter creating circumferential and downward strains similar to parturition. Following this, the animals were euthanized, and the pelvis was fixed in situ for assessment of muscle architectural parameters; muscle fibers length was determined using digital calipers and sarcomere length was measured by light microscopy. Pregnancy induced a significant increase in normalized muscle fiber length in all PFMs compared to non-pregnant animals (Pregnant vs. not pregnant — C: 4.71±0.06 mm vs. 3.37±0.15 mm, p&lt;0.0001; ICa 8.74±0.14 mm vs. 7.50±0.27 mm, p=0.004; PCa 7.13±0.09 mm vs. 6.28±0.34 mm, p=0.04); TA muscle fiber length was unchanged (6.92±0.17 mm vs. 6.73 ± 0.19 mm, p=0.28). Sarcomere length was not affected by pregnancy in any muscle (C: 2.44±0.002 μm vs. 2.45 ± 0.003 μm, p=0.55; ICa: 2.26±0.003 μm vs. 2.26±0.004 μm, p=0.64; PCa: 2.16±0.01 μm vs. 2.16±0.003 μm, p=0.74; TA: 2.55±0.004 μm vs. 2.54±0.003 μm, p=0.28). Balloon-mediated vaginal distention resulted in significantly longer sarcomere lengths in non-pregnant compared to pregnant animals in all PFMs (C: 2.98±0.01 μm vs. 2.43±0.01 μm, p&lt;0.0001; ICa: 2.54±0.004 μm vs. 2.24±0.005 μm, p&lt;0.0001; PCa: 2.85±0.001 μm vs. 2.17±0.001 μm, p&lt;0.0001), indicating protection against sarcomere elongation in pelvic floor muscles of pregnant animals. This study shows that, similar to rats, pregnancy causes architectural changes in mouse pelvic floor muscles, which prevent excessive sarcomere stretching during physiologic vaginal distension that is comparable to fetal delivery. This work was funded by NIH grant #K12 HD000849 (Reproductive Scientist Development Program) to LAB and UC San Diego Senate Grant to LAB. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Myofiber “Lipotoxicity” Does Not Disrupt Cellular Biophysical Properties

Obesity is associated with pathological changes in skeletal muscle that contribute to functional loss and disability. While it is unclear which specific factors cause this impairment in muscle performance, intramyocellular lipid (IMCL) within the muscle fibers, termed “lipotoxicity”, is implicated. Some studies have suggested the mechanism for this association is mitochondrial dysfunction, whereas others propose the increase in IMCL leads to structural changes within the muscle fibers. The objective of this study was to determine whether IMCL, independent of obesity, impacted active force generation and passive viscoelasticity of the myofiber sarcomere lattice. This study utilized soleus muscles from wildtype (WT) and lipodystrophic (LD) mice and calf muscle biopsies from individuals with (DPN) and without (CTL) type 2 diabetes over a range of obesity status to isolate the effects of IMCL from the effects of obesity in general. IMCL was quantified for each fiber type by co-registration of Oil Red O (ORO) stained cryosections or fluorescent BODIPY stained section and myosin heavy chain isoform stained sections. BODIPY stained sections were used with confocal microscopy to quantify individual lipid droplet metrics (average area, total number). Individual muscle fibers were isolated from soleus muscles and calf muscle biopsies and chemically permeabilized to isolate the myofibrillar lattice and were tested in a specialized system (1400A; Aurora Scientific). Active and passive forces were recorded, fit with a 3-element model, and correlated with metrics of IMCL accumulation by fiber type. LD muscle had 2-3 fold higher IMCL accumulation (p&lt;0.05) in type 2a and 2x fibers than WT quantified by ORO and BODIPY. This was due to an increase in both lipid droplet area and number. DPN muscle had ~2 fold higher IMCL accumulation (p&lt;0.05) in type 2 fibers compared with CTL. Both type 1 and type 2 fibers had significantly increased area of lipid droplets, but only in type 2 fibers was there an increase in lipid droplet number and consequently in area fraction. Despite the large accumulation of IMCL, LD permeabilized muscle fibers had no deficit in active force generation and no change in any of the 5 measures of passive viscoelasticity compared with WT. Conversely, in humans, DPN type 2 fibers had significantly lower (-18%) active force generation and both type 1 and type 2 DPN fibers had elevated resting viscosity (+5%) compared with CTL. Across human samples, active force generation was significantly correlated with average lipid droplet area (r2=0.53, p=0.04), but no other correlations were significant. This study suggests that an increase in IMCL accumulation in and of itself does not physically disrupt sarcomere contraction. Dramatic accumulation of IMCL in LD mouse fibers did not impact active or passive forces, likely due to an absence of systemic complications (obesity, advanced diabetes). Human fibers of comparable IMCL accumulation have a deficit in active force generation correlated with IMCL parameters, but we conclude this relationship is more likely correlative than causative as type 1 fibers with similar lipid droplet areas have no association between lipid droplet area and active force generation. These data suggest that while accumulation of IMCL is associated with contractile disfunction across a number of conditions, the mechanism is likely either indirect or biochemical rather than biophysical. Shriners Hospitals for Children, P30 AR074992, AR075773, AG15768, AG46927, AR072999, AR073752. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Physical inactivity following volumetric muscle loss results in a divergence between whole-body and cellular metabolic dysfunction

Volumetric muscle loss (VML) is the frank loss of muscle due to injury or surgery and is characterized by whole-body and cellular metabolic dysfunction. Following VML, prolonged bedrest and life-long disability may worsen metabolic dysfunction. This work aimed to elucidate the impact of VML and physical inactivity on the whole-body, cellular, and metabolomic environment of the remaining uninjured muscle. Adult male C57BI/6J mice (n=40) underwent unilateral VML to the posterior hindlimb compartment or served as age-matched injury naïve controls, then were randomized to standard or restricted activity cages for 8-wks. Physical activity, whole-body metabolism, and glucose tolerance were evaluated at 6- and 7-wks post-VML, respectively. Small molecule metabolites and lipids were measured using liquid chromatography-couple and flow injection tandem mass spectrometry. Differences were evaluated by two-way ANOVA with Tukey’s HSD post hoc. Inactivity following VML resulted in ~7% decrease in 24-hr metabolic rate compared to VML alone (p=0.032). Regardless of injury, 24-hr RER was ~5% greater following inactivity (p=0.001). Over 24 hrs, carbohydrate oxidation was ~23% greater with injury and inactivity (p=0.001); lipid oxidation was largely unchanged (p≥0.068). Change in RER (ΔRER) was ~93% greater in VML-injured mice (p=0.030). Physical activity can influence whole-body metabolism, and inactivity post-VML results in greater whole-body carbohydrate usage. Regardless of activity, blood glucose levels were lower following injury (p&lt;0.001). Adiponectin was greater in VML-injured muscles (p&lt;0.001), which may explain enhanced whole-body glucose tolerance post-VML. Protein expression of localized metabolic signals revealed muscle GLUT4, fatty acid binding protein 4, acetyl-CoA carboxylase (ACC), phosphorylated ACC (pACC) and liver fatty acid synthase (FAS) were unaffected by injury and inactivity (p≥0.117). Muscles of inactive, VML-injured mice exhibited a greater pACC:ACC ratio (p=0.046), suggesting decreased fatty acid synthesis. No effect of injury or inactivity was observed in circulating leptin (p≥0.188). Beta-hydroxyacyl CoA dehydrogenase activity was decreased following injury, suggesting a diminished capacity to oxidize fatty acids (p=0.033). Inactivity alone did not alter the metabolome. Injury resulted in 54 significantly expressed metabolites and/or ratios. The combination of injury and inactivity produced a similar response as VML alone, with 91% of metabolites and/or ratios commonly expressed between groups. Similar metabolite expressions following VML with and without inactivity indicate VML injury alone is regulating an altered metabolome. Collectively, although there was no substantial impact of inactivity on whole-body metabolic dysfunction above VML alone, metabolic changes in VML-injured muscles suggests functional alterations in fatty acid metabolism with inactivity. If the ability to oxidize fatty acids is exhausted following VML, resulting accumulation of triglycerides may contribute to metabolic disease often observed with physical inactivity. Continued work to elucidate mechanisms and functional aspects of fatty acid oxidation following VML is needed. W81XWH-20-1-0885 and R01-AR078903 to JAC &amp; SMG. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Pathological Changes in the Gastrocnemius Muscle throughout Hind Limb Ischemia Modeling in Rats.

We present a two-stage model for the study of chronic hind limb ischemia in rats. In the area of ischemia, sclerotic changes with atrophic rhabdomyocytes and reduced vascularization were revealed. CD31 expression in the endothelium increased proportionally to the number of vessels in the ischemic zone, and at the same time, focal expression of βIII-tubulin was detected in the newly formed nerve fibers. These histological features are equivalent to the development of peripheral arterial disease in humans, which allows using our model in the search for new therapeutic strategies.

The Natural Flavanoid Senolytic Fisetin Mitigates Age-Related Changes in Frailty, Grip Strength, and the Skeletal Muscle Transcriptome in Old Mice

Background: Changes in skeletal muscle (SKM) with aging are characterized, in part, by reduced SKM strength and altered gene expression, both of which contribute to increased frailty. The age-related accumulation of excess senescent cells promotes the sequela of SKM aging and contributes to increased frailty. Thus, reducing senescent cell burden represents a promising therapeutic approach to improve SKM function and reduce frailty with aging. Senolytics are compounds that clear excess senescent cells. Currently available synthetic pharmacological senolytic agents harbor poor safety profiles and have low translational application; thus, new approaches are required. Fisetin (FIS) is a natural flavonoid senolytic compound that may fit this need. However, whether FIS supplementation lowers frailty and mitigates the sequela of SKM aging remains unknown. Hypothesis: FIS supplementation in old mice will ameliorate age-related changes in frailty, SKM strength, and senescence-related gene expression in SKM. Methods: We assessed frailty (via a validated frailty index) and SKM strength (via forelimb grip strength) in old (27 mo) male and female C57BL6/N mice following intermittent oral supplementation of either FIS (OFIS, N=39/19 female; 100 mg/kg/day in vehicle [10% EtOH; 30% PEG400; 60% Phosal 50 PG]; 1 week on — 2 weeks off — 1 week on) or vehicle (OC, N=31/13 female). mRNA expression was assessed in isolated quadriceps SKM via bulk RNA sequencing (N=10/group; 5 female). Results were also compared to a young (6 mo) control reference group (YC, N=10; 5 female). Sex differences were not observed, therefore, data were combined for male and female mice. Data are mean ± SEM. Results: Frailty was higher (OC: 0.27 ± 0.01 vs. YC: 0.01 ± 0.004; p&lt;0.05) and grip strength was lower (OC: 2.9g ± 0.01 vs. YC: 4.4g ± 0.02; p&lt;0.05) in old relative to young mice. Pathways associated with cellular senescence were enriched in SKM of OC compared to YC. Some of the most overly expressed genes with aging were related to cellular senescence (e.g., Ankrd1, Gadd45a, Cdkn1a). FIS supplementation reduced the age-related increase in frailty by ~15% (OFIS, 0.23 ± 0.01; p&lt;0.05 vs. OC) and diminished the age-related decline in grip strength by ~30% (OFIS, 3.3g ± 0.1; p&lt;0.05 vs. OC). FIS altered the overall SKM transcriptome in old mice characterized by (1) a less distinct aging phenotype vs. YC analyzed via principal component analysis; and (2) less or no longer enriched cellular senescence-related pathways. A total of six genes were different in OFIS vs. OC (p&lt;0.05; Log 2-fold change ± 0.5). Notably, Adh1 (alcohol dehydrogenase 1; positively associated with longevity) was higher and Ddit4 (DNA damage inducible transcript 4; positively related to DNA damage-induced senescence) was lower. Conclusions: Intermittent oral supplementation with FIS may be an effective therapeutic strategy to treat the sequela of SKM aging and frailty. However, to elicit greater changes in frailty and SKM strength with aging, a stronger or longer FIS dosing paradigm may be required. F32 HL167552; K01 DK115524; AHA 23CDA1056582; F31 HL165885; F31 HL164004; R01 AG055822-S1; K99 HL159241. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Assessment of Electromyographic Changes in Masseter and Temporalis Muscles for Patients Undergoing Lower Third Molar Surgery: A Prospective Study.

Introduction Lower third molar impaction surgery is one of the most common minor oral surgical procedures done. Trismus has been one of the most common and disturbing postoperative sequelae for patients. The study aimed to evaluate the electrical activity of the masseter and temporalis muscles after mandibular third molar surgery. Materials and methods The research was conducted at Saveetha Dental College and hospitals in the Department of Oral and Maxillofacial Surgery. The study consisted of 20 individuals. The EMG (electromyography) activities of both masseter muscles in each patient were measured before the tooth extraction surgery, postoperatively after 72 hours, and after seven days. The inter-incisal distance was also measured at similar follow-up intervals. Data were analyzed using IBM Corp. Released2015. IBM SPSS Statistics for Windows, Version 23.0. Armonk, NY: IBM Corp., with p-values less than 0.05 considered statistically significant. The Mann-Whitney U test was used for the comparison of electrical activity between masseter and temporalis on both the operated and non-operated sides during preoperative, postoperative, 72-hour, and postoperative seven-day periods. Results It has been found that the electrical activity of the temporalis is higher than that of the masseter muscle measured at all the intervals of the follow-up period, with statistically significant values (p=0.001). It was noted that all the patients have reduced mouth opening when compared with preoperative (mean mouth opening = 45.6 mm), postoperative 72 hours (mean mouth opening = 31.2 mm), and postoperative seven days (mean mouth opening =35.6 mm). When a comparison was done between temporalis and masseter, themasseter took longer to return to pre-operative electrical activity, which might also imply that for prolonged trismus seen in patients after lower third molar surgery, it is the masseter that is affected and needs recovery for trismus to be resolved. Conclusion Based on the results obtained, it can be concluded that there was a reduction in the electrical activity of both the masseter and temporalis post-third molar impaction surgery. It was also found that there was a reduction in mouth opening in patients who underwent lower third molar extraction surgery. Masseter muscle took longer to return to its preoperative electrical activity than temporalis muscle, implying that targeted therapies to accelerate the healing of masseter muscle may prevent prolonged trismus in patients who undergo lower third molar impaction surgery.

Increasing Vertical Dimension of Occlusion (VDO): Review.

The need to increase the Vertical Dimension of Occlusion (VDO) to restore lost dental function or optimise specific dental treatments is a common occurrence in daily dental practice. The common belief that the Vertical Dimension at Rest (VDR) is fixed hinders the development of restorations with a VDO that encroaches on or surpasses the interocclusal rest space (IRS), thereby preventing potential tissue damage to the masticatory apparatus. Recent studies have shown that the mandible rest position falls within a range termed as the "comfort zone". The range of this zone may vary from one person to another and within the same person over time due to factors such as age or health status. In this review, we have concluded that a permanent increase in the VDO, once indicated, is a safe procedure for dentulous patients. However, it is important to minimise the extent of the increase to simplify the prosthodontics treatment process. An inter-incisal increase exceeding 5 mm is seldom needed. Moreover, it is important to consider the functional, aesthetic, and biological elements associated with VDO. The biological and functional environment closely related to the VDO had great adaptive capacities, which have for a historically been underestimated. Patient adaptation has been observed in dentate patients, edentulous patients, and even cases involving implant-supported prostheses. Muscle relaxation and changes in muscle length are likely the primary adaptation mechanisms, rather than the restoration of the original VDO through dentoalveolar maturation. Intervention with a fixed restoration is more predictable and results in a higher and more rapid level of adaptation. Finally, the increase should include the entire arch to prevent relapse of the VDO to its previous value, and changes in VDO should be assessed by utilising temporary diagnostic restorations for a period before implementing definitive prostheses, in order to evaluate the adaptive muscle response.

Evidence for Simultaneous Muscle Atrophy and Hypertrophy in Response to Resistance Training in Humans.

Human skeletal muscle has the profound ability to hypertrophy in response to resistance training (RT). However, this has a high energy and protein cost and is presumably mainly restricted to recruited muscles. It remains largely unknown what happens with nonrecruited muscles during RT. This study investigated the volume changes of 17 recruited and 13 nonrecruited muscles during a 10-wk single-joint RT program targeting upper arm and upper leg musculature. Muscle volume changes were measured by manual or automatic 3D segmentation in 21 RT novices. Subjects ate ad libitum during the study and energy and protein intake were assessed by self-reported diaries. Posttraining, all recruited muscles increased in volume (range: +2.2% to +17.7%, P < 0.05), whereas the nonrecruited adductor magnus (mean: -1.5% ± 3.1%, P = 0.038) and soleus (-2.4% ± 2.3%, P = 0.0004) decreased in volume. Net muscle growth ( r = 0.453, P = 0.045) and changes in adductor magnus volume ( r = 0.450, P = 0.047) were positively associated with protein intake. Changes in total nonrecruited muscle volume ( r = 0.469, P = 0.037), adductor magnus ( r = 0.640, P = 0.002), adductor longus ( r = 0.465, P = 0.039), and soleus muscle volume ( r = 0.481, P = 0.032) were positively related to energy intake. When subjects were divided into a HIGH or LOW energy intake group, overall nonrecruited muscle volume (-1.7% ± 2.0%), adductor longus (-5.6% ± 3.7%), adductor magnus (-2.8% ± 2.4%), and soleus volume (-3.7% ± 1.8%) decreased significantly ( P < 0.05) in the LOW but not the HIGH group. To our knowledge, this is the first study documenting that some nonrecruited muscles significantly atrophy during a period of RT. Our data therefore suggest muscle mass reallocation, that is, that hypertrophy in recruited muscles takes place at the expense of atrophy in nonrecruited muscles, especially when energy and protein availability are limited.