Intramuscular Fat Infiltration Research Articles

Studying intramuscular fat deposition and muscle regeneration: insights from a comparative analysis of mouse strains, injury models, and sex differences

Intramuscular fat (IMAT) infiltration, pathological adipose tissue that accumulates between muscle fibers, is a shared hallmark in a diverse set of diseases including muscular dystrophies and diabetes, spinal cord and rotator cuff injuries, as well as sarcopenia. While the mouse has been an invaluable preclinical model to study skeletal muscle diseases, they are also resistant to IMAT formation. To better understand this pathological feature, an adequate pre-clinical model that recapitulates human disease is necessary. To address this gap, we conducted a comprehensive in-depth comparison between three widely used mouse strains: C57BL/6J, 129S1/SvlmJ and CD1. We evaluated the impact of strain, sex and injury type on IMAT formation, myofiber regeneration and fibrosis. We confirm and extend previous findings that a Glycerol (GLY) injury causes significantly more IMAT and fibrosis compared to Cardiotoxin (CTX). Additionally, females form more IMAT than males after a GLY injury, independent of strain. Of all strains, C57BL/6J mice, both females and males, are the most resistant to IMAT formation. In regard to injury-induced fibrosis, we found that the 129S strain formed the least amount of scar tissue. Surprisingly, C57BL/6J of both sexes demonstrated complete myofiber regeneration, while both CD1 and 129S1/SvlmJ strains still displayed smaller myofibers 21 days post injury. In addition, our data indicate that myofiber regeneration is negatively correlated with IMAT and fibrosis. Combined, our results demonstrate that careful consideration and exploration are needed to determine which injury type, mouse model/strain and sex to utilize as preclinical model especially for modeling IMAT formation.

Intramuscular fat infiltration influences mechanical properties during muscle contraction in older women.

Although evidence suggests that intramuscular fat infiltration may influence muscle strength, the precise mechanisms remain unclear. This study aimed to determine whether intramuscular fat infiltration affects muscle mechanical properties during contraction, and whether these mechanical properties mediate the relationship between intramuscular fat infiltration and muscle strength. Seventy-nine healthy older women aged 75.1±6.8 years were included in this study. The echo intensity (EI) of the vastus lateralis (VL) was measured as an intramuscular fat infiltration index using B-mode ultrasonography. Maximum voluntary isometric contraction strength (MVIC) was assessed using a dynamometer. The VL shear elastic modulus (G), a mechanical property index, was measured using ultrasound shear wave elastography under various muscle contraction conditions, at rest and at 15, 30, and 45% MVIC (G0, G15, G30, and G45). To evaluate the degree of increase in the shear elastic modulus with increasing muscle contraction intensity, the slope of the regression line (Gslope) between muscle contraction and shear elastic modulus was calculated for each participant. The results showed that EI was significantly associated with G30 and G45 but not with G0 or G15. The EI can significantly explain the inter-individual differences in Gslope. Mediation analysis revealed that the effect of EI on MVIC through Gslope was significant (indirect effect = -0.31, 95% confidence interval [-0.57, -0.12]). These findings suggest that a greater EI is associated with a lower G during muscle contraction. Furthermore, our results show that the relationship between EI and MVIC is mediated by Gslope.

P240: Sarcopenia of the lower limb on Magnetic Resonance Imaging in patients with Diabetes Mellitus – a systematic review

Abstract Introduction Sarcopenia is defined by low measures of muscle quantity and quality and physical performance. Accelerated sarcopenic changes in diabetic patients leads to biomechanical changes in the foot and limb loss. Aim To systematically review the literature on Magnetic Resonance Imaging (MRI) and sarcopenia in the lower limb in patients with diabetes. Methods A literature review was conducted in accordance with PRISMA guidelines. Embase and Medline databases were searched with Ovid interface, as well as Pubmed and Cochrane. The grey literature was also reviewed on ClinicalTrials.gov, WHO international clinical trials registry platform, Cochrane library and the NIHR journals library and ProQuest. The MeSH terms “sarcopenia” AND “diabetes mellitus” AND “magnetic resonance imaging” were employed in the primary search string. The articles were reviewed by two independent reviewers. Results 874 studies were screened. 20 articles were included in the final review. Methods of measurement included cross sectional area measurements, stereological muscle measurements, muscle volume estimation, adipose infiltration, signal intensity cut-off, Goutallier grading, semiquantitative 5-point scale. Reduction in cross-sectional area and volumes and greater intramuscular fat infiltration was noted in patients with diabetes Sarcopenia ++ in Diabetic polyneuropathy (DPN) compared to non-diabetic and diabetic but non-DPN counterparts. MRI findings correlate with neuropathy disability scores and physical tests. Single study using a semi-automated process to measure sarcopenia. Conclusion MRI has its merit in providing accurate and detailed information on skeletal muscle volume and assessment of fat infiltration in muscle. This is relevant to reducing complications associated with changes in the biomechanics of the foot.

The utility of a portable muscle ultrasound in the assessment of muscle alterations in children with acute lymphoblastic leukaemia.

During treatment for acute lymphoblastic leukaemia (ALL), children are prone to musculoskeletal deterioration. However, non-invasive tools to measure muscle mass and intramuscular alterations are limited. In this study we explored the feasibility of muscle ultrasound in children with ALL. Additionally, we analysed whether automated ultrasound outcomes of muscle size and intramuscular fat infiltration (IMAT) were associated with appendicular skeletal muscle mass (ASMM), muscle strength and physical performance. Children with ALL, aged 3-18years were included during maintenance therapy. Bilateral images of the rectus femoris muscle were captured using a portable linear array transducer connected to a tablet. Subsequently, an automated image annotation software (MuscleSound) was used to estimate cross-sectional area, muscle thickness and IMAT. Feasibility was assessed using acceptance (percentage of children approached who were enrolled), practicality (percentage of children that completed the ultrasound measurement after enrolment) and implementation (percentage of children that had sufficient imaging to be processed and analysed by the software). Assessments of ASMM by bioimpedance analysis, muscle strength using handheld dynamometry and timed physical performance tests were administered at the same visit. Multivariable linear models were estimated to study the associations between muscle ultrasound outcomes and ASMM, strength and physical performance, adjusted for sex, age, body mass index and ALL treatment week. Muscle ultrasound was performed in 60 out of 73 invited patients (76.9%), of which 37 were boys (61.7%), and median age was 6.1years (range: 3-18.8years). The acceptance was 98.7%, practicality 77.9% and implementation was 100%. Patients who refused the examination (n=13) were younger (median: 3.6, range: 3-11.2years) compared with the 60 examined children (P=0.0009). In multivariable models, cross-sectional area was associated with ASMM (β=0.49 Z-score, 95% confidence interval [CI]:0.3,2.4), knee-extension strength (β=16.9 Newton [N], 95% CI: 4.8, 28.9), walking performance (β=-0.46s, 95% CI: -0.75, -0.18) and rising from the floor (β=-1.07s, 95% CI: -1.71, -0.42). Muscle thickness was associated with ASMM (β=0.14 Z-score, 95% CI: 0.04, 0.24), knee-extension strength (β=4.73N, 95% CI: 0.99, 8.47), walking performance (β=-0.13s, 95% CI: -0.22, -0.04) and rising from the floor (β=-0.28s, 95% CI: -0.48, -0.08). IMAT was associated with knee-extension strength (β=-6.84N, 95% CI: -12.26, -1.41), walking performance (β=0.2s, 95% CI: 0.08, 0.32) and rising from the floor (β=0.54s, 95% CI: 0.27, 0.8). None of the muscle ultrasound outcomes was associated with handgrip strength. Portable muscle ultrasound appears a feasible and useful tool to measure muscle size and intramuscular alterations in children with ALL. Validation studies using magnetic resonance imaging (gold standard) are necessary to confirm accuracy in paediatric populations.

Paper 48: Association of 3D MRI Volumetric Assessment of Rotator Cuff Pathology with Preoperative Patient Reported Outcomes

Paper 48: Association of 3D MRI Volumetric Assessment of Rotator Cuff Pathology with Preoperative Patient Reported Outcomes

Mid-life cyclists preserve muscle mass and composition: a 3D MRI study

Physical activity and a healthy lifestyle are crucial factors for delaying and reducing the effects of sarcopenia. Cycling has gained popularity in the last decades among midlife men. While the cardiovascular benefits of cycling and other endurance exercises have been extensively proved, the potential benefits of lifelong aerobic exercise on muscle health have not been adequately studied. Our aim was to quantify the benefits of cycling in terms of muscle health in middle-aged men, using magnetic resonance imaging. We ran a cross-sectional study involving two groups of middle-aged male adults (mean age 49 years, range 30–65) that underwent Dixon MRI of the pelvis. The groups consisted of 28 physically inactive (PI) and 28 trained recreational cyclists. The latter had cycled more than 7000 km in the last year and have been training for 15 years on average, while the PI volunteers have not practiced sports for an average of 27 years. We processed the Dixon MRI scans by labelling and computing the fat fraction (FF), volume and lean volume of gluteus maximus (GMAX) and gluteus medius (GMED); and measuring the volume of subcutaneous adipose tissue (SAT). We found that the cyclists group had lower FF levels, a measure of intramuscular fat infiltration, compared to the PI group for GMAX (PI median FF 21.6%, cyclists median FF 14.8%, p < 0.01) and GMED (PI median FF 16.0%, cyclists median FF 11.4%, p < 0.01). Cyclists had also larger GMAX and GMED muscles than the PI group (p < 0.01), after normalizing it by body mass. Muscle mass and fat infiltration were strongly correlated with SAT volume. These results suggest that cycling could help preserve muscle mass and composition in middle-aged men. Although more research is needed to support these results, this study adds new evidence to support public health efforts to promote cycling.

A Deep Learning Algorithm for Automatic 3D Segmentation of Rotator Cuff Muscle and Fat from Clinical MRI Scans.

The authors aimed to develop and validate an automated artificial intelligence (AI) algorithm for three-dimensional (3D) segmentation of all four rotator cuff (RC) muscles to quantify intramuscular fat infiltration (FI) and individual muscle volume. The dataset included retrospectively collected RC MRI scans in 232 patients (63 with normal RCs, 169 with RC tears). A two-stage AI model was developed to segment all RC muscles and their FI in each stage. For comparison, single-stage and Otsu filtering models were created. Using the two-stage model, segmentation performance demonstrated high Dice scores (mean, 0.92 ± 0.14 [SD]), low volume errors (mean, 5.72% ± 9.23), and low FI errors (mean, 1.54% ± 2.79) when validated in 30 scans. There was a significant correlation between the 3D FI in the RC tear scans with a Goutallier grade (ρ = 0.53, P < .001) and FI found from a single two-dimensional (2D) section (all muscles, ρ > 0.70; P < .001). However, Bland-Altman analysis of the 3D compared with the 2D analyses of FI demonstrated a proportional bias (all muscles, P < .001). Compared with Goutallier classification or single-image quantification, the AI method allowed for more variability in images and led to objective separate quantifications of muscle volume and FI in all RC muscles. Keywords: Rotator Cuff, Artificial Intelligence, Segmentation, Fat Infiltration, Muscle Volume, MRI, Shoulder Supplemental material is available for this article. © RSNA, 2023.

Sarcopenia and Ageing.

Musculoskeletal ageing is a major health challenge as muscles and bones constitute around 55-60% of body weight. Ageing muscles will result in sarcopenia that is characterized by progressive and generalized loss of skeletal muscle mass and strength with a risk of adverse outcomes. In recent years, a few consensus panels provide new definitions for sarcopenia. It was officially recognized as a disease in 2016 with an ICD-10-CM disease code, M62.84, in the International Classification of Diseases (ICD). With the new definitions, there are many studies emerging to investigate the pathogenesis of sarcopenia, exploring new interventions to treat sarcopenia and evaluating the efficacy of combination treatments for sarcopenia. The scope of this chapter is to summarize and appraise the evidence in terms of (1) clinical signs, symptoms, screening, and diagnosis, (2) pathogenesis of sarcopenia with emphasis on mitochondrial dysfunction, intramuscular fat infiltration and neuromuscular junction deterioration, and (3) current treatments with regard to physical exercises and nutritional supplement.

Growth arrest and DNA damage-inducible alpha regulates muscle repair and fat infiltration through ATP synthase F1 subunit alpha.

Skeletal muscle fat infiltration is a common feature during ageing, obesity and several myopathies associated with muscular dysfunction and sarcopenia. However, the regulatory mechanisms of intramuscular adipogenesis and strategies to reduce fat infiltration in muscle remain unclear. Here, we identified the growth arrest and DNA damage-inducible alpha (GADD45A), a stress-inducible histone folding protein, as a critical regulator of intramuscular fat (IMAT) infiltration. To explore the role of GADD45A on IMAT infiltration and muscle regeneration, the gain or loss function of GADD45A in intramuscular preadipocytes was performed. The adipocyte-specific GADD45A knock-in (KI) mice and high IMAT-infiltrated muscle model by glycerol injection (50μL of 50% v/v GLY) were generated. RNA-sequencing, histological changes, gene expression, lipid metabolism, mitochondrial function and the effect of dietary factor epigallocatechin-3-gallate (EGCG) treatment (100mg/kg) on IMAT infiltration were studied. The unbiased transcriptomics data analysis indicated that GADD45A expression positively correlates with IMAT infiltration and muscle metabolic disorders in humans (correlation: young vs. aged people, Gadd45a and Cebpa, r2 =0.20, P<0.05) and animals (correlation: wild-type [WT] vs. mdx mice, Gadd45a and Cebpa, r2 =0.38, P<0.05; NaCl vs. GLY mice, Gadd45a and Adipoq/Fabp4, r2 =0.80/0.71, both P<0.0001). In vitro, GADD45A overexpression promotes intramuscular preadipocyte adipogenesis, upregulating the expression of adipogenic genes (Ppara: +47%, Adipoq: +28%, P<0.001; Cebpa: +135%, Fabp4: +16%, P<0.01; Pparg: +66%, Leptin: +77%, P<0.05). GADD45A knockdown robustly decreased lipid accumulation (Pparg: -57%, Adipoq: -35%, P<0.001; Fabp4: -37%, P<0.01; Leptin: -28%, P<0.05). GADD45A KI mice exhibit inhibited skeletal muscle regeneration (myofibres: -40%, P<0.01) and enhanced IMAT infiltration (adipocytes: +20%, P<0.05). These KI mice have impaired exercise endurance and mitochondrial function. Mechanistically, GADD45A affects ATP synthase F1 subunit alpha (ATP5A1) ubiquitination degradation (ubiquitinated ATP5A1, P<0.001) by recruiting the E3 ubiquitin ligase TRIM25, which decreases ATP synthesis (ATP production: -23%, P<0.01) and inactivates the cAMP/PKA/LKB1 signalling pathway (cAMP: -36%, P<0.01; decreased phospho-PKA and phospho-LKB1 protein content, P<0.01). The dietary factor EGCG can protect against muscle fat infiltration (triglyceride: -64%, P<0.05) via downregulating GADD45A (decreased GADD45A protein content, P<0.001). Our findings reveal a crucial role of GADD45A in regulating muscle repair and fat infiltration and suggest that inhibition of GADD45A by EGCG might be a potential strategy to combat fat infiltration and its associated muscle dysfunction.

Characteristics of paraspinal muscle degeneration in degenerative diseases of the lumbar spine at different ages

ObjectiveTo analyze the relationship between gender, age, and the degree of lumbar degenerative disease. Methods290 patients with Lumbar spinal stenosis and sciatica were analyzed. Sixty patients without sciatica were collected in the control group. Patient demography including age, gender, body mass index (BMI), serum calcium, and triglyceride level was acquired. The cross-sectional area (CSA) and percentage of fat infiltration area (Intermuscular adipose tissue (IMat%) of paraspinal muscles at the L4–5 level were measured using MRI imaging. The patients were divided into five age groups: A (18–30 years old), B (31–40 years old), C (41–50 years old), D (51–60 years old), and E (> 60 years old). Analysis of variance (ANOVA) and LSD was used to analyze differences among subgroups. Student’s t-test was used to compare MCSA and fat CSA in the two groups. P < 0.05 was statistically significant. ResultsThe paraspinal muscle CSA (MCSA) was significantly smaller in women (P < 0.05). Older age was associated with less MCSA and greater fatty infiltration in erector spinae and multifidus (MF) muscle (P < 0.05). Serum calcium and BMI were positively correlated with CSA of erector spinae muscle (P < 0.05), but not with muscle fat infiltration (P > 0.05). Although there was no significant difference in MCSA between the two groups, the fat infiltration (IMat%) in the disease group was significantly higher than in the control group (p < 0.05). ConclusionLumbar degenerative diseases caused the degeneration of the paravertebral muscles, which mainly resulted in increased intramuscular fat infiltration, rather than changes in the overall MCSA.

Magnetic resonance imaging-based lower limb muscle evaluation in Charcot-Marie-Tooth disease type 1A patients and its correlation with clinical data

We aimed to derive comprehensive MRI parameters that reflect intramuscular fat infiltration severity for designated lower extremity levels, based on semiquantitative analyses in Charcot-Marie-Tooth disease type 1A (CMT1A) patients. We reviewed lower extremity MRIs of 116 CMT1A patients. Intramuscular fat infiltration grading using the Mercuri scale was performed for the non-dominant lower extremity at three levels (proximal, mid, and distal) for the thigh and at two levels (proximal and distal) for the lower leg. Based on MRI results, the following parameters were calculated for each level and for entire muscles: fat infiltration proportion (FIP), significant fat infiltration proportion (SigFIP), and severe fat infiltration proportion (SevFIP). The relationships between the MRI parameters and clinical data were evaluated using Spearman’s correlation analysis. FIP, SigFIP, and SevFIP measured for entire muscles significantly correlated with Charcot-Marie-Tooth Neuropathy Score (p < 0.001), functional disability scale (p < 0.001), 10-m walk test time (p = 0.0003, 0.0010, and 0.0011), and disease duration (p < 0.001). Similar correlations were demonstrated for FIP, SigFIP, and SevFIP acquired from the lower leg. Our MRI parameters obtained through semiquantitative analyses of muscles significantly correlated with clinical parameters in CMT1A patients, suggesting their potential applicability as imaging markers for clinical severity.

Bidirectional roles of skeletal muscle fibro-adipogenic progenitors in homeostasis and disease.

Sarcopenia and myopathies cause progressive muscle weakness and degeneration, which are closely associated with fat infiltration and fibrosis in muscle. Recently, experimental research has shed light on fibro-adipogenic progenitors (FAPs), also known as muscle-resident mesenchymal progenitors with multiple differentiation potential for adipogenesis, fibrosis, osteogenesis and chondrogenesis. They are considered key regulators of muscle homeostasis and integrity. They play supportive roles in muscle development and repair by orchestrating the regulatory interplay between muscle stem cells (MuSCs) and immune cells. Interestingly, FAPs also contribute to intramuscular fat infiltration, fibrosis and other pathologies when the functional integrity of the network is compromised. In this review, we summarize recent insights into the roles of FAPs in maintenance of skeletal muscle homeostasis, and discuss the underlying mechanisms regulating FAPs behavior and fate, highlighting their roles in participating in efficient muscle repair and fat infiltrated muscle degeneration as well as during muscle atrophy. We suggest that controlling and predicting FAPs differentiation may become a promising strategy to improve muscle function and prevent irreparable muscle damage.

Differences in lumbar paraspinal muscle morphology in patients with sagittal malalignment undergoing posterior lumbar fusion surgery.

To investigate whether (1) there is a difference between patients with normal or sagittal spinal and spinopelvic malalignment in terms of their paraspinal muscle composition and (2) if sagittal malalignment can be predicted using muscle parameters. A retrospective review of patients undergoing posterior lumbar fusion surgery was conducted. A MRI-based muscle measurement technique was used to assess the cross-sectional area, the functional cross-sectional area, the intramuscular fat and fat infiltration (FI) for the psoas and the posterior paraspinal muscles (PPM). Intervertebral disc degeneration was graded for levels L1 to S1. Sagittal vertical axis (SVA; ≥ 50mm defined as spinal malalignment), pelvic incidence (PI) and lumbar lordosis (LL) were measured, and PI-LL mismatch (PI-LL; ≥ 10° defined as spinopelvic malalignment) was calculated. A receiver operating characteristic (ROC) analysis was conducted to determine the specificity and sensitivity of the FIPPM for predicting sagittal malalignment. One hundred and fifty patients were analysed. The PI-LL and SVA malalignment groups were found to have a significantly higher FIPPM (PI-LL:47.0 vs. 42.1%; p = 0.019; SVA: 47.7 vs. 41.8%; p = 0.040). ROC analysis predicted sagittal spinal malalignment using FIPPM (cut-off value 42.69%) with a sensitivity of 73.4% and a specificity of 54.1% with an area under the curve of 0.662. Significant differences in the muscle composition between normal and malalignment groups with respect to FIPPM in both sagittal spinal and spinopelvic alignment were found. This work underlines the imminent impact of the paraspinal musculature on the sagittal alignment.

The correlation between types of posterior upper rotator cuff tears and intramuscular fat infiltration based on magnetic resonance imaging: A retrospective observational study.

Objective: This study investigated the correlation between types of posterior upper rotator cuff tears (RCTs) and intramuscular fat infiltration (FI) in magnetic resonance imaging (MRI). Methods: The shoulder joints of 50 adults with a full-thickness posterior upper RCT diagnosed by MRI, from January 2019 to December 2021, were retrospectively analyzed. The patients were divided into three groups according to tear type: 1) an L-shaped tear group; 2) a crescent/U-shaped tear group; 3) a complete tear group. The correlation among age, gender, tear range, trauma history, and the duration of clinical symptoms was analyzed. The MRI images were used by two musculoskeletal imaging physicians to evaluate the type and range of tears, the Goutallier grade of the supraspinatus and infraspinatus, and the correlations and reliability were analyzed. Results: Differences in the tear range (p < 0.001) and the Goutallier grade of the infraspinatus muscle (p = 0.036) among the L-shaped, crescent/U-shaped, and complete tear groups were statistically significant; however, differences in the Goutallier grade of the supraspinatus muscle was not statistically significant (p = 0.356). In the crescent/U-shaped tear group, age was significantly correlated with the Goutallier grade of the supraspinatus muscle (RS = 0.720, p = 0.029) and the infraspinatus muscle (RS = 0.713, p = 0.032). In the complete tear group, tear range was significantly correlated with the Goutallier grade of the supraspinatus muscle (RS = 0.801, p = 0.001) and the infraspinatus muscle (RS = 0.802, p = 0.001). The Goutallier grades of the supraspinatus muscle (kappa, 0.489) and the infraspinatus muscle (kappa, 0.424) presented with interobserver consistency. Conclusion: The type of posterior upper RCT correlates with the degree of FI. There is a positive correlation between the FI of crescent/U-shaped full-thickness RCTs and age. Additionally, the range of complete tears in the posterior upper RC has a positive correlation with FI.

HR-pQCT for the Evaluation of Muscle Quality and Intramuscular Fat Infiltration in Ageing Skeletal Muscle.

Myosteatosis is the infiltration of fat in skeletal muscle during the onset of sarcopenia. The quantification of intramuscular adipose tissue (IMAT) can be a feasible imaging modality for the clinical assessment of myosteatosis, important for the early identification of sarcopenia patients and timely intervention decisions. There is currently no standardized method or consensus for such an application. The aim of this study was to develop a method for the detection and analysis of IMAT in clinical HR-pQCT images of the distal tibia to evaluate skeletal muscle during the ageing process, validated with animal and clinical experimentation. A pre-clinical model of ovariectomized (OVX) rats with known intramuscular fat infiltration was used, where gastrocnemii were scanned by micro-computed tomography (micro-CT) at an 8.4 μm isotropic voxel size, and the images were analyzed using our modified IMAT analysis protocol. IMAT, muscle density (MD), and muscle volume (MV) were compared with SHAM controls validated with Oil-red-O (ORO) staining. Furthermore, the segmentation and IMAT evaluation method was applied to 30 human subjects at ages from 18 to 81 (mean = 47.3 ± 19.2). Muscle-related parameters were analyzed with functional outcomes. In the animal model, the micro-CT adipose tissue-related parameter of IMAT% segmented at −600 HU to 100 HU was shown to strongly associate with the ORO-positively stained area (r = 0.898, p = 0.002). For the human subjects, at an adjusted threshold of −600 to −20 HU, moderate positive correlations were found between MV and MD (r = 0.642, p < 0.001), and between MV and IMAT volume (r = 0.618, p < 0.01). Moderate negative correlations were detected between MD and IMAT% (r = −0.640, p < 0.001). Strong and moderate associations were found between age and MD (r = −0.763, p < 0.01), and age and IMAT (r = 0.559, p < 0.01). There was also a strong correlation between IMAT% and chair rise time (r = 0.671, p < 0.01). The proposed HR-pQCT evaluation protocol for intramuscular adipose-tissue produced MD and IMAT results that were associated with age and physical performance measures, and were of good predictive value for the progression of myosteatosis or sarcopenia. The protocol was also validated on animal skeletal muscle samples that showed a good representation of histological lipid content with positive correlations, further supporting the clinical application for the rapid evaluation of muscle quality and objective quantification of skeletal muscle at the peripheral for sarcopenia assessment.

Modulating Intramuscular Fat Infiltration by Small Molecules

Skeletal muscle has a remarkable ability to regenerate upon injury. However, during aging and in diseases such as muscular dystrophies and diabetes, muscle tissue is replaced by fibrotic scar and fat tissue in a process called fatty fibrosis. Currently, there are no known treatments to prevent fatty fibrosis or the decline in muscle mass and function. Our lab and others have shown that ectopic activation of the Hedgehog (Hh) pathway accelerated muscle regeneration after an acute injury and preserved muscle function with age and disease. In addition, our lab demonstrated that Hh is a potent anti‐adipogenic signal and that activating Hh prevents intramuscular fat formation. However, the cellular and molecular mechanisms by which Hh balances fatty fibrosis and muscle regeneration are unclear. In this project, we use small molecules as a novel approach for modulating intramuscular fat infiltration via Hh signaling: Smoothened agonist (SAG) to activate and Vismodegib to inactivate Hh. We found that SAG (HHON) successfully activates the Hh pathway while Vismodegib (HHOFF) inactivates the pathway, as detected by RT‐qPCR analysis for the expression of key Hh target gene Gli1. Excitingly, by modulating the Hh pathway, SAG and Vismodegib decreased and increased fat infiltration, respectively. We are currently evaluating the effects of SAG and Vismodegib administration on muscle regeneration and fibrosis. Future experiments will focus on using small molecules to modulate the Hh pathway at different time points after injury, as well as looking to therapeutic applications in treating fatty fibrosis in conditions such as Duchenne muscular dystrophy. Together, the results of this project will help uncover the regulatory role and dynamics of Hh signaling in intramuscular fat infiltration, ultimately providing a starting point for developing powerful new therapeutics to treat fatty fibrosis.

The Mitochondria-Targeting Agent MitoQ Improves Muscle Atrophy, Weakness and Oxidative Metabolism in C26 Tumor-Bearing Mice.

Cancer cachexia is a debilitating syndrome characterized by skeletal muscle wasting, weakness and fatigue. Several pathogenetic mechanisms can contribute to these muscle derangements. Mitochondrial alterations, altered metabolism and increased oxidative stress are known to promote muscle weakness and muscle catabolism. To the extent of improving cachexia, several drugs have been tested to stimulate mitochondrial function and normalize the redox balance. The aim of this study was to test the potential beneficial anti-cachectic effects of Mitoquinone Q (MitoQ), one of the most widely-used mitochondria-targeting antioxidant. Here we show that MitoQ administration (25 mg/kg in drinking water, daily) in vivo was able to improve body weight loss in Colon-26 (C26) bearers, without affecting tumor size. Consistently, the C26 hosts displayed ameliorated skeletal muscle and strength upon treatment with MitoQ. In line with improved skeletal muscle mass, the treatment with MitoQ was able to partially correct the expression of the E3 ubiquitin ligases Atrogin-1 and Murf1. Contrarily, the anabolic signaling was not improved by the treatment, as showed by unchanged AKT, mTOR and 4EBP1 phosphorylation. Assessment of gene expression showed altered levels of markers of mitochondrial biogenesis and homeostasis in the tumor hosts, although only Mitofusin-2 levels were significantly affected by the treatment. Interestingly, the levels of Pdk4 and CytB, genes involved in the regulation of mitochondrial function and metabolism, were also partially increased by MitoQ, in line with the modulation of hexokinase (HK), pyruvate dehydrogenase (PDH) and succinate dehydrogenase (SDH) enzymatic activities. The improvement of the oxidative metabolism was associated with reduced myosteatosis (i.e., intramuscular fat infiltration) in the C26 bearers receiving MitoQ, despite unchanged muscle LDL receptor expression, therefore suggesting that MitoQ could boost β-oxidation in the muscle tissue and promote a glycolytic-to-oxidative shift in muscle metabolism and fiber composition. Overall, our data identify MitoQ as an effective treatment to improve skeletal muscle mass and function in tumor hosts and further support studies aimed at testing the anti-cachectic properties of mitochondria-targeting antioxidants also in combination with routinely administered chemotherapy agents.

Phenotypic heterogeneity in patients with NEFL-related Charcot-Marie-Tooth disease.

Charcot–Marie–Tooth disease (CMT) is the most common hereditary peripheral neuropathy. Mutations in the neurofilament light polypeptide (NEFL) gene produce diverse clinical phenotypes, including demyelinating (CMT1F), axonal (CMT2E), and intermediate (CMTDIG) neuropathies. From 2005 to 2020, 1,143 Korean CMT families underwent gene sequencing, and we investigated the clinical, genetic, and neuroimaging spectra of NEFL‐related CMT patients. Ten NEFL mutations in 17 families (1.49%) were identified, of which three (p.L312P, p.Y443N, and p.K467N) were novel. Eight de novo cases were identified at a rate of 0.47 based on a cosegregation analysis. The age of onset was ≤3 years in five cases (13.5%). The patients revealed additional features including delayed walking, ataxia, dysphagia, dysarthria, dementia, ptosis, waddling gait, tremor, hearing loss, and abnormal visual evoked potential. Signs of ataxia were found in 26 patients (70.3%). In leg MRI analyses, various degrees of intramuscular fat infiltration were found. All compartments were evenly affected in CMT1F patients. The anterior and anterolateral compartments were affected in CMT2E, and the posterior compartment was affected in CMTDIG. Thus, NEFL‐related CMT patients showed phenotypic heterogeneities. This study's clinical, genetic, and neuroimaging results could be helpful in the evaluation of novel NEFL variants and differential diagnosis against other CMT subtypes.

An Exploratory Analysis of the Role of Adipose Characteristics in Fulltime Wheelchair Users' Pressure Injury History.

Aim: The goals of this study were 1) to identify the relationship between adipose (subcutaneous and intramuscular) characteristics and pressure injury (PrI) history in wheelchair users and 2) to identify subject characteristics, including biomechanical risk, that are related to adipose characteristics. Materials and Methods: The buttocks of 43 full-time wheelchair users with and without a history of pelvic PrIs were scanned in a seated posture in a FONAR UPRIGHT® MRI. Intramuscular adipose (the relative difference in intensity between adipose and gluteus maximus) and the subcutaneous adipose characteristics (the relative difference in intensity between subcutaneous adipose under and surrounding the ischium) were compared to PrI history and subject characteristics. Results: Participants with a history of PrIs had different subcutaneous fat (subQF) characteristics than participants without a history of PrIs. Specifically, they had significantly darker adipose under the ischium than surrounding the ischium (subQF effect size = 0.21) than participants without a history of PrIs (subQF effect size = 0.58). On the other hand, only when individuals with complete fat infiltration (n = 7) were excluded did individuals with PrI history have more fat infiltration than those without a PrI history. The presence of spasms (μ intramuscular adipose, 95% CI with spasms 0.642 [0.430, 0.855], without spasms 0.168 [−0.116, 0.452], p = 0.01) and fewer years using a wheelchair were associated with leaner muscle (Pearson Corr = −0.442, p = 0.003). Conclusion: The results of the study suggest the hypothesis that changes in adipose tissue under the ischial tuberosity (presenting as darker SubQF) are associated with increased biomechanical risk for pressure injury. Further investigation of this hypothesis, and the role of intramuscular fat infiltration in PrI development, may help our understanding of PrI etiology. It may also lead to clinically useful diagnostic techniques that can identify changes in adipose and biomechanical risk to inform early preventative interventions.

Differences in Abdominal Body Composition According to Glycemic Status: An Inverse Probability Treatment Weighting Analysis.

BackgroundSeveral studies have reported that abdominal fat and muscle changes occur in diabetic patients. However, there are few studies about such changes among prediabetic patients. In this study, we evaluated the differences in abdominal fat and muscles based on abdominopelvic computed tomography in prediabetic and diabetic subjects compared to normal subjects.MethodsWe performed a cross-sectional study using health examination data from March 2014 to June 2019 at Ulsan University Hospital and classified subjects into normal, prediabetic, and diabetic groups. We analyzed the body mass index corrected area of intra-abdominal components among the three groups using inverse probability treatment weighting (IPTW) analysis.ResultsOverall, 8,030 subjects were enrolled; 5,137 (64.0%), 2,364 (29.4%), and 529 (6.6%) subjects were included in the normal, prediabetic, and diabetic groups, respectively. After IPTW adjustment of baseline characteristics, there were significant differences in log visceral adipose tissue index (VATI; 1.22±0.64 cm2/[kg/m2] vs. 1.30±0.63 cm2/[kg/m2] vs. 1.47±0.64 cm2/[kg/m2], P<0.001) and low-attenuation muscle index (LAMI; 1.02±0.36 cm2/[kg/m2] vs. 1.03±0.36 cm2/[kg/m2] vs. 1.09±0.36 cm2/[kg/m2], P<0.001) among the normal, prediabetic, and diabetic groups. Prediabetic subjects had higher log VATI (estimated coefficient=0.082, P<0.001), and diabetic subjects had higher log VATI (estimated coefficient=0.248, P<0.001) and LAMI (estimated coefficient=0.078, P<0.001) compared to normal subjects.ConclusionConsidering that VATI and LAMI represented visceral fat and lipid-rich skeletal muscle volumes, respectively, visceral obesity was identified in both prediabetic and diabetic subjects compared to normal subjects in this study. However, intra-muscular fat infiltration was observed in diabetic subjects only.