Fatty Liver Index and Skeletal Muscle Density

Accumulation of fat in the liver and skeletal muscle is associated with obesity and poor health outcomes. Liver steatosis is a characteristic of non-alcoholic fatty liver disease (NAFLD) and myosteatosis, of poor muscle quality in sarcopenia. In this study of 403 men (33–96 years), we investigated associations between the fatty liver index (FLI) and muscle density, as markers of fat accumulation in these organs. We also investigated associations between the FLI and parameters of sarcopenia, including DXA-derived appendicular lean mass (ALM) and handgrip strength by dynamometry. Muscle density was measured using pQCT at the radius and tibia. FLI was calculated from BMI, waist circumference, and levels of triglycerides and gamma-glutamyltransferase. There was a pattern of decreasing muscle density across increasing quartiles of FLI. After adjusting for age and lifestyle, mean radial muscle density in Q4 was 2.1% lower than Q1 (p < 0.001) and mean tibial muscle density was 1.8% lower in Q3 and 3.0% lower in Q4, compared to Q1 (p = 0.022 and < 0.001, respectively). After adjusting for age and sedentary lifestyle, participants in the highest FLI quartile were sixfold more likely to have sarcopenia. In conclusion, our results suggest that fat accumulation in the liver co-exists with fat infiltration into skeletal muscle.

MiR-320-3p Regulates the Proliferation and Differentiation of Myogenic Progenitor Cells by Modulating Actin Remodeling

Skeletal myogenesis is essential for the maintenance of muscle quality and quantity, and impaired myogenesis is intimately associated with muscle wasting diseases. Although microRNA (miRNA) plays a crucial role in myogenesis and relates to muscle wasting in obesity, the molecular targets and roles of miRNAs modulated by saturated fatty acids (SFA) are largely unknown. In the present study, we investigated the role of miR-320-3p on the differentiation of myogenic progenitor cells. Palmitic acid (PA), the most abundant dietary SFA, suppressed myogenic factors expression and impaired differentiation in C2C12 myoblasts, and these effects were accompanied by CFL2 downregulation and miR-320-3p upregulation. In particular, miR-320-3p appeared to target CFL2 mRNA directly and suppress the expression of CFL2, an essential factor for filamentous actin (F-actin) depolymerization. Transfection of myoblasts with miR-320-3p mimic increased F-actin formation and nuclear translocation of Yes-associated protein 1 (YAP1), a key component of mechanotransduction. Furthermore, miR-320-3p mimic increased myoblast proliferation and markedly impeded the expression of MyoD and MyoG, consequently inhibiting myoblast differentiation. In conclusion, our current study highlights the role of miR-320-3p on CFL2 expression, YAP1 activation, and myoblast differentiation and suggests that PA-inducible miR-320-3p is a significant mediator of muscle wasting in obesity.

The impact of skeletal muscle disuse on distinct echo intensity bands: A retrospective analysis

Echo intensity (EI) is a novel tool for assessing muscle quality. EI has traditionally been reported as the mean of the pixel histogram, with 0 and 255 arbitrary units (A.U.) representing excellent and poor muscle quality, respectively. Recent work conducted in youth and younger and older adults suggested that analyzing specific EI bands, rather than the mean, may provide unique insights into the effectiveness of exercise and rehabilitation interventions. As our previous work showed deterioration of muscle quality after knee joint immobilization, we sought to investigate whether the increase in EI following disuse was limited to specific EI bands. Thirteen females (age = 21 yrs) underwent two weeks of left knee immobilization and ambulated via crutches. B-mode ultrasonography was utilized to obtain images of the immobilized vastus lateralis. The percentage of the total number of pixels within bands of 0–50, 51–100, 101–150, 151–200, and 201–255 A.U. was examined before and after immobilization. We also sought to determine if further subdividing the histogram into 25 A.U. bands (i.e., 0–25, 26–50, etc.) would be a more sensitive methodological approach. Immobilization resulted in a decrease in the percentage of pixels within the 0–50 A.U. band (-3.11 ± 3.98%), but an increase in the 101–150 A.U. (2.94 ± 2.64%) and 151–200 A.U. (0.93 ± 1.42%) bands. Analyses of variance on the change scores indicated that these differences were large and significant (%EI0-50 vs. %EI101-150: p < .001, d = 1.243); %EI0-50 vs. %EI151-200: p = .043, d = 0.831). The effect size for the %EI51-100 versus %EI101-150 comparison was medium/large (d = 0.762), but not statistically significant (p = .085). Further analysis of the 25 A.U. bands indicated that the percentage of pixels within the 25–50 A.U. band decreased (-2.97 ± 3.64%), whereas the 101–125 (1.62 ± 1.47%) and 126–150 A.U. (1.18 ± 1.07%) bands increased. Comparison of the 50 A.U. and 25 A.U. band methods found that 25 A.U. bands offer little additional insight. Though studies are needed to ascertain the factors that may influence specific bands, changes in EI during muscle disuse are not homogeneous across the pixel histogram. We encourage investigators to think critically about the robustness of data obtained from EI histograms, rather than simply reporting the EImean value, in muscle quality research.

Nitrite Stress Induces Oxidative Stress and Leads to Muscle Quality Decreased in Wuchang Bream (Megalobrama amblycephala Yih) Juveniles

To determine the effects of nitrite exposure on muscle quality and physiological functions in Wuchang bream (Megalobrama amblycephala), we exposed M. amblycephala juveniles to acute nitrite (0, 1, 5, 10, 20 mg/L), and the muscle and blood samples were measured at 12, 24, 48, and 96 h. The results showed that when exposed to nitrite for 12 h, the concentrations of blood glucose, cortisol, aspartate aminotransferase (AST), and alanine aminotransferase (ALT) in the 20 mg/L experimental group had the maximum value. The activity of lactate dehydrogenase (LDH) increased significantly in a dose-dependently manner and peaked at 96 h in the 20 mg/L group. During 96 h of exposure to nitrite, the total antioxidant capacity (T-AOC) and catalase (CAT) activity in the liver of the 20 mg/L experimental group were significantly higher than those of the control group, while the concentration of muscle glycogen showed a downtrend. At 12 h and 96 h, the hardness of the four experimental groups were significantly higher than that of the control group. Our research shows that acute sodium nitrite exposure will not only cause oxidative stress and decreased muscle quality in M. amblycephala juveniles but also will be accompanied by changes in serum biochemical index, liver antioxidant capacity, muscle physiological characteristics, and muscle physical characteristics. Preliminary speculation may be that acute nitrite exposure may cause M. amblycephala juveniles to choose to reduce muscle quality and activate antioxidant systems.

Preventive effect of rehabilitation training therapy on muscle quality in patients with stroke: A retrospective study

A retrospective analysis was conducted in 45 patients with stroke. All patients received three weeks of rehabilitation training. Body composition was examined using Bio-impedance analysis methods before and after training. Barthel index was used to evaluate activities of daily living before and after the intervention. After rehabilitation training, total body water, muscle mass, protein content, inorganic salt content, and skeletal muscle content were increased while body fat content and body fat percentage were significantly decreased. Barthel Index scores showed that the ability of daily living was improved after rehabilitation. In conclusion, rehabilitation training therapy may have protective effects on sarcopenia in patients with stroke. Keywords: Stroke, sarcopenia, rehabilitation training

Quality Matters as Much as Quantity of Skeletal Muscle: Clinical Implications of Myosteatosis in Cardiometabolic Health

Although age-related changes in skeletal muscles are closely associated with decreases in muscle strength and functional decline, their associations with cardiometabolic diseases in the literature are inconsistent. Such inconsistency could be explained by the fact that muscle quality—which is closely associated with fatty infiltration of the muscle (i.e., myosteatosis)—is as important as muscle quantity in cardiometabolic health. However, muscle quality has been less explored compared with muscle mass. Moreover, the standard definition of myosteatosis and its assessment methods have not been established yet. Recently, some techniques using single axial computed tomography (CT) images have been introduced and utilized in many studies, as the mass and quality of abdominal muscles could be measured opportunistically on abdominal CT scans obtained during routine clinical care. Yet, the mechanisms by which myosteatosis affect metabolic and cardiovascular health remain largely unknown. In this review, we explore the recent advances in the assessment of myosteatosis and its changes associated with aging. We also review the recent literature on the clinical implication of myosteatosis by focusing on metabolic and cardiovascular diseases. Finally, we discuss the challenges and unanswered questions that need addressing to set myosteatosis as a therapeutic target for the prevention or treatment of cardiometabolic diseases.

Comparison of Muscle Density in Middle-Aged and Older Chinese Adults Between a High-Altitude Area (Kunming) and a Low-Altitude Area (Beijing)

Background and PurposeA high-altitude environment was known to have a negative effect on bone and lead to a higher incidence of hip fracture. However, the dependence of muscle composition on altitude is unclear. Thus, we aimed to compare muscle density and area in plateau and low altitude area and to determine the effect of the altitude on these outcomes.MethodsCommunity dwelling adults over 60 years old living in Beijing (elevation 50 m; 300 subjects,107 men and 193 women) or Kunming (elevation 2000 m; 218 subjects,83 men and 135 women) for more than 10 years were enrolled. Quantitative CT was performed in all subjects and cross-sectional area and attenuation measured in Hounsfield units (HU) were determined for the trunk, gluteus, and mid-thigh muscles.ResultsCompared to Beijing, Kunming adults were slimmer (Beijing men vs Kunming men: 25.08 ± 2.62 vs 23.94 ± 3.10kg/m2, P=0.013; Beijing women vs Kunming women: 25.31 ± 3.1 vs 23.98 ± 3.54 kg/m2, P= 0.001) and had higher muscle density in the L2-trunk and gluteus maximus muscles after adjustment for age and BMI (L2-trunk muscles: Beijing men 29.99 ± 4.17 HU vs Kunming men 37.35 ± 4.25 HU, P&lt; 0.0001; Beijing women 27.37 ± 3.76 HU vs Kunming women 31.51 ± 5.12 HU, P&lt; 0.0001; Gluteus maximus muscle: Beijing men 35.11 ± 6.54 HU vs Kunming men 39.36 ± 4.39 HU, P= 0.0009; Beijing women 31.47 ± 6.26 HU vs Kunming women 34.20 ± 5.87 HU P=0.0375). Age was similar in both cohorts and no differences were observed in the gluteus medius and minimus muscle or the mid-thigh muscle, either in the area or density.ConclusionsCompared with Beijing, the adults in Kunming had higher muscle density of the gluteus maximus and L2 trunk muscles, showing that living at a higher altitude might be beneficial to muscle quality.

Regulation of Myostatin on the Growth and Development of Skeletal Muscle

Myostatin (MSTN), a member of the transforming growth factor-β superfamily, can negatively regulate the growth and development of skeletal muscle by autocrine or paracrine signaling. Mutation of the myostatin gene under artificial or natural conditions can lead to a significant increase in muscle quality and produce a double-muscle phenotype. Here, we review the similarities and differences between myostatin and other members of the transforming growth factor-β superfamily and the mechanisms of myostatin self-regulation. In addition, we focus extensively on the regulation of myostatin functions involved in myogenic differentiation, myofiber type conversion, and skeletal muscle protein synthesis and degradation. Also, we summarize the induction of reactive oxygen species generation and oxidative stress by myostatin in skeletal muscle. This review of recent insights into the function of myostatin will provide reference information for future studies of myostatin-regulated skeletal muscle formation and may have relevance to agricultural fields of study.