Secondary failure of platelet recovery (SFPR), a late decrease in the platelet count after primary platelet recovery that is not due to relapse or graft rejection, occasionally occurs after allogeneic hematopoietic stem cell transplantation (HSCT). The risk factors and impact of SFPR on transplantation outcomes are not well known in the clinical setting. Therefore, we retrospectively evaluated 184 adult patients who underwent their first allogeneic HSCT and achieved primary platelet recovery. The cumulative incidence of SFPR, defined as a decrease in the platelet count to below 20,000/µL for more than 7 days, was 12.2% at 3 years, with a median onset of 81 days (range, 39 to 729) after HSCT. Among patients who developed SFPR (n = 23), 19 (82.6%) showed recovery to a sustained platelet count of more than 20,000/µL without transfusion support, and the median duration of SFPR was 23 days (range, 7 to 1048 days). A multivariate analysis showed that in vivo T cell depletion (hazard ratio [HR], 6.92; 95% confidence interval [CI], 2.31 to 20.7; P < .001), grades II to IV acute graft-versus-host disease (HR, 3.99; 95% CI, 1.52 to 10.5; P = .005), and the use of ganciclovir or valganciclovir (HR, 2.86; 95% CI, 1.05 to 7.77; P = .039) were associated with an increased risk for SFPR. The occurrence of SFPR as a time-dependent covariate was significantly associated with inferior overall survival (HR, 2.29; 95% CI, 1.18 to 4.46; P = .015) in a multivariate analysis. These findings may help to improve the management and treatment strategy for SFPR.

Skeletal muscle is the main tissue of lipid metabolism and accordingly is critical for homeostasis and energy production; however, the determinants of lipid accumulation in skeletal muscle are unknown. Here, we examined whether the soleus muscle (predominantly slow-twitch fibers) has a higher lipid accumulation capacity than that of the extensor digitorum longus (EDL, predominantly fast-twitch fibers) muscle in mice. Soleus and EDL muscles were harvested from male C57BL/6J mice. The mRNA levels of genes involved in fatty acid import and triglyceride synthesis and accumulation were examined in soleus and EDL muscles. The intramyocellular lipid (IMCL) droplets of muscle cross sections and isolated single fibers were visualized by staining with BODIPY493/503, and fiber types were determined by immunofluorescent detection of myosin heavy chain (MyHC) isoforms. We detected higher mRNA expression of genes related to lipid accumulation in the soleus than the EDL. We also observed a marked increase of IMCL in single fibers from the soleus, but not the EDL, after treatment with a high-fat diet plus denervation. Interestingly, greater accumulation of IMCL droplets was observed in type 2A and 2X fibers (MyHC2A- and MyHC2X-positive fibers) than type 1 fibers (MyHC1-positive fibers) in soleus muscles. These results suggest that the soleus contains more IMCL owing to the higher population of type 2A fibers, and the difference in lipid accumulation between the soleus and EDL could depend on fiber type composition.

Dietary fat plays a major role in obesity, lipid metabolism, and cardiovascular diseases. To determine whether the intake of different types of dietary fats affect the muscle fiber types that govern the metabolic and contractile properties of the skeletal muscle, we fed male Wistar rats with a 15% fat diet derived from different fat sources. Diets composed of soybean oil (n-6 polyunsaturated fatty acids (PUFA)-rich), fish oil (n-3 PUFA-rich), or lard (low in PUFAs) were administered to the rats for 4 weeks. Myosin heavy chain (MyHC) isoforms were used as biomarkers to delineate the skeletal muscle fiber types. Compared with soybean oil intake, fish oil intake showed significantly lower levels of the fast-type MyHC2B and higher levels of the intermediate-type MyHC2X composition in the extensor digitorum longus (EDL) muscle, which is a fast-type dominant muscle. Concomitantly, MyHC2X mRNA levels in fish oil-fed rats were significantly higher than those observed in the soybean oil-fed rats. The MyHC isoform composition in the lard-fed rats was an intermediate between that of the fish oil and soybean oil-fed rats. Mitochondrial uncoupling protein 3, pyruvate dehydrogenase kinase 4, and porin mRNA showed significantly upregulated levels in the EDL of fish oil-fed rats compared to those observed in soybean oil-fed and lard-fed rats, implying an activation of oxidative metabolism. In contrast, no changes in the composition of MyHC isoforms was observed in the soleus muscle, which is a slow-type dominant muscle. Fatty acid composition in the serum and the muscle was significantly influenced by the type of dietary fat consumed. In conclusion, dietary fat affects the expression of genes related to the contractile and metabolic properties in the fast-type dominant skeletal muscle, where the activation of oxidative metabolism is more pronounced after fish oil intake than that after soybean oil intake.

In this study, we present a quadruple immunostaining method for rapid muscle fiber typing of mice and rats using antibodies specific to the adult myosin heavy chain (MyHC) isoforms MyHC1, 2A, 2X, and 2B, which are common marker proteins of distinct muscle fiber types. We developed rat monoclonal antibodies specific to each MyHC isoform and conjugated these four antibodies to fluorophores with distinct excitation and emission wavelengths. By mixing the four types of conjugated antibodies, MyHC1, 2A, 2X, and 2B could be distinguished within a single specimen allowing for facile delineation of skeletal muscle fiber types. Furthermore, we could observe hybrid fibers expressing MyHC2X and MyHC2B together in single longitudinal muscle sections from mice and rats, that was not attained in previous techniques. This staining method is expected to be applied to study muscle fiber type transition in response to environmental factors, and to ultimately develop techniques to regulate animal muscle fiber types.

Recently, we found that resident myogenic stem satellite cells upregulate a multi-functional secreted protein, semaphorin 3A (Sema3A), exclusively at the early-differentiation phase in response to muscle injury; however, its physiological significance is still unknown. Here we show that Sema3A impacts slow-twitch fiber generation through a signaling pathway, cell-membrane receptor (neuropilin2-plexinA3) → myogenin-myocyte enhancer factor 2D → slow myosin heavy chain. This novel axis was found by small interfering RNA-transfection experiments in myoblast cultures, which also revealed an additional element that Sema3A-neuropilin1/plexinA1, A2 may enhance slow-fiber formation by activating signals that inhibit fast-myosin expression. Importantly, satellite cell-specific Sema3A conditional-knockout adult mice (Pax7CreER -Sema3A ° activated by tamoxifen-i.p. injection) provided direct in vivo evidence for the Sema3A-driven program, by showing that slow-fiber generation and muscle endurance were diminished after repair from cardiotoxin-injury of gastrocnemius muscle. Overall, the findings highlight an active role for satellite cell-secreted Sema3A ligand as a key "commitment factor" for the slow-fiber population during muscle regeneration. Results extend our understanding of the myogenic stem-cell strategy that regulates fiber-type differentiation and is responsible for skeletal muscle contractility, energy metabolism, fatigue resistance, and its susceptibility to aging and disease. Stem Cells 2017;35:1815-1834.

A recent study demonstrated a positive effect of apple polyphenol (APP) intake on muscle endurance of young-adult animals. While an enhancement of lipid metabolism may be responsible, in part, for the improvement, the contributing mechanisms still need clarification. Here we show that an 8-week intake of 5% (w/w) APP in the diet, up-regulates two features related to fiber type: the ratio of myosin heavy chain (MyHC) type IIx/IIb and myoglobin protein expression in plantaris muscle of 9-week-old male Fischer F344 rats compared to pair-fed controls (P < 0.05). Results were demonstrated by our SDS-PAGE system specialized for MyHC isoform separation and western blotting of whole muscles. Animal-growth profiles (food intake, body-weight gain, and internal-organ weights) did not differ between the control and 5% APP-fed animals (n = 9/group). Findings may account for the increase in fatigue resistance of lower hind limb muscles, as evidenced by a slower decline in the maximum isometric planter-flexion torque generated by a 100-s train of electrical stimulation of the tibial nerve. Additionally, the fatigue resistance was lower after 8 weeks of a 0.5% APP diet than after 5% APP, supporting an APP-dose dependency of the shift in fiber-type composition. Therefore, the present study highlights a promising contribution of dietary APP intake to increasing endurance based on fiber-type composition in rat muscle. Results may help in developing a novel strategy for application in animal sciences, and human sports and age-related health sciences.

In August 2015, the CALorimetric Electron Telescope (CALET), designed for long exposure observations of high energy cosmic rays, docked with the International Space Station (ISS) and shortly thereafter began to collect data. CALET will measure the cosmic ray electron spectrum over the energy range of 1 GeV to 20 TeV with a very high resolution of 2% above 100 GeV, based on a dedicated instrument incorporating an exceptionally thick 30 radiation-length calorimeter with both total absorption and imaging (TASC and IMC) units. Each TASC readout channel must be carefully calibrated over the extremely wide dynamic range of CALET that spans six orders of magnitude in order to obtain a degree of calibration accuracy matching the resolution of energy measurements. These calibrations consist of calculating the conversion factors between ADC units and energy deposits, ensuring linearity over each gain range, and providing a seamless transition between neighboring gain ranges. This paper describes these calibration methods in detail, along with the resulting data and associated accuracies. The results presented in this paper show that a sufficient accuracy was achieved for the calibrations of each channel in order to obtain a suitable resolution over the entire dynamic range of the electron spectrum measurement

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