Dietary oleic acid intake increases the proportion of type 1 and 2X muscle fibers in mice.

Skeletal muscle is one of the largest metabolic tissues in mammals and is composed of four different types of muscle fibers (types 1, 2A, 2X, and 2B); however, type 2B is absent in humans. Given that slow-twitch fibers are superior to fast-twitch fibers in terms of oxidative metabolism and are rich in mitochondria, shift of muscle fiber types in direction towards slower fiber types improves metabolic disorders and endurance capacity. We previously had reported that oleic acid supplementation increases type 1 fiber formation in C2C12 myotubes; however, its function still remains unclear. This study aimed to determine the effect of oleic acid on the muscle fiber types and endurance capacity. An in vivo mouse model was used, and mice were fed a 10% oleic acid diet for 4 weeks. Two different skeletal muscles, slow soleus muscle with the predominance of slow-twitch fibers and fast extensor digitorum longus (EDL) muscle with the predominance of fast-twitch fibers, were used. We found that dietary oleic acid intake improved running endurance and altered fiber type composition of muscles, the proportion of type 1 and 2X fibers increased in the soleus muscle and type 2X increased in the EDL muscle. The fiber type shift in the EDL muscle was accompanied by an increased muscle TAG content. In addition, blood triacylglycerol (TAG) and non-esterified fatty acid levels decreased during exercise. These changes suggested that lipid utilization as an energy substrate was enhanced by oleic acid. Increased proliferator-activated receptor γ coactivator-1ß protein levels were observed in the EDL muscle, which potentially enhanced the fiber type transitions towards type 2X and muscle TAG content. In conclusion, dietary oleic acid intake improved running endurance with the changes of muscle fiber type shares in mice. This study elucidated a novel functionality of oleic acid in skeletal muscle fiber types. Further studies are required to elucidate the underlying mechanisms. Our findings have the potential to contribute to the field of health and sports science through nutritional approaches, such as the development of supplements aimed at improving muscle function.

Treatment strategy at the decision for allogeneic transplantation in patients with myelodysplastic syndrome in the era of azacitidine: A KSGCT prospective study.

The optimal bridge strategy at the decision for allogeneic hematopoietic stem cell transplantation (HSCT) in patients with myelodysplastic syndrome (MDS) is unclear. We performed a prospective observational study in which 110 patients with MDS who were decided to undergo HSCT were enrolled. Among these 110 patients, 77 patients were enrolled in this study within 1 month from the decision for HSCT. Among these 77 patients, 13 patients had a human leukocyte antigen (HLA)-matched sibling, 54 patients started an unrelated donor search, and the other 10 patients directly selected cord blood (CB) at the decision for HSCT, and 13 (100%), 38 (70.4%), and 9 (90%) patients actually underwent HSCT within 1 year, respectively. The overall survival (OS) at 1 year from their enrollment was 70.9%, and the selection of azacitidine use at the decision for HSCT was not associated with OS. Among 60 of the 77 patients who actually underwent HSCT within a year from their enrollment, a lower relapse rate after HSCT was observed in those who selected CB at the decision to undergo HSCT. However, this preferable effect of CB selection disappeared when patients who were enrolled in this study in > 1 month from the decision for HSCT were additionally included in the analyses. In conclusion, the selection of bridge strategy at the decision for HSCT did not affect outcomes in patients with MDS. The immediate performance of HSCT may be associated with better outcomes.

Netrin-4 synthesized in satellite cell-derived myoblasts stimulates autonomous fusion.

Satellite cells are indispensable for skeletal muscle regeneration and hypertrophy by forming nascent myofibers (myotubes). They synthesize multi-potent modulator netrins (secreted subtypes: netrin-1, -3, and -4), originally found as classical neural axon guidance molecules. While netrin-1 and -3 have key roles in myogenic differentiation, the physiological significance of netrin-4 is still unclear. This study examined whether netrin-4 regulates myofiber type commitment and myotube formation. Initially, the expression profiles indicated that satellite cells isolated from the extensor digitorum longus muscle (EDL muscle: fast-twitch myofiber-abundant) expressed slightly more netrin-4 than the soleus muscle (slow-type abundant) cells. As netrin-4 knockdown inhibited both slow- and fast-type myotube formation, netrin-4 may not directly regulate myofiber type commitment. However, netrin-4 knockdown in satellite cell-derived myoblasts reduced the myotube fusion index, while exogenous netrin-4 promoted myotube formation, even though netrin-4 expression level was maximum during the initiation stage of myogenic differentiation. Furthermore, netrin-4 knockdown also inhibited MyoD (a master transcriptional factor of myogenesis) and Myomixer (a myoblast fusogenic molecule) expression. These data suggest that satellite cells synthesize netrin-4 during myogenic differentiation initiation to promote their own fusion, stimulating the MyoD-Myomixer signaling axis.

Effects of the dipeptides comprising leucine and lysine on lifespan and age-related stress in Caenorhabditis elegans.

The aging process is affected by various stressors. An increase in oxidative stress is related to the impairment of physiological functions and enhancement of glycative stress. Food-derived bioactive peptides have various physiological functions, including antioxidant activities. Dipeptides comprising Leu and Lys (LK and KL, respectively) have been isolated from foods; however, their physiological properties remain unclear. In this study, we investigated the antioxidant/antiglycation activity of dipeptides and their antiaging effects using Caenorhabditis elegans (C. elegans). Both dipeptides showed antioxidant activities against several reactive oxygen species (ROS) in vitro. In particular, the scavenging activity of LK against superoxide radicals was higher than KL did. Moreover, dipeptides suppressed advanced glycation end products (AGEs) formation in the BSA-glucose model. In the lifespan assays using wild-type C. elegans, both LK and KL significantly prolonged the mean lifespan by 20.9% and 11.7%, respectively. In addition, LK decreased intracellular ROS and superoxide radical levels in C. elegans. Blue autofluorescence, an indicator of glycation in C. elegans with age, was also suppressed by LK. These results suggest that dipeptides, notably LK, show an antiaging effect by suppressing oxidative and glycative stress. Our findings suggest that such dipeptides can be used as a novel functional food ingredient. Food-derived dipeptide Leu-Lys (LK) and Lys-Leu (KL) exert antioxidant and antiglycation activity in vitro. Treatment with LK prolonged the mean lifespan and maximum lifespan of C. elegans more than that of KL. Intracellular ROS and blue autofluorescence levels (indicator of aging) were suppressed by LK.

Dietary olive oil intake induces female-specific hepatic lipid accumulation without metabolic impairment in mice.

Olive oil is one of the most widely researched Mediterranean diet components in both experimental models and clinical studies. However, the relationship between dietary olive oil intake and liver function in a healthy state of the body remains unclear. Because men are at a greater risk of developing hepatic diseases than women, and because hepatic metabolism is regulated by sex hormones, we hypothesized that olive oil-induced changes in hepatic metabolism would differ by sex. To test our hypothesis, 12-week-old C57BL/6JJcl male and female mice were fed an olive oil diet for 4 weeks. Blood was collected and serum biochemical components were analyzed. Hepatic lipid accumulation was determined via histological analysis using Sudan III staining. Finally, transcript expression levels of hepatic metabolism-related genes were analyzed using quantitative polymerase chain reaction. We observed significant increased hepatic lipid droplet accumulation in olive oil-fed female mice. Serum biochemical and liver messenger RNA expression analyses revealed that the hepatic lipid accumulation was nonpathological and did not involve inflammation. Moreover, the expression of genes related to triacylglycerol and fatty acid synthesis (Dgat1, Dgat2, Agpat3, and Fasn) was significantly upregulated in the liver of olive oil-fed female mice compared with control female mice. Our study demonstrates female-specific hepatic lipid accumulation without liver impairment in a dietary olive oil-fed mouse model. These findings provide a deeper mechanistic understanding of sex-dependent hepatic lipid metabolism of dietary oils.

Comparison of 2,5-dimethyl-4-hydroxy-3(2H)-furanone, a volatile odor compound generated by the Maillard reaction, in cooked meat of various animal species and parts.

2,5-Dimethyl-4-hydroxy-3(2H)-furanone (DMHF), a compound having a sweet caramel-like odor, is one of the major compounds generated by the Maillard reaction. DMHF could affect the palatability of cooked and processed foods such as meat, while its inhalation induces several physiological functions. However, basic findings of DMHF generation in meat remain unclear. In this study, we compared the amount of DMHF in cooked meat of various animal meat (Japanese black cattle beef, Australian beef, pork, and chicken) and parts (round, loin, thigh, and breast). Meat samples were heated at 230°C, and then the amount of DMHF was measured using the solvent extraction methods. Moreover, the substrates (total free amino acid and glucose) used for the Maillard reaction were also measured to elucidate the relation between DMHF generation and nutrients in meat. DMHF was detected in all cooked meat samples, suggesting that DMHF is generated in meat regardless of animal species and parts. A significant positive correlation was observed between the DMHF generation and glucose content in the round and thigh parts. Our results suggest that DMHF generation during meat cooking would be regulated by the glucose content.

Edible insect Locusta migratoria shows intestinal protein digestibility and improves plasma and hepatic lipid metabolism in male rats.

Although edible insect migratory locusts are considered sustainable food resources with proteins and n-3 lipids, their physiological effects on lipid metabolism are not clarified. Here, we clarified the amino acid (AA) value of the edible migratory locust powder (MLP), protein digestibility, and dietary effects of MLP on growth and lipid metabolism in rats. The AA score was 63, which was low score due to the limiting AA (Trp). MLP protein digestibility was resistant to gut pepsin but digestible to intestinal trypsin and chymotrypsin. Dietary MLP represented favorable growth and enhanced intestinal condition and lipid metabolism in rats, particularly, low-density lipoprotein metabolism and arteriosclerosis-related fatty acid profiles. Liver triglyceride accumulation and fatty acid desaturation indices were increased by activating lipids uptake into the liver, while lipogenic protein expression and enzyme activities and liver function indices were reduced by MLP. Conclusively, intestinal digestible MLP is a nutraceutical for the prevention of dyslipidemia.

Comparison of the impact of two post-remission therapy regimens on cardiac events in acute myeloid leukemia patients undergoing allogeneic hematopoietic stem cell transplantation.

High-dose cytarabine (HD-AraC) or anthracycline-containing chemotherapies are used as post-remission therapy for acute myeloid leukemia (AML) patients. However, it remains unclear which regimen would be better as post-remission therapy before allogeneic hematopoietic stem cell transplantation (allo-HSCT). Thus, we compared the incidence of cardiac events and event-free survival (EFS) after allo-HSCT at two Japanese hospitals between HD-AraC and anthracycline-containing post-remission therapy to clarify the safety of post-remission therapy. Of a total of 132 patients, 68 received HD-AraC (HD-AraC group) and 64 received anthracycline-containing chemotherapy (ANT group). HD-AraC was preferentially selected for core-binding factor AML patients (p = 0.008). The median cumulative anthracycline dose was 115.2 mg/m2 in the HD-AraC group and 318.7 mg/m2 in the ANT group (p < 0.0001). Cardiac events were observed in 18 (13.6%) patients during the follow-up period. The 3-year cumulative incidence of cardiac events was 9.1% in the HD-AraC group and 11.0% in the ANT group (p = 0.70). EFS at 3 years after allo-HSCT was 40.9% in the HD-AraC group and 39.6% in the ANT group (p = 0.51). In conclusion, incidence of cardiac events did not differ significantly between post-remission therapy regimens in AML patients who underwent allo-HSCT.

[Low psoas muscle index as independent poor prognostic factor for diffuse large B-cell lymphoma in elderly patients].

Sarcopenia is associated with poor clinical outcomes in elderly patients with diffuse large B-cell lymphoma (DLBCL). However, the clinical significance and optimal assessment of sarcopenia remain unclear. We retrospectively evaluated the prognostic value of low skeletal muscle mass based on the psoas muscle index (PMI) in patients with DLBCL aged 70 years and older treated with R-CHOP therapy. We included 71 patients, including 27 classified under low PMI. There were no differences in baseline characteristics (body mass index, lactate dehydrogenase, performance status [PS], stage, revised-IPI, relative dose intensity) and overall response rate between the low and high PMI groups. The low PMI group had a significantly worse overall survival (OS, p=0.015), but not progression-free survival (PFS, p=0.252), compared with the high PMI group. On multivariate analysis, low PMI and PS were independent negative prognostic factors for OS. Subgroup analysis revealed that the low PS groups had significantly worse PFS regardless of the PMI status. The low PMI and low PS group had markedly poorer OS than all the other groups. However, the poor prognosis associated with low PS was overcome by a high PMI.

Dietary Olive Oil Intake Improves Running Endurance with Intramuscular Triacylglycerol Accumulation in Mice.

Olive oil is a functional food shown to have a variety of bioactive effects. Therefore, we expect it to be a novel functional food with an exercise-mimetic effect on skeletal muscles. This study aimed to investigate the effect of olive oil on the endurance capacity and muscle metabolism in mice. Mice fed a 7% (w/w) olive oil diet for eight weeks showed improved treadmill running endurance and increased intramuscular triacylglycerol (IMTG) accumulation in the gastrocnemius muscle compared to soybean oil diet-fed controls. The increase in running endurance with olive oil intake was independent of the muscle fiber type. To elucidate underlying the mechanism of elevated IMTG levels, we examined the expression levels of the genes related to lipid metabolism. We found that the expression of diacylglycerol O-acyltransferase1 (DGAT1) was significantly upregulated in the muscle of olive oil diet-fed mice. In addition, the olive oil diet-fed mice showed no metabolic impairment or differences in growth profiles compared to the controls. These results suggest that dietary olive oil intake affects muscle metabolism and muscle endurance by increasing energy accumulation.

Inhalation of odors containing DMHF generated by the Maillard reaction affects physiological parameters in rats.

The effects of odors generated by the Maillard reaction from amino acids and reducing sugars on physiological parameters (blood pressure, heart rate, and oxidative stress levels) in Wistar rats were investigated in the present study. The Maillard reaction samples were obtained from glycine, arginine, or lysine of 1.0 mol/L and glucose of 1.0 mol/L with heat treatment. The odor-active compounds in the Maillard reaction samples were identified using the aroma extract dilution analysis. Among the odor-active compounds identified, 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DMHF, FURANEOL and strawberry furanone) had the highest odor activity and its concentration was affected by amino acid types. The Maillard reaction odors generated from glycine or arginine significantly decreased systolic blood pressure and heart rate in rats when inhaled. These physiological effects were associated with DMHF. Furthermore, oxidative stress marker levels in rat plasma were decreased by the inhalation of DMHF. The inhalation of DMHF appears to at least partly affect physiological parameters by decreasing oxidative stress.

Correlation between skeletal muscle fiber type and responses of a taste sensing system in various beef samples.

The difference of muscle fiber type composition affects several parameters related to meat quality; however, the relationship between muscle fiber types and meat taste is unclear. To elucidate this relationship, we determined the taste of various beef samples using a taste sensor (INSENT SA402B) and analyzed its correlation with different muscle fiber type composition. We used 22 kinds of beef samples and measured nine tastes, including the relative and change of membrane potential caused by adsorption (CPA) values, using six sensors (GL1, CT0, CA0, AAE, C00, and AE1). The taste sensor analysis indicated positive value outputs for the relative C00, AAE, and GL1 values as well as for the CPA value of AAE, which corresponded to bitterness, umami, sweetness, and richness, respectively. We found significant positive correlations of the myosin heavy chain 1 (MyHC1) composition with umami taste, and with richness. This result suggests that high levels of slow MyHC1 can induce strong umami taste and richness in beef. We expect that our results will contribute to the elucidation of the relationship between muscle fiber types and meat palatability.

Energy metabolism profile of the effects of amino acid treatment on skeletal muscle cells: Leucine inhibits glycolysis of myotubes.

OBJECTIVES: Amino acids are not only components of proteins, but also can be metabolized to energy substances or be used as signaling molecules. However, basic knowledge of the relationship between amino acid treatment and energy metabolism is still insufficient. The aims of this study was to profile the effects of essential amino acid and alanine treatment on the energy metabolism of both myoblasts and myotubes and to contribute to the understanding of the basic relationship between amino acid treatment and energy metabolism of skeletal muscle cell. METHODS: We profiled whether amino acid (essential amino acids and alanine) treatment can affect the energy metabolism (glycolysis, mitochondrial respiration) of cultured skeletal muscle cells. C2C12 myoblasts and differentiated myotubes were treated with 5 mM each amino acid for 1 h, then the energy metabolism was measured by using extracellular flux analyzer. RESULTS: Although not all of the amino acid treatments could affect the energy metabolism of C2C12 myoblasts, leucine, isoleucine, lysine, phenylalanine, and histidine decreased the extracellular acidification rate, an indirect indicator of glycolysis, in differentiated myotubes without alteration of oxygen consumption rate, an indirect indicator of mitochondrial respiration. By glycolysis stress test, we found that leucine treatment inhibited glycolysis of myotubes when the substrate of glycolysis is sufficient in cultured media. The inhibitory effect of glycolysis by leucine was not canceled by rapamycin (an inhibitor for mTOR). But, 3,6-dichlorobenzo[b]thiophene-2-carboxylic acid (an inhibitor for branched-chain α ketoacid dehydrogenase complex kinase) increased branched-chain amino acid catabolism, which decreased the glycolysis of myotubes. CONCLUSION: Findings from the present study complemented the basic knowledge of amino acid treatment on the energy metabolism of cultured skeletal muscle cells and suggested the inhibitory effects of glycolysis by branched-chain amino acid catabolism.

DMHF (2,5-dimethyl-4-hydroxy-3(2H)-furanone), a volatile food component generated by the Maillard reaction, promotes appetite and changes gene expression in the rat brain through inhalation.

Inhalation of odors can affect physiological parameter and change gene expression-related specific function. 2,5-Dimethyl-4-hydroxy-3(2H)-furanone (DMHF) is one of the major odor compounds generated by the Maillard reaction. We previously reported that the inhalation of DMHF decreased systolic blood pressure via the autonomic nervous system in rats. The autonomic nervous system is also closely related to appetite regulation. The present study investigated the effects of DMHF on dietary intake and gene expression. The inhalation of DMHF increased the dietary intake of rats during the feeding period. However, body weight did not change after 6 weeks feeding. A DNA microarray analysis showed that DMHF altered gene expression associated with feeding behavior and neurotransmission in the rat brain. DMHF inhalation promotes appetite and changes gene expression in rats. Furthermore, phenotypic changes may regulate neurotransmission and appetite at the mRNA level in addition to controlling the autonomic nervous system. PRACTICAL APPLICATION: DMHF is an important flavor component in the food industry. In this study, we first observed that the inhalation of DMHF promotes appetite. This finding is directly connected with the industrial application.

Oleic acid up-regulates myosin heavy chain (MyHC) 1 expression and increases mitochondrial mass and maximum respiration in C2C12 myoblasts.

Skeletal muscle is divided into type 1 and type 2 fibers. Type 1 fibers are rich in mitochondria, have high oxidative metabolism, and are resistant to fatigue. Muscle-specific overexpression of peroxisome proliferator-activated receptor (PPAR)δ drastically increases the number of type 1 fibers. We focused on oleic acid, an omega-9 monounsaturated fatty acid, as a factor that activates PPARδ. In this study, we examined the effects of oleic acid on the muscle fiber type of C2C12 myotubes and its relationship with PPARδ. Our results showed that oleic acid treatment increased the levels of myosin heavy chain (MyHC)1, a known type 1 fiber marker, as well as mitochondrial mass and maximum respiration in C2C12 cells. To confirm the relationship between PPARδ activation and oleic acid-induced MyHC1 increase, we examined the effects of oleic acid in PPARδ knockdown C2C12 myoblasts. We found that oleic acid supplementation increased the mRNA expression of MyHC1 in PPARδ-knockdown C2C12 cells. Our data suggest that oleic acid increases type 1 fiber levels in C2C12 myotubes in a PPARδ-independent manner.

Effect of dietary fish oil intake on ubiquitin ligase expression during muscle atrophy induced by sciatic nerve denervation in mice.

Dietary fish oil intake improves muscle atrophy in several atrophy models however the effect on denervation-induced muscle atrophy is not clear. Thus, the aim of this study was to investigate the effects of dietary fish oil intake on muscle atrophy and the expression of muscle atrophy markers induced by sciatic nerve denervation in mice. We performed histological and quantitative mRNA expression analysis of muscle atrophy markers in mice fed with fish oil with sciatic nerve denervation. Histological analysis indicated that dietary fish oil intake slightly prevented the decrease of muscle fiber diameter induced by denervation treatment. In addition, dietary fish oil intake suppressed the MuRF1 (tripartite motif-containing 63) expression up-regulated by denervation treatment, and this was due to decreased tumor necrosis factor-alpha (TNF-α) production in skeletal muscle. We concluded that dietary fish oil intake suppressed MuRF1 expression by decreasing TNF-α production during muscle atrophy induced by sciatic nerve denervation in mice.

Increase in muscle endurance in mice by dietary Yamabushitake mushroom (Hericium erinaceus) possibly via activation of PPARδ.

Skeletal muscle fiber is largely classified into two types: type 1 (slow-twitch) and type 2 (fast-twitch) fibers. Meat quality and composition of fiber types are thought to be closely related. Previous research showed that overexpression of constitutively active peroxisome proliferator-activated receptor (PPAR)δ, a nuclear receptor present in skeletal muscle, increased type 1 fibers in mice. In this study, we found that hexane extracts of Yamabushitake mushroom (Hericium erinaceus) showed PPARδ agonistic activity in vitro. Eight-week-old C57BL/6J mice were fed a diet supplemented with 5% (w/w) freeze-dried Yamabushitake mushroom for 24 hr. After the treatment period, the extensor digitorum longus (EDL) muscles were excised. The Yamabushitake-supplemented diet up-regulated the PPARδ target genes Pdk4 and Ucp3 in mouse skeletal muscles in vivo. Furthermore, feeding the Yamabushitake-supplemented diet to mice for 8 weeks resulted in a significant increase in muscle endurance. These results indicate that Yamabushitake mushroom contains PPARδ agonistic ligands and that dietary intake of Yamabushitake mushroom could activate PPARδ in skeletal muscle of mice. Unexpectedly, we observed no significant alterations in composition of muscle fiber types between the mice fed control and Yamabushitake-supplemented diets.

Safety of avoiding systemic corticosteroid administration for grade II acute graft-versus-host disease limited to the skin.

We hypothesized that systemic corticosteroid administration would be safely avoided not only in grade I acute graft-versus-host disease (GVHD) but also in selected patients with grade II acute GVHD limited to the skin (grade IIs GVHD). We retrospectively evaluated risk factors for subsequent GVHD progression, defined as the involvement of other organs or progression to grade III to IV GVHD, in 50 patients with acute GVHD of grade IIs at its onset. Sixteen patients received systemic corticosteroid administration before GVHD progression. The cumulative incidence of GVHD progression at 28 days from the onset of grade IIs GVHD was 24%. Twenty-five patients did not require systemic corticosteroid administration throughout the entire episode of acute GVHD. Systemic corticosteroid administration before GVHD progression did not affect GVHD progression, chronic GVHD, or non-relapse mortality. Early onset (less than 26 days from transplantation) of grade IIs GVHD was identified as the only statistically significant risk factor for GVHD progression (hazard ratio 6.73, 95% confidence interval 1.5-31.1, P = 0.01). In conclusion, avoiding systemic corticosteroid administration for selected patients with grade IIs GVHD before GVHD progression did not compromise the transplantation outcomes. Patients with early-onset grade IIs GVHD were at high risk for GVHD progression.

Positive Cytotoxic Crossmatch Predicts Delayed Neutrophil Engraftment in Allogeneic Hematopoietic Cell Transplantation from HLA-Mismatched Related Donors.

Although a positive cytotoxic crossmatch (XM) has been reported to predict graft failure, mainly in solid organ transplantations, its significance in allogeneic hematopoietic cell transplantation (HCT) remains to be elucidated. We retrospectively assessed the impact of positive XM on neutrophil engraftment in 41 patients who underwent HCT with an HLA-mismatched related donor. XM was positive in 22 patients. Six of these 22 patients were also positive for anti-HLA antibody, whereas only 1 was positive for donor-specific anti-HLA antibody. The cumulative incidence of engraftment at day +28 was 89.5% in patients with negative XM versus 59.1% in those with positive XM (P = .08). In particular, positive B cell warm XM was significantly associated with a lower probability of engraftment at day +28 (46.7% versus 88.5%; P = .04). In a multivariate analysis, both positive XM and positive B cell warm XM were significantly associated with delayed engraftment (hazard ratio [HR], .46; P = .02 and HR, .41; P = .01, respectively). There was no significant difference in the achievement of engraftment between those with and without detection of anti-HLA antibodies. In conclusion, positive XM might be associated with a delayed neutrophil engraftment after HCT from HLA-mismatched related donors.

Slow-Myofiber Commitment by Semaphorin 3A Secreted from Myogenic Stem Cells.

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 (Pax7CreERT2 -Sema3Afl °x 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.