Bilaterally Asymmetric Helical Myofibrils in Ascidian Tadpole Larvae

The locomotor system is highly bilateral at the macroscopic level. Homochirality of biological molecules is fully compatible with the bilateral body. However, whether and how single-handed cells contribute to the bilateral locomotor system is obscure. Here, exploiting the small number of cells in the swimming tadpole larva of the ascidian Ciona, we analyzed morphology of the tail at cellular and subcellular scales. Quantitative phase-contrast X-ray tomographic microscopy revealed a high-density midline structure ventral to the notochord in the tail. Muscle cell nuclei on each side of the notochord were roughly bilaterally aligned. However, fluorescence microscopy detected left-right asymmetry of myofibril inclination relative to the longitudinal axis of the tail. Zernike phase-contrast X-ray tomographic microscopy revealed the presence of left-handed helices of myofibrils in muscle cells on both sides. Therefore, the locomotor system of ascidian larvae harbors symmetry-breaking left-handed helical cells, while maintaining bilaterally symmetrical cell alignment. These results suggest that bilateral animals can override cellular homochirality to generate the bilateral locomotor systems at the supracellular scale.

Stress-induced protein dermcidin develops diabetes targeting GLUT4/insulinviaNO/cGMP inhibition

BACKGROUND AND PURPOSE

Diabetes is common in tobacco-consuming individuals, hypoxia-encountering people, and post-menopausal women. The mechanism behind diabetes-associated vascular-dysfunction remains speculative. Dermcidin (DCD), an 11 kDa-protein plays a detrimental role in acute myocardial-infarction through the impairment of endothelial-nitric-oxide-synthase (eNOS).

EXPERIMENTAL APPROACH

DCD mediated genesis of diabetes has been manifested in human and rodent-models under various stress-conditions. Here, plasma levels of DCD have been significantly correlated with the diabetic-conditions in postmenopausal-women, in tobacco-consuming individuals and in hypoxia indicating a common pathway. In mice, DCD infusion augmented the blood glucose with a concomitant reduction of nitric oxide levels. DCD triggers the release of glucose from the liver/muscle/kidney and antagonizes the effects of insulin. This has been demonstrated by the glucose tolerance and insulin tolerance test. Herein our studies showed that DCD inhibited GLUT-4 and impaired NO production.

KEY RESULTS

We showed that tobacco consumption or hypoxia might provoke DCD-induced hyperglycemia by down-regulation of NO-signaling, GLUT4-function, and insulin sensitivity. Tobacco-induced DCD up-regulation has been shown in RT-PCR and qPCR results and DCD-induced lower insulin-sensitivity has been shown by Western-blot. The insulin, GLUT-4, and GANOS expression were missing in postmenopausal women due to DCD. Our FRET-imaging studies demonstrate that DCD-induced NO deregulation impairs cGMP-mediated cellular-signaling.

CONCLUSIONS & IMPLICATIONS

Molecular-docking experiments (AUTODOCK/PATCHDOCK) decisively showed high-affinity binding of DCD to GLUT-4, insulin, and its receptor (Ectodomain1/2). Synergism of all these effects resulted in the breakdown of glucose homeostasis-machinery i.e. insulin-resistance, and further dermcidin induced NO/cGMP down-regulation in individuals under a variety of stressors.

Skeletal Muscle Cell Growth Alters the Lipid Composition of Extracellular Vesicles

We sought to characterize the lipid profile of skeletal muscle cell-derived Extracellular Vesicles (EVs) to determine if a hypertrophic stimulus would affect the lipid composition of C2C12 myotube-derived EVs. Analyses included C2C12 murine myoblasts differentiated into myotubes and treated with Insulin-Like Growth Factor 1 (IGF-1) for 24 h to induce hypertrophic growth. EVs were isolated from cell culture media, quantified using Nanoparticle Tracking Analysis (NTA) and analyzed using Transmission Electron Microscopy (TEM). EVs were homogenized and lipids extracted for quantification by Mass Spectrometry followed by downstream lipid class enrichment and lipid chain analysis. IGF-1 treatment elicited an increase in CD63 and CD81 levels (39% and 21%) compared to the controls (16%), respectively. Analysis revealed that skeletal muscle-derived EVs are enriched in bioactive lipids that are likely selectively incorporated into EVs during hypertrophic growth. IGF-1 treatment of myotubes had a significant impact on the levels of diacylglycerol (DG) and ceramide (Cer) in secreted EVs. Specifically, the proportion of unsaturated DG was two- to three-fold higher in EVs derived from IGF-treated cells, as compared to those from control cells. The levels of saturated DG were unaffected. Selective increases were similarly seen in C16- and C24-Cer but not in other species. Levels of free sphingoid bases tended to decrease, while those of sphingosine-1-phosphate was unaffected. Our results suggest that the lipid composition and biogenesis of skeletal muscle-derived EVs, are specific and highly selective during hypertrophic growth.

Low‑calorie sweetener D‑psicose promotes hydrogen peroxide‑mediated apoptosis in C2C12 myogenic cells favoring skeletal muscle cell injury

Diet and exercise are the most effective approaches used to induce weight loss. D‑psicose is a low‑calorie sweetener that has been shown to reduce weight in obese individuals. However, the effect of D‑psicose on muscle cells under oxidative stress, which is produced during exercise, requires further investigation. The present study aimed to determine the effects of D‑psicose on C2C12 myogenic cells in vitro. Hydrogen peroxide (H₂O₂) was used to stimulate the generation of intracellular reactive oxygen species (ROS) in muscle cells to mimic exercise conditions. Cell viability was analyzed using a MTT assay and flow cytometry was used to analyze the levels of apoptosis, mitochondrial membrane potential (MMP), the generation of ROS and the cell cycle distribution following treatment. Furthermore, protein expression levels were analyzed using western blotting and cell proliferation was determined using a colony formation assay. The results of the present study revealed that D‑psicose alone exerted no toxicity on C2C12 mouse myogenic cells. However, in the presence of low‑dose (100 µM) H₂O₂‑induced ROS, D‑psicose induced C2C12 cell injury and significantly decreased C2C12 cell viability in a dose‑dependent manner. In addition, the levels of apoptosis and the generation of ROS increased, while the MMP decreased. MAPK family molecules were also activated in a dose‑dependent manner following treatment. Notably, the combined treatment induced G₂/M phase arrest and reduced the proliferation of C2C12 cells. In conclusion, the findings of the present study suggested that D‑psicose may induce toxic effects on muscle cells in a simulated exercise situation by increasing ROS levels, activating the MAPK signaling pathway and disrupting the MMP.

Myostatin-1 Inhibits Cell Proliferation by Inhibiting the mTOR Signal Pathway and MRFs, and Activating the Ubiquitin-Proteasomal System in Skeletal Muscle Cells of Japanese Flounder Paralichthys olivaceus

Myostatin (MSTN) is a negative regulator of skeletal muscle growth and development. The mechanisms of fish MSTN involved in muscle growth are not fully understood. In the present study, knockdown and overexpression of mstn-1 was performed in cultured Japanese flounder muscle cells to investigate the molecular function and the underlying mechanism of fish MSTN-1. Results showed that mstn-1 knockdown significantly induced cell proliferation and the mRNA expression of myogenic regulatory factors (MRFs), while overexpression of mstn-1 led to a significant decrease of cell proliferation and a suppression of the MRFs mRNA expression. The overexpression of mstn-1 also significantly increased the mRNA expression of ubiquitin–proteasomal pathway of proteolysis genes including muscle RING-finger protein 1 (murf-1) by 204.1% (p = 0.024) and muscle atrophy F-box protein (mafbx) by 165.7% (p = 0.011). However, mystn-1 overexpression inhibited the activation of mTOR signal pathway and the AKT/FoxO1 pathway through decreasing phosphorylation of AKT at Ser 473 by 56.0% (p = 0.001). Meanwhile, mystn-1 overexpression increased the dephosphorylation and nuclear localization of FoxO1 by 394.9% (p = 0.005). These results demonstrate that mstn-1 in Japanese flounder has the effects of inhibiting cell proliferation and growth, and the mTOR and AKT/FoxO1 pathways participated in these biological effects.

1,25-Dihydroxyvitamin D3 Inhibits Lipopolysaccharide-Induced Interleukin-6 Production by C2C12 Myotubes

Background and Objective: 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) inhibits proinflammatory cytokines in microglial cells and monocytes. However, it is unclear whether 1,25(OH)₂D₃ inhibits proinflammatory cytokines in muscle cells. This study was conducted to investigate whether 1,25(OH)₂D₃ inhibits the production of proinflammatory cytokines, resulting in inhibition of the protein expression of E3 ubiquitin ligases and muscle protein loss. Materials and Methods: C2C12 myoblasts were proliferated in Dulbecco’s modified Eagle medium (DMEM) containing 10% fetal bovine serum, and myoblasts were differentiated into myotubes in DMEM containing 2% horse serum. Myotubes were treated with 1,25(OH)₂D₃ for 24 h, followed by lipopolysaccharide (LPS) stimulation for 48 h. Results: Interleukin (IL)-6 protein concentrations were higher in the culture supernatant following LPS stimulation compared to that without LPS stimulation (p < 0.001). However, the IL-6 concentration was significantly lower in C2C12 myotubes following 1,25(OH)₂D₃ treatment than in C2C12 myotubes without 1,25(OH)₂D₃ treatment (p < 0.001). The myosin heavy chain (MHC), muscle atrophy F-box, and muscle ring-finger protein-1 protein levels did not significantly differ (P = 0.324, 0.552, and 0.352, respectively). We could not compare tumor necrosis factor α (TNFα) protein levels because they were below the limit of detection of our assay in many supernatant samples, including in LPS-stimulated samples. Conclusions: 1,25(OH)₂D₃ inhibited increases in IL-6 protein concentrations in muscle cells stimulated by LPS, suggesting that 1,25(OH)₂D₃ inhibits inflammation in muscle cells. The findings suggest that 1,25(OH)₂D₃ can prevent or improve sarcopenia, which is associated with IL-6. The TNFα protein content could not be measured, and MHC was not decreased despite LPS stimulation of C2C12 myotubes. Further studies are needed to examine the effects of higher doses of LPS stimulation on muscle cells and use more sensitive methods for measuring TNFα protein to investigate the preventive effects of 1,25(OH)₂D₃ on increased TNFα and muscle proteolysis.

PPARδ and FOXO1 Mediate Palmitate-Induced Inhibition of Muscle Pyruvate Dehydrogenase Complex and CHO Oxidation, Events Reversed by Electrical Pulse Stimulation

The mechanisms behind the reduction in muscle pyruvate dehydrogenase complex (PDC)-controlled carbohydrate (CHO) oxidation during chronic high-fat dietary intake are poorly understood, as is the basis of CHO oxidation restoration during muscle contraction. C2C12 myotubes were treated with (300 μM) palmitate or without (control) for 16 h in the presence and absence of electrical pulse stimulation (EPS, 11.5 V, 1 Hz, 2 ms). Compared to control, palmitate reduced cell glucose uptake (p < 0.05), PDC activity (p < 0.01), acetylcarnitine accumulation (p < 0.05) and glucose-derived mitochondrial ATP production (p < 0.01) and increased pyruvate dehydrogenase kinase isoform 4 (PDK4) (p < 0.01), peroxisome proliferator-activated receptor alpha (PPARα) (p < 0.01) and peroxisome proliferator-activated receptor delta (PPARδ) (p < 0.01) proteins, and reduced the whole-cell p-FOXO1/t-FOXO1 (Forkhead Box O1) ratio (p < 0.01). EPS rescued palmitate-induced inhibition of CHO oxidation, reflected by increased glucose uptake (p < 0.01), PDC activity (p < 0.01) and glucose-derived mitochondrial ATP production (p < 0.01) compared to palmitate alone. EPS was also associated with less PDK4 (p < 0.01) and PPARδ (p < 0.01) proteins, and lower nuclear p-FOXO1/t-FOXO1 ratio normalised to the cytoplasmic ratio, but with no changes in PPARα protein. Collectively, these data suggest PPARδ, and FOXO1 transcription factors increased PDK4 protein in the presence of palmitate, which limited PDC activity and flux, and blunted CHO oxidation and glucose uptake. Conversely, EPS rescued these metabolic events by modulating the same transcription factors.

The hidden role of the Sigma1 receptor in muscle cells

This review describes the very specific role of Sigma1 receptor in different types of muscle cells. Sigma1 receptor is a transmembrane protein residing in such structures like MAM. It has chaperoning activity supporting function of many proteins, particularly ion channels, including Ca2+ channels. This latter function is of particular meaning for muscle cells, due to their calcium-based/regulated metabolism. Here we discuss new reports pointing to participation of Sigma1 receptor in muscle specific processes like contraction, EC-coupling, calcium currents and in diseases like left ventricular hypertrophy, transverse aortic stenosis and hypertension-induced heart dysfunction.

Lysophosphatidic Acid Inhibits Simvastatin-Induced Myocytoxicity by Activating LPA Receptor/PKC Pathway

Statins such as simvastatin have many side effects, including muscle damage, which is known to be the most frequent undesirable side effect. Lysophosphatidic acid (LPA), a kind of biolipid, has diverse cellular activities, including cell proliferation, survival, and migration. However, whether LPA affects statin-linked muscle damage has not been reported yet. In the present study, to determine whether LPA might exert potential protective effect on statin-induced myocyotoxicity, the effect of LPA on cytotoxicity in rat L6 myoblasts exposed to simvastatin was explored. Viability and apoptosis of rat L6 myoblasts were detected via 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-5- [(phenylamino)carbonyl]-2H-tetrazolium hydroxide (XTT) assay and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay, respectively. Protein expression levels were detected via Western blotting. Simvastatin decreased viability of L6 cells. Such decrease in viability was recovered in the presence of LPA. Treatment with LPA suppressed simvastatin-induced apoptosis in L6 cells. In addition, treatment with LPA receptor inhibitor Ki16425, protein kinase C (PKC) inhibitor GF109203X, or intracellular calcium chelator BAPTA-AM attenuated the recovery effect of LPA on simvastatin-induced L6 cell toxicity. These findings indicate that LPA may inhibit simvastatin-induced toxicity in L6 cells probably by activating the LPA receptor-PKC pathway. Therefore, LPA might have potential as a bioactive molecule to protect muscles against simvastatin-induced myotoxicity.

miR-206 knockout shows it is critical for myogenesis and directly regulates newly identified target mRNAs

The muscle specific miRNA, miR-206, is important for the process of myogenesis; however, studying the function of miR-206 in muscle development and differentiation still proves challenging because the complement of mRNA targets it regulates remains undefined. In addition, miR-206 shares close sequence similarity to miR-1, another muscle specific miRNA, making it hard to study the impact of miR-206 alone in cell culture models. Here we used CRISPR/Cas9 technology to knockout miR-206 in C2C12 muscle cells. We show that knocking out miR-206 significantly impairs and delays differentiation and myotube formation, revealing that miR-206 alone is important for myogenesis. In addition, we use an experimental affinity purification technique to identify new mRNA targets of miR-206 in C2C12 cells. We identified over one hundred mRNAs as putative miR-206 targets. Functional experiments on six of these targets indicate that Adam19, Bgn, Cbx5, Smarce1, and Spg20 are direct miR-206 targets in C2C12 cells. Our data show a unique and important role for miR-206 in myogenesis.

Microcystin-LR exposure disrupts the insulin signaling pathway in C2C12 mice muscle cell line

Microcystin-LR (MC-LR) is a widely produced monocyclic heptapeptides in eutrophication waterbodies. MC-LR can induce various toxic effects in different cells. Our previous studies have found that MC-LR exposure can disrupt insulin signaling pathway in human liver cells (HL 7702). Skeletal muscle is one of the major organs for glucose disposal and responsive to insulin. However, the effects of MC-LR on insulin signaling pathway in muscle cells have not been fully explored. By using C2C12 mice muscle cells, this study aims to investigate the toxic effects of MC-LR in muscle cells with a focus on its effects on insulin signaling pathways. It was found that MC-LR entered into cells and inhibited protein phosphatase 2A (PP2A) significantly. Furthermore, MC-LR increased phosphorylation of Ser302, Ser307, Ser612 of insulin receptor substrate 1, AKT-Ser473, GSK3α-Ser21, and S6K1-Thr389 by inhibiting the activity of PP2A. The results in this study demonstrate that exposure of MCLR can disrupt the insulin pathway in muscle cells.

Nucleotide excision repair capacity increases during differentiation of human embryonic carcinoma cells into neurons and muscle cells

Embryonic stem cells can self-renew and differentiate, holding great promise for regenerative medicine. They also employ multiple mechanisms to preserve the integrity of their genomes. Nucleotide excision repair, a versatile repair mechanism, removes bulky DNA adducts from the genome. However, the dynamics of the capacity of nucleotide excision repair during stem cell differentiation remain unclear. Here, using immunoslot blot assay, we measured repair rates of UV-induced DNA damage during differentiation of human embryonic carcinoma (NTERA-2) cells into neurons and muscle cells. Our results revealed that the capacity of nucleotide excision repair increases as cell differentiation progresses. We also found that inhibition of the apoptotic signaling pathway has no effect on nucleotide excision repair capacity. Furthermore, RNA-Seq-based transcriptomic analysis indicated that expression levels of four core repair factors, xeroderma pigmentosum (XP) complementation group A (XPA), XPC, XPG, and XPF-ERCC1, are progressively up-regulated during differentiation, but not those of replication protein A (RPA) and transcription factor IIH (TFIIH). Together, our findings reveal that increase of nucleotide excision repair capacity accompanies cell differentiation, supported by the up-regulated transcription of genes encoding DNA repair enzymes during differentiation of two distinct cell lineages.

Adipocytes suppress differentiation of muscle cells in a co-culture system

The development of adipose tissue in skeletal muscle is important for improving meat quality. However, it is still unclear how adipocytes grow in the proximity of muscle fibers. We hypothesized that adipocytes would suppress muscle cell growth so as to grow dominantly within muscle. In this study, we investigated the effect of adipocytes on the differentiation of muscle cells in a co-culture system. The fusion index of C2C12 myoblasts co-cultured with 3T3-L1 adipocytes was significantly lower than that of the control. The expression of myogenin and myosin heavy chain in C2C12 muscle cells co-cultured with 3T3-L1 adipocytes was significantly lower than in the control. Furthermore, the expression of Atrogin-1 and MuRF-1 was higher in C2C12 muscle cells co-cultured with 3T3-L1 adipocytes than the control. These results suggest that 3T3-L1 adipocytes suppress the differentiation of C2C12 myoblasts. In addition, 3T3-L1 adipocytes induced the expression and secretion of IL-6 in C2C12 muscle cells. The fusion index and myotube diameter were higher in C2C12 muscle cells co-cultured with 3T3-L1 cells in medium containing IL-6-neutralizing antibody than the control. Taken together, there is a possibility that adipocyte-induced IL-6 expression in muscle cells could be involved in the inhibition of muscle cell differentiation via autocrine.

Excessive glucocorticoid-induced muscle MuRF1 overexpression is independent of Akt/FoXO1 pathway

The ubiquitin-proteasome system (UPS)-dependent proteolysis plays a major role in the muscle catabolic action of glucocorticoids (GCs). Atrogin-1 and muscle-specific RING finger protein 1 (MuRF1), two E3 ubiquitin ligases, are uniquely expressed in muscle. It has been previously demonstrated that GC treatment induced MuRF1 and atrogin-1 overexpression. However, it is yet unclear whether the higher pharmacological dose of GCs induced muscle protein catabolism through MuRF1 and atrogin-1. In the present study, the role of atrogin-1 and MuRF1 in C2C12 cells protein metabolism during excessive dexamethasone (DEX) was studied. The involvement of Akt/forkhead box O1 (FoXO1) signaling pathway and the cross-talk between anabolic regulator mammalian target of rapamycin (mTOR) and catabolic regulator FoXO1 were investigated. High concentration of DEX increased MuRF1 protein level in a time-dependent fashion (P<0.05), while had no detectable effect on atrogin-1 protein (P>0.05). FoXO1/3a (Thr24/32) phosphorylation was enhanced (P<0.05), mTOR phosphorylation was suppressed (P<0.05), while Akt protein expression was not affected (P>0.05) by DEX. RU486 treatment inhibited the DEX-induced increase of FoXO1/3a phosphorylation (P<0.05) and MuRF1 protein; LY294002 (LY) did not restore the stimulative effect of DEX on the FoXO1/3a phosphorylation (P>0.05), but inhibited the activation of MuRF1 protein induced by DEX (P<0.05); rapamycin (RAPA) inhibited the stimulative effect of DEX on the FoXO1/3a phosphorylation and MuRF1 protein (P<0.05).

Leucine alleviates dexamethasone-induced suppression of muscle protein synthesis via synergy involvement of mTOR and AMPK pathways

Both mTOR and AMPK pathways are involved in the DEX-induced suppression of protein synthesis in muscle cells. Leucine supplementation relieves DEX-induced inhibition on protein synthesis by evoking mTOR and suppressing AMPK pathway.

Glucocorticoids (GCs) are negative muscle protein regulators that contribute to the whole-body catabolic state during stress. Mammalian target of rapamycin (mTOR)-signalling pathway, which acts as a central regulator of protein metabolism, can be activated by branched-chain amino acids (BCAA). In the present study, the effect of leucine on the suppression of protein synthesis induced by GCs and the pathway involved were investigated. In vitro experiments were conducted using cultured C2C12 myoblasts to study the effect of GCs on protein synthesis, and the involvement of mTOR pathway was investigated as well. After exposure to dexamethasone (DEX, 100 μmol/l) for 24 h, protein synthesis in muscle cells was significantly suppressed (P<0.05), the phosphorylations of mTOR, ribosomal protein S6 protein kinase 1 (p70s6k1) and eukaryotic initiation factor 4E binding protein 1 (4EBP1) were significantly reduced (P<0.05). Leucine supplementation (5 mmol/l, 10 mmol/l and 15 mmol/l) for 1 h alleviated the suppression of protein synthesis induced by DEX (P<0.05) and was accompanied with the increased phosphorylation of mTOR and decreased phosphorylation of AMPK (P<0.05). Branched-chain amino transferase 2 (BCAT2) mRNA level was not influenced by DEX (P>0.05) but was increased by leucine supplementation at a dose of 5 mmol/l (P<0.05).

Ginsenoside Rb1 stimulates adiponectin signaling in C2C12 muscle cells through up-regulation of AdipoR1 and AdipoR2 proteins

CONTEXT

Rb1 ginsenoside, the key element of ginseng root, is widely used as an herbal therapeutic drug in diabetic patients. Various hypoglycemic mechanisms have been described for Rb1; however, to date, there has been no report on the effect of Rb1 on adiponectin signaling.

OBJECTIVES

The current study was performed to establish the effects of ginsenoside Rb1 on the gene expression of AdipoR1 and AdipoR2 and their correlation to GLUT4 translocation in C2C12 myocytes.

MATERIALS AND METHODS

C2C12 myotubes were incubated with various concentrations of Rb1 (0.001-100 µM) for different incubation times (1-12 h). Real time PCR and western blot analyses were performed to investigate the expression changes of adiponectin receptors (AdRs) and GLUT4 translocation, respectively. Gene silencing of AdipoR1 using specific siRNA was used to determine whether inhibition of AdipoR1 would reduce Rb1-induced GLUT-4 translocation in C2C12 cells.

RESULTS

Rb1 significantly stimulated basal AdRs expression levels in a time and dose-dependent manner; the maximal effect was attained at a concentration of 100 µM and a time of 3 h (p < 0.05). In muscle cells, Rb1 increased GLUT4 translocations to the cell surface, which was correlated with increasing the adiponectin receptors gene expression. Rb1-induced GLUT4 translocation was inhibited by the silencing of AdipoR1 mRNA.

DISCUSSION AND CONCLUSION

These results suggest that ginsenoside Rb1 promote translocations of GLUT4 by activating the adiponectin signaling pathway. The results can be helpful in understanding the novel antidiabetic mechanism of Rb1 ginsenoside and gain further support for its use as an antidiabetic drug.

Calcitriol enhances fat synthesis factors and calpain activity in co-cultured cells

We have conducted an in vitro experiment to determine whether calcitriol can act as a fat synthesizer and/or meat tenderizer when skeletal muscle cells, adipose tissue, and macrophages are co-cultured. When co-cultured, pro-inflammatory cytokine tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) expression increased, whereas decreased anti-inflammatory cytokine (IL-10 and IL-15) expression decreased in both C2C12 and 3T3-L1 cells. Calcitriol increased reactive oxygen species (ROS) production in the media. While adiponectin gene expression decreased, leptin, resistin, CCAAT-enhancer-binding protein-beta (C/EBP-β), and peroxisome proliferator-activated receptor gamma (PPAR-γ) gene expression was significantly (P < 0.047) increased with calcitriol in 3T3-L1 cells co-cultured with two different cell types. Inducible nitric oxide synthase (iNOS) protein levels were also stimulated in the C2C12 and 3T3-L1 cells, but arginase l was attenuated by calcitriol. Cacitriol highly amplified (P = 0.008) µ-calpain gene expression in co-cultured C2C12 cells. The results showed an overall increase in pro-inflammatory cytokines and a decrease in anti-inflammatory cytokines of C2C12 and 3T3-L1 cells with calcitriol in co-culture systems. µ-Calpain protein was also augmented in differentiated C2C12 cells with calcitriol. These findings suggest that calcitriol can be used as not only fat synthesizer, but meat tenderizer, in meat-producing animals.

Mobilization of calcium from intracellular stores, potentiation of neurotransmitter-induced calcium transients, and capacitative calcium entry by 4-aminopyridine

In this study we analyzed the effect of 4-aminopyridine (4-AP) on free cytosolic calcium concentration ([Ca(2+)](i)) in basal conditions, after stimulation with neurotransmitters, and during capacitative calcium entry. Using fura-2 ratiometric calcium imaging, we found that 4-AP increased [Ca(2+)](i) in type I astrocytes, neurons, and in skeletal muscle cells. The [Ca(2+)](i) elevation induced by 4-AP was concentration-dependent and consisted of two phases: the first was dependent on intracellular calcium mobilization, and the second was dependent on extracellular calcium influx. 4-AP also increased the second messenger inositol trisphosphate in both neurons and astrocytes. In astrocytes, 4-AP treatment potentiated the sustained phase of the [Ca(2+)](i) elevation induced by ATP and bradykinin. In addition, capacitative calcium entry was potentiated severalfold by 4-AP, in astrocytes and muscle cells but not in neurons. These effects of 4-AP were completely and promptly reversible. 4-AP blocked voltage-sensitive K(+) currents in astrocytes. However, voltage-sensitive K(+) channel blockers inhibiting these currents did not affect agonist-induced calcium transients or capacitative calcium entry, indicating that 4-AP effects on [Ca(2+)](i) were not caused by the blockade of voltage-gated K(+) channels. We conclude that 4-AP is able to affect calcium homeostasis at multiple levels, from increasing basal [Ca(2+)](i) to potentiating capacitative calcium entry. The potentiation of capacitative calcium entry in astrocytes or muscle cells may explain some of the therapeutic activities of 4-AP as a neurotransmission enhancer.

Apoptosis of muscle cells causes weight loss prior to impairment of DNA synthesis in tumor-bearing rabbits

The mechanism of weight loss induced by the growth of malignant tumors is still unknown. We investigated it by focusing on apoptosis of skeletal muscle. VX2-tumor was implanted into rabbits and the apoptotic index (AI) of skeletal muscle was measured by in situ end-labeling assay. Plasma of the tumor-bearing rabbits was perfused repeatedly through non-coated charcoal resin. The AI reached 54.6% early after tumor implantation, when weight loss amounted to an 18% decrease in lean body mass (LBM) without change in muscle DNA synthesis or urinary 3-methylhistidine / creatinine ratio (3-MH / Cr). When the decrease of LBM reached 30%, DNA synthesis was decreased by 48% and 3-MH / Cr was increased by 104%, whereas AI was only 4.7%. The plasma perfusion did not prevent apoptosis in muscle, but improved LBM, DNA synthesis, and 3-MH / Cr. There may be two mechanisms of muscle depletion during the tumor growth: apoptosis in the early stage and metabolic abnormalities in muscle in the late stage.