An E-box within the MHC IIB gene is bound by MyoD and is required for gene expression in fast muscle

Identification of Sp1 and GC-boxes as transcriptional regulators of mouse Dag1 gene promoter

Dystroglycan is a widely expressed adhesion complex that anchors cells to the basement membrane and is involved in embryonic development and differentiation. Dystroglycan expression is frequently reduced in human dystrophies and malignancies, and its molecular functions are not completely understood. Several posttranslational mechanisms have been identified that regulate dystroglycan expression and/or function, while little is known about how expression of the corresponding Dag1 gene is regulated. This study aimed to clone the Dag1 gene promoter and to characterize its regulatory elements. Analysis of the mouse Dag1 gene 5'-flanking region revealed a TATA and CAAT box-lacking promoter including a GC-rich region. Transfection studies with serially deleted promoter constructs allowed us to identify a minimal promoter region containing three Specificity protein 1 (Sp1) sites and an E-box. Sp1 binding was confirmed by chromatin immunoprecipitation assay, and Sp1 downregulation reduced dystroglycan expression in muscle cells. Treatment with 5-aza-2'-deoxycytidine and/or the histone deacetylase inhibitor trichostatin A increased Dag1 mRNA expression levels in myoblasts, and methylation decreased promoter activity in vitro. Furthermore, Dag1 gene promoter methylation was reduced while its expression increased during differentiation of C(2)C(12) myoblast cells in myotubes. In conclusion, for the first time we have characterized the activity of the mouse Dag1 gene promoter, confirming a complex regulation by Sp1 transcription factor, DNA methylation, and histone acetylation, which might be relevant for a better understanding of the physiopathology of the dystroglycan complex.

IGF-I activates the mouse type IIb myosin heavy chain gene

IGF-I increases skeletal muscle mass, but whether IGF-I increases type IIb myosin heavy chain (MyHC) transcriptional activity is not known. C2C12 myotubes were cultured with or without IGF-I to determine whether IGF-I increases type IIb MyHC promoter activity, and if so, what region of the promoter might IGF-I signaling regulate. At differentiation days 3 and 4, IGF-I increased type IIb MyHC mRNA and mouse 3.0-kb type IIb MyHC promoter activity. Deletion construct studies identified a potential IGF-I-responsive region between 1.25 and 1.2 kb of the type IIb MyHC promoter, which contained an exact 6-bp T-cell factor/lymphoid enhancer factor (Tcf/Lef) binding site at position -1206 to -1201. Site-specific mutation of the putative Tcf/Lef binding site reduced IGF-I-induced 1.3-kb type IIb MyHC promoter activity. To identify potential IGF-I signaling molecules, the phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin and LY-294002 were both found to markedly attenuate IGF-I activation of the 1.3-kb type IIb MyHC promoter. Downstream signaling of IGF-I can phosphorylate and inactivate GSK-3beta, thereby enhancing beta-catenin protein. The GSK-3beta inhibitor, LiCl, dramatically enhanced IGF-I induction of the 1.3-kb type IIb MyHC promoter, and constitutively active GSK-3beta attenuated IGF-I-induced 1.3-kb type IIb MyHC promoter activity. Finally, IGF-I increased nuclear beta-catenin protein, and small interfering RNA knockdown of beta-catenin attenuated IGF-I-induced 1.3-kb type IIb MyHC promoter activity and type IIb MyHC mRNA. In summary, IGF-I stimulation of C2C12 myotubes increases mouse type IIb MyHC promoter activity, likely through signaling of PI3K, GSK-3beta, beta-catenin, and a Tcf/Lef binding site at -1,206 to -1,201 bp in the promoter.

NFAT isoforms control activity-dependent muscle fiber type specification

The intracellular signals that convert fast and slow motor neuron activity into muscle fiber type specific transcriptional programs have only been partially defined. The calcium/calmodulin-dependent phosphatase calcineurin (Cn) has been shown to mediate the transcriptional effects of motor neuron activity, but precisely how 4 distinct muscle fiber types are composed and maintained in response to activity is largely unknown. Here, we show that 4 nuclear factor of activated T cell (NFAT) family members act coordinately downstream of Cn in the specification of muscle fiber types. We analyzed the role of NFAT family members in vivo by transient transfection in skeletal muscle using a loss-of-function approach by RNAi. Our results show that, depending on the applied activity pattern, different combinations of NFAT family members translocate to the nucleus contributing to the transcription of fiber type specific genes. We provide evidence that the transcription of slow and fast myosin heavy chain (MyHC) genes uses different combinations of NFAT family members, ranging from MyHC-slow, which uses all 4 NFAT isoforms, to MyHC-2B, which only uses NFATc4. Our data contribute to the elucidation of the mechanisms whereby activity can modulate the phenotype and performance of skeletal muscle.

S-nitrosation of proteins duringd-galactosamine-induced cell death in human hepatocytes

Nitric oxide (NO) participates in the cell death induced by d-Galactosamine (d-GalN) in hepatocytes, and NO-derived reactive oxygen intermediates are critical contributors to protein modification and hepatocellular injury. It is anticipated that S-nitrosation of proteins will participate in the mechanisms leading to cell death in d-GalN-treated human hepatocytes. In the present study, d-GalN-induced cell death was related to augmented levels of NO production and S-nitrosothiol (SNO) content. The biotin switch assay confirmed that d-GalN increased the levels of S-nitrosated proteins in human hepatocytes. S-nitrosocysteine (CSNO) enhanced protein S-nitrosation and altered cell death parameters that were related to S-nitrosation of the executioner caspase-3. Fifteen S-nitrosated proteins participating in metabolism, antioxidative defense and cellular homeostasis were identified in human hepatocytes treated with CSNO. Among them, seven were also identified in d-GalN-treated hepatocytes. The results here reported underline the importance of the alteration of SNO homeostasis during d-GalN-induced cell death in human hepatocytes.

Hepatocellular protection by nitric oxide or nitrite in ischemia and reperfusion injury

Ischemia and reperfusion (I/R)-induced liver injury occurs in several pathophysiological disorders including hemorrhagic shock and burn as well as resectional and transplantation surgery. One of the earliest events associated with reperfusion of ischemic liver is endothelial dysfunction characterized by the decreased production of endothelial cell-derived nitric oxide (NO). This rapid post-ischemic decrease in NO bioavailability appears to be due to decreased synthesis of NO, enhanced inactivation of NO by the overproduction of superoxide or both. This review presents the most current evidence supporting the concept that decreased bioavailability of NO concomitant with enhanced production of reactive oxygen species initiates hepatocellular injury and that endogenous NO or exogenous NO produced from nitrite play important roles in limiting post-ischemic tissue injury.

Laennec protects murine from concanavalin A-induced liver injury through inhibition of inflammatory reactions and hepatocyte apoptosis

The effect of Laennec, a hydrolyte of human placenta, on immune-mediated liver injury was investigated in vivo and in vitro in murine. Vena caudalis administration of concanavalin A (Con A) was employed to establish an in vivo liver-injury model, and in vitro hepatotoxicity was induced by 8 h interaction between Con A pre-treated hepatocytes and Con A-stimulated autologous splenic lymphocytes. Laennec was used for pre-treatment in the two models. Laennec decreased biochemical marker activity (alanine aminotransferase, ALT; lactate dehydrogenase, LDH) in serum and recovered the activity of superoxide dismutase (SOD) and myeloperoxidase (MPO), as well as the content of malondialdehyde (MDA) and nitric oxide (NO) in liver tissue. We also found that the DNA ladder induced by Con A in vivo was attenuated by Laennec. Furthermore, the leakage of aspartate aminotransferase (AST) and LDH in the supernatant of the co-culture system was decreased by addition of Laennec. Potential protective mechanisms were elucidated by DNA fragmentation assay and intercellular adhesion molecule-1 (ICAM-1) induction/inhibition experiments. Results showed that ICAM-1, which is related to the interaction between hepatocytes and lymphocytes, was inhibited by Laennec. These findings indicated that Laennec has potent activity against immune-mediated liver injury.

Role of MyoD in denervated, disused, and exercised muscle

The myogenic regulatory factor MyoD plays an important role in embryonic and adult skeletal muscle growth. Even though it is best known as a marker for activated satellite cells, it is also expressed in myonuclei, and its expression can be induced by a variety of different conditions. Several model systems have been used to study the mechanisms behind MyoD regulation, such as exercise, stretch, disuse, and denervation. Since MyoD reacts in a highly muscle-specific manner, and its expression varies over time and between species, universally valid predictions and explanations for changes in MyoD expression are not possible. This review explores the complex role of MyoD in muscle plasticity by evaluating the induction of MyoD expression in the context of muscle composition and electrical and mechanical stimulation.

Morin protects acute liver damage by carbon tetrachloride (CCl(4)) in rat

The purpose of this study was to investigate possible beneficial effects of morin on CCl(4)-induced acute hepatotoxicity in rats. Rats received a single dose of CCl(4) (150 microL/100 g 1:1 in corn oil). Morin treatment (20 mg/kg) was given at 48, 24, and 2 h before CCl(4) administration. CCl(4) challenge elevated serum alanine transaminase (ALT), aspartate transaminase (AST), and alkaline phosphatase (ALP) levels, but these effects were prevented by the pretreatment of rats with morin. To identify the mechanism of protective activity of morin in CCl(4)-induced hepatotoxicity in rats, we investigated expressions of tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), interleukin-6 (IL-6), and inducible nitric oxide (iNOS). The expressions of TNF-alpha, IL-1beta, IL-6, and iNOS were increased by CCl(4) treatment and increased expressions of those were decreased by morin. These findings suggest that morin prevents acute liver damage by inhibiting the production of TNF-alpha, IL-1beta, IL-6, and iNOS.

Expression of myogenic regulatory factors in the muscle-derived electric organ of Sternopygus macrurus

In most groups of electric fish, the current-producing cells of electric organs (EOs) derive from striated muscle fibers but retain some phenotypic characteristics of their precursor muscle cells. Given the role of the MyoD family of myogenic regulatory factors (MRFs) in the transcriptional activation of the muscle program in vertebrates, we examined their expression in the electrocytes of the gymnotiform Sternopygus macrurus. We estimated the number of MRF genes in the S. macrurus genome and our Southern blot analyses revealed a single MyoD, myogenin, myf5 and MRF4 gene. Quantitative RT-PCR showed that muscle and EO transcribe all MRF genes. With the exception of MyoD, the endogenous levels of myogenin, myf5 and MRF4 transcripts in electrocytes were greater than those detected in muscle fibers. These data indicate that MRF expression levels are not sufficient to predict the level to which the muscle program is manifested. Qualitative expression analysis of MRF co-regulators MEF2C, Id1 and Id2 also revealed these genes not to be unique to either muscle or EO, and detected similar expression patterns in the two tissues. Therefore, the partial muscle program of the EO is not associated with a partial expression of MRFs or with apparent distinct levels of some MRF co-factors. In addition, electrical inactivation by spinal cord transection (ST) resulted in the up-regulation of some muscle proteins in electrocytes without an accompanying increase in MRF transcript levels or notable changes in the co-factors MEF2C, Id1 and Id2. These findings suggest that the neural regulation of the skeletal muscle program via MRFs in S. macrurus might differ from that of their mammalian counterparts. Together, these data further our understanding of the molecular processes involved in the plasticity of the vertebrate skeletal muscle program that brings about the muscle-like phenotype of the non-contractile electrogenic cells in S. macrurus.

Down-regulation of MyoD gene expression in rat diaphragm muscle with heart failure

Diaphragm myopathy has been described in patients with heart failure (HF), with alterations in myosin heavy chains (MHC) expression. The pathways that regulate MHC expression during HF have not been described, and myogenic regulatory factors (MRFs) may be involved. The purpose of this investigation was to determine MRF mRNA expression levels in the diaphragm. Diaphragm muscle from both HF and control Wistar rats was studied when overt HF had developed, 22 days after monocrotaline administration. MyoD, myogenin and MRF4 gene expression were determined by RT-PCR and MHC isoforms by polyacrylamide gel electrophoresis. Heart failure animals presented decreased MHC IIa/IIx protein isoform and MyoD gene expression, without altering MHC I, IIb, myogenin and MRF4. Our results show that in HF, MyoD is selectively down-regulated, which might be associated with alterations in MHC IIa/IIx content. These changes are likely to contribute to the diaphragm myopathy caused by HF.

Inhibition of inducible nitric oxide synthase activity prevents liver recovery in rat thioacetamide-induced fibrosis reversal

BACKGROUND

Stimulation of nitric oxide (NO) synthesis similar to the application of NO donors could be of benefit in liver fibrosis. Many authors believe that activation of NO synthesis by pharmacological agents is promising in the treatment of liver fibrosis. However, there is considerable controversy in understanding the role of NO in fibrogenesis and fibrolysis. The aims of our study were to evaluate the effects of L-arginine, as an NO metabolic precursor, and those of NO synthase (NOS) inhibitors, L-nitroarginine methyl ester (L-NAME) and aminoguanidine (AG) in rats with thioacetamide (TAA)-induced liver fibrosis reversal.

MATERIALS AND METHODS

Male Wistar rats, 230-240 g, received TAA (200 mg kg(-1), intraperitoneally) twice a week for 3 months. Liver resolution was simulated by withdrawal of TAA administration. Thereafter the animals were subdivided into five groups and treated by intragastric intubation with: L-arginine (100 and 300 mg kg(-1)); L-NAME as an inhibitor of both constitutively expressed NOS (eNOS) and inducible NOS (iNOS) (20 mg kg(-1)), AG as a specific inhibitor of iNOS (100 mg kg(-1)) or placebo. The severity of liver fibrosis was assessed by morphometric evaluation of liver slides stained with Azan-Mallory, hydroxyproline (Hyp) determination and mRNA steady state levels of collagen I, transforming growth factor (TGF)-beta1, metalloproteinases (MMP)-13, -14, tissue inhibitor of MMP (TIMP)-1 and plasminogen activator inhibitor (PAI)-1 were quantified by real time PCR. The activities of serum marker enzyme, alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase, were measured.

RESULTS

TAA treatment during 3 months induced micronodular liver fibrosis with a pronounced deposition of collagen fibres. L-Arginine did not affect this deposition nor did it affect both relative and total liver hydroxyproline content. Both NOS inhibitors significantly increased the square of the liver connective tissue stained by Azan-Mallory and the above parameters characterizing liver hydroxyproline content. Both NOS inhibitors up-regulated procollagen alpha1 (I), MMP-13, TIMP-1 and PAI-1 mRNA expression. The AG effects were more pronounced. than those of L-NAME. AG treatment also increased mRNA expression of TGF-beta1 and PAI-1.

CONCLUSIONS

Both NOS inhibitors developed a clear pro-fibrotic effect in the liver. Aminoguanidine was more fibrotic than L-NAME. Our data suggest a significant anti-fibrotic role for iNOS rather than for eNOS. L-Arginine did not show any anti-fibrotic properties in the TAA-model used.

alpha-melanocyte-stimulating hormone gene transfer attenuates inflammation after bile duct ligation in the rat

Cholestasis occurs in a wide variety of human liver diseases, and hepatocellular injury is an invariant feature of cholestasis causing liver dysfunction and inflammation, promoting fibrogenesis, and ultimately leading to liver failure. alpha-Melanocyte-stimulating hormone (alpha-MSH) is a potent anti-inflammatory agent in many models of inflammation, suggesting that it inhibits a critical step common to different forms of inflammation. The aim of this study was to investigate whether the gene transfer of alpha-MSH could attenuate hepatic inflammation after bile duct ligation in the rat. Studies were performed in bile duct-ligated (BDL) rats. Hydrodynamic-based gene transfection with alpha-MSH plasmid via rapid tail vein injection was performed 30 min after ligation of bile duct. The endpoints were studied as markers of inflammation 7 days after bile duct ligation. alpha-MSH expression in liver via a single administration of naked plasmid was demonstrated. Liver inflammation index, including neutrophil infiltration and serum alanine aminotransferase, were significantly reduced in alpha-MSH gene transfer rats. Markers for liver inflammation, including expression of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and inducible NO synthase (iNOS) mRNA, as assessed by real-time PCR, were also attenuated by alpha-MSH gene therapy. Expression of iNOS protein in liver diminished after alpha-MSH gene transfer. Consistent with these data, hepatic stellate cells (HSC) and Kupffer cells were markedly inhibited in alpha-MSH gene-treated rats. Our findings show that gene transfer of alpha-MSH could attenuate hepatic inflammation after bile duct ligation in the rat.

Myostatin preferentially down-regulates the expression of fast 2x myosin heavy chain in cattle

Myostatin is involved in an inhibitor of muscular growth and differentiation. Myoblasts derived from double-muscled Japanese shorthorn cattle (DM myoblasts) with absence of functional myostatin had higher abilities to proliferate and differentiate than myoblasts derived from normal-muscled cattle (NM myoblasts). In DM myoblasts, mRNA expressions of fetal myosin heavy chain (MyHC) in growth medium and of fast 2a and 2x MyHC in fusion medium were significantly greater than that in NM myoblasts. No significant difference existed in expressions of embryonic and slow MyHC mRNA between DM and NM myoblasts. The expression of MyoD mRNA was suppressed in myoblasts by administration of myostatin. Two cloned DM myoblast strains (DMc) were established. Addition of myostatin for DMc resulted in less myotube formation and suppression of mRNA expression of fast 2x MyHC. These findings suggest that the endogenous myostatin preferentially down-regulates the expression of the fast 2x MyHC and participates in differentiation of myofiber types during early bovine myogenesis.

Allopurinol in rat chronic pancreatitis: effects on pancreatic stellate cell activation

OBJECTIVES

Activation of pancreatic stellate cells (PSCs) is a key event in pancreatic fibrosis. Xanthine oxidase-derived free radicals are involved in the mechanism of chronic pancreatitis (CP). We here searched the in vivo effects of allopurinol on PSC activation and its relation to tissue oxidative stress and histological findings in rat CP.

METHODS

Rat CP was induced with intraductal trinitrobenzene sulfonic acid in groups 1 (n = 16) and 2 (n = 10). Group 3 (n = 10) received intraductal saline. Four weeks after induction, group 1 received allopurinol (200 mg/kg, s.c.), and groups 2 and 3 received saline. After 4 weeks, oxidative stress parameters, histological evaluation, and immunostaining for alpha-smooth muscle actin (+) PSCs were performed in the pancreata.

RESULTS

Oxidative stress parameters improved significantly in group 1 compared with groups 2 and 3. Collagen deposition and lobular/sublobular atrophy were significantly lower in group 1 than in group 2. Alpha-smooth muscle actin (+) PSCs counts in group 1 were significantly lower than in group 2, and were in correlation with the degree of fibrosis and atrophy.

CONCLUSIONS

Allopurinol inhibits PSC activation in vivo. Pancreatic fibrosis can be prevented, at least in part, by antioxidant treatment through xanthine oxidase metabolism. Long-term use of allopurinol and its analogs may be considered in clinical trials with CP.

Inhaled NO accelerates restoration of liver function in adults following orthotopic liver transplantation

Ischemia/reperfusion (IR) injury in transplanted livers contributes to organ dysfunction and failure and is characterized in part by loss of NO bioavailability. Inhalation of NO is nontoxic and at high concentrations (80 ppm) inhibits IR injury in extrapulmonary tissues. In this prospective, blinded, placebo-controlled study, we evaluated the hypothesis that administration of inhaled NO (iNO; 80 ppm) to patients undergoing orthotopic liver transplantation inhibits hepatic IR injury, resulting in improved liver function. Patients were randomized to receive either placebo or iNO (n = 10 per group) during the operative period only. When results were adjusted for cold ischemia time and sex, iNO significantly decreased hospital length of stay, and evaluation of serum transaminases (alanine transaminase, aspartate aminotransferase) and coagulation times (prothrombin time, partial thromboplastin time) indicated that iNO improved the rate at which liver function was restored after transplantation. iNO did not significantly affect changes in inflammatory markers in liver tissue 1 hour after reperfusion but significantly lowered hepatocyte apoptosis. Evaluation of circulating NO metabolites indicated that the most likely candidate transducer of extrapulmonary effects of iNO was nitrite. In summary, this study supports the clinical use of iNO as an extrapulmonary therapeutic to improve organ function following transplantation.

Ectopic expression of myostatin induces atrophy of adult skeletal muscle by decreasing muscle gene expression

Myostatin is a master regulator of myogenesis and early postnatal skeletal muscle growth. However, myostatin has been also involved in several forms of muscle wasting in adulthood, suggesting a functional role for myostatin in the regulation of skeletal muscle mass in adult. In the present study, localized ectopic expression of myostatin was achieved by gene electrotransfer of a myostatin expression vector into the tibialis anterior muscle of adult Sprague Dawley male rats. The corresponding empty vector was electrotransfected in contralateral muscle. Ectopic myostatin mRNA was abundantly present in muscles electrotransfected with myostatin expression vector, whereas it was undetectable in contralateral muscles. Overexpression of myostatin elicited a significant decrease in muscle mass (10 and 20% reduction 7 and 14 d after gene electrotransfer, respectively), muscle fiber cross-sectional area (15 and 30% reduction 7 and 14 d after gene electrotransfer, respectively), and muscle protein content (20% reduction). No decrease in fiber number was observed. Overexpression of myostatin markedly decreased the expression of muscle structural genes (myosin heavy chain IIb, troponin I, and desmin) and the expression of myogenic transcription factors (MyoD and myogenin). Incidentally, mRNA level of caveolin-3 and peroxisome proliferator activated receptor gamma coactivator-1alpha was also significantly decreased 14 d after myostatin gene electrotransfer. To conclude, our study demonstrates that myostatin-induced muscle atrophy elicits the down-regulation of muscle-specific gene expression. Our observations support an important role for myostatin in muscle atrophy in physiological and physiopathological situations where myostatin expression is induced.

Inhibitory and enhancing effects of NO on H(2)O(2) toxicity: dependence on the concentrations of NO and H(2)O(2)

Nitric oxide (NO) has been shown to both enhance hydrogen peroxide (H(2)O(2)) toxicity and protect cells against H(2)O(2) toxicity. In order to resolve this apparent contradiction, we here studied the effects of NO on H(2)O(2) toxicity in cultured liver endothelial cells over a wide range of NO and H(2)O(2) concentrations. NO was generated by spermine NONOate (SpNO, 0.001-1 mM), H(2)O(2) was generated continuously by glucose/glucose oxidase (GOD, 20-300 U/l), or added as a bolus (200 microM). SpNO concentrations between 0.01 and 0.1 mM provided protection against H(2)O(2)-induced cell death. SpNO concentrations >0.1 mM were injurious with low H(2)O(2) concentrations, but protective at high H(2)O(2) concentrations. Protection appeared to be mainly due to inhibition of lipid peroxidation, for which SpNO concentrations as low as 0.01 mM were sufficient. SpNO in high concentration (1 mM) consistently raised H(2)O(2) steady-state levels in line with inhibition of H(2)O(2) degradation. Thus, the overall effect of NO on H(2)O(2) toxicity can be switched within the same cellular model, with protection being predominant at low NO and high H(2)O(2) levels and enhancement being predominant with high NO and low H(2)O(2) levels.

Molecular cloning and characterization of the Myf5 gene in sea perch (Lateolabrax japonicus)

The cDNA of myogenic factor (Myf5) was isolated from sea perch (Lateolabrax japonicus) using Reverse-transcription Polymerase Chain Reaction (RT-PCR) and rapid amplification of cDNA ends (RACE). The 5' flanking sequence of the cDNA contains a TATA box, GC box, CAAT box, several E box sites and muscle-specific regulatory elements determined by genome walking. The Myf5 gene consists of 3 exons and 2 introns. The open reading frame was found to code a protein with 238 amino-acid residues, containing the conserved basic helix-loop-helix domain (bHLH). RT-PCR indicated the Myf5 was highly expressed in muscle, and weakly expressed in brain, eyes, spleen, gill, liver, kidney, intestine and heart. In early embryonic stages, Myf5 mRNA transcripts are highly detectable in the early gastrula stage while decreasing up to a low level at the late gastrula stage, subsequently greatly increased up to the highest level in the somites stage, then gradually decreases from the tail-bud stage to 15 d larvae after hatching, but they are still detectable. Further, Myf5 mRNA was expressed in several sea perch cell lines such as LJES1, LJHK, LJH-1, LJH-2, LJS, LJL, although its expression level varied greatly among different cell lines.

Mechanisms of protection by melatonin against acetaminophen-induced liver injury in mice

The present study was performed to determine whether melatonin protects mouse liver against severe damage induced by acetaminophen (APAP) administration and where melatonin primarily functions in the metabolic pathway of APAP to protect mouse liver against APAP-induced injury. Treatment of mice with melatonin (50 or 100 mg/kg, p.o.) 8 or 4 hr before APAP administration (750 mg/kg, p.o.) suppressed the increase in plasma alanine aminotransferase and aspartate aminotransferase activities in a dose- and a time-dependent manner. Melatonin treatment (100 mg/kg, p.o.) 4 hr before APAP administration remarkably inhibited centrilobular hepatic necrosis with inflammatory cell infiltration and increases in hepatic lipid peroxidation and myeloperoxidase activity, an index of tissue neutrophil infiltration, as well as release of nitric oxide and interleukin-6 into blood circulation at 9 hr after APAP administration. However, melatonin neither affected hepatic reduced glutathione (GSH) content nor spared hepatic GSH consumption by APAP treatment. Moreover, pretreatment with melatonin 4 hr before APAP administration did not influence the induction of hepatic heat shock protein 70 (HSP70) by APAP and melatonin alone did not induce HSP70 in mouse liver. These results indicate that exogenously administered melatonin exhibits a potent hepatoprotective effect against APAP-induced hepatic damage probably downstream of the activity of cytochrome P450 2E1, which works upstream of GSH conjugation in the pathway of APAP metabolism, via its anti-nitrosative and anti-inflammatory activities in addition to its antioxidant activity.

Multifunctional roles of MT1-MMP in myofiber formation and morphostatic maintenance of skeletal muscle

Sequential activation of muscle-specific transcription factors is the critical basis for myogenic differentiation. However, the complexity of this process does not exclude the possibility that other molecules and systems are regulatory as well. We observed that myogenic differentiation proceeded through three distinct stages of proliferation, elongation and fusion, which are distinguishable by their cellular morphologies and gene expression patterns of proliferation- and differentiation-specific markers. Treatment of the differentiating myoblasts with inhibitors of matrix metalloproteinases (MMPs) revealed that MMP activity at the elongation stage is a critical prerequisite to complete the successive myoblast cell fusion. The MMP regulated the myogenic differentiation independently from the genetic program that governs expression of the myogenic genes. Membrane-type 1 matrix metalloproteinase (MT1-MMP) was identified as a major contributor to this checkpoint for morphological differentiation and degraded fibronectin, a possible inhibitory factor for myogenic cell fusion. A MT1-MMP deficiency caused similar myogenic impediments forming smaller myofibers in situ. Additionally, the mutant mice demonstrated some central nucleation of the myofibers typically found in muscular dystrophy and MT1-MMP was found to cleave laminin-2/4 in the basement membrane. Thus, MT1-MMP is a new multilateral regulator for muscle differentiation and maintenance through processing of stage-specific distinct ECM substrates.

Heart failure alters MyoD and MRF4 expressions in rat skeletal muscle

Heart failure (HF) is characterized by a skeletal muscle myopathy with increased expression of fast myosin heavy chains (MHCs). The skeletal muscle-specific molecular regulatory mechanisms controlling MHC expression during HF have not been described. Myogenic regulatory factors (MRFs), a family of transcriptional factors that control the expression of several skeletal muscle-specific genes, may be related to these alterations. This investigation was undertaken in order to examine potential relationships between MRF mRNA expression and MHC protein isoforms in Wistar rat skeletal muscle with monocrotaline-induced HF. We studied soleus (Sol) and extensor digitorum longus (EDL) muscles from both HF and control Wistar rats. MyoD, myogenin and MRF4 contents were determined using reverse transcription-polymerase chain reaction while MHC isoforms were separated using polyacrylamide gel electrophoresis. Despite no change in MHC composition of Wistar rat skeletal muscles with HF, the mRNA relative expression of MyoD in Sol and EDL muscles and that of MRF4 in Sol muscle were significantly reduced, whereas myogenin was not changed in both muscles. This down-regulation in the mRNA relative expression of MRF4 in Sol was associated with atrophy in response to HF while these alterations were not present in EDL muscle. Taken together, our results show a potential role for MRFs in skeletal muscle myopathy during HF.

MyoD, Myf5, and the calcineurin pathway activate the developmental myosin heavy chain genes

Myogenesis is accompanied by the activation of two developmental myosin heavy chains (MyHCs), embryonic and perinatal, followed by a dramatic decrease in their expression during early postnatal life. The pathways that control the transcription of these genes have not been previously determined. In this study, we identified cis-acting elements and trans-acting factors that regulate the expression of these two developmental MyHCs in the mouse. Between 800 and 1000 bp of proximal promoter sequence is sufficient to drive muscle-specific expression in cell culture. Further, these same regions contain sequences that confer downregulation in postnatal life in vivo. For the embryonic MyHC gene, the region between -791 bp and -626 bp contains the majority of activating elements. In the proximal promoter regions of both genes, we identified two E-box elements that work in conjunction to activate transcription, but only the embryonic MyHC E-boxes bind a complex containing MyoD. In addition, our results reveal activation by calcineurin that is transduced only partially by its conventional downstream effectors, MEF2 and NFAT. Some common features are shared between the promoters of these two genes; however, the mechanisms of their regulation appear distinct.

Blockade of the receptor for advanced glycation end products attenuates acetaminophen-induced hepatotoxicity in mice

BACKGROUND AND AIM

Severe injury to the liver, such as that induced by toxic doses of acetaminophen, triggers a cascade of events leading to hepatocyte death. It is hypothesized that activation of the receptor for advanced glycation end products (RAGE) might contribute to acetaminophen-induced liver toxicity by virtue of its ability to generate reactive oxygen species, at least in part via nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, and thereby activate downstream signaling pathways leading to cellular injury.

METHODS

A model was employed in which toxic doses of acetaminophen (1125 mg/kg) were administered to C57BL/6 mice. To block RAGE, mice received murine soluble (s) RAGE, the extracellular ligand binding domain of the receptor that acts as a decoy to interrupt ligand-RAGE signaling.

RESULTS

Animals treated with sRAGE displayed increased survival compared with vehicle treatment, and markedly decreased hepatic necrosis. Consistent with an important role for RAGE-triggered oxidant stress in acetaminophen-induced injury, a significant reduction of nitrotyrosine protein adducts was observed in hepatic tissue in sRAGE-treated versus vehicle-treated mice receiving acetaminophen, in parallel with significantly increased levels of glutathione. In addition, pro-regenerative cytokines tumor necrosis factor-alpha and interleukin-6 were increased in sRAGE-treated versus vehicle-treated mice.

CONCLUSION

These findings implicate RAGE-dependent mechanisms in acetaminophen-induced liver damage and suggest that blockade of this pathway may impart beneficial effects in toxin-induced liver injury.

Cachexia: pathophysiology and clinical relevance

Cachexia causes weight loss and increased mortality. It affects more than 5 million persons in the United States. Other causes of weight loss include anorexia, sarcopenia, and dehydration. The pathophysiology of cachexia is reviewed in this article. The major cause appears to be cytokine excess. Other potential mediators include testosterone and insulin-like growth factor I deficiency, excess myostatin, and excess glucocorticoids. Numerous diseases can result in cachexia, each by a slightly different mechanism. Both nutritional support and orexigenic agents play a role in the management of cachexia.

Pathophysiological basis for antioxidant therapy in chronic liver disease

Oxidative stress is a common pathogenetic mechanism contributing to initiation and progression of hepatic damage in a variety of liver disorders. Cell damage occurs when there is an excess of reactive species derived from oxygen and nitrogen, or a defect of antioxidant molecules. Experimental research on the delicately regulated molecular strategies whereby cells control the balance between oxidant and antioxidant molecules has progressed in recent years. On the basis of this evidence, antioxidants represent a logical therapeutic strategy for the treatment of chronic liver disease. Clinical studies with large numbers of patients have not yet been performed. However, results from several pilot trials support this concept and indicate that it may be worth performing multicentre studies, particularly combining antioxidants with anti-inflammatory and/or antiviral therapy. Oxidative stress plays a pathogenetic role in liver diseases such as alcoholic liver disease, chronic viral hepatitis, autoimmune liver diseases and non-alcoholic steatohepatitis. The use of antioxidants (e.g. S-adenosylmethionine [SAMe; ademetionine], tocopherol [vitamin E], polyenylphosphatidylcholine or silymarin) has already shown promising results in some of these pathologies.

Molecular and cellular defects of skeletal muscle in an animal model of acute quadriplegic myopathy

Muscle denervation and concomitant high-dose dexamethasone treatment in rodents produces characteristic pathologic features of severe muscle atrophy and selective myosin heavy filament (MyHC) depletion, identical to those seen in acute quadriplegic myopathy (AQM), also known as critical illness myopathy. We tested the hypothesis that defective pre-translational processes contribute to the atrophy and selective MyHC depletion in this model. We examined the effects of combined glucocorticoid-denervation treatment on MyHC and actin mRNA populations; we also studied mRNA expression of the myogenic regulatory factors (MRFs), primary transcription factors for MyHC. Adult female rats were subjected to proximal sciatic denervation followed by high-dose dexamethasone (DD) treatment (5 mg/kg body weight daily) for 7 days. Disease controls included rats treated with denervation alone (DN) or dexamethasone alone (DX). At 1 week the plantaris atrophied by approximately 42% in DD muscles. DD treatment resulted in selective MyHC protein depletion; actin protein concentration was not significantly changed. Despite an increase in total RNA concentration in DN and DD muscles, MyHC and actin mRNA concentrations were significantly decreased in these muscles. MyHC mRNA showed a significantly more extensive depletion relative to actin mRNA in DD muscles. Glucocorticoid treatment did not influence a denervation-induced increase in the mRNA expression of the MRFs. We conclude that a deleterious interaction between glucocorticoid and denervation treatments in skeletal muscle is responsible for pre-translational defects that reduce actin and MyHC mRNA substrates in a disproportionate fashion. The resultant selective MyHC depletion contributes to the severe muscle atrophy.

Protective Effects of Broccoli (Brassica oleracea) against Oxidative Damage in Vitro and in Vivo

The antioxidative effect and protective potential against diabetes of the broccoli flower were investigated both in vitro and in a diabetic rat model. Among fractions of MeOH, CH2Cl2, BuOH, and H2O, the BuOH fraction exerted the strongest inhibitory activities on 1,1-diphenyl-2-picrylhydrazyl radical, radical-induced protein oxidation, and nitric oxide generation by sodium nitroprusside. The in vitro results suggest that the BuOH fraction from the broccoli flower has a protective potential against oxidative stress. The rat model with diabetes induced by streptozotocin was employed to evaluate the protective effect of the BuOH fraction in vivo. Diabetic rats showed reduced body weight gain and heavier kidney and liver weights than normal rats, while oral administration of the BuOH fraction at an oral dose of 100 or 200 mg/kg body weight/d for 20 d attenuated the physiological changes induced by diabetes. In addition, oral administration of the BuOH fraction to diabetic rats led to significant decreases in serum glucose and glycosylated protein, while it resulted in the increase of serum albumin, implying that the BuOH fraction improves the abnormal metabolism of glucose and protein that leads to oxidative stress. Moreover, it significantly reduced thiobarbituric acid-reactive substance levels in serum, hepatic and renal mitochondria. This suggests that the BuOH fraction would alleviate the oxidative stress associated with diabetes through the inhibition of lipid peroxidation. The present study demonstrates that the BuOH fraction has an antioxidative effect in vitro and it protects against oxidative stress induced by diabetes in an in vivo model.

Nitric oxide synthase inhibition in sepsis? Lessons learned from large-animal studies

Nitric Oxide (NO) plays a controversial role in the pathophysiology of sepsis and septic shock. Its vasodilatory effects are well known, but it also has pro- and antiinflammatory properties, assumes crucial importance in antimicrobial host defense, may act as an oxidant as well as an antioxidant, and is said to be a "vital poison" for the immune and inflammatory network. Large amounts of NO and peroxynitrite are responsible for hypotension, vasoplegia, cellular suffocation, apoptosis, lactic acidosis, and ultimately multiorgan failure. Therefore, NO synthase (NOS) inhibitors were developed to reverse the deleterious effects of NO. Studies using these compounds have not met with uniform success however, and a trial using the nonselective NOS inhibitor N(G)-methyl-l-arginine hydrochloride was terminated prematurely because of increased mortality in the treatment arm despite improved shock resolution. Thus, the issue of NOS inhibition in sepsis remains a matter of debate. Several publications have emphasized the differences concerning clinical applicability of data obtained from unresuscitated, hypodynamic rodent models using a pretreatment approach versus resuscitated, hyperdynamic models in high-order species using posttreatment approaches. Therefore, the present review focuses on clinically relevant large-animal studies of endotoxin or living bacteria-induced, hyperdynamic models of sepsis that integrate standard day-to-day care resuscitative measures.

Response of the ubiquitin-proteasome pathway to changes in muscle activity

The ubiquitin-proteasome pathway plays a critical role in the adaptation of skeletal muscle to persistent decreases or increases in muscle activity. This article outlines the basics of pathway function and reviews what we know about pathway responses to altered muscle use. The ubiquitin-proteasome pathway regulates proteolysis in mammalian cells by attaching ubiquitin polymers to damaged proteins; this targets the protein for degradation via the 26S proteasome. The pathway is constitutively active in muscle and continually regulates protein turnover. Conditions of decreased muscle use, e.g., unloading, denervation, or immobilization, stimulate general pathway activity. This activity increase is caused by upregulation of regulatory components in the pathway and leads to accelerated proteolysis, resulting in net loss of muscle protein. Pathway activity is also increased in response to exercise, a two-phase response. An immediate increase in selective ubiquitin conjugation by constitutive pathway components contributes to exercise-stimulated signal transduction. Over hours-to-days, exercise also stimulates a delayed increase in general ubiquitin conjugating activity by inducing expression of key components in the pathway. This increase mediates a late-phase rise in protein degradation that is required for muscle adaptation to exercise. Thus the ubiquitin-proteasome pathway functions as an essential mediator of muscle remodeling, both in atrophic states and exercise training.

Differential regulation of rodent hepatocyte and oval cell proliferation by interferon gamma

Hepatocytes and intrahepatic progenitor cells (oval cells) have similar responses to most growth factors but rarely proliferate together. Oval cells constitute a reserve compartment that is activated when hepatocyte proliferation is inhibited. Interferon gamma (IFN-gamma) increases in liver injury that involves oval cell responses, but it is not upregulated during liver regeneration after partial hepatectomy. Based on these observations, we used well-characterized lines of hepatocytes (AML-12 cells) and oval cells (LE-6 cells) to investigate the potential mechanisms that regulate differential growth responses in hepatocytes and oval cells. We show that IFN-gamma blocks hepatocyte proliferation in vivo, and that in combination with either tumor necrosis factor (TNF) or lipopolysaccharide (LPS), it causes cell cycle arrest in hepatocytes but stimulates oval cell proliferation in cultured cells. The hepatocyte cell cycle arrest is reversible, is p53-independent, and is not associated with apoptosis. Treatment of AML-12 hepatocytes with IFN-gamma/LPS or IFN-gamma/TNF, but not with individual cytokines, induced NO synthase and generated NO, while similarly treated oval cells produced little if any NO. Generation of NO by an NO donor reproduced the inhibitory effect of the cytokine combinations on AML-12 cell replication, while NO inhibitors abolish the replication deficiency. In conclusion, we propose that IFN-gamma, in conjunction with TNF or LPS, can both inhibit hepatocyte proliferation through the generation of NO and stimulate oval cell replication. The response of hepatocytes and oval cells to cytokine combinations may contribute to the differential proliferation of these cells in hepatic growth processes.

Reversibility of caspase activation and its role during glycochenodeoxycholate-induced hepatocyte apoptosis

The accumulation of glycochenodeoxycholate (GCDC) induced hepatocyte apoptosis in cholestasis. However, many hepatocytes still survived GCDC-induced apoptosis. The molecular mechanism for the survival of hepatocytes remains unclear. In the present study, isolated rat hepatocytes were cultured in William's E medium and treated with 50 microM GCDC. DNA, RNA, cell lysate, and nuclear proteins were collected at different intervals for DNA fragmentation assay, reverse transcription PCR, Western blotting, and gel mobility shift assay, respectively. GCDC-induced active caspases were detected as early as 2 h by Western blotting and kinetic caspase assay, whereas hepatocyte apoptosis was found at 4 h by DNA fragmentation and terminal deoxynucleotidyl transferase-mediated dUPT nick-end labeling assay. When GCDC was removed, the increased caspases as well as NF-kappaB could be restored to control level. A1/Bfl-1 and inducible nitric oxide synthase (iNOS) were up-regulated in 2 h of GCDC stimulation. After GCDC was removed, hepatocytes decreased expression of A1/Bfl-1, but not iNOS, to the control level. NF-kappaB activation coincided with the change of A1/Bfl-1. Survivin, cIAP1, cIAP2, XIAP, and A1/Bfl-1, but not iNOS, were down-regulated by pan-caspase inhibitor benzyloxycarbonyl-VAD-fluoromethyl ketone. In addition, benzyloxycarbonyl-VAD-fluoromethyl ketone inhibited release of cytochrome c and suppressed NF-kappaB activation. Our data suggested that caspase pathway is an important regulatory factor during hepatocyte apoptosis. GCDC-induced caspase response is reversible, which may activate anti-apoptotic genes to protect hepatocytes from apoptosis.

Myocyte enhancer factor-2 and serum response factor binding elements regulate fast Myosin heavy chain transcription in vivo

Adult fast muscle fibers express distinct myosin heavy chains (MyHC) in differing proportions, but the mechanisms underlying their differential expression remain undefined. We used a variety of in vitro and in vivo approaches to explore the contribution of transcriptional regulation to adult fast MyHC expression. Here we show that 800-1000 bp of a sequence upstream of the three mouse adult fast MyHC genes (Ia, IIb, and IId/x) are sufficient to drive muscle-specific and fiber-specific expression in vivo. We show that the upstream promoter region of the gene most abundantly expressed in mouse skeletal muscles, IIb MyHC, retains binding activity and transcriptional activation for three positive transcription factors, the serum response factor, Oct-1, and myocyte enhancer factor-2, whereas the other two genes (IIa and IId/x) have nucleotide substitutions in these sites that reduce binding and transcriptional activation. Finally, we demonstrate that regions upstream of 300 bp modulate the effects of these elements. Together, these data demonstrate that the quantitative differences in MyHC expression in mouse skeletal muscle have evolved at least in part through the elimination of positive-acting transcription factor binding sites.

Structure and function of the upstream promotor of the humanMafbx gene: The proximal upstream promotor modulates tissue-specificity

Muscle loss has been linked to increased expression of an ubiquitin ligase termed muscle atrophy F-box (MAFbx), a nuclear protein involved in degradation of MyoD. To gain insights into mechanisms by which the human MAFbx gene is controlled, the structure of its upstream promotor were studied, and its expression in cultured cells was characterized. Expression of MAFbx was found only in cells of muscle lineage. A reporter gene controlled by 948 bases of human MAFbx upstream promotor displayed similar cell-type selectivity. MAFbx levels were greatly enhanced upon myogenic differentiation of C2C12 myoblasts, and differentiation markedly increased activity of a reporter gene constructed with 400 bp of upstream promotor from the MAFbx gene. The core promotor spanned approximately 160 bases beginning at -241 bp upstream of the first codon, included potential binding sites for MyoD and myogenin, and was highly conserved among mouse, rat, and humanMAFbx genes. The major transcription start site for the human MAFbx gene was 340 bases upstream of the ATG and was localized the highly conserved region of 140 bp. The findings indicate an important role for the immediate upstream promotor of the human MAFbx gene in mediating its developmental expression and tissue specificity.

Activity-unrelated neural control of myogenic factors in a slow muscle

The properties of skeletal muscles are modulated by neural and nonneural factors, and the neural factors can be modulated by activity-independent as well as activity-dependent mechanisms. Given that daily activation of fast muscles is considerably less than of slow muscles, we hypothesized that the myogenic properties of the rat soleus (a slow muscle) would be more dependent on activity-dependent than activity-independent factors. Muscle mass, MyoD, and myogenin mRNA and protein levels, and satellite cell proliferation and differentiation rates (bromodeoxyuridine incorporation) were examined at 3, 14, and 28 days after either spinal cord isolation (SI, neuromuscular connectivity intact with minimal activation) or denervation (no neural influence). Soleus atrophy was similar in the SI and denervated groups at each time point, although increases in whole-muscle expression of myogenin and, to a lesser degree, MyoD were lower (P < 0.05) in SI than denervated soleus muscles. Proliferation and differentiation of satellite cells, as well as mitotic activity of connective tissue cells, were lower (P < 0.05) in SI than denervated soleus muscles. In some instances, these changes were not observed until the later time points, i.e., 14 or 28 days. These results demonstrate that the motoneurons that innervate the slow soleus muscle have a significant modulatory influence on some muscle properties via mechanisms that are independent of activation. These activity-independent modulatory influences, however, are less in the slow soleus than previously observed in fast muscles.

Ectopic Expression of p73α, but Not p73β, Suppresses Myogenic Differentiation

The TRP73 gene, a member of the p53 family, encodes several variants through differential splicing and use of alternative promoters. At the N terminus, two different promoters generate the full-length and the DeltaN isoforms, with or without the transactivating domain. At the C terminus, seven isoforms generated through alternative splicing have been cloned. Previous studies have demonstrated that DeltaN-p73 interferes with p73-induced apoptosis. However, there has been no evidence for functional diversity of the C-terminal p73 variants. In this study, we found that p73alpha and p73beta exerted differential effect on the differentiation of C2C12 myoblasts. Although p73beta lacked any detectable effect on differentiation, p73alpha caused a substantial delay in the expression of muscle-specific genes. In co-transfection experiments p73alpha, but not p73beta, attenuated the transcriptional activity of MyoD. Microarray-based gene profiling confirmed the protraction of MyoD-dependent gene expression in C2C12 cells stably expressing p73alpha. Notwithstanding the differential effect on differentiation, p73alpha and p73beta showed similar activity in sensitizing C2C12 myoblasts to cisplatin-induced cell death. These results demonstrated a functional diversity between the two C-terminal variants of p73 and suggested that p73alpha can regulate cellular differentiation in addition to its role in stimulating cell death.

Enhanced inducible nitric oxide synthase expression and nitrotyrosine accumulation in experimental granulomatous hepatitis caused by Toxocara canis in mice

The involvement of inducible nitric oxide synthase (iNOS) and nitrotyrosine (NT) in pathogenesis of toxocaral granulomatous hepatitis (TGH) in a murine host was quantitatively determined by biochemical, parasitological, pathological, and immunohistochemical assessments in a 42-week investigation. Mice were sacrificed for serum collection and histological processing as well as acid-pepsin digestion of the liver in a larval recovery study. Significantly increased levels of total serum NO were found in the trial, indirectly suggesting iNOS activation in the liver. iNOS reactivity was predominantly observed in infiltrating leucocytes in lesions and normal and apocrine-like cholangiocytes; in contrast, hepatocytes and multinucleated giant cells showed negative cytoplasmic staining in TGH. Strong iNOS-like reactivity was also detected on the body wall of larvae. The locations of NT reactivity were nearly identical to those of iNOS expression; infiltrating leucocytes or cholangiocytes stained for iNOS were also stained for NT in TGH. Enhanced iNOS expression, but not invading larvae (r = 0.256, P = 0.211), seemed to play a certain role in pathological damage in TGH due to a significant correlation between iNOS expression and serum alanine aminotransferase (ALT) levels (r =0.593, P = 0.021) in the trial. Our present results indicate a potential therapeutic strategy for treatment of GH caused by other nematodes through manipulation of iNOS expression.

Effect of unloading on type I myosin heavy chain gene regulation in rat soleus muscle

Slow-twitch soleus, a weight-bearing hindlimb muscle, predominantly expresses the type I myosin heavy chain (MHC) isoform. However, under unloading conditions, a transition in MHC expression occurs from slow type I toward the fast-type isoforms. Transcriptional processes are believed to be involved in this adaptation. To test the hypothesis that the downregulation of MHC1 in soleus muscle following unloading is controlled through cis element(s) in the proximal region of the promoter, the MHC1 promoter was injected into soleus muscles of control rats and those subjected to 7 days of hindlimb suspension. Mutation analyses of six putative regulatory elements within the -408-bp region demonstrated that three elements, an A/T-rich, the proximal muscle-type CAT (betae3), and an E-box (-63 bp), play an important role in the basal level of MHC1 gene activity in the control soleus and function as unloading-responsive elements. Gel mobility shift assays revealed a diminished level of complex formation of the betae3 and E-box probes with nuclear extract from hindlimb suspension soleus compared with control soleus. Supershift assays indicated that transcriptional enhancer factor 1 and myogenin factors bind the betae3 and E-box elements, respectively, in the control soleus. Western blots showed that the relative concentrations of the transcriptional enhancer factor 1 and myogenin factors were significantly attenuated in the unloaded soleus compared with the control muscle. We conclude that the downregulation of MHC1 in response to unloading is due, in part, to a significant decrease in the concentration of these transcription factors available for binding the positive regulatory elements.

Nitric oxide attenuates ischaemia-reperfusion (I/R) injury in the diabetic liver

BACKGROUND

Liver ischaemia-reperfusion (I/R) occurs during resuscitation from haemorrhagic shock, hepatic transplantation and anatomic resection of the liver. This injury is associated with hepatocellular enzyme release and hepatocyte necrosis. The impact of chronic illnesses such as diabetes mellitus (DM) on hepatic I/R is unknown. This study determines the effect of DM on liver I/R using a murine model of type II DM in which the leptin receptor is defective. Preliminary studies suggest that animal models of DM have impaired endothelial nitric oxide (NO) release. Other studies suggest that NO attenuates hepatic I/R in phenotypically normal animals. We postulated that DM exacerbates hepatic I/R and that exogenous NO administration will attenuate hepatocellular injury.

METHODS

Non-diabetic and diabetic (db/db) mice were anaesthetized and underwent laparotomy with the placement of a microvascular clip on the hepatic artery and portal vein supplying the medial and left lateral lobes of the liver rendering about 70% of the liver ischaemic. Hepatic ischaemia was maintained for 45 min after which time the clip was removed and the liver segments reperfused. The abdomen was closed and the animals maintained for 5 h of reperfusion. Hepatic injury was then assessed by measuring serum alanine and aspartate transaminases (ALT, AST) spectrophotometrically. Sections of liver reperfused for 24 h were stained with haematoxylin and eosin and the percentage of hepatocyte necrosis evaluated using morphometric techniques. Other animals undergoing hepatic I/R received the NO donor (DETA 100 micro g/kg, i.v. 5 min prior to reperfusion). Time-matched, sham-operated animals served as controls. The data are expressed as mean +/- SEM and analysed by ANOVA.

RESULTS

Serum AST and ALT levels were significantly higher in db/db animals vs. non-diabetics, even in the absence of hepatic I/R (P < 0.01). Serum AST and ALT levels in db/db mice undergoing hepatic I/R were nearly five times greater than that of non-diabetic animals (P < 0.01). Histologic examination of the livers of the diabetic animals undergoing I/R demonstrated significantly greater hepatocellular necrosis (zone III; 30-40%) when compared with non-diabetic animals sustaining the same injury (zone III; 3-10%). The NO donor DETA totally prevented the increase in serum ALT and AST release associated with I/R in both the diabetic and non-diabetic mice when compared with animals not receiving this agent (P < 0.01).

CONCLUSION

This is the first study suggesting that DM exacerbates hepatic I/R and that NO donors will prevent this hepatocellular injury in the diabetic. Sixteen million Americans have DM. Understanding the effect of this chronic illness on the inflammatory response to injury is essential to improving clinical outcomes in these medically compromised patients.

Cancer cachexia is regulated by selective targeting of skeletal muscle gene products

Cachexia is a syndrome characterized by wasting of skeletal muscle and contributes to nearly one-third of all cancer deaths. Cytokines and tumor factors mediate wasting by suppressing muscle gene products, but exactly which products are targeted by these cachectic factors is not well understood. Because of their functional relevance to muscle architecture, such targets are presumed to represent myofibrillar proteins, but whether these proteins are regulated in a general or a selective manner is also unclear. Here we demonstrate, using in vitro and in vivo models of muscle wasting, that cachectic factors are remarkably selective in targeting myosin heavy chain. In myotubes and mouse muscles, TNF-alpha plus IFN-gamma strongly reduced myosin expression through an RNA-dependent mechanism. Likewise, colon-26 tumors in mice caused the selective reduction of this myofibrillar protein, and this reduction correlated with wasting. Under these conditions, however, loss of myosin was associated with the ubiquitin-dependent proteasome pathway, which suggests that mechanisms used to regulate the expression of muscle proteins may be cachectic factor specific. These results shed new light on cancer cachexia by revealing that wasting does not result from a general downregulation of muscle proteins but rather is highly selective as to which proteins are targeted during the wasting state.

Transcription of MyoD and myogenin in the non-contractile electrogenic cells of the weakly electric fish, Sternopygus macrurus

The MyoD family of basic helix-loop-helix (bHLH) myogenic regulatory factors (MRFs) are transcriptional activators of skeletal muscle gene expression and are pivotal in inducing the full myogenic program. The expression of these factors after muscle differentiation is complete and the mechanism by which they modulate (or maintain) the muscle phenotype is less well understood. The myogenically derived electric organ (EO) of the electric fish Sternopygus macrurus is an excellent model to address this question. The electrocytes, i.e., the electrogenic cells of the EO, are not contractile but they do retain some muscle proteins. In order to examine the molecular regulatory pathways that control the muscle-to-electrocyte cell conversion, we have cloned the MyoD and myogenin cDNAs from S. macrurus. Clustal-based alignments showed that the functional domains observed in mammalian MyoD and myogenin are highly conserved in these MRF homologs. Expression analyses revealed that mature electrocytes, which retain the muscle proteins dystrophin, desmin, acetylcholine receptors (AChRs), alpha-actin, and alpha-actinin, also transcribe the MyoD and myogenin genes. RT-PCR studies confirmed that expression of these MRFs is confined to the myogenic lineage. Surprisingly, the levels of MyoD and myogenin transcripts in skeletal muscle and EO could not be used to predict the level to which a cell manifests the muscle program. We conclude that expression of multiple MRFs is not sufficient to induce non-contractile cells to fully express the skeletal muscle program. These data also suggest that the MRF transcriptional program in S. macrurus may be distinct from MRF-dependent myogenesis in other vertebrate systems.

The Effect of the β2-Adrenoceptor Agonist Prodrug BRL-47672 on Cardiovascular Function, Skeletal Muscle Myosin Heavy Chain, and MyoD Expression in the Rat

The intracellular mechanisms that regulate changes in postnatal myosin heavy chain (MHC) expression are not well established. The major objective of this study was to examine the acute and chronic effects of administration of BRL-47672, the prodrug of the beta2-adrenoceptor agonist clenbuterol on MHC and MyoD transcription factor expression to determine whether or not changes in MHC composition are preceded by changes in MyoD protein expression. To assess to what extent the use of BRL-47672 minimized cardiovascular effects, its hemodynamic actions were compared with those of clenbuterol. The effect of BRL-47672 on heart rate, mean arterial blood pressure, and hindquarters vascular conductance was significantly less than that of clenbuterol after a single i.p. injection (250 microg kg(-1) body mass). In the main study, 4-week old rats were given BRL-47672 (900 microg kg(-1) body mass) or an equivalent volume of saline (control) daily for 1, 28, or 56 days. Soleus muscle (SOL) was excised and MHC and MyoD expression analyzed. After 4 weeks, SOL from the BRL-47672-treated animals had significantly faster MHC composition (49 +/- 2% MHCIIA) compared with those from the control animal (39 +/- 3% MHCIIA, P <0.05). MyoD expression increased by 40% after 1 day of BRL-47672 administration (P <0.05) before a change in MHC composition. In conclusion, these data suggest that increased expression of fast-type MHCIIA expression in rat SOL induced by BRL-47672 administration is preceded by changes in the level of MyoD transcription factor expression.

Hepatotoxicity and mechanism of action of haloalkanes: carbon tetrachloride as a toxicological model

The use of many halogenated alkanes such as carbon tetrachloride (CCl4), chloroform (CHCl3) or iodoform (CHI3), has been banned or severely restricted because of their distinct toxicity. Yet CCl4 continues to provide an important service today as a model substance to elucidate the mechanisms of action of hepatotoxic effects such as fatty degeneration, fibrosis, hepatocellular death, and carcinogenicity. In a matter of dose,exposure time, presence of potentiating agents, or age of the affected organism, regeneration can take place and lead to full recovery from liver damage. CCl4 is activated by cytochrome (CYP)2E1, CYP2B1 or CYP2B2, and possibly CYP3A, to form the trichloromethyl radical, CCl3*. This radical can bind to cellular molecules (nucleic acid, protein, lipid), impairing crucial cellular processes such as lipid metabolism, with the potential outcome of fatty degeneration (steatosis). Adduct formation between CCl3* and DNA is thought to function as initiator of hepatic cancer. This radical can also react with oxygen to form the trichloromethylperoxy radical CCl3OO*, a highly reactive species. CCl3OO* initiates the chain reaction of lipid peroxidation, which attacks and destroys polyunsaturated fatty acids, in particular those associated with phospholipids. This affects the permeabilities of mitochondrial, endoplasmic reticulum, and plasma membranes, resulting in the loss of cellular calcium sequestration and homeostasis, which can contribute heavily to subsequent cell damage. Among the degradation products of fatty acids are reactive aldehydes, especially 4-hydroxynonenal, which bind easily to functional groups of proteins and inhibit important enzyme activities. CCl4 intoxication also leads to hypomethylation of cellular components; in the case of RNA the outcome is thought to be inhibition of protein synthesis, in the case of phospholipids it plays a role in the inhibition of lipoprotein secretion. None of these processes per se is considered the ultimate cause of CCl4-induced cell death; it is by cooperation that they achieve a fatal outcome, provided the toxicant acts in a high single dose, or over longer periods of time at low doses. At the molecular level CCl4 activates tumor necrosis factor (TNF)alpha, nitric oxide (NO), and transforming growth factors (TGF)-alpha and -beta in the cell, processes that appear to direct the cell primarily toward (self-)destruction or fibrosis. TNFalpha pushes toward apoptosis, whereas the TGFs appear to direct toward fibrosis. Interleukin (IL)-6, although induced by TNFalpha, has a clearly antiapoptotic effect, and IL-10 also counteracts TNFalpha action. Thus, both interleukins have the potential to initiate recovery of the CCl4-damaged hepatocyte. Several of the above-mentioned toxication processes can be specifically interrupted with the use of antioxidants and mitogens, respectively, by restoring cellular methylation, or by preserving calcium sequestration. Chemicals that induce cytochromes that metabolize CCl4, or delay tissue regeneration when co-administered with CCl4 will potentiate its toxicity thoroughly, while appropriate CYP450 inhibitors will alleviate much of the toxicity. Oxygen partial pressure can also direct the course of CCl4 hepatotoxicity. Pressures between 5 and 35 mmHg favor lipid peroxidation, whereas absence of oxygen, as well as a partial pressure above 100 mmHg, both prevent lipid peroxidation entirely. Consequently, the location of CCl4-induced damage mirrors the oxygen gradient across the liver lobule. Mixed halogenated methanes and ethanes, found as so-called disinfection byproducts at low concentration in drinking water, elicit symptoms of toxicity very similar to carbon tetrachloride, including carcinogenicity.

Molecular analysis of fiber type-specific expression of murine myostatin promoter

Myostatin is a negative regulator of muscle growth, and absence of the functional myostatin protein leads to the heavy muscle phenotype in both mouse and cattle. Although the role of myostatin in controlling muscle mass is established, little is known of the mechanisms regulating the expression of the myostatin gene. In this study, we have characterized the murine myostatin promoter in vivo. Various constructs of the murine myostatin promoter were injected into the quadriceps muscle of mice, and the reporter luciferase activity was analyzed. The results indicate that of the seven E-boxes present in the 2.5-kb fragment of the murine myostatin promoter, the E5 E-box plays an important role in the regulation of promoter activity in vivo. Furthermore, the in vitro studies demonstrated that MyoD preferentially binds and upregulates the murine myostatin promoter activity. We also analyzed the activity of the bovine and murine promoters in murine skeletal muscle and showed that, despite displaying comparable levels of activity in murine myoblast cultures, bovine myostatin promoter activity is much weaker than murine myostatin promoter in mice. Finally, we demonstrate that in vivo, the 2.5-kb region of the murine myostatin promoter is sufficient to drive the activity of the reporter gene in a fiber type-specific manner.

Oxidative stress impairs skeletal muscle repair in diabetic rats

Alongside increased proteolysis, the inability to repair damaged skeletal muscle is a characteristic feature of uncontrolled diabetes. This study evaluates the role of oxidative stress in muscle-specific gene regulatory regions and myosin chain synthesis in streptozotocin (STZ)-induced diabetic and ZDF rats. In the gastrocnemius muscle of diabetic rats, prooxidant compounds were seen to increase while antioxidant levels fell. Myogenic regulatory factors--Myo, myogenin, and Jun D--were also reduced, and muscle enhancer factor (MEF)-1 DNA binding activity was impaired. Moreover, synthesis of muscle creatine kinase and both heavy and light chains of myosin were impaired, suggesting that oxidative stress triggers the cascade of events that leads to impaired muscle repair. Dehydroepiandrosterone has been reported to possess antioxidant properties. When it was administered to diabetic rats, in addition to an improved oxidative imbalance there was a recovery of myogenic factors, MEF-1 DNA binding activity, synthesis of muscle creatine kinase, and myosin light and heavy chains. Vitamin E administration to STZ-induced diabetic rats reverses oxidative imbalance and improves muscle gene transcription, reinforcing the suggestion that oxidative stress may play a role in diabetes-related impaired muscle repair.

Vasodilator mRNA levels are increased in the livers of portal hypertensive NO-synthase 3-deficient mice

BACKGROUND/AIMS

Nitric oxide synthase (NOS) 3-deficient (NOS-3 KO) mice have an increased systemic arterial pressure but develop portal hypertension to the same extent as wildtype (WT) mice. We hypothesized that other vasodilators in the portal circulation compensate for the lack in NOS-3 activity. We used quantitative PCR as a screening method to identify mediators that possibly compensate for NOS-3 in NOS-3 KO mice.

METHODS

Mean arterial pressure (MAP) and portal venous pressure (PVP) were measured in the anaesthetized animal. mRNA levels in whole liver tissue were determined by quantitative RT-PCR.

RESULTS

NOS-3 KO mice had a significantly higher mean arterial pressure than WT mice, but portal venous pressure did not differ. Bile duct ligation (BDL) induced a drop in MAP and a rise in PVP in both groups. Bile duct ligation induced a significant increase in mRNA levels of the cannabinoid receptor (CB)-1, adrenomedullin and NOS-2 in the liver of NOS-3 KO and WT mice. Nitric oxide synthase-1 and NOS-3 mRNA levels were elevated in BDL WT mice compared with sham-operated WT mice. Higher mRNA levels of CB-1, NOS-1 and the adrenomedullin receptor were found in sham-operated NOS-3 KO mice compared with sham-operated WT mice.

CONCLUSIONS

We used quantitative PCR as a screening method to identify vasodilative mediators that might be involved in the compensation for the lack of NOS-3 activity in NOS-3 KO mice. Elevated mRNA levels in sham-operated NOS-3 KO mice compared with sham-operated WT mice were demonstrated for CB-1, NOS-1 and the adrenomedullin receptor.

In vivo characterisation of the human UCP3 gene minimal promoter in mice tibialis anterior muscles

Transcriptional mechanisms controlling human UCP3 gene expression in skeletal muscle remain poorly understood. Experiments based on plasmid electrotransfer into tibialis anterior muscle of C57/BL6 male mice were set up in order to functionally analyze the hUCP3 gene promoter. These transfection experiments showed that a 6300 bp region upstream of the transcription initiation site was sufficient to mediate maximal promoter activity. Further analyses with a series of 5(')-deleted constructs demonstrated that the hUCP3 gene minimal promoter was located between nucleotides -284 and -40. Furthermore, an essential region was identified between nucleotides -284 and -224. The analysis of this region revealed a putative response element for PPAR located between nucleotides -281 and -269. Finally, mutations of potential cis-acting elements within the hUCP3 minimal promoter showed the presence of two TATA boxes (-198/-194 and -45/-41) required for constitutive UCP3 gene expression. To our knowledge, this is the first time that molecular characterization of the UCP3 promoter has been achieved using an in vivo experimental model.