Physiology - Research Publications
Now showing items 1-12 of 155
Glycine Protects Muscle Cells From Wasting in vitro via mTORC1 Signaling
(FRONTIERS MEDIA SA, 2019-11-13)
Glycine supplementation can protect skeletal muscles of mice from cancer-induced wasting, but the mechanisms underlying this protection are not well-understood. The aim of this study was to determine whether exogenous glycine directly protects skeletal muscle cells from wasting. C2C12 muscle cells were exposed to non-inflammatory catabolic stimuli via two models: serum withdrawal (SF) for 48 h; or incubation in HEPES buffered saline (HBS) for up to 5 h. Cells were supplemented with glycine or equimolar concentrations of L-alanine. SF- and HBS-treated myotubes (with or without L-alanine) were ~20% and ~30% smaller than control myotubes. Glycine-treated myotubes were up to 20% larger (P < 0.01) compared to cells treated with L-alanine in both models of muscle cell atrophy. The mTORC1 inhibitor rapamycin prevented the glycine-stimulated protection of myotube diameter, and glycine-stimulated S6 phosphorylation, suggesting that mTORC1 signaling may be necessary for glycine's protective effects in vitro. Increasing glycine availability may be beneficial for muscle wasting conditions associated with inadequate nutrient intake.
Lentiviral transduction of rat Sertoli cells as a means to modify gene expression.
(Informa UK Limited, 2012-10-01)
Primary cell culture is an established and widely used technique to study Sertoli cell function in vitro. However, the relative difficulty of stably overexpressing or knocking down genes in Sertoli cell culture has limited progress in the field. In this technical report, we present a method to transduce 20 dpp rat Sertoli cell cultures with VSV-G pseudotyped lentiviral based vectors at a high rate (~80%), with stable reporter gene expression. Although high transgene expression is desirable, it was noted that at transduction rates > 60% inter-Sertoli cell tight junction integrity and, hence, Sertoli cell function, were transiently compromised. We envisage that this optimized procedure has the potential to stimulate Sertoli cell research, and motivate the use of Sertoli cells in various cell therapy applications.
Generation of MicroRNA-34 Sponges and Tough Decoys for the Heart: Developments and Challenges
(FRONTIERS MEDIA SA, 2018-09-21)
Heart failure (HF) is a debilitating and deadly chronic disease, with almost 50% of patients with HF dying within 5 years of diagnosis. With limited effective therapies to treat or cure HF, new therapies are greatly needed. microRNAs (miRNAs) are small non-coding RNA molecules that are powerful regulators of gene expression and play a key role in almost every biological process. Disruptions in miRNA gene expression has been functionally linked to numerous diseases, including cardiovascular disease. Molecular tools for manipulating miRNA activity have been developed, and there is evidence from preclinical studies demonstrating the potential of miRNAs to be therapeutic targets for cardiovascular disease. For clinical application, miRNA sponges and tough decoys have been developed for more stable suppression and targeted delivery of the miRNA of choice. The aim of this study was to generate miRNA sponges and tough decoys to target miR-34 in the mouse heart. We present data to show that using both approaches we were unable to get significant knockdown of miR-34 or regulate miR-34 target genes in the heart in vivo. We also review recent applications of this method in the heart and discuss further considerations for optimisation in construct design and testing, and the obstacles to be overcome before they enter the clinic.
Using AAV vectors expressing the beta 2-adrenoceptor or associated G alpha proteins to modulate skeletal muscle mass and muscle fibre size
(NATURE PUBLISHING GROUP, 2016-03-14)
Anabolic β2-adrenoceptor (β2-AR) agonists have been proposed as therapeutics for treating muscle wasting but concerns regarding possible off-target effects have hampered their use. We investigated whether β2-AR-mediated signalling could be modulated in skeletal muscle via gene delivery to the target tissue, thereby avoiding the risks of β2-AR agonists. In mice, intramuscular administration of a recombinant adeno-associated virus-based vector (rAAV vector) expressing the β2-AR increased muscle mass by >20% within 4 weeks. This hypertrophic response was comparable to that of 4 weeks' treatment with the β2-AR agonist formoterol, and was not ablated by mTOR inhibition. Increasing expression of inhibitory (Gαi2) and stimulatory (GαsL) G-protein subunits produced minor atrophic and hypertrophic changes in muscle mass, respectively. Furthermore, Gαi2 over-expression prevented AAV:β2-AR mediated hypertrophy. Introduction of the non-muscle Gαs isoform, GαsXL elicited hypertrophy comparable to that achieved by AAV:β2-AR. Moreover, GαsXL gene delivery was found to be capable of inducing hypertrophy in the muscles of mice lacking functional β1- and β2-ARs. These findings demonstrate that gene therapy-based interventions targeting the β2-AR pathway can promote skeletal muscle hypertrophy independent of ligand administration, and highlight novel methods for potentially modulating muscle mass in settings of disease.
Transduction of Skeletal Muscles with Common Reporter Genes Can Promote Muscle Fiber Degeneration and Inflammation
(PUBLIC LIBRARY SCIENCE, 2012-12-12)
Recombinant adeno-associated viral vectors (rAAV vectors) are promising tools for delivering transgenes to skeletal muscle, in order to study the mechanisms that control the muscle phenotype, and to ameliorate diseases that perturb muscle homeostasis. Many studies have employed rAAV vectors carrying reporter genes encoding for β-galactosidase (β-gal), human placental alkaline phosphatase (hPLAP), and green fluorescent protein (GFP) as experimental controls when studying the effects of manipulating other genes. However, it is not clear to what extent these reporter genes can influence signaling and gene expression signatures in skeletal muscle, which may confound the interpretation of results obtained in experimentally manipulated muscles. Herein, we report a strong pro-inflammatory effect of expressing reporter genes in skeletal muscle. Specifically, we show that the administration of rAAV6:hPLAP vectors to the hind limb muscles of mice is associated with dose- and time-dependent macrophage recruitment, and skeletal muscle damage. Dose-dependent expression of hPLAP also led to marked activity of established pro-inflammatory IL-6/Stat3, TNFα, IKKβ and JNK signaling in lysates obtained from homogenized muscles. These effects were independent of promoter type, as expression cassettes featuring hPLAP under the control of constitutive CMV and muscle-specific CK6 promoters both drove cellular responses when matched for vector dose. Importantly, the administration of rAAV6:GFP vectors did not induce muscle damage or inflammation except at the highest doses we examined, and administration of a transgene-null vector (rAAV6:MCS) did not cause damage or inflammation at any of the doses tested, demonstrating that GFP-expressing, or transgene-null vectors may be more suitable as experimental controls. The studies highlight the importance of considering the potential effects of reporter genes when designing experiments that examine gene manipulation in vivo.
miR-206 Represses Hypertrophy of Myogenic Cells but Not Muscle Fibers via Inhibition of HDAC4
(PUBLIC LIBRARY SCIENCE, 2013-09-02)
microRNAs regulate the development of myogenic progenitors, and the formation of skeletal muscle fibers. However, the role miRNAs play in controlling the growth and adaptation of post-mitotic musculature is less clear. Here, we show that inhibition of the established pro-myogenic regulator miR-206 can promote hypertrophy and increased protein synthesis in post-mitotic cells of the myogenic lineage. We have previously demonstrated that histone deacetylase 4 (HDAC4) is a target of miR-206 in the regulation of myogenic differentiation. We confirmed that inhibition of miR-206 de-repressed HDAC4 accumulation in cultured myotubes. Importantly, inhibition of HDAC4 activity by valproic acid or sodium butyrate prevented hypertrophy of myogenic cells otherwise induced by inhibition of miR-206. To test the significance of miRNA-206 as a regulator of skeletal muscle mass in vivo, we designed recombinant adeno-associated viral vectors (rAAV6 vectors) expressing miR-206, or a miR-206 "sponge," featuring repeats of a validated miR-206 target sequence. We observed that over-expression or inhibition of miR-206 in the muscles of mice decreased or increased endogenous HDAC4 levels respectively, but did not alter muscle mass or myofiber size. We subsequently manipulated miR-206 levels in muscles undergoing follistatin-induced hypertrophy or denervation-induced atrophy (models of muscle adaptation where endogenous miR-206 expression is altered). Vector-mediated manipulation of miR-206 activity in these models of cell growth and wasting did not alter gain or loss of muscle mass respectively. Our data demonstrate that although the miR-206/HDAC4 axis operates in skeletal muscle, the post-natal expression of miR-206 is not a key regulator of basal skeletal muscle mass or specific modes of muscle growth and wasting. These studies support a context-dependent role of miR-206 in regulating hypertrophy that may be dispensable for maintaining or modifying the adult skeletal muscle phenotype--an important consideration in relation to the development of therapeutics designed to manipulate microRNA activity in musculature.
Abnormal Mitochondrial L-Arginine Transport Contributes to the Pathogenesis of Heart Failure and Rexoygenation Injury
(PUBLIC LIBRARY SCIENCE, 2014-08-11)
BACKGROUND: Impaired mitochondrial function is fundamental feature of heart failure (HF) and myocardial ischemia. In addition to the effects of heightened oxidative stress, altered nitric oxide (NO) metabolism, generated by a mitochondrial NO synthase, has also been proposed to impact upon mitochondrial function. However, the mechanism responsible for arginine transport into mitochondria and the effect of HF on such a process is unknown. We therefore aimed to characterize mitochondrial L-arginine transport and to investigate the hypothesis that impaired mitochondrial L-arginine transport plays a key role in the pathogenesis of heart failure and myocardial injury. METHODS AND RESULTS: In mitochondria isolated from failing hearts (sheep rapid pacing model and mouse Mst1 transgenic model) we demonstrated a marked reduction in L-arginine uptake (p<0.05 and p<0.01 respectively) and expression of the principal L-arginine transporter, CAT-1 (p<0.001, p<0.01) compared to controls. This was accompanied by significantly lower NO production and higher 3-nitrotyrosine levels (both p<0.05). The role of mitochondrial L-arginine transport in modulating cardiac stress responses was examined in cardiomyocytes with mitochondrial specific overexpression of CAT-1 (mtCAT1) exposed to hypoxia-reoxygenation stress. mtCAT1 cardiomyocytes had significantly improved mitochondrial membrane potential, respiration and ATP turnover together with significantly decreased reactive oxygen species production and cell death following mitochondrial stress. CONCLUSION: These data provide new insights into the role of L-arginine transport in mitochondrial biology and cardiovascular disease. Augmentation of mitochondrial L-arginine availability may be a novel therapeutic strategy for myocardial disorders involving mitochondrial stress such as heart failure and reperfusion injury.
Silencing of miR-34a Attenuates Cardiac Dysfunction in a Setting of Moderate, but Not Severe, Hypertrophic Cardiomyopathy
(PUBLIC LIBRARY SCIENCE, 2014-02-27)
Therapeutic inhibition of the miR-34 family (miR-34a,-b,-c), or miR-34a alone, have emerged as promising strategies for the treatment of cardiac pathology. However, before advancing these approaches further for potential entry into the clinic, a more comprehensive assessment of the therapeutic potential of inhibiting miR-34a is required for two key reasons. First, miR-34a has ∼40% fewer predicted targets than the miR-34 family. Hence, in cardiac stress settings in which inhibition of miR-34a provides adequate protection, this approach is likely to result in less potential off-target effects. Secondly, silencing of miR-34a alone may be insufficient in settings of established cardiac pathology. We recently demonstrated that inhibition of the miR-34 family, but not miR-34a alone, provided benefit in a chronic model of myocardial infarction. Inhibition of miR-34 also attenuated cardiac remodeling and improved heart function following pressure overload, however, silencing of miR-34a alone was not examined. The aim of this study was to assess whether inhibition of miR-34a could attenuate cardiac remodeling in a mouse model with pre-existing pathological hypertrophy. Mice were subjected to pressure overload via constriction of the transverse aorta for four weeks and echocardiography was performed to confirm left ventricular hypertrophy and systolic dysfunction. After four weeks of pressure overload (before treatment), two distinct groups of animals became apparent: (1) mice with moderate pathology (fractional shortening decreased ∼20%) and (2) mice with severe pathology (fractional shortening decreased ∼37%). Mice were administered locked nucleic acid (LNA)-antimiR-34a or LNA-control with an eight week follow-up. Inhibition of miR-34a in mice with moderate cardiac pathology attenuated atrial enlargement and maintained cardiac function, but had no significant effect on fetal gene expression or cardiac fibrosis. Inhibition of miR-34a in mice with severe pathology provided no therapeutic benefit. Thus, therapies that inhibit miR-34a alone may have limited potential in settings of established cardiac pathology.
Forced expression of muscle specific kinase slows postsynaptic acetylcholine receptor loss in a mouse model of MuSK myasthenia gravis
We investigated the influence of postsynaptic tyrosine kinase signaling in a mouse model of muscle-specific kinase (MuSK) myasthenia gravis (MG). Mice administered repeated daily injections of IgG from MuSK MG patients developed impaired neuromuscular transmission due to progressive loss of acetylcholine receptor (AChR) from the postsynaptic membrane of the neuromuscular junction. In this model, anti-MuSK-positive IgG caused a reduction in motor endplate immunolabeling for phosphorylated Src-Y418 and AChR β-subunit-Y390 before any detectable loss of MuSK or AChR from the endplate. Adeno-associated viral vector (rAAV) encoding MuSK fused to enhanced green fluorescent protein (MuSK-EGFP) was injected into the tibialis anterior muscle to increase MuSK synthesis. When mice were subsequently challenged with 11 daily injections of IgG from MuSK MG patients, endplates expressing MuSK-EGFP retained more MuSK and AChR than endplates of contralateral muscles administered empty vector. Recordings of compound muscle action potentials from myasthenic mice revealed less impairment of neuromuscular transmission in muscles that had been injected with rAAV-MuSK-EGFP than contralateral muscles (empty rAAV controls). In contrast to the effects of MuSK-EGFP, forced expression of rapsyn-EGFP provided no such protection to endplate AChR when mice were subsequently challenged with MuSK MG IgG. In summary, the immediate in vivo effect of MuSK autoantibodies was to suppress MuSK-dependent tyrosine phosphorylation of proteins in the postsynaptic membrane, while increased MuSK synthesis protected endplates against AChR loss. These results support the hypothesis that reduced MuSK kinase signaling initiates the progressive disassembly of the postsynaptic membrane scaffold in this mouse model of MuSK MG.
Functional Deficits in nNOS mu-Deficient Skeletal Muscle: Myopathy in nNOS Knockout Mice
(PUBLIC LIBRARY SCIENCE, 2008-10-13)
Skeletal muscle nNOSmu (neuronal nitric oxide synthase mu) localizes to the sarcolemma through interaction with the dystrophin-associated glycoprotein (DAG) complex, where it synthesizes nitric oxide (NO). Disruption of the DAG complex occurs in dystrophinopathies and sarcoglycanopathies, two genetically distinct classes of muscular dystrophy characterized by progressive loss of muscle mass, muscle weakness and increased fatigability. DAG complex instability leads to mislocalization and downregulation of nNOSmu; but this is thought to play a minor role in disease pathogenesis. This view persists without knowledge of the role of nNOS in skeletal muscle contractile function in vivo and has influenced gene therapy approaches to dystrophinopathy, the majority of which do not restore sarcolemmal nNOSmu. We address this knowledge gap by evaluating skeletal muscle function in nNOS knockout (KN1) mice using an in situ approach, in which the muscle is maintained in its normal physiological environment. nNOS-deficiency caused reductions in skeletal muscle bulk and maximum tetanic force production in male mice only. Furthermore, nNOS-deficient muscles from both male and female mice exhibited increased susceptibility to contraction-induced fatigue. These data suggest that aberrant nNOSmu signaling can negatively impact three important clinical features of dystrophinopathies and sarcoglycanopathies: maintenance of muscle bulk, force generation and fatigability. Our study suggests that restoration of sarcolemmal nNOSmu expression in dystrophic muscles may be more important than previously appreciated and that it should be a feature of any fully effective gene therapy-based intervention.
Site-Specific Glycation and Chemo-enzymatic Antibody Sortagging for the Retargeting of rAAV6 to Inflamed Endothelium
(CELL PRESS, 2019-09-13)
Gene therapy holds great potential for conditions such as cardiovascular disease, including atherosclerosis and also vascular cancers, yet available vectors such as the adeno-associated virus (rAAV) transduce the vasculature poorly. To enable retargeting, a single-chain antibody (scFv) that binds to the vascular cell-adhesion molecule (VCAM-1) overexpressed at areas of endothelial inflammation was site specifically and covalently conjugated to the exterior of rAAV6. To achieve conjugation, the scFv was functionalized with an orthogonal click chemistry group. This conjugation utilized site-specific sortase A methodology, thus preserving scFv binding capacity to VCAM-1. The AAV6 was separately functionalized with 4-azidophenyl glyoxal (APGO) via covalent adducts to arginine residues in the capsid's heparin co-receptor binding region. APGO functionalization removed native tropism, greatly reducing rAAV6-GFP transduction into all cells tested, and the effect was similar to the inhibition seen in the presence of heparin. Utilizing the incorporated functionalizations, the scFv was then covalently conjugated to the exterior of rAAV6 via strain-promoted azide-alkyne cycloaddition (SPAAC). With both the removal of native heparin tropism and the addition of VCAM-1 targeting, rAAV6 transduction of endothelial cells was greatly enhanced compared to control cells. Thus, this novel and modular targeting system could have further application in re-directing AAV6 toward inflamed endothelium for therapeutic use.
Regulation of Tissue Growth by the Mammalian Hippo Signaling Pathway
(FRONTIERS MEDIA SA, 2017-11-24)
The integrative control of diverse biological processes such as proliferation, differentiation, apoptosis and metabolism is essential to maintain cellular and tissue homeostasis. Disruption of these underlie the development of many disease states including cancer and diabetes, as well as many of the complications that arise as a consequence of aging. These biological outputs are governed by many cellular signaling networks that function independently, and in concert, to convert changes in hormonal, mechanical and metabolic stimuli into alterations in gene expression. First identified in Drosophila melanogaster as a powerful mediator of cell division and apoptosis, the Hippo signaling pathway is a highly conserved regulator of mammalian organ size and functional capacity in both healthy and diseased tissues. Recent studies have implicated the pathway as an effector of diverse physiological cues demonstrating an essential role for the Hippo pathway as an integrative component of cellular homeostasis. In this review, we will: (a) outline the critical signaling elements that constitute the mammalian Hippo pathway, and how they function to regulate Hippo pathway-dependent gene expression and tissue growth, (b) discuss evidence that shows this pathway functions as an effector of diverse physiological stimuli and