Muscle Creatine Kinase Promoter Research Articles

A modified mouse model of Friedreich's ataxia with conditional Fxn allele homozygosity delays onset of cardiomyopathy.

Friedreich's ataxia (FA) is an autosomal recessive disorder caused by a deficiency in frataxin (FXN), a mitochondrial protein that plays a critical role in the synthesis of iron-sulfur clusters (Fe-S), vital inorganic cofactors necessary for numerous cellular processes. FA is characterized by progressive ataxia and hypertrophic cardiomyopathy, with cardiac dysfunction as the most common cause of mortality in patients. Commonly used cardiac-specific mouse models of FA use the muscle creatine kinase (MCK) promoter to express Cre recombinase in cardiomyocytes and striated muscle cells in mice with one conditional Fxn allele and one floxed-out/null allele. These mice quickly develop cardiomyopathy that becomes fatal by 9-11 wk of age. Here, we generated a cardiac-specific model with floxed Fxn allele homozygosity (MCK-Fxnflox/flox). MCK-Fxnflox/flox mice were phenotypically normal at 9 wk of age, despite no detectable FXN protein expression. Between 13 and 15 wk of age, these mice began to display progressive cardiomyopathy, including decreased ejection fraction and fractional shortening and increased left ventricular mass. MCK-Fxnflox/flox mice began to lose weight around 16 wk of age, characteristically associated with heart failure in other cardiac-specific FA models. By 18 wk of age, MCK-Fxnflox/flox mice displayed elevated markers of Fe-S deficiency, cardiac stress and injury, and cardiac fibrosis. This modified model reproduced important pathophysiological and biochemical features of FA over a longer timescale than previous cardiac-specific mouse models, offering a larger window for studying potential therapeutics.NEW & NOTEWORTHY Previous cardiac-specific frataxin knockout models exhibit rapid and fatal cardiomyopathy by 9 wk of age. This severe phenotype poses challenges for the design and execution of intervention studies. We introduce an alternative cardiac-specific model, MCK-Fxnflox/flox, with increased longevity and delayed onset of all major phenotypes. These phenotypes develop to the same severity as previous models. Thus, this new model provides the same cardiomyopathy-associated mortality with a larger window for potential studies.

Abstract P1097: Foxk1 Is A Regulator Of Cardiomyocyte Proliferation And Heart Regeneration

While the adult mammalian heart has limited regenerative potential, the neonatal mouse heart has a remarkable regenerative capacity. Our goal focused on defining new factors and mechanisms that could enhance repair and regeneration in the adult mouse heart. FOXK1 is a transcription factor that regulates cell cycle kinetics, myogenic stem cell proliferation and skeletal muscle regeneration. During development, its expression is restricted to progenitors, somites and the heart. However, its role in neonatal heart regeneration is unknown and warrants investigation. Here, we describe a novel role for FOXK1 as a regulator of cardiomyocyte (CM) proliferation and regeneration. Using computational analysis of single nucleus RNAseq datasets of neonatal CMs, we determined that FOXK1 was expressed in CMs. qPCR analysis of P1 hearts from control or Foxk1 null mice demonstrated that the absence of FOXK1 led to the dysregulation of Ccne1 and p21 expression, suggesting that FOXK1 could play a role in cell cycle kinetics in the neonatal heart. Control or Foxk1 null mice were pulsed with EdU which demonstrated that the absence of FOXK1 led to a decrease in CM proliferation in vivo. We then engineered a transgenic mouse model that overexpressed FOXK1 using the muscle creatine kinase ( MCK-Foxk1 ) promoter and isolated and cultured control or MCK-Foxk1 CMs (72 hrs), and determined that overexpression of FOXK1 led to a significant increase in CM proliferation. Furthermore, EdU pulsing studies in adult control or MCK-Foxk1 mice demonstrated a significant increase in EdU incorporation in adult CMs of MCK-Foxk1 unperturbed mice compared to control. We then performed LAD ligation surgeries in control and MCK-Foxk1 adult mice. Echocardiography 2 months following LAD ligations showed a significant increase in both ejection fraction and fractional shortening in MCK-Foxk1 mice compared to controls. Single nucleus RNAseq analysis of control and MCK-Foxk1 adult hearts highlighted two distinct CM populations by UMAP analysis, with the latter demonstrating a higher expression of myoblast proliferative pathways. These results identify FOXK1 as a regulator of CM proliferation and heart regeneration by employing both knockout and transgenic mouse models.

Kcnma1 is involved in mitochondrial homeostasis in diabetes-related skeletal muscle atrophy.

Uncontrolled diabetes causes a catabolic state with multi-organic complications, of which impairment on skeletal muscle contributes to the damaged mobility. Kcnma1 gene encodes the pore-forming α-subunit of Ca2+ - and voltage-gated K+ channels of large conductance (BK channels), and loss-of-function mutations in Kcnma1 are in regards to impaired myogenesis. Herein, we observed a time-course reduction of Kcnma1 expression in the tibialis anterior muscles of leptin receptor-deficient (db/db) diabetic mice. To investigate the role of Kcnma1 in diabetic muscle atrophy, muscle-specific knockdown of Kcnma1 was achieved by mice receiving intravenous injection of adeno-associated virus-9 (AAV9)-encoding shRNA against Kcnma1 under the muscle creatine kinase (MCK) promoter. Impairment on muscle mass and myogenesis were observed in m/m mice with AAV9-shKcnma1 intervention, while this impairment was more obvious in diabetic db/db mice. Simultaneously, damaged mitochondrial dynamics and biogenesis showed much severer in db/db mice with AAV9-shKcnma1 intervention. RNA sequencing revealed the large transcriptomic changes resulted by Kcnma1 knockdown, and changes in mitochondrial homeostasis-related genes were validated. Besides, the artificial alteration of Kcnma1 in mouse C2C12 myoblasts was achieved with an adenovirus vector. Consistent results were demonstrated by Kcnma1 knockdown in palmitate-treated cells, whereas opposite results were exhibited by Kcnma1 overexpression. Collectively, we document Kcnma1 as a potential keeper of mitochondrial homeostasis, and the loss of Kcnma1 is a critical event in priming skeletal muscle loss in diabetes.

Skeletal muscle-specific overexpression of miR-486 limits mammary tumor-induced skeletal muscle functional limitations

miR-486 is a myogenic microRNA, and its reduced skeletal muscle expression is observed in muscular dystrophy. Transgenic overexpression of miR-486 using muscle creatine kinase promoter (MCK-miR-486) partially rescues muscular dystrophy phenotype. We had previously demonstrated reduced circulating and skeletal muscle miR-486 levels with accompanying skeletal muscle defects in mammary tumor models. To determine whether skeletal muscle miR-486 is functionally similar in dystrophies and cancer, we performed functional limitations and biochemical studies of skeletal muscles of MMTV-Neu mice that mimic HER2+ breast cancer and MMTV-PyMT mice that mimic luminal subtype B breast cancer and these mice crossed to MCK-miR-486 mice. miR-486 significantly prevented tumor-induced reduction in muscle contraction force, grip strength, and rotarod performance in MMTV-Neu mice. In this model, miR-486 reversed cancer-induced skeletal muscle changes, including loss of p53, phospho-AKT, and phospho-laminin alpha 2 (LAMA2) and gain of hnRNPA0 and SRSF10 phosphorylation. LAMA2 is a part of the dystrophin-associated glycoprotein complex, and its loss of function causes congenital muscular dystrophy. Complementing these beneficial effects on muscle, miR-486 indirectly reduced tumor growth and improved survival, which is likely due to systemic effects of miR-486 on production of pro-inflammatory cytokines such as IL-6. Thus, similar to dystrophy, miR-486 has the potential to reverse skeletal muscle defects and cancer burden.

H19X-encoded miR-322(424)/miR-503 regulates muscle mass by targeting translation initiation factors.

BackgroundSkeletal muscle atrophy is a debilitating complication of many chronic diseases, disuse conditions, and ageing. Genome‐wide gene expression analyses have identified that elevated levels of microRNAs encoded by the H19X locus are among the most significant changes in skeletal muscles in a wide scope of human cachectic conditions. We have previously reported that the H19X locus is important for the establishment of striated muscle fate during embryogenesis. However, the role of H19X‐encoded microRNAs in regulating skeletal mass in adults is unknown.MethodsWe have created a transgenic mouse strain in which ectopic expression of miR‐322/miR‐503 is driven by the skeletal muscle‐specific muscle creatine kinase promoter. We also used an H19X mutant mouse strain in which transcription from the locus is interrupted by a gene trap. Animal phenotypes were analysed by standard histological methods. Underlying mechanisms were explored by using transcriptome profiling and validated in the two animal models and cultured myotubes.ResultsOur results demonstrate that the levels of H19X microRNAs are inversely related to postnatal skeletal muscle growth. Targeted overexpression of miR‐322/miR‐503 impeded skeletal muscle growth. The weight of gastrocnemius muscles of transgenic mice was only 54.5% of the counterparts of wild‐type littermates. By contrast, interruption of transcription from the H19X locus stimulates postnatal muscle growth by 14.4–14.9% and attenuates the loss of skeletal muscle mass in response to starvation by 12.8–21.0%. Impeded muscle growth was not caused by impaired IGF1/AKT/mTOR signalling or a hyperactive ubiquitin–proteasome system, instead accompanied by markedly dropped abundance of translation initiation factors in transgenic mice. miR‐322/miR‐503 directly targets eIF4E, eIF4G1, eIF4B, eIF2B5, and eIF3M.ConclusionsOur study illustrates a novel pathway wherein H19X microRNAs regulate skeletal muscle growth and atrophy through regulating the abundance of translation initiation factors, thereby protein synthesis. The study highlights how translation initiation factors lie at the crux of multiple signalling pathways that control skeletal muscle mass.

AAV1.NT-3 gene therapy in a CMT2D model: phenotypic improvements in GarsP278KY/+ mice.

Glycyl–tRNA synthetase mutations are associated to the Charcot–Marie–Tooth disease type-2D. The GarsP278KY/+ model for Charcot–Marie–Tooth disease type-2D is known best for its early onset severe neuropathic phenotype with findings including reduced axon size, slow conduction velocities and abnormal neuromuscular junction. Muscle involvement remains largely unexamined. We tested the efficacy of neurotrophin 3 gene transfer therapy in two Gars mutants with severe (GarsP278KY/+) and milder (GarsΔETAQ/+) phenotypes via intramuscular injection of adeno-associated virus setoype-1, triple tandem muscle creatine kinase promoter, neurotrophin 3 (AAV1.tMCK.NT-3) at 1 × 1011 vg dose. In the GarsP278KY/+ mice, the treatment efficacy was assessed at 12 weeks post-injection using rotarod test, electrophysiology and detailed quantitative histopathological studies of the peripheral nervous system including neuromuscular junction and muscle. Neurotrophin 3 gene transfer therapy in GarsP278KY/+ mice resulted in significant functional and electrophysiological improvements, supported with increases in myelin thickness and improvements in the denervated status of neuromuscular junctions as well as increases in muscle fibre size along with attenuation of myopathic changes. Improvements in the milder phenotype GarsΔETAQ/+ was less pronounced. Furthermore, oxidative enzyme histochemistry in muscles from Gars mutants revealed alterations in the content and distribution of oxidative enzymes with increased expression levels of Pgc1a. Cox1, Cox3 and Atp5d transcripts were significantly decreased suggesting that the muscle phenotype might be related to mitochondrial dysfunction. Neurotrophin 3 gene therapy attenuated these abnormalities in the muscle. This study shows that neurotrophin 3 gene transfer therapy has disease modifying effect in a mouse model for Charcot–Marie–Tooth disease type-2D, leading to meaningful improvements in peripheral nerve myelination and neuromuscular junction integrity as well as in a unique myopathic process, associated with mitochondria dysfunction, all in combination contributing to functional outcome. Based on the multiple biological effects of this versatile molecule, we predict neurotrophin 3 has the potential to be beneficial in other aminoacyl-tRNA synthetase-linked Charcot–Marie–Tooth disease subtypes.

Sema3a-Nrp1 Signaling Mediates Fast-Twitch Myofiber Specificity of Tw2+ Cells.

We previously identified a unique population of interstitial muscle progenitors, marked by expression of the Twist2 transcription factor, which fuses specifically to type IIb/x fast-twitch myofibers. Tw2+ progenitors are distinct from satellite cells, a muscle progenitor that expresses Pax7 and contributes to all myofiber types. Through RNA sequencing and immunofluorescence, we identify the membrane receptor, Nrp1, as a marker of Tw2+ cells but not Pax7+ cells. We also found that Sema3a, a chemorepellent ligand for Nrp1, is expressed by type I and IIa myofibers but not IIb myofibers. Using stripe migration assays, chimeric cell-cell fusion assays, and a Sema3a transgenic mouse model, we identify Sema3a-Nrp1 signaling as a major mechanism for Tw2+ cell fiber-type specificity. Our findings reveal an extracellular signaling mechanism whereby a cell-surface receptor for a chemorepellent confers specificity of intercellular fusion of a specific muscle progenitor with its target tissue.

Syntaxin 4 (STX4) Enrichment in Skeletal Muscle Remediates Insulin Resistance via and Improving Mitochondrial Function

Type 2 diabetes afflicts 10% of the US population and is the result of both peripheral insulin resistance (skeletal muscle and adipose tissue) as well as insulin secretion defects (pancreas). Insulin resistance, also commonly termed ‘pre‐diabetes’ is estimated to impact more than 30% of our population, and is caused by the inability of skeletal muscle to clear excess blood glucose from the circulation. Human skeletal muscle accounts for over 80% of glucose clearance in the body, a process important in maintaining glucose homeostasis. Currently the only therapeutics that directly improve muscle glucose uptake are diet and exercise. However, with only 3% of the population leading a “healthy lifestyle”, including exercise, directed therapeutics are required to restore skeletal muscle function in pre‐diabetics. Several studies have identified correlations between insulin resistance and reduced levels of a SNARE protein named Syntaxin 4 (STX4) in human skeletal muscle. STX4 interacts with other SNARE proteins to facilitate the fusion of glucose transporter 4 (GLUT4) vesicles with the plasma membrane, to then channel extracellular glucose to the interior of the muscle cell, ultimately clearing glucose from the circulation.To further define the function of STX4 in muscle, we developed a doxycycline Tet‐on inducible skeletal muscle specific STX4 overexpressing mouse model, under the muscle creatine kinase promoter (skm‐STX4 mice). Chow fed female mice overexpressing STX4 exhibited enhanced insulin sensitivity and improved glucose tolerance. Serum insulin levels from these mice were also reduced compared to littermate controls, concordant with their improved glucose tolerance. The data recapitulated the global overexpression model that we had previously published, suggesting that skeletal muscle is the primary driver in modulating glucose homeostasis. To establish that enriching STX4 can remediate insulin resistance, male skm‐STX4 mice were fed a 45% high fat diet (HF; to mimic a typical western diet), until they became insulin resistant. Upon establishing pre‐diabetes in the mice, STX4 enrichment was induced in the skeletal muscle (HFD+STX4 mice). Remarkably HFD+STX4 mice had the insulin sensitivity of a chow‐fed mouse, resolving the HFD‐linked insulin resistance in full. Moreover, the HFD+STX4 mice had significantly improved voluntary movement and increased respiratory exchange ratio, indicating increased reliance on carbohydrate rather than fat oxidation. The maximal oxygen consumption rate was also increased in primary myotubes from these HFD+ STX4 mice.Taken together, these results suggest that STX4 enrichment carries the potential as a therapeutic to remedy obesity‐linked insulin resistance, potentially via improving mitochondrial function. These results suggest that STX4 could be a viable therapeutic target for treatment of pre‐diabetes.Support or Funding InformationResearch was supported by the NIH (DK067912, DK102233, and DK112917) to D.C.T and by the H.N. & Frances C. Berger Foundation, and Helen & Payson Chu Fellowships to K.E.MThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Germline or inducible knockout of p300 or CBP in skeletal muscle does not alter insulin sensitivity.

Akt is a critical mediator of insulin-stimulated glucose uptake in skeletal muscle. The acetyltransferases, E1A binding protein p300 (p300) and cAMP response element-binding protein binding protein (CBP) are phosphorylated and activated by Akt, and p300/CBP can acetylate and inactivate Akt, thus giving rise to a possible Akt-p300/CBP axis. Our objective was to determine the importance of p300 and CBP to skeletal muscle insulin sensitivity. We used Cre-LoxP methodology to generate mice with germline [muscle creatine kinase promoter (P-MCK and C-MCK)] or inducible [tamoxifen-activated, human skeletal actin promoter (P-iHSA and C-iHSA)] knockout of p300 or CBP. A subset of P-MCK and C-MCK mice were switched to a calorie-restriction diet (60% of ad libitum intake) or high-fat diet at 10 wk of age. For P-iHSA and C-iHSA mice, knockout was induced at 10 wk of age. At 13-15 wk of age, we measured whole-body energy expenditure, oral glucose tolerance, and/or ex vivo skeletal muscle insulin sensitivity. Although p300 and CBP protein abundance and mRNA expression were reduced 55%-90% in p300 and CBP knockout mice, there were no genotype differences in energy expenditure or fasting glucose and insulin concentrations. Moreover, neither loss of p300 or CBP impacted oral glucose tolerance or skeletal muscle insulin sensitivity, nor did their loss impact alterations in these parameters in response to a calorie restriction or high-fat diet. Muscle-specific loss of either p300 or CBP, be it germline or in adulthood, does not impact energy expenditure, glucose tolerance, or skeletal muscle insulin action.

Bone-Targeted Alkaline Phosphatase Treatment of Mandibular Bone and Teeth in Lethal Hypophosphatasia via an scAAV8 Vector

Hypophosphatasia is an inherited disease caused by mutations in the gene encoding tissue-nonspecific alkaline phosphatase (TNALP), the major symptom of which is hypomineralization of the bones and teeth. We had recently demonstrated that TNALP-deficient (Akp2−/−) mice, which mimic the phenotype of the severe infantile form of hypophosphatasia, can be treated by intramuscular injection of a self-complementary (sc) type 8 recombinant adeno-associated virus (rAAV8) vector expressing bone-targeted TNALP with deca-aspartates at the C terminus (TNALP-D10) via the muscle creatine kinase (MCK) promoter. In this study, we focused on the efficacy of this scAAV8-MCK-TNALP-D10 treatment on the mandibular bone and teeth in neonatal Akp2−/− mice. Upon scAAV8-MCK-TNALP-D10 injection, an improvement of mandibular growth was observed by X-ray analysis. Micro-computed tomography analysis revealed progressive mineralization of the molar root in the treated Akp2−/− mice, and morphometric parameters of the alveolar bone were improved. These results suggest that the mandibular bones and teeth of hypophosphatasia were effectively treated by muscle directed rAAV-mediated TNALP-D10 transduction. Our strategy would be promising for future hypophosphatasia gene therapy because it induces dentoalveolar mineralization and reduces the risk of tooth exfoliation.

TH.I.9 - Development of microdystrophins for gene therapy of DMD

Gene therapy represents a promising approach to treat DMD as it has the potential to circumvent the primary cause of the disorder, a mutant gene. Gene replacement therapies have focused on methods to deliver expression cassettes encoding the dystrophin protein. Challenges to this approach have included the enormous size of the dystrophin gene (2.2 MB), its muscle mRNA (14 kb) and difficulties in safely delivering vectors to muscles bodywide. We and others have shown that vectors derived from specific serotypes of adeno-associated virus (AAV) can systemically deliver genes to muscles after intravascular infusion. However, AAV vectors have a limited carrying capacity of approximately 5 kb, necessitating the design of miniaturized cDNAs and gene regulatory elements that enable expression of “microdystrophins”. Early generation microdystrophins displayed functional limitations due to their small size (<4 kb) and the absence of some protein interaction domains. To develop improved vectors we tested a variety of novel microdystrophins lacking the C-terminal domain but carrying 4–6 spectrin-like repeats, including the nitric oxide synthase localization domain. We also tested a set of powerful gene regulatory elements based on the muscle creatine kinase (MCK) enhancer plus promoter. These novel microdystrophins were evaluated by AAV-mediated delivery to dystrophic mdx4cv mice followed by extensive analysis of muscle pathophysiology. We identified a 5 repeat vector that when driven by the CK8 regulatory cassette leads to stable expression and profound reductions in muscle pathophysiology. This AAV/CK8-µDys5 vector performs better than previously tested microdystrophin cassettes and represents a promising clinical candidate. We have also been testing AAV vectors to deliver components of the CRISPR/Cas9 system as a method to potentially repair, rather than replace, the mutant dystrophin gene. While this gene editing approach shows promise, its efficiency remains low and as currently applied is less effective than direct delivery of microd

Muscle-specific expression of the RNA-binding protein Staufen1 induces progressive skeletal muscle atrophy via regulation of phosphatase tensin homolog.

Converging lines of evidence have now highlighted the key role for post-transcriptional regulation in the neuromuscular system. In particular, several RNA-binding proteins are known to be misregulated in neuromuscular disorders including myotonic dystrophy type 1, spinal muscular atrophy and amyotrophic lateral sclerosis. In this study, we focused on the RNA-binding protein Staufen1, which assumes multiple functions in both skeletal muscle and neurons. Given our previous work that showed a marked increase in Staufen1 expression in various physiological and pathological conditions including denervated muscle, in embryonic and undifferentiated skeletal muscle, in rhabdomyosarcomas as well as in myotonic dystrophy type 1 muscle samples from both mouse models and humans, we investigated the impact of sustained Staufen1 expression in postnatal skeletal muscle. To this end, we generated a skeletal muscle-specific transgenic mouse model using the muscle creatine kinase promoter to drive tissue-specific expression of Staufen1. We report that sustained Staufen1 expression in postnatal skeletal muscle causes a myopathy characterized by significant morphological and functional deficits. These deficits are accompanied by a marked increase in the expression of several atrophy-associated genes and by the negative regulation of PI3K/AKT signaling. We also uncovered that Staufen1 mediates PTEN expression through indirect transcriptional and direct post-transcriptional events thereby providing the first evidence for Staufen1-regulated PTEN expression. Collectively, our data demonstrate that Staufen1 is a novel atrophy-associated gene, and highlight its potential as a biomarker and therapeutic target for neuromuscular disorders and conditions.

A Noninvasive In Vitro Monitoring System Reporting Skeletal Muscle Differentiation.

Monitoring of cell differentiation is a crucial aspect of cell-based therapeutic strategies depending on tissue maturation. In this study, we have developed a noninvasive reporter system to trace murine skeletal muscle differentiation. Either a secreted bioluminescent reporter (Metridia luciferase) or a fluorescent reporter (green fluorescent protein [GFP]) was placed under the control of the truncated muscle creatine kinase (MCK) basal promoter enhanced by variable numbers of upstream MCK E-boxes. The engineered pE3MCK vector, coding a triple tandem of E-Boxes and the truncated MCK promoter, showed twentyfold higher levels of luciferase activation compared with a Cytomegalovirus (CMV) promoter. This newly developed reporter system allowed noninvasive monitoring of myogenic differentiation in a straining bioreactor. Additionally, binding sequences of endogenous microRNAs (miRNAs; seed sequences) that are known to be downregulated in myogenesis were ligated as complementary seed sequences into the reporter vector to reduce nonspecific signal background. The insertion of seed sequences improved the signal-to-noise ratio up to 25% compared with pE3MCK. Due to the highly specific, fast, and convenient expression analysis for cells undergoing myogenic differentiation, this reporter system provides a powerful tool for application in skeletal muscle tissue engineering.

PGC-1α Coordinates Mitochondrial Respiratory Capacity and Muscular Fatty Acid Uptake via Regulation of VEGF-B.

Vascular endothelial growth factor (VEGF) B belongs to the VEGF family, but in contrast to VEGF-A, VEGF-B does not regulate blood vessel growth. Instead, VEGF-B controls endothelial fatty acid (FA) uptake and was identified as a target for the treatment of type 2 diabetes. The regulatory mechanisms controlling Vegfb expression have remained unidentified. We show that peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) together with estrogen-related receptor α (ERR-α) regulates expression of Vegfb Mice overexpressing PGC-1α under the muscle creatine kinase promoter (MPGC-1αTG mice) displayed increased Vegfb expression, and this was accompanied by increased muscular lipid accumulation. Ablation of Vegfb in MPGC-1αTG mice fed a high-fat diet (HFD) normalized glucose intolerance, insulin resistance, and dyslipidemia. We suggest that VEGF-B is the missing link between PGC-1α overexpression and the development of the diabetes-like phenotype in HFD-fed MPGC-1αTG mice. The findings identify Vegfb as a novel gene regulated by the PGC-1α/ERR-α signaling pathway. Furthermore, the study highlights the role of PGC-1α as a master metabolic sensor that by regulating the expression levels of Vegfa and Vegfb coordinates blood vessel growth and FA uptake with mitochondrial FA oxidation.

Promoter analysis of bovine cardiomyopathy-associated protein 1 gene.

The CMYA1 (cardiomyopathy-associated protein 1) is an actin-binding protein that plays a vital role in cardiac morphogenesis. CMYA1 is expressed specifically in the myocardial and skeletal muscle and is up-regulated in injured muscle. We therefore speculated that the bovine CMYA1 promoter might be muscle-specific. In this study, the promoter (+20/-1135) region of the bovine CMYA1 gene was cloned into a pEGFP-1 vector, and we found that the EGFP was observed only in C2C12 and myoblast cells. Thus, the CMYA1 promoter is muscle-specific. Thereafter, eight pGL3-basic vectors with various truncated CMYA1 promoter fragments were transfected into C2C12 cells, to identify the core promoter region using a Dual-Luciferase Reporter Assay System. The results showed that the promoter region from -457 to +20 bp was essential for CMYA1 to maintain the promoter activity, implying that this region may be the CMYA1 core promoter. We thus illustrate that the core promoter is muscle-specific. To evaluate the activity of the CMYA1 core promoter, the CMYA1 core and muscle creatine kinase (MCK) promoters were cloned into a pcDNA3.1 vector. The expression levels of their target genes were measured in C2C12 cells using real-time polymerase chain reaction. The CMYA1 promoter drove the expression of the target gene six times higher than did the MCK promoter. The results thus suggest that the CMYA1 promoter could be an effective muscle-specific promoter, which may be useful in further studies of cardiomyopathy treatment and transgenic animal research.

Treatment of hypophosphatasia by muscle-directed expression of bone-targeted alkaline phosphatase via self-complementary AAV8 vector

Hypophosphatasia (HPP) is an inherited disease caused by genetic mutations in the gene encoding tissue-nonspecific alkaline phosphatase (TNALP). This results in defects in bone and tooth mineralization. We recently demonstrated that TNALP-deficient (Akp2−/−) mice, which mimic the phenotype of the severe infantile form of HPP, can be treated by intravenous injection of a recombinant adeno-associated virus (rAAV) expressing bone-targeted TNALP with deca-aspartates at the C-terminus (TNALP-D10) driven by the tissue-nonspecific CAG promoter. To develop a safer and more clinically applicable transduction strategy for HPP gene therapy, we constructed a self-complementary type 8 AAV (scAAV8) vector that expresses TNALP-D10 via the muscle creatine kinase (MCK) promoter (scAAV8-MCK-TNALP-D10) and examined the efficacy of muscle-directed gene therapy. When scAAV8-MCK-TNALP-D10 was injected into the bilateral quadriceps of neonatal Akp2−/− mice, the treated mice grew well and survived for more than 3 months, with a healthy appearance and normal locomotion. Improved bone architecture, but limited elongation of the long bone, was demonstrated on X-ray images. Micro-CT analysis showed hypomineralization and abnormal architecture of the trabecular bone in the epiphysis. These results suggest that rAAV-mediated, muscle-specific expression of TNALP-D10 represents a safe and practical option to treat the severe infantile form of HPP.

Retinol as a cofactor for PKCδ-mediated impairment of insulin sensitivity in a mouse model of diet-induced obesity.

We previously defined that the mitochondria-localized PKCδ signaling complex stimulates the conversion of pyruvate to acetyl-coenzyme A by the pyruvate dehydrogenase complex. We demonstrated in vitro and ex vivo that retinol supplementation enhances ATP synthesis in the presence of the PKCδ signalosome. Here, we tested in vivo if a persistent oversupply of retinol would further impair glucose metabolism in a mouse model of diet-induced insulin resistance. We crossed mice overexpressing human retinol-binding protein (hRBP) under the muscle creatine kinase (MCK) promoter (MCKhRBP) with the PKCδ(-/-) strain to generate mice with a different status of the PKCδ signalosome and retinoid levels. Mice with a functional PKCδ signalosome and elevated retinoid levels (PKCδ(+/+)hRBP) developed the most advanced stage of insulin resistance. In contrast, elevation of retinoid levels in mice with inactive PKCδ did not affect remarkably their metabolism, resulting in phenotypic similarity between PKCδ(-/-)hRBP and PKCδ(-/-) mice. Therefore, in addition to the well-defined role of PKCδ in the etiology of metabolic syndrome, we present a novel PKCδ signaling pathway that requires retinol as a metabolic cofactor and is involved in the regulation of fuel utilization in mitochondria. The distinct role in whole-body energy homeostasis establishes the PKCδ signalosome as a promising target for therapeutic intervention in metabolic disorders.

389. Assessment of Sensorimotor Skills of the MCK Model of Friedreich Ataxia

Friedreich ataxia (FA) is the most common autosomal recessive disorder of the cerebellum, causing degeneration of spinal sensory neurons and spinocerebellar tracts. The disease is caused by severely reduced levels of frataxin, a mitochondrial protein involved in iron metabolism. We tested an experimental model generated by Dr. Puccio's group by crossing mice homozygous for a conditional allele of the Fxn gene with mice heterozygous for a deleted exon 4 of Fxn carrying a tissue-specific Cre transgene under control of the muscle creatine kinase promoter. Relative to wild-type, the MCK-Cre conditional mutants were impaired on tests of motor coordination comprising horizontal bar, vertical pole, and the rotorod as well as displaying gait anomalies and the hindlimb clasping response. Thus this MCK-Cre model reproduces some key features of muscle dysfunction in patients with Friedreich ataxia and provides an opportunity of ameliorating their symptoms with experimental therapies.

Sensorimotor skills in Fxn KO/Mck mutants deficient for frataxin in muscle

Friedreich ataxia is the most common autosomal recessive disorder of the cerebellum, causing degeneration of spinal sensory neurons and spinocerebellar tracts. The disease is caused by severely reduced levels of frataxin, a mitochondrial protein involved in iron metabolism. An experimental model has been generated by crossing mice homozygous for a conditional allele of the Fxn gene with mice heterozygous for a deleted exon 4 of Fxn carrying a tissue-specific Cre transgene under control of the muscle creatine kinase promoter. Relative to wild-type, Fxn null mutants were impaired on tests of motor coordination comprising horizontal bar, vertical pole, and the rotorod as well as displaying gait anomalies and the hindlimb clasping response. The Fxn KO/Mck model reproduces some key features of patients with Friedreich ataxia and provides an opportunity of ameliorating their symptoms with experimental therapies.

Contrasting roles for MyoD in organizing myogenic promoter structures during embryonic skeletal muscle development.

Among the complexities of skeletal muscle differentiation is a temporal distinction in the onset of expression of different lineage-specific genes. The lineage-determining factor MyoD is bound to myogenic genes at the onset of differentiation whether gene activation is immediate or delayed. How temporal regulation of differentiation-specific genes is established remains unclear. Using embryonic tissue, we addressed the molecular differences in the organization of the myogenin and muscle creatine kinase (MCK) gene promoters by examining regulatory factor binding as a function of both time and spatial organization during somitogenesis. At the myogenin promoter, binding of the homeodomain factor Pbx1 coincided with H3 hyperacetylation and was followed by binding of co-activators that modulate chromatin structure. MyoD and myogenin binding occurred subsequently, demonstrating that Pbx1 facilitates chromatin remodeling and modification before myogenic regulatory factor binding. At the same time, the MCK promoter was bound by HDAC2 and MyoD, and activating histone marks were largely absent. The association of HDAC2 and MyoD was confirmed by co-immunoprecipitation, proximity ligation assay (PLA), and sequential ChIP. MyoD differentially promotes activated and repressed chromatin structures at myogenic genes early after the onset of skeletal muscle differentiation in the developing mouse embryo.