Follistatin-based ligand trap ACE-083 induces localized hypertrophy of skeletal muscle with functional improvement in models of neuromuscular disease

Skeletal muscle is under inhibitory homeostatic regulation by multiple ligands of the transforming growth factor-β (TGFβ) superfamily. Follistatin is a secreted protein that promotes muscle growth and function by sequestering these ligands extracellularly. In the present study, we evaluated the potential of ACE-083 – a locally acting, follistatin-based fusion protein – as a novel therapeutic agent for focal or asymmetric myopathies. Characterization of ACE-083 in vitro revealed its high affinity for heparin and extracellular matrix while surface plasmon resonance and cell-based assays confirmed that ACE-083 binds and potently neutralizes myostatin, activin A, activin B and growth differentiation factor 11 (GDF11). Intramuscular administration of ACE-083 caused localized, dose-dependent hypertrophy of the injected muscle in wild-type mice and mouse models of Charcot-Marie-Tooth disease (CMT) and Duchenne muscular dystrophy, with no evidence of systemic muscle effects or endocrine perturbation. Importantly, ACE-083 also increased the force of isometric contraction in situ by the injected tibialis anterior muscle in wild-type mice and disease models and increased ankle dorsiflexion torque in CMT mice. Our results demonstrate the potential of ACE-083 as a therapeutic agent for patients with CMT, muscular dystrophy and other disorders with focal or asymmetric muscle atrophy or weakness.

Effect of a soluble activin receptor type IIB on androgen-deprivation-induced effects on body composition

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Background: Androgen deprivation therapy (ADT) is a well-established treatment for hormone sensitive prostate cancer, but is associated with adverse side effects including loss of bone and lean mass and increased adipose mass. Activin receptor type IIB (ActRIIB) signaling is necessary for the negative regulation of lean tissue mass and treatment with a non-signaling, decoy ActRIIB results in a robust increase in lean tissue mass. Methods: Similar to ADT patients, orchiectomized (ORX) mice lose bone and lean mass and gain fat mass. To determine the therapeutic potential of inhibiting ActRIIB signaling to reduce the negative effects associated with ADT, we treated sham-operated (SHAM) and orchiectomized (ORX) mice with RAP-031, a fusion protein comprised of a form of the extracellular domain of ActRIIB linked to a murine Fc. Mice received twice weekly injections for 10 weeks with either vehicle (VEH) or 10 mg/kg RAP-031 (RAP). NMR scanning was used to determine body composition and whole body DEXA scans were performed to determine bone mineral density (BMD). Results: ORX resulted in a 4.4% decrease in BMD, an 18% reduction in lean tissue and a 41.6% increase in adiposity compared to the VEH-SHAM cohort. Both RAP-031treated groups of mice had significantly increased BMD and lean tissue mass and decreased adipose mass compared to their respective VEH groups. However, BMD, lean tissue and adiposity were not significantly different between the VEH-SHAM and RAP-ORX groups. These data illustrate that RAP-031 treatment completely attenuates ORX-induced alterations in bone, lean and fat mass. Conclusions: These data support the hypothesis that treatment with a form of soluble ActRIIB can offset negative side effects of ADT and have significant therapeutic implications for the treatment of patients with prostate cancer.

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Profiling proteins from azoxymethane-induced colon tumors at the molecular level by matrix-assisted laser desorption/ionization mass spectrometry

New developments in mass spectrometry allow for the profiling of the major proteomic content of fresh tissue sections. Briefly, fresh tissue sections are sampled and blotted onto a polyethylene membrane for protein transfer and then subsequently analyzed by matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). Using this technology, we have compared the protein expression of normal and cancerous mouse colon tissue obtained from the same animal. By difference, several protein signals specific to cancerous tissue were observed. A protein extract obtained from the tumors was fractionated by high-performance liquid chromatography and the individual fractions analyzed by MALDI-MS. The fractions containing the targeted proteins were subjected to trypsin digestion. The resulting tryptic peptides were sequenced by tandem mass spectrometry, and based on the recovered partial amino acid sequences, three of the tumor specific protein markers were identified as calgranulin A (S100A8), calgranulin B (S100A9) and calgizzarin (S100A11).

Profiling proteins from azoxymethane-induced colon tumors at the molecular level by matrix-assisted laser desorption/ionization mass spectrometry

New developments in mass spectrometry allow for the profiling of the major proteomic content of fresh tissue sections. Briefly, fresh tissue sections are sampled and blotted onto a polyethylene membrane for protein transfer and then subsequently analyzed by matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS). Using this technology, we have compared the protein expression of normal and cancerous mouse colon tissue obtained from the same animal. By difference, several protein signals specific to cancerous tissue were observed. A protein extract obtained from the tumors was fractionated by high-performance liquid chromatography and the individual fractions analyzed by MALDI-MS. The fractions containing the targeted proteins were subjected to trypsin digestion. The resulting tryptic peptides were sequenced by tandem mass spectrometry, and based on the recovered partial amino acid sequences, three of the tumor specific protein markers were identified as calgranulin A (S100A8), calgranulin B (S100A9) and calgizzarin (S100A11).

Comparative genomic sequence analysis and isolation of human and mouse alternative EGFR transcripts encoding truncated receptor isoforms

This study presents the annotated genomic sequence and exon-intron organization of the human and mouse epidermal growth factor receptor (EGFR) genes located on chromosomes 7p11.2 and 11, respectively. We report that the EGFR gene spans nearly 200 kb and that the full-length 170-kDa EGFR is encoded by 28 exons. In addition, we have identified two human and two mouse alternative EGFR transcripts of 2.4-3.0 kb using both computational and experimental methods. The human 3.0-kb and mouse 2.8-kb EGFR mRNAs are predominantly expressed in placenta and liver, respectively, and both transcripts encode 110-kDa truncated receptor isoforms containing only the extracellular ligand-binding domain. We also have demonstrated that the aberrant 2.8-kb EGFR transcript produced by the human A431 carcinoma cell line is generated by splicing to a recombinant 3'-terminal exon located in EGFR intron 16, which apparently was formed as a result of a chromosomal translocation. Finally, we have shown that the human, mouse, rat, and chicken 1.8- to 3.0-kb alternative EGFR transcripts are generated by distinct splicing mechanisms and that each of these mRNAs contains unique 3' sequences that are not evolutionarily conserved. The presence of truncated receptor isoforms in diverse species suggests that these proteins may have important functional roles in regulating EGFR activity.

Genetic analysis of testis weight and fertility in an interspecies hybrid congenic strain for Chromosome X

A hybrid congenic strain, C57BL/6J.SPRET-Hprt(a), carrying 17 map units of Chromosome (Chr) X from Mus spretus on a background of C57BL/6J. has the novel phenotype of low fertility associated with small testis weight. In histological cross-section, many of the tubules in the testes of these congenic mice are empty except for Sertoli cells, while the other tubules appear to be normal. The gene, interspecific hybrid testis weight 1 (Ihtw1) causing this phenotype, has been fine mapped by using the strategy of generating subcongenic strains from recombinants within the congenic region. Genetic and phenotypic analysis of the subcongenic strains has defined a critical region of 1.8 map units for Ihtw1. This region of the genetic map is orthologous to the region on human Chr X containing the gene for the Borjeson-Forssman-Lehman syndrome, an inherited disease in which males show microorchidism.

Genetic dissection of X-linked interspecific hybrid placental dysplasia in congenic mouse strains

Interspecific hybridization in the genus Mus results in male sterility and X-linked placental dysplasia. We have generated several congenic laboratory mouse lines (Mus musculus) in which different parts of the maternal X chromosome were derived from M. spretus. A strict positive correlation between placental weight and length of the M. spretus-derived part of the X chromosome was shown. Detailed analysis was carried out with one congenic strain that retained a M. spretus interval between 12.0 and 30.74 cM. This strain consistently produced hyperplastic placentas that exhibited an average weight increase of 180% over the weight of control placentas. In derived subcongenic strains, however, increased placental weight could no longer be observed. Morphometric analysis of these placentas revealed persistence of abnormal morphology. Fully developed placental hyperplasia could be reconstituted by recombination of proximal and central M. spretus intervals with an intervening M. musculus region. These results may suggest that placental dysplasia of interspecific mouse hybrids is caused by multiple loci clustered on the X chromosome that act synergistically. Alternatively, it is possible that changes in chromatin structure in interspecific hybrids that influence gene expression are dependent on the length of the alien chromosome.

A direct repeat sequence at the Rasgrf1 locus and imprinted expression

Genomic imprinting is an epigenetic modification that can lead to parental-specific monoallelic expression of specific autosomal genes. While methylation of CpG dinucleotides is thought to be a strong candidate for this epigenetic modification, little is known about the establishment or maintenance of parental origin-specific methylation patterns. We have recently identified a portion of mouse chromosome 9 containing a paternally methylated region associated with a paternally expressed imprinted gene, Ras protein-specific guanine nucleotide-releasing factor 1 (Rasgrf1). This area of chromosome 9 also contains a short, direct tandem repeat in close proximity to a paternally methylated NotI site 30 kb upstream of Rasgrf1. Short, direct tandem repeats have been found associated with other imprinted genes and may act as important regulatory structures. Here we demonstrate that two rodent species (Mus and Rattus) contain a similar direct repeat structure associated with a region of paternal-specific methylation. In both species, the Rasgrf1 gene shows paternal-specific monoallelic expression in neonatal brain. A more divergent rodent species (Peromyscus) appears to lack a similar repeat structure based on Southern Blot analysis. Peromyscus animals show biallelic expression of Rasgrf1 in neonatal brain. These results suggest that direct repeat elements may play an important role in the imprinting process.

A methylation imprint mark in the mouse imprinted gene Grf1/Cdc25Mm locus shares a common feature with the U2afbp-rs gene: an association with a short tandem repeat and a hypermethylated region

We identified a sperm-specific methylation imprint mark (Site II) associated with a short tandem repeat sequence and a site/region methylated in both gametes (Site I) in the Grf1 locus on mouse chromosome 9, which shared a common feature with the U2afbp-rs gene. Sites or regions of gamete-specific methylation in imprinted genes are strong candidates for carrying information regarding the parental origin of alleles. The gamete-specific methylation pattern of Sites I and II was conserved after fertilization, but attained the somatic cell pattern by the blastocyst stage. In primordial germ cells, Site I was methylated, but Site II was unmethylated in both male and female embryos, suggesting that the sperm-specific methylation imprint mark in Site II was established during spermatogenesis. These common features in methylation imprint regions may be a clue to identifying regions carrying primary information for the imprinting regulation.

Divergently transcribed overlapping genes expressed in liver and kidney and located in the 11p15.5 imprinted domain

Human chromosomal band 11p15.5 has been shown to contain genes involved in the development of several pediatric and adult tumors and in Beckwith-Wiedemann syndrome (BWS). Overlapping P1 artificial chromosome clones from this region have been used as templates for genomic sequencing in an effort to identify candidate genes for these disorders. PowerBLAST identified several matches with expressed sequence tags (ESTs) from fetal brain and liver cDNA libraries. Northern blot analysis indicated that two of the genes identified by these ESTs encode transcripts of 1-1.5 kb with predominant expression in fetal and adult liver and kidney. With RT-PCR and RACE, full-length transcripts were isolated for these two genes, with the largest open reading frames encoding putative proteins of 253 and 424 amino acids. Database comparison of the predicted amino acid sequence of the larger transcript indicated homology to integral membrane organic cation transporters; hence, we designate this gene ORCTL2 (organic cation transporter-like 2). An expressed sequence polymorphism provided evidence that the ORCTL2 gene exhibits "leaky" imprinting in both human fetal kidney and human fetal liver. The mouse orthologue (Orctl2) was identified, and a similar polymorphism was used to demonstrate maternal-specific expression of this gene in fetal liver from interspecific F1 mice. The predicted protein of the smaller gene showed no significant similarity in the database. Northern and RACE analyses suggest that this gene may have multiple transcription start sites. Determination of the genomic structure in humans indicated that the 5'-end of this transcript overlaps in divergent orientation with the first two exons of ORCTL2, suggesting a possible role for antisense regulation of one gene by the other. We, therefore, provisionally name this second transcript ORCTL2S (ORCTL2-antisense). The expression patterns of these genes and the imprinted expression of ORCTL2 are suggestive of a possible role in the development of Wilms tumor (WT) and hepatoblastoma. Although SSCP analysis of 62 WT samples and 10 BWS patients did not result in the identification of any mutations in ORCTL2 or ORCTL2S, it will be important to examine their expression pattern in tumors and BWS patients, since epigenetic alteration at these loci may play a role in the etiology of these diseases.

Absence of imprinting in U2AFBPL, a human homologue of the imprinted mouse gene U2afbp-rs

The mouse gene U2 auxiliary factor binding protein related sequence (U2afbp-rs) has previously been shown to be genomically imprinted with monoallelic expression from the paternal allele. To determine if the human homologue is imprinted and contains conserved structural features which regulate imprinting, we isolated genomic clones from a human P1-derived artificial chromosome (PAC) library that map to human chromosome 5q22-31, a region syntenic to the proximal portion of mouse chromosome 11 where U2afbp-rs resides. A genomic subclone was isolated which contained an open reading frame with high homology to the mouse gene. This subclone also maintained the intronless character of the mouse gene. A KpnI polymorphism within the open reading frame of the gene was found to occur in 21% (8/38) of the alleles tested from human placental tissue samples. RT-PCR analysis of human placentas using the KpnI polymorphism to determine the parental origin of the alleles indicates biallelic expression of the human chromosome 5 U2AFBPL gene.