New insights into molecular changes in skeletal muscle aging and disease: Differential alternative splicing and senescence

Progressive loss of muscle mass and function due to muscle fiber atrophy and loss in the elderly and chronically ill is now defined as sarcopenia. It is a major contributor to loss of independence, disability, need of long-term care as well as overall mortality. Sarcopenia is a heterogenous disease and underlying mechanisms are not completely understood. Here, we newly identified and used Tmem158, alongside Cdkn1a, as relevant senescence and denervation markers (SDMs), associated with muscle fiber atrophy. Subsequent application of laser capture microdissection (LCM) and RNA analyses revealed age- and disease-associated differences in gene expression and alternative splicing patterns in a rodent sarcopenia model. Of note, genes exhibiting such differential alternative splicing (DAS) are mainly involved in the contractile function of the muscle. Many of these splicing events are also found in a mouse model for myotonic dystrophy type 1 (DM1), underscoring the premature aging phenotype of this disease. We propose to add differential alternative splicing to the hallmarks of aging.

A High-Throughput Screening Identifies MICU1 Targeting Compounds

Mitochondrial Ca²⁺ uptake depends on the mitochondrial calcium uniporter (MCU) complex, a highly selective channel of the inner mitochondrial membrane (IMM). Here, we screen a library of 44,000 non-proprietary compounds for their ability to modulate mitochondrial Ca²⁺ uptake. Two of them, named MCU-i4 and MCU-i11, are confirmed to reliably decrease mitochondrial Ca²⁺ influx. Docking simulations reveal that these molecules directly bind a specific cleft in MICU1, a key element of the MCU complex that controls channel gating. Accordingly, in MICU1-silenced or deleted cells, the inhibitory effect of the two compounds is lost. Moreover, MCU-i4 and MCU-i11 fail to inhibit mitochondrial Ca²⁺ uptake in cells expressing a MICU1 mutated in the critical amino acids that forge the predicted binding cleft. Finally, these compounds are tested ex vivo, revealing a primary role for mitochondrial Ca²⁺ uptake in muscle growth. Overall, MCU-i4 and MCU-i11 represent leading molecules for the development of MICU1-targeting drugs.

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An HTS identifies MCU-i4 and MCU-i11 as negative modulators of the MCU

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MCU-i4 and MCU-i11 bind MICU1

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MICU1 is required for the activity of MCU-i4 and MCU-i11

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MCU-i4 and MCU-i11 impair muscle cell growth

Protein kinase A activation inhibits DUX4 gene expression in myotubes from patients with facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is among the most prevalent of the adult-onset muscular dystrophies. FSHD causes a loss of muscle mass and function, resulting in severe debilitation and reduction in quality of life. Currently, only the symptoms of FSHD can be treated, and such treatments have minimal benefit. The available options are not curative, and none of the treatments address the underlying cause of FSHD. The genetic, epigenetic, and molecular mechanisms triggering FSHD are now quite well-understood, and it has been shown that expression of the transcriptional regulator double homeobox 4 (DUX4) is necessary for disease onset and is largely thought to be the causative factor in FSHD. Therefore, we sought to identify compounds suppressing DUX4 expression in a phenotypic screen using FSHD patient-derived muscle cells, a zinc finger and SCAN domain-containing 4 (ZSCAN4)-based reporter gene assay for measuring DUX4 activity, and ∼3,000 small molecules. This effort identified molecules that reduce DUX4 gene expression and hence DUX4 activity. Among those, β₂-adrenergic receptor agonists and phosphodiesterase inhibitors, both leading to increased cellular cAMP, effectively decreased DUX4 expression by >75% in cells from individuals with FSHD. Of note, we found that cAMP production reduces DUX4 expression through a protein kinase A-dependent mode of action in FSHD patient myotubes. These findings increase our understanding of how DUX4 expression is regulated in FSHD and point to potential areas of therapeutic intervention.

Development of Selective, Orally Active GPR4 Antagonists with Modulatory Effects on Nociception, Inflammation, and Angiogenesis

A novel, selective, and efficacious GPR4 antagonist 13 was developed starting from lead compound 1a. While compound 1a showed promising efficacy in several disease models, its binding to a H₃ receptor as well as a hERG channel prevented it from further development. Therefore, a new round of optimization addressing the key liabilities was performed and led to discovery of compound 13 with an improved profile. Compound 13 showed significant efficacy in the rat antigen induced arthritis as well as in the hyperalgesia and angiogenesis model at a well-tolerated dose of 30 mg/kg.

Orally active 7-substituted (4-benzylphthalazin-1-yl)-2-methylpiperazin-1-yl]nicotinonitriles as active-site inhibitors of sphingosine 1-phosphate lyase for the treatment of multiple sclerosis

Sphingosine 1-phosphate (S1P) lyase has recently been implicated as a therapeutic target for the treatment of multiple sclerosis (MS), based on studies in a genetic mouse model. Potent active site directed inhibitors of the enzyme are not known so far. Here we describe the discovery of (4-benzylphthalazin-1-yl)-2-methylpiperazin-1-yl]nicotinonitrile 5 in a high-throughput screen using a biochemical assay, and its further optimization. This class of compounds was found to inhibit catalytic activity of S1PL by binding to the active site of the enzyme, as seen in the cocrystal structure of derivative 31 with the homodimeric human S1P lyase. 31 induces profound reduction of peripheral T cell numbers after oral dosage and confers pronounced protection in a rat model of multiple sclerosis. In conclusion, this novel class of direct S1P lyase inhibitors provides excellent tools to further explore the therapeutic potential of T cell-targeted therapies in multiple sclerosis and other autoimmune and inflammatory diseases.

Targeting ceramide metabolism with a potent and specific ceramide kinase inhibitor

Ceramide kinase (CerK) produces the bioactive lipid ceramide-1-phosphate (C1P) and appears as a key enzyme for controlling ceramide levels. In this study, we discovered and characterized adamantane-1-carboxylic acid (2-benzoylamino-benzothiazol-6-yl)amide (NVP-231), a potent, specific, and reversible CerK inhibitor that competitively inhibits binding of ceramide to CerK. NVP-231 is active in the low nanomolar range on purified as well as cellular CerK and abrogates phosphorylation of ceramide, resulting in decreased endogenous C1P levels. When combined with another ceramide metabolizing inhibitor, such as tamoxifen, NVP-231 synergistically increased ceramide levels and reduced cell growth. Therefore, NVP-231 represents a novel and promising compound for controlling ceramide metabolism that may provide insight into CerK physiological function.

Inhibition of Vascular Endothelial Growth Factor Cotranslational Translocation by the Cyclopeptolide CAM741

The cyclopeptolide CAM741 inhibits cotranslational translocation of vascular cell adhesion molecule 1 (VCAM1), which is dependent on its signal peptide. We now describe the identification of the signal peptide of vascular endothelial growth factor (VEGF) as the second target of CAM741. The mechanism by which the compound inhibits translocation of VEGF is very similar or identical to that of VCAM1, although the signal peptides share no obvious sequence similarities. By mutagenesis of the VEGF signal peptide, two important regions, located in the N-terminal and hydrophobic segments, were identified as critical for compound sensitivity. CAM741 alters positioning of the VEGF signal peptide at the translocon, and increasing hydrophobicity in the h-region reduces compound sensitivity and causes a different, possibly more efficient, interaction with the translocon. Although CAM741 is effective against translocation of both VEGF and VCAM1, the derivative NFI028 is able to inhibit only VCAM1, suggesting that chemical derivatization can alter not only potency, but also the specificity of the compounds.

The translocation inhibitor CAM741 interferes with vascular cell adhesion molecule 1 signal peptide insertion at the translocon

The cyclopeptolide CAM741 selectively inhibits cotranslational translocation of vascular cell adhesion molecule 1 (VCAM1), a process that is dependent on its signal peptide. In this study we identified the C-terminal (C-) region upstream of the cleavage site of the VCAM1 signal peptide as most critical for inhibition of translocation by CAM741, but full sensitivity to the compound also requires residues of the hydrophobic (h-) region and the first amino acid of the VCAM1 mature domain. The murine VCAM1 signal peptide, which is less susceptible to translocation inhibition by CAM741, can be converted into a fully sensitive signal peptide by two amino acid substitutions identified as critical for compound sensitivity of the human VCAM1 signal peptide. Using cysteine substitutions of non-critical residues in the human VCAM1 signal peptide and chemical cross-linking of targeted short nascent chains we show that, in the presence of CAM741, the N- and C-terminal segments of the VCAM1 signal peptide could be cross-linked to the cytoplasmic tail of Sec61beta, indicating altered positioning of the VCAM1 signal peptide relative to this translocon component. Moreover, translocation of a tag fused N-terminal to the VCAM1 signal peptide is selectively inhibited by CAM741. Our data indicate that the compound inhibits translocation of VCAM1 by interfering with correct insertion of its signal peptide into the translocon.

Selective inhibition of cotranslational translocation of vascular cell adhesion molecule 1

Increased expression of vascular cell adhesion molecule 1 (VCAM1) is associated with a variety of chronic inflammatory conditions, making its expression and function a target for therapeutic intervention. We have recently identified CAM741, a derivative of a fungus-derived cyclopeptolide that acts as a selective inhibitor of VCAM1 synthesis in endothelial cells. Here we show that the compound represses the biosynthesis of VCAM1 in cells by blocking the process of cotranslational translocation, which is dependent on the signal peptide of VCAM1. CAM741 does not inhibit targeting of the VCAM1 nascent chains to the translocon channel but prevents translocation to the luminal side of the endoplasmic reticulum (ER), through a process that involves the translocon component Sec61beta. Consequently, the VCAM1 precursor protein is synthesized towards the cytosolic compartment of the cells, where it is degraded. Our results indicate that the inhibition of cotranslational translocation with low-molecular-mass compounds, using specificity conferred by signal peptides, can modulate the biosynthesis of certain secreted and/or membrane proteins. In addition, they highlight cotranslational translocation at the ER membrane as a potential target for drug discovery.

The 3D-structure of a natural inhibitor of cell adhesion molecule expression

The three-dimensional structure of cyclopeptolide HUN-7293, a naturally-occurring inhibitor of cell adhesion molecule expression, has been determined from nuclear magnetic resonance data recorded in solution and from X-ray diffraction analysis of single crystals. The backbone conformation of HUN-7293 is characterized by two cis-peptide bonds in both the solution and crystalline state. Differences between the solution and crystal structure are visible for the orientation of some side chains and the strength of two transannular hydrogen bonds. Such structural information helps to provide insight into the molecular architecture of HUN-7293 on the atomic level and opens the way for structure-based modifications of this novel inhibitor of cell adhesion molecule expression.

The influence of endosome-disruptive peptides on gene transfer using synthetic virus-like gene transfer systems

The process by which viruses destabilize endosomal membranes in an acidification-dependent manner has been mimicked with synthetic peptides that are able to disrupt liposomes, erythrocytes, or endosomes of cultured cells. Peptides containing the 20 amino-terminal amino acid sequence of influenza virus hemagglutinin as well as acidic derivatives showed erythrocyte lysis activity only when peptides were elongated by an amphipathic helix or by carboxyl-terminal dimerization. Interestingly, peptides consisting of the 23 amino-terminal amino acids of influenza virus hemagglutinin were also active in erythrocyte lysis. When peptides were incorporated into DNA complexes that utilize a receptor-mediated endocytosis pathway for uptake into cultured cells, either by ionic interaction with positively charged polylysine-DNA complexes or by a streptavidin-biotin bridge, a strong correlation between pH-specific erythrocyte disruption activity and gene transfer was observed. A high-level expression of luciferase or interleukin-2 was obtained with optimized gene transfer complexes in human melanoma cells and several cell lines.

Effective incorporation of 2'-O-methyl-oligoribonucleotides into liposomes and enhanced cell association through modification with thiocholesterol

Cholesterol was linked to 2'-O-methyl-oligoribonucleotides (2'-OMe-RNA) via a disulfide bond by reacting the 3'-(pyridyldithio)-modified 2'-OMe-RNA with thiocholesterol in dichloromethane-methanol solution. This ligation reaction was made possible by a novel strategy in which the highly charged oligonucleotide was rendered soluble in nonaqueous solvent through conversion to a lipophilic amidinium salt. The biodegradable lipophilic modification of 2'-OMe-RNA resulted in a large increase in incorporation of such oligonucleotides into liposomes prepared by reversephase evaporation. Furthermore, association of these modified oligonucleotides with cultured TIB 73 cells was 100-fold higher than that seen with unmodified 2'-OMe-RNA in serum-free medium and about 10 to 30-fold higher in the presence of 10% calf serum. During incubation with cells, release of the internalized oligonucleotide from the thiocholesteryl moiety can be demonstrated.

A simple procedure for the preparation of protected 2'-O-methyl or 2'-O-ethyl ribonucleoside-3'-O-phosphoramidites

Protected 2'-O-methyl and 2'-O-ethyl ribonucleoside-3'-O-phosphoramidites were prepared via alkylation of the ribonucleosides at an early stage in the synthesis. Utilizing a strategy of minimal protection, the alkylation was performed with unprotected cytidine and adenosine, or with O6-protected guanosine and N3,5'-O-protected uridine using methyl or ethyl iodide and sodium hydride. In subsequent steps, the introduction of standard protective groups for oligonucleotide synthesis and the concomitant separation from 3'-O-alkylated isomers was accomplished. A modification of the phosphitylation procedure permitted facile isolation of the desired phosphoramidites which show high coupling efficiencies in oligomer assembly.

2'-O-methyl, 2'-O-ethyl oligoribonucleotides and phosphorothioate oligodeoxyribonucleotides as inhibitors of the in vitro U7 snRNP-dependent mRNA processing event

We describe the synthesis of 2'-O-methyl, 2'-O-ethyl oligoribonucleotides and phosphorothioate oligodeoxyribonucleotides and demonstrate their utility as inhibitors of the in vitro U7 snRNP-dependent mRNA processing event. These 2'-O-modified compounds were designed to possess the binding affinity of an RNA molecule towards a complementary RNA target with an enhanced stability against nucleases. The 2'-O-methyl and 2'-O-ethyl antisense compounds function as potent inhibitors of the reaction at 1-10 nM, approximately 5-fold more effective than a natural antisense RNA molecule and requiring an approximate 5-fold excess over the target RNA for 80% inhibition of the processing reaction.

[Sports and diet--an ambulatory program for obese children]

In an out-patient programme, 18 obese children aged 9-13 years were attended to for 1 year. The project consisted of an exercise programme performed 3 times per week, dietary restriction to 1200 kcal/d and psychological approach. The aim, besides weight reduction and acquisition of a healthy individual nutrition habit, was to improve physical performance and to increase self-confidence. All children improved physical and coordinative capacity and staying power and showed considerably more self-confidence. Weight reduction to a level below 20% overweight was achieved in the group of 12-13 years of age, whereas younger children showed minor weight loss. In the early period of treatment, HDL-cholesterol generally decreased but increased within 4-5 months exceeding pretreatment levels. No vitamin deficiencies occurred.

[Prevention and therapy of obesity with diet and sports, an ambulatory therapy program for overweight children]

Dietary restriction together with ongoing power-orientated training provide best results in the therapy and prevention of obesity. Diet can reduce the resting metabolic rate by up to 20% within 14 days. Physical activity stimulates the resting metabolic rate and counteracts this energy saving effect, but is especially important for maintaining a steady state after weight reduction. Exercise reduces the risk factors accompanying obesity by favorable adaptation of the sympathoadrenergic system to physical activity. This can be seen in the effects on heart rate, stroke volume, blood pressure, as well as glycogenolytic and lipolytic activities. Body fat especially in the abdominal area, which is particularly connected with atherogenic risk, is diminished. Weight reduction is accompanied by a decrease of the cardioprotective cholesterol fraction. Diets high in unsaturated fatty acids combined with a staying power training have a synergistic effect: they reduce a decrease of HDL. It is difficult to demonstrate risk factors connected with overweight children. However, from the preventive medicine point of view it is advisable to start with therapeutic measures during childhood. In an out-patient pilot project we surveyed 18 obese children aged 9 to 13 years. The therapy plan consisted of dietary restriction (1200 kcal/d), an exercise program performed 3 times a week, and psychological assistance. All children of 12 to 13 years arrived at an overweight level less than 20%, the younger ones displayed a lower weight reduction effect. All 18 improved their aerobic capacity. In the 1st months of treatment, HDL-cholesterol decreased slightly, but increased above pre-treatment level, later on. We did not see any vitamin deficiencies during the therapeutic regimen.