Fragments of bovine insulin-like growth factors I and II stimulate proliferation of rat L6 myoblast cells

Therapeutic approaches for muscle wasting disorders

Muscle wasting and weakness are common in many disease states and conditions including aging, cancer cachexia, sepsis, denervation, disuse, inactivity, burns, HIV-acquired immunodeficiency syndrome (AIDS), chronic kidney or heart failure, unloading/microgravity, and muscular dystrophies. Although the maintenance of muscle mass is generally regarded as a simple balance between protein synthesis and protein degradation, these mechanisms are not strictly independent, but in fact they are coordinated by a number of different and sometimes complementary signaling pathways. Clearer details are now emerging about these different molecular pathways and the extent to which these pathways contribute to the etiology of various muscle wasting disorders. Therapeutic strategies for attenuating muscle wasting and improving muscle function vary in efficacy. Exercise and nutritional interventions have merit for slowing the rate of muscle atrophy in some muscle wasting conditions, but in most cases they cannot halt or reverse the wasting process. Hormonal and/or other drug strategies that can target key steps in the molecular pathways that regulate protein synthesis and protein degradation are needed. This review describes the signaling pathways that maintain muscle mass and provides an overview of some of the major conditions where muscle wasting and weakness are indicated. The review provides details on some therapeutic strategies that could potentially attenuate muscle atrophy, promote muscle growth, and ultimately improve muscle function. The emphasis is on therapies that can increase muscle mass and improve functional outcomes that will ultimately lead to improvement in the quality of life for affected patients.

Efficiency of a high-titer retroviral vector for gene transfer into skeletal myoblasts

BACKGROUND

Genetic transformation of skeletal myoblasts for myocardial repair is dependent on an efficient gene transfer system that integrates the genes of interest into the genome of the target cell and its progeny. The aim of this investigation was to evaluate the use of a new retrovirally based gene transfer system for this purpose.

METHODS

MFGnlslacZ retroviral vector, packaged in high-titer, split-genome packaging cell line (FLYA4) was used to transduce the skeletal myoblast cell line L6. L6 cells, cultured in 10% fetal calf serum, were transduced with the MFGnlslacZ vector by means of filtered supernatant from FLYA4 cells. Transduced L6 cells were divided into four groups. Group I cells were fixed as myoblasts 3 days after transduction. Group II cells were allowed to differentiate into myotubes. Group III cells were split every 3 days for 4 months. Group IV cells were split as in group III but then allowed to differentiate into myotubes. All samples were fixed and stained for beta-galactosidase activity. The effects on gene transfer of transforming growth factor-beta, insulin-like growth factor-I, and platelet-derived growth factor were determined by spectrophotometric assay of beta-galactosidase activity in cells transduced in the presence or absence of serum with 0 to 200 ng/ml of each growth factor.

RESULTS

Morphometric analysis showed that 66.3% +/- 3% to 69.6% +/- 6% of cells in group I to IV expressed the lacZ reporter gene. In the presence of serum, transforming growth factor-beta significantly inhibited gene transfer, whereas insulin-like growth factor-I and platelet-derived growth factor significantly enhanced gene transfer. In absence of serum, however, only platelet-derived growth factor enhanced retrovirally mediated gene transfer into skeletal myoblasts.

CONCLUSION

MFG retroviral vectors packaged in FLYA4 cells are efficient in gene transfer into skeletal myoblasts and result in transgenic expression that is maintained after repeated cell division, differentiation, or both. Platelet-derived growth factor enhances retrovirally mediated gene transfer into skeletal myoblasts.

Neurotrophic factor therapy for nervous system degenerative diseases

The ability of neurotrophic factors to regulate developmental neuronal survival and adult nervous system plasticity suggests the use of these molecules to treat neurodegeneration associated with human diseases. Solid rationales exist for the use of NGF and neurotrophin-3 in the treatment of neuropathies of the peripheral sensory system, insulin-like growth factor and ciliary neurotrophic factor in motor neuron atrophy, and NGF in Alzheimer's disease. Growth factors have been identified for neurons affected in Parkinson's disease, Huntington's disease, and acute brain and spinal cord injury. Various strategies are actively pursued to deliver neurotrophic factors to the brain, and develop therapeutically useful molecules that mimic neurotrophic factor actions or stimulate their production or receptor mechanisms.

Nucleotide sequence of the central coding region of bovine erythrotropin/insulin-like growth factor II cDNA from fetal intestine and northern analysis of the major IGF II transcripts at the time of hepatic erythropoiesis

1. cDNA for insulin-like growth factor II (IGF II) was synthesized from poly A(+)-RNA from fetal bovine intestine and amplified. 2. The sequence corresponding to amino acids 6-62 was identical to a published ovine IGF II sequence cDNA with the exception of a single nucleotide change (G to A). 3. Northern blot analysis of intestine, liver, kidney and spleen from bovine fetuses showed multiple IGF II RNA species which are more similar to the human than to the rodent mRNAs. 4. Under the hybridization conditions used, synthesis of antisense strands, as described in embryonic chicken IGF II transcripts, was undetectable.