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Gene therapy techniques may build muscle, performance

guss

guss

MuscleHead
Aug 11, 2010
380
179
#1
Bryan Haycock's Research Update column recently described a gene therapy experiment in which an adenovirus was reprogrammed to carry genes for IGF-1 and myosin light chain mRNA. When mice were transfected with the engineered virus, young mice gained new muscle, and more significantly, old mice regained muscle lost in the aging process.

Remarkable as this experiment is, it is by no means unique. Gene therapy is showing potential in fighting cancer, renewing damaged hearts, overcoming muscular dystrophy, and in a myriad of other fields. For those of us interested in the scientific aspects of bodybuilding there are new applications showing up on almost a monthly basis that could revolutionize the sport if applied properly. Nor are these techniques always so high-tech and expensive that they are beyond the means of athletes.

HGF Gene Transfer

Apart from its near-miraculous effects healing liver and ulcers and raising the level of HDL ("good cholesterol") [Ueki1999, Tahara1999, Takahashi1996], Hepatocyte Growth Factor (HGF) is the first of the growth factors to activate satellite cells after injury (including traumatic exercise). [Gal-Levi1998, Tatsumi1998]. Under the influence of HGF, satellite cells proliferate, differentiate, and form new muscle. One of the ways in which prostaglandins build muscle is by inducing secretion of HGF.

In addition to its mitogenic effect, HGF has a potent chemotactic and chemokinetic effect on satellite cells. Muscle regeneration is not solely dependent on satellite cells in the vicinity of the affected muscle. When muscle is crushed for example, it releases HGF, which acts as a chemical distress signal to summon muscle precursors from other locations.

Scientists at Osaka University in Japan have used the Hemaglutinating Virus of Japan (HVJ, also known as the "Sendai" virus) as a vector to transduce HGF into the muscles and liver of rats. HVJ has a big advantage over replication-defective adenovirus (RDAd),which has been favored by Americans. RDAd presents antigens, leading to attack by cells of the immune system [Hirano1998]. This results in loss of persistence of the effect desired. HVJ on the other hand can be repeatedly injected with only the most minor immune system response [Kafri1998].

In the experiment, rats were injected with a poison called dimethylnitrosamine (DMN) for three days each week. DMN selectively damages the liver, causing cell destruction and fibrous scarring similar to liver cirrhosis in humans. The illness was progressive, causing death of all rats by the seventh week, unless they received the HVJ virus with its recombinant human HGF payload.

Beginning after the fourth weekly administration of DMN, at a time when damage to the livers was already widespread, rats were injected once weekly with either 20 mg. of a HVJ-liposome mix, 40 mg. of HVJ-liposome, or a placebo. Analyses showed the serum level of human HGF rose quickly, remained at the higher level for a week, and rose to an even higher level after a second injection. As well, the rats' own endogenous HGF rose after the injections, and remained elevated (see figures).

HGF gene therapy (from Ueki et al., 1999)

Physiologically, treatment with HVJ-HGF reduced fibrosis by 70% and prevented apoptosis caused by DMN. Rats given the smaller dose of HVJ-HGF survived 26% longer, and those given the higher dose were completely cured. All were free of cirrhosis 50 days after the beginning of the experiment.

So this therapy cures cirrhosis, a disease that kills tens of thousands of people each year. More relevantly for bodybuilders, it provides a safe and reliable method for increasing HGF levels in muscles. Although very high levels of HGF can result in tumor formation [Takayama1997], experiments at the U.S. National Cancer Institute show that in transgenic mice with HGF levels 200-300% over normal, tumors were suppressed. The transfection experiment we've described here also produced increased HGF at this lower level. Hence treatment by transfection is likely to be safe.

If this treatment for cirrhosis becomes widespread, it is just a matter of time before it is used by bodybuilders to produce new gains in muscle -- not just hypertrophy, but actual increases in the number of muscle fibers due to activation and proliferation of satellite cells and other muscle precursors by Hepatocyte Growth Factor.

Leptin Gene Transfer

It's not enough for a bodybuilder to have massive muscles, there also must be a bare mimimum of fat for the seperation of the muscles to be evident. What better way to remove fat than to increase leptin, the main substance controlling body composition?

Scientists at Merk Laboratories in Pennsylvania have used a second-generation helper-dependent adenovirus (HDAd) to deliver leptin genes to both normal and genetically obese mice [Morsy1998]. Whereas first-generation adenovirus vectors produced immune reactions and liver toxicity, the HDAd delivery system had significantly improved safety and produced a prolonged increase in serum leptin levels, resulting in weight loss. Actually the real problem with this system is that it accepts such a large genetic payload (37 kilobases) that it is tempting to insert a few more genes just for good measure...

Erythropoietin Gene Transfer

What will the Tour de France be like when the muscles of bicycle racers can be transduced with erythropoietin (EPO),the doping substance that gives them greater endurance by creating more blood cells? That day may not be far off, judging from recent reports.

Credible EPO gene therapy experiments have been reported since 1994 [Tripathy1994, Kessler1996]. Recently, a team from Chiron Corporation showed that a single injection of an adeno- associated virus (AAV) encoded with the EPO gene produced sustained high circulating EPO levels in monkeys. By week #10 after the injection, the monkey's hematocrit had doubled.

However, having a hematocrit that is too high can be as dangerous as anemia. Therefore new experiments reported in the last two years have sought to transfer the EPO gene in a way that production of EPO can be fine-tuned. This is accomplished by adding a transcription factor that can be regulated by dosing with a harmless drug like tetracycline [Ye1999, Bohl1998, Rendahl1998].

The Future

Gene therapy is attracting some of the best minds in science, and the potential rewards in fighting disease are almost beyond imagining. On the way to the lofty goals of suppressing cancer, rebuilding damaged hearts and so on, there will be opportunities for those of us who simply want to get stronger and look better. Imagine a clinic in Brazil that you visit once a year to get your HGF and leptin genes reset. Imagine a scientist at the Pasteur Institute with a lucrative but secret practice catering to bicyclists. These technologies exist today. They just require a modest laboratory capable of sustaining a viral culture. It won't be long.

References

1. Bohl D, Salvetti A, Moullier P, Heard JM. 1998 Sep 1. Control of erythropoietin delivery by doxycycline in mice after intramuscular injection of adeno-associated vector. Blood. 92(5):1512-1517.
2. Gal-Levi R, Leshem Y, Aoki S, Nakamura T, Halevy O. 1998 Mar 12. Hepatocyte growth factor plays a dual role in regulating skeletal muscle satellite cell proliferation and differentiation. Biochim Biophys Acta. 1402(1):39-51.
3. Hirano T, Fujimoto J, Ueki T, Yamamoto H, Iwasaki T, Morisita R, Sawa Y, Kaneda Y, Takahashi H, Okamoto E. 1998 Apr. Persistent gene expression in rat liver in vivo by repetitive transfections using HVJ-liposome. Gene Ther. 5(4):459-464.
4. Kafri T, Morgan D, Krahl T, Sarvetnick N, Sherman L, Verma I. 1998 Sep 15. Cellular immune response to adenoviral vector infected cells does not require de novo viral gene expression: implications for gene therapy. Proc Natl Acad Sci U.S.A. 95(19):11377-11382.
5. Kessler PD, Podsakoff GM, Chen X, McQuiston SA, Colosi PC, Matelis LA, Kurtzman GJ, Byrne BJ. 1996 Nov 26. Gene delivery to skeletal muscle results in sustained expression and systemic delivery of a therapeutic protein. Proc.Natl.Acad.Sci.U.S.A. 93(24):14082-14007.
6. Lattanzi L, Salvatori G, Coletta M, Sonnino C, et al. 1998 May High Efficiency Myogenic Conversion of Human Fibroblasts by Adenoviral Vector-mediated MyoD Gene Transfer. J Clin Invest. 101(10):2119-2128. Full text]
7. Morsy MA, Gu M, Motzel S, Zhao J, Lin J, Su Q, Allen H, et al. 1998 Jul 7. An adenoviral vector deleted for all viral coding sequences results in enhanced safety and extended expression of a leptin transgene. Proc Natl Acad Sci U S A. 95(14):7866-7871.
 
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