Therapy (2008) 15, 1075–1076 NEWS AND COMMENTARY & 2008 Macmillan Publishers Limited All rights reserved 0969-7128/08 $30.00 www.nature.com/gt expression of the FS-344 isoform ...... AAV-dependent targeting of function and its derivative FS-315 did not affect fertility neither were found histological alterations in the gonads. Follistatin strikes back at muscular In addition, an increase in the muscle mass was observed both in the dystrophy directly injected muscles and in C Colussi, C Gaetano and MC Capogrossi surrounding tissues, suggesting a ...... potential paracrine effect of the (2008) 15, 1075–1076; doi:10.1038/gt.2008.95; circulating isoform. Unfortunately, published online 5 June 2008 it was not determined whether the FS-344 follistatin isoform had any positive effect on heart function; this Muscular dystrophies are muscle- functional improvement of dys- is a relevant issue as currently more wasting diseases due to mutations trophic muscle in mice7 raising the then 30% of all deaths among DMD of , which modulate skeletal possibility that myostatin blocking patients results from cardiac involve- muscle function and, in the case of therapies may represent an alterna- ment. Further, it remains to be dystrophin, form a link between the tive to gene replacement. established the molecular mechan- cytoskeleton and the basal lamina. Very recently, the identification of ism of action of FS-344, including its Dystrophin-deficient myopathies are myostatin-binding proteins capable ability to inhibit activins, proteins the most common genetically of regulating myostatin activity that regulate myostatin function, the determined skeletal muscle diseases further expanded the number of level of muscle maturation as well as and, although a clinically effective potential therapeutic targets in mus- the possible side effects in distal therapy is still lacking, two new cular dystrophy. In this regard, the organs, such as the liver and brain. therapeutic approaches are being study published in PNAS by Haidet Haidet et al.8 used an AAV vector investigated in animal models of et al.8 describes the beneficial effect to deliver the myostatin inhibitor the disease. In one case, the objective of different myostatin-binding pro- proteins cDNAs. AAV are in general is to reconstitute dystrophin gene teins delivered by one-time postnatal safe and efficient tools for gene expression either by cell therapy, intramuscular injection of AAV vec- transfer and maintain for a pro- gene transfer or endogenous gene tors to mdx mice. Specifically, the longed time, even years, high levels repair by exon skipping. The latter authors expressed known secreted of in vivo transgene expression in the can be achieved by adeno-associated myostatin-inhibiting , that is, absence of significant inactivating viral (AAV) vectors expressing small the growth and differentiation fac- immune responses. In this regard, nuclear ribonucleoproteins that tar- tor-associated serum 1, the Haidet et al.8 clearly showed that a get the mutated exons and form a follistatin-related gene and the follis- single injection of the myostatin shorter but in-frame transcript that is tatin splicing variant FS-344. Each inhibitor proteins encoding AAVs translated into functional dystro- and all these molecules increased the enhanced locally the muscle mass phin.1,2 The other approach consists muscle body mass and led to func- for approximately 2 years. However, in targeting molecular pathways tional improvement. In this experi- local intramuscular injection is not a downstream of the primary genetic ment, the FS-344 isoform showed the feasible strategy for a disease in defect, that is, the dystrophin muta- greatest efficacy during a 2-year which the majority of muscles have tion. As an example, pharmacologi- follow-up and the injected animals to be reached by the therapeutic cal administration of histone displayed muscle fibers hypertrophy, agent. Thus, AAV delivery into the deacetylase inhibitors3 or nitric oxide reduced connective tissue deposition systemic circulation, it is recent the donors4,5 have been shown to coun- and increased muscle strength com- discovery that AAV serotype 8 is teract the progression of muscular pared to controls. This beneficial more efficient than other serotypes dystrophy in the mdx mouse model effect could be achieved in young for gene delivery in skeletal and of duchenne muscular dystrophy as well as aged animals, a result that cardiac muscles,9 and the use of (DMD). The beneficial effect of these could have particular relevance for skeletal and cardiac muscle-specific treatments relies, at least in part, on older DMD patients with signifi- promoters need to be examined to the transcriptional activation of the cantly compromised muscle struc- move these interesting results to myostatin antagonist follistatin. Pre- ture and regenerative capacity. clinical evaluation. In addition, it vious studies have shown the role of It is noteworthy that Follistatin has to be kept in mind that early myostatin, a member of the trans- generates the FS-344 and FS-317 iso- clinical studies with AAV vectors forming growth factor-beta family, as forms by . By have shown complications related a negative regulator of muscle devel- subsequent cleavage FS-344 and FS- to unexpected immune responses opment, thus indicating this mole- 317 give rise to FS-315 and FS-288 against the vectors,10 moreover cule and its interactors as possible polypeptides respectively; FS-315 AAV might not be administered to new therapeutic targets. Deletion of is found in the circulation, whereas patients who are already immunized the myostatin gene from mdx mice FS-288 exhibits high tissue affinity against the natural virus.10 significantly enlarged the muscle and may decrease reproductive ability In conclusion, Haidet et al.8 pro- mass and increased strength and because it locates in the gonads and vide new and valuable data about a performance.6 Notably, the develop- interferes with pituitary follicle-sti- novel and potentially clinically rele- ment of antibodies that specifically mulating hormone. Interestingly, in vant strategy for muscle regenera- target and inhibit myostatin led to the study by Haidet et al.8 the tion in DMD. A number of issues, News and Commentary 1076 however, remain to be addressed to model. Proc Natl AcadSci USA 2006; 103: severity of muscular dystrophy in mdx move their results from the bench to 3758–3763. mice. Ann neurol 2002; 52: 832–836. the bedside. ’ 3 Minetti GC, Colussi C, Adami R, Serra 7 Bogdanovich S, Krag TO, Barton ER, C, Mozzetta C, Parente V et al. Func- Morris LD, Whittemore LA, Ahima RS Dr MC Capogrossi and C Gaetano are at the tional and morphological recovery of et al. Functional improvement of dys- Istituto Dermopatico dell’Immacolata-IDI, dystrophic muscles in mice treated with trophic muscle by myostatin blockade. Laboratory of Vascular Pathology Isntituto deacetylase inhibitors. Nat med 2006; 12: Nature 2002; 420: 418–421. Dermopatico Dell’Immacolata, V. Monti di 1147–1150. 8 Haidet AM, Rizo L, Handy C, Umapathi Creta, Rome 167, Italy. 4 Pisconti A, Brunelli S, Di Padova M, De P, Eagle A, Shilling C et al. Long-term E-mail: [email protected] and C Colussi is at the Palma C, Deponti D, Baesso S et al. enhancement of skeletal muscle mass Centro Cardiologico Monzino, Milano, Italy. Follistatin induction by nitric oxide and strength by single gene administra- through cyclic GMP: a tightly regulated tion of myostatin inhibitors. Proc Natl 1 Alter J, Lou F, Rabinowitz A, Yin H, signaling pathway that controls myo- Acad Sci USA 2008; 105: 4318–4322. Rosenfeld J, Wilton SD et al. Systemic blast fusion. J cell biol 2006; 172: 233–244. 9 Wang Z, Zhu T, Qiao C, Zhou L, Wang B, delivery of morpholino oligonucleotide 5 Sciorati C, Galvez BG, Brunelli S, Taglia- Zhang J et al. Adeno-associated virus restores dystrophin expression body- fico E, Ferrari S, Cossu G et al. Ex vivo serotype 8 efficiently delivers genes to wide and improves dystrophic pathol- treatment with nitric oxide increases muscle and heart. Nat biotechnol 2005; 23: ogy. Nat med 2006; 12: 175–177. mesoangioblast therapeutic efficacy in 321–328. 2 Denti MA, Rosa A, D0Antona G, Sthan- muscular dystrophy. J cell sci 2006; 119: 10 Zaiss AK, Muruve DA. Immunity to dier O, De Angelis FG, Nicoletti C et al. 5114–5123. adeno-associated virus vectors in ani- Body-wide gene therapy of Duchenne 6 Wagner KR, McPherron AC, Winik N, mals and humans: a continued chal- muscular dystrophy in the mdx mouse Lee SJ. Loss of myostatin attenuates lenge. Gene Therapy 2008; 15: 808–816.

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