Salmonella enterica serotype Typhimurium (S. Typhimurium) causes acute gut inflammation by using its virulence factors to invade the intestinal epithelium and survive in mucosal macrophages. The inflammatory response enhances the transmission success of S. Typhimurium by promoting its outgrowth in the gut lumen through unknown mechanisms. Here we show that reactive oxygen species generated during inflammation reacted with endogenous, luminal sulphur compounds (thiosulfate) to form a new respiratory electron acceptor, tetrathionate. The genes conferring the ability to utilize tetrathionate as an electron acceptor produced a growth advantage for S. Typhimurium over the competing microbiota in the lumen of the inflamed gut. We conclude that S. Typhimurium virulence factors induce host-driven production of a new electron acceptor that allows the pathogen to use respiration to compete with fermenting gut microbes. Thus, the ability to trigger intestinal inflammation is crucial for the biology of this diarrhoeal pathogen.

Attempts to develop gene therapy for Duchenne muscular dystrophy (DMD) have been complicated by the enormous size of the dystrophin gene. We have performed a detailed functional analysis of dystrophin structural domains and show that multiple regions of the protein can be deleted in various combinations to generate highly functional mini- and micro-dystrophins. Studies in transgenic mdx mice, a model for DMD, reveal that a wide variety of functional characteristics of dystrophy are prevented by some of these truncated dystrophins. Muscles expressing the smallest dystrophins are fully protected against damage caused by muscle activity and are not morphologically different from normal muscle. Moreover, injection of adeno-associated viruses carrying micro-dystrophins into dystrophic muscles of immunocompetent mdx mice results in a striking reversal of histopathological features of this disease. These results demonstrate that the dystrophic pathology can be both prevented and reversed by gene therapy using micro-dystrophins.

A major obstacle limiting gene therapy for diseases of the heart and skeletal muscles is an inability to deliver genes systemically to muscles of an adult organism. Systemic gene transfer to striated muscles is hampered by the vascular endothelium, which represents a barrier to distribution of vectors via the circulation. Here we show the first evidence of widespread transduction of both cardiac and skeletal muscles in an adult mammal, after a single intravenous administration of recombinant adenoassociated virus pseudotype 6 vectors. The inclusion of vascular endothelium growth factor/vascular permeability factor, to achieve acute permeabilization of the peripheral microvasculature, enhanced tissue transduction at lower vector doses. This technique enabled widespread muscle-specific expression of a functional micro-dystrophin in the skeletal muscles of dystrophin-deficient mdx mice, which model Duchenne muscular dystrophy. We propose that these methods may be applicable for systemic delivery of a wide variety of genes to the striated muscles of adult mammals.Human mortality and quality of life are significantly affected by diseases of the striated musculature. Genetic treatments that are being developed for conditions such as heart disease, aging-associated muscle wasting and the muscular dystrophies have been limited by an inability to achieve widespread and efficient gene transfer to the heart and dispersed skeletal muscles of an adult organism 1-4 . For example, anesthesia, invasive surgery and hazardous cofactors are required to transduce varying fractions of the cardiomyocyte population efficiently 1,5 . Similarly, the transfer of genes to the muscles of individual limbs using various vectors requires either direct injection of individual muscles, or complex surgical procedures performed under anesthesia to distribute vectors via the circulation 2-4,6-10 . Here we describe a simple and highly efficient method to transfer genes systemically to the cardiac and skeletal muscles of adult mammals. This approach uses intravenous administration of recombinant adeno-associated virus pseudotype 6 (rAAV6-pseudotyped vectors) 11 , which are extremely effective at transducing skeletal muscles after intramuscular injection 12 .Correspondence should be addressed to J.S.C. (jsc5@u.washington.edu).. 4 These authors contributed equally to this work.Note: Supplementary information is available on the Nature Medicine website. COMPETING INTERESTS STATEMENTThe authors declare competing financial interests (see the Nature Medicine website for details). NIH Public Access RESULTS Systemic transduction of skeletal muscles by rAAV6First, we examined the potential for systemic gene transfer after intravenous administration of rAAV6 vectors at the whole-body level in young adult (6-8 wk) C57Bl/10J mice (Fig. 1). The muscles of mice examined 11 days after administration through the tail vein of ~2 × 10 11 vector genomes of rAAV6 vector containing a CMV-lacZ expression cassette, did not show obvious exogenous β-galactosidase (...

Many neuromuscular conditions are characterized by an exaggerated exercise-induced fatigue response that is disproportionate to activity level. This fatigue does not necessarily correlate with elevated central or peripheral fatigue in patients1, and some patients experience severe fatigue without any demonstrable somatic disease2. Except in myopathies that are due to specific metabolic defects, the mechanism underlying this type of fatigue remains unknown2. With no treatment available, this form of inactivity is a major determinant of disability3. Here we show, using mouse models, that this exaggerated fatigue response is distinct from a loss in specific force production by muscle, and that sarcolemma-localized nNOS signaling in skeletal muscle is required to maintain activity after mild exercise. Of significance, we show that nNOS-null mice do not have muscle pathology and have no loss of muscle specific-force after exercise, but do display this exaggerated fatigue response to mild exercise. In mouse models of nNOS mislocalization from the sarcolemma, prolonged inactivity was only relieved by pharmacologically enhancing the cGMP signal that results from muscle nNOS activation during the nitric oxide signaling response to mild exercise. Our findings suggest that the mechanism underlying the exaggerated fatigue response to mild exercise is a lack of contraction-induced signaling from sarcolemma-localized nNOS, which reduces cGMP-mediated vasomodulation in the vessels that supply active muscle after mild exercise. Notably, sarcolemmal nNOS was reduced in patient biopsies from a large number of distinct myopathies, suggesting a common mechanism of fatigue. Our results suggest that patients with an exaggerated fatigue response to mild exercise would show clinical improvement in response to treatment strategies aimed at improving exercise-induced signaling.