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Duchenne muscular dystrophy (DMD) is an inherited severe muscle wasting disorder with, thus far, no effective therapy. DMD causes respiratory and cardiac failure as well as muscle wastage. Among the various symptoms, respiratory insufficiency is a major cause of death in DMD patients at about 20 years of age. So, naturally, the improvement of respiratory function will extend the patient's life. We report here, for the first time, a sensitive procedure using whole-body plethysmography to monitor respiratory parameters detected in the utrophin/dystrophin double knockout mouse (dko mouse), showing quite similar systemic symptoms to human DMD including restrictive ventilatory impairment. Furthermore, we show that a highly efficient dystrophin-transduction to the dko's diaphragm--achieved by simple intraperitoneal injection of a helper-dependent adenovirus vector (HDAdv) containing the full-length dystrophin expression cassette--provided beneficial results. In spite of dystrophin expression only in the diaphragm, this focal gene transfer could result in the rescue from ventilatory impairment (increased tidal volume (TV) and improvement of compensatory hyperpnea). Our result suggests that a DMD patient's mortal ventilatory impairment may be improved via technically easy means through the intraperitoneal injection of HDAdv.

Variations in gene promoter/enhancer activity in different muscle fiber types after gene transduction was noticed previously, but poorly analyzed. The murine stem cell virus (MSCV) promoter drives strong, stable gene expression in hematopoietic stem cells and several other cells, including cerebellar Purkinje cells, but it has not been studied in muscle. We injected a lentiviral vector carrying an MSCV-EGFP cassette (LvMSCV-EGFP) into tibialis anterior muscles and observed strong EGFP expression in muscle fibers, primary cultured myoblasts, and myotubes isolated from injected muscles. We also generated lentiviral-mediated transgenic mice carrying the MSCV-EGFP cassette and detected transgene expression in striated muscles. LvMSCV-EGFP transgenic mice showed fiber type-dependent variations in expression: highest in types I and IIA, intermediate in type IID/X, and lowest in type IIB fibers. The soleus and diaphragm muscles, consisting mainly of types I and IIA, are most severely affected in the mdx mouse model of muscular dystrophy. Further analysis of this promoter may have the potential to achieve certain gene expression in severely affected muscles of mdx mice. The Lv-mediated transgenic mouse may prove a useful tool for assessing the enhancer/promoter activities of a variety of different regulatory cassettes.

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