Functional substitution by TAT-utrophin in dystrophin-deficient mice

Background: The loss of dystrophin compromises muscle cell membrane stability and causes Duchenne muscular dystrophy and/or various forms of cardiomyopathy. Increased expression of the dystrophin homolog utrophin by gene delivery or pharmacologic up-regulation has been demonstrated to restore membrane integrity and improve the phenotype in the dystrophin-deficient mdx mouse. However, the lack of a viable therapy in humans predicates the need to explore alternative methods to combat dystrophin deficiency. We investigated whether systemic administration of recombinant full-length utrophin (Utr) or DR4-21 ‘‘micro’ ’ utrophin (mUtr) protein modified with the cell-penetrating TAT protein transduction domain could attenuate the phenotype of mdx mice. Methods and Findings: Recombinant TAT-Utr and TAT-mUtr proteins were expressed using the baculovirus system and purified using FLAG-affinity chromatography. Age-matched mdx mice received six twice-weekly intraperitoneal injections of either recombinant protein or PBS. Three days after the final injection, mice were analyzed for several phenotypic parameters of dystrophin deficiency. Injected TAT-mUtr transduced all tissues examined, integrated with members of the dystrophin complex, reduced serum levels of creatine kinase (11,2906920 U versus 5,95061,120 U; PBS versus TAT), the prevalence of muscle degeneration/regeneration (54%65 % versus 37%64 % of centrally nucleated fibers; PBS versus TAT), the susceptibility to eccentric contraction-induced force drop (72%65 % versus 40%68 % drop; PBS versus TAT), an