The early steps of adeno-associated virus (AAV) infection involve attachment to a variety of cell surface receptors (heparan sulfate, integrins, and fibroblast growth factor receptor 1) followed by clathrin-dependent or independent internalization. Here we have studied the subsequent intracellular trafficking of AAV particles from the endosomal compartment to the nucleus. Human cell lines were transduced with a recombinant AAV (rAAV) carrying a reporter gene (luciferase or green fluorescent protein) in the presence of agents that affect trafficking. The effects of bafilomycin A 1 , brefeldin A, and MG-132 were measured. These drugs act at the level of endosome acidification, early-to-late endosome transition, and proteasome activity, respectively. We observed that the transducing virions needed to be routed as far as the late endosomal compartment. This behavior was markedly different from that observed with adenovirus particles. Antiproteasome treatments with MG-132 led to a 50-fold enhancement in transduction efficiency. This effect was accompanied by a 10-fold intracellular accumulation of single-stranded DNA AAV genomes, suggesting that the mechanism of transduction enhancement was different from the one mediated by a helper adenovirus, which facilitates the conversion of the rAAV single-stranded DNA genome into its replicative form. MG-132, a drug currently in clinical use, could be of practical use for potentializing rAAV-mediated delivery of therapeutic genes.

The molecular events by which eccentric muscle contractions induce muscle damage and remodelling remain largely unknown. We assessed whether eccentric exercise modulates the expression of proteinases (calpains 1, 2 and 3, proteasome, cathepsin B+L), muscle structural proteins (α‐sarcoglycan and desmin), and the expression of the heat shock proteins Hsp27 and αB‐crystallin. Vastus lateralis muscle biopsies from twelve healthy male volunteers were obtained before, immediately after, and 1 and 14 days after a 30 min downhill treadmill running exercise. Eccentric exercise induced muscle damage as evidenced by the analysis of muscle pain and weakness, creatine kinase serum activity, myoglobinaemia and ultrastructural analysis of muscle biopsies. The calpain 3 mRNA level was decreased immediately after exercise whereas calpain 2 mRNA level was increased at day 1. Both mRNA levels returned to control values by day 14. By contrast, cathepsin B+L and proteasome enzyme activities were increased at day 14. The α‐sarcoglycan protein level was decreased immediately after exercise and at day 1, whereas the desmin level peaked at day 14. αB‐crystallin and Hsp27 protein levels were increased at days 1 and 14. Our results suggest that the differential expression of calpain 2 and 3 mRNA levels may be important in the process of exercise‐induced muscle damage, whereas expression of α‐sarcoglycan, desmin, αB‐crystallin and Hsp27 may be essentially involved in the subsequent remodelling of myofibrillar structure. This remodelling response may limit the extent of muscle damage upon a subsequent mechanical stress.

Calpain 3 is known as the skeletal muscle–specific member of the calpains, a family of intracellular nonlysosomal cysteine proteases. It was previously shown that defects in the human calpain 3 gene are responsible for limb girdle muscular dystrophy type 2A (LGMD2A), an inherited disease affecting predominantly the proximal limb muscles. To better understand the function of calpain 3 and the pathophysiological mechanisms of LGMD2A and also to develop an adequate model for therapy research, we generated capn3-deficient mice by gene targeting. capn3-deficient mice are fully fertile and viable. Allele transmission in intercross progeny demonstrated a statistically significant departure from Mendel's law. capn3-deficient mice show a mild progressive muscular dystrophy that affects a specific group of muscles. The age of appearance of myopathic features varies with the genetic background, suggesting the involvement of modifier genes. Affected muscles manifest a similar apoptosis-associated perturbation of the IκBα/nuclear factor κB pathway as seen in LGMD2A patients. In addition, Evans blue staining of muscle fibers reveals that the pathological process due to calpain 3 deficiency is associated with membrane alterations.

Calpain 3 is a nonlysosomal cysteine protease whose biological functions remain unknown. We previously demonstrated that this protease is altered in limb girdle muscular dystrophy type 2A patients. Preliminary observations suggested that its gene is subjected to alternative splicing. In this paper, we characterize transcriptional and posttranscriptional events leading to alterations involving the NS, IS1, and IS2 regions and/or the calcium binding domains of the mouse calpain 3 gene (capn3). These events can be divided into three groups: (i) splicing of exons that preserve the translation frame, (ii) inclusion of two distinct intronic sequences between exons 16 and 17 that disrupt the frame and would lead, if translated, to a truncated protein lacking domain IV, and (iii) use of an alternative first exon specific to lens tissue. In addition, expression of these isoforms seems to be regulated. Investigation of the proteolytic activities and titin binding abilities of the translation products of some of these isoforms clearly indicated that removal of these different protein segments affects differentially the biochemical properties examined. In particular, removal of exon 6 impaired the autolytic but not fodrinolytic activity and loss of exon 16 led to an increased titin binding and a loss of fodrinolytic activity. These results are likely to impact our understanding of the pathophysiology of calpainopathies and the development of therapeutic strategies.Study of calpain 3 received an important impetus after the demonstration of its involvement in limb girdle muscular dystrophy type 2A (Mendelian Inheritance in Man [MIM] 253600) (24). This neuromuscular disorder is characterized mainly by symmetrical atrophy and weakness of proximal limb muscles, by elevated creatine kinase in serum, and by a dystrophic pattern in muscle biopsies (4). Calpains are members of a family of intracellular nonlysosomal cysteine proteases (for reviews, see references 35 and 36). They are comprised of three ubiquitous calpains (, m, and /m); a skeletal musclespecific calpain (calpain 3, CAPN3, nCL-1, or p94 [31]), a variant of which is also expressed in a lens-specific manner (17, 18); a digestive tract-specific calpain ); and the stomach-specific calpains (nCL-2 and nCL-2Ј [33]).The human calpain 3 gene was reported to consist of 24 exons spanning approximately 45 kb (24). It encodes a 3.5-kb mRNA expressed predominantly in skeletal muscle tissues. The 821-amino-acid-long calpain 3 protein can be subdivided, like the other calpains, into four domains that include a proteolytic (domain II) and a calcium binding (domain IV) domain (26, 31). In addition, three short calpain 3-specific sequences (NS, IS1, and IS2 [36]) are present. These are located, respectively, at the N terminus, in the protease domain, and between domains III and IV. IS2 includes a titin (connectin) binding site (11, 34) as well as a putative nuclear localization signal (31). Calpain 3 differs from the ubiquitous calpains by its rapid autolysis, at least when it is expre...

Wiskott-Aldrich syndrome (WAS) is an immune deficiency with thrombopenia resulting from mutations in the WASP gene. This gene normally encodes the Wiskott-Aldrich syndrome protein (WASP), a major cytoskeletal regulator expressed in hematopoietic cells. Gene therapy is a promising option for the treatment of WAS, requiring that clinically applicable WASP gene transfer vectors demonstrate efficacy in preclinical studies. Here, we describe a selfinactivating HIV-1-derived lentiviral vector encoding human WASP and show that it effectively transduced bone marrow progenitor cells of WASP knockout (WKO) mice. Transplantation of these transduced cells into lethally irradiated WKO recipients led to stable expression of WASP and correction of immune, inflammatory and cytoskeletal defects. Splenic T-cell proliferation was restored, podosomes were reinstated on bone-marrow-derived dendritic cells and colon inflammation was reduced. This shows for the first time (a) that cytoskeletal defects can be corrected in WKO mice, (b) that human WASP is biologically active in mice and (c) that a lentiviral vector is effective to express human WASP in vivo over several months. These data support further development of such lentiviral vectors for the gene therapy of WAS. Gene Therapy (2005) 12, 597-606.

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BackgroundThe spontaneous emergence of phenotypic heterogeneity in clonal populations of mammalian cells in vitro is a rule rather than an exception. We consider two simple, mutually non-exclusive models that explain the generation of diverse cell types in a homogeneous population. In the first model, the phenotypic switch is the consequence of extrinsic factors. Initially identical cells may become different because they encounter different local environments that induce adaptive responses. According to the second model, the phenotypic switch is intrinsic to the cells that may occur even in homogeneous environments.Principal FindingsWe have investigated the “extrinsic” and the “intrinsic” mechanisms using computer simulations and experimentation. First, we simulated in silico the emergence of two cell types in a clonal cell population using a multiagent model. Both mechanisms produced stable phenotypic heterogeneity, but the distribution of the cell types was different. The “intrinsic” model predicted an even distribution of the rare phenotype cells, while in the “extrinsic” model these cells formed small clusters. The key predictions of the two models were confronted with the results obtained experimentally using a myogenic cell line.ConclusionsThe observations emphasize the importance of the “ecological” context and suggest that, consistently with the “extrinsic” model, local stochastic interactions between phenotypically identical cells play a key role in the initiation of phenotypic switch. Nevertheless, the “intrinsic” model also shows some other aspects of reality: The phenotypic switch is not triggered exclusively by the local environmental variations, but also depends to some extent on the phenotypic intrinsic robustness of the cells.

Individual cells take lineage commitment decisions in a way that is not necessarily uniform. We address this issue by characterising transcriptional changes in cord blood-derived CD34+ cells at the single-cell level and integrating data with cell division history and morphological changes determined by time-lapse microscopy. We show that major transcriptional changes leading to a multilineage-primed gene expression state occur very rapidly during the first cell cycle. One of the 2 stable lineage-primed patterns emerges gradually in each cell with variable timing. Some cells reach a stable morphology and molecular phenotype by the end of the first cell cycle and transmit it clonally. Others fluctuate between the 2 phenotypes over several cell cycles. Our analysis highlights the dynamic nature and variable timing of cell fate commitment in hematopoietic cells, links the gene expression pattern to cell morphology, and identifies a new category of cells with fluctuating phenotypic characteristics, demonstrating the complexity of the fate decision process (which is different from a simple binary switch between 2 options, as it is usually envisioned).