Gene therapy olTers a radically different approach to the treatment of arthritis. We demonstrated that cDNA coding for human interleukin-1 receptor-antagonist protein (IL-1Ra) and cDNA coding for human interleukin-I0 (IL-10) can be delivered. by ex vivo techniques, to the synovial lining of joints, intra-articular expression of gene significantly reduced cartilage matrix degradation and cartilage breakdown. To achieve this, lapine synoviocytes were first transduced in culture by retroviral infection. The genetically modified synoviocytes were then transplanted by intra-articular injection into the knee joints of OA rabbits, assay of joint lavages confirmed that the gene expression was not lost 14 days after transfer. Knees receiving the IL-IRa gene had significantly reduced cartilage breakdown. Delivery of the IL-I0 gene was less effective, having only a moderate effect on cartilage breakdown. When both genes were injected together, there was a greater inhibition of cartilage breakdown, suggesting that simultaneous gene delivery may be necessary to treat OA by targeting the activities of multiple inflammatory effectors.

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Ciliary neurotrophic factor (CNTF) is primarily known for its important cellular effects within the nervous system. However, recent studies indicate that its receptor can be highly expressed in denervated skeletal muscle. Here, we investigated the direct effect of CNTF on skeletal myoblasts of adult human. Surprisingly, we found that CNTF induced the myogenic lineage-committed myoblasts at a clonal level to dedifferentiate into multipotent progenitor cells-they not only could proliferate for over 20 passages with the expression absence of myogenic specific factors Myf5 and MyoD, but they were also capable of differentiating into new phenotypes, mainly neurons, glial cells, smooth muscle cells, and adipocytes. These "progenitor cells" retained their myogenic memory and were capable of redifferentiating into myotubes. Furthermore, CNTF could activate the p44/p42 MAPK and down-regulate the expression of myogenic regulatory factors (MRFs). Finally, PD98059, a specific inhibitor of p44/p42 MAPK pathway, was able to abolish the effects of CNTF on both myoblast fate and MRF expression. Our results demonstrate the myogenic lineage-committed human myoblasts can dedifferentiate at a clonal level and CNTF is a novel regulator of skeletal myoblast dedifferentiation via p44/p42 MAPK pathway. INTRODUCTIONAdult skeletal myoblasts have long been considered as myogenic lineage-committed cells with either self-renewing or differentiating into multinucleated myotubes in vitro (Jankowski et al., 2002;Tamaki et al., 2003). Myoblast fate is critically dependent on the myogenic regulatory factors (MRFs): MyoD, Myf5, myogenin, and Mrf4, which have a well-defined role in orchestrating skeletal muscle development and differentiation. Gene targeting in mice has illustrated the essential role for MRFs: Myf5 and MyoD is critical to establishing the myogenic cell lineage and producing committed, undifferentiated myoblasts (Kablar et al., 1999), whereas myogenin has an important role in initiating differentiation (Hasty et al., 1993); Mrf4 regulates terminal differentiation and myofiber maintenance (Patapoutian et al., 1995). Gene targeting in mice has illustrated the essential role for Myf5 and MyoD in myoblast fates. In MyoDϪ/Ϫ and/or Myf5Ϫ/Ϫ knockout mice, muscle precursors acquire nonmuscle cell fates (Kablar et al., 1999) and become multipotential stem cells or a progenitor compartment (Parker et al., 2003). Early histological studies indicated that muscle fibers at the amputation plane of urodele amphibians might dedifferentiate by budding off mononucleate cells from syncytial muscle cells (Echeverri and Tanaka, 2002). Recent studies suggest that dedifferentiation may be also possible in mammalian system (Odelberg et al., 2000;Tsai et al., 2002;Chen et al., 2004). Especially, the recent reports have shown that ectopic expression of msx1 in C2C12 myotubes can induce dedifferentiation of the myotubes to produce multipotent mononucleated cells (Odelberg et al., 2000), and a 2,6-disubstituted purine, reversine, can also induce dedifferentia...