The 2010 Annual Meeting of the International Society for Stem Cell Research (ISSCR) was held in San Francisco in June with an exciting program covering a wealth of stem cell research from basic ...science to clinical research.
Direct lineage reprogramming is a promising approach for human disease modeling and regenerative medicine with poorly understood mechanisms. Here we reveal a hierarchical mechanism in the direct ...conversion of fibroblasts into induced neuronal (iN) cells mediated by the transcription factors Ascl1, Brn2, and Myt1l. Ascl1 acts as an “on target” pioneer factor by immediately occupying most cognate genomic sites in fibroblasts. In contrast, Brn2 and Myt1l do not access fibroblast chromatin productively on their own; instead Ascl1 recruits Brn2 to Ascl1 sites genome-wide. A unique trivalent chromatin signature in the host cells predicts the permissiveness for Ascl1 pioneering activity among different cell types. Finally, we identified Zfp238 as a key Ascl1 target gene that can partially substitute for Ascl1 during iN cell reprogramming. Thus, precise match between pioneer factor and the chromatin context at key target genes is determinative for trans-differentiation to neurons and likely other cell types.
1. The goals of this study were to evaluate the immunogenicity of myogenic cells (MCs) (1) immediately after implantation
into regenerating muscles, and (2) following their maturation under initial ...immunosuppression. Implanted mouse soleus muscles
were evaluated by isometric tension recordings in vitro followed by histological investigations on frozen sections. 2. Implantation
of non-histocompatible myoblasts into cryodamaged soleus muscles of CBA/J mice induced immune rejection which caused large
and permanent deficits in muscle force: 4-42 weeks postimplantation maximal tetanic tension was 50-60% that of intact or regenerated
cryodamaged control muscles without tendency for recovery or histological signs of muscle regeneration. Specific tension (force
per unit muscle weight) was also significantly reduced. 3. On frozen sections, only 62 +/- 12% of the total area was desmin-positive,
that is, occupied by muscle fibres, versus 90 +/- 4% in regenerated and 92 +/- 3% in intact muscles. Also, the total number
of muscle fibre profiles was significantly reduced. 4. Under immune suppression with cyclosporin A (CsA), large muscles developed
within 4 weeks. Following CsA withdrawal, muscle weight and force, in addition to desmin-positive areas on cross-sections,
gradually declined over several months despite continual regeneration, indicating retarded immune rejection. 5. Initial application
of CsA for 8 weeks after implantation, instead of 4 weeks, did not result in better survival of the implants, nor did a higher
initial dose of CsA (100 instead of 50 mg kg-1 day-1). Prolonged continuous application of a reduced dose (25 mg kg-1 day-1)
did not prevent muscle wasting but caused an additional delay. 6. It is concluded that histoincompatible myoblasts are highly
immunogenic and that immune rejection causes large and permanent muscle deficits indicating elimination of host muscle tissue.
Initial transient immunosuppression protects the incompatible cells, but after withdrawal, prolonged immune rejection and
retarded muscle wasting occur.
Design of efficient transplantation strategies for myoblast-based gene therapies in humans requires animal models in which xenografts are tolerated for long periods of time. In addition, such ...recipients should be able to withstand pretransplantation manipulations for enhancement of graft growth. Here we report that a newly developed immunodeficient mouse carrying two known mutations (the recombinase activating gene 2, RAG2, and the common cytokine receptor gamma, gammac) is a candidate fulfilling these requirements. Skeletal muscles from RAG2(-/-)/gammac(-/-) double mutant mice recover normally after myotoxin application or cryolesion, procedures commonly used to induce regeneration and improve transplantation efficiency. Well-differentiated donor-derived muscle tissue could be detected up to 9 weeks after transplantation of human myoblasts into RAG2(-/-)/gammac(-/-) muscles. These results suggest that the RAG2(-/-)/gammac(-/-) mouse model will provide new opportunities for human muscle research.
We have studied the contractile properties, structure, fiber-type composition, and myosin heavy chain (MyHC) expression pattern of regenerating and intact soleus muscles of adult CBA/J mice treated ...with cyclosporin A (CsA) or vehicle solutions (Cremophor, saline). A comparison of muscles after 4-7 weeks drug application with those receiving vehicle showed that the isometric contractile force of intact drug-treated muscles was reduced (tetanus, -21%; twitch, -34%) despite normal mass and muscle cross-sectional area. The frequency of fast-twitch fibers was increased, whereas no innervation deficits, histopathological alterations, or changes in fiber numbers were observed. Regeneration after cryolesion of the contralateral soleus proceeded more slowly in CsA-treated than in vehicle-treated animals. Despite this, when muscle properties reached mature levels (4-7 weeks), muscle mass recovery was better in CsA-treated animals (30% higher weight, 50% more fiber profiles in cross-sections). The force production per unit cross-sectional area was deficient, but not the maximum tension. Twitch time-to-peak and half-relaxation time were shorter than controls correlating with a predominance of fast-twitch fibers (98% Type II fibers versus 16%-18% in control muscles) and fast MyHC isoforms. Partial reversal of this fast phenotype and an increase in muscle force were observed when the animals were left to recover without treatment for 5-8 weeks after CsA application over 7 weeks. The high numbers of fiber profiles in CsA-treated regenerated muscles and increased mass remained unchanged after withdrawal. Thus, CsA treatment has a hyperplastic effect on regenerating muscles, and drug-induced phenotype alterations are much more prominent in regenerated muscles.
Approximately 50% of patients with essential thrombocythemia (ET) or myelofibrosis (MF) lack activating mutations in JAK2. Among these patients, ~10% harbor an activating mutation in the ...thrombopoietin receptor, MPLW515L. We have reported that expression of MPLW515L in a murine bone marrow transplant model recapitulates many features of ET and MF, including severe fibrosis and thrombocytosis, that are not observed in the JAK2V617F model. These observations provide an opportunity to assess the efficacy of small molecule JAK2 inhibitors on a myeloproliferative disease (MPD) induced by MPLW515L in vivo, and to determine whether such inhibitors attenuate thrombocytosis. We have tested EXEL-8232 for efficacy in suppression of thrombocytosis in vivo, and for its ability to attenuate JAK2V617F-negative MPD mediated by MPLW515L. EXEL-8232 is a potent small molecule inhibitor of JAK2 and is structurally similar to XL019, a compound currently in clinical trials for MF and polycythemia vera. EXEL-8232 is selective for JAK2 with a biochemical IC50 of 2 nM, and abolished constitutive phosphorylation of JAK2 and STAT5, as well as cytokine-independent growth, of Ba/F3 cells in vitro. After disease was established 12 days post-bone marrow transplantation, EXEL-8232 was administered for 28 days q12h by oral gavage at doses of 30mg/kg or 100mg/kg respectively. Animals treated with 100mg/kg normalized high platelet counts in excess of2 million/ml and normalized leukocytosis from a median of 134,000/ml in vehicle treated controls. Furthermore, drug treatment eliminated extramedullary hematopoiesis in the spleen, as well as bone marrow fibrosis. Of note, EXEL-8232 had no impact on erythrocytosis in diseased animals or in wild type controls, and wild type animals treated with either dosage of 30mg/kg or 100mg/kg did not develop thrombocytopenia. Consistent with these clinical responses, the surrogate endpoints for response to treatment included a reduction of genomic disease burden in the 100mg/kg treated arm (p<0.05) as assessed by quantitative PCR, a reduction of endogenous colony growth, as well as a inhibition of activation of P-STAT5, P-STAT3 and P-S6K1 kinase as assessed by flow cytometry in immature erythroid and myeloid primary cells both in vitro and upon treatment in vivo. We conclude that EXEL-8232 has efficacy in treatment of thrombocytosis in vivo in a murine model of ET and MF, and may be of therapeutic benefit for patients with JAK2V617F-negative MPD.
Tumor necrosis factor (TNF) plays a central role in the state of insulin resistance leading to type II diabetes. We here describe the crosstalk of TNF with insulin signaling cascades in the mouse ...muscle cell line pmi28. TNF downregulated insulin induced insulin receptor kinase activity and insulin induced activation of the transcription factor STAT5. Our results provide evidence that the inhibitory crosstalk between TNF and insulin in skeletal muscle cells comprises an interference with the expression of STAT5 regulated genes which may play an important role in the manifestation and/or progression of insulin resistance in muscle cells.
Primary aldosteronism (PA) is the most prevalent form of secondary hypertension and is most commonly caused by an adrenal adenoma or bilateral adrenal hyperplasia. Minimally invasive adrenalectomy is ...the treatment of choice for unilateral disease. Here, we report the case of a 57-year-old man with previous bladder cancer who was referred for evaluation of resistant hypertension and hypokalemia. Diagnostic workup indicated PA with computed tomography imaging revealing a left adrenal adenoma and adrenal venous sampling lateralizing to the left adrenal. He was therefore referred for a left adrenalectomy using a retroperitoneoscopic approach. However, surgery was complicated by significant perinephritis related to previous bladder cancer immunotherapy and, in view of an identifiable adrenal adenoma, a partial adrenalectomy was performed. Despite histology confirming removal of an adrenal adenoma, he remained hypertensive and hypokalemic with persistent PA. He underwent a computed tomography-guided percutaneous thermal (microwave) ablation of the residual adrenal nodule with immediate biochemical reversal of PA. Six years postprocedure, he remains biochemically and clinically cured from PA. This article presents the details of the case and reviews the literature on long-term outcomes for patients undergoing thermal ablation and adrenalectomy, suggesting that thermal ablation may be a viable alternative for selected patients.
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