Genetics
Citation Information: J Clin Invest. 2003;111(12):1913-1921. https://doi.org/10.1172/JCI17828.
Abstract
Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an autosomal recessive disorder caused by loss-of-function mutations in the gene encoding thymidine phosphorylase (TP). This deficiency of TP leads to increased circulating levels of thymidine (deoxythymidine, dThd) and deoxyuridine (dUrd) and has been associated with multiple deletions and depletion of mitochondrial DNA (mtDNA). Here we describe 36 point mutations in mtDNA of tissues and cultured cells from MNGIE patients. Thirty-one mtDNA point mutations (86%) were T-to-C transitions, and of these, 25 were preceded by 5′-AA sequences. In addition, we identified a single base-pair mtDNA deletion and a TT-to-AA mutation. Next-nucleotide effects and dislocation mutagenesis may contribute to the formation of these mutations. These results provide the first demonstration that alterations of nucleoside metabolism can induce multiple sequence-specific point mutations in humans. We hypothesize that, in patients with TP deficiency, increased levels of dThd and dUrd cause mitochondrial nucleotide pool imbalances, which, in turn, lead to mtDNA abnormalities including site-specific point mutations.
Authors
Yutaka Nishigaki, Ramon Martí, William C. Copeland, Michio Hirano
Abstract
The inward rectifier current IK1 is tightly regulated regionally within the heart, downregulated in heart failure, and genetically suppressed in Andersen syndrome. We used in vivo viral gene transfer to dissect the role of IK1 in cardiac repolarization and maintenance of the resting membrane potential (RMP) in guinea pig ventricular myocytes. Kir2.1 overexpression boosted Ba2+-sensitive IK1 by more than 100% (at –50mV), significantly shortened action potential durations (APDs), accelerated phase 3 repolarization, and hyperpolarized RMP compared with control cells (nongreen cells from the same hearts and green cells from GFP-transduced hearts). The dominant-negative Kir2.1AAA reduced IK1 by 50–90%; those cells with less than 80% reduction of IK1 exhibited prolonged APDs, decelerated phase 3 repolarization, and depolarization of the RMP. Further reduction of IK1 resulted in a pacemaker phenotype, as previously described. ECGs revealed a 7.7% ± 0.9% shortening of the heart rate–corrected QT interval (QTc interval) in Kir2.1-transduced animals (n = 4) and a 16.7% ± 1.8% prolongation of the QTc interval (n = 3) in Kir2.1AAA-transduced animals 72 hours after gene delivery compared with immediate postoperative recordings. Thus, IK1 is essential for establishing the distinctive electrical phenotype of the ventricular myocyte: rapid terminal repolarization to a stable and polarized resting potential. Additionally, the long-QT phenotype seen in Andersen syndrome is a direct consequence of dominant-negative suppression of Kir2 channel function.
Authors
Junichiro Miake, Eduardo Marbán, H. Bradley Nuss
Citation Information: J Clin Invest. 2003;111(9):1347-1356. https://doi.org/10.1172/JCI16887.
Abstract
Gene replacement therapy is an attractive approach for treatment of genetic disease, but may be complicated by the risk of a neutralizing immune response to the therapeutic gene product. There are examples of humoral and cellular immune responses against the transgene product as well as absence of such responses, depending on vector design and the underlying mutation in the dysfunctional gene. It has been unclear, however, whether transgene expression can induce tolerance to the therapeutic antigen. Here, we demonstrate induction of immune tolerance to a secreted human coagulation factor IX (hF.IX) antigen by adeno-associated viral gene transfer to the liver. Tolerized mice showed absence of anti-hF.IX and substantially reduced in vitro T cell responses after immunization with hF.IX in adjuvant. Tolerance induction was antigen specific, affected a broad range of Th cell subsets, and was favored by higher levels of transgene expression as determined by promoter strength, vector dose, and mouse strain. Hepatocyte-derived hF.IX expression induced regulatory CD4+ T cells that can suppress anti-hF.IX formation after adoptive transfer. With a strain-dependent rate of success, tolerance to murine F.IX was induced in mice with a large F.IX gene deletion, supporting the relevance of these data for treatment of hemophilia B and other genetic diseases.
Authors
Federico Mingozzi, Yi-Lin Liu, Eric Dobrzynski, Antje Kaufhold, Jian Hua Liu, YuQin Wang, Valder R. Arruda, Katherine A. High, Roland W. Herzog
Abstract
Revertant mosaicism due to true back mutations or second-site mutations has been identified in several inherited disorders. The occurrence of revertants is considered rare, and the underlying genetic mechanisms remain mostly unknown. Here we describe somatic mosaicism in two brothers affected with Wiskott-Aldrich syndrome (WAS). The original mutation causing disease in this family is a single base insertion (1305insG) in the WAS protein (WASP) gene, which results in frameshift and abrogates protein expression. Both patients, however, showed expression of WASP in a fraction of their T cells that were demonstrated to carry a second-site mutation causing the deletion of 19 nucleotides from nucleotide 1299 to 1316. This deletion abrogated the effects of the original mutation and restored the WASP reading frame. In vitro expression studies indicated that mutant protein encoded by the second-site mutation was expressed and functional, since it was able to bind to cellular partners and mediate T cell receptor/CD3 downregulation. These observations were consistent with evidence of in vivo selective advantage of WASP-expressing lymphocytes. Molecular analysis revealed that the sequence surrounding the deletion contained two 4-bp direct repeats and that a hairpin structure could be formed by five GC pairs within the deleted fragment. These findings strongly suggest that slipped mispairing was the cause of this second-site mutation and that selective accumulation of WASP-expressing T lymphocytes led to revertant mosaicism in these patients.
Authors
Taizo Wada, Akihiro Konno, Shepherd H. Schurman, Elizabeth K. Garabedian, Stacie M. Anderson, Martha Kirby, David L. Nelson, Fabio Candotti
Abstract
The extracellular calcium-sensing receptor (CaR; alternate gene names, CaR or Casr) is a membrane-spanning G protein–coupled receptor. CaR is highly expressed in the parathyroid gland, and is activated by extracellular calcium (Ca2+o). Mice homozygous for null mutations in the CaR gene (CaR–/–) die shortly after birth because of the effects of severe hyperparathyroidism and hypercalcemia. A wide variety of functions have been attributed to CaR. However, the lethal CaR-deficient phenotype has made it difficult to dissect the direct effect of CaR deficiency from the secondary effects of hyperparathyroidism and hypercalcemia. We therefore generated parathyroid hormone–deficient (PTH-deficient) CaR–/– mice (Pth–/–CaR–/–) by intercrossing mice heterozygous for the null CaR allele with mice heterozygous for a null Pth allele. We show that genetic ablation of PTH is sufficient to rescue the lethal CaR–/– phenotype. Pth–/–CaR–/– mice survive to adulthood with no obvious difference in size or appearance relative to control Pth–/– littermates. Histologic examination of most organs did not reveal abnormalities. These Pth–/–CaR–/– mice exhibit a much wider range of values for serum calcium and renal excretion of calcium than we observe in control littermates, despite the absence of any circulating PTH. Thus, CaR is necessary for the fine regulation of serum calcium levels and renal calcium excretion independent of its effect on PTH secretion.
Authors
Claudine H. Kos, Andrew C. Karaplis, Ji-Bin Peng, Matthias A. Hediger, David Goltzman, Khalid S. Mohammad, Theresa A. Guise, Martin R. Pollak
Abstract
While mast cells and basophils constitutively express the high-affinity IgE receptor (FcεRI), it is absent or weakly expressed on APCs from normal donors. FcεRI is strongly upregulated on APCs from atopic donors and involved in the pathophysiology of atopic diseases. Despite its clinical relevance, data about FcεRI regulation on APCs are scarce. We show that in all donors intracellular α chain of the FcεRI (FcεRIα) accumulates during DC differentiation from monocytes. However, expression of γ chains of the FcεRI (FcεRIγ), mandatory for surface expression, is downregulated. It is low or negative in DCs from normal donors lacking surface FcεRI (FcεRIneg DCs). In contrast, DCs from atopics express surface FcεRI (FcεRIpos DCs) and show significant FcεRIγ expression, which can be coprecipitated with FcεRIα. In FcεRIneg DCs lacking FcεRIγ, immature and core glycosylated FcεRIα accumulates in the endoplasmic reticulum. In FcεRIpos DCs expressing FcεRIγ, an additional mature form of FcεRIα exhibiting complex glycosylation colocalizes with FcεRIγ in the Golgi compartment. IgE binding sustains surface-expressed FcεRI on DCs from atopic donors dependent on baseline protein synthesis and transport and enhances their IgE-dependent APC function. We propose that enhanced FcεRI on DCs from atopic donors is driven by enhanced expression of otherwise limiting amounts of FcεRIγ and is preserved by increased IgE levels.
Authors
Natalija Novak, Carmen Tepel, Susanne Koch, Klaudia Brix, Thomas Bieber, Stefan Kraft
Citation Information: J Clin Invest. 2003;111(6):887-895. https://doi.org/10.1172/JCI15475.
Abstract
We performed a genetic and epigenetic study of the hMLH1 and hMSH2 mismatch repair genes in resected primary tumors from 77 non-small cell lung cancer (NSCLC) patients. The molecular alterations examined included the loss of mRNA and protein expression as well as promoter methylation, and the allelic imbalance of the chromosomal regions that harbor the genes. We found that 78% and 26% of patients showed at least one type of molecular alteration within the hMLH1 and hMSH2 genes, respectively. Promoter methylation of the hMLH1 gene was present in 55.8% of tumors, and was significantly associated with the reduction in mRNA and protein expression (P = 0.001). A 72% concordance of aberrant methylation in sputum samples with matched resected tumors was found. In addition, a 93% consistency between the promoter methylation and the mRNA expression of the hMSH2 gene was found in 14 female NSCLC patients. However, no correlation was found between the expression of hMLH1 and hMSH2 proteins and the allelic imbalance of five microsatellite markers closely linked to the genes. Our results suggest that hMLH1 is the major altered mismatch repair gene involved in NSCLC tumorigenesis, and that promoter methylation is the predominant mechanism in hMLH1 and hMSH2 deregulation. In addition, promoter methylation of the hMLH1 gene may be identified in sputum samples to serve as a potential diagnostic marker of NSCLC.
Authors
Yi-Ching Wang, Yung-Pin Lu, Ruo-Chia Tseng, Ruo-Kai Lin, Jer-Wei Chang, Jung-Ta Chen, Chuen-Ming Shih, Chih-Yi Chen
Citation Information: J Clin Invest. 2003;111(5):717-725. https://doi.org/10.1172/JCI15830.
Abstract
Although lymphedema is a common clinical condition, treatment for this disabling condition remains limited and largely ineffective. Recently, it has been reported that overexpression of VEGF-C correlates with increased lymphatic vessel growth (lymphangiogenesis). However, the effect of VEGF-C–induced lymphangiogenesis on lymphedema has yet to be demonstrated. Here we investigated the impact of local transfer of naked plasmid DNA encoding human VEGF-C (phVEGF-C) on two animal models of lymphedema: one in the rabbit ear and the other in the mouse tail. In a rabbit model, following local phVEGF-C gene transfer, VEGFR-3 expression was significantly increased. This gene transfer led to a decrease in thickness and volume of lymphedema, improvement of lymphatic function demonstrated by serial lymphoscintigraphy, and finally, attenuation of the fibrofatty changes of the skin, the final consequences of lymphedema. The favorable effect of phVEGF-C on lymphedema was reconfirmed in a mouse tail model. Immunohistochemical analysis using lymphatic-specific markers: VEGFR-3, lymphatic endothelial hyaluronan receptor-1, together with the proliferation marker Ki-67 Ab revealed that phVEGF-C transfection potently induced new lymphatic vessel growth. This study, we believe for the first time, documents that gene transfer of phVEGF-C resolves lymphedema through direct augmentation of lymphangiogenesis. This novel therapeutic strategy may merit clinical investigation in patients with lymphedema.
Authors
Young-sup Yoon, Toshinori Murayama, Edwin Gravereaux, Tengiz Tkebuchava, Marcy Silver, Cynthia Curry, Andrea Wecker, Rudolf Kirchmair, Chun Song Hu, Marianne Kearney, Alan Ashare, David G. Jackson, Hajime Kubo, Jeffrey M. Isner, Douglas W. Losordo
Citation Information: J Clin Invest. 2003;111(3):399-407. https://doi.org/10.1172/JCI15737.
Abstract
The availability of mice lacking the mitochondrial uncoupling protein UCP1, has provided an opportunity to analyze the relationship between the capacity for energy expenditure and the development of obesity in response to a high-fat, high-sucrose diet. Congenic UCP1-deficient mice on a C57BL/6J genetic background show a temperature-dependent resistance to diet-induced obesity when compared with wild-type mice. This resistance, which occurs at 20°C, is quickly reversed when the ambient temperature is increased to 27°C. At 20°C, total oxygen consumption and physical activity of mutant and wild-type mice are indistinguishable; however, body temperature is higher in UCP1-deficient mice by 0.1–0.3°C, and respiratory quotient is slightly reduced. A reduced respiratory quotient, together with elevated β-hydroxybutyrate and reduced plasma fatty acid levels, suggests that the mutants oxidize a greater proportion of fat than wild-type mice, and that this possibly accounts for the resistance to diet-induced obesity. Although shivering is one alternative mechanism of thermogenesis that is probably used in UCP1-deficient mice, whether there are others remains to be determined. Nevertheless, our study underscores the paradox that elimination of the major thermogenic mechanism in the animal reduces rather than increases metabolic efficiency. We propose that in the absence of nonshivering thermogenesis, alternative, calorically more costly pathways of metabolism must be used to maintain body temperature.
Authors
Xiaotuan Liu, Martin Rossmeisl, Jennifer McClaine, Leslie P. Kozak
Abstract
IGF-II is a mitogenic peptide that has been implicated in hepatocellular oncogenesis. Since the silencing of gene expression is frequently associated with cytosine methylation at cytosine-guanine (CpG) dinucleotides, we designed a methylated oligonucleotide (MON1) complementary to a region encompassing IGF2 promoter P4 in an attempt to induce DNA methylation at that locus and diminish IGF2 mRNA levels. MON1 specifically inhibited IGF2 mRNA accumulation in vitro, whereas an oligonucleotide (ON1) with the same sequence but with nonmethylated cytosines had no effect on IGF2 mRNA abundance. MON1 treatment led to the specific induction of de novo DNA methylation in the region of IGF2 promoter hP4. Cells from a human hepatocellular carcinoma (HCC) cell line, Hep 3B, were implanted into the livers of nude mice, resulting in the growth of large tumors. Animals treated with MON1 had markedly prolonged survival as compared with those animals treated with saline or a truncated methylated oligonucleotide that did not alter IGF2 mRNA levels in vitro. This study demonstrates that a methylated sense oligonucleotide can be used to induce epigenetic changes in the IGF2 gene and that inhibition of IGF2 mRNA accumulation may lead to enhanced survival in a model of HCC.
Authors
Xiaoming Yao, Ji-Fan Hu, Mark Daniels, Hadas Shiran, Xiangjun Zhou, Huifan Yan, Hongqi Lu, Zhilan Zeng, Qingxue Wang, Tao Li, Andrew R. Hoffman
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