The mitochondrial ADP/ATP carrier (AAC) is a major transport protein of the inner mitochondrial membrane. It exchanges mitochondrial ATP for cytosolic ADP and controls cellular production of ATP. In ...addition, it has been proposed that AAC mediates mitochondrial uncoupling, but it has proven difficult to demonstrate this function or to elucidate its mechanisms. Here we record AAC currents directly from inner mitochondrial membranes from various mouse tissues and identify two distinct transport modes: ADP/ATP exchange and H
transport. The AAC-mediated H
current requires free fatty acids and resembles the H
leak via the thermogenic uncoupling protein 1 found in brown fat. The ADP/ATP exchange via AAC negatively regulates the H
leak, but does not completely inhibit it. This suggests that the H
leak and mitochondrial uncoupling could be dynamically controlled by cellular ATP demand and the rate of ADP/ATP exchange. By mediating two distinct transport modes, ADP/ATP exchange and H
leak, AAC connects coupled (ATP production) and uncoupled (thermogenesis) energy conversion in mitochondria.
Recent advances in DNA sequencing technologies are revealing how human genetic variations associate with differential health risks, disease susceptibilities, and drug responses. Such information is ...now expected to help evaluate individual health risks, design personalized health plans and treat patients with precision. It is still challenging, however, to understand how such genetic variations cause the phenotypic alterations in pathobiologies and treatment response. Human induced pluripotent stem cell (iPSC) technologies are emerging as a promising strategy to fill the knowledge gaps between genetic association studies and underlying molecular mechanisms. Breakthroughs in genome editing technologies and continuous improvement in iPSC differentiation techniques are particularly making this research direction more realistic and practical. Pioneering studies have shown that iPSCs derived from a variety of monogenic diseases can faithfully recapitulate disease phenotypes in vitro when differentiated into disease-relevant cell types. It has been shown possible to partially recapitulate disease phenotypes, even with late onset and polygenic diseases. More recently, iPSCs have been shown to validate effects of disease and treatment-related single nucleotide polymorphisms identified through genome wide association analysis. In this review, we will discuss how iPSC research will further contribute to human health in the coming era of precision medicine. Stem Cells 2017;35:545-550.
The mitochondrial permeability transition pore (MPTP) has resisted molecular identification. The original model of the MPTP that proposed the adenine nucleotide translocator (ANT) as the inner ...membrane pore-forming component was challenged when mitochondria from Ant1/2 double null mouse liver still had MPTP activity. Because mice express three
genes, we reinvestigated whether the ANTs comprise the MPTP. Liver mitochondria from
,
, and
deficient mice were highly refractory to Ca
-induced MPTP formation, and when also given cyclosporine A (CsA), the MPTP was completely inhibited. Moreover, liver mitochondria from mice with quadruple deletion of
,
,
, and
(cyclophilin D, target of CsA) lacked Ca
-induced MPTP formation. Inner-membrane patch clamping in mitochondria from
,
, and
triple null mouse embryonic fibroblasts showed a loss of MPTP activity. Our findings suggest a model for the MPTP consisting of two distinct molecular components: The ANTs and an unknown species requiring CypD.
Nanog is a critical homeodomain factor responsible for maintaining embryonic stem (ES) cell self-renewal and pluripotency. Of interest, Nanog expression is not homogeneous in the conventional culture ...of murine ES cells. A Nanog-high population expresses markers for pluripotent ES cells, whereas a Nanog-low population expresses markers for primitive endoderm, such as Gata6. Since the inner cell mass of early blastocysts has recently been reported to be heterogeneous in terms of Nanog and Gata6 expression, ES cells appear to closely resemble the developing stage from which they originate. We further demonstrate that Nanog can directly repress Gata6 expression through its binding to the proximal promoter region of the Gata6 gene and that overexpression of Nanog reduces heterogeneity during ES cell maintenance. Interestingly, Nanog heterogeneity does not correlate with the heterogeneous expression of stage-specific embryonic antigen-1, suggesting that multiple but overlapping levels of heterogeneity may exist in ES cells. These findings provide insight into the factors that control ES cell self-renewal and the earliest lineage commitment to primitive endoderm while also suggesting methods to promote homogeneity during ES cell maintenance. Disclosure of potential conflicts of interest is found at the end of this article.
Myotonic dystrophy type 1 (DM1) is caused by expanded Cytosine-Thymine-Guanine (CTG) repeats in the 3′-untranslated region (3′ UTR) of the Dystrophia myotonica protein kinase (DMPK) gene, for which ...there is no effective therapy. The objective of this study is to develop genome therapy in human DM1 induced pluripotent stem (iPS) cells to eliminate mutant transcripts and reverse the phenotypes for developing autologous stem cell therapy. The general approach involves targeted insertion of polyA signals (PASs) upstream of DMPK CTG repeats, which will lead to premature termination of transcription and elimination of toxic mutant transcripts. Insertion of PASs was mediated by homologous recombination triggered by site-specific transcription activator-like effector nuclease (TALEN)-induced double-strand break. We found genome-treated DM1 iPS cells continue to maintain pluripotency. The insertion of PASs led to elimination of mutant transcripts and complete disappearance of nuclear RNA foci and reversal of aberrant splicing in linear-differentiated neural stem cells, cardiomyocytes, and teratoma tissues. In conclusion, genome therapy by insertion of PASs upstream of the expanded DMPK CTG repeats prevented the production of toxic mutant transcripts and reversal of phenotypes in DM1 iPS cells and their progeny. These genetically-treated iPS cells will have broad clinical application in developing autologous stem cell therapy for DM1.
Mitochondria contain cardiolipin (CL), an organelle-specific phospholipid that carries four fatty acids with a strong preference for unsaturated chains. Unsaturation is essential for the stability ...and for the function of mitochondrial CL. Surprisingly, we found tetrapalmitoyl-CL (TPCL), a fully saturated species, in the testes of humans and mice. TPCL was absent from other mouse tissues but was the most abundant CL species in testicular germ cells. Most intriguingly, TPCL was not localized in mitochondria but was in other cellular membranes even though mitochondrial CL was the substrate from which TPCL was synthesized. During spermiogenesis, TPCL became associated with the acrosome, a sperm-specific organelle, along with a subset of authentic mitochondrial proteins, including Ant4, Suox, and Spata18. Our data suggest that mitochondria-derived membranes are assembled into the acrosome, challenging the concept that this organelle is strictly derived from the Golgi apparatus and revealing a novel function of mitochondria.
Myotonic dystrophy type 1 (DM1) is caused by a CTG nucleotide repeat expansion within the 3′ UTR of the Dystrophia Myotonica protein kinase gene. In this study, we explored therapeutic genome editing ...using CRISPR/Cas9 via targeted deletion of expanded CTG repeats and targeted insertion of polyadenylation signals in the 3′ UTR upstream of the CTG repeats to eliminate toxic RNA CUG repeats. We found paired SpCas9 or SaCas9 guide RNA induced deletion of expanded CTG repeats. However, this approach incurred frequent inversion in both the mutant and normal alleles. In contrast, the insertion of polyadenylation signals in the 3′ UTR upstream of the CTG repeats eliminated toxic RNA CUG repeats, which led to phenotype reversal in differentiated neural stem cells, forebrain neurons, cardiomyocytes, and skeletal muscle myofibers. We concluded that targeted insertion of polyadenylation signals in the 3′ UTR is a viable approach to develop therapeutic genome editing for DM1.
Myotonic dystrophy type 1 is caused by toxic RNAs with expanded CUG repeats in the 3′ UTR of the DMPK gene. Wang et al. developed a strategy to eliminate the toxic repeats by insertion of polyadenylation signals upstream of the expanded repeats for personalized cell-based therapy and in vivo therapeutic genome editing.
Embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) have promise in regenerative medicine because of their ability to differentiate into all 3 primary germ layers. This review ...describes recent advances in the understanding of the link between the metabolism of ESCs/iPSCs and their maintenance/differentiation in the cell culture setting, with particular emphasis on amino acid (AA) metabolism. ESCs are endowed with unique metabolic features with regard to energy consumption, metabolite flux through particular pathways, and macromolecular synthesis. Therefore, nutrient availability has a strong influence on stem cell growth, self-renewal, and lineage specification, both in vivo and in vitro. Evidence from several laboratories has documented that self-renewal and differentiation of mouse ESCs are critically dependent on proline metabolism, with downstream metabolites possibly serving as signal molecules. Likewise, catabolism of either threonine (mouse) or methionine (human) is required for growth and differentiation of ESCs because these AAs serve as precursors for donor molecules used in histone methylation and acetylation. Epigenetic mechanisms are recognized as critical steps in differentiation, and AA metabolism in ESCs appears to modulate these epigenetic processes. Recent reports also document that, in vitro, the nutrient composition of the culture medium in which ESCs are differentiated into embryoid bodies can influence lineage specification, leading to enrichment of a specific cell type. Although research designed to direct tissue specification of differentiating embryoid bodies in culture is still in its infancy, early results indicate that manipulation of the nutrient milieu can promote or suppress the formation of specific cell lineages.
Trithorax proteins and long-intergenic noncoding RNAs are critical regulators of embryonic stem cell pluripotency; however, how they cooperatively regulate germ layer mesoderm specification remains ...elusive. We report here that HoxBlinc RNA first specifies Flk1(+) mesoderm and then promotes hematopoietic differentiation through regulation of hoxb pathways. HoxBlinc binds to the hoxb genes, recruits Setd1a/MLL1 complexes, and mediates long-range chromatin interactions to activate transcription of the hoxb genes. Depletion of HoxBlinc by shRNA-mediated knockdown or CRISPR-Cas9-mediated genetic deletion inhibits expression of hoxb genes and other factors regulating cardiac/hematopoietic differentiation. Reduced hoxb expression is accompanied by decreased recruitment of Set1/MLL1 and H3K4me3 modification, as well as by reduced chromatin loop formation. Re-expression of hoxb2-b4 genes in HoxBlinc-depleted embryoid bodies rescues Flk1(+) precursors that undergo hematopoietic differentiation. Thus, HoxBlinc plays an important role in controlling hoxb transcription networks that mediate specification of mesoderm-derived Flk1(+) precursors and differentiation of Flk1(+) cells into hematopoietic lineages.
The IFN‐stimulated gene ubiquitin‐specific proteinase 18 (USP18) encodes a protein that negatively regulates T1 IFN signaling via stearic inhibition of JAK1 recruitment to the IFN‐α receptor 2 ...subunit (IFNAR2). Here, we demonstrate that USP18 expression is induced by HIV‐1 in a T1 IFN‐dependent manner. Experimental depletion of USP18 by clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR‐associated protein 9 (Cas9) gene editing results in a significant restriction of HIV‐1 replication in an induced pluripotent stem cell (iPSC)‐derived macrophage model. In the absence of USP18, macrophages have increased responsiveness to stimulation with T1 IFNs with prolonged phosphorylation of STAT1 and STAT2 and increased expression of IFN‐stimulated genes that are key for antiviral responses. Interestingly, HIV‐1 requires some signaling through the T1 IFN receptor to replicate efficiently because a neutralizing antibody that inhibits T1 IFN activity reduces HIV‐1 replication rate in monocyte‐derived macrophages. USP18 induction by HIV‐1 tunes the IFN response to optimal levels allowing for efficient transcription from the HIV‐1 LTR promoter while minimizing the T1 IFN‐induced antiviral response that would otherwise restrict viral replication and spread. Finally, iPSC and CRISPR/Cas9 gene targeting offer a powerful tool to study host factors that regulate innate immune responses.
USP18 promotes HIV‐1 replication by negatively regulating expression of antiviral genes induced by T1 IFN signaling.
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