Almudena Martinez-Fernandez

Somatic oxidative bioenergetics transitions into pluripotency-dependent glycolysis to facilitate nuclear reprogramming

The bioenergetics of somatic dedifferentiation into induced pluripotent stem cells remains largely unknown. Here, stemness factor-mediated nuclear reprogramming reverted mitochondrial networks into cristae-poor structures. Metabolomic footprinting and fingerprinting distinguished derived pluripotent progeny from parental fibroblasts according to elevated glucose utilization and production of glycolytic end products. Temporal sampling demonstrated glycolytic gene potentiation prior to induction of pluripotent markers. Functional metamorphosis of somatic oxidative phosphorylation into acquired pluripotent glycolytic metabolism conformed to an embryonic-like archetype. Stimulation of glycolysis promoted, while blockade of glycolytic enzyme activity blunted, reprogramming efficiency. Metaboproteomics resolved upregulated glycolytic enzymes and downregulated electron transport chain complex I subunits underlying cell fate determination. Thus, the energetic infrastructure of somatic cells transitions into a required glycolytic metabotype to fuel induction of pluripotency.

Repair of Acute Myocardial Infarction by Human Stemness Factors Induced Pluripotent Stem Cells

Background— Nuclear reprogramming provides an emerging strategy to produce embryo-independent pluripotent stem cells from somatic tissue. Induced pluripotent stem cells (iPS) demonstrate aptitude for de novo cardiac differentiation, yet their potential for heart disease therapy has not been tested. Methods and Results— In this study, fibroblasts transduced with human stemness factors OCT3/4, SOX2, KLF4, and c-MYC converted into an embryonic stem cell–like phenotype and demonstrated the ability to spontaneously assimilate into preimplantation host morula via diploid aggregation, unique to bona fide pluripotent cells. In utero, iPS-derived chimera executed differentiation programs to construct normal heart parenchyma patterning. Within infarcted hearts in the adult, intramyocardial delivery of iPS yielded progeny that properly engrafted without disrupting cytoarchitecture in immunocompetent recipients. In contrast to parental nonreparative fibroblasts, iPS treatment restored postischemic contractile performance, ventricular wall thickness, and electric stability while achieving in situ regeneration of cardiac, smooth muscle, and endothelial tissue. Conclusions— Fibroblasts reprogrammed by human stemness factors thus acquire the potential to repair acute myocardial infarction, establishing iPS in the treatment of heart disease.BACKGROUND Nuclear reprogramming provides an emerging strategy to produce embryo-independent pluripotent stem cells from somatic tissue. Induced pluripotent stem cells (iPS) demonstrate aptitude for de novo cardiac differentiation, yet their potential for heart disease therapy has not been tested. METHODS AND RESULTS In this study, fibroblasts transduced with human stemness factors OCT3/4, SOX2, KLF4, and c-MYC converted into an embryonic stem cell-like phenotype and demonstrated the ability to spontaneously assimilate into preimplantation host morula via diploid aggregation, unique to bona fide pluripotent cells. In utero, iPS-derived chimera executed differentiation programs to construct normal heart parenchyma patterning. Within infarcted hearts in the adult, intramyocardial delivery of iPS yielded progeny that properly engrafted without disrupting cytoarchitecture in immunocompetent recipients. In contrast to parental nonreparative fibroblasts, iPS treatment restored postischemic contractile performance, ventricular wall thickness, and electric stability while achieving in situ regeneration of cardiac, smooth muscle, and endothelial tissue. CONCLUSIONS Fibroblasts reprogrammed by human stemness factors thus acquire the potential to repair acute myocardial infarction, establishing iPS in the treatment of heart disease.

Induced pluripotent stem cells: developmental biology to regenerative medicine.

Nuclear reprogramming of somatic cells with ectopic stemness factors to bioengineer pluripotent autologous stem cells signals a new era in regenerative medicine. The study of developmental biology has provided a roadmap for cardiac differentiation from embryonic tissue formation to adult heart muscle rejuvenation. Understanding the molecular mechanisms of stem-cell-derived cardiogenesis enables the reproducible generation, isolation, and monitoring of progenitors that have the capacity to recapitulate embryogenesis and differentiate into mature cardiac tissue. With the advent of induced pluripotent stem (iPS) cell technology, patient-specific stem cells provide a reference point to systematically decipher cardiogenic differentiation through discrete stages of development. Interrogation of iPS cells and their progeny from selected cohorts of patients is an innovative approach towards uncovering the molecular mechanisms of disease. Thus, the principles of cardiogenesis can now be applied to regenerative medicine in order to optimize personalized therapeutics, diagnostics, and discovery-based science for the development of novel clinical applications.

iPS Programmed Without c-MYC Yield Proficient Cardiogenesis for Functional Heart Chimerism

Rationale: Induced pluripotent stem cells (iPS) allow derivation of pluripotent progenitors from somatic sources. Originally, iPS were induced by a stemness-related gene set that included the c-MYC oncogene. Objective: Here, we determined from embryo to adult the cardiogenic proficiency of iPS programmed without c-MYC, a cardiogenicity-associated transcription factor. Methods and Results: Transgenic expression of 3 human stemness factors SOX2, OCT4, and KLF4 here reset murine fibroblasts to the pluripotent ground state. Transduction without c-MYC reversed cellular ultrastructure into a primitive archetype and induced stem cell markers generating 3-germ layers, all qualifiers of acquired pluripotency. Three-factor induced iPS (3F-iPS) clones reproducibly demonstrated cardiac differentiation properties characterized by vigorous beating activity of embryoid bodies and robust expression of cardiac Mef2c, α-actinin, connexin43, MLC2a, and troponin I. In vitro isolated iPS-derived cardiomyocytes demonstrated functional excitation-contraction coupling. Chimerism with 3F-iPS derived by morula-stage diploid aggregation was sustained during prenatal heart organogenesis and contributed in vivo to normal cardiac structure and overall performance in adult tumor-free offspring. Conclusions: Thus, 3F-iPS bioengineered without c-MYC achieve highest stringency criteria for bona fide cardiogenesis enabling reprogrammed fibroblasts to yield de novo heart tissue compatible with native counterpart throughout embryological development and into adulthood.

Disease-causing mitochondrial heteroplasmy segregated within induced pluripotent stem cell clones derived from a patient with MELAS.

Mitochondrial diseases display pathological phenotypes according to the mixture of mutant versus wild‐type mitochondrial DNA (mtDNA), known as heteroplasmy. We herein examined the impact of nuclear reprogramming and clonal isolation of induced pluripotent stem cells (iPSC) on mitochondrial heteroplasmy. Patient‐derived dermal fibroblasts with a prototypical mitochondrial deficiency diagnosed as mitochondrial encephalomyopathy with lactic acidosis and stroke‐like episodes (MELAS) demonstrated mitochondrial dysfunction with reduced oxidative reserve due to heteroplasmy at position G13513A in the ND5 subunit of complex I. Bioengineered iPSC clones acquired pluripotency with multilineage differentiation capacity and demonstrated reduction in mitochondrial density and oxygen consumption distinguishing them from the somatic source. Consistent with the cellular mosaicism of the original patient‐derived fibroblasts, the MELAS‐iPSC clones contained a similar range of mtDNA heteroplasmy of the disease‐causing mutation with identical profiles in the remaining mtDNA. High‐heteroplasmy iPSC clones were used to demonstrate that extended stem cell passaging was sufficient to purge mutant mtDNA, resulting in isogenic iPSC subclones with various degrees of disease‐causing genotypes. On comparative differentiation of iPSC clones, improved cardiogenic yield was associated with iPSC clones containing lower heteroplasmy compared with isogenic clones with high heteroplasmy. Thus, mtDNA heteroplasmic segregation within patient‐derived stem cell lines enables direct comparison of genotype/phenotype relationships in progenitor cells and lineage‐restricted progeny, and indicates that cell fate decisions are regulated as a function of mtDNA mutation load. The novel nuclear reprogramming‐based model system introduces a disease‐in‐a‐dish tool to examine the impact of mutant genotypes for MELAS patients in bioengineered tissues and a cellular probe for molecular features of individual mitochondrial diseases. STEM Cells2013;31:1298–1308

Stem Cell Platforms for Regenerative Medicine

The pandemic of chronic degenerative diseases associated with aging demographics mandates development of effective approaches for tissue repair. As diverse stem cells directly contribute to innate healing, the capacity for de novo tissue reconstruction harbors a promising role for regenerative medicine. Indeed, a spectrum of natural stem cell sources ranging from embryonic to adult progenitors has been recently identified with unique characteristics for regeneration. The accessibility and applicability of the regenerative armamentarium has been further expanded with stem cells engineered by nuclear reprogramming. Through strategies of replacement to implant functional tissues, regeneration to transplant progenitor cells or rejuvenation to activate endogenous self‐repair mechanisms, the overarching goal of regenerative medicine is to translate stem cell platforms into practice and achieve cures for diseases limited to palliative interventions. Harnessing the full potential of each platform will optimize matching stem cell‐based biologics with the disease‐specific niche environment of individual patients to maximize the quality of long‐term management, while minimizing the needs for adjunctive therapy. Emerging discovery science with feedback from clinical translation is therefore poised to transform medicine offering safe and effective stem cell biotherapeutics to enable personalized solutions for incurable diseases.

Nuclear Reprogramming with c-Myc Potentiates Glycolytic Capacity of Derived Induced Pluripotent Stem Cells

Reprogramming strategies influence the differentiation capacity of derived induced pluripotent stem (iPS) cells. Removal of the reprogramming factor c-Myc reduces tumorigenic incidence and increases cardiogenic potential of iPS cells. c-Myc is a regulator of energy metabolism, yet the impact on metabolic reprogramming underlying pluripotent induction is unknown. Here, mitochondrial and metabolic interrogation of iPS cells derived with (4F) and without (3F) c-Myc demonstrated that nuclear reprogramming consistently reverted mitochondria to embryonic-like immature structures. Metabolomic profiling segregated derived iPS cells from the parental somatic source based on the attained pluripotency-associated glycolytic phenotype and discriminated between 3F versus 4F clones based upon glycolytic intermediates. Real-time flux analysis demonstrated a greater glycolytic capacity in 4F iPS cells, in the setting of equivalent oxidative capacity to 3F iPS cells. Thus, inclusion of c-Myc potentiates the pluripotent glycolytic behavior of derived iPS cells, supporting c-Myc-free reprogramming as a strategy to facilitate oxidative metabolism-dependent lineage engagement.

Induced Pluripotent Reprogramming from Promiscuous Human Stemness-Related Factors

Ectopic expression of pluripotency gene sets provokes nuclear reprogramming in permissive somatic tissue environments, generating nduced pluripotent stem (iPS) cells. The evolutionary conserved function of sternness orthologs was tested here through interspecies transduction. A spectrum of human immunodeficiency virus (HIV)‐based lentiviral vectors was designed, and point mutations in the HIV‐1 capsid region were identified for efficient infectivity and expanded transspecies tropism. Human pluripotent gene sequences, OCT3/4, SOX2, KLF4, and c‐MYC, packaged into engineered lentiviral expression vectors achieved consistent expression in nonhuman fibroblasts. Despite variation in primary amino acid sequence between species, introduction of human pluripotent genes produced cell lines with embryonic stem cell‐like morphology. Transduced fibroblasts differentiated in vitro into all three germ layers according to gastrulation gene expression profiles, and formed in vivo teratoma with multilineage potential. Reprogrammed progeny incorporated into nonhuman morula to produce blastomeres capable of developing into chimeric embryos with competent organogenesis. This model system establishes a prototypic approach to examine consequences of human sternness factors‐induced reprogramming in the context of normal embryonic development by exploiting nonhuman early‐stage embryos. Thus, ectopic xenotransduction across species unmasks the promiscuous nature of sternness induction, suggesting evolutionary selection of core processes for somatic tissue reprogramming.

Induced pluripotent stem cells: advances to applications

Induced pluripotent stem cell (iPS) technology has enriched the armamentarium of regenerative medicine by introducing autologous pluripotent progenitor pools bioengineered from ordinary somatic tissue. Through nuclear reprogramming, patient-specific iPS cells have been derived and validated. Optimizing iPS-based methodology will ensure robust applications across discovery science, offering opportunities for the development of personalized diagnostics and targeted therapeutics. Here, we highlight the process of nuclear reprogramming of somatic tissues that, when forced to ectopically express stemness factors, are converted into bona fide pluripotent stem cells. Bioengineered stem cells acquire the genuine ability to generate replacement tissues for a wide-spectrum of diseased conditions, and have so far demonstrated therapeutic benefit upon transplantation in model systems of sickle cell anemia, Parkinson’s disease, hemophilia A, and ischemic heart disease. The field of regenerative medicine is therefore primed to adopt and incorporate iPS cell-based advancements as a next generation stem cell platforms.

Induced pluripotent stem cell intervention rescues ventricular wall motion disparity, achieving biological cardiac resynchronization post-infarction

•  The pumping function of the heart depends on ordered initiation and propagation of myocardial excitation. Cardiac output is compromised by inconsistent timing and direction of wall motion, leading to dyssynchrony and organ failure. •  Myocardial infarction induces irreversible heart damage. Extensive damage hampers effective pacemaker‐based cardiac resynchronization therapy, the current standard‐of‐care. Establishment of alternative approaches is thus warranted. •  High‐resolution imaging was here utilized to non‐invasively map suitable therapeutic targets within a dyssynchronous heart. Speckle‐tracking echocardiography unmasked the source of progressive cardiac dyssynchrony within the primary infarcted region. •  Bioengineered stem cells with a capacity to induce a regenerative response were implanted into infarcted areas. Speckle‐tracking echocardiography and histology assessment revealed that cell therapy achieved cardiac resynchronization and long‐term repair. •  This proof‐of‐concept study thus introduces a stem cell‐based regenerative solution to address cardiac dyssynchrony post‐infarction.