Diego Fraidenraich

IGF-II promotes stemness of neural restricted precursors.

Insulin‐like growth factor (IGF)‐I and IGF‐II regulate brain development and growth through the IGF type 1 receptor (IGF‐1R). Less appreciated is that IGF‐II, but not IGF‐I, activates a splice variant of the insulin receptor (IR) known as IR‐A. We hypothesized that IGF‐II exerts distinct effects from IGF‐I on neural stem/progenitor cells (NSPs) via its interaction with IR‐A. Immunofluorescence revealed high IGF‐II in the medial region of the subventricular zone (SVZ) comprising the neural stem cell niche, with IGF‐II mRNA predominant in the adjacent choroid plexus. The IGF‐1R and the IR isoforms were differentially expressed with IR‐A predominant in the medial SVZ, whereas the IGF‐1R was more abundant laterally. Similarly, IR‐A was more highly expressed by NSPs, whereas the IGF‐1R was more highly expressed by lineage restricted cells. In vitro, IGF‐II was more potent in promoting NSP expansion than either IGF‐I or standard growth medium. Limiting dilution and differentiation assays revealed that IGF‐II was superior to IGF‐I in promoting stemness. In vivo, NSPs propagated in IGF‐II migrated to and took up residence in periventricular niches while IGF‐I‐treated NSPs predominantly colonized white matter. Knockdown of IR or IGF‐1R using shRNAs supported the conclusion that the IGF‐1R promotes progenitor proliferation, whereas the IR is important for self‐renewal. Q‐PCR revealed that IGF‐II increased Oct4, Sox1, and FABP7 mRNA levels in NSPs. Our data support the conclusion that IGF‐II promotes the self‐renewal of neural stem/progenitors via the IR. By contrast, IGF‐1R functions as a mitogenic receptor to increase precursor abundance. STEM CELLS2012;30:1265–1276

Increased sarcolipin expression and decreased sarco(endo)plasmic reticulum Ca2+ uptake in skeletal muscles of mouse models of Duchenne muscular dystrophy

Abnormal intracellular Ca2+ handling is an important factor in the progressive functional decline of dystrophic muscle. In the present study, we investigated the function of sarco(endo)plasmic reticulum (SR) Ca2+ ATPase (SERCA) in various dystrophic muscles of mouse models of Duchenne muscular dystrophy. Our studies show that the protein expression of sarcolipin, a key regulator of the SERCA pump is abnormally high and correlates with decreased maximum velocity of SR Ca2+ uptake in the soleus, diaphragm and quadriceps of mild (mdx) and severe (mdx:utr−/−) dystrophic mice. These changes are more pronounced in the muscles of mdx:utr−/− mice. We also found increased expression of SERCA2a and calsequestrin specifically in the dystrophic quadriceps. Immunostaining analysis further showed that SERCA2a expression is associated both with fibers expressing slow-type myosin and regenerating fibers expressing embryonic myosin. Together, our data suggest that sarcolipin upregulation is a common secondary alteration in all dystrophic muscles and contributes to the abnormal elevation of intracellular Ca2+ concentration via SERCA inhibition.

Nitric oxide signalling pathway in Duchenne muscular dystrophy mice: up-regulation of L-arginine transporters.

DMD (Duchenne muscular dystrophy) is an incurable rapidly worsening neuromuscular degenerative disease caused by the absence of dystrophin. In skeletal muscle a lack of dystrophin disrupts the recruitment of neuronal NOS (nitric oxide synthase) to the sarcolemma thus affecting NO (nitric oxide) production. Utrophin is a dystrophin homologue, the expression of which is greatly up-regulated in the sarcolemma of dystrophin-negative fibres from mdx mice, a mouse model of DMD. Although cardiomyopathy is an important cause of death, little is known about the NO signalling pathway in the cardiac muscle of DMD patients. Thus we used cardiomyocytes and hearts from two month-old mdx and mdx:utrophin-/- (double knockout) mice (mdx:utr) to study key steps in NO signalling: L-arginine transporters, NOS and sGC (soluble guanylyl cyclase). nNOS did not co-localize with dystrophin or utrophin to the cardiomyocyte membrane. Despite this nNOS activity was markedly decreased in both mdx and mdx:utr mice, whereas nNOS expression was only decreased in mdx:utr mouse hearts, suggesting that utrophin up-regulation in cardiomyocytes maintains nNOS levels, but not function. sGC protein levels and activity remained at control levels. Unexpectedly, L-arginine transporter expression and function were significantly increased, suggesting a novel biochemical compensatory mechanism of the NO pathway and a potential entry site for therapeutics.

Stem cell transplant into preimplantation embryo yields myocardial infarction-resistant adult phenotype.

Stem cells are an emerging strategy for treatment of myocardial infarction, limited however to postinjury intervention. Preventive stem cell‐based therapy to augment stress tolerance has yet to be considered for lifelong protection. Here, pluripotent stem cells were microsurgically introduced at the blastocyst stage of murine embryo development to ensure stochastic integration and sustained organ contribution. Engineered chimera displayed excess in body weight due to increased fat deposits, but were otherwise devoid of obesity‐related morbidity. Remarkably, and in sharp contrast to susceptible nonchimeric offspring, chimera was resistant to myocardial infarction induced by permanent coronary occlusion. Infarcted nonchimeric adult hearts demonstrated progressive deterioration in ejection fraction, while age‐matched 12–14‐months‐old chimera recovered from equivalent ischemic insult to regain within one‐month preocclusion contractile performance. Electrical remodeling and ventricular enlargement with fibrosis, prominent in failing nonchimera, were averted in the chimeric cohort characterized by an increased stem cell load in adipose tissue and upregulated markers of biogenesis Ki67, c‐Kit, and stem cell antigen‐1 in the myocardium. Favorable outcome in infarcted chimera translated into an overall benefit in workload capacity and survival. Thus, prenatal stem cell transplant yields a cardioprotective phenotype in adulthood, expanding cell‐based indications beyond traditional postinjury applications to include pre‐emptive therapy. STEM CELLS 2009;27:1697–1705

Developmental ablation of Id1 and Id3 genes in the vasculature leads to postnatal cardiac phenotypes

The Id1 and Id3 genes play major roles during cardiac development, despite their expression being confined to non-myocardial layers (endocardium-endothelium-epicardium). We previously described that Id1Id3 double knockout (dKO) mouse embryos die at mid-gestation from multiple cardiac defects, but early lethality precluded the studies of the roles of Id in the postnatal heart. To elucidate postnatal roles of Id genes, we ablated the Id3 gene and conditionally ablated the Id1 gene in the endothelium to generate conditional KO (cKO) embryos. We observed cardiac phenotypes at birth and at 6 months of age. Half of the Id cKO mice died at birth. Postnatal demise was associated with cardiac enlargement and defects in the ventricular septum, trabeculation and vasculature. Surviving Id cKO mice exhibited fibrotic vasculature, cardiac enlargement and decreased cardiac function. An abnormal vascular response was also observed in the healing of excisional skin wounds of Id cKO mice. Expression patterns of vascular, fibrotic and hypertrophic markers were altered in the Id cKO hearts, but addition of Insulin-Like Growth Factor binding protein-3 (IGFbp3) reversed gene expression profiles of vascular and fibrotic, but not hypertrophic markers. Thus, ablation of Id genes in the vasculature leads to distinct postnatal cardiac phenotypes. These findings provide important insights into the role/s of the endocardial network of the endothelial lineage in the development of cardiac disease, and highlight IGFbp3 as a potential link between Id and its vascular effectors.

Embryonic stem cells prevent developmental cardiac defects in mice

The potential therapeutic use of embryonic stem cells (ESCs) has gathered the attention of the scientific and medical communities recently. We report that in addition to their unique capacity to populate defective cardiac tissues, ESCs secrete factors that correct gene expression profiles in the defective neighboring cells. Id (inhibitor of DNA binding) gene knockout (KO) mouse embryos die at midgestation because of multiple cardiac defects, but injection of ESCs into preimplantation Id KO embryos prevents these defects and corrects gene expression profiles throughout the heart. ESCs injected into expectant mothers only partially rescue cardiac defects in the Id KO embryos. Two secreted factors are implicated in the rescue process: insulin-like growth factor I accounts for the long-range action of the ESCs, and Wnt5a, a short-range factor, corrects gene expression profiles in the Id KO hearts. Future studies are discussed.

Selective Connexin43 Inhibition Prevents Isoproterenol-Induced Arrhythmias and Lethality in Muscular Dystrophy Mice.

Duchenne muscular dystrophy (DMD) is caused by an X-linked mutation that leads to the absence of dystrophin, resulting in life-threatening arrhythmogenesis and associated heart failure. We targeted the gap junction protein connexin43 (Cx43) responsible for maintaining cardiac conduction. In mild mdx and severe mdx:utr mouse models of DMD, and human DMD tissues, Cx43 was found to be pathologically mislocalized to lateral sides of cardiomyocytes. In addition, overall Cx43 protein levels were markedly increased in mouse and human DMD heart tissues examined. Electrocardiography on isoproterenol challenged mice showed that both models developed arrhythmias and died within 24 hours, while wild-type mice were free of pathology. Administering peptide mimetics to inhibit lateralized Cx43 function prior to challenge protected mdx mice from arrhythmogenesis and death, while mdx:utr mice displayed markedly improved ECG scores. These findings suggest that Cx43 lateralization contributes significantly to DMD arrhythmogenesis and that selective inhibition may provide substantial benefit.

Blastocyst Injection of Embryonic Stem Cells: A Simple Approach to Unveil Mechanisms of Corrections in Mouse Models of Human Disease

Embryonic stem cell (ESC) research is a promising area of investigation with enormous therapeutic potential. We have injected murine wild type (WT) ESCs into a variety of mutant murine blastocysts, which are predisposed to develop a human-like disease, such as muscular dystrophy or the embryonic lethal “thin myocardial syndrome”. In this review, we summarize data indicating that partial incorporation of ESCs is sufficient to prevent disease from occurring. We also present data indicating that blastocyst incorporation of ESCs may aid in the prevention of heart failure in stressed WT mice. In some cases, the rescue observed is predominantly non-cell autonomous and relies on the production of secreted factors from the ES-derived cells, but in others, cell replacement is required. Thus, congenital or acquired disease can be pre-emptively averted in mice by developmental injection of ESCs.

A Novel Lamin A Mutant Responsible for Congenital Muscular Dystrophy Causes Distinct Abnormalities of the Cell Nucleus.

A-type lamins, the intermediate filament proteins participating in nuclear structure and function, are encoded by LMNA. LMNA mutations can lead to laminopathies such as lipodystrophies, premature aging syndromes (progeria) and muscular dystrophies. Here, we identified a novel heterozygous LMNA p.R388P de novo mutation in a patient with a non-previously described severe phenotype comprising congenital muscular dystrophy (L-CMD) and lipodystrophy. In culture, the patient’s skin fibroblasts entered prematurely into senescence, and some nuclei showed a lamina honeycomb pattern. C2C12 myoblasts were transfected with a construct carrying the patient’s mutation; R388P-lamin A (LA) predominantly accumulated within the nucleoplasm and was depleted at the nuclear periphery, altering the anchorage of the inner nuclear membrane protein emerin and the nucleoplasmic protein LAP2-alpha. The mutant LA triggered a frequent and severe nuclear dysmorphy that occurred independently of prelamin A processing, as well as increased histone H3K9 acetylation. Nuclear dysmorphy was not significantly improved when transfected cells were treated with drugs disrupting microtubules or actin filaments or modifying the global histone acetylation pattern. Therefore, releasing any force exerted at the nuclear envelope by the cytoskeleton or chromatin did not rescue nuclear shape, in contrast to what was previously shown in Hutchinson-Gilford progeria due to other LMNA mutations. Our results point to the specific cytotoxic effect of the R388P-lamin A mutant, which is clinically related to a rare and severe multisystemic laminopathy phenotype.

Neuronal nitric oxide synthase localizes to utrophin expressing intercalated discs and stabilizes their structural integrity

The neuronal nitric-oxide synthase (nNOS) splice variant nNOSµ is essential for skeletal muscle function. Its localization is dependent on dystrophin, which stabilizes the dystrophin glycoprotein complex (DGC) at the sarcolemma of skeletal muscle fibers. In Duchenne muscular dystrophy (DMD) dystrophin is absent and sarcolemmal nNOS is lost. This leads to functional ischemia due to a decrease in contraction-induced vasodilation. In cardiomyocytes, nNOSµ is believed to be the predominant NOS isoform. However, the association of nNOS with the DGC in the heart is unclear. Here, we report nNOS localization at the intercalated discs (IDs) of cardiomyocytes, where utrophin is highly expressed. In mdx, mdx:utr, nNOSµ knock-out (KO), and mdx:nNOSµ KO mice, we observed a gradual reduction of nNOS at IDs and disrupted ID morphology, compared to wild-type. In mdx:nNOSµ KO mice, but not in mdx or nNOSµ KO mice, we also observed an early development of cardiac fibrosis. These findings suggest that nNOS localization in the heart may not depend exclusively on the presence of dystrophin. Additionally, the β1 subunit of soluble guanylyl cyclase (sGC), responsible for the production of cGMP through nitric oxide (NO) signaling, was also detected at the IDs. Together, our results suggest a new role of nNOS at the IDs for the cGMP-dependent NO pathway and the maintenance of ID morphology.