IVan Velasco - Academia.edu (original) (raw)

Papers by IVan Velasco

Background and Purpose-Because fibroblast growth factor 2 is a mitogen for central nervous system... more Background and Purpose-Because fibroblast growth factor 2 is a mitogen for central nervous system stem cells, we explored whether long-term fibroblast growth factor 2 delivery to the brain can improve functional outcome and induce cortical neurogenesis after ischemia. Methods-Rats underwent permanent distal middle cerebral artery occlusion resulting in an ischemic injury limited to the cortex. We used an adeno-associated virus transfection system to induce long-term fibroblast growth factor 2 expression and monitored behavioral and histological changes. Results-Treatment increased the number of proliferating cells and improved motor behavior. Neurogenesis continued throughout 90 days after the ischemia, and the occurrence of newly generated cells with characteristics of neural precursors and immature neurons was most evident 90 days after treatment. Conclusions-Focal cortical ischemia elicits an ongoing neurogenic response that can be enhanced with fibroblast growth factor 2 leading to improved functional outcome. (Stroke. 2007;38:153-161.)

Stroke, 2006

Background and Purpose-Because fibroblast growth factor 2 is a mitogen for central nervous system... more Background and Purpose-Because fibroblast growth factor 2 is a mitogen for central nervous system stem cells, we explored whether long-term fibroblast growth factor 2 delivery to the brain can improve functional outcome and induce cortical neurogenesis after ischemia. Methods-Rats underwent permanent distal middle cerebral artery occlusion resulting in an ischemic injury limited to the cortex. We used an adeno-associated virus transfection system to induce long-term fibroblast growth factor 2 expression and monitored behavioral and histological changes. Results-Treatment increased the number of proliferating cells and improved motor behavior. Neurogenesis continued throughout 90 days after the ischemia, and the occurrence of newly generated cells with characteristics of neural precursors and immature neurons was most evident 90 days after treatment. Conclusions-Focal cortical ischemia elicits an ongoing neurogenic response that can be enhanced with fibroblast growth factor 2 leading to improved functional outcome. (Stroke. 2007;38:153-161.)

Science, 2001

Although the source of embryonic stem (ES) cells presents ethical concerns, their use may lead to... more Although the source of embryonic stem (ES) cells presents ethical concerns, their use may lead to many clinical benefits if differentiated cell types can be derived from them and used to assemble functional organs. In pancreas, insulin is produced and secreted by specialized structures, islets of Langerhans. Diabetes, which affects 16 million people in the United States, results from abnormal function of pancreatic islets. We have generated cells expressing insulin and other pancreatic endocrine hormones from mouse ES cells. The cells self-assemble to form three-dimensional clusters similar in topology to normal pancreatic islets where pancreatic cell types are in close association with neurons. Glucose triggers insulin release from these cell clusters by mechanisms similar to those employed in vivo. When injected into diabetic mice, the insulin-producing cells undergo rapid vascularization and maintain a clustered, islet-like organization.

The International Journal of Developmental Biology, 2009

Neural stem cells (NSC) self-renew and generate specialized cell types. There are reports indicat... more Neural stem cells (NSC) self-renew and generate specialized cell types. There are reports indicating that Notch and Leukemia Inhibitory Factor (LIF) signaling are involved in cell determination of NSC, either preventing differentiation or promoting astrocytic fate. In this work, we aimed to compare the astrocytogenic effect of activated Notch with that induced by LIF. To this end, rat cerebral cortex neural progenitors/NSC were transduced with retroviral vectors in order to express green fluorescent protein (GFP), or a fusion protein of GFP with the active Notch1 intracellular domain (NICD). In parallel, other cultures were treated with increasing concentrations of LIF. We confirmed, in proliferating NSC, that LIF activated intracellular effectors by measuring STAT3 phosphorylation and Socs3 transcription.

Developmental Biology, 2007

This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apol... more This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause.The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy

Developmental Biology, 2009

Developmental Biology, 2009

Background: Histamine (HA) regulates the sleep-wake cycle, synaptic plasticity and memory in adul... more Background: Histamine (HA) regulates the sleep-wake cycle, synaptic plasticity and memory in adult mammals. Dopaminergic specification in the embryonic ventral midbrain (VM) coincides with increased HA brain levels. To study the effect of HA receptor stimulation on dopamine neuron generation, we administered HA to dopamine progenitors, both in vitro and in vivo.

Journal of Materials Science-materials in Medicine, 2000

Chemotropic proteins guide neuronal projections to their final target during embryo development a... more Chemotropic proteins guide neuronal projections to their final target during embryo development and are useful to guide axons of neurons used in transplantation therapies. Site-specific delivery of the proteins however is needed for their application in the brain to avoid degradation and pleiotropic affects. In the present study we report the use of Poly (ethylene glycol)-Silica (PEG-Si) nanocomposite gel with thixotropic properties that make it injectable and suitable for delivery of the chemotropic protein semaphorin 3A. PEG-Si gel forms a functional gradient of semaphorin that enhances axon outgrowth of dopaminergic neurons from rat embryos or differentiated from stem cells in culture. It is not cytotoxic and its properties allowed its injection into the striatum without inflammatory response in the short term. Long term implantation however led to an increase in macrophages and glial cells. The inflammatory response could have resulted from non-degraded silica particles, as observed in biodegradation assays.

Brain Research Bulletin, 1999

The hexacationic dye ruthenium red produce neuronal death in primary cultures. We injected messen... more The hexacationic dye ruthenium red produce neuronal death in primary cultures. We injected messenger RNA (mRNA) from cultured neurons into Xenopus laevis oocytes to test whether this treatment can make oocytes sensitive to the damaging action of ruthenium red. Two-microelectrode voltage clamp and resting membrane potential were used to evaluate mRNA expression and to assess the effect of the dye on oocyte survival, when added to the medium or when injected into the cells, at 20, 50, or 100 μM concentrations. Injection of mRNA from cultured cortical or cerebellar granule neurons produced both new outward currents and membrane hyperpolarization. Exposure of mRNA-injected oocytes to extracellular ruthenium red for 24 h induced a remarkable depolarization, but no significant damage was observed. Injection of the dye into buffer-injected oocytes did not cause any change in membrane potential or cell survival, whereas in mRNA-injected oocytes an important depolarization was observed at 24 h after ruthenium red introduction, and 29% of the cells showed serious damage. The results suggest that oocytes become sensitive to intracellular ruthenium red toxicity because they express neuronal-specific proteins involved in cell death.

Cell Transplantation, 2009

Embryonic stem (ES) cells can be induced to differentiate into motor neurons (MN). Animal models ... more Embryonic stem (ES) cells can be induced to differentiate into motor neurons (MN). Animal models resembling MN degeneration and paralysis observed in familial amyotrophic lateral sclerosis (ALS) have been previously reported. In this work, we aimed to investigate whether transplanted MN could prevent motor deterioration in transgenic rats expressing a mutant form of human superoxide dismutase 1 (hSOD1(G93A)) associated with inherited ALS. Mouse ES cells were differentiated to neurons that express green fluorescent protein (GFP) under the promoter of the MN-specific gene hb9, as well as molecular markers indicative of MN identity. Cells were grafted into the lumbar spinal cord of adult wild-type (WT) or hSOD1(G93A) rats at 10 weeks of age, when transgenic animals are presymptomatic. Grafted cells with MN phenotype can survive for at least 1 week in hSOD1(G93A) animals. To quantitatively evaluate motor performance of WT and transgenic rats, we carried out weekly rotarod tests starting when the animals were 14 weeks old. Sham and grafted WT animals showed no decline in their ability to sustain themselves on the rotating rod. In contrast, sham hSOD1(G93A) rats decreased in motor performance from week 16 onwards, reaching paralysis by week 19 of age. In grafted transgenic animals, there was a significant improvement in rotarod competence at weeks 16 and 17 when compared to sham hSOD1(G93A). However, in the following weeks, transplanted hSOD1(G93A) rats showed motor deterioration and eventually exhibited paralysis by week 19. At end-stage, we found only a few endogenous MN in sham and grafted hSOD1(G93A) rats by cresyl violet staining; no choline acetyl transferase-positive nor GFP-positive MN were present in grafted transgenic subjects. In contrast, WT rats analyzed at the same age possessed grafted GFP-positive MN in their spinal cords. These results strongly suggest that the transgenic hSOD1(G93A) environment is detrimental to grafted MN in the long term.

Developmental Biology, 2007

Developmental Biology, 2007

This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apol... more This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause.The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy

Developmental Biology, 2007

Developmental Biology, 2007

Molecular Brain, 2014

Background: Histamine (HA) regulates the sleep-wake cycle, synaptic plasticity and memory in adul... more Background: Histamine (HA) regulates the sleep-wake cycle, synaptic plasticity and memory in adult mammals. Dopaminergic specification in the embryonic ventral midbrain (VM) coincides with increased HA brain levels. To study the effect of HA receptor stimulation on dopamine neuron generation, we administered HA to dopamine progenitors, both in vitro and in vivo.

International Journal of Developmental Neuroscience, 2009

Estradiol protects dopamine neurons of the substantia nigra from toxic insults. Such neurons succ... more Estradiol protects dopamine neurons of the substantia nigra from toxic insults. Such neurons succumb in Parkinson's disease; one strategy for restoring dopamine deficiency is cell therapy with neurons differentiated from embryonic stem cells. We investigated the effects of 17b-estradiol on dopaminergic induction of embryonic stem cells using the 5-stage protocol. Cells were incubated with different steroid concentrations during the proliferation (stage 4) or differentiation (stage 5) phases. Estradiol added at nM concentrations only during stage 4 increases the proliferation of dopaminergic precursors expressing Lmx1a, inducing a higher proportion of dopamine neurons at stage 5. These actions were mediated by activation of estrogen receptors, because co-incubation of cells with estradiol and ICI 182,780 completely abolished the positive effect on both proliferation of committed precursors, and subsequent differentiation to dopaminergic neurons. Our results suggest that estradiol should be useful in producing higher proportions of dopamine neurons from embryonic stem cells aimed for treating Parkinson's disease.

STEM CELLS, 2014

Access to healthy or diseased human neural tissue is a daunting task and represents a barrier for... more Access to healthy or diseased human neural tissue is a daunting task and represents a barrier for advancing our understanding about the cellular, genetic, and molecular mechanisms underlying neurogenesis and neurodegeneration. Reprogramming of somatic cells to pluripotency by transient expression of transcription factors was achieved a few years ago. Induced pluripotent stem cells (iPSC) from both healthy individuals and patients suffering from debilitating, life-threatening neurological diseases have been differentiated into several specific neuronal subtypes. An alternative emerging approach is the direct conversion of somatic cells (i.e., fibroblasts, blood cells, or glial cells) into neuron-like cells. However, to what extent neuronal direct conversion of diseased somatic cells can be achieved remains an open question. Optimization of current expansion and differentiation approaches is highly demanded to increase the differentiation efficiency of specific phenotypes of functional neurons from iPSCs or through somatic cell direct conversion. The realization of the full potential of iPSCs relies on the ability to precisely modify specific genome sequences. Genome editing technologies including zinc finger nucleases, transcription activator-like effector nucleases, and clustered regularly interspaced short palindromic repeat/CAS9 RNA-guided nucleases have progressed very fast over the last years. The combination of genome-editing strategies and patient-specific iPSC biology will offer a unique platform for in vitro generation of diseased and corrected neural derivatives for personalized therapies, disease modeling and drug screening.

Developmental Biology, 2007

Background and Purpose-Because fibroblast growth factor 2 is a mitogen for central nervous system... more Background and Purpose-Because fibroblast growth factor 2 is a mitogen for central nervous system stem cells, we explored whether long-term fibroblast growth factor 2 delivery to the brain can improve functional outcome and induce cortical neurogenesis after ischemia. Methods-Rats underwent permanent distal middle cerebral artery occlusion resulting in an ischemic injury limited to the cortex. We used an adeno-associated virus transfection system to induce long-term fibroblast growth factor 2 expression and monitored behavioral and histological changes. Results-Treatment increased the number of proliferating cells and improved motor behavior. Neurogenesis continued throughout 90 days after the ischemia, and the occurrence of newly generated cells with characteristics of neural precursors and immature neurons was most evident 90 days after treatment. Conclusions-Focal cortical ischemia elicits an ongoing neurogenic response that can be enhanced with fibroblast growth factor 2 leading to improved functional outcome. (Stroke. 2007;38:153-161.)

Stroke, 2006

Background and Purpose-Because fibroblast growth factor 2 is a mitogen for central nervous system... more Background and Purpose-Because fibroblast growth factor 2 is a mitogen for central nervous system stem cells, we explored whether long-term fibroblast growth factor 2 delivery to the brain can improve functional outcome and induce cortical neurogenesis after ischemia. Methods-Rats underwent permanent distal middle cerebral artery occlusion resulting in an ischemic injury limited to the cortex. We used an adeno-associated virus transfection system to induce long-term fibroblast growth factor 2 expression and monitored behavioral and histological changes. Results-Treatment increased the number of proliferating cells and improved motor behavior. Neurogenesis continued throughout 90 days after the ischemia, and the occurrence of newly generated cells with characteristics of neural precursors and immature neurons was most evident 90 days after treatment. Conclusions-Focal cortical ischemia elicits an ongoing neurogenic response that can be enhanced with fibroblast growth factor 2 leading to improved functional outcome. (Stroke. 2007;38:153-161.)

Science, 2001

Although the source of embryonic stem (ES) cells presents ethical concerns, their use may lead to... more Although the source of embryonic stem (ES) cells presents ethical concerns, their use may lead to many clinical benefits if differentiated cell types can be derived from them and used to assemble functional organs. In pancreas, insulin is produced and secreted by specialized structures, islets of Langerhans. Diabetes, which affects 16 million people in the United States, results from abnormal function of pancreatic islets. We have generated cells expressing insulin and other pancreatic endocrine hormones from mouse ES cells. The cells self-assemble to form three-dimensional clusters similar in topology to normal pancreatic islets where pancreatic cell types are in close association with neurons. Glucose triggers insulin release from these cell clusters by mechanisms similar to those employed in vivo. When injected into diabetic mice, the insulin-producing cells undergo rapid vascularization and maintain a clustered, islet-like organization.

The International Journal of Developmental Biology, 2009

Neural stem cells (NSC) self-renew and generate specialized cell types. There are reports indicat... more Neural stem cells (NSC) self-renew and generate specialized cell types. There are reports indicating that Notch and Leukemia Inhibitory Factor (LIF) signaling are involved in cell determination of NSC, either preventing differentiation or promoting astrocytic fate. In this work, we aimed to compare the astrocytogenic effect of activated Notch with that induced by LIF. To this end, rat cerebral cortex neural progenitors/NSC were transduced with retroviral vectors in order to express green fluorescent protein (GFP), or a fusion protein of GFP with the active Notch1 intracellular domain (NICD). In parallel, other cultures were treated with increasing concentrations of LIF. We confirmed, in proliferating NSC, that LIF activated intracellular effectors by measuring STAT3 phosphorylation and Socs3 transcription.

Developmental Biology, 2007

This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apol... more This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause.The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy

Developmental Biology, 2009

Developmental Biology, 2009

Background: Histamine (HA) regulates the sleep-wake cycle, synaptic plasticity and memory in adul... more Background: Histamine (HA) regulates the sleep-wake cycle, synaptic plasticity and memory in adult mammals. Dopaminergic specification in the embryonic ventral midbrain (VM) coincides with increased HA brain levels. To study the effect of HA receptor stimulation on dopamine neuron generation, we administered HA to dopamine progenitors, both in vitro and in vivo.

Journal of Materials Science-materials in Medicine, 2000

Chemotropic proteins guide neuronal projections to their final target during embryo development a... more Chemotropic proteins guide neuronal projections to their final target during embryo development and are useful to guide axons of neurons used in transplantation therapies. Site-specific delivery of the proteins however is needed for their application in the brain to avoid degradation and pleiotropic affects. In the present study we report the use of Poly (ethylene glycol)-Silica (PEG-Si) nanocomposite gel with thixotropic properties that make it injectable and suitable for delivery of the chemotropic protein semaphorin 3A. PEG-Si gel forms a functional gradient of semaphorin that enhances axon outgrowth of dopaminergic neurons from rat embryos or differentiated from stem cells in culture. It is not cytotoxic and its properties allowed its injection into the striatum without inflammatory response in the short term. Long term implantation however led to an increase in macrophages and glial cells. The inflammatory response could have resulted from non-degraded silica particles, as observed in biodegradation assays.

Brain Research Bulletin, 1999

The hexacationic dye ruthenium red produce neuronal death in primary cultures. We injected messen... more The hexacationic dye ruthenium red produce neuronal death in primary cultures. We injected messenger RNA (mRNA) from cultured neurons into Xenopus laevis oocytes to test whether this treatment can make oocytes sensitive to the damaging action of ruthenium red. Two-microelectrode voltage clamp and resting membrane potential were used to evaluate mRNA expression and to assess the effect of the dye on oocyte survival, when added to the medium or when injected into the cells, at 20, 50, or 100 μM concentrations. Injection of mRNA from cultured cortical or cerebellar granule neurons produced both new outward currents and membrane hyperpolarization. Exposure of mRNA-injected oocytes to extracellular ruthenium red for 24 h induced a remarkable depolarization, but no significant damage was observed. Injection of the dye into buffer-injected oocytes did not cause any change in membrane potential or cell survival, whereas in mRNA-injected oocytes an important depolarization was observed at 24 h after ruthenium red introduction, and 29% of the cells showed serious damage. The results suggest that oocytes become sensitive to intracellular ruthenium red toxicity because they express neuronal-specific proteins involved in cell death.

Cell Transplantation, 2009

Embryonic stem (ES) cells can be induced to differentiate into motor neurons (MN). Animal models ... more Embryonic stem (ES) cells can be induced to differentiate into motor neurons (MN). Animal models resembling MN degeneration and paralysis observed in familial amyotrophic lateral sclerosis (ALS) have been previously reported. In this work, we aimed to investigate whether transplanted MN could prevent motor deterioration in transgenic rats expressing a mutant form of human superoxide dismutase 1 (hSOD1(G93A)) associated with inherited ALS. Mouse ES cells were differentiated to neurons that express green fluorescent protein (GFP) under the promoter of the MN-specific gene hb9, as well as molecular markers indicative of MN identity. Cells were grafted into the lumbar spinal cord of adult wild-type (WT) or hSOD1(G93A) rats at 10 weeks of age, when transgenic animals are presymptomatic. Grafted cells with MN phenotype can survive for at least 1 week in hSOD1(G93A) animals. To quantitatively evaluate motor performance of WT and transgenic rats, we carried out weekly rotarod tests starting when the animals were 14 weeks old. Sham and grafted WT animals showed no decline in their ability to sustain themselves on the rotating rod. In contrast, sham hSOD1(G93A) rats decreased in motor performance from week 16 onwards, reaching paralysis by week 19 of age. In grafted transgenic animals, there was a significant improvement in rotarod competence at weeks 16 and 17 when compared to sham hSOD1(G93A). However, in the following weeks, transplanted hSOD1(G93A) rats showed motor deterioration and eventually exhibited paralysis by week 19. At end-stage, we found only a few endogenous MN in sham and grafted hSOD1(G93A) rats by cresyl violet staining; no choline acetyl transferase-positive nor GFP-positive MN were present in grafted transgenic subjects. In contrast, WT rats analyzed at the same age possessed grafted GFP-positive MN in their spinal cords. These results strongly suggest that the transgenic hSOD1(G93A) environment is detrimental to grafted MN in the long term.

Developmental Biology, 2007

Developmental Biology, 2007

This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apol... more This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause.The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy

Developmental Biology, 2007

Developmental Biology, 2007

Molecular Brain, 2014

Background: Histamine (HA) regulates the sleep-wake cycle, synaptic plasticity and memory in adul... more Background: Histamine (HA) regulates the sleep-wake cycle, synaptic plasticity and memory in adult mammals. Dopaminergic specification in the embryonic ventral midbrain (VM) coincides with increased HA brain levels. To study the effect of HA receptor stimulation on dopamine neuron generation, we administered HA to dopamine progenitors, both in vitro and in vivo.

International Journal of Developmental Neuroscience, 2009

Estradiol protects dopamine neurons of the substantia nigra from toxic insults. Such neurons succ... more Estradiol protects dopamine neurons of the substantia nigra from toxic insults. Such neurons succumb in Parkinson's disease; one strategy for restoring dopamine deficiency is cell therapy with neurons differentiated from embryonic stem cells. We investigated the effects of 17b-estradiol on dopaminergic induction of embryonic stem cells using the 5-stage protocol. Cells were incubated with different steroid concentrations during the proliferation (stage 4) or differentiation (stage 5) phases. Estradiol added at nM concentrations only during stage 4 increases the proliferation of dopaminergic precursors expressing Lmx1a, inducing a higher proportion of dopamine neurons at stage 5. These actions were mediated by activation of estrogen receptors, because co-incubation of cells with estradiol and ICI 182,780 completely abolished the positive effect on both proliferation of committed precursors, and subsequent differentiation to dopaminergic neurons. Our results suggest that estradiol should be useful in producing higher proportions of dopamine neurons from embryonic stem cells aimed for treating Parkinson's disease.

STEM CELLS, 2014

Access to healthy or diseased human neural tissue is a daunting task and represents a barrier for... more Access to healthy or diseased human neural tissue is a daunting task and represents a barrier for advancing our understanding about the cellular, genetic, and molecular mechanisms underlying neurogenesis and neurodegeneration. Reprogramming of somatic cells to pluripotency by transient expression of transcription factors was achieved a few years ago. Induced pluripotent stem cells (iPSC) from both healthy individuals and patients suffering from debilitating, life-threatening neurological diseases have been differentiated into several specific neuronal subtypes. An alternative emerging approach is the direct conversion of somatic cells (i.e., fibroblasts, blood cells, or glial cells) into neuron-like cells. However, to what extent neuronal direct conversion of diseased somatic cells can be achieved remains an open question. Optimization of current expansion and differentiation approaches is highly demanded to increase the differentiation efficiency of specific phenotypes of functional neurons from iPSCs or through somatic cell direct conversion. The realization of the full potential of iPSCs relies on the ability to precisely modify specific genome sequences. Genome editing technologies including zinc finger nucleases, transcription activator-like effector nucleases, and clustered regularly interspaced short palindromic repeat/CAS9 RNA-guided nucleases have progressed very fast over the last years. The combination of genome-editing strategies and patient-specific iPSC biology will offer a unique platform for in vitro generation of diseased and corrected neural derivatives for personalized therapies, disease modeling and drug screening.

Developmental Biology, 2007