During embryogenesis, serotonin has been reported to be involved in craniofacial and cardiovascul... more During embryogenesis, serotonin has been reported to be involved in craniofacial and cardiovascular morphogenesis. The detailed molecular mechanisms underlying these functions, however remain unknown. From mouse and human species, we have recently reported the cloning of 5-HT2B receptors which share signal transduction pathways with other 5-HT2 receptor subtypes (5-HT2A and 5-HT2C). In addition to phospholipase C stimulation, it appears that these three subtypes of receptor transduce a common serotonin-induced mitogenic activity, which could be important for cell differentiation and proliferation. We have first investigated the expression of 5-HT2 receptor mRNAs in the mouse embryo. Interestingly, a peak of 5-HT2B receptor mRNA expression was detected 8-9 days postcoitum, whereas there was only low level 5-HT2A and no 5-HT2C receptor mRNA expression at this stage. Expression of this receptor was confirmed by binding assays using a 5-HT2-specific ligand which revealed a peak of bindi...
Background Background: Spinocerebellar ataxia type 7 (SCA7) is primarily characterized by progres... more Background Background: Spinocerebellar ataxia type 7 (SCA7) is primarily characterized by progressive cerebellar degeneration with major alteration of Purkinje cells (PC) due to polyglutamine expansion in ATXN7, a subunit of SAGA transcriptional co-regulator complex. Additional neural tissues are affected and contribute to diverse symptoms. Current animal models were insufficient to recapitulate the broad spectrum of SCA7 pathology and the mechanisms of PC degeneration remain poorly explored. Methods: To delineate spatio-temporal features of SCA7, we performed a longitudinal characterization of a new knock-in mice line expressing ATXN7 with 140 glutamines (SCA7 140Q/5Q ) using a battery of analyses including motor tests, brain and retina imaging, morphometry, electrophysiology, electron microscopy and immunohistochemistry of disease tissues. We also determined the cerebellar transcriptome and cell-type specific gene deregulation. Results: Here we describe the first SCA7 knock-in mic...
Knock-out of the mouse RXRa gene was previously shown to result in a hypoplastic heart ventricula... more Knock-out of the mouse RXRa gene was previously shown to result in a hypoplastic heart ventricular wall, histologically detectable in 12.5 dpc fetuses. We show here that a precocious differentiation can be detected as early as 8.5 dpc in ventricular cardiomyocytes of RXRα−/− mutants. This precocious differentiation, which is characterized by the presence of striated myofibrils, sarcoplasmic reticulum and intercalated disks, is found after 9.5 dpc in about 50% of RXRα−/− subepicardial myocytes. In contrast, wild-type subepicardial myocytes remain morphologically undifferentiated up to at least 16.5 dpc. A similar precocious differentiation was observed in 9.5 dpc subepicardial myocytes of several RXR0α−/− and RARα−/− mutants, as well as in vitamin A-deficient embryos. The proportion of differentiated subepicardial myocytes almost reached 100% in RXRα/RXRβ double null mutants, indicating a partial functional redundancy between RXRα and RXRβ. This differentiation defect was always para...
Obesity is a major risk factor for insulin resistance (IR) and its attendant complications. The p... more Obesity is a major risk factor for insulin resistance (IR) and its attendant complications. The pathogenic mechanisms linking them remain poorly understood, partly due to a lack of intermediary monogenic human phenotypes. Here, we report on a monogenic form of IR-prone obesity, Alström syndrome (ALMS). Twenty-three subjects with monogenic or polygenic obesity underwent hyperinsulinemic-euglycemic clamping with concomitant adipose tissue (AT) microdialysis and an in-depth analysis of subcutaneous AT histology. We have shown a relative AT failure in a monogenic obese cohort, a finding supported by observations in a novel conditional mouse model (Almsflin/flin) and ALMS1-silenced human primary adipocytes, whereas selective reactivation of ALMS1 gene in AT of an ALMS conditional knockdown mouse model (Almsflin/flin; Adipo-Cre+/−) restores systemic insulin sensitivity and glucose tolerance. Hence, we show for the first time the relative AT failure in human obese cohorts to be a major det...
Centronuclear myopathies (CNM) are non-dystrophic muscle diseases for which no effective therapy ... more Centronuclear myopathies (CNM) are non-dystrophic muscle diseases for which no effective therapy is currently available. The most severe form, X-linked CNM, is caused by myotubularin 1 (MTM1) loss-of-function mutations, while the main autosomal dominant form is due to dynamin2 (DNM2) mutations. We previously showed that genetic reduction of DNM2 expression in Mtm1 knockout (Mtm1KO) mice prevents development of muscle pathology. Here we show that systemic delivery of Dnm2 antisense oligonucleotides (ASOs) into Mtm1KO mice efficiently reduces DNM2 protein level in muscle and prevents the myopathy from developing. Moreover, systemic ASO injection into severely affected mice leads to reversal of muscle pathology within 2 weeks. Thus, ASO-mediated DNM2 knockdown can efficiently correct muscle defects due to loss of MTM1, providing an attractive therapeutic strategy for this disease.
The epicardium plays an essential role in coronary artery formation and myocardial development. H... more The epicardium plays an essential role in coronary artery formation and myocardial development. However, signals controlling the developing epicardium and epicardial-mesenchymal transition (EMT) in the normal and diseased adult heart are studied less rigorously. Here we investigated the role of angiogenic hormone, prokineticin-2 and its receptor PKR1 in the epicardium of developing and adult heart. Genetic ablation of PKR1 in epicardium leads to partial embryonic and postnatal lethality with abnormal heart development. Cardiac developmental defects are manifested in the adult stage as ischemic cardiomyopathy with systolic dysfunction. We discovered that PKR1 regulates epicardial-mesenchymal transition (EMT) for epicardial-derived progenitor cell (EPDC), formation. This event affects at least three consequential steps during heart development: (i) EPDC and cardiomyocyte proliferation involved in thickening of an outer compact ventricular chamber wall, (ii) rhythmicity, (iii) formatio...
Background Reciprocal relationships between endothelial dysfunction and insulin resistance result... more Background Reciprocal relationships between endothelial dysfunction and insulin resistance result in a vicious cycle of cardiovascular, renal, and metabolic disorders. The mechanisms underlying these impairments are unclear. The peptide hormones prokineticins exert their angiogenic function via prokineticin receptor‐1 ( PKR 1). We explored the extent to which endothelial PKR 1 contributes to expansion of capillary network and the transcapillary passage of insulin into the heart, kidney, and adipose tissues, regulating organ functions and metabolism in a specific mice model. Methods and Results By combining cellular studies and studies in endothelium‐specific loss‐of‐function mouse model (ec‐PKR1 −/− ), we showed that a genetically induced PKR 1 loss in the endothelial cells causes the impaired capillary formation and transendothelial insulin delivery, leading to insulin resistance and cardiovascular and renal disorders. Impaired insulin delivery in endothelial cells accompanied with...
Summary Friedreich's ataxia (FRDA) is a recessive neurodegenerative disorder commonly associa... more Summary Friedreich's ataxia (FRDA) is a recessive neurodegenerative disorder commonly associated with hypertrophic cardiomyopathy. FRDA is due to expanded GAA repeats within the first intron of the gene encoding frataxin, a conserved mitochondrial protein involved in iron-sulphur cluster biosynthesis. This mutation leads to partial gene silencing and substantial reduction of the frataxin level. To overcome limitations of current cellular models of FRDA, we derived induced pluripotent stem cells (iPSCs) from two FRDA patients and successfully differentiated them into neurons and cardiomyocytes, two affected cell types in FRDA. All FRDA iPSC lines displayed expanded GAA alleles prone to high instability and decreased levels of frataxin, but no biochemical phenotype was observed. Interestingly, both FRDA iPSC-derived neurons and cardiomyocytes exhibited signs of impaired mitochondrial function, with decreased mitochondrial membrane potential and progressive mitochondrial degenerati...
Src homology and collagen A (ShcA) is an adaptor protein that binds to tyrosine kinase receptors.... more Src homology and collagen A (ShcA) is an adaptor protein that binds to tyrosine kinase receptors. Its germ line deletion is embryonic lethal with abnormal cardiovascular system formation, and its role in cardiovascular development is unknown. To investigate its functional role in cardiovascular development in mice, ShcA was deleted in cardiomyocytes and vascular smooth muscle cells by crossing ShcA flox mice with SM22a-Cre transgenic mice. Conditional mutant mice developed signs of severe dilated cardiomyopathy, myocardial infarctions, and premature death. No evidence of a vascular contribution to the phenotype was observed. Histological analysis of the heart revealed aberrant sarcomeric Z-disk and M-band structures, and misalignments of T-tubules with Z-disks. We find that not only the ErbB3/Neuregulin signaling pathway but also the baroreceptor reflex response, which have been functionally associated, are altered in the mutant mice. We further demonstrate that ShcA interacts with ...
Proceedings of the National Academy of Sciences, 2009
Bardet-Biedl syndrome (BBS) is an inherited ciliopathy generally associated with severe obesity, ... more Bardet-Biedl syndrome (BBS) is an inherited ciliopathy generally associated with severe obesity, but the underlying mechanism remains hypothetical and is generally proposed to be of neuroendocrine origin. In this study, we show that while the proliferating preadipocytes or mature adipocytes are nonciliated in culture, a typical primary cilium is present in differentiating preadipocytes. This transient cilium carries receptors for Wnt and Hedgehog pathways, linking this organelle to previously described regulatory pathways of adipogenesis. We also show that the BBS10 and BBS12 proteins are located within the basal body of this primary cilium and inhibition of their expression impairs ciliogenesis, activates the glycogen synthase kinase 3 pathway, and induces peroxisome proliferator-activated receptor nuclear accumulation, hence favoring adipogenesis. Moreover, adipocytes derived from BBS-patients' dermal fibroblasts in culture exhibit higher propensity for fat accumulation when c...
During embryogenesis, serotonin has been reported to be involved in craniofacial and cardiovascul... more During embryogenesis, serotonin has been reported to be involved in craniofacial and cardiovascular morphogenesis. The detailed molecular mechanisms underlying these functions, however remain unknown. From mouse and human species, we have recently reported the cloning of 5-HT2B receptors which share signal transduction pathways with other 5-HT2 receptor subtypes (5-HT2A and 5-HT2C). In addition to phospholipase C stimulation, it appears that these three subtypes of receptor transduce a common serotonin-induced mitogenic activity, which could be important for cell differentiation and proliferation. We have first investigated the expression of 5-HT2 receptor mRNAs in the mouse embryo. Interestingly, a peak of 5-HT2B receptor mRNA expression was detected 8-9 days postcoitum, whereas there was only low level 5-HT2A and no 5-HT2C receptor mRNA expression at this stage. Expression of this receptor was confirmed by binding assays using a 5-HT2-specific ligand which revealed a peak of bindi...
Background Background: Spinocerebellar ataxia type 7 (SCA7) is primarily characterized by progres... more Background Background: Spinocerebellar ataxia type 7 (SCA7) is primarily characterized by progressive cerebellar degeneration with major alteration of Purkinje cells (PC) due to polyglutamine expansion in ATXN7, a subunit of SAGA transcriptional co-regulator complex. Additional neural tissues are affected and contribute to diverse symptoms. Current animal models were insufficient to recapitulate the broad spectrum of SCA7 pathology and the mechanisms of PC degeneration remain poorly explored. Methods: To delineate spatio-temporal features of SCA7, we performed a longitudinal characterization of a new knock-in mice line expressing ATXN7 with 140 glutamines (SCA7 140Q/5Q ) using a battery of analyses including motor tests, brain and retina imaging, morphometry, electrophysiology, electron microscopy and immunohistochemistry of disease tissues. We also determined the cerebellar transcriptome and cell-type specific gene deregulation. Results: Here we describe the first SCA7 knock-in mic...
Knock-out of the mouse RXRa gene was previously shown to result in a hypoplastic heart ventricula... more Knock-out of the mouse RXRa gene was previously shown to result in a hypoplastic heart ventricular wall, histologically detectable in 12.5 dpc fetuses. We show here that a precocious differentiation can be detected as early as 8.5 dpc in ventricular cardiomyocytes of RXRα−/− mutants. This precocious differentiation, which is characterized by the presence of striated myofibrils, sarcoplasmic reticulum and intercalated disks, is found after 9.5 dpc in about 50% of RXRα−/− subepicardial myocytes. In contrast, wild-type subepicardial myocytes remain morphologically undifferentiated up to at least 16.5 dpc. A similar precocious differentiation was observed in 9.5 dpc subepicardial myocytes of several RXR0α−/− and RARα−/− mutants, as well as in vitamin A-deficient embryos. The proportion of differentiated subepicardial myocytes almost reached 100% in RXRα/RXRβ double null mutants, indicating a partial functional redundancy between RXRα and RXRβ. This differentiation defect was always para...
Obesity is a major risk factor for insulin resistance (IR) and its attendant complications. The p... more Obesity is a major risk factor for insulin resistance (IR) and its attendant complications. The pathogenic mechanisms linking them remain poorly understood, partly due to a lack of intermediary monogenic human phenotypes. Here, we report on a monogenic form of IR-prone obesity, Alström syndrome (ALMS). Twenty-three subjects with monogenic or polygenic obesity underwent hyperinsulinemic-euglycemic clamping with concomitant adipose tissue (AT) microdialysis and an in-depth analysis of subcutaneous AT histology. We have shown a relative AT failure in a monogenic obese cohort, a finding supported by observations in a novel conditional mouse model (Almsflin/flin) and ALMS1-silenced human primary adipocytes, whereas selective reactivation of ALMS1 gene in AT of an ALMS conditional knockdown mouse model (Almsflin/flin; Adipo-Cre+/−) restores systemic insulin sensitivity and glucose tolerance. Hence, we show for the first time the relative AT failure in human obese cohorts to be a major det...
Centronuclear myopathies (CNM) are non-dystrophic muscle diseases for which no effective therapy ... more Centronuclear myopathies (CNM) are non-dystrophic muscle diseases for which no effective therapy is currently available. The most severe form, X-linked CNM, is caused by myotubularin 1 (MTM1) loss-of-function mutations, while the main autosomal dominant form is due to dynamin2 (DNM2) mutations. We previously showed that genetic reduction of DNM2 expression in Mtm1 knockout (Mtm1KO) mice prevents development of muscle pathology. Here we show that systemic delivery of Dnm2 antisense oligonucleotides (ASOs) into Mtm1KO mice efficiently reduces DNM2 protein level in muscle and prevents the myopathy from developing. Moreover, systemic ASO injection into severely affected mice leads to reversal of muscle pathology within 2 weeks. Thus, ASO-mediated DNM2 knockdown can efficiently correct muscle defects due to loss of MTM1, providing an attractive therapeutic strategy for this disease.
The epicardium plays an essential role in coronary artery formation and myocardial development. H... more The epicardium plays an essential role in coronary artery formation and myocardial development. However, signals controlling the developing epicardium and epicardial-mesenchymal transition (EMT) in the normal and diseased adult heart are studied less rigorously. Here we investigated the role of angiogenic hormone, prokineticin-2 and its receptor PKR1 in the epicardium of developing and adult heart. Genetic ablation of PKR1 in epicardium leads to partial embryonic and postnatal lethality with abnormal heart development. Cardiac developmental defects are manifested in the adult stage as ischemic cardiomyopathy with systolic dysfunction. We discovered that PKR1 regulates epicardial-mesenchymal transition (EMT) for epicardial-derived progenitor cell (EPDC), formation. This event affects at least three consequential steps during heart development: (i) EPDC and cardiomyocyte proliferation involved in thickening of an outer compact ventricular chamber wall, (ii) rhythmicity, (iii) formatio...
Background Reciprocal relationships between endothelial dysfunction and insulin resistance result... more Background Reciprocal relationships between endothelial dysfunction and insulin resistance result in a vicious cycle of cardiovascular, renal, and metabolic disorders. The mechanisms underlying these impairments are unclear. The peptide hormones prokineticins exert their angiogenic function via prokineticin receptor‐1 ( PKR 1). We explored the extent to which endothelial PKR 1 contributes to expansion of capillary network and the transcapillary passage of insulin into the heart, kidney, and adipose tissues, regulating organ functions and metabolism in a specific mice model. Methods and Results By combining cellular studies and studies in endothelium‐specific loss‐of‐function mouse model (ec‐PKR1 −/− ), we showed that a genetically induced PKR 1 loss in the endothelial cells causes the impaired capillary formation and transendothelial insulin delivery, leading to insulin resistance and cardiovascular and renal disorders. Impaired insulin delivery in endothelial cells accompanied with...
Summary Friedreich's ataxia (FRDA) is a recessive neurodegenerative disorder commonly associa... more Summary Friedreich's ataxia (FRDA) is a recessive neurodegenerative disorder commonly associated with hypertrophic cardiomyopathy. FRDA is due to expanded GAA repeats within the first intron of the gene encoding frataxin, a conserved mitochondrial protein involved in iron-sulphur cluster biosynthesis. This mutation leads to partial gene silencing and substantial reduction of the frataxin level. To overcome limitations of current cellular models of FRDA, we derived induced pluripotent stem cells (iPSCs) from two FRDA patients and successfully differentiated them into neurons and cardiomyocytes, two affected cell types in FRDA. All FRDA iPSC lines displayed expanded GAA alleles prone to high instability and decreased levels of frataxin, but no biochemical phenotype was observed. Interestingly, both FRDA iPSC-derived neurons and cardiomyocytes exhibited signs of impaired mitochondrial function, with decreased mitochondrial membrane potential and progressive mitochondrial degenerati...
Src homology and collagen A (ShcA) is an adaptor protein that binds to tyrosine kinase receptors.... more Src homology and collagen A (ShcA) is an adaptor protein that binds to tyrosine kinase receptors. Its germ line deletion is embryonic lethal with abnormal cardiovascular system formation, and its role in cardiovascular development is unknown. To investigate its functional role in cardiovascular development in mice, ShcA was deleted in cardiomyocytes and vascular smooth muscle cells by crossing ShcA flox mice with SM22a-Cre transgenic mice. Conditional mutant mice developed signs of severe dilated cardiomyopathy, myocardial infarctions, and premature death. No evidence of a vascular contribution to the phenotype was observed. Histological analysis of the heart revealed aberrant sarcomeric Z-disk and M-band structures, and misalignments of T-tubules with Z-disks. We find that not only the ErbB3/Neuregulin signaling pathway but also the baroreceptor reflex response, which have been functionally associated, are altered in the mutant mice. We further demonstrate that ShcA interacts with ...
Proceedings of the National Academy of Sciences, 2009
Bardet-Biedl syndrome (BBS) is an inherited ciliopathy generally associated with severe obesity, ... more Bardet-Biedl syndrome (BBS) is an inherited ciliopathy generally associated with severe obesity, but the underlying mechanism remains hypothetical and is generally proposed to be of neuroendocrine origin. In this study, we show that while the proliferating preadipocytes or mature adipocytes are nonciliated in culture, a typical primary cilium is present in differentiating preadipocytes. This transient cilium carries receptors for Wnt and Hedgehog pathways, linking this organelle to previously described regulatory pathways of adipogenesis. We also show that the BBS10 and BBS12 proteins are located within the basal body of this primary cilium and inhibition of their expression impairs ciliogenesis, activates the glycogen synthase kinase 3 pathway, and induces peroxisome proliferator-activated receptor nuclear accumulation, hence favoring adipogenesis. Moreover, adipocytes derived from BBS-patients' dermal fibroblasts in culture exhibit higher propensity for fat accumulation when c...
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