Biomedical subjects

Pierre Chambon

Publications and source records attributed to Pierre Chambon.

At least 19 recordsLinked to original sources

PubMed2007

Effects of loss of classical estrogen response element signaling on bone in male mice.

The role of estrogen signaling in the male skeleton via estrogen receptor (ER)-alpha is now well established. ERalpha can elicit responses through either classical estrogen response elements (ERE) pathways or nonclassical, non-ERE pathways. In the present study, we examined the effects of either the attenuation or loss of classical ERalpha signaling on the murine male skeleton. To accomplish this, we crossed male mice heterozygous for a knock-in mutation [nonclassical ERalpha knock-in (NERKI)], which abolishes the ERE-mediated pathway with female heterozygous ERalpha knockout mice (ERalpha+/-) and studied the F1 generation ERalpha+/+, ERalpha+/-, ERalpha+/NERKI, and ERalpha-/NERKI male progeny longitudinally using bone density and histomorphometry. The only ERalpha allele present in ERalpha-/NERKI mice is incapable of classical ERE-mediated signaling, whereas the heterozygous ERalpha+/NERKI mice have both one intact ERalpha and one NERKI allele. As compared with ERalpha+/+ littermates (n=10/genotype), male ERalpha+/NERKI and ERalpha-/NERKI mice displayed axial and appendicular skeletal osteopenia at 6, 12, 20, and 25 wk of age, as demonstrated by significant reductions in total bone mineral density (BMD) at representative sites (areal BMD by dual-energy x-ray absorptiometry at the lumbar vertebrae and femur and volumetric BMD by peripheral quantitative computed tomography at the tibia; P<0.05-0.001 vs. ERalpha+/+). The observed osteopenia in these mice was evident in both trabecular and cortical bone compartments. However, these decreases were more severe in mice lacking classical ERalpha signaling (ERalpha-/NERKI mice), compared with mice in which one wild-type ERalpha allele was present (ERalpha+/NERKI mice). Collectively, these data demonstrate that classical ERalpha signaling is crucial for the development of the murine male skeleton.

Animals↗

PubMed2006

Insidious adrenocortical insufficiency underlies neuroendocrine dysregulation in TIF-2 deficient mice.

The transcription-intermediary-factor-2 (TIF-2) is a coactivator of the glucocorticoid receptor (GR), and its disruption would be expected to influence glucocorticoid-mediated control of the hypothalamo-pituitary-adrenal (HPA) axis. Here, we show that its targeted deletion in mice is associated with altered expression of several glucocorticoid-dependent components of HPA regulation (e.g., corticotropin-releasing hormone, vasopressin, ACTH, glucocorticoid receptors), suggestive of hyperactivity under basal conditions. At the same time, TIF-2(-/-) mice display significantly lower basal corticosterone levels and a sluggish and blunted initial secretory response to brief emotional and prolonged physical stress. Subsequent analysis revealed this discrepancy to result from pronounced aberrations in the structure and function of the adrenal gland, including the cytoarchitectural organization of the zona fasciculata and basal and stress-induced expression of key elements of steroid hormone synthesis, such as the steroidogenic acute regulatory (StAR) protein and 3beta-hydroxysteroid dehydrogenase (3beta-HSD). In addition, altered expression levels of two nuclear receptors, DAX-1 and steroidogenic factor 1 (SF-1), in the adrenal cortex strengthen the view that TIF-2 deletion disrupts adrenocortical development and steroid biosynthesis. Thus, hyperactivity of the hypothalamo-pituitary unit is ascribed to insidious adrenal insufficiency and impaired glucocorticoid feedback.

3-Hydroxysteroid Dehydrogenases↗

PubMed2006

Prepubertal testis development relies on retinoic acid but not rexinoid receptors in Sertoli cells.

Sertoli cells (SC) are instrumental to stem spermatogonia differentiation, a process that critically depends on retinoic acid (RA). We show here that selective ablation of RA receptor alpha (RARalpha) gene in mouse SC, singly (Rara(Ser-/-) mutation) or in combination with RARbeta and RARgamma genes (Rara/b/g(Ser-/-) mutation), abolishes cyclical gene expression in these cells. It additionally induces testis degeneration and delays spermatogonial expression of Stra8, two hallmarks of RA deficiency. As identical defects are generated upon inactivation of RARalpha in the whole organism, our data demonstrate that all the functions exerted by RARalpha in male reproduction are Sertoli cell-autonomous. They further indicate that RARalpha is a master regulator of the cyclical activity of SC and controls paracrine pathways required for spermatogonia differentiation and germ cell survival. Most importantly, we show that the ablation of all RXR (alpha, beta and gamma isotypes) in SC does not recapitulate the phenotype generated upon ablation of all three RARs, thereby providing the first evidence that RARs exert functions in vivo independently of RXRs.

Aging↗

PubMed2006

CYP26A1 and CYP26C1 cooperatively regulate anterior-posterior patterning of the developing brain and the production of migratory cranial neural crest cells in the mouse.

The appropriate regulation of retinoic acid signaling is indispensable for patterning of the vertebrate central nervous system along the anteroposterior (A-P) axis. Although both CYP26A1 and CYP26C1, retinoic acid-degrading enzymes that are expressed at the anterior end of the gastrulating mouse embryo, have been thought to play an important role in central nervous system patterning, the detailed mechanism of their contribution has remained largely unknown. We have now analyzed CYP26A1 and CYP26C1 function by generating knockout mice. Loss of CYP26C1 did not appear to affect embryonic development, suggesting that CYP26A1 and CYP26C1 are functionally redundant. In contrast, mice lacking both CYP26A1 and CYP26C1 were found to manifest a pronounced anterior truncation of the brain associated with A-P patterning defects that reflect expansion of posterior identity at the expense of anterior identity. Furthermore, Cyp26a1-/-Cyp26c1-/- mice fail to produce migratory cranial neural crest cells in the forebrain and midbrain. These observations, together with a reevaluation of Cyp26a1 mutant mice, suggest that the activity of CYP26A1 and CYP26C1 is required for correct A-P patterning and production of migratory cranial neural crest cells in the developing mammalian brain.

Animals↗

PubMed2006

Skin epidermis lacking the c-Myc gene is resistant to Ras-driven tumorigenesis but can reacquire sensitivity upon additional loss of the p21Cip1 gene.

The target gene(s) required for Myc-mediated tumorigenesis are still elusive. Here we show that while endogenous c-Myc is surprisingly dispensable for skin homeostasis and TPA-induced hyperplasia, c-Myc-deficient epidermis is resistant to Ras-mediated DMBA/TPAinduced tumorigenesis. This is mechanistically linked to p21(Cip1), which is induced in tumors by the activated Ras-ERK pathway but repressed by c-Myc. Acute elimination of c-Myc in established tumors leads to the up-regulation of p21(Cip1), and epidermis lacking both p21(Cip1) and c-Myc reacquires normal sensitivity to DMBA/TPA-induced tumorigenesis. This identifies c-Myc-mediated repression of p21(Cip1) as a key step for Ras-driven epidermal tumorigenesis.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed2006

Topical vitamin D3 and low-calcemic analogs induce thymic stromal lymphopoietin in mouse keratinocytes and trigger an atopic dermatitis.

We have demonstrated that cytokine thymic stromal lymphopoietin (TSLP), whose expression is rapidly induced upon keratinocyte-selective ablation of retinoid X receptors (RXRs) -alpha and -beta in the mouse (RXRalphabeta(ep-/-) mice), plays a key role in initiating a skin and systemic atopic dermatitis-like phenotype. We show here that topical application of the physiologically active ligand [1alpha,25-(OH)(2)D(3); calcitriol] of the vitamin D receptor, or of its low-calcemic analog MC903 (calcipotriol; Dovonex), induces TSLP expression in epidermal keratinocytes, which results in an atopic dermatitis-like syndrome mimicking that seen in RXRalphabeta(ep-/-) mutants and transgenic mice overexpressing TSLP in keratinocytes. Furthermore, topical application of retinoic acid receptor RARgamma-selective agonist BMS961 also induces TSLP expression either on its own or synergistically with 1alpha,25-(OH)(2)D(3). Our data demonstrate that RXR/vitamin D receptor and RXR/retinoic acid receptor-gamma heterodimers and their ligands cell-autonomously control the expression of TSLP in epidermal keratinocytes of the mouse. We propose molecular mechanisms through which vitamin D3 and retinoic acid signalings could be involved in the pathogenesis of atopic diseases.

Administration, Topical↗

PubMed2006

Genetic and pharmacological evidence that a retinoic acid cannot be the RXR-activating ligand in mouse epidermis keratinocytes.

Using genetic and pharmacological approaches, we demonstrate that both RARgamma/RXRalpha heterodimers involved in repression events, as well as PPARbeta(delta)/RXRalpha heterodimers involved in activation events, are cell-autonomously required in suprabasal keratinocytes for the generation of lamellar granules (LG), the organelles instrumental to the formation of the skin permeability barrier. In activating PPARbeta(delta)/RXRalpha heterodimers, RXRalpha is transcriptionally active as its AF-2 activation function is required and can be inhibited by an RXR-selective antagonist. Within repressing RARgamma/RXRalpha heterodimers, induction of the transcriptional activity of RXRalpha is subordinated to the addition of an agonistic ligand for RARgamma. Thus, the ligand that possibly binds and activates RXRalpha heterodimerized with PPARbeta(delta) cannot be a retinoic acid, as it would also bind RARgamma and relieve the RARgamma-mediated repression, thereby yielding abnormal LGs. Our data also demonstrate for the first time that subordination of RXR transcriptional activity to that of its RAR partner plays a crucial role in vivo, because it allows RXRs to act concomitantly, within the same cell, as heterodimerization partners for repression, as well as for activation events in which they are transcriptionally active.

Animals↗

PubMed2006

A G-protein-coupled estrogen receptor is involved in hypothalamic control of energy homeostasis.

Estrogens are involved in the hypothalamic control of multiple homeostatic functions including reproduction, stress responses, energy metabolism, sleep cycles, temperature regulation, and motivated behaviors. The critical role of 17beta-estradiol (E2) is evident in hypoestrogenic states (e.g., postmenopause) in which many of these functions go awry. The actions of E2 in the brain have been attributed to the activation of estrogen receptors alpha and beta through nuclear, cytoplasmic, or membrane actions. However, we have identified a putative membrane-associated estrogen receptor that is coupled to desensitization of GABAB and mu-opioid receptors in guinea pig and mouse hypothalamic proopiomelanocortin neurons. We have synthesized a new nonsteroidal compound, STX, which selectively targets the Galphaq-coupled phospholipase C-protein kinase C-protein kinase A pathway, and have established that STX is more potent than E2 in mediating this desensitization in an ICI 182, 780-sensitive manner in both guinea pig and mouse neurons. Both E2 and STX were fully efficacious in estrogen receptor alpha,beta knock-out mice. Moreover, in vivo treatment with STX, similar to E2, attenuated the weight gain in hypoestrogenic female guinea pigs. Therefore, this membrane-delimited signaling pathway plays a critical role in the control of energy homeostasis and may provide a novel therapeutic target for treatment of postmenopausal symptoms and eating disorders in females.

Animals↗

PubMed2006

RARgamma is critical for maintaining a balance between hematopoietic stem cell self-renewal and differentiation.

Hematopoietic stem cells (HSCs) sustain lifelong production of all blood cell types through finely balanced divisions leading to self-renewal and differentiation. Although several genes influencing HSC self-renewal have been identified, to date no gene has been described that, when activated, enhances HSC self-renewal and, when inactivated [corrected] promotes HSC differentiation. We observe that the retinoic acid receptor (RAR)gamma is selectively expressed in primitive hematopoietic precursors and that the bone marrow of RARgamma knockout mice exhibit markedly reduced numbers of HSCs associated with increased numbers of more mature progenitor cells compared with wild-type mice. In contrast, RARalpha is widely expressed in hematopoietic cells, but RARalpha knockout mice do not exhibit any HSC or progenitor abnormalities. Primitive hematopoietic precursors overexpressing RARalpha differentiate predominantly to granulocytes in short-term culture, whereas those overexpressing RARgamma exhibit a much more undifferentiated phenotype. Furthermore, loss of RARgamma abrogated the potentiating effects of all-trans retinoic acid on the maintenance of HSCs in ex vivo culture. Finally, pharmacological activation of RARgamma ex vivo promotes HSC self-renewal, as demonstrated by serial transplant studies. We conclude that the RARs have distinct roles in hematopoiesis and that RARgamma is a critical physiological and pharmacological regulator of the balance between HSC self-renewal and differentiation.

Animals↗

PubMed2006

Paracrine signaling through the epithelial estrogen receptor alpha is required for proliferation and morphogenesis in the mammary gland.

Estradiol is a major regulator of postnatal mammary gland development and thought to exert its effects through estrogen receptor alpha (ERalpha) expressed in the mammary gland stroma and epithelium. Previous studies, however, were confounded by the use of an ERalpha mutant strain that retains some of the protein with transactivation activity. Here, we use an ERalpha-/- mouse strain in which no ERalpha transcript can be detected to analyze mammary gland development in the complete absence of ERalpha signaling. The ERalpha-/- females show no development beyond a rudimentary ductal system. By grafting ERalpha-/- epithelium or stroma in combination with ERalpha WT stroma or epithelium, we show that the primary target for estradiol is the mammary epithelium, whereas a direct response of the mammary stroma is not required for mammary gland development to proceed normally. Mammary glands reconstituted with ERalpha-/- mammary epithelium exposed to pregnancy hormones show increased transcription of milk protein genes, indicating that ERalpha signaling is not an absolute requirement for a transcriptional response to pregnancy hormones. When ERalpha-/- mammary epithelial cells are in close vicinity to ERalpha WT cells, they proliferate and contribute to all aspects of mammary gland development, indicating that estradiol, like progesterone, orchestrates proliferation and morphogenesis by a paracrine mechanism, affecting nearby cells in the mammary epithelium.

Animals↗

PubMed2006

Distinct roles for retinoic acid receptors alpha and beta in early lung morphogenesis.

Retinoic acid (RA) signaling is required for normal development of multiple organs. However, little is known about how RA influences the initial stages of lung development. Here, we used a combination of genetic, pharmacological and explant culture approaches to address this issue, and to investigate how signaling by different RA receptors (RAR) mediates the RA effects. We analyzed initiation of lung development in retinaldehyde dehydrogenase-2 (Raldh2) null mice, a model in which RA signaling is absent from the foregut from its earliest developmental stages. We provide evidence that RA is dispensable for specification of lung cell fate in the endoderm. By using synthetic retinoids to selectively activate RAR alpha or beta signaling in this model, we demonstrate novel and unique functions of these receptors in the early lung. We show that activation of RAR beta, but not alpha, induces expression of the fibroblast growth factor Fgf10 and bud morphogenesis in the lung field. Similar analysis of wild type foregut shows that endogenous RAR alpha activity is required to maintain overall RA signaling, and to refine the RAR beta effects in the lung field. Our data support the idea that balanced activation of RAR alpha and beta is critical for proper lung bud initiation and endodermal differentiation.

Aldehyde Oxidoreductases↗

PubMed2006

Skin lesion development in a mouse model of incontinentia pigmenti is triggered by NEMO deficiency in epidermal keratinocytes and requires TNF signaling.

NF-kappaB essential modulator (NEMO), the regulatory subunit of the IkappaB kinase, is essential for NF-kappaB activation. Mutations disrupting the X-linked NEMO gene cause incontinentia pigmenti (IP), a human genetic disease characterized by male embryonic lethality and by a complex pathology affecting primarily the skin in heterozygous females. The cellular and molecular mechanisms leading to skin lesion pathogenesis in IP patients remain elusive. Here we used epidermis-specific deletion of NEMO in mice to investigate the mechanisms causing the skin pathology in IP. NEMO deletion completely inhibited NF-kappaB activation and sensitized keratinocytes to tumor necrosis factor (TNF)-induced death but did not affect epidermal development. Keratinocyte-restricted NEMO deletion, either constitutive or induced in adult skin, caused inflammatory skin lesions, identifying the NEMO-deficient keratinocyte as the initiating cell type that triggers the skin pathology in IP. Furthermore, genetic ablation of tumor necrosis factor receptor 1 (TNFRI) rescued the skin phenotype demonstrating that TNF signaling is essential for skin lesion pathogenesis in IP. These results identify the NEMO-deficient keratinocyte as a potent initiator of skin inflammation and provide novel insights into the mechanism leading to the pathogenesis of IP.

Animals↗

PubMed2006

Retinoids and spermatogenesis: lessons from mutant mice lacking the plasma retinol binding protein.

Using Rbp4-null mice as models, we have established for the first time the kinetics of the spermatogenetic alterations during vitamin A deficiency (VAD). Our data demonstrate that the VAD-induced testicular degeneration arises through the normal maturation of germ cells in a context of spermatogonia differentiation arrest. They indicate that retinoic acid (RA) appears dispensable for the transition of premeiotic to meiotic spermatocytes, meiosis, and spermiogenesis. They confirm that RA plays critical roles in controlling spermatogonia differentiation, spermatid adhesion to Sertoli cells, and spermiation, and suggest that the VAD-induced arrest of spermatogonia differentiation results from simultaneous blocks in RA-dependent events mediated by RA receptor gamma (RARgamma) in spermatogonia and by RARalpha in Sertoli cells. They also provide evidence that expression of major RA-metabolizing enzymes is increased in mouse Sertoli cells upon VAD and that vitamin A-deficient A spermatogonia differ from their RA-sufficient counterparts by the expression of the Stra8 gene.

Animals↗

PubMed2006

Temporal regulation of Cre recombinase activity in neural stem cells.

Neural stem cells are known to give rise to distinct subtypes of neurons and glial cells over time by changing their competency. However, precise characterization of neural stem cells at various developmental stages remains to be performed. For such analysis, a tool to manipulate neural stem cells at different time points is necessary. Here, we generated transgenic mice that express Cre-ER(T2) in the ventricular zone of the developing nervous system under the control of the nestin promoter and enhancer (Nes-CreER(T2)). In mice expressing Cre-ER(T2) at appropriate levels, Cre recombinase activity was mostly inactive but efficiently activated by tamoxifen within 1 day. When such mice were crossed with the ROSA-26 or Z/EG reporter mice, neural stem cells were permanently labeled after administration of tamoxifen. Thus, Nes-CreER(T2) mice offer a powerful tool to manipulate neural stem cells genetically at desired time points.

Animals↗

PubMed2006

Conditional (loxP-flanked) allele for the gene encoding the retinoic acid-synthesizing enzyme retinaldehyde dehydrogenase 2 (RALDH2).

Retinoic acid, the active vitamin A derivative, has pleiotropic functions during vertebrate development and postnatal life. Retinaldehyde dehydrogenase 2 (RALDH2) acts as the main retinoic acid-synthesizing enzyme during development. Mouse Raldh2 germline null mutants are early embryonic lethal and exhibit complex abnormalities that include defective heart looping morphogenesis. To investigate later functions of this enzyme, we have engineered a "floxed" (loxP-flanked) allele allowing Cre-mediated somatic gene inactivations. Mice heterozygous or homozygous for the floxed Raldh2 allele are viable and fertile. We tested whether the novel Raldh2 allele behaves as a null mutation after Cre-mediated in vivo excision by crossing the conditional mutants with CMV-Cre transgenic mice. An embryonic lethal phenotype indistinguishable from that of germline mutants was obtained. The conditional allele described herein is a genetic tool for studying tissue-specific, RALDH2-dependent functions of retinoic acid during development and in adult life.

Aldehyde Oxidoreductases↗

PubMed2006

PGC1alpha expression is controlled in skeletal muscles by PPARbeta, whose ablation results in fiber-type switching, obesity, and type 2 diabetes.

Mice in which peroxisome proliferator-activated receptor beta (PPARbeta) is selectively ablated in skeletal muscle myocytes were generated to elucidate the role played by PPARbeta signaling in these myocytes. These somatic mutant mice exhibited a muscle fiber-type switching toward lower oxidative capacity that preceded the development of obesity and diabetes, thus demonstrating that PPARbeta is instrumental in myocytes to the maintenance of oxidative fibers and that fiber-type switching is likely to be the cause and not the consequence of these metabolic disorders. We also show that PPARbeta stimulates in myocytes the expression of PGC1alpha, a coactivator of various transcription factors, known to play an important role in slow muscle fiber formation. Moreover, as the PGC1alpha promoter contains a PPAR response element, the effect of PPARbeta on the formation and/or maintenance of slow muscle fibers can be ascribed, at least in part, to a stimulation of PGC1alpha expression at the transcriptional level.

Animals↗

PubMed2006

Localized inflammatory skin disease following inducible ablation of I kappa B kinase 2 in murine epidermis.

Skin inflammation is a complex process that involves interactions between various cell types residing in different skin compartments. Using mice with conditionally targeted I kappa B kinase 2 (IKK2) alleles, we have previously shown that epidermal keratinocytes can play a dominant role in the initiation of an inflammatory reaction. In order to investigate long-term consequences of IKK2 deletion in adult skin, we have generated mice with floxed IKK2 alleles in which expression of a Tamoxifen-inducible Cre recombinase construct is targeted to epidermal keratinocytes (K14-Cre-ER(T2)IKK2(fl/fl) mice). K14-Cre-ER(T2)IKK2(fl/fl) mice are born normally and do not show signs of a skin disease until the age of 6 months. Deletion of IKK2 can be observed after Tamoxifen application to the back skin or spontaneously, without Tamoxifen application, in mice older than 6 months. This deletion is accompanied by dramatic, localized skin changes that are characterized by invasion of inflammatory cells, hair follicle disruption, and pseudoepitheliomatous hyperplasia of the epidermis, but not by tumor formation. The hyperplastic epithelium shows increased phosphorylation of signal transducer and activator of transcription 3 and extracellular signal-regulated protein kinase 1/2, typical features of psoriatic epidermis. Our results identify a primary role for IKK2 in the development of skin inflammation and confirm its requirement for the maintenance of skin homeostasis.

Animals↗

PubMed2006

International Union of Pharmacology. LX. Retinoic acid receptors.

Retinoid is a term for compounds that bind to and activate retinoic acid receptors (RARalpha, RARbeta, and RARgamma), members of the nuclear hormone receptor superfamily. The most important endogenous retinoid is all-trans-retinoic acid. Retinoids regulate a wide variety of essential biological processes, such as vertebrate embryonic morphogenesis and organogenesis, cell growth arrest, differentiation and apoptosis, and homeostasis, as well as their disorders. This review summarizes the considerable amount of knowledge generated on these receptors.

Animals↗