Gain-of-function mutant of angiotensin II receptor, type 1A, causes hypertension and cardiovascular fibrosis in mice.

The role of the renin-angiotensin system has been investigated by overexpression or inactivation of its different genes in animals. However, there is no data concerning the effect of the constitutive activation of any component of the system. A knockin mouse model has been constructed with a gain-of-function mutant of the Ang II receptor, type 1A (AT(1A)), associating a constitutively activating mutation (N111S) with a C-terminal deletion, which impairs receptor internalization and desensitization. In vivo consequences of this mutant receptor expression in homozygous mice recapitulate its in vitro characteristics: the pressor response is more sensitive to Ang II and longer lasting. These mice present with a moderate (~20 mmHg) and stable increase in BP. They also develop early and progressive renal fibrosis and cardiac fibrosis and diastolic dysfunction. However, there was no overt cardiac hypertrophy. The hormonal parameters (low-renin and inappropriately normal aldosterone productions) mimic those of low-renin human hypertension. This new model reveals that a constitutive activation of AT(1A) leads to cardiac and renal fibrosis in spite of a modest effect on BP and will be useful for investigating the role of Ang II in target organs in a model similar to some forms of human hypertension.

Magnetic resonance imaging and histological studies of corpus callosal and hippocampal abnormalities linked to doublecortin deficiency.

Mutated doublecortin (DCX) gives rise to severe abnormalities in human cortical development. Adult Dcx knockout mice show no major neocortical defects but do have a disorganized hippocampus. We report here the developmental basis of these hippocampal abnormalities. A heterotopic band of neurons was identified starting at E17.5 in the CA3 region and progressing throughout the CA1 region by E18.5. At neonatal stages, the CA1 heterotopic band was reduced, but the CA3 band remained unchanged, continuing into adulthood. Thus, in mouse, migration of CA3 neurons is arrested during development, whereas CA1 cell migration is retarded. On the Sv129Pas background, magnetic resonance imaging (MRI) also suggested abnormal dorsal hippocampal morphology, displaced laterally and sometimes rostrally and associated with medial brain structure abnormalities. MRI and cryosectioning showed agenesis of the corpus callosum in Dcx knockout mice on this background and an intermediate, partial agenesis in heterozygote mice. Wild-type littermates showed no callosal abnormalities. Hippocampal and corpus callosal abnormalities were also characterized in DCX-mutated human patients. Severe hippocampal hypoplasia was identified along with variable corpus callosal defects ranging from total agenesis to an abnormally thick or thin callosum. Our data in the mouse, identifying roles for Dcx in hippocampal and corpus callosal development, might suggest intrinsic roles for human DCX in the development of these structures.

New targets of beta-catenin signaling in the liver are involved in the glutamine metabolism.

Inappropriate activation of the Wnt/beta-catenin signaling has been implicated in the development of hepatocellular carcinoma (HCC), but exactly how beta-catenin works remains to be elucidated. To identify, in vivo, the target genes of beta-catenin in the liver, we have used the suppression subtractive hybridization technique and transgenic mice expressing an activated beta-catenin in the liver that developed hepatomegaly. We identified three genes involved in glutamine metabolism, encoding glutamine synthetase (GS), ornithine aminotransferase (OAT) and the glutamate transporter GLT-1. By Northern blot and immunohistochemical analysis we demonstrated that these three genes were specifically induced by activation of the beta-catenin pathway in the liver. In different mouse models bearing an activated beta-catenin signaling in the liver known to be associated with hepatocellular proliferation we observed a marked up-regulation of these three genes. The cellular distribution of GS and GLT-1 parallels beta-catenin activity. By contrast no up-regulation of these three genes was observed in the liver in which hepatocyte proliferation was induced by a signal-independent of beta-catenin. In addition, the GS promoter was activated in the liver of GS(+/LacZ) mice by adenovirus vector-mediated beta-catenin overexpression. Strikingly, the overexpression of the GS gene in human HCC samples was strongly correlated with beta-catenin activation. Together, our results indicate that GS is a target of the Wnt/beta-catenin pathway in the liver. Because a linkage of the glutamine pathway to hepatocarcinogenesis has already been demonstrated, we propose that regulation of these three genes of glutamine metabolism by beta-catenin is a contributing factor to liver carcinogenesis.

Thymus, kidney and craniofacial abnormalities in Six 1 deficient mice.

Six genes are widely expressed during vertebrate embryogenesis, suggesting that they are implicated in diverse differentiation processes. To determine the functions of the Six1 gene, we constructed Six1-deficient mice by replacing its first exon by the beta-galactosidase gene. We have previously shown that mice lacking Six1 die at birth due to thoracic skeletal defects and severe muscle hypoplasia affecting most of the body muscles. Here, we report that Six1(-/-) neonates also lack a kidney and thymus, as well as displaying a strong disorganisation of craniofacial structures, namely the inner ear, the nasal cavity, the craniofacial skeleton, and the lacrimal and parotid glands. These organ defects can be correlated with Six1 expression in the embryonic primordium structures as revealed by X-Gal staining at different stages of embryogenesis. Thus, the fetal abnormalities of Six1(-/-) mice appear to result from the absence of the Six 1 homeoprotein during early stages of organogenesis. Interestingly, these Six1 defects are very similar to phenotypes caused by mutations of Eya 1, which are responsible for the BOR syndrome in humans. Close comparison of Six1 and Eya 1 deficient mice strongly suggests a functional link between these two factors. Pax gene mutations also lead to comparable phenotypes, suggesting that a regulatory network including the Pax, Six and Eya genes is required for several types of organogenesis in mammals.

Functional type I PTH/PTHrP receptor in freshly isolated newborn rat keratinocytes: identification by RT-PCR and immunohistochemistry.

The presence of identical or distinct type I parathyroid hormone (PTH)/parathyroid hormone-related peptide (PTHrP) receptors in keratinocytes is still a matter of debate. We studied the expression and functionality of PTHrP receptors in freshly isolated keratinocytes from newborn rat skin. Four overlapping primers, amplifying different regions in the rat PTH receptor, were used for reverse transcriptase-polymerase chain reaction (RT-PCR). The first region corresponded to the N-terminal extracellular region and the first transmembrane domain (S/M1), the second region amplified the connecting intracellular and extracellular loops transmembrane domain (E2/M5), the third spanned the range from the transmembrane to the intracellular domain (M4/T), and the fourth region amplified the C-terminal tail (M6/7/T). The PCR products from the keratinocyte RNA were identical to those from kidney RNA of the same rats. The cloned four transcripts showed 100% of homologies with the cDNA sequence from bone ROS cells. Keratinocytes, freshly isolated or present in situ in the epidermis, recognized an anti-PTH receptor antibody (PTH-II) directed against the receptor extracellular domain. Western blotting showed the same protein patterns in keratinocytes, kidney, and ROS cell extracts. Low doses of PTHrP(1-34) (10(-12)-10(-9) M) increased the cell number studied by [3H]thymidine incorporation and DNA content. Treatment with the PTH/PTHrP receptor antagonist [Asn10, Leu11, D Trp12] PTHrP(7-34) or two different PTH receptor antibodies inhibited the increase in cell proliferation induced by PTHrP(1-34). All these findings indicate that newborn rat epidermis and keratinocytes express functional PTHrP receptors, which are identical to type I PTH/PTHrP receptor and are recognized by PTHrP(1-34).

Neuroanatomical distribution of ARX in brain and its localisation in GABAergic neurons.

Recent human genetics approaches identified the Aristaless-related homeobox (ARX) gene as the causative gene in X-linked infantile spasms, Partington syndrome, and non-syndromic mental retardation as well as in forms of lissencephaly with abnormal genitalia. The ARX predicted protein belongs to a large family of homeoproteins and is characterised by a C-terminal Aristaless domain and an octapeptide domain near the N-terminus. In order to learn more about ARX function, we have studied in detail Arx expression in the central nervous system during mouse embryonic development as well as in the adult. During early stages of development, Arx is expressed in a significant proportion of neurons in the cortex, the striatum, the ganglionic eminences and also in the spinal cord. In the adult, expression of Arx is still present and restricted to regions that are known to be rich in GABAergic neurons such as the amygdala and the olfactory bulb. A possible role for Arx in this type of neurons is further reinforced by the expression of Arx in a subset of GABAergic interneurons in young and mature primary cultures of cortical neuronal cells as well as in vivo. Moreover, these data could explain the occurrence of seizures in the great majority of patients with an ARX mutation, due to mislocalisation or dysfunction of GABAergic neurons. We also performed ARX wild-type and mutant over-expression experiments and found that the different ARX mutations tested did not modify the morphology of the cells. Moreover, no abnormal cell death or protein aggregation was observed, hence suggesting that more subtle pathogenic mechanisms are involved.

Rapid dissemination of SIV follows multisite entry after rectal inoculation.

Receptive ano-rectal intercourse is a major cause of HIV infection in men having sex with men and in heterosexuals. Current knowledge of the mechanisms of entry and dissemination during HIV rectal transmission is scarce and does not allow the development of preventive strategies. We investigated the early steps of rectal infection in rhesus macaques inoculated with the pathogenic isolate SIVmac251 and necropsied four hours to nine days later. All macaques were positive for SIV. Control macaques inoculated with heat-inactivated virus were consistently negative for SIV. SIV DNA was detected in the rectum as early as four hours post infection by nested PCR for gag in many laser-microdissected samples of lymphoid aggregates and lamina propria but never in follicle-associated epithelium. Scarce SIV antigen positive cells were observed by immunohistofluorescence in the rectum, among intraepithelial and lamina propria cells as well as in clusters in lymphoid aggregates, four hours post infection and onwards. These cells were T cells and non-T cells that were not epithelial cells, CD68(+) macrophages, DC-SIGN(+) cells or fascin(+) dendritic cells. DC-SIGN(+) cells carried infectious virus. Detection of Env singly spliced mRNA in the mucosa by nested RT-PCR indicated ongoing viral replication. Strikingly, four hours post infection colic lymph nodes were also infected in all macaques as either SIV DNA or infectious virus was recovered. Rapid SIV entry and dissemination is consistent with trans-epithelial transport. Virions appear to cross the follicle-associated epithelium, and also the digestive epithelium. Viral replication could however be more efficient in lymphoid aggregates. The initial sequence of events differs from both vaginal and oral infections, which implies that prevention strategies for rectal transmission will have to be specific. Microbicides will need to protect both digestive and follicle-associated epithelia. Vaccines will need to induce immunity in lymph nodes as well as in the rectum.

Eya1 and Eya2 proteins are required for hypaxial somitic myogenesis in the mouse embryo.

In mammals, Pax3, Six4, Six1 and Six5 genes are co-expressed with Eya1, Eya2 and Eya4 genes during mouse somitogenesis. To unravel the functions of Eya genes during muscle development, we analyzed myogenesis in Eya2-/- and in Eya1-/- embryos. A delay in limb myogenesis was observed between E10 and E13 in Eya1-/- embryos only, that is later compensated. Compound E18 Eya1-/-Eya2-/+ fetuses present a muscle phenotype comparable with that of Six1-/- fetuses; lacking a diaphragm and with a specific absence of limb muscles, suggesting either genetic epistasis between Six and Eya genes, or biochemical interactions between Six and Eya proteins. We tested these two non-exclusive possibilities. First, we show that Six proteins recruit Eya proteins to drive transcription during embryogenesis in the dermomyotomal epaxial and hypaxial lips of the somites by binding MEF3 DNA sites. Second, we show that Pax3 expression is lost in the ventrolateral (hypaxial) dermomyotomes of the somite in both Eya1-/-Eya2-/- embryos and in Six1-/-Six4-/- embryos, precluding hypaxial lip formation. This structure, from which myogenic cells delaminate to invade the limb does not form in these double mutant embryos, leading to limb buds without myogenic progenitor cells. Eya1 and Eya2, however, are still expressed in the somites of Six1Six4 double mutant and in splotch embryos, and Six1 is expressed in the somites of Eya1Eya2 double mutant embryos and in splotch embryos. Altogether these results show that Six and Eya genes lie genetically upstream of Pax3 gene in the formation of ventrolateral dermomyotome hypaxial lips. No genetic links have been characterized between Six and Eya genes, but corresponding proteins activate key muscle determination genes (Myod, Myogenin and Mrf4). These results establish a new hierarchy of genes controlling early steps of hypaxial myogenic commitment in the mouse embryo.

PDE4 inhibition prevents preterm delivery induced by an intrauterine inflammation.

The aim of this study was to explore the anti-inflammatory properties of phosphodiesterase-4 (PDE4) inhibitors in vivo and their potential ability to prevent inflammation-induced preterm delivery. Indeed, intrauterine inflammation is the major etiology of very preterm delivery, the leading cause of neonatal mortality and morbidity. Intrauterine injection of Escherichia coli LPS in 15-day-pregnant mice induced an increase of PDE4 activity and PDE4B expression at the maternofetal interface, a rise of amniotic fluid levels of TNF-alpha, IL-1beta, IL-6, and IL-10 and provoked massive preterm delivery and fetal demise. Selective PDE4 inhibition by rolipram prevented the rise in the proinflammatory cytokines. Following the nuclear translocation of the transcription factor NFkappaB, as a marker of cellular activation after the inflammatory challenge, showed a time-dependent sequential activation of the gestational tissues, from the uterine mesometrial to the fetal compartment, particularly in the glycogen-trophoblastic cells of the placenta. This activation was disrupted by PDE4 inhibition, and inflammation-induced preterm delivery and fetal demise were prevented. PDE4 selective inhibitors may thus represent a novel effective treatment to delay inflammation-induced preterm delivery and to prevent adverse outcomes in infants.

Six1 and Six4 homeoproteins are required for Pax3 and Mrf expression during myogenesis in the mouse embryo.

In mammals, Six5, Six4 and Six1 genes are co-expressed during mouse myogenesis. Six4 and Six5 single knockout (KO) mice have no developmental defects, while Six1 KO mice die at birth and show multiple organ developmental defects. We have generated Six1Six4 double KO mice and show an aggravation of the phenotype previously reported for the single Six1 KO. Six1Six4 double KO mice are characterized by severe craniofacial and rib defects, and general muscle hypoplasia. At the limb bud level, Six1 and Six4 homeogenes control early steps of myogenic cell delamination and migration from the somite through the control of Pax3 gene expression. Impaired in their migratory pathway, cells of the somitic ventrolateral dermomyotome are rerouted, lose their identity and die by apoptosis. At the interlimb level, epaxial Met expression is abolished, while it is preserved in Pax3-deficient embryos. Within the myotome, absence of Six1 and Six4 impairs the expression of the myogenic regulatory factors myogenin and Myod1, and Mrf4 expression becomes undetectable. Myf5 expression is correctly initiated but becomes restricted to the caudal region of each somite. Early syndetomal expression of scleraxis is reduced in the Six1Six4 embryo, while the myotomal expression of Fgfr4 and Fgf8 but not Fgf4 and Fgf6 is maintained. These results highlight the different roles played by Six proteins during skeletal myogenesis.

Altered myogenesis in Six1-deficient mice.

Six homeoproteins are expressed in several tissues, including muscle, during vertebrate embryogenesis, suggesting that they may be involved in diverse differentiation processes. To determine the functions of the Six1 gene during myogenesis, we constructed Six1-deficient mice by replacing its first exon with the lacZ gene. Mice lacking Six1 die at birth because of severe rib malformations and show extensive muscle hypoplasia affecting most of the body muscles in particular certain hypaxial muscles. Six1(-/-) embryos have impaired primary myogenesis, characterized, at E13.5, by a severe reduction and disorganisation of primary myofibers in most body muscles. While Myf5, MyoD and myogenin are correctly expressed in the somitic compartment in early Six1(-/-) embryos, by E11.5 MyoD and myogenin gene activation is reduced and delayed in limb buds. However, this is not the consequence of a reduced ability of myogenic precursor cells to migrate into the limb buds or of an abnormal apoptosis of myoblasts lacking Six1. It appears therefore that Six1 plays a specific role in hypaxial muscle differentiation, distinct from those of other hypaxial determinants such as Pax3, cMet, Lbx1 or Mox2.

Hyperthermia assists survival of astrocytes from oxidative-mediated necrotic cell death.

In response to many stresses and pathologic states, including different models of nervous system injury, cells synthesize a variety of proteins, most notably the inducible 72 kDa heat shock protein 70 (Hsp70), which plays important roles in maintaining cellular integrity and viability. We report here that cultured astrocytes from rat diencephalon express high levels of Hsp70 upon exposure to elevated temperatures, and are less vulnerable to a subsequent oxidative stress. Complex oxidative stress was induced by exposure of astrocytes to an aqueous extract of tobacco smoke. This resulted in both glutathione and ATP depletion, along with cell death that proceeded through a necrotic pathway. Pretreatment of cultures with the glutathione replenishing agent, N-acetyl-L-cysteine, prevented glutathione and ATP loss as well as necrotic cell death. Thermal stress also protected astrocytes from necrotic cell death but without affecting glutathione or ATP levels. We propose that heat shock protects astrocytes from necrosis induced by oxidative stress, probably as a result of Hsp70 synthesis, through an antioxidant-ATP independent mechanism. As Hsp70 may transfer from glial to neuronal cells, its synthesis by astrocytes may represent an important survival mechanism by which astrocytes protect neurons against oxidative-mediated cell death.