Tie2-Cre Transgenic Mice: A New Model for Endothelial Cell-Lineage Analysis in Vivo

AbstractEndocardial cells are thought to contribute at least in part to the formation of the endocardial cushion mesenchyme. Here, we created Tie2-Cre transgenic mice, in which expression of Cre recombinase is driven by an endothelial-specific promoter/enhancer. To analyze the lineage of Cre expressing cells, we used CAG-CAT-Z transgenic mice, in which expression of lacZ is activated only after Cre-mediated recombination. We detected pan-endothelial expression of the Cre transgene in Tie2-Cre;CAG-CAT-Z double-transgenic mice. This expression pattern is almost identical to Tie2-lacZ transgenic mice. However, interestingly, we observed strong and uniform lacZ expression in mesenchymal cells of the atrioventricular canal of Tie2-Cre;CAG-CAT-Z double-transgenic mice. We also detected lacZ expression in the mesenchymal cells in part of the proximal cardiac outflow tract, but not in the mesenchymal cells of the distal outflow tract and branchial arch arteries. LacZ staining in Tie2-Cre;CAG-CAT-Z embryos is consistent with endocardial–mesenchymal transformation in the atrioventricular canal and outflow tract regions. Our observations are consistent with previously reported results from Cx43-lacZ, Wnt1-Cre;R26R, and Pax3-Cre;R26R transgenic mice, in which lacZ expression in the cardiac outflow tract identified contributions in part from the cardiac neural crest. Tie2-Cre transgenic mice are a new genetic tool for the analyses of endothelial cell-lineage and endothelial cell–specific gene targeting

Differential roles of orexin receptor-1 and -2 in the regulation of Non-REM and REM sleep

金沢大学医薬保健研究域医学系Orexin-A and orexin-B are hypothalamic neuropeptides that play critical roles in the maintenance of wakefulness. Intracerebroventricular (ICV) administration of orexin-A has been shown to promote wakefulness and suppress both rapid eye movement (REM) sleep and non-REM (NREM) sleep through the orexin receptor-1 (OX1R) and orexin receptor-2 (OX2R). Here, we elucidated the differential roles of orexin receptors in the regulation of sleep and wakefulness by comparing the effects of ICV orexin-A administration in wild-type, OX1R, and OX2R mice. The effects of orexin-A on wakefulness and NREM sleep were significantly attenuated in both knock-out mice as compared with wild-type mice, with substantially larger attenuation in OX2R mice than in OX1R mice. These results suggest that although the OX2R-mediated pathway has a pivotal role in the promotion of wakefulness, OX1R also plays additional roles in promoting arousal. In contrast, suppression of REM sleep by orexin-A administration was slightly and similarly attenuated in both OX1R and OX2R mice, suggesting a comparable contribution of the two receptors to REM sleep suppression. Histological studies demonstrated differential distributions of each receptor subtype in distinct neuronal populations with specific neurotransmitter identities in brainstem cholinergic/monoaminergic neurons. In the laterodorsal tegmental and pedunculopontine tegmental nuclei especially, cholinergic neurons exclusively expressed OX1R mRNA, but OX2R mRNA was expressed mainly in GABAergic putative interneurons. Thus, each orexin receptor subtype plays differential roles in gating NREM and REM sleep through distinct neuronal pathways. © 2011 by the authors

Cholinergic Modulation of Narcoleptic Attacks in Double Orexin Receptor Knockout Mice

To investigate how cholinergic systems regulate aspects of the sleep disorder narcolepsy, we video-monitored mice lacking both orexin (hypocretin) receptors (double knockout; DKO mice) while pharmacologically altering cholinergic transmission. Spontaneous behavioral arrests in DKO mice were highly similar to those reported in orexin-deficient mice and were never observed in wild-type (WT) mice. A survival analysis revealed that arrest lifetimes were exponentially distributed indicating that random, Markovian processes determine arrest lifetime. Low doses (0.01, 0.03 mg/kg, IP), but not a high dose (0.08 mg/kg, IP) of the cholinesterase inhibitor physostigmine increased the number of arrests but did not alter arrest lifetimes. The muscarinic antagonist atropine (0.5 mg/kg, IP) decreased the number of arrests, also without altering arrest lifetimes. To determine if muscarinic transmission in pontine areas linked to REM sleep control also influences behavioral arrests, we microinjected neostigmine (50 nl, 62.5 µM) or neostigmine + atropine (62.5 µM and 111 µM respectively) into the nucleus pontis oralis and caudalis. Neostigmine increased the number of arrests in DKO mice without altering arrest lifetimes but did not provoke arrests in WT mice. Co-injection of atropine abolished this effect. Collectively, our findings establish that behavioral arrests in DKO mice are similar to those in orexin deficient mice and that arrests have exponentially distributed lifetimes. We also show, for the first time in a rodent narcolepsy model, that cholinergic systems can regulate arrest dynamics. Since perturbations of muscarinic transmission altered arrest frequency but not lifetime, our findings suggest cholinergic systems influence arrest initiation without influencing circuits that determine arrest duration

Mice with cardiomyocyte-specific disruption of the endothelin-1 gene are resistant to hyperthyroid cardiac hypertrophy

Endothelin 1 (ET-1), a potent vasoconstrictor peptide expressed by endothelium, is also produced in the heart in response to a variety of stresses. It induces hypertrophy in cultured cardiac myocytes but only at concentrations far greater than those found in plasma. We tested whether ET-1 generated by cardiac myocytes in vivo is a local signal for cardiac hypertrophy. To avoid the perinatal lethality seen in systemic ET-1-null mice, we used the Cre/loxP system to generate mice with cardiac myocyte-specific disruption of the ET-1 gene. We used the α-myosin heavy chain promoter to drive expression of Cre and were able to obtain 75% reduction in ET-1 mRNA in cardiac myocytes isolated from these mice at baseline and after stimulation, in vivo, for 24 h with tri-iodothyronine (T3). Necropsy measurements of cardiac mass indexed for body weight showed a 57% reduction in cardiac hypertrophy in response to 16 days of exogenous T3 in mice homozygous for the disrupted ET-1 allele compared to siblings with an intact ET-1 gene. Moreover, in vivo MRI showed only a 3% increase in left ventricular mass indexed for body weight in mice with the disrupted allele after 3 weeks of T3 treatment versus a 27% increase in mice with an intact ET-1 gene. A reduced hypertrophic response was confirmed by planimetry of cardiac myocytes. We conclude that ET-1, produced locally by cardiac myocytes, and acting in a paracrine/autocrine manner, is an important signal for myocardial hypertrophy that facilitates the response to thyroid hormone

The role of endothelial insulin signaling in the regulation of vascular tone and insulin resistance

Insulin receptors (IRs) on vascular endothelial cells have been suggested to participate in insulin-regulated glucose homeostasis. To directly address the role of insulin action in endothelial function, we have generated a vascular endothelial cell IR knockout (VENIRKO) mouse using the Cre-loxP system. Cultured endothelium of VENIRKO mice exhibited complete rearrangement of the IR gene and a more than 95% decrease in IR mRNA. VENIRKO mice were born at the expected Mendelian ratio, grew normally, were fertile, and exhibited normal patterns of vasculature in the retina and other tissues. Glucose homeostasis under basal condition was comparable in VENIRKO mice. Both eNOS and endothelin-1 mRNA levels, however, were reduced by approximately 30–60% in endothelial cells, aorta, and heart, while vascular EGF expression was maintained at normal levels. Arterial pressure tended to be lower in VENIRKO mice on both low- and high-salt diets, and on a low-salt diet VENIRKO mice showed insulin resistance. Thus, inactivation of the IR on endothelial cell has no major consequences on vascular development or glucose homeostasis under basal conditions, but alters expression of vasoactive mediators and may play a role in maintaining vascular tone and regulation of insulin sensitivity to dietary salt intake