Estrogen blocks M-CSF gene expression and osteoclast formation by regulating phosphorylation of Egr-1 and its interaction with Sp-1

Central to the pathogenesis of osteoporosis is the ability of estrogen deficiency to increase osteoclast formation by enhancing stromal cell production of the osteoclastogenic cytokine macrophage colony-stimulating factor (M-CSF). We report that stromal cells from ovariectomized mice exhibit increased casein kinase II-dependent phosphorylation of the nuclear protein Egr-1. Phosphorylated Egr-1 binds less avidly to the transcriptional activator Sp-1 and the resulting higher levels of free Sp-1 stimulate transactivation of the M-CSF gene. Estrogen replacement fails to block M-CSF mRNA expression and osteoclast formation in ovariectomized mice lacking Egr-1, confirming the critical role played by this transcription factor in mediating the antiosteoclastogenic effects of estrogen. Thus, by downregulating formation of a novel Egr-1/Sp-1 complex in stromal cells, estrogen deficiency results in enhanced levels of free Sp-1 and increased M-CSF gene expression and osteoclast formation.

[Intramural blood vessels of the large intestine of the horse (Equus przewalskii f. caballus)]

The vascular system of the large intestine of 12 horses was examined by means of vascular corrosion casts, histology and transmission electron microscopy providing the following results. The Aa. et Vv. breves et longae leave the mesenteric vessels, respectively the subserously on the teniae lying cecal vessels to reach the tela subserosa at the mesenteric margin. The short vessels enter the deeper layers of the wall instantly, whereas the Aa. et Vv. longae move towards the submucosa by penetrating the muscular layers after a variable subserous course. The tela submucosa contains an arterial and a venous vascular plexus. In broader areas of the submucosa a three-dimensional vascular network can be found. This consists of a deep and a superficial vascular plexus, which are closely interconnected. The deep plexus is applied to the inner circular muscles, whereas the superficial plexus is adjacent to the muscularis mucosae. The (deep) arterial plexus receives its afflux from the Aa. breves et longae and supplies parts of the circular muscle layer with recurrent muscle branches. The vascularisation of the mucosa also originates from the submucosal (superficial) plexus. In the basal tunica mucosa, the ascending arteries form a transversal network from which arterioles branch into periglandular capillaries around each Lieberkühn crypt. Close to the lumen, a polygonal subepithelial capillary system is formed. The capillaries turn into postcapillary venules immediately below the epithelium of the mucosal surface. Veins move vertically through the submucosa to enter the submucosal plexus after few inflowing side branches. Branches of the subserous-submucosal connections form an intermuscular plexus between the circular and longitudinal muscular layer. This plexus supplies the capillaries of the tunica muscularis. The subepithelial capillaries are predominantly lined with a fenestrated endothelium, whereas the capillaries of the pericryptal mucosa mainly show a continuous endothelial lining. The latter contain multiple vesicles, which may fuse in order to form transcytoplasmic channels. Sphincter-like muscle bundles at the transition points from capillaries to venules may provide hemodynamic regulatory structures in the submucosa of the horse. Veins with circumferential cushions of smooth muscle fibres, so-called 'throttle veins', are also found.

[Vascular system in the large intestine of the dog (Canis lupus f. familiaris)]

The vascular system of the large intestine of 10 dogs was examined by means of vascular corrosion casts, histology and transmission-electron microscopy. The tela submucosa contains an arterial and a venous vascular plexus. In broader areas of the submucosa, a deep and a superficial vascular plexus, which are interconnected, can be found. The plexus are orientated parallel to the layers of the intestinal wall. On the one hand, these vessels naturally provide self-sufficiency and drainage of the submucosa, and, moreover, direct branches to the stratum circulare of the muscular layer. On the other hand, the submucosal vascular plexus is the 'distributional network' for the functional plexus of the tunica mucosa. The arteries, which ascend to the tunica mucosa, supply a flat arterial network underneath the intestinal glands. Bundles of only a few arteriolae originate from this in order to supply the pericryptal capillaries. In the vicinity of the cryptal orifices, these turn into a network of subepithelial capillaries, which is post-connected to the periglandular capillary plexus. From this 'terminal circulatory pathway', the blood is drained off by veins that enter the submucosal plexus. It is characteristic that the postcapillary venules often begin as part of the capillary network. As in other species, the subepithelial capillaries are pre-dominantly lined with a 'fenestrated endothelium', whereas the capillaries of the pericryptal areas show a continuous endothelium. The latter contains multiple vesicles that may fuse in order to form transcytoplasmic channels as a morphological equivalent for transcappillar-epithelial and vice versa occurring transport of substances.

[The blood vessel system of the large intestine of swine (Sus scrofa f. domestica)]

The circulatory system of the large intestine of 27 pigs was examined by means of corrosion anatomy (vascular casts), histology and electron microscopy. The results were as follows: The Aa. et Vv. breves et longae leave the mesenteric vessels and reach the wall of the intestine at the mesenteric margin. The short vessels enter the deeper layers of the wall, whereas the Aa. et Vv. longae, by taking a variable subserous course, reach the submucosa after penetrating the muscular layers. The tela submucosa contains an arterial and a venous vascular plexus. Where the submucosa is larger, there is a three-dimensional vascular network, a deep and superficial vascular plexus that are closely interconnected. The deep plexus is applied to the inner circular muscles, whereas the superficial plexus is adjacent to the muscularis mucosae. The deep arterial plexus receives its afflux from the Aa. breves et longae and provides part of the circular muscle layers with recurrent muscle branches. The vascularization of the mucosa is derived from the (superficial) submucosal plexus. The arteries that ascend the tunica mucosa ramify, in the form of a brush, into some arterioles. In the basal part of the mucosa, they turn into a periglandular capillary system, i.e. a network around each Lieberkühn crypt. Close to the lumen, a polygonal subepithelial capillary system is formed. Below the epithelium of the mucosal surface, the capillaries turn into postcapillary venules. These are running vertically through the submucosa, with few inflowing side branches, and finally enter the submucosal plexus An intermuscular plexus is formed by anastomoses between the circular and the longitudinal muscular layers from the branches of the subserous-submucosal connections. This intermuscular plexus provides the capillaries for the tunica muscularis. The subepithelial capillaries are, above all, furnished with a so-called fenestrated endothelium, whereas the capillaries of the pericryptal mucosa mainly show a continuous endothelium. The latter contains multiple vesicles that can fuse to form transcytoplasmic channels. In the wall of the large intestine of the pig, there are no sure indications as to the existence of either arterio-venous anastomoses or haemodynamic regulatory structures.