Beta2-adrenergic receptors expressed on murine chondrocytes stimulate cellular growth and inhibit the expression of Indian hedgehog and collagen type X.
The sympathetic nervous system has been demonstrated to have a role in regulating bone remodeling through beta-adrenergic receptors (beta-AR) expressed on osteoblasts. Studies using beta(2)-adrenergic receptor agonists in vivo have also suggested an effect on endochondral bone development; however, it was not clear if this effect was mediated through osteoblasts or chondrocytes. To more thoroughly examine the role of beta-AR in chondrocytes we characterized the expression and signal transduction systems activated by beta-AR in growth plate chondrocytes prepared from ribs of embryonic E18.5 mice. Using RT-PCR and immunohistochemistry we found that the chondrocytes expressed only beta(2)-AR. The receptors were coupled to stimulation of adenylyl cyclase, phosphorylation of the cyclic AMP response element binding protein (CREB) and extracellular signal-regulated kinase (ERK1/2). Stimulation of ERK1/2 was transient and limited by the concomitant stimulation of the mitogen-activated protein kinase phosphatase (MKP-1). Isoproterenol stimulated the growth of chondrocytes as assessed by increased incorporation of [(3)H]-thymidine into the cells. The cellular expression of two markers of chondrocyte differentiation, Indian hedgehog, expressed in pre-hypertrophic cells and collagen type X, expressed in hypertrophic chondrocytes, were both significantly inhibited after incubation with isoproterenol. Collectively, these findings demonstrate regulation of chondrocytes through beta(2)-AR expressed on the cells that stimulate their growth and inhibit their differentiation, indicating that the sympathetic nervous system may be an important regulator of embryonic cartilage development.
Lai
Lick Pui
LP
Department of Pharmacology, University of Toronto, Toronto, Ontario, Canada.
Mitchell
Jane
J
D000818:Animals; D002356:Cartilage / Q000196:embryology / Q000254:growth & development; D002454:Cell Differentiation; D049109:Cell Proliferation; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology*; D024121:Collagen Type X / Q000037:antagonists & inhibitors*; D004622:Embryo, Mammalian; D053823:Hedgehog Proteins / Q000037:antagonists & inhibitors*; D051379:Mice; D018343:Receptors, Adrenergic, beta-2 / Q000502:physiology*; D015398:Signal Transduction
D024121:Collagen Type X; D053823:Hedgehog Proteins; D018343:Receptors, Adrenergic, beta-2; C514061:ihh protein, mouse