title: Glutamate Receptor Agonists and Glutamate Transporter Antagonists Regulate Differentiation of Osteoblast Lineage Cells.
abstract: Development and function of osteoblast lineage cells are regulated by a complex microenvironment consisting of the bone extracellular matrix, cells, systemic hormones and cytokines, autocrine and paracrine factors, and mechanical load. Apart from receptors that transduce extracellular signals into the cell, molecular transporters play a crucial role in the cellular response to the microenvironment. Transporter molecules are responsible for cellular uptake of nutritional components, elimination of metabolites, ion transport, and cell-cell communication. In this report, the expression of molecular transporters in osteoblast lineage cells was investigated to assess their roles in cell development and activity. Low-density arrays, covering membrane and vesicular transport molecules, were used to assess gene expression in osteoblasts representing early and late differentiation states. Receptors and transporters for the amino acid glutamate were found to be differentially expressed during osteoblast development. Glutamate is a neurotransmitter in the central nervous system, and the mechanisms of its release, signal transduction, and cellular reabsorption in the synaptic cleft are well understood. Less clear, however, is the control of equivalent processes in peripheral tissues. In primary osteoblasts, inhibition of glutamate transporters with nonselective inhibitors leads to an increase in the concentration of extracellular glutamate. This change was accompanied by a decrease in osteoblast proliferation, stimulation of alkaline phosphatase, and the expression of transcripts encoding osteocalcin. Enzymatic removal of extracellular glutamate abolished these pro-differentiation effects, as did the inhibition of PKC- and Erk1/2-signaling pathways. These findings demonstrate that glutamate signaling promotes differentiation and activation of osteoblast lineage cells. Consequently, the glutamate system may represent a putative therapeutic target to induce an anabolic response in the skeletal system. Known antagonists of glutamate transporters will serve as lead compounds in developing new and specific bioactive molecules.
authors.affiliation: Bone Biology & Orthopaedic Research, Department Clinical Research, University of Bern, Murtenstrasse 35, 3010, Bern, Switzerland.|Swiss National Centre of Competence in Research, NCCR TransCure, University of Bern, Bern, Switzerland.|Graduate School for Cellular and Biomedical Sciences, University of Bern, Bern, Switzerland.
authors.forename: Wenjie
authors.initials: W
authors.lastname: Xie
authors.affiliation: Bone Biology & Orthopaedic Research, Department Clinical Research, University of Bern, Murtenstrasse 35, 3010, Bern, Switzerland.
authors.forename: Silvia
authors.initials: S
authors.lastname: Dolder
authors.affiliation: Bone Biology & Orthopaedic Research, Department Clinical Research, University of Bern, Murtenstrasse 35, 3010, Bern, Switzerland.
authors.forename: Mark
authors.initials: M
authors.lastname: Siegrist
authors.affiliation: Bone Biology & Orthopaedic Research, Department Clinical Research, University of Bern, Murtenstrasse 35, 3010, Bern, Switzerland.
authors.forename: Antoinette
authors.initials: A
authors.lastname: Wetterwald
authors.affiliation: Bone Biology & Orthopaedic Research, Department Clinical Research, University of Bern, Murtenstrasse 35, 3010, Bern, Switzerland. hofstetter@dkf.unibe.ch.|Swiss National Centre of Competence in Research, NCCR TransCure, University of Bern, Bern, Switzerland. hofstetter@dkf.unibe.ch.
authors.forename: Willy
authors.initials: W
authors.lastname: Hofstetter
mesh_terms: D027322:Amino Acid Transport System X-AG / Q000037:antagonists & inhibitors* / Q000378:metabolism; D000818:Animals; D001842:Bone and Bones / Q000378:metabolism; D002450:Cell Communication / Q000502:physiology; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D019070:Cell Lineage / Q000187:drug effects* / Q000502:physiology; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology*; D005971:Glutamates / Q000378:metabolism / Q000494:pharmacology; D008810:Mice, Inbred C57BL; D010006:Osteoblasts / Q000166:cytology* / Q000187:drug effects; D015675:Osteocalcin / Q000378:metabolism; D010012:Osteogenesis / Q000187:drug effects / Q000502:physiology; D017470:Receptors, Glutamate / Q000378:metabolism*
chemical_list: D027322:Amino Acid Transport System X-AG; D018690:Excitatory Amino Acid Agonists; D005971:Glutamates; D017470:Receptors, Glutamate; D015675:Osteocalcin
keywords: Anabolic response; Glutamate; Membrane transporter; Osteoblast lineage cells