title: NELL-1 increases pre-osteoblast mineralization using both phosphate transporter Pit1 and Pit2.
abstract: NELL-1 is a potent osteoinductive molecule that enhances bone formation in multiple animal models through currently unidentified pathways. In the present manuscript, we hypothesized that NELL-1 may regulate osteogenic differentiation accompanied by alteration of inorganic phosphate (Pi) entry into the osteoblast via sodium dependent phosphate (NaPi) transporters. To determine this, MC3T3-E1 pre-osteoblasts were cultured in the presence of recombinant human (rh)NELL-1 or rhBMP-2. Analysis was performed for intracellular Pi levels through malachite green staining, Pit-1 and Pit-2 expression, and forced upregulation of Pit-1 and Pit-2. Results showed rhNELL-1 to increase MC3T3-E1 matrix mineralization and Pi influx associated with activation of both Pit-1 and Pit-2 channels, with significantly increased Pit-2 production. In contrast, Pi transport elicited by rhBMP-2 showed to be associated with increased Pit-1 production only. Next, neutralizing antibodies against Pit-1 and Pit-2 completely abrogated the Pi influx effect of rhNELL-1, suggesting rhNELL-1 is dependent on both transporters. These results identify one potential mechanism of action for rhNELL-1 induced osteogenesis and highlight a fundamental difference between NELL-1 and BMP-2 signaling.
authors.affiliation: Department of Bioengineering, University of California, Los Angeles, 420 Westwood Plaza,7523 Boelter Hall, Los Angeles, CA 90095, USA.
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Cowan
authors.forename: Xinli
authors.initials: X
authors.lastname: Zhang
authors.forename: Aaron W
authors.initials: AW
authors.lastname: James
authors.forename: T Mari
authors.initials: TM
authors.lastname: Kim
authors.forename: Nichole
authors.initials: N
authors.lastname: Sun
authors.forename: Benjamin
authors.initials: B
authors.lastname: Wu
authors.forename: Kang
authors.initials: K
authors.lastname: Ting
authors.forename: Chia
authors.initials: C
authors.lastname: Soo
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000378:metabolism; D002113:Calcification, Physiologic / Q000187:drug effects / Q000502:physiology*; D002135:Calcium-Binding Proteins; D002460:Cell Line; D005109:Extracellular Matrix / Q000378:metabolism / Q000502:physiology; D006801:Humans; D051379:Mice; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D010012:Osteogenesis / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction; D050611:Sodium-Phosphate Cotransporter Proteins, Type III / Q000378:metabolism*
chemical_list: D055396:Bone Morphogenetic Protein 2; D002135:Calcium-Binding Proteins; C104144:NELL1 protein, human; D009419:Nerve Tissue Proteins; D050611:Sodium-Phosphate Cotransporter Proteins, Type III; D000469:Alkaline Phosphatase