1990-1994: B.S., Molecular and Cell Biology, The Pennsylvania State University.
1996-2000: Ph.D., Biochemistry, Microbiology and Molecular Biology,The Pennsylvania State University.
2001-2004: Post Doctoral fellow in the lab of Roberto Civitelli, Washington University in St. Louis.
2004-present: Assistant Professor in Orthopaedics, University of Maryland, School of Medicine
The major focus in my laboratory is the study of intercellular communication among the cells of bone. Primarily, we examine the role of the gap-junction protein connexin43 in transmitting signals among bone-forming osteoblasts.
Gap junctions are intercellular channels formed by hexamers of connexins in one cell that dock with a hexameric array of connexins on an adjacent cell, forming an aqueous pore between the two cells. Gap junctions permit the direct intercellular exchange of small molecules, such as ions, metabolites and second messengers.
In bone, osteoblasts and osteocytes are highly interconnected via gap junctions composed primarily of connexin43. In these cells, connexin43 has been shown to play an important role in transmitting hormonal-, mechanical load- and growth factor-induced signals and, ultimately, in bone mass acquisition. In addition, mutations in Gja1, the gene encoding Cx43, result in the pleiotropic disorder oculodentodigital dysplasia, which includes skeletal manifestations.
Despite the clear importance of connexin43 in skeletal function, key molecular details of how connexin43 regulates bone mass acquisition, osteoblast differentiation and osteoblast/osteocyte function are unknown. My work is focused on answering key questions, such as what are the identities of the second messengers communicated by connexin43 gap junctions, what are the targets of these second messengers, and how do they regulate osteoblast/osteocyte function?
In my lab, we use in vivo models, as well as molecular, biochemical and cell biological approaches to determine the role of connexin43 in bone and to elucidate the molecular mechanisms underpinning the impact of connexin43 on osteoblast gene transcription, signal transduction and bone formation.
(A) Gap junctions are composed of connexin monomers. Six connexin monomers assemble to form a connexon or hemichannel in the plasma membrane of one cell. A hemichannel can then dock with a hemichannel on an adjacent cell to form a permeable channel between the cells. (B) Immunofluorescence of the gap junction protein connexin43 in osteoblast cells. Connexin43, green; actin, red; nuclei, blue. (C) Gap junctional communication (the exchange of low molecular weight molecules) between osteoblasts can be visualized by the scrape loading dye transfer assay. (D) Immunohistochemistry of connexin43 (reddish-brown) in osteoblasts during bone formation.
Lab Techniques and Equipment:
Real time PCR, luciferase reporter assays, western blotting, cell transfections, cell culture, chromatin immunoprecipitations (ChIP), fluorescence microscopy, immunohistochemistry, skeletal histology, bone histomorphometry, and micro computed tomography.
Niger C, Buo AM, Hebert C, Duggan BT, Williams MS, Stains JP (2012) ERK acts in parallel to PKC delta to mediate the Cx43-dependent potentiation of Runx2 activity by FGF2 in MC3T3 osteoblasts. Am J Physiol Cell Physiol 302:C-1035-1044.
Nanjundaiah SM, Venkatesha SH, Yu H, Tong L, Stains JP, Moudgil KD (2012) Celastrus and its bioactive Celastrol protect against bone damage in autoimmune arthritis by modulating the osteo-immune crosstalk. J Biol Chem, 287:22216-22226.
Niger C, Lima F, Yoo DJ, Gupta RR, Buo AM, Hebert C, Stains JP (2011) The Transcriptional Activity of Osterix Requires the Recruitment of Sp1 to the Osteocalcin Proximal Promoter. Bone 49:683-692.
Gupta RR, Yoo DJ, Hebert C, Niger C, Stains JP (2010) Induction of an osteocyte-like phenotype by fibroblast growth factor-2. Biochem Biophys Res Commun, 402:258-264.
Niger C, Hebert C, Stains JP (2010) Interaction of Connexin43 and Protein Kinase C-delta during FGF2 Signaling. BMC Biochem, 11:14.
Niger C, Howell FD, Stains JP (2010) Interleukin-1Î² increases gap junctional communication among synovial fibroblasts via the extracellular signal regulated kinase pathway. Biol Cell, 102:37-49.
Lima F, Niger C, Hebert C, Stains JP (2009) Connexin43 potentiates osteoblast responsiveness to fibroblast growth factor 2 via a protein kinase C-delta/Runx2-dependent mechanism. Mol Biol Cell 20:2697-2708.
Yu, M; Moreno JL, Stains JP, Keegan, AD (2009) Complex regulation of tartrate-resistant acid phosphatase (TRAP) expression by interleukin 4 (IL-4): IL-4 indirectly suppresses receptor activator of NF -kappaB ligand (RANKL)- mediated TRAP expression but modestly induces its expression directly. J. Biol Chem 284:32986-32979.
Chung DJ, Castro CH, Watkins M, Stains JP, Chung MY, Szejnfeld VL, Willecke K, Theis M, Civitelli R (2006) Low peak bone mass and attenuated anabolic response to parathyroid hormone in mice with an osteoblast-specific deletion of connexin43. J Cell Sci 119:4187-4198.
Stains JP, Civitelli R (2005) Gap junctions regulate extracellular signal-regulated kinase (ERK) signaling to affect gene transcription. Mol Biol Cell 16:64-72.
Stains JP, Lecanda F, Screen J, Towler DA, Civitelli R (2003) Gap junctional communication modulates gene transcription by altering recruitment of Sp1 and Sp3 to connexin-response elements in osteoblast promoters. J Biol Chem 278:24377-24387.
Links of Interest:Orthopaedics Research at the University of Maryland
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