Gap junctions formed by connexin 43 (Cx43) play an important role in transmitting signals betweenbone cells such as osteoblasts and osteoclasts, cells responsible for bone formation and bone remodeling.However, osteocytes express extremely large amounts of Cx43 compared with other bone cell types and thisprotein is located both on the membrane cell surface as well as in the cytoplasm. Osteocytes, unlike othercell types, only connect and form gap junctions with other cells through the tips of their dendritic processes.This is a very small percentage of the total cell surface area compared to other cells. Our data shows that inaddition to gap junctions, primary osteocytes and osteocyte-like MLO-Y4 cells express functional Cx43-forming hemichannels and that these hemichannels mediate the immediate release of prostaglandin byosteocytes in response to fluid flow shear stress. The central hypothesis of the project based on oursignificant preliminary findings is that hemichannels formed by Cx43 have essential, yet distinct functionsfrom gap junctions in the mediation and regulation of the osteocytic response to mechanical strain.
Three specific aims will be pursued: 1). Determine the importance of Cx43 in osteocytes in vivo in response tomechanical strain by the generation of targeted deletion and overexpression of Cx43 in osteocytes intransgenic mouse models; 2). Determine the function of hemichannels in osteocytes by the specific blockingof hemichannel function, but not gap junction function; and 3). Determine the role alpha5 Integrin plays in theregulation of the opening of hemichannels induced by fluid flow shear stress. This last specific aim will beaccomplished by blocking either expression of aSintegrin or blocking protein interaction with Cx43. One ofthe innovative aspects of this proposal is the discovery of a novel, unconventional function for hemichannelsin osteocytes and regulation of Cx43-forming hemichannels in osteocytes in response to mechanical strain.Moreover, this study combines comprehensive biochemical, molecular, transgenic and functionalapproaches with unique mechanical engineering applications. It is our expectation that our experimentalfindings will have a major impact on our understanding of the novel roles hemichannels play in regulatingosteocyte response to mechanical strain. Our experimental outcomes will be significant because the newknowledge obtained will contribute to our understanding of how mechanical signals are transduced andmodulated between osteocytes and cells on the bone surface. Furthermore, completion of these threespecific aims should provide novel contributions to the development of strategies for the treatment of bonediseases such as osteoporosis by providing clues for potential targets for drug action and development.
Showing the most recent 10 out of 97 publications
