Browsing by Author "Harris, Stephen E."

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    Characterization of a novel murine Sost ERT2 Cre model targeting osteocytes
    (Springer Nature, 2019-02-21) Maurel, Delphine B.; Matsumoto, Tsutomu; Vallejo, Julian A.; Johnson, Mark L.; Dallas, Sarah L.; Kitase, Yukiko; Brotto, Marco; Wacker, Michael J.; Harris, Marie A.; Harris, Stephen E.; Bonewald, Lynda F.; Anatomy and Cell Biology, IU School of Medicine
    Transgenic mice are widely used to delete or overexpress genes in a cell specific manner to advance knowledge of bone biology, function and disease. While numerous Cre models exist to target gene recombination in osteoblasts and osteoclasts, few target osteocytes specifically, particularly mature osteocytes. Our goal was to create a spatial and temporal conditional Cre model using tamoxifen to induce Cre activity in mature osteocytes using a Bac construct containing the 5' and 3' regions of the Sost gene (Sost ERT2 Cre). Four founder lines were crossed with the Ai9 Cre reporter mice. One founder line showed high and specific activity in mature osteocytes. Bones and organs were imaged and fluorescent signal quantitated. While no activity was observed in 2 day old pups, by 2 months of age some osteocytes were positive as osteocyte Cre activity became spontaneous or 'leaky' with age. The percentage of positive osteocytes increased following tamoxifen injection, especially in males, with 43% to 95% positive cells compared to 19% to 32% in females. No signal was observed in any bone surface cell, bone marrow, nor in muscle with or without tamoxifen injection. No spontaneous signal was observed in any other organ. However, with tamoxifen injection, a few positive cells were observed in kidney, eye, lung, heart and brain. All other organs, 28 in total, were negative with tamoxifen injection. However, with age, a muscle phenotype was apparent in the Sost-ERT2 Cre mice. Therefore, although this mouse model may be useful for targeting gene deletion or expression to mature osteocytes, the muscle phenotype may restrict the use of this model to specific applications and should be considered when interpreting data.
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    Cx43 Overexpression in Osteocytes Prevents Osteocyte Apoptosis and Preserves Cortical Bone Quality in Aging Mice
    (Wiley, 2018-02-26) Davis, Hannah M.; Aref, Mohammad W.; Aguilar‐Perez, Alexandra; Pacheco‐Costa, Rafael; Allen, Kimberly; Valdez, Sinai; Herrera, Carmen; Atkinson, Emily G.; Mohammad, Arwa; Lopez, David; Harris, Marie A.; Harris, Stephen E.; Allen, Matthew; Bellido, Teresita; Plotkin, Lilian I.; Anatomy and Cell Biology, School of Medicine
    Young, skeletally mature mice lacking Cx43 in osteocytes exhibit increased osteocyte apoptosis and decreased bone strength, resembling the phenotype of old mice. Further, the expression of Cx43 in bone decreases with age, suggesting a contribution of reduced Cx43 levels to the age-related changes in the skeleton. We report herein that Cx43 overexpression in osteocytes achieved by using the DMP1-8kb promoter (Cx43OT mice) attenuates the skeletal cortical but not trabecular bone phenotype of aged, 14-month-old mice. The percentage of Cx43-expressing osteocytes was higher in Cx43OT mice, whereas the percentage of Cx43-positive osteoblasts remained similar to wild-type (WT) littermate control mice. The percentage of apoptotic osteocytes and osteoblasts was increased in aged WT mice compared with skeletally mature, 6-month-old WT mice, and the percentage of apoptotic osteocytes, but not osteoblasts, was decreased in age-matched Cx43OT mice. Aged WT mice exhibited decreased bone formation and increased bone resorption as quantified by histomorphometric analysis and circulating markers compared with skeletally mature mice. Further, aged WT mice exhibited the expected decrease in bone biomechanical structural and material properties compared with young mice. Cx43 overexpression prevented the increase in osteoclasts and decrease in bone formation on the endocortical surfaces and the changes in circulating markers in the aged mice. Moreover, the ability of bone to resist damage was preserved in aged Cx43OT mice both at the structural and material level. All together, these findings suggest that increased Cx43 expression in osteocytes ameliorates age-induced cortical bone changes by preserving osteocyte viability and maintaining bone formation, leading to improved bone strength. © 2018 American Society for Bone and Mineral Research.
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    Podoplanin is dispensable for mineralized tissue formation and maintenance in the Swiss outbred mouse background
    (Wiley, 2021) Nakamura, Masako Toda; Zhang, Honghao; Guo, Dayong; Ueharu, Hiroki; Pan, Haichun; Scott, Greg; Harris, Marie; Ray, Manas; Feng, Jiang Q.; Harris, Stephen E.; Bonewald, Lynda F.; Mishina, Yuji; Anatomy, Cell Biology and Physiology, School of Medicine
    Podoplanin, PDPN, is a mucin-type transmembrane glycoprotein widely expressed in many tissues, including lung, kidney, lymph nodes, and mineralized tissues. Its function is critical for lymphatic formation, differentiation of type I alveolar epithelial lung cells, and for bone response to biomechanical loading. It has previously been shown that Pdpn null mice die at birth due to respiratory failure emphasizing the importance of Pdpn in alveolar lung development. During the course of generation of Pdpn mutant mice, we found that most Pdpn null mice in the 129S6 and C57BL6/J mixed genetic background die at the perinatal stage, similar to previously published studies with Pdpn null mice, while all Pdpn null mice bred with Swiss outbred mice survived. Surviving mutant mice in the 129S6 and C57BL6/J mixed genetic background showed alterations in the osteocyte lacunocanalicular network, especially reduced osteocyte canaliculi in the tibial cortex with increased tibial trabecular bone. However, adult Pdpn null mice in the Swiss outbred background showed no overt differences in their osteocyte lacunocnalicular network, bone density, and no overt differences when challenged with exercise. Together, these data suggest that genetic variations present in the Swiss outbred mice compensate for the loss of function of PDPN in lung, kidney, and bone.