Powrnima Joshi

Publications (8) View all

• Article: In Vivo Transplantation of Autogenous Marrow-Derived Cells Following Rapid Intraoperative Magnetic Separation Based on Hyaluronan to Augment Bone Regeneration.

  Tonya Caralla, Powrnima Joshi, Sean Fleury, Viviane Luangphakdy, Kentaro Shinohara, Hui Pan, Cynthia Boehm, Amit Vasanji, Theresa E Hefferan, Esteban Walker, Michael Yaszemski, Vincent Hascall, Maciej Zborowski, George F Muschler
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  ABSTRACT: Introduction: This project was designed to test the hypothesis that rapid intraoperative processing of bone marrow based on hyaluronan (HA) could be used to improve the outcome of local bone regeneration if the concentration and prevalence of marrow-derived connective tissue progenitors (CTPs) could be increased and nonprogenitors depleted before implantation. Methods: HA was used as a marker for positive selection of marrow-derived CTPs using magnetic separation (MS) to obtain a population of HA-positive cells with an increased CTP prevalence. Mineralized cancellous allograft (MCA) was used as an osteoconductive carrier scaffold for loading of HA-positive cells. The canine femoral multidefect model was used and four cylindrical defects measuring 10 mm in diameter and 15 mm in length were grafted with MCA combined with unprocessed marrow or with MS processed marrow that was enriched in HA(+) CTPs and depleted in red blood cells and nonprogenitors. Outcome was assessed at 4 weeks using quantitative 3D microcomputed tomography (micro-CT) analysis of bone formation and histomorphological assessment. Results: Histomorphological assessment showed a significant increase in new bone formation and in the vascular sinus area in the MS-processed defects. Robust bone formation was found throughout the defect area in both groups (defects grafted with unprocessed marrow or with MS processed marrow.) Percent bone volume in the defects, as assessed by micro-CT, was greater in defects engrafted with MS processed cells, but the difference was not statistically significant. Conclusion: Rapid intraoperative MS processing to enrich CTPs based on HA as a surface marker can be used to increase the concentration and prevalence of CTPs. MCA grafts supplemented with heparinized bone marrow or MS processed cells resulted in a robust and advanced stage of bone regeneration at 4 weeks. A greater new bone formation and vascular sinus area was found in defects grafted with MS processed cells. These data suggest that MS processing may be used to enhance the performance of marrow-derived CTPs in clinical bone regeneration procedures. Further assessment in a more stringent bone defect model is proposed.
  Tissue Engineering Part A 10/2012; · 4.64 Impact Factor
• Article: Hair cell BK channels interact with RACK1, and PKC increases its expression on the cell surface by indirect phosphorylation.

  Alexei Surguchev, Jun-Ping Bai, Powrnima Joshi, Dhasakumar Navaratnam
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  ABSTRACT: Large conductance (BK) calcium activated potassium channels (Slo) are ubiquitous and implicated in a number of human diseases including hypertension and epilepsy. BK channels consist of a pore forming α-subunit (Slo) and a number of accessory subunits. In hair cells of nonmammalian vertebrates these channels play a critical role in electrical resonance, a mechanism of frequency selectivity. Hair cell BK channel clusters on the surface and currents increase along the tonotopic axis and contribute significantly to the responsiveness of these hair cells to sounds of high frequency. In contrast, messenger RNA levels encoding the Slo gene show an opposite decrease in high frequency hair cells. To understand the molecular events underlying this paradox, we used a yeast two-hybrid screen to isolate binding partners of Slo. We identified Rack1 as a Slo binding partner and demonstrate that PKC activation increases Slo surface expression. We also establish that increased Slo recycling of endocytosed Slo is at least partially responsible for the increased surface expression of Slo. Moreover, analysis of several PKC phosphorylation site mutants confirms that the effects of PKC on Slo surface expression are likely indirect. Finally, we show that Slo clusters on the surface of hair cells are also increased by increased PKC activity and may contribute to the increasing amounts of channel clusters on the surface of high-frequency hair cells.
  AJP Cell Physiology 04/2012; 303(2):C143-50. · 3.54 Impact Factor
• Article: CDK5 interacts with Slo and affects its surface expression and kinetics through direct phosphorylation.

  Jun-Ping Bai, Alexei Surguchev, Powrnima Joshi, Liza Gross, Dhasakumar Navaratnam
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  ABSTRACT: Large-conductance calcium-activated potassium (BK) channels are ubiquitous and play an important role in a number of diseases. In hair cells of the ear, they play a critical role in electrical tuning, a mechanism of frequency discrimination. These channels show variable kinetics and expression along the tonotopic axis. Although the molecular underpinnings to its function in hair cells are poorly understood, it is established that BK channels consist of a pore-forming α-subunit (Slo) and a number of accessory subunits. Here we identify CDK5, a member of the cyclin-dependent kinase family, as an interacting partner of Slo. We show CDK5 to be present in hair cells and expressed in high concentrations in the cuticular plate and in the circumferential zone. In human embryonic kidney cells, we show that CDK5 inhibits surface expression of Slo by direct phosphorylation of Slo. Similarly, we note that CDK5 affects Slo voltage activation and deactivation kinetics, by a direct phosphorylation of T847. Taken together with its increasing expression along the tonotopic axis, these data suggest that CDK5 likely plays a critical role in electrical tuning and surface expression of Slo in hair cells.
  AJP Cell Physiology 11/2011; 302(5):C766-80. · 3.54 Impact Factor
• Conference Proceeding: Amyloid precusor protein is required for convergent-extension movments during Zebrafish development

  Po-Nien Lu, Powrnima Joshi, Jennifer Liang, Kristine DiMonte, John Sullivan, Sanjay Pimplikar
  2010 International Conference on Zebrafish Development and Genetics, Madison, WI 53706; 01/2010
• Article: Amyloid precursor protein is required for convergent-extension movements during Zebrafish development.

  Powrnima Joshi, Jennifer O Liang, Kristine DiMonte, John Sullivan, Sanjay W Pimplikar
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  ABSTRACT: Amyloid precursor protein (APP) has been a focus of intense investigation because of its role in Alzheimer's disease (AD), however, its biological function remains uncertain. Loss of APP and APP-like proteins results in postnatal lethality in mice, suggesting a role during embryogenesis. Here we show that in a zebrafish model system, knock down of APP results in the generation of fish with dramatically reduced body length and a short, curly tail. In situ examination of gene expression suggests that the APP morphant embryos have defective convergent-extension movements. We also show that wild-type human APP rescues the morphant phenotype, but the Swedish mutant APP, which causes familial AD (fAD), does not rescue the developmental defects. Collectively, this work demonstrates that the zebrafish model is a powerful system to define the role of APP during embryonic development and to evaluate the functional activity of fAD mutant APP.
  Developmental Biology 09/2009; 335(1):1-11. · 4.07 Impact Factor