gms | German Medical Science

Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU 2018)

23.10. - 26.10.2018, Berlin

Periprosthetic hypoxia as consequence of TRPM7 mediated cobalt influx in osteoblasts

Meeting Abstract

  • presenting/speaker Constantin Römmelt - Department of Orthopaedic Surgery, Otto-von-Guericke University, Magdeburg, Germany
  • Thomas Munsch - Institute of Physiology, Otto-von-Guericke University, Magdeburg, Germany
  • Andreas Drynda - Department of Orthopaedic Surgery, Otto-von-Guericke University, Magdeburg, Germany
  • Volkmar Lessmann - Institute of Physiology, Otto-von-Guericke University, Magdeburg, Germany
  • Christoph Lohmann - Department of Orthopaedic Surgery, Otto-von-Guericke University, Magdeburg, Germany
  • Jessica Bertrand - Department of Orthopaedic Surgery, Otto-von-Guericke University, Magdeburg, Germany

Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU 2018). Berlin, 23.-26.10.2018. Düsseldorf: German Medical Science GMS Publishing House; 2018. DocGF11-1053

doi: 10.3205/18dkou442, urn:nbn:de:0183-18dkou4428

Veröffentlicht: 6. November 2018

© 2018 Römmelt et al.
Dieser Artikel ist ein Open-Access-Artikel und steht unter den Lizenzbedingungen der Creative Commons Attribution 4.0 License (Namensnennung). Lizenz-Angaben siehe http://creativecommons.org/licenses/by/4.0/.


Gliederung

Text

Objectives: The reasons for the high number of loosened metal-on-metal (MoM) hip implants are still not fully understood. It is assumed that adverse reactions to metal wear debris generated from endoprosthesis are one of the major reasons. Interestingly, cobalt-ions have been used in experimental designs for a long time now to simulate hypoxia by induction of HIF-1α. HIF-1 mediated signaling pathways, which normally modulate tissue metabolism under hypoxic circumstances, could be also triggered by prosthetic wear debris and influence bone metabolism favoring osteolysis. The aim of this study was to investigate the uptake mechanism of cobalt ions and the subsequent effects on the induction of chemical hypoxia.

Methods: Immunhistochemical staining of periprosthetic tissues of failed MoM and MoP hip implants in comparison to OA tissues was conducted to evaluate debris-dependent HIF-1α expression. Calcium imaging experiments using the ratiometric indicator fura-2 were performed to find out about Co2+ influx in MG-63 osteoblast-like cells based on cobalt mediated quenching effects. Standard PCR and qRT-PCR were conducted to determine the general expression of TRPM6 and TRPM7 as potential cobalt influx pathways in osteoblasts. The inhibitor 2-APB and TRPM7-specific siRNA were applied to quantify the importance of TRPM7 for cobalt uptake. To correlate the influx with intracellular effects and to find out about the hypoxic effects of cobalt ions, western blots were conducted determining HIF-1α activity in MG-63 cells.

Results and conclusion: Tissues harvested from MoM patients showed a significantly increased number of HIF-1α positive cells in comparison to the PE (p = .009) and OA (p = .007) group. The calcium imaging data indicate a clear dependency of cobalt influx on the applied CoCl2 concentration (F(5,37) = 21.95, p < .001). Absolute mRNA quantification revealed a significantly higher expression (t(48) = -3.20, p = .002) of TRPM7 in comparison to TRPM6 in MG-63 cells. Experiments applying 2-APB revealed a highly significant inhibitory effect on the extent of Co2+ influx (F(1,76) = 14.41, p < .001) and the expression of HIF-1α (t(6) = -2.44, p = .05). Finally, also specific TRPM7 knockdown had a highly significant, inhibitory effect on the Co2+ influx (F(1,14) = 91.93, p < .001) in MG-63 osteoblast-like cells.

The results indicate TRPM7 as a major influx pathway for Co2+ ions in osteoblasts and underline the potential importance of HIF-1α in periprosthetic bone homeostasis. This hypoxic signaling could be of great significance for the pathomechanism leading to implant loosening.