Eine Hyperglykämie hemmt die Osteoblastenfunktionen in vitro

Zusammenfassung

Einleitung/Ziel der Studie

Diabetes mellitus ist eine der häufigsten Volkskrankheiten, die zu einem erhöhten Frakturrisiko und einer verschlechterten Frakturheilung führen. Obwohl die zugrundeliegenden zellulären und molekularen Mechanismen noch nicht abschließend geklärt sind, scheint eine verminderte Osteoblastenfunktion beteiligt zu sein. Vor Kurzem konnten wir zeigen, dass eine Stimulation der Osteoblastenfunktion durch Aktivierung des Wnt-Signalwegs die Knochenqualität und -regeneration in diabetischen Ratten verbessert. Das Ziel dieser Studie war es, diabetische Konditionen in vitro zu simulieren, um die molekularen Mechanismen der verminderten Osteoblastenfunktion zu untersuchen.

Methoden

Osteoblasten-ähnliche UMR- 106-Zellen wurden in Zellkulturmedium mit normalen (6 mM) oder erhöhten (30–150 mM) Glukosekonzentrationen kultiviert. Anschließend wurde die Vitalität, Proliferation und Mineralisierung sowie die Expression von Osteoblastenmarkern und Wnt- Signalmolekülen untersucht.

Ergebnisse

Nach vier Tagen in einem erhöhten Glukosemilieu nahm die Proliferation der UMR-106-Zellen bei gleichbleibender Zellzahl signifikant ab (–42 %). Ferner verringerte sich das Mineralisierungspotenzial der UMR-106-Zellen um 43 %. Die Genexpression der Osteoblastenmarker Osteokalzin und Osteopontin sank um 38 % bzw. 27 %. Die Expression von Connexin-43 und des Wnt-Inhibitors Dickkopf-1 stieg hingegen unter hyperglykämischen Bedingungen an (+15 % und +20 %). Die Konzentration von zyklischem Adenosinmonophosphat (cAMP), einem intrazellulären, ubiquitären Second messenger, nahm mit steigender Glukosemenge signifikant ab (–61 %). Die Proteinkonzentration der nachgeschalteten aktiven Proteinkinase A war in einem erhöhten Glukosemilieu reduziert.

Fazit

Unsere Ergebnisse weisen darauf hin, dass eine erhöhte Glukosekonzentration in vitro die Osteoblastenfunktion massiv beeinträchtigt. Eine Reduktion von cAMP sowie Veränderungen der Expression Osteoblasten-spezifischer Differenzierungsmarker sind mögliche Grundlagen dieses Defektes.

Summary

Introduction/Aim of the study

Diabetes mellitus is one of the most common metabolic diseases and leads to an increased fracture risk and impaired fracture healing. The underlying cellular and molecular mechanisms are not fully understood, but a decreased osteo - blastic function seems to be operative. Previously, we showed that blocking of inhibitors of the Wnt signaling pathway stimulated osteoblast function and increased bone quality and bone regeneration in diabetic rats. The aim of this study was to mimic diabetic conditions in vitro to understand the molecular mechanisms underlying decreased osteoblast function.

Methods

Osteoblast-like UMR-106 cells were cultured in normal (6 mM) and high (30–150 mM) glucose conditions. Cell vitality, proliferation, and mineralization status as well as gene expression of osteoblastic markers and Wnt molecules were assessed.

Results

After four days under high glucose conditions, the proliferation rate of the UMR-106 cells decreased significantly (–42 %), while cell number remained stable. In addition, the mineralization capacity of UMR-106 cells was reduced (43 %). The gene expression of the bone formation marker osteocalcin was significantly diminished (–38 %) similar to the expression of osteopontin (–27 %). The expression of connexin 43 and the Wnt inhibitor Dickkopf-1 was increased (+15 % and +20 %). The concentration of cyclic adenosine monophosphate (cAMP), an ubiquitous intracellular second messenger, decreased with increasing glucose amounts (–61 %). The concentration of activated downstream target protein kinase A was reduced under high glucose conditions.

Conclusion

These data indicate that high concentrations of glucose suppressed osteoblastic function in vitro. Reduction of cAMP and interference with Wnt signaling represent potential mechanisms.

Schlüsselwörter

Diabetes mellitus - Osteoblastenfunktion - Wnt-Signalweg

Keywords

Diabetes mellitus - osteoblastic function - Wnt signaling pathway

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