Volume 25, Issue 113, July 2021

Mechanisms of C2-ceramide-induced apoptosis in osteoblasts

Turki Y Alhazzazi¹, Raghad A Al-Dabbagh^2♦, Nadia A Al-Hazmi¹, Sahar Bukhary¹, Dania F Bogari³, Daniel Weekes⁴, Fraser Mc Donald⁵, Peter Hill⁶, Agamemnon E Grigoriadis⁵

¹Department of Oral Biology, Faculty of Dentistry, KingAbdulaziz University, Jeddah, Saudi Arabia
²Department of Oral and Maxillofacial Prosthodontics, Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia
³Department of Endodontics, Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia
⁴The Institute of Cancer Research, London, Greater London, UK
⁵Department of Craniofacial and Regenerative Biology, Dental Institute, King’s College London, London, UK
⁶Belmont Park Dental Care, Lewisham, London, UK

^♦Corresponding author
Assistant Professor and Consultant in Prosthodontics, Department of Oral and Maxillofacial Prosthodontics, Faculty of Dentistry, King Abdulaziz University, Jeddah, Saudi Arabia

ABSTRACT

Dysregulated osteoblast programmed cell death (PCD) is implicated in metabolic bone diseases such as osteoporosis. Ceramide, a precursor to all complex sphingolipids, is a secondary messenger in PCD. However, the mechanisms of ceramide induced-PCD are poorly characterized. Thus, the aim of this study was to investigate the nature and mechanism of ceramide-induced PCD in osteoblasts. The MTT assay, propidium iodide uptake with flow cytometric analysis, and TUNEL staining were used to assess the effect of exogenous ceramide on cell viability and apoptosis in MC3T3-E1 cells and primary murine osteoblasts. Western blotting and immunofluorescence approaches were used to elucidate the underlying signaling mechanisms. Ceramide reduced MC3T3-E1 and primary osteoblast viability and induced apoptosis in a dose-dependent manner. Ceramide failed to activate the executioner caspases-3 and -7 and poly (ADP-ribose) polymerase (PARP), while a selective inhibitor of caspase-8 abrogated ceramide effects on osteoblast viability. Ceramide induced p38 and ERK activation, but only p38 was involved in ceramide-induced osteoblast PCD. Our study highlights a novel role for ceramide in inducing caspase-8 and p38-dependent osteoblast PCD. Understanding cell death mechanisms in osteoblasts could help in the development of new targeted therapeutics that selectively identify cells with pathogenic programmed cell death pathways.

Keywords: Apoptosis, cell biology, osteoblasts

Medical Science, 2021, 25(113), 1530-1541

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