Abstract
ABSTRACTDuring orthodontic tooth movement, the periodontal ligament (PDL) is exposed to continuous mechanical strain. However, many researchers have applied cyclic tensile strain, not continuous tensile strain, to PDL cells in vitro because there has been no adequate device to apply continuous tensile strain to cultured cells. In this study, we contrived a novel device designed to apply continuous tensile strain to cells in culture. The continuous tensile strain was applied to human immortalized periodontal ligament cell line (HPL cells) and the cytoskeletal structures of HPL cells were examined by immunohistochemistry. The expression of both inflammatory and osteogenic markers was also examined by real-time reverse transcription polymerase chain reaction. The osteogenic protein, Osteopontin (OPN), was also detected by western blot analysis. The actin filaments of HPL cells showed uniform arrangement under continuous tensile strain. The continuous tensile strain increased the expression of inflammatory genes such as IL-1β, IL-6, COX-2 and TNF-α, and osteogenic genes such as RUNX2 and OPN in HPL cells. It also elevated the expression of OPN protein in HPL cells. These results suggest that our new simple device is useful for exploring the responses to continuous tensile strain applied to the cells.
Highlights
Continuous tensile strain from the device apparently influenced the direction of actin filaments in Human immortalized periodontal ligament cell lines (HPL) cells
Immunohistochemistry demonstrated that actin filaments were unidirectionally arranged in HPL cells exposed to the continuous tensile strain, though filaments were randomly arranged in HPL cells in the control group (Fig. 2C and D)
It has been reported that the expression levels of inflammatory genes were upregulated in periodontal ligament (PDL) cells under mechanical strain (Iwasaki et al, 2001; Jacobs et al, 2014; Shimizu et al, 1998; Yamamoto et al, 2006); we examined the effects of continuous tensile strain on inflammatory gene expression in HPL cells
Summary
Cells in the body are usually exposed to several types of mechanical stimulation, such as shear stress (Li et al, 2005), compressive stress (MacKelvie et al, 2003; Tschumperlin et al, 2004) and tensile stress (Thomas et al, 2006). To investigate the cellular response to mechanical stress, numerous researchers have contrived devices to apply mechanical strain, such as shear stress (Jacobs et al, 1998; Yoo et al, 2014), tensile strain (Beckmann et al, 2014; Kanzaki et al, 2006; Shah et al, 2013; Tsuji et al, 2004; Zhu et al, 2008), compression (Kanzaki et al, 2002; Tschumperlin et al, 2004) and hydrostatic pressure (Swartz et al, 2001), to cultured cells in order to mimic the in vivo environment. Much of the mechanical strain in the living body is cyclic in nature, and continuous mechanical strain is only applied in limited situations, such as in orthodontic tooth movement and distraction osteogenesis (Beertsen et al, 1997; Meikle, 2006; Peltomaki, 2009)
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