Effects of hypoxia on the proliferation, mineralization and ultrastructure of human periodontal ligament fibroblasts in vitro

Abstract

This study aimed to investigate the effects of hypoxia on the proliferation, mineralization and ultrastructure of human periodontal ligament fibroblasts (HPLFs) at various times in vitro in order to further study plateau-hypoxia-induced periodontal disease. HPLFs (fifth passage) cultured by the tissue culture method were assigned to the slight (5% O2), middle (2% O2), and severe hypoxia (1% O2) groups and the control (21% O2) group, respectively. At 12, 24, 48 and 72 h, the proliferation and alkaline phosphatase (ALP) activities were detected. The ultrastructure of the severe hypoxia group was observed. HPLFs grew more rapidly with an increase in the degree of hypoxia at 12 and 24 h, and significant levels of proliferation (P<0.05) were observed in the severe hypoxia group at 24 h. Cell growth was restrained with an increase in the degree of hypoxia at 48 and 72 h, and the restrictions were clear (P<0.05) in the middle and severe hypoxia groups. ALP activity was restrained with increasing hypoxia at each time point. The restrictions were marked (P<0.05) in the severe hypoxia group at 24 h and in the middle and severe hypoxia groups at 48 and 72 h. However, the restriction was more marked (P<0.05) in the severe hypoxia group at 72 h. An increase was observed in the number of mitochondria and rough endoplasmic reticula (RER), with slightly expanded but complete membrane structures, in the severe hypoxia group at 24 h. At 48 h, the number of mitochondria and RER decreased as the mitochondria increased in size. Furthermore, mitochondrial cristae appeared to be vague, and a RER structural disorder was observed. At 72 h, the number of mitochondria and RER decreased further when the mitochondrial cristae were broken, vacuolar degeneration occurred, and the RER particles were reduced while the number of lysosomes increased. HPLF proliferation and mineralization was restrained. Additionally, HPLF structure was broken for a relatively long period of time in the middle and severe hypoxia groups. This finding demonstrated that hypoxia was capable of damaging the metabolism, reconstruction and recovery of HPLFs. The poor state of HPLFs under hypoxic conditions may therefore initiate or aggravate periodontal disease.

Hypoxia increases the expression of enamel genes and cytokines in an ameloblast‐derived cell line

“…It is known from animal studies that ALP is present at elevated levels during mineralization of enamel, and ALP can be found in stratum intermedium and ameloblast cells within the enamel organ (41,42). In this study, we measured the activity of secreted ALP in the cell-culture medium, and the results showed reduced activity after 24 and 48 h of hypoxia, which was consistent with previous findings in fibroblasts (43). Despite the fact that the function of ALP in enamel mineralization is indirect through regulating transport of nutrients and/or ionic transport (44), ALP is essential for optimal enamel mineralization.…”

Hypoxia enhances periodontal ligament stem cell proliferation via the MAPK signaling pathway

“…Hypoxia can promote osteoblast proliferation in the periodontal microenvironment (Li et al, 2015), as well as periodontal ligament fibroblast proliferation (Zhang et al, 2013), revealing that hypoxic environments may affect PDLSC proliferation. Therefore, PDLSCs were cultured under hypoxia and normoxia to examine the influence of hypoxia on PDLSCs.…”

External cervical resorption‐part 1: histopathology, distribution and presentation

“…Recent evidence suggests that hypoxia also might play a role in the activation of osteoclastogenesis (Knowles & Athanasou ), as it can disturb the metabolism and impede the recovery of human periodontal ligament fibroblasts (Zhang et al . ). The synergetic effect of hypoxia and bacteria in the PDL may also accelerate the inflammation (Gölz et al .…”

“…RANKL binds to RANK receptors of clastic precursor cells, which will then become mature clastic cells by means of fusion (Kanzaki et al 2001, Fukushima et al 2003, Belibasakis et al 2007, Uchiyama et al 2009). Recent evidence suggests that hypoxia also might play a role in the activation of osteoclastogenesis (Knowles & Athanasou 2009), as it can disturb the metabolism and impede the recovery of human periodontal ligament fibroblasts (Zhang et al 2013). The synergetic effect of hypoxia and bacteria in the PDL may also accelerate the inflammation (G€ olz et al 2015).…”