So detected in all cells of the five donors, whereas CYP2R1 was not detected, with the premise that anti-CYP2R1 antibody was able to recognize the protein in PC-3 cells, which were used as a positive control (Fig. 2). This indicated that Vitamin D2 web CYP27A1 might be the key 25-hydroxylase in hGF and hPDLC. After 1326631 confirming the expression of 25-hydroxylase in hGF and hPDLC, the function of 25-hydroxylase was investigated. Whereas 1000 nM vitamin D3 did not have a significant cytotoxic effect on any of the cells within 48 h, hGF and hPDLC generated 25OHD3 in response to vitamin D3 (Figs. 3A, B). The fact that extra- and intracellular 25OHD3 was generated in the presence of vitamin D3 provides direct and convincing evidence of the existence of 25hydroxylase in hGF and hPDLC. At all time points, there was no significant difference in the levels of intracellular and extracellular 25OHD3 between the two cell types. Additionally, exposure to vitamin D3 also resulted in the synthesis of 1,25OH2D3 in hGF and hPDLC (Fig. 4). The observation that hGF and hPDLC could synthesize 1,25OH2D3 when exposed to 25OHD3 [29] is further evidence of 25hydroxylase activity in hGF and hPDLC. Based on the above direct evidence for 25-hydroxylase activity in hGF and hPDLC, we examined the effect of 25-hydroxylase knockdown. The efficiency of RNA interference against both CYP27A1 and CYP2R1 was both over 70 (Fig. 5). The generation of 25OHD3 increased with increasing vitamin D3 concentrations, but dropped significantly when CYP27A1 was knocked down using specific siRNA (Figs. 6A ). However, knockdown of CYP2R1 did not significantly influence 25OHD3 generation by hGF (Figs. 6A, C), and only slightly influenced 25OHD3 generation by hPDLC (Figs. 6B, D). These results suggest that CYP27A1 might be the key 25-hydroxylase in hGF and hPDLC. In addition, knockdown of CYP27A1 resulted in asignificant reduction of 1,25OH2D3 generation (Figs. 7A ). This is additional evidence for the activity of CYP27A1 as the 25hydroxylase in hGF and hPDLC. After the comprehensive confirmation of 25-hydroxylase activity in hGF and hPDLC, and the verification of CYP27A1 as the key 25-hydroxylase, the regulation of CYP27A1 in hGF and hPDLC was investigated. Interleukin-1b (IL-1b) and Porphyromonas gingivalis lipopolysaccharide (Pg-LPS) strongly induced CYP27A1 expression (Fig. 8). Additionally, dose-dependent increases in expression of CYP27A1 mRNA in hGF and hPDLC following incubation with IL-1b or Pg-LPS were demonstrated (Fig. 8). By contrast, sodium butyrate did not influence significantly CYP27A1 mRNA expression in hGF and hPDLC (Fig. 8). In addition, no significant differences between hGF and hPDLC were observed in the regulation of CYP27A1.DiscussionIn the present study, our hypothesis that hGF and hPDLC have 25-hydroxylase activity, and that they can synthesize 25OHD3 was verified. Therefore, the origin of high 25OHD3 concentrations in gingival crevicular fluid [27,28] might be hGF and hPDLC. Having demonstrated 1a-hydroxylase activity in hGF and hPDLC [29], we could consider that the conversion of vitamin D3 to 1,25OH2D3 in hGF and hPDLC consisted of two steps: s from vitamin D3 to 25OHD3, under the HDAC-IN-3 biological activity action of 25-hydroxylase CYP27A1; t from 25OHD3 to 1,25OH2D3, under the action of 1a-hydroxylase CYP27B1. This two-step conversion is similar to that observed in human keratinocytes [7,19,30,31,32]. In addition, Slominski et al. reported an alternate pathway of vitamin D3 metabolism by cytochrome P45.So detected in all cells of the five donors, whereas CYP2R1 was not detected, with the premise that anti-CYP2R1 antibody was able to recognize the protein in PC-3 cells, which were used as a positive control (Fig. 2). This indicated that CYP27A1 might be the key 25-hydroxylase in hGF and hPDLC. After 1326631 confirming the expression of 25-hydroxylase in hGF and hPDLC, the function of 25-hydroxylase was investigated. Whereas 1000 nM vitamin D3 did not have a significant cytotoxic effect on any of the cells within 48 h, hGF and hPDLC generated 25OHD3 in response to vitamin D3 (Figs. 3A, B). The fact that extra- and intracellular 25OHD3 was generated in the presence of vitamin D3 provides direct and convincing evidence of the existence of 25hydroxylase in hGF and hPDLC. At all time points, there was no significant difference in the levels of intracellular and extracellular 25OHD3 between the two cell types. Additionally, exposure to vitamin D3 also resulted in the synthesis of 1,25OH2D3 in hGF and hPDLC (Fig. 4). The observation that hGF and hPDLC could synthesize 1,25OH2D3 when exposed to 25OHD3 [29] is further evidence of 25hydroxylase activity in hGF and hPDLC. Based on the above direct evidence for 25-hydroxylase activity in hGF and hPDLC, we examined the effect of 25-hydroxylase knockdown. The efficiency of RNA interference against both CYP27A1 and CYP2R1 was both over 70 (Fig. 5). The generation of 25OHD3 increased with increasing vitamin D3 concentrations, but dropped significantly when CYP27A1 was knocked down using specific siRNA (Figs. 6A ). However, knockdown of CYP2R1 did not significantly influence 25OHD3 generation by hGF (Figs. 6A, C), and only slightly influenced 25OHD3 generation by hPDLC (Figs. 6B, D). These results suggest that CYP27A1 might be the key 25-hydroxylase in hGF and hPDLC. In addition, knockdown of CYP27A1 resulted in asignificant reduction of 1,25OH2D3 generation (Figs. 7A ). This is additional evidence for the activity of CYP27A1 as the 25hydroxylase in hGF and hPDLC. After the comprehensive confirmation of 25-hydroxylase activity in hGF and hPDLC, and the verification of CYP27A1 as the key 25-hydroxylase, the regulation of CYP27A1 in hGF and hPDLC was investigated. Interleukin-1b (IL-1b) and Porphyromonas gingivalis lipopolysaccharide (Pg-LPS) strongly induced CYP27A1 expression (Fig. 8). Additionally, dose-dependent increases in expression of CYP27A1 mRNA in hGF and hPDLC following incubation with IL-1b or Pg-LPS were demonstrated (Fig. 8). By contrast, sodium butyrate did not influence significantly CYP27A1 mRNA expression in hGF and hPDLC (Fig. 8). In addition, no significant differences between hGF and hPDLC were observed in the regulation of CYP27A1.DiscussionIn the present study, our hypothesis that hGF and hPDLC have 25-hydroxylase activity, and that they can synthesize 25OHD3 was verified. Therefore, the origin of high 25OHD3 concentrations in gingival crevicular fluid [27,28] might be hGF and hPDLC. Having demonstrated 1a-hydroxylase activity in hGF and hPDLC [29], we could consider that the conversion of vitamin D3 to 1,25OH2D3 in hGF and hPDLC consisted of two steps: s from vitamin D3 to 25OHD3, under the action of 25-hydroxylase CYP27A1; t from 25OHD3 to 1,25OH2D3, under the action of 1a-hydroxylase CYP27B1. This two-step conversion is similar to that observed in human keratinocytes [7,19,30,31,32]. In addition, Slominski et al. reported an alternate pathway of vitamin D3 metabolism by cytochrome P45.
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