[Effect and mechanism of intermittent alkaline stimulation on high phosphorus induced calcification in vascular smooth muscle cells of rats].

Objective

To explore the effect and possible mechanisms of intermittent alkaline on rat vascular smooth muscle cells (VSMCs) calcification induced by high phosphorus.

Methods

VSMCs were isolated from rat thoracic aorta and cultured in vitro. The fourth generation VSMCs were randomly divided into control group, high phosphorus+ pH7.4, high phosphorus+ pH7.5, high phosphorus+ pH7.6 and high phosphorus+ pH7.7 group with random number table. The control group was cultured in DMEM with 10% fetal bovine serum. Other groups were cultured in DMEM with 10 mmol/L β-glycerophosphate and alkalized by 7.4% NaHCO(3) to adjust the pH respectively. After the intervention of 4 hours, the control group was replaced with the normal medium containing 10% fetal bovine serum, the other 4 groups were replaced with high phosphorus based on the pH value of the culture medium, and then replaced the culture medium every other day. After 4 days intervention, the mRNA and protein expression of L type calcium channel β(3) subunit(LTCC β(3)) and Runt related transcription factor 2 (Runx2) were detected by RT-PCR and Western blot. After 4 days intervention, the level of VSMC calcium ion was detected by Fluo-3/AM. After 14 days intervention, alkaline phosphatase (ALP) activity was measured by enzyme linked immunosorbent assay (ELISA) and the calcification was observed by measuring calcium content.

Results

(1) Compared with control group, the gene and protein expressions of LTCC β(3) were higher in high phosphorus+ pH7.4 group (0.49±0.03 vs. 0.23±0.02 and 0.45±0.03 vs. 0.26±0.02 respectively, all P<0.05). Compared with high phosphorus+ pH7.4 group, the mRNA(0.86±0.05) and protein(0.62±0.04) expressions of LTCC β(3) were higher in high phosphorus+ pH7.5 group (P<0.05). Compared with high phosphorus+ pH7.5 group, the mRNA(0.99±0.05) and protein(0.80±0.03) expressions of LTCC β(3) were higher in high phosphorus+ pH7.5 group (all P<0.05). Compared with high phosphorus+ pH7.6 group, the mRNA(1.16±0.05) and protein(0.93±0.03) expressions of LTCC β(3) were higher in high phosphorus+ pH7.7 group (all P<0.05). (2) Compared with control group, calcium ion influx were higher in high phosphorus+ pH7.4 group (124.61±6.06 vs. 75.68±7.82, P<0.05). Compared with high phosphorus+ pH7.4 group, calcium ion influx was higher in high phosphorus+ pH7.5 group(210.85±9.75, P<0.05). Compared with high phosphorus+ pH7.5 group, calcium ion influx was higher in high phosphorus+ pH7.6 group(298.44±11.42, P<0.05). Compared with high phosphorus+ pH7.6 group, calcium ion influx was higher in high phosphorus+ pH7.7 group(401.13±11.41, P<0.05). (3) Compared with control group, the mRNA and protein expressions of Runx2 and ALP were higher in high phosphorus+ pH7.4 group (0.60±0.04 vs. 0.34±0.03, 0.42±0.04 vs. 0.21±0.02, 67.2±4.3 vs. 23.2±2.3 respectively, all P<0.05). Compared with high phosphorus+ pH7.4 group, the mRNA(0.76±0.05) and protein(0.68±0.03) expressions of Runx2 and ALP(102.1±5.4) were higher in high phosphorus+ pH7.5 group (all P<0.05). Compared with high phosphorus+ pH7.5 group, the mRNA(0.90±0.05) and protein(0.90±0.05) expressions of Runx2 and ALP(139.3±4.9) were higher in high phosphorus+ pH7.6 group (all P<0.05). Compared with high phosphorus+ pH7.6 group, the mRNA(1.11±0.05) and protein(1.08±0.06) expressions of Runx2 and ALP(197.0±6.7) were higher in high phosphorus+ pH7.7 group (all P<0.05). (4) Compared with control group, the calcium content were higher in high phosphorus+ pH7.4 group ((75.4±4.3)mg/g pro vs.(25.2±2.1)mg/g pro, P<0.05). Compared with high phosphorus+ pH7.4 group, the calcium content were higher in high phosphorus+ pH7.5 group ((100.8±5.7) mg/g pro, P<0.05). Compared with high phosphorus+ pH7.5 group, the calcium content were higher in high phosphorus+ pH7.6 group ((143.5±6.1) mg/g pro, P<0.05). Compared with high phosphorus+ pH7.6 group, the calcium content were higher in high phosphorus+ pH7.7 group ((205.1±8.2) mg/g pro, P<0.05).

Conclusion

Intermittent alkaline stimulation can promote high phosphorus induced rat VSMCs calcification possibly through upregulating LTCC β(3) subunit gene and protein expression, increasing calcium ion influx and enhancing VSMCs phenotypic transformation.