AIM   AIM To observe the effects of simulated weightlessness on protein expressions and distribution of sphingosine-1-phosphate (S1P) and its receptor (S1PRs) in the thoracic aorta (TA) and abdominal aorta (AA) of rats.

  METHODS   Hindlimb unloading tail suspension (HU) was performed in rats to simulate the effect of weightlessness on vascular system. Thoracic aorta (TA) and abdominal aorta (AA) were isolated and collected. Hematoxylin-eosin (HE) staining was conducted for evaluation of intima-media thickness (IMT) and cross section area (CSA). Western blotting and immunohistochemical staining were carried out to detect protein expressions and distribution of sphingosine kinase 1 (SphK1) and 2 (SphK2), S1P lyase 1 (SGPL1), S1P receptors (S1PR1, S1PR2 and S1PR3), proliferating cell nuclear antigen (PCNA) and collagen 1 (COL1).

  RESULTS   After 4 weeks’ (wk) tail suspension, no significant changes were found in protein expressions of SphK1 and S1P receptors in TA, while those of SphK2 and SGPL1 decreased significantly (P<0.05). IMT, CSA and PCNA were significantly increased in TA of HU rats. In contrast to those in TA, protein expressions of SphK1, SphK2 and SGPL1 in AA significantly increased (P<0.05) in HU relative to control (CON), and those of S1PR1 and S1PR3 significantly decreased (P<0.05). No significant changes were found in IMT, CSA and PCNA content after tail suspension, but COL1 expression decreased significantly (P<0.05). Moreover, we found protein expressions of SphK1, SphK2, SGPL1, S1PR3, PCNA and COL1 were significantly higher and S1PR1 lower in TA than those in AA.

  CONCLUSION   Simulated weightlessness results in regional-specific remodeling of synthesis and degradation of S1P in AA and TA. Besides, there is notable intrinsic discrepancy in S1P/S1PRs between AA and TA.