Background: Familial Mediterranean Fever (FMF) is an autoinflammatory disease due to mutations of MEFV gene which encodes for Pyrin, a protein expressed in white blood cells, mainly neutrophils and monocytes. The Pyrin mutation results in the assembly of the NLRP3 inflammasome, leading to caspase 1-mediated proteolytic activation of the interleukin-1β (IL-1β) and interleukin-18 (IL-18). Aquaporin-3 (AQP3) is a membrane channel facilitating the movement of water, glycerol, and hydrogen peroxide into and out of cells and whose expression has been also correlated with several inflammatory conditions with suggested involvement in redox signalling, cell migration, and NLRP3 activation. Here, we characterize the expression and subcellular localization of AQP3 in human peripheral blood mononuclear cells (PBMCs) and evaluate its expression in monocytes of FMF patients against those of control healthy subjects.
Materials and Methods: BMCs from both FMF patients and control healthy subjects were isolated by density gradient centrifugation using a SepMate™ technology. The isolated PBMCs were used to assess the transcriptional expression of AQP3 against that of the housekeeping ßactin gene and to analyse the extent and distribution of the related protein by confocal immunofluorescence.
Results: By RT-PCR the AQP3 mRNA level was higher in the PBMCs from FMF patients than healthy control subjects. By immunofluorescence, AQP3 was localized at the plasma membrane in the form of punctuated immunolabeling. AQP3 immunoreactivity was much higher in monocytes than in lymphocytes. In line with the RT-PCR analysis, AQP3 appeared to be of higher extent in FMF than control monocytes. No difference in AQP3 immunoreactivity was seen between FMF and control lymphocytes.
Conclusions: In human PBMCs, AQP3 is much more expressed in monocytes than in lymphocytes. Monocytes of FMF patients show higher levels of AQP3 than control healthy subjects. Work is in progress to see whether the increased expression of AQP3 in FMF monocytes has correlations with the NLRP3 dysfunction underlying this autoinflammatory disease.