The phosphatidylserine receptor mediates phagocytosis by vascular smooth muscle cells

Abstract

Apoptosis participates in every step of atherogenesis, but the process of clearance of apoptotic cells by phagocytosis has been underestimated. Rapid removal of apoptotic cells is critical for tissue homeostasis, in order to avoid accumulation of necrotic material and subsequent inflammation in the pathological vascular wall. We have demonstrated by RT-PCR, western blot and immunocytofluorescence that vascular smooth muscle cells (VSMCs) express the phosphatidylserine receptor (PSR). We then tested the involvement of PSR in the ability of VSMCs to bind and engulf apoptotic cells. We used a model of senescent erythrocytes, which expose PS after 4 days of culture (85% of cells relative to 8% in freshly isolated erythrocytes). The pseudo-peroxidase activity of haemoglobin contained within erythrocytes allowed us to quantify per se both binding and phagocytosis by VSMCs. We have also shown by light and confocal microscopy that VSMCs were able to ingest aged erythrocytes. Addition of a blocking antibody or transfection of VSMCs by a siRNA directed against PSR reduced the binding and engulfment of aged erythrocytes by more than 90%. These results suggest that PSR is involved in phagocytosis of PS-presenting cells. Incubation of aged erythrocytes with VSMCs also significantly increased the expression of PSR, suggesting that the tethering/ingestion of apoptotic cells triggers this process. Immunostaining for PSR in complicated atherosclerotic plaques shows positivity in the media and macrophage-rich areas. The mechanisms underlying phagocytosis and involving PSR in vivo, within the pathological arterial wall, deserve further investigation.

Endogenous Jmjd6 gene product is expressed at the cell surface and regulates phagocytosis in immature monocyte‐like activated THP‐1 cells

“…It is also established that the phagocytic function of THP-1 cells enhances with time after activation (Reyes et al, 1999). Taken together with the previous report that anti-Jmjd6 Ab or downregulation of Jmjd6 protein expression significantly reduced cumulative accumulation of dead cell products in vascular smooth muscle cells (Kolb et al, 2007), our data indicate that Jmjd6 gene product may serve as a surface receptor and play a role in low-rate phagocytosis in immature macrophages and non-professional phagocytes.…”

“…In addition, lymphoid cells transfected with recombinant Jmjd6 protein acquired ability to bind the apoptotic cells (Fadok et al, 2000). Furthermore, downregulation of the Jmjd6 gene with antisense sequence or siRNA significantly reduced uptake of dead cells in NIH3T3 cells and vascular smooth muscle cells, respectively (Hoffmann et al, 2001;Kolb et al, 2007). Moreover, in C. elegans and zebrafish the Jmjd6 gene knockout produced marked cell corpse accumulation in early embryos (Wang et al, 2003;Hong et al, 2004).…”

“…Surface expression of Jmjd6 gene product was confirmed by immunostaining and flow cytometry using variety of anti-Jmjd6 Ab (Fadok et al, 2000;Monks et al, 2005;Otsuka et al, 2005;Kolb et al, 2007;Zakharova et al, 2007) and a major function of Jmjd6 was attributed to be a surface receptor for recognition and engulfment of apoptotic cells. It was reported that polyclonal anti-Jmjd6 Ab reduced phagocytosis of phosphatidylserine-exposing T cell exosomes and aged red blood cells by immature macrophages and vascular smooth muscle cells, respectively (Kolb et al, 2007;Zakharova et al, 2007). In addition, lymphoid cells transfected with recombinant Jmjd6 protein acquired ability to bind the apoptotic cells (Fadok et al, 2000).…”

Peripheral Artery Disease Is Associated With a High CD163/TWEAK Plasma Ratio

“…Immunofluorescence was performed on 4-m-thick sections as previously described. 31 Primary antibodies were goat anti-TWEAK polyclonal antibody (AF1090; R&D Systems) and mouse anti-CD163 monoclonal antibody (EDhu-1; Serotec) followed by a secondary antibody respectively conjugated with Alexa 488 and Alexa 455 (Invitrogen). Nuclei were stained with 4Ј,6-diamidino-2-phenylindole (0.1 g/mL).…”

“…Red blood cells were obtained from healthy volunteers with informed consent, as previously described. 31 …”