Abstracts (complete list) - Wissenschaft Online

Connie Schulze, Petra Heyder, Sandra Franz, Kerstin Sarter, Luis Munoz, Stefan
Pöhlmann, Hanns-Martin Lorenz, Martin Herrmann, Martin Schiller
Alteration of glycocalyx and exposition of mannose residues
during apoptosis are essential for the clearance of apoptotic
marterial
Apoptosis and removal of apoptotic cells are essential for the maintenance of
homeostasis in multicellular organisms. Defects in these processes lead to the
development of autoimmune diseases. To date, a variety of receptors regulating uptake
of apoptotic cells are known. Recently, alterations of sugar residues on the surface of
apoptozing cells were observed. Thus, we wanted to characterize changes in the
glycocalyx of dying lymphocytes. Further, we wanted to analyze whether these changes
are important for the clearance of apoptotic cells. We analyzed the binding of lectins to
apoptotic lymphocytes and subcellular fragments shed from these cells. A receptor for
poly-mannose residues expressed on dendritic cells is DC-SIGN (DCS). To substantiate
the role of DCS for the engulfment of apoptotic material we used Raji cells stably
transfected with DCS (Raji-DCS). Engulfment by Raji-DCS and untransfected Raji cells
of apoptotic material was compared.
Apoptozing lymphocytes showed an early binding of Maakia amurensis lectin I (MAL I)
and Sambuccus nigra agglutinine (SNA) (2h after apoptosis induction). These lectins
recognize sialic acid residues. Further, on we detected a time dependent increase in the
binding of Narcissus pseudonarcissus lectin (NPn), Griffonia simplificolia lectin II (GSL
II) and Ulex europaeus agglutinine I (UEA I). NPn recognizes poly-mannose, GSL II is
specific for N-acetyl-glucosamine, and UEA I for fucose residues. These lectins also
bound to subcellular fragments shed from apoptozing cells. Co-incubation of subcellular
fragments with Raji-DCS as well as untransfected Raji cells revealed that the uptake of
subcellular fragments depends on the presence of DCS. Untransfected Raji cells showed
a significantly attenuated and delayed engulfment of apoptotic material.
Taken together we found an alteration of the glycocalyx on the surface of apoptotic cells
as well as subcellular fragments shed from these cells during apoptosis. The recognition
of altered glycocalyx especially of mannose residues by DCS is crucial for the
engulfment of apoptotic material.