Expression and role of mannose receptor/terminal high-mannose type oligosaccharide on osteoclast precursors during osteoclast formation

Abstract

Osteoclasts are formed from hematopoietic precursors via cell-cell fusion. We have previously reported that mannose residues are expressed on the outer membranes of monocytes during osteoclast differentiation. In the present study, we have attempted to demonstrate the pattern of expression levels of terminal high-mannose type oligosaccharide and to show that the mannose receptor is expressed on osteoclast precursor cells. Osteoclasts were formed using three different systems, namely mouse bone marrow cell culture, co-culture of mouse spleen cells with stromal cells, and RAW264·7 cell cultures. During osteoclast differentiation, the expression of terminal highmannose type oligosaccharide gradually increased and then peaked at the stage of fusion in all three systems. Expression of the mannose receptor gradually increased during osteoclast differentiation in bone marrow cells and the co-culture system. In contrast, that in RAW264·7 cells had already been detected in the absence of the soluble receptor activator of NF-B ligand and did not change during osteoclast differentiation. To ascertain whether expression of high-mannose type oligosaccharide is involved in tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cell (MNC) formation, glycosidase inhibitors were used on RAW264·7 cell culture. Castanospermine, an inhibitor of glucosidase I, inhibited the TRAP-positive MNCs, and deoxymannojirimycin, an inhibitor of -mannosidase I, increased the TRAPpositive MNC formation. These results indicate that the binding of terminal high-mannose and mannose receptor is important for the process of cellular fusion in osteoclast formation.

SPECT Imaging of Joint Inflammation with Nanobodies Targeting the Macrophage Mannose Receptor in a Mouse Model for Rheumatoid Arthritis

“…Other cells, isolated from bone marrow, lymph nodes, and spleen, showed various degrees of MMR expression levels corresponding to what has been described before (12,(34)(35)(36). Osteoclast cells that were generated in vitro stained positively for MMR, and these data are in line with findings reported by Morishima et al (15). However, in comparison with mature macrophages, the expression was only modest on osteoclasts; therefore, we concluded that MMR was not an ideal marker for this population.…”

“…Among the infiltrating cells in synovial tissues and fluid, macrophages constitute a subset of cells that differentiate into multinuclear osteoclasts, which are responsible for bone destruction in RA (32,33). In the present study, we imaged in an animal model of RA the distribution of MMR, a marker expressed by a subpopulation of macrophages and by osteoclasts (14,15). In our study, we confirmed the presence of macrophages in synovium and synovial fluid of arthritic mice.…”

“…Its primary functions are endocytic clearance of certain glycoproteins and phagocytosis of unopsonized microorganisms (13). Interestingly, MMR was found to be involved in the formation of multinucleated osteoclasts by binding to terminal high-mannose-type oligosaccharides expressed on osteoclast precursor cells (14,15). Osteoclasts are derived from the monocyte or macrophage lineage and are responsible for the progressive destruction of bone tissue in RA and in collagen-induced arthritis (CIA) (16,17), a frequently used animal model for human RA (18,19).…”

Extensive Determination of Glycan Heterogeneity Reveals an Unusual Abundance of High Mannose Glycans in Enriched Plasma Membranes of Human Embryonic Stem Cells

“…4) (40). More generally, high mannose glycans are not commonly observed on the surfaces of mammalian cells (41), with the exception of macrophages (42). High mannose glycans are involved in initial steps in N-glycan processing and control of protein folding in the endoplasmic reticulum.…”

“…Thus, investigations of the role of high mannose glycans have been mostly directed to their involvement in initiating the innate immune system or in protein folding in the endoplasmic reticulum. A few studies, however, have suggested that high mannose glycans mediate cell-cell fusion (42,44), mediating sperm-egg fusion, myoblast fusion, and osteoclast formation. Thus, high mannose glycans on hESCs may play a role in cellular binding and recognition.…”