Characteristic localization of carbohydrates in osteoclasts by lectin cytochemistry

Lectin cytochemistry was performed to clarify the process of glycosylation and the localization of glycocalyx in osteoclasts. Microslicer sections of decalcified rat tibiae were incubated in the presence of HRP-conjugated lectins (Con A, PNA, MPA, WGA, UEA-1). Lectin reactions in cell organelles revealed that glucose (Glc) and mannose (Man) are transferred to carbohydrate chains in nuclear envelopes, rough endoplasmic reticuli, and the cis and medial sides of the Golgi apparatus. N-acetylgalactosamine (GalNAc), N-acetylglucosamine (GlcNAc), and/or N-acetylneuraminic acic (NANA) residues are transferred, in turn, in the Golgi apparatus. Lectin reactions detected in lysosomal structures suggest that some sugar residues are incorporated into carbohydrate chains of hydrolytic enzymes, such as acid phosphatase and arylsulfatase. Others would be transported to plasma membranes as glycocalyx. PNA and MPA reactions were most evident on ruffled borders of osteoclasts. On the other hand, cement-line-like structures on bone surfaces displayed Con A, MPA, and WGA positive reactions. The following factors suggest that osteoclasts actively metabolize sugar: characteristic localization of glycocalyx in osteoclasts reflect the polarity of osteoclasts, and carbohydrate complexes in cement-line-like structures seem to play an important role in the coupling phenomenon in bone tissue.