In Vitro Differentiation of CD14 Cells From Osteopetrotic Subjects: Contrasting Phenotypes With TCIRG1, CLCN7, and Attachment Defects

Abstract

CD14 cells from all subjects had similar lysosomal and nonspecific esterase activity. With the exception of cells from one osteopetrotic subject, CD14 cells from osteopetrotic and control monocytes attached similarly to bone or tissue culture substrate. Cells from one osteopetrotic subject, with normal CLCN7 and TCIRG1, did not attach to bone, did not multinucleate, and formed no podosomes or actin rings in RANKL and CSF-1. Attachment defects are described in osteopetrosis, most commonly mild osteopetrosis with Glantzman's thrombasthenia. However, this case, with abnormal integrin alphavbeta3 aggregates and no osteoclasts, seems to be unique. Two subjects were compound heterozygotes for TCIRG1 defects; both had CD14 cells that attached to bone but did not acidify attachments; cell fusion and attachment occurred, however, in RANKL and CSF-1. This is consistent with TCIRG1, essential for H+-ATPase assembly at the ruffled border. A compound heterozygote for CLCN7 defects had CD14 cells that fused in vitro, attached to bone, and secreted acid, TRACP, and cathepsin K. However, lacunae were shallow and retained demineralized matrix. This suggests that CLCN7 may not limit H+-ATPase activity as hypothesized, but may be involved in control of organic matrix degradation or removal.