Osteopetrosis with micro-lacunar resorption because of defective integrin organization.
In vitro differentiated monocytes were used to characterize the cellular defect in a type of osteopetrosis with minimally functional osteoclasts, in which defects associated with common causes of osteopetrosis were excluded by gene sequencing. Monocytes from the blood of a 28-year-old patient were differentiated in media with RANKL and CSF-1. Cell fusion, acid compartments within cells, and tartrate resistant acid phosphatase (TRAP) activity were normal. However, the osteoclasts made abnormally small pits on the dentine. Phalloidin labeling showed that the cell attachments lacked the peripheral ring structure that supports lacunar resorption. Instead, the osteoclasts had clusters of podosomes near the center of cell attachments. Antibody to the alphavbeta3 integrin pair or to the C-terminal of beta3 did not label podosomes, but antibody to alphav labeled them. Western blots using antibody to the N-terminal of beta3 showed a protein of reduced size. Integrins beta1 and beta5 were upregulated, but, in contrast to observations in beta3 defects, alpha2 had not increased. The rho-GTP exchange protein Vav3, a key attachment organizing protein, did not localize normally with peripheral attachment structures. Vav3 forms of 70 kD and 90 kD were identified on western blots. However, the proteins beta3 integrin, Vav3, Plekhm1, and Src, implicated in attachment defects, had normal exon sequences. In this new type of osteopetrosis, the integrin-organizing complex is dysfunctional, and at least two attachment proteins may be partially degraded.
Blair
Harry C
HC
Department of Pathology, University of Pittsburgh, and Veteran's Affairs Medical Center, Pittsburgh, PA 15261, USA. hcblair@imap.pitt.edu
Yaroslavskiy
Beatrice B
BB
Robinson
Lisa J
LJ
Mapara
Markus Y
MY
Pangrazio
Alessandra
A
Guo
Lida
L
Chen
Ka
K
Vezzoni
Paolo
P
Tolar
Jakub
J
Orchard
Paul J
PJ
D000135:Acid Phosphatase / Q000235:genetics / Q000378:metabolism; D000328:Adult; D001798:Blood Proteins / Q000235:genetics / Q000378:metabolism; D015153:Blotting, Western; D001862:Bone Resorption / Q000473:pathology* / Q000503:physiopathology; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002454:Cell Differentiation; D002478:Cells, Cultured; D022001:Focal Adhesions / Q000502:physiology; D006801:Humans; D016023:Integrins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D007963:Leukocytes, Mononuclear / Q000378:metabolism / Q000473:pathology*; D010010:Osteoclasts / Q000378:metabolism / Q000473:pathology*; D010022:Osteopetrosis / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D051567:Proto-Oncogene Proteins c-vav / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D000071681:Tartrate-Resistant Acid Phosphatase; D019061:src-Family Kinases / Q000235:genetics / Q000378:metabolism
D001798:Blood Proteins; D015815:Cell Adhesion Molecules; D016023:Integrins; D007527:Isoenzymes; D010750:Phosphoproteins; D051567:Proto-Oncogene Proteins c-vav; C496621:VAV3 protein, human; C039077:platelet protein P47; D019061:src-Family Kinases; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase