Non-invasive optical detection of cathepsin K-mediated fluorescence reveals osteoclast activity in vitro and in vivo.
Osteoclasts degrade bone matrix by demineralization followed by degradation of type I collagen through secretion of the cysteine protease, cathepsin K. Current imaging modalities are insufficient for sensitive observation of osteoclast activity, and in vivo live imaging of osteoclast resorption of bone has yet to be demonstrated. Here, we describe a near-infrared fluorescence reporter probe whose activation by cathepsin K is shown in live osteoclast cells and in mouse models of development and osteoclast upregulation. Cathepsin K probe activity was monitored in live osteoclast cultures and correlates with cathepsin K gene expression. In ovariectomized mice, cathepsin K probe upregulation precedes detection of bone loss by micro-computed tomography. These results are the first to demonstrate non-invasive visualization of bone degrading enzymes in models of accelerated bone loss, and may provide a means for early diagnosis of upregulated resorption and rapid feedback on efficacy of treatment protocols prior to significant loss of bone in the patient.
Kozloff
Kenneth M
KM
Center for Molecular Imaging Research, Harvard Medical School, Massachusetts General Hospital, 149 13th Street, Room 5406, Charlestown, MA 02129-2060, USA.
Quinti
Luisa
L
Patntirapong
Somying
S
Hauschka
Peter V
PV
Tung
Ching-Hsuan
CH
Weissleder
Ralph
R
Mahmood
Umar
U
D000818:Animals; D000831:Animals, Newborn; D001846:Bone Development; D001862:Bone Resorption / Q000201:enzymology; D002113:Calcification, Physiologic; D056657:Cathepsin K; D002403:Cathepsins / Q000235:genetics / Q000378:metabolism*; D002470:Cell Survival; D002478:Cells, Cultured; D016616:Cryoultramicrotomy; D005260:Female; D005269:Femur / Q000473:pathology; D005453:Fluorescence; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D015336:Molecular Probe Techniques; D015335:Molecular Probes / Q000378:metabolism; D010010:Osteoclasts / Q000166:cytology / Q000201:enzymology*; D010052:Ovariectomy; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation
D015335:Molecular Probes; D012333:RNA, Messenger; D002403:Cathepsins; C534130:CTSK protein, human; D056657:Cathepsin K; C534132:Ctsk protein, mouse