title: Pit- and trench-forming osteoclasts: a distinction that matters.
abstract: Osteoclasts (OCs) seeded on bone slices either drill round pits or dig long trenches. Whereas pits correspond to intermittent resorption, trenches correspond to continuous and faster resorption and require a distinct assembly of the resorption apparatus. It is unknown whether the distinction between pits and trenches has any biological relevance. Using OCs prepared from different blood donors, we found that female OCs achieved increased resorption mainly through pit formation, whereas male OCs did so through trench formation. Trench formation went along with high collagenolytic activity and high cathepsin K (CatK) expression, thereby allowing deeper demineralization. A specific CatK inhibitor abrogated the generation of trenches, while still allowing the generation of pits. OCs obtained from bone marrow were more prone to generate trenches than those obtained from blood. Scanning electron microscopy of bone surfaces eroded in vivo showed trenches and pits of similar size as those made by OCs in culture. We conclude that the distinction between trench- and pit-forming OCs is relevant to the differences among OCs from different skeletal sites, different individuals, including gender, and results from differences in collagenolytic power. This indicates a biological relevance and highlights the importance of discriminating between pits and trenches when assessing resorption.
authors.affiliation: Department of Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, Institute of Regional Health Research, University of Southern Denmark , Vejle, Denmark.
authors.forename: Ditte Mh
authors.initials: DM
authors.lastname: Merrild
authors.affiliation: Department of Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, Institute of Regional Health Research, University of Southern Denmark , Vejle, Denmark.
authors.forename: Dinisha C
authors.initials: DC
authors.lastname: Pirapaharan
authors.affiliation: Orthopaedic Research Laboratory, Department of Orthopedic Surgery and Traumatology, Odense University Hospital, University of Southern Denmark , Odense C, Denmark.
authors.forename: Christina M
authors.initials: CM
authors.lastname: Andreasen
authors.affiliation: Department of Orthopedic Surgery, Vejle Hospital/Lillebaelt Hospital , Vejle, Denmark.
authors.forename: Per
authors.initials: P
authors.lastname: Kjærsgaard-Andersen
authors.affiliation: Department of Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, Institute of Regional Health Research, University of Southern Denmark , Vejle, Denmark.
authors.forename: Anaïs Mj
authors.initials: AM
authors.lastname: Møller
authors.affiliation: Orthopaedic Research Laboratory, Department of Orthopedic Surgery and Traumatology, Odense University Hospital, University of Southern Denmark , Odense C, Denmark.
authors.forename: Ming
authors.initials: M
authors.lastname: Ding
authors.affiliation: Department of Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, Institute of Regional Health Research, University of Southern Denmark , Vejle, Denmark.
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Delaissé
authors.affiliation: Department of Clinical Cell Biology, Vejle Hospital/Lillebaelt Hospital, Institute of Regional Health Research, University of Southern Denmark , Vejle, Denmark.
authors.forename: Kent
authors.initials: K
authors.lastname: Søe