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Biomolecules 2019, 9(1), 17; https://doi.org/10.3390/biom9010017

Specialized Roles for Actin in Osteoclasts: Unanswered Questions and Therapeutic Opportunities

1
Department of Oral Geriatrics, School and Hospital of Stomatology, Jilin University, Changchun 130021, China
2
Department of Orthodontics, College of Dentistry, University of Florida, Gainesville, FL 32610, USA
3
Department of Anatomy & Cell Biology, College of Dentistry, University of Florida, Gainesville, FL 32610, USA
*
Author to whom correspondence should be addressed.
Received: 10 December 2018 / Revised: 3 January 2019 / Accepted: 4 January 2019 / Published: 9 January 2019
(This article belongs to the Special Issue Key Biomolecules in Bone Resorption)
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Abstract

Osteoclasts are cells of the hematopoietic lineage that are specialized to resorb bone. In osteoclasts, the actin cytoskeleton engages in at least two unusual activities that are required for resorption. First, microfilaments form a dynamic and structurally elaborate actin ring. Second, microfilaments bind vacuolar H+-ATPase (V-ATPase) and are involved in forming the V-ATPase-rich ruffled plasma membrane. The current review examines these two specialized functions with emphasis on the identification of new therapeutic opportunities. The actin ring is composed of substructures called podosomes that are interwoven to form a cohesive superstructure. Studies examining the regulation of the formation of actin rings and its constituent proteins are reviewed. Areas where there are gaps in the knowledge are highlighted. Microfilaments directly interact with the V-ATPase through an actin binding site in the B2-subunit of V-ATPase. This binding interaction is required for ruffled membrane formation. Recent studies show that an inhibitor of the interaction blocks bone resorption in pre-clinical animal models, including a model of post-menopausal osteoporosis. Because the unusual actin-based resorption complex is unique to osteoclasts and essential for bone resorption, it is likely that deeper understanding of its underlying mechanisms will lead to new approaches to treat bone disease. View Full-Text
Keywords: actin; microfilament; vacuolar H+-ATPase; V-ATPase; anti-resorptives; bone; bone remodeling; actin polymerization actin; microfilament; vacuolar H+-ATPase; V-ATPase; anti-resorptives; bone; bone remodeling; actin polymerization
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Han, G.; Zuo, J.; Holliday, L.S. Specialized Roles for Actin in Osteoclasts: Unanswered Questions and Therapeutic Opportunities. Biomolecules 2019, 9, 17.

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