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Mechanics of OsteoClast bone degradation machinery: Deciphering the architecture, force and functional relationship of podosomes in human osteoclasts – MechanOCs

Mechanics of human OsteoClast bone degradation machinery

Osteoclasts are specialized cells that have developed efficient and unique machinery to tightly adhere to the bone surface and perform bone resorption: the sealing zone. The sealing zone is composed of highly inter-connected podosomes. Here, we hypothesized that the specific continuous podosome structure in osteoclasts exerts a coordinated protrusive force and probes bone biomechanical properties, which is instrumental for efficient sealing to bone and bone degradation.

Objective

Importantly, defects in sealing zone formation or dynamics lead to altered bone resorption, and ultimately to bone diseases, the most common being osteoporosis. In a context where the number of people suffering from osteoporosis is dramatically increasing worldwide, in particular with due to general population aging, there is a need to better characterize, at the fundamental level, the structure and function of the sealing zone. The sealing zone is composed of highly inter-connected podosomes, which are dynamic F-actin adhesion structures. In MechanOCs, we hypothesized that the specific continuous podosome structure in osteoclasts exerts a coordinated protrusive force and by this mean probes bone biomechanical properties, which is instrumental for efficient sealing to bone and bone degradation. The main objective of this proposal was to characterize how the architecture and mechanics of the sealing zone are essential for bone resorption.

The main objective of this proposal was to characterize how the architecture and mechanics of the sealing zone are essential for bone resorption. The is conducted with human osteoclasts and was organized in 4 objectives that aimed to:
1/ define the 3D architecture of the sealing zone at the nano-scale, by combining cutting-edge techniques in electronic and optical imaging (cryo-electron tomography and super-resolution microscopy);
2/ analyze the forces that the sealing zone exert on substrates of controlled stiffness and composition
3/ study the collective behavior of podosomes inside this structure
4/ identify molecular actors controlling the relationship between the nano-architecture, the mechanics and the osteolytic activity of the sealing zone.

This project got insights into an integrated portrait of the sealing zone from the molecular scale up to the biological context of bone resorption, thus producing unprecedented fundamental knowledge in mechanobiology. In addition, we published that HIV-1-infection of osteoclasts, via the viral protein Nef, modify the organization of the sealing zone, thus increasing bone degradation and participating in bone defects observed in patients.

Finally, the MechanOCs project is relevant for human physiology with a high societal impact. In fact, a better characterization of the mechanisms by which the sealing zone drive bone resorption is a crucial step to expect determining new therapeutic approaches dedicated to osteoclast-linked pathologic situations, including age- and HIV-1-related osteoporosis.

Article :
Raynaud-Messina B, Bracq L, Dupont M, Souriant S, Usmani SM, Proag A, Pingris K, Soldan V, Thibault C, Capilla F, Al Saati T, Gennero I, Jurdic P, Jolicoeur P, Davignon JL, Mempel TR, Benichou S, Maridonneau-Parini I*, Vérollet C*. Bone de

Background: Osteoclasts are specialized cells that have developed efficient and unique machinery to tightly adhere to the bone surface and perform bone resorption: the sealing zone. Importantly, defects in sealing zone formation or dynamics lead to altered bone resorption, and ultimately to bone diseases, the most common being osteoporosis. In a context where the number of people suffering from osteoporosis is dramatically increasing worldwide, in particular with due to general population aging, there is a need to better characterize, at the fundamental level, the structure and function of the sealing zone, in order to identify novel therapeutic approaches.

The sealing zone is composed of highly inter-connected podosomes, which are dynamic F-actin adhesion structures. Recently, my team has revealed that macrophage podosomes possess mechanosensing properties through the development of a homemade method, we called Protrusion Force Microscopy (PFM), which allows the measurement of the force exerted by podosomes on a substrate.

Hypothesis: In MechanOCs, we hypothesize that the specific continuous podosome structure in osteoclasts exerts a coordinated protrusive force and by this mean probes bone biomechanical properties, which is instrumental for efficient sealing to bone and bone degradation.

Objectives and approaches: The main objective of this proposal is to characterize how the architecture and mechanics of the sealing zone are essential for osteoclast attachment to bone and bone resorption. The project is organized in 3 aims that will: 1/ define the 3D architecture of the sealing zone at the nano-scale, by combining cutting-edge techniques in electronic and optical imaging (Cryo-electron tomography and super-resolution microscopy); 2/ analyze the forces that the sealing zone exerts on substrates of controlled stiffness and composition, and study the collective behavior of podosomes inside this structure, mainly by using our home-made new PFM technology and; 3/ study the relationship between the nano-architecture, the mechanics and the osteolytic activity of the sealing zone, by modulating the level of regulatory or structural proteins of the sealing zone.

Importantly, this project will be carried out in primary human osteoclasts, which are difficult to work with but represent the most relevant model to study osteoclast biology.

Relevance and Strategy: The articulation of mechanical and architectural insights into an integrated portrait of the sealing zone from the molecular scale up to the biological context of bone resorption constitutes a challenging project that will produce unprecedented fundamental knowledge in mechanobiology. In addition, the MechanOCs project is relevant for human physiology with a high societal impact. In fact, a better characterization of the mechanisms by which the sealing zone drives bone resorption is a crucial step to expect determining new therapeutic approaches dedicated to osteoclast-linked pathologic situations, including age-related osteoporosis. These applications are a tenet of ANR Défi 4.

Finally, the MechanOCs program will set up a solid foundation for establishing a “jeune chercheuse” research program for the next three years. Undoubtedly, it will enable me to carve a niche within the field of mechanobiology of osteoclasts and represent a stepping-stone for my career.

Project coordinator

Madame Christel Vérollet (Centre National de la Recherche Scientifique/Institut de Pharmacologie et de Biologie Structurale)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

CNRS/IPBS Centre National de la Recherche Scientifique/Institut de Pharmacologie et de Biologie Structurale

Help of the ANR 199,999 euros
Beginning and duration of the scientific project: September 2016 - 36 Months

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