Osteocytes are critical to the maintenance of tissue quality and mechanical integrity of bone. As the primary mechanosensing cells, osteocytes orchestrate bone's adaptation processes under mechanical cues such as load-induced fluid flow. However, the in vivo mechanisms by which osteocytes, deeply embedded in mineralized matrix, detect and transduce mechanical signals remain elusive. Filling this knowledge gap is essential to the development of new osteoporosis treatments that exploit bone's intrinsic sensitivity to mechanical loading (a potent anabolic factor). Recent studies have found a fibrous pericellular matrix (PCM) that spans the entire fluid annulus (~80nm) within the lacunar-canalicular system (LCS) and tethers the cell processes to the canalicular wall matrix. Evidence increasingly suggests that these PCM tethering fibers act as mechanical sensors, capturing fluid drag force and initiating mechanotransduction cascades in osteocytes. However, rigorous testing of this concept has been hindered by a lack of quantitative tools for measuring the PCM ultrastructure and by the scarcity of data regarding PCM composition. Breakthroughs from our previous award cycle have overcome these barriers, allowing us to precisely define the functional roles of the PCM in bone. First, we invented a tracer velocimetry approach based on fluorescence recovery after photobleaching (FRAP) to quantify osteocytic PCM in intact bone. Second, we identified perlecan/HSPG2, a large heparan sulfate (HS) proteoglycan, to be an essential structural component of the PCM. Using a perlecan-deficient mouse model that mimics human Schwartz-Jampel syndrome (SJS) we discovered that perlecan deficiency results in not only decreased PCM fiber density but also attenuated responses to in vivo loading and unloading. These preliminary studies formed the cornerstone of our hypothesis that the osteocytic PCM regulates bone's adaptation to mechanical cues through mechanosensing in the LCS, which will be tested at the tissue, cellular, and molecular levels in the following three specific aims: 1) Quantify the effects of PCM alterations on bone adaptation to mechanical cues in vivo; 2) Quantify the effects of PCM alterations on osteocyte mechanosensing ex vivo; 3) Determine the mechanisms by which PCM perlecan forms functional mechanosensing tethers in the LCS in vitro. The proposed studies are important because PCM is the critical interface between osteocytes and the extracellular environment. Identifying the functional roles of the osteocytic PCM and one of its major components, perlecan, in bone adaptation could lead to the development of new osteoporosis treatments that exploit bone's intrinsic sensitivity to mechanical stimuli, a potent non- pharmaceutical factor in promoting bone formation. These studies will also advance our knowledge of the fundamental functions of the PCM, a uniquely functioning but overlooked structure found in nearly all mammalian cells including osteocytes.
The proposal aims to elucidate the functional roles of osteocyte pericellular matrix (PCM) and one of its major components (perlecan) in bone (re)modeling. The work is important because PCM, as the critical interface between bone osteocytes and the extracellular environment, controls how bone perceives and responds to mechanical loading, which is one of the most potent anabolic factors in promoting bone formation. These proposed studies will not only guide the development of novel strategies such as patient-specific exercise regimens and new interventions for the treatment of osteoporosis, but also advance the fundamental knowledge on the PCM, a uniquely functioning but overlooked structure found in nearly all mammalian cells, in skeletal mechanobiology and certain pathologies.
|Wang, Bin; Sun, Xuanhao; Akkus, Ozan et al. (2017) Elevated solute transport at sites of diffuse matrix damage in cortical bone: Implications on bone repair. J Orthop Res :|
|Lv, Mengxi; Zhou, Yilu; Chen, Xingyu et al. (2017) Calcium signaling of in situ chondrocytes in articular cartilage under compressive loading: Roles of calcium sources and cell membrane ion channels. J Orthop Res :|
|Chiu, Yu-Chieh; Fong, Eliza L; Grindel, Brian J et al. (2016) Sustained delivery of recombinant human bone morphogenetic protein-2 from perlecan domain I - functionalized electrospun poly (?-caprolactone) scaffolds for bone regeneration. J Exp Orthop 3:25|
|Fan, Lixia; Pei, Shaopeng; Lucas Lu, X et al. (2016) A multiscale 3D finite element analysis of fluid/solute transport in mechanically loaded bone. Bone Res 4:16032|
|Wijeratne, Sithara S; Martinez, Jerahme R; Grindel, Brian J et al. (2016) Single molecule force measurements of perlecan/HSPG2: A key component of the osteocyte pericellular matrix. Matrix Biol 50:27-38|
|Parajuli, Ashutosh; Liu, Chao; Li, Wen et al. (2015) Bone's responses to mechanical loading are impaired in type 1 diabetes. Bone 81:152-160|
|Srinivasan, Padma P; Parajuli, Ashutosh; Price, Christopher et al. (2015) Inhibition of T-Type Voltage Sensitive Calcium Channel Reduces Load-Induced OA in Mice and Suppresses the Catabolic Effect of Bone Mechanical Stress on Chondrocytes. PLoS One 10:e0127290|
|Lai, Xiaohan; Price, Christopher; Modla, Shannon et al. (2015) The dependences of osteocyte network on bone compartment, age, and disease. Bone Res 3:|
|Jing, Da; Baik, Andrew D; Lu, X Lucas et al. (2014) In situ intracellular calcium oscillations in osteocytes in intact mouse long bones under dynamic mechanical loading. FASEB J 28:1582-92|
|Gong, Xiaoyuan; Yang, Weidong; Wang, Liyun et al. (2014) Prostaglandin E2 modulates F-actin stress fiber in FSS-stimulated MC3T3-E1 cells in a PKA-dependent manner. Acta Biochim Biophys Sin (Shanghai) 46:40-7|
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