Selective patterning of netrin-1 as a novel guiding cue for anisotropic dendrogenesis in osteocytes

Pathways Controlling Formation and Maintenance of the Osteocyte Dendrite Network

PURPOSE OF REVIEW

The purpose of this review is to discuss the molecular mechanisms involved in osteocyte dendrite formation, summarize the similarities between osteocytic and neuronal projections, and highlight the importance of osteocyte dendrite maintenance in human skeletal disease.

RECENT FINDINGS

It is suggested that there is a causal relationship between the loss of osteocyte dendrites and the increased osteocyte apoptosis during conditions including aging, microdamage, and skeletal disease. A few mechanisms are proposed to control dendrite formation and outgrowth, such as via the regulation of actin polymerization dynamics. This review addresses the impact of osteocyte dendrites in bone health and disease. Recent advances in multi-omics, in vivo and in vitro models, and microscopy-based imaging have provided novel approaches to reveal the underlying mechanisms that regulate dendrite development. Future therapeutic approaches are needed to target the process of osteocyte dendrite formation.

Control of osteoblast arrangement by osteocyte mechanoresponse through prostaglandin E2 signaling under oscillatory fluid flow stimuli

Anisotropic collagen/apatite microstructure is a prominent determinant of bone tissue functionalization; in particular, bone matrix modulates its anisotropic microstructure depending on the surrounding mechanical condition. Although mechanotransduction in bones is governed by osteocyte function, the precise mechanisms linking mechanical stimuli and anisotropic formation of collagen/apatite microstructure are poorly understood. Here we developed a novel anisotropic mechano-coculture system which enables the understanding of the biological mechanisms regulating the oriented bone matrix formation, which is constructed by aligned osteoblasts. The developed model provides bone-mimetic coculture platform that enables simultaneous control of mechanical condition and osteoblast-osteocyte communication with an anisotropic culture scaffold. The engineered coculture device helps in understanding the relationship between osteocyte mechanoresponses and osteoblast arrangement, which is a significant contributor to anisotropic organization of bone tissue. Our study showed that osteocyte responses to oscillatory flow stimuli regulated osteoblast arrangement through soluble molecular interactions. Importantly, we found that prostaglandin E2 is a novel determinant for oriented collagen/apatite organization of bone matrix, through controlling osteoblast arrangement.

Superior Alignment of Human iPSC-Osteoblasts Associated with Focal Adhesion Formation Stimulated by Oriented Collagen Scaffold

Human-induced pluripotent stem cells (hiPSCs) can be applied in patient-specific cell therapy to regenerate lost tissue or organ function. Anisotropic control of the structural organization in the newly generated bone matrix is pivotal for functional reconstruction during bone tissue regeneration. Recently, we revealed that hiPSC-derived osteoblasts (hiPSC-Obs) exhibit preferential alignment and organize in highly ordered bone matrices along a bone-mimetic collagen scaffold, indicating their critical role in regulating the unidirectional cellular arrangement, as well as the structural organization of regenerated bone tissue. However, it remains unclear how hiPSCs exhibit the cell properties required for oriented tissue construction. The present study aimed to characterize the properties of hiPSCs-Obs and those of their focal adhesions (FAs), which mediate the structural relationship between cells and the matrix. Our in vitro anisotropic cell culture system revealed the superior adhesion behavior of hiPSC-Obs, which exhibited accelerated cell proliferation and better cell alignment along the collagen axis compared to normal human osteoblasts. Notably, the oriented collagen scaffold stimulated FA formation along the scaffold collagen orientation. This is the first report of the superior cell adhesion behavior of hiPSC-Obs associated with the promotion of FA assembly along an anisotropic scaffold. These findings suggest a promising role for hiPSCs in enabling anisotropic bone microstructural regeneration.

Crosstalk between Bone and Nerves within Bone

For the past two decades, the function of intrabony nerves on bone has been a subject of intense research, while the function of bone on intrabony nerves is still hidden in the corner. In the present review, the possible crosstalk between bone and intrabony peripheral nerves will be comprehensively analyzed. Peripheral nerves participate in bone development and repair via a host of signals generated through the secretion of neurotransmitters, neuropeptides, axon guidance factors and neurotrophins, with additional contribution from nerve-resident cells. In return, bone contributes to this microenvironmental rendezvous by housing the nerves within its internal milieu to provide mechanical support and a protective shelf. A large ensemble of chemical, mechanical, and electrical cues works in harmony with bone marrow stromal cells in the regulation of intrabony nerves. The crosstalk between bone and nerves is not limited to the physiological state, but also involved in various bone diseases including osteoporosis, osteoarthritis, heterotopic ossification, psychological stress-related bone abnormalities, and bone related tumors. This crosstalk may be harnessed in the design of tissue engineering scaffolds for repair of bone defects or be targeted for treatment of diseases related to bone and peripheral nerves.

3D Printing of Anisotropic Bone-Mimetic Structure with Controlled Fluid Flow Stimuli for Osteocytes: Flow Orientation Determines the Elongation of Dendrites

Although three-dimensional (3D) bioprinting techniques enable the construction of various living tissues and organs, the generation of bone-like oriented microstructures with anisotropic texture remains a challenge. Inside the mineralized bone matrix, osteocytes play mechanosensing roles in an ordered manner with a well-developed lacunar-canaliculi system. Therefore, control of cellular arrangement and dendritic processes is indispensable for construction of artificially controlled 3D bone-mimetic architecture. Herein, we propose an innovative methodology to induce controlled arrangement of osteocyte dendritic processes using the laminated layer method of oriented collagen sheets, combined with a custom-made fluid flow stimuli system. Osteocyte dendritic processes showed elongation depending on the competitive directional relationship between flow and substrate. To the best of our knowledge, this study is the first to report the successful construction of the anisotropic bone-mimetic microstructure and further demonstrate that the dendritic process formation in osteocytes can be controlled with selective fluid flow stimuli, specifically by regulating focal adhesion. Our results demonstrate how osteocytes adapt to mechanical stimuli by optimizing the anisotropic maturation of dendritic cell processes.

Preparation of a Biofunctionalized Surface on Titanium for Biomedical Applications: Surface Properties, Wettability Variations, and Biocompatibility Characteristics

This study developed a promising approach (low-temperature plasma polymerization with allylamine) to modify the titanium (Ti) surface, which helps the damaged tissue to heal faster. The Ti surface was first cleaned by argon (Ar) plasma, and then the functional amino-groups were coated on the Ti surface via plasma polymerization. The topography characteristics, wettability, and optimal plasma modification parameters were investigated through atomic force spectroscopy, secondary ion mass spectroscopy, and response surface methodology (RSM). Analytical results showed that the formation of a porous surface was found on the Ar plasma-modified Ti surfaces after Ar plasma modification with different parameters. The Ar plasma modification is an effective approach to remove surface contaminants and generate a porous topography on the Ti surface. As the Ti with Ar plasma modification was at 100 W and 190 m Torr for 12 min, the surface exhibited the maximum hydrophilic performance. In the allylamine plasma modifications, the contact angle values of the allylamine plasma-modified Ti surfaces varied between 70.15° and 88.26° in the designed parameters. The maximum concentration of amino-groups (31.58 nmole/cm2) can be obtained from the plasma-polymerized sample at 80 W and 150 mTorr for 22 min. Moreover, the cell response also demonstrated that the allylamine plasma-modified Ti sample with an optimal modification parameter (80 W, 22 min, and 150 mTorr) possessed great potential to increase cell adhesion ability. Thus, the optimal parameters of the low-temperature plasma polymerization with allylamine can be harvested using the RSM design. These data could provide new scientific information in the surface modification of Ti implant.

Robotic Cell Printing for Constructing Living Yeast Cell Microarrays in Microfluidic Chips

Living cell microarrays in microfluidic chips allow the non-invasive multiplexed molecular analysis of single cells. Here, we developed a simple and affordable perfusion microfluidic chip containing a living yeast cell array composed of a population of cell variants (green fluorescent protein (GFP)-tagged Saccharomyces cerevisiae clones). We combined mechanical patterning in 102 microwells and robotic piezoelectric cell dispensing in the microwells to construct the cell arrays. Robotic yeast cell dispensing of a yeast collection from a multiwell plate to the microfluidic chip microwells was optimized. The developed microfluidic chip and procedure were validated by observing the growth of GFP-tagged yeast clones that are linked to the cell cycle by time-lapse fluorescence microscopy over a few generations. The developed microfluidic technology has the potential to be easily upscaled to a high-density cell array allowing us to perform dynamic proteomics and localizomics experiments.