Effect of mechanical perturbation on the release of PGE(2) by macrophages in vitro

Bioreactors for Vocal Fold Tissue Engineering

It is estimated that almost one-third of the United States population will be affected by a vocal fold (VF) disorder during their lifespan. Promising therapies to treat VF injury and scarring are mostly centered on VF tissue engineering strategies such as the injection of engineered biomaterials and cell therapy. VF tissue engineering, however, is a challenging field as the biomechanical properties, structure, and composition of the VF tissue change upon exposure to mechanical stimulation. As a result, the development of long-term VF treatment strategies relies on the characterization of engineered tissues under a controlled mechanical environment. In this review, we highlight the importance of bioreactors as a powerful tool for VF tissue engineering with a focus on the current state of the art of bioreactors designed to mimic phonation in vitro. We discuss the influence of the phonatory environment on the development, function, injury, and healing of the VF tissue and its importance for the development of efficient therapeutic strategies. A concise and comprehensive overview of bioreactor designs, principles, operating parameters, and scalability are presented. An in-depth analysis of VF bioreactor data to date reveals that mechanical stimulation significantly influences cell viability and the expression of proinflammatory and profibrotic genes in vitro. Although the precision and accuracy of bioreactors contribute to generating reliable results, diverse gene expression profiles across the literature suggest that future efforts should focus on the standardization of bioreactor parameters to enable direct comparisons between studies. Impact statement We present a comprehensive review of bioreactors for vocal fold (VF) tissue engineering with a focus on the influence of the phonatory environment on the development, function, injury, and healing of the VFs and the importance of mimicking phonation on engineered VF tissues in vitro. Furthermore, we put forward a strong argument for the continued development of bioreactors in this area with an emphasis on the standardization of bioreactor designs, principles, operating parameters, and oscillatory regimes to enable comparisons between studies.

Regenerative Medicine Technologies to Treat Dental, Oral, and Craniofacial Defects

Additive manufacturing (AM) is the automated production of three-dimensional (3D) structures through successive layer-by-layer deposition of materials directed by computer-aided-design (CAD) software. While current clinical procedures that aim to reconstruct hard and soft tissue defects resulting from periodontal disease, congenital or acquired pathology, and maxillofacial trauma often utilize mass-produced biomaterials created for a variety of surgical indications, AM represents a paradigm shift in manufacturing at the individual patient level. Computer-aided systems employ algorithms to design customized, image-based scaffolds with high external shape complexity and spatial patterning of internal architecture guided by topology optimization. 3D bioprinting and surface modification techniques further enhance scaffold functionalization and osteogenic potential through the incorporation of viable cells, bioactive molecules, biomimetic materials and vectors for transgene expression within the layered architecture. These computational design features enable fabrication of tissue engineering constructs with highly tailored mechanical, structural, and biochemical properties for bone. This review examines key properties of scaffold design, bioresorbable bone scaffolds produced by AM processes, and clinical applications of these regenerative technologies. AM is transforming the field of personalized dental medicine and has great potential to improve regenerative outcomes in patient care.

Shifts in Biochemical Markers Associated with Wound Healing in Laryngeal Secretions following Phonotrauma: A Preliminary Study

The current study sought to determine whether shifts in key components of the inflammatory process could be detected from laryngeal secretions sampled before and after vocal loading. A healthy 44-year-old woman served as the subject. The vocal folds were swabbed to collect baseline secretions. Ten and 20 minutes after nearly constant loud phonation for 1 hour, the vocal folds were swabbed again. The findings indicated strong shifts in several key inflammatory mediators: interleukin-1beta, tumor necrosis factor alpha, and matrix metalloproteinase 8. The concentrations of those mediators continued to increase from the 10- to 20-minute postloading time-points. Transforming growth factor beta and prostaglandin E2 did not demonstrate clear shifts. In summary, mediators reflecting the acute inflammatory process could be detected from laryngeal secretions in an awake human. The upward slope of the curves at the 20-minute time interval indicates the need for longer follow-up sampling to determine the full biological response of the vocal folds to acute phonotrauma.

Aggravation of inflammatory response by costimulation with titanium particles and mechanical perturbations in osteoblast- and macrophage-like cells

The interface between bone tissue and metal implants undergoes various types of mechanical loading, such as strain, compression, fluid pressure, and shear stress, from daily activities. Such mechanical perturbations create suboptimal environments at the host bone-implant junction, causing an accumulation of wear particles and debilitating osseous integration, potentially leading to implant failure. While many studies have focused on the effect of particles on macrophages or osteoprogenitor cells, differential and combined effects of mechanical perturbations and particles on such cell types have not been extensively studied. In this study, macrophages and osteoprogenitor cells were subjected to physiological and superphysiological mechanical stimuli in the presence and absence of Ti particles with the aim of simulating various microenvironments of the host bone-implant junction. Macrophages and osteoprogenitor cells were capable of engulfing Ti particles through actin remodeling and also exhibited changes in mRNA levels of proinflammatory cytokines under certain conditions. In osteoprogenitor cells, superphysiological strain increased proinflammatory gene expression; in macrophages, such mechanical perturbations did not affect gene expression. We confirmed that this phenomenon in osteoprogenitor cells occurred via activation of the ERK1/2 signaling pathway as a result of damage to the cytoplasmic membrane. Furthermore, AZD6244, a clinically relevant inhibitor of the ERK1/2 pathway, mitigated particle-induced inflammatory gene expression in osteoprogenitor cells and macrophages. This study provides evidence of more inflammatory responses under mechanical strains in osteoprogenitor cells than macrophages. Phagocytosis of particles and mechanical perturbation costimulate the ERK1/2 pathway, leading to expression of proinflammatory genes.

Uniaxial cyclic tensile stretch inhibits osteogenic and odontogenic differentiation of human dental pulp stem cells

As the most important organs of occlusion, teeth are subjected to a variety of mechanical stresses. These stresses are transmitted into the dental pulp tissue and affect the dental pulp stem cells. In this study, human dental pulp stem cells were isolated from human impacted third molars and their multilineage differentiation abilities were tested. Human dental pulp stem cells were then exposed to cyclic tensile stretch. The results showed that the cyclic tensile stretch inhibited the expression of osteogenic marker genes and proteins such as BMP-2, OCN and ALP. Simultaneously, odontogenic marker genes and proteins such as DSPP, DSP and BSP were also inhibited by the mechanical stress. It was concluded that cyclic tensile stretch inhibits the osteogenic and odontogenic differentiation of dental pulp stem cells.

Prostaglandin E2 synthesis in cartilage explants under compression: mPGES-1 is a mechanosensitive gene

Knee osteoarthritis (OA) results, at least in part, from overloading and inflammation leading to cartilage degradation. Prostaglandin E2 (PGE₂) is one of the main catabolic factors involved in OA. Its synthesis is the result of cyclooxygenase (COX) and prostaglandin E synthase (PGES) activities whereas NAD+-dependent 15 hydroxy prostaglandin dehydrogenase (15-PGDH) is the key enzyme implicated in the catabolism of PGE₂. For both COX and PGES, three isoforms have been described: in cartilage, COX-1 and cytosolic PGES are constitutively expressed whereas COX-2 and microsomal PGES type 1 (mPGES-1) are inducible in an inflammatory context. COX-3 (a variant of COX-1) and mPGES-2 have been recently cloned but little is known about their expression and regulation in cartilage, as is also the case for 15-PGDH. We investigated the regulation of the genes encoding COX and PGES isoforms during mechanical stress applied to cartilage explants. Mouse cartilage explants were subjected to compression (0.5 Hz, 1 MPa) for 2 to 24 hours. After determination of the amount of PGE₂ released in the media (enzyme immunoassay), mRNA and proteins were extracted directly from the cartilage explants and analyzed by real-time RT-PCR and western blotting respectively. Mechanical compression of cartilage explants significantly increased PGE₂ production in a time-dependent manner. This was not due to the synthesis of IL-1, since pretreatment with interleukin 1 receptor antagonist (IL1-Ra) did not alter the PGE₂ synthesis. Interestingly, COX-2 and mPGES-1 mRNA expression significantly increased after 2 hours, in parallel with protein expression, whereas COX-3 and mPGES-2 mRNA expression was not modified. Moreover, we observed a delayed overexpression of 15-PGDH just before the decline of PGE₂ synthesis after 18 hours, suggesting that PGE₂ synthesis could be altered by the induction of 15-PGDH expression. We conclude that, along with COX-2, dynamic compression induces mPGES-1 mRNA and protein expression in cartilage explants. Thus, the mechanosensitive mPGES-1 enzyme represents a potential therapeutic target in osteoarthritis.

The functional response of U937 macrophage-like cells is modulated by extracellular matrix proteins and mechanical strain

Extracellular matrix proteins (ECMs) play a significant role in the transfer of mechanical strain to monocyte-derived macrophages (MDMs) affecting morphological changes in a foreign body reaction. This study investigated how the functional responses of U937 macrophage-like cells differed when subjected to 2 dynamic strain types (nonuniform biaxial or uniform uniaxial strain) while cultured on siloxane membranes coated with either collagen type I or RGD peptide repeats (ProNectin®). Biaxial strain caused an increase in intracellular esterase and acid phosphatase (AP) activities, as well as monocyte-specific esterase (MSE) protein levels in cells that were seeded on either uncoated surfaces (shown previously) or collagen, but not ProNectin®. Released AP activity, but not released esterase activity, was increased on all surfaces. Biaxial strain increased IL-6, but not IL-8 on all surfaces. When cells were subjected to uniaxial strain, intracellular esterase increased on coated surfaces only, whereas intracellular AP activity was unaffected. Both esterase and AP released activities increased on all surfaces. Uniaxial strain increased the release of IL-6 on all surfaces, but IL-8 on coated surfaces only. This study demonstrated for the first time that ECM proteins could specifically modulate cellular responses to different types of strain. Using this approach with an in vitro cell system may help to unravel the complex function of MDMs in the foreign-body reaction.

Particulate endocytosis mediates biological responses of human mesenchymal stem cells to titanium wear debris

Continual loading and articulation cycles undergone by metallic (e.g., titanium) alloy arthroplasty prostheses lead to liberation of a large number of metallic debris particulates, which have long been implicated as a primary cause of periprosthetic osteolysis and postarthroplasty aseptic implant loosening. Long-term stability of total joint replacement prostheses relies on proper integration between implant biomaterial and osseous tissue, and factors that interfere with this integration are likely to cause osteolysis. Because multipotent mesenchymal stem cells (MSCs) located adjacent to the implant have an osteoprogenitor function and are critical contributors to osseous tissue integrity, when their functions or activities are compromised, osteolysis will most likely occur. To date, it is not certain or sufficiently confirmed whether MSCs endocytose titanium particles, and if so, whether particulate endocytosis has any effect on cellular responses to wear debris. This study seeks to clarify the phenomenon of titanium endocytosis by human MSCs (hMSCs), and investigates the influence of endocytosis on their activities. hMSCs incubated with commercially pure titanium particles exhibited internalized particles, as observed by scanning electron microscopy and confocal laser scanning microscopy, with time-dependent reduction in the number of extracellular particles. Particulate endocytosis was associated with reduced rates of cellular proliferation and cell-substrate adhesion, suppressed osteogenic differentiation, and increased rate of apoptosis. These cellular effects of exposure to titanium particles were reduced when endocytosis was inhibited by treatment with cytochalasin D, and no significant effect was seen when hMSCs were treated only with conditioned medium obtained from particulate-treated cells. These findings strongly suggest that the biological responses of hMSCs to wear debris are triggered primarily by the direct endocytosis of titanium particulates, and not mediated by secreted soluble factors. In this manner, therapeutical approaches that suppress particle endocytosis could reduce the bioreactivity of hMSCs to particulates, and enhance long-term orthopedic implant prognosis by minimizing wear-debris periprosthethic osteolysis.

Wear-particle-induced osteoclast osteolysis: the role of particulates and mechanical strain

Periprosthetic osteolysis involves osteoclast activation by wear particulates and their exposure to mechanical perturbation through exposure to shear forces generated by periprosthetic fluid as well as interface micromotion. This study aimed to determine the interactions between wear particulates, mechanical stimulation, and osteoclasts. In static cultures, wear particulates increased osteoclast differentiation. Addition of neutralizing antibodies to RANKL (receptor activator of nuclear factor kappa ligand) inhibited the particle-induced increase in osteoclast numbers. Cyclic 5000 microstrains were applied with the use of a custom-built device to marrow-derived cultures to assess the effect on osteoclast differentiation. Mechanical strain application alone decreased osteoclast differentiation, which was further decreased by the addition of particles despite increases in the soluble RANKL to osteoprotegerin (OPG) ratio. Mechanical strain alone induced mature osteoclast apoptosis in a dose-dependent manner. In contrast, in the mature osteoclast model, the addition of nonmetal particulates protected the osteoclasts from becoming apoptopic. Titanium (Ti) and cobalt chromium (CoCr) particles, however, induced osteoclast apoptosis, whereas polyethylene (PE) and polymethylmethacrylate (PMMA) did not. Wear particulates and mechanical stimulation interact via an eicosanoid-dependent pathway to alter osteoclast function and survival. The addition of mechanical perturbation to a particle-laden system thus appears to enhance the potential for osteolytic activity by enhancing osteoclast survival.

Effect of cyclic mechanical stretch and titanium particles on prostaglandin E2 production by human macrophages in vitro

Early implant instability has been proposed as a critical factor in the onset and progression of aseptic loosening and periprosthetic osteolysis in total joint arthroplasties. Previous in vitro studies have reported that macrophages stimulated with cyclic mechanical strain release inflammatory mediators. Little is known, however, about the response of these cells to mechanical strain with particles, which is often a component of the physical environment of the cell. We therefore studied the production of prostaglandin E(2) (PGE(2)), an important mediator in aseptic loosening and periprosthetic osteolysis in total joint arthroplasties, for human macrophages treated with mechanical stretch alone, titanium particles alone, and mechanical stretch and particles combined. A combination of mechanical stretch and titanium particles resulted in a statistically synergistic elevation of levels of PGE(2) compared with the levels found with either stretch or particles alone. Exposure of human macrophages to mechanical stretch with particles upregulated the expression of cyclooxygenase (COX)-2 mRNA but not COX-1 mRNA, this expression resulting in a 97-fold increase in PGE(2) production compared to the nonstimulated cells. The current study is the first to investigate the effects of mechanical stretch with particles on cultured macrophages and include an investigation of the time course of PGE(2) production and COX-2 mRNA expression. Our results suggest that, while mechanical strain may be one of the primary factors responsible for macrophage activation and periprosthetic osteolysis, mechanical strain with particles load may contribute significantly to the osteolytic potential of macrophages in vitro. The synergistic effect observed between mechanical stretch and particles could accelerate implant loosening and implies that reduction in either cyclic mechanical strain or wear debris load would lead to a reduction of osteolysis.