Articular cartilage is a tissue exposed to various mechanical stimuli. Normal mechanical stimuli play an important role in chondrocyte activity inside the tissue by modulating extracellular matrix production, differentiation, and proliferation. However, excessive mechanical stimulation induces inflammation in cartilage, which leads to decreased expression of genes involved in chondrocyte homeostasis, accelerated degradation of the extracellular matrix, and apoptosis. Low-intensity mechanical stimulation is also used in physical therapy to promote functional tissue recovery, and the effects of mechanical stimulation on cartilage tissue are diverse. Though the effects of individual stimuli on chondrocytes have been extensively studied, the effects of combined stimuli on chondrocytes in a three-dimensional environment are still unknown. Recently, we developed a new bioreactor that could simultaneously and independently apply hydrostatic pressure and compressive strain to cells embedded in a 3D construct. In this study, we investigated the expression levels of genes involved in inflammation and osteoarthritis when compressive stress and hydrostatic pressure were applied to a 3D tissue model in which mouse chondrocytes (ATDC5 cells) were included in a 3D gel. We found that different trends were obtained between single stimulation and compound stimulation. Therefore, the simultaneous application of compressive stress and hydrostatic pressure, which was used to mimic the main mechanical environment of cartilage, is expected to greatly contribute to the elucidation of cartilage pathogenesis and homeostasis. The model developed in this study is believed to be an important tool as an alternative model for animal experiments on cartilage tissue.

Evaluations of the toxicity of hazardous substances in foods and other products are essential. Metals are severely neurotoxic to humans. To date, neurotoxicity has mainly been examined in animal experiments using rodents; however, the importance of using in vitro systems has recently been reported. Although the brain also contains glial cells, in vitro assessments of neurotoxicity have mainly been performed using neurons. Therefore, we established a high-throughput evaluation system by creating a mixed culture system of microglia, a type of glial cell, and neurons using BV2 and Neuro2A cells. The mixed culture showed changes in gene expression compared to the monoculture. Furthermore, in examinations of the toxicities of various metals, some exhibited different toxicities in the mixed culture from those in the single culture. These results suggest that the conventional evaluation system using single cultures is insufficient and also that the use of glial cells to accurately assess neurotoxicity may be necessary.