Modeling Joint Pain on a Chip: integrating sensory neurons in the microJoint to model osteoarthritis

The development of safe and effective methods for the treatment of osteoarthritis(OA)-associated pain is a critical need. Recently, our team successfully modeled OA-like pathology in an in vitro multi-component joint-on-a-chip (microJoint), which integrates engineered osteochondral complex, synovium, adipose tissue and given their crucial role in joint pain, macrophages. In the present project, we introduce the sensory neurons into the established microJoint to generate the neu-microJoint, enabling the dynamic interplay between the peripheral nervous system and joint tissues. By recording activity in sensory neurons, joint integrity as well as therapeutic efficacy can be monitored in real time. The neu-microJoint is a hybrid PDMS/3D printed system where microchannels establish a diffusion barrier but enable sensory neuron innervation of joint tissues. Neural activity is assessed with micro electrode arrays (MEAs) and fura2-based calcium imaging. With the use of L4 and L5 dorsal root ganglion (DRG) neurons recovered from organ donors, the neu-microJoint can be fully humanized. DRG neurons cultured for 4 days were screened with increasing concentrations of KCl (10, 30, and 50mM) to detect spiking in the MEAs. There was little to no spontaneous activity under baseline conditions, but activity was detected in response to 30mM KCl. Rodent and human DRG neurons plated in the neu-microJoint cultured between 10 – 28 days showed substantial axonal growth through the microchannels as visualized through DiI or fura2 labeling. Moreover, electrical stimulation applied to the neurites evoked an increase in calcium in the corresponding soma. Conditioned media from the OA-modeled microJoint applied to the neurons caused an increase in calcium in a subpopulation of neurons. These data suggest the potential to apply an in vitro microphysiological system to study OA pain. These results also indicate that a subset of neurons, now undergoing specific characterization, is potentially responsible for OA pain modeled in the neu-microJoint. F32 1F32NS110148-01A1, UG3TR003090.