Background/Objectives: Osteoarthritis (OA) is a progressive joint disease characterized by inflammation, cartilage degradation, and subchondral bone changes, for which effective disease-modifying therapies are lacking. Messenger RNA (mRNA)-based therapeutics offer a versatile approach to modulate joint pathology, but their application to OA remains limited. Methods: We evaluated intra-articular delivery of therapeutic mRNAs using polyplex nanomicelles, a non-inflammatory and minimally invasive carrier system, in a rat model of inflammation-driven OA induced by monosodium iodoacetate (MIA). Results: IL-1 receptor antagonist (IL-1Ra) mRNA reduced synovial inflammation and alleviated pain and swelling. RUNX1 mRNA, a transcription factor critical for chondrogenesis, supported chondrocyte viability, type II collagen expression, and cartilage structure. Under conditions of pronounced inflammation, however, the protective effects of RUNX1 mRNA alone were modest. Notably, combined administration of IL-1Ra and RUNX1 mRNAs produced synergistic therapeutic benefits, with enhanced chondroprotection and preservation of subchondral bone integrity. Conclusions: These findings suggest that while RUNX1 is essential for maintaining cartilage homeostasis, effective control of joint inflammation is required for its therapeutic activity. Dual mRNA therapy delivered by polyplex nanomicelles therefore represents a promising strategy to address the multifactorial pathology of OA.

Osteoarthritis (OA) is a prevalent degenerative joint disease characterized by the progressive breakdown of cartilage. Here, we sought to define a pre-osteoarthritis (pre-OA) state using nanoindentation-based mechanical testing and evaluation of collagen organization in cartilage matrix. The reductions in elastic modulus and impaired viscoelasticity preceded any overt histological degeneration. This mechanical dysfunction was primarily driven by early disorganization of type II collagen, occurring before substantial depletion of cartilage components. We subsequently identified type IX collagen (Col IX), which played a critical role at the pre-OA stage. Intra-articular administration of Col9 mRNAs delivered by polymer-based nanomicelle restored pre-OA cartilage to a healthy, native-like collagen network architecture and preserved cartilage mechanical integrity, ultimately halting OA progression in the rat model. These findings identify viscoelastic dysfunction as an early biomechanical hallmark of pre-OA cartilage and establish Col9 mRNA as a potential anti-OA drug to prevent its onset. Together, these results provide a translatable framework in which quantitative mechanical-ultrastructural metrics guide ultra-early, presymptomatic intervention for degenerative diseases.

Hypothesis: This study aimed to evaluate the effectiveness of a less invasive drug delivery device, the pyro-drive jet injector-intratympanic (PJI-IT), as an alternative to the conventional intratympanic injection (ITI). Background: Conventional ITI using fine needles can cause damage to the tympanic membrane and hearing loss. A safer, less invasive delivery platform would be valuable for the local treatment of inner-ear disorders. Methods: Lipid nanoparticles (LNPs) containing firefly luciferase (Fluc) mRNA were injected into the middle ears of male guinea pigs (n=30) using the needle-free PJI-IT, which created a small, temporary perforation of the tympanic membrane through a high-pressure liquid jet. Conventional fine [30-gauge (30G)] needle injection was used as control. Perforation size and closure time were measured microscopically. Bioluminescence imaging was performed to evaluate Fluc protein production. Auditory brainstem responses (ABRs) were recorded before and after the injection to assess auditory function. Results: The PJI-IT and the 30G needle provided comparable amounts of Fluc protein in the tympanic cavity and cochlea. Compared with the conventional needle, the PJI-IT caused a smaller perforation of the tympanic membrane, which was closed faster. Auditory function was virtually preserved after injection using the PJI-IT, whereas injection using the conventional fine needle induced significant ABR threshold elevations. Conclusions: The PJI-IT has the potential to be a safe and minimally invasive instrument for intratympanic injections. The preserved auditory function and rapid healing of the perforated tympanic membrane suggest its clinical availability, especially for the repeated administration of biological agents such as mRNA regenerative medicine.