Role of NOTCH2 in Articular Inflammation

PROJECT SUMMARY/ABSTRACT Osteoarthritis is a chronic inflammatory and degenerative disease of the joint affecting the cartilage, synovium and subchondral bone. Notch signal activation has been associated with the development of osteoarthritis, and inactivation of its canonical signaling prevents the osteoarthritis that follows destabilization of the medial meniscus (DMM). These findings indicate a role of Notch in the pathogenesis of osteoarthritis. However, the mechanisms responsible are not understood. We created a mouse model harboring a moderate gain-of-NOTCH2 function mutation and termed Notch2tm1.1Ecan. Notch2tm1.1Ecan mice are sensitized to the development of osteoarthritis following DMM surgeries, and chondrocytes from mutant mice are sensitized to the actions of tumor necrosis factor α (TNFα) and interleukin 1β (IL1β). The induction of interleukin (IL)6 and IL1β by TNFα and IL1β is amplified significantly in Notch2tm1.1Ecan chondrocytes, an effect that is independent of canonical signaling indicating the existence of novel signaling pathways operating in osteoarthritis. Our findings demonstrate a new role for Notch in the inflammatory response and osteoarthritis, but the cell and mechanisms responsible are not known. To explore the consequences of the NOTCH2 gain-of-function in specific articular cells, we created a Notch2 conditional by inversion (COIN) mouse model. The goal of our research is to establish the cell and mechanisms responsible for osteoarthritis and the enhanced inflammatory response to NOTCH2. Our specific aims are: Aim 1. To define the cell responsible for the NOTCH2-dependent osteoarthritis. To this end, we will utilize a conditional Notch2 mouse model to induce the NOTCH2 gain-of- function in specific articular cells; Aim 2. To establish the mechanisms responsible for NOTCH2 dependent osteoarthritis by defining transcriptome profiles and pathways responsible for osteoarthritis in the context of a NOTCH2 gain-of-function; and Aim 3. To establish the mechanisms responsible for NOTCH2-dependent inflammation by defining signaling pathways influenced by NOTCH2 to enhance the inflammatory response. The overarching goal of the proposed work is to discover novel mechanisms of Notch signaling operational in osteoarthritis and interrogate undiscovered Notch-related pathways and mechanisms responsible for an enhanced inflammatory response to Notch in cartilage.