Cellular Stress in Pain and Tissue Damage

Summary Osteoarthritis (OA) is influenced by factors like joint injury, age, and gender. Chronic pain is the primary debilitating symptom, and current treatments are ineffective and do not reduce disease progression. Understanding OA and developing therapies is challenging because pain does not always correlate with joint damage. Targeting mechanisms that regulate joint tissue integrity and inflammation simultaneously may be necessary to alleviate pain and limit further physical deterioration. Our research identified the role of IRE1α- XBP1 in inflammatory pain and showed that leukocyte-specific IRE1α deficiency reduced pain and inflammatory mediators. We have uncovered that XBP1 transactivates NUPR1, which, when expressed in chondrocytes, leads to apoptosis and cartilage degradation. Furthermore, our studies demonstrate that global deletion of NUPR1 reduced OA pain and structural changes in mice, suggesting that the IRE1α-XBP1-NUPR1 axis regulates inflammation and tissue damage in OA. Thus, we hypothesize that IRE1α-XBP1-NUPR1 drives OA by promoting inflammatory programs in synovial immune cells while fostering joint cartilage damage via catabolic changes in chondrocytes. We will implement our plan through these specific aims: 1. Define how IRE1α-XBP1-NUPR1 signaling in immune cells and chondrocytes differentially contributes to synovial inflammation, cartilage damage, and OA pain. Two knee OA models (an injured model and an aging model) will be used in conditional knockout (cKO) mice lacking IRE1 or NUPR1 exclusively in leukocytes (Vavcre Ern1fl/fl) or chondrocytes (Col2a1cre Ern1fl/fl). Pain related behaviors and structural and molecular changes in the knee will be evaluated over time. 2. Determine how the IRE1α-XBP1-NUPR1 axis programming affects immune cell and chondrocyte function to drive OA joint structural damage, inflammation, and sensory neuron hyperactivity. We will use transgenic reporter mice that exhibit Venus-green fluorescent protein expression upon IRE1α-XBP1 activation to define the anatomical, cellular, and temporal IRE1α activation in the injury-link OA knee and study the functional phenotype of FACS sorted immune cells based on IRE1α activation. Then, we will discern how intrinsic leukocyte or chondrocyte IRE1α (cKO) sculpts the transcriptomic landscape and pathological microenvironment of the OA joint, and how IRE1α dictates leukocyte-chondrocyte interactions via single cell RNA sequencing and interactome bioinformatic analyses. 3. Test the translational hypothesis that inhibiting IRE1α or NUPR1 prevents or limits the progression of OA. We will use pharmacological blockers of IRE1α or NUPR1 to prevent or reverse OA-related pain behaviors and joint structural damage. Our project will establish IRE1α-XBP1-NUPR1 axis as a disease modifying target that would reduce pain and enhance joint functionality. Our unique transgenic mouse lines enable precise dissection of this specific OA molecular mechanism. Our multidisciplinary team is uniquely equipped to successfully complete these studies as we combine expertise in neuroimmunology and pain, cartilage and chondrocyte biology, and genomics coupled with advanced bioinformatic analytical tools.