SAT-665 - Defining the Role of Leptin in Fat-Sensory Nerve-Joint Crosstalk in Osteoarthritis

Introduction: Osteoarthritis (OA) is a painful joint disease, and obesity is a major risk factor for OA. We previously demonstrated that adipose-derived leptin promotes cartilage structural damage, but the downstream mechanisms and cellular targets of leptin driving OA-related pain remain poorly defined. The purpose of this study was to determine if cartilage is directly modified by leptin in OA.

Methods: Global leptin knockout (JAX #000632) (Ob/Ob), heterozygous (Ob/+), and wildtype (WT) mice were used as a model of genetic obesity. Chondrocyte-specific leptin knockout mice were generated by crossing aggrecan-creERT2 (JAX #019148) mice with leptin receptor knockout mice (JAX #008327) and treated with tamoxifen for 4 days at 12 weeks of age to induce cre expression. At 16 weeks, mice underwent destabilization of the medial meniscus (DMM) to model OA in the left hindlimb, and the right hindlimb remained naive. Pain and behavior testing, including algometer testing for pressure-pain hyperalgesia and static weight bearing, were performed before euthanizing at 28 weeks. Luminex assays on serum and synovial fluid were performed. Lumbar L3-L5 dorsal root ganglia neurons were assessed via bulk RNA sequencing. To assess leptin’s role in human DRGs, 10ng/mL leptin was added to human DRG culture media, followed by bulk RNA sequencing after 24 hours. Data were analyzed using 1- or 2-way ANOVA with post hoc testing.

Results: Ob/Ob mice displayed increased body mass and fat compared to WT. While Ob/Ob, Ob/+, and WT mice all sustained cartilage damage after DMM injury, only Ob/Ob mice were protected from hyperalgesia (p < 0.001). Synovial fluid from Ob/Ob mice showed trends toward reduced IL-6 (p=0.10) and IL-1alpha (p=0.14) in the injured limb versus the non-injured limb. In serum from Ob/Ob and Ob/+ mice, MCP-1 and TNF-alpha were significantly elevated compared to WT mice. Loss of leptin receptor in chondrocytes did not prevent OA or pain following knee injury in male or female animals. DRG sequencing from injured Ob/Ob limbs revealed changes in KEGG pathways tied to PPARgamma signaling, linoleic acid metabolism, and complement signaling via PLA2G2D and membrane attack complex components. When treated with leptin for 24 hours, human DRG mRNA levels for the inflammatory genes, CCL3, CCL7, and ICAM-1 significantly downregulated.

Conclusion: Leptin contributes to knee pain via neuro-immune crosstalk mechanisms linking fat and sensory neurons, rather than direct effects on chondrocytes. Cartilage-specific deletion of leptin receptor did not prevent pain or OA, aligning with data showing leptin signaling is necessary but insufficient for driving cartilage damage in OA.