Spatial Transcriptomics of TMJ Reveals a Remodeling Fibroblast‐Immune Microenvironment Driving Arthritis Pain

ABSTRACT Temporomandibular joint (TMJ) arthritis remodels the cartilage, subchondral bone, and synovial tissue with diverse cell changes. The functional importance of the anatomical organization of TMJ cell types and cellular microenvironment in painful arthritis remains largely unknown. Here, we applied seqFISH (sequential Fluorescence In Situ Hybridization) spatial transcriptomics to examine the adult mouse TMJ. We uncovered new cell types and comprehensively mapped anatomical locations of diverse cell types with distinct neighborhoods, revealed arthritis‐induced cell number and cell status changes, and discovered microenvironment remodeling of fibroblast‐immune cells, which are confirmed in patient synovial tissues. Functional and mechanistic studies showed that macrophage‐specific knockout of mouse Igf1 promotes its immune activation and upregulates Il33 in adjacent synovial fibroblasts, resulting in inflammatory fibroblast expansion. In turn, fibroblast‐specific deletion of Il33 alleviates inflammatory macrophages and inflammation, leading to pain mitigation. Thus, spatial transcriptomics maps diverse cell types in TMJ and reveals a remodeling of synovial fibroblast‐immune microenvironment via the Igf1‐Il33 axis, which drives arthritis pain with therapeutic potentials.