10th International Conference on Osteoimmunology: Interactions of the Immune and Skeletal Systems

Abstract

The first day of the conference chaired by Iannis Adamopoulos and Hiroshi Takayanagi highlighted how rapidly the field of osteoimmunology is expanding beyond classical bone resorption and formation, toward a more integrated view of bone as a dynamic immune, vascular, metabolic and stem cell organ.Across Sessions I and II, speakers explored how specialized niches in bone marrow, growth plate, vasculature and stromal compartments shape skeletal homeostasis, inflammation, regeneration and disease.The session opened with Noriaki Ono who presented new insights into the endosteal niche at the crossroads of bone and immune cells.Building on the concept that PTHrP positive resting zone chondrocytes serve as skeletal stem cells in the postnatal growth plate, his talk emphasized how PTHrP controls the orderly transition of chondrocyte differentiation and prevents ectopic hypertrophic conversion through GDF5 pathways.Andrei Chagin further expanded this theme by describing a dual stem cell organization in growth plates.His presentation distinguished two resting zone stem cell subsets, including a Wnt enriched, highly stem like GP1 population and a GP2 population marked by different molecular features.This concept provides a new framework for understanding how the growth plate sustains longitudinal bone growth while balancing stemness, proliferation and hypertrophic differentiation.Anjali Kusumbe's lecture focused on skeletal vasculature and vascular niches, emphasizing endothelial diversity across space, time and function.Her work has been central to defining specialized bone vessels as niche structures that regulate bone formation, hematopoiesis and tissue aging.Earlier studies showed that age associated decline of niche forming skeletal vessels can impair bone and hematopoietic environments, while more recent work continues to reveal site specific vascular and stromal heterogeneity in skull, vertebral and long bone marrow niches.The second session shifted toward inflammatory and regenerative mechanisms in stromal, stem and progenitor cell biology.Masayuki Tsukasaki presented a vascular derived RANKL and OPG axis controlling arterial calcification independently of the skeleton, illustrating how classical bone regulatory molecules can act in vascular disease.Ritu Chakravarti introduced multilevel regulation of osteoclastogenesis by 14-3-3ζ at the inflammation and bone interface.Several talks emphasized bone as an active systemic responder to inflammation.Stavroula Kousteni described bone-derived inflammatory SAA1 as a regulator of stem cell state and persistence in myeloid malignancies.Yasuhiro Kobayashi addressed inflammaging, focusing on endothelial RANK signaling.A recurring theme was the intimate connection between immune cells and skeletal repair.Salwa Suliman and colleagues highlighted regulatory T cells as orchestrators of mesenchymal stromal cell mediated bone regeneration.Kazutaka Nakamura and colleagues described a stromal niche supporting osteoclastogenesis in giant cell tumor of bone.Daniela Paternina Martinez showed that IL 17RA blockade can uncover alternative osteogenic pathways driven by IL 17F through BMP and Wnt signaling.Jessica De Angelis presented evidence that bone can rapidly sense inflammation and secrete Lipocalin 2, reinforcing the concept that skeletal tissue participates actively in immune communication.Together, the session portrayed bone as a highly organized, immune responsive and metabolically adaptable organ.Stem cells, stromal cells, endothelial cells, immune cells and osteoclasts do not act in isolation.They form interconnected niches that determine skeletal growth, inflammatory bone loss, regeneration, vascular calcification, aging and malignancy.This integrated view captures the current direction of osteoimmunology: from bone and immune crosstalk toward a broader biology of tissue niches, systemic inflammation and organ level adaptation. Day 2: New insights in Osteoclast biology, Inflammation and BoneD