Two paths to healing: organoids reveal sex-specific bone regeneration mechanisms

Recent findings in bone regeneration research, highlights the significant impact of biological sex and donor variability on healing processes, offering promising new approaches to personalized medicine. By modeling cartilage-to-bone transition with innovative callus organoids, scientists discovered two distinct pathways—hypertrophic cartilage and fibrocartilage—driven by early progenitor cell activation. Notably, male-derived organoids favored larger, cartilage-rich structures, while female-derived organoids developed denser fibrous tissues. Despite these differences, both pathways successfully resulted in the formation of bone upon implantation, underlining the importance of a shared set of secreted proteins in the healing process. The findings pave the way for the development of personalized bone implants and noninvasive biomarkers to predict therapeutic outcomes.

Bone regeneration continues to be a critical challenge in tissue engineering, with unpredictable outcomes often hindering clinical application. Current strategies overlook key factors such as donor differences and biological sex, both of which play a significant role in fracture healing. While cartilage intermediates have shown promise, the transition from cartilage to functional bone remains poorly understood, and a lack of quality metrics that are predictive of bone regeneration across patients hinder clinical implementation. Moreover, the influence of biological sex on bone repair, particularly in younger patients, remains an underexplored area. These challenges highlight the urgent need to understand how donor and sex-specific mechanisms affect bone regeneration.

Published (DOI: 10.1038/s41413-025-00418-z) on March 26, 2025, in Bone Research, a groundbreaking study led by KU Leuven in collaboration with international researchers examined bone-forming callus organoids derived from human periosteal cells. The team compared organoids from male and female donors, analyzing their extracellular matrix composition, transcriptomes, and secreted proteins. Their findings unveiled sex-dependent pathways in the cartilage-to-bone transition, offering fresh insights into personalized tissue engineering.

The study revealed striking differences between male and female-derived organoids in terms of cartilage formation. Male-derived organoids predominantly produced hypertrophic cartilage (HyC), featuring large, transparent structures rich in glycosaminoglycans and collagen II. Female-derived organoids, on the other hand, tended to develop fibrocartilage (FiC), consisting of smaller, denser tissues that lacked hypertrophic markers. Transcriptomic analysis uncovered a shared set of chondrogenic genes but distinct progenitor markers, suggesting early divergence in the differentiation process.

A key highlight of the study was the identification of 84 secreted proteins common to both cartilage-to-bone pathways, but not present in non bone-forming tissue, including agrin (AGRIN), osteopontin (SPP1), angiopoietin-like 4 (ANGPL4), autotaxin (NPP2) and bone morphogenic protein 1 (BMP1). These proteins are critical in driving bone maturation, angiogenesis and matrix remodeling.Despite their morphological differences, both male and female organoids successfully regenerated bone in mice, though the HyC organoids produced larger volumes. Notably, male cells exhibited faster proliferation and deposited more extracellular matrix, highlighting the role of biological sex in progenitor cell activation.

Prof. Ioannis Papantoniou, senior author of the study, emphasized the significance of these findings: "Our work bridges the gap between developmental biology and clinical translation. By decoding sex-specific repair mechanisms, we can design smarter living implants tailored to individual but also groups of patients. The secreted protein panel is a game-changer for monitoring implant quality without invasive sampling."

The implications of this research are profound, offering the potential to revolutionize treatments for bone defects with sex-specific or donor-matched therapies. The identification of secreted protein biomarkers could streamline the manufacturing process, reducing costs and enhancing the reliability of advanced therapeutic products. Clinically, these advancements could benefit younger patients (aged 25-45), who often struggle with non-union fractures. Moving forward, future research will focus on validating these biomarkers in larger animal models and exploring the influence of hormones. Ultimately, this study underscores the crucial role of biological sex in regenerative medicine, advocating for a shift toward personalized approaches in tissue engineering.

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References

DOI

10.1038/s41413-025-00418-z

Original Source URL

https://doi.org/10.1038/s41413-025-00418-z

Funding information

The micro (or nano)-CT images were generated on the X-ray computed tomography facility of the Department of Development and Regeneration of the KU Leuven, financed by the Hercules Foundation (project AKUL/13/47). The project leading to this publication has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 874837. This work was supported by the Flemish Government (department of Economy, Science and Innovation) through the Regenerative Medicine Crossing Borders initiative. Images were recorded on a Zeiss LSM 780 – SP Mai Tai HP DS (Cell and Tissue Imaging Cluster (CIC), Supported by Hercules AKUL/11/37 and FWO G.0929.15 to Pieter Vanden Berghe, University of Leuven. This work was supported by Interne Fondsen KU Leuven/Internal Funds KU Leuven grant numbers C24M/22/058.

About Bone Research

Bone Research was founded in 2013. As a new English-language periodical, Bone Research focuses on basic and clinical aspects of bone biology, pathophysiology and regeneration, and supports the foremost discoveries resulting from basic investigations and clinical research related to bone. The aim of the Journal is to foster the worldwide dissemination of research in bone-related physiology, pathology, diseases and treatment.