Angiogenesis is the process of forming new blood vessels and is closely linked to osteogenesis—the formation of new bone tissue, which is essential for skeletal development and homeostasis. Recent studies have shown that endothelial-to-osteoblast conversion(EC-to-OSB) plays a critical role in cancer bone metastasis and heterotopic ossification. However, this view remains controversial. It is still unclear whether and how EC-to-OSB regulates bone formation and homeostasis under physiological or aging conditions. Therefore, there is an urgent need to investigate the role of EC-to-OSB in osteoporosis (OP).

Recently, Professor Chen Di(Faculty of Pharmacy, Shenzhen University of Advanced Technology & Shenzhen Institutes of Advanced Technology (SIAT), Chinese Academy of Sciences) and ProfessorCao Huiling (Southern University of Science and Technology) co-published a paper entitled “Endothelial-to-Osteoblast Conversion maintains bone homeostasis through Kindlin-2/Piezo1/TGFβ/Runx2 axis” in Protein & Cell. The study reveals thatendothelial cells serve as an important source of osteoblasts, a process regulated by the Kindlin-2/Piezo1/TGFβ/Runx2 signaling axis, and that targeting this axis can treat osteoporosis.

The researchers first analyzed skeletal single-cell lineages and identified a subpopulation of MSCs highly expressing endothelial markers that also co-expressed osteoblast-related genes. These endothelial-marker-positive MSCs were phylogenetically closest to endothelial cells. Further experiments showed that knocking out Runx2—a core osteoblast differentiation gene—in endothelial cells significantly reduced bone mass in mice. Fluorescence staining confirmed a marked decrease in endothelium-derived osteoblasts on bone surfaces after Runx2 knockout, demonstrating their critical contribution to bone homeostasis.

The team also found that knocking down Kindlin-2 in endothelial cells significantly increased bone mass in mice, an effect mediated by EC-to-OSB. Using TGFβ inhibitors revealed that Kindlin-2-mediated EC-to-OSB is TGFβ-dependent, driven by elevated Piezo1 levels upon Kindlin-2 knockdown.

Mechanistic studies showed that Kindlin-2 directly interacts with Trim28 (an E3 ubiquitin ligase) and Piezo1, enhancing Trim28–Piezo1 interaction to promote Piezo1 ubiquitination and degradation. AlphaFold-Multimer predictions and experiments confirmed that the K1334 site of Piezo1 is critical for this ubiquitination. Endothelial-specific Kindlin-2 knockdown markedly stabilized Piezo1, thereby activating TGFβ/Runx2 signaling to drive EC-to-OSB. All mechanisms were validated by in vivo specific knockout experiments.

Furthermore, EC-to-OSB was significantly downregulated in aged and OVX-induced OP mouse models as well as in OP patients. CasRx-mediated editing of Kindlin-2 mRNA significantly attenuated ovariectomy (OVX)-induced and age-related osteoporosis progression in mice, suggesting that targeting Kindlin-2-mediated EC-to-OSB holds therapeutic promise for osteoporosis (OP).

This study proposes a novel perspective and mechanism for EC-to-OSB in regulating physiological and age-related bone homeostasis. In particular, the interaction between Kindlin-2 and Piezo1 highlights extensive crosstalk between Kindlin-2-mediated integrin signaling and Piezo1 mechanosensing—two major mechanotransduction pathways—providing critical theoretical support for elucidating in vivo mechanical signal transduction.

Cao Huiling and Chen Di are co-corresponding authors. Dr. Ma Guixing and Master’s student Han Yingying (Faculty of Medicine, Southern University of Science and Technology) are co-first authors.