Section for Pharmacology and Pharmaceutical Biosciences, Department of Pharmacy, University of Oslo, Oslo, Norway.
Department of Cellular and Molecular Medicine, University of Copenhagen, Copenhagen, Denmark.
Front Endocrinol (Lausanne). 2024 Sep 19;15:1445049. doi: 10.3389/fendo.2024.1445049. eCollection 2024.
Transforming growth factor-beta 1 (TGF-β1) is a critical regulator of skeletal homeostasis and has diverse effects on osteoblastogenesis. To date, the mechanisms behind the intriguing inhibitory effect of TGF-β1 on osteoblast maturation are not fully understood. Here, we demonstrate a novel mechanism by which TGF-β1 modulates osteoblast maturation through the lysosomal protease legumain. We observed that addition of TGF-β1 to osteogenic cultures of human bone marrow derived mesenchymal stromal (stem) cells enhanced legumain activity and secretion, in-spite of decreased legumain mRNA expression, suggesting post-transcriptional regulation. We further showed that osteogenic cells internalize and activate prolegumain, associated with inhibited osteoblast maturation, revealing legumain as a paracrine regulator of osteoblast maturation. Interestingly, TGF-β1 treatment exacerbated legumain internalization and activity, and showed an additive effect on legumain-induced inhibition of osteoblast maturation. Importantly, pharmacological inhibition of legumain abolished the inhibitory effect of TGF-β1 on osteoblast maturation. Our findings reveal that TGF-β1 inhibits osteoblast maturation by stimulating secretion and activity of endogenous legumain, as well as enhancing internalization and activation of extracellular prolegumain. Therefore, our study provides a deeper understanding of the complex regulation of osteoblastogenesis and unveils a novel TGF-β1-legumain axis in regulation of osteoblast maturation, offering novel insights for possible therapeutic interventions related to bone diseases associated with aberrant TGF-β1 signaling.
转化生长因子-β1（TGF-β1）是骨骼动态平衡的关键调节因子，对成骨细胞生成有多种影响。迄今为止，TGF-β1 对成骨细胞成熟的这种有趣的抑制作用的机制尚未完全阐明。在这里，我们通过溶酶体蛋白酶半胱氨酸天冬氨酸蛋白酶（legumain）证实了 TGF-β1 调节成骨细胞成熟的新机制。我们观察到，向人骨髓间充质基质（干）细胞的成骨培养物中添加 TGF-β1 会增强 legumain 活性和分泌，尽管 legumain mRNA 表达降低，这表明存在转录后调控。我们进一步表明，成骨细胞内化并激活 prolegumain，与抑制成骨细胞成熟有关，揭示 legumain 是成骨细胞成熟的旁分泌调节剂。有趣的是，TGF-β1 处理加剧了 legumain 的内化和活性，并显示出与 legumain 诱导的成骨细胞成熟抑制的相加作用。重要的是，legumain 的药理学抑制消除了 TGF-β1 对成骨细胞成熟的抑制作用。我们的发现表明，TGF-β1 通过刺激内源性 legumain 的分泌和活性，以及增强细胞外 prolegumain 的内化和激活，来抑制成骨细胞成熟。因此，我们的研究提供了对成骨细胞生成复杂调节的更深入了解，并揭示了 TGF-β1 调节成骨细胞成熟的新的 TGF-β1-legumain 轴，为与 TGF-β1 信号传导异常相关的骨骼疾病的可能治疗干预提供了新的见解。
