[Activation of Notch signaling in bone marrow stromal cells promotes osteogenesis in mice in vitro].

Objective To investigate the osteogenic differentiation of bone marrow stromal cells (BMSC) with Notch signaling activation in vitro. Methods The BMSC derived from Notch1-NICDflox/flox mice were infected with recombinant adenovirus expressing Cre or GFP respectively, and designated as Ad-Cre group and Ad-GFP group. The expression of Notch1 was evaluated by Western blot analysis. Alkaline phosphatase (ALP) activity was determined by ALP staining and biochemical quantification, and the calcium deposition was analyzed with Alizarin red S staining. Real-time fluorescence quantitative PCR (qPCR) was used to quantify the expression of Notch target genes(Hes1, Hey1, Hey2, HeyL), osteogenic differentiation-related genes(ALP, RUNX2, osterix, osteocalcin), and angiogenesis factors(VEGF, HIF-1α). Results Notch signaling in BMSC of Notch1-NICDflox/flox mice was activated successfully by Ad-Cre, as was evidenced by the significantly elevated expression of Notch1 and Notch target genes. Compared with the Ad-GFP group, ALP activity and the late calcium deposition were significantly increased upon treatment with Ad-Cre. qPCR results demonstrated that the expression of ALP, RUNX2, osterix, osteocalcin, VEGF, HIF-1α in the Ad-Cre group were significantly upregulated. Conclusion Activation of Notch signaling in BMSC in vitro significantly promotes osteogenic differentiation.

Canonical Wnt signaling works downstream of iron overload to prevent ferroptosis from damaging osteoblast differentiation.

Excessive iron has emerged in a large population of patients suffering from degenerative or hematological diseases with a common outcome, osteoporosis. However, its underlying mechanism remains to be clarified in order to formulate effective prevention and intervention against the loss of bone-forming osteoblasts. We show herein that increased intracellular iron by ferric ammonium citrate (FAC) mimicking the so-called non-transferrin bound iron concentrations leads to ferroptosis and impaired osteoblast differentiation. FAC upregulates the expression of Trfr and DMT1 genes to increase iron uptake, accumulating intracellular labile ferrous iron for iron overload status. Then, the excessive ferrous iron generates reactive oxygen species (ROS) and lipid peroxidation products (LPO), causing ferroptosis with its typical mitochondrial morphological changes, such as shrinkaged and condensed membrane with diminution and loss of crista and outer membrane rupture. We further examined that ferroptosis is the main cause responsible for FAC-disrupted osteoblast differentiation, although apoptosis and senescence are concurrently induced as well. Mechanistically, we revealed that iron dose-dependently down-regulates the expression of Wnt target genes and inhibits the transcription of Wnt reporter TopFlash construct, so as to inhibit the canonical Wnt signaling. Wnt agonist, ferroptosis inhibitor, or antioxidant melatonin reverses iron-inhibited canonical Wnt signaling to restore osteoblast differentiation by reducing ROS and LPO production to prevent ferroptosis notably without reducing iron overload. This study proposes a working model against excessive iron-induced osteoporosis: iron chelator deferoxamine or the above three drugs prevent ferroptosis, restore traditional Wnt signaling to maintain osteoblast differentiation no matter whether iron overload is removed or not. Additionally, iron chelator should be used to a suitable extent because iron itself is necessary for osteogenic differentiation.