An angiogenic approach to osteoanabolic therapy targeting the SHN3-SLIT3 pathway

Endothelial-mesenchymal crosstalk drives osteogenic differentiation of human osteoblasts through Notch signaling

BACKGROUND

Angiogenesis and osteogenesis are closely interrelated. The interaction between endothelial and bone-forming cells, such as osteoblasts, is crucial for normal bone development and repair. Juxtacrine and paracrine mechanisms play key roles in cell differentiation towards the osteogenic direction, assuming the direct effect of endothelium on osteogenic differentiation. However, the mechanisms of this interplay have yet to be thoroughly studied.

METHODS

Isolated endothelial cells (EC) from human umbilical vein and human osteoblasts (OB) from the epiphysis of the femur or tibia were cultured in direct and indirect (separated by membrane) contact in vitro under the osteogenic differentiation conditions. Osteogenic differentiation was verified by RT-PCR, and alizarin red staining. Shotgun proteomics and RNA-sequencing were used to compare both EC and OB under different co-culture conditions to assess the mechanisms of EC-OB interplay. To verify the role of Notch signaling, experiments with Notch modulation in EC were performed by EC lentiviral transduction with further co-cultivation with OB. Additionally, the effect of Notch modulation in EC was assessed by RNA-sequencing.

RESULTS

EC have opposite effects on osteogenic differentiation depending on the co-culture conditions with OB. In direct contact, EC enhance osteogenic differentiation, but in indirect cultures, EC suppress it. Our proteotranscriptomic analysis revealed that the osteosuppressive effect is related to the action of paracrine factors secreted by EC, while the osteoinductive properties of EC are mediated by the Notch signaling pathway, which can be activated only upon a physical contact of EC with OB. Indeed, in the direct co-culture, the knockdown of Notch1 and Notch3 receptors in EC has an inhibitory effect on the OB osteogenic differentiation, whereas activation of Notch by intracellular domain of either Notch1 or Notch3 in EC has an inductive effect on the OB osteogenic differentiation.

CONCLUSION

The data indicate the dual role of the endothelium in regulating osteogenic differentiation and highlight the unique role of the Notch signaling pathway in inducing osteogenic differentiation during cell-to-cell interactions. The findings of the study emphasize the importance of intercellular communication in the regulation of osteoblast differentiation during bone development and maintenance.

Sarsasapogenin stimulates angiogenesis and osteogenesis coupling to treat estrogen deficiency-induced osteoporosis by activating the GPX4/SLIT3/ROBO1 axis

BACKGROUND

Promoting the coupling of osteogenesis and angiogenesis is a crucial strategy for the treatment of postmenopausal osteoporosis (PMOP). Estrogen deficiency induces ferroptosis, which is closely associated with the pathophysiology of PMOP. Sarsasapogenin (SAR) is a natural sapogenin with anti-oxidative effects. However, it is unclear whether SAR has a protective role against the impaired osteogenesis and angiogenesis coupling in PMOP. In this study, we evaluated the efficacy of SAR in estrogen deficiency-induced osteoporosis and explored the underlying mechanisms.

METHODS

Bone marrow mesenchymal stem cells (BMSCs) and human umbilical vein endothelial cells (HUVECs) were utilized to assess the in vitro effects of SAR on the coupling of osteogenesis and angiogenesis. In vivo experiments involved bilateral ovariectomy (OVX)-induced osteoporosis in mice and glutathione peroxidase 4 (GPX4)-knockout (KO) mice. Mice were orally administered SAR (5 or 10 mg/kg/d) for a duration of 12 weeks. The direct target of SAR was investigated through molecular docking, a cellular thermal shift assay, and surface plasmon resonance. Additionally, RNA sequencing was employed to elucidate the underlying mechanisms.

RESULTS

SAR treatment improved cell viability and osteogenic differentiation while inhibiting ferroptosis in iron dextran-induced BMSCs. Furthermore, SAR enhanced the production of slit guidance ligand 3 (SLIT3) in these cells, which stimulated angiogenesis by activating its receptor, roundabout human homolog 1 (ROBO1), in HUVECs. An in vitro model of ferroptosis induced by erastin demonstrated that SAR promoted the coupling of osteogenesis and angiogenesis by upregulating the BMSCs-SLIT3/HUVECs-ROBO1 axis. Activation of GPX4 was identified as a contributing factor to the effects of SAR on this coupling. Transfection of GPX4 small interfering RNA (siRNA) in BMSCs negated the impact of SAR on the BMSCs-SLIT3/HUVECs-ROBO1 axis. Additionally, SAR was found to directly interact with GPX4, enhancing protein stability, with an equilibrium dissociation constant of 44.6 μM. Notably, SAR did not increase SLIT3, ROBO1, or indicators of osteogenesis or angiogenesis in GPX4-KO mice.

CONCLUSIONS

These findings underscore the significance of restoring the GPX4/SLIT3/ROBO1 axis in promoting the coupling of angiogenesis and osteogenesis. SAR mitigates PMOP, in part, by activating the BMSCs-SLIT3/HUVECs-ROBO1 axis, with GPX4 serving as an upstream signaling modulator responsible for SLIT3 production. Our observations provide experimental evidence supporting the clinical application of SAR in the treatment of PMOP.

Inhibition of Slit3/Robo1 signaling alleviates osteoarthritis in mice by reducing abnormal H-type vessel formation in subchondral bone

BACKGROUND

The aberrant H-type vessel formation was found to be intimately linked to subchondral bone remodeling during osteoarthritis (OA) development. Herein, we investigated the role and mechanism of osteoblast-secreted slit guidance ligand 3 (Slit3) in H-type vessel formation during OA progression.

METHODS

Slit3 protein levels in subchondral bone samples of OA patients were detected. The isolated osteoblasts were transfected with Slit3 overexpression or knockdown plasmids, and their conditioned medium was cultured with endothelial progenitor cells (EPCs). The migration, tube formation, VEGF, and H-type vessel marker protein CD31 and endomucin (EMCN) levels in EPCs were accessed. The interactions between Slit3 and roundabout (Robo) family members were validated by Co-IP assay. Besides, whether the Slit3/Robo signaling affects the transforming growth factor β1 (TGF-β1)/SMADs pathway was determined. Additionally, sh-Slit3 was injected into OA mice, followed by the detection of articular cartilage degradation, subchondral bone remodeling, and H-type vessel formation.

RESULTS

Slit3 was upregulated in subchondral bone tissues of OA patients. Slit3 overexpression in osteoblasts intensified the migration and H-type vessel formation of EPCs, while Slit3 knockdown showed the opposite results. Slit3 overexpression enhanced Robo1 protein level. Robo1 knockdown abrogated Slit3-mediated migration and H-type vessel formation in EPCs. Slit3 activated the TGF-β1/SMADs pathway in EPCs, which might be associated with H-type vessel formation in EPCs. Additionally, Slit3 silencing restrained articular cartilage degradation, aberrant subchondral bone formation, and H-type vessel formation in OA mice.

CONCLUSION

Inhibition of Slit3/Robo1 signaling alleviates osteoarthritis in mice by reducing abnormal H-type vessel formation in the subchondral bone.

Bone controls browning of white adipose tissue and protects from diet-induced obesity through Schnurri-3-regulated SLIT2 secretion

The skeleton has been suggested to function as an endocrine organ controlling whole organism energy balance, however the mediators of this effect and their molecular links remain unclear. Here, utilizing Schnurri-3-/- (Shn3-/-) mice with augmented osteoblast activity, we show Shn3-/-mice display resistance against diet-induced obesity and enhanced white adipose tissue (WAT) browning. Conditional deletion of Shn3 in osteoblasts but not adipocytes recapitulates lean phenotype of Shn3-/-mice, indicating this phenotype is driven by skeleton. We further demonstrate osteoblasts lacking Shn3 can secrete cytokines to promote WAT browning. Among them, we identify a C-terminal fragment of SLIT2 (SLIT2-C), primarily secreted by osteoblasts, as a Shn3-regulated osteokine that mediates WAT browning. Lastly, AAV-mediated Shn3 silencing phenocopies the lean phenotype and augmented glucose metabolism. Altogether, our findings establish a novel bone-fat signaling axis via SHN3 regulated SLIT2-C production in osteoblasts, offering a potential therapeutic target to address both osteoporosis and metabolic syndrome.

Chondroitin sulfate/silk fibroin hydrogel incorporating graphene oxide quantum dots with photothermal-effect promotes type H vessel-related wound healing

Chronic wounds with bacterial infection present formidable clinical challenges. In this study, a versatile hydrogel dressing with antibacterial and angiogenic activity composite of silk fibroin (SF), chondroitin sulfate (CS), and graphene oxide quantum dots (GOQDs) is fabricated. GOQDs@SF/CS (GSC) hydrogel is rapidly formed through the enzyme catalytic action of horseradish peroxidase. With the incorporation of GOQDs both gelation speed and mechanical properties have been enhanced, and the photothermal characteristics of GOQDs in GSC hydrogel enabled bacterial killing through photothermal treatment (PTT) at ∼51 °C. In vitro studies show that the GSC hydrogels demonstrate excellent antibacterial performance and induce type H vessel differentiation of endothelial cells via the activated ERK1/2 signaling pathway and upregulated SLIT3 expression. In vivo results show that the hydrogel significantly promotes type H vessels formation, which is related to the collagen deposition, epithelialization and, ultimately, accelerates the regeneration of infected skin defects. Collectively, this multifunctional GSC hydrogel, with dual action of antibacterial efficacy and angiogenesis promotion, emerges as an innovative skin dressing with the potential for advancing in infected wound healing.

Angiogenesis-related immune response may be the prelude to the syndesmophyte formation in Ankylosing spondylitis

BACKGROUND

Ankylosing spondylitis (AS) is a chronic autoimmune arthritis that mainly affects spine joints. To date, the pathogenesis of AS remains unclear, although immune cells and innate immune response cytokines have been suggested to be crucial players.

METHODS

By adopting a single-cell RNA sequencing approach in the AS cynomolgus model, we profiled and characterized PBMC proportions along disease progression.

RESULTS

Here, our primary focus was on the activation of an immune cascade-initiating lymphocyte subtype known as CD4+CXCR5+ T follicular helper (Tfh) cells. These Tfhs demonstrated a localized residence in AS bone lesion as an ectopic lymphoid structure. Moreover, Tfhs would serve as an upstream initiator for a pro-angiogenic cascade. Then, an expansion in CD14+ monocytes and DC cells subsets resulted in enhanced expression of angiogenesis genes in these AS cynomolgus monkeys. With a confirmed higher abundance of TNF-α accompanying H-type vascular invasion in the osteophytic region, pronounced expansion of Tfhs at such lesion site signaling for monocytes and DCs intrusion is considered as the prelude to the characteristic angiogenic bony outgrowth in AS known as syndesmophytes.

CONCLUSIONS

We explored the intimate relationship between local inflammation and bone formation in AS from the perspective of nascent vascularisation. Hence, our study lays the foundation for elucidating a unified AS pathogenesis through the immune-angiogenesis-osteogenesis axis.

Mesenchymal stem cell-derived extracellular vesicles: a regulator and carrier for targeting bone-related diseases

The escalating threat of bone-related diseases poses a significant challenge to human health. Mesenchymal stem cell (MSC)-derived extracellular vesicles (MSC-EVs), as inherent cell-secreted natural products, have emerged as promising treatments for bone-related diseases. Leveraging outstanding features such as high biocompatibility, low immunogenicity, superior biological barrier penetration, and extended circulating half-life, MSC-EVs serve as potent carriers for microRNAs (miRNAs), long no-code RNAs (lncRNAs), and other biomolecules. These cargo molecules play pivotal roles in orchestrating bone metabolism and vascularity through diverse mechanisms, thereby contributing to the amelioration of bone diseases. Additionally, engineering modifications enhance the bone-targeting ability of MSC-EVs, mitigating systemic side effects and bolstering their clinical translational potential. This review comprehensively explores the mechanisms through which MSC-EVs regulate bone-related disease progression. It delves into the therapeutic potential of MSC-EVs as adept drug carriers, augmented by engineered modification strategies tailored for osteoarthritis (OA), rheumatoid arthritis (RA), osteoporosis, and osteosarcoma. In conclusion, the exceptional promise exhibited by MSC-EVs positions them as an excellent solution with considerable translational applications in clinical orthopedics.