Inhibiting WNT secretion reduces high bone mass caused by Sost loss-of-function or gain-of-function mutations in Lrp5

AUTHORS

Cassandra R. Diegel, Ina Kramer, Charles Moes, Gabrielle E. Foxa, Mitchell J. McDonald, Zachary B. Madaj, Sabine Guth, Jun Liu, Jennifer L. Harris, Michaela Kneissel & Bart O. Williams

ABSTRACT

Proper regulation of Wnt signaling is critical for normal bone development and homeostasis. Mutations in several Wnt signaling components, which increase the activity of the pathway in the skeleton, cause high bone mass in human subjects and mouse models. Increased bone mass is often accompanied by severe headaches from increased intracranial pressure, which can lead to fatality and loss of vision or hearing due to the entrapment of cranial nerves. In addition, progressive forehead bossing and mandibular overgrowth occur in almost all subjects. Treatments that would provide symptomatic relief in these subjects are limited. Porcupine-mediated palmitoylation is necessary for Wnt secretion and binding to the frizzled receptor. Chemical inhibition of porcupine is a highly selective method of Wnt signaling inhibition. We treated three different mouse models of high bone mass caused by aberrant Wnt signaling, including homozygosity for loss-of-function in Sost, which models sclerosteosis, and two strains of mice carrying different point mutations in Lrp5 (equivalent to human G171V and A214V), at 3 months of age with porcupine inhibitors for 5–6 weeks. Treatment significantly reduced both trabecular and cortical bone mass in all three models. This demonstrates that porcupine inhibition is potentially therapeutic for symptomatic relief in subjects who suffer from these disorders and further establishes that the continued production of Wnts is necessary for sustaining high bone mass in these models.

MACF1 overexpression in BMSCs alleviates senile osteoporosis in mice through TCF4/miR-335–5p signaling pathway

AUTHORS

Kewen Zhang, Wuxia Qiu, Hui Li, Jun Li, Pai Wang, Zhihao Chen, Xiao Lin, Airong Qian

ABSTRACT

Background

The decreased osteogenic differentiation ability of mesenchymal stem cells (MSCs) is one of the important reasons for SOP. Inhibition of Wnt signaling in MSCs is closely related to SOP. Microtubule actin crosslinking factor 1 (MACF1) is an important regulator in Wnt/β-catenin signal transduction. However, whether the specific expression of MACF1 in MSC regulates SOP and its mechanism remains unclear.

Methods

We established MSC-specific Prrx1 (Prx1) promoter-driven MACF1 conditional knock-in (MACF-KI) mice, naturally aged male mice, and ovariectomized female mice models. Micro-CT, H&E staining, double calcein labeling, and the three-point bending test were used to explore the effects of MACF1 on bone formation and bone microstructure in the SOP mice model. Bioinformatics analysis, ChIP-PCR, qPCR, and ALP staining were used to explore the effects and mechanisms of MACF1 on MSCs’ osteogenic differentiation.

Results

Microarray analysis revealed that the expression of MACF1 and positive regulators of the Wnt pathway (such as TCF4, β-catenin, Dvl) was decreased in human MSCs (hMSCs) isolated from aged osteoporotic than non-osteoporotic patients. The ALP activity and osteogenesis marker genes (Alp, Runx2, and Bglap) expression in mouse MSCs was downregulated during aging. Furthermore, Micro-CT analysis of the femur from 2-month-old MSC-specific Prrx1 (Prx1) promoter-driven MACF1 conditional knock-in (MACF-cKI) mice showed no significant trabecular bone changes compared to wild-type littermate controls, whereas 18- and 21-month-old MACF1 c-KI animals displayed increased bone mineral densities (BMD), improved bone microstructure, and increased maximum compression stress. In addition, the ovariectomy (OVX)-induced osteoporosis model of MACF1 c-KI mice had significantly higher trabecular volume and number, and increased bone formation rate than that in control mice. Mechanistically, ChIP-PCR showed that TCF4 could bind to the promoter region of the host gene miR-335–5p. Moreover, MACF1 could regulate the expression of miR-335–5p by TCF4 during the osteogenic differentiation of MSCs.

Conclusion

These data indicate that MACF1 positively regulates MSCs osteogenesis and bone formation through the TCF4/miR-335-5p signaling pathway in SOP, suggesting that targeting MACF1 may be a novel therapeutic approach against SOP.

The translational potential of this article

MACF1, an important switch in the Wnt signaling pathway, can alleviate SOP through the TCF4/miR-335-5p signaling pathway in mice model. It might act as a therapeutic target for the treatment of SOP to improve bone function.