Sustained notch signaling inhibition with a gamma-secretase inhibitor prevents traumatic heterotopic ossification

Eupalinolide A attenuates trauma-induced heterotopic ossification of tendon in mice by promoting YAP degradation through TOLLIP-mediated selective autophagy

BACKGROUND

Inhibiting the aberrant osteogenic differentiation of tendon-derived stem cells (TDSCs) is an effective strategy for treating traumatic heterotopic ossification (HO) in tendons.

PURPOSE

This study aimed to investigate whether eupalinolide A (EA) could prevent tendon HO progression by suppressing the osteogenic differentiation of TDSCs.

METHODS

The effects of EA on osteogenic differentiation and key signaling pathways in TDSCs were examined in vitro to assess its therapeutic potential and elucidate the underlying molecular mechanisms. Furthermore, the therapeutic efficacy of EA was evaluated in a mouse model of trauma-induced tendon HO via local injection therapy.

RESULTS

EA significantly inhibited the osteogenic differentiation of TDSCs by targeting YAP in vitro. Specifically, EA facilitated the recruitment of E3 ubiquitin ligase HECW1, which mediated K27-linked polyubiquitination of YAP, leading to its degradation via the TOLLIP-mediated selective autophagy pathway. In vivo, EA mitigated trauma-induced tendon HO by inhibiting the YAP pathway.

CONCLUSIONS

EA could be a potential therapeutic agent for treating traumatic tendon HO. The therapeutic target HECW1 involved in YAP degradation via autophagy presents a new therapeutic avenue to attenuate the progression of traumatic tendon HO.

Estrogen Deficiency Exacerbates Traumatic Heterotopic Ossification in Mice

Background

Traumatic heterotopic ossification (HO) is a devastating sequela of orthopedic surgeries and traumatic injuries; however, few studies have explored the effects of the estrogen-deficient state on HO formation. In the present study, we investigated the impact of estrogen deficiency on ectopic cartilage and bone formation in tendon after Achilles tenotomy in an ovariectomized mouse model.

Methods

A total of 45 female C57BL/6 mice were randomly divided into three groups: sham-operated (control), estrogen depletion by ovariectomy (OVX) and OVX with 17β-estradiol supplementation (OVX + E2), with 15 animals in each group. Three weeks after OVX, all mice were subjected to an Achilles tenotomy using a posterior midpoint approach to induce HO. At 1, 3 and 9 weeks after tenotomy, the left hind limbs were harvested for histology, immunohistochemistry and immunofluorescence evaluations. The volume of ectopic bone was assessed by micro-CT.

Results

Mice in the OVX group formed more ectopic cartilage 3 weeks after tenotomy, as well as ectopic bone 9 weeks after tenotomy, compared to the control group. Estrogen deficiency resulted in more severe inflammatory infiltration at the injury sites 1 week after tenotomy, involving the recruitment of more macrophages and mast cells, as well as increasing the expressions of pro-inflammatory mediators, including IL-1β, IL-6, and TNF-α. Moreover, the local TGF-β/SMAD signaling pathway was dysregulated after OVX, which manifested as upregulated expressions of TGF-β and pSMAD2/3. E2 supplementation protected against OVX-induced HO deterioration, inhibited inflammatory infiltration, and downregulated the TGF-β/SMAD signaling pathway.

Conclusion

Estrogen deficiency exacerbated HO formation in the Achilles tenotomy model. These findings might be attributable to the disturbance of the inflammatory response and the activation of TGF-β/SMAD signaling at the injury sites during the early stages of HO development.