RhoA/Rock activation represents a new mechanism for inactivating Wnt/β-catenin signaling in the aging-associated bone loss

The Wnt/β-catenin signaling pathway appears to be particularly important for bone homeostasis,whereas nuclear accumulation ofβ-catenin requires the activation of Rac1,a member of the Rho small GTPase family.The aim of the present study was to investigate the role of RhoA/Rho kinase(Rock)-mediated Wnt/β-catenin signaling in the regulation of aging-associated bone loss.We find that Lrp5/6-dependent and Lrp5/6-independent RhoA/Rock activation by Wnt3a activates Jak1/2 to directly phosphorylate Gsk3βat Tyr216,resulting in Gsk3βactivation and subsequentβ-catenin destabilization.In line with these molecular events,RhoA loss-or gain-of-function in mouse embryonic limb bud ectoderms interacts genetically with Dkk1 gain-of-function to rescue the severe limb truncation phenotypes or to phenocopy the deletion ofβ-catenin,respectively.Likewise,RhoA loss-of-function in pre-osteoblasts robustly increases bone formation while gain-of-function decreases it.Importantly,high RhoA/Rock activity closely correlates with Jak and Gsk3βactivities but inversely correlates withβ-catenin signaling activity in bone marrow mesenchymal stromal cells from elderly male humans and mice,whereas systemic inhibition of Rock therefore activates theβ-catenin signaling to antagonize aging-associated bone loss.Taken together,these results identify RhoA/Rock-dependent Gsk3βactivation and subsequentβ-catenin destabilization as a hitherto uncharacterized mechanism controlling limb outgrowth and bone homeostasis.

Hippo signaling activates hedgehog signaling by Taz-driven Gli3 processing

The overlapping roles of Hippo and Hedgehog signaling in biological functions and diseases prompt us to inves-tigate their potential interactions.Activation of Hippo signaling enhances the transcriptional output of Hedgehog signaling,and the role of Hippo signaling in regulating Hedgehog signaling relies on the Hippo pathway key effector,Taz.Interestingly,Taz exhibits a gradient expression across the posterior-to-anterior of limb bud mesoderms,similar to Sonic hedgehog(Shh).Importantly,Taz drives PKA to phosphorylate Gli3,resulting in the Gli3 processing into its repressor and attenuation of Hedgehog signaling in the Shh-independent manner.Specifically,Taz deletion in mouse embryonic limb bud mesenchyme not only enhances the Hedgehog signaling but partially restores the phenotypes from Shh deletion in causing severe defects of anteroposterior patterning and digit number and identity.Together,these results uncover Taz-dependent Gli3 processing as a hitherto uncharacterized mechanism controlling Hedgehog signaling,highlighting its cross-regulation by Hippo signaling.

Correction:RhoA/Rock activation represents a new mechanism for inactivating Wnt/β-catenin signaling in the aging-associated bone loss

Following publication of the original article(Shi et al.2021),the authors have identified errors in Figs.1d and 3i which occurred during the figure assembly process.Theβ-actin bands in Fig.1d were mistakenly compiled from similar experiments in a previous publication by the same group(Gong et al.2014),conducted within the same time frame as the experiments in Fig.1d.To address this,the authors made corrections in Fig.1d in this revision.Furthermore,theβ-catenin band in Fig.3a was inadvertently reused in Fig.3i,and the new Fig.3 containing the correctβ-catenin in Fig.3i has been provided below.It’s important to note that despite these corrections,all the results and conclusions in this article remain consistent and unaffected.The authors deeply regret any inconvenience caused by these errors and sincerely apologize for them.