Human HAND1 inhibits the conversion of cholesterol to steroids in trophoblasts

Steroidogenesis from cholesterol in placental trophoblasts is fundamentally involved in the establishment and maintenance of pregnancy.The transcription factor gene heart and neural crest derivatives expressed1(Hand1)promotes differentiation of mouse trophoblast giant cells.However,the role of HAND1 in human trophoblasts remains unknown.Here,we report that HAND1 inhibits human trophoblastic progesterone(P4)and estradiol(E2)from cholesterol through downregulation of the expression of steroidogenic enzymes,including aromatase,P450 cholesterol side-chain cleavage enzyme(P450 scc),and 3β-hydroxysteroid dehydrogenase type 1(3β-HSD1).Mechanically,although HAND1 inhibits transcription of aromatase by directly binding to aromatase gene promoter,it restrains transcription of P450 scc by upregulation of the methylation status of P450 scc gene promoter through its binding to ALKBH1,a demethylase.Unlike aromatase and P450 scc,HAND1 decreases 3β-HSD1 m RNA levels by the reduction of its RNA stability through binding to and subsequent destabilizing protein Hu R.Finally,HAND1 suppresses circulating P4 and E2 levels derived from JEG-3 xenograft and attenuates uterine response to P4 and E2.Thus,our results uncover a hitherto uncharacterized role of HAND1 in the regulation of cholesterol metabolism in human trophoblasts,which may help pinpoint the underlying mechanisms involved in supporting the development and physiological function of the human placenta.

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.