ABSTRACT Rett syndrome (RTT) is a rare neurodevelopmental disorder caused by loss‐of‐function mutations in the gene encoding methyl‐CpG‐binding protein 2 (MECP2) that is located on the X chromosome. Affected individuals also exhibit a variety of non‐neurological symptoms such as kyphoscoliosis and osteoporosis. Thus, MECP2 may play a functional role in bone remodeling and osteoblast differentiation. This study aimed to clarify the molecular mechanisms underlying the deregulation of bone remodeling in RTT. Human deciduous tooth‐derived mesenchymal stem cells that exhibit osteoblast plasticity were used as a cellular model of RTT. Using a small interfering RNA‐mediated MECP2 (MECP2‐siR) knockdown system, we quantitatively analyzed the RUNX2‐dependent and canonical Wnt signaling pathways during osteoblast differentiation. Expression of active β‐catenin, RUNX2, and their downstream targets (osteocalcin and alkaline phosphatase) and mineralization were decreased in MECP2‐siR‐treated osteoblasts compared to that in control osteoblasts. In contrast, the MECP2‐siR‐treated osteoblasts exhibited an increase in the endogenous Wnt antagonist DKK1. Notably, MECP2/DKK1 double‐knockdown osteoblasts possessed greater β‐catenin and RUNX2 levels than MECP2 single‐knockdown osteoblasts. Furthermore, microRNA126‐3p was upregulated in MECP2‐siR‐treated osteoblasts, and an antagomir of microRNA126‐3p prevented DKK1 upregulation, thereby improving the levels of active β‐catenin and other osteoblastic phenotypes. These results suggest that MECP2 insufficiency enhances DKK1 expression via the upregulation of microRNA126‐3p, suppressing the canonical Wnt signaling and subsequent RUNX2‐dependent osteoblast differentiation. The present study provides insights into the molecular mechanisms involved in impaired osteoblast differentiation that contribute to the development of osteoporosis in RTT.
Dong et al. (2026) studied this question.