Summary: Rett syndrome is usually described as a disorder of neurons, but new research shows that the brain’s vascular system — the “plumbing” that surrounds and supports neurons — may be equally important. A landmark study finds that mutations in the MECP2 gene drive overexpression of a particular microRNA, miR-126-3p, which weakens blood-vessel structure and produces a leakier brain environment. Using 3D microvascular networks grown from patient-derived stem cells, the investigators show that reducing this microRNA can restore elements of the blood-brain barrier, pointing to a potential new therapeutic target for Rett syndrome.
Researchers used advanced human tissue models to trace how two different MECP2 mutations compromise vessel integrity. They identified miR-126-3p as a central mediator of the vascular defect and demonstrated that blocking this microRNA increases expression of the junctional protein ZO-1 and partially rescues barrier function in vitro.
Key Facts
- Vascular vulnerability: MECP2 mutations weaken the structural integrity of brain blood vessels, producing increased leakiness during the critical developmental window around ages 2–3.
- The miRNA culprit: The study pinpoints miR-126-3p as overexpressed downstream of MeCP2 dysfunction. This overexpression contributes to reduced levels of the junctional protein ZO-1.
- Tight junction breakdown: ZO-1 helps form tight junctions between endothelial cells; its reduction impairs the seal between vessel cells, allowing unwanted molecules to cross into brain tissue.
- Neural disruption: Neurons exposed to media from Rett vasculature cultures display reduced electrical activity, indicating that vascular leakiness can directly impair neuronal function.
- Therapeutic potential: An antisense strategy that lowers miR-126-3p levels partially restores vessel barrier properties. A miR-126 inhibitor is already undergoing clinical testing in other conditions, making it a promising candidate for further preclinical study in Rett models.
Source: Picower Institute at MIT
Overview of the findings
Rett syndrome is a severe neurodevelopmental disorder caused by mutations in the widely expressed MECP2 gene. Although MeCP2 affects many cell types, symptoms in affected children typically appear between ages two and three — a period when brain blood vessels are maturing. Scientists at the Picower Institute for Learning and Memory at MIT modeled how two common MECP2 mutations affect vascular development and how those vascular changes could contribute to the neurological features of Rett syndrome.
To study these effects, lead author Tatsuya Osaki and senior author Mriganka Sur created three-dimensional microvascular networks using induced pluripotent stem (iPS) cells derived from Rett patients. These cells were driven to an endothelial fate, embedded in matrix with supporting fibroblasts, and connected to microfluidic flow to recreate aspects of developing microvasculature. The team generated isogenic controls by editing the same patient-derived cells so that genetic background was matched and the only difference was the presence or absence of the MECP2 mutation.
The researchers examined two distinct MECP2 mutations, R306C and R168X, chosen because each is relatively common and they disrupt MeCP2 function in different ways. Despite the molecular differences between those mutations, both produced a similar downstream effect: upregulation of miR-126-3p, loss and mislocalization of ZO-1 at endothelial junctions, and increased vessel permeability compared with their isogenic controls.
Mechanism and functional consequences
MeCP2 normally represses gene expression, so the team hypothesized that removal of MeCP2-mediated repression could permit expression of regulators that indirectly reduce ZO-1. MicroRNAs, which modulate gene expression post-transcriptionally, were primary candidates. Profiling revealed significant overexpression of miR-126-3p in Rett endothelial cells. RNA sequencing further identified dysregulation of molecular pathways that support vascular integrity.
Functionally, microvascular networks carrying MECP2 mutations showed reduced ZO-1 expression and impaired localization to cell junctions, consistent with a compromised physical barrier. When neurons were exposed to conditioned medium from the mutant vasculature cultures, their electrical activity was diminished, implying that secreted factors or altered extracellular conditions from leaky vessels can disrupt neuronal function.
Rescue experiments and therapeutic implications
To test causality, the team applied an antisense approach to lower miR-126-3p levels in the Rett endothelial cultures. This intervention increased ZO-1 expression, partially restored barrier function, and shifted dysregulated pathways toward control-like states. These results support a model in which MECP2 mutation drives miR-126-3p upregulation, which in turn contributes to endothelial dysfunction and blood-brain barrier impairment.
Because pharmacological inhibitors of miR-126 are already under clinical investigation for other diseases, the authors plan to evaluate such compounds in animal models of Rett syndrome to determine whether correcting vascular leakiness can improve behavioral or neurological outcomes.
Authors and funding
In addition to Tatsuya Osaki and Mriganka Sur, co-authors include Zhengpeng Wan, Koji Haratani, Ylliah Jin, Marco Campisi, David A. Barbie, and Roger D. Kamm. Funding came from the National Institutes of Health, a MURI grant, The Freedom Together Foundation, and the Simons Center for the Social Brain.
Key Questions Answered:
A: This study expands that view by showing that healthy neurons may still fail to function properly when the surrounding vasculature is defective. A compromised blood-brain barrier can disrupt the brain’s extracellular environment and impair neuronal electrical activity.
A: That age range corresponds to a critical window when brain vasculature matures. If MECP2 mutations interfere with vascular development at that time, the resulting barrier defects can produce the first observable symptoms.
A: While not a cure, identifying miR-126-3p as a specific downstream target offers a promising therapeutic avenue. A miR-126 inhibitor is in clinical trials for other diseases, and researchers are testing vascular-targeted approaches in animal models to assess their potential to improve Rett-related dysfunction.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full.
- Additional context was added by staff.
About this Rett syndrome and neuroscience research news
Author: David Orenstein
Source: Picower Institute at MIT
Contact: David Orenstein – Picower Institute at MIT
Image: The image is credited to Neuroscience News
Original Research: Open access. “miR126-mediated alteration of vascular integrity in Rett syndrome” by Tatsuya Osaki, Zhengpeng Wan, Koji Haratani, Ylliah Jin, Marco Campisi, David A. Barbie, Roger D. Kamm & Mriganka Sur. DOI: 10.1038/s41380-026-03492-9
Abstract
miR126-mediated alteration of vascular integrity in Rett syndrome
Rett syndrome (RTT) results from mutations in methyl-CpG binding protein 2 (MeCP2). MeCP2 is expressed across multiple cell types, so its mutation affects not only neurons but also non-neuronal cells such as endothelial cells that support the brain vasculature. Vascular integrity is essential for brain homeostasis, and its disruption may contribute to neurodevelopmental and neurodegenerative pathologies. Using RTT patient-derived iPS cells carrying MeCP2[R306C] or MeCP2[R168X], the authors developed a microvascular network model to study early vascular impact. By inducing endothelial differentiation and constructing perfused microvascular networks, they observed increased permeability in RTT cultures versus isogenic controls, indicating compromised barrier function. MicroRNA profiling and RNA sequencing linked the hyperpermeability to upregulation of miR-126-3p, and restoring miR-126-3p levels rescued barrier properties. These findings implicate miR-126-3p–mediated vascular impairment in RTT and suggest potential therapeutic strategies for restoring vascular and neural function.