A tiny strand of genetic material is taking center stage in a new MIT study on Rett syndrome. Researchers report that two common MECP2 mutations that cause Rett appear to make developing brain blood vessels leaky by overactivating a vascular microRNA called miR-126-3p. When the team dialed down this microRNA in lab-grown human vessel models, levels of the tight-junction protein ZO-1 improved and permeability dropped. In three-dimensional microvascular networks built from patient-derived induced pluripotent stem (iPS) cells carrying the R306C or R168X mutations, the scientists saw reduced ZO-1 and leakier vessels compared with controls.
How The Lab Model Showed Leakiness
To probe what was going wrong at the vessel wall, the investigators used microfluidic 3-D microvascular networks and engineered endothelial networks from Rett syndrome patient iPS cells. They then measured barrier function and protein expression. Cultures with MeCP2[R306C] or MeCP2[R168X] mutations showed higher permeability and weaker ZO-1 localization at cell junctions than control networks.
Transcriptomic profiling pointed to a likely culprit. The defective barrier was linked to up-regulation of miR-126-3p and downstream changes in TEK and EDN1 signaling pathways, according to a report in Molecular Psychiatry.
MicroRNA 126 Emerges As A Culprit
The authors argue that miR-126-3p is acting as a mediator between MeCP2 dysfunction and endothelial breakdown rather than as a passive downstream bystander. Senior author Mriganka Sur put it this way in a statement to the Picower Institute:
“A role for microRNAs in Rett syndrome has been shown, but now demonstrating that miRNA-126-3p is actually downstream of MeCP2 and directly implicated in the endothelial cell dysfunction is an important piece of the Rett syndrome puzzle.”
In other words, the work ties a specific microRNA to the vascular problems linked to MECP2 mutations, which gives researchers a more concrete target to chase.
A Drug Already In Trials
Adding a twist that will catch drug developers’ attention, the paper and press release note that an anti-miR-126 therapy called miRisten is already being tested in adults with relapsed or refractory acute myeloid leukemia, under ClinicalTrials.gov identifier NCT07025564, according to ClinicalTrials.gov.
Preclinical oncology studies have reported that depleting miR-126 can reduce leukemia stem cell activity and that pharmacological inhibition of miR-126 can enhance the activity of venetoclax in acute myeloid leukemia models, which helped spur the first-in-human study, according to PubMed.
Why This Matters To Families
Rett syndrome is a rare, X-linked neurodevelopmental disorder caused by MECP2 mutations. Symptoms usually emerge between ages two and three and include loss of spoken language, loss of hand skills and loss of motor control, according to the National Institute of Neurological Disorders and Stroke.
That early-childhood window overlaps with a critical period of vascular maturation in the brain. The MIT team suggests that if blood vessels are already leaky at that time, the resulting vascular disruption could alter neuronal activity and contribute to how the syndrome progresses. For families who often see skills suddenly slip away in toddlers, any credible lead on what is happening inside the brain draws close scrutiny.
Caution: Early Results, Not A Therapy Yet
So far, all of the experiments were done in engineered human tissues in the lab. Antisense knockdown of miR-126-3p in those models partially restored ZO-1 and reduced leakiness, but the fix was not complete. The authors stress that moving from this kind of in vitro success to animals and then to humans will take substantial additional work.
The Molecular Psychiatry paper concludes that the findings outline a “promising therapeutic avenue” rather than a ready-made treatment. There is still no evidence yet of benefit in living animals or in patients, a reminder that the path from petri dish to clinic is long and full of ways for early ideas to fall apart.
Next Steps At MIT
Lead author Tatsuya Osaki and Sur say their next move is to test miRisten in mouse models of Rett syndrome to see whether shoring up the vasculature can improve neuronal activity and behavior. Successful rescue in animals would be a prerequisite before anyone even contemplates human trials.
Even if the mouse data look encouraging, clinicians and patient advocates point out that any repurposed therapy would still have to clear safety testing and years of clinical trials. Still, the study offers a sharper molecular target and a drug already in development that could, in theory, be pointed in a new direction, the team told the Picower Institute.
