Science1 publisher2 min readPublished
Removing NSF from D2-receptor cells left mice with a smaller striatum and less dopamine
A University of Fukui group deleted the membrane fusion protein NSF only in dopamine D2 receptor cells. The mice lost those cells during development, ended up with a smaller striatum, and behaved like an ADHD model.
The Scientist · Science desk
What happened
- A University of Fukui team built conditional knockout mice with Nsf deleted specifically from dopamine D2 receptor-expressing cells, to test in living animals an NSF-D2R interaction known only from earlier work.
- The knockouts had fewer D2R-expressing cells, more cell death early in development, and a smaller striatum than the deletion was expected to leave untouched.
- Dopamine levels in the striatum of the modified mice were markedly lower.
- Those brain changes came with ADHD-like behaviors in the same animals.
Compiled by The ScientistSomething wrong?How this is made
Why it matters
- capability A cell-type-restricted knockout turns a question about what maintains D2R-expressing neurons into an experiment with a manipulated variable, which the human dopamine-ADHD literature cannot supply.
- constraint Because the deletion is in place through development, the study cannot separate a permanent loss of cells from an ongoing fault in the cells that remain, and only the second is something a drug could address.
- decision The clinical direction Xie points to is D2R function and striatal dopamine signaling, territory existing compounds already occupy, so the near-term test is pharmacological.
- precedent With NSF already reported as reduced in autism and schizophrenia and aggregated in Parkinson's, a D2R-cell knockout invites the same deletion being read across those literatures.
In the knockouts, D2 receptor-expressing cells died off during early development and the striatum came out smaller [13]. Dopamine in that region was markedly lower [14].
That leaves two candidate explanations for the ADHD-like behavior. One is structural: fewer D2R cells in a smaller striatum. The other is functional, because NSF moves proteins within cell membranes and helps neurons release their chemical messengers [7], so the cells that survive may handle their D2 receptors badly. The published title asserts both, impaired striatal development and impaired dopaminergic function [6]. Which one carries the behavior matters for the treatment claim, since a drug given later can only act on cells that are still there.
The design is the reason this goes past another dopamine association. Xie's group generated D2R-specific Nsf conditional knockout mice, Nsf f/f;D2R-Cre, to examine NSF function in those cells in vivo [11], and D2R-expressing cells sit in the striatum, the region tied to movement and behavioral control [16]. "Although D2R has been extensively studied, the upstream mechanisms regulating its function and localization remain unclear," the authors wrote [8]. Deleting a candidate upstream regulator from one cell population is an intervention. The cell loss and the dopamine deficit are consequences of that deletion.
The human NSF evidence the authors cite comes from other diagnoses: "NSF dysfunction is implicated in neuropsychiatric disorders, with reduced expression in autism spectrum disorder (ASD) and schizophrenia and aggregates in Parkinson's disease," they noted [9]. The starting hypothesis came by the same indirect route. "NSF was known to interact with D2R; however, the role of this interaction in vivo remained unclear," Xie said [10]. Xie was blunt about the distance to a clinic: "This is basic research and will not immediately lead to a new treatment" [4].
The team also tested whether drugs affecting dopamine signaling could reduce the behavioral changes in the mutants [12]. The report does not name those drugs, the doses, or the tasks used to score the ADHD-like phenotype [17]. That is the result with clinical bearing, because the direction Xie names is "new therapeutic strategies targeting D2R function and striatal dopamine signaling, especially for treatment-resistant ADHD" [5].
What to watch
- The Neuropsychopharmacology paper itself: which dopamine-signaling drugs were given to the mutants, at what dose, and how much of the behavior they corrected.
- An adult-onset deletion of Nsf in D2R-expressing cells would test whether the behavior depends on the developmental cell loss.
- Human genetic or postmortem data tying NSF levels to ADHD, not only to autism, schizophrenia and Parkinson's.