Assessing the effects of methylphenidate in proliferation and Wnt activity of neuronal stem cells from attention deficit/hyperactivity disorder patients

As the most common neurodevelopmental and mental disorder around the world, attention-deficit/hyperactivity disorder (ADHD) affects primarily children and adolescents. Both genetic (polygenicity) and environmental variables interplay in the etiology of this disorder. The Wnt signaling pathway, which regulates proliferation and differentiation during neurodevelopment, has been implicated in ADHD. Clinically, individuals with ADHD may exhibit delays in structural and functional brain development. Available evidence suggests that methylphenidate (MPH) treatment can potentially improve these delays. However, the molecular and cellular mechanisms underlying ADHD and the therapeutic targets of MPH are not yet completely elucidated. In a pilot investigation, the proliferation of neural stem cells (NSCs) derived from induced pluripotent stem cells (iPSCs) was significantly lowered in ADHD male patients. Yet, we did not observe any variations in proliferation rates during the iPSC stage. To extend the earlier results, we increased the sample size to include females, explored whether MPH may improve NSC proliferation in ADHD and clarified the role of the Wnt pathway. To do so, iPSC and NSC proliferation from five ADHD patients and five controls was assessed. The results corroborated our previous findings of decreased proliferation in ADHD NSCs. Conversely, ADHD NSC proliferation was modestly regulated by MPH treatment at 10 nM, which also showed modulatory effects on Wnt signaling in this group. Interestingly, no increase in proliferation was seen when DKK1 blocked Wnt signaling before MPH treatment. These findings suggest MPH regulates the canonical Wnt pathway and may partially explain ADHD-related neurodevelopmental abnormalities and MPH-specific benefits.