Zinc deficiency and low enterocyte zinc transporter expression in human patients with autism related mutations in SHANK3

Phelan McDermid Syndrome (PMDS) is a genetic disorder characterized by features of Autism spectrum disorders. Similar to reports of Zn deficiency in autistic children, we have previously reported high incidence of Zn deficiency in PMDS. However, the underlying mechanisms are currently not well understood. Here, using inductively coupled plasma mass-spectrometry to measure the concentration of Zinc (Zn) and Copper (Cu) in hair samples from individuals with PMDS with 22q13.3 deletion including SHANK3 (SH3 and multiple ankyrin repeat domains 3), we report a high rate of abnormally low Zn/Cu ratios. To investigate possible underlying mechanisms, we generated enterocytes from PMDS patient-derived induced pluripotent stem cells and used Caco-2 cells with knockdown of SHANK3. We detected decreased expression of Zn uptake transporters ZIP2 and ZIP4 on mRNA and protein level correlating with SHANK3 expression levels, and found reduced levels of ZIP4 protein co-localizing with SHANK3 at the plasma membrane. We demonstrated that especially ZIP4 exists in a complex with SHANK3. Furthermore, we performed immunohistochemistry on gut sections from Shank3αβ knockout mice and confirmed a link between enterocytic SHANK3, ZIP2 and ZIP4. We conclude that apart from its well-known role in the CNS, SHANK3 might play a specific role in the GI tract.