SLC20A2 variants cause dysfunctional phosphate transport activity in endothelial cells induced from Idiopathic Basal Ganglia Calcification patients-derived iPSCs.

Idiopathic Basal Ganglia Calcification (IBGC) is a rare neuropsychiatric illness also known as Fahr's disease or Primary Familial Brain Calcification (PFBC). IBGC is caused by SLC20A2 variants, which encodes the inorganic phosphate (Pi) transporter PiT-2, a transmembrane protein associated with Pi homeostasis. We have reported novel SLC20A2 variants in the Japanese population and established an induced pluripotent stem cells (iPSCs) from an IBGC patient carrying a SLC20A2 variant. To investigate the effect of these SLC20A2 variants identified in our previous study, we used Chinese hamster ovary (CHO) cells expressing these variant proteins using the Flp-In system (Flp-In CHO cells), and showed that variant SLC20A2 proteins significantly disrupted the Pi transport activity in Flp-In CHO cells. Endothelial cells (ECs) represent important target cells for elucidating the pathology of IBGC. Using patient-derived iPSCs in this study, we differentiated these cells into ECs and found no significant difference in their differentiation capacity into ECs compared with control iPSCs. However, the Pi transport activity of IBGC patient-derived iPS-ECs was significantly decreased compared with that of control iPS-ECs without changing the gene expression of the other SLC 20 family members. We confirmed that SLC20A2 variants caused the loss of function of the Pi transport activity in both Flp-In CHO cells and disease-specific iPSCs. This is the first report to show an in vitro model of iPSCs in IBGC with patient-identified SLC20A2 variants. These useful tools will help in elucidating IBGC pathogenesis and can be used for screening drug candidates.