A phosphate transporter in VIPergic neurons of the suprachiasmatic nucleus gates locomotor activity during the light/dark transition in mice.

The suprachiasmatic nucleus (SCN) encodes time of day through changes in daily firing; however, the molecular mechanisms by which the SCN times behavior are not fully understood. To identify factors that could encode day/night differences in activity, we combine patch-clamp recordings and single-cell sequencing of individual SCN neurons in mice. We identify PiT2, a phosphate transporter, as being upregulated in a population of Vip+Nms+ SCN neurons at night. Although nocturnal and typically showing a peak of activity at lights off, mice lacking PiT2 (PiT2-/-) do not reach the activity level seen in wild-type mice during the light/dark transition. PiT2 loss leads to increased SCN neuronal firing and broad changes in SCN protein phosphorylation. PiT2-/- mice display a deficit in seasonal entrainment when moving from a simulated short summer to longer winter nights. This suggests that PiT2 is responsible for timing activity and is a driver of SCN plasticity allowing seasonal entrainment.

Novel findings in a Swedish primary familial brain calcification cohort.

INTRODUCTION: Brain calcifications are frequent findings on imaging. In a small proportion of cases, these calcifications are associated with pathogenic gene variants, hence termed primary familial brain calcification (PFBC). The clinical penetrance is incomplete and phenotypic variability is substantial. This paper aims to characterize a Swedish PFBC cohort including 25 patients: 20 from seven families and five sporadic cases. METHODS: Longitudinal clinical assessment and CT imaging were conducted, abnormalities were assessed using the total calcification score (TCS). Genetic analyses, including a panel of six known PFBC genes, were performed in all index and sporadic cases. Additionally, three patients carrying a novel pathogenic copy number variant in SLC20A2 had their cerebrospinal fluid phosphate (CSF-Pi) levels measured. RESULTS: Among the 25 patients, the majority (76%) displayed varying symptoms during the initial assessment including motor (60%), psychiatric (40%), and/or cognitive abnormalities (24%). Clinical progression was observed in most patients (78.6%), but there was no significant difference in calcification between the first and second scans, with mean scores of 27.3 and 32.8, respectively. In three families and two sporadic cases, pathogenic genetic variants were identified, including a novel finding, in the SLC20A2 gene. In the three tested patients, the CSF-Pi levels were normal. CONCLUSIONS: This report demonstrates the variable expressivity seen in PFBC and includes a novel pathogenic variant in the SLC20A2 gene. In four families and three sporadic cases, no pathogenic variants were found, suggesting that new PFBC genes remain to be discovered.

Mechanisms of PiT2-loop7 Missense Mutations Induced Pi Dyshomeostasis / 神经科学通报·英文版

PiT2 is an inorganic phosphate (Pi) transporter whose mutations are linked to primary familial brain calcification (PFBC). PiT2 mainly consists of two ProDom (PD) domains and a large intracellular loop region (loop7). The PD domains are crucial for the Pi transport, but the role of PiT2-loop7 remains unclear. In PFBC patients, mutations in PiT2-loop7 are mainly nonsense or frameshift mutations that probably cause PFBC due to C-PD1131 deletion. To date, six missense mutations have been identified in PiT2-loop7; however, the mechanisms by which these mutations cause PFBC are poorly understood. Here, we found that the p.T390A and p.S434W mutations in PiT2-loop7 decreased the Pi transport activity and cell surface levels of PiT2. Furthermore, we showed that these two mutations attenuated its membrane localization by affecting adenosine monophosphate-activated protein kinase (AMPK)- or protein kinase B (AKT)-mediated PiT2 phosphorylation. In contrast, the p.S121C and p.S601W mutations in the PD domains did not affect PiT2 phosphorylation but rather impaired its substrate-binding abilities. These results suggested that missense mutations in PiT2-loop7 can cause Pi dyshomeostasis by affecting the phosphorylation-regulated cell-surface localization of PiT2. This study helps understand the pathogenesis of PFBC caused by PiT2-loop7 missense mutations and indicates that increasing the phosphorylation levels of PiT2-loop7 could be a promising strategy for developing PFBC therapies.