Golgi damage caused by dysfunction of PiT-2 in primary familial brain calcification

Computational molecular characterization of a novel SLC20A2 variant associated with primary familial brain calcification

SLC20A2, encoding human type III sodium-dependent phosphate transporter 2 (hPiT2), is the gene most frequently associated with primary familial brain calcification (PFBC). The mechanism by which a SLC20A2 mutation causes phosphate transporter dysfunction may depend on the functional region of hPiT2 being affected. We presented clinical and brain imaging data of a patient with idiopathic brain calcification. Genetic testing detected a novel, de novo and in silico-predicted deleterious variant, c.1891 C > T (p.Pro631Ser), in SLC20A2. Computational simulations revealed that, compared to the wild type, this variant hPiT2 was associated with a higher root mean square deviation in molecular dynamics, a smaller value with a wider range for the kink angle of transmembrane helix 8 (TM8), and a less flexible TM8 structural conformation. These molecular characteristics were also observed in the known pathogenic missense variants in the TM8 of hPiT2. The pathogenicity of the novel SLC20A2 variant p.Pro631Ser is supported by the computational simulations for molecular characteristics of the variant hPiT2. The findings also highlight the role of TM8 helix in maintaining normal hPiT2 functions.

Astrocytes in Primary Familial Brain Calcification (PFBC): Emphasis on the Importance of Induced Pluripotent Stem Cell-Derived Human Astrocyte Models

Primary familial brain calcification (PFBC) is a rare, progressive central nervous system (CNS) disorder without a cure, and the current treatment methodologies primarily aim to relieve neurological and psychiatric symptoms of the patients. The disease is characterized by abnormal bilateral calcifications in the brain, however, our mechanistic understanding of the biology of the disease is still limited. Determining the roles of the specific cell types and molecular mechanisms involved in the pathophysiological processes of the disease is of great importance for the development of novel and effective treatment methodologies. There is a growing interest in the involvement of astrocytes in PFBC, as recent studies have suggested that astrocytes play a central role in the disease and that functional defects in these cells are critical for the development and progression of the disease. This review aims to discuss recent findings on the roles of astrocytes in PFBC pathophysiology, with a focus on known expression and roles of PFBC genes in astrocytes. Additionally, we discuss the importance of human astrocytes for PFBC disease modeling, and astrocytes as a potential therapeutic target in PFBC. Utilization of species-specific and physiologically relevant PFBC model systems can open new avenues for basic research, drug development, and regenerative medicine.