DISRUPTED ASTROCYTE HOMEOSTASIS DRIVES MYORG-ASSOCIATED PRIMARY FAMILIAL BRAIN CALCIFICATION

Primary familial brain calcification (PFBC) is a rare neurodegenerative disorder characterized by bilateral intra- and perivascular calcium phosphate deposits, frequently affecting basal ganglia and cerebellum. Biallelic mutations in the myogenesis-regulating glycosidase (MYORG) gene, an endoplasmic reticulum (ER)–resident a-galactosidase enriched in astrocytes, account for approximately 13 percent of PFBC cases, yet the underlying mechanisms remain poorly defined.
Here, we investigated shared pathomechanisms across various MYORG mutations using heterologous overexpression systems, primary mouse astrocytes isolated from a MYORG knock-in (KI) mouse model, and human induced pluripotent stem cell (iPSC)-derived models.
Cycloheximide chase assay and proteasomal inhibition revealed reduced protein stability and half-life of MYORG variants and enhanced ER-associated degradation, accompanied by increased ER chaperone BiP levels. Mutant MYORG triggered aberrant expression of autophagy-related proteins p62 and LC3B-II, suppressed PI3K-AKT-mTORC1 signalling, and impaired lysosomal clearance. Additionally, matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) further uncovered for the first time a global reduction in N-linked glycosylation in cerebellar astrocytes. Comparative analyses identified a cerebellar-specific astrocytic vulnerability at both transcriptomic and proteomic levels. Finally, we established the first human iPSC-derived spheroid model of MYORG-PFBC, which revealed early patterning defects and astrocytic morphological abnormalities.
Altogether, these findings redefine and expand the pathogenic spectrum of MYORG-PFBC as an astrocyte–driven disorder of proteostasis, autophagic–lysosomal dysfunction and glycosylation failure, with region-specific vulnerability, opening the gate to new translational avenues. Additionally, the established iPSC-derived 3D model can serve as a unique human-relevant preclinical platform for high-throughput screening, allowing for discovery of disease-modifying mechanisms.