ABSTRACT: Amelogenesis imperfecta type 1G (AI1G), also known as Enamel-Renal-Gingival Syndrome (ERGS), is an autosomal recessive disorder caused by variants in FAM20A, encoding a Golgi apparatus protein crucial for protein processing and secretion. AI1G presents with enamel defects, nephrocalcinosis, and gingival overgrowth. Building upon our previous findings demonstrating the impact of FAM20A insufficiency on deciduous dental pulp cells, this study investigated the molecular mechanisms underlying gingival fibromatosis in AI1G. RNA sequencing of gingival fibroblasts from an AI1G patient revealed widespread differential gene expression (DEG). Gene Ontology (GO) analysis demonstrated enrichment of DEGs in biological processes related to cell adhesion, differentiation, proliferation (including positive regulation and cell division), cell cycle regulation, apoptosis, and signal transduction. Furthermore, enriched molecular functions included protein, ATP, and calcium ion binding, protein homodimerization and kinase activity, and receptor binding. Pathway analysis (Reactome and KEGG) further highlighted the dysregulation of signaling pathways, including Wnt, TGF-β, cell cycle, DNA replication, Rho GTPase signaling, and extracellular matrix organization. Functional assays confirmed these findings, revealing delayed initial attachment and spreading, impaired osteogenic differentiation (evidenced by reduced mineralization and downregulation of DLX5, OCN, RUNX2, and OPN), enhanced cell cycle progression and proliferation (increased colony size and proliferation rates, along with a shift from G0/G1 to G2/M phase), and suppressed apoptosis in FAM20A-insufficient fibroblasts. These results suggest that FAM20A plays a critical role in regulating fundamental processes in gingival fibroblasts, and its insufficiency contributes to the gingival fibromatosis phenotype observed in AI1G through the disruption of cell adhesion, differentiation, proliferation, and apoptosis. This study proposes novel insights into the pathogenesis of AI1G and highlights potential therapeutic targets for this complex disorder.
