ESPE Abstracts

Acromicric dysplasia AD）is a relatively rare congenital disease characterized by server short stature、short extremities、and progressive joint limitation. The skeletal dysplasia significantly affects the physical and mental health of children and adolescents. FBN1 heterozygous point mutations in TB5 domain have been proposed as the predominant cause of AD. While upregulation of TGF-β signaling has been proposed as the underlying molecular mechanism of FBN1 gene variants causing short stature, this hypothesis has been challenged. Here, we identified two typical three-generation family pedigrees with AD due to the FBN1 variants c.5263 T>C and c.5179 C>G. We reprogrammed patient peripheral blood mononuclear cells (PBMCs) into induced pluripotent stem cells (iPSCs) by nucleofecting with episomal plasmids. The patient-specific iPSCs were corrected through CRISPR/Cas9 RNP technology to generate gene-corrected isogenic iPSCs. These iPSCs were further differentiated into chondroblast via mesenchymal stem cell (MSCs). We detected that the FBN1 variant associated with AD led to a significant reduction in chondrogenic potential. MSCs RNA-seq results suggested FBN1 variants lead to aberrant expression patterns of extracellular matrix (ECM) protein, increasing matrix degradation, decreasing matrix synthesis and promoting the cross-linking of collagen and elastic fibers. ECM Structural disorder caused aberrant mechano-transduction. At the early stages of chondrocyte differentiation, vinculin as the hallmark of focal adhesions was reduced with the cell cytoskeleton changed. Moreover, disrupted F-actin dynamics inhibited YAP nuclear translocation which decreased proliferation and increased apoptosis. Excessive apoptosis is pathological and harmful in chondrogenic differentiation of MSCs. In vivo, we generated orthologous mutant mice harboring alleles with human FBN1 c.5263 T>C. In agreement with the clinical manifestation, mutant mice have the shortened body length and affected the growth plate formation. Growth plate immunohistochemistry show consistent trends with cellular studies. These findings will provide a theoretical foundation for accurate diagnosis and development of drugs targeting acromicric dysplasia caused by FBN1 variation in the future.