OMICS Profiling Identifies Signatures of Senescence in Osteogenesis Imperfecta Osteoblasts Counteracted by 4-PBA

Mutations in collagen I are the most common cause of osteogenesis imperfecta (OI), leading to delayed protein folding and structurally abnormal molecules. While some aberrant collagen is secreted into the extracellular matrix (ECM), impairing bone quality, a significant fraction is retained intracellularly, disrupting osteoblast homeostasis. 4-phenylbutyrate (4-PBA) has been shown to improve osteoblast function and ECM composition in OI models. To investigate the intracellular consequences of mutant collagen retention and the mechanisms of 4-PBA, we analysed the secretome and transcriptome of two dominant OI mouse models, Col1a1^+/G349C and Col1a2^+/G610C. MS/MS proteomic analysis of conditioned media revealed senescence-associated secretory phenotype proteins, together with components linked to altered cytoskeletal organization and cell adhesion. Transcriptomic analysis identified P53 as a central hub gene, supporting premature senescence activation. Increased senescence-associated β-galactosidase activity, elevated expression of the cyclin-dependent kinase inhibitor P16, and reduced Ki67 levels further supported a senescent phenotype. Notably, senescence-associated proteins were absent from the secretome following 4-PBA treatment, which also modulated cytoskeletal and adhesion-related protein expression. Moreover, 4-PBA significantly reduced senescence marker expression and decreased the number of senescent cells. Overall, these findings indicate that cellular senescence underlies osteoblast dysfunction in OI and uncover a novel contribution of 4-PBA to osteoblast homeostasis.